| Geopolymer is a kind of inorganic aluminosilicate polymer synthesized by natural materials such as metakaolin, fly ash, slag and other furnace industrial by-products. Its basic structure is a three-dimensional network that is connected with the oxygen atoms shared by silicon oxide and aluminum tetrahedron oxygen tetrahedra. Owing to the characters of abundant in sources, no pollution, low price, energy conservancy and anticorrosion etc., it has been widely applied to making fireproof and thermal protection materials, decorate stones, repairing infrastructure, casting metals and so on. The discovered references demonstrate that there exist zeolite structures in geopolymer materials. Under certain crystallization conditions, geopolymer could be converted to the zeolites molecular siever.In this paper, metakaolin and water glass were utilized to prepare a series of Na2O-XSiO2-Al2O3 geopolymer material (X=2.4～4), and certain experimental conditions were set to translate them into zeolites. This study found that when X is 3.0, the Na2O-3.0SiO2-Al2O3 geopolymer material can be transformed into zeolite molecular sieve with sandwich layer structure; When X is 4, Na2O-4SiO2-Al2O3 geopolymer materials can be transformed into ZSM-20 zeolites under certain crystallization conditions. This project used SEM, XRD, BET, XRF tests to study the surface morphology, phase composition and specific surface area of the zeolites molecular siever. In addition, this project confirmed the optiumn technological parameters of the synthesized sandwich layer zeolite and ZSM-20 zeolite.(1) The important factors affecting preparation of zeolites including:the volume of activity silica-alumina in the reaction system and the silica to alumina ratio, alkalinity, hydrothermal temperature and hydrothermal time. In the reaction system, less active silica-alumina content make it difficult to form crystalline structures. Different silica to alumina ratio can decide the type of molecular sieve to some degree. Alkali, as an activator of the reaction system, will affect the distribution and aggregation state of raw material in the synthesis. Hydrothermal temperature and hydrothermal time are important energetic factors that provide energy during the process where the geopolymer is transformed into zeolites. During the hydrothermal process, only a sufficient energy supply could enable geopolymer to be transformed into zeolites molecular sieves.(2) The Na2O-3.0SiO2-Al2O3 geopolymer materials was used to synthesize sandwich layer zeolites in this paper and we have figure out the optimum conditions for preparation of sandwich zeolites as follows:the hydrothermal temperature was 180℃, the hydrothermal time was 10h, the aging temperature was 60℃, the aging time was 3 days, water galss module was 1.0, H2O/Na2O ratio was 9.5. The forming mechanism of the sandwich-type zeolite molecular service was firstly geological polymer membrane had a certain thickness itself. Under this condition, different material component’concentration varies between inside and outside the membrance, which leads to different crystal order. That’s why a unique sandwich structure was formed during the curing and hydrothermal process.(3) The confirmed optium technological condition under which the Na20-4SiO2-Al2O3 geopolymer is transformed into ZSM-20 zeolite molecular sieve is 140℃ of hydrothermal temperature, 10h of hydrothermal process,40℃ of aging temperature,3 days of aging time,1.1 water galss module and 7.5 H2O/Na2O ratio. |
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