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Neutron diffraction with magnesium isotope substitution, high energy x-ray diffraction, and 29Si, 27Al, and 25Mg solid-state nuclear magnetic resonance (NMR) spectroscopy were used to measure the structure of glassy diopside (CaMgSi2O6), enstatite (MgSiO3), and four (MgO) x(Al2O3) y(SiO2)1−x−y glasses, with x = 0.375 or 0.25 along the 50 mol. % silica tie-line (1 − x − y = 0.5) or with x = 0.3 or 0.2 along the 60 mol. % silica tie-line (1 − x − y = 0.6). The bound coherent neutron scattering length of the isotope 25Mg was remeasured, and the value of 3.720(12) fm was obtained from a Rietveld refinement of the powder diffraction patterns measured for crystalline 25MgO. The diffraction results for the glasses show a broad asymmetric distribution of Mg–O nearest-neighbors with a coordination number of 4.40(4) and 4.46(4) for the diopside and enstatite glasses, respectively. As magnesia is replaced by alumina along a tie-line with 50 or 60 mol. % silica, the Mg–O coordination number increases with the weighted bond distance as less Mg2+ ions adopt a network-modifying role and more of these ions adopt a predominantly charge-compensating role. 25Mg magic angle spinning (MAS) NMR results could not resolve the different coordination environments of Mg2+ under the employed field strength (14.1 T) and spinning rate (20 kHz). The results emphasize the power of neutron diffraction with isotope substitution to provide unambiguous site-specific information on the coordination environment of magnesium in disordered materials.

An electron paramagnetic resonance (EPR) study has been carried out on the hybrid layered nanocomposite formed by TiO2 and myristic acid. The samples were characterized by means of X-ray diffractio...

It is crucial to control the tuning and improve the emission of a quantum emitter at the nanoscale. We report multiple Fano resonances in metallic nanostructures on an Er3+-doped tellurite glass. Periodic nanoslits were fabricated with a focused gallium ion beam on a gold thin film deposited on the tellurite glass. Is proposed a coupling function with Fano line-shape form, and the asymmetric parameter q for each resonance wavelength in the 515 to 535 nm region was calculated. This asymmetric resonance effect is a consequence of the quantum interaction between the continuum state, generated in the nanostructure, and the Stark splits of the $$^2$$ 2 H$$_{11/2}$$ 11 / 2 state.

The melt-quenching method was used to synthesize a series of neodymium-doped zinc tellurite glass systems. The ultrasonic velocities, elastic moduli and other elastic parameters of the prepared glasses showed non-linear variations with an increase of Nd2O3 in the glass system. The non-linear variation is associated with the presence of non-bridging and bridging oxygen caused by the network modifier of Nd2O3. Theoretical data sets for the elastic properties of the glass systems were obtained by using the Makishima and Mackenzie theory and the Rocherulle, bond compression and ring deformation models. The values retrieved for the elastic moduli by using the Makishima and Mackenzie, and Rocherulle models are in great agreement with the corresponding experimental data. The recorded bond compression model data for the glass has much higher values for elastic moduli when compared to the corresponding experimental values. Therefore, in this glass system, only the bond compression model is not favoured.

Network former mixing (NFM) effects on ionic conductivities have been characterized in ternary germanotellurite glasses of composition (A2O)0.3[(TeO2)x(GeO2)1-x]0.7 (A = Li, Na), revealing an interesting cation dependence. While the results demonstrate a weak positive NFM effect in the Li-containing system, the electrical conductivities of the Na-containing systems correspond to the weighted average values observed in their binary endmembers. The structural origins of these differing effects have been explored by Raman scattering and 125Te solid-state NMR spectroscopy, indicating no significant differences in the structural organization of these materials. Overall, the data suggest that the concentration of heteroatomic connectivities is relatively low. For the Li-containing system, an analysis of the motional narrowing effects observed in temperature-dependent static 7Li NMR spectra confirms the existence of a weak positive NFM effect at the local atomic level. Accordingly, the absence of an NFM effect for the Na-containing system is corroborated by low-temperature 23Na spin-echo decay spectroscopy, showing very similar network modifier distributions in those glasses.

In this work, fluorophosphate glass samples with the composition 35NaPO3-30Ba(PO3)2-25MgF2-(10- x)YF3–x[EuF3 or Dy2O3] with x = 0–4.0 mol% EuF3, or x = 0–1.0 mol% Dy2O3, were fabricated by the melt quenching technique. The glasses were characterized from the structural, thermal and optical-spectroscopic points of view. Emission spectra were measured in the visible range upon UV excitation. Luminescence decay curves were registered by monitoring the most intense emissions of Eu3+ (5D0→7F2) and of Dy3+ (4F9/2→6H13/2) in the red and green, respectively, and from them the average lifetime values of the excited states 5D0 of Eu3+ (2.5 ms) and 4F9/2 of Dy3+ (0.71 ms) were determined. Emission spectra measured under variable excitation power yielded calibration curves for Eu3+ and Dy3+-doped glasses. The response to X-ray excitation was evaluated through radioluminescence measurements. The results indicate the promising application of these glasses in scintillators and for X-ray sensing devices.

This work investigates the influence of transition metals oxides (Ta2O5 and ZrO2) on the nonlinear refraction of niobium-borotellurite glasses prepared by melt-quenching technique. The closed-aperture Z-scan technique was used to measure the nonlinear refractive index (n2) spectrum from 470 nm to 800 nm. Also, the BGO (Boling, Glass, and Owyoung) approach was used to model nonlinear spectra, considering the oxygens present in the sample as the major contribution to the nonlinearity. The samples’ molar electronic polarizability was determined to further understanding the effect of the transition metals oxides on the optical properties. Structural analysis was performed by differential scanning calorimetry, Raman and Infrared spectroscopies. The results indicate that although the modifier oxides affect the structural units and glass polarizability, they are not enough to change the behavior of the nonlinear refractive index spectra, being the glass-matrix the main responsible for optical nonlinearity in the system studied here.

[EN] By the first time the correlation between glass stability (GS), activation energy for crystallization (E) and structural data was investigated for some TiOdoped CaO-SrO-BO-SiO glasses obtained from the same batch. B NMR spectra demonstrated that the boron changes from tetragonal to trigonal configuration for TiO contents higher than 4 mol%, while the Si NMR spectra showed the absence of Q species, in addition to an increase in Q at the expense of Q units. Both observations are consistent with Ti acting as a network modifier. It was demonstrated that all these glasses crystallize mainly from the surface, and the crystal growth changes with the TiO content. Most of the GS parameters increase with the TiO content, while E decreases for larger TiO contents. This dramatic reduction in E is strongly correlated to the change in the role of Ti cation in the glass matrix., The authors are indebted to the Maranh ̃o Foundation for Scientific Research and Development (FAPEMA), Processes # 2014/01469, #2014/00260 and # 2015/00773. MVSA and GVPB also thank the cholarships of the Federal Agency for the Support and Improvement of Higher Education (CAPES). JFS acknowledges financial support from FAPESP (grant CEPID 2013/07793-6) and CNPq (grant 311520/2018-9). We are grateful to Benjamin J.A. Moulton for his valuable suggestions.

Glasses in the ternary xLi2O + (33-x)CaO + 67B2O3 tetraborate system, with x = 0, 5, 10, 15, 20, 25, 30 and 33 mol%, were prepared by melting and casting. The glass structure, and thermal, and electrical response of highly transparent and homogeneous glasses were evaluated by X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), Fourier Transform Infrared Spectroscopy (FTIR) and Impedance Spectroscopy (IS). The glass transition temperature (Tg) decreases as CaO is substituted by Li2O (increasing x), while the thermal stability against crystallization to the supercooled liquid in the region Tg

Optical thermometry via luminescence intensity ratio (LIR) is often explored in the visible spectrum range of trivalent rare earth doped materials but much less so in the near infrared region. This work range, which can be explored in Nd3+ and Yb3+ doped materials, overlaps with the first and second biological window thus making these thermometers interesting for bio applications. In this work, proof of concept is given by developing highly sensitive optical thermometers based on Nd3+-singly doped and Nd3+/Yb3+-co-doped fluorophosphate glasses with superior optical properties than phosphate and fluoride glasses. The developed systems offer the possibility of simultaneously using two LIR as thermometric parameters with high measurement accuracy, in wide temperature ranges. The Nd3+-based thermometer operating via three energy level sets emitting in the 730–950 nm range has relative sensitivities spanning from 1.7% K−1 (at room temperature) to 0.6% K−1 (at 520 K). The Nd3+/Yb3+ system presents, in addition to the use of Nd3+ transitions LIR, a new possibility of temperature detection up to 520 K. A decreased intensity of the zero-phonon line of Yb3+ at 975 nm was detected and used by comparison to the Nd3+ emission around 800 nm, resulting in relative sensitivities of ~2% K−1 at room temperature.

Eu3+-, Er3+-doped and Er3+/Yb3+-codoped niobium alkali germanate glasses, in the compositional host system GeO2-Nb2O5-K2O were synthesized by the conventional melt-quenching technique. Glass-ceramics were manufactured by controlled heat treatment of the precursor glasses. Homogeneous glasses and nanocrystalline glass-ceramics were investigated by DSC, XRD, TEM and spectroscopic analysis. K2Nb14O36 crystals are formed in the prepared glass-ceramics. This crystalline phase has low phonon energy as compared to the precursor glass and a variety of chemical sites for rare-earth ions. In glass-ceramics, the rare-earth ions occupy higher symmetry sites of the K2Nb14O36 nanocrystals resulting in inhomogeneous broadband emissions. Judd-Ofelt parameters were obtained for the Eu3+- and Er3+-doped samples. Glass-ceramics heat-treated for 20 h exhibited the highest photoluminescence quantum efficiency. The increased quantum efficiency is due to the decrease of nonradiative decay processes, that depopulate the excited levels, as well as the decrease in hydroxyl content and overall phonon energy. However, luminescence quenching is verified for samples with longer crystallization times, which emphasizes the importance of optimized heat treatment parameters. The gain coefficient and upconversion data were obtained and corroborate the potential application of these materials as photonic devices, such as visible and NIR laser and optical amplifiers.

Borosilicate glass samples singly- and co-doped with Er3+ and ZnSe, were obtained via the melt quenching technique. Structural and morphological characterization confirmed the formation of ZnSe nanoparticles (NPs) during glass preparation. The glassy samples present the characteristic absorption bands of the respective species. Optical band gap values indicate quantum confinement effect in ZnSe-doped glasses. Excitation spectra of the co-doped glasses also display the characteristic bands of both ZnSe and Er3+. Intensity depleted regions at 377 and 521 nm observed in the excitation band of ZnSe indicate absorption by Er3+, that is, energy transfer from the ZnSe NPs to Er3+ ion. Upon excitation at 367, 447 and 498 nm, ZnSe doped glasses give broad emission bands centered around 696 nm. This reveals a broad multiple-band structure due to the overlap of emissions from NPs (electron-hole recombination) and from defect to traps, formed owing to Se and Zn vacancies. The Er3+-doped glasses display green (526 and 550 nm) and NIR (1530 nm) emissions when excited at 377 nm. The co-doped glasses show emission bands of both Er3+ and ZnSe. When compared to ZnSe and Er3+ singly doped glasses, a decrease is observed in the overall red emission while the green and NIR emissions from Er3+ increase. The intensity enhancement of Er3+ emissions increase with increasing ZnSe content which is attributed to the energy transfer from ZnSe NPs to Er3+. It was also observed that the color of the emitted light from the co-doped glasses, changes with change in excitation slit width.

Made available in DSpace on 2021-06-25T10:21:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-25 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Glass-ceramics containing rare earth gallium garnets were obtained using glass compositions as reactional medium. This work reports on the synthesis, and structural, morphological, and optical characterizations of Er3+ and Tm3+-doped Yb3Ga5O12 crystals prepared from controlled cooling of heavy metal oxide glass melts. Micrometric cubic crystals were obtained by controlling the cooling of a rare earth-supersaturated glassy composition melted at high temperature. Crystals with sizes ranging between 5 and 150 µm were formed into the glass matrix. A gallium garnet phase corresponding to space group Ia-3d was identified by X-ray diffraction and confirmed by Rietveld simulations. The morphology of crystals was studied by optical and scanning electron microscopies, while chemical elements were mapped by electron dispersive X-Ray spectroscopy. The glass phase was studied by XRD, thermal analysis and Raman spectroscopy. The optical properties of both glass and glass-ceramic materials were evaluated by UV–Vis and luminescence spectroscopies. Micro-luminescence measurements confirmed that rare earths were incorporated into the crystalline phase. Intense upconversion emissions of Er3+ (550 and 660 nm) and Tm3+ (800 nm) were observed when the glass-ceramics were pumped at 980 nm. These new glass-ceramics are excellent candidates for the development of photonic devices. Institute of Chemistry – São Paulo State University – UNESP São Carlos Institute of Physics University of São Paulo University of Bordeaux CNRS ICMCB UPR 9048 University of Bordeaux CNRS ISM UPR 5803 Institute of Chemistry – São Paulo State University – UNESP FAPESP: 2013/07793-6 FAPESP: 2019/01223-0 CNPq: 502391/2014-6

International audience; In this report, Ti3+, 4+/Eu2+, 3+ co-doped OH− free low silica calcium aluminosilicate glasses (LSCAS) were synthesized and their optical properties investigated aiming applications as phosphors for white light generation. This research explores the possibility of combining the broad emission bands in the visible of these glasses co-doped with Ti3+,4+/Eu2+ ions with those in the red emitted by Eu3+, in addition to the high luminescence quantum yield they present. The excitation and emission results show that exciting the samples at 300 nm, a broad emission band is generated, embracing very well the visible region. The emission spectra were analyzed by (x-y) CIE-1931 chromaticity diagram and the color rendering index (CRI) presented Ra values up to 80, with the correlate color temperature (CCT) varying from 4995 to 6609 K. The luminescence quantum yield determined by Thermal Lens Spectroscopy showed values of 38 and 42% for the samples with (in wt%) 0.1Eu2O3-2.0TiO2 and 0.5Eu2O3-2.0TiO2, respectively. Finally, the energy transfer processes between these luminescent ions were discussed, highlighting the potential of the Eu–Ti LSCAS glasses as candidates for the development of devices for white light generation.

At the present time there is no doubt that almost every country is experiencing a revolutionary change in the used devices for artificial lighting whether for public, for domestic or for work place illumination. This movement is taking place towards the substitution of fluorescent lamps to LED-phosphor based devices under the justification of reduction in energy consumption and mitigation of the contamination of environment produced by the mercury of fluorescent lamps. In this aspect, despite of the great effort of worldwide scientists to obtain a white lighting source with the emitting spectrum similar to that of the sunlight, it is recognized that there is still a challenge to be faced of getting luminescent materials with broad band excitation in the UV–Vis regions and large emission in the visible in order to allow tunable white lighting generation. Motivated by this interest, in this paper, Eu2+,3+/Pr3+ co-doped calcium aluminosilicate glasses were synthesized and spectroscopically investigated aiming at the development of smart white lighting devices. A prototype was developed to study the sample with excitation at 445 nm light emission diode (LED). The results indicate high color rendering index (CRI Ra ∼92–95) and tunable correlated color temperature (CCT from 5700 to 6600 K), covering the whole spectral daylight range. By using a second 405 nm LED together with the 445 nm one, the calculated Du’v’ values are suitable for indoor illumination. In this configuration, by adjusting the LEDs intensities it is possible to tune the CCT close to the white lighting region with CRI Ra nearly 95. These characteristics demonstrate that the Eu2+,3+/Pr3+ co-doped OH− calcium aluminosilicate glass is a strong candidate for smart white lighting with LEDs.

The fluorine motional dynamics in fluorosilicate glasses and glass-ceramics of the SiO2–PbF2–CdF2 system was investigated by complex impedance spectroscopy and 19F nuclear magnetic resonance (NMR) spectroscopy, and the coordination environment of a Cu2+ paramagnetic probe was examined by electron paramagnetic resonance (EPR) spectroscopy. Glass-ceramics were obtained by heat treatment of glass at a temperature between the glass-transition (Tg) and the onset of crystallization (Tx). Ionic conductivity of about 1.6 × 10–4 S/cm was obtained at 500 K for glass. The conductivity of the glass-ceramics was found to be lower than that obtained for the glass. The temperature dependence of the 19F NMR spin–lattice relaxation times was investigated between 300 and 770 K. The 19F NMR results of glass exhibit the qualitative features associated with fluorine mobility, namely, the presence of a relaxation rate maximum below Tg. The NMR relaxation data of the glass-ceramics were analyzed assuming two fluorine dynamics. ...

Mixed-network former effects upon glass transition temperatures, densities and electrical conductivities have been studied in glasses in the system (Na 2 O) 1/3 [(2TeO 2 ) x (B 2 O 3 ) 1 − x ] 2/3 . Mixing of network formers B 2 O 3 and TeO 2 has a negative effect on ionic conductivities. Possible structural origins of this behavior have been studied by 11 B, 23 Na, and 125 Te high-resolution and dipolar solid state nuclear magnetic resonance (NMR) techniques, O-1s X-ray photoelectron spectroscopy and Raman spectroscopy. A quantitative structural model has been developed that is consistent with all of the experimental data, and provides a detailed description of network modification processes, interactions and connectivities. All the O-1s XP spectra can be satisfactorily fitted with two line shape components with the parameters of the binary end-member glasses, providing no evidence for the possible formation of B–O–Te linkages. In addition, none of the 125 Te and 11 B NMR data shows significant proof of such linkages, even though their formation cannot be explicitly excluded. 23 Na NMR data indicate a monotonic chemical shift trend consistent with proportional sharing of the network modifier between the two network former species. The experimental data suggest a tendency towards an avoidance of B–O–Te linkages, even though no macroscopic phase separation is observed. Nevertheless, the negative mixed network former effect can be rationalized in terms of compositionally segregated sodium borate and sodium tellurite nano-domains.

Niobium alkali germanate glasses were synthesized by the melt-quenching technique. The ternary system (90-x)GeO2-xNb2O5-10K2O forms homogeneous glasses with x ranging from 0 to 20mol%. Samples were investigated by DSC and XRD analysis, FTIR and Raman spectroscopy, and optical absorption. Structural and physical features are discussed in terms of Nb2O5 content. The niobium content increase in the glass network strongly modifies the thermal, structural and optical properties of alkali germanate glasses. DSC, Raman and FTIR analysis suggest niobium addition promotes NbO6 groups insertion close to GeO4 units of the glass network. XRD analysis also pointed out that samples containing high niobium oxide contents exhibit preferential niobium oxide rich phase after crystallization after heat treatment, which is similar to orthorhombic Nb2O5. Absorption spectra revealed high transmission range between 400nm to 6.2μm, added to a considerably decreased hydroxyl group content as the addition of niobium in the alkali germanate network. The niobium oxide rich phase crystallization process was studied and activation energy was determined, as well as nucleation and crystal growth temperatures and time for obtaining transparent glass-ceramics. This article is protected by copyright. All rights reserved.

This paper reports a study on linear and nonlinear optical properties in a series of lithium‑calcium tetraborate (CaLiBO) glasses in the presence of two rare earth ions, Tb3+ and Yb3+. The nonlinear index of refraction (n2) was determined in a wide wavelength range (470–1500 nm) through femtosecond Z-scan technique. Such results were modeled by BGO approach, in which the optical nonlinearity was related to the oxygens present in the glasses. Also, the molar electronic polarizability evidenced that there is a strong influence of the polarizability of the rare earth ions in the nonlinear optical properties. Thus, we can infer that the cooperation of oxygens and the polarizability of rare earth ions are responsible for the nonlinearity present in the investigated vitreous system.

Made available in DSpace on 2018-12-11T16:59:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-02-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Physicochemical characteristics of a biomaterial directly influence its biological behavior and fate. However, anatomical and physiological particularities of the recipient site also seem to contribute with this process. The present study aimed to evaluate bone healing of maxillary sinus augmentation using a novel bioactive glass ceramic in comparison with a bovine hydroxyapatite. Bilateral sinus augmentation was performed in adult male rabbits, divided into 4 groups according to the biomaterial used: BO—particulate bovine HA Bio-Oss® (BO), BO+G—particulate bovine HA + particulate autogenous bone graft (G), BS—particulate glass ceramic (180–212 μm) Biosilicate® (BS), and BS+G—particulate glass ceramic + G. After 45 and 90 days, animals were euthanized and the specimens prepared to be analyzed under light and polarized microscopy, immunohistochemistry, scanning electron microscopy (SEM), and micro-computed tomography (μCT). Results revealed different degradation pattern between both biomaterials, despite the association with bone graft. BS caused a more intense chronic inflammation with foreign body reaction, which led to a difficulty in bone formation. Besides this evidence, SEM and μCT confirmed direct contact between newly formed bone and biomaterial, along with osteopontin and osteocalcin immunolabeling. Bone matrix mineralization was late in BS group but became similar to BO at day 90. These results clearly indicate that further studies about Biosilicate® are necessary to identify the factors that resulted in an unfavorable healing response when used in maxillary sinus augmentation. Department of Dentistry Endodontics and Dental Materials Bauru School of Dentistry University of São Paulo – FOB/USP, Al. Octávio Pinheiro Brisola, 9-75 Oral Biology Master’s Program Sagrado Coração University – USC, Rua Irmã Arminda 10-50 Oral Biology Doctoral’s Program Bauru School of Dentistry University of São Paulo – FOB/USP, Al. Octávio Pinheiro Brisola, 9-75 Department of Bioscience Federal University of Sao Paulo, Campus Baixada Santista – UNIFESP, Avenida Ana Costa, 95 Department of Basic Sciences Araçatuba School of Dentistry São Paulo State University FOA/UNESP, Rua José Bonifácio 1193 Oral Biology Doctoral’s Program Sagrado Coração University USC CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) Department of Basic Sciences Araçatuba School of Dentistry São Paulo State University FOA/UNESP, Rua José Bonifácio 1193 FAPESP: 2008/11485-8; 2009

Mechanical and tribological properties of a partially crystallized sintered glass-ceramic were compared to two commercial floor tiles: black granite and porcelainized stoneware. Mechanical properties, hardness and elastic modulus were evaluated by instrumented indentation. Friction coefficient and wear characterization were evaluated using a reciprocating ball-on-flat tribometer in two controlled environments: air with relative humidity of 53% and under running water at 23 °C. The sintered glass-ceramic and porcelainized stoneware presented similar mechanical and tribological properties. Regarding the mechanical and tribological properties, the results suggest that this glass-ceramic is suitable to be used as industrial tile.

Relatório de projecto Programa Operacional Ciência e Inovação 2010 Relatório de estágio realizado na FEUP orientado pela Drª Anabela Gregório Dias

Mestrado em Ciência e Engenharia de Materiais A mineralização em meio acelular de vidros e vidros cerâmicos está relacionada com a capacidade de formação de uma camada apatitica à sua superfície. Vidros e vidros cerâmicos apresentam diferenças significativas na formação dessa camada, estando estas intimamente ligadas a diferenças na respectiva reactividade superficial. A reactividade superficial, por sua vez, está relacionada com a taxa de dissolução do vidro e com a natureza e quantidade de fases cristalinas presentes no vidro cerâmico. Neste trabalho estudou-se o comportamento de vidros e correspondentes vidros cerâmicos, quando imersos em fluidos fisiológicos sintéticos. As amostras em estudo foram seleccionadas no sistema 3CaO.P2O5-SiO2-MgO e preparadas a partir de Ca(H2PO4).H2O, CaCO3, SiO2 e MgO. Algumas foram sujeitas a tratamentos térmicos adicionais para obter vidros cerâmicos. Testes de imersão em meio acelular foram realizados, tanto nos vidros como nos vidros cerâmicos, usando a solução de fluido fisiológico sintético de Kokubo (SBF) e tempos de ensaio até 30 dias. A análise por DRX evidenciou a natureza amorfa do vidro enquanto que os vidros cerâmicos apresentam adicionalmente duas fases cristalinas distintas, um fosfato de cálcio e magnésio e um silicato de magnésio. A observação da microestrutura por microscopia electrónica de varrimento (SEM) permitiu distinguir claramente as fases cristalinas da fase amorfa, e diferenciar com alguma dificuldade as fases cristalinas entre si. A observação em SEM com espectroscopia de dispersão de energia das amostras após imersão em SBF permitiu identificar uma camada apatítica sobre as suas superfícies, rapidamente formada no vidro e mais lentamente nos vidros cerâmicos. A técnica de microscopia electrónica de varrimento constitui uma ferramenta indispensável, quer no acompanhamento do processo de cristalização de vidros quer na avaliação da reactividade superficial dos vidros e vidros cerâmicos, fundamental para a compreensão do processo de mineralização desses materiais. Procurou-se utilizar a microscopia de força atómica para complementar os estudos in vitro; os resultados obtidos sustentaram as observações feitas por SEM. ABSTRACT: The mineralization of glasses and glass-ceramics in an acellular medium is related with the ability to form an apatite layer on their surfaces. Glassceramics and glasses have significant differences in the formation of this layer due to distinct surface reactivities. The surface reactivity is related with the rate of glass dissolution and with the nature and amount of crystalline phases in the glass-ceramics. In this work the behaviour of glasses and corresponding glass-ceramics in simulated body fluid has been studied. The samples with compositions in the 3CaO.P2O5-SiO2-MgO system were prepared from reagent grade Ca(H2PO4).H2O, CaCO3, SiO2 and MgO. Some samples were submitted to additional heat treatments to obtain glassceramics. Immersion tests in an acellular medium have been carried out using the Kokubo’s simulated body fluid (SBF) with incubation times up to 30 days. XRD analysis confirmed the amorphous nature of the glass while the glassceramic exhibited additionally two distinct crystalline phases, a calcium magnesium phosphate and a magnesium silicate. SEM observation of microstructures allowed to distinguish the amorphous phase from the crystalline phases, although these were difficult to differentiate between themselves. SEM and EDS analysis of the samples after immersion in SBF showed an apatite layer on their surfaces, which formed fast on the glass and more slowly on the glass-ceramics. SEM technique revealed to be a powerful tool to follow the crystallization process of glasses and to evaluate the surface reactivity of glasses and glassceramic, essential for the understanding of the mineralization process of these materials. Atomic Force microscopy was used to complete the in vitro tests, results obtained by this technique confirmed the results obtained in the SEM observations.

Mestrado em Engenharia de Materiais Este relatório descreve o trabalho desenvolvido no estágio realizado na unidade industrial da Vista Alegre S.A., Ílhavo, produtora de porcelana dura. O objetivo do estágio foi identificar a origem e corrigir uma variação de tonalidade no vi-drado preto brilhante observada durante a cozedura. No decorrer do estágio foi analisado um outro problema, com o vidrado branco mate, que apresentava um ligeiro brilho. Caracterizou-se o pigmento preto realizando vários ensaios entre os quais uma análise granulométrica. Esta permitiu observar que a maioria das partículas tem um tamanho inferior a 2 μm. Noutros ensaios, fizeram-se difrações de raios X ao pigmento em cru e após tratamento térmico em diferentes atmosferas, para se ver qual a influência que esta tem no comportamento do pigmento. O pig-mento é composto por NiFe2O4 e apresenta reação na presença de sílica. Quando a atmosfera é redutora, aparece níquel metálico. Realizaram-se en-saios em vidrados com diferentes quantidades de pigmento (de 3 a 8% em massa) e observou-se que a redução na quantidade de pigmento faz com que o vidrado adquira uma cor esverdeada, resultante, possivelmente, da dissolução parcial do pigmento na fase vítrea, que pode ser favorecida pelo reduzido tama-nho das partículas. Foram feitos ensaios para se ver qual a evolução dos vidrados com a tempera-tura. O resultado destes ensaios permitiu verificar que o pigmento preto retarda o desenvolvimento do vidrado. Recorrendo-se a caracterizações microscópicas, nomeadamente SEM e EDS (acoplado ao SEM), foi possível observar o desen-volvimento dos vidrados brancos mate, verificando-se que a cristalização só ocorre acima de 1300 °C. Com base nestes resultados e com o intuito de melhorar as características dos vidrados foram feitas três curvas de cozedura. As diferentes cozeduras permiti-ram concluir que a quantidade de pigmento preto utilizada no vidrado deveria aumentar e desse modo aumentar também o tempo de cozedura (patamar) para que o desenvolvimento do vidrado fosse completo. O vidrado branco mate ne-cessita apenas de um prolongamento no patamar de temperatura máxima. Con-cluiu-se que as variações no vidrado preto brilhante estão associadas à dissolu-ção parcial do pigmento e a um tempo de cozedura reduzido. O estágio serviu, também, para adquirir um conhecimento prático do funciona-mento de uma empresa, ao permitir acompanhar o processo produtivo desde a criação dos moldes até à escolha final da louça, compreender e visualizar a uti-lização dos diversos métodos de conformação das peças, assim como os dife-rentes métodos de aplicação de vidrados, até aos de aplicação de decoração. Este estágio permitiu ainda observar e participar na resolução de pequenos pro-blemas na produção diária da empresa. This report describes the work carried out during the internship at the industrial unit Vista Alegre S.A., Ílhavo, which produces continental porcelain. The objec-tive of the internship was to identify the origin and to correct a tonality variation observed during firing of the bright black glaze. During the internship, another problem related to the brightness of a matte white glaze was also investigated. The black pigment was characterized in several tests, among which a granulo-metric analysis. This allowed to observe that most of the particles have a size smaller than 2 μm. Other tests, namely X-ray diffraction analysis, were carried out on the pigment before and after thermal treatment under different atmos-pheres in order to see the atmosphere influence on the pigment behavior. The pigment is composed by NiFe2O4 and only reacts in the presence of silica. When fired under a reducing atmosphere, metallic nickel was detected. Tests were car-ried out on glazes with different pigment contents (from 3 to 8 wt. %) and it was observed that decreasing the pigment content leads to greenish coloration, likely due to the partial dissolution of the pigment in the vitreous phase, which can be promoted by low particle size. Some tests were performed in order to understand the glaze development with temperature. The results showed that the black pigment delays the glaze devel-opment. Through microscopic characterization, namely SEM and EDS (coupled to SEM) analysis, it was possible to observe the development of the matte white glazes, in which crystallization only occurs above 1300 °C. Based on these results, three firing curves were made aimed at improving the glazes characteristics. The different firings showed that the content of black pig-ment used in the glaze should be increased as well as the dwell time during firing in order to ensure that the glaze development is complete. In the case of the matte white glaze, the results demonstrated that the dwell time must be longer. It was also concluded that the changes observed in the bright black glaze are associated with the partial dissolution of the pigment and with the short firing time. The internship also provided a practical knowledge about the production process of the company, which was followed from the molds production to the final ware sorting. Seeing the various shaping methods available, as well as the different glaze application and decoration methods, was helpful to understand them. Fur-thermore, this internship was also the opportunity to closely follow the company daily routine and allowed the participation on the resolution of the small day-to-day production problems.

Tese de doutoramento. Faculdade de Engenharia. Universidade do Porto. 1998