306 research outputs found
Alkali-free bioactive glass composition, U.S. Patent 9,238,044
No full textThe present invention relates to development of bioactive glass/glass-ceramic composition that are able to promote a fast deposition layer of carbonated hydroxyapatite upon immersion in simulated body fluid (SBF) for time periods as short as one hour. Such composition might include fluorides, and a variety of oxides (or their precursor compounds), such as Na2O—Ag2O—SrO—CaO—MgO—ZnO—P2O5—SiO2—Bi2O3—B2O3—CaF2, be prepared by the melt route or by the sol-gel process, with the specific composition and the preparation route selected according to the intended functionalities, which can present controlled biodegradation rate and bactericidal activity. The powders derived from glass melts purred in cold water (frits) may completely densify by sintering at temperatures up to 800° C. without devitrification, resulting in bioglass compacts with high flexural strength (˜85 MPa). The bioactive glass powders prepared by sol-gel densify at lower temperatures due to their higher specific surface area and reactivity
Clinopyroxene based glasses and glass-ceramics for functional applications
No full textDoutoramento em Ciência e Engenharia de MateriaisAs piroxenas são um vasto grupo de silicatos minerais encontrados em muitas rochas ígneas e metamórficas. Na sua forma mais simples, estes silicatos são constituídas por cadeias de SiO3 ligando grupos tetrahédricos de SiO4. A fórmula química geral das piroxenas é M2M1T2O6, onde M2 se refere a catiões geralmente em uma coordenação octaédrica distorcida (Mg2+, Fe2+, Mn2+, Li+, Ca2+, Na+), M1 refere-se a catiões numa coordenação octaédrica regular (Al3+,
Fe3+, Ti4+, Cr3+, V3+, Ti3+, Zr4+, Sc3+, Zn2+, Mg2+, Fe2+, Mn2+), e T a catiões em coordenação tetrahédrica (Si4+, Al3+, Fe3+). As piroxenas com estrutura monoclínica são designadas de clinopiroxenes. A estabilidade das
clinopyroxenes num espectro de composições químicas amplo, em conjugação com a possibilidade de ajustar as suas propriedades físicas e químicas e a durabilidade química, têm gerado um interesse mundial devido a suas
aplicações em ciência e tecnologia de materiais. Este trabalho trata do desenvolvimento de vidros e de vitro-cerâmicos baseadas de clinopiroxenas
para aplicações funcionais. O estudo teve objectivos científicos e tecnológicos; nomeadamente, adquirir conhecimentos fundamentais sobre a formação de fases cristalinas e soluções sólidas em determinados sistemas vitro-cerâmicos, e avaliar a viabilidade de aplicação dos novos materiais em diferentes áreas tecnológicas, com especial ênfase sobre a selagem em células de combustível de óxido sólido (SOFC). Com este intuito, prepararam-se vários vidros e
materiais vitro-cerâmicos ao longo das juntas Enstatite (MgSiO3) - diopsídio (CaMgSi2O6) e diopsídio (CaMgSi2O6) - Ca - Tschermak (CaAlSi2O6), os quais foram caracterizados através de um vasto leque de técnicas. Todos os vidros
foram preparados por fusão-arrefecimento enquanto os vitro-cerâmicos foram obtidos quer por sinterização e cristalização de fritas, quer por nucleação e cristalização de vidros monolíticos. Estudaram-se ainda os efeitos de várias substituições iónicas em composições de diopsídio contendo Al na estrutura, sinterização e no comportamento durante a cristalização de vidros e nas propriedades dos materiais vitro-cerâmicos, com relevância para a sua aplicação como selantes em SOFC. Verificou-se que Foi observado que os vidros/vitro-cerâmicos à base de enstatite não apresentavam as características necessárias para serem usados como materiais selantes em SOFC, enquanto as melhores propriedades apresentadas pelos vitro-cerâmicos à base de
diopsídio qualificaram-nos para futuros estudos neste tipo de aplicações. Para além de investigar a adequação dos vitro-cerâmicos à base de clinopyroxene como selantes, esta tese tem também como objetivo estudar a influência dos
agentes de nucleação na nucleação em volume dos vitro-cerâmicos resultantes á base de diopsídio, de modo a qualificá-los como potenciais
materiais hopedeiros de resíduos nucleares radioactivos.The pyroxenes are a wide spread group rock-forming silicate minerals found in many igneous and metamorphic rocks. They are silicates that, in their simplest form, contain single SiO3 chains of linked SiO4 tetrahedra. The general chemical formula for pyroxenes is M2M1T2O6, where M2 refers to cations in a generally distorted octahedral coordination (Mg2+, Fe2+, Mn+, Li+, Ca2+, Na+), M1 to cations in a regular octahedral coordination (Al3+, Fe3+, Ti4+, Cr3+, V3+, Ti3+, Zr4+, Sc3+, Zn2+, Mg2+, Fe2+, Mn2+), and T to tetrahedrally coordinated cations (Si4+, Al3+, Fe3+). Monoclinic pyroxenes are called clinopyroxenes. The stability
of clinopyroxenes over a broad spectrum of chemical compositions, in conjunction with the possibility of achieving desired physical properties and high chemical durability, has generated a worldwide interest due to their applications in material science and technology. The present work deals with the development of clinopyroxene based glasses and glass-ceramics for functional applications. The objective of the study was dual, both scientific and technological; particularly to gain fundamental knowledge on the formation of
crystalline phases and solid solutions in selected glass-ceramic systems, and to evaluate the feasibility for application of new materials in different
technological areas with emphasis on sealing in solid oxide fuel cells (SOFC).
In this pursuit, various glasses and glass-ceramics along Enstatite (MgSiO3) - Diopside (CaMgSi2O6) and Diopside (CaMgSi2O6) – Ca – Tschermak
(CaAlSi2O6) joins have been prepared and characterized by a wide array of characterization techniques. All the glasses were prepared by melt-quenching technique while glass-ceramics were produced either by sintering and crystallization of glass powders or by nucleation and crystallization in monolithic glasses. Furthermore, influence of various ionic substitutions/additions in Alcontaining
diopside on the structure, sintering and crystallization behaviour of glasses and properties of resultant glass-ceramics has been investigated, in relevance with final application as sealants in SOFC. It has been observed that enstatite based glasses/glass-ceramics do not exhibit requisite characteristics in order to qualify for the job of sealing in SOFC while the superior properties
exhibited by diopside based glass-ceramics qualify them for further experimentation as SOFC sealants. Apart from investigating the suitability of
clinopyroxene based glass-ceramics as sealants, this thesis also aims to study the influence of nucleating agents on the volume nucleation in the resultant diopside based glass-ceramics so as to qualify them for further experimentation as hosts for radioactive nuclear wastes
Assessment of interatomic parameters for the reproduction of borosilicate glass structures via DFT‐GIPAW calculations
No full textBorates and borosilicates are potential candidates for the design and development of glass formulations with important industrial and technological applications. A major challenge that retards the pace of development of borate/borosilicate based glasses using predictive modeling is the lack of reliable computational models to predict the structure‐property relationships in these glasses over a wide compositional space. A major hindrance in this pursuit has been the complexity of boron‐oxygen bonding due to which it has been difficult to develop adequate B–O interatomic potentials. In this article, we have evaluated the performance of three B–O interatomic potential models recently developed by Bauchy et al [J. Non‐Cryst. Solids, 2018, 498, 294–304], Du et al [J. Am. Ceram. Soc. https://doi.org/10.1111/jace.16082] and Edèn et al [Phys. Chem. Chem. Phys., 2018, 20, 8192–8209] aiming to reproduce the short‐to‐medium range structures of sodium borosilicate glasses in the system 25 Na2O x B2O3 (75 − x) SiO2 (x = 0‐75 mol%). To evaluate the different force fields, we have computed at the density functional theory level the NMR parameters of 11B, 23Na, and 29Si of the models generated with the three potentials and the simulated MAS NMR spectra compared with the experimental counterparts. It was observed that the rigid ionic models proposed by Bauchy and Du can both reliably reproduce the partitioning between BO3 and BO4 species of the investigated glasses, along with the local environment around sodium in the glass structure. However, they do not accurately reproduce the second coordination sphere of silicon ions and the Si–O–T (T = Si, B) and B‐O‐T distribution angles in the investigated compositional space which strongly affect the NMR parameters and final spectral shape. On the other hand, the core‐shell parameterization model proposed by Edén underestimates the fraction of BO4 species of the glass with composition 25Na2O 18.4B2O3 56.6SiO2 but can accurately reproduce the shape of the 11B and 29Si MAS‐NMR spectra of the glasses investigations due to the narrower B–O–T and Si‐O‐T bond angle distributions. Finally, the effect of the number of boron atoms (also distinguishing the BO3 and BO4 units) in the second coordination sphere of the network former cations on the NMR parameters have been evaluated
Impact of mixed-alkaline earth effect on the structure and dissolution behavior of borate glasses
No full textA suite of state-of-the-art spectroscopic techniques has been employed to understand theimpact of varying the Sr2+/ Ca2+ ratio on the structure and dissolution behavior (pH = 7) of borate glasses. The glasses tend to dissolve congruently leading to a complete breakdown of the borate network. Dissolution kinetics were found to increase with increasing Sr2+/Ca2+ ratio, but the trend was not a linear function of glass composition. Raman and 11B MAS NMR spectroscopy results indicate that varying the Sr2+/Ca2+ ratios has a minimal impact on borate speciation in the glass structure. However, it does impact the superstructural arrangement of borate units in the glass structure. Therefore, the dissolution kinetics appear to be governed by the impact of the ionic field strength of the alkaline-earth modifier on the volume of the borate network, which in turn dictates the kinetics of hydration reactions in the glass structure.M.S.Includes bibliographical reference
Biovidros de diópsido-pirofosfafto de cálcio dopados com alguns aditivos
No full textMestrado em Materiais e Dispositivos BiomédicosO objectivo do presente trabalho é o de mostrar a influência de vários iões
funcionais (Y3+, Cu2+, F1-, Mn2+ e Ti4+) na capacidade de formação de vidro, na
sua estrutura, aptidão para serem sinterizados, no comportamento na
cristalização e nas várias propriedades termofísicas de vidros e vitro-cerâmicos
obtidos a partir de um vidro base formulado no sistema diópsido – pirofosfato
de cálcio.
Ao vidro base foram adicionadas três quantidades diferentes de cinco
compostos dopantes de modo a obter cinco séries de vidros por fusão. A
análise estrutural dos vidros foi feita por ressonância magnética nuclear (NMR)
dos elementos 29Si e 31P e por espectroscopia de infravermelho associada a
transformas de Fourier (FTIR). A rede de silicato em todos os vidros
investigados encontra-se predominantemente coordenada em unidades Q2
(Si), enquanto o fósforo tende a permanecer no seu ambiente de ortofosfato
(Q°). Todos os vidros apresentaram taxas rápidas de biomineralização,
tornando-os bons candidatos para aplicações biomédicas.
Os comportamentos dos pós de vidro na sinterização e na cristalização foram
estudados por análise termal diferencial (DTA), enquanto a dilatometria foi
usada para determinar os valores do coeficiente de expansão térmica de todos
os vidros. A evolução das fases cristalinas e a microestrutura dos vitrocerâmicos
foram analisadas por difracção de raio x (XRD) e por microscopia
de electrónica de varrimento (SEM). Os vitro-cerâmicos foram obtidos por
sinterização e cristalização dos pós dos vidros respectivos por tratamento
térmico a 800, 850, e 900 °C durante 1 h.The aim of the present work is to show the influence of various functional ions
(Y3+, Cu2+, F1-, Mn 2+ and Ti4+) on the glass forming ability, structure, sintering
ability, crystallization behaviour and various thermo-physical properties of
glasses and glass-ceramics in the diopside–calcium pyrophosphate system.
Five series of glasses have been prepared by melt-quenching technique, by
doping the parent glass with 3 different percentages for each doping additive.
The structural analysis of glasses has been made by 29Si and 31P-nuclear
magnetic resonance (NMR) and Fourier transforms infrared spectroscopy
(FTIR). The silicate network in all the investigated glasses is predominantly
coordinated in Q2 (Si) units while phosphorus tends to remain in
orthophosphate (Qº) environment. All glasses exhibited fast biomineralization
rates, making them promising candidates for biomedical applications.
The sintering and crystallization behaviours of glass powders were studie by
differential thermal analysis (DTA), while dilatometry was used to get the
results about the coefficient of thermal expansion for all glasses. Crystalline
phase evolution and microstructure of glass-ceramics has been followed by Xray
diffraction (XRD) and scanning electron microscopy (SEM). Glass ceramics
were obtained by sintering and crystallization of glass powder compacts from
all the glasses at 800,850 and 900 ºC for 1 h
Study of calcium–magnesium–aluminum–silicate (CMAS) glass and glass-ceramic sealant for solid oxide fuel cells
No full textA parent glass within the CaO-MgO-Al2O3-SiO2 system and resulting glass-ceramics (GCs) have been appraised for solid oxide fuel cells (SOFCs) sealing applications. The sintering behavior was investigated by differential thermal analysis and hot stage microscopy. The glass composition exhibited single-stage shrinkage behavior with high sintering ability, and a suitable viscosity of 107.1 dPa s at the SOFCs operating temperature 900 °C. X-ray diffraction in conjunction with the Rietveld-RIR technique were employed to quantify the crystalline and amorphous phases in the GCs sintered at 900 °C for 1 h and 850 °C for 300 h. The coefficients of thermal expansion (CTE) measured were 9.7 × 10-6 K-1 (200-500 °C) and ~10.1 × 10-6 K-1 (200-700 °C) for glass and GCs, respectively, in good agreement with those typical for SOFC components. Weibull analysis was applied on the three-point bend data of GCs in order to obtain the mechanical strength distribution, characteristic strength and Weibull modulus. Well matching CTE, flexural strength values, good sintering behavior and adhesion to the other components in air atmosphere allow proposing this glass composition as promising candidate for further experimentation as sealant for SOFCs
Composition-structure-property relationships in magnesium yttrium aluminoborate glasses
No full textThere is an increasing need for light-weight, strong and crack-resistant glasses for industrial applications. In order to design new glasses, a thorough understanding of relationships between composition, structure, and properties is required. This study attempts to shed more light on the composition-structure-property relationships in alumina-rich aluminoborate glasses. In the present work, MgO-Y2O3-Al2O3-B2O3 glasses have been fabricated by melt-quenching at temperatures ranging from 1600°C to 1650°C. The influence of the substitution of B2O3 by Al2O3 on the structure, thermal and mechanical properties of the glasses (hardness and crack resistance) have been investigated using magic angle spinning – nuclear magnetic resonance (MAS-NMR), differential scanning calorimetry (DSC) and Vickers indentation. Hardness and crack resistance of the glasses were found to correlate with their structure and composition. Furthermore, with Al2O3/B2O3 substitution, fragility, density and hardness were found to increase while glass forming ability as well as crack resistance decreased.M.S.Includes bibliographical referencesIncludes vitaby Anne Elisabeth Rebecc
Preparação e caracterização de biovidros dopados com Sr e Zn
No full textMestrado em Ciência e Engenharia dos MateriaisOs vidros e vitro-cerâmicos do sistema ternário diopsite (CaO·MgO·2SiO2;
posteriormente mencionado como Di) – fluorapatite (9CaO·3P2O5·CaF2;
posteriormente mencionado como FA) e fosfato tricálcico (3CaO·P2O5;
posteriormente mencionado como TCP) são potenciais candidatos para várias
aplicações biomédicas incluindo estruturas de suporte para engenharia de
tecido ósseo.
O presente trabalho teve como objectivo investigar os vidros e os vitrocerâmicos
do sistema Di-FA-TCP quanto à sua estrutura e capacidades de
formação, sinterização e cristalização. Estudou-se também a influência da
variação das razões SrO/CaO e ZnO/MgO na estrutura e em várias
propriedades termo-físicas nos mesmos vidros, nos quais o CaO foi
parcialmente substituído pelo SrO e o MgO pelo ZnO (0-10 mol.%). Todos os
vidros estudados foram preparados pela técnica de fusão-arrefecimento rápido.
A análise estrutural dos vidros foi feita por Ressonância Magnética Nuclear 29Si
e 31P (NMR) e Espectroscopia de Infra-Vermelho (FTIR). Em todos os vidros a
rede de silicato é coordenada predominantemente nas unidades Q2 (Si)
enquanto que o fósforo tende a permanecer no ambiente do ortofosfato (Q0). O
comportamento dos pós dos vidros na sinterização e cristalização foi estudado
por Microscopia de Aquecimento (Hot Stage Microscopy - HSM) e por Análise
Térmica Diferencial (DTA), respectivamente, enquanto a evolução das fases
cristalinas e da microestrutura dos vitro-cerâmicos foi seguida por Difracção de
Raios-X (XRD) e por Microscopia Electrónica de Varrimento (SEM). Na maioria
das composições dos vidros investigados, a sinterização precedeu a
cristalização tendo a DI e a FA cristalizado como fases primárias em todos os
vitro-cerâmicos após sinterização a 850ºC durante 1 h.The glasses and glass-ceramics in ternary system of diopside
(CaO·MgO·2SiO2; hereafter referred as Di) – fluorapatite [9CaO·3P2O5·CaF2;
hereafter referred as FA] – tricalcium phosphate (3CaO·P2O5; hereafter
referred as TCP) system are potential candidates for various biomedical
applications including scaffolds for bone tissue engineering. The present work
investigates the glass forming ability, structure, sintering ability and
crystallization behaviour of some glasses along Di-FA-TCP join. Further,
influence of varying SrO/CaO and ZnO/MgO ratio has been studied on
structure and various thermo-physical properties of glasses in the above
mentioned system where CaO has been partially substituted by SrO and MgO
has been partially substituted by ZnO (0 – 10 mol.%). All the glasses have
been prepared by melt-quenching technique. The structural analysis of glasses
has been made by 29Si and 31P-nuclear magnetic resonance (NMR) and
infrared spectroscopy (FTIR). The silicate network in all the investigated
glasses is predominantly coordinated in Q2 (Si) units while phosphorus tends to
remain in orthophosphate (Q0) environment. The sintering and crystallization
behaviour of glass powders has been studied by hot stage microscopy (HSM)
and by differential thermal analysis (DTA), respectively while crystalline phase
evolution and microstructure of glass-ceramics has been followed by X-ray
diffraction (XRD) and scanning electron microscopy (SEM). The sintering
preceded crystallization in majority of the glass compositions and Di and FA
crystallized as the primary crystalline phases in all the investigated glassceramics
after sintering at 850ºC for 1 h
Vidros bioactivos isentos de alcalinos para regeneração óssea
No full textDoutoramento em Ciência e Engenharia dos MateriaisBioactive glasses and glass-ceramics are a class of third generation
biomaterials which elicit a special response on their surface when in contact
with biological fluids, leading to strong bonding to living tissues. The purpose of
the present study was to develop diopside based alkali-free bioactive glasses in
order to achieve good sintering behaviour, high bioactivity, and a dissolution/
degradation rates compatible with the target applications in bone regeneration
and tissue engineering. Another aim was to understand the structure-property
relationships in the investigated bioactive glasses. In this quest, various glass
compositions within the Diopside (CaMgSi2O6) – Fluorapatite (Ca5(PO4)3F) –
Tricalcium phosphate (3CaO•P2O5) system have been investigated. All the
glasses were prepared by melt-quenching technique and characterized by a
wide array of complementary characterization techniques. The glass-ceramics
were produced by sintering of glass powders compacts followed by a suitable
heat treatment to promote the nucleation and crystallization phenomena.
Furthermore, selected parent glass compositions were doped with several
functional ions and an attempt to understand their effects on the glass
structure, sintering ability and on the in vitro bio-degradation and biomineralization
behaviours of the glasses was made. The effects of the same
variables on the devitrification (nucleation and crystallization) behaviour of
glasses to form bioactive glass-ceramics were also investigated. Some of the
glasses exhibited high bio-mineralization rates, expressed by the formation of a
surface hydroxyapatite layer within 1–12 h of immersion in a simulated body
fluid (SBF) solution. All the glasses showed relatively lower degradation rates in
comparison to that of 45S5 Bioglass®. Some of the glasses showed very good
in vitro behaviour and the glasses co-doped with zinc and strontium showed an
in vitro dose dependent behaviour. The as-designed bioactive glasses and
glass–ceramic materials are excellent candidates for applications in bone
regeneration and for the fabrication of scaffolds for tissue engineering.Os vidros e vitrocerâmicos bioactivos fazem parte da chamada terceira
geração de biomateriais, i.e., materiais que estimulam uma resposta especial
quando em contacto com fluidos biológicos, capaz de conduzir ao
estabelecimento de ligações fortes entre a sua superfície e os tecidos vivos. O
presente estudo visou o estudo e desenvolvimento de vidros bioactivos à base
de diópsido e isentos de metais alcalinos que apresentem um bom
comportamento na sinterização, elevados índices de bioactividade, e taxas de
dissolução / degradação compatíveis com as almejadas aplicações em
regeneração óssea e em engenharia de tecidos. Procurou-se ainda entender
as relações entre a estrutura e as propriedades dos vidros bioactivos
estudados. De acordo com esta perspectiva, estudaram-se várias
composições de vidros bioactivos pertencentes ao sistema Diópsido
(CaMgSi2O6) – Fluorapatite (Ca5(PO4)3F) – Fosfato de tricálcico (3CaO•P2O5).
Todas as composições vítreas foram preparados por fusão, seguida de
fritagem em água fria, e caracterizados através de um conjunto de técnicas
complementares de caracterização. Os vitrocerâmicos foram obtidos por
sinterização das fritas de vidro moídas e compactadas, seguida de tratamento
térmico adequado para promover os fenómenos de nucleação e cristalização.
Além disso, algumas composições vítreas seleccionadas foram dopadas com
vários iões funcionais e os seus efeitos na estrutura vítrea, na sua propensão
para a sinterização, e nos comportamentos in vitro em termos de biodegradação
e bio-mineralização foram avaliados. Os efeitos das mesmas
variáveis no processo de devitrificação (nucleação e cristalização) dos vidros e
formação de materiais vitrocerâmicos foram também investigados. Algumas
composições de vítreas apresentaram taxas de bio-mineralização elevadas,
expressas através da formação de camadas superficiais de hidroxiapatite após
1-12 h de imersão num fluido fisiológico simulado (SBF).
Todas as composições vítreas apresentaram taxas de degradação mais baixas
quando comparadas com a do 45S5 Bioglass®. Alguns vidros bioactivos
revelaram comportamentos in vitro excelentes, sendo a taxa de biomineralização
dos co-dopados com zinco e estrôncio dependente da dose
incorporada de dopantes. Os materiais estudados demostraram boa aptidão
para aplicações em regeneração óssea e para o fabrico de estruturas de
suporte em engenharia de tecidos
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