An aqueous synthesis of photocatalyst by selective dissolution of titanium oxide/hydroxyapatite composite

A novel synthesis method of a highly active photocatalyst was proposed. Titanium dioxide (TiO₂) nano-particles were prepared by three-step procedure, precipitation of hydroxyapatite (HAp) on TiO₂ particles, heat treatment of the TiO₂/HAp composites, and acid treatment in hydrochloric acid. The unique point of this procedure is the selective dissolution of HAp to obtain exposed TiO₂ surfaces. The HAp precipitation was achieved by stirring TiO₂ powders in the mixtures of Ca(NO₃)₂ and NH₄H₂PO₄ aqueous solutions at pH 8.5. Then, the heat-treated TiO₂/HAp composites were treated with hydrochloric acid. The precipitated HAp avoided the direct contact of TiO₂ particles and suppressed the phase transformation from anatase-to-rutile >200 °C. The HAp also suppressed a decrease of specific surface area of TiO₂ during the heat treatment. The photocatalytic activities were evaluated from an absorbance decrease of methylene blue (MB) under ultraviolet (UV) irradiation. The MB photodecomposition was approximated to the first-order reaction and the reaction rate constants of the obtained TiO₂ powders heated at various temperatures were higher than those of conventional TiO₂ powders heated at same temperatures. The enhanced photocatalytic activity is attributed to the suppression effects for the phase transformation to rutile phase and the decreasing of specific surface area in the heat treatment.     

Microstructure and mechanical properties of in situ produced SiC/TiSi2 nanocomposites

The microstructure and mechanical properties of in situ produced SiC/TiSi₂ nanocomposites have been studied. The results indicate that SiC/TiSi₂ composites can be fabricated by reactively hot pressing mixed powders of TiC, elemental Si and elemental Ti. The in situ produced SiC particles are close to nanosize. Without elemental Ti powder, the composite obtained consists of TiSi₂ 66 vol% and SiC 34 vol% without residual Si or TiC. At ambient temperature, the highest bending strength of SiC/TiSi₂ composites was 400 MPa, twice that of monolithic TiSi₂. Also fracture toughness of SiC/TiSi₂ composites exceeds that of pure TiSi₂. At 1200°C, the yield strength of composites was improved due to the presence of the SiC particles.     

Formation of hydroxyapatite on CaSiO3 powders in simulated body fluid

CaSiO₃ powders were prepared from ethanol solutions of Ca(NO₃)₂·4H₂O and Si(OC₂H₅)₄ using NaOH as a precipitant. The resultant powders were heated at three different temperature regimes, (1) 500°C, (2) 500 and 1000^oC and (3) 500 and 1400°C, to obtain the amorphous phase (amorphous-CS), low temperature phase (β-CS), and high temperature phase (α-CS) of CaSiO₃, respectively. The different amorphous and crystalline phases exhibited different microtextures and specific surface areas of the powders. The rough, porous particles of amorphous-CS and β-CS have higher specific surface areas than the smooth, dense particles of α-CS. These CaSiO₃ powders were soaked in a simulated body fluid (SBF) at 36.5°C for 2 h to 30 days. Formation of hydroxyapatite (HAp) was observed on the surfaces of all samples, but the formation behavior and microstructures were different, resulting the differences in microstructure and crystal structure of the starting powders as well as particle size and specific surface area. The HAp formed on the amorphous-CS was a loose porous layer consisting of uniformly-sized tiny ball-like agglomerated particles, while that formed on the β-CS and α-CS was a dense layer consisting of larger ball-like agglomerated particles.     

Synthesis and characterization of bioactive zirconia toughened alumina doped with HAp and fluoride compounds

Alumina–zirconia nanostructured composites (ZrO₂ addition by 20 wt%) were prepared using combined gelation–precipitation process. A modified sol–gel process has been developed to prepare nano structured spinel [MgAl₂O₄], Al₂O₃, ZrO₂ and their composite materials. This process is useful in retaining tetragonal phase of zirconia at room temperature, which provides transformation toughening in the nano composites. Dried gels powders were calcined up to 1250 °C. Similarly, hydroxyapatite powders were produced by wet-chemical method and calcined at different temperatures. All the dried gel and calcined powders were characterized by using X-ray diffraction, DTA/TGA and SEM. Samples were prepared by uniaxial pressing the composites powders using ZTA, HAp, MgF₂ and CaF₂ in different ratio. Incorporation of CaF₂ and MgF₂ as a source for fluorine was also done to improve the sinterability of composites. The samples were sintered at 1400 °C for three hours. Densification and mechanical behaviour of sintered samples were observed. Bioactivities of all compositions were tested using SBF solution and then characterizing by FTIR. The main objective of work was to dope ZTA nano composites with HAp and fluoride compounds to obtain better sinterability at lower temperatures. Then evaluate the obtained ZTA based bioactive composite ceramics that have high mechanical strengths. This study verifies the bioactivities of HAp-added ZTA composites.     

Fabrication of structure-controlled hydroxyapatite/zirconia composite

The structure-controlled hydroxyapatite/zirconia (HAp/ZrO₂) composites were fabricated. At first, cylindrical hydroxyapatite (HAp) samples were prepared by the extrusion process, and then the extruded HAp cylindrical samples were coated with 3 mol% of Y₂O₃ partially stabilized ZrO₂ slurry, dried and aligned unidirectionally to form a composite bulk. The volume fraction of ZrO₂ in the HAp/ZrO₂ composite was estimated to be about 23 vol%. Bulk density and bending strength of the composites increased with sintering temperature. Fracture energy of HAp/ZrO₂ composite sintered at 1350 °C was approximately 1.6 times higher than that of monolithic HAp. Although the bending strength of HAp/ZrO₂ composite prepared in this study was relatively low, it exhibited high fracture energy than HAp monolithic and a non-brittle fracture behavior was obtained without using fiber as the reinforcement.     

Synthesis of Nanocrystalline Hydroxyapatite Nanorods via Hydrothermal Conditions

The effect of Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ primary solutions as the starting materials in the synthesis of a calcium phosphate phase was examined. Therefore, wet chemical reactions were investigated in solution at different temperatures by hydrothermal conditions aimed at hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) synthesis. The powders were investigated by XRD, SEM, FE‐TEM, HRTEM, EDAX, SAED, and FTIR. It is found that the HAp have diameters of 25–50 nm and lengths of 120�30 nm with different morphologies. As a matter of fact, the hydrothermal method guarantees the production of HAp for different applications.     

Preparation and in vitro apatite-forming ability of hydroxyapatite and β-wollastonite composite materials

This paper provides a one-step method of preparation of the ceramic powders, containing various amounts of hydroxyapatite (HA) and β-wollastonite (WT), based on the salt coprecipitation and subsequent thermal treatment of the synthesis products at 1000?°C. Aqueous solutions of Ca(OH)₂, H₃PO₄ and Na₂SiO₃ were used as precursors of Ca₁₀(PO₄)₆(OH)₂ and β-CaSiO₃, as a minimal amount of by-product is formed during such an interaction of reagents. Variation of the concentration of the initial reagents allows the preparation of ceramic powders containing from 0 to 100?wt% of apatite. All composites were examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), laser diffraction analysis and an adsorption method (BET). Degradability of composite powders was analyzed in the Tris-HCl buffer solution. The apatite-forming ability of synthetic composites was investigated by soaking composite ceramics in a simulated body fluid (SBF). The results that were obtained reveal an increase in the dissolution rate of powders with wollastonite addition. Soaking of the composite ceramics in SBF leads to the formation of a bone-like apatite spherical particle layer on their surfaces, which become thicker while the content of β-СаSiO₃ in the samples increases.     

Synthesis and dissolution behavior of β-TCP and HA/β-TCP composite powders

Calcium phosphate powders, β-TCP and biphasic HA/β-TCP, were synthesized by calcining the powders obtained from the co-precipitation method using Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄. The effects of the initial Ca/P ratio and pH of the solution on the phase evolution and in vitro dissolution behavior of the powders in a Ringer's solution were investigated. The Ca/P ratio of the resulting powders was strongly dependent on the pH of the solution and weakly dependent on the initial Ca/P ratio. Single phase TCP powder was obtained at pH=7.4 and the initial Ca/P ratio had a little effect on the resulting Ca/P ratio. Biphasic composite powders were prepared at pH=8.0 and the Ca/P ratio of resulting powder was controllable by adjusting the initial Ca/P ratio. TCP powder showed the highest dissolution rate in the Ringer's solution and biphasic composite powder exhibited an intermediate dissolution behavior between that of HA and TCP.     

Physico-chemical and biological properties of novel Eu-doped carbonization modified tricalcium silicate composite bone cement

This paper introduces a novel composite bone cement (Eu:HAp/V-C₃S), which is composed of carbonated tricalcium silicate (V-C₃S) and europium-doped hydroxyapatite (Eu:HAp), and Eu:HAp was generated by hydrothermal synthesis. The physical and chemical properties, mineralization in vitro, biocompatibility and bacteriostasis of the composite bone cement were evaluated. The results show that the Eu:HAp/V-C₃S composite bone cement has good setting properties and a relatively low pH value. The composite bone cement with 0.1 wt% Eu has a higher compressive strength than pure V-C₃S (141.06% higher than pure V-C₃S), which can greatly improve the mechanical properties of the materials. The in vitro immersion test shows that composite bone cement has good mineralization ability. The cell test proves that it has good cell proliferation ability and low cytotoxicity. In addition, the bacteriostatic experiment also verifies that composite bone cement has bacteriostatic effect to some degree. These results indicate that Eu:HAp/V-C₃S composite bone cement is a promising biomedical material.     

Hydroxyapatite/tricalcium silicate composites cement derived from novel two-step sol-gel process with good biocompatibility and applications as bone cement and potential coating materials

Tricalcium silicate (C₃S) and hydroxyapatite (HAp) composites were fabricated through the sol-gel process. The aim of this research is to improve the biocompatibility of C₃S through HAp addition and study the potential of using this as coating materials. The composites (HAp/C₃S) were characterised by Fourier transform infrared spectrometry, thermal gravity-differential thermal analysis and X-ray diffraction. The working and setting times of cement pastes were tested using Gillmore needle. Mechanical properties were examined by nanoindentation and material testing system. In vitro biocompatibility of the materials were studied by cell attachment and viability of L929 and MG-63 cells. HAp/C₃S as a coating material on gelatin film were measured with the surface roughness and imaged by scanning electron microscope. With the addition of HAp, no undesirable free CaO was detected with the synthesis by the sol-gel preparation. The pH values of HAp added groups were between 7.54 and 8.76, which were much lower than pure C₃S group (pH?=?11.75). For in vitro studies, the presence of HAp could effectively enhance the cell attachment and viability of both L929 and MG-63 cells grown in the extract or directly on the composites. However, the mechanical properties of the composites were impaired as compared to pure C₃S. Lastly, HAp/C₃S cement could be evenly coated on gelatin film. HAp is successfully demonstrated to improve C₃S biocompatibility with this new composites HAp/C₃S. C-75 (75% C₃S and 25% HAp), in particular, has good biocompatibility, relatively high compressive strength and can be uniformly coated onto gelatin film. Thus, C-75 is a promising material for further investigation as a coating on other biopolymers.     

Preparation of Al2O3–SiC composite powder from kyanite tailings via carbothermal reduction process

ABSTRACT

Al₂O₃–SiC composite powders were prepared from kyanite tailings mixed with 20% excess carbon coke via carbothermal reduction (CR) reaction. The optimised synthesis condition for synthesising Al₂O₃–SiC composite powders was at 1600°C for 6?h. The equilibrium relationship curves of the condensed phases were presented and the temperature dependence of the phase composition was also studied. The results show that irregular Al₂O₃ and SiC grains first formed at 1500°C, and the elements C, O, Al, and Si randomly distributed in the each crystal particles. The amount of Al₂O₃–SiC composites increased with the increasing synthesis temperature and reaction time. Finally, Al₂O₃–SiC composite bulk materials were further prepared by pressureless sintering using the synthesised Al₂O₃–SiC composite powders as raw materials, and their mechanical properties were investigated in detail. All these results indicate that the CR method can offer a niche application for the development of kyanite tailings.     

Natural and synthetic hydroxyapatite/zirconia composites: A comparative study

Zirconia precursor was precipitated in a HAp particles suspension using two HAp powders of natural origin and a synthetic powder. The first natural HAp was extracted from animal bones by treatment with hot NaOH solution and the second one by treatment under hydrothermal conditions with water.Hydrous zirconia was precipitated in the HAp suspension. Pressureless sintering was performed at 1000–1300 °C and hot pressing at 1050–1300 °C.It was found that zirconia additive promotes decomposition of both HAp of natural origin as well as the synthetic one. The most stable HAp was the one extracted from bovine bones by treatment with water in an autoclave. This reaction leads to the formation of β–TCP and the CaO–ZrO₂ solid solution.The hot pressed composites show essentially higher strength and fracture toughness as compared to the pure hydroxyapatite polycrystals.     

Morphological and thermal characterization of zirconia/hydroxyapatite composites prepared via sol-gel for biomedical applications

The thermal behavior of pure ZrO₂ and hydroxyapatite (denoted as Z and HAp, respectively), as well as three composites with different content of Z and HAp (Z90HAp10, Z70HAp30 and Z50HAp50) prepared via sol-gel method has been studied by thermogravimetry (TG) and first-order derivative of TG up to 1200?°C under inert gas atmosphere. Dehydration, loss of alcohol and acetylacetone and a multi-step thermal decomposition processes has been identified by analyzing the gases evolved in each step by Fourier transform infrared spectroscopy (FTIR). Fresh samples of Z-rich composites undergo an abrupt ejection of material from the crucible around 200?°C with noticeable increase of the sample temperature. During the occurrence of this phenomenon FTIR spectra demonstrated the evolution of gases (CO, CO₂, acetone and ethylene) due to the simultaneous decomposition of acetylacetone and ethanol, not present in the samples calcined at 120?°C. As far as the structural study is concerned, pure Z crystallizes at 1000?°C in the monoclinic system, but the presence of HAp in the composite materials enables the crystallization of Z in the tetragonal phase. Finally, the amorphization degree increases with increasing the content of Z in all the composites treated at 600 and 1000?°C.     

Mechanical properties of HAp–ZrO2 composites

Hydroxyapatite is a well-known and valuable implant material with bioactive properties. Full utilisation of the unique properties of hydroxyapatite ceramics is, however, possible only after its proper reinforcement, i.e., by preparation of composites. In the present work zirconia reinforced hydroxyapatite composites were obtained by hot pressing method. The reinforcing phase in the form of ZrO₂ particles was selected due to the satisfactory biocompatibility of ZrO₂ and also because of its exceptional mechanical properties.Our investigations were aimed at assessing the influence of varying ZrO₂ on the phase composition and mechanical properties of HAp–ZrO₂ composites. In order to produce dense sinters, we used three types of initial zirconia powders which differed in morphology and contents of the tetragonal and monoclinic phases. We studied the influence of these oxides on thermal stability of hydroxyapatite matrix as well as on the phase composition and mechanical properties of the composite materials produced.     

Piezoelectric and mechanical properties of hydroxyapatite/titanium oxide composites

Hydroxyapatite (HAp) is the most common bioactive ceramic used to replace hard tissue in the body. Because of its low resistance and fragile nature, more attention is being given to composites based on HAp such as HAp/TiO₂ composites. This study aims at reporting the synthesis of HAp/TiO₂ composites (hereafter named HT composite) by sol-gel and co-precipitation methods assisted by ultrasonic radiation. The structural characterization was carried out by X-ray Diffraction (XRD) and Scanning Transmission X-ray Microscopy (STXM) techniques using synchrotron radiation, which allowed a mixture of phases to be identified separately in the two materials once the composite was formed. A Rietveld refinement for XRD data determined the phase percentage and structural parameters obtained for each material. In addition, crystallite size using the modified Scherrer equation was determined. A piezoelectric character of the two materials was confirmed by Piezoresponse Force Microscopy (PFM) to determine the piezoelectric coefficient (d_eff). Finally, PinPoint-AFM force curves confirmed an increase in the Young's modulus value for the HT composite.     

The influence of CNTs on the thermoelectric properties of a CNT/Bi2Te3 composite

CNT/Bi₂Te₃ composites were prepared from composite powders in which CNTs were implanted in the Bi₂Te₃ matrix powders by a novel chemical route. It was found that the fabricated composite had a microstructure of a homogeneous dispersion of CNTs in the Bi₂Te₃ matrix due to interfacial bonding agents of oxygen atoms attaching to the surface of CNTs. The dimensionless figure of merit (ZT) of the composite shows significantly increased values compared to those of pure binary Bi₂Te₃ in the temperature range of 298–498 K and a maximum ZT of 0.85 was obtained at 473 K. It is considered that the improved thermoelectric performance of the composite mainly originated from thermal conductivity that was reduced by active phonon-scattering at the CNT/Bi₂Te₃ interface.     

Densification additives for hydroxyapatite ceramics

The present work is aimed at the elucidation of the role played by CaCl₂ and NH₄NO₃ (the latter is a by-product of the solution synthesis of hydroxyapatite, hereinafter referred to as HAp) in the densification of nano-sized HAp powder in the course of the pressureless sintering. Nanocrystalline HAp powder was fabricated via the wet-precipitation technique by the dropwise addition of an (NH₄)₂HPO₄ solution to a Ca(NO₃)₂ mother solution at a pre-adjusted pH at 60 °C. The pH of the aqueous mixture was maintained at a constant value (either 7 or 9) by the addition of an appropriate amount of NH₄OH. The Ca/P ratio was set to 1.67, 1.61, and 1.48; 10 wt% of CaCl₂ was added to dry HAp powder. NH₄NO₃ remaining in unwashed HAp powder can act as a fluxing agent that promotes partial melting at a relatively low temperature (150–250 °C) thus allowing the particles to rearrange into a denser packing. Several mechanisms of the CaCl₂ action as a densification additive might be envisaged: (i) a decrease in the melting temperature; (ii) the surface wetting of grains; (iii) a change in the growth morphology owing to the high-temperature surfactant properties; (iv) a possible reaction with HAp on the surface of grains giving rise to the decomposition of HAp and yielding chlorapatite (ClAp), which can convert back to HAp over a wide temperature range and at any level of H₂O.     

Processing of hydroxyapatite and its composites using ceramic fused filament fabrication (CF3)

In this article, we report the fabrication of hydroxyapatite (HAp) and its composites with 7.75 vol% Si₃N₄ (HAp10SN) using ceramic fused filament fabrication (CF³). Homogeneous feedstock with 40 vol% ceramic powder was prepared and used to extrude filaments for further printing using a desktop printer. Our results showed that the addition of Si₃N₄ to HAp increases the feedstock viscosity. However, the filaments and CF³ parts made using HAp and HAp10SN feedstocks exhibited comparable densities without gross defects. We have obtained relatively smoother CF³ parts with HAp10SN than pure HAp, which is attributed to their high feedstock viscosity and formation of liquid phase during sintering. Sintering at 1250 °C for 4 h in air, after thermal debinding, resulted in a relative density of ~85% with HAp and tricalcium phosphate (TCP) as major constituents. Sintered HAp10SN samples also revealed almost 70% reduction in the grain size and 4-fold increase in the hardness compared to pure HAp. Our results indicate that the CF³ processed HAp10SN samples containing ~15% porosity, Si₃N₄ particles and Si-substituted HAp/TCP have strong potential as bone replacements.     

Preparation and electrochemical properties of polyaniline/α‐RuCl3.xH2O composites for supercapacitor

Polyaniline/α‐RuCl₃.xH₂O composites were successfully synthesized by an in‐situ chemical polymerization and employed as new electrode materials in supercapacitors. The synthesized composites were characterized physically by scanning electronic microscope (SEM). The electrochemical capacitance performance of these composites was investigated by cyclic voltammetry, galvanostatic charge–discharge tests and AC impedance spectroscopy with a three‐electrode system in 1 mol l⁻¹ NaNO₃ aqueous solution electrolyte. The polyaniline/α‐RuCl₃.xH₂O composites electrodes showed much higher specific capacitance, better power characteristics and were more promising for application in capacitor than pure polyaniline electrode. The effect and role of α‐RuCl₃.xH₂O in the composite electrode were also discussed in detail. POLYM. COMPOS., 34:2142–2147, 2013. © 2013 Society of Plastics Engineers     

Quaternary bioactive glass-derived powders presenting submicrometric particles and antimicrobial activity

The biomedical engineering advances in the last years have been rising demand for multifunctional biomaterials. Bioactive glass (BG) submicron particles are potential candidates for the formulation of composites with improved dispersion and homogeneity between the constituents. This work presents the preparation of SiO₂–Na₂O–CaO–P₂O₅ glass-derived powders composed of particles with homogenous shapes and sizes between 300 and 500 nm. Two types of synthesis were employed for the preparation of the BG powders, the melt-quenching method, and a citric acid-assisted sol-gel route at a low citric acid concentration (0.005 mol L^?1). The morphology of the particles was achieved by a low-energy process using a ball mill. These powders were characterized for their structure and surface area and evaluated for in vitro mineralization and antibacterial behavior. X-ray diffraction (XRD) analysis revealed different crystalline silicate phases in the sol-gel-derived powder and confirmed the amorphous structure of the melt-quenching-derived one. The surface of the particles was covered by hydroxycarbonate-apatite (HCA) after five days in simulated body fluid (SBF). The antibacterial activity against Staphylococcus aureus was higher for the sol-gel-derived powder, showing inhibition >99% of the bacteria growth in 24 h for all concentrations studied. These BG-based powders present a set of characteristics useful for the formulation of multifunctional composites for orthopedic applications.