A Study On The Mechanism Of Formation Of Sphericle Xonotlite Agglomerates During Dynamic Hydrothermal Synthesis

Xonotlite-based material is a very useful insulation material, because spherical xonotlite agglomerates which are synthesized with dynamic hydrothermal rrocess consist of many pores. In the article, the mechanism of formation of s~herical xonotlite agglomerates during dynamic hydrothermal synthesis is presented.The slurry of xonotlite is a suspension containing high volume of solid. Apparent viscosity of xonotlite slurry depends on the shape and concentration of spherical xonotlite agglomerates, and decreased with increasing shear rate. The slurry of xonotlite is classified into pseudoplastic liquid. During dynamic hydrothermal synthesis, C-S-H gel forms firstly, and followed by formaion of fibrous crystal in C-S-H gel. The agglomerates size and the apparent viscosit?of the slurry increase due to the growth of fibrous crystal. The apparent viscosity of the slurries in an autoclave can be estimated by measuring the resistant torques on the blender leaves at constant temperature during dynamic hydrothermal syitthesis. Apparent activation energies for nucleation and growth of xonotlitle n be calculated by analyzing the apparent viscosity of slurries. Then the formation process during dynamic hydrothermal synthesis of xonotlite can be monitored.The revolution of blending should be high enoungh at heating stage during dynamic hydrothermal synthesis, so that it is favorable for heat and mass trasportations, and formation of suspension. The shear stress makes fibrous crystals grow at the surfaces of C-S-H gel, and finally spherical xonotlite agglomerates form because of development of fibrous crystal from the sueface of the C-S-LI gel to inside of that. It is favorable for formation of spherical xonotlite agglomerates when Reynold number is in the range from 1.65 >~ to 1.42 x ~The effect of Sr(N03)2 as a mineralizer, on the formation of spherical xonotlite agglomerates during hydrothermal synthesis was studied . It showed that, Sr(N03)2 that was added into slurry before hydrothermal increased the ionic strength of slurry, leading to retarding the formation of xonotlite from C-S-H gel. Sr(N0j2 reducedabsolute values of ~ potential and particle sizes of the C-S-H gel. Sr promotedgrowth of fibrous crystal and formation of larger spherical xonotlite agglomerates.