Key Engineering Materials Vols. 602-603

Abstract: A facile onestep in situ chemical deposition method was introduced to synthesize Ni coated SiC composite powders, which used NiCl₂·6H₂O as nickel source and N₂H₄·H₂O as reductant, respectively. SiC(Ni)/Fe composites were prepared by current-vacuum hot-pressed sintering at 850°C, 40MPa for 30min. Scanning electronic microscope (SEM) and X-ray diffraction (XRD) were used to characterize the structure, morphology and composition of the prepared Ni/SiC core/shell composite powders. It is found that the Ni coated SiC is favorable to improve the dispersion and compatibility of SiC(Ni)/ Fe composites. By a series of contrast experiments, it is shown that the sintering sample with 5wt% of SiC(Ni) has the best mechanical properties. The relative density, Vickers hardness and bending strength is 91.67%, 4.72GPa and 508MPa, respectively.

Abstract: In this study, functionally gradient aluminum reinforced by Silicon carbide particles (FGMSiCp/Al) composites are prepared by microwave sintering and pressureless sintering processing. The sintering behaviors, mechanical properties of composites were measured, and microstructure was observed by optical microscope and SEM. The results showed that the density of sintered samples which prepared by microwave sintering were better than that presureless sintering one. The highest density of sintered sample by microwave sintering reached 2.64 g/cm3, the relative density was 95.65%. Whatever preparing process, the mechanical properties of sintered samples were related to the temperature. The distribution of silicon carbide particles is uniform in the aluminum matrix, however, slight agglomeration can be observed. The interface between other layers is not obvious except interface between Al and 5% SiC/Al layer.

Abstract: In this study, glassy phase is formed by SiO₂-K₂O addition to serve as amorphous grain boundary transition layer. SiC (SiO₂-K₂O) / Cu composite material were prepared by two-step coating method and hot pressing sintered below 770°C, 30MPa for 1.5h, using α-SiC as main reinforced phase, SiO₂-K₂O as grain boundary and Cu as matrix. The Cu-SiC volume ratio was 75:25. The SiO₂ contents were 5vol.%, 10vol.%, 15vol.%, 20vol.% and 25vol.% of the total volume of the SiC / Cu. XRD and SEM techniques were used to characterize the composite particles and the sintered compacts; Archimedes method, Vickers hardness tester, universal testing machine to test the apparent porosity of the composite materials, the Vickers hardness and the bending strength, respectively. The results showed that with increasing of glassy phase contents, the Vickers hardness and the bending strength first rise and then drop, at the same time, it shows the opposite tendency for the apparent porosity. The sintering samples with the SiO₂ content of 15vol.% have the optimum mechanical properties, the Vickers hardness reached 1.49 GPa, and the bending strength was close to 235 MPa.

Abstract: SiC_p/Cu composites were prepared by vacuum hot-pressing at 770°C for 1.5 h under the pressure of 30MPa. The composites were enhanced by CNTs with different volume fractions from 0 vol. % to 4 vol. %. Three-step approach wrapping process was introduced to prepare composite powders. XRD and SEM techniques were used to characterize the samples. It is found that the core-shell structure composed of SiC core and Cu shell was formed in the composite particles. Optimized volume fraction of CNTs is 1 vol. %. Minimum Porosity and maximum Hardness is about 0.84% and 2.31GPa, respectively. But maximum Flexural strength was measured as 248MPa for samples containing 2 vol. % CNTs. Flexural strength was improved by the bridge effect caused by the increased CNTs.

Abstract: The effects of Pr₆O₁₁ and Er₂O₃ dopants on microstructure and mechanical properties of zirconia ceramics were investigated. The phase composition and microstructure analysis indicate that samples are all tetragonal phase and grain size is about 50-100 nm. The relative density of zirconia ceramics was above 99.1%, linear shrinkage was nearly 20%, while Vickers hardness was over 12.5 GPa. Three-points bending strength was over 850 MPa which was slightly lower than that of the pure samples, and fracture toughness was above 4.9 MPa*m^1/2. The results show that the dopants can be used to obtain the colored zirconia ceramic, and also have effects on its mechanical properties.

Abstract: The hydroxyapatite (HA)/ TiO₂ composite ceramic coatings were formed by micro-arc oxidation (MAO) on pure titanium in mixed electrolyte of calcium glycerophosphate and calcium acetate with DC pulse power. Microstructure, phase composition, porosity and thickness of the coatings were examined using SEM, XRD, Image-Pro Plus 6.0 Image analysis system and Eddy current thickness gauge. Results indicate that MAO coatings containing calcium and phosphorus were formed in situ on pure titanium surface. Pores formed by the discharge channels distribute uniformly on the coatings surface, and the inner layer is dense. The principal crystalline phases of the MAO coatings are anatase TiO₂, rutile TiO₂, HA, Ca₃(PO₄)₂ and matrix Ti. The interface is metallurgical bonding and the bonding strength is strong. And reaction time makes a greater influence than voltage in thickness and voltage makes a greater influence than time in porosity.

Abstract: To evaluate the effect of three surface treatments and two resin cements on microtensile bond strength of zirconia to dentin. Sixty human molars were embedded in acrylic resin and sectioned 3 mm below the occlusal plane. Teeth specimens and sixty zirconia specimens were randomized into 3 groups according to the following surface treatments (n=20): no treatment (control), sandblasting and silane application (SB+SI), sandblasting then silica coating and silane application (SB+SC+SI). In each group, half of the ceramic-tooth assemblies were cemented with PanaviaTM F (Kurary Dental), the rest with RelyX Unicem (3M ESPE). All specimens were cut into microtensile sticks that were loaded in tension until failure. Data were analyzed using two-way ANOVA and Tukey’s HSD test (α=0.05). The SB+SC+SC group presented higher values than SB+SI and the control group (P<0.05). Bond strength in PanaviaTM F groups were significantly higher than those in RelyX Unicem regardless of the surface treatment (P<0.05). Data indicated that both surface treatment and resin cement have significant effects on bond strength of zirconia to dentin.

Abstract: To study the effect of different core thickness on the flexural strength of zirconia and feldspathic ceramics. Bilayered zirconia-feldspathic samples of three commercial brands were made in three different thickness(n=10): 0.5 mm, 0.8 mm and 1.0 mm respectively. On zirconia core specimens of each thickness, feldspathic dentin porcelain was added to reach a total crown thickness of 2 mm. Samples were stored in artificial saliva with neutral pH for 10 days at 37°C. Flexural strength was conducted with 3-point bending test. Data were analyzed by one-way ANOVA, and multiple comparisons were performed using Student-Newman-Keuls test(α=0.05). The measurement of 1.0 mm group was higher than the other groups, and 0.5 mm group was the lowest(P＜0.05), regardless of any commercial brand. Commercial dental zirconia blocks had varied flexural strength, Zirkonzahn expressed highest value in any thickness group compared with the other materials. Moreover, the fracture mode of zirconia bilayered composites was different in this study, 0.5 mm and 0.8 mm groups exhibited higher number of fragments and appeared to delamination compared with 1.0 mm group. So we infer that the thickness of core can have an effect on the flexural strength of bilayered zirconia-feldspathic crown, as well as different kinds of materials.

Abstract: The use of zirconia crown has attracted considerable attention due to its good mechanical and optimal biocompatility. The white color of zirconia does not allow for perfect aesthetic characteristics though. Colorized zirconia blocks with Pr₆O₁₁, Er₂O₃ and Fe₂O₃ gradient concentration and the shade stability were investigated. Chromatic values of the samples were presented in CIELab system, and the shade stability was evaluated by color comparison of samples in the same group. The value of L* from 68.2-84.0, a* from-1.8-5.9, and b* from 18.6-33.2 can be obtained. These values can be comparable to the Vita 3D master system. The E between the samples of every group was below 2.2. The results showed that by adding combined oxides of gradient concentration could reproduce the tooth-like color of zirconia ceramics, and the shade stability was satisfied.

Abstract: Objective: To compare the effectiveness of different proportional nHA / PLA application in alveolar bone preservation. Methods: After extraction, apply extraction socket filling based on the alveolar bone defect model due to absorption in Beagle dog. Implant materials are divided into 3 different groups: nHA / PLAI, nHA / PLAII and the control group. Samples of the alveolar bone were collected at Week 4 and 8, respectively for the bone resorption assessment, bone density measurement, and histological examination. Results: After nHA / PLA implantation, the alveolar bone preservation was significantly improved. There was no difference in the alveolar bone preservation between the nHA / PLAI and nHA / PLAII groups. However, the sample which are 8w from group I, have higher bone density and have complete absorption in their dental material nest .Therefore group I is better than group II. Conclusions: The results can provide a reliable basis for the application of alveolar bone preservation in basic research and selection of clinical materials.