Decomposition Of HAp Research Articles

Enhanced Sinterability and Mechanical Strength of Beta-type Tricalcium Phosphates Ceramics through Reaction Sintering with Hydroxyapatite

Beta-tricalcium phosphate (β-TCP) ceramics were fabricated via reaction sintering at 1100 °C, utilizing various phosphate salts and calcium compounds as raw materials. The sintering characteristics, reaction sintering behavior and mechanical properties of the resulting β-TCP ceramics were investigated. Reaction sintering with a Ca/P molar ratio of 1.50 consistently generated β-TCP. In addition, a notable variance in physical properties was observed contingent on the presence or absence of stoichiometric hydroxyapatite (HAp; Ca10(PO4)6(OH)2) in raw materials. Sintered bodies produced with HAp−β-Ca2P2O7 (β-CPP), HAp− CaHPO4·2H2O (DCPD) and HAp−(NH4)2H(PO4) all exhibited densification and enhanced mechanical strength, correlated with higher bulk densities. In contrast, conventional sintered bodies prepared from β-TCP and reaction sintered bodies prepared using β-CPP−Ca(OH)2 or β-CPP−CaCO3 were not as dense. Comprehensive assessments by thermogravimetry-differential thermal analysis, X-ray diffraction and scanning electron microscope together with the evaluation of shrinkage behavior were used to monitor the sintering of β-TCP with HAp. This process was found to involve thermal decomposition of HAp and crystal transitions leading to the formation and sintering of β-TCP with significant shrinkage. These findings underscore the efficacy of employing HAp as a raw material in reaction sintering. This technique allows the formation of sintered β-TCP bodies exhibiting exceptional sintering characteristics, superior bulk density and high mechanical strength.

Sintering behavior and mechanical properties of hydroxyapatite ceramics prepared from Nile Tilapia (Oreochromis niloticus) bone and commercial powder for biomedical applications

In this work, Nile tilapia (Oreochromis niloticus) bone was calcined at 800 °C for 5 h in an air atmosphere to obtain hydroxyapatite powder (FB powder). The elemental composition, phase structure, and morphology of the FB powder were investigated and compared with commercial hydroxyapatite powder (SM powder). The FB-powder exhibited 1.01 at. % of Mg while the SM-powder showed Mg in ppm-level. Carbonate groups were detected in the two powders. Both HAp and β-tricalcium phosphate (β-TCP) structures were found in the FB powder, but the SM powder exhibit only the HAp phase. Irregular-shaped particles were observed in the FB powder. After the two HAp powders were sintered at 1200 °C and 1250 °C for 2 h (FB-1200, FB-1250, SM-1200, and SM-1250), the β-TCP intensity peaks of the FB-ceramic samples significantly increased with increasing sintering temperature. The highest relative density, well-packed grains, and β-TCP stabilization by Mg at the Ca5 site of the FB-1250 structure were the dominant factors governing the highest mechanical properties. Although high density was observed in the SM-1200 sample, Vickers hardness of the SM-1200 sample is lower than the FB-1250 sample. This may be attributed to the partial decomposition of HAp into β-TCP, α-tricalcium phosphate (α-TCP), and Ca10(PO4)6O phases. In addition, the increase of grain size was the main factor that governs the increasing compressive strength and Young's modulus instead of density and phase decomposition of the SM-ceramic samples.

Thermal physical processes during forming of biocompatible Ca-P coatings by detonation spraying

Carbon-carbon composites with calcium phosphate (Ca-P) coatings (with a thickness up to of ≈100 μm) are considering as prospective grafts for defect bone substitution. Detonation spraying of Ca-P layers allows to fulfil a deposition mode with relative low temperature loads (up to a temperature of the processed surface of ≈850…1100 K) under a pulsed pressure of ≈2…6 bar. Such deposition conditions could promote to minimal thermal decomposition of feedstock HAp.

Functionally Graded Antibacterial Biomaterial Coatings for Titanium Base Alloy

Metal implants made of titanium and its alloys need surface modification operations because they are weak in terms of osseointegration and to protect them from corrosive body fluids and the growth of harmful bacteria that prevent them from performing their function and cause their failure. Hydroxyapatite and titanium dioxide have proven high efficiency by using them as biological and anti-bacterial coating. The basis of the current study is to deposit a functionally graded ceramic coating of titanium dioxide and hydroxyapatite on a Ti6Al4V substrate by electrophoretic deposition (EPD) method at room temperature with optimal conditions of 20 volts and a deposition time of 1 minute, and then sintering in an atmosphere of argon at a temperature of 950°C for one hour. In addition, polarisation, open circuit, anti-bacterial activity, XRD, SEM, EDS was conducted. The laboratory results showed that the corrosion rate decreases for the coated samples compared to the uncoated. As for the SEM examination, the cross-section images showed that the gradient coating is dense, cohesive and free from microscopic cracks. Also, the surface images showed that the surface was uniform. In terms of XRD, the results showed the presence of rutile, anatase, and hydroxyapatite phases in addition to α_CaPO and β_TCP as a result of HAp decomposition. For the anti-bacterial examination, the findings revealed that the coating is anti-bacterial.

Chemical and Electronic Investigation of Buried NiO1-δ, PCBM, and PTAA/MAPbI3-xClx Interfaces Using Hard X-ray Photoelectron Spectroscopy and Transmission Electron Microscopy.

Identification and profiling of molecular fragments generated over the lifespan of halide perovskite solar cells are needed to overcome the stability issues associated with these devices. Herein, we report the characterization of buried CH3NH3PbI3-xClx (HaP)-transport layer (TL) interfaces. By using hard X-ray photoelectron spectroscopy in conjunction with transmission electron microscopy, we reveal that the chemical decomposition of HaP is TL-dependent. With NiO1-δ, phenyl-C61-butyric acid methyl ester (PCBM), or poly(bis(4-phenyl) (2,4,6-trimethylphenyl)amine) (PTAA) as TLs, probing depth analysis shows that the degradation takes place at the interface (HaP/TL) rather than the HaP bulk area. From core-level data analysis, we identified iodine migration toward the PCBM- and PTAA-TLs. Unexpected diffusion of nitrogen inside NiO1-δ-TL was also found for the HaP/NiO1-δ sample. With a HaP/PCBM junction, HaP is dissociated to PbI2, whereas HaP/PTAA contact favored the formation of CH3I. The low stability of HaP solar cells in the PTAA-TL system is attributed to the formation of CH3I and iodide ion vacancies. Improved stability observed with NiO1-δ-TL is related to weak dissociation of stoichiometric HaP. Here, we provide a new insight to further distinguish different mechanisms of degradation to improve the long-term stability and performance of HaP solar cells.

Thermal behaviour of TiOy/HAp nanocomposites

The structural and microstructural characteristics and thermal behaviour of TiOy/HAp nanocomposite materials used for tissue engineering have been studied by differential and thermal gravimetric analyses (DTA–TGA), X-ray diffraction (XRD) phase analysis and scanning electron microscopy (SEM) methods. Substoichiometric TiO0.92 and superstoichiometric TiO1.23 were used in amounts of 10 and 20 wt %, respectively, to reinforce HAp. When the temperature increased as a result of interactions between the matrix and the introduced nanoparticles, titanium monoxide was oxidized to titanium dioxide. Comparing the DTA–TGA and XRD results allowed us to determine the temperature intervals of the beginning of the titanium valence variation and phase transitions occurring in the nanocomposites. The onset temperatures of HAp decomposition and TiOy oxidation depend on the initial stoichiometry of titanium monoxide and the composition of the reinforcing additive. The TiOy additives have a stabilizing effect on HAp. The effect of the additive stoichiometry on the interactions between the matrix and nanoparticles in the whole temperature range is shown.

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.

Bioactive, nanostructured Si-substituted hydroxyapatite coatings on titanium prepared by pulsed laser deposition.

The aim of this work was to deposit silicon-substituted hydroxyapatite (Si-HAp) coatings on titanium for biomedical applications, since it is known that Si-HAp is able to promote osteoblastic cells activity, resulting in the enhanced bone ingrowth. Pulsed laser deposition (PLD) method was used for coatings preparation. For depositions, Si-HAp targets (1.4 wt % of Si), made up from nanopowders synthesized by wet method, were used. Microstructural and mechanical properties of the produced coatings, as a function of substrate temperature, were investigated by scanning electron and atomic force microscopies, X-ray diffraction, Fourier transform infrared spectroscopy, and Vickers microhardness. In the temperature range of 400-600°C, 1.4-1.5 µm thick Si-HAp films, presenting composition similar to that of the used target, were deposited. The prepared coatings were dense, crystalline, and nanostructured, characterized by nanotopography of surface and enhanced hardness. Whereas the substrate temperature of 750°C was too high and led to the HAp decomposition. Moreover, the bioactivity of coatings was evaluated by in vitro tests in an osteoblastic/osteoclastic culture medium (α-Modified Eagle's Medium). The prepared bioactive Si-HAp coatings could be considered for applications in orthopedics and dentistry to improve the osteointegration of bone implants.

Spark plasma sintering of graphene reinforced hydroxyapatite composites

Hydroxyapatite (prepared from eggshell)/graphene (HAP/GNPs) composites were prepared by spark plasma sintering (SPS). Pure HAP does not have good mechanical properties so it is necessary to combine them with other materials, which endow them acceptable strength. Sintering was carried out at various temperatures (700°C and 900°C) and holding times (5 and 10min). Rapid processing time and low sintering temperatures was of importance to avoid HAP decomposition. Mechanical and structural properties of the sintered bodies were studied with different methods. The highest relative density ~96% was obtained at 700°C sintering temperature regardless of the holding time. Composite with the best mechanical properties (hardness ~4GPa, 3-point bending strength ~119MPa) consisted of HAP elongated grains with average length of 300nm. The GNPs were agglomerated and located on grain boundaries closed to porosities. The structural observation confirmed increased fraction of hexagonal shaped grains, and poorer mechanical properties with increased sintering time and temperature.

Consolidation of different hydroxyapatite powders by SPS: Optimization of the sintering conditions and characterization of the obtained bulk products

The difference in purity, particle size, microstructure, and thermo-chemical stability of three commercially available hydroxyapatite powders are found to play an important role during their consolidation using spark plasma sintering (SPS) as well as strongly affect the characteristics of the resulting sintered bodies. A fully dense material without secondary phases was obtained by SPS at 900°C, when using the relatively small sized, with refined grains and high purity powders. The sintered product, consisting of sub-micrometer sized hydroxyapatite grains, displayed optical transparency and good mechanical properties.In contrast, the higher temperature levels (up to 1200°C) needed to sinter powders with larger particles, or finer ones which contain additional phases, lead to products with coarser microstructures and/or significant amount of β-TCP as a result of HAp decomposition. Optical characteristics, hardness and elastic modulus of the resulting sintered samples are correspondingly worsened.

Mechanical Properties of Microwave Sintered 60YSZ-Al<sub>2</sub>O<sub>3</sub>/10HAP Bioceramics Composites

Microwave heating technology promising shorter processing times and less energy consumption beneficial for economic perspective with improved properties and better microstructural control. This study focussed on microwave sintered bioceramics material of 60YSZ-Al2O3/10HAP mixture fabricated by powder metallurgy route. The study was conducted based on three different sintering temperatures, starting with 900 °C, 1000°C ended with 1100°C. Mechanical properties of materials such as porosity, density, hardness and compressive strength were then determined for each composites. Results showed that lowest porosity was obtained at 1000°C which promoting to higher density, hardness and compressive strength. However, the increasing sintering temperature up to 1100 °C was initiated the decomposition of HAP and constitutes the formation of CaZrO3determined by X-ray Diffraction (XRD) analysis. Microstructure characterization by Scanning Electron Microscope (SEM) observed the growth of large particles and pores result in excessive grain coarsening. Better sinterability was achieved through an adequate sintering temperature of 1000°C with no reaction reported between HA and ZrO2during the sintering process facilitate by microwave hybrid heating. The pores was found to be interconnected for each composites via microwave heating expected to be useful for biomedical application which was favorable to osteo-integration.

A novel two-step sintering for nano-hydroxyapatite scaffolds for bone tissue engineering.

In this study, nano-hydroxyapatite scaffolds with high mechanical strength and an interconnected porous structure were prepared using NTSS for the first time. The first step was performed using a laser characterized by the rapid heating to skip the surface diffusion and to obtain the driving force for grain boundary diffusion. Additionally, the interconnected porous structure was achieved by SLS. The second step consisted of isothermal heating in a furnace at a lower temperature (T2) than that of the laser beam to further increase the density and to suppress grain growth by exploiting the difference in kinetics between grain-boundary diffusion and grain-boundary migration. The results indicated that the mechanical properties first increased and then decreased as T2 was increased from 1050 to 1250°C. The optimal fracture toughness, compressive strength and stiffness were 1.69 MPam1/2, 18.68 MPa and 245.79 MPa, respectively. At the optimal point, the T2 was 1100°C, the grain size was 60 nm and the relative density was 97.6%. The decrease in mechanical properties was due to the growth of grains and the decomposition of HAP. The cytocompatibility test results indicated that cells adhered and spread well on the scaffolds. A bone-like apatite layer formed, indicating good bioactivity.

Poly (l-lactide acid) improves complete nano-hydroxyapatite bone scaffolds through the microstructure rearrangement

Cracks often occur when nano-hydroxyapatite bone scaffolds are fabricated with selective laser sintering, which affect the performance of scaffolds. In this study, a small amount of poly (l-lactide acid) (PLLA) was added into nano-hydroxyapatite (nano-HAP) powder by mechanical blending in order to improve the sintering properties. The nano-HAP powder combined with 1wt % PLLA was sintered under different laser power (5W, 7.5W, 10W, 12.5W, 15W and 20W). The fabricated scaffolds were characterized using Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Micro Hardness Tester. The results showed that nano-HAP particles grew up quickly with the laser power increasing, and there were many strip-like cracks on the surface of sintering zone. The cracks gradually reduced until disappeared when the laser power increased to 15W, together with a great improvement of density. Large pores were observed on the specimen when the laser power further increases, accompanied with the decomposition of HAP into β-tricalcium phosphate (β-TCP) and tetracalcium phosphate (TTCP). And the optimum parameters were eventually obtained with laser power of 15W, scanning speed of 1000 mm/min, powder bed temperature of 150ºC, laser spot diameter of 2 mm and layer thickness of 0.2 mm. We summarized that the molten PLLA enhanced the particle rearrangement of nano-HAP by capillary force and may absorb thermal stress in laser sintering process, while PLLA would be oxidized gradually until completely excluded from the sintered nano-HAP scaffolds, which was confirmed by FTIR analysis. This study provides a novel method to improve the sintering properties of nano-HAP with no adverse effects which would be used in the application of bone tissue engineering potentially.

Hydroxyapatite Matrix Composites by Hot Isostatic Pressing: Part 2. Zirconia Fibre and Powder Reinforced

The Aim of the Project Was to Enhance the Fracture Toughness of Hydroxyapatite to a Level Comparable to that of Natural Bone for in Vivo Applications. to this Aim, the Effect of Various Parameters, Were Studied. Fully Dense Decomposition-Free Hap Matrix Composite Was Produced Using Hot Isostatic Pressing Technique. A Graphite/stainless Steel Encapsulation System Was Found to Be an Appropriate Method. Glass Encapsulation Was Unsuccessful Technique due to the Excessive Low-Temperature Volatilisation, which Aerated the Glass. Toughness Improvement Was 2.7 Times for PSZ Fibres, and 2.4 Times for PSZ Powder. the Optimal Addition Level of PSZ Fibre and PSZ Powder Was 20 Vol% and ~30 Vol% Respectively. Further, it Was Found that the Hap Decomposition Temperature Was Higher at 100 Mpa (the Hiping Pressure) than for Pressureless Sintering. the Toughening Effect of the Additives Induced Plastic Deformation and Ductile Fracture.

Hydroxyapatite Matrix Composites by Hot Isostatic Pressing: Part 1. Alumina Fibre Reinforced

Fracture Toughness Improvement of the Hydroxyapatite Matrix Composite, to a Level Comparable to that of Natural Bone for in Vivo Applications, Was the Aim of the Present Work. Hot Isostatic Press Using a Graphite/stainless Steel Encapsulation System Enabled the Production of Fully Dense Decomposition-Free Hap with Toughness Improvements of: 2.4 Times (Al2O3 Fibres, Optimally 20 Vol%). Glass Encapsulation of Fibre-Reinforced Hap Resulted in Aeration from Sample Volatilization. Further, it Was Found that the Hap Decomposition Temperature Was Higher at 100 Mpa (the Hiping Pressure) than for Pressureless Sintering. the Toughening Effect of the Al2o3 Fibre Additive Induced Plastic Deformation and Ductile Fracture.

Argon atmospheric plasma sprayed hydroxyapatite/Ti composite coating for biomedical applications

20wt.% hydroxyapatite/Ti composite coatings were fabricated via an in-house developed argon atmospheric plasma spraying (AAPS) system on Ti substrates. The phase and morphologies of the coatings were identified by X-ray diffraction and scanning electron microscopy. The electrochemical corrosion behavior of the coatings was evaluated in a simulated biomedical environment by using potentiodynamic polarization and electrochemical impedance spectroscope techniques. The bioactivity of the composite coatings was studied by immersing the coatings in simulated body fluid (SBF) for up to 8months. The mechanical properties such as microhardness, friction and bonding strength were also investigated. Results demonstrate that dense composite coatings with a typical morphology of HAP homogenously distributed in Ti matrix are obtained and the decomposition of HAP during plasma spraying process is avoided. The bonding strength is significantly higher than that of HAP or Ti reinforced HAP coatings and the frictional property is comparable to Ti substrate. A relatively higher corrosion current of HAP/Ti composite than that of pure Ti coating in simulated body fluid indicates a good bioactivity for composite coating, which is also testified by the formation of apatite layer in vitro test. After eight months immersion, a thick, tortoise-shell like apatite layer covered the entire top surface of composite coating. The study indicates the potential of AAPS deposited HAP/Ti composites as load bearing implant materials.

MA-SPSプロセスで作製したチタン–ハイドロキシアパタイト複合材料の特性

Ti-x HAp (x=0, 10, 20 and 30 mass%) composite powders were synthesised by mechanical alloying (MA) using a vibrational ball mill, and MAed composite powders were consolidated into bulk composite materials by spark plasma sintering (SPS). The hardness and constituent phase of the MAed powder and SPS materials were investigated by hardness measurements and X-ray diffraction (XRD) , respectively. Mean particle size of the MAed powders and microstructure of the SPSed materials were characterised by scanning electron microscopy (SEM) and optical microscopy, respectively. No decomposition of HAp in the MAed Ti-10 and 20 HAp composite powders occurred. However, decomposition of HAp in the MAed Ti-30 HAp composite powders occurred to form both CaO and CaTiO3. Formation of both TiC and CaO was observed in the all SPSed materials. In addition, formation of both CaO and CaTiO3 was also observed in the Ti-30 HAp SPSed materials. The hardness of the SPSed materials increased by both an increase in the amount of HAp and in the MA time. The results thus imply that the Ti-HAp composite materials exhibiting the high hardness can be obtained by a controlling of the amount of HAp powder and MA time.

Effect of Mechanical Alloying Conditions on Mechanical Properties of Ti-HAp Composite Materials

Ti-x HAp (x=10, 20 and 30 mass%) composite powders were synthesised by mechanical alloying (MA) using a vibrational ball mill, and MAed composite powders were consolidated into bulk composite materials by spark plasma sintering (SPS). Effects of MA conditions on the hardness and constituent phase of the MAed powder and SPS materials were investigated by hardness measurements and X-ray diffraction (XRD), respectively. No decomposition of HAp in the Ti-HAp composite powders was observed, whereas formation of CaO was observed in all the SPSed materials. In addition, formation of TiC occurred in the Ti-10 and 20 HAp SPSed materials. On the other hand, both CaTiO3 and TiN was formed in the Ti-30 HAp SPSed materials. The hardness of the Ti-HAp SPSed materials fabricated from the 0.5, 1 and 2 h MAed powders were higher than that of the pure Ti SPSed materials fabricated from the none MAed powder. A maximum value of Vickers hardness was 1101 HV when the Ti-20 HAp SPSed material was fabricated from 1 h MAed powder.

Behaviour of bone origin hydroxyapatite at elevated temperatures and in O 2 and CO 2 atmospheres

In the present work the behaviour of HAp extracted from pig bones at elevated temperatures up to 1000 °C in O 2 and CO 2 atmospheres has been studied. It has been found that CO 2 atmosphere arrests HAp decomposition. Chemical analysis and infrared spectroscopy reveal that no free CaO appears and no decrease of CO 3 −2 group concentration occurs in the material calcined in CO 2 atmosphere. In the O 2 atmosphere at elevated temperatures, CaO and CO 2 are emitted from the samples, although the remaining material retains the HAp structure as indicated by the X-ray diffraction.

Densification additives for hydroxyapatite ceramics

The present work is aimed at the elucidation of the role played by CaCl 2 and NH 4NO 3 (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 (NH 4) 2HPO 4 solution to a Ca(NO 3) 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 NH 4OH. The Ca/P ratio was set to 1.67, 1.61, and 1.48; 10 wt% of CaCl 2 was added to dry HAp powder. NH 4NO 3 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 CaCl 2 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 H 2O.