Key Engineering Materials Vols. 434-435

Abstract: A SiC coating was chemical vapour deposited (CVD) on a Cf/SiC composite with the ratio of H2 and methyltrichlorosilane (MTS) changed gradually from 6:1 to 12:1 during the CVD processing. Energy-dispersive spectrometry (EDS) of the coating showed that the content of C decreased while Si increased continuously from the interface between coating and Cf/SiC substrate to the outside surface of coating. The obtained compositionally graded structure effectively reduced the generation of microcracks by releasing the mismatch of CTE of the coating and the composite.

Abstract: The Ce3+-doped and undoped nanocrystalline TiO2 films were prepared on glass substrates surface by sol-gel dip coating technique. The crystal structure and surface morphology of TiO2 films were characterized by means of X-ray diffractometer (XRD), transmission electron microscopy (TEM) and atomic force microscope (AFM). The results indicated that the Ce3+-doped TiO2 films were solely composed of the anatase phase whereas in the undoped films small amount of the rutile phase of TiO2 were present. The average crystallite size of the undoped TiO2 films was about 30nm and was decreased with Ce3+-doping in the TiO2 films. Moreover, the grains distributed more uniform and the surface roughness was smaller in the Ce3+-doped TiO2 films than in the undoped one. The action mechanism of Ce3+-doping inhibits the crystallization of the rutile phase and decreases the anatase granularity of TiO2 films is associated with its physicochemical properties, as well as ionic diffusion and valance change of Ce3+ to Ce4+ in the sintering process.

Abstract: The process of Electron Beam-Physical Vapor Deposition (EB-PVD) preparing SiC coating with liquid evaporation was firstly discussed from a thermodynamic viewpoint. The results showed that the ratio of SiC in the as-deposited coating gradually increases and tends to reach a stable maximum of 0.73 with the evaporation temperature increase from 2500 K to 3400 K. To verify the thermodynamic analysis, amorphous SiC coating was deposited on Si substrate by EB-PVD at 3100 K. SiC concentration across the cross section of coating was calculated from the area of elements spectrum in X-ray photoelectron spectroscopy (XPS) depth profile analysis. The results showed that the average SiC concentration was about 0.7.

Abstract: Calcium phosphate based glasses and glass-ceramics in the system of 54CaO-36P2O5- (10-x)Na2O-xSrO were fabricated by sol-gel method. The structures of the glasses were investigated by Fourier transform infrared spectroscopy and X-ray diffraction has been used to determine the crystallize phase from glass matrix. The synthesized glass matrix shows a metaphosphate-like structure which consists of a chain and /or ring structure. After sintered at 1150 °C, the crystalline phase -Ca2P2O7 and a small quantity of amorphous glass were observed clearly. With 1.0 mol% addition of SrO, the average grain size of -Ca2P2O7 was obviously decreased and some of them were covered with amorphous glass. When the content of strontium reached to 5.0 mol%, only a little crystalline phase -Ca2P2O7 can be found in the glass matrix, while the grain size has no significant change, compared with that of the sample containing 1.0 mol% SrO. The results showed that SrO addition to 54CaO-36P2O5-10Na2O system can inhibit the crystallization of -Ca2P2O7 and decrease the grain size, and then adjust the degradation rate in body fluid by controlling the ratio of -Ca2P2O7 to amorphous glass.

Abstract: Titania layer is deposited on polyethylene substrates when they are soaked in TiOSO4/H2O2 solution and aged in hot water. The aging in hot water promoted the precipitation of anatase and rutile in the surface layer, indicating that cleavage and recombination of the Ti-O-Ti bond took place. The Ti-OH functional groups were rearranged and emerged accompanying the structure relaxation in the layer. Moreover, the aging in hot water enhanced crystalline of titania and then obtained well apatite-forming ability on the polyethylene substrates in SBF. This was accounted for by the removal of residual impurities due to TiOSO4/H2O2 treatment. They had an anatase/rutile dual layer microstructure: the dense bottom layer predominantly consisted of rutile, while the upper layer consisted of loosely packed aggregation of anatase particles. The titania deposition was the results of compromise among two conflicting processes: 1) hydrolysis of titanium oxysulfate to yield either soluble titanol-complexes or titania, 2) dissolution of the titania under the presence of hydrogen peroxide to yield similar complexes or compounds. Various soaking periods were carried out to investigate the dissolution-deposition equilibrium in the solution. Anatase/rutile dual layers were thus deposited on titanium and polyethylene substrates when they were soaked in TiOSO4/H2O2 solution and aged in hot water. The proper soaking time in the treating solution is the other key factors to control the formation of dense titania layers. The resulted titania layers have apatite-forming ability.

Abstract: The TiO2 nanopowder was prepared with TiOSO4 as raw material at low temperature by hydrolysis method, and microspheres coated polyethylene and TiO2 were then fabricated on titanium by layer-by-layer self-assembly technology. Using ultraviolet irradiation of titanium coating in distilled water for some time, titanium with enhanced bioactivity was achieved when immersed in simulated body fluid (SBF). The morphology, size and crystal shape before and after ultraviolet irradiation were characterized by scanning electron microcopy (SEM) and X-ray diffraction (XRD). UV irradiation of titanium results in the conversion of Ti4+ to Ti3+ and the generation of oxygen vacancies, which could react with the absorbed water to form basic Ti–OH groups. Compared with the coating non-UV irradiation, the UV-irradiated coatings do not present any obvious differences in morphology, surface roughness, grain size and phase component; however, they have more abundant basic Ti–OH groups thus the water contact angle decreases greatly so the surface become much more hydrophilic.

Abstract: The aim of this study was to explored the effects of Fe2O3 and Bi2O3 on the color properties of a 3Y-TZP zirconia ceramics for dental application. Pigmented dental ZrO2 powders were prepared by mixing different concentration of Fe2O3 and Bi2O3, also in their combinations with 3Y-TZP powders. The mixture was compacted by isostastic pressure, then densely sintered. Color parameters were measured by Minolta CM2600d spectrophotometer. XRD was used to exam the structure of colored 3Y-TZP. Experimental results showed that the hue of the materials shift from yellow-green to yellow-red with the increasing concentration of the Fe2O3 and Bi2O3. Combined use of Fe2O3 and Bi2O3 could further decrease the L* value, which color scope was suitable for dental color matching. The XRD spectra showed only tetragonal phase was detected.

Abstract: The calcium phosphate bioceramic coating was fabricated on titanium alloy (Ti-6Al-4V) substrate by a 5kW continuous transverse flow CO2 laser. Due to the peculiar role of rare earth oxide in laser cladding, the effect of ceria additive on the microstructure and properties of laser-cladded bioceramic coating was investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), microhardness and corrosion resistance testing. The results indicate that the appearance of rare earth oxide ceria in the precursor powders has an impact on the microstructure and properties of the laser-cladded bioceramic coating. Calcium phosphate bioceramic such as hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) are synthesized on the top surface of laser-cladded specimens. And the addition of rare earth oxide ceria in pre-placed powders has an influence on the formation of calcium phosphate bioceramic phases. Furthermore, it reveals that the laser-cladded bioceramic coating of ceria additive in pre-placed powders has more favorable microhardness and corrosion resistance compared with the coating without rare earth oxide.

Abstract: The aim of this study was to develop a novel injectable hydroxyapatite for bone repair materials. This study was based on the in situ setting properties of calcium phosphate cement (CPC), which properties were improved. The solid phase consisted of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA). The liquid phase was the weak acidic solution of chitosan. The CPC powder was mixed with the chitosan solution to form a paste that could conform to the bone cavity even for irregularly shaped cavities. All the by-production disappeared by neutralization reaction. The CPC paste could then set in situ to form hydroxyapatite (HA) as the final product. The chemical process of CPC hydration was studied. The process was controlled by dissolution and precipitation chemical reaction. The kinetic model of hydration reaction was established. The effects of preparing conditions, such as powder to liquid ratio and particle size, on setting time and compressive strength were investigated systematically. The optimal condition was that the liquid phase contained 3% chitosan, 5% citric acid and 15% glucose (wt%), powder to liquid ratio was 0.8 g/ml, and powders were respectively ground for 40 hours.

Abstract: ZrO2 nanocomposites were prepared and studied by microstructure observation and mechanical property detection. First, yttria stabilized zirconia (3Y-TZP) nanopowders were synthesized by sol-gel method. TEM photograph showed that the addition of yttria restrained the growth of the grain, but caused the agglomeration of the nanopowder. XRD analysis showed that the amount of yttria influenced the phase character of the materials, and the monoclinic zirconia changed gradually into tetragonal and cubic phase with increasing yttria content. Second, the micro-size 3Y-TZP materials was mixed with the former prepared nano-size particles and pressed by cold isostatic pressing, and then sintered at 1300 °C to prepare ZrO2 ceramic nanocomposites. The results of microstructure analysis showed that the amount of nano-size powder affected the fracture mode of nanocomposites, thus changed the fracture toughness. The mechanical testing results indicated that both the flexural strength and the hardness decreased with increasing nano-size powder, whereas fracture toughness increased and decreased subsequently. ZrO2 ceramic nanocomposites with 20% nano-size powder would be a promising kind of dental restoration material due to its low hardness, high fracture toughness and moderate flexural strength.