The role of CaF2 on the structure, crystallization behaviour and properties of a relatively simpl... more The role of CaF2 on the structure, crystallization behaviour and properties of a relatively simple non-stoichiometric lithium disilicate (Li2Si2O5) based glass composition was studied. Different x amounts (x = 0, 1, 3 and 5 mol{\%}) of CaF2 were added to (100 - x) of a parent glass (22.96Li2O-2.63K2O-2.63Al2O3-71.78SiO2) composition. The glasses were produced by conventional melt-quenching technique, whilst glass-ceramics were produced via crystallization of monolithic bulk glasses. A scanning electron microscopy (SEM) examination of as cast non-annealed monolithic glasses revealed precipitation of nanosize droplet phase in glassy matrices suggesting the occurrence of liquid phase separation in all investigated compositions. The extent of phase segregation, as judged from the mean droplet diameter and the packing density of droplets, decreased with increasing CaF2 content in the glasses. A slight depolymerisation of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for CaF2. The presence of CaF2 enhanced the crystallization at lower temperatures in comparison to CaF2-free glass.
The structural role of Mn was investigated in a relatively simple non-stoichiometric lithium disi... more The structural role of Mn was investigated in a relatively simple non-stoichiometric lithium disilicate (Li2Si2O 5) based glass composition. Glasses were prepared by partially replacing SiO2 by MnO2 from the base glass belonging to the system Li2O-K2O-Al2O3-SiO 2. An overall depolymerization of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for Mn. However, thermal analysis, phase segregation and nucleation in the glasses suggested that Mn might also act as network former. Moreover, calculated crystal field parameters from UV-Visible spectroscopy, showing high ligand field strength ($\Delta$o) and Racah inter electronic repulsion (B) indicate the possible existence of Mn as individual molecular entities in the interstitials of the glass network. This paper discusses the implications of this structural role of Mn on the crystallization of bulk glasses and on the sintering behaviour and crystallization of glass powder compacts. This journal is {\textcopyright} the Partner Organisations 2014.
The aim of this work is to evaluate the effects of incorporating river silt originated from washi... more The aim of this work is to evaluate the effects of incorporating river silt originated from washing silica sands extracted in "Ria de Aveiro" as a raw material in the manufacturing process of traditional ceramic building products such as bricks and tiles and on their final properties. The solid river silt waste was physicochemicaliy characterized for particle size distribution, morphology and XRF. The thermal behaviour was investigated by DTA and TCA analysis, and the mineralogical phases were identified by XRD. Testing bars made of several compositions incorporating amounts in the range of 0 to 10-wt% of river silt and of an industrial standard paste were produced in a pilot-plant extruder, and fired at different temperatures in the range of 950-1100 °C. The characterisation results of sintered specimens (water absorption, linear shrinkage and mechanical bending strength) have shown that products with final properties similar to those obtained from the standard industrial...
The role of CaF2 on the structure, crystallization behaviour and properties of a relatively simpl... more The role of CaF2 on the structure, crystallization behaviour and properties of a relatively simple non-stoichiometric lithium disilicate (Li2Si2O5) based glass composition was studied. Different x amounts (x = 0, 1, 3 and 5 mol{\%}) of CaF2 were added to (100 - x) of a parent glass (22.96Li2O-2.63K2O-2.63Al2O3-71.78SiO2) composition. The glasses were produced by conventional melt-quenching technique, whilst glass-ceramics were produced via crystallization of monolithic bulk glasses. A scanning electron microscopy (SEM) examination of as cast non-annealed monolithic glasses revealed precipitation of nanosize droplet phase in glassy matrices suggesting the occurrence of liquid phase separation in all investigated compositions. The extent of phase segregation, as judged from the mean droplet diameter and the packing density of droplets, decreased with increasing CaF2 content in the glasses. A slight depolymerisation of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for CaF2. The presence of CaF2 enhanced the crystallization at lower temperatures in comparison to CaF2-free glass.
The structural role of Mn was investigated in a relatively simple non-stoichiometric lithium disi... more The structural role of Mn was investigated in a relatively simple non-stoichiometric lithium disilicate (Li2Si2O 5) based glass composition. Glasses were prepared by partially replacing SiO2 by MnO2 from the base glass belonging to the system Li2O-K2O-Al2O3-SiO 2. An overall depolymerization of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for Mn. However, thermal analysis, phase segregation and nucleation in the glasses suggested that Mn might also act as network former. Moreover, calculated crystal field parameters from UV-Visible spectroscopy, showing high ligand field strength ($\Delta$o) and Racah inter electronic repulsion (B) indicate the possible existence of Mn as individual molecular entities in the interstitials of the glass network. This paper discusses the implications of this structural role of Mn on the crystallization of bulk glasses and on the sintering behaviour and crystallization of glass powder compacts. This journal is {\textcopyright} the Partner Organisations 2014.
The aim of this work is to evaluate the effects of incorporating river silt originated from washi... more The aim of this work is to evaluate the effects of incorporating river silt originated from washing silica sands extracted in "Ria de Aveiro" as a raw material in the manufacturing process of traditional ceramic building products such as bricks and tiles and on their final properties. The solid river silt waste was physicochemicaliy characterized for particle size distribution, morphology and XRF. The thermal behaviour was investigated by DTA and TCA analysis, and the mineralogical phases were identified by XRD. Testing bars made of several compositions incorporating amounts in the range of 0 to 10-wt% of river silt and of an industrial standard paste were produced in a pilot-plant extruder, and fired at different temperatures in the range of 950-1100 °C. The characterisation results of sintered specimens (water absorption, linear shrinkage and mechanical bending strength) have shown that products with final properties similar to those obtained from the standard industrial...
Uploads
articles by Hugo Fernandes
Papers by Hugo Fernandes