Temperature sintering

Other Reactions. Dry hydrated lime adsorbs halogen gases, eg, CI2 and F2, to form hypochlorites and fluorides. It reacts with hydrogen peroxide to form calcium peroxide, a rather unstable compound. At sintering temperatures, quicklime combines with iron to form dicalcium ferrite. 

In sintering, the green compact is placed on a wide-mesh belt and slowly moves through a controlled atmosphere furnace (Fig. 3). The parts are heated to below the melting point of the base metal, held at the sintering temperature, and cooled. Basically a solid-state process, sintering transforms mechanical bonds, ie, contact points, between the powder particles in the compact into metallurgical bonds which provide the primary functional properties of the part. 

Fig. 6. Effects on the pressed compact of (a) speed, where A is low and B, high speed compacting (b) powders, where A is soft and B, hard powders (c) dimensional change after sintering and (d) sintering temperatures, where A is high, B, medium, and C room temperature.

Liquid-Ph se Sintering. Sintering ia the Hquid state refers to the sintering of a powder mixture of two or more components, of which at least one has a melting temperature lower than the others. The sintering temperature is then selected ia such a manner that a Hquid phase is formed ia which the soHd powder particles of the other components rearrange. A high density powder compact is the result. 

Fig. 6. Dependence of stmctural density of alkoxide-derived porous silica gels as a function of sintering temperature held for 12 h for three different...

Other Uses. The production of finished shapes from iron powder by compacting and sintering utilizes about 100,000 t of iron powder aimuaHy copper powder (2—10 wt %) is normally added as a sintering aid. Addition of 2% tin powder or equal amounts of tin and copper powder considerably lowers the sintering temperature and time of sintering at a cost saving. The tin addition also improves dimensional control. Iron powder plus 10 wt % powdered lead—tin metal is pressed and siatered to make pistons for use ia automotive hydrauHc brake cylinders. 

Hydraulic Limes. These materials are produced by heating below sintering temperature a limestone containing considerable clay, duriag which some combination takes place betweea the lime and the oxides of the clay to form hydrauHc compounds. 

The potential technological importance of nanoparticles is due to the increase in sinterability widr a substantial decrease in the sintering temperature... 

An example where one metal melts before the densihcation process, is the formation of bronze from a 90 10 weight percentage mixture of copper and tin. The tin melts at a temperature of 505 K, and the liquid immediately wets the copper particles, leaving voids in the compact. The tin then diffuses into the copper particles, leaving further voids due to dre Kirkendall effect. The compact is therefore seen to swell before the hnal sintering temperature of 1080 K is reached. After a period of homogenization dictated by tire criterion above, the alloy shrinks on cooling to leave a net dilatation on alloy formation of about 1%. 

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