Carlos Araújo Queiroz

Universidade NOVA de Lisboa | NOVA · Research Unit Glass and Ceramic for the Arts (VICARTE)

Historically, glass is often viewed as a remarkable translucent substance though usually made from the simplest raw materials upon the effect of firing. Nature, itself, is the best instance to learn how different temperature changes can provide various glassy states, altering from very slow rates occurring within geological time scales (e.g. obsidi...

Contemporary stained glass models were developed in this work using colourless float glass with luminescent glass threads or flecks, and painted with luminescent enamels. CO2 laser engraving was also used to explore the image effects on float glass coated with layers of luminescent glass.

The study of SiO2–MgO–Na2O glasses is of particular relevance because some compositions can exhibit adequate properties for their use in biomedical applications.The influence of substitution of divalent Mg2+ ions for monovalent Na+ in the structure of silicate glasses which contain 55mol% SiO2 was investigated by Magic-Angle Spinning (MAS) Nuclear...

Disordered matter still presents stringent conceptual difficulties. The often confused concepts of amorphous and glassy states (and corresponding material substances) were re-examined and previous attempts to trace a distinction are revised and thoroughly discussed. We examine several rheological and thermodynamical aspects of glasses in the glass...

Carta ao Editor: comentário ao artigo «As provas escritas de Química do Exame Nacional do Ensino Secundário do 12.º Ano de Escolaridade – 2006» publicado Química / Boletim da Sociedade Portuguesa de Química, Nº 102, Julho-Setembro 2006, pp. 15-21.

Impedance spectroscopy was used to monitor the non-isothermal crystallisation of a phosphate phase in bulk samples of a glass with the molar composition 0.45SiO2–0.36MgO–0.09K2O–0.1(3CaO⋅P2O5), intended for biomedical applications. The K+ alkali ions are probably the main charge carriers in glass of this composition. Impedance spectra were obtained...

Impedance spectroscopy was used to measure the changes of electrical properties during the isothermal crystallisation of the phosphate phase in bulk samples of a glass with nominal molar composition (3CaO⋅P2O5)20(SiO2)35(MgO)38.354(K2O)6.646, developed for biomedical applications. Crystallization studies were performed in isothermal conditions at 8...

We propose new theoretical models, which generalize the classical Avrami-Nakamura models. These models are suitable to describe the kinetics of nucleation and growth in transient regime, and/or with overlapping of nucleation and growth. Simulations and predictions were performed for lithium disilicate based on data reported in the literature. One r...

The European quest for the hard paste porcelain lasted until about 1710, when the first production unit was built at Meissen in Saxony. Although, it is generally believed that Bottger discovered the European porcelain technology, this work shows that the German porcelain quest was a State affair; a collective project directed by Tschirnhaus and sup...

An investigation on the crystallisation of a whitlockite type orthophosphate phase in a calcium phosphosilicate glass frit with the molar composition (3CaO.P2O5)20(SiO2)35(MgO)38.354(K2O)6.646 was made. Isothermal heat treatments at different temperatures combined with XRD and SEM analysis of the glass ceramics have shown that in glass frits of thi...

This work investigates the structure of phosphosilicate glasses from the SiO2-–MgO-–K2O-–3CaO.P2O5 system, as determined by 29Si and 31P MAS-NMR. According to the 29Si NMR, the actual network connectivity of the glasses generally exhibits a tendency for decreasing with increasing the alkali additive content. 31P NMR shows that the glass structure i...

Impedance spectroscopy is used to measure the changes in electrical properties during the crystallisation of a phosphate phase in a glass with nominal molar composition 0·45 SiO2.0·405 MgO.0·045K2O.0· (3CaO.P2O5) being developed for biomedical applications. The results show that changes in electrical resistivity can be used to monitor the onset of...

The kinetics of crystallization have been re-examined by taking into account the transient nucleation time and numerical methods were used to obtain the dependence of fraction crystallized on temperature, heating rate and nucleation conditions (temperature and time). These solutions were used to analyze the applicability of approximate models which...

The effects of nucleation temperature and time on the kinetics of non-isothermal glass crystallization have been re-examined to demonstrate the limitations of some approximate solutions used to extract kinetic parameters from differential thermal analysis (DTA) experiments. Those features were analyzed by numerical solutions of equations describing...

In this work glasses with nominal molar compositions 0.45SiO2–(0.45-x)MgO–xK2O–0.1(3CaO.P2O5) (x=0 and 0.09) were heat-treated according to adequate time-temperature schedules to obtain glass-ceramics (GCs) with phosphate phases. The GCs were immersed for different periods of time in SBF at 37ºC. The morphology, crystallinity, and adhesion of the a...

Differential thermal analyses of glass frits with nominal molar composition 0.45SiO2–0·405MgO–0.045K2O–0.1(3CaO·P2O5) showed two main exothermic peaks. X-ray diffraction was used to ascribe these peaks to the crystallisation of a whitlockite related phosphate phase Ca9MgK(PO4)7 at temperatures close to 900°C and mainly forsterite (Mg2SiO4) at highe...

Laboratory technique dealing with steel hardness for materials science and engineering education.

English title: Fermentation Dissolved Oxygen Control for Minimum Energy Consumption Abstract: A strategy for adaptive control and energetic optimization of aerobic fermentors was implemented, with both air flow and agitation speed as manipulated variables. This strategy is separable in its components: control, optimization, estimation. We optimiz...