Oxidation carbide

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. 

M. Levenson, J. V. C. Trice, and W. J. Mecham, Comparative Cost Study of the Processing of Oxide, Carbide, and MetalFast Breeder Reactor Fuels by Aqueous, Uolatility andPyrochemicalMethods, ANL-7137, Argonne National Laboratory, Argonne, lU., 1966. 

The materials deposited by PVD techniques include metals, semiconductors (qv), alloys, intermetaUic compounds, refractory compounds, ie, oxides, carbides, nitrides, borides, etc, and mixtures thereof. The source material must be pure and free of gases and inclusions, otherwise spitting may occur. 

Refractory Compounds. Refractory compounds resemble oxides, carbides, nitrides, borides, and sulfides in that they have a very high melting point. In some cases, they form extensive defect stmctures, ie, they exist over a wide stoichiometric range. For example, in TiC, the C Ti ratio can vary from 0.5 to I.O, which demonstrates a wide range of vacant carbon lattice sites. 

T oxides, carbides via high iatensity arc metallic powders via vacuum or catalytic reactions... 

Porous filament wound composite of oxide fibers and an inorganic adhesive, impregnated with an organic resin Hot pressed oxide, carbide, or nitride in a metal honeycomb... 

Ceramics (single and mixed oxides, carbides, nitrides, borides, glasses, and traditional ceramics)... 

The deposition of a binary compound can be achieved by a coreduction reaction. In this manner, ceramic materials such as oxides, carbides, nitrides, borides, and silicides can be produced readily and usually more readily than the parent metal. A common example is the deposition of titanium diboride ... 

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). 

The pulsed molecular beam cluster source has produced clusters of virtually every material—we have made clusters of even the most refractory transition metals, of group IIIB and IVB elements, and numerous oxides, carbides, and intermetallic alloys of these elements. 

According to Ref. [12], template for synthesis of nanomaterials is defined as a central structure within which a network forms in such a way that removal of this template creates a filled cavity with morphological or stereochemical features related to those of the template. The template synthesis was applied for preparation of various nanostructures inside different three-dimensional nanoporous structures. Chemically, these materials are presented by polymers, metals, oxides, carbides and other substances. Synthetic methods include electrochemical deposition, electroless deposition, chemical polymerization, sol-gel deposition and chemical vapor deposition. These works were reviewed in Refs. [12,20]. An essential feature of this... 

The electroextraction process for molybdenum involves the use of its oxides, carbides or sulfides as soluble anodes in a potassium chloride-potassium hexachloromolybdate (K3MoCl6) molten electrolyte. An inert atmosphere electrolytic cell, with a provision for semicontinuous electrolysis, is used for this purpose. The process operation consists of the following steps. 

Along with compound semiconductor nanoparticles, nanoparticles of many other materials, including metals, metal oxides, carbides, borides, nitrides, silicon, and other elemental... 

Although most of the fluorine calorimetry has been done with the elements, it has been used to burn oxides, carbides, nitrides, and chal-cogenides and hence determine their heats of formation. In some instances it has proved superior to oxygen bomb calorimetry. Thus the oxidation of boron tends to be incomplete because of oxide coating, whereas fluorination produces gaseous boron trifluoride without surface inhibition. A summary of modem fluorine calorimetry results is assembled in Table III. 

In many studies the chemisorption and the surface reaction is just the first step in a series of solid state reactions that take place as atoms from the surface move into the bulk. Corrosion, oxide, carbide and other compound formations are generally initiated at the surface and then propagate into the bulk. There may be a concentration gradient of certain constituents at the surface in a multicomponent system that would influence the mechanical or chemical properties of the system. Hardening of materials and other forms of passivation treatment frequently involve introduction of certain substances only in the near surface region. For the investigation of these problems RHEED is a powerful technique. 

We need to develop methods to understand trends for complex reactions with many reaction steps. This should preferentially be done by developing models to understand trends, since it will be extremely difficult to perform experiments or DFT calculations for all systems of interest. Many catalysts are not metallic, and we need to develop the concepts that have allowed us to understand and develop models for trends in reactions on transition metal surfaces to other classes of surfaces oxides, carbides, nitrides, and sulfides. It would also be extremely interesting to develop the concepts that would allow us to understand the relationships between heterogeneous catalysis and homogeneous catalysis or enzyme catalysis. Finally, the theoretical methods need further development. The level of accuracy is now so that we can describe some trends in reactivity for transition metals, but a higher accuracy is needed to describe the finer details including possibly catalyst selectivity. The reliable description of some oxides and other insulators may also not be possible unless the theoretical methods to treat exchange and correlation effects are further improved. 

Carbonic acid, carbonic oxide, carbide of hydrogen, anduncondcnsed water,. 87 to 30... 

Foot from top HlfrOgCIL Cittoonli) aold fttttonlo oxide. Carbide of Jiydrotpa< UydregeiL Gtoftrttri guA ... 

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