Study On "Clay Figure Zhang" Non-crack & Quick Hardening

As for the problems existing in the drying process of clay sculptures of"Clay Figure Zhang", a new technology of"Non-crack and quick hardening"was studied from two aspects, one was improving the proportion of composition, the other was optimizing original drying process. Without changing the main ingredients, gelling agent (mixed power-MPC contains of MgO and NH₄H₂PO₄) was added. It initiated hydration reaction which fixed the moisture, resulted in drying and hardening in short-time, and reducing the shrinkage ratio of volume at the same time. The influence of the ratio of gelling agent on drying time and effect of clay drying (shrinkage ratio, microstructure and flexural strength) was studied. The mechanism of rapid drying of clay added MPC was also clarified. Moreover, the influence of vacuum drying on drying-time and properties was discussed in this paper. The results showed that:Without adding any new ingredients, MPC could accelerate the hardening of clay. Adding 1²%MPC could result in a shorter primary setting time which was suitable for the kneading of clay sculptures and lower shrinkage ratio. Meantime, adding MPC could improve the pore size distribution effectively. The total volume of pore decreases with the increase of MPC content. The flexural strength changed little with MPC content 1²%. However, the flexural strength decreased by 30% with MPC content over 3%.As soon as water added to the mixed power of MPC and clay, MgO particles adhered to the matrix of clay at first. And then, MgO hydrated and formed Mg²⁺ ions and a small quantity of Mg(OH)₂. Mg²⁺ with H₂O around formed hydration of Mg, and be absorbed on clay surface. NH₄H₂PO₄ could ionize out NH4+, H+ and PO43- when it went into solution. Ions NH4+ and PO43- and hydration of Mg complexed molecules of struvite, and these complexes developed a struvite network, connected by hydrogen bonds. The network developed and connected on the matrix of clay, and filled into the interspace of clay microstructure, which fixed the water and reached the purpose of quick drying.Vacuum drying could reduce drying-time greatly without effecting the process of kneading. The flexural strength of clay increased than before. At the same time, the pore size was refined, the total pore volume decreased. The shrinkage ratio decreased with the increase of vacuum. Every direction of shrinkage was relatively uniform; the phenomenon of warping deformation was not significant.In addition, according to the drying property of clay, a new equipment was invented to measure drying-time, and proved to be usable.