The aim of the undertaken experiments was to investigate the regularity of surface layers
structure and the composition of colorless container glass from different glass manufacturers,
using section etching by HF solution.
The subjects of investigation were bottles and jars of different capacity. The investigation
was made using sectional glass-forming machines (IS-8-2, IS-6-2, AL-106-2) and rotor glassforming
machines (BB-7, BB-12). The variations of chemical composition of glasses is the
following (weight %): 72.0-72.8 SiO2, 1.0-1.9 Al2O3, 0.07-0.10 Fe2O3, 7.5-8.0 CaO, 3.7-4.0
MgO, 13.6-13.9 Na2O, 0.2-0.4 K2O and 0.2-0.4 SO3.
The analyses of glass surface layers have been carried out with the help of section etching
by HF solution. Three glass samples were fixed in fluorocarbon polymer cassettes and then fused
with a polymer wheel and put into a weak HF solution. The samples were rotated in the solution
with a speed of 100 rotations per minute. In the following experiments samples were kept in
solution in stationary position, i. e. without rotation. After etching the samples were washed with
distilled water, dried and weighed. The duration of etching changed within 3 to 120 minutes. The
thickness of the dissolved layer and rate of dissolution in HF solution of glass surface layers
were calculated based on mass losses of the samples before and after etching. The concentration
of Na+, K+ and Ca2+ was measured in extracts after etching by the method of flame photometry.
Preliminary experiments showed that the rate of dissolution of glass depends on the
temperature of the HF solution and its concentration, on the volume of solution and on the time
the samples were exposed to it, as well as on hydrodynamics conditions. The temperature of the
HF solution, its volume and concentration remained unchanged in all the experiments. The
dissolution of surface layer with the necessary thickness has been achieved through different
time of etching and changes of hydrodynamics conditions (the samples were rotated in solution
or kept in stationary position). The analysis of samples was carried out at the depth 100 μm. The
section etching was supplemented by light microscopy and determination of microhardness. The
samples were viewed under the microscope with magnification from 100 to 500 times.
The experiments showed that the rate of dissolution of all the samples in HF solution is
not stable. The medium rate of dissolution of the samples from jars and bottles is at the same
level, regardless of the method of glass-forming. It has also been established that there is a direct
correlation between the stability of the dissolution rate of glass surface layers and the thickness
of dissolved layer during one etching. We think, this shows the stratified structure of colorless
glass for container.
A correlation between the microhardness of glass and the rate of its dissolution has been
determined. The higher the glass microhardness is the lower its rate of dissolution in HF
solution. It has been revealed with the help of light microscopy that the bottles and jars consist of
layers without any determined orientation. The thickness of separate layers makes small parts of
μm. The character of stratification depends on the homogeneity of the glass, on the method and
conditions of its manufacture. The increase of glass homogeneity reduces its stratification.