Glass melting conditioning

Under commercial glass-melting conditions, the dissolution of S1O2 is a highly complex process. Its study and interpretation is usually based on simplified models, such as (1) dissolution of a spherical particle in a quasi-infinite static medium, (2) dissolution of a spherical particle in an excess of extensively agitated liquid. 

Polarizing power of network modifier (z/r ) Concentration of nonbridging oxygens Coordination number of certain cations Type of structural groupings in glass Melting conditions Photochemical reactions Multivalent additives Impurities... 

Benefits resulting from better control of glass melting ate lower fuel consumption, better glass quality, more efficient production time, and better pollution control. Fewer operators are needed and working conditions are better. 

Heat treatment of related glasses melted under reducing conditions can yield a unique microfoamed material, or "gas-ceramic" (29). These materials consist of a matrix of BPO glass-ceramic filled with uniformly dispersed 1—10 p.m hydrogen-filled bubbles. The hydrogen evolves on ceranarning, most likely due to a redox reaction involving phosphite and hydroxyl ions. These materials can have densities as low as 0.5 g/cm and dielectric constants as low as 2. 

Glass-melting furnaces are built nf refractory materials of various types, which will withstand the severe conditions to which they are exposed. The lower portion ill the inciter section, liir instance, must be of the highest quality to withstand the corrosive action of the glass as well as the high temperutures used. Some sections may use lower-quality refractories because the temperature or corrosion conditions are not as severe. 

If flow in a physical model is to have the same character as that in large-scale melting practice, the conditions required by the similarity theory have to be met. The properties of the model liquid have to bear a certain ratio to those of the glass melt. Mere geometrical similarity of the model and the furnace (scaling down) is not sufficient it is also necessary to observe the similarity with respect to forces acting on the corresponding masses of liquids in tlie model and in the actual furnace. 

The control of glass melting furnaces is based in particular on correct setting and maintenance of the temperature conditions. The temperature maximum usually occurs at one half or two thirds of the melting zone and the melting itself should be completed before this point is reached. Convection can be promoted and stabilized by eletric boosting or bubbling. 

Sample Preparation. Two methods were used to produce sodium silicate glass samples for this study. The primary method used conventional glass melting techniques to produce compositions ranging from 12 to 21 wt. % Na20. Batch ingredients, African sand, sodiiam carbonate, and sodium nitrate, were melted at 1600 C for six hours in platinum crucibles, poured into patties and fine ground into 1 1/2" diameter discs with thickness of one to four millimeters. These anhydrous discs were fully hydrated in a one cubic foot autoclave under saturated steam conditions and stored in controlled relative hiimidity desiccators at room temperature. 

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