Sintering process

Trapped gas in closed pores often limits densification when sintering witlr a liquid or viscous (glass) phase because rapid material transport tlirough tlie liquid often results in pore closure early in tlie sintering process. 

Thummler F and Thomma W 1967 The sintering process J. Inst. Metals 12 69-108... 

Sintering aid Sintering ores Sintering processes Si02... 

Sodamide Soda-silica glass Soda-sinter process Sodatol... 

In 1990, appioximately 66,000 metric tons of alumina trihydiate [12252-70-9] AI2O2 3H20, the most widely used flame retardant, was used to inhibit the flammabihty of plastics processed at low temperatures. Alumina trihydrate is manufactured from either bauxite ore or recovered aluminum by either the Bayer or sinter processes (25). In the Bayer process, the bauxite ore is digested in a caustic solution, then filtered to remove siUcate, titanate, and iron impurities. The alumina trihydrate is recovered from the filtered solution by precipitation. In the sinter process the aluminum is leached from the ore using a solution of soda and lime from which pure alumina trihydrate is recovered (see Aluminum compounds). 

Fig. 17. Sol—gel and simple sintering process used to make ceramic membranes.

Post-Sintering Treatments. The sintering process concludes the powder metallurgy processes of production and consoHdation. However, some P/M parts may require a number of further operations. 

Another preparation method is a sintering process where phosphate ore, sand, and coal are blended together and ignited on the grates of a sintering machine. Air is pulled through the blend, and the entire mass is allowed to bum. The resulting fused bed of material is then cmshed and screened to the appropriate size distribution, and the undersized material is reprocessed. 

Aluminum hydroxides are technically the most widely used members of the alurnina chemicals family. The most important source of aluminum hydroxides is the bauxite refining plant for alurnina production. A small amount of somewhat purer aluminum hydroxide is produced by the Sinter process. 

White Hydroxide. Tlie soda sinter process appHed to bauxite or bauxite residue produces a hydroxide that is completely free from organic coloring matter and is very wliite. A value of more than 95% is obtained on the GE brightness scale relative to Ti02 as followed in the paper (qv) industry. Tliis compares to about 70% on the same scale for the nomial Bayer product. Tlie wliite hydroxide is preferred in the paper, toothpaste, and artificial marble industries. 

Extra-Fine Precipitated Hydroxide. Very fine (< 1 /im-diameter) particle size hydroxide is produced by precipitation under carefully controlled conditions using specially prepared hydroxide seed. Precipitation is usually carried out at low (30 —40°C) temperatures causing massive nucleation of fine, uniform hydroxide particles (Fig. 5). Tray or tumiel Ape dry ers are used to dry the thorouglily washed filter cake to a granular product wliich is easily pulverized to obtain the fine hydroxide. Alternatively, the washed product is spray dried. Precipitation from an organic-free aluniinate Hquor, such as that obtained from the soda—sinter process, fields a very wliite product. Tlie fine precipitated hydroxide is used by the paper and plastic industries as fillers. 

Commercial production of bayerite is relatively small and employs CO2 neutralization of caustic aluminate Hquor obtained from either Bayer or sinter processes. The product obtained is about 90% crystalline bayerite having small amounts of gibbsite, pseudoboehmite, and amorphous aluminum hydroxides. 

In contrast to triaxial porcelains, packaging materials such as 99% AI2O2 prepared by a soHd-state sintering process, display significantly lower dielectric loss. In these materials, there is no residual glassy phase with its associated mobile ion content, and therefore, conduction losses are minimized. 

Thermal Degradation and Sintering Thermally iaduced deactivation of catalysts may result from redispersion, ie, loss of catalytic surface area because of crystal growth ia the catalyst phase (21,24,33) or from sintering, ie, loss of catalyst-support area because of support coUapse (18). Sintering processes generally take... 

There is a material to process compatibility risk for impact extrusion, cold forging, cold extmsion, sheet metalworking, machining and powder metal sintering processes because their respective process capability maps relate to the ideal material case. 

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