Silicides properties

More than half of the elements in the Periodic Table react with silicon to form one or more silicides. The refractory metal and noble metal silicides ate used in the electronics industry. Silicon and ferrosilicon alloys have a wide range of applications in the iron and steel industries where they are used as inoculants to give significantly improved mechanical properties. Ferrosilicon alloys are also used as deoxidizers and as an economical source of silicon for steel and iron. 

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. 

The theoretical studies " have been focused on TiSi2. Some attempts, with use of high-symmetry crystal structures, have been made to understand some of the other titanium silicides. This paper deals vith Ti,5Si.3. Because of the crucial interplay between structure and bonding we have studied the proposed stable low-symmetry crystal structure. This will give a better picture of the electronic structure and the bonding properties in this system. An investigation of seven members in the Ti-Si system will be presented in a future publication. ... 

The general understanding of the electronic structure and the bonding properties of transition-metal silicides is in terms of low-lying Si(3.s) and metal-d silicon-p hybridization. There are two dominant contributions to the bonding in transition-metal compounds, the decrease of the d band width and the covalent hybridization of atomic states. The former is caused by the increase in the distance between the transition-metal atoms due to the insertion of the silicon atoms, which decreases the d band broadening contribution to the stability of the lattice. 

In general, many metals and alloys (e.g. of Al, Ta and Mo) can be deposited on metallic and some non-metallic substrates. M may also be a metal compound having special useful properties (e.g. borides, nitrides, oxides, silicides and carbides), or even a non-metal such as Si (as in Ihrigising ). 

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). 

Tsai, J. Y., etal., Silicide-ThinFilms,Fabrication,Properties, and Applications, m Proc. of MRS Symposium, 4102 245-250 (1996)... 

I. Tomaszkiewicz, G. A. Hope, C. M. Beck II, P. A. G. O Hare. Thermodynamic Properties of Silicides. VI. Pentamolybdenum Trisilicide (Mo Sf). Fluorine Combustion Calorimetric Determination of the Standard Molar Enthalpy of Formation at the Temperature of 298.15 K. J. Chem. Thermodynamics 1997, 29, 87-98. 

Aluminium-Silicon.—Vanadium possesses the property in common with a large number of other metals of forming complex alloys with aluminium and silicon.7 Several of these vanadium-aluminium-silicides, each possessing different crystalline form, have been obtained... 

Metallurgy. The strong affinity for oxygen and sulfur makes the rare-earth metals useful in metallurgy (qv). Mischmetal acts as a trap for these Group 16 (VIA) elements, which are usually detrimental to the properties of steel (qv) or cast iron (qv). Resistance to high temperature oxidation and thermomechanical properties of several metals and alloys are thus significandy improved by the addition of small amounts of mischmetal or its silicide... 

It has to be mentioned that the chemical analysis of the impurities often is insufficient for an adequate powder characterisation because of their very specific influence on the properties of the powder compacts (sintered bodies). On the one hand, particle size and particle distribution of the impurity inclusions are important for instance it has been shown that the same impurity contents of Fe cause a drastic decrease in strength of the compacts if concentrated in few inclusions with diameters >50 pm, but have nearly no influence as inclusions <5-10 pm [238]. On the other hand, most metallic impurities form silicides which cause a remarkable volume increase [238]. 

Klemm H, Tangermann K, Reich T, Herrmann M, Schubert C, Hermel W (1995) High-Temperature Properties of Silicon Nitride Molybdenum Silicide Composites. In Bellosi A (ed) Fourth Europ Ceramics, Vol 4, Grupp Editoriale faenca Editrice, Faenza, p 233... 

In this article the intention is to place the main emphasis on studies of molecular silicon-transition-metal compounds, in particular those from the author s laboratory and those that have been reported since the comprehensive reviews noted above. As, however, it is now known that these molecular compounds can act as convenient precursors for certain transition-metal silicides, aspects of the properties of silicides will also be outlined, and relationships between the two classes of compounds examined. Compounds with bonds between transition metals... 

V.N. Yeremenko, G.M. Lukashenko, V.R. Sidorko. Thermodynamic properties of vanadium, chromium and manganese silicides at elevated temperatures // Rev.Intern. Haut.Temp.Refract.- 1975.- V.12, No.3.- P.237-240. 

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