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Ceramic Raw Materials VIII 1

Advanced Ceramic Raw Materials

Advanced Ceramic Raw Advanced Ceramic Raw MaterialsMaterials

Part VIIIPart VIII


Advanced Ceramics

Mechanical properties

Thermal properties

OpticalProperties

Biologicalproperties

Electronic and magnetic

• varistor• sensor• piezoelectric• ferroelectric• electronic parts• ate…

• Light emitting• translucent porcelain• cable• optical fiber

• artificial bone and teeth• bone substitute• dental materials

• Abrasive• machine parts• turbines• blades

• refractory • furnace lining, bricks• heating elements• high temp. machine parts


Advanced Ceramic Raw Materials

• Oxide

• Nitride

• Carbide

• BorideReference: 1.Materials Science and Technology Vol. 11: Structure and properties of ceramics, edited by R.W. Cahn, P. Haasen and E.J. Kramer, VCH, 19942. Dibyendu Ganguli and Minati Chatterjee, Ceramic powder preparation: a handbook, Kluwer academic publishers,1997


Application areas for representative engineering ceramics

1.Materials Science and Technology Vol. 11: Structure and properties of ceramics, edited by R.W. Cahn, P. Haasen and E.J. Kramer, VCH, 1994


�� Advanced ceramic �� 2001

• Electronic 68.1%

• Coatings 8.1%

• Chemical & Environmental 17.9% Structural 5.9%

• Source: Business Communications Co., Inc.


Oxide CeramicsOxide CeramicsOxide Ceramics

TiOTiO22, SiO, SiO22, , mullitemullite, , MgOMgO, , Barium Barium titanatetitanate and lead and lead titanatetitanate


Titanium oxideTitanium oxideTitanium oxide

TiOTiO22


Polymorphic forms

• Anatase (tetragonal)

• Rutile (tetragonal)

• Brookite (ortho-rhombic)


Uses:

• Pigments: brightness and very high refractive index (n=2.4). TiO2is also an effective opacifier in powder form, where it is employed as a pigment to provide whiteness and opacity to products such as paints, coatings, plastics, papers, inks, foods, and most toothpastes. In cosmetic and skin care products, titanium dioxide is used both as a pigment and a thickener. In ceramic glazestitanium dioxide acts as an opacifier and seeds crystal formation.

• Photocatalyst: anatase form is a photocatalyst under ultraviolet light. It is used for anti-fogging coatings or self-cleaning windows. TiO2 incorporated into outdoor building materials can substantially reduce concentrations of airborne pollutants such as volatile organic compounds and nitrogen oxides.

• Waste water remediation• Oxygen sensor


ก�� TiO2

�ก ilmenite (FeTiO3) ��

• Digestion of ilmenite ore in H2SO4

• Separation of the less soluble iron sulphate, FeSO4.7H2O

• Thermal hydrolysis of the titanium-containing species, i.e. TiO(SO4) to obtain hydrous titania

• Washing and calcination of the hydrous oxide to obtain TiO2


�ก TiCl4• Chlorination of natural rutile to obtain TiCl4

• Purification of TiCl4 by distillation

• Reaction between vaporized TiCl4 and O2 to obtain TiO2

ก�� TiO2


• Hydrothermal synthesis:

200-700°C, 10-150 MPa and 0-120 h.

Ti + 2H2O � TiO2 + 2H2

Ti + x/2 H2 � TiHx (x~1.9)

TiHx + 2H2O � TiO2 + (2+x/2) H2

ก�� TiO2


Barium titanateBarium Barium titanatetitanate

BaTiOBaTiO33


Structure

• Hexagonal (high temp. form)

• Perovskite (low temp. form)

• Tetragonal (< 130°)


Uses:

• Dielectric materials: capacitor

• Piezoelectric materials: microphones, transducers

• Positive temperature coefficient: Thermistors and self-regulating electric heating systems.

• Thin films of barium titanate display electrooptic modulation to frequencies over 40 GHz.[3]


ก�� BaTiO3

• Solid state reaction: 1000-1300°C

BaCO3 + TiO2 � BaTiO3 + CO2

BaCO3 + BaTiO3 � Ba2TiO4 + CO2

Ba2TiO4 + TiO2 � 2BaTiO3


• Commercial techniques: barium titanyl oxalate BaCl2 + TiCl4 + 2H2C2O4 + 5H2O �BaTiO(C2O4)2.4H2O + 6HCl

25-225°C

BaTiO(C2O4)2.4H2O� BaTiO(C2O4)2 +4H2O225-465°C

BaTiO(C2O4)2 + 0.5H2O � BaCO3 + TiO2 + CO + 2CO2

465-700°C

BaCO3 + TiO2 � BaTiO3 + CO2

ก�� BaTiO3


Lead titanateLead Lead titanatetitanate

PbTiOPbTiO33


Polymorphs of PbTiO3

• Tetragonal (low temp.)

• Cubic (high temp.)

• Transformation at 490°C


ก�� PbTiO3

• Co-precipitation

Pb(NO3)2 + TiCl4 at pH~ 10, 40-45°C� precipitate � washing� drying and calcined at 400-800°C �Tetragonal PT

• Decomposition of lead titanyl oxalate precursor at 600°C

• Hydrothermal: treatment of an aqueous solution containing lead and titanium ions for 130-250°C under pressure.


Uses:• Piezoelectric• Thin film ferroelectric• PZT is used to make ultrasound transducers and

other sensors and actuators, as well as high-value ceramic capacitors. PZT is also used in the manufacture of ceramic resonators for reference timing in electronic circuitry.


Nitride Ceramic

• Transition metal nitride (Ex. TiN, VN, ZrN)high hardness and stiffness� wear resistance application and coating

• Si3N4

• Sialon (Si-Al-O-N) for cutting tools• Aluminium nitride (AlN): high thermal conductivity�� :• ��!��"��#� • $�$�� ก��%�� &'()#��*�+��• �,!��+ ��• ��!&'��$�ก�� !��"��#�$�% &'()#��#�• $�*- $�!��+ ��ก


Silicon nitrideSilicon nitrideSilicon nitride

SiSi33NN44


Application of silicon nitride

• .��$�%/.+ก��%�01�/��'$�%��!��+ ��#�

• ��&��

• .��$�%�+ ��ก��$�% &'()#��#�


α-β Silicon Nitride Phase Transformation

• ��ก/� liquid phase sintering $�% &'()#��#�ก�� 1400°C ��3% α phase $�%*�+��!��+ �/��ก4$�%�� ก0��#� � ��ก�� meta-silicon-oxynitride ��%�!3

1400°C, P of O2 = 10-20 atm

α Si3N4 (+Si2N2O) � β-Si3N4 + Si2N2O (Wild et al,1972)

β-form �ก��*�+/��ก4$�%�� ก0��%,α-from �ก��*�+/��ก4$�%�� ก0��#� (Roberts et.al., 1972)


AB layers in the crystal structure of β-Si3N4(after Hampshire et al., 1978)

After Redington, 1989)


The ABCD stacking of layers in the α silicon nitride structure giving rise to two closed

interstices per unit cell(after Hampshire et al., 1978)

(after Redington, 1989)

C layer

D layer


ก�� Silicon nitride

1. The nitridation of silicon 3Si + 2N2 �� Si3N4

2. Chemical vapor deposition 3SiCl4 + 4NH3 �� Si3N4 + 12HCl �� ก (amorphous) �� 1300°°°°C ก��

��ก�� !3. Carbo-thermal reduction of silica

1300-1700°°°°C3SiO2 + 6C + 2N2 �� Si3N4 + 6CO �%&��'��()�*�%�� +��!��ก,ก%�-�,-.��(/�,ก%�*0%ก%�%�� !+�'� 1��(��'��-� SiO 1��

SiC ,ก%�+�'�� 2��3��1��3 /4��%��,-��-� 4. Silicon diimide precipitation

1200-1500SiCl4 + 6NH3 �� Si(NH)2 + 4NH4Cl 3Si(NH)2 �� Si3N4 + 2NH3


Vapor-phase ammonolysis of silicon tetrachloride

• in DC plasma, RF plasma • 3SiCl4 + 4NH3 → Si3N4 (α-phase) + 12HCl↑

1100-1400°C

• 3 Si3N4 + 4 NH3 → Si3N4 + 12H2

• 3 SiCl4 + 16 NH3 → Si3N4 + 12NH4Cl• 3 SiCl4 + 4 NH3 → Si3N4 + 12HCl

Raw materials SiCl4 or SiH4

Pulverizing(refining)

Pyrolysis: Production of Si3N4

ClassificationRefiningProducts


Thermal decomposition �ก silicon diimide

SiCl4 + 6NH3 � Si(NH)2 + 4NH4Cl

1200-1500 °c

• 3Si(NH)2 → Si3N4+2NH3 ↑

• To minimize contamination with C, O and various metallic impurities.

• ก��+�� method (�3 process $�%��ก�� $,/(+*�+ product $�%��ก��ก��+�� .�� shape, size of particles, impurities and phases


�ก7' � �� Si3N4 $�%��• ��#��$�%��%,�� 3% /(+��8 ��ก��*�+��3% �,*��1��#�

• ��"ก ��3��$�%��ก��3% /(+�ก��9�ก��*�+�� 3% ��ก�� *�+��3� $�%��

• ��-� α �ก ��3% $,/(+�ก��ก�sintering �� • ��%��3 ��%,��3% (�ก��%��ก��ก��9�ก��:�� 3%��

$,/(+!��"�� )�';<��


Characteristics of Si3N4 powders, processed by different preparation methods (Wötting and Ziegler, 1986)



Silicon nitride ceramics

• Monolithic Silicon Nitride

• Reaction bonding (RBSN)

• Sintering and gas-pressure-assisted sintering (SSN)

• Hot pressing (HPSN) and hot isostatic pressing (HIPSN)


Reaction-bonded silicon nitride (RBSN)

• .��*��(�� ก ��$��$��)�';<

• ��#��&�)�/�� ' 20-30 %

• ��!��"��+ �ก�� SSN, HPSN

• �-�$�%�ก��1��:�*�+$�� α � β �1�� #�ก�� gas composition, pressure, temperature, heating rate

Silicon powder �&)!�"กก�� 10 *�!� �

High temperature,N2 gas atmosphere


Typical analysis of a commercial silicon powder used for RBSN (Stuart Hampshire, 1994)



��)�ก��ก��silicon nitride /��9�ก�� Reaction-bonding process. Model by Atkinson et al. (1976):ก��ก�� Silicon nitride ?��ก��ก��ก��!3% ��+� silicon ?�� evaporation-condensation or surface diffusion �+�$,�9�ก��ก��ก@0 Oxygen $,/(+*�+ SiO vapor 01%�� $,�9�ก��ก��ก@0 N2 *�+��:� silicon nitride $,/(+�ก��#��&�ก�+��1�� ก�� silicon nitride � �A )�/��#��&�� N2 �+�� 3% �9�ก��,��*� ก"� *�+ silicon nitride $�%�ก��ก� �B��#��&��(��


RBSN ��!3 silicon, ��$!3 nitride ��,!3 �#��&� (after Atkinson et al. 1974)


Hot-pressed Si3N4 (HPSN)

α-Si3N4+ 1 wt% MgO

1650-1850°C for 1-4 h.,N2 gas for 15-30 MPa

• ��+ �,ก�� #��• �,��:��+ ��ก��ก��.�� • ��ก��-�$�%*��+ �ก��3% ��กก��!��.��/�ก� sintering HPSN (after Ziegler et al.,1987)


Sintered silicon nitride (SSN)

• �!8#ก � *�+��)�';<$�%��#��0��0+ �• ��3% ��ก*��/.+!��/�ก��1ก� $,/(+�ก��ก��

� � silicon nitride *�+$�% &'()#��#� �$,ก��1ก/�+ �� +�� boron nitride ��3% �ก�� (� ก*� (Wötting and Hausner, 1983)

Microstructure of SSN


Si3N4 powder+ MgO, Y2O3

�� boron nitride ��3% �ก�� (�

1700-1800°C N2 gas for 0.1 MPa


Sintered Reaction-bonded Silicon Nitride (SRBSN)

• �� silicon nitride ��(��A�+��,*��1ก/(+��!��(��#��1�� ?��ก�(�� 45-55% $,*�+?��ก�� silicon ก�� MgO or Y2O3 ก� ��,*��1��#� �+��ก� ��ก� nitriding ��:� RBSN

• /(+!��+ ��81� 1800-2000°C /��ก4*�?��$�% 0.1-8 MPa �+�FG��/� inert boron nitride � *�+!��(�� ' 98% theoretical density

Scanning electron micrograph of a polished and etched section of SRBSN (after Kleebe and Ziegler, 1989)

Si powder+ MgO, Y2O3

1800-2000°C N2 gas for 0.1-8 MPa


Hot Isostatically Pressed Silicon Nitride (HIPSN)

• ��:��ก��1��#�� $,ก��1ก*��+ �Aก�� P = 200 MPa /� Autoclave &'()#��#��กก�� 1700°C /��ก4 Ar (�3 N2 /��!��.�� ก��1��#��:�.��$�%��!��&�� #� �+��,�� HIP �ก!��*�+ ��3% ��ก��J��/.+ additive ��'�+ ��1�$,/(+*�+.��$�%!��"��ก��J� 3%�

• RBSN, SSN, SRBSN ��8�,��ก� ��ก��*�+��3% /(+��!��(��ก�1�� ก

Transmission electron micrograph of HIPSN (after Rouxel, 1990)

1700-1900°C N2 gas for 200 MPa RBSN, SSN, SRBSN

ก� �� ก+�


Mechanical properties of silicon nitride

R.W. Cahn, P. Haasen and E.J. Kramer, Materials Science and Technology, Vol.11, VCH, 1994


Aluminium NitrideAluminiumAluminium NitrideNitride

AlNAlN


Aluminium nitride, AlN• Covalent of nitride• Crystal structure = wurzite structure with nitrogen atoms in

a close-packed hexagonal arrangement and with aluminiumatoms occupying half of the tetrahedral interstitial sites in the structure (a= 3.114 °A and C = 4.986 °A)

Bruce G. Hyde, John G. Thompson and Ray L. Withers, 1994


!&'��$�%�,!�K� � AlN

• �,!��+ �*�+��

• �� $J�ก��%,

• ��!��+�$�*--L�#�

• ��!�ก�ก� ��!��+ ��#�

• �!8#ก *��:��7


Application of AlN

• Insulating substrate

• Packing material for high power, high-speed microelectronic, high packaging density integrated circuits (ICs)


��J�ก�� AlN• Nitridation

> 1200°C

2Al + N2 � 2AlN High exothermic and high purity• Carbothermal reduction of alumina

>1400°C

Al2O3 + 3C + N2 � 2AlN + 3CO�+ � calcined �ก!��$�% 1200°C ��3% *�!�<� �$�%�ก�ก�� ก*� (Kuramoto and Taniguchi, 1986)

• Ammonia reaction with aluminum compoundAlCl3 + NH3 � AlN + 3HClAlN *��8 self-sintering ��3% /(+��!��(��#�'<*�+ (3.2 g/cm3) �+ �

�� additives �.�� CaO, MgO, Y2O3

• Carbonitridation (J.M. Haussonne et al., 1993) > 1100°C

Al + C + 2N2 � AlN


AlN Ceramics

• AlN + CaO, Y2O3 (�3 rare earth oxide

• �1��#�?��ก� ��(�3 tape casting

• sintering at 1650-1900°C in N2 gas • ��8�1��#�?��/.+ hot pressing


Aluminium oxynitride(AlON)

• Transparent � optical transparency in infra red and visible regions

• Electromagnetic window

• AlN + Al2O3 � AlON

(2025°C under N2 gas)

• Sintering: AlON + rare earth oxide (Y2O3, La2O3) at 1930°C for 24-48 hr. (Gentilman et.al.,1985)


ตื่นกอน!อยาเพิ่งนอน....


Boron NitrideBoron NitrideBoron Nitride

BNBN


Boron nitride (BN)Crystal structure:Crystal structure:Crystal structure:Crystal structure:• hhhh----BN [HBN] = hexagonal (graphiteBN [HBN] = hexagonal (graphiteBN [HBN] = hexagonal (graphiteBN [HBN] = hexagonal (graphite----

like) like) like) like) ใชกระบวนการขึน้รปูโดยใชกระบวนการขึน้รปูโดยใชกระบวนการขึน้รปูโดยใชกระบวนการขึน้รปูโดย hothothothot----pressing pressing pressing pressing หรอืเคลอืบผวิดวยวธิีหรอืเคลอืบผวิดวยวธิีหรอืเคลอืบผวิดวยวธิีหรอืเคลอืบผวิดวยวธิี CVDCVDCVDCVD

• CCCC----BN [CBN] = cubic (diamondBN [CBN] = cubic (diamondBN [CBN] = cubic (diamondBN [CBN] = cubic (diamond----like): like): like): like): นยิมทาํเปนวสัดขุัดนยิมทาํเปนวสัดขุัดนยิมทาํเปนวสัดขุัดนยิมทาํเปนวสัดขุัด มคีวามแขง็มากมคีวามแขง็มากมคีวามแขง็มากมคีวามแขง็มาก เตรยีมไดเตรยีมไดเตรยีมไดเตรยีมไดจากจากจากจาก HBN HBN HBN HBN ทีค่วามดนัและอณุหภมูิสงูทีค่วามดนัและอณุหภมูิสงูทีค่วามดนัและอณุหภมูิสงูทีค่วามดนัและอณุหภมูิสงู คลายคลายคลายคลายกบัการสงัเคราะหเพชรกบัการสงัเคราะหเพชรกบัการสงัเคราะหเพชรกบัการสงัเคราะหเพชร จงึนาํไปใชในงานขดัจงึนาํไปใชในงานขดัจงึนาํไปใชในงานขดัจงึนาํไปใชในงานขดัหรอืงานตดัโลหะหรอืงานตดัโลหะหรอืงานตดัโลหะหรอืงานตดัโลหะ


ก��!� (< BN

• Direct nitridation of boron in nitrogen at 1400-1900°C and ammonium chloride and thiocyanate are used to increase the reaction rate � HBN

• Reaction between BCl3 + NH3 at -70°C� B(NH2)3 or Cl3B3N3H3. and then powder is heated at 1100°C under N2 atmosphere � BN

• Reaction between BCl3 and NH4Cl at a reflux temperature of 200°C� Cl3B3N3H3 then powder is heated at 1100°C under N2 atmosphere � BN

• Reaction between NaBH4 and NH4Cl at 170-180°C. then powder is heated at 1100°C under N2 atmosphere � BN

R.S. Kalyoncu, Ceram. Eng. Sci. Proc., 6, 1356-64 (1985)


Properties of AlN, AlON and BN

From David W. Richerson, Modern Ceramic Engineering, 1992


Carbide CeramicsCarbide CeramicsCarbide Ceramics


Carbide Ceramics

• Ex. SiC, TiC, B4C, Al4C3, WC etc• Other transition metal-carbon system: ex. Zr-C, Cr-C, Mo-C, W-C, Mn-C system

• ��:� covalent bonding ( �� ionic(�3 metallic bond)

Ceramic Raw Materials VIII 57From David W. Richerson, Modern Ceramic Engineering, 1992


Silicon CarbideSilicon CarbideSilicon Carbide

SiCSiC


Silicon Carbide (SiC)

• Intermediate solid compound in Si-C system• Cubic β-from• Hexagonal α-formคณุสมบัต ิ• สลายตวัที่ at 2500 °C /��ก4�ก��• มีความแข็งมาก• นําความรอนไดดี• ทนตอการคบืที่อุณหภมู ิสงู• มีคณุสมบัตเิปนสารกึ่งตวันํา• ทนทานตอการกัดกรอนในบรรยากาศทีม่ีออกซิเจน (Oxidation and

Corrosion resistance)


Atomic arrangement in the most common SiC polytypes(Ryan et al., 1968)


Si-C phase diagram (Massalski, 1990)


Synthesis of SiC powder

1. Acheson Method2500 °C

SiO2(s) + 3C(s) → SiC(s) + 2CO (g)electrical heating

• Low cost• !��&$J�M 97-99%2. Low Temperature Carbonization of SiO2

1400-1800 °C

SiO2 + C (powder) → SiC + 2CO• *�+ Crystals ��:� β-SiC ��&$J�M >98%, 99%• Fine grain3. Vapor Phase Reaction3.1 sublimation in an inert atmosphous

Si(s) + C �1300°C �β-SiCSi(g) + C �2500°C � β-SiC


3.2 vapor phase reaction with methaneSi(g) + CH4 � SiC + 2H2

3.3 Silane in hydrogen SiH4 + carbon-containing compounds � SiC

3.4 Vapor phase reaction of silicon tetrachloride with toluene or other hydrocarbons in hydrogen such as methane, hexane or chloroform

SiCl4 + C6H5-CH3 � 1200-1800°C in H2 atmosphere� SiC + 4HCl (+C)

7SiCl4 + C7H8 + 10H2 → 7SiC + 28HCl (hydrocarbon)

•/.+(�กก� Chemical Vapor Deposition (CVD) *�+ β-SiC ��&$J�M 94-97%แตมีราคาสูง *��(� $,/�ก��.��'�.�< �(� �,(�� SiC coating graphite �� substrate


Large, elongated, lath-like α-SiC particles in pressureless sintered material grown at 2100°C at

the expense of β-SiC (Mitchell et al., 1978)


Typical properties of dense SiC

From David W. Richerson, Modern Ceramic Engineering, 1992


Application of SiC

• ��&ก��%�01�$�% &'()#��#�• ��&�� • Heating element �#�81� 1600°C

figures from JJISCO


Titaniun CarbideTitaniunTitaniun CarbideCarbide

TiCTiC


Titanium Carbide (TiC)

• Crystal structure: Cubic �� FCC (NaCl structure)

Crystal structure of TiCwith orbital overlapping: Black= titanium, white = carbon (Neckel, 1990) Every metal and carbon atom is surrounded by eight next- neighbors of the respective other species in an octahedral configuration


!&'��:

• �,!��+ �*�+��

•$�$�� ก��%�� &'()#��ก

• ��!��"��ก

Titanium Carbide


Applications of TiC

• Redding Titanium Carbide Pistol Dies

• Cutting tools

• Cutting wheel

• Semiconductor

Figures from 10ring.com, Kyocera


การสงัเคราะห TiC Powder

• 1. Conversion of titanium tetrachloride + methaneH2

TiCl4 + CH4 → TiC + 4HCl 1600-2000°C

2. Decomposition of TiCl4 with acetylene in H2 plasmaTiCl4 + 1/2 C2H2 + 3/2 H2 ↔ TiC + 4HCl

3. Reaction of titanium trichloride with metallic Al powder + C700-1100 °C

TiCl3 + Al + C → TiC + AlCl3

��J�1, 3 *�+ particle size ~10-100 nm.



Boron CarbideBoron CarbideBoron Carbide

BB44CC


Crystals structure of boron carbide



ก�� B4C �,(��3% ก�!+

1. Carbothermic reduction of boron oxide with C 1500-2500°C

2B2O3 +7C � B4C + 6CO (g)2. Hydroboric acid reacts with acetylene black/ethylene glycol in a vented

tube furnace1600-1800°C

4H3BO3 + 7C � B4C +6H2O + 6CO3. Exothemic magnesiothermic reduction in the presence of carbon black

1000-1800°C2B2O3 + 6Mg + C � B4C + 6MgO

4. Reaction with aluminium metal particles (J.B. Holt, 1987)2B2O3 + 4Al � 4B + 2Al2O3

4B + C � B4C


1. Self-propagation above 1100°C or melting by arc at 2500°C4B + C � B4C

2. Chemical vapor deposition4BCl3 + 6H2 + C � B4C + 12HCl

3. Pyrolysis of boron trihalides with methane or carbon tetradiodide as carbon carriers in high-frequency furnace

900-1800°C

4B(Cl,Br)3 + CH4 + 4H2 � B4C + 12HCl (HBr)900-1100°C

4BI3 + CI4 �B4C + 8 I2

ก�� B4C �,(��$�%��!��&$J�M�#�


Borides ceramicsBorides ceramicsBorides ceramics


Boride Ceramics

• Higher melting point (3260 c°)• Chemically less reactive

• Strongly anisotropic thermal expansion

• High oxidation resistance

• High strength at high temperature


Application of Boride Ceramic

• Electron microscope filaments (Lanthanum boride)

• Aerospace• Refractory• Part in piston engines• Abrasive• High-Temp electrical

conductor,Superconductor (magnesium boride, lanthanum boride)

• Boride cermet• High corrosion resistance

(zirconium boride)

Figures from Asahi glass ceramic Co. Ltd.


Crystal structure of Borides

Structural classification units of the borides (Spear, 1977)

Isolated boron or pairs: Ni3B, Ru7B3, Fe2B, Cr5B3

Double chains: Cr3B4

Two-dimensional nets: M2B3

and MB4


Preparation of Boride

1. Carbothermic reductionMO2 + B2O3 + 5C → MB2 + 5CO↑M = metal → TiB2, ZrB2 �� C < 3wt %

2. Reduction of metal oxide with carbon (B4C): boron carbide process

H2 or Vacuum

2MO2 + B4C +3C → 2MB2 + 4CO↑1600-2000°C

M2O3 + 3B4C � MB6 +3COMC + MO2 + B4C � 2MB2 + 2CO (g)

3. Aluminothermic, silicothermic, magesiothermic reduction of mixtures of metal oxides and hydroboric acid

MO2 + B2O3 + Al(Si,Mg) � MB2 + Al2O3(SiO2,MgO)


Laboratory-scale methods1. �กJ�&(�3 metal hydrides ?��ก�( �/��*--L(�3 ?��ก��/��ก��1ก(�3

hot pressing M +2B � MB2

MH2 + 2B � MB2 +H2

2. Borothermic reduction of metal oxides MO2 + 4B � MB2 + B2O3 (g)

3. Conversion of metal carbides with boron and/or boron carbideMC + 2B � MB2 + CMC + 6B � MB2 + B4C2MC + B4C � 2MB2+ 3C

4. Electrolysis of fused salts containing metal oxides, boron oxide or hydroboric acid plus alkaline borates and fluorides.

5. Chemical vapor reaction of metal halides and boron halides in a hydrogen atmosphere under plasma conditions.

�+ �,ก��/�ก��3% ก�!+!3 �!� ��8&��#�� ก��%,


�� Zirconium Diboride (ZrB2) (Kobayashi et al.1992) ZrO2 + B2O3 + 5Mg � ZrB2 + 5MgO ZrO2 + 2B + 2Mg � ZrB2 + 2MgO

Titanium diboride (TiB2) - mechanochemical synthesis - self-propagating high temperature synthesis - TiCl4 + 2BCl3 + 10Na � TiB2 (amorphous) + 10NaCl

(in n-heptane, 110-160°C) (ref: H.R. Baumgartner, 1984)


ก�!,��'�� (Batch determination)

• Weight percent

• Volume percent

• Mole percent

• Atomic percent


Example 1

• Mullite shows up on a phase equilibrium diagram as 3Al2O3.2SiO2. What is the mol% of Al2O3 and SiO2?

• Answer: Mullite consists of 3 mol of Al2O3 and 2 mol of SiO2

Mol% Al2O3 = 3 / (3+2) *100 = 60 mol%

Mol%SiO2 = 2/(3+2) * 100 = 40 mol%


Example 2• What is the wt% of Al2O3 and SiO2 in mullite? (atomic

weight of Al = 27.0, Si = 28.1, O = 16)• Answer: calculate the equivalent weight of

3 mol Al2O3: 3[(2)(27) +(3)(16)] = 306and 2 mol SiO2: 2[(28.1)+(2)(16)] = 120.2Thus, wt% Al2O3 = wt Al2O3 x 100 = 306 x 100 = 71.8 wt%

total wt 426.2And

wt%SiO2 = 120.2 x 100 = 28.2 wt%426.2

Therefore, to end up with 100 g of mullite, we must mix 71.8 g of Al2O3 and 28.2 g of SiO2


Example 3

• We wish to prepare a composite consisting of 80 vol% Al2O3and 20vol% SiC whiskers. We want a 1000-g batch. How much Al2O3 and SiC whiskers do we mix?

• Answer: density of pure Al2O3 = 3.98 g/cm3, density of SiC

= 3.19 g/cm3

Wt of Al2O3 = 0.8 x 3.98 = 3.18 gWt of SiO2 = 0.2 x 3.19 = 0.64 g

Wt% of Al2O3 = 3.18/(3.18+0.64) x 100 = 83.2 wt%Wt % of SiO2 whiskers = 0.64 / (3.18+0.64) x 100 = 16.8 wt%

Thus, 1000 g batch will consist of 832 g of Al2O3 powder and 168 g of SiC whiskers.

8 advanced ceramic raw materials - suranaree university of...

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