Dear El Mahdi Bouabdalli

The occurrence of bubbles/blisters/seeds is somehow a complicated problem, and unfortunately, there is no direct solution for eliminating those. However, you may do the following ways:

1- Increasing the melting temperature so that the viscosity decreases which in turn facilitates the bubble removal.

2- Adding some fluxing agents (i.e. soda ash) or increasing their amounts if this will not cause a compositional problem. Thus, the glass viscosity will decrease to remove bubbles.

3- Inserting some agents such as sodium sulfate or sodium nitrate will aid to enlarge the size of the bubbles/blisters/seeds. This situation will lead to eliminating bubbles from the glass melt.

Hope these alternatives will solve your existing problems.

Regards.

The primary objective of this work has been to further the understanding of bubble migration in granular porous media. This study has produced the first quantitative measurement of the terminal velocity of an air bubble rising in a stationary porous medium. As a result of our investigations, we make the following comments: 1. The results presented in this study are valid for a saturated porous medium consisting of 4-mm glass beads and should only be extended to gravel aquifers. 2. The motion of single air bubbles has been observed for emerging bubble sizes ranging from one to three grain diameters. 3. For a particular radius the rise velocity is independent of the depth of the single bubble within the granular porous medium; that is, the bubble has a relatively constant rise velocity. 4. The air bubble velocities in the porous medium range from 16.7 to 20.2 cm/s, which is -4 cm/s slower than the velocities measured for single bubbles in the water-filled column. 5. The bubble velocities in the porous medium are 17.4- 27.4% smaller than those in an infinite water medium. Values for an infinite liquid medium have been obtained by correcting our data in the water-filled 3.6-cm-ID column for the wall effect. 6. Although it is common to treat a porous medium as a bundle of capillary tubes, our results have shown that there are significant differences in the physical phenomena governing the rise of a bubble in a granular porous medium and its motion in a capillary tube. 7. The velocity of a chain of bubbles in the porous medium is decreased in comparison with that of a single bubble.

Use carbonates instead of oxide as your raw materials

Dear El Mahdi Bouabdalli

1. It is important via which component the phosphate was added to melt. Solid phosphate compounds using lead to hugh quantity of bubbles in the melt. We recommended use phosphate acid (H3PO4) for liquid batch prepearing.

2. In this case it need to use two stage glass production.

First state is production of fritt in a ceramic crucible.

Second stage is production of pure glass. For this aim it need to use platinum or platinum-rodium crucibles.

This method can help to reach minimum bubbles precense in the glass.

If You need information about temperature regimes or batch compounds don't hesitate to ask me.