230,748 research outputs found
Novel sol–gel preparation of (PO)–(CaO)–(NaO)–(TiO) bioresorbable glasses (X = 0.05, 0.1, and 0.15)
No full textQuaternary phosphate-based glasses in the PO–CaO–NaO–TiO system with a fixed PO and CaO content of 40 and 25 mol% respectively have been successfully synthesised via sol–gel method and bulk, transparent samples were obtained. The structure, elemental proportion, and thermal properties of stabilised sol–gel glasses have been characterised using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), P nuclear magnetic resonance (P NMR), titanium K-edge X-ray absorption near-edge structure (XANES), fourier transform infrared (FTIR) spectroscopy, and differential thermal analysis (DTA). The XRD results confirmed the amorphous nature for all stabilized sol–gel derived glasses. The EDX result shows the relatively low loss of phosphorus during the sol–gel process and Ti K-edge XANES confirmed titanium in the glass structure is in mainly six-fold coordination environment. The P NMR and FTIR results revealed that the glass structure consist of mainly Q and Q phosphate units and the Ti cation was acting as a cross-linking between phosphate units. In addition DTA results confirmed a decrease in the glass transition and crystallisation temperature with increasing NaO content. Ion release studies also demonstrated a decrease in degradation rates with increasing TiO content therefore supporting the use of these glasses for biomedical applications that require a degree of control over glass degradation. These sol–gel glasses also offer the potential to incorporate proactive molecules for drug delivery application due to the low synthesis temperature employed
Sol-gel derived lead zirconate titanate thick films and their improved pyroelectric properties
No full textThe single-layer thickness of Pb(Zr0.3Ti0.7)O3(PZT 30/70) thin films made by the sol-gel process is often restricted by the appearance of cracks when a single layer is thicker than 100 nm. Making a film with 1μm thick needs more than 10 times coating cycles, which is sometimes unacceptable. In this study, a sol modified with an additive was used for the preparation of thick PZT films. The thickness of the films depends upon the rotation rate. Up to 700 nm crack-free single layers could be obtained. The deposited films crystallised as the perovskite structure on platinum-buffered silicon by heating at 550°C. The porosity of the thick films was a function of the single layer thickness. A dense PZT film with a single layer 140 nm thick was found to have a very high pyroelectric coefficient (p=2.36×10− 4CK− 1m− 2) and figure of merit (1.88×10− 5Pa− 0.5). The introduction of pores in the films reduced p. However, the figure of merit of the films exhibited a reasonably high value due to a dramatic reduction of dielectric constant
Fabrication of high temperature piezoelectric ceramics by sol gel method
No full textThis research covers the fabrication of piezoelectric ceramics using a sol gel
method. Commercial high temperature transducers are typically fabricated by a
milled oxide method. The sol gel method presented here produced purer samples that
can be prepared at lower temperatures than conventional milled oxide preparations.
The performance of the samples as piezoelectric transducers was also investigated,
with the samples produced by sol gel method exceeding the piezoelectric response of
the commercial samples
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
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
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
Films based on bacteriorhodopsin in sol-gel matrices
No full textThe bacteriorhodopsin film in gelatin matrixes which are used as sensitive
elements of integrated optic and fibre-optic sensors of various vapor and gases
components will not be able to carry out the chemical control of aqueous
solutions. In the given paper the results of technological development of
obtaining the bacteriorhodopsin (bR) films in a sol-gel matrix are represented.
The films are obtained in a broad thickness range (from 0.5 to 20 microns) with
various bR concentrations and photosensitize additives. The optimal
technological conditions of obtaining of uniform films with given optical
parameters are defined. The surface morphology and cross section of the obtained
films was studied using an AFM and SEM. The films have a reasonable surface
roughness (~ 100 nm) and a uniform distribution of the purple membrane fragments
in the nanostructured sol-gel glass matrix along the films surface and
thickness. The transmission spectrums have the characteristic for bR the
absorption band, the value of which depends on bR concentration and
technological features of the films deposition. The investigated photosensitive
properties of the obtained films and influence on them of chemical components of
aqueous solutions, allow recommending the thin bR films in sol-gel matrixes for
creation of planar waveguides in the role of components of the chemical sensors
of liquid solutions
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)
Preparation of sub-micron PZT particles with the sol-gel technique
No full textThis paper describes the production of Pb1.0Zr0.9Ti0.1 ceramic powder, by using metal organic precursors as starting materials. In this study polyvinylpyrrolidone, PVP, was used to create a PZT–PVP sol and then also added as a secondary stage to control the particle size of the powder.
Two different sol–gel routes were used to create PZT powder. Both routes gave similar primary particle sizes in the range, 30–70 nm, but different agglomerate formations. Perovskite PZT powder was created with both routes
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
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