A process for metallisation and bonding of silicon carbide surfaces

Abstract

The present disclosure relates to a process to metallise and bond silicon carbide ceramic surfaces. The process comprises hydrophilising the silicon carbide surface with a hydrophilising agent to form a hydrophilised silicon carbide surface; contacting the hydrophilised silicon carbide surface with a solution comprising one or more monovalent metal ions; reducing the one or more monovalent metal ions to form metal nanoparticles on the hydrophilised silicon carbide surface by the application of energy to the one or more monovalent metal ions and the hydrophilised silicon carbide surface; to provide the nanoparticle seeded silicon carbide surface. Also disclosed herein is a process to produce a hermetically sealed diffusion bond between silicon carbide surface.

Description

A process for metallisation and bonding of silicon carbide surfacesTechnical Field

[0001] The present invention relates to a process to metallise and bond silicon carbide (SiC) ceramic surfaces.Background

[0002] SiC is a wide bandgap semiconductor material that is often used in high power devices because it has high thermal conductivity and low coefficients of thermal expansion. Demand for SiC devices is growing, especially due to the rise of electric vehicles, but may also find uses in fields including structural ceramics, solar inverters, high-temperature turbine components and aerospace applications. Additionally, SiC serves as a functional material in fields like fusion and nuclear reactors for its radiation resistance, mechanical stability and its ability to withstand very high temperatures.

[0003] A significant technological challenge for high-performance SiC-device manufacturing is in the area of metallisation. Particularly in the effective control of metal / SiC contact properties to create low resistivity, and high stability ohmic contacts. The choice of metals and processes significantly impacts device performance and reliability.

[0004] Current technology for metallising SiC ceramic surfaces involves toxic chemicals, is expensive, energy intensive and time consuming.

[0005] Common metallisation methods used in the industry include physical vapour deposition (PVD), chemical vapour deposition (CVD) and electroplating. PVD is a widely used method for depositing metal films on SiC substrates. Techniques like sputtering and evaporation are often employed to deposit metals such as titanium (Ti), aluminium (Al), nickel (Ni), and gold (Au) for ohmic and Schottky contacts. CVD is used for depositing metal films under specific conditions of temperature and pressure. It is commonly applied for barrier metals like titanium nitride (TiN) or tungsten (W) in SiC devices. Electroplating is often used forthick metallisation layers, such as copper (Cu) for heat dissipation and conductivity; however, an initialconductive seed layer is typically deposited via PVD which is costly and lacks specificity, i.e. PVD deposits on all surfaces not only the target surface.

[0006] In addition, to ensure proper adhesion and reduced contact resistance, annealing at high temperatures (e.g. 600 °C - 1000 °C) is necessary to form strong ohmic contacts.

[0007] In order to bond SiC to metal, or SiC to SiC, the technological challenge lies in finding a diffusion bonding layer that is compatible with the SiC matrix, produces high integrity bonds, is compatible with the high neutron fluxes associated with fusion reactor environments and can be processed at low temperatures and pressures.

[0008] Existing methods for bonding may include calcium-alumina glass-ceramics, Ti3SiC2,SiC nano-powder with AI2O3-Y2O3 and Iridium, which all use expensive materials, high pressures and elevated temperatures and often require vacuum processing to bond the materials.

[0009] For example, US 10,406,774 describes a method of using an iridium foil between two SiC layers with high temperature and low pressures. This is heated at 1500 °C under a vacuum of less than 10“5torr and a pressure between 1 ksi and 7 ksi for 6-10 hours. This process forms a hermetic seal with a leak rate below 3*10“9cm3 / sec, mainly attributed to the formation of iridium-silicides in a reaction zone at the SiC / iridium interface.

[0010] WO 2016131861 further describes a method for diffusion bonding silicon infiltrated SiSiC using high heat and high pressure. This achieves a strong bond between rough surfaces, specifically focusing on achieving a thin joint seam. This method requires heating near the melting point of silicon (1300 -1380 °C) under an inert gas atmosphere or vacuum with a contact pressure of 0.1 - 5.0 MPa for 1 hr. This method emphasizes reducingthe reliance on precise surface polishing, a common requirement in conventional diffusion bonding processes.

[0011] US 20140326403 for example, describes a method of solid-state bonding of high purity SiC made via CVD using toxic chemicals, high pressures, and high temperatures. The method comprises cleaning the surfaces to be bonded with a combination of HF and nitric acids, bonding the surfaces with a force of 0.35 MPa,heating the articles to a temperature of between 1900°C to 2200°C in a vacuum or inert atmosphere for between 2 and 4 hours.

[0012] US 11 ,728,287 discloses methods for bonding obstructive elements to semiconductor elements for security purposes. More specifically, US 11 ,728,287 explores direct bonding techniques to achieving bonding without use of adhesives.

[0013] JPH06105722 describes a ceramic bonding method using an aluminium-silicon brazing material to join alumina or other ceramics to a silicon carbide ceramic for semiconductor packaging applications. JPH06105722 utilises high thermal conductivity and airtightness by forming a eutectic alloy region at the interface.

[0014] US 10,995,408 describes an electroless nickel plating of silicon carbide powder for enhancing wear resistance and other properties, which could potentially be relevant for pre-treatment before diffusion bonding. The process differs from the current disclosure in requiring an oxidised surface and then using hydrofluoric acid to hydrophilise the surface which produces inferior performance compared to the current disclosed method. The process describes depositing palladium on the surface as a catalyst after sensitisation in a tin solution which is a complex two-step process compared to the disclosed single step reduction of metal ions directly on the hydrophilised surface.

[0015] JP 7229852 details a method for processing silicon carbide wafers and devices, highlighting the use of specialized techniques for splitting and bonding SiC wafers.

[0016] Muellerdescribes a room temperature SiC bonding process using sodium silicate.The method provided for extremely low strength bonds (~2 MPa) through development of hydroxyls on the SiC surfaces which subsequently reduced the silicate to SiO2. However, bonds provided by Mueller have low strength which may be attributed to low reactivity. Further, while Mueller demonstrates the bond has an ability to withstand temperatures as low as 77 K, its upper temperature limit is only 130 °C . As such Mueller does not achieve high bonding strength suitable for high- temperature applications.

[0017] Matsuda et al., 2018 further describes a low temperature (between 300 °C and 500°C), low bond strength (~18 MPa) method for adhesion of various silicon-based materials using silver nanoparticles (AgNPs), which are derived from in-situdecomposition of silver oxide (Ag2O) paste. While the method of Matsuda does not require surface pre-treatment / activation, it relies on formation of a silicon oxide interlayer containing AgNPs to provide intimate contact of the surfaces to be bonded. This silicon oxide interlayer forms due to the high affinity of Si for oxygen, leading to Si oxidation during thermal redox decomposition of Ag2O during bonding. And while Matsuda provides for a bond strength of about 18 MPa, the silicon oxide interlayer is detrimental to fracture strength of the bond / adhesion making it unsuitable for certain applications. Furthermore, the method of Matsuda is performed under vacuum and provision of such processes under vacuum requires expensive specialised equipment which makes such processes less economical.

[0018] Thus, there is a need in the art for improved metallisation and / or bonding processes for the provision of adhesive metallic coatings between silicon carbide surfaces.

[0019] It is therefore an object of the present invention to provide a process that provides for metallisation and / or bonding of silicon carbide surfaces having improved fracture strength, or to at least provide the public with a useful choice.

[0020] It is a further object of the invention to provide a method that minimises use of high energy and high toxicity chemicals, or to at least provide the public with a useful choice.Statements of invention

[0021] In one aspect, there is provided a process to create a nanoparticle seeded surface on a silicon carbide (SiC) surface, the process comprising the steps of:a. providing a silicon carbide surface;b. optionally pre-treating the silicon carbide surface;c. hydrophilisingthe silicon carbide surface with a hydrophilising agent to form a hydrophilised silicon carbide surface;d. contacting the hydrophilised silicon carbide surface with a solution comprising one or more monovalent metal ions;e. reducing the one or more monovalent metal ions to form metal nanoparticles on the hydrophilised silicon carbide surface by the application of energy to the one or more monovalent metal ions and the hydrophilised silicon carbide surface; to provide the nanoparticle seeded silicon carbide surface.

[0022] In one example, the silicon carbide surface may be selected from the group comprising: sintered silicon carbide surface, sintered silicon carbide fibre composite, crystalline silicon carbide surface, and silicon carbide nanopowder.

[0023] In one example, the optional pre-treatment step comprises one or more techniques selected from: polishing the silicon carbide surface with a polishing media having a hardness value greater than silicon carbide; etching the silicon carbide surface; and a combination thereof.

[0024] In one example, polishing the silicon carbide surface comprises grindingthe silicon carbide surface once or a plurality of times.

[0025] In one example, polishing the silicon carbide surface comprises polishing with a polishing media at about 6 pm, about 3 pm, or about 1 pm.

[0026] In one example, polishing the silicon carbide surface comprises polishing successively with a polishing media at about 6 pm, then about 3 pm, and then about 1 pm.

[0027] In one example, the polishing media comprises diamond.

[0028] In one example, the polishing media is a diamond paste.

[0029] In one example, etching the silicon carbide surface comprises immersing the silicon carbide surface in one or more of the following solutions selected from:i. ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2) and water (H2O); ii. hydrochloric acid, hydrogen peroxide (H2O2) and water (H2O);iii. sulfuric acid (H2SO4) and hydrogen peroxide (H2O2);iv. hydrofluoric acid;v. nitric acid; andvi. a combination thereof.

[0030] In one example, the pre-treatment step comprises providing a surface roughness value of Ra <3.

[0031] In one example, the pre-treatment step comprises providing a surface roughness value of Ra <1, preferably about 0.2.

[0032] In one example, the pre-treatment step comprises providing a surface flatness value of AFrms of about 3.

[0033] In one example, the pre-treatment step comprises providing a surface flatness value of AFrms of about 2.

[0034] In one example, the pre-treatment step comprises providing a surface flatness value of AFrms of about 1.

[0035] In one example, the hydrophilising agent comprises: at least one inorganic oxidising agent and at least one acid.

[0036] In one example, the hydrophilising agent forms a hydroxyl moiety on the silicon carbide surface.

[0037] In one example, the at least one inorganic oxidising agent is selected from a compound having a standard reduction potential above +1.23eV.

[0038] In one example, the at least one inorganic oxidising agent is selected from:permanganate salts, potassium permanganate (KMnO4); high-valent chlorine compounds, HCIO, HCIO4; chromium compounds, hexavalent chromium compounds, sodium dichromate (Na2Cr2O7), pyridinium chlorochromate; potassium chlorate; and any combination thereof.

[0039] In one example, the at least one inorganic oxidising agent has a concentration of between about 0.01 mol / L and about 1 mol / L.

[0040] In one example, the at least one acid is a mineral acid that does not react with the at least one oxidising agent.

[0041] In one example, the at least one acid is selected from: phosphoric acid, sulfuric acid, and a combination thereof.

[0042] In one example, the at least one acid is an aqueous acid.

[0043] In one example, the aqueous acid comprises a concentration of between about 10 % and about 60 %.

[0044] In one example, the aqueous acid comprises a concentration selected from: about 10 %, about 20 %, about 30 %, about 40 %, about 50 %, and about 60 %.

[0045] In one example, the hydrophilising agent further comprises at least one stabilising agent.

[0046] In one example, the hyd rop hilisi ng agent comprises:i. at least one permanganate compound,ii. at least one acid; andiii. at least one stabilising agent.

[0047] In one example, the at least one stabilising agent is selected from: phosphorus containing species, phosphate, phosphonate, pyrophosphate, and etidronate.

[0048] In one example, the at least one stabilising agent is a phosphorus containing species selected from: Na3PO4, Na2PO3CH2, Na4P2O, and C2H6Na2O7P2.

[0049] In one example, the at least one stabilising agent comprises a concentration of between about 0.01 mol / L and about 1 mol / L.

[0050] In one example the hydrophilising agent comprises:i. KMnO4at a concentration of about 20 g / L (about 0.1 mol / L); andii. about 40 % aq. H2SO4; andiii. Na4P2O7at a concentration of about 20 g / L (about 0.08 mol / L); or iv. Na3PO4.12H2O at a concentration of about 200 g / L (about 0.6 mol / L); or v. C2H6Na2O7P2at a concentration of about 24 g / L (about 0.1 mol / L); or vi. Na2PO3CH2at a concentration of about 13 g / L (about 0.1 mol / L).

[0051] In one example, the hydrophilisation step is performed over a period of between about 30 minutes and about 90 minutes.

[0052] In one example, the hydrophilisation step is performed over a period of about 60 minutes.

[0053] In one example, the hydrophilisation step is performed at a temperature between about 10 °C and about 30 °C.

[0054] In one example, the solution comprisingthe one or more monovalent metal ions further comprises at least one complexing agent selected from: ammonia, cyanide, ethylenediamine, pyridine, and ethylenediamine tetraacetic acid (EDTA).

[0055] In one example, the solution comprisingthe one or more monovalent metal ions comprises at least one complexing agent that is a hydroxide containing species.

[0056] In one example, the at least one complexing agent may be the same or different from the stabilisation agent used in the hydrophilisation step.

[0057] In one example, the solution comprisingthe one or more monovalent metal ions further comprises a surfactant selected from: polyvinylpyrrolidinone (PVP), sodium dodecyl sulfate (SDS), sodium laureth sulfate (SLS), polyvinyl alcohol (PVA), cetrimonium bromide (CTAB), polyethylene glycol (PEG), Tween-20 (also known as polysorbate 20), and a combination thereof.

[0058] In one example, the solution comprisingthe one or more monovalent metal ions is provided as an aqueous solution.

[0059] In one example, the solution comprisingthe one or more monovalent metal ions has a concentration of the one or more monovalent metal ions between about 0.001 mol / L and about 1 mol / L.

[0060] In one example, the solution comprisingthe one or more monovalent metal ions has a concentration of the one or more monovalent metal ions between about 0.005 mol / L and about 0.1 mol / L.

[0061] In one example, the one or more monovalent metal ions may be selected from:copper ions, gold ions, lithium ions, potassium ions, rubidium ions, silver ions, sodium ions, and a combination thereof.

[0062] In one example, the one or more monovalent metal ions are selected from: silver ions, copper ions, and a combination thereof.

[0063] In one example, the one or more monovalent metal ions are silver ions.

[0064] In one example, the silver ions are provided as an aqueous solution of silver nitrate.

[0065] In one example, the one or more monovalent metal ions are copper ions.

[0066] In one example, the copper ions are provided as an aqueous solution of copper cyanide.

[0067] In one example, the step of contacting the hydrophilised silicon carbide surface with the solution comprising the one or more monovalent metal ions is maintained at a temperature of between about 10 °C and about 40 °C.

[0068] In one example, the step of reducing the monovalent metal ions comprises low temperature thermal processing.

[0069] In one example, the step of reducing the monovalent metal ions comprises heating at a temperature of between about 30 °C and about 120 °C.

[0070] In one example, the step of reducing the monovalent metal ions comprises heating at a temperature of between about 60 °C and about 80 °C.

[0071] In one example, the step of reducing the monovalent metal ions comprises heating at a temperature selected from: about 60 °C, about 70 °C, and about 80 °C.

[0072] In one example, the step of reducing the monovalent metal ions comprises application of a hot air flow stream; exposure to hot air environment, such as heating in an oven.

[0073] In one example, the step of reducing the monovalent metal ions comprises holding the temperature for a period of between about 1 and about 5 minutes, preferably about 2 minutes.

[0074] In one example, the step of reducing the monovalent metal ions comprises an oxidation step for oxidation of reduced monovalent metal ions.

[0075] In one example, the oxidation step comprises heating at a temperature greater than 120 °C.

[0076] In one example, the oxidation step comprises heating at a temperature of about 200°C.

[0077] In one example, the oxidation step comprises heating for a period of time of between about 1 minute and about 5 hours; for between about 5 minutes and about 1 hour; or for about 30 minutes.

[0078] In one example, the oxidation step comprises heating at a temperature of about 200°C for between about 1 minute and about 5 hours.

[0079] In one example, the oxidation step comprises heating at a temperature of about 200 °C for between about 5 minutes and about 1 hour.

[0080] In one example, the oxidation step comprises heating at a temperature of about 200°C for about 30 minutes.

[0081] In one example, the nanoparticle seeded silicon carbide surface has a percentage surface area that is free of metal nanoparticles of between about 20% and about 70%; or between about 30% and about 60%; between about 35% and about 50%; or about 40%.

[0082] In one example, the metal nanoparticle has a surface area of between about 0.5 cm2and 5 cm2, per cm2of silicon carbide area; or about 3 cm2of nanoparticle per cm2of SiC area.

[0083] In one example, the metal nanoparticles cover an area of the total silicon carbide surface of between about 30% and about 80%; or between about 40% and about 70%; or between about 65 and 50 %; or about 60%.

[0084] In one example, between about 30% and about 80%; or between about 40% and about 70%; or between about 65 and 50 %; or about 60% of the total silicon carbide surface is seeded with the metal nanoparticles.

[0085] In some examples, there is a surface area ratio of nanoparticle to SiC surface of between about 1.5 : about 1 and about 4.5 : about 1. Preferably, there is a surface area ratio of nanoparticle : SiC surface of about 3 : about 1.

[0086] In a second aspect, there is provided a process to create a first metal plating surface on a nanoparticle seeded silicon carbide surface to provide a plated silicon carbide surface, the process comprising the steps of:a. providing a nanoparticle seeded silicon carbide surface as described above; and b. contacting the nanoparticle seeded silicon carbide surface with an electroless plating solution to thereby provide a first metal plating on the nanoparticle seeded silicon carbide surface; andthereby producing the plated silicon carbide surface.

[0087] In one example, the electroless plating solution comprises a reducing agent.

[0088] In one example, the electroless plating solution is selected from an electroless nickel plating solution, an electroless silver plating solution, an electroless copper plating solution, and a combination thereof.

[0089] In one example, the reducing agent is selected from: tartrate, amine borane,gluconate, formaldehyde, borohydride, and a combination thereof.

[0090] In one example, the electroless nickel plating solution comprises: electroless nickel boron and the reducing agent is amine borane.

[0091] In one example, the nanoparticle seeded silicon carbide surface is seeded with silver nanoparticles, the electroless plating solution comprises electroless silver, and the reducing agent is sodium gluconate.

[0092] In one example, the silver nanoparticle seeded silicon carbide surface is plated in an electroless silver plating bath for a period of between about 2 and about 10 minutes.

[0093] In one example, the silver nanoparticle seeded silicon carbide surface is plated in an electroless silver plating bath for a period of about 5 minutes

[0094] In one example, the silver nanoparticle seeded silicon carbide surface is plated in an electroless silver plating bath to provide a first metal plating surface having total silver thickness of 1 pm or less.

[0095] In one example, the nanoparticle seeded silicon carbide is seeded with copper nanoparticles, the electroless plating solution is an electroless copper plating solution, and the reducing agent is EDTA.

[0096] In a third aspect, there is provided a process to deposit a second plating surface on the first metal plating surface, the process comprising the steps of:a. providing the first metal plating surface as described above;b. depositing a second plating surface on the first metal plating surface by electrodeposition or electroless deposition;thereby providing a plated silicon carbide surface having a second plating.

[0097] In one example, the second plating surface is selected from silver, gold, copper, nickel, composite coatings, alloy coatings, and combinations thereof.

[0098] In one example, the second plating surface is an electrodeposited metal-ceramic composite.

[0099] In one example, the metal-ceramic composite comprises a ceramic selected from Al2O3, TiO2, SiO2, and WO2, or the like, and a metal selected from silver, gold, nickel, titanium, orthe like, and any combination thereof.[000100] In a fourth aspect, there is provided a process to produce a hermetically sealed diffusion bond between:i. two silicon carbide surfaces selected from: a plated silicon carbide surface, a nanoparticle seeded silicon carbide surface, and a hydrophilised silicon carbide surface, each produced as described herein;the process comprising the steps of:a. contacting i (above) and applying pressure to provide contacted surfaces; and b. heating the contacted surfaces in an oxygen containing atmosphere at a temperature exceeding 400 °C;to thereby provide a hermetically sealed diffusion bond.[000101] In one example, and accordingto any of the aspects described herein, priorto the step of contacting the silicon carbide surfaces, the process comprises a further step of applying an oxidation accelerator to one or more silicon carbide surfaces to thereby provide an oxidation accelerator layer.[000102] In one example, the oxidation accelerator comprises a solution comprising alkali metal ions selected from: sodium ions (Na+), potassium ions (K+), rubidium ions (Rb+), and caesium ions (Cs), or any combination thereof.[000103] In one example, the oxidation accelerator is selected from: sodium hydroxide (NaOH), sodium nitrate (NaNO3), sodium fluoride (NaF), potassium hydroxide (KOH), potassium carbonate (K2CO3), rubidium carbonate (Rb2CO3), caesium carbonate (Cs2CO3), and a combination thereof.[000104] In one example, the oxidation accelerator layer is a monolayer.[000105] In one example, and accordingto any of the aspects mentioned herein the process comprises applying a filler to the silicon carbide surface.[000106] In one example, the filler is applied after applying the oxidation accelerator.[000107] In one example, the filler comprises: a SOL.[000108] In one example the SOL is applied in an amount of between about 0.001 mL / cm2and about 0.02 mL / cm2, preferably about 0.01 mL / cm2.[000109] In one example, the SOL is a mixed oxide SOL.[000110] In one example, the mixed oxide SOL comprises a combination of precursor reagents designed to produce one or more oxides selected from: yttria (Y2O3), alumina (Al2O3), calcia (CaO), magnesia (MgO), titania (TiO2), copper oxide (Cu2O), and silica (SiO2).[000111] In one example, the precursor reagents comprise the combination: aluminium-tri- sec butoxide, yttrium nitrate, acetylacetone, and ethanol.[000112] In one example, the process further comprises a gelling step to partially or substantially gel the filler.[000113] In one example, the filler is gelled to form a paste.[000114] In one example, the gelling step comprises heatingthe silicon carbide surface comprising the filler in an oven at a temperature of between about 50 °C and about 150°C.[000115] In one example, the gelling step comprises heatingthe silicon carbide surface comprising the filler for a period of between about 10 minutes and about 120 minutes.[000116] In one example, the contacting step comprises applying a pressure greater than 0.1MPa.[000117] In one example, the contacting step comprises applying a pressure of between about 1 MPa and about 30 MPa.[000118] In one example, contacting step comprises applying a pressure of about 10 MPa.[000119] In one example, the heating step is performed at a temperature close to the melting point of the metal nanoparticles.[000120] In one example, the heating step is performed between about 400 °C and about 1000[000121] In one example, the heating step is performed between about 700 °C and about 800 o[000122] In one example, the heating step is performed between about 400 °C and about 1000°C and the nanoparticles are silver nanoparticles.[000123] In one example, the heating step is performed fora period greater than about 30 minutes.[000124] In one example, the heating step is performed for a period between about 30minutes and about 48 hours.[000125] In one example, the heating step is performed for a period between about 1 hour and about 24 hours.[000126] In one example, the heating step is performed for a period between about 6 hours and about 18 hours[000127] In one example, the heating step is performed for a period that is about 6 hours;about 10 hours.[000128] In a fifth aspect, there is provided a process to produce a hermetic diffusion bond between a plated silicon carbide surface or a nanoparticle seeded silicon carbide surface and a metal surface to provide a bonded silicon carbide material, the process comprising the steps of:a. providing a nanoparticle seeded silicon carbide surface or a plated silicon carbide surface as described above;b. providing a metal surface;c. contacting the metal surface with an alkaline solution to remove any native oxides or surface contaminants, and then further contacting the metal surface with an acid solution and de-smutting the metal surface in the acid solution; d. contacting the metal surface with the nanoparticle seeded silicon carbide surface or contacting the metal surface with the plated silicon carbide surface to provide contacted surfaces;e. applying pressure to the contacted surfaces; andf. heating at a temperature greater than about 400 °C in an oxygen containing environment;to provide the bonded silicon carbide material.[000129] In one example, the metal surface may be selected from tungsten, stainless steel, copper, and a combination thereof.[000130] In one example, the step of applying pressure comprises: applying a pressure between about 0.1 GPa and 1 GPa.[000131] In one example, the heating step is performed at a temperature of between about 400 °C and 1000 °C.[000132] In one example, the heating step is performed at a temperature of between about 500 °C and 850 °C.[000133] In one example, the oxygen containing environment is ambient air.[000134] In one example, the oxygen containing environment is at atmospheric pressure.[000135] In one example, the heating step comprises heating for a period of between about 30 minutes and 48 hours.[000136] In one example, the heating step comprises heating for a period of between about 1 hours and 24.[000137] In one example, the heating step comprises heating for a period about less than 6 hours.[000138] In a sixth aspect there is provided a process to bond two silicon carbide surfaces, the process comprising the steps of:a. providing two or more silicon carbide surfaces;b. hydrophilising the two or more silicon carbide surfaces with a hydrophilising agent to form hydrophilised silicon carbide surfaces where the hydrophilisation step is described above;c. contacting the hydrophilised silicon carbide surface with a solution comprising one or more monovalent metal ions;d. reducing the one or more monovalent metal ions by the application of energy to form nanoparticles on the hydrophilised silicon carbide surface thereby providing a nanoparticle seeded silicon carbide surface;e. bondingthe two or more hydrophilised or nanoparticle seeded silicon carbide surfaces comprising: application of a nanoparticle seeded silicon carbide nanopowder to at least one of the silicon carbide surfaces, and contacting withthe other silicon carbide surface to form a contacted surface, and where the nanoparticle seeded silicon carbide nanopowder is prepared according to the following steps:i. providing a silicon carbide nanopowder;ii. hydrophilisin the silicon carbide nanopowder with a hyd rop hilising agent to form a hydrophilised silicon carbide nanopowder where the hydrophilising step is described herein;iii. forming the nanoparticle seeded silicon carbide nanopowder by contacting the hydrophilised silicon carbide nanopowder with a solution comprising one or more monovalent metal ions;iv. reducing the monovalent metal ions to form nanoparticles on the hydrophilised silicon carbide surface by the application of energy and thereby providing the nanoparticle seeded silicon carbide nanopowder; andf. applying of pressure to the contacted surfaces to thereby form a bond.[000139] In one example, the step of hydrophilisingthe silicon carbide nanopowder is followed by the step of separating the hydrophilised silicon carbide nanopowder from any liquids.[000140] In one example, the step of separating the hydrophilised silicon carbide nanopowder from any liquids is followed by washing the hydrophilised silicon carbide nanopowder.[000141] In one example, the step of separatingthe hydrophilised silicon carbide nanopowder from any liquids comprises one or more techniques selected from: centrifugation, decantation, filtration, sedimentation, drying, vacuum drying, freeze drying, magnetic separation, membrane separation, vacuum filtration, and a combination thereof.[000142] In one example, the step of forming the nanoparticle seeded nanopowder is followed by the step of separatingthe nanoparticle seeded nanopowder from any liquids.[000143] In one example, the step of separatingthe nanoparticle seeded nanopowder from any liquids comprises one or more techniques selected from: centrifugation, decantation, filtration, sedimentation, drying, vacuum drying, freeze drying, magnetic separation, membrane separation, vacuum filtration, and a combination thereof.[000144] In one example, the nanoparticle seeded silicon carbide nanopowder is applied as paste.[000145] In one example, the nanoparticle seeded silicon carbide nanopowder is applied as an aqueous paste.[000146] In one example, the bonding step comprises application of pressure greaterthan 0.1MPa.[000147] In one example, the pressure applied in step f is between about 1 MPa and about 30MPa.[000148] In one example, pressure applied in step f is about 10 MPa.[000149] In one example, step f is followed by the step of heating the contacted surfaces in an oxygen containing atmosphere at a temperature exceeding 400 °C.[000150] In one example, the heating of the contacted surfaces is performed at a temperature of between about 400 °C and about 1000 °C.[000151] In one example, the heating of the contacted surfaces is performed at a temperature of about 800 °C.[000152] In one example, the heating of the contacted surfaces is performed for a period greater than about 30 minutes.[000153] In one example, the heating of the contacted surfaces is performed for a period between about 30 minutes and about 48 hours.[000154] In one example, the heating of the contacted surfaces is performed for a period between about 1 hour and about 24 hours.[000155] In one example, the heating of the contacted surfaces is performed for a period that is less than about 6 hours.[000156] In one example, the energy is applied for a period of between about 2 minutes and about 10 minutes.[000157] In one example, the nanoparticles on the silicon carbide nanopowder are silver.[000158] In one example, the heating of the contacted surfaces is performed at about 800°C for a period about 10 hours in an oxygen containing atmosphere.[000159] In one example, the oxygen containing atmosphere is an air atmosphere.[000160] In one example, the oxygen containing atmosphere is at ambient pressure.[000161] In one example the silicon carbide nanopowder is about 99 % pure.[000162] In one example, the silicon carbide nanopowder is substantially spherical.[000163] In one example, the silicon carbide nanopowder has a particle size between about 200 nm and about 2 pm.[000164] In one example, the silicon carbide nanopowder has a particle size about 1 m.Brief description of the figures[000165] Figure 1 shows images of water droplets on a SiC sintered surface prepared according to aspects of the invention.[000166] Figure 2 shows an image of Ni plated SiC substrate showing ASTM D3359 test results.[000167] Figure 3 shows low resolution SEM image and SEM / EDS map of silver seeded surface.[000168] Figure 4 shows high resolution SEM image and SEM / EDS map of silver seeded surface.[000169] Figure 5 shows apparatus to bond SiC surfaces.[000170] Figure 6 shows an image of bonded SiC material.[000171] Figure 7 shows a layered SEM / EDS Image and associated EDS results for silver seeded surface.[000172] Figure 8 shows SEM / EDS map of separated bonded material.[000173] Figure 9 shows a series of SEM / EDS maps of the bonding surface.[000174] Figure 10 shows a cross-section SEM / EDS layered image of a bonding interface.[000175] Figure 11 provides a series of SEM / EDS maps shown surface of a SiC bonded samples using the YAG enhanced process after tensile testing and shows composition and distribution of elements formingthe bond.[000176] Figures 12 A and B provides TG and DSC analysis plots analysing the effect of silver on the SiC bond formation.[000177] Figure 13 shows an SEM of a nanoparticle seeded silicon carbide surface, seeded with silver nanoparticles and which has been plated for a period of about 10 minutes.Detailed description[000178] Any discussion of the prior art throughout the description and / or claims should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.Definitions[000179] Chemical terminologies as used herein have their standard meaning known in the art in accordance with the IUPAC Goldbook, unless explicitly stated.[000180] As used in the description and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.[000181] As used herein throughout the description and the appended claims, the term “about” is intended to mean ± 10 % of the stated value.[000182] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising” and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.[000183] The term “monolayer” as used herein is intended to mean a single, closely packed layer of ions, atoms, molecules.[000184] The present invention is predicated on hydrophilisation of a SiC surface. It has been surprisingly found by the present inventors that use of a hydrophilising agent provides unexpected activation of the SiC surface, which is believed to be superior to the existing art which adopts HF etching.[000185] Without wishing to be bound by theory, it is believed that hydrophilisation of the SiC surface in an acidic solution forms hydroxyl radicals on the SiC surface. The hydrophilised surface is then treated with monovalent metal ions to deposit these monovalent metal ions on the hydrophilised SiC surface as nanoparticles. It isbelieved that the SiC surface is seeded with these nanoparticles. Furthermore, the nanoparticle seeded surface is not believed to be conductive due to the dispersion of the nanoparticles. It should be further appreciated that the nanoparticles are directly bonded to the SiC surface. However, those of skill in the art will also readily appreciate that in depositing metal nanoparticles, this means that a percentage of the SiC surface is available for oxidation reactions.[000186] Referring to Figure 1 , Figure 1 A (101) shows the contact angle of an untreated SiC surface and it can be seen how deionised water beads on an untreated SiC surface. Figure 1 B (102) shows the contact angle of a SiC surface that has been etched using a 10 % aq. HF solution for a period of 1 hour according to the current art. As can be seen in Figure 1 B, deionised water also beads in the SiC surface in a similar fashion to Figure 1 A. Figure 1C (103) shows the contact angle on a SiC surface hydrophilised according to the current invention. As can be seen, the contact angle is very low in comparison to the untreated SiC surface and HF treated surface.[000187] Suitable hydrophilising agents may preferably comprise at least one inorganic oxidising agent and at least one acid, and optionally at least one stabilising agent.[000188] For example, inorganic oxidising agents may be selected from: permanganate salts, such as potassium permanganate (KMnO4); high-valent chlorine compounds, such as HCIO, HCIO4; chromium compounds, such as hexavalent chromium compounds, sodium dichromate (Na2Cr2O7), pyridinium chlorochromate; potassium chlorate; and a combination thereof. The inorganic oxidising agent may be provided having a concentration of between about 0.01 mol / L and about 1 mol / L. Suitable acids may be acids that do not react with the at least one inorganic oxidising agent. That is the inorganic oxidising agents, and the acid must be stable together. This would be readily apparent to those of skill in the art. Suitable acids may be sulfuric acid, phosphoric acid, and a combination of these acids.[000189] Suitable stabilising agents may comprise phosphate and pyrophosphate.[000190] After SiC surface hydrophilisation, the hydrophilised SiC surface may be seeded with nanoparticles according to the present invention.[000191] The seeding with nanoparticles is achieved by contacting the hydrophilised silicon carbide surface with a solution comprising one or more monovalent metal ions. This is done using solutions comprising copper ions, gold ions, lithium ions, potassiumions, rubidium ions, silver ions, sodium ions, and a combination thereof. The solution comprising one or more monovalent metal ions may comprise at least one complexing agent. Without wishing to be bound by theory, the presence of the at least one complexing agent enables for formation of ions which are not normally stable in a monovalent oxidation state. For example, the hydrophilisation step generates hydroxyl ions which are sufficient to the facilitate reduction of the monovalent ion to form nanoparticles. For divalent metal ions (e.g. M2+), the hydroxyl ions would be insufficient to reduce those divalent ions to form metal nanoparticles. As such, the presence of at least one complexing agent achieves the formation of monovalent ions, when divalent ions are present.[000192] Suitable examples of monovalent ion solutions comprise aqueous solutions of silver nitrate (AgNO3) or copper cyanide solutions. These solutions may take the form of a plating bath. The solutions from which the nanoparticles are formed may further have a concentration in a range that is between about 0.001 mol / L and about 1 mol / L.[000193] Once the nanoparticle seeded SiC surface is formed, on removal from the solution comprising the monovalent metal ions, it is dried by the application of external energy. Suitable means for the application of energy to dry would comprise for example, drying in an oven, or drying with a hot airstream. This preferentially done at ambient pressure, i.e. at atmospheric pressure. The temperature at which the nanoparticle seeded SiC surface may be dried may be between about 30 °C to about 120 °C, or between about 60 °C and 120 °C; or about 80 °C. Suitable drying times would also be between a period of between 1 and 5 minutes, preferably 2 minutes.[000194] It will be readily appreciated that due to the inherent nature of seeding a surface, and seeding the SiC surface, the metal nanoparticles cover an area of the SiC surface but also provide for areas of the SiC surface without nanoparticles. The metal nanoparticle on the nanoparticle seeded silicon carbide surface may have a surface area of between about 0.5 cm2and 5 cm2per cm2of silicon carbide area; or about 3 cm2of nanoparticle per cm2of SiC area. The metal nanoparticles may cover a total area of the silicon carbide surface of between about 30% and about 80%; or between about 40% and about 70%; or between about 65 and 50 %; or about 60%. That is, between about 30% and about 80%; or between about 40% and about 70%; or between about 65 and 50 %; or about 60% of the total silicon carbide surface isseeded with the metal nanoparticles. The area that is unseeded is further available for oxidation reactions as part of the bond forming process. That is, the nanoparticle seeded silicon carbide surface has a percentage surface area that is free of metal nanoparticles of between about 20% and about 70%; or between about 30% and about 60%; between about 35% and about 50%; or about 40 %. It is theorized that a surface area ratio of the metal nanoparticles to the SiC, preferably, of about 3 : about 1 is helpful in the formation of a bond; however this may be between about 1.5 : about 1 and about 4.5 : about 1.[000195] Referring to Figure 3, A and B, Figure 3 depicts a SEM image (301 ) of a nanoparticle seeded SiC surface prepared according to the inventions, in this specific case, a silver nanoparticle seeded SiC surface. This shows that the nanoparticles seeded SiC surface contains well adhered silver nanoparticles. The nanoparticle seed may be concentrated on intergranular boundaries of the SiC surface (see 303). The silver nanoparticle seeds may also agglomerate on the hydrophilised SiC surface (see 305). SEM / EDS map as shown in Figure 3B (302) highlights the formed nanoparticles (in this case silver) on the surface - light areas in the SEM image relates to silver nanoparticles. The SEM / EDS map, see Figure 3B (302), also shows a wide distribution of silver nanoparticles over the hydrophilised SiC surface, 304.[000196] Without wishing to be bound by theory the inventors believe that hydrophilisation develops surface hydroxyl groups, specifically on carbon atoms present on the SiC surface. The hydroxyl groups are believed to reduce the monovalent metal ions such as silver ions. And, as such, the monovalent metal ions covalently bond to the carbon to seed the hydrophilised SiC surface. However as described above, monovalent metal ions can be formed from typically divalent ions when at least one complexing agent is used in the solution comprising the monovalent metal ions.[000197] Furthermore, when using sintered SiC surfaces, intergranular boundaries of the sintered SiC surface comprise more exposed carbon compared to crystalline silicon carbide, and consequently, concentrate the metal nanoparticle seed such as silver nanoparticles, 303 of Figure 3. The EDS analysis for this surface shown in Table 1, detected 6.56 wt. % Ag.Table 1 ; SEM / EDS of Ag SiC seeded surface[000198] In certain examples of the present invention, the nanoparticle seeded SiC surface may be further metallised to develop a plated surface.[000199] To substantially, completely, or partially metallise a surface, the nanoparticle seeded SiC surface is contacted with an electroless plating bath, which deposits a first metal plating surface on the nanoparticle seeded SiC surface to form the first metal plating surface. The monovalent metal ions may form nanoparticles which are covalently bonded to the hydrophilised SiC surface. The nanoparticles act as seeds on which the first metal plating surface is deposited from the electroless plating solution.[000200] The electroless plating solution may include an electroless nickel bath, an electroless copper bath, an electroless silver bath, or any electroless bath compatible with the nanoparticle seeded SiC surface. Suitable electroless plating solutions would be readily apparent to one of skill in the art. For example, if a nickel electroplated surface as the conductive surface is desired, an electroless nickel boron plating solution may be selected.[000201] The first metal plating surface may have a thickness between about 0.5 pm to 2 pm, preferably 1 pm, or a thickness sufficient to form a continuous plating surface over the nanoparticle seeded silicon carbide surface. The feature of the first metal plating surface being continuous imparts conductivity. Plating surfaces having this thickness range are preferred so as to minimise the deposition time, however those of skill in the art will appreciate that this can be varied depending on the thickness desired forthe plating surface, and the intended end application. Furthermore, aplating surface of this thickness provides for effective bonding to the nanoparticle seeded SiC surface.[000202] The first metal plating surface may be further conditioned to increase bonding strength between the first metal plating surface and the nanoparticle seeded SiC surface.[000203] Conditioning may be performed at low temperature, between about 60 °C and about 200 °C preferably less than about 100 °C for between about 1 hour and about 24 hours, preferably between about 2 and about 10 hours, more preferably about 6 hours. Conditioned metal surfaces are then optionally re-immersed in the electroless plating solution for about 2 to about 5 minutes before undergoing electrolytic plating to form second plating surface.[000204] The second plating surface may comprise any metal coating in any thickness as required by the intended end use. Figure 2, for example shows a SiC surface that has been plated with a 1 pm electroless nickel-boron coating after being seeded with silver and a 5 pm semi-bright nickel surface. The nickel-boron coating was conditioned for 24 hours before depositing the semi-bright nickel. Adhesion of the nickel coating in Figure 2, 201 was tested according to the process specified in ASTM D3359 and showed excellent (5B) adhesion between the SiC surface and metal layers, which was determined by no peel of scribed metal squares.[000205] In certain examples, the nanoparticle seeded SiC surface may also function as an interstitial layer which may facilitate the bonding of two SiC surfaces. In such examples, the monovalent ions are preferred to be silver. Without wishing to be bound by theory, intimate contact, facilitated by the interstitial layer, between surfaces to be bonded may enhance bonding.[000206] Referring to Figure 13, Figure 13 shows a preferred nanoparticle seeded SiC surface to provide an interstitial layer which facilitates bonding of two SiC surfaces. As seen, the nanoparticle seeded SiC surface comprises a high surface area of nanoparticles with areas of the SiC surface available to form the bond through oxidation reaction(s). Preferably the nanoparticles cover between about 40% and about 70% of the total SiC surface area, preferably about 60% . Preferably, there is a surface area ratio of nanoparticle to SiC surface of between about 1.5 : 1 and about 4.5 : 1.Preferably, there is a surface area ratio of nanoparticle : SiC surface of about 3: about 1.[000207] Furthermore, pre-treating SiC surfaces prior to the hydrophilisation step may improve the bonding facet contact. Pre-treatment, such as polishing is believed to lower surface roughness (Ra). A surface roughness of about 0.2 pm is preferred. Appropriate pre-treatment may also increase surface flatness. A flatness, AFrms of 1 pm is also preferred. Increasing the thickness of the interstitial layer, especially where the interstitial metal is soft, like silver, also increases the surface contact. Preferably, the nanoparticle is plated on one of the two contact surfaces. Preferably, the interstitial layer is a deposit of electroless silver of between 0.2 pm and 2 pm, preferably 0.05 pm.[000208] It will be appreciated that the monovalent metal such as silver or other metal (seeded or plated) does not form a strong bond between the SiC surface but rather facilitates the development of a bond by acting as a catalyst. Without wishing to be bound by theory, the present inventors theorise that the following reactions occur:Ag(s)+O2(g AgO2(s) (1)2AgO2(s) 2AgO(s) + 20 (2)AgO(s Ag(s) + O (3)SiC(s)+4O^ SiO2(s) +CO2(g) (4)[000209] Without wishing to be bound by theory, the inventors have surprisingly established that the silver nanoparticles or the silver-plating acts as a catalyst for formation of silica, which creates the bond through the above-mentioned oxidation reactions. Excessive silver on the SiC surface lowers the bond strength by reducing the SiC surface area available to be oxidised. Furthermore, a higher Ag surface area, such as that provided by silver nanoparticles increases the rate of SiC decomposition and Si oxidation. As the silver nanoparticles or the plating is thermally oxidised, the silver particle size decreases via reaction (2) above, the melting temperature of the silver is also decreased. Consequently, nanosilver escapes the bond interface. However, silver is required to facilitate developing complete, substantial or partial coverage of the contacting surfaces with SiO2, to create the bond.[000210] It will be further appreciated that inclusion of oxidation accelerators such alkali metal ions, can speed up reactions (1 ) - (3) above. Suitable alkali metal ions may be provided as a solution comprising one or more alkali metal ions selected from: sodium ions (Na+), potassium ions (K+), rubidium ions (Rb+), caesium ions (Cs+), and a combination thereof.[000211] It will be further appreciated that the monovalent metal, such as silver, can catalyse other oxidation reactions and that the introduction of additional elements into the bonding interfaces can strengthen the bond by diffusing into the SiC matrix. For example, it is known in the art that materials such as yttrium, aluminium, titanium, silicon, magnesium and calcium can assist the formation of strong SiC bonds at elevated temperatures and pressures, typically in a vacuum. However, the present inventors have established that introduction of these materials as a filler such as a SOL into the bond between two SiC surfaces comprising nanoparticles or a plating of a monovalent ions (such as silver) allows strong bonds to form at lower temperatures and pressures.[000212] One example of such a SOL filler, which is a precursor to an Yttrium Alumina Garnet (YAG), comprises ratios of: 6.16 g of aluminium-tri-sec butoxide, 5.75 g of yttrium nitrate, 1.25 g of acetylacetone and 50 mL of ethanol. Those of skill in the art will appreciate that this SOL can be suitably scaled as required. Partial, substantial, or complete hydrolysis of the SOL on the SiC bonding surface to produce a gel by heating at about 80 °C for about 20 minutes improves its effectiveness. Normally YAG forms at temperatures above 1300 °C. However, the present inventors have established that a filler such as YAG bonding layer is formed well below typical temperatures in the presence of silver nanoparticles or a silver plating on a SiC surface.[000213] It will be appreciated that application of pressure also further facilitates bonding between the nanoparticle seeded SiC or the plated surfaces. Figure 5 for example shows a schematic of an apparatus for applying pressure to bond surfaces. Here, the two nanoparticle seeded SiC surfaces, or a nanoparticle seeded and first metal plated surface 504 are contacted. Pressure is applied from between two stainless steel plates 502 by four bolts and nuts 503. Those of skill in the art will appreciate that the plates used to apply pressure do not need to be stainless steel, provided they are suited to the conditions. The bolts specifically used in this system haveBelville washers under the nuts to maintain the pressure when the bolts lengthen in the oven. Tightening the nuts uniformly applies a calibrated pressure over the bonding surfaces. A bonding pressure of about 10 MPa is preferred although bonding pressures of between about 1 MPa and about 40 MPa are effective. Tightening the nuts to about 2 NM produces the appropriate contact force between the surfaces 504. The preferred metal coating thickness on one surface is sufficient to fill any voids caused by unevenness on the surface and the compression force is sufficient to mechanically migrate the deposited metal to create an intimate metal SiC interface[000214] The inventors of the present invention have further ascertained that excessive contact force between bonding surfaces eliminates oxygen diffusion routes into the hermetically sealed diffusion bond which results in formation of a weaker bond. Conversely, too little contact force prevents development of a strong hermetically sealed diffusion bond since there is insufficient formation of oxide to bridge any gap between contacted SiC surfaces 504. Apparatus 500 is subsequently placed in an electric furnace to heat the contacted SiC surfaces to a temperature of between about 600°Cto 1000 °C, preferably about 700 °C to about 850 °C, more preferably 800°C to bond the contacted SiC surfaces . Without wishing to be bound by theory, the temperature selected should be close to but below the melting point of the nanoparticle seed for efficient bonding while not creating substantial grain change in the SiC.[000215] Those of skill in the art will readily appreciate that adopting an electric furnace is not mandatory for any of the heating steps, and any method of heating the contacted SiC surfaces to the appropriate temperature is sufficient for the heating steps described above. For example, an induction heating system could be used instead of an electric furnace. In certain examples of the current invention, the temperature of the substrates 501 of Figure 5 is ramped to prevent excessive thermal stress and cracking of the substrates. The ramping temperature may be from about room temperature to up to about 1000 °C and may be ramped at a rate of about 4-10 °C per minute, preferably about 5 °C / minute. It will be appreciated that bond formation occurs over time as the monovalent metal ions form nanoparticles on the hydrophilised SiC surface, and oxidation occurs.[000216] Figure 7 shows and SEM / EDS of a partially bonded silver nanoparticle seeded SiC surface and first silver-plated SiC surface. Here, the SiC surface comprises silver nanoparticles with oxygen rich interfaces, 703, shown as dots on the metal surface. This demonstrates oxidation occurs during the process. Growth of nanoparticles from the monovalent metal ions is fostered by electrons from adjacent surface hydroxyl groups. During the reduction step of the process monovalent metal ions form nanoparticles. And, during bonding the nanoparticles grow by diffusion of the monovalent metal ions to adjacent nanoparticles or the first metal plating surface. The nanoparticle seeded surface may be fully or partially decorated with carbon, as shown in 703 in an EDS overlay map 700. This is virtually coincident with the oxygen and shows that carbon also migrates to the surface of nanoparticle seeded surface during bonding. Without wishing to be bound by theory, this carbon migration is believed to provide a mechanism for the nanoparticle to diffuse into the SiC. Finally, the area 704 of the overlay EDS map 700 shows an area of unbonded SiC. Image 701 of FIG. 7 shows the associated EDS spectrum from the SEM / EDS analysis.[000217] Figure 6 shows an image of two 2 cm x 2 cm sintered silicon carbide blocks, 602, bonded using the process of the invention. The bonded interface is denoted 601.[000218] Figure 8 shows SEM / EDS results of elemental analysis which validates the nature of the SiC-SiC bond a layer as catalytically developed SiO2. The bonded blocks 602 of Figure 6 were cut with a diamond saw to expose the bonded interface. A focussed ion beam (FIB) created a 7 pm xIO pm trench, 805, exposing a section of the interface allowing nature to the bond to be examined. The features of the interface are labelled 801 ,802, 803 and 804. The EDS / Map shows a metal nanoparticle, in this case silver, 801 , that has migrated into the SiC, to about 500 nm beneath the SiC surface. The high silicon / oxygen content at the bond interface 802, shows the development of SiO2at the bond interface replacing the silver deposited by the metal seeding a plating process described above.[000219] Silicon dioxide provides high bonding strength approaching the fracture strength of silicon carbide. Here the joint sections where the completely bridges the interface, 803, provide a strong bond. While the areas where SiO2does not completely fill the interface a less strong bond. Without wishing to be bound by theory the inventors believe that degree of bonding is determined by the surface topology of the bondedinterface the thickness of the metal plated layer, the bond between the metal seed layer and the SiC, the temperature and time of the bonding process.[000220] Figure 9 shows a series of SEM / EDS maps of the bonding surface, i.e. the interface 601 of Figure. 6. SiC blocks, i.e. the blocks 602 of Figure 6 were separated and the surfaces imaged using SEM EDS. Each surface was baked in an over for a different time with 901 being 6 hours, 902 being 14 hours and 903 being 24 hours. The maps show evolution of the nanoparticles during the bonding process. At time 0, nanoparticles substantially cover the surface (not shown). As the bonding process develops the nanoparticles contract to smaller and smaller islands and diffuse into the SiC (as seen in in 801 of Figure 8). As the nanoparticles contract and diffuse oxygen (O2) is drawn onto the surface and is disassociated by the exposed metal to become atomic oxygen (O) which reacts with any exposed SiC to form Si-O-Si and SiO2which bonds the two surfaces. Composite SEM / EDS map mages 904 and 905 of Figure 9 show an increase oxygen in the interface, initially around the metal islands (904) and later filling the interface and covering the metal islands (905).Examples[000221] Reagents and solvents used herein were purchased from commercially available suppliers.1. Hydrophilised SiC Surface Preparation[000222] A 0.5 cm thick SiC surface was cut into five 2.5 cm x 2.5 cm portions. One surface of the substrate was pre-treated by polishing using a diamond paste to achieve a surface finish roughness (Ra) of 1 and a flatness A Frms of between about 0.5 pm-1 pm.[000223] After polishing, each SiC surface was cleaned in an ultrasonic bath containing IPA for 15 minutes.[000224] Each SiC surface was independently subjected to hydrophilisation using one bath selected from a-e.a. as received, unpolished SiC substrate - no treatment,b. cleaned SiC substrate, where the surface was degreased in NH4OH / H2O2ZH2O1:1:5at 65 °C,c. 10 % aq. HF solution,d. a permanganate-HF solution comprising:- KMnO420 g / L, 40 % aq. H2SO4and 1% by volume of concentrated HF (48%),e. permanganate - KMnO420 g / L + 40 % H2SO4.[000225] Bath d. containing permanganate was prepared by dissolving the KMnO4in deionised water and adding a concentrated sulphuric acid (98 %) dropwise to the bath during the hydrophilisation process until the acid concentration reached the desired value. The process was continued until the time noted.[000226] In the case of the HF-Permanganate bath, HF was added to the DI water before the permanganate was dissolved.[000227] Contact angles were calculated by imaging the hydrophilised surfaces with 0.05 mL of water against an opaque lighted white background. The images were processed with ImageJ to calculate the angle, and the results are shown in Figure 1 and Table 2.Table 2: Hydrophilisation experiments2. Silver Nanoparticle Seeded Surface Preparation[000228] Sintered SiC surfaces were hydrophilised according to Table 2, Test 7 above. The hydrophilised surfaces were suspended in a bath comprising 10 g / L silver nitrate (AgNO3) solution at room temperature for 10 minutes followed by hot air drying at around 80 °C for 2 minutes to form a silver nanoparticle seeded SiC surface.[000229] The nanoparticle seeded surfaces were examined by SEM / EDS to determine the distribution of silver nanoparticles on the surface. The SEM images Figure 3, 303 show silver concentrated in the intergranular boundaries of the sintered SiC surface and shows, 304, a good distribution of silver nanoparticles across the SiC surface.[000230] Silver plating the nanoparticle seeded surface as, described in example 3 fora period of 10 minutes increases the size of the nanoparticle seeds to a preferred size for SiC- to-SiC bonding. Figure 13 shows a SEM image of a nanoparticle seeded surface preferred for bonding. Here the silver particles (white area) range in size from about 10 nm to over 1 micron with the average size being about 300 nm. The available reaction (oxidation) surface of the SiC (dark area) is about 40% of the total SiC surface area with the remainder covered by silver nanoparticles. The high surface area of the silver nanoparticles provides a silver reaction(oxidation) area that is about 3 times that of the SiC.3. Silver Plated Surface Preparation[000231] Silver nanoparticle seeded SiC surfaces prepared according to example 2 above and were plated to form a first metal plating surface for 20 minutes at room temperature in an electroless Ag plating bath comprising:- AgNC310g / L- KOH 6g / L- 28% NH4OH 60mL / L- Ethylenediamine 20mL / L- Ethanol 40 mL / L- Na gluconate 8g / L- K Na tartrate 2.5g / L[000232] The plating produced a uniform first metal plating surface of silver of approximately 1 micrometre.[000233] The surfaces were then conditioned at a temperature of 80 °C for between 24 and 48 hours to improve adhesion, however the surface as plated with silver was sufficient.[000234] Adhesion of the silver first metal plating surface was tested following the procedure outlined in ASTM-D3359. The 5B performance demonstrates good adhesion between the silver and the nanoparticle seeded SiC surface, Figure 2.4. Nickel Plated Surface Preparation[000235] Silver nanoparticle seeded SiC surfaces were prepared according to example 2above and were electroless nickel plated in a solution comprisingNiSO4.6H2O 50 g / L- Na4P2O7100 g / L- 28 %aq. NH4OH 40 mL / L- DMAB (as a reducing agent) 1.5 g / L.[000236] The bath temperature was maintained at 32°C and plating was conducted for 10 minutes to provide nickel first metal plating surface.[000237] The nickel-plated surface was rinsed in DI water and conditioned in an oven at 80°C for 48 hours to improve the adhesion between the nickel and the nanoparticle seeded SiC surface.[000238] The conditioned nickel-plated surfaces were then plated in a commercial semi- bright nickel-plating solution at 60 °C for 5 minutes at 5 A / dm2to deposit about 2 pms of semi-bright nickel to provide the second plating surface.[000239] After rinsing the second plating surface was further plated in a commercial bright nickel-plating solution 60°C for 5 minutes at 2 A / dm2, to deposit about 1 pm of bright nickel to deposit a third plating surface.[000240] The plated surfaces were adhesion tested according to ASTM D3359 with the result shown in Figure 2 as 5B adhesion.5. Gold Plated Surface Preparation[000241] Nickel plated surfaces were prepared according to above and were electroplated with gold in a 40 °C commercial gold cyanide bath at 1 A / dm2for 5 mins to produce a bright gold surface on the nickel surface.6. SiC / SiC Bonding Examples[000242] 2.5 cm x 2.5 cm x 0.5 cm SiC substrates of polished sintered silicon carbide were identically prepared as in example 1.7 above. Substrate pairs were selected for coplanarity by evaluating the strength of the Casimir effect between the surfaces.[000243] As described, some experiments adopted 2 cm x 2 cm pre-ground SiC substrates 0.8 cm thick, here the purchased specification included an Ra of 0.2 microns and a coplanarity or surface levelness of 1 micron.[000244] The surface pairs are shown in Table 3 below where the entries denote the treatment of each surface. The treatments were:- A- 2.5 cm substrates as noted above,- B- 2 cm substrates as noted above,- H - hydrophilisation only,- NP - nano particle seeded surface as explained in example 2 above,- Ag surface electroless plated with silver as explained in example 3 above (with the silver thickness is microns noted),- YAG - Hydrophilised surface treated with SOL which was cured at 80°C for 20 minutes priorto bonding, Table 3 shows the mL / cm2of SOL.[000245] NP and silver surfaces were oxidised by placing in an oven at 200 degrees for 30 minutes before joining.[000246] The surface pairs were clamped immediately in clamping apparatus after preparation and clamped with a force of about 10 MPa shown in Figure 5. The clamping force was provided by bolts and Belville washers to maintain the joining force at temperature.[000247] The contacted SiC pairs were placed in a furnace in an air atmosphere and the temperature was ramped to the target temperature over 2 hours to prevent thermal stresses.[000248] Sample pairs were maintained at the target temperature for the times shown in Table 3. At the end of the time period, the oven was turned off and the pairs allowed to return the room temperature.[000249] The clamping apparatus was carefully removed, and bond strength of sample pairs were tested using a sheer test apparatus. The maximum force to break the bond was recorded and converted to MPa as reported in Table 3.[000250] The de-bonded surfaces were analysed optically and using SEM to estimate the bond surface percentage as reported in Table 3.[000251 ] Successfully bonded samples were repeated and cross section prepared to evaluate the penetration of the bond into the substrate using SEM-EDS with the results reported in Table 3.Table 3[000252] It has been surprisingly established that successful bonding depends on four factors:(1 ) the presence of nanoparticles (e.g. silver) on one or more of the SiC surfaces to be bonded; (2) the availability of any exposed silicon carbide on one or more of the surfaces to be bonded; (3) the temperature; and (4) the time at temperature. Without wishing to be bound by theory, the inventors believe that oxidised nanoparticles (e.g. silver) have a lower melting temperature than pure silver. Thus, the nanoparticles melt, and the silver and oxygen disassociate releasing oxygen atoms. The oxygen atoms react with exposed SiC surface, oxidising both silicon and carbon. The oxidisation creates the bond, and the oxidised carbon creates carbon monoxide or carbon dioxide, which is believed to escape from the bonding surface. The newly exposed metal surface is immediately re-oxidised by oxygen molecules diffusing intothe bonding surface. Some of the metallic silver volatilised and escape from the bonded interface while other silver diffuses into the SiC matrix.[000253] The process progress is demonstrated by Figure 9, where over time the amount of silver and carbon on the bonding surface decreased, 901 to 903, while the quantity of oxygen increases, 904 and 905.[000254] The results in Table 3 demonstrate the effect of the processing parameters on the Si- O-Si bond formation. Firstly, while bonds form at all joining pressures, the percentage of the area bonded depends on the pressure, as shown in Table 3, rows 1-4.[000255] Without wishing to be bound by theory, the inventors believe that as the pressure applied to bond the surfaces increases, the gap between the SiC surfaces decreases on average and the bonded area increases. Substrate B bonding in Table 3, rows 11 and 12 show a more bonded area is produced despite a lower bonding pressure. It is believed that substrate flatness of < 1 micron contributed to the extent of bonding.[000256] Referring to Figure 10, 1004 shows a cross-section SEM / EDS map of a bond between two polished SiC substrates, 1001 and 1004. Here the bond dimension, 1003 is about 400 nm which suggests that the thickness of the SiC formed spans narrow interfacial gaps.[000257] Table 3, rows 12 and 13 show the effect of silver concentration on the bonding surfaces. The experiment reported in Row 13 produced a lower bonding area compared to that in row 12 which has less silver. The inventors believe that silver plays a limited role in bond strength. It is currently believed that silver remaining in the bonded area may detract from the bonding area. Thus, the strength of the bond and the % bonded area are believed to depend on the ability of silver to escape from the bond interface.[000258] Row 1 and row 12 of Table 3 demonstrate the impact of the substrate in providing an escape route from the bond interface for the silver. Substrate A had a higher porosity than substrate B and allowed easier escape for the silver which produces a higher bond strength per unit area.[000259] Table 3, row 14 demonstrates the impact of introducing a filler into the bonding interface. A partially gelled SOL precursor to Yttrium Aluminium Garnet (YAG) wasintroduced onto the hydrophilised surface of a SiC bonding pair. 0.05 mL of the SOL per cm2of bonding surface was utilised. The inventors surprisingly established that the YAG SOL filler improved bonding through two mechanisms. Firstly, the YAG facilitated the escape of silver from the bond interface with silver accumulating at the bond edge. In row 14, the quantity of silver on the bonded surface reduced by about 80 % from that in row 12. Secondly, the YAG contributed to the bonding process.[000260] Figure 11 shows a series of SEM / EDS maps of the bonding surface after debonding during tensile testing. Here, the individual maps are carbon (1101), oxygen (1102), aluminium (1103), silicon (1104), yttrium (1105), and silver 1106. Figure 11, (1108) provides individual counts for each element. About 6 wt. % silver was uniformly plated on one of the two bonding surfaces (Table 1), and the YAG precursor was uniformly spread on the other surface. After bonding the silver was reduced and the silver was partially or substantially expelled from the bond interface. Furthermore, any remaining silver became concentrated in islands having clear boundaries (1107) shown between the islands and the bonded area. It was ascertained that the bonded area comprises about 60 % of the sample surface, and the bond was poor in carbon but rich is silicon, yttrium, and oxygen. The present inventors believe that the bond is a combined ceramic oxide diffused into the SiC matrix which provides a strength of about 148 MPa (see Table 3, row 14), and shows superior bond strength.7. Bonding Mechanism Examination[000261] To examine the reactions involved in developing the SiC-to-SiC bond,thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis of powders containing the bonding materials was carried out.[000262] Three TG / DSC sample powders were prepared, each containing 10-micron SiC particles (purchased from Sigma Aldrich), 50 nm silver particles (purchased from Novacentrix), and dried YAG sol residue (described below).[000263] The YAG sol was prepared by dissolving separately, 5.75g of Y(NO3)3in 25 mLof ethanol, and 6.16g of aluminium tri-sec butoxide (ATSB) in 25 mL of ethanol. 1.25g of acetylacetone was mixed into the ATSB ethanol solution. The Y(NO3) ethanolic solution and the ATSB solutions were gradually combined in a solution with stirring at 55°C for 1 hour. The combined solution was hydrolysed by gradually adding 1.8 mL ofdeionised water, and the volume of water adjusted as required to prevent rapid gelation of the YAG sol.[000264] The sample powders were prepared by heating 10 mLof the YAG sol in a beaker at 80°C for 2 hours to gel and then dehydrated. The dehydrated SOL from the bottom of the beaker was collected and ground in a mortar to produce a powder.[000265] The powder combinations were prepared, in the ratios indicated:1) SiC powder with Ag powder (2:1),2) SiC powder with Y-Al sol-gel powder and Ag powder (2:1:1),3) SiC powder with Y-Al sol-gel powder (2:1) as a reference.[000266] The above SiC powder combinations 1), 2) and 3) were each placed in a TG crucible, and TG / DSC analysis was performed at temperatures between room temperature and about 950 °C in ambient atmosphere, at a scanning rate of about 10 °C per minute.[000267] Figure 12 A and B shows the TG / DSC analysis results. Curves 1202 relates to 1) SiC / Ag; 1203 relates to 2) SiC / sol / Ag; and 1204 relates to 3) sol / SiC.[000268] Figure 12B shows the DSC analysis with three regions of interest, which are identified as 1206, 1207, 1208 and 1209. The DSC curves are identified usingthe same numbering as the TG in Figure 12A.[000269] Feature 1206 shows significant weight loss and heat absorption in samples 2) and 3) containing Y-Al sol-gel powders. This is attributed to the release of outer-layer water content from aluminum hydroxide and yttrium hydroxide.[000270] Figure 12A shows a gradual weight loss from samples, up to a temperature of about 400 °C. Without wishing to be bound by any theory, this is theorized to be due to loss of lattice-bound hydroxyl groups from the activated SiC surface. However, sample 1) exhibits minimal weight change in this region, which is theorised to be due to oxidation of Ag.[000271] Figure 12B, and feature 1207 indicates thermal oxidation reactions of Ag at around 280 °C, which is accompanied by minor weight loss. An additional, unidentified peak is shown at around 320 °C without any significant weight change.[000272] As described above, the theorized oxidation reactions, are believed to be:Ag(s)+O2(g) - AgO2(s) (1)2AgO2(s) - 2AgO(s) + 20 (2)AgO(s) — >■ Ag(s) +O (3)[000273] Without wishing to be bound by theory, it is theorised that the reaction pathway likely involves initial formation of atomic oxygen (O) before the emergence of molecular oxygen (O2), thereby increasing local oxygen activity. Due to its more negative standard Gibbs free energy of oxide formation compared to silver, silicon carbide can preferentially react with the atomic oxygen prior to its release of O2gas:SiC(s)+4O— ► SiO2(s) +CO2(g) (4)[000274] Figure 12B, feature 1208 shows ongoing decomposition of Ag2O, production of SiO2, and release of CO2with minor weight loss.[000275] Arrow 1210 in Figure 12B indicates that the Y-Al sol-gel delays decomposition of Ag2O from about 420 °C to about 480 °C.[000276] A weight increase in the SiC + Ag powder sample (1) -1202 of Figure 12), above about 600 °C, as well as the heat absorption peak between 550 °C and 700 °C, are theorised to be associated with ongoing absorption of oxygen and elimination of carbon from the SiC surface through reactions (1) -(4) identified above.[000277] Minor heat absorption peak at feature 1209, in Figure 12B, is associated with the YAG phase transformation. This peak is absent from samples 1) and 2) containing Ag and indicates that silver delays YAG formation. Without wishing to be bound by theory, it is possible that YAG formation occurs above 950 °C, which is beyond the testing range.[000278] Where reference has been made to integers having known equivalents thereof, those equivalents are herein incorporated as if individually set forth. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is appreciated that further modifications may be made to the invention as described herein without departing from the spirit and scope of the invention.References[000279] Preston, A., Mueller, G., Bonding SiC to SiC Using a Sodium Silicate Solution. Int J Appl Ceram Technol. 2012, 8(4) 764-774, https: / / doi.Org / 10.1111 / j.1744- 7402.2011.02644.x[000280] Hijikata, D. G. (2016). Unified theory of silicon carbide oxidation based on the Si and C emission Mode. J of Phys D: Appl. Phys.[000281] Matsuda, T., Inami, K., Motoyama, K., Sano, T., & Hirose, A. (2018). Silver oxide decomposition mediated direct bonding of silicon-based materials. Scientific Reports, 8(1). https: / / doi.org / 10.1038 / s41598-018-28788-x

Claims

Claims1. A process to create a nanoparticle seeded surface on a silicon carbide (SiC) surface, the process comprising the steps of:a. providing a silicon carbide surface;b. optionally pre-treating the silicon carbide surface;c. hydrophilisingthe silicon carbide surface with a hydrophilising agent to form a hydrophilised silicon carbide surface;d. contacting the hydrophilised silicon carbide surface with a solution comprising one or more monovalent metal ions;e. reducing the one or more monovalent metal ions to form metal nanoparticles on the hydrophilised silicon carbide surface by the application of energy to the one or more monovalent metal ions and the hydrophilised silicon carbide surface; to provide the nanoparticle seeded silicon carbide surface.

2. The process according to claim 1 , wherein the silicon carbide surface may be selected from the group comprising: sintered silicon carbide surface, sintered silicon carbide fibre composite, crystalline silicon carbide surface, and silicon carbide nanopowder.

3. The process according to claim 1 or claim 2, wherein the optional pre-treatment step comprises one or more techniques selected from: polishingthe silicon carbide surface with a polishing media having a hardness value greater than silicon carbide; etching the silicon carbide surface; and a combination thereof.

4. The process according to claim 3, wherein polishing the silicon carbide surface comprises grinding the silicon carbide surface once or a plurality of times.

5. The process according to any one of claims 2 - 3, wherein polishing the silicon carbide surface comprises polishing with a polishing media at about 6 pm, about 3 pm, or about 1 pm.

6. The process according to any one of claims 2-5, wherein polishing the silicon carbide surface comprises polishing successively with a polishing media at about 6 pm, then about 3 pm, and then about 1 pm.

7. The process according to any one of claims 2-6, wherein the polishing media comprises diamond.

8. The process according to any one of claims 2-7, wherein the polishing media is a diamond paste.

9. The process according to any one of claims 2-8, wherein etching the silicon carbide surface comprises immersing the silicon carbide surface in one or more of the following solutions:i. ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2) and water (H2O); ii. hydrochloric acid, hydrogen peroxide (H2O2) and water (H2O); iii. sulfuric acid (H2SO4) and hydrogen peroxide (H2O2);iv. hydrofluoric acid;v. nitric acid; anda combination thereof.

10. The process according to anyone of claims 1 -9, wherein the pre-treatment step comprises providing a surface roughness value of Ra <3.

11. The process according to any one of claims 1 -10, wherein the pre-treatment step comprises providing a surface roughness value of Ra <1.

12. The process according to anyone of claims 1 -11, wherein the pre-treatment step comprises providing a surface flatness value of AFrms of about 3.

13. The process according to anyone of claims 1 -12, wherein the pre-treatment step comprises providing a surface flatness value of AFrms of about 2.

14. The process according to anyone of claims 1 -13, wherein the pre-treatment step comprises providing a surface flatness value of AFrms of about 1.

15. The process according to anyone of claims 1 -14, wherein the hydro hilising agent comprises: at least one inorganic oxidising agent and at least one acid.

16. The process according to anyone of claims 1 -15, wherein the hydrophilising agent forms a hydroxyl moiety on the silicon carbide surface.

17. The process according to anyone of claims 1 -16, wherein the at least one inorganic oxidising agent is selected from a compound having a standard reduction potential above +1.23eV.

18. The process according to claim 17, wherein the at least one inorganic oxidising agent is selected from permanganate salts, potassium permanganate (KMnO4); high-valent chlorine compounds, HCIO, HCIO4; chromium compounds, hexavalent chromium compounds, sodium dichromate (Na2Cr2O7), pyridinium chlorochromate; potassium chlorate; and a combination thereof.

19. The process according to anyone of claims 15 - 18, wherein the at least one inorganic oxidising agent is provided having a concentration of between about 0.01 mol / L and about 1 mol / L.

20. The process according to anyone of claims 15-19, wherein the at least one acid is a mineral acid that does not react with the at least one oxidising agent.

21. The process according to anyone of claims 15-20, wherein the at least one acid is selected from: phosphoric acid, sulfuric acid, and a combination thereof.

22. The process according to anyone of claims 15-21, the at least one acid is an aqueous acid.

23. The process according to claim 22, wherein the aqueous acid comprises a concentration of between about 10 % and about 60 %.

24. The process according to claim 22 or 23, wherein the aqueous acid comprises a concentration of about 10 %, about 20 %, about 30 %, about 40 %, about 50 %, or about 60 %.

25. The process according to anyone of claims 1- 24, wherein the hydrophilising agent further comprises at least one stabilising agent.

26. The process according to anyone of claims 1- 25, the hydrophilising agent comprises:i. at least one permanganate compound,ii. at least one acid; andiii. at least one stabilising agent.

27. The process according to anyone of claims 25 or 26, wherein the at least one stabilising agent is selected from phosphorus containing species, such as phosphate, phosphonate, and pyrophosphate.

28. The process according to anyone of claims 25 - 27, wherein the at least one stabilising agent comprises a concentration of between about 0.01 mol / L and about 1 mol / L.

29. The process according to anyone of claims 1 -28, wherein the hydrophilising agent comprises:i. KMnO4at a concentration of about 20 g / L (about 0.1 mol / L); andii. about 40 % aq. H2SO4; andiii. Na4P2O7at a concentration of about 20 g / L (about 0.08 mol / L); oriv. Na3PO4.12H2O at a concentration of about 200 g / L (about 0.6 mol / L); or v. C2H6Na2O7P2at a concentration of about 24 g / L (about 0.1 mol / L); or vi. Na2PO3CH2at a concentration of about 13 g / L (about 0.1 mol / L).

30. The process according to anyone of claims 1 -29, wherein the hydrophilisation step comprises a period of between about 30 minutes and about 90 minutes.

31. The process according to anyone of claims 1 -30, wherein the hydrophilisation step comprises a period of about 60 minutes.

32. The process according to anyone of claims 1 -31 , wherein the hydrophilisation step is performed at a temperature between about 10 °C and about 30 °C.

33. The process according to anyone of claims 1 -32, wherein the solution comprising the one or more monovalent metal ions further comprises at least one complexing agent selected from ammonia, cyanide, ethylenediamine, pyridine, and ethylenediamine tetraacetic acid (EDTA).

34. The process according to anyone of claims 1 -32, wherein the solution comprising the one or more monovalent metal ions comprises at least one complexing agent that is a hydroxide containing species.

35. The process according to anyone of claims 1 -34, wherein at least one complexing agent may be the same or different from the at least one stabilisation agent used in the hydrophilisation step.

36. The process according to anyone of claims 1 -35, wherein the solution comprising the one or more monovalent metal ions further comprises a surfactant selected from: polyvinylpyrrolidinone (PVP), sodium dodecyl sulfate (SDS), sodium laureth sulfate (SLS), polyvinyl alcohol (PVA), cetrimonium bromide (CTAB), polyethylene glycol (PEG), Tween-20 (also known as polysorbate 20), and a combination thereof.

37. The process according to anyone of claims 1 -36, wherein the solution comprising the one or more monovalent metal ions is provided as an aqueous solution.

38. The process according to anyone of claims 1 -37, wherein the solution comprising the one or more monovalent metal ions has a concentration of the one or more monovalent metal ions between about 0.001 mol / L and about 1 mol / L.

39. The process according to anyone of claims 1 -38, wherein the solution comprising the one or more monovalent metal ions has a concentration of the one or more monovalent metal ions between about 0.005 mol / L and about 0.1 mol / L.

40. The process according to anyone of claims 1 -39, wherein the one or more monovalent metal ions may be selected from: copper ions, gold ions, lithium ions, potassium ions, rubidium ions, silver ions, sodium ions, and a combination thereof.

41. The process according to anyone of claims 1 -40, wherein the one or more monovalent metal ions are selected from: silver ions, copper ions, and a combination thereof.

42. The process according to anyone of claims 1 -41 , wherein the one or more monovalent metal ions are silver ions.

43. The process according to anyone of claims 40 - 42, wherein the silver ions are provided as an aqueous solution of silver nitrate.

44. The process according to anyone of claims 40 or 41, wherein the one or more monovalent metal ions are copper ions.

45. The process according to anyone of claims 40, 41 or 44, wherein the copper ions are provided as an aqueous solution of copper cyanide.

46. The process according to anyone of claims 1 - 45, wherein the step of contacting the hydrophilised silicon carbide surface with the solution comprising the one or more monovalent metal ions is maintained at a temperature of between about 10 °C and about 40 °C.

47. The process according to anyone of claims 1 - 46, wherein the step of reducing the monovalent metal ions comprises low temperature thermal processing.

48. The process according to anyone of claims 1 - 47, wherein the step of reducing the monovalent metal ions comprises heating at a temperature of between about 30 °C and about 120 °C.

49. The process according to anyone of claims 1 - 48, wherein the step of reducing the monovalent metal ions comprises heating at a temperature of between about 60 °C and about 80 °C.

50. The process according to anyone of claims 1 - 49, wherein the step of reducing the monovalent metal ions comprises heating at a temperature selected from: about 60 °C, about 70 °C, and about 80 °C.

51. The process according to anyone of claims 1 - 50, wherein the step of reducing the monovalent metal ions comprises application of a hot air flow stream; exposure to hot air environment, such as heating in an oven.

52. The process according to anyone of claims 1 - 51, wherein the step of reducing the monovalent metal ions comprises holding at the temperature for a period of between about 1 and about 5 minutes, preferably about 2 minutes.

53. The process according to anyone of claims 1 - 50, wherein the step of reducing the monovalent metal ions further comprises an oxidation step for oxidation of the reduced monovalent metal ions.

54. The process according to claim 53, wherein the oxidation step comprises heating at a temperature greater than 120 °C.

55. The process according to claim 53 or 54, wherein the oxidation step comprises heating at a temperature of about 200 °C.

56. The process according to anyone of claims 53 - 55, wherein the oxidation step comprises heating for between about 1 minute and about 5 hours; for between about 5 minutes and about 1 hour; for about 30 minutes.

57. The process according to anyone of claims 53 - 56, wherein the oxidation step comprises heating at a temperature of about 200 °C for between about 1 minute and about 5 hours.

58. The process according to anyone of claims 53 - 57, wherein the oxidation step comprises heating at a temperature of about 200 °C for between about 5 minutes and about 1 hour.

59. The process according to anyone of claims 53 - 58, wherein the oxidation step comprises heating at a temperature of about 200 °C for about 30 minutes.

60. A process to create a first metal plating surface on a nanoparticle seeded silicon carbide surface, the process comprising the steps of:a. providing a nanoparticle seeded silicon carbide surface as claimed in any one of claims 1 -59; andb. contacting the nanoparticle seeded silicon carbide surface with an electroless plating solution to thereby provide a first metal plating on the nanoparticle seeded silicon carbide surface; andthereby producing a plated silicon carbide surface.

61. The process according to claim 60, wherein the electroless plating solution comprises a reducing agent.

62. The process according to anyone of claims 60 or 61, wherein the electroless plating solution is selected from: an electroless nickel plating solution, an electroless silver plating solution, an electroless copper plating solution, and a combination thereof.

63. The process according to anyone of claims 61 or 62, wherein the reducing agent is selected from: tartrate, amine borane, gluconate, formaldehyde, borohydride, and a combination thereof.

64. The process according to anyone of claims 62 or 63, wherein the electroless nickel plating solution comprises: electroless nickel boron and the reducing agent is amine borane.

65. The process according to anyone of claims 60-64, wherein the nanoparticle seeded silicon carbide surface is seeded with silver nanoparticles, the electroless plating solution comprises electroless silver, and the reducing agent is sodium gluconate.

66. The process according to claim 65, wherein the silver nanoparticle seeded silicon carbide surface is plated in an electroless silver plating bath for a period of between about 2 and about 10 minutes.

67. The process according to claim 65 or 66, wherein the silver nanoparticle seeded silicon carbide surface is plated in an electroless silver plating bath for a period of about 5 minutes.

68. The process according to anyone of claims 65 - 67, wherein the silver nanoparticle seeded silicon carbide surface is plated in an electroless silver plating bath to provide a first plating surface having total silver thickness of 1 pm or less.

69. The process according to anyone of claims 61 - 63, wherein the nanoparticle seeded silicon carbide surface is seeded with copper nanoparticles, the electroless plating solution is an electroless copper plating solution, and the reducing agent is EDTA.

70. A process to deposit a second plating surface on a first plating surface, the process comprising the steps of:a. providing the first plating surface as claimed in any one of claims 60- 69; b. depositing a second plating surface on the first plating surface by electrodeposition or electroless deposition; andthereby providing a plated silicon carbide surface.

71. The process according to claim 70, wherein the second plating surface is selected from silver, gold, copper, nickel, composite coatings, alloy coatings, and combinations thereof.

72. The process according to anyone of claims 70 or 71, wherein the second plating surface is an electrodeposited metal-ceramic composite, and wherein the ceramic is selected from Al2O3, TiO2, SiO2, WO2and the like; and a metal selected from silver, gold, nickel, titanium, and the like; and any combination thereof.

73. A process to produce a hermetically sealed diffusion bond between:i. two selected from: a plated silicon carbide surface prepared according to any one of claims 60 - 72, or a hydrophilised silicon carbide surface prepared according claim 1 ;the process comprising the steps of:a. contacting i (above) and applying pressure to provide contacted surfaces; and b. heating the contacted surfaces in an oxygen containing atmosphere at a temperature exceeding 400°C;to thereby provide a hermetically sealed diffusion bond.

74. The process according to claim 73, wherein the contacting step comprises applying a pressure greater than 0.1 MPa.

75. The process according to anyone of claims 73 or 74, wherein the contacting step comprises applying a pressure of between about 1 MPa and about 5 MPa.

76. The process according to anyone of claims 73 - 75, wherein the contacting step comprises applying a pressure of about 2 MPa.

77. The process according to anyone of claims 73 - 76, wherein the heating step is performed at a temperature close to the melting point of the metal nanoparticles.

78. The process according to anyone of claims 73 - 77, wherein the heating step is performed at a temperature of between about 400 °C and about 1000 °C.

79. The process according to anyone of claims 73-78, wherein the heating step is performed between about 700 °C and about 800 °C.

80. The process according to anyone of claims 73-79, wherein the heating step is performed between about 400 °C and about 1000 °C and the nanoparticles are silver nanoparticles.

81. The process according to anyone of claims 73-80, wherein the heating step is performed for a period greater than about 30 minutes.

82. The process according to anyone of claims 73-81, wherein the heating step is performed for a period of between about 30 minutes and about 48 hours.

83. The process according to anyone of claims 73-82, wherein the heating step is performed for a period between about 1 hour and about 24 hours.

84. The process according to anyone of claims 73-83, wherein the heating step is performed for a period between about 6 hours and about 18 hours85. The process according to anyone of claims 73-84, wherein the heating step is performed for a period that about 6 hours; about 10 hours.

86. A process to produce a hermetic diffusion bond between a plated silicon carbide surface or a nanoparticle seeded silicon carbide surface and a metal surface to provide a bonded silicon carbide material, the process comprising the steps of:a. providing a nanoparticle seeded silicon carbide surface according to anyone of claims 1 - 59 or a plated silicon carbide surface according to anyone of claims 60 -72;b. providing a metal surface;c. contacting the metal surface with an alkaline solution to remove any native oxides or surface contaminants, and then further contacting the metal surface with an acid solution and de-smuttingthe metal surface in the acid solution; d. contacting the metal surface with the nanoparticle seeded silicon carbide surface or contacting with the plated silicon carbide surface to provide contacted surfaces;e. applying pressure to the contacted surfaces; andf. heating at a temperature greater than about 400 °C in an oxygen containing environment;to provide the bonded silicon carbide material.

87. The process according to claim 86, wherein the metal surface may be selected from tungsten, stainless steel, copper, and a combination thereof.

88. The process according to anyone of claims 86 or 87, wherein applying pressure comprises: applying a pressure between about 0.1 GPa and about 1 GPa.

89. The process according to anyone of claims 86 - 88, wherein the heating step comprises heating at a temperature of between about 400 °C and about 1000 °C.

90. The process according to anyone of claims 86 - 89, wherein the heating step comprises heating at a temperature of between about 500 °C and about 850 °C.

91. The process according to anyone of claims 86 - 90, wherein the oxygen containing environment is ambient air.

92. The process according to anyone of claims 86 - 91 , wherein the oxygen containing environment is at atmospheric pressure.

93. The process according to anyone of claims 86 - 92, wherein the heating step comprises heating for a period of between about 30 minutes and about 48 hours.

94. The process according to anyone of claims 86 - 93, wherein the heating step comprises heating for a period of between about 1 hours and about 24 hours.

95. The process according to anyone of claims 86 - 94, wherein the heating step comprises heating for a period about less than about 6 hours.

96. A process to bond two silicon carbide surfaces, the process comprising the steps of:a. providing two or more silicon carbide surfaces;b. hydrophilisingthe two or more silicon carbide surfaces with a hydrophilising agent to form hydrophilised silicon carbide surfaces wherein the hydrophilisation step is according to anyone of claims 15 - 32 ;c. contacting the hydrophilised silicon carbide surfaces with a solution comprising one or more monovalent metal ions ;d. reducing the one or more monovalent metal ions by the application of energyto form nanoparticles on the hydrophilised silicon carbide surface thereby providing nanoparticle seeded silicon carbide surfaces ;e. bonding the two or more hydrophilized or nanoparticle seeded silicon carbide surfaces comprising: application of a nanoparticle seeded silicon carbide nanopowder to at least one of the silicon carbide surfaces, and contacting withthe other silicon carbide surface to form a contacted surface, and where the nanoparticle seeded silicon carbide nanopowder is prepared according to the following steps:i. providing a silicon carbide nanopowder;ii. hydrophilisin the silicon carbide nanopowder with a hydrophilising agent to form a hydrophilised silicon carbide nanopowder wherein the hydrophilising step is accordingto anyone of claims 15 - 32;iii. formingthe nanoparticle seeded silicon carbide nanopowder by contacting the hydrophilised silicon carbide nanopowder with a solution comprising one or more monovalent metal ions;iv. reducing the monovalent metal ions to form nanoparticles on the hydrophilised silicon carbide surface by the application of energy and thereby providing the nanoparticle seeded silicon carbide nanopowder; andf. application of pressure to the contacted surfaces to thereby bond the two silicon carbide surfaces.

97. The process according to claim 96, wherein the step of hydrophilising the silicon carbide nanopowder is followed by the step of separating the hydrophilised silicon carbide nanopowder from any liquids.

98. The process accordingto anyone of claims 96 or 97, wherein the step of separating the hydrophilised silicon carbide nanopowder from any liquids is followed by washing the hydrophilised silicon carbide nanopowder.

99. The process accordingto anyone of claims 96 - 98, wherein the step of separating the hydrophilised silicon carbide nanopowder from any liquids comprises one or more techniques selected from: centrifugation, decantation, filtration, sedimentation, drying, vacuum drying, freeze drying, magnetic separation, membrane separation, vacuum filtration, and a combination thereof.

100. The process accordingto anyone of claims 96 - 99, wherein the step of forming the nanoparticle seeded nanopowder is followed by the step of separating the nanoparticle seeded nanopowder from any liquids.

101. The process according to anyone of claims 96 - 100, wherein the step of separating the nanoparticle seeded nanopowder from any liquids comprises one or more techniques selected from: centrifugation, decantation, filtration, sedimentation, drying, vacuum drying, freeze drying, magnetic separation, membrane separation, vacuum filtration, and a combination thereof.

102. The process according to anyone of claims 96 - 101, wherein the nanoparticle seeded silicon carbide nanopowder is applied as paste.

103. The process according to anyone of claims 96 - 102, wherein the nanoparticle seeded silicon carbide nanopowder is applied as an aqueous paste.

104. The process according to anyone of claims 96 - 103, wherein the bonding step comprises application of a pressure greater than 1 MPa.

105. The process according to anyone of claims 96 - 104, wherein the application of pressure comprises applying a pressure of between about 1 MPa and about 5 MPa.

106. The process according to anyone of claims 96 - 105, wherein the application of pressure comprises applying a pressure of about 2 MPa.

107. The process according to anyone of claims 96 - 106, wherein the application of pressure is followed by the step of heating the contacted surfaces in an oxygen containing atmosphere at a temperature exceeding 400 °C.

108. The process according to claim 107, wherein the heating step comprises heating the contacted surfaces at a temperature of between about 400 °C and about 1000 °C.

109. The process according to anyone of claims 107 - 108, wherein the heating step comprises heating the contacted surfaces at a temperature of about 800 °C.

110. The process according to anyone of claims 107 - 109, wherein the heating step comprises heating the contacted surfaces for a period of greater than about 30 minutes.

111. The process according to anyone of claims 107 - 110, wherein the heating step comprises heating the contacted surfaces for a period of between about 30 minutes and about 48 hours.

112. The process according to anyone of claims 107 - 111, wherein the heating step comprises heating the contacted surfaces for a period of between about 1 hour and about 24 hours.

113. The process according to anyone of claims 107 - 112, wherein the heating step comprises heating the contacted surfaces for a period that is less than about 6 hours.

114. The process according to anyone of claims 96- 113, wherein the energy is applied for a period of between about 2 minutes and about 10 minutes.

115. The process according to anyone of claims 96- 114, wherein the nanoparticles on the nanoparticle seeded silicon carbide nanopowder are silver.

116. The process according to anyone of claims 96- 115, wherein heating the contacted surfaces is performed at a temperature of about 800°C for a period about 10 hours in an oxygen containing atmosphere.

117. The process according to anyone of claims 96- 116, wherein the oxygen containing atmosphere is an air atmosphere.

118. The process according to anyone of claims 96- 117, wherein the oxygen containing atmosphere is at ambient pressure.

119. The process according to anyone of claims 96- 118, wherein the silicon carbide nanopowder is about 99 % pure.

120. The process according to anyone of claims 96- 119, wherein the silicon carbide nanopowder is substantially spherical.

121. The process according to anyone of claims 96 - 120, wherein the silicon carbide nanopowder has a particle size of between about 200 nm and about 2 pm.

122. The process according to anyone of claims 96 - 121, wherein the silicon carbide nanopowder has a particle size of about 1 pm.

123. The process according to anyone of claims 1-122, wherein prior to the step of contacting the silicon carbide surfaces, the process comprises a further step of applying an oxidation accelerator to one or more silicon carbide surfaces to thereby provide an oxidation accelerator layer.

124. The process according to claim 123, wherein the oxidation accelerator comprises a solution comprising alkali metal ions selected from: sodium ions (Na+), potassium ions (K+), rubidium ions (Rb+), and caesium ions (Cs), or any combination thereof.

125. The process according to anyone of claims 123 or 124, wherein the oxidation accelerator layer is a monolayer.

126. The process according to anyone of claims 123 -125, wherein the process comprises applying a filler to the silicon carbide surface.

127. The process according to claim 126, wherein the filler is applied after applying the oxidation accelerator.

128. The process according to anyone of claims 126 or 127, wherein the filler comprises a SOL.

129. The process accordingto claim 128, wherein the SOL is applied in an amount of between about 0.001 mL / cm2and about 0.02 mL / cm2.

130. The process accordingto claim 128 or 129, wherein the SOL is a mixed oxide SOL.

131. The process accordingto claim 130, wherein the mixed oxide SOL comprises a combination of precursor reagents designed to produce one or more oxides selectedfrom: yttria (Y2O3), alumina (Al2O3), calcia (CaO), magnesia (MgO), titania (TiO2), copper oxide (Cu2O), and silica (SiO2).

132. The process according to claim 131, wherein the precursor reagents comprise the combination: aluminium-tri-sec butoxide, yttrium nitrate, acetylacetone, and ethanol.

133. The process according to anyone of claims 126 - 132, wherein the process further comprises a gelling step to partially or substantially gel the filler.

134. The process according to claim 133, wherein the gelling step comprises heating in an oven at a temperature of between about 50°C and about 150°C.

135. The process according to claim 133 or 134, wherein the gelling step comprises heating for a period of between about 10 minutes and about 120 minutes.

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