Yin Zhang

Influence of Powder Particle Size of Slurries on Mechanical Properties of Porous Hydroxyapatite Ceramics

The effect of different particle sizes on the flexural strength and microstructure of three different types of hydroxyapatite (HAp) powders was studied. The powder characteristics of laboratory synthesized HAp powder (Lab1 and Lab2) were obtained through a wet milling method, and the median particle size and the specific surface area of powders are different with the dryness period. The median particle sizes of Lab1 and Lab2 are 0.34 µm and 0.74 µm, and the specific surface areas of Lab1 and Lab2 are 38.01 m2/g and 19.77 m2/g. The commercial HAp had median particle size of 1.13 µm and specific surface area of 11.62m2/g. The different powder characteristics affected the slip characteristics, and the flexural strength and microstructure of the sintered porous HAp bodies are also different. The optimum value for the minimum viscosity in these present HAp slip with respect to its solid loading and the optimum amount of the deflocculant were investigated. The flexural strengths of the porous HAp ceramics prepared by heating at 1200°C for 3 hrs in air were 17.59 MPa for Lab1 with a porosity of 60.48％, 10.51 MPa for Lab2 with a porosity of 57.75％, and 3.92 MPa for commercial HAp with a porosity of 79.37％.

Preparation of Biphasic Calcium Phosphate Porous Ceramics Prepared from Fine Powders with Different Particle Size and its Dissolution Behavior in Simulated Body Fluid

Biphasic calcium phosphate (BCP) ceramics, a mixture of hydroxyapatite (HAp) and betatricalcium phosphate (β-TCP), of varying HAp/β-TCP ratios was prepared. One kinds of HAp and one kind of β-TCP powders were used to produce porous BCP bioceramics with HAp/β-TCP weight rations of 20/80, 40/60, and 80/20. A slip was obtained by adding a mixed powders of HAp and β-TCP to a solution 1.5% of deflocculant and 0.5 wt% of foaming agent. The optimum value for the minimum viscosity in these present slips with respect to its solid loading and the optimum amount of the deflocculant were investigated. The specimen obtained by casting a polyurethane foam with 1.5 wt% of deflocculant into a slip, and drying it under vacuum, was heated at 1150°C for 3 hours. The resultant porous BCP sintered body had large spherical pores of 300 /m with interconnecting rectangular voids. Many small pores in the size range of 2-3 /m or below were observed in the specimen obtained by heating at 1150°C for 3 hours. The dissolution test was done as follows. The obtained porous ceramics samples about 0.5g individually soaked into 30 mL of simulated body fluid (SBF) solution at 36.5°C. The calcium and phosphorous content of the SBF solution was analyzed by ICP. The porous body was dried, and characterized using SEM, XRD, and FT-IR.

Bimodal Porous Bi-Phasic Calcium Phosphate Ceramics and Its Dissolution in SBF Solution

Biphasic calcium phosphate (BCP) ceramics, a mixture of hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP), of varying HAp/β-TCP ratios were prepared from fine powders. Porous BCP ceramic materials with HAp/β-TCP weight rations of 20/80, 40/60, and 80/20 were prepared. In this study, the bioactivity is reduced at a larger HAp content rate, which is likely related to the high driving pore for the formation of a new phase, and the reaction rate was proportional to the β-TCP. The porous BCP ceramics having a bigger porosity rate can easily under up dissolution. The powder having a larger β-TCP content rate can easily generate a new phase. The dissolution results confirmed that the biodegradation of calcium phosphate ceramics could be controlled by simply adjusting the amount of HAp or β-TCP in the ceramics and porosity rate.

The Influence of Conditions on Synthesis Hydroxyapatite By Chemical Precipitation Method

Particles of Hydroxyapatite (HAp) were synthesized by means of chemical precipitation method, under atmosphere pressure. The starting solution with the Ca/P ratio of 1.67 was prepared by mixing 0.167 mol?dm?3 Ca(NO3)2?4H2O, 0.100 mol?dm?3 (NH4)2HPO4, 0.500 mol?dm?3 (NH2)2CO and 0.10 mol?dm?3 HNO3 aqueous solutions. The hydroxyapatite were prepared by heating the solution at 80 ?C for 24 hour and then at 90?C for 72 hour. Then followed, the dry powers were heat treatment at 660?C temperatures for 8 hour. The obtained powder was analyzed using XRD, XRF, FT-IR, SEM, TG-DTA. The results showed that obtained HAp powers were greatly influenced by synthetic conditions. HAp powders with various morphologies, such as sphere, rod, layered, dumbbell, fibre, scaly, were obtained by controlling the synthetic conditions.

Preparation of Bimodal Porous Apatite Ceramics through Slip Casting Using Fine Hydroxyapatite Powders

A bimodal porous hydroxyapatite (HAp) body with high flexural strength was prepared through slip casting. HAp fine powder used in this study was synthesized by wet milling, drying and heating of a mixture of calcium hydrogen phosphate di-hydrate and calcium carbonate. The synthesized HAp powder was 0.320.05 μm in size and 38.10.8m2/g in specific surface area. The slip was prepared by adding deflocculant and foaming reagent. The optimum value for the minimum viscosity in the present HAp slip with respect to its solid loading and the optimum amount of the deflocculant were studied. The total porosity of the specimens obtained from a slip of 48 wt% HAp solid loading is in the range of 49 – 61vol %, and the resultant porous HAp sintered body had large spherical pores of 300 -m with interconnecting rectangular voids. Many small pores in the size range of 2-3 -m or below were observed in the specimen obtained by heating at 1100, and 1200 . The flexural strength of the bimodal porous HAp ceramics sintered at 1200 C showed a large value of 17.6 MPa, with a porosity of 60.5vol.

Hyperstructured Hydroxyapatite Ceramics as a Carrier for Cell and Protein

The preparation of hyperstructured hydroxyapatite (HAp) ceramics is reported. Mesoporous silica with nano size pore was coated on the bi-modal type porous HAp ceramics with pore size 100-200 µm and 1-2 µm. The mesoporous silica coating was done using two different procedures and the ceramics were characterized by XRD, N2 Sorption, SEM/EDX, and TEM. The results clearly showed the formation of mesoporous coating on the large pores of parent HAp ceramics. SEM images reveal that the mesoporous coatings consists of almost spherical particles with relatively uniform sizes of ~1 µm. Protein adsorption and release behavior on these mesoporous coated HAp ceramics was evaluated using UV-VIS spectrometry. The large pores are suitable for cell immobilization, and the mesopores several nm in size were found to enhance protein encapsulation ability.

Preparation of Bimodal Porous Biphasic Calcium Phosphate Ceramics and Their Dissolution Behavior in Simulated Body Fluid

Biphasic calcium phosphate (BCP) ceramics, a mixture of hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP), of varying HAp/β-TCP ratios were prepared from fine powders. Porous BCP ceramic materials with HAp/β-TCP weight rations of 20/80, 40/60, and 80/20 were prepared. In this study, the bioactivity is reduced at a bigger HAp content rate, which is likely related to the high driving pore for the formation of a new phase, and the reaction rate was proportional to the β-TCP. The porous BCP ceramics having a bigger porosity rate can easily under up dissolution. The powder having a bigger β-TCP content rate can easily generate a new phase. The dissolution results confirmed that the biodegradation of calcium phosphate ceramics could be controlled by simply adjusting the amount of HAp or β-TCP in the ceramics and porosity rate.

The effect of phosphoric acid concentration on the synthesis of nano-whiskers of calcium metaphosphate by chemical precipitation Method

Calcium metaphosphate (CMP) nano-whiskers were produced by a chemical precipitation method. In order to produce nano-powders, CMP was prepared by the mixing of two precursors, calcium oxide (CaO) and phosphate acid (H3PO4). Sparingly soluble chemicals, the Ca/P ratio of the mixture was set to be 0.50 to produce stoichiometric CMP, were chemical agitated in phosphate acid solution. At least 3 hours of pre-hydrolysis of phosphorus precursor were required to obtain CMP phase. The CMP powders were dried in a drying oven at 60 °C for 7 days and then followed by a heat treatment at 390 °C for 8hours. The obtained powder was analyzed using XRD, XRF, FT-IR, SEM, TG-DTA, Zeta Potential Meter, Specific Surface Area, and Particle Size Analyzer. The results showed that obtained CMP nano-whiskers have a significantly powder characteristics.

Study on the Propertyies of Magnesium-Doped Calcium Polyphosphate Scaffolds Ceramics

This Magnesium-doped calcium polyphosphate (MCPP) porous bioceramics of different magnesium content were prepared by the method of solid reaction sintering. The effect of magnesium on the structure and density of magnesium-doped calcium polyphosphate bioceramics was studied. Phases, cross section morphologies and porosity of MCPP bioceramics were analyzed with X-ray diffraction(XRD) and scanning electron microscopy (SEM). The results show that MCPP ceramics were successfully prepared by the solid reaction sintering, and the bending strength of ceramics began to increase and then to decrease with increasing amounts of magnesium content apart with the improvement of the stability improved.

Synthesis of Calcium Metaphosphates Fine Powders by Chemical Precipitation Methods

Calcium metaphosphate (CMP) fine powders were produced by a chemical precipitation method. In order to produce the powders, CMP was prepared by the mixing of two precursors, such as calcium oxide (CaO) and phosphate acid (H3PO4). Sparingly soluble chemicals, the Ca/P ratio of the mixture was set to be 0.50 to produce stoichiometric CMP, were chemical agitated in phosphate acid solution. At least 3 hours of pre-hydrolysis of phosphorus precursor were required to obtain CMP phase. The CMP powders were dried in a drying oven at 60°C for 72 hours and then heat-treated at various temperatures at a ramp of 1°C /min in air for various hours. The obtained powder was analyzed using XRD, XRF, FT-IR, SEM, TG-DTA, Zeta Potential Meter, Specific Surface Area, and Particle Size Analyzer. The results showed that obtained CMP powders have a significantly powder characteristics.