Peptisation

If a dilute acid is added to this solution, a white gelatinous precipitate of the hydrated tin(IV) oxide is obtained. It was once thought that this was an acid and several formulae were suggested. However, it now seems likely that all these are different forms of the hydrated oxide, the differences arising from differences in particle size and degree of hydration. When some varieties of the hydrated tin(IV) oxide dissolve in hydrochloric acid, this is really a breaking up of the particles to form a colloidal solution—a phenomenon known as peptisation. 

The process for manufacture of a chloroprene sulfur copolymer, Du Pont type GN, illustrates the principles of the batch process (77,78). In this case, sulfur is used to control polymer molecular weight. The copolymer formed initially is carried to fairly high conversion, gelled, and must be treated with a peptising agent to provide a final product of the proper viscosity. Key control parameters are the temperature of polymerisation, the conversion of monomer and the amount/type of modifier used. 

Peptisator, m. peptizer, peptizing agent, peptisch, a. peptic, peptisieren. v.t. peptize. 

Phosphates are another common ingredient of alkali cleaners. They have both detergent and peptisation properties. The pyro- and polyphosphates in particular have water softening capabilities. 

In general, pure water should not be used unless it is certain that it will not dissolve appreciable amounts of the precipitate or peptise it. If the precipitate... 

Problems which arise with certain precipitates include the coagulation or flocculation of a colloidal dispersion of a finely divided solid to permit its filtration and to prevent its re-peptisation upon washing the precipitate. It is therefore desirable to understand the basic principles of the colloid chemistry of precipitates, for which an appropriate textbook should be consulted (see the Bibliography, Section 11.80). However, some aspects of the colloidal state relevant to quantitative analysis are indicated below. 

The process of dispersing a gel or a flocculated solid to form a sol is called peptisation, and is briefly dealth with on page 421 and in Section 11.8. 

The precipitate should be washed with the appropriate dilute solution of an electrolyte. Pure water may tend to cause peptisation. (For theory of washing, see Section 11.8 below.)... 

Procedure. Precipitation is therefore made by adding a very dilute solution, say 0.05M, of silver nitrate slowly and with constant stirring to a dilute ammoniacal solution of the iodide until precipitation is complete, and then adding excess of nitric acid (1 per cent by volume). The precipitate is collected in the usual manner, washed with 1 per cent nitric acid, and finally with a little water to remove nitric acid. Peptisation tends to occur with excess of water. Other details of the determination will be found in Section 11.57. 

In view of the selective character of many colorimetric reactions, it is important to control the operational procedure so that the colour is specific for the component being determined. This may be achieved by isolating the substance by the ordinary methods of inorganic analysis double precipitation is frequently necessary to avoid errors due to occlusion and co-precipitation. Such methods of chemical separation may be tedious and lengthy and if minute quantities are under consideration, appreciable loss may occur owing to solubility, supersaturation, and peptisation effects. Use may be made of any of the following processes in order to render colour reactions specific and/or to separate the individual substances. 

Palladium, D. of as dimethylglyoximate. (g) 463 as nioximate, (g) 474 by EDTA, (ti) 329 Paper chromatography 229 see Thin layer chromatography Parallax errors due to, 85 Parallel determinations 132 Partial ionic equations 850, (T) 851 Partition chromatography 13. 217 Partition coefficient 162 Patton and Reeder s indicator 317, 328 Peptisation 419. 421... 

In preparing the membrane, a clear sol was obtained by the addition of acid into the aluminum sec-butoxide sol to peptise the sol and obtain a stable colloid solution. Aluminum monohydroxides formed by the hydrolysis of aluminum alkoxides, which are peptisable to a clear sol. Peptisation was performed by the addition of acid and heat treatment for a sufficient time. It was found that stable sols cannot be obtained when the concentration of the peptisation acid is too low. The critical range for inorganic acids such as nitric, hydrochloric and perchloric acids is 0.03-0.1 mole/mole of hydroxide. In this study, nitric acid was used as the peptising agent. The resulting sols are poured into Petri dishes and dried in an oven at a controlled drying rate to obtain a gel layer. The molar ratio of zirconia salt... 

PVA was used as a temporary binder owing to its water solubility, excellent binding strength and clean burning characteristics. To prepare the PVA solution, 4 g of PVA were added to 100ml distillated water. The mixture was heated and stirred vigorously until all the PVA was dissolved in the water. This took about half an hour. Peptisation was done by addition of 5 ml 1M HN03 to the solution. Finally, the solution was refluxed for 4 hours. The PVA solution was used in the preparation of the zirconia-alumina sol-gel solution. The preparation of the PVA solution can be summarised as follows ... 

Additives (antioxidants, antiozonants, softeners, tacfdfiers, peptisers, scorch inhibitors, colorants, flame retardants, blowing agents, process aids, etc.)... 

Natural rubber which has been reduced to an easy flowing consistency by prolonged mastication in the presence of peptising agents. Suitably compounded, DPR may be cast into moulds and vulcanised ebonite products from DPR are also possible. 

Natural rubber to which has been added on the plantation a quantity of a peptising agent. Such pre-softened and easily-softened rubbers... 

A substance which added to rubber in very small amounts (0.1-0.2 phr) speeds up the normal mastication process and produces rubber of a given plasticity in a shorter time and with less power consumption. The accelerator MBT has a peptising action but certain thiophenols, mercaptans and particularly o-o-dibenzoylaminodiphenyl disulphide are much more effective. 

Substances used to assist in the reclaiming of rubber. Many plasticisers and some peptisers function as reclaiming agents. 

Compounding ingredients added to elastomers (2-5 phr) to increase plasticity and facilitate processing. In larger proportions (20-50 phr) certain oil softeners are classed as extenders. See Peptising Agent. 

An efficient peptising agent for natural rubber it is also used as a bleaching agent in the preparation of pale crepe rubber. 

Peptisers are often used to facilitate breakdown of the rubber during mixing, although quantities of greater than 0.6 phr can cause a reduction in the final level of physical properties. 

The polymerisation of butadiene results in a polymer with a narrow molecular weight distribution which can be difficult to process. Indeed, commercially available grades present a compromise between processibility and performance. Most polybutadiene rubbers are inherently difficult to break down during mixing and milling, have low inherent tack, and the inherent elasticity of the polymer gives poor extrudability. Peptisers can be used to facilitate breakdown and hence aid processing. 

The A and FA types both require peptisation to ensure ease of processing, and this is normally accomplished by the addition of MBTS and DPG onto a two roll mill maintained at 160°F prior to the addition of other ingredients. 

DNPT is flammable, so it must be stored carefully to avoid contact with heat sources. It must also be kept dry as moisture reduces its activity. It is activated by peptisers and curing agents and therefore care must be taken at the weighing out stage of mixing. 

Dry hydrogen sulphide interacts with selenium oxychloride with the formation of yellow selenium sulphide and evolution of hydrogen chloride. There is a development of heat which dissociates the selenium sulphide into sulphur and red selenium. Sulphur dioxide has no action on the hot anhydrous oxychloride, but if water is present there is a deposition of selenium. Sulphur trioxide is soluble in selenium oxychloride, forming a thick solution which is a very powerful solvent for the oxides of the rare earth metals. When the oxychloride is brought into contact with finely divided barium sulphate, the latter is at once peptised and becomes gelatinous in appearance,1 but when subsequently treated with water the sulphate immediately changes back to the ordinary form. 

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