Cadmium oxidative addition

Liquid- and vapor-phase processes have been described the latter appear to be advantageous. Supported cadmium, zinc, or mercury salts are used as catalysts. In 1963 it was estimated that 85% of U.S. vinyl acetate capacity was based on acetylene, but it has been completely replaced since about 1982 by newer technology using oxidative addition of acetic acid to ethylene (2) (see Vinyl polymers). In western Europe production of vinyl acetate from acetylene stiU remains a significant commercial route. 

Cadmium is usually plated from a cyanide bath that consists of an aqueous solution of cadmium oxide (35 g/L) and sodium cyanide (75 g/L). An additive and a brightener are used to produce smooth, fine-grain deposits. Current density ranges from 1.4 to 3.7 A/dm, depending on the concentration of cadmium cations in the electrolyte. 

Dimethylsilicone rubbers show a high compression set which can be reduced to some extent by additives such as mercurous oxide and cadmium oxide. These materials are undesirable, however, because of their toxicity. Substantially reduced compression set values may be obtained by using a polymer containing... 

The high reactivity of the cadmium metal powder is clearly demonstrated by the ready oxidative addition of a variety of alkyl and aryl halides. 

Cadmium, as cadmium oxide, is obtained mainly as a by-product during the processing of zinc-bearing ores and also from the refining of lead and copper from sulfide ores (USPHS 1993). In 1989, the United States produced 1.4 million kg of cadmium (usually 0.6 to 1.8 million kg) and imported an additional 2.7 million kg (usually 1.8 to 3.2 million kg). Cadmium is used mainly for the production of nickel-cadmium batteries (35%), in metal plating (30%), and for the manufacture of pigments (15%), plastics and synthetics (10%), and alloys and miscellaneous uses (10%) (USPHS 1993). 

Cadmium oxide is used in storage battery electrodes. Its solution, mixed with sodium cyanide, is used in electroplating baths. Other uses are in PVC heat stabilizers as an additive to nitrile rubbers and plastics to improve heat resistance and in ceramic glazes and phosphors. 

Production. The raw material for the production of cadmium yellow pigments is high-purity cadmium metal (99.99 %), cadmium oxide, or cadmium carbonate. If the metal is used it is first dissolved in mineral acid. A zinc salt is then added to the solution the amount added depends on the desired shade. The zinc salt is followed by addition of sodium sulfide solution. An extremely finely divided cadmium sulfide or cadmium zinc sulfide precipitate is formed, which does not possess any pigment properties. This intermediate product can also be obtained by mixing the cadmium or cadmium-zinc salt solution with sodium carbonate solution. An alkaline cadmium carbonate or cadmium zinc carbonate precipitate is formed which reacts in suspension with added sodium sulfide solution. 

In pocket plate cells, the active materials are a mixture of finely powdered metallic iron and Fe304. The preparation of this mixture varies from manufacturer to manufacturer, but generally involves a final process in which controlled air oxidation of iron powder or reduction of Fe304 with hydrogen is used to form the appropriate composition. Additives such as cadmium, cadmium oxide or graphite are commonly included to improve the capacity retention and electronic conductance. The performance of the electrode is improved by the addition of up to 0.5% of FeS the mechanism of the sulphide involvement is not well understood. If sulphide is lost by oxidation after prolonged use, small amounts of soluble sulphide may be added to the electrolyte,... 

In addition to those dusts producing lung injury are dusts which are systemic in their effects. Common examples of these dusts are the lead compounds, manganese dioxide, cadmium oxide, etc. On inhalation, the effect of these dusts is much more severe than if they were ingested. They are easily absorbed into the blood stream and act directly on many vital organs. 

Cadmium pigments have been manufactured by both a direct calcination process and a precipitation-calcination process. In the first instance, a mixture of cadmium carbonate and sulfur (and zinc oxide and selenium if the hue to be produced requires their addition) is calcined at 520-600°C for 1-2 h. This direct calcination process is complicated by the volatility of cadmium oxide and selenium, both of which are toxic and require special handling. In the precipitation process, an alkali sulfide solution is added to a solution of cadmium and (in the case of green-shade yellows) zinc salts or to a solution of cadmium and (in the case of deep oranges, reds, and maroon) selenium metal to precipitate the appropriate compound. The precipitate is washed, dried, and calcined at 600-700°C in an inert or reducing atmosphere to convert the precipitated cubic structure to a more stable wurtzite crystal. The calcination conditions control particle size, which ranges from 0.2 to 1.0pm. 

Many other substances have been tested for use as additives for molybdenum disulphide films, including silver, tin, lead, lead oxide, bismuth trioxide and boron nitride , alumina, arsenic oxide, cadmium oxide, cuprous oxide, molybdic oxide. 

In the powder process, finely divided cadmium carbonate or cadmium oxide is subjected to intensive mechanical mixing with sulfur and mineralizers and then calcined in the absence of oxygen. The addition of zinc or selenium produces the same effects as in the precipitation process. The product is worked up in the same way as in the precipitation process. The main producer of cadmium pigments is Millenium (USA). 

Derivation (a) Addition of sodium cyanide and formaldehyde to a basic solution of ethy lenediamine (forms the tetrasodium salt) (b) heating tetrahydroxyethylethylenediamine with sodium hydroxide or potassium hydroxide with cadmium oxide catalyst. 

Other alkaline earth metal oxides and related Group II metal oxides were screened for activity. Tests indicated that magnesia-zinc oxide combinations were about as efficient as magnesia alone. Calcium oxide, zinc oxide, and cadmium oxide were all catalysts for the reaction but were not as effective as magnesium oxide. Efficiencies of these oxides were increased by supporting them on activated alumina. In addition, it was found that sodium and lithium compounds deposited on activated alumina were active cat-... 

A series of runs was made in which from 0.3 to 1.5% by weight each of cadmium oxide and titanium oxide was added as a catalyst. In both cases 0.6 to 0.7% by weight of catalyst was sufficient to give maximum catalytic effect. The addition of catalysts in greater amounts did not change the composition of the product. 

Hydrogenation is generally carried out at tanperatures of 250-280°C and pressures of 20-25 MPa. Catalysts include zinc oxide in conjunction with aluminum oxide, chromium oxide, or iron oxide, and possibly, other promoters copper chromite whose activity has been reduced by the addition of cadmium compounds and cadmium oxide on an alumina carrier. Selective hydrogenation can also be carried out in a homogenous phase with metallic soaps as catalysts. 

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