Preparation of Slurries

A good dispersant must allow the preparation of slurries that provide the highest solids content with the lowest (or at least acceptable) viscosity. 

Slurries An alternative to dry and wet decompositions is the preparation of slurries, which have been shown to provide a convenient way to introduce solid material into the plasma torch. The solid sample is not digested rather, it is finely ground and suspended in a liquid to be then introduced as an aerosol of fine, hydrated, solid particles. Thus, the direct analysis of solid samples as slurries reduces both the risk of sample contamination and the time required for sample preparation. 

Table 1 Conditions of pretreatment of metal support and preparation of slurry and the weight gains after dip-coating and calcination of the samples...

A third method for the preparation of slurry oxide is the thermal decomposition of thorium formate [28]. In this procedure, thorium nitrate in solution is decomposed on adding it to concentrated formic acid at 95°C [29,30]. The precipitated thorium formate is washed free of excess acid and decomposed by calcination at 500 to 800 C. The oxide from the formate procedure is similar in its slurry behavior to that produced by thorium oxalate thermal decomposition however, less is known about its handling characteristics. Because of this, the oxalate preparation method is preferred at the present time. 

Systematic studies to investigate the effect of concentration of impregnating reagent, temperature, and pH to optimize the separation conditions have been reported by different workers. These showed that the best resolution for ( )-ibuprofen was at 0.1 g of (—)-brucine for every preparation of slurry of silica gel (30 g), at 24 2°C and between pH 6 and 7 [13]. 

Hafnium Carbonate. Basic hafnium carbonate [124563-80-0], Hf2(0H)4C02 XH20, is prepared as a wet paste by reaction of a slurry of basic hafnium sulfate [139290-14-5], Hf 02(S0 2 XH20, and sodium carbonate, then filtering. The basic carbonate has a short shelf life and is preferably prepared as needed. It is a starting material for the preparation of various hafnium carboxylates. 

Hquid—soHd preparing homogeneous slurries of light and heavy soHds such as polymers, catalyst, etc dissolving, crystallization, Hquid—soHd reactions, solvent extraction... 

The general manufacturing scheme for phosphate salts is shown in Figure 11. Condensed phosphates are prepared from the appropriate orthophosphate or mixture of orthophosphates, so the preparation of orthophosphates must be considered first for the manufacture of any phosphate salt. Phosphoric acid is neutralized to form a solution or slurry with a carefully adjusted acid/base ratio according to the desired orthophosphate product. The orthophosphate may be recovered either by crystallization from solution, or the entire solution or slurry may be evaporated to dryness. The dewatering (qv) method is determined by the solubihty properties of the product and by its desired physical properties such as crystal size and shape, bulk density, and surface area. Acid orthophosphate salts may be converted to condensed phosphates by thermal dehydration (calcination). 

Cements and Ceramics. Refractory cements and ceramics (qv) are prepared from slurries of siUca, 2irconia, alumina, or magnesia and a prehydroly2ed siUcate (see Cement). Calcining at 1000°C yields cured refractory shapes (48,49). 

In industrial production of acid-modified starches, a 40% slurry of normal com starch or waxy maize starch is acidified with hydrochloric or sulfuric acid at 25—55°C. Reaction time is controlled by measuring loss of viscosity and may vary from 6 to 24 hs. For product reproducibiUty, it is necessary to strictly control the type of starch, its concentration, the type of acid and its concentration, the temperature, and time of reaction. Viscosity is plotted versus time, and when the desired amount of thinning is attained the mixture is neutralized with soda ash or dilute sodium hydroxide. The acid-modified starch is then filtered and dried. If the starch is washed with a nonaqueous solvent (89), gelling time is reduced, but such drying is seldom used. Acid treatment may be used in conjunction with preparation of starch ethers (90), cationic starches, or cross-linked starches. Acid treatment of 34 different rice starches has been reported (91), as well as acidic hydrolysis of wheat and com starches followed by hydroxypropylation for the purpose of preparing thin-hoiling and nongelling adhesives (92). 

In this method, a metal oxide or hydroxide is slurried in an organic solvent, neodecanoic acid is slowly added, and the mixture is refluxed to remove the water. Salts that are basic can be prepared by using less than stoichiometric amounts of acid. This method has been used in the preparation of metal salts of silver (80) and vanadium (81). The third method of preparation is similar to the fusion process, the difference is the use of finely divided metal as the starting material instead of the metal oxide or hydroxide. This method has been appHed to the preparation of cobalt neodecanoate (82). Salts of tin (83) and antimony (84) have been prepared by the fusion method, starting with lower carboxyHc acids, then replacing these acids with neodecanoic acid. 

Several modifications of the preparation of neutral Ca(OCl)2 2H20 do not involve intermediates. In a continuous process, lime slurry containing caustic and Ca(OCl)2 mother Hquor is chlorinated under reduced pressure to remove the heat of reaction, and the resulting slurry is separated in a classifier into Ca(OCl)2— and NaCl-rich regions from which slurry is withdrawn to obtain Ca(OCl)2 filter cake and soHd salt (204). 

Two solvent processes for preparation of Ca(OCl)2 have been described. In one, a CCl solution of /-C H OCl is allowed to react with a thin lime slurry and the aqueous phase, a solution of Ca(OCl)2, is evaporated to a product with a purity of >95% (217). In the other, a solution of HOCl in methyl ethyl ketone reacts with either CaO or Ca(OH)2 (133). FoUowing filtration, the residual solvent in the product is removed under vacuum. 

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