José Martinho Marques de Oliveira

Glass–Glass Laser-Assisted Glass Frit Bonding

A novel sealing method is proposed for encapsulating devices comprised of glass substrates. This sealing method is based on applying a glass frit paste cord onto the substrate and then using a laser beam to locally supply the necessary energy to allow the formation of a hermetic bonding layer. A detailed description of the laser bonding technique, the necessary equipment and method, and a preliminary study is carried out. The need to apply mechanical pressure during the bonding step is averted, thus facilitating the manufacturing process. The glass bonding cord obtained by the laser-assisted process was found to have an excellent contact with both substrates and no gas inclusions or voids were detected, indicating that an effective sealing was achieved. Preliminary hermeticity tests of the laser-bonded cells yielded encouraging results. The developed laser-assisted glass frit bonding process is a promising technique for obtaining hermetic sealing of photoelectronic and electrochemical devices, as it allows temperature-sensitive materials to be used inside them.

Development and characterization of 3CaO·P2O5-SiO2-MgO glass-ceramics with different crystallization degree

The CaO-P2O5-SiO2-MgO system presents several compounds used as biomaterials such as hydroxyapatite (HA), tricalcium phosphate (TCP) and TCP with magnesium substituting partial calcium (TCMP). The β-TCMP phase with whitlockite structure has interesting biological features and mechanical properties, meeting the requirements of a bioactive material for bone restoration. In this work, the production of Mg-doped TCP, β-TCMP, has been investigated by crystallization from a glass composed of 52.75 wt% 3CaO·P2O5, 30 wt% SiO2 and 17.25 wt% MgO (i.e., 31.7 mol% CaO, 10.6 mol% P2O5, 26.6 mol% MgO and 31.1 mol% SiO2) using heat treatments between 775 °C and 1100 °C for up to 8 h. The devitrification process of the glass has been accompanied by differential scanning calorimetry (DSC), high-resolution X-ray diffraction (HRXRD), relative density and bending strength measurements. The characterization by HRXRD and DSC revealed the occurrence of whitlockite soon after the bulk glass preparation, a transient non-cataloged silicate between 800 °C and 1100 °C, and the formation of diopside in samples treated at 1100 °C as crystalline phases. The overall crystalline fraction varied from 26% to 70% depending on the heat treatments. Furthermore, contraction of the a-axis lattice parameter and expansion of the c-axis lattice parameter of the whitlockite structure have been observed during the heat treatments, which were attributed to the β-TCMP formation with the partial substitution of Ca2+ by Mg2+. Relative densities near 99% and 97% for the glass and glass-ceramics respectively indicated a discrete reduction as a function of the devitrification treatment. Bending strengths of 70 MPa and 120 MPa were determined for the glass and glass-ceramic material crystallized at 975 °C for 4 h, respectively.