Fusibility. Surface

Base material Composition Fusibility Surface tension Rheological characteristics... 

One example of the utilization of adsorption-induced strength lowering in these processes is the use of small amounts of fusible surface-active metals in the treatment of hardened steels and solid alloys. The powder of a fusible metal is introduced into the polymeric binder of grinding wheels along with the diamond powder (Figure 7.50). Due to the increase in temperature in the course of the grinding, the microamounts of active metal are melted and lower the strength of hard metals and... 

Before this treatment, the cassiterite content of the ore is increased by removing impurities such as clay, by washing and by roasting which drives off oxides of arsenic and sulphur. The crude tin obtained is often contaminated with iron and other metals. It is, therefore, remelted on an inclined hearth the easily fusible tin melts away, leaving behind the less fusible impurities. The molten tin is finally stirred to bring it into intimate contact with air. Any remaining metal impurities are thereby oxidised to form a scum tin dross ) on the surface and this can be skimmed off Very pure tin can be obtained by zone refining. 

Coating Theory. This theory includes fire retardants which form an impervious skin on the fiber surface. This coating may be formed during normal chemical finishing, or subsequently when the fire retardant and substrate are heated. It excludes the air necessary for flame propagation and traps any tarry volatiles produced during pyrolysis of the substrate. Examples of this type of agent include the easily fusible salts such as carbonates or borates. 

Developments. A variety of process modifications aimed at improving surface finish or weld line integrity have been described. They include gas assisted, co-injection, fusible core, multiple Hve feed, and push—pull injection mol ding (46,47). An important development includes computer-aided design (CAD) methods, wherein a proposed mold design is simulated by a computer and the melt flow through it is analy2ed (48). 

Low viscosity cellulose propionate butyrate esters containing 3—5% butyryl, 40—50% propionyl, and 2—3% hydroxyl groups have excellent compatibihty with oil-modified alkyd resins (qv) and are used in wood furniture coatings (155). Acetate butyrate esters have been used in such varied apphcations as hot-melt adhesive formulations (156), electrostatically spray-coated powders for fusible, non-cratering coatings on metal surfaces (157—159), contact lenses (qv) with improved oxygen permeabiUty and excellent wear characteristics (160—162), and as reverse-osmosis membranes for desalination of water (163). 

Enamels used on cast iron and aluminum have traditionally been composed of SiO., B Oi. PjOs, and PbO. The lead oxide produces good surface quality, fusibility, and acid resistance when properly formulated with other oxides. More recently some non lead-bearing compositions have been developed for both cast-iron and aluminum metals. Glasses containing lead oxide are not recommended for food contact surfaces. 

Magnesium Chromate. [CAS 13423-fil-5. MgCiCC SH.o, small readily soluble, yellow cryslals. formed by reaction ol magnesium carbonate and chromic acid solution. Use Since it does not produce a fusible alkaline residue when thermally decomposed, it is used as a corrosion inhibitor in the water coolant of gas turbine engines. Insoluble basic magnesium chromates also arc available. Their potential applications arc in the treatment of light metal surfaces. 

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