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2001 | PATENTS
| INTERNET
|
Barsoum M. W., El-Raghy T. Synthesis and Characterization
of a Remarkable Ceramic: Ti3SiC2
// J. Amer. Cer. Soc. - 1996. - 79(7). - 1953-1956. Polycrystalline bulk samples of Ti3SiC2 were fabricated by reactively hot pressing Ti, graphite and SiC powders at 40 MPa and 1600 °C for 4 hours. This compound has remarkable properties. Its compressive strength, measured at room temperature, was 600 MPa, and dropped to 260 MPa at 1300 °C in air. Although the room temperature failure was brittle, the high temperature load-displacement curve shows significant plastic behavior. The oxidation is parabolic and at 1000 and 1400 °C the parabolic rate constants were, respectively, 2 x 10-8 and 2 x 10-5 kg2m-4s-1. The activation energy for oxidation is thus divide; 300 kJ/mol. The room temperature electrical conductivity is 4.5 x 106 ohm-1 m-1, roughly twice that of pure Ti. The thermal expansion coefficient in the temperature range 25 to 1000 °C, the room temperature thermal conductivity, and heat capacity are respectively, 10 x 10-6 øC-1, 43 W/m.K, and 588 J/kg K. With a hardness of 4 GPa and a Young's modulus of 320 GPa, it is relatively soft, but reasonably stiff. Furthermore, Ti3SiC2 does not appear to be susceptible to thermal shock; quenching from 1400 °C into water does not affect the post-quench bend strength. As significantly, this compound is as readily machinable as graphite. Scanning electron microscopy of polished and fractured surfaces leaves little doubt as to the its layered nature. |
| El-Raghy
T., Zavaliangos
A., Barsoum
M. W., Kalidindi
S. R. Processing and Properties of
Ti3SiC2
/ Process. Fabr. Adv. Mater. V, Proc. Symp., 5th. - Warrendale, Pa.,
1996. - 631-640. Recently we were able to fabricate fully dense, single phase samples of Ti3SiC2 in bulk form. In this paper we present results from the preliminary characterization of this ternary compd. which has an impressive set of properties: machinability similar to that of graphite, oxidn. resistance at 1000 °C comparable to chromium, a compressive yield strength of over 300 MPa at 1300°C accompanied by significant high temp. ductility, and non-susceptibility to thermal shock. Microscopic studies indicate that this material exhibits behavior and properties akin to those of a nanocomposite. |
|
Hasegawa M., Itatani K., Aizawa M., Howell S. F., Kishioka A. Low-Temperature
Synthesis of Aluminum Silicon Carbide Using Ultrafine Aluminum Carbide
and Silicon Carbide Powders // J. Am. Ceram. Soc. - 1996. -
79(1). - 275-278. The conditions for preparing a-aluminum silicon carbide (a-Al4SiC4) were examined by heating stoichiometric mixtures of ultrafine Al4C3 and SiC powders with sizes of <0.1 mm at and below 1600 °C. The starting Al4C3 powder was obtained by the pyrolysis of trimethylaluminum; the starting SiC powders were obtained by the pyrolyzes of triethylsilane (3ES), tetraethylsilane (4ES), and hexamethyldisilane (6MDS). The reactivity of SiC with Al4C3 to form a-Al4SiC4 varies according to the kind of starting alkyl-silane: 3ES > 4ES > 6MDS. The reaction of 3ES-derived SiC with Al4C3 produced a-Al4SiC4 at temperatures as low as 1400 °C for 240 min, regardless of the presence of Al4C3 (trace). Only a-Al4SiC4 was formed at and above 1500 °C for 60 min; the crystal growth was appreciable. |
| Ivanovskii
A. L., Gusev A. I., Shveikin G. P. Quantum Chemistry
in Materials Science. Ternary Carbides and Nitrides Based on Transition
Metals and IIIb, IVb Subgroup Elements. - Ekaterinburg: Ural
Div. RAS, 1996. (Russian). This monograph presents a systematic description of the modern state of investigations of phase relationships and crystal chemistry in M-X-C,N systems (M - d,f-metals, X - IIIb, IVb subgroup elements). The material available on theoretical quantum chemical and experimental study of the electronic structure, chemical bonding, charge states and physico-chemical properties of ternary carbides and nitrides based on transition metals and IIIb, IVb subgroup non-transition elements has been generalized. For specialists working on the field of physico-chemistry of solid state, physical chemistry and materials science. |
| Lihrmann J.-M., Tirlocq J. A New Silicon Carbide - based
Material // Mutations - 1996. - 12. [no abstract] |
| Morgiel
J., Lis J., Pampuch R. Microstructure of Ti3SiC2-based
Ceramics // Mater. Lett. - 1996. - 27(3).
- 85-89. The Ti3SiC2-based ceramic produced by self-propagating high-temp. synthesis (SHS) has been investigated by means of anal. electron microscopy (AEM). The observations have proved that the elongated slabs with rounded corners of well-fused Ti3SiC2 grains form a matrix within which some rounded TiC and less frequent angular SiC inclusions are present. A TiSi2 phase filling up a remaining free space between carbide grains, has been also detected. The Ti3SiC2 grains are characterized by a high d. of dislocations, while the TiC ones contain mostly stacking faults. Cracks forming in the material are situated predominantly at the Ti3SiC2/TiC interface. |
| Naka
M., Feng J., Schuster J. C. Phase Formation
in SiC/Metal Joints at High Temperatures // Mater. Trans.,
JIM - 1996. - 37(3). - 394-398. Joining of SiC to SiC was performed using Ti and Nb foils at 1373-1790 K in vacuum. The change in microstructures of the SiC/Ti and SiC/Nb interfaces was investigated in detail at 1673 K and 1790 K, resp. At a bonding time of 0.3 ks, TiC at the Ti side and a mixt. of Ti5Si3Cx + TiC at the SiC side were formed. Furthermore, a Ti5Si3Cx layer phase appeared between SiC and mixt. of Ti5Si3Cx + TiC, upon the formation of Ti3SiC2 after the bonding time of 3.6 ks, and the diffusion path was obsd. as follows: .beta.-Ti/Ti + TiC/TiC + Ti5Si3Cx/Ti5Si3Cx/Ti3SiC2/SiC. At 1790K, the diffusion path between SiC and Nb was established as Nb/Nb2C/NbC/Nb5Si3C/NbC/SiC, and the NbSi2 phase appeared at the interface between NbC adjacent to SiC and Nb5Si3C at the longer time of 2 k 7s. |
| Naka
M., Feng J., Schuster J. C. Structure and Strength
of a SiC/Ti Bonding Interface // Yosetsu Gakkai Ronbunshu -
1996. - 14(2). - 338-343. (Japanese). The solid state bonding of pressureless-sintered SiC to SiC using 20 .mu.m Ti foil was conducted at bonding temps. 1373-1673 K for 0.3-72 ks in vacuum. For a const. bonding time of 3.6 ks, the granular TiC next to Ti and a mixt. of Ti5Si3Cx + TiC phases next to SiC were formed. Increasing the bonding temp. in 100 K intervals from 1473 to 1773 K, the Ti5Si3Cx single phase, Ti3SiC2 phase and TiSi2 phase sequentially appeared. Fracture shear testing was used to measure bonding strength. The bonding strength was found to increase up to a max. of 153 MPa at 1473 K. At higher temps. it decreases to 54 MPa at 1573 K. At still higher temps. bonding strength again increases. The highest strength of 250 MPa was measured at 1773 K. This variation of bonding strength with bonding temp. is correlated with the microstructure obsd. at the interface of the joints. The SiC/Ti joint with a duplex phase of Ti3SiC2 + TiSi2 shows the stable strength up to testing temp. 973 K. |
| Qiu
C., Metselaar R. Thermodynamic Evaluation of
the Al2O3
- Al4C3
System and Stability of Al-Oxycarbides //
Z. Metallkd. - 1995. - 86(3). - 198-205. Thermodynamic properties of the pseudo-binary Al2O3-Al4C3 system have been evaluated based on thermodynamic models. An ionic-liquid model was applied to the liquid slag phase and a compound-energy model to Al2OC. Both the models are with two sublattices' and latter one can be extended to describe the solid solution phases formed among Al2OC, AlN, and SiC. A description of the system was obtained and then used to calculate the Al2O3-Al4C3 phase diagram which shows satisfactory agreement with experimental observation. A series of potential diagrams was also calculated for the Al-C-O system, which illustrate the effect of partial pressures of Al, CO, and CO2 gas on the stability of Al4C3, Al2O3, Al4O4C, and Al2OC at different temperatures. These diagrams can provide an important basis for the carbothermic reduction of alumina to produce Al4C3. |
| Radhakrishnan
R., Henager Jr. C. H., Brimhall J. L., Bhaduri S. B. Synthesis
of Ti3SiC2/SiC
and TiSi2/SiC Composites
Using Displacement Reactions in the Ti-Si-C System
// Scripta Materialia - 1996. - 34(12). - 1809-1814. [no abstract] |
| Shveikin
G. P., Istomin
P. V., Goldin
B. A., Ryabkov
Yu. I. Stable Phase States of the
TiO2–SiO2–C
System in Vacuo // Dokl. Acad. Nauk - 1996.
- 350(2). - 223-225. (Russian). [no abstract] |
| Tamai
F., Natka M. Joining of Silicon-Containing Ceramics
with Active Brazes. 2. Microstructure and Strength of SiC/SiC Joints
Brazed with Cu-Ti Alloys // Yosetsu Gakkai Ronbunshu - 1996.
- 14(2). - 333-337. (Japanese). Pressureless sintered SiC ceramic was brazed to SiC with Cu-Ti alloys contg. Ti content up to 50 at% at 1373 K for 1.8 ks in vacuum. The strength of SiC/SiC joints was measured by 4-point bending test at room temp. and elevated temp. The microstructures and elemental distribution and reaction phases in the joining layers were investigated by means of electron probe micro-analyzer and x-ray diffraction. The strength of SiC/SiC joint increases with increasing Ti content in Cu-Ti alloys for Ti content up to 34 at%, and shows the max. of 208 MPa at Ti content of 34 at%. Ti in the alloys with Ti content up to 15 at% reacts with SiC and forms TiC, Ti5Si3 and TiSi. Ti in the alloys with Ti content of 34 at% or more reacts with SiC and forms TiC, Ti3SiC2, TiSi and TiSi2. The formation of TiC and Ti5Si3 at the interface between SiC and Cu-Ti alloy prevents the direct reaction of copper with SiC, and reduces the thickness of the brittle copper penetrating layer. The formation of thick carbide layer of Ti3SiC2 is attributable to the max. strength of SiC/SiC joint. The SiC/SiC joint brazed with Cu-34 at% Ti alloy represents the strength of 208 MPa up to testing temp. of 723 K, and the degrdn. of strength with further increase in temp. |
| Tian
Q., Virkar A. V. Interdiffusion in SiC-AlN and
AlN-Al2OC
System // J. Am. Ceram. Soc. - 1996. - 79(8).
- 2168-2174. AlN, Al2OC, and the 2H form of SiC are isostructural. Both SiC-AlN and AlN-Al2OC form homogeneous solid solutions above 2000° and 1950°C, respectively. The kinetics of phase separation in the two systems, however, are quite different. Interdiffusion in both SiC-AlN and AlN-Al2OC systems was examined in the solid-solution regime in an attempt to elucidate differences in the kinetics of phase separation that occur in the two systems when annealed at lower temperatures. Diffusion couples of (SiC)0.3(AlN)0.7 / (SiC)0.7(AlN)0.3 and (AlN)0.7(Al2OC)0.3 / (AlN)0.3(Al2OC)0.7 were fabricated by hot pressing and were annealed at high temperatures by encapsulating them in sealed SiC crucibles to suppress loss due to evaporation. Interdiffusion coefficients in (SiC)0.3(AlN)0.7 / (SiC)0.7(AlN)0.3 diffusion couples were measured at 2373, 2473, and 2573 K, and the corresponding activation energy was determined to be 632 kJ/mol. (AlN)0.7(Al2OC)0.3 / (AlN)0.3(Al2OC)0.7 samples were annealed at 2273 K. The interdiffusion coefficient measured in the AlN-Al2OC system was much larger than that in the SiC-AlN system. |
| Tong
X., Yano T., Iseki T. Sintering Behavior of
TiC Reinforced SiC Composites Doped with Ti and C // J. Ceram.
Soc. Jpn. - 1996. - 104 (July). - 594-598. SiC-TiC composites with different C/Ti ratio were hot-pressed at 2050°C for 1 h under vacuum. The ratio of C/Ti was controlled by the addn. of Ti or C. D. of the sintered bodies decreased with increasing C content. The SiC-TiC composite with a low C/Ti ratio, i.e., doped with 2 mass% Ti, could be densified up to 98%. On the other hand, relative d. of the specimens with higher C/Ti ratio reached only about 80%. D. of the monolithic SiC doped with 2 mass% Ti was measured to be 73%. The presence of free Si and Ti3SiC2 phases was confirmed by XRD for the composites with lower C/Ti ratio. Diffraction intensity of these peaks decreased with increasing C content, and finally disappeared. Plastic deformation of TiC and formation of Si and Ti3SiC2 phases are believed to be the main factors to control the sintering behavior of SiC-TiC composite contg. C deficiency. |
| Zhang
S., Yamaguchi A. Hydration Resistences and Reactions
with CO of Al4O4C
and Al2OC Formed in Carbon-Containing
Refractories with Al // J. Ceram. Soc. Japan.
- 1996. - 104(5). - 393-398. Two of fundamental properties of carbon-containing refractories with Al, hydration resistances and reactions with CO of Al4O4C and Al2OC formed in the refractories at high temperatures were investigated. Al4O4C is formed from a mixture of Al2O3 : Al : C = 4 : 4 : 3 (molar ratio) adove 1300°C. Al2OC is formed from a mixture of Al2O3 : Al : C = 1 : 4 : 3 (molar ratio) above 1400°C. The hydratation resistances of Al4O4C are much better than that of Al4C3. Al4O4C and Al2OC react with CO to form Al2O3 and C at temperatures above 900°C. |
| Zhou Y., Jiang D. L., Tan S. H., Guo J. K. Fabrication
of Multiphase Ceramics by Reaction - Pyrolyzing Polycarbosilane-Titanium
Mixtures in Different Atmospheres // Ceram. Trans. - 1996.
- 74 (Advances in Ceramic-Matrix Composites III). - 179-187. Using polycarbosilane as polymeric precursor and Ti powder as a reactive filler phase, three kinds of multiphase ceramics were fabricated via reaction pyrolysis of a polycarbosilane/60 vol.% Ti mixt. in a N2, NH3 or Ar atm. Chem. reactions which took place during pyrolysis in the different atms. were sep. analyzed. The influence of atm. on chem. and crystallog. compn., microstructure and some properties, such as bulk d., flexural strength, porosity and linear shrinkage, of the resulting ceramics were investigated. Low-shrinkage porous TiN / SiC1+y ceramics were obtained in N2 or NH3 atms., while high-shrinkage dense TiC1+x/Ti3SiC2 ceramic was obtained in the Ar atm. However, the flexural strength of the latter was higher than that of the former. |
