Silicon phosphate

K. B. Babb, D.A. Lindquist, S.S. Rooke, W.E. Young, and M.G. Kleeve, Porous Solids of Boron Phosphate, Aluminum Phosphate, and Silicon Phosphate, eds. S. Komarneni, D.M. Smith, and J.S. Beck, Advances in Porous Materials, vol. 371. (Materials Research Society, 1995), pp. 279-290. 

The octahedral arrangement in pyridinium tris-(o-phenylendioxy)-siliconate [C5HgNH]2[CgH402)3Si] has been confirmed by the crystal structure determination. The mineral thaumasite belongs also to this group, as well as various silicon phosphates, which can be synthesized at atmospheric pressure. In stishovite and in 16]... 

K(A1q 2sSio.75)40g (hoUandite structure) 46) octahedra are connected by edges and corners to give the three-dimensional structure, in that way while in silicon phosphates and in thaumasite they are separated by anions. 

Phosphate rock preparation—Domestic phosphate rocks are essentially fluorapatite admixed with various proportions of other compounds of calcium, fluorine, iron, aluminum, and silicon. Phosphate rock preparation involves beneficiation to remove impurities, drying to remove moisture, and grinding to improve reactivity. Phosphate rock, when very finely pulverized, has limited direct use as a fertilizer. However, it is mainly used as a raw material for the manufacture of phosphate acid, superphosphate, phosphorus, and phosphorus compounds. 

Silicon phosphates. These compounds contain silicon with an octahedral coordination of O atoms, as in Si2P207, Si50(P04)g and (NH4)2SiP40i3. In these compounds measured Si-0 distances are about 10% greater than when tetrahedral coordination is involved, and ionic character for the bonds, with SP+ present, is indicated (Chapter 3.4). Neither P nor S has any tendency to form such octahedral arrangements, although arsenic has. 

The effect of phosphoric acid on silica has been examined by Mitsyuk (193), who found that HjPO is adsorbed on silica gel from water. The amount corresponds to about one HjPO molecule per surface silicon atom, indicating formation of a surface compound of silicon phosphate. Once treated with as little as 0.06% HjPO, the rate of dissolution of the silica in water is greatly reduced. The addition of H2SO to the dilute H,PO< solution prevents the formation of an adsorbed film and accelerates dissolution. In strong HjPO there is further reaction as silica is converted to SiPjOr in which silicon is coordinated with six oxygen atoms. 

Silica has long been known to react with anhydrous H3PO4 but the wide variety of possible compounds has not been investigated. The reaction is, in effect, a condensation, with water eliminated. For example, by heating amorphous silica with HjPO at a molar ratio of 1 2 for a week at 80-180 C, silicon phosphate is formed. Excess HjPO is removed with dioxane and the product is dried at 100 C. A 10% solution can be made in water, giving a 2.7% concentration of silica (59a). Silicon phosphate has long been known but this example of a water-soluble material is mentioned because it probably hydrolyzes to SifOH). ... 

Colloids of silicophosphoric acid derivatives have not been further investigated, but silicon phosphates have been studied. Jacoby (172) found that at atmospheric pressure, melts of SiO, and P,0, could be made in which 21 compounds were detected. Physical properties of SiO,-P,Oj and 3SiO, 2P,Os were reported. Dissolu tion of some compounds of this type in water or alcohols would probably give aqueous dispersions of colloidal silica, or mixed acid esters similar to that described above. 

Protective agents prevent interference by forming sfable but volatile species with the analyte Three common reagents for this purpose are elhylenedi-aminetetraacetic acid (EDTA). 8-hydroxyquinoline, and APCD, which is the ammonium salt of 1-pyrro-lidinecarbodithioic acid. The presence of EDTA has been shown to eliminate the interference of aluminum, silicon, phosphate, and sulfate in the determination of calcium. Similarly. 8-hydroxyquinoline suppresses the interference of aluminum in the determination of calcium and magnesium. 

Fig. 3.81 Calculated charge densities for the clusters representing (a) boron phosphate, (b) aluminum phosphate and (c) silicon phosphate.

Replacement materials may need to be generated [13]. In the case of PCB, the need for stability, fire resistance, and good electrical characteristics has restricted the search to compounds that may still have the same properties of persistence and bioaccumulation, that led to the concern about PCB in the first place principal contenders are alkylated biphenyls and terphenyls, silicones, phosphate esters and high molecular weight phthalates. 

In the geochemistry of fluorine, the close match in the ionic radii of fluoride (0.136 nm), hydroxide (0.140 nm), and oxide ion (0.140 nm) allows a sequential replacement of oxygen by fluorine in a wide variety of minerals. This accounts for the wide dissemination of the element in nature. The ready formation of volatile silicon tetrafluoride, the pyrohydrolysis of fluorides to hydrogen fluoride, and the low solubility of calcium fluoride and of calcium fluorophosphates, have provided a geochemical cycle in which fluorine may be stripped from solution by limestone and by apatite to form the deposits of fluorspar and of phosphate rock (fluoroapatite [1306-01 -0]) approximately CaF2 3Ca2(P0 2 which ate the world s main resources of fluorine (1). 

Coesite. Coesite, the second most dense (3.01 g/cm ) phase of silica, was first prepared ia the laboratory by heating a mixture of sodium metasibcate and diammonium hydrogen phosphate or another mineraliser at 500—800°C and 1.5—3.5 GPa (14,800—34,540 atm). Coesite has also been prepared by oxidation of silicon with silver carbonate under pressure (67). The stmcture is monoclinic = 717 pm, Cg = 1.238 pm, and 7 = 120°. 

Other limitations on phytoplankton growth are chemical in nature. Nitrogen, in the form of nitrate, nitrite and ammonium ions, forms a basic building material of a plankton s cells. In some species silicon, as silicate, takes on this role. Phosphorus, in the form of phosphate, is in both cell walls and DNA. Iron, in the form of Fe(III) hydroxyl species, is an important trace element. Extensive areas of the mixed layer of the upper ocean have low nitrate and phosphate levels during... 

Formulations for one-shot polyether systems are similar to those used for flexible foams and contain polyether, isocyanate, catalyst, surfactant and water. Trichloroethyl phosphate is also often used as a flame retardant. As with polyesters, diphenylmethane di-isocyanate is usually preferred to TDI because of its lower volatility. Tertiary amines and organo-tin catalysts are used as with the flexible foams but not necessarily in combination. Silicone oil surfactants are again found to be good foam stabilisers. Volatile liquids such as trichlorofluoro-methane have been widely used as supplementary blowing agents and give products of low density and of very low thermal conductivity. 

Fluorides and dust are emitted to the air from the fertilizer plant. All aspects of phosphate rock processing and finished product handling generate dust, from grinders and pulverizers, pneumatic conveyors, and screens. The mixer/reactors and dens produce fumes that contain silicon tetrafluoride and hydrogen fluoride. A sulfuric acid plant has two principal air emissions sulfur dioxide and acid mist. If pyrite ore is roasted, there will also be particulates in air emissions that may contain heavy metals such as cadmium, mercury, and lead. 

Fluor-jod, n. iodine fluoride, -kalium, n. potassium fluoride, -kalzium, n. calcium fluoride, -kiesel, m. silicon fluoride, -kie-selsaure,/. fluosilicic acid, -kohlenstoff, m. carbon fluoride, -lithium, n. lithium fluoride. -metall, n. metallic fluoride, -natrium, n. sodium fluoride, -phosphat, n. fluophosphate. -phosphor, m. phosphorus fluoride, -salz, n. fluoride, -schwefel, m. sulfur fluoride, -selen, n. selenium fluoride, -silber, n. silver fluoride, -silikat, n. fluo-silicate. -silizium, n. silicon fluoride, -sili-ziumverbindung, /. fluosilicate. -tantal-sMure, /. fluotantalic acid, -tellur, n. tellurium fluoride, -titan, n. titanium fluoride, -toluol, n. fluorotoluene, fluotoluene. 

Salts giving an alkaline reaction may be corrosive to the irons, and while neutral solutions can be handled safely there is usually little point in using high-silicon irons for these relatively innocuous solutions. The irons are useful in handling acidic solutions, subject to the restrictions already referred to regarding the halide, sulphite and phosphate ions. 

Both acids form compounds of silicon as a result of attack on the network, silicon fluoride from hydrofluoric acid and silicyl phosphate from phosphoric acid. 

Heating with the following solids, their fusions, or vapours (a) oxides, peroxides, hydroxides, nitrates, nitrites, sulphides, cyanides, hexacyano-ferrate(III), and hexacyanoferrate(II) of the alkali and alkaline-earth metals (except oxides and hydroxides of calcium and strontium) (b) molten lead, silver, copper, zinc, bismuth, tin, or gold, or mixtures which form these metals upon reduction (c) phosphorus, arsenic, antimony, or silicon, or mixtures which form these elements upon reduction, particularly phosphates, arsenates,... 

Other anticaking ingredients include ferric ammonium citrate, silicon dioxide, sodium ferrocyanide, magnesium silicate, magnesium carbonate, propylene glycol, aluminum calcium silicate, sodium aluminosilicate (also called sodium silicoaluminate), and calcium phosphate. 

FIG. 2 Results of white-light interferometric microscopy observation near the triple line of a drop of tricresyl phosphate (TCP) on a soft silicone rubber (RTV 615, General Electric Co.). 

Equation (52) allows us to estimate the impact of viscoelastic braking on the capillary flow rate. As an example, we will consider that the liquid is tricresyl phosphate (TCP, 7 = 50 mN-m t = 0.07 Pa-s). The viscoelastic material is assumed to have elastic and viscoelastic properties similar to RTV 615 (General Electric, silicone rubber), i.e., a shear modulus of 0.7 MPa (E = 2.1 MPa), a cutoff length of 20 nm, and a characteristic speed, Uo, of 0.8 mm-s [30]. TCP has a contact angle at equilibrium of 47° on this rubber. 

Fig. 1 shows the reactor setup used for continuous precipitation of lanthanum phosphate. A tube made of silicone rubber was used as a reactor. The inner diameter of the reactor tube... 

The iron formed in a blast furnace, called pig iron, contains impurities that make the metal brittle. These include phosphorus and silicon from silicate and phosphate minerals that contaminated the original ore, as well as carbon and sulfur from the coke. This iron is refined in a converter furnace. Here, a stream of O2 gas blows through molten impure iron. Oxygen reacts with the nonmetal impurities, converting them to oxides. As in the blast furnace, CaO is added to convert Si02 into liquid calcium silicate, in which the other oxides dissolve. The molten iron is analyzed at intervals until its impurities have been reduced to satisfactory levels. Then the liquid metal, now in the form called steel, is poured from the converter and allowed to solidify. 

In the previous paragraph, it has been stated that minerals have the same structure but different compositions (phenomenon of isomorphism of minerals) while some minerals have the same composition but different structures (phenomenon of polymorphism of minerals). Mineral composition and structure are both important in studying and classifying minerals. The major class of minerals - based on composition and structure - include elements, sulfides, halides, carbonates, sulfates, oxides, phosphates, and silicates. The silicate class is especially important, because silicon makes up 95% of the minerals, by volume, in the Earth s crust. Mineral classes are divided into families on the basis of the chemicals in each mineral. Families, in turn, are made of groups of minerals that have a similar structure. Groups are further divided into species. 

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