# How to furnace-melt bismuth oxide into optical glass?

I have been experimenting with a furnace at my house and am looking to attempt the more difficult process of creating bismuth-oxide based optical glass for the purposes of creating optical elements (think lenses and reflective glasses).

I'm having trouble finding what the raw material inputs to create the best mixture should be, as well as best practices for an amateur such as myself. Most of the literature on how to produce good results are either pay walled or too esoteric for me to understand. I was able to find a helpful paper, with the following excerpt:

The raw materials of tellurium dioxide, TeO2 (Aldrich 99.5%), and bismuth (iii) oxide Bi2O3 (Aldrich 99.0%) were used to synthesize the glass sample. The glass sample was prepared by using a melt quenching method [32,33]. The bismuth (iii) oxide, x = 5, 8, 10, 12, 15 in mol% was added into the tellurite oxide and was weighed using a digital weighing machine with an accuracy of ±0.01 g and then mixed together by using a mortar and pestle. The mixture was poured into an alumina crucible and put into an electric furnace set at 100 °C for a period of 30 min. The alumina crucible was used because it can withstand high temperatures and does not react with the raw materials during the melting process as opposed to porcelain crucibles. The temperature was then increased by 10 °C/min until 900 °C and the then maintained for 2 h. When the melting process was completed, the molten liquid was cast into a stainless steel cylindrical shape mould which had been preheated at 400 °C for 30 min. The sample was annealed at 400 °C in a second furnace for 1 h, then the furnace was turned off. The glass sample was cut at a thickness of about 2 mm for the required measurements [33].

I have pulled a few assumptions from this paragraph which it would be helpful for me to verify before testing this out:

1. I'm assuming the passage

the glass sample was prepared by using a melt quenching method [32,33]. The bismuth (iii) oxide, x = 5, 8, 10, 12, 15 in mol% was added into the tellurite oxide

is simply stating that the end concoction consists of a combination between 85-95% TeO2 and 5-15% Bi2O3, correct?

2. What is the purpose of annealing for in this context? My end case for the result pieces are simply for prototyping, but my guess is I will have to polish the pieces with cerium oxide without destroying them so they can not be too brittle. Is annealing required?

3. I'm lost for understanding what the quenching method is, results online are sparse and the linked papers are pay walled. What is the process for this like?

Are there other things I should know? I have this furnace and have had success with simple metals but not sure what else I need to know for something a bit more chemically involved like optical glass.

Thank you.

• Unfortunately, this is none of my bismuth... – niels nielsen Jan 14 '20 at 23:16