Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Cations polyvalent

Other Reactants. Other reactants are used in smaller amounts to provide phenoHc resins that have specific properties, especially coatings appHcations. Aniline had been incorporated into both resoles and novolaks but this practice has been generally discontinued because of the toxicity of aromatic amines. Other materials include rosin (abietic acid), dicyclopentadiene, unsaturated oils such as tung oil and linseed oil, and polyvalent cations for cross-linking. [Pg.293]

Orthophosphate salts are generally prepared by the partial or total neutralization of orthophosphoric acid. Phase equiUbrium diagrams are particularly usehil in identifying conditions for the preparation of particular phosphate salts. The solution properties of orthophosphate salts of monovalent cations are distincdy different from those of the polyvalent cations, the latter exhibiting incongment solubiUty in most cases. The commercial phosphates include alkah metal, alkaline-earth, heavy metal, mixed metal, and ammonium salts of phosphoric acid. Sodium phosphates are the most important, followed by calcium, ammonium, and potassium salts. [Pg.331]

Many orthophosphate salts, in particular those of polyvalent cations, exhibit incongment solubihty where disporportionation occurs in solution to yield a more basic orthophosphate salt and phosphoric acid. This hydrolytic disproportionation of orthophosphates should not be confused with the... [Pg.333]

Alkali Meta.IPhospha.tes, A significant proportion of the phosphoric acid consumed in the manufacture of industrial, food, and pharmaceutical phosphates in the United States is used for the production of sodium salts. Alkali metal orthophosphates generally exhibit congment solubility and are therefore usually manufactured by either crystallisation from solution or drying of the entire reaction mass. Alkaline-earth and other phosphate salts of polyvalent cations typically exhibit incongment solubility and are prepared either by precipitation from solution having a metal oxide/P20 ratio considerably lower than that of the product, or by drying a solution or slurry with the proper metal oxide/P20 ratio. [Pg.341]

Silicate Grouts. Sodium silicate [1344-09-8] h.3.s been most commonly used in the United States. Its properties include specific gravity, 1.40 viscosity, 206 mPa-s(=cP) at 20°C Si02 Na20 = 3.22. Reaction of sodium silicate solutions with acids, polyvalent cations, such organic compounds as formamide, or their mixtures, can lead to gel formation at rates, which depend on the quantity of acid or other reagent(s) used. [Pg.227]

The hot-water separation process involves extremely compHcated surface chemistry with interfaces among various combinations of soUds (including both silica sand and alurninosilicate clays), water, bitumen, and air. The control of pH is critical. The preferred range is 8.0—8.5, achievable by use of any of the monovalent bases. Polyvalent cations must be excluded because they tend to flocculate clays and thus raise viscosity of the middlings in the separation cell. [Pg.359]

When a potential is appHed across the ceU, the sodum and other cations are transported across the membrane to the catholyte compartment. Sodium hydroxide is formed in the catholyte compartment, because of the rise in pH caused by the reduction of water. Any polyvalent cations are precipitated and removed. The purified NaOH may be combined with the sodium bicarbonate from the sodium dichromate process to produce soda ash for the roasting operation. In the anolyte compartment, the pH falls because of the oxidation of water. The increase in acidity results in the formation of chromic acid. When an appropriate concentration of the acid is obtained, the Hquid from the anolyte is sent to the crystallizer, the crystals are removed, and the mother Hquor is recycled to the anolyte compartment of the ceU. The electrolysis is not allowed to completely convert sodium dichromate to chromic acid (76). Patents have been granted for more electrolytic membrane processes for chromic acid and dichromates manufacture (86). [Pg.138]

Ghelants and Precipitation Inhibitors vs Dispersants. Dispersants can inhibit crystal growth, but chelants, such as ethylenediaminetetraacetic acid [60-00-4] (EDTA), and pure precipitation inhibitors such as nitrilotris(methylene)tris-phosphonic acid [6419-19-8], commonly known as amino trismethylene phosphonic acid (ATMP), can be more effective under certain circumstances. Chelants can prevent scale by forming stoichiometric ring stmctures with polyvalent cations (such as calcium) to prevent interaction with anions (such as carbonate). Chelants interact... [Pg.149]

Poly(vinyl chloride) is commercially available in the form of aqueous colloidal dispersions (latices). They are the uncoagulated products of emulsion polymerisation process and are used to coat or impregnate textiles and paper. The individual particles are somewhat less than 1 p,m in diameter. The latex may be coagulated by concentrated acids, polyvalent cations and by dehydration with water-miscible liquids. [Pg.355]

The formation of a single complex species rather than the stepwise production of such species will clearly simplify complexometric titrations and facilitate the detection of end points. Schwarzenbach2 realised that the acetate ion is able to form acetato complexes of low stability with nearly all polyvalent cations, and that if this property could be reinforced by the chelate effect, then much stronger complexes would be formed by most metal cations. He found that the aminopolycarboxylic acids are excellent complexing agents the most important of these is 1,2-diaminoethanetetra-aceticacid (ethylenediaminetetra-acetic acid). The formula (I) is preferred to (II), since it has been shown from measurements of the dissociation constants that two hydrogen atoms are probably held in the form of zwitterions. The values of pK are respectively pK, = 2.0, pK2 = 2.7,... [Pg.55]

The nature of chemical coagulants are such that the macrofloc may possess certain charges for example lime (CaO), alum (A1203) and flocculating polyvalent cations cany positive charges, which interact with proteins. The interactions are simply illustrated in Figure 7.6. [Pg.179]

The investigation of plutonium chemistry in aqueous solutions provides unique challenges due in large part to the fact that plutonium exhibits an unusually broad range of oxidation states -from 3 to 7-and in many systems several of these oxidation states can coexist in equilibrium. Following the normal pattern for polyvalent cations, lower oxidation states of plutonium are stabilized by more acidic conditions while higher oxidation states become more stable as the basicity increases. [Pg.214]

The ability of polyvalent cations leached from the glass to suppress the free-fluoride ion concentration in basalt ground water is difficult to assess. Fluoride definitely enhances leaching and is the primary cause of the high concentrations of dissolved plutonium in the basalt ground-water leachate. Once the plutonium is dissolved, however, it is not possible to determine what fraction is stabilized by fluoride as opposed to other species leached from the glass. [Pg.342]

Alkylphosphonates are surface-active agents. But the main use of these substances lies in their ability to form stable complexes with bi- or polyvalent cations. Thus, besides the identification of the P-C bond and the determination of the amount of phosphorus in the molecule by one of the previously mentioned methods, measurement of their sequestering ability is carried out. [Pg.617]

In the present experiments, MTX markedly increased the tissue Ca content, Ca uptake, and intracellular free Ca concentration of smooth or cardiac mus cles. These Ca -mobilizing effects of MTX as well as its vasoconstrictive, cardio tonic, and cardiotoxic effects were profoundly suppressed or abolished by Ca entry blockers, polwalent cations, or Ca -free medium. It has been reported that MTX produces Ca -dependent excitatory effects on neuronal (10,11,18) or pituitary (26) cells and smooth (12,13), cardiac (14,15,17), or skeletal (16) muscles, and that all these actions of MTX were antagonized by Ca antagonists or polyvalent cations. These observations suggest that the enhanced Ca influx and the subsequent increase in cytoplasmic free Ca concentration play a dominant role in the excitatory effects of MTX. [Pg.142]

For chemical and electrostatic reasons, some ions are bound more strongly than others. Polyvalent cations are much more strongly bound than univalent cations the same holds for anions. Thus, when a solution containing Ca ions (hard water) is passed through a cation exchanger which is present in its Na or H+ form, the Ca ions are held back in it and the Na or H+ ions leave instead. Similarly, an anion exchanger in the OH form will retain Cl or SO ions from the solution. By a cation and anion exchanger in series, the former in the H+ and the latter in the OH... [Pg.452]

Figure 8. Variation in with cation charge (Z ) for lattice sites in elinopyroxene (Blundy and Dalton 2000 Brooker et al. 2003) and wollastonite (Law et al. 2000), eompared to change in ionie radius with eharge for some polyvalent cations (Am, U, Np and Pu in Vt-, Vtl- and Vtll-fold... Figure 8. Variation in with cation charge (Z ) for lattice sites in elinopyroxene (Blundy and Dalton 2000 Brooker et al. 2003) and wollastonite (Law et al. 2000), eompared to change in ionie radius with eharge for some polyvalent cations (Am, U, Np and Pu in Vt-, Vtl- and Vtll-fold...
Although it is possible, by the loss of several electrons, for certain metal atoms to form polyvalent cations upto a maximum valency of four (e.g., tin forms the tetravalent stannic ion, Sn4+), the formation of polyvalent anions is extremely difficult since for the acquisition of each additional electron the attractive force exerted by the nucleus on each individual electron becomes progressively smaller. It is for this reason that the maximum valency for a simple anion is found to be two. [Pg.7]

Soils containing polyvalent cations having high valence and high electrolyte concentration have a high conductivity, whereas the soils containing monovalent cations, such as sodium, have a low k. Distilled water at the extreme end of the spectrum is free of electrolytes. In the Gouy-Chapman equation, the electrolyte concentration na would be 0. The denominator, therefore, would go to 0 and the T value to infinity. [Pg.1117]

The strong interaction of polyvalent cations with polyions is well known to strongly alter the rheological properties of hydrolyzed polyacrylamide used in the tertiairy oil recovery process (1-4). The influence of divalent cations have already been studied(5-7) but the role played by the presence of small quantities of aluminium ions has never been investigated. [Pg.129]

Solutions of TKPP were mixed with aqueous fluids commonly encountered in drilling or completion of wells. Unlike saturated zinc bromide, concentrated TKPP solutions can be mixed in any proportion with fresh water with the only result being a decrease in solution density. Similar results were obtained with conventional oil field brines containing as much as 400 parts per million polyvalent cations, mostly calcium. Saturated solutions of calcium hydroxide also can be added to TKPP in any proportion without promoting precipitation as can concentrated hydrochloric acid solutions, conventionally used for well stimulation. The acid tends to generate a slight haze as the pH is reduced from 11.5 to approximately 8 however, this haze rapidly disappears as the pH is lowered by further addition of acid. [Pg.630]


See other pages where Cations polyvalent is mentioned: [Pg.440]    [Pg.449]    [Pg.502]    [Pg.445]    [Pg.490]    [Pg.238]    [Pg.534]    [Pg.150]    [Pg.2057]    [Pg.285]    [Pg.99]    [Pg.899]    [Pg.178]    [Pg.179]    [Pg.208]    [Pg.302]    [Pg.152]    [Pg.341]    [Pg.309]    [Pg.40]    [Pg.75]    [Pg.224]    [Pg.227]    [Pg.624]    [Pg.626]    [Pg.16]    [Pg.17]    [Pg.254]    [Pg.3]    [Pg.52]   
See also in sourсe #XX -- [ Pg.29 ]

See also in sourсe #XX -- [ Pg.7 ]

See also in sourсe #XX -- [ Pg.409 ]




SEARCH



Polyvalent

© 2024 chempedia.info