Study On Liquid-Phase Opacified Frit For Low-Temperature Fast Firing

In the production of ceramic glazed tiles for architectural ceramics,the quality of raw materials used for the body is usually low.The opaque glaze can not only cover the natural color of body,but also provide opalescent "canvas" for the color decoration on the glazed surface.In the production of ceramics glazed tile,opaque frit is often used to prepare glaze,among which zirconium is the most widely used one.It is a kind of solid-phase opaque frit with zircon as opacifier.It has the advantages of strong adaptability and good opacification effect.However,it also has some disadvantages such as high temperature viscosity,high melting temperature and more zircon consumption.China belongs to a zircon-poor country and needs to import a large amount of zircon every year.In this paper,Zircon-Free or low-zirconium opaque frits with liquid-phase opacification are studied to reduce the amount of zircon in opacified frits and enrich the types of opacified frits.In this paper,potassium feldspar,dolomite,calcite,potassium carbonate,zinc oxide,boric acid,apatite,quartz and zircon are used as raw materials to prepare frit,and the frit and kaolin are grinded in proportion to form glaze slurry.The frit is glazed on pottery bricks and fired in a low-temperature fast-firing roller kiln.By adjusting the composition of the frit’s raw material ratio,the effect of the frit’s luster,smoothness and opacity on the glaze surface is explored.The brightness L value,red-green a value and yellow-blue b value of the glaze were measured by spectrophotometer,and the effect of the change of raw material composition on the glaze effect was comprehensively analyzed.The variation of glaze effect and thermal shock resistance of the best frit sample under different firing systems of roller kiln and the adaptability of different ceramic ink were observed and analyzed.XRD,SEM and EDS were used to test the glaze surface,and the opacification mechanism of opaque frit was discussed.The results show that the optimum chemical composition of the opaque frit in R2O-RO-Al2O3-B2O3-P2O5-SiO2 system is 4.93K2 O,0.57Na2 O,12.64 CaO,2.62 MgO,5.65 ZnO,4.86Al2O3,5.33B2O3,0.79P2O5,62.61SiO2.The properties of the glaze are as follows: L=92.49,a=-0.65,b=0.41;The glaze has good gloss,smoothness and opacity.The glaze quality and thermal shock resistance of the glaze prepared by the opaque frit are obviously affected by the firing system of roller kiln,and are sensitive to the color of ceramic ink,so the frit has a narrow range of application.The optimum chemical composition of the low-zirconium opaque frit in R2O-RO-Al2O3-B2O3-P2O5-SiO2-ZrO2 system is 4.75K2 O,0.31Na2 O,13.37 CaO,1.13 MgO,7.02 ZnO,4.33Al2O3,5.25B2O3,0.83P2O5,61.17SiO2,1.84ZrO2.The properties of the glaze are as follows: L=93.96,a=-0.62,b=0.81;The gloss and smoothness of glaze surface are good,and the opacity effect is better.The glaze effect and thermal shock resistance are less affected by the change of sintering system of roller kiln.When using different ceramic inks,the glaze has bright colors and clear patterns.The frit has a wide range of adaptability.Through XRD analysis,it is found that the glaze made of the opaque frit of R2O-RO-Al2O3-B2O3-P2O5-SiO2 system and the low zirconium opaque frit of R2ORO-Al2O3-B2O3-P2O5-SiO2-ZrO2 system is a typical glass body with gentle variation of diffraction pattern curve and no obvious crystal characteristic peak.The results of SEM and EDS analysis show that three kinds of liquid phases can be formed in the glaze prepared from the opaque frit of R2O-RO-Al2O3-B2O3-P2O5-SiO2 system.one is low-silicon liquid phase enriched with boron phosphorus and alkali metals,the other is Low-alkali and low-silicon liquid phase enriched with boron and phosphorus,and the other is low phosphorus and low boron liquid phase enriched with silicon and alkaline earth metals.The first two are staggered worm-like distribution,and the other is blocky distribution surrounded by worm-like liquid phase.The glaze prepared by using the opaque frit of R2O-RO-Al2O3-B2O3-P2O5-SiO2-ZrO2 system can form two kinds of liquid phases,one is the low alkali metal and low silicon liquid phase enriched with boron,phosphorus and zirconium,the other is the low boron,low phosphorus and low zirconium liquid phase enriched with alkali metal and silicon.The two kinds of liquid phases are interlaced with each other and present worm-like distribution.The results show that the opaque glaze is made from the opaque frit of the R2O-ROAl2O3-B2O3-P2O5-SiO2 system or the low zirconium opaque frit of the R2O-RO-Al2O3-B2O3-P2O5-SiO2-ZrO2 system.The interaction of P2O5 and B2O3 in the glaze at high temperature results in the phase separation of the glaze melt and the worm-like distribution after the liquid phase enrichment.When the size of worm-like liquid phase approaches the wavelength range of visible light,worm-like liquid phase strongly scatters visible light,which is a typical liquid-phase opaque glaze.