Papers by Carlos Araújo Queiroz
Disordered matter still presents stringent conceptual difficulties. The often confused concepts o... more 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 transformation region as well as the dynamics of associated relaxation processes.
Bookmarks Related papers MentionsView impact
C. M. Queiroz, S. Agathopoulos, in: M. I. Prudêncio, M. I. Dias, Waerenborgh, J. C. (Eds), Understanding people through their pottery, Trabalhos de Arqueologia, N.º 42, Instituto Português de Arqueologia, Lisboa (Lisbon), 2005, 211-215 [ISSN: 0871-2581; ISBN: 972-8662-25-4]
The European quest for the hard paste porcelain lasted until about 1710, when the first productio... more 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 supported by August the Strong. It also aims to shed light to the reasons that led to Tschirnhaus's relative oblivion. Considering three distinct temporal stages, we re-examine the roles of the main contributors to the porcelain project, referring to the role of the Mercantilism system and to the philosophical roots of Tschirnhaus's method.
Bookmarks Related papers MentionsView impact
GLASSAC 11 / Glass science in art and conservation: Innovative technologies in glass art, design and conservation from the 19th to the 21st century - the role of the sciences, 10-12 May 2011, Ed. by Sabrina Rota and Katrin Wittstadt, pp. 99-100.
Contemporary stained glass models were developed in this work using colourless float glass with l... more 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.
Bookmarks Related papers MentionsView impact
Rosa Barovier and Cristina Tonini (Eds.), Study Days on Venetian Glass: Approximately 1600's; Instituto Veneto di Scienze, Lettere ed Arti; ATTI - Classe di Scienze Fisiche, Matematiche e Naturali (ISSN 0392-6680), CLXXII-I, 2013-2014, 177-181
Bookmarks Related papers MentionsView impact
C. M. Queiroz, M. H. V. Fernandes, J. R. Frade, in: P. M. Vilarinho (Ed.), Proc. of 'Materiais 2005 – III Int. Mater. Symp. and XII Portuguese Mater. Soc. Meeting', 2005, or: Materials Science Forum, Vols. 514-516 (2006), 1078-1082.
Impedance spectroscopy was used to monitor the non-isothermal crystallisation of a phosphate phas... more 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 as a function of temperature, following non-isothermal heat treatments at 2ºCmin-1. It is shown that suitable analysis of impedance spectra can be used to evaluate the crystallization peak of a orthophosphate phase, Ca9MgK(PO4)7. Results obtained by this method are comparable to those obtained by differential thermal analysis (DTA) of the corresponding glass frits. Impedance spectroscopy is thus suitable to study the crystallization of bulk samples, and can be used both with variable temperature and under isothermal conditions.
Bookmarks Related papers MentionsView impact
C. M. Queiroz, M. H. V. Fernandes, J. R. Frade, in: P. M. Vilarinho (Ed.), Proc. of 'Materiais 2005' – III Int. Materials Symposium and XII Portuguese Materials Society Meeting, University of Aveiro, 2005, or: Materials Science Forum, 514-516 (2006), 1073-1077.
Impedance spectroscopy was used to measure the changes of electrical properties during the isothe... more 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 800ºC and 860ºC, and were monitored by impedance spectroscopy. XRD shows that a stable orthophosphate phase, Ca9MgK(PO4)7 crystallizes at about 860ºC, after formation of earlier phosphate precursors formed at lower temperatures, namely oxyapatite (Ca5(PO4)3O) and tricalcium phosphate (Ca3(PO4)2). The conductivity of bulk glass samples decreases at 800ºC, as the phosphate precursors phases crystallize. The opposite trend is observed on crystallizing the orthophosphate phase, at 860ºC.
Bookmarks Related papers MentionsView impact
C. M. Queiroz, F. M. Figueiredo, M. H. Fernandes, J. R. Frade, Proc. VII Symp. on Crystallisation in Glasses and Liquids, Sheffield, 6-9 July 2003 / Part B: Physics and Chemistry of Glasses, 45(2) April 2004, 71-74.
Impedance spectroscopy is used to measure the changes in electrical properties during the crystal... more 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.0.1(3CaO·P2O5) being developed for biomedical applications. The results show that changes in electrical resistivity can be used to monitor the onset of crystallisation and the crystallisation peak in bulk samples.
Bookmarks Related papers MentionsView impact
C. M. Queiroz, J. R. Frade, M. H. V. Fernandes, in: M. A. Barbosa, F. J. Monteiro, R. Correia, B. Leon (Eds.), Proc. 16th Int. Symp. on Ceram. in Med. – Bioceramics, Vol. 16: Key Engineering Materials, 254-256 (2004), 155-158.
In this work glasses with nominal molar compositions 0.45SiO2–(0.45-x)MgO–xK2O–0.1(3CaO⋅P2O5) (x=... more 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 apatite layers thus formed are compared and discussed for the glasses and the GCs. Adhesion measurements were performed for the GCs using the scratch test technique. Distinct adhesion behaviours of the newly formed apatite layers to the substrate were observed when the GCs composition is K-free or when it contains K. Adhesion parameters for the apatite coating on the K-containing GCs showed to be affected by the immersion time in SBF but were not time dependent in the case of the K-free GCs.
Bookmarks Related papers MentionsView impact
Jorge R. Frade, Carlos M. Queiroz, Maria H. Fernandes, Journal of Non-Crystalline Solids, 333(3) 2004, 271-277.
The effects of nucleation temperature and time on the kinetics of non-isothermal glass crystalliz... more 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 the dependence of fraction crystallized on the rates of nucleation and growth, and the corresponding transient time, reported for lithium disilicate. It was shown that the temperature of maximum nucleation rate varies on changing the nucleation time. Some guidelines were established to assist the selection of suitable conditions to perform crystallization studies by DTA, and to extract the values of activation energy and dimensionality of growth from the dependences of crystallization peak temperature on heating rate, and nucleation time. The main limitations of these methods were identified and discussed.
Bookmarks Related papers MentionsView impact
Jorge R. Frade, C. M. Queiroz, M. H. Fernandes, Journal of Non-Crystalline Solids, 333(3), 2004, 263-270.
The kinetics of crystallization have been re-examined by taking into account the transient nuclea... more 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 were based on the assumption of steady state nucleation. The transient nucleation time, which precedes nucleation in as quenched samples, was taken into account to reexamine the deviations expected for relatively short nucleation time, and/or for cases when the actual nucleation temperature is displaced from the corresponding nucleation peak. Additional solutions were computed to obtain the dependence of crystallization peak temperature on the nucleation temperature. It was found that the crystallization peak temperature reaches its lowest value after nucleation at a temperature which can be significantly higher than the peak temperature of steady state nucleation.
Bookmarks Related papers MentionsView impact
C. M. Queiroz, M. H. Fernandes, J. R. Frade, in: Proc. of the II Inter. Mater. Symp. 'Materiais 2003' and 'XI Encontro da Sociedade Portuguesa de Materiais', Advanced Materials Forum II, Materials Science Forum, 455-456 (2004), 402-405.
An investigation on the crystallisation of a whitlockite type orthophosphate phase in a calcium p... more 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 this composition the whitlockite type orthophosphate phase, Ca9MgK(PO4)7 develops from earlier crystalline phosphate phase precursors, namely from oxyapatite (OAp), the ideal composition being Ca5(PO4)3O. This OAp phase seems to evolve from a previous tricalcium phosphate phase, Ca3(PO4)2 (TCP).
Bookmarks Related papers MentionsView impact
C. M. Queiroz, S. Agathopoulos, J. R. Frade, M. H. V. Fernandes, in: Proc. of the II Inter. Mater. Symp. 'Materiais 2003' and 'XI Encontro da Sociedade Portuguesa de Materiais', Advanced Materials Forum II, Materials Science Forum, 455-456 (2004), 383-387.
This work investigates the structure of phosphosilicate glasses from the SiO2-MgO-K2O-3CaO⋅P2O5 s... more 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 includes orthophosphate groups (PO43-) closer to Ca2+ ions than to Mg2+ ions, which are probably deeply inserted within the silicate network. Structural features were related with acellular bioactivity performance, in terms of in vitro capability of glass surface for inducing apatite mineralization in simulated body fluid. Needle-like apatite precipitates at the surface of the investigated bulk glass samples. A relatively flat and poorly crystallised hydroxyapatite (HAp) layer forms on the K-enriched glasses. For glasses without or with smaller K content, nearly amorphous octacalciumphosphate (OCP) seems to predominate over HAp. In this case apatite balls, built up from thin needles, are spread over the glass surface. Both the crystallinity degree and the thickness of the apatite precipitates, as observed by SEM, seem to evolve with increasing K content, consistently with the decrease in the average network connectivity detected by NMR.
Bookmarks Related papers MentionsView impact
C. M. Queiroz, M. H. Fernandes, J. R. Frade, in: M. D. Ingram (Ed.), Proc. of the XIX Int. Congr. on Glass, Edinburgh, Scotland, 1-6 July 2001, Society of Glass Technology and International Commission on Glass [ISBN 0 900682 39 6]: Physics and Chemistry of Glasses, Vol. 43C (2002) 281-285.
Differential thermal analyses of glass frits with nominal molar composition 0.45SiO2–0.405MgO–0.0... more 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 higher temperatures. The DTA phosphate peak was nearly independent of the particle size of frits and scanning electron microscopy suggests that Ca9MgK(PO4)7 crystallises in the bulk, mainly with plate like shape. The silicate peak was strongly dependent on the grain size suggesting surface crystallisation for the smaller particle sizes; this might be related to surface crystallisation of diopside in samples with small grain sizes as found by x-ray diffraction.
Bookmarks Related papers MentionsView impact
A. M. B. Silva, C. M. Queiroz, S. Agathopoulos, R. N. Correia, M. H. V. Fernandes, J. M. Oliveira, Journal of Molecular Structure, 986(1-3) 2011, 16-21.
The study of SiO2–MgO–Na2O glasses is of particular relevance because some compositions can exhib... more 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 55 mol% SiO2 was investigated by Magic-Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), Raman spectroscopy and Fourier Transformed Infrared Spectroscopy (FTIR), in both qualitative and quantitative basis. According to the results, the structure of the glasses predominantly comprised Q2 and Q3 structural species. In glasses with more than 25% molar MgO, the substitution of Na2O by MgO promotes a significant change in the main silicate chain through a disproportionation reaction 2Q2 = Q1 + Q3, while glasses with less than 20% molar MgO show no evidence of silicate chain modifications.
Information about the glass structure is of major importance for the understanding of the parameters that can control the biomedical properties, such as the chemical dissolution rate, pH and cell viability.
Bookmarks Related papers MentionsView impact
Book Chapters by Carlos Araújo Queiroz
Jaroslav Šesták, Carlos A. Queiroz, Jirı J. Mareš, Miroslav Holecek, Chap. 4 in: “Glassy, Amorphous and Nano-crystalline Material: Thermal Physics, Analysis, Structure and Properties”, Hot Topics in Thermal Analysis and Calorimetry, Vol. 8, Springer, 2011, pp. 59-75
The differences between amorphous and glassy state are discussed and the methods of their prepara... more The differences between amorphous and glassy state are discussed and the methods of their preparation reviewed. The role of crystallization during fast cooling is analyzed and nucleation-growth process is shown in two attitude models, which characterization are depicted on DTA curves. Specificity of non- and nano-crystalline metallic glasses is revealed.
Bookmarks Related papers MentionsView impact
Jaroslav Šesták, Carlos A. Queiroz and Bronislav Foller, Chapter 3 in: Dana Křemenáková, Rajesh Mishra, Jiří Militký, Jaroslav Šesták (key authors and Eds.), "Selected topics of textile and material science", Publishing House of WBU (West Bohemian University), Pilsen, 2011, pp. 53-75.
Bookmarks Related papers MentionsView impact
Carlos A. Queiroz, Jaroslav Šesták, in: Jaroslav Šesták, Miroslav Holeček, Jiří Málek, Dana Křemenáková (Eds.), "Thermodynamic, Structural and Behavioral Aspects of Materials Accentuating Non-crystalline States”, 2nd ed., 2011, pp. 8-28 (introductory chapter)
Please see the attached file (which refers to the 1st ed. of this book) for the outline of this c... more Please see the attached file (which refers to the 1st ed. of this book) for the outline of this chapter.
Bookmarks Related papers MentionsView impact
Carlos A. Queiroz, Jaroslav Šesták, in: Jaroslav Šesták, Miroslav Holeček, Jiří Málek (Eds.), “Some Thermodynamic, Structural and Behavioral Aspects of Materials Accentuating Non-crystalline States”, 2009, 8-28 (introductory chapter)
Please see the attached file for the index of this chapter.
Bookmarks Related papers MentionsView impact
Thesis by Carlos Araújo Queiroz
Carlos Manuel Gomes de Araújo Queirós, (Pre-Bologna) Master Thesis in Biotechnology (Biochemistry Engineering), Instituto Superior Técnico, Universidade Técnica de Lisboa (now: Universidade de Lisboa), Lisboa, 1997 (xvi+150pp). Submitted July 21, 1997; argued Sept. 11, 1997. In Portuguese.
A strategy for adaptive control and energetic optimization of aerobic fermentors was implemented,... more 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 optimized parameter’s estimation (from the usual KLa correlation) using sinusoidal excitation of air flow and agitation speed. We have implemented parameter’s estimation trough recursive least squares algorithm with forgetting factor. We carried separate essays on control, optimization and estimation algorithms. We carried our essays using an original computational simulation environment, with noise and delay generating facilities for data sampling and filtering.
Our results show the convergence and robustness of the estimation algorithm used, improved with use of both forgetting factor and KLa dead-band facilities. Control algorithm used in our work compares favorably with PID using the integrated area criteria for deviation between oxygen molarity and critical molarity (set point). Optimization algorithm clearly reduces energetic consumption, respecting critical molarity. Integration of control, optimization and adaptive algorithms was implemented, but future work is needed for stability. Methods were defined and implemented for stability improvement. We have implemented data acquisition and computer manipulation of air flow and agitation speed for actual fermentors.
Bookmarks Related papers MentionsView impact
Carlos Manuel Gomes de Araújo Queiroz, Ph.D Thesis in Science and Engineering of Materials, Universidade de Aveiro – Departamento de Engenharia Cerâmica e do Vidro, Aveiro, 2005 (xxviii + 270 pp).
We propose new theoretical models, which generalize the classical Avrami-Nakamura models. These m... more 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 re-examined the limitations of the models currently used to interpret DTA or DSC results, and to extract the relevant kinetic parameters.
Glasses and glass-ceramics with molar formulation 0.45SiO2(0.45-x)MgO–xK2O–0.1(3CaO⋅P2O5) (0 ≤ x ≤ 0.090) were prepared, crystallized and studied as potential materials for biomedical applications. Substitution of K+ for Mg2+ were used to prevent devritification on cooling, to adjust the kinetics of crystallization and to modify the in vitro behaviour of resulting biomaterials.
The crystallization of the glass frits was studied by DTA, XRD and SEM. Exothermic peaks were detected corresponding to bulk crystallization of whitlockite-type phosphate, Ca9MgK(PO4)7, at approximately 900ºC, and surface crystallization of a predominant forsterite phase (Mg2SiO4) at higher temperatures. XRD also revealed the presence of diopside (CaMgSi2O6) in some samples. The predominant microstructure of the phosphate phase is of the plate-type, seemingly crystallizing by a 2-dimensional growth mechanism. Impedance spectroscopy revealed significant changes in electrical behaviour, associated to crystallization of the phosphate phase. This showed that electrical measurements can be used to study the kinetics of crystallization for cases when DTA or DSC experiments reveal limitations, and to extract estimates of relevant parameters from the dependence of crystallization peak temperature, and its width at half height.
In vitro studies of glasses and glass-ceramics in acelular SBF media showed bioactivity and the development of apatite layers The morphology, composition and adhesion of the apatite layer could be changed by substitution of Mg2+ by K+. Apatite layers were deposited on the surface of glass-ceramics of the nominal compositions with x=0 and 0.09, in contact with SBF at 37ºC. The adhesion of the apatite layer was quantified by the scratch test technique, having been related with SBF’s immersion time, with composition and structure of the glass phase, and with the morphology of the crystalline phase of the glass-ceramics. The structure of three glasses (x = 0, 0.045 and 0.090) were investigated by MAS-NMR (29Si and 31P), showing that the fraction of Q3 structural units increases with the contents of Mg, and that the structure of these glasses includes orthophosphate groups (PO43-)preferentially connected to Ca2+ ions. Mg2+ ions show preference towards the silicate network. Substitution of Mg2+ by K+ allowed one to change the bioactivity. FTIR data revealed octacalcium phosphate precipitation (Ca8H2(PO4)6⋅5H2O) in the glass without K, while the morphology of the layer acquires the shape of partially superimposed hemispheres, spread over the surface. The glasses with K present a layer of acicular hidroxyapatite, whose crystallinity and needles thickness tend to increase along with K content.
Bookmarks Related papers MentionsView impact
Uploads
Papers by Carlos Araújo Queiroz
The influence of substitution of divalent Mg2+ ions for monovalent Na+ in the structure of silicate glasses which contain 55 mol% SiO2 was investigated by Magic-Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), Raman spectroscopy and Fourier Transformed Infrared Spectroscopy (FTIR), in both qualitative and quantitative basis. According to the results, the structure of the glasses predominantly comprised Q2 and Q3 structural species. In glasses with more than 25% molar MgO, the substitution of Na2O by MgO promotes a significant change in the main silicate chain through a disproportionation reaction 2Q2 = Q1 + Q3, while glasses with less than 20% molar MgO show no evidence of silicate chain modifications.
Information about the glass structure is of major importance for the understanding of the parameters that can control the biomedical properties, such as the chemical dissolution rate, pH and cell viability.
Book Chapters by Carlos Araújo Queiroz
Thesis by Carlos Araújo Queiroz
Our results show the convergence and robustness of the estimation algorithm used, improved with use of both forgetting factor and KLa dead-band facilities. Control algorithm used in our work compares favorably with PID using the integrated area criteria for deviation between oxygen molarity and critical molarity (set point). Optimization algorithm clearly reduces energetic consumption, respecting critical molarity. Integration of control, optimization and adaptive algorithms was implemented, but future work is needed for stability. Methods were defined and implemented for stability improvement. We have implemented data acquisition and computer manipulation of air flow and agitation speed for actual fermentors.
Glasses and glass-ceramics with molar formulation 0.45SiO2(0.45-x)MgO–xK2O–0.1(3CaO⋅P2O5) (0 ≤ x ≤ 0.090) were prepared, crystallized and studied as potential materials for biomedical applications. Substitution of K+ for Mg2+ were used to prevent devritification on cooling, to adjust the kinetics of crystallization and to modify the in vitro behaviour of resulting biomaterials.
The crystallization of the glass frits was studied by DTA, XRD and SEM. Exothermic peaks were detected corresponding to bulk crystallization of whitlockite-type phosphate, Ca9MgK(PO4)7, at approximately 900ºC, and surface crystallization of a predominant forsterite phase (Mg2SiO4) at higher temperatures. XRD also revealed the presence of diopside (CaMgSi2O6) in some samples. The predominant microstructure of the phosphate phase is of the plate-type, seemingly crystallizing by a 2-dimensional growth mechanism. Impedance spectroscopy revealed significant changes in electrical behaviour, associated to crystallization of the phosphate phase. This showed that electrical measurements can be used to study the kinetics of crystallization for cases when DTA or DSC experiments reveal limitations, and to extract estimates of relevant parameters from the dependence of crystallization peak temperature, and its width at half height.
In vitro studies of glasses and glass-ceramics in acelular SBF media showed bioactivity and the development of apatite layers The morphology, composition and adhesion of the apatite layer could be changed by substitution of Mg2+ by K+. Apatite layers were deposited on the surface of glass-ceramics of the nominal compositions with x=0 and 0.09, in contact with SBF at 37ºC. The adhesion of the apatite layer was quantified by the scratch test technique, having been related with SBF’s immersion time, with composition and structure of the glass phase, and with the morphology of the crystalline phase of the glass-ceramics. The structure of three glasses (x = 0, 0.045 and 0.090) were investigated by MAS-NMR (29Si and 31P), showing that the fraction of Q3 structural units increases with the contents of Mg, and that the structure of these glasses includes orthophosphate groups (PO43-)preferentially connected to Ca2+ ions. Mg2+ ions show preference towards the silicate network. Substitution of Mg2+ by K+ allowed one to change the bioactivity. FTIR data revealed octacalcium phosphate precipitation (Ca8H2(PO4)6⋅5H2O) in the glass without K, while the morphology of the layer acquires the shape of partially superimposed hemispheres, spread over the surface. The glasses with K present a layer of acicular hidroxyapatite, whose crystallinity and needles thickness tend to increase along with K content.
The influence of substitution of divalent Mg2+ ions for monovalent Na+ in the structure of silicate glasses which contain 55 mol% SiO2 was investigated by Magic-Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), Raman spectroscopy and Fourier Transformed Infrared Spectroscopy (FTIR), in both qualitative and quantitative basis. According to the results, the structure of the glasses predominantly comprised Q2 and Q3 structural species. In glasses with more than 25% molar MgO, the substitution of Na2O by MgO promotes a significant change in the main silicate chain through a disproportionation reaction 2Q2 = Q1 + Q3, while glasses with less than 20% molar MgO show no evidence of silicate chain modifications.
Information about the glass structure is of major importance for the understanding of the parameters that can control the biomedical properties, such as the chemical dissolution rate, pH and cell viability.
Our results show the convergence and robustness of the estimation algorithm used, improved with use of both forgetting factor and KLa dead-band facilities. Control algorithm used in our work compares favorably with PID using the integrated area criteria for deviation between oxygen molarity and critical molarity (set point). Optimization algorithm clearly reduces energetic consumption, respecting critical molarity. Integration of control, optimization and adaptive algorithms was implemented, but future work is needed for stability. Methods were defined and implemented for stability improvement. We have implemented data acquisition and computer manipulation of air flow and agitation speed for actual fermentors.
Glasses and glass-ceramics with molar formulation 0.45SiO2(0.45-x)MgO–xK2O–0.1(3CaO⋅P2O5) (0 ≤ x ≤ 0.090) were prepared, crystallized and studied as potential materials for biomedical applications. Substitution of K+ for Mg2+ were used to prevent devritification on cooling, to adjust the kinetics of crystallization and to modify the in vitro behaviour of resulting biomaterials.
The crystallization of the glass frits was studied by DTA, XRD and SEM. Exothermic peaks were detected corresponding to bulk crystallization of whitlockite-type phosphate, Ca9MgK(PO4)7, at approximately 900ºC, and surface crystallization of a predominant forsterite phase (Mg2SiO4) at higher temperatures. XRD also revealed the presence of diopside (CaMgSi2O6) in some samples. The predominant microstructure of the phosphate phase is of the plate-type, seemingly crystallizing by a 2-dimensional growth mechanism. Impedance spectroscopy revealed significant changes in electrical behaviour, associated to crystallization of the phosphate phase. This showed that electrical measurements can be used to study the kinetics of crystallization for cases when DTA or DSC experiments reveal limitations, and to extract estimates of relevant parameters from the dependence of crystallization peak temperature, and its width at half height.
In vitro studies of glasses and glass-ceramics in acelular SBF media showed bioactivity and the development of apatite layers The morphology, composition and adhesion of the apatite layer could be changed by substitution of Mg2+ by K+. Apatite layers were deposited on the surface of glass-ceramics of the nominal compositions with x=0 and 0.09, in contact with SBF at 37ºC. The adhesion of the apatite layer was quantified by the scratch test technique, having been related with SBF’s immersion time, with composition and structure of the glass phase, and with the morphology of the crystalline phase of the glass-ceramics. The structure of three glasses (x = 0, 0.045 and 0.090) were investigated by MAS-NMR (29Si and 31P), showing that the fraction of Q3 structural units increases with the contents of Mg, and that the structure of these glasses includes orthophosphate groups (PO43-)preferentially connected to Ca2+ ions. Mg2+ ions show preference towards the silicate network. Substitution of Mg2+ by K+ allowed one to change the bioactivity. FTIR data revealed octacalcium phosphate precipitation (Ca8H2(PO4)6⋅5H2O) in the glass without K, while the morphology of the layer acquires the shape of partially superimposed hemispheres, spread over the surface. The glasses with K present a layer of acicular hidroxyapatite, whose crystallinity and needles thickness tend to increase along with K content.
References:
[1] Jorge Custódio, A Real Fábrica de Vidros de Coina (1719-1747) e o Vidro em Portugal nos séculos XII e XVII. Ed. Instituto Português do Património Arquitectónico, Lisboa, Portugal, 2002
[2] António Pires de Matos, Carlos Queiroz, Filipa Lopes, Andreia Ruivo, Augusta Lima, Márcia Vilarigues, Glass colours at Marinha Grande by the last quarter of the 18th century, Annual Meeting of The Society of Glass Technology, Cambridge, September, 2009.
References
[1] C. Rüssel, Redox Behavior and Electrochemical Behavior of Glass Melts, in Propeties of Glass-Forming Melts, Edited by L. D. Pye, A. Montenero and I. Joseph, Taylor and Francis, 2005, 27-55.
[2] M. W. Medlin, K. D. Sienerth and H. D. Schreiber, J. Non Crystalline Solids, 1998, 240, 193-201.
[3] G. Gordoba, C. Caravaca, J. Electroanal. Chem., 2004, 572, 36-41.
References:
[1] Jorge Custódio, A Real Fábrica de Vidros de Coina (1719-1747) e o Vidro em Portugal nos séculos XII e XVII. Ed. Instituto Português do Património Arquitectónico, Lisboa, Portugal, 2002
[2] António Pires de Matos, Carlos Queiroz, Filipa Lopes, Andreia Ruivo, Augusta Lima, Márcia Vilarigues, Glass colours at Marinha Grande by the last quarter of the 18th century, Annual Meeting of The Society of Glass Technology, Cambridge, September, 2009.
Glasses and glass-ceramics with molar formulation 0.45SiO2–(0.45-x)MgO–xK2O–0.1(3CaO⋅P2O5) (0 ≤ x ≤ 0.090) were prepared, crystallized and studied as potential materials for biomedical applications. Substitution of K+ for Mg2+ were used to prevent devritification on cooling, to adjust the kinetics of crystalli zation and to modify the in vitro behaviour of resulting biomaterials.
The crystallization of the glass frits was studied by DTA, XRD and SEM. Exothermic peaks were detected corresponding to bulk crystallization of whitlockite-type phosphate, Ca9MgK(PO4)7, at approximately 900ºC, and surface crystallization of a predominant forsterite phase (Mg2SiO4) at higher temperatures. XRD also revealed the presence of diopside (CaMgSi2O6) in some samples. The predominant microstructure of the phosphate phase is of the plate-type, seemingly crystallizing by a 2-dimensional growth mechanism. Impedance spectroscopy revealed significant changes in electrical behaviour, associated to crystallization of the phosphate phase. This showed that electrical measurements can be used to study the kinetics of crystallization for cases when DTA or DSC experiments reveal limitations, and to extract estimates of relevant parameters from the dependence of crystallization peak temperature, and its width at half height.
In vitro studies of glasses and glass-ceramics in acelular SBF media showed bioactivity and the development of apatite layers The morphology, composition and adhesion of the apatite layer could be changed by substitution of Mg2+ by K+. Apatite layers were deposited on the surface of glass-ceramics of the nominal compositions with x=0 and 0.09, in contact with SBF at 37ºC. The adhesion of the apatite layer was quantified by the scratch test technique, having been related with SBF’s immersion time, with composition and structure of the glass phase, and with the morphology of the crystalline phase of the glass-ceramics. The structure of three glasses (x=0, 0.045 and 0.090) were investigated by MAS-NMR (29Si and 31P), showing that the fraction of Q3 structural units increases with the contents of Mg, and that the structure of these glasses includes orthophosphate groups (PO4 3-)preferentially connected to Ca2+ ions. Mg2+ ions show preference towards the silicate network. Substitution of Mg2+ by K+ allowed one to change the bioactivity. FTIR data revealed octacalcium phosphate precipitation (Ca8H2(PO4)6⋅5H2O) in the glass without K, while the morphology of the layer acquires the shape of partially superimposed hemispheres, spread over the surface. The glasses with K present a layer of acicular hidroxyapatite, whose crystallinity and needles thickness tend to increase along with K content.
Ficou demonstrada a robustez e a convergência do algoritmo utilizado na adaptação, especialmente com recurso conjugado a banda morta de KLa e factor de esquecimento. O algoritmo de controlo mostra-se favorável relativamente ao PID segundo o critério da área integrada de desvio da molaridade de oxigénio face à molaridade crítica (ponto de ajuste). O algoritmo de optimização reduz significativamente o consumo energético, respeitando a molaridade de oxigénio crítica. A integração dos algoritmos de controlo, optimização e adaptação, encontra-se implementada. Requer trabalho futuro de estabilização, mediante métodos definidos e implementados. Implementou-se aquisição de dados e manipulação de variáveis para fermentações reais.