Function and Properties of Mineralizer in Glass Kiln Silica Brick Production

The role of the mineralizer is to accelerate the transformation of quartz into low-density quartz variants (tridylquartz and square quartz) during firing without significantly reducing its refractoriness. It also prevents loosening and cracking of silica brick adobe due to rapid expansion during firing.

When quartz is converted into tridylquartz or square quartz, α-quartz forms α-square quartz without or with little mineralizer. This transformation is called "dry transformation". During dry transformation, due to the large uneven volume expansion inside the brick body and the lack of liquid phase buffering stress, the structure of the silica brick is loose and cracked, and good products cannot be obtained. However, in the presence of enough mineralizers, α-quartz, mineralizers, etc. form a liquid phase and invade into the cracks formed during the transformation process, causing t-quartz, etc. to continue to dissolve into the formed liquid phase, making It becomes a supersaturated solution of silicon oxide, and then crystallizes from the solution in a stable tridymite form. This transformation speed depends on the nature and quantity of the added mineralizer. The formed liquid phase buffers the stress caused by volume expansion, improves the heating volume stability and strength of the adobe, and prevents the loosening and cracking of the product during the roasting process..

The ability of the mineralizer to promote quartz mainly depends on the quantity and nature of the melt formed by the added mineralizer and the silica in the adobe at high temperature, that is, the temperature at which the liquid phase begins to form, the number of liquid phases, the viscosity, the wetting ability and its structure. The lower the co-melting temperature between the mineralizer and the silicon oxide to form the liquid phase, the more favorable it is for the square quartz formed during sintering to transform into tridymite through the liquid phase. The stronger the role of the mineralizer, the more tridymite, and the larger the grain.

The ability of mineralizers to act is also related to the ease of being saturated by SiO2 when the liquid phase is produced, that is, the crystallization ability of the liquid phase.

There are many kinds of mineralizers that can promote the transformation of quartz to pyroquartz through the liquid phase, and their mineralization capabilities are listed in Table 1.

The strength of mineralization ability is not the only criterion for the selection of mineralizers. In actual production, it must be determined according to the chemical composition and properties of silica raw materials. The ideal mineralizer should have the following conditions.

① It can form a liquid phase with SiO2 at a temperature not too high (generally below 1300~ 1350 ° C), and at the same time has little effect on the refractoriness of the product.

② A sufficient amount of liquid phase can be formed. The viscosity of the liquid phase should be low, and it has a strong wetting ability to quartz particles, and the amount of liquid phase does not change much with the increase of temperature.

③ Mineralization is not too intense, and there are no cracks in the burned product.

In the production process of silicon bricks, a single mineralizer is generally rarely used, and two oxide composite mineralizers are often used. For example, CaO + FeO mineralizer is used. The addition amount of mineralizer should generally not exceed 3% to 4%. If the amount is too large, the fire resistance of silicon bricks will be reduced.