Pastes and Dispersions

Dispersions have previously been described in Chapter 9 in the context of volatile liquids designed to supply powder to a system. But dispersions in non-volatile liquids are also used as a means of feeding a high concentration of molybdenum disulphide into a system while still maintaining some degree of flow. 

There are three main types of application for which molybdenum disulphide pastes and concentrated dispersions are used. They are used as anti-seize compounds for threaded fittings, pipes, flanges, and so on. They are also used to assist assembly, and to a lesser extent running-in, of many different types of mechanical euqipment. Finally, they are used in high-load metalforming processes. 

Pastes can be made with the same carrier liquids by simply increasing the concentration of powder to achieve a paste-like semi-solid consistency. More stable pastes are obtained by using a carrier which is inherently semi-solid, such as a grease, petrolatum (soft petroleum wax) or a semi-fluid polymer. The concentration of powder in a paste or a dispersion may be anything between 35 and 75%, depending on the application. The British military specification Def Stan 80-81/1 requires not less than 50% of molybdenum disulphide in a mineral oil grease for an anti-seize and anti-scuffing compound for use up to 250 C. This is probably a fairly typical level for anti-seize use. 

The Government of the German Democratic Republic published a standard TGL 10596/03 in 1977 for a product containing not less than 40% in a stabilised paste with mineral oil and adhesive components . This material was recommended for a wide range of applications, including - 

Installation and removal of bearings and seals. Loosening of threaded joints. 

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Slade, L. and Levine, H. 1985. Intermediate moisture systems concentrated and supersaturated solutions pastes and dispersions water as plasticizer the mystique of bound water thermodynamics versus kinetics (Number 24). Presented at Faraday Division, Royal Society of Chemistry Discussion Conference - Water Activity A Credible Measure of Technological Performance and Physiological Viability Cambridge, July 1-3. 

Table 13.9 lists some of the many commercial molybdenum disulphide greases. 13.4 PASTES AND DISPERSIONS... 

Pastes and dispersions have also been recommended for running-in ("breaking equipment after assembly, but there are limitations on the extent to which this... 

In addition to being used as a textile assistant, dye paste and dispersant, SMA was reacted with polyethylene oxide (Carbowax) to produce bonded fabrics (14). Heavy metal salts of SMA were also used as controlled release biocides (15). 

TEM has been applied to the analysis of dry powder pigments, flushes, pastes and dispersions. In most cases the sample preparation is quite simple. 

Disk-and-Cone Agitator n A mixing device comprised of disks or cones rotating at speeds between 20 and 60 rev/s or higher. The disks/cones displace fluid contacting their surfaces by centrifugal force. They are used in preparing pastes and dispersions. 

Pigments are available ia a number of commercial forms including dry powders (either surface treated or untreated), presscakes, flushed colors (thick pastes), fluidi2ed dispersions (pourable pastes), resia predispersed pigments (powders), and plastic color concentrates or master batches (granules) (see PiGLffiNTDISPERSIONS). 

Suspended Particle Techniques. In these methods of size enlargement, granular soHds are produced direcdy from a Hquid or semiliquid phase by dispersion in a gas to allow solidification through heat and/or mass transfer. The feed Hquid, which may be a solution, gel, paste, emulsion, slurry, or melt, must be pumpable and dispersible. Equipment used includes spray dryers, prilling towers, spouted and fluidized beds, and pneumatic conveying dryers, all of which are amenable to continuous, automated, large-scale operation. Because attrition and fines carryover are common problems with this technique, provision must be made for recovery and recycling. 

Nonfood Uses. Native com starch is principally used in nonfood appHcations in mining, adhesives, and paper industries. Pregelatinized starch is chemically unmodified, but it is physically modified. Pregelatinized starches are used to decrease water losses in oil-weU drilling muds, in cold water-dispersable wallpaper pastes, and in papermaking as an internal fiber adhesive. 

Liquids. Liquids (33) are common forming additives in plastic, paste, and slurry processing. In plastic forming operations, the Hquid aids forming and serves as the binder/plasticizer for the system. In pastes and slurries, other additives are also dissolved or dispersed in the Hquid/solvent. Water is a good, inexpensive solvent that can be recycled. Organic Hquids such as alcohols are used to process water-sensitive materials and to dissolve water-insoluble forming additives, however, at considerably more expense. 

Two-fluid nozzles do not operate efficiently at high capacities and consequently are not used widely on plant-size spray diyers. Their chief advantage is that they operate at relatively low pressure, the hq-uid being 0 to 400 kPa/m" pressure, while the atomizing fluid is usually no more than 700 kPa/m" pressure. The atomizing fluid may be steam or air. Two-fluid nozzles nave been employed for the dispersion of thick pastes and filter cakes not previously capable of being handled in ordinaiy atomizers [Baran, Ind. Eng. Chem., 56(10), 34-36 (1964) andTurba, Brit. Chem. Eng., 9(7), 457-460 (1964)]. 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

The environmental problem of sulfur dioxide emission, as has been pointed out, is very much associated with sulfidic sources of metals, among which a peer example is copper production. In this context, it would be beneficial to describe the past and present approaches to copper smelting. In the past, copper metallurgy was dominated by reverberatory furnaces for smelting sulfidic copper concentrate to matte, followed by the use of Pierce-Smith converters to convert the matte into blister copper. The sulfur dioxide stream from the reverberatory furnaces is continuous but not rich in sulfur dioxide (about 1%) because it contains carbon dioxide and water vapor (products of fuel combustion), nitrogen from the air (used in the combustion of that fuel), and excess air. The gas is quite dilute and unworthy of economical conversion of its sulfur content into sulfuric acid. In the past, the course chosen was to construct stacks to disperse the gas into the atmosphere in order to minimize its adverse effects on the immediate surroundings. However, this is not an en-... 

Starch glues are water dispersions for libraiy paste and wallpaper paste. They coat paper for better receptivity of inks and keep the inks held out on the paper surface. They are also used in corrugated cardboard and paper laminating. 

The water-soluble EHEC is used in water-borne paints, pastes, polymer dispersions, ceramics and cosmetics, and pharmaceuticals,whereas organic soluble EHEC is used in inks, lacquers, and as coatings. 

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