PHOSPHIDES AND SILICIDES

Phosphides and silicides frequently behave in an analogous manner. Thus, calcium phosphide, CaaP2, is decomposed by water yielding phosphorus trihydnde, PH3, and liquid phosphoretted hydrogen, P2H4, which is spontaneously inflammable. 

Inorganic non-oxide materials, such as III-V and II-VI group semiconductors, carbides, nitrides, borides, phosphides and silicides, are traditionally prepared by solid state reactions or gas-phase reaction at high temperatures. Some non-oxides have been prepared via liquid-phase precipitation or pyrolysis of organometallic precursors. However, amorphous phases are sometimes formed by these methods. Post-treatment at a high temperature is needed for crystallization. The products obtained by these processes are commonly beyond the manometer scale. Exploration of low temperature technique for preparing non-oxide nanomaterials with controlled shapes and sizes is very important in materials science. 

Non-oxide ceramic nanomaterials, such as carbides, nitrides, borides, phosphides and silicides, have received considerable attention due to their potential applications in electronics, optics, catalysis, and magnetic storage. In contrast with the traditional processes, such as solid state reactions, CVD, MOCVD and PVD, which involve using high temperatures, toxic organometallic precursors, or complicated reactions and posttreatments, solvothermal method is a low temperature route to these materials with controlled shapes and sizes. 

PdSe/72137-76-7], PdSe2 [60672-19-7], PdTe [12037-94-4], and PdTe2 [12037-95-5]. Borides, silicides, phosphides, and arsenides are also known (23,24). 

II-VI and III-V compounds, borides, carbides, nitrides and silicides of transition metals, as well as sulphides, phosphides, aluminides, etc. A1203, AIN, B203, BN, SiC, Si3N4, U02, Y203, Zr02, etc. 

IRON, Fe (Ar 55 85) - IRON(II) Chemically pure iron is a silver-white, tenacious, and ductile metal. It melts at 1535°C. The commercial metal is rarely pure and usually contains small quantities of carbide, silicide, phosphide, and sulphide of iron, and some graphite. These contaminants play an important role in the strength of iron structures. Iron can be magnetized. Dilute or concentrated hydrochloric acid and dilute sulphuric acid dissolve iron, when iron(II) salts and hydrogen gas are produced. 

Two different types of reactors are used depending on the product synthesized. The first type can maintain pressures up to 150 atm, and is widely used for production of powders in gasless and gas-solid systems. Carbides, borides, silicides, intermetallics, chalcogenides, phosphides, and nitrides are usually produced in this type of reactor. The second type, a high-pressure reactor (up to 2000 atm), is used for the production of nitride-based articles and materials, since higher initial sample densities require elevated reactant gas pressures for full conversion. For example, well-sintered pure BN ceramic with a porosity of about 20-35% was synthesized at 100 to 5000-atm nitrogen pressure (Merzhanov, 1992). Additional examples are discussed in Section III. 

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. 

Metals in a finely divided state bum spontaneously in chlorine. Solid metals (nonpow-dered form) bum spontaneously at elevated temperatures. Metal carbides react with chlorine with incandescence. Metal hydrides bum spontaneously in chlorine. Diborane explodes with chlorine at ordinary temperature silane, phosphine, arsine, or stibine produce a flame. The latter compounds react explosively with chlorine at elevated temperatures. Metal sulfides, silicides, nitrides, phosphides, and oxides bum in chlorine. Phosphorus undergoes a highly exothermic reaction with chlorine. White phosphorus explodes with liquid chlorine white phosphorus and finely divided red phosphorus bum spontaneously in chlorine gas with a pale green light (NFPA 1997). 

The metal-rich transition metal phosphides (<60% P) are dark coloured and insoluble in water, they have high chemical and thermal stability, they are dense, hard and brittle and have high thermal and electrical conductivities. These properties they have in common with the transition metal borides and silicides (and in some cases carbides and nitrides) to which they are often structurally related. With few exceptions, the transition metal phosphides, borides and silicides are not attacked by dilute acids and bases and may remain unaffected by hot concentrated mineral acids. 

In some cases close structural relationships exist between phosphides, borides, silicides and even carbides. Isostructural arrangements based on nine-fold coordination of the metallide atom are listed in Table 8.5. 

Bulk moduli for ambient conditions (with index o ) are listed in Tables 10.7 for elements, SlO.l for compounds MX, S10.2 for MX2, S10.3 for MX3, S10.4 for binary oxides, S10.5 for binary nitrides, S10.6 for binary borides, S10.7 for binary carbides and silicides, S10.8 for binary phosphides and arsenides, S10.9 for ternary oxides and coordination compounds, SIO.IO for molecular substances and polymers, SlO.l 1 for characteristics of polymorphous modifications of elements and the MX compounds, S10.12 for various phases ofMX2 crystals. 

The word ceramics is derived from the Greek keramos, meaning solid materials obtained from the firing of clays. According to a broader modern definition, ceramics are either crystalline or amorphous solid materials involving only ionic, covalent, or iono-covalent chemical bonds between metallic and nonmetallic elements. Well-known examples are silica and silicates, alumina, magnesia, calcia, titania, and zirconia. Despite the fact that, historically, oxides and silicates have been of prominent importance among ceramic materials, modern ceramics also include borides, carbides, silicides, nitrides, phosphides, and sulfides. 

The volume edited by Quill contains ten papers by various authors, dealing with liquid-solid equilibria, temperature-composition diagrams of metal-metal halide systems, and properties of the elements, carbides, sulphides, silicides, phosphides, and halides. 

B. Aronsson, T. Lundstrom, and S. Rundqvist, Borides, Silicides and Phosphides, Methuen, London, U.K., 1965. 

Low-temperature solvents are not readily available for many refractory compounds and semiconductors of interest. Molten salt electrolysis is utilized in many instances, as for the synthesis and deposition of elemental materials such as Al, Si, and also a wide variety of binary and ternary compounds such as borides, carbides, silicides, phosphides, arsenides, and sulfides, and the semiconductors SiC, GaAs, and GaP and InP [16], A few available reports regarding the metal chalcogenides examined in this chapter will be addressed in the respective sections. Let us note here that halide fluxes provide a good reaction medium for the crystal growth of refractory compounds. A wide spectrum of alkali and alkaline earth halides provides... 

Aronsson B, Lundstrom T, Rundqvist S (1965) Borides, silicides and phosphides. Methuen, London... 

The Badische AniKn- und Soda-Fabrik prepared a nitride of undetermined composition by heating a mixture of silica and carbon in an atm. of nitrogen. The reaction proceeds at a relatively low temp, if a hydroxide or salt of a metal be added. The product contains silicon nitride mixed with the nitride of the metal. The Badische Anilin- und Soda-Fabrik also removed many of the impurities—iron, carbon, silicates, carbides, silicides, and phosphides—by treatment with acids or mild oxidizing agents which do not affect the silicon nitride. A. S. Larsen and O. J. Storm prepared the nitride by the action of nitrogen on molten silicides—e.g. ferrosilicon. 

The oxides, hydrides, halides, sulphides, sulphate , carbonates, nitrates, and phosphates are considered with the basic elements the other compounds are taken in connection with the aoidio element. The double or complex salts in connection with a given element include those associated with elements previously discussed. The carbides, silicides, titanides, phosphides, arsenides, etc., are considered in connection with carbon, silicon, titanium, etc. The intermetallic compounds of a given element include those associated with elements previously considered. 

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