Glass - Back to the Future!

Presenting Author:
Elena Krekhova

article posted 7 April 2016

Elena Krekhova is a Leading Engineer Technologist at Lytkarino Optical Glass Factory in Moscow, and she is also a Senior Lecturer at the Moscow Technical University. Her PhD was awarded in 2000 for research in the chemical technology of refractory non-metallic materials at the University of Chemical Technology of Russia in Moscow.

Development of Special Flint Glass Production Technology

A.V. Zolikov, E.Y. Krekhova, V.I. Molev, A.B. Nikonov & S.P. Belousov
JSC LZOS, H.1, Parkovay str., Lytkarino, 140080, Russia

One of the components of apochromatic lenses are the glasses of type called Special Flint (OF), characterized by blue spectral line relative partial dispersion which is lower than in ordinary flints. While for the most part of optical glass types, the correlation of relative partial dispersion (Px,y) vs. Abbe value (nue) is close to linear one, special flints are out of the so called normal line, and are in below-zero area (see Figure 1).

Figure 1. Location of OF10 glass in diagram P~f(nue): (a) for area F'e; (b) for area gF'

In order to create special flints which could be used for building the apochromatic lenses, two main tasks should be solved:
- develop the composition of glass characterized by the required set of optical properties;
- master the method of production of the glass with such composition at industrial level.
Traditionally, OF composition with lowered relative partial dispersions were borate-based. It was found out that flint could be made on borosilicate basis with addition of germanium oxide, which lead to the development of glass type OF10, which, together with already known glass OK4 (Special Crown), creates perfect apochromatic lens, due to virtually equal relative partial dispersion values at (F'e) and (gF') spectrum areas as well as big difference between Abbe values (see Table 1).

Table 1. Basic characteristics of glasses OK4 and OF10

The main problems in the production of glass OF10 were the high percentage of striae and opalescence of blocks after rough annealing. After detecting the opalescence-inducing crystal phase, glass composition was corrected. This fact in combination with special manufacturing methods, allowed not only eliminating the opalescence but also reducing striae up to 15%.