Sintering characteristics of talc in the presence of phosphatic and alkali carbonate sintering activators

The sintering characteristics of three-layer monoclinic natural talc sample occurring in Jabalpur District of Madhya Pradesh (India) have been investigated in the presence of sintering activators. The mineral is observed to undergo dehydroxylation reaction on heat treatment. The dehydroxylation reaction occurs at a lower temperature in the presence of added activator of sintering. The dehydroxylate species react with sodium carbonate to form Na2Si2O5 and Na2MgSiO4 phases leading to mechanical strength in the sintered body. In the case of phosphatic species (H3PO4/sodium hexametaphosphate (SHMP)) added to serve as activators of sintering, Mg3(PO4)2/Mg(PO3)2/NaMgPO4 phases are formed. The impact strength of the tile-shaped samples made in the presence of phosphoric acid is observed to be higher than that of those made with only sodium carbonate. The impact strength of samples is observed to increase with increase in SHMP content. The SEM micrographs show the formation of fairly large size crystals when talc is sintered with H3PO4. In the case of other activators of sintering (viz. Na2CO3 and SHMP), significant amount of smaller crystals are also observed to be present.