Ceramic Mechanism And Thermal Properties Of Sodium And Lithium Substituted Cubic Cesium Leucite Compounds Using Geopolymer Method

Cubic pollucite-based compounds, Cs(1-x)NaxAl Si2O6(x=0.1,0.2,0.3,0.4) and Cs(1-x)LixAl Si2O6(x=0.1,0.2,0.3), were synthesized through Geopolymer Technology. Thermal evolution and thermal expansion behavior of the prepared pollucite ceramics were systermatically invesitigated.Mixing with alkali silicate solution, Metakaolin firstly hydrolyzed into Silicon-oxygen tetrahedron [Si(OH)4]- and Alumina tetrahedron [Al(OH)4]-, then the Si species condense with Al species to form aluminosilicate with 3D-network structure. Alkali activator and powder providing Al-Si will affect the organization structure and the phase of aluminosilicate. There are two types of powder providing Al-Si, one is nature metakaolin(NMK) and another one is synthesis metakaolin(SMK). SMK is of higher reactivity than NMK, so part of amorphous aluminosilicate using SMK transform to pollucite phase after curing at 50oC. Na+ is helpful to the crystallization of pollucite, where pollucite and Analcime were observed inboth Cs(1-x)NaxGP-NMK and Cs(1-x)NaxGP-SMK(x≥0.1). Effective electropositivity of Na+, Li+ is greater than Cs+, so the size of the polymer particles is increasing with the increase in Na+ and Li +contents.Cs(1-x)LixAl Si2O6(x=0.1,0.2, 0.3) were synthesized through heat treating Li+ partially substituted Cs+-based geopolymer(Cs(1-x)LixGP(x=0.1,0.2,0.3)). With the increase in Li+, the pollucite crystallization temperature(Tc) is gradually reduced, 1165℃、1021℃、923℃和 919℃. With the higher activity of SMK, Tc of Cs GP-SMK is 1024℃, which is 140℃ lower than Cs GP-NMK. For Cs(1-x)LixGP-SMK(x=0.1,0.2,0.3), part of amorphous has transformed into pollucite by solid-phase reaction and the peak intensity of crystallization reduced significantly. The phase composition of Cs0.7Li0.3GP-NMK is changed after heat treatment in different temperature. Before heat treatment, Cs0.7Li0.3GP-NMK is amorphous after curing at 50℃; heating at 800℃ for 2h, the peaks corresponding to pollucite can be observed; at 900℃ for 2h, peaks of spodumene began to appear and relative intensity peaks reached the maximum at 1100 ℃. For Cs0.7Li0.3Al Si2O6-SMK, the crystallization temperature and max temperature of spodumene reduces about 100℃, 800℃ and 1000℃. After heating at 1300 ℃ for 2h, a dense cesium lithium leucites can be obtained. For Cs(1-x)LixAl Si2O6(x=0,0.1,0.2,0.3), when x=0.2, peak of spodumene began to appear, and Li+ exists in spodumene rather than displacement of Cs in pollucite. It confirmed the organizational structure of Cs(1-x)LixAl Si2O6 is pollucite and melted spodumene by SEM and TEM, and melted spodumene fills the void between pollucite grains. With the increase in Li+ content, coefficient of resulted pollucite decreased significantly.Cs(1-x)NaxAl Si2O6(x=0.1,0.2, 0.3,0.4) were synthesized by the same heat treatment. Na is more helpful than Li+ to the crystallization of pollucite, so the amorphous phase is rarely and intensity of crystallization peak of pollucite is reduced or disappeared. For Cs(1-x)NaxAl Si2O6-NMK, When x=0, 0.1 0.2, the temperature of crystallization is 1165℃、925℃和 887℃, while no peak for crystallization were observed with x continuing to increase. It is same to Cs(1-x)NaxAl Si2O6-SMK(x=0,0.1,0.2,0.3,0.4) that the crystallization temperature gradually reduce with Na increase, 1024℃、853℃、830℃和 757℃, and no peak of crystallization when x=0.4. Cs0.6Na0.4Al Si2O6 is heat treated in different temperatures, and similar phase composition is noted containing pollucite and analcime. In SEM, we can observe octahedral analcime at 1000℃, and at 1100℃ the number of analcime grains is max, while at 1200℃ octahedral analcime gradually transformed into irregular poor crystallinity polyhedral. Cs(1-x)NaxGP-SMK(x=0,0.1,0.2,0.3,0.4)were heated at 1300℃ for 2h. With the increase of Na, in XRD the peak of pollucite move to high angle, indicating Na+ substituting at the Cs+ sites in pollucite. The size of pollucite grains is reduced with the increase of Na+.So Geopolymer technology provides a novel and low const way to prepare pollucite ceramics of complex shape combining high-performance. With Na+, Li+ partially substitution at the Cs+ site, the crystallization temperature and coefficient of thermal expansion of pollucite is decreased significantly.