2- SPCTS, ENSCI, Europeen Ceramic Center, 12 rue Atlantis, 87068 Limoges cedex, France
3- LMACE, FSSM, Cadi Ayyad University, Av. Prince My Abdallah – B.P. 2390, 40000 Marrakech, Morocco
firstname.lastname@example.org The opacifying effect of an inorganic filler in a glassy matrix is essentially due to two factors, namely, either a local devitrification result of recrystallization of some oxides of the matrix, either simply to the insolubility of the filler incorporated in glassy matrix. In both cases, this results in a local discontinuity in the refractive index which leads to the formation of an optical contrast between the glass phase (refractive index ng) and the particles (powder or insoluble crystals - index refraction np). Then the result is the appearance of the phenomenon of diffusion responsible for the increase of the reflection and by following the decrease in light transmission.
In the present work we are interested in studying the opacifying effect of phosphates on borosilicate glass matrix for possible valorization of phosphates in the production of opaque enamels. To do this, and at first, we studied the effect of adding different concentrations of calcium phosphate on the optical properties of a transparent borosilicate glass. Indeed, the transmission was measured in the visible range between 450 and 800 nm for glass samples containing increasing percentages (0, 1, 5, 10, 20 and 30wt %) of calcium phosphate. The microstructural observation of the samples is in perfect harmony with the optical measurements. It shows that for a very low incorporation (1wt %), the glass matrix is perfectly homogeneous. Calcium phosphates are incorporated perfectly miscible in the bulk. A 5 wt %, the inclusions in the matrix is clearly visible and become more and more significant with the increase of phosphate incorporated. Chemical analysis by EDS (Energy Dispersive Spectrometry) show that these inclusions are calcium phosphates, which suggests that the opacifying effect, in this case, comes from the light scattering of calcium phosphate particles insoluble in the vitreous matrix.