Hugo Fernandes - Academia.edu (original) (raw)

articles by Hugo Fernandes

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.

Papers by Hugo Fernandes

Journal of Thermal Analysis and Calorimetry, 2011

This article aims to shed some light on the structure and thermo-physical properties of lithium d... more This article aims to shed some light on the structure and thermo-physical properties of lithium disilicate glasses in the system Li 2 O-SiO 2 -Al 2 O 3 -K 2 O. A glass with nominal composition 23Li 2 O-77SiO 2 (mol%) (labelled as L 23 S 77 ) and glasses containing Al 2 O 3 and K 2 O with SiO 2 /Li 2 O molar ratios (3.13-4.88) were produced by conventional melt-quenching technique in bulk and frit forms. The glass-ceramics (GCs) were obtained from nucleation and crystallisation of monolithic bulk glasses as well as via sintering and crystallisation of glass powder compacts. The structure of glasses as investigated by magic angle spinning-nuclear magnetic resonance (MAS-NMR) depict the role of Al 2 O 3 as glass network former with fourfold coordination, i.e., Al(IV) species while silicon exists predominantly as a mixture of Q 3 and Q 4 (Si) structural units. The qualitative as well as quantitative crystalline phase evolution in glasses was followed by differential thermal analysis (DTA), X-ray diffraction (XRD) adjoined with Rietveld-reference intensity ratio (R.I.R.) method, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The possible correlation amongst structural features of glasses, phase composition and thermo-physical properties of GCs has been discussed.

Journal of Thermal Analysis and Calorimetry, 2013

The crystallisation kinetics of experimental glasses in 3 different systems: (were studied under ... more The crystallisation kinetics of experimental glasses in 3 different systems: (were studied under non-isothermal conditions. The DTA results revealed a stronger tendency to crystallisation of binary compositions in comparison to the ternary and quaternary compositions comprising Al 2 O 3 and K 2 O which present the lower crystallisation, i.e. the crystallisation propensity follows the trend A [ B [ C. The devitrification process in the Li 2 O-SiO 2 and Li 2 O-Al 2 O 3 -SiO 2 systems began earlier and the rate was higher in comparison to that of glasses in the quaternary Li 2 O-K 2 O-Al 2 O 3 -SiO 2 system. Thus, addition of Al 2 O 3 and K 2 O to glasses of Li 2 O-SiO 2 system was demonstrated to promote glass stability against crystallisation. However, the activation energy for crystallisation was shown to depend also on the SiO 2 /Li 2 O ratio with the binary system showing a decreasing trend with increasing SiO 2 / Li 2 O ratio, while the opposite tendency was being observed for compositions with added Al 2 O 3 and K 2 O.

Journal of the European Ceramic Society, 2012

Glass compositions with formula (71.78 − x)SiO 2 -2.63Al 2 O 3 -(2.63 + x)K 2 O-23.7Li 2 O (mol.%... more Glass compositions with formula (71.78 − x)SiO 2 -2.63Al 2 O 3 -(2.63 + x)K 2 O-23.7Li 2 O (mol.%, x = 0-10) and SiO 2 /Li 2 O molar ratios far beyond that of stoichiometric lithium disilicate (Li 2 Si 2 O 5 ) were prepared by conventional melt-quenching technique to investigate the influence of K 2 O content on structural transformations and devitrification behaviour of glasses in the Li 2 O-SiO 2 system. The scanning electron microscopy (SEM) examination of as cast non-annealed glasses revealed the presence of nanosized droplets in glassy matrices suggesting occurrence of liquid-liquid phase separation. An overall trend towards depolymerization of the silicate glass network with increasing K 2 O content was demonstrated by employing magic angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopy. The distribution of structural units in the experimental glasses was estimated using 29 Si MAS-NMR spectroscopy suggesting the appearance of Q 2 , enhancement of Q 3 and diminishing of Q 4 groups with increasing K 2 O contents. X-ray diffraction (XRD) and differential thermal analysis (DTA) were used to assess the influence of K 2 O on devitrification process and formation of lithium disilicate (Li 2 Si 2 O 5 ) and/or lithium metasilicate (Li 2 SiO 3 ) crystalline phases. (H.R. Fernandes). GC manufacture, 4 the GCs derived from this parent binary system exhibit some unfavourable characteristics in terms of their mechanical and chemical properties which hinder their potential applications in several technological areas.

Journal of the European Ceramic Society, 2004

The production of glasses whose composition ranged between tetrasilicic mica and fluorapatite-dio... more The production of glasses whose composition ranged between tetrasilicic mica and fluorapatite-diopsite 50/50 (in wt.%) was investigated. Glass-ceramics were obtained by both bulk crystallization and sintering of glass powder compacts. The experimental results showed that increasing amount of apatite and diopsite components in the ternary system until 50% mica content generally caused decrease of melting temperature and increasing stability of glass against spontaneous crystallization during cooling after casting. Liquid immiscibility, whose features depend on the particular glass composition, characterized all the investigated glasses but it was more pronounced in the glasses with higher amount of apatite and diopsite components. The investigated glasses are preferably crystallized in bulk form between 700 and 900 • C, resulting in formation of different combinations between mica, fluorapatite and diopsite, depending on the particular composition. The obtained glass-ceramics exhibited attractive aesthetics, structural integrity and dense structure.

Journal of the American Ceramic Society, 2006

The phase transformations in Li 2 O-doped model formulations (using 1-7% Li 2 CO 3 ), which compr... more The phase transformations in Li 2 O-doped model formulations (using 1-7% Li 2 CO 3 ), which comprised 50% kaolin, 25% feldspar, and 25% quartz (in wt%), were investigated experimentally and with the aid of thermodynamic calculations between 9001 and 13501C. Experimental and theoretical approaches agree fairly well with another and indicated that the presence of Li 2 O and other alkalis, such as K 2 O, in aluminosilicate matrices plays an important role in the phase transformations that occur at different temperatures during firing. Discrepancies in experimental results from thermodynamics have been attributed to slow kinetics, also likely because of the nature of the raw materials used.

Journal of Porous Materials, 2006

High compressive strength glass foams were produced using sheet glass cullet with the aid of 1 wt... more High compressive strength glass foams were produced using sheet glass cullet with the aid of 1 wt.% SiC powder, as gassing agent, and the incorporation of small amounts of an alkali earth aluminosilicate glass powder (AD), which is intrinsically prone to be crystallised to anorthite and diopside. The amount of SiC used as well as the mean particle sizes of the powders of both glasses and SiC were lower than those used in earlier studies. The experimental results showed that homogenous microstructures of large pores could be obtained by adding 1 wt.% SiC. The compressive strength of the glass foams was considerably increased when the incorporated AD-glass was higher than 1 wt.%. It is concluded that the presence of the AD glass is beneficial for the produced glass foams because of the formation of a well packed honeycomb structure which features an optimal distribution of pentagonal-and hexagonal-like shaped pores surrounded by dense struts. The crystallization of wollastonite and diopside inside the struts should also have a positive impact on the mechanical behaviour of the produced porous glass foams.

Journal of Non-Crystalline Solids, 2013

The aim of the present study is to investigate the apatite formation process from glasses in the ... more The aim of the present study is to investigate the apatite formation process from glasses in the fluorapatitediopside-anorthite-albite system. The effects of partial and total replacement of anorthite fraction by albite in the ternary composition 26 Ca 5 (PO 4 ) 3 F−44 CaAl 2 Si 2 O 8 − 30 CaMgSi 2 O 6 (wt.%) on the properties of glasses and glass-ceramics were evaluated. The scanning electron microscopy (SEM) examination of glasses revealed the precipitation of a nanosize droplet phase in the glassy matrices suggesting the occurrence of amorphous phase separation in all annealed glasses. An overall trend towards polymerization of the glass network with increasing albite content was demonstrated by employing MAS-NMR and FTIR spectroscopy. X-ray diffraction (XRD) and differential thermal analysis (DTA) were used to assess the effect of albite content on the devitrification process and formation of fluorapatite crystalline phase (Ca 5 (PO 4 ) 3 F).

Journal of Materials Science, 2013

The aim of this study was to investigate the effects of different nucleating agents (P 2 O 5 , Ti... more The aim of this study was to investigate the effects of different nucleating agents (P 2 O 5 , TiO 2 and ZrO 2 ) on the crystallization behaviour and the properties of a parent glass with composition 23.7 Li 2 O-2.63 K 2 O-2.63 Al 2 O 3 -71.78 SiO 2 (mol%) and SiO 2 /Li 2 O molar ratio far beyond that of stoichiometric lithium disilicate (LD, Li 2 Si 2 O 5 ). The scanning electron microscopy examination of the as-cast non-annealed glasses revealed the occurrence of liquidliquid phase separation for all the compositions. P 2 O 5 revealed to be effective in promoting bulk crystallization of LD, while TiO 2 and ZrO 2 led to surface crystallization. Moreover, ZrO 2 enhances the glass polymerization and shifts T p to higher temperatures, hindering crystallization. At 900°C, TiO 2 -containing glasses feature LD and lithium metasilicate (LMS, Li 2 SiO 3 ), while P 2 O 5 -and ZrO 2 -containing ones present monophasic LD and LMS glassceramics, respectively.

Ceramics International, 2009

Glass foams were produced using sheet glass cullet and fly ashes from thermal power plant with ad... more Glass foams were produced using sheet glass cullet and fly ashes from thermal power plant with added carbonates (commercial dolomite-and calcite-based sludges) as foaming agents. The influence of type and amount of carbonates as well as of the sintering temperature on the apparent density, compressive strength, microstructure and crystalline phases was evaluated. The experimental results showed that homogenous microstructures of large pores could be obtained by adding just 1-2 wt.% carbonates and using low sintering temperature (850 8C), leading to foams presenting apparent density and compressive strength values of about 0.36-0.41 g/cm 3 and 2.40-2.80 MPa, respectively. Good correlations between compressive strength, apparent density and microstructure (pore size, struts' thickness and internal porosity) were observed. #

Ceramics International, 2006

Glass-ceramics were produced by crystallization of glasses in the SiO 2 -Al 2 O 3 -B 2 O 3 -MgO-C... more Glass-ceramics were produced by crystallization of glasses in the SiO 2 -Al 2 O 3 -B 2 O 3 -MgO-CaO-Na 2 O-F system. The experimental results showed that bulk glasses are prone to surface crystallization. Hence, crystallization of bulk glasses resulted in non-homogeneous crystalline materials, which comprised relatively coarse crystals. Therefore, processing was realized using glass-powder compacts. Maximum densification was reached at 700-750 8C. This interval is positioned at relatively lower temperatures than those often reported for similar sintered glass-ceramics. Doping with P 2 O 5 improved sintering behaviour and broadened sintering temperature range. Sintering between 750 and 800 8C resulted in materials, which exhibited dense crystalline microstructure and the maximum flexural strength. #

Advances in Applied Ceramics, 2009

Glass foams were produced exclusively from industrial residues, namely from sheet glass cullet an... more Glass foams were produced exclusively from industrial residues, namely from sheet glass cullet and fly ashes from thermal power plant as the main components, and from burned wastes of silicon carbide (SiC) abrasive papers. The experimental results showed that homogenous microstructures of large pores could be obtained by adding an optimum amount (1 wt-%) of a commercial SiC powder (SiC C ) after sintering at 950uC. The SiC C was then replaced by equivalent amounts of SiC abrasive paper ashes of different grain sizes. The SiC containing foams led to apparent density and compressive strength values of about 0?18-0?35 g cm 23 and 0?9-1?8 MPa. Good correlations between compressive strength, apparent density and microstructure (pore size, strut thickness and internal porosity) were observed.

Industrial Ceramics

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...

Bayesian statistics defines how new information, given by a likelihood, should be combined with p... more Bayesian statistics defines how new information, given by a likelihood, should be combined with previously acquired information, given by a prior distribution. Many experiments have shown that humans make use of such priors in cognitive, perceptual, and motor tasks, but where do priors come from? As people never experience the same situation twice, they can only construct priors by generalizing from similar past experiences. Here we examine the generalization of priors over stochastic visuomotor perturbations in reaching experiments. In particular, we look into how the first two moments of the prior-the mean and variance (uncertainty)-generalize. We find that uncertainty appears to generalize differently from the mean of the prior, and an interesting asymmetry arises when the mean and the uncertainty are manipulated simultaneously.

Ceramics International, 2014

Panel (P) and funnel (F) glasses from Cathode Ray Tube (CRT) have been used to obtain glass foams... more Panel (P) and funnel (F) glasses from Cathode Ray Tube (CRT) have been used to obtain glass foams by a simple and economic processing route, consisting of direct heating the glass powders at relatively low temperatures (650-750 1C) using different foaming agents (FA) such as egg shells, calcite, dolomite. Mixtures in different proportions of P and F glass powders were tested and the effects of composition and heat treatment temperature on the foaming behaviour were evaluated. Glass foams featuring apparent density and compressive strength values of 0.29 g/cm 3 and 2.34 MPa, respectively, could be produced from a P/F ratio ¼1 with added 3 wt% of egg shells upon heat treating at 700 1C for 15 min. The P/F ratio was found to strongly influence the foaming behaviour and, consequently, the physical properties of the final foam glass. The relative performance of other foaming agents under a given set of experimental conditions revealed to be dependent on the type of glass (composition and thermal properties).

PLoS Computational Biology, 2009

A large number of experiments have asked to what degree human reaching movements can be understoo... more A large number of experiments have asked to what degree human reaching movements can be understood as being close to optimal in a statistical sense. However, little is known about whether these principles are relevant for other classes of movements. Here we analyzed movement in a task that is similar to surfing or snowboarding. Human subjects stand on a force plate that measures their center of pressure. This center of pressure affects the acceleration of a cursor that is displayed in a noisy fashion (as a cloud of dots) on a projection screen while the subject is incentivized to keep the cursor close to a fixed position. We find that salient aspects of observed behavior are well-described by optimal control models where a Bayesian estimation model (Kalman filter) is combined with an optimal controller (either a Linear-Quadratic-Regulator or Bang-bang controller). We find evidence that subjects integrate information over time taking into account uncertainty. However, behavior in this continuous steering task appears to be a highly non-linear function of the visual feedback. While the nervous system appears to implement Bayes-like mechanisms for a full-body, dynamic task, it may additionally take into account the specific costs and constraints of the task.

Journal of the European Ceramic Society, 2012

The effects of K 2 O content on sintering and crystallization of glass powder compacts in the Li ... more The effects of K 2 O content on sintering and crystallization of glass powder compacts in the Li 2 O-K 2 O-Al 2 O 3 -SiO 2 system were investigated. Glasses featuring SiO 2 /Li 2 O molar ratios of 2.69-3.13, far beyond the lithium disilicate (LD-Li 2 Si 2 O 5 ) stoichiometry, were produced by conventional melt-quenching technique. The sintering and crystallization behaviour of glass powders was explored using hot stage microscopy (HSM), scanning electron microscopy (SEM), differential thermal (DTA) and X-ray diffraction (XRD) analyses. Increasing K 2 O content at the expense of SiO 2 was shown to lower the temperature of maximum shrinkage, eventually resulting in early densification of the glass-powder compacts. Lithium metasilicate was the main crystalline phase formed upon heat treating the glass powders with higher amounts of K 2 O. In contrast, lithium disilicate predominantly crystallized from the compositions with lower K 2 O contents resulting in strong glass-ceramics with high chemical and electrical resistance. The total content of K 2 O should be kept below 4.63 mol% for obtaining LD-based glass-ceramics.

Journal of the European Ceramic Society, 2009

The present work aimed at studying the incorporation of wastes from natural rock cutting and poli... more The present work aimed at studying the incorporation of wastes from natural rock cutting and polishing to produce roof tiles. The sintered products incorporating the sludge were targeted to have similar or even enhanced properties in comparison to those made of a standard reference paste industrially used to fabricate concurrent products available in the market. Firstly, the raw materials, including the sludge, were characterised by particle size distribution, density, X-ray diffraction (XRD), thermal properties and loss on ignition. Different formulations were prepared to evaluate the effects of each component on plasticity of pastes, drying and firing processes, and on the final properties of the tiles. Finally, the most promising formulations were selected and characterised for sintered density, water absorption, and flexural bending strength. The results obtained made it possible to conclude about the possibility of producing roof tiles incorporating 10% of granite wastes having excellent properties (water absorption <6%, lower pyroplastic deformation index, and bending strength values of about 14 MPa and 38 MPa for the green and sintered products, respectively). Therefore, the sludge derived from the granite cutting and polishing industries can be classified as a by-product suitable to replace natural non-plastic raw material in traditional ceramic formulations. This will contribute to preserve non-renewable natural resources, while it allows minimization of the negative environmental impact due to its disposal.

Journal of Thermal Analysis and Calorimetry, 2011

Journal of Thermal Analysis and Calorimetry, 2013

Journal of the European Ceramic Society, 2012

Journal of the European Ceramic Society, 2004

Journal of the American Ceramic Society, 2006

Journal of Porous Materials, 2006

Journal of Non-Crystalline Solids, 2013

Journal of Materials Science, 2013

Ceramics International, 2009

Ceramics International, 2006

Advances in Applied Ceramics, 2009

Industrial Ceramics

Ceramics International, 2014

PLoS Computational Biology, 2009

Journal of the European Ceramic Society, 2012

Journal of the European Ceramic Society, 2009

Journal of the European Ceramic Society, 2007

In the present work, industrial sludges derived from cutting and polishing natural stones (granit... more In the present work, industrial sludges derived from cutting and polishing natural stones (granite and quartzite) were characterised in terms of particles size distribution, chemical and mineralogical composition, and thermal behaviour and their potential to be incorporated as main components in red-clay-based stoneware tiles was evaluated. High levels (60-70 wt.%) of incorporation were attempted aiming at designing new formulations intended to be less expensive and possess better final properties (lower water absorption and higher flexural strength) in comparison to an industrial reference body used in the production of rustic tiles by extrusion, characterised 8-9% water absorption and a flexural strength of 17-18 MPa. Extruded rods of different formulations were produced and fired at 1100 • C, 1125 • C, 1150 • C and 1200 • C. The experimental results showed that all the new formulations performed better with the most significant improvements being obtained with incorporation of granite sludge. Flexural strength values more than triplicate and water absorption decreased by more than one order of magnitude in comparison to the reference paste. The new products fulfil the requirements of the ISO 13006 standard, group BIa (porcelain tiles).

Journal of the European Ceramic Society, 2010