Chen Ma

Calcium and Phosphate Biocoatings on Magnesium Alloy Fabricated by Micro-Arc Oxidation

Calcium phosphate biocoatings were fabricated on the surface of magnesium alloy by micro-arc oxidation (MAO) technique. The properties of biocoatings related with MAO technics parameters and the electrolyte constitute. The surface morphology, constitute and friction coefficient were studied by SEM XRD and fret test machine. The results indicated that the optimum electrolyte was CaCO3-Na3PO4 contained 20g/L phosphate ions and 1.5 Ca/P ratio, and the optimum technics parameters was 350V oxidation voltage for10min, 500HZ pulse frequency and 1:10 in duty cycle. The main phase constitutes of the porous biocoatings contained were Mg, MgO, Mg3(PO4)2 and CaNaPO4. The anode polarization potential of the coating was -1.36V and enhanced about 0.29V compared with that of magnesium alloy substrate, which indicated that the biocoatings had better corrosion resistant properties. The friction coefficient of the biocoatings was 0.23 and decreased 0.15 compared with that of magnesium alloy substrate, which indicated that the biocoatings had better wear resistant properties. The biocoatings could induce hydroxyapatite to form on its surface after soaked in body fluid, which showed that the composite coatings owned good bioactivity.

Bioactive and Stability of Calcium Phosphate-Polypyrrole Composite Coatings by Electrochemical Deposition

This study examined the bioactive and stability of calcium phosphate- polypyrrole(ppy) composite coatings on titanium alloys by electrochemically deposition in simulated body fluid (SBF). Change of coatings mass and SBF pH during coatings soaked in SBF indicated that ppy reduces the decomposition of coatings. The surface morphology of coatings characterized by SEM showed that the stability of composition coating was superior to that of single coating. XRD indicated that ppy induces CO3 2- enter calcium phosphate coating, which showed that the composite coatings possess better bioactive. Thus, this electrochemical deposition provides an effective method of ppy incorporation at physiological temperature, which can offer excellent bioactive and stability of coatings, with a potential for sustained release of therapeutic agents as required for metallic implant fixation.

The Effect of n-TiO2 on Corrosion and Biological Activity of Biocoatings Coated by Ultrasound Micro-Arc Oxidation on Pure Magnesium

In order to improve the corrosion resistance and bioactivity of magnesium alloy coated by ultrasound micro-arc oxidation (UMAO), different content of n-TiO2 was added into silicate electrolyte. Electrochemical corrosion and simulated body fluid (SBF) soaking were conducted, and the surface morphology, phase structure and composition also were analyzed. The results indicated that Ecorr and Icorr of UMAO biocoatings with n-TiO2 increased and decreased an order of magnitude with increase of n-TiO2, respectively. The corrosion resistance of coatings with adding 4.8g/L n-TiO2 into electrolyte was the best. After soaking in SBF, the samples increased loose weight firstly and then increased weight to form Mg3Ca (CO3)4, Mg10Cl (OH)18·5H2O and Na4Mg2(PO4) ·2H2O new phases and Mg, MgO, MgSiO3 were still exit, which showed that good bioactivity of the UMAO coatings with n-TiO2.

The Effects of TiO2 Addition on the Crystallization of Molybdenum Slag Glass

The glass ceramics were prepared by using molybdenum slag (90wt% added) as the raw materials, in which TiO2 functioned as the nucleation agent. The effect of TiO2 additions on the crystallization was studied. The crystallization process was investigated by DTA, XRD and SEM. It was showed that TiO2 can effectively promote the glass formation when the content of TiO2 is 5wt %. The activation energy for crystal growth E=280.46kJ/mol was evaluated by DTA and kinetic method. The glass ceramic has good properties with main crystal phase of wollastonite.

Research on Structural Composition and Seismic of Gypsum - Adobe Wall Dwellings

Gypsum-adobe wall structure is a new type of green earth building. The feature of its structure is that the wall uses adobe and plaster as its main materials.The wall is erected by putting rods or stems of plants between layers of adobe, and is poured gypsum slurry into the gaps between adobe bricks and on the wall surface. Then adobe and plaster solidify and come to a composite wall structure. Finally，Gypsum and adobe bricks interact and bear stress together. This paper focuses on fully describing the shaking table test of a 1/4 scale house model of the structure. The Test results and engineering practice show that the single-storey gypsum-adobe wall structure has a good seismic performance and is worth promoting in residential construction of the drought areas.

Magnetite and Anti-Microbial Properties of Ag2O-CaO-Fe2O3-SiO2 Glass-Ceramic by Sol-Gel Method

Ag2O-CaO-Fe2O3-SiO2 glass-ceramic was prepared by the sol-gel method. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) were used to investigate crystallization process of Ag2O-CaO-Fe2O3-SiO2 glass. The kinetic results show that the values of the activation energy and frequency factor of the glass are 441.991 KJ/ mol and 1.58×1020, respectively. And the dimensionality of crystal growth, n, decreases as the heating rate increases. The crystalline phases of the glass-ceramic are magnetite, wollastonite and minor hematite. The saturation magnetization and coercive force of the heat-treated glass are 0.08 Wb/m2 and 14 KA/m at room temperature. The glass-ceramic has some capacity of anti-microbial.

Bioactivity, Wear and Corrosion Resistant Properties of Rare Earth/Calcium Phosphate Composite Coatings

Rare earth/calcium phosphate composite coatings were fabricated on the surface of Ti-6Al-4V by micro-arc oxidation (MAO) technique. The wear properties and corrosion resistant of rare earth/ calcium phosphate composite coatings in the simulated body fluid (SBF) have been investigated and the bioactivity of the composite coatings were evaluated. The results show that the friction coefficient of the composite coatings in the SBF is only 0.15~0.18 and the anode polarization potential of the coating has been obviously enhanced about 0.18V compared with that of coatings of calcium phosphate coatings. So the composite coatings have excellent wear and corrosion resistant properties. XRD analysis indicates that the composite coatings can induce hydroxyapatite to form on its surface after soaked in SBF for 9d, which shows that the composite coatings own good bioactivity.

Electrochemically Assisted Co-Precipitation of Electrically Conducting Polymer with Calcium Phosphate Coatings on Ti Alloys

Electrically conducting polymer containing calcium phosphate coating (ppy/brushite) was made on the Ti-6Al-4V surface by means of electrochemically assisted co-precipitation. This study examined the effects of the electrically conducting polymer on electrochemically assisted co-precipitation of ppy/ brushite onto titanium alloys. Electrochemically assisted co-precipitation of ppy/ brushite coatings resulted in an increase in the thickness and adhesion of coatings compared to those of coatings of single calcium phosphate at the same deposition conditions. The surface morphology of coatings characterized by SEM showed that the morphology of ppy/ brushite was superior to that of brushite. XRD indicated that ppy did not change the phase of brushite. Thus, this electrochemically assisted co-precipitation technique provides an effective method of polypyrrole incorporation at physiological temperature, which can offer excellent thickness, adhesion and structure of coatings, with a potential for sustained release of therapeutic agents as required for metallic implant fixation.

Study on the Subsonic Thermal Sprayed Ti/Bioglass Composite Coatings on Titanium Alloy

Ti/bioglass composite coatings on titanium alloy were prepared by a subsonic thermal spraying technology. Mixtures of titanium and bioglass powders with different proportions were used as feedstock. The effect of soaking of bioglass on the bond strength of between coatings and substrate was discussed. The bond strength and residual stress were investigated. The morphology was observed using scanning electron microscopy (SEM). The results showed that TiO2, CaTi4(PO4)6, CaTiO3, NaTi2(PO4)3 formed during thermal spraying process and the residual stress in the coatings was in compressive state. After the coatings were heat-treated, soaking of bioglass made some particles achieve metallurgical bond. Furthermore, new bioglass was formed and the compressive stress was increased. The phenomenon of bioglass healing up the cracks in the heat-treated coatings was observed through SEM, which reduced the porosity of the interface layer resulting in the significant increase of the bond strength.

Effects of Ingredients and Post-Heat Treatment on Phase Transformation and Structure of Bioactive Composite Coatings

Bioactive composite coatings containing sub-layer and working-layer with different ingredients were prepared using subsonic thermal spraying technology and then heat-treated at 700°C for 1h. Two types of bioglasses, named BG1 and BG2, and Y2O3 were used as additives of the sublayer and working layer respectively. Phase transformation and structure changes of the coatings were investigated with XRD, DSC and SEM. Results showed that the phases of as-sprayed Ti/BG1 sub-layer were TiN, TiO2 (rutile and anatase), etc. Post-heat treatment changed the phase composition. TiN and anatase transformed into rutile and some new phases generated, which often enriched at pores and cracks. In the working-layer, part of nano-hydroxyapatite powders decomposed during coating preparation. Y2O3 impaired the decomposition to some extent and BG2 enhanced greatly. Post-heat treatment increased the crystallinity of all coatings effectively. The analysis of TG-DSC showed that BG2 added in working-layer crystallized at 700°