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SiO2 melting
2

SiO2 melting

SiO2 melting

(OP)
I'm searching information about melting of high silica glasses in laboratory scale.
Any reference would be helpful.

RE: SiO2 melting

(OP)
We already thought of the H2-O2 flame, but you need good refractory for the walls, and the Pt melts above 1736°C!!!!

RE: SiO2 melting

The 'best' solution probably depends upon the quantity you want, the purpose and the source of the material.

If you are starting with sand (with or without other materials) and are melting a tiny quantity, you can start with a ceramic crucible that is available from many lab supply catalogs.  This can be heated in a high temperature oven or over a high temperature flame

If you are wanting to remelt and reform existing glass via 'lampworking' a glass rod, you can do that with a common lab burner.

RE: SiO2 melting

Your best bet is melting in a platinum crucible for purity reasons. You can then remove any residual material that solidifies in the crucible by dissolving in HF. Your furnace could be lined with high alumina ceramic fibre, however, be careful to avoid too much direct flame impingement on the lining or your walls will suffer from excess shrinkage. Some possible suppliers of 1800C ceramic fibre can be found at www.azom.com/details.asp?articleid=1300. Your other alternative would be to melt in an electric furnace equiupped with MoSi2 elements and a similar refractory lining.

RE: SiO2 melting

(OP)
Dear Bugman,
the problem with Pt-crucible is that it melts above 1736°C!!!!!!!!
Meanwhile we tried some induction melting and that seems to work out quite good.

RE: SiO2 melting

I'm also interested in melting sand directly to produce high SiO2 glass, and I will start with about 3kg of sand. I though of using oxy torch (or torches) to melt it and some zirconia based castable cermaic. I found on InterNET this site: http://cotronics.com/vo/cotr/cm_castable.htm

RE: SiO2 melting

Dear YM,
High Silica glass is not enough to have the understanding of what would be the best way to melt the glass. Do you have any compositional aspect in mind?
If it is in the range of 96% sio2 then the route is totally different. There is a type of glass called Vycor glass.This has 96 to 97% silica,1.5% Na2O and may be another 1.5% B2O3.
The normal way to produce this glass is to make a batch having more than 22% B2O3 content Na2O higher than 18%. The glass so formed is again leached out with Acid. The acid leaches out the soda and boron content of glass leaving back the high silica rich skeleton structure of the glass.The so leached glass is then fired in a MoSi2 fired furnace to fuse out the Silica structure to almost 97 to 96% SiO2 glass.
Hope that is a new option for you.
ERegards
shudipto

RE: SiO2 melting

(OP)
Dear all,
I knew about the vicor process, but there is still too much sodium in the glass at the end.
I found some papers about preparing a glass in a hot press: Ceramics International, 23 (1997) 291-296.

RE: SiO2 melting

I'm  not a scientist, but being an art glassblower I know a little about refractories and crucibles.  The highest temp insulation I'm aware of is graphite felt which melts above 5000f.  As for crucibles, graphite and quartz both have hi temp ratings.  I don't know if they are suitble for your hi-silica glass.  I'd avoid platinum because of the $$$ if possible.  I don't know about contamination, but there are high alumina castables rated to 3400f.  National Refractories sells a 99% alumina castable called Kricron 34.

The guys above mentioned using H2-O2 or Moly elements.  Just for curiosity, have you considered carbon arcs?  

BTW, What size is "laboratory scale"?  We art glass guys melt soda-lime glass at around 2300f in ceramic crucibles between 100-300 lbs.  Science to us is mixing in metalic oxides to make pretty colors and adjusting the COE's to "fit" each other.

Good Luck,
Glenn

RE: SiO2 melting

YM,
If you need high purity and therefore do not want to melt in ceramic refracory crucibles, there is an option.  A crucible of 80%Pt/20%Rh alloy is much more refractory than Pt itself (melting point 1900 C).  Currently the price for Rhodium is quite close to Pt so there is no monetary penelty.  Rhodium can impart a slight color to your glass however, so if color is a problem then Pt/Rh may not be your answer.
Hope this helps.

RE: SiO2 melting

GlassMann: you mention some carbon arcs for melting. Could you detail a little bit? It seems an interesting ideea. In fact I don't know how I could produce the arcs to melt the glass.

RE: SiO2 melting

Delta2112,
I don't really know any details.  I do know steel mills use carbon electrodes which melt using an electric arc.  I once visited  a plate glass factory that had an electric furnace but I'm not positive that the elements were  the arcing type,  maybe they were "normal" heat radiating elements.  They were submerged in the glass, I do know that.

RE: SiO2 melting

As far as I know the arcs uses the conductivity of metal ore (iron ore or whatevere) as an resitive space between the electrods. There are the arcs coming from (if I'm not wrong).

There might be thow an electric way to heat the glass, but don't know how expensive would be not only the "furnance", but also the electric power used.

This spring I'll start experimenting with the H2-O2 as I said before and I'll tell you the results. There is still one thing that bothers me with that: The heat accumulated in the "new born" glass might heat the gear of the H2-O2 torch (torch, hoses, etc.) over the saftey limit...

RE: SiO2 melting

Why do you want to produce this fused silica glass yourself? This is not really a do it yourself process due to all the problems previously stated by others.

If you are looking for high purity natural fused silica (99.8% SiO2), fused quartz (99.99%+ SiO2) or synthetic fused silica (99.9999%+ SiO2) you are better off buying a suitable commercially produced material.

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