Carbide -boride and in-SITU boride composite material with thermoelectric properties

Abstract

The invention relates to a surface modification method for in-situ transition metal boride-coated semiconductor silicon carbide, boron carbide and silicon carbide-boron carbide composite granules ( 2 ) and to composite material s having a segregated network structure and thermoelectric properties. The production method for composite materials with thermoelectric properties includes mechanical alloying, grinding and sieving of the coating material mixture ( 1 ), preparing a surface activating liquid phase solution and dispersing the said solution on the surface of the granules, coating of the coating material mixture ( 1 ) on the surface of the composite granules ( 2 ) and sintering of the material. The final product has a conductive segregated network structure.

Description

[0001] DESCRIPTION

[0002] CARBIDE -BORIDE AND IN-SITU BORIDE COMPOSITE MATERIAL WITH THERMOELECTRIC PROPERTIES

[0003] The Subject of the Invention

[0004] The invention is related to a surface modi fication method of in-situ transition metal boride coated semiconductor silicon carbide , boron carbide and silicon carbide-boron carbide composite granules , which allows electrical energy to be obtained by a gradient of thermal energy applied to the material , with simultaneously increased electrical conductivity and reduced thermal conductivity to improve thermoelectric performance in thermoelectric materials and composite materials with segregated network structure obtained as a result of this method .

[0005] State of the Art

[0006] Today, increasing energy consumption and cost due to the rapidly growing world population has confronted humanity with problems such as global warming, climate change , environmental pollution and energy crisis . In this context , thermoelectric technology, which converts heat energy directly obtained from waste heat sources into electrical energy with the help of the Seebeck ef fect discovered by Thomas Johann Seebeck in 1821 , is considered as an important solution to the present environmental pollution and global energy crisis by providing cleaner energy by reducing greenhouse gas emissions while contributing to the worldwide energy demand . A thermoelectric module consists of a combination of n-type and p-type semiconductor thermoelectric materials connected electrically in series and thermally in parallel . When a temperature gradient is applied to the thermoelectric material , the mobile charge carriers at the hot end tend to di f fuse to the cold end . The accumulation of charge carriers results in a net charge at the cold end (negative for electrons , ( e~) , positive for electron holes , (h+) ) and causes a potential di f ference (voltage ) between the two ends . This phenomenon is called the Seebeck ef fect or thermoelectric ef fect . This phenomenon creates the basis of thermoelectric energy conversion .

[0007] In 1948 , the first commercial thermoelectric power generator was developed by Abram Fedorovich Iof fe . In the stated work, the heat emitted by an oil lamp energi zed a radio by converting into electrical energy through the use of ZnSb and constantan ( 55% Cu-45% Ni alloy) thermoelectric materials . A study implemented by S zybist et al . in 2018 aimed to convert the waste heat of high-temperature exhaust gas into electrical energy by using quasi-Heusler thermoelectric materials . Scutterudites , quasi-Heusler alloys and Si-Ge alloys are attractive material groups for thermoelectric studies , however these materials have disadvantages such as having rare element content and relatively high thermal conductivity that limit their potential applications . Besides this , Bi2Te3- based materials , known for their high thermoelectric performance , exhibit negative characteristics , including expensive elemental content and low thermal strength, which prevent them from being used in high-temperature applications .

[0008] Driven by the pursuit of sustainable energy sources and the pressing threat of energy crisis , many studies have been carried out with the aim of increasing the ef ficiency of existing thermoelectric materials and producing new ones . The documents on the studies aimed at providing clean energy through the use of thermoelectric materials are mentioned below . Patent document TR 2012 / 15684 can be given as an example of the state of the art . The invention described in the document aims to produce bismuth oxide nanocrystalline composite ceramic materials , incorporating nanocrystals , graphene and alkaline earth metals such as Ca, Sr, Ba in pellet form, using polyvinyl alcohol polymer solution by electro-spinning technique . A key aspect of the invention is to enhance its ef ficiency by adding graphene to the bismuth oxide structure , which exhibits superior thermoelectric properties when doped with alkali earth metal .

[0009] Another example of the state of the art can be found in the patent document TR 2018 / 04602 . The invention described in the document aims to utili ze the physical properties of graphene and boron materials to produce high quality thermoelectric materials by doping them with metal oxides having high thermoelectric properties , such as calcium cobalt oxide ( CaCoOs ) , thereby improving the thermoelectric performance of these metal oxides . Electro-spinning method was used for the synthesis of CaCoOs thermoelectric nanocrystalline ceramic composites doped with graphene and boron .

[0010] Patent document US 10964872B2 can be mentioned as another example of the state of the art . The document discloses a method for improving the thermoelectric properties of CaMnCh metal oxide material , wherein, in addition to doping the material with metals and metal oxides , 13- 16th group elements and rare earth elements are doped at the grain boundaries through the use of a liquid phase sintering method . The document further states that the thermoelectric performance of Cai-xBixMnCuy03 composition increases in certain temperature ranges . The patent document US20160104554A1 may be listed as another example of the state of the art . The document aims to produce porous polymer nanocomposites with a three-dimensional network structure in order to enhance their functionality for use in di f ferent energy applications . The main obj ective of the mentioned document is to tailor the properties of the produced material to match those of the secondary material based on the intended application area .

[0011] Another example of the state of the art can be found in the patent document JP2017135159A. The document relates to a thermoelectric element made of boron carbide ceramics with thermoelectric properties and a production method thereof . Amorphous boron and amorphous carbon are mixed, the powder mixture is molded, and a sintering operation is performed .

[0012] A material with high thermoelectric performance should have high electrical conductivity and low thermal conductivity . However, electrical conductivity and thermal conductivity properties , the two key properties that af fect thermoelectric performance , exhibit directly proportional behavior with respect to each other . Therefore , one of the main challenges is to simultaneously reduce the thermal conductivity of thermoelectric materials without negatively af fecting their electrical conductivity . A lot of methods have been developed to improve the performance of thermoelectric materials such as grain si ze reduction, nano-deposition technique , two- dimensional material synthesis , conventional composite approach (mixing at least two di f ferent materials ) and surf ace / interf acial modi fication . These known state of the art studies highlight the need for the production of cost- ef fective materials , with high temperature resistance and high thermoelectric performance , driven by factors such as the high-cost and extensive use of secondary materials doped into the main material , the limitations of materials suitable for high-temperature thermoelectric applications , and the complexity and high costs associated with production methods .

[0013] Commonly used thermoelectric materials have disadvantages such as high cost and complex production methods , the use of expensive / rare element content , toxicity to the environment and low thermal strength . Therefore , there is a need for developing easily accessible and cost-ef fective high temperature thermoelectric materials . To address these disadvantages , a surface modi fication method of silicon carbide , boron carbide and silicon carbide-boron carbide composite granules was developed . This method led to the creation of composite materials with a segregated network structure .

[0014] Detailed Description of the Invention

[0015] The invention relates to a surface modi fication method of in- situ transition metal boride-coated semiconductor silicon carbide ( SiC ) , boron carbide (BxC ) and silicon carbide-boron carbide ( SiC-BxC ) composite granules with increased electrical conductivity and reduced thermal conductivity in order to increase the thermoelectric performance of thermoelectric materials , allowing for the generation of electrical energy from the thermal energy gradient applied to the material , and composite materials with segregated network structure obtained by the use of the said method .

[0016] An obj ect of the invention is to obtain composites with thermoelectric properties having a transition metal-boride segregated network structure that simultaneously increases electrical conductivity and decreases thermal conductivity . Another obj ect o f the invention is to provide a method for producing composite materials exhibit both low thermal conductivity properties through increased phonon scattering, and high electrical conductivity enhanced by segregated conductive network structure .

[0017] Another obj ect of the invention is to provide a low-cost and simple production method, and a material from which superior thermoelectric properties can be obtained by means of the said method .

[0018] Another obj ect of the invention is the use of readily accessible and cheap components as an alternative to materials with expensive and rare elemental components used in high- temperature thermoelectric applications .

[0019] The invention is , in its most general form, a method of producing SiC, BXC and SiC-BxC composite materials having thermoelectric properties , wherein the method comprises the process steps of grinding of a coating material mixture ( 1 ) containing metallic boron, boron carbide , boron nitride and boron oxide particles and transition metals , transition metal carbide , transition metal nitride and solid solutions thereof or transition metal oxide to micron-si ze , preparation of a surface activating liquid phase solution and dispersion of the obtained surface activating liquid phase solution on the surface of SiC, BXC and SiC-BxC composite granules ( 2 ) , homogeneous coating of the coating solution obtained by mixing the said coating material mixture ( 1 ) and surface activator liquid phase solution on SiC, BXC and SiC-BxC composite particles and sintering operation . In an embodiment , the particles of the coating material mixture ( 1 ) are mechanically alloyed .

[0020] In an embodiment of the invention, the particle si ze of the coating material mixture ( 1 ) is below 25 pm .

[0021] In an embodiment of the invention, transition metals are Sc, Y, Ti , Zr, Hf , transition metal carbide ScC, YC2 , TiC, ZrC, HfC, transition metal nitride ScN, YN, TiN, ZrN, HfN and their solid solutions of TiCN, transition metal oxide SC2O3, Y2O3, TiO2, ZrO2, Hf 02•

[0022] In an embodiment of the invention, the coating is made by mechanical mixing, mechanical alloying, atomic layer deposition, residue precipitation, thermal spray, magnetron sputtering, physical vapor deposition, chemical vapor deposition and / or sol-gel technique .

[0023] In an embodiment of the invention, the coating solution comprises a solid phase comprising 0 . 5-35% by weight of the matrix material o f the coating material mixture ( 1 ) and 0 . 1- 5% by weight of the matrix material of the surfactant liquid phase .

[0024] In an embodiment of the invention, the surfactant liquid phase comprises organic materials such as PEG, CTAB, CTAC, Polyethyleneimine , SDS and combinations thereof and solvents such as distilled water, ethyl alcohol , isopropyl alcohol and / or combinations thereof .

[0025] In an embodiment of the invention, the surfactant liquid phase comprises 0 . 1- 10 wt% organic material . In an embodiment of the invention, the sintering is pressureless sintering, hot pressing, spark plasma sintering or hot isostatic pressing sintering.

[0026] In an embodiment of the invention, the sintering temperature value in spark plasma sintering is 1500-2300°C, the heating rate is 20-250°C per minute, the sintering time is 1-60 minutes, and the sintering pressure is 10-80 MPa.

[0027] In an embodiment of the invention, the spark plasma sintering is carried out under vacuum, argon and / or nitrogen atmosphere conditions .

[0028] SiC, BXC and SiC-BxC composites obtained by the inventive method are also encompassed by the protective scope of the invention .

[0029] The composite obtained by the inventive method comprises 65- 99.5 wt% matrix, 0-9.5 wt% boron source, 0-24.5 wt% transition metal source as solid phase, 0-5 wt% solvent and 0-0.5 wt% organic matter as liquid phase. The composite obtained by said method comprises SiC, BxC and / or SiC-BxC as matrix. In an embodiment of the invention, the matrix is SiC, the boron source is B4C, the transition metal source is Tie, the solvent is ethyl alcohol, and the organic material is PEG.

[0030] The invention relates to obtain silicon carbide, boron carbide or silicon carbide-boron carbide based composites with a transition metal boride (ScBx, YBX, TiB2, ZrB2, HfB2) segregated network structure that simultaneously increases electrical conductivity and decreases thermal conductivity with silicon carbide (SiC) and boron carbide (BXC) based granules and composite granules (SiC-BxC) , preferably mechanically alloyed with metallic boron (B) , boron carbide (BXC) , boron nitride (BN) and boron oxide (B2O3) particles and transition metal (Sc, Y, Ti, Zr, Hf) transition metal carbide (ScC, YC2, TiC, ZrC, HfC) , transition metal nitride (ScN, YN, TiN, ZrN, HfN) and solid solutions thereof (such as TiCN) or transition metal oxide (SC2O3, Y2O3, TiCh, ZrO2, HfCh) particles, preferably during pressure sintering.

[0031] The invention is based on the use of a p-type semiconductor material in thermoelectric modules that provide electrical energy to be obtained by using the Seebeck effect with the thermal energy gradient applied to the material.

[0032] The same or superior thermoelectric properties are obtained by using approximately 1 / 3 secondary phase compared to previous techniques by coating mechanically alloyed boron carbide (BXC) , metallic boron (B) , boron nitride (BN) or boron oxide (B2O3) with transition metals (Sc, Y, Ti, Zr, Hf ) , transition metal carbides (ScC, YC2, TiC, ZrC, HfC) , transition metal nitrides (ScN, YN, TiN, ZrN, HfN) and their solid solutions (such as TiCN) or transition metal oxides (SC2O3, Y2O3, Ti02, ZrO2, HfO2) , and obtaining SiC and BXC composites showing thermoelectric properties with transition metal boride (ScBx, YBX, TiB2, ZrB2, HfB2) segregated network structure by in-situ reactions carried out during sintering, which generally increase electrical conductivity and decrease thermal conductivity simultaneously.

[0033] The invention is a surface modification method for in-situ transition metal boride-coated semiconductor silicon carbide and boron carbide or silicon carbide-boron carbide composite with simultaneously increased electrical conductivity and reduced thermal conductivity to improve thermoelectric performance. Surface coating process can be realized by more than one method. The surface coating process can be implemented by more than one method . These methods are mixing methods , mechanical alloying method, sol-gel method, atomic layer deposition method, residue precipitation method, thermal spray method or magnetron sputtering methods . In order to increase the electrical conductivity with in-situ transition metal boride segregated network structure , the coating must be homogeneously dispersed in the microstructure to provide electron movement . In order to reduce thermal conductivity with in-situ transition metal boride segregated network structure , the coating should be homogeneously dispersed in the microstructure to increase phonon scattering . An optimum thickness of surface coating ( 0 . 1 pm- 10 pm) is predicted by mechanical alloying and coating methods .

[0034] Detailed information about the studies carried out is given below .

[0035] Table 1 . In-situ TiEk segregated networked SiC compositions

[0036] Example 1 : SiC, BXC and SiC-BxC composite granules without segregated network structure ( 2 )

[0037] In the present example , no coating material mixture ( 1 ) was applied on SiC, BXC and SiC-BxC composite granules ( 2 ) . This composition can be used as a reference sample . Example 2: SiC granules containing in-situ TiE>2 segregated network structure

[0038] In the present example, the coating material mixture (1) containing a mixture of 3% B4C and 6% Tie by weight was used.

[0039] Table 2. Comparison of the reference sample (Sample 1) and the composition coated with a mixture of 3 wt% B4C and 6 wt% TiC ( S amp 1 e 2 )

[0040] The electrical conductivity, thermal conductivity and ZT values of the samples without segregated network structure (Sample 1) and with segregated network structure (Sample 2) are compared in Table 2. It is considered that the electrical conductivity is improved by about 3000 times with the segregated network structure and the thermal conductivity is improved by about 2.5 times simultaneously. In this context, the present inventors consider that the ZT value, which determines the performance of thermoelectric materials, is improved by about 300 times with the in-situ TiB2 segregated network structure formed. The schematic representation of the in-situ HB2 segregated network formation process is shown in Figure-1 and the image of the TiB2 segregated network sample (Sample 2) analyzed by scanning electron microscopy is shown in Figure-2. Figure-1 shows the coating material mixture (1) , SiC, BXC and SiC-BxC composite granules (2) and conductive network structure (3) . The conductive network structure (3) is also shown in the image obtained by scanning electron microscopy in Figure-2. An advantage of the surface modi fication method of the invention is that the composites obtained by this method have high electrical conductivity and low thermal conductivity through the segregated network structure . These properties provide the composites to show superior thermoelectric properties .

[0041] Another advantage of the surface modi fication method of the invention is that it provides a low-cost and simple production method for producing composites with high thermoelectric properties .

[0042] Another advantage of the surface modi fication method of the invention is that it is free from toxic structures that could harm the environment .

[0043] Another advantage of the surface modi fication method of the invention is to obtain a composite with thermal resistance suitable for use as a high temperature thermoelectric material by means of the said method .

[0044] Description of Figures

[0045] Figure- 1 : Schematic representation of the in-situ TiEk segregated network formation process

[0046] Figure-2 : Scanning electron microscopy image of a sample with in-situ TiEk segregated network structure

[0047] Description of Reference Numbers in Figures

[0048] 1 . Coating material mixture

[0049] 2 . Composite granules

[0050] 3 . Conductive network structure

Claims

CLAIMS1. A production method for producing SiC, BXC and SiC-BxC composites with thermoelectric properties, wherein the method is characterized by comprising the process steps of: grinding of a coating material mixture (1) containing metallic boron, boron carbide, boron nitride and boron oxide particles and transition metals, transition metal carbide, transition metal nitride and solid solutions thereof or transition metal oxide to micron-size, preparing a surface activating liquid phase solution and dispersing the obtained surface activating liquid phase solution on the surface of SiC, BXC and SiC-BxC composite granules ( 2 ) , homogeneous coating of the coating solution obtained by mixing the mentioned coating material mixture (1) and surface activator liquid phase solution on SiC, BXC and SiC-BxC composite granules and subjecting to sintering process.2 . A method according to claim 1, wherein the particles of the coating material mixture (1) are mechanically alloyed.

3. A method according to claim 2, wherein the coating material particle size is below 25 pm.

4. A method according to claim 1, wherein transition metals are Sc, Y, Ti, Zr, Hf, transition metal carbides are ScC, YC2, TiC, ZrC, HfC, transition metal nitrides are ScN, YN, TiN, ZrN, HfN and solid solutions thereof are TiCN or transition metal oxides are SC2O3, Y2O3, TiCh, ZrCh, HfCh.

5. A method according to claim 1, wherein coating is done by mechanical mixing, mechanical alloying, atomic layerdeposition, residue precipitation, thermal spray, magnetron sputtering, physical vapor deposition, chemical vapor deposition and / or sol-gel technique.

6. A method according to claim 1, wherein coating solvent comprises- the solid phase containing 0.5-35% by weight of the matrix material of the coating material mixture (1) 0.1-5% by weight of the matrix material of the surfactant liquid phase.

7. A method according to claim 1 or 6, wherein the surfactant liquid phase contains organic materials such as PEG, CTAB, CTAC, Polyethyleneimine, SDS and combinations thereof and distilled water, ethyl alcohol, isopropyl alcohol solvents and / or combinations thereof.

8. A method according to claim 7, wherein the surfactant liquid phase contains 0.1-10 wt% of organic material.

9. A method according to claim 1, wherein the sintering includes pressureless sintering, hot pressing, spark plasma sintering or hot isostatic pressing sintering.

10. A method according to claim 9, wherein in the spark plasma sintering the sintering temperature is 1500-2300°C, the heating rate is 20-250°C per minute, the sintering time is 1-60 minutes, the sintering pressure is 10-80 MPa.

11. A method according to claim 9, wherein the spark plasma sintering is performed under vacuum, argon and / or nitrogen atmosphere conditions.

12. The SiC, BXC and SiC-BxC composite obtained by a suitable method according to any one of the preceding claims.

13. A composite according to claim 12, comprising 65-99.5 wt% of matrix, 0-9.5 wt% of boron source, 0-24.5 wt% of transition metal source, 0-5 wt% of solvent and 0-0.5 wt% of organic matter as solid phase.

14. A composite according to claim 13, wherein the matrix isSiC, the boron source is B4C, the transition metal source is Tie, the solvent is ethyl alcohol and the organic matter is PEG.

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