Phosphorous, amorphous

Figure 3.09 (a) Time variation of , the potential energy per atom in a 150-atom niekel-phosphorous amorphous deposit, as simulated by computer, (b) Logarithm of the distribution of potential energy minima, plotted against potential energy per atom. (After Stillinger and Weber, 1984). 

The only clearly defined crystalline compositions are three forms of phosphoric acid and hemihydrate, pyrophosphoric acid, and crystalline P O q. The phosphoric acids obtained in highly concentrated solutions or by mixing phosphoric acid with phosphoms pentoxide are members of a continuous series of amorphous (excluding [Y OO]) condensed phosphoric acid mixtures. Mixtures having more than 86% P2O5 contain some cyclic metaphosphoric... 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

Properties and Structure. Phosphoms(V) oxide, the extremely hygroscopic acid anhydride of the phosphoric acids, exists in several forms but is often referred to by its empirical formula, P2O3. Three crystalline polymorphs, two distinct Hquids, and several amorphous or glassy soHds are recogni2ed. Some properties of the various forms of phosphoric oxide are Hsted in Table 10. 

Silver [7440-22-4]—The coloi additive silvei (EEC No. E 174) is a crystaUine powdei of high purity silver prepared by die reaction of silver nitrate with ferrous sulfate in the presence of nitric, phosphoric, and sulfuric acids. Poly(vinyl alcohol) is used to prevent the agglomeration of crystals and the formation of amorphous silver. 

Komrska Satava (1970) showed that these accounts apply only to the reaction between pure zinc oxide and phosphoric acid. They found that the setting reaction was profoundly modified by the presence of aluminium ions. Crystallite formation was inhibited and the cement set to an amorphous mass. Only later (7 to 14 days) did XRD analysis reveal that the mass had crystallized directly to hopeite. Servais Cartz (1971) and Cartz, Servais Rossi (1972) confirmed the importance of aluminium. In its absence they found that the reaction produced a mass of hopeite crystallites with little mechanical strength. In its presence an amorphous matrix was formed. The amorphous matrix was stable, it did not crystallize in the bulk and hopeite crystals only grew from its surface under moist conditions. Thus, the picture grew of a surface matrix with some tendency for surface crystallization. 

Several allotropic forms of phosphorus are known, the most common of which are the white, red, and black forms. Heating the white form at 400 °C for several hours produces red phosphorus, which is known to include several forms. A red form that is amorphous can be prepared by subjecting white phosphorus to ultraviolet radiation. In the thermal process, several substances (I2, S8, and Na) are known to catalyze the conversion of phosphorus to other forms. Black phosphorus consists of four identifiable forms that result when white phosphorus is subjected to heat and pressure. Phosphorus is used in large quantities in the production of phosphoric acid and other chemicals. White phosphorus has been used extensively in making incendiary devices, and red phosphorus is used in making matches. 

Addition of a soluble Zr(IV) salt to phosphoric acid results in the precipitation of a gelatinous amorphous solid. The stoichiometric crystalline zirconium phosphate can be prepared by refluxing zirconium phosphate-gel in concentrated phosphoric acid [5]. The procedures for synthesis of zirconium phosphate have been described in detail elsewhere [6]. 

The theoretical endproduct of the dehydration of phosphoric acid is phosphorus (V) oxide, which has three crystalline forms with known structures (65,66,128,180) and two amorphous forms (135). All of them contain only tertiary P04 tctrahedra and represent the nonacidic final product of the series of cross-linked or ultra phosphates. Only the readily volatile hexagonal crystalline form has been studied in any detail chemically. This form consists of P401() molecules with four P04 tetrahedra joined together (47). Formula (53)]. When this form of the oxide is treated with water or... 

Bahr.Ber 61,2178-83(1928) 63,99(1930) Phosphorus Carbide, PaCj, wh amorph ppt, which spontaneously ignites when gently warmed. Was prepd by treating an ethereal soln of acetylene-bis-magnesium iodide, MgI.C CMgI with phosphorous trichloride Refs l)Beil l,[22l] 2)E- deMahler, BullFr... 

In industrial procedures catalyst preparation in organic solvents is preferred, producing a more amorphous precursor with high density of active sites.1022 In addition, phosphorous compounds are usually injected into the feed to replenish phosphorous lost through hydrolysis. In this way an appropriate surface phosphorous vanadium ratio is maintained ensuring prolonged catalytic activity and selectivity. 

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