Tellurite And Fluorotellurite Glasses For Active And Passive

7. Surface properties; MDO 257
sides of the sample. For etchants based on HF, the experiments were carried out in a fume
cupboard at room temperature in polyethylene containers.
The environmental durability studies were performed on fluorotellurite glass samples
of dimension 3 × 5 × 5 mm (see section 6.1.1.1. for polishing details), in a polypropylene
sealed container with 50 ml distilled water (filled to capacity). The experiment at 60°C
was carried out in an oven.
Samples were removed from the etchant / water with polyethylene tweezers after the
appropriate time (measured by a stopwatch) and immediately placed in a 250 ml beaker
containing 50 ml acetone (Fisher analytical reagent grade), and dried to constant weight
using a hotplate at 70°C. The mass difference after treatment was measured on electronic
scales (Sartorius BP211D), which nominally read to five decimal places (i.e. to the
nearest 1×10 -5 g).
The volume of acid or alkali, VA, required to produce the total volume of etchant, Vtotal,
of concentration [A]final, is given by equation (7.5).
V
A
[ A]
final
= Vtotal
×
(7.5)
[ A]
initial
where [A]initial is the initial concentration of the undiluted acid or alkali. The acid or alkali
was made up to the volume Vtotal with distilled water, i.e. Vtotal = VA + Vdw, where Vdw =
volume of distilled water. For example, to make up a 1000 ml solution of 1M H2SO4,
from 18M undiluted sulphuric acid, 55.56 ml (1000/18) was added to a 1000 ml
container, and made up to 1000 ml with distilled water. Table (7.1) summarises the