Oxides and Other Binary Compounds

Black AgO is prepared by oxidation of silver salts with O3, S20 and, most recently, S02/air mixtures, as well as by anodic oxidation [31]. Neutron diffraction shows it to be Ag Ag 02 with 2-coordinate Ag and square planar Ag sites. It is stable to around 100°C and gives solutions of Ag when dissolved in dilute acid. Treatment with alkaline periodate retains the disproportionation 

Less important oxides are Ag203, obtained impure by extended anodic oxidation of silver, and Ag30, obtained hydrothermally from Ag/AgO at 80°C, 4000 bar, which is a metallic conductor with the anti-Bil3 structure containing an hep array of silvers with oxide ions occupying 2/3 of the octahedral holes [32]. 

Au(OH)4. There have been claims for an AUO2, which may have been impure AU2O3. 

The ternary oxides M3AUO (M = Rb, Cs) contain Au , however [34]. Other binary compounds include the very insoluble black Ag2S 

Gold forms no simple phosphide AU2P3 is Au4(P6 ) with P—Au—P angles of 171 and 180 . 

---

When atomic theory developed to the point where it was possible to write specific formulae for the various oxides and other binary compounds, names reflecting composition more or less accurately then became common no names reflecting the composition of the oxosalts were ever adopted, however. As the number of inorganic compounds rapidly grew, the essential pattern of nomenclature was little altered until near the end of the 19th century. As a need arose, a name was proposed and nomenclature grew by accretion rather than by systematization. 

Howe, A. T., and P. J. Fenshaw, Quart. Rev., 1967, 21, 507 (electronic properties of oxides and other binary compounds of first-row transition metals). 

The chemistry required to convert the oxide to other binary compounds is independent of the scale of operation. However, with microscale synthetic methods applied to radioactive materials, successful preparations are achieved more readily by carrying out the chemistry in situ, that is, in such a manner that eliminates, or at least minimizes, the necessity of having to "handle" the sample during or following its synthesis. Thus, actinide compounds are usually prepared in silica capillary tubes which can be flame sealed at the conclusion of a synthesis to provide the desired sample for study in a small volume, quartz container. A special feature of the preparation/vacuum system in the TRL is the capability to interrupt a synthesis, isolate (by means of a stopcock) and remove the sample, examine it in... 

SiC has greater thermal stability than any other binary compound of Si and decomposition by loss of Si only becomes appreciable at 2700°. It resists attack by most aqueous acids (including HE but not H3PO4) and is oxidized in air only above 1000° because of the protective layer of Si02 this can be removed by molten hydroxides or carbonates and oxidation is much more rapid under these conditions, e.g. ... 

Most chemical properties of technetium are similar to those of rhenium. The metal exhibits several oxidation states, the most stable being the hep-tavalent, Tc +. The metal forms two oxides the black dioxide Tc02 and the heptoxide TC2O7. At ambient temperature in the presence of moisture, a thin layer of dioxide, Tc02, covers the metal surface. The metal burns in fluorine to form two fluorides, the penta- and hexafluorides, TcFs and TcFe. Binary compounds also are obtained with other nonmetaUic elements. It combines with sulfur and carbon at high temperatures forming technetium disulfide and carbide, TcS2 and TcC, respectively. 

The next five chapters deal with deposition of specific groups of semiconductors. In Chapter 4, II-VI Semiconductors, all the sulphides, selenides, and (what little there is on) tellurides of cadmium (most of the chapter), zinc (a substantial part), and mercury (a small part). (Oxides are left to a later chapter.) This chapter is, understandably, a large one, due mainly to the large amount of work carried out on CdS and to a lesser extent on CdSe. Chapter 5, PbS and PbSe, provides a separate forum for PbS and PbSe, which provided much of the focus for CD in earlier years. The remaining sulphides and selenides are covered in Chapter 6, Other Sulphides and Selenides. There are many of these compounds, thus, this is a correspondingly large chapter. Chapter 7, Oxides and Other Semiconductors, is devoted mainly to oxides and some hydroxides, as well as to miscellaneous semiconductors that have only been scantily studied (elemental selenium and silver halides). These previous chapters have been limited to binary semiconductors, made up of two elements (with the exception of elemental Se). Chapter 8, Ternary Semiconductors, extends this list to semiconductors composed of three elements, whether two different metals (most of the studies) or two different chalcogens. 

Attention will then be turned to the major oxide minerals MgO, AljOj, and SiOj and the binary transition-metal oxides of Ti, Mn, and Fe, with some brief discussion of the series of transition-metal monoxides (MnO, FeO, CoO, NiO) and complex oxides (FeCr204, FeTiOj, etc.), and of the problem of the calculation of Mossbauer parameters in iron oxides (and other compounds). 

This chapter is concerned with the thermal decompositions of oxides and peroxides. There are obviously very important connections with the reactions of hydroxides (Chapter 8) and so-called peroxysalts, which contain hydrogen peroxide of crystallization (included in Chapter 7 on hydrates). Hydrated oxides vary from compounds accurately represented by the stoichiometric formula M(OH) , to phases which contain discrete HjO molecules. The chemistry of oxides should also be considered in the context of the other binary compounds (e.g. hydrides, nitrides, carbides, sulphides etc.) dealt with in Chapter 10. 

Reaction rates may be determined by the ease of intracrystalline transport to the surface, or by the chemical change on the surface. These surface reactions often resemble behaviour described in modelling heterogeneous catalytic processes and are usually reversible so that decomposition rates are sensitive to any gases present. Behaviour of reactants of the present group is similar to that of the oxides (Chapter 9), which are in the same class. Little information is available for other binary compounds, fluorides, chlorides, etc., which usually melt rather than decompose. 

Other Binary Compounds. Direct reaction of uranium with B, C, Si, N, P, As, Sb, Se, S, Te, etc., leads to semimetallic compounds that are often non-stoichiometric, resembling the oxides. Some of them, for example, the silicides, are chemically inert, and the sulfides,35 notably US, can be used as refractories. 

---