Nitride dissociation

W. Muthmann and co-workers also reported that finely divided vanadium reacts with nitrogen at a red-heat. The reaction is so slow that 20-24 hrs. are needed for the increase in weight to become constant nitrogen is also absorbed at dull redness, but the action is still slower. In contradistinction to H. E. Roscoe, the composition of the product approximated vanadium heminitride, V2N. R. E. Slade and G. I. Higson found that vanadium nitride dissociates at 1203° and 02 mm. press. According to N. Whitehouse, at a white-heat vanadium forms the mononitride. The velvety-black powder is unchanged in air when heated in air, however, it forms vanadium pentoxide water, and dil. hydrochloric acid, hot or cold, have no action, but it dissolves in cold dil. nitric acid. G. Gore found that vanadium nitride is insoluble in liquid ammonia. It is not affected by alkali-lye, but with fused potassium hydroxide, ammonia is evolved. 

The product is described as a powder, white to dark red in colour according to the time of heating at 250° C. The density was 2-5. The nitride was tasteless, odourless, and chemically inactive at ordinary temperatures. The heat of formation (from white phosphorus) is given as +81-5 Cals, per mol.3 The molar heat of combustion was 474-7 Cals, (at constant pressure). The nitride dissociated into its elements in a vacuum at about 760° C.4 It was reduced to phosphorus and ammonia by hydrogen at a red heat, and burned when heated in oxygen or chlorine. It was hydrolysed by boiling water, thus... 

It is clear from the above that h-BN materials possess a variety of unique properties and demands on such ceramics consistently increase. However, the production methods are energy and time consuming and thus expensive. Indeed, being extremely refractory material, similar to graphite, with nitride dissociation, it is difficult to sinter this type of compound. Can one suggest a novel approach to produce BN ceramics The author truly believes that direct synthesis of boron nitride net shape articles by combustion-based approach described below is an effective alternative to the conventional technologies. 

Sihcon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between sihcon carbide and a variety of compounds at relatively high temperatures. Sodium sihcate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal sihcide. Sihcon carbide decomposes in fused alkahes such as potassium chromate or sodium chromate and in fused borax or cryohte, and reacts with carbon dioxide, hydrogen, ak, and steam. Sihcon carbide, resistant to chlorine below 700°C, reacts to form carbon and sihcon tetrachloride at high temperature. SiC dissociates in molten kon and the sihcon reacts with oxides present in the melt, a reaction of use in the metallurgy of kon and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new sihcon nitride-bonded type exhibits improved resistance to cryohte. 

Several elements react with the N atoms in active nitrogen to form nitrides. The excited Ni molecules are also highly reactive and can cause the dissociation of molecules that are normally stable to attack either by ordinary N2 or even N atoms, e.g. ... 

In many CVD reactions for the deposition of nitrides, ammonia (NH3) is used as a source of nitrogen, rather than nitrogen. This is preferable from a thermodynamic standpoint but may present a problem in that any NH3 — either unreacted or present in the regions of furnace where the temperature is below its dissociation temperature— tends to combine with the HCl effluent gas and forms NH4CI, which may clog the exhaust line. 

Compounds such as the refractory carbides, nitrides, and oxides have extremely high boiling points and generally dissoci-... 

Puurunen et al. have investigated the effect of surface nitridation of y-AI2O3 supports by the atomic layer deposition process on the activity of chromium catalysts for isobutane dehydrogenation. Nitridation was observed to suppress activity and it was argued that oxide ions were more active for the dissociation of isobutane. 

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