Preparation And Properties Of Porous Glass-ceramics Based On Pegmatite

Liaoning Province is very rich in non-metallic mineral resources, such as quartz ore, quartz sand, kaolin, limestone, dolomite, wollastonite, pegmatite, and some mineral resources have been used efficiently, but the efficient use of pegmatite (a mineral resource from Benxi, Liaoning Province) which was only used as mineral stone was an urgent need to resolve. In this paper, SiO₂-Al₂O₃-CaO-ZnO-R₂O porous glass-ceramics was prepared from pegmatite, and the porous glass-ceramics was attempted to be used in the field of building insulation.The chemical constitutions of Pegmatite was determinded with XRF. The results of qualitative and quantitative analysis indicated that the main components of Pegmatite were SiO₂, Al₂O₃, Fe₂O₃, R₂O, CaO and MgO. Through the theoretical analysis, the total content of SiO₂ and Al₂O₃ can reach more than 90% of the total ingredient of Pegmatite, thus Pegmatite was suitable to prepare SiO₂-Al₂O₃-CaO family porous glass-ceramics. Sintered process and addition of pore-forming agent were adopted to prepare porous glass-ceramics. In order to determine the heat treating regime for preparing porous glass-ceramics, the thermal-properties of Pegmatite, pore-forming agent-stearic acid and the binder-polyvinyl alcohol were analyzed through the TGA/SDTA method.The physical, chemical and mechanical properties of porous glass-ceramics are dependent on the crystalline phase, so it is a very important task to control the crystallization of glass. The glass crystallization dynamic equation as well as the crystallization index were introduced in the paper, and the crystallization active energy E and the frequency factorγfor 5 glass samples were calculated according to the modified JMA equation, the crystallization kinetic parameter k(Tp) of samples were obtained. Finally, the crystallization index n for all samples was got via Augis-Bennett equation. The results indicated that k of the sample, whose ratio of SiO₂ to Al₂O₃ is 61:6, was the largest one in 5 samples, and it increased faster than the others with the temperature increasing. It can be concluded that the crystallization of this sample happened easily in all samples. The crystallization form of porous glass-ceramics belong to volume crystallization; the parawollastonite which was the main phase was monocline chain structure ZM type wollastonite, with long needle crystal or short rodlike crytal. SiO₂2,Al₂O₃ and CaO are the main ingredients of SiO₂-Al₂O₃-CaO family porous glass-ceramics. The varied contents of SiO₂,Al₂O₃ and CaO can affect the properties of Porous glass-ceramics. The relationship between the properties of porous glass-ceramics with the ratios of CaO to SiO₂ and Al₂O₃ to SiO₂ were discussed in this article. The results indicated: the main crystal phase maintained with the increasing of CaO/SiO₂, while the length-diameter ratio of parawollastonite decreased gradually; the compressive strength and the flexural strength of porous glass-ceramics increased to maximum and then decreased with the increasing of CaO/SiO₂; the maximum flexural strength loss rates of l#-5# samples under acid and alkali condition were 0.30 and 0.32, respectively. The main crystal phase maintained with the increasing of Al₂O₃/SiO₂, while the amount of crystals decreased; the compressive strength and the flexural strength of porous glass-ceramics decreased with the increasing of Al₂O₃/SiO₂; and the maximum flexural strength loss rates of 6#-10# samples under acid condition and alkali condition were 0.29 and 0.30, respectively.The heat preservation performance of porous glass-ceramics was investigated as well. Considering the internal composition and the porosity of porous glass-ceramics based on pegmatite, three heat conduction ideal equivalent physical models were proposed by the author, and a mathematical formula was deduced to testify the thermal conductivity of porous glass-ceramics. The results showed that the thermal conductivity of porous glass-ceramics obtained from experiments coincided well with the theory value. Along with the porosity increase, the porous glass-ceramics thermal conductivity inclined to decrease. According to the thermal insulation material definition, D# and E# sample's thermal conductivity had met the definition requirements. At present, research on heat conduction performance of porous glass-ceramics is relatively rare.