359,497 research outputs found
Effect of calcium source on structure and properties of sol–gel derived bioactive glasses
No full textThe aim was to determine the most effective calcium precursor for synthesis of sol–gel hybrids and for improving homogeneity of sol–gel bioactive glasses. Sol–gel derived bioactive calcium silicate glasses are one of the most promising materials for bone regeneration. Inorganic/organic hybrid materials, which are synthesized by incorporating a polymer into the sol–gel process, have also recently been produced to improve toughness. Calcium nitrate is conventionally used as the calcium source, but it has several disadvantages. Calcium nitrate causes inhomogeneity by forming calcium-rich regions, and it requires high temperature treatment (>400 °C) for calcium to be incorporated into the silicate network. Nitrates are also toxic and need to be burnt off. Calcium nitrate therefore cannot be used in the synthesis of hybrids as the highest temperature used in the process is typically 40–60 °C. Therefore, a different precursor is needed that can incorporate calcium into the silica network and enhance the homogeneity of the glasses at low (room) temperature. In this work, calcium methoxyethoxide (CME) was used to synthesize sol–gel bioactive glasses with a range of final processing temperatures from 60 to 800 °C. Comparison is made between the use of CME and calcium chloride and calcium nitrate. Using advanced probe techniques, the temperature at which Ca is incorporated into the network was identified for 70S30C (70 mol % SiO2, 30 mol % CaO) for each of the calcium precursors. When CaCl2 was used, the Ca did not seem to enter the network at any of the temperatures used. In contrast, Ca from CME entered the silica network at room temperature, as confirmed by X-ray diffraction, 29Si magic angle spinning nuclear magnetic resonance spectroscopy, and dissolution studies. CME should be used in preference to calcium salts for hybrid synthesis and may improve homogeneity of sol–gel glasses
Nonoxide Sol-Gel Synthesis of Terbium-Doped Silicon Nitride Phosphors
No full textExposure of solutions of Tb(N(SiMe3)2)3 with SiCl(NEt2)3 in tetrahydrofuran to dry ammonia results in polymeric xerogels. Heating these gels in ammonia leads to amorphous Tb:SiNx phosphors that exhibit bright green luminescence under UV irradiation. MAS-NMR and combustion analysis reveal that the phosphors are silicon nitride materials analogous to those typically produced by sol–gel routes. Photoluminescence behavior is similar to that of Tb:SiNx or Tb:SiO2 films produced by ion implantation that show good electroluminescence activity
Entrapment of glucoamylase by sol-gel technique in PhTES/TEOS hybrid matrixes
No full textMesoporous silica particles were prepared by the sol-gel method from different alkoxysilane precursors and
used as a host matrix for encapsulation of glucoamylase, an enzyme widely used in fermentative industry. The
aim was to investigate the physico-chemical properties of the different silica powders and their effect on the
enzyme kinetics. The encapsulated enzymes followed Michaelis-Menten kinetics. The Michaelis constant (KM)
and the maximum rate of starch hydrolysis reaction (Vmax) were calculated according to the Michaelis-Menten
and Lineweaver-Burke plots. The values of the Michaelis constant (KM) of the encapsulated enzymes were
higher than those of the free enzyme. The temperature and pH infl uence on the activity of free and immobilized
glucoamylase were also compared. The results of this study show that the enzymes immobilized in organic/inorganic
hybrid silica matrixes (obtained by the sol-gel method), allowing the entrapped glucoamylase to retain
its biological activity, are suitable for many different applications, (medicinal, clinical, analytical)
Galería
No full text- 44° Aniversario del IBONE- Finalizó una nueva edición del Programa “Los Científicos van a la Escuela”- Jóvenes Investigadores de la UNNE premiados en Jornadas de AUGM 2017- “Café científico e innovación”, una propuesta de la UNNE para difundir las ciencias- Premio al Valor Científico del Senado de la Nació
Characterizing the hierarchical structures of bioactive sol-gel silicate glass and hybrid scaffolds for bone regeneration
No full textBone is the second most widely transplanted tissue after blood. Synthetic alternatives are needed that can reduce the need for transplants and regenerate bone by acting as active temporary templates for bone growth. Bioactive glasses are one of the most promising bone replacement/regeneration materials because they bond to existing bone, are degradable and stimulate new bone growth by the action of their dissolution products on cells. Sol-gel-derived bioactive glasses can be foamed to produce interconnected macropores suitable for tissue ingrowth, particularly cell migration and vascularization and cell penetration. The scaffolds fulfil many of the criteria of an ideal synthetic bone graft, but are not suitable for all bone defect sites because they are brittle. One strategy for improving toughness of the scaffolds without losing their other beneficial properties is to synthesize inorganic/organic hybrids. These hybrids have polymers introduced into the sol-gel process so that the organic and inorganic components interact at the molecular level, providing control over mechanical properties and degradation rates. However, a full understanding of how each feature or property of the glass and hybrid scaffolds affects cellular response is needed to optimize the materials and ensure long-term success and clinical products. This review focuses on the techniques that have been developed for characterizing the hierarchical structures of sol-gel glasses and hybrids, from atomicscale amorphous networks, through the covalent bonding between components in hybrids and nanoporosity, to quantifying open macroporous networks of the scaffolds. Methods for non-destructive in situ monitoring of degradation and bioactivity mechanisms of the materials are also included. © 2012 The Royal Society
Sol-gel derived hydroxyapatite, fluorhydroxyapatite and fluorapatite coatings for titanium implants
No full textCurrently, most titanium implant coatings are made using hydroxyapatite and a
plasma-spraying technique. There are however limitations associated with the
plasma-spraying process including; poor adherence, high porosity and cost. An
alternative - the sol-gel technique offers many potential advantages but is
currently lacking research data for this application.
Hydroxyapatite (HA), fluorhydroxyapatite (FHA) and fluorapatite (FA) have
been synthesised by a sol-gel method. Calcium nitrate and triethyl phosphite
were used as precursors under an ethanol-water based solution. Different
amounts of ammonium fluoride (NH4F) were incorporated for the preparation of
the FHA and FA sol-gels. Optimisation and characterisation of the sol-gels was
carried out using, X-ray Diffraction (XRD), High Temperature X-Ray Diffraction
(HTXRD), Fourier Transform Infrared Analysis (FTIR) and Differential Thermal
Analysis (DTA).
Rheology and hydrophilicity of the sol-gels showed that increasing fluoride ion
substitution caused an increase in viscosity and contact angle.
The dissolution (Ca2+ and PO4
3-rates) rates of the fluoride-substituted powders
from the sol-gels were considerably lower than that of HA and all rates could be
decreased by increasing the sintering temperature. This suggests the
possibility of tailoring the solubility of any coatings made from the sol-gels
through fluoride ion substitution and increased sintering temperature.
A spin coating protocol has been established for coating the sol-gels onto
titanium. Increasing the coating speed decreased the porosity and thickness of
the coatings. Bond strengths to titanium were investigated. Fluoride substitution
and sintering temperature were shown to be important factors. Cellular proliferation studies revealed that increasing the level of fluoride
substitution in the apatite structure significantly increased the biocompatibility
of the material.
The sol-gel technique may be an alternative to plasma spraying for coating
titanium implants. Furthermore it may also be suitable for producing HA, FHA
and FA as bone grafting materials
Pôr do sol químico
No full textO vídeo apresenta uma demonstração, utilizando retroprojetor, que simula o pôr do sol. A reação entre tiossulfato de sódio e um ácido produz partículas muito pequenas, de enxofre sólido, dispersas na solução (colóide chamado de sol). Parte da luz branca do retroprojetor ao atravessar o colóide é espalhada, de modo que a luz azul sofre um desvio de 90 graus e a luz vermelha atravessa a mistura e pode ser vista projetada na tela, simulando o pôr do sol. O vídeo mostra ainda que usando soluções reagentes mais concentradas ocorre aumento da velocidade da reação, produzindo mais rapidamente o precipitado de enxofreEnsino Médio::Químic
PRELIMINARY STUDY FOR USING VINYLTRIACETOXYSILANE AS PRECURSOR IN ENZYME IMMOBILIZATION BASED ON SOL-GEL METHOD
No full textDuring the last years, sol-gel technology has become a well-established method
for the preparation of catalytic active monoliths, bulk, particles and thin films. One reason
for the increasing research activities in this field is the opportunity to obtain versatile
hybrid materials by incorporation of different molecules, like dyes, enzymes, whole cells,
chemicals and drugs. The aim of this research was to evaluate the suitability of
vinyltriacetoxysilane (VTAS) as precursor in sol-gel enzyme immobilization and the
physicochemical characterization of the final products (silica xerogels)
Pôr do sol químico
No full textEnsino Médio::QuímicaO vídeo apresenta uma demonstração, utilizando retroprojetor, que simula o pôr do sol. A reação entre tiossulfato de sódio e um ácido produz partículas muito pequenas, de enxofre sólido, dispersas na solução (colóide chamado de sol). Parte da luz branca do retroprojetor ao atravessar o colóide é espalhada, de modo que a luz azul sofre um desvio de 90 graus e a luz vermelha atravessa a mistura e pode ser vista projetada na tela, simulando o pôr do sol. O vídeo mostra ainda que usando soluções reagentes mais concentradas ocorre aumento da velocidade da reação, produzindo mais rapidamente o precipitado de enxofr
Custo de produção de cultivos de Coffea canephora agroecológico sombreado e a pleno sol, no assentamento padre Ezequiel, Rondônia
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Agrárias, Programa de Pós-Graduação em Agroecossistemas, Florianópolis, 2015.Esta pesquisa analisou os custos da força de trabalho de agroecossistemas de café Coffea canephora, da variedade robusta e conilon, sombreado e a pleno sol. O trabalho teve como objetivo compreender a dinâmica do cultivo agroecológico nos diferentes agroecossistemas para indicação de sistemas de produção mais sustentáveis e economicamente viáveis para a cafeicultura na região norte do Brasil. A pesquisa foi realizada no assentamento Padre Ezequiel, município de Mirante da Serra, estado de Rondônia onde foram investigados oito agroecossistemas de café, quatro em cultivo sombreado e quarto em cultivo a pleno sol. Observou-se que o café é adaptado ao cultivo em sistemas sombreados, com menores custos de produção em relação ao cultivo a pleno sol. O custo total em mão de obra foi mais vantajoso nos cultivos sombreados. Portanto o cultivo de café sombreado representa uma alternativa viável economicamente e ecologicamente, sendo recomendado aos pequenos cafeicultores da região norte do Brasil.Abstract : We analyzed the effect of shade on the yield, gross income, net margin of agroecological coffee farms in Brazilian Amazon region. The survey was conducted in the settlement Father Ezekiel municipality of Mirante da Serra, State of Rondônia, and eight coffee agroecosystems were investigated; four in shading system and four the unshaded. Neither net income nor total production cost differed from shaded and sun systems. On the other hand, it was observed that shade coffee has higher net margins, highlighting the efficiency of these systems. The shaded coffee agroecosystems presented as an economically viable alternative and environmentally friendly practice in the northern Brazil
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