Sodium feldspar is one of the minerals in the feldspar family, which is mainly anhydrous aluminum silicate with the frame crystal structure of potassium, sodium and calcium. It has three basic types and five transition types. The three basic types are soda feldspar (NaAISi308), potassium feldspar (KAISi308) and calcium feldspar (CaAl2Si208).
The ionic radius of Na+ (97pm) is quite different from that of K+ (133pm), and the charge numbers are the same, so although sodium feldspar and potassium feldspar can be completely dissolved at high temperatures, they will gradually dissolve as they cool and crystallize. Melting, separation, and finally only partial solid solution, forming the so-called intermediate transition type sodium potassium feldspar, which is characteristic of the so-called alkaline feldspar series.
Albite feldspar occurring in nature is mostly low-temperature albite feldspar which is stable below 500C. The basic unit of the crystal structure of soda feldspar is a four-membered ring composed of three silico-oxygen tetrahedrons and one alumino-oxygen tetrahedron (which basically occupies a fixed position). The theoretical structural formula of albite is NaAISi308 and the theoretical chemical formula is Na20A12036sio2 accounting for 68.7%. A1203 accounted for 19.5%, and Na20 accounted for 11.8%. The color of sodium feldspar is mostly white to colorless, transparent to translucent, with glass luster, and sometimes pearl luster. In the two groups of complete cleavage, the intersection Angle is about 86° (not vertical, which is different from orthoclase), the specific gravity of 2.60~2.65g/cm3, and Mohs hardness of 6~6.5.
Soda feldspar Compared with potassium feldspar
Soda feldspar not only has a lower melting temperature but also has a narrower melting range and a lower melt viscosity. And the viscosity decreases faster as the temperature increases, it shows a more obvious fast melting sex or short melting. Therefore, when using sodium feldspar powder in the ceramic body, attention should be paid to its influence on deformation and firing range. However, albite powder is a common and effective mineral raw material in terms of lowering the melting temperature, increasing the fluxing ability, and improving the melting ability of quartz, clay minerals, and mullite. Soda feldspar powder plays a more prominent role than potassium feldspar in improving the vitrification ability of ceramic tiles and accelerating the melting of the glaze.