Carbide nitride halides

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

Boric oxide is used as a catalyst in many oiganic reactions. It also serves as an intermediate in the production of boron halides, esters, carbide, nitride, and metallic borides. 

A large variety of catalysts, both homogeneous and heterogeneous, has been found active for dehydrohalogenation. The catalysts include a number of Br nsted and Lewis acids (liquid or soluble, as well as solid), metal oxides, active carbon, carbides, nitrides and some metals. However, in the latter case, the actual catalysts are most probably surface metal halides... 

CVD processes have a greater flexibility of using a wide range of chemical precursors such as halides, hydrides, organo-metallic compounds and so forth which enable the deposition of a large spectrum of materials, including metals, non-metallic elements, carbides, nitrides, oxides, sulphides, as well as polymers. Up to now, around 70% of elements in the periodic table have been deposited by the CVD technique, some of which are in the form of the pure element, however, more often the compound materials. 

A variety of precursor materials including halides, hydrides, and organometallics can be used, which enables deposition of metals, carbides, nitrides, and oxides. 

The reactant gases, also referred to as precursor molecules, are chosen to react and produce a specific film. Properties necessary for a good precursor include thermal stability at its vaporization temperature and sufficient vapor pressure (at least —125 Pa) at a reasonable temperature (—300°C) for effective gas phase delivery to the growth surface. In addition, the molecules must be obtainable at high purity and must not undergo parasitic or side reactions which would lead to contamination or degradation of the film (10). Examples of the classes of precursor molecules (e.g., hydrides, halides, carbonyls, hydrocarbons, and organ-ometallics) and the types of chemical reaction (pyrolysis, oxidation/hydrolysis, reduction, carbidization/nitridation, and disproportionation) are summarized in Table 1.3. 

Gerasimov et have provided a reference book on the thermodynamic properties of tungsten, molybdenum, titanium, zirconium, niobium, and tantalum, and their more important compounds, viz. oxides, sulphides, halides, carbides, nitrides, silicates, borides, and hydrides. 

Methods of preparation for silicides and aluminides are very similar to those used for carbides, nitrides and borides (1) synthesis by fusion or sintering, (2) reduction of the metal oxide by silicon or aluminum, (3) reaction of the metal oxide with SiOj and carbon, (4) reaction of the metal with silicon halide or (5) fused salt electrolysis. The simplest preparation method consists of... 

Plasmas have been used to produce a wide range of materials, many of which are described in reviews by Hamblyn and Reuben [126] and by Johnson [12]. As indicated by the examples listed in Table 2, products include metals from pyrolysis of halides, oxides from oxidation of halides, and a variety of nonoxides, including carbides, nitrides, and borides. The powders have submicron particles, are generally agglomerated, and are either amorphous or crystallized into nonequilibrium phases. 

There are perovskite structures of halides, hydrides, carbides, nitrides. 

Wicks, C. E. and Block, F. E. "Thermodynamic Properties of 65 Elements - Their Oxides, Halides, Carbides, and Nitrides", Bureau of Mines, Bulletin 605, 1963. 

Binary rare-earth compounds such as carbides, sulfides, nitrides, and hydrides have been used to prepare anhydrous trihalides, but they offer no special advantage. Treating these compounds at a high temperature with a halogen (98) or hydrogen halide (115) produces the trihalide, e.g.,... 

The term S] is defined by the authors as an ionicity factor and assumes a value of 0.5 for oxides and silicates, 0.75 for halides, 0.40 for calcogenides, 0.25 for phosphides and arsenides, and 0.2 for nitrides and carbides (Z is the anion charge). Equation 1.94 is based on the thermal expansion data listed in table 1.15. 

Plutonium reacts with hydrogen at high temperatures forming hydrides. With nitrogen, it forms nitrides, and with halogens, various plutonium hahdes form. Halide products also are obtained with halogen acids. Reactions with carbon monoxide yields plutonium carbides, whde with carbon dioxide, the products are both carbides and oxides. Such reactions occur only at high temperatures. 

In the group, the most familiar members are the oxides, halides, hydrides (including the hydrocarbons), nitrides, sulfides, and carbides. Many methods are available for the preparation of binary compounds, and the most general ones will be illustrated by exercises. 

Block, Thermodynamic Properties of 65 Elements Their Oxides, Halides, Carbides and Nitrides , US BuMines Bull 608 (1963)... 

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