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REFINING EFFICIENCY IN RELATION TO THE OXYGEN ACTIVITY OF THE MELT (P9913)

The aim is to learn more about the refining process, by studying the oxygen activity in the melt and its relation to the composition.

Background
When producing glass refining is a very important step. It is when the glass melt gets rid of the gaseous bubbles, which are formed when the glass raw materials are heated. As a rule a refining agent is added, which sets oxygen free in the melt.

When the refining starts in a glass melt the bubbles are rising with different speed depending on their size. The big bubbles rise most rapidly. The refining agent helps the oxygen to set free and to draw the bubbles out of the melt.

Ordinary refining agents are: antimony oxide and sodium sulphate. However, antimony as refining agent can be questioned because of its influence on the environment. But it is complicated to replace antimony with for example sulphate, as they do not give the same effect.

In earlier projects (“Batch for refining without nitrate”, “Refining with cerium oxide” and “Refining with sulphate combinations”) various problems related to refining have been studied. When refining in the same glass we found that the bubbles seem to be smaller at sulphate refining than at antimony refining. There have also been indications that a glass with less broken network, than for example an ordinary soda glass, yields a better result at sulphate refining.

The traditional refining agents do not always function so well when the glass is changed radically. For example it could be when the melting temperature has been lowered a lot, or when the sodium/potassium proportion is very much varied. Today we do not have enough knowledge to foresee or explain this, which can lead to problem with the refining when new glass compositions are developed.

Oxygen activity in relation to composition
The refining is depending on the amount of oxygen and the mobility of the oxygen in the melt. This is described by the oxygen activity. It varies a lot with the temperature, but it is also very dependent on which refining agent that is used.

The oxygen activity is one way to describe the refining in the melt quantitatively. We intend to measure the oxygen activity. By that we hope to be able to follow the changes influencing the refining, e.g. varying composition of the glass. The properties are changed if the composition is varied. To understand how this will influence the refining process, important glass properties like surface tension and viscosity should be measured in a number of representative samples.

CURRENT PROJECTS