Phosphorus vapor pressure

The upper glow limit corresponds to about 0.5 atm pressure of O2 if the phosphorus vapor pressure is about 10 torr. [02]2) the upper limiting pressure of O2, is essentially independent of temperature or the size of the reactor, but is reduced by the addition of foreign gases. If the upper and lower limits are not near each other then [02]2 is approximately 4 x 10" [P4]. 

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). 

C14-0078. Using data from Appendix D, calculate the vapor pressure of P4(g) over solid white phosphorus at 298 K. 

Phosphorus vapor consists of tetrahedral P4 molecules, and at higher temperatures also of P2 molecules (P=Pbond length 190 pm). White phosphorus forms by condensation of the vapor it also consists of P4 molecules. Liquid phosphorus normally consists of P4 molecules, but at a pressure of 1 GPa and 100 °C polymeric liquid phosphorus is formed which is not miscible with liquid P4. 

By irradiation with light or by heating it to temperatures above 180 °C, white phosphorus is transformed to red phosphorus. Its tint, melting point, vapor pressure and especially its density depend on the conditions of preparation. Usually, it is amorphous or microcrystalline, and it is rather laborious to grow crystals. 

The hazards associated with occupational exposure to phosphoric acid depend on its acidic nature. Concentrated phosphoric acid is corrosive to exposed tissue, and lower concentrations are irritating to the skin, eyes, and mucous membranes. Phosphoric acid has a low vapor pressure at room temperature and is unlikely to present an inhalation hazard unless introduced into the atmosphere as a spray or mist. Unacclimated workers could not endure exposure to fumes of phosphorus pentoxide (the anhydride of phosphoric acid) at a concentration of lOOmg/m exposure to concentrations between 3.6 and 11.3mg/m produced cough, whereas concentrations of... 

The tricaldum phosphate in phosphate rock, mixed with coke and silica, is thermally reduced to yield P2 vapor. The phosphorus vapors condense to a liquid and the carbon monoxide produced is returned for burning in the furnace. The process requires much heat and, in addition to the heat provided by the combustion of the coke and the heating value of the recycled carbon monoxide, an electric arc also is used. The reaction takes place in very large furnaces at a temperature of 1,300-1,500°C and at atmospheric pressure. A 70-MW furnace will produce 44,000 short tons (39,600 metric tons) of P4 per year, equivalent to 100.000 tons (90,000 metric tons) of P2O5 (if converted to acid). Although there are numerous intermediate and side reactions, the overall reaction is Caj(P04)2 + 5C +... 

Reactants should be weighed in the atomic ratio of 1 Si/ 2.0-2.5P. The presence of excess phosphorus has been found to enhance reaction and impede the formation of silicon monophosphide. Since a large excess of phosphorus increases the chance of explosion from its vapor pressure, an optimum ratio is... 

P (c, red). The exact thermodynamic status of the solid forms of phosphorus other than yellow has not yet been determined. The vapor pressure of red phosphorus was measured by Chapman1 and Troost and Hautefeuille1 and the latter calculated, from the difference in the temperature coefficients of the vapor pressures of the yellow and red forms, the heat of transition from yellow to red to be 4.2 at 700°. From the difference in the heats of combustion of the yellow and red forms of phosphorus, Giran1 found T=3.7. A more direct measurement of the heat of transition is that from the data of Giran1 on the heats of reaction of the two forms with bromine in carbon disulfide, (2 = 38.79 and 43.01 for the red and yellow forms, respectively. These data yield T=4.22. Giran1 found that the so-called violet or black phosphorus had a heat of reaction of 38.56 with bromine in carbon disulfide. Apparently this form is thermochemically identical with the red form. 

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. 

Black phosphorus is thermodynamically the most stable form of the element and exists in three known crystalline modifications orthorhombic, rhombohedral, and cubic, as well as in an amorphous form. Unlike white phosphorus, the black forms are all highly polymeric, insoluble, and practically non-flammable, and have comparatively low vapor pressures. The black phosphorus varieties represent the densest and chemically the least reactive of all known forms of the element. 

In this important class of additives, the halogen contributes to some extent to the flame retardancy although this contribution is offset by the lower phosphorus content. The halogens generally reduce vapor pressure and water solubility, thus aiding retention of these additives. Thus, more efficient and effective blending/manufacturing processes involved usually lead to a favorable economics of polymer flame retardation.26... 

Tetraalkylstannanes and phosphorus pentafluoride are commercially available. Commercial phosphorus pentafluoride contains a small amount of phosphoryl fluoride, but its presence does not hinder the exchange reaction or cause any subsequent difficulties in workup of the products. It may be removed if desired, however, by carefully fractionating the commercial sample through —112° (CS2 slush) and —196° traps. The former trap will retain the phosphoryl fluoride, whereas the pentafluoride will pass this trap and collect at —196°. The vapor pressure of phosphorus pentafluoride at —96° (toluene slush) is 335 mm. Hg the purity of the sample may be checked by comparison of its vapor pressure against this value. 

Hydrogen chloride generated in situ is insoluble in AHF and leaves the reactor spontaneously. After the reaction is over, excess anhydrous HF is decanted and LiPF6 salt is dried very carefully as the dry salt has PF5 vapor pressure at ambient temperature. Exposure of the salt to air or moisture produces white smokes due to a reaction between PF5 and water present in the air. Phosphorus pentafluoride reacts with water and produces POF3 and HF. A continuous vacuum drying of LiPF6 above 100°C fully decomposes LiPF6 to LiF and PF5. ... 

Kowalsky reported that the oxidation of phosphorus vapor occurred only between certain upper and lower limits of O2 pressure. At the lower limit [02]i varied inversely with the phosphorus pressure. The upper pressure limit was independent of T between —40 and +15° C, with [Ozh about 4 x 10" [P4]. Between the lower and upper critical pressures oxidation occurred and was accompanied by chemiluminescence. The results were interpreted in terms of Semenov s theory of branched-chain reactions. ° ° . Kowalsky s experimental work was consistent with eqn. (c) and Semenov himself discarded eqn (b). 

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. 

Thus if liquid white phosphorus is heated to 440, for example, as was done by Troost and Hautefeuille, the vapor pressure attains quickly 7.76 atmos., which is, at this temperature, the... 

If red phosphorus is heated to 440 , the vapor pressure increases slowly up to 1.75 at. and remains stationary when this value has been reached. 

If we enclose in a flask a mass of white or red phosphorus, and if we keep this flask at a fixed high temperature T long enough for equilibrium to be established, we shall have, at the end of the experiment, the flask filled wilb phosphorus vapor, whose tension will be equal to the tension. of saturated vapor from red phosphorus at the temperature of tiie experiment, and the mass of solid in excess will be in the form of red phosphorus. If, for instance, the temperature is 440 C., we shall have a mass of phosphorus vapor which will fill the flask at a pressure of 1.75 at. this mass will be equal to as many times 3.6 gr. as there are litres in the volume of the flask the rest of the phosphorus will be in the red form. By suddenly cooling the flask we shall find a mass of phosphorus, soluble in carbon bisulphide, equal to 3.6 gr. per litre the rest will be insoluble in carbon bisulphide. 

The condensation of phosphorus vapor to the state of white phosphorus conforms to this law it is not the same with the condensation of phosphorus vapor to the state of red phosphorus at the ordinary temperature saturated white phosphorus vapor has a tension greatly exceeding the tension of saturated red phosphorus vapor, the latter being practically zero nevertheless the saturated vapor of white phosphorus remains indefinitely, at least in the dark without changing into red phosphorus. This phenomenon of false equilibrium makes it possible to predict the realization of an enclosure imequally heated, filled with phosphorus vapor at a high pressure, and in which phosphorus would condense, in the state of red phosphorus, otherwhere than on the coldest waUs of the enclosure this experiment was realized by Troost and Hautefeuille it is the more convincing as the condensation of vapors to the state of white phosphorus, modification free from... 

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... 

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