Zinc Systems

The basic metal salts and soaps tend to be less cosdy than the alkyl tin stabilizers for example, in the United States, the market price in 1993 for calcium stearate was about 1.30— 1.60, zinc stearate was 1.70— 2.00, and barium stearate was 2.40— 2.80/kg. Not all of the coadditives are necessary in every PVC compound. Typically, commercial mixed metal stabilizers contain most of the necessary coadditives and usually an epoxy compound and a phosphite are the only additional products that may be added by the processor. The requited costabilizers, however, significantly add to the stabilization costs. Typical phosphites, used in most flexible PVC formulations, are sold for 4.00— 7.50/kg. Typical antioxidants are bisphenol A, selling at 2.00/kg Nnonylphenol at 1.25/kg and BHT at 3.50/kg, respectively. Pricing for ESO is about 2.00— 2.50/kg. Polyols, such as pentaerythritol, used with the barium—cadmium systems, sells at 2.00, whereas the derivative dipentaerythritol costs over three times as much. The P-diketones and specialized dihydropyridines, which are powerful costabilizers for calcium—zinc and barium—zinc systems, are very cosdy. These additives are 10.00 and 20.00/kg, respectively, contributing significantly to the overall stabilizer costs. Hydrotalcites are sold for about 5.00— 7.00/kg. 

Figure A1.19 shows the phase diagram for the copper-zinc system. It is more complicated than you have seen so far, but all the same rules apply. The Greek letters (conventionally) identify the single-phase fields. 

The copper-zinc system (which includes brasses) has one eutectoid reaction. Mark the eutectoid point on the phase diagram (Fig. A 1.38). 

The copper-zinc system shown in Fig. A1.38 has no fewer than five peritectic reactions. Locate them and ring the peritectic points. (Remember that when a single-phase field closes above at a point, the point is a peritectic point.)... 

How far the formulation of a phosphating bath influences The Ratio is not entirely clear. Nitrite alone or in combination with chlorate has been the most widely used accelerator system for many years but more recently nitrite-free chlorate/organic systems have been increasingly favoured. Low zinc systems in which the bath is starved of zinc to promote a high iron content in the coating, originally introduced in Japan, have become widespread. 

Let us first consider, as an example, the copper-zinc system of alloys.1 The ordinary yellow brass of commerce is restricted in composition to the first (copper-rich) phase of the system. This phase, which has the face-centered cubic structure characteristic of copper, is followed successively, as the zinc content is increased, by the /3-phase (body-centered cubic),... 

Phase diagram studies of the magnesium-al uminum-zinc system have shown that there exists a ternary phase, which has been given the name A phase or T phase (Egar, 1913 Koster Wolf, 1936 Koster ... 

Of the tin additives studied, the anhydrous and hydrated zinc stannates, ZnSnO and ZnSn(OH), respectively, are considerably more effective flame-retardant synergists with the bromine present in the plastic than 8-stannic acid (Figure 1). In line with this observation, oxidic tin-zinc systems have previously been found to exhibit superior flame-retardant properties to tin oxides alone (19-22). In addition, ZnSnO, gives higher values of 01 than Sb20, incorporation levels studied, and, in fact, the 1% ZnSnO - containing plastics outperform samples containing 2% Sb O,. 

There are several possible soluble and insoluble zinc species in a chemical bath containing OH", S2, NH3, and NH2-NH2. The probable species and relevant equilibrium of the zinc system in an ammonium-based solution is as follows35 ... 

The coupling of two azinyl halides, in the presence of an appropriate electron source, also leads to the formation of diaryl compounds. 2-Iodopyrimidine and its derivatives were converted into the symmetrical 2,2 -bipyrimidines (7.88.) using activated copper. This method was found to give superior results,111 compared to the earlier reported nickel chloride-zinc system.112... 

For general zinc plating in the United States, estimates of the zinc baths in use in 1970 showed cyanide at over 90%, chloride at 3%, and noncyanide alkaline (zincate) baths at 4%. By 1990, cyanide zinc was 20%, chloride 50%, and zincate 30% (138). In 1992 (139) the cyanide was 16%, chloride 48%, and zincate 36%. Moreover, the cyanide zinc baths of 1992 were more likely to be run at 15—30 g/L sodium cyanide in contrast to the 100 g/L normal in 1970. Each of the three zinc systems uses proprietary brighteners. 

The problems concerning reaction equilibrium and kinetics description based on chemical potentials rather than on concentrations are extensively discussed in Refs. 54 and 55, using the zinc system. The latter is recommended as a reactive liquid-liquid reference extraction test system by the European Federation of... 

Thus, participation of solvent may be critical in this type of system, as in the magnesium and zinc systems. 

It may be noted that all of the homosteric catalysts were chiral zinc systems, the composition of which was expressed as [RZnOR ]x[R,OZnOR,]J,(v/y < 1). Antisteric catalysts were chiral zinc- or cadmium-based systems of a common compositional feature expressed as [RZnOR ]x[R OZnOR ]>, or [RCdOR ]x [R OCdOR ]) (x/y > 2). The nature of homosteric and antisteric stereoelection has not yet been elucidated fully at the molecular level because the structure of the operating species and the polymerisation mechanism with these catalysts are not clearly established [52]. 

Reductive coupling of iodonium salts catalysed by a palladium-zinc system also produced biaryls in good yield [38]. Also very effective was the palladium-catalysed cross-coupling of iodonium salts with sodium tetraphenylborate in water [39]. The reaction of 3-indolyl phenyliodonium trifluoroacetate with several alkyl and aryl lithium reagents gave 3-substituted indoles [40] ... 

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