Figs. 5 and 6 are plots of the partial pressure of carbon
monoxide versus temperature for several oxides
commonly encountered in glasses. Fig. 5 is for metal oxides
of the type Me2Ox and Fig. 6 for metal oxides of the
type MeO. Calculations were performed for three different
oxide molar concentrations (1%, 10% and 50%) in
order to see its impact on gas production. Formation
of bubbles can only occur if pCO is greater than atmospheric
pressure, i.e., P105Pa in our experiments. For
example, according to Figs. 5 and 6, the oxides Al2O3,
CaO and MgO cannot be responsible for the production
of gas. These oxides should then be preferred over PbO
or Na2O, for example, since these last two are shown to
produce CO in large quantities. The concentration of an
oxide in a given glass may have a larger effect depending
on their type (e.g., Cu2O shows a larger dependency on
concentration compared to B2O3). A reduction in bubbling
rate with time could be linked with the depletion
of the glass in certain oxides. The probability of a reaction
continuing would then depend on the amount of
reacting oxides still present in the glass.