On glass fining methods ― Several approaches may possibly be considered, depending on glass composition and on the adopted melting technology, such as: (i) adding some suitable chemical fining agent to melt composition; (ii) blowing air or water vapour stream into the bottom of the tank/pot; (iii) shortly increasing the temperature, to decrease melt viscosity, thus promoting the expulsion of larger gas bubbles ('blisters'); being that followed by lowering the temperature to increase gas resorption from smaller bubbles ('seeds') to the melt; (iv) promoting natural convection (e.g. deeper tank/pot/crucible); (v) considering alternative raw materials; (vi) reconsidering (possibly increasing) the melting/fining temperature and/or time.

For somewhat related RG discussions: https://www.researchgate.net/post/How_can_I_avoid_bubbles_during_cooling_in_float_glass_production https://www.researchgate.net/post/How_can_I_get_rid_of_the_foam_aspect_in_an_enamel_glass_coating_containing_zinc_sulfide https://www.researchgate.net/post/Why_do_ZnO_nanoparticles_in_glaze_swell_and_lift_up_from_the_surface

About other glass defects at RG: https://www.researchgate.net/post/What_causes_Striae_in_float_glass

According to my little experience, in order to remove bubbles from the glass there are two important process which are very necessary to do before melting process, they are mixing well the composition and preheating the mixture. The other way is to do shaking for the melt every few minutes.

Thank you for your contribution.

However I want to add some chemicals to the melt gob to shrink or enlarge bubbles.

Usually the bubbles have gases such as N2, CO2, O2, Ar, ... .

What chemicals can reacts specifically with this reagents to remove them?

Dear Dr. Saad

Regarding remove this bubbles from molten glass

Answer

The fusion of glass consists of three separate steps which follow each other: melting, refining and the cooling down period.

As its name indicates, the purpose of refining is to clean out of the fused glass air bubbles which it might contain. Most of these gasses are CO and CO2 which arise from sodium, calcium and magnesium carbonates decomposition.

Nevertheless, refining is classified into mechanical, physical, chemical and the like. This is what actually takes place in general refining methods.

a) Physical refining

The temperature is raised. During refining, glass is at the highest temperature of the entire process of glass-making

b) Mechanical refining

This involves stirring in the optical glass industry and blocking hand made glass.

c) Chemical refining

Chemical refining agents are:

1. Sodium nitrate

2. Sulphates

3. Manganese dioxide

Best regards

Prof. Dr. G.A. Khater

Read the chapter on glass melting in my book Introduction to Glass Science and Technology. It covers the various methods discussed in the answers above, which are quite good. You can also find a lot of information in another of my books, Diffusion of Gases in Solids and Melts, particularly dealing with carbon dioxide. Incidentally, N2 and Ar bubbles are due to physically trapped atmospheric gases which were trapped between the batch particles. CO2 is due to decomposition of carbonates. Oxygen can be due to either trapped or decomposition sources. Fining agents include arsenic and antimony oxides, sodium sulfate, CeO2, and others, depending on the type of glass. Bubbling the melts with steam or helium can also help remove bubbles. The answer to your questions is not trivial, since it depends on the composition and melting conditions you are using. It can even depend on the type of container, i.e. platinum or other metals, refractories, etc.

You can alter the redox of your melt. Reduced melts have lower optimal fining temperatures.

dear dr saad

in my exoerience you cab=n reduce the amount of soda ass in your glass. you can also controling the moisutre of your bach bellow 4 percent

If this helps, based in my experience in glass container industry, there are some points to take into consideration:

What is the size and location of the bubbles;

Appearance of the bubbles: do they have deposits, condensation, etc.;

After that, start looking at the process: recipe and batch preparation, batch transportation (segregation can cause bubbles), storing and delivering to the furnace, batch charging, furnace stability, conditioning and forming processes. If necessary, in parallel, gas analysis from bubbles has to be requested. Based in the results, it is possible to find re source, which sometimes can surprise you, like metallic (ferrous and non-ferrous) contamination, refractory quality/damage/wear in furnace or conditioning processes, damage thermocouple, etc.