Study On The Process And Mechanism Of Toughened Ceramics With Calcium Silicate Hydrate

Calcium silicate hydrate has been widely used as a type of inorganic nonmetal material in metallurgical industry, building industry and chemical industry because of its low thermal expansion, low bulk density, fine high-temperature thermal property and structural diversity. Generally, ceramic materials exhibit excellent physical properties, however, the main drawback of ceramics is the lack of sufficient brittleness. Thus the toughening of ceramics has been the research hotspot and a problem to be solved. In this study, calcium silicate hydrates were prepared by dynamic hydrothermal synthesis method which could easily control the phase and chemical composition, especially the microstructure of the materials. The raw material was sodium silicate alkaline solution which was the byproduct during utilization of fly ash. Calcium silicate hydrates were then studied in toughening of ceramics. The main results obtained in this paper are as follows:(1) The influence of several different factors on crystal phase compositions and morphologies of calcium silicate hydrate products was obtained and the controlling method of crystal phase compositions and morphologies of different calcium silicate hydrates was successfully established. The relatively optimal reaction condition of calcium silicate hydrate whisker preparation with desilicication liquid of fly ash was determined:Na2O concentration under 80 g/L, reaction temperature 220 ℃, reaction time 6 h, mass ratio of alumina to silica under 0.06 and mass ratio of calcium oxide to silica 0.9. The results showed that the length of calcium silicate whisker could be over 20 μm and the purity could be as high as 80%.(2) New process of preparation of anorthite ceramics with different calcium silicate hydrates as raw material was developed. The effect of composition, particle size and thermal properties of raw materials on the performance of ceramics was investigated. It was confirmed that ceramic samples which added calcium silicate whisker as reinforcement material had the highest flexural strength and the lowest water absorption. Toughening ceramics with flexural strength as high as 45 MPa were successfully obtained.(3) Toughening mechanism of ceramics with calcium silicate hydrate whisker was systemically studied. The results indicated that wollastonite was formed after dehydration process of calcium silicate hydrate. Then wollastonite and metakaolinite were consumed and anorthite together with cristobalite were formed. The difference was that the whisker structure could support skeleton of ceramic body when whisker was used as raw material during sintering. Most whisker was consumed in reaction and the rest could supply strength to the structure of ceramic body together with anorthite. Besides, whisker could induce formation of acicular anorthite crystal, which successfully improved btittleness of ceramic body.(4) The extended-scale experimentation was successfully conducted. The results showed that new process of preparation of ceramics with calcium silicate hydrate wisker was in good connection with the traditional ceramic production process. The performance of products completely satisfied national standard.