MoSi 2 -Based High-Temperature Structural Silicides
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Li Si Li2Si
range of applications in the industrial, aerospace, and automotive arenas. A few of the industrial uses for such materials are furnace elements and components, power generation components, high-temperature heat exchangers, gas burners and igniters, and high-temperature filters. Aerospace applications include turbine aircraft engine
hot-section components such as blades, vanes, combustors, nozzles, and seals. Automotive applications involve components such as turbocharger rotors, valves, glow plugs, and advanced turbine engine parts. There is increasing interest in silicidebased compounds for high-temperature structural uses under oxidizing conditions in the range of 1200-1600°C. In this temperature range, for oxidation and strength reasons, the choice of materials is limited to the silicon-based structural ceramics such as Si3N4 and SiC, and the new class of "high-temperature structural silicides." An extensive survey of progress in the area of high-temperature structural silicides has recently been published.1 A pseudoperiodic table of known silicides is shown in Figure 1. While a large number of silicides have been identified, currently most are little characterized. Potential silicides for elevated-temperature applications are those based on refractory and transition metals. A tabulation of some interesting high-temperature structural silicides is given in Table I. Of such materials, MoSi2 is presently considered the most promis-
NaSi
KSi
RbSi
CsSi
LaSi 2
Ca 2 Si CaSi CaSi
Sc,.Si3
Sr 2 Si SrSi SrSij,
CeSi CeSi 2
Zlj Si Zt,Si ZSi
Y5Si3 YSi YSi*2
BaSi BaSi*2
ZrSi ZrSi2 Hf 2 Si Hf 3 Si 2 HfSi HfSb
LaSi
PrSi*2
Th 3 Si 2 ThSi Th 2 Si 3 ThSi*2
Ti-Si Ti s Si 3 TiSi TiSi 2
NdSi^
U3Si U 3 Si 2 USi* U3Si5 USi* 2
SmSi*2
NpSi 2
V3Si
VSi
Nb,Si Si* NbSi 2
Cr 3 Si Cr5Si3 CrSi CrSi 2
Mn 3 Si MnSi MnSLL,
7
Mo-Si
Fe 3 Si Fe5Si3 FeSi FeSii
Ru2Si RuSi* Ru 2 Si 3
MOgSi
MoSL
Co2Si CoSi CoSi 2
Rh2Si Rh 5 Si 3 S
Ni 3 Si Ni5Si Ni 2 Si*
b NiSi NiSL,
K(CuSi) P(CuSi) Cu 3 1 Si 8
Pd2Si PdSi
RhSi
Ta3Si Ta 2 Si3 Ta 5 Si* 3 TaSi 2
EuSi2
Pu 5 S^ PuSi Pu2Si PuSi2
W-Sig 2
Gd 2 Si 3 TbzSi GdSi 2 - TbSi 2
% ReSi ReSi 2
Dy2Si DySi* 2
OsSi
Ir.Si lr2 Si lr3Si2 IrSi
PtSi* PtjSi* S RSi
HOzSig Er 2 Si 3 Tm 2 Si 3 Yb 2 Si 3 LUjSig HoSi 2
*There is more than one phase with or near this composition.
Figure 1. Pseudoperiodic table of known silicides.'
MRS BULLETIN/JULY 1993
35
MoSi2-Based High-Temperature Structural Silicides
Table I: List of Interesting High-Temperature Structural Silicides. Silicide MoSi2 WSi 2 TiSi2 CrSi2 CoSi2 Mo 5 Si 3 Ti5Si3
Melting Point (°C) 2030 2160 1500 1490 1326 2160 2130
ing due to its combination of high melting point, superb elevated-temperature oxidation resistance, brittle-to-ductile transition, and electrical conductivity.2 Potential structural uses for MoSi2 include its application as a matrix in structural silicide composites, as a reinforcement for structural ceramic matrix composites, as a high-temperature joining material for structural ceramic com
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