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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