Salts mixed-metal

A large number of crystalline phosphates contain two or more cations, and many phosphate minerals are mixed metal salts. 

Heat stabilisers for PVC act by HC1 scavenging and include organotins, mixed metal salt blends, and lead compounds. The latter account for nearly 64 % of volume (in 1994), followed by barium/cadmium and organotin compounds. Cadmium-based heat stabilisers are rapidly being replaced due to environmental concerns. Barium/zinc and calcium/zinc compounds show a high growth rate. It is expected that methyltin stabilisers will soon dominate the growing PVC pipe market. 

One of the difficulties with the classical solid-state reaction is that mechanical mixing methods are relatively ineffective in bringing the solid reactants in contact with one another. Diffusion lengths, on an atomic scale, are still enormous and the temperatures required may preclude the formation of phases that might be stable at intermediate temperatures. One method, called a precursor method, involves the formation of a mixed-metal salt of a volatile organic oxyanion such as oxalate by wet chemical methods, which result in mixing essentially on the atomic level. The salt is then ignited at relatively low temperatures to form the mixed-metal oxide. The method has been applied successffilly to the preparation of a number of ternary transition metal oxides with the spinel structure. ... 

Oxidation of a mixture of potassium and silver(I) halides with fluorine in alkaline solution produces yellow potassium tetrafluoroargentate, KAgp4, which is very sensitive to moisture. The corresponding yellow sodium and cesium salts are also known. All contain the diamagnetic square-planar [Agp4] ion. There are mixed-metal salts such as KCs2Agp6, which contains the octahedral [AgP ] " ion. Pluorination of a mixture of CsCl and AgCl under pressure yields a complex salt of tetravalent silver Cs2[Ag p6]. 

Transmetallation of zinc organometallics with manganese(II) salts does not occur and cannot be used to produce functionalized organomanganese compounds. The reaction of unsaturated alkyl bromides furnishes, in the presence of a mixed metal-salt system composed of copper(I) chloride and manganese(Il) bromide [32], cyclization products in satisfactory yields (see Section 9.6.17 Scheme 9-55) [94]. 

Mixed oxides can also be reduced to the mixed metal catalysts by hydrogen reduction. Such oxides have been prepared by sodium nitrate fusion of mixed metal salts, primarily those of the noble metals, following the procedure used for the prepeiration of Adams catalyst, platinum oxide. 31-136 Non-noble metal alloy powders are prepared by heating mixed nitrates, carbonates or hydroxides in air to convert them to the mixed oxides which are then reduced. The hydroxides can be prepared by coprecipitation from a mixed metal salt solution. ... 

A solution of appropriate salts can also be reduced in the liquid phase by the addition of an appropriate reducing agent. Sodium borohydride has been used but care must be taken to remove the boron from the catalyst, particularly for the mixed noble metals. This has been accomplished by adding a dilute borohydride solution to the mixed metal salt solution under rapid agitation followed by a thorough washing of the precipitated metal black with warm water.The use of hydrazine, formaldehyde or formic acid is preferred to borohydride since the byproducts of the reduction do not contaminate the catalyst. Another procedure is to use a ternary alloy and to leach out one component as in the preparation of Raney nickel and similar catalysts. 

Acid-to-base precipitation is used for batch operation, in which the mixed metal salt solution is fed into the basic solution (precipitation agent) in the reactor. During the acid-to-base operation, the pH continuously decreases to a predetermined lower value. The end pH can be further adjusted by adding an additional amount of acid or base. Base-to-acid precipitation is also an alternative, with the pH continuously increasing during the precipitation. 

These builders are generally available as sodium, potassium, or mixed-metal salts, the latter being more soluble in water but also more costly. The widespread use of sodium TPP (STPP) in LADD formulations can be attributed to the many functions it performs during the wash cycle. Besides its efficient sequestration of hardness ions, STPP works to disperse and suspend soils, enhance the surface action of anionic surfactants, solubilize proteinaceous soils, and provide alkalinity and buffering action. Pyrophospates have been included in some LADD formulations because of its better solubility properties relative to tripolyphosphate [20],... 

Procedure 1 - NaOH(3M) was added to a mixed metal salt solution until pH of 10 is reached. The precipitate was washed several times and dried at 100"C. The solid was crushed and calcinated at 300 C for 3 hr. ... 

The most important costabilizers in PVC formulations used mainly in combination with mixed metal salts are alkyl-aryl-phosphites to improve early color. Epoxy compounds, for example, epoxidized fatty esters such as epoxidized soy bean oil, react directly with HCl or substitute labile chlorine atoms, for example, in the presence of zinc ions. Furthermore, the epoxidized fatty esters act as plasticizers. Polyols such as pentaerythritol or dipentaerythritol and P-diketones act as complexing agents and deactivate the negative effect of the formed zinc chloride. Hydrotalcites... 

Heat stabilizers may be classified as either primary or secondary. Primary heat stabilizers inhibit dehydrochlorination in chlorine-containing polymers and react with any liberated hydrogen chloride to delay further degradation. Mixed metal salts are primary heat stabilizers and form metal chlorides with hydrogen chloride. However, mixed metal salts have a destabilizing effect which results in discolouration of the polymer. This effect is counteracted by the introduction of secondary heat stabilizers such as organophosphites and epoxy compounds. Organotin and lead primary heat stabilizers can be used alone. 

Many types of additives are used to stabilise PVC. For example, mixed metal salts of fatty acids, such as barium and cadmium stearates, are added at a 2 or 3% level. Metal stearates (MSti) react with and remove free hydrogen chloride, slowing down the degradation. 

Precipitation at increasing pH A simple way to prepare a mixed metallic hydroxide consists of carrying out a potentiometric titration of a mixed metallic salts solution with a l sic solution of an alkali metal hydroxide or alkali metal carbonate (Ross, and Kodama 1967 Hemandez-Moreno, Ulibarri, Rendon, and Serna 1985 Yamaoka, Abe, and Tsuji 1989). We have recently prepared by the addition of a NaOH solution at a constant rate to a mixed solution of ZnCl2 and CrCla, and NiCh and CrCls,... 

Several hundred mixed-metal pyrophosphates are known in the solid state. Many of these may be prepared by melting together two pyrophosphates (5.125), or orthophosphoric acid with the appropriate mixture of oxides, or a mixture of metal nitrates with dianunonium phosphate. When solutions of equivalent quantities of a soluble metal salt and sodium pyrophosphate are mixed, a precipitate of a mixed-metal salt is produced. These precipitates are often amorphous and reluctant to crystallise, and sometimes ill defined with a variable water content. In other cases, however, a crystalline compound with a definite composition can be isolated (5.126). Molten nitrates will react with some acid salts to produce double salts [30] (5.127). 

When mixed metal salts are used as primary heat stabilizers, metallic chlorides are formed by the reaction with labile Cl. These materials have a destabilizing effect that sometimes result in color formation in... 

Mixed-Metal Sulfides. Mixed-metal sulfides are generally prepared by one of the four following methods 1) comaceration, (2) homogeneous sulfide precipitation, (3) mixed-metal salts or organometallic clusters decomposition, and 4) impregnation of a binary sulfide. Most of these techniques were developed for the synthesis of Co/Mo or Ni/Mo catalysts but are applicable to other systems. 

In the IJS 2()0 million US market, the main heat stabilizers include lead compounds, organotin compounds, and mixed metal/salt blends based on chemicals such as barium, cadmium, and zinc, and significant changes are expected. Over US 75 million of the business is in lead- and cadmium-containing stabilizers, but these are under increasing scrutiny on health and safety grounds. 

Mixed Metal Salts (or Soaps). These consist of Ba/Cd salts (once the most widely used because of their effectiveness but now declining owing to regulatory pressure), Ba/Zn, and Ca/Zn salts. The efficacy of these mixed metal salts as thermal stabilizers follows that order. Mainly used in flexible or semirigid PVC, they are available in solid and liquid versions. Solids are typically salts of fatty acids such as stearates and laurates while liquid versions are octoate, phenolate, and neodecanoate salts. Mixed metal salts are almost always used in the presence of secondary stabilizers such as organophosphites, epoxies (eg, epoxidized soyabean oil), and j8-diketones. This is particularly the case for the less active Ba and Ca/Zn. The ratio of metal salt to secondary stabilizer is typically 4 1. Mixed metal salts or soaps are available from Akros, Baerlocher, Ferro, and Rohm Haas in North America. 

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