Metallic powders, hydrogenation

Chlorosulfonic acid Saturated and unsaturated acids, acid anhydrides, nitriles, acrolein, alcohols, ammonia, esters, HCl, HF, ketones, hydrogen peroxide, metal powders, nitric acid, organic materials, water... 

Hafnium hydride is brittle and easily cmshed to very fine particle sizes. It is usually produced as an intermediate in the process of making hafnium powder from massive hafnium metal. The hydrogen can be removed by high vacuum pumping above 600°C. 

Manufacturing Processes. Ammonium molybdate or molybdenum trioxide is reduced to molybdenum metal powder by hydrogen in a two-stage process. In the first stage, MoO or ammonium molybdate is reduced to molybdenum dioxide, M0O2, at temperatures around 600°C in the... 

Bina Selenides. Most biaary selenides are formed by beating selenium ia the presence of the element, reduction of selenites or selenates with carbon or hydrogen, and double decomposition of heavy-metal salts ia aqueous solution or suspension with a soluble selenide salt, eg, Na2Se or (NH 2S [66455-76-3]. Atmospheric oxygen oxidizes the selenides more rapidly than the corresponding sulfides and more slowly than the teUurides. Selenides of the alkah, alkaline-earth metals, and lanthanum elements are water soluble and readily hydrolyzed. Heavy-metal selenides are iasoluble ia water. Polyselenides form when selenium reacts with alkah metals dissolved ia hquid ammonia. Metal (M) hydrogen selenides of the M HSe type are known. Some heavy-metal selenides show important and useful electric, photoelectric, photo-optical, and semiconductor properties. Ferroselenium and nickel selenide are made by sintering a mixture of selenium and metal powder. 

Reduction to Metal Powder. The metal powder is obtained from APT by stepwise reduction with carbon or hydrogen. The intermediate products are the yeUow oxide, WO blue oxide, (see Tungsten compounds) and brown oxide, WO2. Because carbon introduces impurities,... 

Includes only hydrogen-reduced metal powder and chemicals. 

Mercury, chlorine, calcium hypochlorite, iodine, bromine or hydrogen fluoride Acids, metal powders, flammable liquids, chlorates, nitrites, sulphur, finely-divided organics or combustibles Nitric acid, hydrogen peroxide... 

In the previous Sections, bulk specimens were alloyed with hydrogen from the gas phase. It was interesting to see whether hydrogen affects the mechanical properties of titanium in a similar way if metal is in a powder state and hydrogen is introduced by mechanical mixing of the metal powder with titanium dihydride, or the interparticle boundaries axe an insurmountable obstacle for hydrogen an eliminate the effects observed in bulk specimens. 

No binary hydrides have been characterized, but reactions of the metal powders with alkali metal hydrides in a hydrogen atmosphere lead to Li3RhH4 (planar RhH4 ) and M3MH6 (M = Li, Na M = Rh, Ir) with octahedral MHj [34],... 

Activation methods can be divided into two groups. Activation by addition of selected metals (a few wt%), mainly transition metals, e.g., fine powders of Fe, Ni, Co, Cr, Pt, Pd, etc. ", or chlorides of these metals when these are reducible to the metal by hydrogen during presintering. The mechanism of activation is not understood (surface tension, surface diffusion, etc.) but is related to the electronic structure of the metal additive. Activation by carbon is also effective. Alternatively, activation utilizes powders in a specially activated state, e.g., very fine (submicronic) powders. ... 

Praseodymium tri-iodide, Prl3, as the starting material for reduction reactions, might be easily produced by the oxidation of praseodymium metal with elemental iodine [17]. With catalytic amounts of hydrogen dissolved in praseodymium metal powder, the reaction temperature can be as low as 230 °C [18]. Sublimation in high vacuum in tantalum tubes yields pure Prl3. 

At least rune manufacturing technologies are available for the production of caprolactam and, in most, hydroxylamine (hyam) is one of the important raw materials. In particular, in the HPO process the hydroxylamine is made by using a precious metal powdered catalyst to selectively hydrogenate nitric acid. Evonik... 

Plasma processes have been successfully demonstrated for production of metals from their oxides and chlorides intermediates. Reducing agents are, of course, to be used. Thus, a plasma-based process involving reduction of tantalum chloride in hydrogenous atmosphere has been claimed to yield highly pure metal powder suitable for making of porous capacitor of high capacitance. 

Tungstic oxide —- Hydrogen reduction — Tungsten metal powder Figure 5.39 Processing of tungsten resources. 

Metallic powders are made several different ways. They can be prepared by reducing salts in a stream of a reducing gas, such as hydrogen chlorides of metals are commonly used but oxides are used too. Thermal decomposition in a vacuum of metal carbonyls or metal salts of organic acids, such as formates, produces metal powders. Surface areas of such powders are around 1.5 m2/g. Powders can also be made from electrolytic reduction of salts in organic solvents and by atomization of the metal. 

Alloys of zinc with iridium, platinum or rhodium, after extraction with acid, leave residues which explode on warming in air, owing to the presence of occluded hydrogen (or oxygen) in the catalytic metal powders so produced. 

The activity of metals other than platinum for skeletal reactions of larger molecules is not well documented, particularly in a mechanistic sense. Carter, Cusumano, and Sinfelt (157) have recently studied the reaction of n-heptane on a series of group VIII metals in the form of hydrogen-reduced (300°C) metal powders. The nature of the reaction pathways is summarized in Table IX. Although many metals have been... 

ESCA and AUGER have been carried out on several metals and in all cases the metal has been shown to be in the zerovalent state. Bulk analysis also clearly shows that the metal powders are complex materials containing in many cases significant quantities of carbon, hydrogen, oxygen, halogens, and alkali metal. 

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