Self Propagating High Temperature Synthesis Method
Self Propagating High Temperature Synthesis (SHS) is a new technology which uses the high reaction heat produced between reactants and synthesis of materials in a short time.
In 1967, Soviet scientists began to study the SHS technology system and apply it to industry. Self propagating high temperature synthesis is the reaction with certain gases in vacuum or filled (N2, H2, Ar2 etc.) combustion reaction container, then the combustion products were crushed and grinded by different specifications of powder technology. The technological process is as follows: material preparation, briquetting, preheating, ignition, self propagating, high temperature synthesis, mechanical fragmentation, product performance test.
The process of preparing tungsten powder by SHS is carried out in a home-made reactor and argon atmosphere, and tungsten filament parallel to the surface of the sample is used as the ignition source. After combustion, the product was soaked in 10% HCl (excess 30%) solution for a certain period of time and then washed to neutral by deionized water, At the same time, no Ca2+ and Mg2+ were identified in the filtrate, and then dried to remove MgO and CaO. The resulting filter residue was leached with 5% NaOH and then filtered, washed with water to neutral and rinsed with 10% HCl. After repeated drying, the tungsten powder was obtained. The XRD, SEM and particle size distributions of the products after combustion and after leaching showed that: By means of self propagating reduction method, the average particle size was 0.87 um and the specific surface area was 1.09m2/g, the purity bigger or equal to 99.0% tungsten powder.
By self propagating high temperature synthesis method to produce ultrafine tungsten powder, it has the advantages of high efficiency, energy saving, economy and environmental protection. However, there are some shortcomings such as fast reaction speed and difficult to control, but there is no doubt that SHS is very promising.
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