Silicide melting points

Silicon is soluble in aluminum in the solid state to a maximum of 1.62 wt % at 577°C (2). It is soluble in silver, gold, and 2inc at temperatures above their melting points. Phase diagrams of systems containing silicides are available (2,3). 

The nozzle of original design was fabricated from a niobium alloy coated with niobium silicide and could not operate above 1320°C. This was replaced by a thin shell of rhenium protected on the inside by a thin layer of iridium. The iridium was deposited first on a disposable mandrel, from iridium acetylacetonate (pentadionate) (see Ch. 6). The rhenium was then deposited over the iridium by hydrogen reduction of the chloride. The mandrel was then chemically removed. Iridium has a high melting point (2410°C) and provides good corrosion protection for the rhenium. The nozzle was tested at 2000°C and survived 400 cycles in a high oxidizer to fuel ratio with no measurable corrosion.O l... 

On a metal surface, silicide layers can be formed by two methods. In the first, Si atoms are vapor deposited by heating either a well degassed silicon wafer or a silicon rod to near its melting point. In the second method the metal is heated in 10 to 50 mTorr of silane for a desired length of time, usually about 10 to 60 s at a desired temperature, usually about 300 to 700°C. The first method is better suited for studying very early stages of silicide formation, the second more convenient for growing thick layers of silicides. Chemical vapor deposition or laser enhanced chemical vapor deposition may probably be used also, but have not yet been explored. 

Chemical Vapor Deposition. Deposition of tungsten, molybdenum, and their silicides by chemical yapor deposition (CVD) is of relatively recent interest in the microelectronics industry. These materials arc useful for gates and interconnects in metal oxide semiconductors (MOS) devices. Aluminum, the widely used interconnect material, has a comparatively low melting point (600°C) and a markedly different coefficient of thermal expansion (compared to silicon), so that over a period of years researchers have been seeking an alternative for aluminum,... 

A suitable metal solvent should provide high solubility for the reactants. In addition, it should either not form compounds with the reactants or only those with heats of formation that are low with respect to the desired silicide. Finally, the solvent should have a relatively low melting point and vapor pressure, and separate easily from the product silicide. 

Si3N4/other silicides Less important due to less stability against oxidation or low melting point Under sintering conditions liquid silicides can concentrate in big defects, Fe silicide can improve the wear behaviour in engine applications [564]... 

Nitrides, borides and silicides. Nitrides have the highest melting points next to carbides. They are brittle, hard, and oxidize above 1000 °C. The nitrides mentioned below are efficient electrical insulators even at high temperatures, whereas others (e.g. TiN) are good conductors. 

The silicides exhibit the lowest melting points and hardness values of the metallic hard materials (see Table 5.6-5). Their brittleness makes them unsuitable for utilization in hard metal alloys. Silicides have only been utilized industrially in metallurgical fields in which their scaling resistance and chemical resistance are important. They are also deposited using the CVD process e.g. as protective layers on high melting metallic surfaces. 

Many carbides and silicides of composition AX are formed by transition metals. These carbides and silicides are characterized by very high melting points, extreme hardness, optical opacity and relatively high electrical conductivity. Many of them have the sodium chloride structure but they are not ionic compounds rather do they resemble the corresponding nitrides and phosphides in simulating alloy systems in many of their properties. For this reason they will be discussed later. 

---