Sodium silicate solute foaming in a flat slot-type capillary under microwave radiation influence

Abstract

Purpose. A mass transferring mechanism during liquid glass foaming in flat slot-type capillary under microwave radiation influence has been determined. Methodology. Sodium soda silicate solute with silicate module of 2.8–3.0 and specific gravity of 1.43–1.46 g/cm3 is used in the studies. For sodium silicate solute coloring, red ink is added. Treatment of sodium silicate solute water solution with microwave radiation is carried out in a furnace with a working chamber volume of 23 liters, with nominal magnetron power of 700 W and radiation frequency of 2450 MHz. Investigation of the structure of foamed sodium silicate solute is done by the optical microscopy method with magnifications of 25 to 200 times. Microwave furnace internal temperature is measured using non-contact electronic infrared thermometer Temperature AR 320. Mass determination is carried out on electronic balance with 0.01 g accuracy. Liquid glass foaming is organized in a flat slot-type capillary with thickness of 30 to 900 μm formed by two glass plates parallel to each other. Findings. A mechanism of sodium silicate solute mass transferring during its foaming in a flat slot-type capillary when heated by microwave radiation description is developed. It is established that sodium silicate solute transferring in a capillary proceeds in stages according to a scheme similar to a chain reaction. The scheme includes: sodium silicate solute self-encapsulation due to appearance of shell on free surface of partially dehydrated sodium silicate solute; vapor bubble in capsule formation; increasing steam pressure in capsule; capsule shell destruction and ejection of part of unhardened sodium silicate solute out of the capsule; complete removal of sodium silicate solute from the capsule and its destruction under high vapor pressure influence; movement finalization of stream of sodium silicate solute ejected outside the capsule, its repeated self-encapsulation, and so on. This process repeats until water removal from the treated sodium silicate solute will be completed. Sodium silicate solute foam structure formation staging and certain cyclical nature under microwave radiation effects is the main cause of substantial no uniformity of pore dispersion and resulting foam permeability. Originality. For the first time, description of a mechanism of mass transferring of sodium silicate solute foamed in a flat slottype capillary when heated by microwave radiation has been developed. For the first time it has been determined that sodium silicate solute with silica modulus of 2.8 to 3.0 microwave radiation processing allows reducing water content in dried sodium silicate solute to value less than 0.1 % (wt.). Practical value. Sodium silicate solute foaming by microwave radiation is a perspective process from the point of view of developing new methods and approaches for solving the problem of optimization of granular material structuring and, in particular, for manufacturing molds and cores. Understanding of sodium silicate solute foaming mechanism will allow increasing the accuracy of predicting the structure of foams produced on sodium silicate solute basis and properties, optimizing the process parameters for their pores formation, expanding the knowledge concerning technological possibilities of implementing sodium silicate solute in porous environments structuring, dehydration by microwave radiation, and so on.