Cheng Long Yu

Preparation of Porous Hydroxyapatite-Zirconia Composite Scaffolds by Combination of Gel-Casting and Polymer Sponge Methods

Hydroxyapatite (HA) doped with 3%yttria-stabilized 20wt% zirconia (ZrO2) ceramic were developed in order to produce a porous composite biomaterial by integrating the gel-casting technique with polymer sponge method with improved mechanical strength and controllable porous structure. The pore morphology, size, and distribution of the scaffolds were characterized using an electron microscope. The scaffolds prepared have an open, uniform and interconnected porous structure with a pore size of 300~500m. The porosity of the open pores in the scaffold can be controlled by changing HA-ZrO2 composite concentration and it is between 87%~35%. A compressive strength of 12MPa for HA-ZrO2 porous scaffolds with HA-ZrO2 concentration of 55wt% was achieved, which is comparable to that of cortical bone.

The Effects of Calcium Fluoride Addition on Crystallization Characteristics of Hydroxyapatite-Zirconia Composite

Hydroxyapatite (HA) doped with 3% Yttria-stabilized 20vol%m-ZrO2 composite were synthesized by solid state reaction between tricalcium phosphate (TCP) and Ca(OH)2 at various temperature(1000 to 1200°C) for 3h with adding 5~20wt% calcium fluoride (CaF2), respectively. The effects of various amount of CaF2 on crystallization characteristics of HA-20vol%ZrO2 composite were investigated in details. The results show that when small amount of CaF2 was added, the reactions of HA with CaF2 occurs, which leads to the formation of fluorapatite (FA). With the increasing of the amount of CaF2, the decomposition of HA to β-TCP decreases gradually and the CaZrO3 peaks disappear, while t-ZrO2 increases because of the formation of thermally stable FHA solid solutions. When the sintered temperature is above 1100°C and the addition of CaF2 is about 10wt%, the main phases are FHA and t-ZrO2 with a negligible amount of Ca5P8, which suppress the reaction between HA and ZrO2. From SEM, it can be seen that with 10wt% of CaF2 addition, the morphology of the composite powder is a mixture of spherical ZrO2 particles embedded within agglomerated HA shaped like a small rod.

Crystallization Characteristics and Microstructure of Yttria-Stabilized Zirconia / Hydroxyapatite Composite

Good crystallized Hydroxyapatite was synthesized using H3PO4 and Ca(OH)2 as raw materials by wet chemical method and sintered at 800°C for 3h. The as-prepared HA powders were mixed with 15%, 20%, 25% yttria-stabilized m-ZrO2, respectively, and sintered at 900°C- 1200°C for 1h, respectively. The main phases and rules of phases changing with the content of yttria-stabilized m-ZrO2 and sintered temperature was investigated by XRD and the microstructure features of the composite powders were analysed by scanning electron microscopy. The results show that when the temperature is at 1000°C, HA starts to decompose to β-TCP and CaO, the m-ZrO2 is then partly converted into t-ZrO2 by partial consumption of CaO, which in turn results in a mixture of β-TCP and HA further. The CaO produced reacts further with m-ZrO2 generating a mixture of t-ZrO2 and CaZrO3 in different proportions. The microstructure of the HA-ZrO2 composite further indicates that when sintered at 1000°C for 1h, gray slice area represent a mixture of HA and a small amount of β-TCP. While in the white area, some spheric ZrO2 mixed with a negligible amount of CaO. When sintered at 1200°C, distinguished reduced spherical ZrO2 particles embed within mixed HA and β-TCP, which change from slice to agglomeration. As a result, when the sintered temperature is about 1000°C and the addition of m-ZrO2 reaches 20wt%, superior main phases are HA and t-ZrO2, which improves the combination of mechanical and biological properties.

Preparation of Glass-Alumina Functionally Gradient Materials by Rapid Prototyping Technology

A novel rapid prototyping manufacturing technology for glass-alumina functionally gradient materials (G-A FGMs) based on the quick solidification of wax was proposed. The feature of the technology came from its layer-by-layer fabrication of the wax-glass/alumina composite layer carved in accordance with the shape of each layer of the computer designed model and in situ casting of wax into the carved area. Removal of the wax in the G-A FGMs green body was investigated based on differential scanning calorimetry (DSC) analysis. Sintering properties of the G-A FGMs were discussed. Bending strength of the G-A FGMs was measured by a three-point flexural test. Microstructures of the prepared G-A FGMs were observed using environmental scanning electron microscope (ESEM) and the compositional distribution was determined according to energy dispersive spectrum (EDS). Samples were preliminarily and respectively held at 200°C and 300°C for a long time based on the DSC analysis. The range of the optimal sintering temperature is determined to be from 710°C to 720°C and the holding time is 30min. With the increasing alumina content, the bending strength increases and the maximum bending strength is 67.5MPa. There is no delamination of the G-A FGMs via ESEM. Homogeneous distribution of the ingredient materials is confirmed through EDS.

Molten Salt Synthesis of Ni0.5Zn0.5Fe2O4 Ferrites

In this paper, Ni0.5Zn0.5Fe2O4ferrite ceramics were produced with Ni0.5Zn0.5Fe2O4powders prepared by reaction in a molten salt using Fe2O3, NiO and ZnO powders as raw materials. Ni-Zn powders were characterized by X-ray diffraction (XRD). Density and shrinkage in diameter of Ni0.5Zn0.5Fe2O4ceramics were measured. MicroSubscript text structures were observed using field emission scanning electron microscopy (FESEM), and magnetic properties were examined by HP4291B impedance analyzer. XRD pattern indicated that the powders synthesized at 900°C for 1h were pure spinel Ni0.5Zn0.5Fe2O4phase. Via the measurement of density and shrink in diameter, optimal temperature was 1200°C and holding time was 2h, which was in accord with the results concluded from micrographs. FESEM images illustrated that the average grain size increased with increasing holding time, which followed the Ostwald liquid growth mechanism. At lower frequencies, the initial permeability (μi) increased from 86.65 to 183.48 with increasing holding time, while the threshold frequency decreased from 13.3MHz to 8.52MHz, which implied the initial permeability (μi) variation complied with the Snoek law to some extent.

Aluminium Induced Sub-Microsized α-Al2O3 Platelets in the Soda-Lime-Silica Glass

α-Al2O3 platelets were prepared in the interface of Na2O-CaO-SiO2 glass induced by Al. The morphology of the platelets was observed by Environmental Scanning Electron Microscopy (ESEM). The platelets are irregularly shaped at 720°C for 30mins and share mean thickness of 200nm. EDS shows that the platelets are rich in Si, reasonably due to the formation of Al-Si eutectic. At 1200°C, the prepared platelets have mean diameters between 400nm and 1000nm, most of which are aggregated and part through intergrowth. The crystals develop from the glass and can form good moistening with the glass matrix.

Novel Temperature Dependent Process for α-Al2O3 Platelets

α-Al2O3 platelets were prepared in the interface of Na2O-CaO-SiO2 glass induced by Al. Phase identification was accomplished by X-ray diffraction analysis. The morphology of the platelets was observed using an Environmental Scanning Electron Microscopy (ESEM). The changes for the mixtures of the Al powders and the glass powders that occurred during heating were characterized by a combination of differential scanning calorimetry (DSC) and thermalgravimety(TG) on a multi-functional instrument. Confirmed by XRD and ESEM, at 1200°C, the prepared platelets have mean diameters between 400nm and 1000nm. Most of them are aggregated and part of them through intergrowth. The crystals develop from the interface between glass and Al, and can form good moistening with the glass matrix. DSC/TG shows that γ-Al2O3 formed by oxidation of Al, transforms into α-Al2O3 and grow into the platelet α-Al2O3 crystals owing to the molten Al and the molten glass. On the other hand, part of the molten Al erodes into the glass and makes the deviation of the Na2O-CaO-SiO2 ternary system into Na2O-Al2O3-SiO2 ternary system, resulting in the formation of NaAlSiO4.

Crystallization Characteristics and Thermal Stability of Fluor-Hydroxyapatite Composites with Zirconia

Hydroxyapatite (HA) was synthesized in presence of 20wt% m-ZrO2 by solid state reaction between tricalcium phosphate(TCP) and Ca(OH)2 at 1000 °C for 2h. Similarily, Fluorine hydroxyapatite(FA) was synthesized using tricalcium phosphate and calcium fluoride as raw materials at 1000 °Cfor 3h. The as-prepared HA was mixed with 10%,25%,45%,55%,70wt% FA and the mixture was sintered at 1000°C-1400°C for 2h. The main phase and bulk density was measured. The results show that when the relative amount of FA to HA increased, the decomposition of the composite is decreased gradually because of the formation of thermally stable FHA solid solutions. Low temperature would effect the exchange of ionic between FA and HA,while high temperature would impact synthesis of composites, because high temperature would lead to dissolution of HA ,which has to react with FA. Increase the content of HA would be advantage for synthesis FHA-ZrO2 composite.

Orthogonal Experiment of Glass-Alumina Functionally Gradient Materials Produced with Rapid Prototyping

A novel rapid prototyping technology for glass-alumina functionally gradient materials (G-A FGMs) based on the quick solidification of wax was proposed. The feature of the technology came from its layer-by-layer fabrication of the wax-glass/alumina composite layer. With the help of orthogonal experiment method, the influence of different parameters (sintering temperature, component ratio (the glass and the alumina), and number of layers) on the flexural strength of FGMs was discussed. Optimum conditions obtained from the above experiments were applied to prepare the G-A FGM with three layers. The G-A FGM was analyzed in detail, by observing it under an environmental scanning electron microscope (ESEM) coupled with an X-ray energy dispersive spectrometer (X-EDS). The results of orthogonal experiment show that number of layers is the principal parameter to the flexural strength of FGMs, component ratio is the secondary factor, and sintering temperature may be not an important factor. The special microstructure appears in the cross section of the G-A FGM, observed by ESEM. It is from the X-EDS graph concluded that alumina and glass probably react to form the special microstructure with part removal of wax.

Modeling on Falling Velocity of Sodiumtetraborate Aqueous Solution Drops before the Gelation of PVA-TiO2 Suspensions by the Runge-Kutta Method in Matlab 6.5

Numerical modeling on falling of sodiumtetraborate aqueous solution drops as the initiator before the gelation of PVA-TiO2 suspensions was conducted. Effect of time and elevation angle of the PVA-TiO2 suspensions on the falling velocity of the sodiumtetraborate aqueous solution drops was analyzed. An ordinary differential equation was given. Integration of the ordinary differential equation was fulfilled using the fourth-order Runge-Kutta method in Matlab 6.5. From the model, a two-order nonlinear effect of time on the velocity of the drops during falling is determined and the quadratic term -3.408t2 serves as the time dependent air resistance. The component of the falling velocity along the suspensions increases with the increasing of the elevation angle. However, for the component vertical to the suspensions, with elevation angle increasing, it decreases.