Phosphorus compounds, vapor pressure

Phosphorus Pentoxide. This compound, P2O55 (Class 1, nonregenerative) is made by burning phosphoms ia dry air. It removes water first by adsorptioa, followed by the formation of several forms of phosphoric acid (2). Phosphoms peatoxide [1314-56-3] has a high vapor pressure and should only be used below 100°C. Its main drawback is that as moisture is taken up, the surface of the granules becomes wetted and further moisture removal is impeded. For this reason, phosphoms pentoxide is sometimes mixed with an iaert material (see Phosphoric acids and phosphates). 

The determination of specific phosphorus compounds in thin films is important. Only through wet chemical analysis was it possible to first discover the presence and then to accurately measure the quantities of P2Os, P203, and phosphine found in plasma, plasma-enhanced, LPO-LTO (low-pressure oxide-low-temperature oxide), and CVD (chemical vapor deposition) processes (3). Methods such as X-ray or FTIR spectroscopy would have seen all phosphorus atoms and would have characterized them as totally useful phosphorus. In plasma and plasma-enhanced CVD films, phosphine is totally useless in doping processes. 

Gallium(III) bromide is a hygroscopic, white solid which sublimes readily and melts at 122.5° to a covalent, dimeric liquid. The solid is ionic and its electrical conductivity at the melting point is twenty-three times that of the liquid.5 The vapor pressure of the liquid at T°K is given by the equation log p(mm.) = 8.554 — 3129/T and the heat of dissociation of the dimer in the gas phase is 18.5 kcal./mol.3 At 125° the liquid has the following properties 5,6 density, 3.1076 dynamic viscosity, 2.780 c.p. surface tension, 34.8 dynes/cm. and specific conductivity, 7.2 X 10-7 ohm-1 cm.-1 Gallium(III) bromide readily hydrolyzes in water and forms addition compounds with ligands such as ammonia, pyridine, and phosphorus oxychloride. 

The formation of mixed Mo — P —S compounds is thermodynamically restricted at temperatures lower than 1000°C (70). This restriction implies that the sulfur atoms in M0S2 are not directly replaced by phosphorus atoms. In the same way, phosphorus does not regularly occupy the edges of the M0S2 platelets through bonds with sulfur atoms as in the case of the promoted CoMoS or NiMoS phases. The presence of P(white), P(red), and P(black) on catalysts can also be excluded because they have extremely high vapor pressures under hydrotreating conditions. 

Direct reaction is feasible for the IVA-VA compounds. This is surprising, since a low vapor pressure element, such as silicon, would be expected to passivate on exposure to phosphorus or arsenic. The valve metal analogy to electrochemical reactions may be invoked here fresh silicon probably diffuses rapidly through the compound, providing a continuous supply of reactant. A cold zone with a temperature of less than 500°C supplies phosphorus to the silicon, kept slightly near the 1 1 SiP melting point of 1166°Ck... 

An analysis was made of the published experimental and calculated values of the theimochemical constants of gallium phosphide (the standard entropy and the specific heat, the enthalpy, and the free energy of formation of diis compound) and of the equilibrium constants and vapor pressure of phosphorus. Approximate methods were used to calculate the remaining constants the specific heat was found by the Landiya method and the standard entropy was deduced from the Eastman equation and by summing the entropies of elemental group IV semiconductors. 

Phosphorus exists as white and red phosphorus. The former allotrope may be preserved in the dark at low temperatures but otherwise reverts to the more stable red form. The white form is a waxy, translucent, crystalline, highly-toxic solid subliming at room temperature and inflaming in air at 35°C, so it is handled under water. The red form is a reddish violet crystalline solid which vaporizes if heated at atmospheric pressure and condenses to give white phosphorus. The red form ignites in air at 260°C. Both are insoluble in water, and white phosphorus can be stored beneath it. Phosphorus forms a host of compounds such as phosphine, tri- and penta-halides, tri-, tetra- and penta-oxides, oxyacids including hypophosphorous, orthophosphorous and orthophosphoric acids. 

The reaction of adipic acid with ammonia in either liquid or vapor phase produces adipamide as an intermediate which is subsequently dehydrated to adiponitrile. The most widely used catalysts are based on phosphorus-containing compounds, but boron compounds and silica gel also have been patented for this use (52—56). Vapor-phase processes involve the use of fixed catalyst beds whereas, in liquid—gas processes, the catalyst is added to the feed. The reaction temperature of the liquid-phase processes is ca 300°C and most vapor-phase processes mn at 350—400°C. Both operate at atmospheric pressure. Yields of adipic acid to adiponitrile are as high as 95% (57). 

In the second stage of the process, the reaction mass is added to bitumen at a starting temperature of 130°C-140°C that is subsequently increased to 180°C under reduced pressure. This results in the formation of low volatility, low toxicity phosphorus-containing compounds and the vaporization of isobutanol and N-methylpyrrolidinone. The vapor stream is condensed to form a distillate that contains isobutanol and N-methylpyrrolidinone. Upon cooling, a solid bitumen-salt end product is formed. The joint evalu-... 

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