article posted 30 March 2016
Guglielmo Macrelli is senior scientist in an industrial R&D laboratory.
He has been active since 1990 in many glass science areas: ion exchange in silicate
glasses, thin film optical coatings and mechanical glass properties.
He worked in the development of industrial chemical strengthening plants and
processes for sodium alumina-silicate glasses, soda-lime glasses and
lithium alumina-silicate glasses and in the development of electrochromic
coatings based in all solid state thin film inorganic layers.
He has authored about 15 papers in peer reviewed international journals and
he has presented several oral contributions in international conferences.
Guglielmo Macrelli is member of the American Ceramic Society
Some "unconventional" analytical solutions to diffusion equations
in thermal ion exchange in silicate glasses
Isoclima SpA R&D Department - 35042 Este (PD) Italy
Ion exchange in silicate glasses is becoming a widely used process for both glass
strengthening and modifications of near surface refractive index.
Process configurations can be purely thermal or may be assisted by an external electric field.
Ion sources can be molten salts reservoirs or thick film deposited on the glass surface.
In process analysis or process predictions the classical diffusion solutions are generally
considered: erfc-like in case of wide ions reservoir or Gaussian-like in case of thick
surface layers sources. These solutions may be considered, in some way, "conventional"
because they are often proposed in spite of the implicit approximations included in the
assumptions of the boundary conditions (instantaneous constant equilibrium concentration
attained at glass surface and constant initial concentration) under which they are derived.
"Unconventional" solutions may be considered for time dependent boundary conditions
or for not constant initial conditions. Such solutions are significant when the sudden
surface equilibrium condition is a not acceptable approximation or when a subsequent
thermal treatment is coupled to ion exchange. Other relevant case is when ion diffusion
coefficient in the reservoir medium is significant and may influence the ion concentration
distribution in glass.
Such unconventional solutions may be helpful to analyse efficiency
or contamination issues in ion exchange processes. A review of these unconventional
solutions will be presented and discussed in connection to specific process analysis or