Physical silicides

Titanium Silicides. The titanium—silicon system includes Ti Si, Ti Si, TiSi, and TiSi (154). Physical properties are summarized in Table 18. Direct synthesis by heating the elements in vacuo or in a protective atmosphere is possible. In the latter case, it is convenient to use titanium hydride instead of titanium metal. Other preparative methods include high temperature electrolysis of molten salt baths containing titanium dioxide and alkalifluorosiUcate (155) reaction of TiCl, SiCl, and H2 at ca 1150°C, using appropriate reactant quantities for both TiSi and TiSi2 (156) and, for Ti Si, reaction between titanium dioxide and calcium siUcide at ca 1200°C, followed by dissolution of excess lime and calcium siUcate in acetic acid. 

Table 18. Structure and Physical Constants of Titanium Silicides ...

Limitations of Plasma CVD. With plasma CVD, it is difficult to obtain a deposit of pure material. In most cases, desorption of by-products and other gases is incomplete because of the low temperature and these gases, particularly hydrogen, remain as inclusions in the deposit. Moreover, in the case of compounds, such as nitrides, oxides, carbides, or silicides, stoichiometry is rarely achieved. This is generally detrimental since it alters the physical properties and reduces the resistance to chemical etching and radiation attack. However in some cases, it is advantageous for instance, amorphous silicon used in solar cells has improved optoelectronic properties if hydrogen is present (see Ch. 15). 

Parth6, E. and Chabot, B. (1984) Crystal structures and crystal chemistry of ternary rare earth-transition metal borides, silicides and homologues. In Handbook on the Physics and Chemistry of Rare Earths, ed. Gschneidner Jr., K.A. and Eyring, L. (North-Holland, Amsterdam), Vol. 6, p. 113. 

A totally different but nevertheless exciting field is the solid state chemistry of silicides and of Zintl anions aimed on the optimization of the physical properties (e.g. conductivity) and their derivatization to give molecular species. 

Although the silicon atom has the same outer electronic structure as carbon its chemistry shows very little resemblance to that of carbon. It is true that elementary silicon has the same crystal structure as one of the forms of carbon (diamond) and that some of its simpler compounds have formulae like those of carbon compounds, but there is seldom much similarity in chemical or physical properties. Since it is more electro-positive than carbon it forms compounds with many metals which have typical alloy structures (see the silicides, p. 789) and some of these have the same structures as the corresponding borides. In fact, silicon in many ways resembles boron more closely than carbon, though the formulae of the compounds are usually quite different. Some of these resemblances are mentioned at the beginning of the next chapter. Silicides have few properties in common with carbides but many with borides, for example, the formation of extended networks of linked Si (B) atoms, though on the other hand few silicides are actually isostructural with borides because Si is appreciably larger than B and does not form some of the polyhedral complexes which are peculiar to boron and are one of the least understood features of boron chemistry. 

The present paper describes the complex lattice structures, the physical and mechanical properties of the refractory silicides Ti5Si3, TiSi2 as well as a-Ti/Ti5Si3 composite materials of higher strength as function of the temperature. The results will be discussed with respect to microstructural features. 

This Datareview has described the known surface phases which exist on both a- and P-SiC. Surface treatments by annealing in UHV, by ion bombardment and by laser irradiation are not suitable to prepare SiC surfaces for further study. Chemical reduction of surface oxides is the preferred route to surface preparation, particularly using a Si flux at temperatures < 1000°C. A distinction is drawn between ideal surfaces prepared in UHV and practical ones where substrates are chemically treated or ion bombarded prior to metallisation. Processes occurring during deposition of the first few monolayers of metal and subsequent treatments are discussed in terms of chemical and physical properties. A total of 15 metal-SiC combinations are reviewed and discussed in terms of silicide and carbide formation. 

Unlike most other aluminides which are considered for high temperature applications, NiAl with a B2 structure exhibits excellent oxidation resistance since a protective AI2O3 scale is readily formed during oxidation (Doychak et al., 1989 Nesbitt and Lowell, 1993). According to present knowledge, NiAl seems to be the only really oxidation resistant intermetallic, apart from some silicides (Meier et al., 1993). The physical reason for this high oxidation resistance is that the Al content... 

Naito, M., Nakanishi, R., Machida, N. et al. 2012. Growth of higher manganese silicides from amorphous manganese-silicon layers synthesized by ion implantation. Nuclear Instruments and Methods in Physics Research B 272 446 49. 

Hard materials are used as thin hard coatings of some microns thickness for wear protection of tools and machine parts because of their high abrasive wear resistance. For the selection of the coating material the physical, mechanical, and technological properites of these coatings, required by the application, are decisive. The following data collection presents fundamental and available material properties for approximately 130 hard materials as a result of a literature search on carbides, nitrides, borides, silicides, and oxides. 

Parthd, E. Chabot, B. (1984). Crystal Structures and Crystal Chemistry of Ternary Rare Earth - Transition Metal Borides, Silicides and Homologues in "Handbook on the Physics and Chemistry of The Rare Earths", edited by K.Gschneidner, Jr. and L. R. Eyring, Vol. 6, ppl 13-334, Amsterdam North Holland. 

---