Phosphor physical properties

Extensive hydrogen bonding takes place in phosphoric acid solutions. In concentrated (86% H PO solutions, as well as in the crystal stmctures of the anhydrous acid and the hemihydrate, the tetrahedral H PO groups are linked by hydrogen bonding. At lower (75% H PO concentrations, the tetrahedra are hydrogen-bonded to the water lattice. Physical properties of phosphoric acid solutions of various concentrations are Hsted in Table 2 the vapor pressure of aqueous H PO solutions at various temperatures is given in Table 3. 

Table 2. Physical Properties of Aqueous Solutions of Phosphoric Acid...

The general manufacturing scheme for phosphate salts is shown in Figure 11. Condensed phosphates are prepared from the appropriate orthophosphate or mixture of orthophosphates, so the preparation of orthophosphates must be considered first for the manufacture of any phosphate salt. Phosphoric acid is neutralized to form a solution or slurry with a carefully adjusted acid/base ratio according to the desired orthophosphate product. The orthophosphate may be recovered either by crystallization from solution, or the entire solution or slurry may be evaporated to dryness. The dewatering (qv) method is determined by the solubihty properties of the product and by its desired physical properties such as crystal size and shape, bulk density, and surface area. Acid orthophosphate salts may be converted to condensed phosphates by thermal dehydration (calcination). 

Flame retardants designated for nylon include halogenated organic compounds, phosphorous derivatives, and melamine cyanurate (160—163). Generally, flame retardants are difficult to spin in nylon because of the high loading required for effectiveness and their adverse effects on melt viscosity and fiber physical properties. 

Within the limitations on the physical properties which generally restrict plastics to low precision optics, plastics materials have found wide applications in optical products that range from lights to binders for electroluminescent phosphors to fiber optics and lasers. They represent an easily worked material with a wide range of desirable optical properties in simple to complex shapes. In this review the discussion has been limited to the differences between plastics and optical glass materials and to some of the unique design possibilities that are especially important for plastics. Using the optical arts and the... 

Elemental composition P 37.78%, H 3.69%, 0 58.54%. The acid in solid form may be identified by its physical properties. Aqueous solution may be heated and phosphorus acid is converted to phosphoric acid which is measured for orthophosphate ion by ion chromatography or colorimetry (see Phosphoric Acid). A cold aqueous solution may be analyzed for phosphite ion by ion chromatography, following appropriate dilution. Strength of the acid in an aqueous solution may be measured by acid-base titration using a standard solution of alkali. Also, titration against a standard solution of silver nitrate using potassium chromate as indicator may serve as an additional confirmatory test. 

Sodium is analyzed in aqueous solution by AA or ICP methods. Phosphate anion is measured by colorimetric methods (See Phosphoric Acid) or ion chromatography. The solution must be diluted appropriately. The compound is also identified from its physical properties. 

Table II lists several physical properties of various phosphors as compared to those for an ideal phosphor. The refractive index should be fairly low so that in a polymeric system (polymer Rl 1.5) the number of scattering phenomena are decreased. In this respect, BaFCI Eu is best. To reduce structure mottle and improve phosphor packing, spherical or polyhedral shaped particles are most desireable. Further, to improve phosphor packing, narrow particle distributions are best.

No easy comparisons can be made of commercial screens regarding quantum mottle, resolution and speed since different screen constructions are used and particle sizes differ. Other factors cannot be easily compared. The intent of the previous discussions was to compare several physical properties of rare earth x-ray phosphors which have an important effect on final image quality. Other benefits of rare earth screens include ... 

Some physical properties of metaphosphoric acid.—Metaphosphoric acid is a transparent, vitreous solid sometimes called glacial phosphoric add. E. Brescius2 said that the glacial acid is soft and flexible, and the presence of sodium phosphate makes it hard. The commercial acid is sold in sticks, and, according to A. Betten-dorff, it often contains some sodium salts and some ortho- and pyro-acids as impurities. The dry acid deliquesces rapidly in air, and it readily dissolves in water with the development of much heat. The acid solidifies to a vitreous mass without crystallization from solutions with less than 63 per cent, of water. 

Some elements exist in various forms. These forms have different physical properties but have the same chemical properties. They are called allotropes of the element. Carbon, phosphorous and sulfur have allotropes. 

The extraction of zinc with the cation exchanger di(2-ethylhexyl)phosphoric acid, RH, is recommended by the EFCE as a test system for RE. Physical properties, handling, equilibrium data, etc. are documented on the internet (http // www. dechema.de/Extraction, http //www.icheme.org/leaming). 

Pure deuterophosphoric acid is stable indefinitely as a solid but in the fused state always contains traces of pyro-and other polyphosphates which depress the freezing point of the compound. Its chemical properties are similar to those of phosphoric acid. The more important physical properties of the two compounds (supercooled) are compared in the following table.3... 

Physical Properties.—Phosphorus trichloride is a colourless liquid which boils at 76° C. and freezes at about -100° C. The vapour density and the analysis correspond to the molecule PC13. The liquid fumes in moist air with decomposition. It is immiscible with water, but is completely hydrolysed by it forming hydrochloric and phosphorous acids. 

Orthophosphorio Acid —Preparation—Physical Properties of Solid Hydrates of P2Os—Solubilities, Melting-points and Eutectics of the System HjP04-Ha0—Densities of Aqueous Solutions—Vapour Pressures—Conductivities of Concentrated and Dilute Solutions—Viscosities—Refractive Index—Basicity and Neutralisation of the Phosphoric Acids—Constitution... 

Pure lead has low creep and fatigue resistance, but its physical properties can be improved by the addition of small amounts of silver, copper, antimony, or tellurium. Lead-clad equipment is in common use in many chemical plants. The excellent corrosion-resistance properties of lead are caused by the formation of protective surface coatings. If the coating is one of the highly insoluble lead salts, such as sulfate, carbonate, or phosphate, good corrosion resistance is obtained. Little protection is offered, however, if the coating is a soluble salt, such as nitrate, acetate, or chloride. As a result, lead shows good resistance to sufuric acid and phosphoric acid, but it is susceptible to attack by acetic acid and nitric acid. 

Table 5 Some physical properties and P NMR chemical shifts S of phosphoric and thiophosphoric trihahdes and mixed halides ...

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