Sol–Gel Preparation and Properties of Fluoride-Substituted Hydroxyapatite Powders

Hydroxyapatite (HA) and fluor-hydroxyapatite (FHA) powders were synthesized by a sol–gel method for usage as bone filler and drug carrier. 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 FHA powders. With heat treatment above 400°C, a characteristic apatite phase was observed for all the sol–gel powders. However, the crystallization temperature decreased with increasing fluoride addition. The tricalcium phosphate (TCP) phase formed in the pure HA powder above 800°C was attenuated in the FHA powders, confirming an enhanced phase stability of the FHA powders. Increasing the F⁻ addition improved crystallinity and increased the crystallite size, as was determined from X-ray diffraction (XRD) analyses. The lattice parameters of the heat-treated powders varied corresponding to the fluoride addition, i.e., a gradual decrease in the a -axis, while little change in the c -axis was observed with increasing fluoride addition, indicating a nearly complete substitution of fluoride within the apatite lattice. However, little difference was observed with heat-treatment temperatures (400°–1000°C). The powders substituted with fluoride exhibited reduced dissolution rates in an in vitro solution as compared with the pure HA powder, suggesting the possibility of tailoring bioactivity with fluoride substitution.     

Characterization of Nanocrystalline Forsterite Fiber Synthesized via the Sol–Gel Process

An alkoxide sol–gel route was developed to prepare forsterite fibers. Transparent precursor gel fibers were converted to the crystalline phase of forsterite by heating above 550°C. Fibers heated at 1100°C for 2 h showed a porous microstructure with nanocrystalline sizes of about 50–100 nm. The structural evolution of fibrous gel was characterized. Effects of water and ethanol content on microstructures and strengths of fired fibers are also discussed. Some properties of the fired fibers were investigated.     

Synthesis of Bismuth Sodium Titanate Nanosized Powders by Solution/Sol–Gel Process

(Bi_1/2Na_1/2)TiO₃ (BNT) is a prominent candidate for a lead-free piezoelectric material. In this study, BNT was synthesized using the solution/sol–gel method, in which a solution of Bi₂O₃ and Na₂CO₃ was dissolved in HNO₃ as starting materials. The solution then was mixed with ethylene glycol and titanium tetraisopropoxide. The obtained BNT powder was analyzed using FT-IR, DTA-TG, Raman spectroscopy, and high-temperature XRD. Results showed that BNT crystallization occurred above 600°C. TEM investigation showed that 100–200 nm BNT particles were formed by heat-treating the sol–gel-derived BNT sol at 700°C for 6 h.     

Synthesis of a Hydroxyapatite/Collagen/Chondroitin Sulfate Nanocomposite by a Novel Precipitation Method

A hydroxyapatite/collagen/chondroitin sulfate nanocomposite that partly mimicked the composition of cartilage was synthesized through a novel precipitation method, using a calcium hydroxide suspension and phosphoric acid solutions that contained several mixing ratios of type II collagen (Col) and chondroitin sulfate (ChS). The precipitates were shaped and consolidated via filter pressing and subsequent cold isostatic pressing, respectively. A preferential alignment of the crystallographic c -axis of the hydroxyapatite nanocrystals along the longitudinal direction of the Col and ChS mixture was observed. The fracture strength and Vickers hardness of the nanocomposites were in the ranges of 35–50 and 119–219 MPa, respectively. This nanocomposite may be applicable for use as a bone substitute, because of its potential capability of bone remodeling through endochondral ossification.     

Synthesis of Nanosized and Microporous Precipitated Hydroxyapatite in Synthetic Polymers and Biopolymers

In situ precipitation of microporous and nanosized hydroxyapatite particles (5–40 nm) has been conducted in poly(vinyl alcohol) and bovine serum albumin gels. The process, which is similar to biomineralization, is highly controlled with respect to microstructural features, such as size and shape, and to precipitation of hydroxyapatite phase having a calcium:phosphorus stoichiometric ratio of 1.67. Nanosized precipitated hydroxyapatite particles show remarkable thermal stability and do not decompose to other calcium phosphate phases, even at higher temperatures.     

Sol–Gel Synthesis of Cadmium Telluride-Microcrystal-Doped Silica Glasses

The sol–gel process has been applied to the preparation of small-sized CdTe-doped silica glasses. Gels synthesized by the hydrolysis of a complex solution of Si(OC₂H₅)₄, Cd(CH₃COO)₂· 2H₂O, and Te were heated from 350° to 600°C in a H₂─N₂ atmosphere to form fine cubic CdTe crystals. The size of CdTe crystals, determined from the line broadening of X-ray diffraction pattern, increases from 4 to 9 nm in diameter with increasing heat-treatment temperature. The optical absorption edge shifts to the higher-energy side as the size of the CdTe crystals decreases. This phenomenon is interpreted in terms of a quantum confinement effect of electron and hole in the CdTe microcrystals.     

Preparation of Mesoporous Silicon Nitride via a Nonaqueous Sol–Gel Route

A silicon diimide gel Si(NH) _x (NH₂) _y (NMe₂) _z was prepared by an acid-catalyzed ammonolysis of tris(dimethylamino)silylamine. Pyrolysis of the gel at 1000°C under NH₃ flow led to the formation of an amorphous silicon nitride material without carbon contamination. All of the gel and pyrolyzed products exhibited a mesoporous structure with a high surface area and narrow pore-size distribution. The effective surface area of the pyrolyzed silicon nitride residues decreases with increasing temperature, but the heating rate during pyrolysis has little influence on the surface area and pore-size distribution of the final mesoporous ceramic Si₃N₄ products because of the highly cross-linked structures of the precursor silicon diimide gel.     

Phase Analysis and Thermal Stability of Hot Isostatically Pressed Zirconia–Hydroxyapatite Composites

Composites of zirconia and hydroxyapatite (OHAp) have been processed via hot isostatic pressing (HIP) or sintering in air. When the composites were sintered in air at a temperature of 950°C, decomposition of the OHAp to tricalcium phosphate occurred. Using the HIP technique, composites without any detectable degradation of the OHAp phase were produced at 1200°C. The reactivity between zirconia and OHAp was dependent on both the amount of water lost from OHAp and the geometry of the interaction. The phase composition of the materials prepared was evaluated from their powder X-ray diffraction patterns, and their microstructures were studied via electron microscopy.     

Sol–Gel Processing of Tetramethylammonium Silicate

A new sol–gel silica material based on tetramethylammonium silicate (TMAS) is reported here. Both xerogels and aerogels were produced by gelling a solution of 18.7 wt% TMAS using a series of esters. The gelation kinetics was controlled by varying the type and concentration of the ester. The supercritically dried TMAS aerogel was seen to have a larger pore size distribution with high porosity (>90%). In contrast, the conventionally dried gel showed a narrow distribution of mesopores, indicating its potential as a host matrix for protein encapsulations and catalysts.     

Micropatterning on Methylsilsesquioxane– Phenylsilsesquioxane Thick Films by the Sol–Gel Method

Prismatic patterns with a pitch of 30 μm and a slant height of 30 μm were embossed successfully in 70:30 (in mol%) methylsilsesequioxane:phenylsilsesqeioxane (MeSiO_3/2–PhSiO_3/2) thick films on glass substrates by laminating an organic polymer sheet as a stamper with the patterns against the films. The embossed shape of the prismatic patterns precisely agreed with the negative shape of those of the stamper that was used. The resultant MeSiO_3/2–PhSiO_3/2 films were transparent, and the refractive index of the films was adjusted to 1.51, to match that of the glass substrate.     

Synthesis of Porous Silica Foams via a Novel Vacuum-Induced Sol–Gel Method

Mesoporous silica foams having a macroporous skeleton and well-ordered internal mesoporous structure were synthesized by a novel vacuum-induced sol–gel process. This contrasts with the usual route involving expensive sacrificial microspheres. The resulting materials had a tri-modal pore size distribution and were characterized by nitrogen physisorption, X-ray diffraction, transmission electron microscopy.     

Sol–Gel Alumina-Coated Carbon Film

A simple method for dipcoating porous reticular carbon foam with aluminum oxide thin-film coatings is presented. Weight gain versus temperature and number of dipcoatings is presented along with scanning electron micrographs of uniform, adherent alumina thin films. Composite foam structures of up to 57% alumina have been prepared.     

Nucleation of Hydroxyapatite Crystal through Chemical Interaction with Collagen

The nucleation of hydroxyapatite (HAp) crystal through chemical interaction with collagen was investigated. A collagen membrane was soaked in a supersaturated simulated body fluid (1.5 SBF) solution with ion concentrations at 1.5 times that of normal simulated body fluid (1.0 SBF). A few carbonate-containing HAp crystals were formed mostly on the edge-side of the collagen membrane after 4 weeks. In the Fourier-transform infrared spectometry (FTIR) results, the carboxylate band of the collagen membrane showed red chemical shifts after the formation of HAp crystals, which coincided well with the decrease of the calculated bond orders of the carboxylate group when chelated with a calcium ion, which emulated the first-step nucleation of HAp crystal on the carboxylate group of collagen. The result implies that the binding of a calcium ion to the carboxylate group of collagen is one of the key factors for the nucleation of HAp crystals in a 1.5 SBF solution.     

琼脂糖-普鲁兰凝胶体系中羟基磷灰石的仿生合成

根据生物矿化的原理,采用二元凝胶法,在琼脂糖-普鲁兰凝胶体系中,以Ca(NO3)2和(NH4)3PO4为钙源和磷源,通过双扩散得到花簇状的羟基磷灰石(HA)。用X射线衍射仪(XRD)、傅立叶变换红外光谱(FTIR)、扫描电镜(SEM)和热重示差热分析仪(TG-DTA)对晶体的结构、组成、形貌和热性能进行表征。结果表明,普鲁兰在很大程度上改变了HA的形貌。当普鲁兰浓度较低时,形成的是不规则的棒状晶体,当普鲁兰浓度较高时,形成的是花簇状晶体。探讨了在琼脂糖-普鲁兰凝胶体系中HA的生长机理。     

Encapsulation of Hydroxyapatite Microspheres with Fluorapatite Using a Diffusion Process

Modification of hydroxyapatite surfaces can improve the properties of biomedical devices. The objective of this work was to encapsulate hydroxyapatite particles with a fluorapatite layer. A suspension of hydroxyapatite microspheres was prepared in a solution at different pH and treated with ammonium fluoride. pH, calcium, and fluoride were monitored in real time and particles subjected to fluoride analysis. After addition of fluoride, it was found that more material is released from the particle surface at low pH conditions, but leads to a high fluoride uptake from solution. Low solution fluoride levels produce a fluorapatite layer, but higher fluoride levels produce calcium fluoride.     

Dip Coating of Calcium Hydroxyapatite on Ti-6Al-4V Substrates

Ti-6Al-4V alloy is the most commonly used metallic material in the manufacture of orthopedic implants. The main inorganic phase of human bone is calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA). To achieve better biocompatibility with bone, metal implants made of Ti-6Al-4V are often coated with bioceramics. Dip-coating techniques scarcely are used to apply HA onto metallic implants. New dipping-solution recipes to be used for HA coatings are described in this work. Scanning electron microscopy and X-ray diffractometry have been used for sample characterization.     

Nonepitaxial Orientation in Sol–Gel Bismuth Titanate Films

Control over crystallographic orientation in ceramic thin films is important for highly anisotropic structures. Layered perovskites, like Bi₄Ti₃O₁₂, have interesting properties associated with their ferroelectric nature, which may be fully exploited only when films are highly textured. Textured films of this titanate were fabricated via a sol–gel technique without using epitaxial growth. Orientation in the film is confirmed by XRD and SEM, and supported by refractive index and dielectric measurements. In an attempt to explain the orienting effect, light scattering experiments were conducted to yield information about the molecular size, shape, and conformation of macromolecules as the sol–gel solution ages and condensation reactions proceed. These experiments clearly show an increase in the size of molecular clusters with time. We believe that it is the organization of these large clusters during spin coating, and the relationship of the backbone chemistry to the crystal structure of Bi₄Ti₃O₁₂, that are responsible for the observed orientation.     

Synthesis of Platinum/Silica Nanocomposite Particles by Reverse Micelle and Sol–Gel Processing

Pt/SiO₂ nanosized particles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles and the thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethoxysilane (TEOS) within the microemulsion. The average size of synthesized particles was in the size range of 21–42 nm. The effects of synthesis parameters, such as the molar ratio of water to TEOS and the molar ratio of water to surfactant, are discussed.     

Synthesis and Characterization of Lead Zirconate Titanate Fibers Prepared by the Sol–Gel Method: The Role of the Acid

Lead zirconate titanate (PZT) fibers are prepared by the sol–gel method using acetic acid and methacrylic acid to control the pH of the PZT precursor sol. The chemical evolution of the precursors, the thermal and crystallization behavior of the PZT gel fibers, and the microstructure of the samples with and without acid addition are analyzed and compared. It is observed that the properties of the fibers are improved when acids are used; particularly longer PZT ceramic fibers (4–5 cm) are obtained after heat treatment and a single perovskite phase is obtained at 550°C when using methacrylic acid. The mechanisms of the acid effect on the strengthening and crystallization of PZT fibers are discussed.     

透辉石复合的羟基磷灰石生物陶瓷材料的制备及性能

介绍了透辉石复登在磷灰石生物陶瓷材料的工艺条件,讨论了影响其抗折强度的主要因素。