Researche influence of holding time on the rheological properties of alumina slips containing with dispersing and hardening additives and the properties of corundum ceramics samples which made from them
The researches influence of holding time on the rheological properties of the slips and the properties of corundum ceramics samples based on alumina of the MARTOXID MR70 brand with dispersing and hardening additives (for casting thin-walled products) and only with the dispersing additive (for casting of thick-walled products) which made of them were carried out. The holding time has a significant effect on the rheological properties of the slips were established. The destruction of aggregates in initial alumina on particles were begining with increasing the holding time the slips to 24 hours as a result the dynamic viscosity of these slips decreases and reaches a minimum value. In the slips with combined additive (dispersing and hardening) with increasing the holding time more than 24 hours beginning the formation of a coagulation-condensation structure. In the slip with only a dispersing additive and in the slips without additive beginning the formation of a coagulation structure the dynamic viscosity of the slips increases and this process does not end at 672 hours. However, with a little mechanical mixing in all three slips their structure are fragile and easily almost completely destroyed and such slips are suitable for making quality products from them. The samples which made from the slips after a holding time of 24 hours and 720 hours have practically the same properties, so the increasing the holding time for more than 24 hours does not affect the properties of the samples. For making quality products the fresh slips are also suitable and it is necessary to choose the holding time of slips according to the size and configuration of products, their service conditions and production volumes. According to the electronicmicroscopic studies the formation a gel-like substance that envelops alumina particles and thereby prevents its settling in the slip which contains the hardening additive.