Dried laid composite article

Abstract

The present invention relates to a process for producing a composite article comprising: A. batching together raw materials comprising: i. refractory fibres; ii. a high temperature binder; iii. an optional low temperature binder; iv. an optional filler B. mixing the raw materials to form a mixture consisting of solid particles; C. feeding the mixture into a mould; D. vibrating the mixture; E. pressing the mixture; and F. curing the pressed mixture to form the composite article.

Description

[0001] Dried Laid Composite Article

[0002] Field

[0003] The present invention relates to the process of producing dried laid composite articles and said dried laid composite articles, including dried laid boards.

[0004] Background

[0005] Conventional refractory boards are typically produced using a slurry - mould forming method in which a mixture of water, inorganic fibres, colloidal silica and starch form a slurry which flows over a screened surface mould, with vacuum used to remove excess liquid prior to a drying step. There has been long felt desire to improve refractory board manufacture to reduce energy consumption as well as water usage and processing costs.

[0006] A number of technology developments have been directed at this objective. US2002 / 0098336 discloses blowing fibres and a powder water soluble binder onto a conveyor belt; spraying the mixture with about 20 wt% water prior to hot pressing the board.

[0007] US2011 / 0091721 teaches the use of fine silica (e.g. fumed silica) as a binder in a humid environment to form dry pressed fibrous compacts having a bulk density of 190 - 600 kg / m3. Whilst these boards have reduced water and energy consumption, the quality of the resultants boards has limited their adoption within industry.

[0008] EP0305209A1 discloses a method of forming fibre reinforced cement composites. The method comprises steps of preparing a mixture including dry solids and not more than 30% water by mass based upon the total mass of dry solids, the dry solids include hydraulic cement, chemical pulp lignocellulosic fibre and at least one selected siliceous substance; forming and pressing the mixture to predetermined density and / or dimension; and maintaining conditions of high humidity for sufficient time to advance setting reactions in the mixture to produce a fibre reinforced product. EP0305209A1 teaches use of at least 50% silica along with humid environment. Further the density of the product obtained is as high as 1200 kg / m3along with high modulus of rupture (MOR).

[0009] EP2001522B1 discloses a process for making composite products comprising fibrous material from domestic waste material, the process comprising a) obtaining fibrous material produced by the thermal treatment of waste materials with pressurised steam; b) mixing the fibrous material with a binding material; c) forming the resulting mixture into a shape; and d) curing the shaped mixture; wherein the fibrous material obtained in step a) has a moisture content in the range of from 4 to 10% by mass; and wherein the process also comprises the steps of the separating out the fibrous material and deodorising the fibrous material. The process disclosed in the patent document is not suitable for obtaining dried refractory fibres. Though the product obtained has medium density, it showed high MOR.

[0010] US20020098336A1 discloses a process for producing a high temperature rigid fibre board comprising steps of providing a fibrous material, the fibrous material including alumina silica fiber, soluble fiber, mineral wool or a combination thereof; performing fiberization; forming a fibrous mat; accumulating layers of built-up fibrous mat; heating and pressing the fibrous mat to achieve a desired thickness; and drying the fibrous mat to form a fibrous high temperature pressed board product. A preferred embodiment of the document discloses a watering step to dissolve binders. The resultant boards have poor thermal shock characteristics, which is likely connected to the high fibre orientation in the layered construction.

[0011] US5827797A discloses a process of producing filament of refractory material comprising preparing a dispersion of particles of refractory material; preparing a spin mix by mixing said dispersion with a carrier solution; wet spinning said spin mix to form filament of cellulose; heating said filament to sufficient temperatures and over sufficient durations thereby forming the filament of refractory material. However, the process begins by preparing a dispersion of particles of refractory material wherein liquid or dispersion medium is usually water. Thus, the process disclosed in this document is also not environment friendly.

[0012] Therefore, there is a need in the state of the art for more environmentally sustainable refractory boards which are able to still meet the mechanical and high temperature performance requirements of many end-use applications.

[0013] Summary of the invention

[0014] In a first aspect of the present invention, there is provided a process for producing a composite article comprising:

[0015] A. batching together raw materials comprising: i. refractory fibres, ii. an inorganic binder, ill. an optional organic binder, iv. an optional filler;

[0016] B. mixing the raw materials to form a mixture of solid particles;

[0017] C. feeding the mixture into a mould;

[0018] D. vibrating the mixture; E. pressing the mixture; and

[0019] F. curing the pressed mixture to form the composite article.

[0020] The composite article may be a planar board with a typical thickness in the range of 5 to 200 mm. In some embodiments, the board is at least 50 mm or at least 70 mm or at least 90 mm or at least 100 mm thick. However, it would be appreciated that other shaped products may also be formed, depending upon the dimensions of the mould.

[0021] The process of the present invention provides an environmentally sustainable means to generate composite articles without the need of excessive quantities of water, which is required for alternative processes known in the art including vacuum forming and fourdrinier based techniques. Further, through a combination of sufficient fibre alignment along multiple axes and reduced microstructural variation, the composite articles have good multi-directional properties, including excellent thermal shock performance.

[0022] The batched mixture is typically substantially randomly orientated. The refractory fibres of the mixture may be separably, such that the vibration process separates and re-orientates at least a portion of the refractory fibres. The vibration process enables the raw materials to sufficiently reorientate to generate a composite with a medium degree of fibre orientation. The vibration process typically re-orientates a portion of the fibres into a X-Y plane, perpendicular to the direction of vibration Z, whilst a sufficient portion of fibres are positioned in a transverse direction to enable a degree of fibre entanglement between X-Y planar layers. This avoids the formation of highly anisotropic material, which is mechanically vulnerable in at least one direction. Such anisotropic behaviour is found in composite articles formed via the pressing of fibrous blankets, such as disclosed in US7413797. Composite articles formed via vacuum moulding, as disclosed in US6987076, use chopped ( / .e. short fibres) to form a flocculated suspension which is able to drain water under vacuum. The resultant composite articles have higher porosity and reduced mechanical properties (e.g. compression strength and / or modulus of rupture).

[0023] Although the mechanical properties may be improved through the addition of filler materials, the addition of filler materials also limits the maximum thickness of boards formed as fillers reduce the effectiveness of the vacuum drawing liquid through the drainage screen. The layered floc formation of vacuum boards also make the boards vulnerable to delaminating after repeated high temperature cycling. Even though fibre alignment may be low within the flocs, the flocs are arranged in layers, with bonding between floc layers susceptible to delamination. Further, the relatively high proportion of filler materials may result in a mismatch in the co-efficient of expansion between the fibres and the filler materials making the composite susceptible to poor thermal shock performance. A summary of the relative properties of the boards of the present invention and convention vacuum formed boards (wet processing) and pressed blankets (dry processing) is presented in Table 1. As illustrated, the boards of the present invention have particularly strong thermal shock characteristics, whilst still possessing good mechanical and insulative properties. Table 1

[0024] Where:

[0025] O represents- acceptable performance in some applications

[0026] 00 represents-good (where good is better than acceptable) performance in most applications

[0027] 000 represents-excellent (where excellent is better than good) performance in most applications Refractory fibres

[0028] Refractory fibres may be any fibres, when in the form of a blanket, comprise a linear shrinkage of 5% or less after 24 hrs exposure at 1000°C measured in accordance with EN ISO 10635:1999.

[0029] The refractory fibres may include, but not be limited to, the group consisting of aluminosilicate (RCF) fibers and / or alumino zirconia silicate (AZS) fibres, alkaline earth silicate (AES) fibres, alkali aluminosilicates (AAS) fibres and combinations thereof. Suitable fibres may be available from Thermal

[0030] Ceramics Inc. under the mark SUPERWOOL™(e.g. AES fibres) or KA0W00L™ (RCF fibres). Alternatively, suitable fibres may be available from Unifrax under the mark ISOFRAX™, and / or high temperature ceramic fibers such as high alumina fibers, such as those available from Unifrax under the mark FIBERMAX™.

[0031] The refractory fibre may comprise shot components which are globules formed during the formation of the refractory fibres. The shot content (> 45pm) is typically between 30 and 60 wt% of the total weight of the refractory fibre, depending upon the manufacturing method; the fibre composition and whether the refractory fibre has gone through any de-shotting processes. In some embodiments, deshotted refractory fibre is used, with a shot content of less than 30 wt% or less than 20 wt% or less than 10 wt%.

[0032] Suitable AES fibres, which are soluble in bodily fluids, may be found in W087 / 05007, WO89 / 12032, WO93 / 15028, WO94 / 15883, WO96 / 02478, and WO97 / 49643.

[0033] The refractory fibres preferably have good temperature resistance after 24 hrs at 1000°C or more or 1100°C or more or 1150°C or more or 1200°C or more or 1260°C or more. The linear shrinkage of the fibres, when in the form of a blanket, is preferably less than 5% or less than 4% or less than 3% or less than 2% after 24 hrs at 1100°C or at 1150°C or at 1200°C or at 1260°C.

[0034] The arithmetic average fibre length of the refractory fibres may be in the range of 0.2 mm or 0.3 mm or 0.4 mm or 0.5 mm or 0.75 mm or 1 mm or more and 150 mm or less. In some embodiments, the arithmetic average fibre length may be at least 3 mm at least 5 mm at least 8 mm or at least 10 mm or at least 12 mm or at least 15 mm or at least 20 mm or at least 30 mm or more. In some embodiments, at least some of the refractory fibres are at least 5 mm or at least 10 mm or at least 20 mm or at least 30 mm or more. Having at least some fibres of the lengths (e.g at least 0.5 wt% or at least 1.0 wt%) enables the composite article to have more robust mechanical properties. In some embodiments, the arithmetic average fibre length may be less than 120 mm or less than 100 mm or less than 80 mm or less than 60 mm or less than 40 mm or less than 20 mm or less than 10 mm. When the arithmetic average fibre length is low (e.g. less than 0.2 mm), it may not be possible to suitably align or entangle the inorganic fibre. As a result, the mechanical strength of the thermal insulation may be insufficient. When the arithmetic average fibre length is high (e.g. more than 150 mm), the material flow property of the raw material during processing may be impaired. The refractory fibres preferably comprise at least some fibres (e.g. at least 1 wt% or at least 5 wt%) which are at least 10 mm in length to improve the mechanical integrity of the composite article.

[0035] In some embodiments, the arithmetic average fibre diameter of the refractory fibre is 25 pm or less or 20 pm or less or 15 pm or less. To be more specific, the arithmetic average fiber diameter is preferably 1.5 pm or 2.0 pm or 2.5 pm or more and 15 pm or 12 pm or 10 pm or 8 pm or 6 pm or 4 pm or 3 pm or less. When the arithmetic average fibre diameter is more than 15 pm, the inorganic fibre becomes liable to break in some cases. As a result, the strength of the thermal insulation may be insufficient.

[0036] In some embodiments, the refractory fibres may be defined as fibres with a minimum length of 0.1 mm or 0.3 mm or 0.5 mm. In these embodiments, the refractory fibres with a length below this threshold are regarded as filler material.

[0037] High temperature binder

[0038] High temperature binders are used in the form of inorganic binders. The high temperature binder is preferably able to withstand (i.e. maintain mechanical performance and exhibit a linear shrinkage of less than 5%) temperatures of at least 800°C or at least 900°C or at least 1000°C or at least 1100°C. The high temperature binder may include, but not be limited, to the group consisting of colloidal silica, colloidal alumina, fine silica particles, precipitated silica, alkali metal silicates and combinations thereof. The high temperature binder is preferably a solvent activated binder (i.e. the presence of a solvent (e.g. water) is required to initiate a reaction with the binder to enable the binder to adhere to other components with the raw materials, such as the refractory fibre).

[0039] Low temperature binder

[0040] Low temperature binders are typically organic binders, which serve to improve the handling characteristics of the product concerned at low temperatures (e.g. less than 300°C) but which burn off at higher temperatures. Organic binders may include such materials as starch or resin. During high temperature operation in end-use applications, the low temperature binder may degrade resulting in an increase in porosity.

[0041] Fillers

[0042] The fillers may include low density fillers including, but not limited to, perlite, vermiculite, porous ceramic spheres, expanded clay, foamed lightweight geological materials, microporous silica, microporous alumina, expanded glass, hollow ceramic, glass spheres and combinations thereof.

[0043] The filler may comprise high density fillers including, but not limited to, alumina, wollastonite, talc, fumed silica, mullite and clay.

[0044] The fillers may also include opacifiers including, but not limited to, chromium oxide, zirconium oxide, iron oxide, titanium oxide, manganese dioxide, ilmenite, quartz powder, silicon carbide, boron carbide, tantalum carbide, carbon black, graphite and combinations thereof. In some embodiments, the composite article is substantially free of fillers (e.g. less than 2 wt% or less than a detectable amount).

[0045] Other additives

[0046] Other additives may include processing aids (including flow agents) and water proofing agents, such as hydrophobic coatings.

[0047] Water / Liquid

[0048] Any liquid present in the mixture is insufficient to form a paste or slurry. In addition to being used to activate the high temperature binders, liquids (e.g. water) may also be optionally added as a solvent or dispersant to better disperse the binders, such as starch or colloidal silica.

[0049] Mixing

[0050] The batched raw materials are preferably mixed to form a homogenous mixture. Mixing time may vary according to the amounts of raw materials and the mixing equipment used. However, typical mixing time may range from 10 seconds to 10 minutes, although higher times (e.g. 30 minutes) are possible. For the purposes of the present invention, mixing encompasses mixing batched raw materials in which the mixture is preferably flowable or sievable solid particles rather than a paste or slurry. In some embodiments, binder components may be added as a solution or dispersion to assist in the dispersion of the binder within the fibres and filler materials. However, even though a portion of the raw material may be liquid, the resultant mixture is still solid particles, with any liquid being absorbed / adsorbed into the other raw material components and, in particular, the inorganic binder, such as colloidal silica which has a high surface area and ability to absorb / adsorb liquid while being maintained in the solid form.

[0051] The mixing process of the present invention may be categorised as a "dry mixing process" or a "dry blending process" which is a commonly used term with specific meaning in a variety of industries such as the pharmaceutical, food, chemical and fertiliser industries, amongst others. In a dry mixing process, the mixture consists essentially of solid ingredients (e.g. flowable solid particles) and the blend has been prepared by dry mixing said raw materials. While the mixture does not contain a discrete liquid phase, the mixture may contain molecules of one or more liquids at 20° C. (e.g. water and organic solvents) adsorbed on the surface of the solids (e.g. moisture adsorbed from a humid air environment or from a raw material component disperse within a liquid phase). To facilitate dry mixing, the mixing is preferably conducted at a relative humidity of no more than 50% relative humidity or no more than 40% relative humidity. These conditions limit the degree of moisture absorption from the atmosphere affecting the drying mixing process.

[0052] The total moisture (or other liquid) content of the mixture is dictated by the ability of the mixture to absorb / adsorb the liquid without a separate liquid phase (e.g. slurry) forming or without the mixture agglomerating together, such that the refractory fibres cannot separate from each and re-oreintate during the vibration process. For mixtures comprising highly liquid absorbent binders, such as colloidal silica, the mixture may be able to comprise a significant amount of water within the binders.

[0053] Sievability of the solid particles of the mixture is preferred to enable the refractory fibres to separate from other solid particles and re-orientate during the vibration process. Typically, the total level of water (or other liquid) in the mixture is less than 60 wt% or less than 50 wt% or less than 40 wt% or less than 30 wt% or less than 25 wt% or less than 20 wt% or less than 10 wt% or less than 5 wt% relative to the total weight of the mixture (wet weight basis). The lower the water content the more environmentally friendly the process is with a lower water and energy consumption. The maximum level of water will be determined by the specific additives, binders and filler used and their ability to absorb / adsorb moisture whilst the solid particles are able to maintain flowability or sievability, such that the refractory fibres can re-orientate during vibration. The moisture / liquid level of at least 1 wt% or at least 2 wt% or at least 3 wt% (wet basis) may be required to activate the binding capabilities of the inorganic binder, such as colloidal silica.

[0054] Dry mixing is differentiated from wet mixing which generally comprises mixing a wet paste (an agglomerated mixture of particles and a liquid with a malleable consistency) or slurry (particles and a discrete liquid phase).

[0055] Sievability of the solid particles in the mixture should be such that the refractory fibres can be separated from the other components of the mixture through manually vibrating the mixture through a sieve under gravity force.

[0056] Feeding the mixture into the mould

[0057] The mixture may be fed into a mould defining the shape of the composite article. The act of feeding results in the flowing of solid particles into the mould. For clarity, the act of feeding in not inclusive of casting, in which a liquid phase flows into the mould. The mould may be board shaped, such as 500 mm x 500 mm x 30 mm.

[0058] Vibrating the mixture The moulded mixture is then subject to vibration. This may occur through the mould being integrated into a vibration - press machine, such as a Maxibrator™, which enables the moulded mixture to be subject to controlled vibration. The vibration conditions are sufficient such that the density of the resultant composite article is at least 3% or at least 5% or at least 8% or at least 10% or at least 12% greater than the composite article that would be produced without being subject to the vibration conditions. The vibration conditions are such that the mixture is able to re-orientate into a more efficient packing order. The vibration may conform to sinusoidal, square, triangular or other nonrandom or random wave patterns.

[0059] In some embodiments, the moulded mixture may be vibrated with a frequency of at least 0.1 Hertz or at least 1 Hertz or at least 5 or at least 10 or at least 20 or at least 30 Hertz or at least 40 Hertz or at least 50 Hertz or at least 60 Hertz. The upper vibration frequency may be 100 Hertz or greater. Lower frequencies have been found to not effectively re-distribute and align the mixture into a more efficient packaging arrangement (i.e. high bulk density). Whilst higher frequencies may be used, they have been found not to provide any further beneficial effect. The amplitude of the vibration (horizontal axis to peak) may be at least 1 mm or at least 2 mm or at least 3 mm or at least 4 mm. Lower amplitude of vibrations may not enable the mixture to re-align and redistribute. Excessive amplitudes may result in excessive segregation of the mixture of components.

[0060] The duration of the vibration time should be sufficient to realign and redistribute the mixture without resulting in segregation of the mixture components. The realignment and redistribution results in a lowering of anisotropic properties of the result composite article. The duration of vibration may be in the range of at least 1 seconds or at least 2 seconds or at least 3 seconds or at least 4 seconds or at least 5 seconds or at least 10 seconds or at least 15 seconds to no more than 40 seconds or no more than 50 seconds to no more than 60 seconds or no more than 120 seconds or no more than 300 seconds or no more than 500 seconds. Lower vibration times may not be sufficient to realign and redistribute the mixture, whilst higher vibration times may result in segregation of the mixture components. For compositions with higher proportions of filler material, the vibration time may be reduced to avoid segregation in which the heavier particles may gravitate towards the bottom of the mould (or lighter materials may segregate to the top of the mould). In some embodiments, the vibration time is no more than 30 seconds or no more than 20 seconds or no more than 10 seconds for compositions comprises more than 10 wt% filler material. The specific vibration settings may be optimised by measuring the properties of the resultant composition article.

[0061] Pressing the mixture The vibrated mixture is then pressed. The mixture may be dry pressed or steam pressed depending upon the moisture level of the mixture and the type of binders in the formulation. In some embodiment, isostatic pressing may be used. The pressure used may vary according to the desired density of the resultant composite article.

[0062] The composite article may be pressed at a pressure ranging from about 1 to about 20 MPa (or higher) or 5 to 15 MPa. In certain embodiments, pressures ranging from about 7 to about 12 MPa may be used. Pressures may be varied by one of skill in the art as required to achieve the properties desired for composite articles, such as boards, without undue experimentation. Any conventional press used to press ceramic composites may be employed. It is known to use moulds when pressing ceramic composite articles. The use of higher pressure may increase the density of boards (or other composite articles) and reduce its insulating properties.

[0063] The composite article may be kept in the press for a time ranging from about 1 to about 120 minutes. In another embodiment, the composite article may be kept in the press for a time ranging from about 1 to about 5 minutes.

[0064] Curing

[0065] The composite article may be cured in an oven at a temperature ranging from about 40° to about 350° C. In another embodiment, temperatures can be used ranging from about 80° to about 150° C. In some embodiments, the composite article is dried at a temperature ranging from about 40° to about 350° C, for a time period ranging from about 2 minutes to about 1 hour. The curing time will be dependent upon the type of inorganic binder used and the dimensions of the composite article. Curing enables the binder to ensure bonding of the fibres.

[0066] Curing is defined as a process whereby the inorganic binder composition undergoes a physical and / or chemical reaction which in case of a chemical reaction usually increases the molecular weight of the compounds in the binder composition. The cured binder composition binds the fibres to form a structurally coherent matrix of fibres. Curing encompasses a range of processes including those disclosed in US20110091721, US2002 / 0098336 and EP0305209, which are incorporated herein by reference. Typically, the inorganic binders require moisture and heat to chemically transform though polymerisation or cross-linking to bond to the fibres.

[0067] Finishing the article / board

[0068] The composite article may be required to have a flat profile (e.g. board) to enable the article to fit into a pre-determined structure. Alternatively, the surface of the article may need to have a specific finish (e.g. roughness). Therefore, the board may also require levelling, smoothing or texturing. In respect to the levelling of boards, the reduced variation of density in the vibration pressed (also referred to as vibro-pressed) boards resulted in a lower degree of levelling required to obtain a level board. In some embodiments, the process further comprises the step of levelling the board from a board with a height variation of up to 3 % or 4% or 5% or 6% or 7% to a height variation less than 2% or less than 1.5% or less than 1.0 % of the thickness of the resultant levelled board.

[0069] Composite article

[0070] In a second aspect of the present invention, there is provided a composite article produced obtained by or obtainable by a process according to the first aspect of the present invention. The process of the first aspect of the invention provides a composite with an excellent combination of mechanical and thermal properties. This is achieved through producing a composite article with a low structural variation and sufficient fibre alignment.

[0071] In a third aspect of the present invention there is provided a composite article comprising a composite article comprising:

[0072] 20.0 to 95.0 wt% refractory fibres;

[0073] 3.0 to 60.0 wt% high temperature binder;

[0074] 0 to 20.0 wt% (or 0 to 10.0 wt%) optional low temperature binder; and

[0075] 0 to 40.0 wt% optional filler,

[0076] In some embodiments, a major component of refractory fibres is orientated in parallel planes and a minor component of refractory fibres are orientated in a transverse direction thereto.

[0077] The refractory fibre content may be at least 40 wt% or at least 50 wt% or at least 60 wt% or at least 70 wt% or at least 80 wt% or at least 90 wt% or at least 92 wt%. The upper limit of the refractory fibre content may be no more than 90 wt% or no more than 80 wt% or no more than 70 wt%. Higher proportions of fibres in the composite articles, when sufficiently entangled, provide mechanical and high temperature properties. A sufficient proportion of refractory fibre is required for the benefits of the vibration step to be realised.

[0078] The high temperature (or inorganic) binder content may be no more than 50 wt% or no more than 40 wt% or no more than 30 wt% high temperature binder or no more than 20 wt% high temperature binder or no more than 10 wt% high temperature binder. Too high a content of high temperature binder may increase the rigidity of the composite article making the composite article less resilient to thermal shock. In some embodiments, the high temperature binder content is at least 5wt% or at least 8 wt%. Too low a level of high temperature binder may not be sufficient to adhere the fibres together to maintain the mechanical properties (such as compression strength) of the composite article.

[0079] The low temperature (or organic) binder content, when present, may be no more than 10 wt% or no more than 8 wt% or no more than 6 wt% high temperature binder. In some embodiments, the low temperature binder content is at least lwt% or at least 2 wt% or at least 4 wt%. A small amount of organic binder may be required to increase the "green strength" of the composite article to assist in the ease of manufacturing of the composite article.

[0080] The formulations of the present invention span a range of densities from 300 to 1600 kg / m3, with composite articles able to comprise lower and higher end densities through the use of low and high densities filler materials.

[0081] Through the articles comprising at least a minor portion of the refractory fibres being orientated in transverse directions relative to a major portion of the refractory fibres, the anisotropic behaviour of the articles may be moderated.

[0082] The refractory fibres preferably comprise a portion of fibres greater than 1mm or greater than 2mm or greater than 3mm or greater than 4 mm or greater than 5mm in length or greater than 6mm or greater than 8 mm or greater than 10mm in length. The entanglement of these longer fibres contributes to more uniform mechanical properties measured in each direction.

[0083] Whilst the orientation of fibres may be assessed qualitatively, it was not possible to reliably measure the fibre orientation on a quantitative basis. However, the differences in functional performance may be directly linked back to fibre orientation.

[0084] The sum of the refractory fibres, high temperature binder, low temperature binder and filler is preferably at least 70 wt% or 80 wt% or 90 wt% or 95 wt% of the total weight of the composite article,

[0085] In a further aspect of the present invention, there is provided: a medium (M) density composition comprising:

[0086] 20 to 95 wt% refractory fibres;

[0087] 3.0 to 60 wt% high temperature binder;

[0088] 0 to 20 wt% or 0 to 10 wt% optional low temperature binder; and a density of between 600 and 950 kg / m3(or 650 to 900 kg / m3or 680 to 870 kg / m3) and wherein the sum of the refractory fibres and high temperature binder is at least 70wt% or 80wt% or 90wt% of the total weight of the composite article;

[0089] • a low (L) density composition comprising:

[0090] 20 to 95 wt% refractory fibres;

[0091] 3.0 to 60 wt% high temperature binder;

[0092] 0 to 20 wt% or 0 to 10 wt% optional low temperature binder; and

[0093] 0.2 to 40 wt% low density filler, said filler comprising a bulk density of less than 900 kg / m3or less than 800 kg / m3or less than 600 kg / m3or less than 500 kg / m3or less than 400 kg / m3or less than 300 kg / m3or less than 250 kg / m3and the filler may have a bulk density of at least 50 kg / m3; a density of between 300 and 650 kg / m3(or 350 to 600 kg / m3or 380 to 570 kg / m3) and wherein the sum of the refractory fibres, high temperature binder and low density filler is at least 70wt% or 80wt% or 90wt% of the total weight of the composite article; or

[0094] • a high (H) density composition comprising:

[0095] 20 to 95 wt% ( or to 80 wt% or to 60 wt% or to 50 wt%) refractory fibres;

[0096] 3.0 to 60 wt% high temperature binder;

[0097] 0 to 20 wt% or 0 to 10 wt% optional low temperature binder; and

[0098] 0.5 to 40 wt% high density filler, said high density fillers comprising a bulk density of greater than 900 kg / m3or greater than 1000 kg / m3or greater than 1500 kg / m3or greater than 1800 kg / m3or greater than 2000 kg / m3or greater than 2500 kg / m3or greater than 2800 kg / m3or greater than 3000 kg / m3and the filler may have a bulk density of no more than 5000 kg / m3; a density of between 900 and 1600 kg / m3(or 950 to 1500 kg / m3or 1000 to 1400 kg / m3) and wherein the sum of the refractory fibres, high temperature binder and filler is at least 70wt% or 80wt% or 90wt% of the total weight of the composite article.

[0099] In some embodiments, the sum of the refractory fibres, high temperature binder and filler in the composite article is at least 92wt% or at least 94wt% or at least 96 wt%. The composite article may comprise at least 35.0 wt% or at least 40 wt% or least 45 wt% or at least 50.0 wt% or at least 55.0 wt% or at least 60.0 wt% refractory fibre. In some embodiments, the composite article comprises less than 90 .0 wt% or less than 85.0 wt% refractory fibre.

[0100] In a specific aspect of the present invention, there is provided a composite article having a composition comprising:

[0101] 50.0 to 95.0 wt% refractory fibres;

[0102] 3.0 to 30.0 wt% high temperature binder;

[0103] 0 to 20 wt% or 0 to 10 wt% wt% optional low temperature binder; and

[0104] 0 to 10.0 wt% optional filler, wherein the density of the composite article is in the range 600 to 950 kg / m3(or 650 to 900 kg / m3or 680 to 870 kg / m3).

[0105] The composition is able to provide excellent mechanical properties (e.g. MOR and compression strength) without the need of excessive filler or inorganic binders. This is achieved through the refractory fibres being more homogeneously distributed and orientated compared to vacuum formed and pressed blanket composite articles. The effect of the vibration of the mixture is a denser and more isotropic composite article.

[0106] In the preferred embodiment, the medium density composite articles comprise no more than 10 wt% or no more than 5 wt% or substantially no filler materials (e.g. < 2 wt% or 0 wt%). Within this embodiment, the composite article may comprise 70 to 95 wt% refractory fibres and 3.0 to 30 wt% binders (high temperature and optionally low temperature binders). Due to the even distributions of fibres, boards which excellent mechanical and thermal shock characteristics may be obtained with a relatively low proportion of binders and filler materials (if present). In some embodiments, the weight ratio of refractory fibres to binders is at least 3:1 or at least 4:1 or at least 5:1 or at least 6:1 or at least 7:1 or at least 8:1 or at least 9:1 or at least 10:1 or at least 11:1.

[0107] In some embodiments, the refractory fibres comprises an alkaline earth silicate, an alkali silicate or a alumino-silicate and the high temperature binder comprises an inorganic binder comprises silica or silicate (e.g. colloidal silica). The combination of a silica / silicate based refractory fibre and inorganic binder reduces thermal stresses due to mis-matches in the co-efficient of thermal expansion.

[0108] The low-density composition may comprise at least 0.5 wt% or at least 1.0 wt% of at least 2.0 wt% or at least 5.0 wt% low-density filler. The low-density composition may comprise less than 35.0 wt% or less than 30.0 wt% or less than 25.0 wt% or less than 20.0 wt% low-density filler. The high-density composition may comprise at least 0.5 wt% or at least 1.0 wt% of at least 2.0 wt% or at least 5.0 wt% or at least 10.0 wt% or at least 15.0 wt% or at least 20.0 wt% high-density filler. The high-density composition may comprise less than 35.0 wt% or less than 30.0 wt% or less than 25.0 wt% or less than 20.0 wt% high-density filler.

[0109] In some embodiments, the composite article comprises at least 1.0 wt% or at least 2.0 wt% or at least 3.0 wt% low temperature binder.

[0110] In some embodiments, the composite article comprises at least 18.0 wt% or at least 20.0 wt% or at least 25.0 wt% or at least 30.0 wt% or at least 35.0 wt% high temperature binder. In some embodiments, the composite article comprises less than 65.0 wt% or less than 60.0 wt% or less than 55.0 wt% or less than 50.0 wt% or less than 40.0 wt% or less than 30.0 wt% or less than 25.0 wt% high temperature binder.

[0111] Apparent Porosity

[0112] The apparent porosity is the ratio of the total volume of the open pores of a product, expressed as a percentage of the bulk volume. The apparent porosity of the composite article may be at least 55% or at least 56% or at least 57% or at least 58% or at least 59% or at least 60%. The apparent porosity of the composite article may be no more than 70% or no more than 69% or no more than 68% or no more than 67% or no more than 66% or no more than 65% or no more than 64%. A higher apparent porosity promotes low thermal conductivity but may make the composite article more susceptible from failure due to thermal shock.

[0113] Microstructure

[0114] The microstructure of the composite articles preferably comprises an open fibrous network which is substantially homogeneous compared to the layered structures present in pressed blankets and vacuum formed articles. The open fibrous network is thought to enable the composite article to withstand repetitious thermal shock cycles (e.g. room temperature to 1200°C), whilst maintaining mechanical integrity, due to the network of fibres comprising a low proportion of closed pores, whereby the repetitive expansion and contraction of gases within the microstructure do not exert excessive stresses on the microstructure. In contrast, pressed boards and vacuum formed articles, particularly with high filler contents have layered microstructures with a more closed microstructure structure.

[0115] For the purposes of the present invention, a homogeneous microstructure means that the microstructure does not comprise a layered structured or a non-homogeneous concentration of fibrous or particle matter. Thermal conductivity

[0116] The low density (300-650 kg / m3) composite articles may have a thermal conductivity in the range between 0.12 and 0.18 W / m.K at 800°C. The upper limit of thermal conductivity may be no more than 0.17 W / m.K or no more than 0.16 W / m.K or no more than 0.15 W / m.K or no more than 0.14 W / m.K at 800°C.

[0117] The medium density (600-950 kg / m3) composite articles may have a thermal conductivity in the range between 0.15 and 0.25 W / m.K at 800°C. The upper limit of thermal conductivity may be no more than 0.24 W / m.K or no more than 0.23 W / m.K or no more than 0.22 W / m.K or no more than 0.21 W / m.K or no more than 0.20 W / m.K or no more than 0.20 W / m.K at 800°C.

[0118] The high density (900-1600 kg / m3) composite articles may have a thermal conductivity in the range between 0.22 and 0.40 W / m.K at 800°C. The upper limit of thermal conductivity may be no more than 0.38 W / m.K or no more than 0.36 W / m.K or no more than 0.34 W / m.K or no more than 0.32 W / m.K or no more than 0.30 W / m.K or no more than 0.28 W / m.K at 800°C. The thermal conductivity will be dependent upon the porosity of the composite and the material used.

[0119] Compressive strength

[0120] The compressive strength of the board is a measure of the board's resistance to deformation under load and an important design consideration. The compressive strength may be related to the composition of the board and the binder strength. Whilst the addition of dense filler material may increase the compressive strength of a composite, the thermal conductivity properties may also increase.

[0121] The 5% compressive strength of composite articles may be at least 100 KPa for low density composite articles or at least 1000 KPa for medium density composite articles or at least 2000 KPa for high density composite articles.

[0122] The 10% compressive strength of composite articles may be at least 300 KPa for low density composite articles or at least 3000 KPa for medium density composite articles or at least 5000 KPa for high density composite articles.

[0123] The maximum compressive strength of the composite articles is the strength at which the article fails (e.g. cracks). The maximum compressive strength of composite articles may be at least 500 KPa for low density composite articles or at least 5000 KPa for medium density composite articles or at least 7000 KPa for high density composite articles. In some embodiments, the ratio of the maximum compressive strength (MCS) to density is at least 9.0 KPa.m3 / kg or at least 10.0 KPa.m3 / kg or at least 11.0 KPa.m3 / kg or at least 12.0 KPa.m3 / kg.

[0124] In some embodiments, the compressive strength (@10% displacement compression) in the D (depth) x W (width) plane is at least 50% or at least 60% or at least 70% of the compressive strength in the L (length) x W (width) plane. Typically, the compressive strength in the D x W plane is less than 100% or less than 95% or less than 90% or less than 85% of the compressive strength (@10% displacement compression) in the L x W plane. Thus, the composite articles of the present invention whilst being anisotropic in nature, still have sufficient mechanical properties in their D x W or D x L plane to maintain the composite article's mechanical integrity, even during exposure to events placing stresses within all directional planes within the composite, such as during exposure to thermally induced stresses. In the formation of the board, the mixture is placed within a mould of L x W dimensions and pressed to obtain a board thickness D.

[0125] Modulus of Rupture

[0126] The modulus of rupture or flexural strength is a measure of a board's resistance to a bending load. Flexural strength may be reduced by defects or variations in the composite's microstructure which results in a concentration of stresses resulting in failure. In some embodiments, the modulus of rupture of the composite article is at least 200 KPa or at least 400 KPa or at least 600 KPa or at least 700 KPa or at least 750 KPa or at least 800 KPa or at least 1000 KPa or at least 1200 KPa or at least 1400 KPa or at least 1600 KPa or at least 1800 KPa or at least 2000 KPa or at least 2200 KPa or at least 2400 KPa or at least 2600 KPa. Generally, lower density composite articles comprise a lower modulus of rupture values (e.g. greater than 200 KPa or greater than 400 KPa or greater than 600 KPa or greater than 700 KPa or greater than 750 KPa and less than 1200 KPa). Medium and high density composite articles may have a minimum modulus of rupture of at least 1000 KPa.

[0127] High Temperature Performance

[0128] The high temperature performance of the composite articles may be measured by a combination of the thermal shock test and the linear shrinkage test. The thermal shock test measures the ability of the composite article to withstand cyclic variations in temperature, similar to that experienced when the composite article is used in high temperature environments, such as furnaces, which are routinely cooled and reheated during batch operations or routine maintenance. The thermal shock test may be reflective of the structural homogeneity (e.g. density variation) and / or differences in the thermal coefficient of expansion of the different components forming the composite article. Higher density variations and higher differences between the thermal coefficient of expansion between components may be expected to result in poorer thermal shock test results.

[0129] In some embodiments, after 20 or 25 or 30 cycles of in the thermal shock test (room temperature to 1200°C), the composite article retains at least 99.0 wt% or at least 99.1 wt% or at least 99.2 wt% or at least 99.3 wt% or at least 99.4 wt% or at least 99.5 wt% or at least 99.6 wt% of the original weight of the composite article prior to the thermal shock test. In another embodiment, after 5 or 10 or 20 or 25 or 30 cycles of the thermal shock test, the composite article displays no substantive visual signs of cracking or delamination (e.g. no visual signs of cracking or delamination when visually inspected from 1.0 metres from the composite article).

[0130] The composite article is deemed to have passed the thermal shock test if the composite article, after cycling between room temperature and 1200°C (being held at 15 minutes at each temperature) for at least 20 or 25 or 30 cycles retains at least 99.0 wt% of the composite article's original weight prior to the thermal shock test; and / or the composite article has not delaminated or cracked during the thermal cycling after at least 4 or at least 8 or at least 10 or least 15 or at least 20 or at least 30 thermal cycles (as described above).

[0131] A linear shrinkage test may also be used to assess the ability of the composite article to maintain its structural dimensions after prolonged periods at high temperature (e.g. 1000°C or above). In fibre based composites, increased linear shrinkage may be dependent upon the composition and dimensions (e.g. diameter) of the fibres in addition to the orientation of the fibres. Composite articles with low linear shrinkages are desirable particularly when the composite articles are used in insulating and / or sealing applications in which the dimensional stability of the composite article is important. In some embodiments, the composite article comprises a linear thermal shrinkage (after 1100°C for 24 hours) of no more than 5.0% or no more than 4.5% or no more than 4.0% or no more than 3.8% or no more than 3.5%. The linear thermal shrinkage performance is preferably obtainable across each orthogonal dimension (e.g. length, width and thickness).

[0132] Dimensions

[0133] The composite article typically has a thickness in the range between 5 and 200 mm. In contrast to vacuum forming techniques in which water is required to drain through the composite, the process of the present invention enables the thickness of composite article to be formed without this limitation. Optionally, the composite article may have a thickness of at least 80 mm or at least 100 mm or at least 120 mm or at least 140 mm. The shape of the composite article may be dependent upon the shape of the mould used. However, in a preferred embodiment, the composite article comprises a planar board. The composite article may have any suitable width and length as required by its intended use. In one embodiment, the board dimensions are in the range of 100 mm to 10,000 mm wide and 100 mm to 10,000 mm long.

[0134] Structural variation

[0135] The composite article may have a density variation of no more than 5.0% standard deviation as determined by the variation in density across the composite article from a minimum of 8 samples and preferably at least 10 samples. In some embodiments the standard deviation of the density of the composite article is no more than 4.5% or no more than 4.0% or no more than 3.5% or no more than 3% or no more than 2.5% or no more than 2.0%. The standard deviation is preferably derived from a minimum of 8 or 9 or 10 samples. A lower standard deviation in the density of the composite article typically results in a lower variation in the resultant functional mechanical and thermal properties. The lower structural variation may also contribute to improved mechanical properties.

[0136] For the purpose of the present invention:

[0137] • low density refers to a density between 300 and 650 kg / m3or between 350 and 650 kg / m3;

[0138] • medium density refers to a density between 600 and 950 kg / m3; and

[0139] • high density refers to a density between 900 and 1600 kg / m3.

[0140] As the density definitions comprise an overlapping range, a composite article may be classified as belonging to more than one density classification.

[0141] Unless otherwise indicated compositions are expressed on a dry weight basis. The formulations in Table 10 are not expressed on a dry weight basis, with the moisture of specific ingredients specified.

[0142] The sum of all components shall not exceed more than 100 wt% of the total weight of the composite article.

[0143] BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0144] Figure 1 is a schematic diagram of a prior art process of producing vacuum formed boards.

[0145] Figure 2 is a schematic block diagram of a process of the present invention.

[0146] Figure 3 is a photograph showing a cross sectional view of boards made through pressing (A); vibration and pressing as indicated in Figure 2 (B); and through a vacuum forming process as indicated in Figure 1.

[0147] Figures 4a to 4d are SEM images of a cross section of a vacuum formed board (prior art). Figures 5a to 5c are SEM images of a cross section of a pressed blanket board (prior art).

[0148] Figures 6a and 6d are SEM images of a cross section of a vibration and pressed board.

[0149] Figures 7a and 7d are SEM images of a cross section of a vibration and pressed board.

[0150] Figure 8 is a graph of the weight loss of a pressed board versus a board of the present invention (vibropressed) after undergoing a cyclic thermal shock test.

[0151] Figure 9 is a schematic diagram of the microstructure of a composite article of the present invention.

[0152] Figure 10 is an X-ray CT scan image illustrating the microstructure of a prior art board.

[0153] Figure 11 is a photograph of the composite article samples after 4 thermal shock cycles.

[0154] DETAILED DESCRIPTION

[0155] With reference to Figure 1, traditional vacuum formed boards are produced through weighing out raw materials and dispersing them into an aqueous solution to form a slurry containing about 5 wt% solids ( / .e. about 95% liquid). The slurry typically undergoes high shear mixing to form flocculates of fibres, binders and filler materials. The board is formed by passing the slurry over a wire mesh which enables the aqueous solution to drain away leaving a layer of flocculated material which builds up to a thickness which still enables the solution to drain through. Board thicknesses over 50 mm for high density and 80-100 mm for low density are difficult to obtain due to the requirement of the solution to drain through the accumulated layer of flocculants. The layer is then pressed and dried, before further finishing processes are performed, such as machining to maintain the boards within their desired tolerances.

[0156] The process of the present invention (Figure 2) dispenses with the high water consumption and energy costs associated with drying the board and achieves superior product properties. This is achieved through first batching the raw materials together and mixing the ingredients to form a mixture comprising predominantly refractory fibres and binders. The binders may contain water as a carrier or dispersant to distribute the binder more homogeneously, however the amount of water is not sufficient to prevent the mixing of the ingredients together and enables the mixture to flow freely. Relative to the vacuum formed process, the mixing process is gentle with minimal reduction in fibre length due to the mixing process. The mixture is fed into moulds defining the dimensions of the green boards to be produced. The moulds are mounted upon a rotatory vibrator device which vibrates the loaded mould at a specified amplitude and frequency. Through controlling these parameters and the duration of vibration, the raw materials are more evenly distributed, resulting in a board with uniform density, mechanical and thermal insulative properties. The vibration filled form is then pressed, preferably at elevated temperatures. The residual water in the mixture typically reacts with the inorganic high temperature binders to activate ("cure") the binders and ensure bonding of the fibres within the board, thereby contributing to the excellent flexural and compressive strength of the resultant boards.

[0157] Due to the more even distribution of raw materials, the thickness of the cured boards is more uniform compared to conventional air laid processes and, as such, the amount of additional finishing processes to meet tolerance requirements is typically less.

[0158] The difference in microstructure of the traditional vacuum formed and air laid board versus the board / composite article of the present invention is illustrated in Figure 3. Board A is an air laid board in which the fibres do not possess a well-defined axis of orientation (i.e. no vibration step). Whilst this feature may favour isotropic composite behaviour, the variation in density associated with the randomly orientated fibres is also associated with a detrimental impact on mechanical and thermal shock functionality of the material. Board C is a conventional vacuum formed board, in which the fibre length in significantly reduced compared to Boards A and B. Board B represents a board made under the scope of the present disclosure. The main difference in processing between Boards A and B is the use of vibrational packing of the mould in Board B. This results in a greater alignment of the fibres with there being a bias towards a parallel (e.g. horizontal) orientation of the fibres as a consequent of the vibration of the fibres which tends to favour a higher packing density. Whilst there may be a distinct bias in fibre orientation, there are still sufficient fibres (e.g. at least 5% or at least 10% or at least 15% or at least 20% of the fibres) at cross angle to the horizontal / parallel orientation to reduce the degree of directional dependency on mechanical properties. The board may be considered to have a major horizontal / parallel orientation and a minor cross horizontal or transverse orientation, for example 10 or 15 or 20 or 25 or 30 to 90 degrees or 45 to 90 degrees to the horizonal / parallel orientation.

[0159] The microstructure of cross-sectional edge (D x W) of vacuum formed, pressed blanket, pressed, and vibration pressed boards are provided in Figures 4a to 4d, Figures 5a to 5c; Figures 6a to 6d; and Figures 7a to 7d respectively.

[0160] As illustrated in Figure 4a, the sedimentary process under which the board is formed results in a layered microstructure. Figure 4b to 4d illustrate an increasing magnification of the vacuum formed board. It is apparent that the board microstructure is dominated with the inorganic binder and filler materials, as the refractory fibre only making up 20wt% of the board. The microstructure appears to be more closed, with void spaces being covered by layers of filler / inorganic filler, indicating that the microstructure is not suited to resisting repetitive thermal shock cycles, in which gases expand and contract within the void space.

[0161] The pressed blankets are shown in increasing magnification from Figures 5a to 5c. The images also reveal a layered structured in which layers of binder encased fibres are separated by void space. The encased fibres appears to be substantially orientated horizontally, indicating that the properties of the board would exhibit anisotropic behaviour.

[0162] The pressed boards represent boards derived from pressing of the mixture without vibration. Figures 6a to 6d are images of the resultant microstructure under increasing magnification. In comparison to the vibro-pressed (Figures 7a to 7d), the microstructure is less homogeneous with variations in density apparent from some regions comprising greater void space.

[0163] The vibro-pressed boards of the present invention are shown in increasing magnification in Figure 7a to 7d. It is immediately apparent that the microstructure contains much less binder material compared to pressed and vacuum formed boards, leaving the structure having a more open porosity compared to the vacuum formed and pressed blanket microstructures. The spherical globules in the images are "shot" particles, which are produced as a by-product of melt spun refractory fibres. Also, in contrast to the vacuum formed and pressed blanket microstructures, the vibro-pressed board microstructure does not possess any well-defined layered structures, with no large void spaces apparent. This is indicative of the low variation in density observed across the board. The open homogeneous microstructure would indicate that the microstructure would be suitable to handling repeated thermal shock cycles, with gases able to more freely move and escape through the microstructure.

[0164] With reference to Figure 9, the microstructure of a board (W x D plane) 10 of the present invention comprises a minor component of refractory fibres 110, 120, 130, 140, 150, which are orientated in transverse planes / axes to that of a major component of refractory fibres 30, which run in parallel planes / axes. The two components of fibres may intertangle with each other thereby strengthening the mechanical properties of the article in both the parallel and transverse directions. The microstructure may also comprise filler components 20 disperse throughout. In comparison, Figure 10 illustrates the microstructure of a prior art board (W x D plane) in which the fibres 200 are more uniformly orientated within a matrix of filler material 210.

[0165] With reference to Figure 10, a CT image of a Fiberfrax™ refractory fibre based insulation material.

[0166] "Thermal conductivity measurements and modelling of the ceramic fibre insulation materials" Headley et al, US Department of Energy, 2019. The CT scan highlights the fibre alignment, which appear to have a similar microstructure of the pressed blankets (Figures 5a to 5c).

[0167] Variations and adaptions to the disclosed process and resultant products beyond that previously described and defined is well within the scope of the skilled artisan and is also within the scope of the present invention.

[0168] Experiments

[0169] Sample preparation

[0170] Base composition for vacuum form boards (VF1, VF2)

[0171] CERA™ refractory fibre 20 mm granulated - 40 kgs (20 wt% dry basis)

[0172] Colloidal silica (30wt% solid) - 36 kgs (13 wt% dry basis)

[0173] Alumina - 80 kgs (41 wt% dry basis)

[0174] Wollastonite - 40 kgs (20 wt% dry basis)

[0175] Cationic starch - 11.3 kgs (6 wt% dry basis)

[0176] Additional Water - 5000 kgs

[0177] Composition: Example 2 (US6,987,076)

[0178] Fibre: 73.3 wt%

[0179] Colloidal Silica (30wt% solid) 22.8 wt%

[0180] Cationic Starch 3.9 wt%

[0181] The vacuum formed boards (including VF1 & VF2) were made according to the procedures disclosed in US6987076 which is included herein by reference.

[0182] Base composition for blanket pressed boards (BP1)

[0183] Blanket pressed board was made according to Example 1 of US7,413,797 using CERA™ blanket (128 kg / m3density). The formulation on a dry weight basis is:

[0184] Fibre: 59.0 wt%

[0185] Colloidal Silica (30wt% solid) 33.3 wt%

[0186] Starch and gelling agent 7.7 wt%

[0187] Base Composition for VP1, VP2, Pl and P2:

[0188] Granulated CERA™ refractory fibre (<20 pm diameter): 4158 grams (74wt% dry basis) Colloidal silica solution (30 wt% solids): 3500 grams (1050 grams of colloidal silica - 19wt% dry basis)

[0189] Cationic starch: 400 grams (7wt% dry basis)

[0190] Moisture content of mixture = 2450 / 8058 = 30.4 wt%

[0191] The components are added to a vessel and mixed for approximately 10 minutes to form a homogeneous mixture.

[0192] The mixture was fed into a mould (dimensions) on a vibration - pressing machine (Maxibrator™ available from Unicraft (Chennai, India)

[0193] Vibrated and pressed board (VP1, VP2): the mixture was placed into a mould and vibrated for between 10 and 15 seconds at 50 Hertz at an amplitude of 2 to 2.5 mm. The vibrated mixture was then hydraulically pressed at about 10 MPa for 1-3 minutes. VP1 was then cured at 110°C for to 4 to 6 hours to remove any residual moisture.

[0194] The pressed board (Pl, P2) was produced using a similar method, except that there was no vibration of the mixture prior to pressing.

[0195] Methodology

[0196] Unless otherwise specified and where applicable methodology and terminology is consistent with EN 1094-1:2008 and EN ISO 10635:1999.

[0197] Compression Strength (CS)

[0198] Samples of 35 mm length x 35 mm width and 25 mm thickness were obtained with the sample placed in a compression testing machine (Universal Testing Machine from Fuel Instruments and Engineers Pvt. Ltd (FIE), model Unitek 9450). A compression rate of 5 mm / minute was used with the compression load recorded as the board displacement reached 5%, 10% and 50% compression of the original thickness. Unless otherwise indicated the compression strength is measured in the length x width (L x W) or face plane. The test was performed at room temperature.

[0199] Modulus of Rupture (MOR)

[0200] The Universal Testing Machine from FIE (model Unitek 9450) was used to determine the MOR. A test sample of 250 mm length, 75 mm width and 25 mm thickness is dried to constant weight. The test sample is placed flat across the width on bearing cylinders with a span of 150 mm. A load is applied at a rate between 5 to 10 mm / minute and the peak load recorded.

[0201] Variation in density Boards are dried at 110°C for 4-6 hrs to remove moisture from the board. After drying, thickness and weight of the board is measured. From the weight of individual boards, variation density is measured. The 500 x 520 x 25 mm board is cut into 10 pieces of approximately 250 x 100 x 25 mm. The samples are taken at approximately evenly spaced locations including samples adjacent the corners. The samples are weighed, and the density determined therefrom.

[0202] Thermal Shock

[0203] A furnace was maintained at a temperature of 1200°C. Board samples (100 mm x 100 mm x 25 mm), at room temperature, were placed into the furnace in a vertical position for 15 minutes and then taken out of the furnace and allowed to cool at room temperature conditions for 15 minutes. The samples are not covered and are spaced sufficiently apart to enable dimensional changes and deterioration of individual samples to occur without impacting neighbouring samples. The samples were then visually inspected for cracking and then weighed. The samples were then returned to the furnace at 1200°C, after 15 minutes of cooling at room temperature, and the cycle was repeated.

[0204] Apparent Porosity

[0205] The apparent porosity was determined in accordance with British Standard 1902-308 / A. The reported values in Table 5 are the average of 4 samples. The variation in the porosity of the pressed boards was significantly higher than the variation in porosity of the vibration / pressed boards of the present invention.

[0206] Structural and functional variation

[0207] The structural and functional variation of the composite articles of the present invention were evaluated against air laid composite articles formed without vibration of the raw material mixture prior to pressing. The results (Table 2) indicate that the vibration step:

[0208] • increases the density of the result board;

[0209] • reduces the variation in density and porosity;

[0210] • increases the mechanical properties; and

[0211] • reduces the variation in the mechanical properties.

[0212] Table 2

[0213] *an outlying value was omitted.

[0214] As the results indicate, the vibration of the raw material prior to pressing reduces the variation in density by nearly 3 times. This results not only in an increase in the functional performance of the board, as determined by the modulus of rupture (MOR) and confined compressive strength (CCS) values, but also in the variations of these parameters. Due to the higher variation in functional performance of pressed board, design criteria would need to take into account not only the lower performance, but also the increased probability of obtaining a significantly lower than average performing board compared to the boards of the present invention. With greater certainty in the performance of the boards of the present invention, a lower safety margin may be incorporated into the specification of these boards in end-use applications.

[0215] Effect of vibration frequency

[0216] The effect of vibration frequency was evaluated by varying the vibration frequency of a VP1 formulation and processed board, with the only difference to the standard formulation and processing being the frequency of vibration. As indicated in the results in Table 3, an increase in the vibration frequency resulted in an increase in density and associated mechanical properties. It would be expected that the benefits of increasing frequency would begin to diminish and therefore frequency above 100 hertz may not represent any advantage than a frequency below 100 hertz or below 80 hertz.

[0217] Table 3 1

[0218] Effect of vibration duration

[0219] The effect of the duration of vibration of sample VP1 was studied, with the results provided in Table 4 below. The results indicate that an increase in densification and associated functional properties occurred by at least 15 seconds of vibration. Continued vibration after this point resulted in an oscillation in values comprising lower points at the 20 seconds and the 90 seconds mark. This oscillation in density and functional properties may be a result of the continued vibration resulting in stratification of the components, with high density components progressing towards the bottom of the layer. The skilled artisan would understand that the minimum and maximum duration of vibration may be dependent upon the nature of material used and the vibration conditions used, with the optimal duration of vibration readily obtainable through routine experimentation.

[0220] Table 4

[0221] Effect of process on mechanical properties Duplicate samples of boards of the present invention (VP1, VP2) were compared to pressed boards (Pl, P2) and vacuum pressed boards (VF1, VF2) in terms of mechanical properties (Table 5). The results indicated that the boards of the present invention had superior mechanical properties compared to just pressed boards. The vacuum formed boards had superior MOR values due to the increased levels of filler material, which also was reflected in the sample's increased density.

[0222] However, the composite article of the present invention possessed a higher compression strength to density ratio compared to vacuum formed or pressed board. This may be attributable to a more homogenous distribution of components, enabling a more even level of bonding, thereby reducing "weak spots" within the board which may result in premature mechanical failure in pressed boards. The vacuum formed boards higher filler content and layered microstructure may also be intrinsically of lower compressive strength for composites of the same density.

[0223] When a vacuum formed board without fillers (Example 2 from US6,987,076) was compared with a board of similar composition made using the process of the present invention (sample 9), the boards under the present invention were significantly denser and had significantly higher MOR values. Table 5

[0224] The variation in the apparent porosity of the pressed boards (Pl, P2) was significantly higher than the variation in porosity of the vibration / pressed boards (VP1, VP2) of the present invention.

[0225] Anisotropic Properties

[0226] The structural differences in the boards of the present invention results in lower anisotropic properties compared to boards derived from pressed blanket (Table 6). The compressive strength of boards measured against the face plane (L x W) and the edge plane (D x W) revealed that the while the vibration pressed board of the present invention was more anisotropic compared to a pressed board, the compressive strength was considerably greater in the edge direction compared to a pressed blanket sample. The pressed blanket also was exhibited anisotropic behaviour in terms of its linear shrinkage results (Table 7).

[0227] This reduction in anisotropic behaviour is also reflective in the superior thermal shock properties of the boards of the present invention versus pressed blanket boards. Lower anisotropy is also reflected in the thermal shock results (Table 9), in which vacuum formed composite articles performed poorly.

[0228] Compressive strength

[0229] As illustrated in Table 6, the pressed board exhibited isotropic behaviour with the 10% displacement compression strength result being within 2% of each other in the face and edge direction. In comparison, the vibration pressed board of the present invention exhibited more anisotropic behaviour, although the difference in directional compression strength between the Edge and Face direction of the boards were a modest 27.5%. In contrast, the pressed blanket board (PB), whilst having good compression strength in the face direction had very low compression strength in the edge direction to the extent the compression value was difficult to measure. As such, the difference in face to edge compression strength was estimated to be at least 90%.

[0230] Table 6

[0231] The results reflect the fact that the vibration pressed board (VP1) have an increased fibre alignment in the face plane relative to the pressed board (Pl). However, in contrast to the pressed blanket (PB), there is still sufficient portion of fibres with alignment in the edge plane to provide the vibration pressed board with acceptable compression strength properties in the edge plane. Linear shrinkage

[0232] Linear shrinkage was measured in accordance with EN ISO 10635:1999. Samples of boards with dimensions of approximately 120 mm x 60 mm x 25 mm were subjected to 1100°C for 24 hours with the linear shrinkage recorded in table 7 below. The results confirm that the vacuum formed board (VF1) had the lowest linear shrinkage overall, which may be attributable to the additional additives and higher density of this board. The vibration pressed board (VP1) of the present invention had a compared linear shrinkage to the pressed board (Pl), indicating that the effects of differences in fibre orientation and density (see Table 2) may have cancelled each other out. The blanked pressed board (PB1) had good linear shrinkage results in the W - L plane, however the linear shrinkage in the thickness dimension was about 7 times the shrinkage observed in the W - L plane. This factor can be attributed to the high degree of fibre alignment in the W-L plane.

[0233] Table 7

[0234] Thermal Conductivity

[0235] As indicated in Table 8, the thermal conductivity of the boards of the present invention (VP1) is comparable to vacuum formed boards (VF1) and superior to boards derived from pressed blankets (US7413797 - Example 1) or pressed vacuum formed board (US7413797 - Example 3). Table 8

[0236] A- 750°C

[0237] Effect of vibration on resultant composite article's thermal shock properties

[0238] The vacuum formed board exhibited cracking (along an edge plane) after the 3rdthermal cycle and after the 6ththermal cycle the board was considered to have failed due to delamination of the board being observed.

[0239] Sample VP1 and Pl continued to undergo thermal cycling for 34 cycles. After the 22ndcycle the board's weight was recorded and the percentage reduction in weight depicted in Figure 8. The increase in weight loss of Pl was also reflected by the roughened surface appearance of the board compared to VP1. The improved thermal shock performance of VP1 over Pl is attributed to the lower density variation obtained in boards formed by vibration / pressed process compared to just the pressed process. Increased differences in porosity and density are thought to result in increased thermal induced stresses which lead to fracturing and deterioration of the composite over repeated thermal cycles. The boards of the present invention have been found to be both superior to vacuum formed boards and conventional air laid boards (e.g. pressed blankets or pressed fibre mixture).

[0240] Table 9

[0241] X - signifies failure of the sample due to visual signs of cracking. With reference to Table 9, the mechanical properties of the vibro-pressed (VP1) boards maintained their superior properties of the pressed boards after 4 thermal shock cycles. In comparison the vacuum formed board started to show visual signs of cracking after 3 thermal shock cycles and visual signs of delamination after 6 thermal shock cycles. A photograph of the pressed board sample 300, vibro-pressed sample of the present invention 310 and the vacuum formed board 320 after 4 thermal shock cycles is provided in Figure 11, with clear visual cracking 330 observed along an edge plane. In contrast, no signs of cracking were observed for the pressed and vibro-pressed boards nor after 34 thermal shock cycles (images not shown).

[0242] Formula variations

[0243] As indicated in Table 10, the formulation of the composite article may be varied by adjusting the relative amounts and types of refractory fibre and binders. The type and amount of filler may be varied to produce either a low-density board, through the addition of low-density filler material or a high-density board, through the addition of a high-density filler material. In general, medium density board may be produced without the additional of fillers. Table 10 (Formulation and properties)

[0244] Ingredient list

[0245] Refractory fibre:

[0246] CERA™ refractory alumino-silicate fibre available Murugappa Morgan Thermal Ceramics Ltd (India)

[0247] Fillers:

[0248] A: ball clay - less than 3 wt% retention left on 325# mesh, Loss on ignition less than 11%, Moisture less than 1%, density: 2450-2650 kg / m3.

[0249] B: alumina spheres (small) - density less than 0.2 g / cc, size 1-2 mm

[0250] C: alumina spheres (large) - density less than 0.2 g / cc, size 1-5 mm

[0251] D: cellulose fibre - length less than 6 mm, cotton based

[0252] E: quartz - density: 3800 kg / m3moisture content max 0.2%, Loss on ignition less than 1%, purity Min 98%

[0253] F: alumina - density: 2400 - 2800 kg / m3, moisture content max 0.2%, Loss on ignition less than 1%, purity Min 98%

[0254] G: Wollastonite - moisture content max 2%, purity Min 95%

[0255] H: Perlite - density less than 0.4 g / cc, size: less than 3 mm

[0256] I: Water repellent - stearic acid dissolved in isopropyl alcohol / methylsiloxanes or mixture thereof.

[0257] J: glass wool

[0258] Inorganic binder:

[0259] A: colloidal silica (default unless otherwise indicated) - 30 wt% solids in aqueous solution

[0260] B: sodium silicate -(solids 40 % wt in aqueous solution) purity minimum 98 wt%.

[0261] C: ball clay - - less than 3 wt% retention left on 325# mesh, Loss on ignition less than 11%, Moisture less than 1%, density: 2450-2650 kg / m3.

[0262] Organic binder:

[0263] A: Starch (default unless otherwise indicated) - Cationic starch, supplier Wesbond™

[0264] B: epoxy resin - supplied by CUMI (India)

[0265] Patent Scope

[0266] The particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

[0267] For the avoidance of doubt it should be noted that in the present specification the term "comprise" in relation to a composition is taken to have the meaning of include, contain, or embrace, and to permit other ingredients to be present. The terms "comprises" and "comprising" are to be understood in like manner. It should also be noted that no claim is made to any composition in which the sum of the components exceeds 100%.

[0268] Although the invention herein provided a description with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope thereof. Thus, it is intended that the present invention include modifications and variations that are within the scope of the appended claims and their equivalents.

Claims

CLAIMS1. A process for producing a composite article comprising:A. batching together raw materials comprising: i. refractory fibres; ii. an inorganic binder; ill. an optional organic binder; iv. an optional fillerB. mixing the raw materials to form a mixture consisting of solid particles;C. feeding the mixture into a mould;D. vibrating the mixture;E. pressing the mixture; andF. curing the pressed mixture to form the composite article.

2. The process according to claim 1, wherein the mixture is vibrated under conditions sufficient to result in an increase in density of the resultant composite article of at least 3% compared to the resultant composite article without being subjected to vibration.

3. The process according to claim 1 or 1, wherein the mixture is vibrated at an amplitude in the range of 1 to 100 mm.

4. The process according to any one of the preceding claims, wherein the mixture is vibrated at a frequency of at least 0.1 hertz.

5. The process according to any one of the preceding claims, wherein the mixture is vibrated for in the range 0.5 to 500 seconds.

6. The process according to any one of the preceding claims, wherein the mixture does not comprise a discrete liquid phase.

7. The process according to any one of the preceding claims, wherein vibrating the mixture separates and re-orientates at least a portion of the refractory fibres.

8. The process according to any one of the preceding claims, wherein the refractory fibres, when in the form of a blanket, comprise a linear shrinkage of 5% or less after 24 hrs exposure at 1000°C measured in accordance with EN ISO 10635:1999.

9. The process according to any one of the preceding claims wherein the raw materials comprise: a. 20.0 to 95.0 wt% refractory fibres; b. 3.0 to 60.0 wt% inorganic binder; c. 0 to 20.0 wt% organic binder; and d. 0 to 40.0 wt% optional fillers, wherein the sum of the abovementioned components is at least 90 wt% of the total weight of the raw materials.

10. The process according to claim 9, wherein the sum of refractory fibres and inorganic binder is at least 80 wt% of the total weight of the composite article.

11. The process according to any one of the preceding claims, wherein the inorganic binder comprises an inorganic binder selected from the group consisting of colloidal silica, colloidal alumina, fine silica particles, precipitated silica or alkali metal silicates or any combinations thereof.

12. The process according to any one of the preceding claims, wherein the inorganic binder comprises colloidal silica.

13. The process according to any one of the preceding claims, wherein the organic binder comprises an organic binder selected from the group consisting of starch, catonic starch or resin.

14. The process according to any one of the preceding claims, wherein the refractory fibres have an arithmetic average diameter of between 1.5 and 10 pm.

15. The process according to any one of the preceding claims, wherein the mixture comprises an absorbed and or adsorbed liquid content of less than 30 wt% relative to the total weight of the mixture on a wet weight basis.

16. The process according to any one of the preceding claims, wherein the composite article is a board.

17. The process according to claim 16, further comprising the step of levelling the board from a board with a height variation of up to 7.0 % to a height variation less than 2.0% of the resultant levelled board.

18. A composite article comprising:20.0 to 95.0 wt% refractory fibres;3.0 to 70.0 wt% inorganic binder;0 to 20.0 wt% optional organic binder; and0 to 40.0 wt% optional filler, wherein the composite article has a linear shrinkage after exposure to 1100°C for 24 hours of less than 5% in each orthogonal dimension.

19. A composite article obtained or obtainable according to the process according to any one of claims 1 to 17.

20. A composite article according to claim 18 or 19,A) having a composition comprising:20.0 to 95.0 wt% refractory fibres;3.0 to 60.0 wt% inorganic binder;0 to 20.0 wt% optional organic binder; and the composition having a density of between 600 and 950 kg / m3and wherein the sum of the refractory fibres and inorganic binder is at least 80 wt% of the total weight of the composite article; orB) having a composition comprising:20.0 to 95.0 wt% refractory fibres;3.0 to 60.0 wt% inorganic binder;0 to 20.0 wt% optional organic binder; and0.2 to 40.0 wt% filler having a bulk density of less than 900 kg / m3, the composition having a density of between 300 and 650 kg / m3and wherein the sum of the refractory fibres, high temperature binder and low-density filler is at least 80 wt% of the total weight of the composite article; orC) having a composition comprising:20.0 to 95.0 wt% refractory fibres;3.0 to 60.0 wt% inorganic binder;0 to 20.0 wt% optional organic binder; and0.5 to 40.0 wt% high-density filler comprising a bulk density of greater than 900 kg / m3; and the composition having a density of between 900 and 1600 kg / m3and wherein the sum of the refractory fibres, inorganic binder and high-density filler is at least 90wt% of the total weight of the composite article.

21. The composite article according to claim 20, wherein:• the composition B) has a modulus of rupture (MOR) of at least 400 KPa;• the composition A) has a MOR of at least 1200 KPa; and• the composition C) has a MOR of at least 2000 KPa.

22. A composite article according to any one of claims 18 to 21 having a composition of:50.0 to 95.0 wt% refractory fibres;3.0 to 30.0 wt% inorganic binder;0 to 20.0 wt% optional organic binder; and0 to 10.0 wt% optional filler, wherein the density of the composite article is in the range 600 to 950 kg / m3.

23. The composite article of claim 22, wherein the weight ratio of the refractory fibres to the inorganic binder is at least 2:1.

24. The composite article according to claims 22 or 23, wherein the composition comprises at least 70 wt% refractory fibres.

25. The composite article according to any one of claims 22 to 24, wherein the compressive strength (@10% displacement) in the face plane (L x W) after four thermal cycles between room temperature and 1200°C is at least 600 KPa.

26. The composite article according to any one of claims 22 to 25, wherein the composition is substantially free of fillers.

27. The composite article according to any one of claims 18 to 26, wherein the standard deviation in density over the composite article is less than 5%.

28. The composite article according to any one of claims 18 to 27, wherein a compressive strength (@10% displacement compression) in the depth x width (edge) plane is at least 50% of the compressive strength in the length x width (face) plane.

29. The composite article according to any one of claims 18 to 28, wherein there are no signs of visual cracks from a 100 mm x 100 mm x 25 mm sample of the composite article after being placed a furnace at 1200°C for 15 minutes and then taken out of the furnace and allowed to cool at room temperature conditions for 15 minutes and the cycle repeated at 4 times.

30. The composite article according to any one of claims 18 to 29, wherein a ratio of a maximum compressive strength (MCS) to density of the composite article is at least 9.0 kPa.m3 / kg31. The composite article according to any one of claims 18 to 26, wherein the composite article has at least one or at least two or at least three or all of the properties:• standard deviation of density variation over the composite article less than 5%;• a compressive strength (@10% displacement compression) of the composite article in the depth x width plane is at least 50% of the compressive strength in the length x width plane;• no signs of visual cracks from a 100 mm x 100 mm x 25 mm sample of the composite article after being placed in a furnace at 1200°C for 15 minutes and then taken out of the furnace and allowed to cool at room temperature conditions for 15 minutes and the cycle repeated at 4 times; or• the ratio of a maximum compressive strength (MCS) to density of the composite article at least 9.0 kPa.m3 / kg.

32. The composite article according to any one of claims 18 to 31, wherein the refractory fibres have an arithmetic average length of between 0.2 mm and 150 mm.

33. The composite article according to any one of claims 18 to 32, wherein the refractory fibres comprise some fibres of at least 10 mm length.

34. The composite article according to any one of claims 18 to 33, wherein the composite article is between 5 mm to 200 mm thick.

35. The composite article according to any one of claims 18 to 34, wherein the composite article is at least 100 mm thick.

36. The composite article according to claim 20, wherein the filler having a bulk density of less than 900 kg / m3is selected from the group consisting of perlite, vermiculite, porous ceramic spheres, expanded clay, foamed lightweight geological materials, microporous silica, microporous alumina, expanded glass, hollow ceramic, glass spheres and combinations thereof.

37. The composite article according to any one of claims 18 to 36, in which the filler further comprises opacifier selected from the group consisting of chromium oxide, zirconium oxide, iron oxide, titanium oxide, manganese dioxide, ilmenite, quartz powder, silicon carbide, boron carbide, tantalum carbide, carbon black, graphite and combinations thereof.

38. The composite article according to any one of claims 18 to 37, comprising an apparent porosity of no more than 68%.

39. The composite article according to any one of claims 18 to 37, comprising an apparent porosity of no more than 65%.

40. A composite article as defined in claim 18 having a composition of:50.0 to 95.0 wt% refractory fibres;3.0 to 30.0 wt% inorganic binder;0 to 20.0 wt% optional organic binder; and0 to 10.0 wt% optional filler, the article having a density in the range 600 to 950 kg / m3and wherein the composite article has a linear shrinkage after exposure to 1100°C for 24hrs of less than 5% in each orthogonal dimension.

41. The composite article of claim 40 comprising:70.0 to 90.0 wt% refractory fibres; and10.0 to 30.0 wt% inorganic binder, wherein the sum of refractory fibres and inorganic binder is at least 90 wt% of the total weight of the composite article.

42. The composite article of claim 41 further comprising at least 1.0 wt% organic binder.

43. The composite article of claim 40, having an apparent porosity of no more than 68%.

44. The composite article according to any one of claims 18 to 43, having a homogeneous microstructure.

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