Mixing should require no special precautions other than gloves and segregating your waste for disposal. At 1100 C you need to be careful of volatility of the PbO. Your final glass composition may not be exactly what you batched. At minimum you should have a lid on your crucible and do the melting in a hood. You should carefully choose your crucible material as well. We have had lead alloy with platinum crucibles before.

Pt crucible is fine to made PbO-SiO2 glass, but you need to use furnace with vapor extraction and filtration to storage Pb vapor !

Indeed, Pt crucible is the best one. However, at high temperatures PbO dissolves Pt, so that glass melting could result in Pt lost. To avoid this, perform glass synthesis through frit. Prepare fine powders of both reagents, mix them carefully, put the mixture in Pt crucible and then heat it up to about 700-800 C. Stand the mixture at this temperature (for an hour or two) until the mixture becomes frit (it looks like a stone with big pores). Then you can increase temperature to the one necessary for glass melting (about 1000 C).

Actually PbO forms eutectic system with SiO2, check the PbO-SiO2 phase diagram. So you don't need to heat up to super high temperature to completely melt your mixed powder, a heating up to 950C should be enough to give you a liquid phase for your composition (8% SiO2 additive), at this temperature , actually, the volitization of PbO oxide is not too strong (however, for safety, it is better for the Pt crucible to be coverd with a lid) and a Pt crucible is absolutely fine, there is almost no attack of the PbO to Pt at such a low temperature. I used Pt crucibles for crystal growth of piezoelectric single crystal using PbO-B2O3 as flux, the Pt crucible can be reused many times for piezoelectric crystal growth with growth temperature around 1200C before sent to refurbish.

If you are using a fine particle size lead oxide, do your mixing in a hood as well. The Pb will form an alloy with Pt under reducing conditions. The batch you are working with should not have this problem. When there is a risk of going reducing, you can bubble O2 into your melt through a Pt tube; this also provides some mixing.

If you need a glass with high density and low viscosity but want to avoid safety hazards caused by the use of PbO, you could use Bi2O3 instead. The melting point in Bi2O3-B2O3 binary should be low enough for your application (M. Hoch, Calphad Vol. 20, No. 4, pp. 511-519, 1996), otherwise you could add boron oxide to a Bi2O3-SiO2 glass (phase diagram in Y. Fei, Progress in Crystal Growth and Characterization of Materials, 2000 183-188).

Pt crucible is fine. I suggest you can heat the Pt crucible,sat on a refractory base, up to eutectic point, then put the PbO--SiO2 mixture into the crucible in hot condition, consequently, increase the furnace temperature about 50-100C higher than the eutectic point to make sure a homogeneous glass frit.

For your PbO containing glass preparation, normal precautions such as mixing glass batch using hand gloves and face mask is more than enough. The evaporation during melting process is more hazardous to health and environment. So you use a lid during melting process. Platinum crucible is fine for the above melting. I think your glass could be melted at lower temperature than the 1100 0C. Bi2O3 containing glasses are suitable substitutes for PbO from view point of health and environment, and the other optical, thermal properties also be achieved in comparison with PbO. Fore more details, you can read my paper and a book chapter on Bismuth glasses such as S. P. Singh and B. Karmakar, Materials Characterization, 62 (2011) 626-634 and S. P. Singh and B. Karmakar, Chapter 9 in Bismuth: Characteristics, Production and Applications, Nova Science Publication, New York, USA, 2011 ISBN: 978-1-61470-768-4.

.

You must ensure that the Pt crucible is clean enough such that no impurities would affect the outcome. PbO and any heavy metal/ oxides are known to be unhealthy for us. So, the use of lid during the melting process is very much recommended. If the high temperature furnace is a problem, the melting temperature can be lowered by adding some light metal oxides.

To add to the useful advice given above, I would suggest that you may need to quench your melt quite rapidly, given that 8 wt.% silica (~75.6 mol% PbO) is close to the practical limit of glass formation.

A lower melt temperature (~900 degrees C) and shorter melt time (~30 mins) would also be sufficient, and would reduce volatilization losses of PbO.

Using Pb3O4 as a starting material is also useful for creating an oxidising environment (Pb3O4 decomposes at ~500 degrees C to PbO and O).

I found most of the above info quite useful! Just to add some of our experience in melting PbO.SiO2 (50%mol) glass; we have once used a so called " joule heating" funrace, where the Pt crucible is directly heated by an electrical current in open air. In this way we noticed that the silica + Pb3O4 mixture was molten in about 4-5 minutes, We then homogenized the melt by stirring with a Pt rod for about 3 minutes. The resulting glass was quite good and due to the very short time used, Pb volatilization was minimized - BUT volatilization of Oxygen and perhaps Pb was clearly (visually) observed. Please be carefull when melting these glasses...

EDZ (lamav.weebly.com).

The most important point for making this glass I think is to wear a protective respiratory mask during the quenching as some nasty fumes will be formed during melting, even if your furnace has a fume hood (and it should!).

I used to weight the sample in a fume hood as well because you'll be manipulating an important amount of lead oxide. The mixing should not generate any problem if you have the adapted equipment.

I personally use alumina-silica crucibles to prepare my high content PbO glasses and it was just fine. You might pick up some alumina during melting, but less than 1 mol.%.

The temperature doesn't need to be that high though, I think 950 degres would be enough for this glass, maybe lower.

Good luck!

I used to melt PbCl2-Sb2O3 composition in order to get the higher viscosity of the melt, thus using slightly lower temperature, usually around 900C. However, some normal safety precautions have to applied such as using mask during melting process. However, it depends really on what you want Pb to be in the glass network.

Dear Mehdi, to add to the already excellent range of advice presented, based on my experience of melting high-lead glasses including binaries, I would suggest the following: (1) if you are going to use a Pt crucible then please do so carefully as I have seen Pt crucibles destroyed melting such glasses. Do not add As or Sb compounds as refining agents, instead consider using a little nitrate as an oxidising refiner. This can help prevent reduction and attack of the crucible (2) If you are going to use a ceramic crucible, then Al2O3 is fine although it will, of course, contaminate your glass with a little Al2O3; (3) Binary lead silicate glasses are notoriously difficult glasses to homogenise, owing to the large differences in density between SiO2-rich and PbO-rich regions which form early in melting. If a truly homogeneous glass is required then I strongly advise stirring in situ during melting. An alternative is frit/remelt but this is imperfect.. Kind Regards and good luck, Paul.