Key Engineering Materials Vol. 492

Abstract: The relationship among the composition, microstructure and strength of materials is always one of the hotspots for scholars of materials research. The influence of curing time on the compressive strength and flexural strength of the foam concrete with the cement, cement-slag and cement-steel slag as main binder respectively was studied in this paper. The microstructure of these foam concrete was analyzed by SEM and the mineral phases of the foam concrete was analyzed by XRD. The relationship among the binders, microstructure, mineral phases and strength of the foam concrete were explored and the reasons of why the strength of the cement foam concrete and cement-slag foam concrete is much higher than that of the cement-steel slag foam concrete are proposed.

Abstract: Measuring mechanism of true density measurement of refractory through gas replacement technology by the AccyPyc1330 automatic true density analyzer was introduced. Compared with the current liquid immersion method, the gas replacement technology had many advantages in time, temperature, diversity and permeability of specimens. The results indicated that it had features of accurate data, fast measurement and less factors by the gas displacement technology.

Abstract: Pyramid shaped pyrolysis flame is a new method for carbon nanotubes (CNTs) synthesis, using this method has successfully produced high properties carbon nanotubes. But, because at the first 1min of sampling time, there are not tubes produced, so catalyst particles and carbon atom clusters assemble on the sampling substrate in the first 1min. Also, lots of amorphous carbon, deformity tubes, and graphite segment were produced in the experimental. In order to eliminate these impurities, ultrasonic treatment, aether cleaning, acid pickling, and co-processing were used. Ultrasonic treatment can separate particles from tubes, aether can clear amorphous carbon and graphite segment while acid pickling can dissolve catalyst particles. Using ultrasonic oscillation separation and aether as diluent can gain pure sample. Ultrasonic oscillation and nitric acid as diluent can purify products also, but not as good as aether as diluent. Concentrated nitric acid and long time immersion will destroy the structure of carbon nanotubes.

Abstract: In many manufacturing industries, e.g. powder metallurgy, pharmaceuticals, ceramics and foodstuff, die compaction is widely applied. Although die filling has attracted increasing attention recently, very few published studies are available to predict powder flow rate from a moving feed shoe to dies. In this research, a feed shoe with three wheels of a high-speed rotary tablet press was studied. The powder discharge rates from the feed shoe and the tablet weight variability at different feeding wheel paddle speeds were investigated experimentally and numerically. The results of the two methods were in good agreement. According to the experimental results, the minimum deviation of tablet weight was obtained at the speed of 60 rpm. However, the wheel speed of 55 rpm was likely to be the better one on account of the calculations, which will be studied in the future experiments.

Abstract: Objectives: To compare the permeability of human dentin and a porous ceramic with two different compositions of perfusion fluid, in vitro. Methods: Dentin discs were cut from extracted third molar at a level close to the pulp chamber and ceramic discs were cut from a porous ceramic block. The convective permeability of the discs was measured in a fluid transport model using de-ionised water or 1:3 diluted bovine serum and the hydraulic conductance was determined. Results: In the negative controls, no flow was detected. The hydraulic conductance values for the dentin discs and the ceramic discs when water was used as the perfusion fluid were 0.069±0.023and 0.047±0.019ml min^-1 cm^-2 cm H₂O^-1, respectively. When the discs were perfused with the diluted bovine serum the mean (standard error of the mean) hydraulic conductance values for the dentin and the ceramic discs were 0.036±0.016 and 0.012±0.0055 ml min^-1 cm^-2 cm H₂O^-1, respectively. Conclusion: Basing on the modern technique it is possible to fabricate discs of hydroxylapatite ceramic to act as substitutes for dentin barriers in cytotoxicity test.

Abstract: Objective: To evaluate the biological safety of a colored zirconia ceramic regarding its hemolytic activity and short-term systemic toxicity. Methods: Fresh anti-coagulating rabbit blood was mixed with test materials and the hemolytic activities detected spectrophotometrically. Suspensions of the ceramic were fed to rats for one week while monitoring food consumption and relative growth rate and with subsequent pathology examinations of vital organs and tissues. Results: The hemolytic activity of the ceramics was <5%, and rats in all groups showed weekly relative growth rates of food utilization and body weight with no statistically significant differences. There were also no pathological changes observed among the various examined organs between the experimental and control groups. Conclusions: This colored ceramic showed good biocompatibility in terms of hemolytic activity and short-term systemic toxicity.

Abstract: Objective: To evaluate the biological safety of a colored zirconia ceramic in terms of cellular toxicity and a skin sensitivity test. Methods: the cytotoxicity of the ceramic was evaluated by a molecular filtration method and skin irritation activity of the composite was assessed via intradermal injection of a guinea pig test solution, by inducing, enhancing, and stimulating an allergic response after local tissue exposure. Results: cell-coated filter paper in contact with test material showed the appearance of intracellular blue dye at the same staining density as in control samples, leading to a 0 toxicity rating. Guinea pigs showed no obvious erythema or edema from the irritation test, such that the assessment of colored zirconia ceramic skin allergy response in guinea pig was 0%. Conclusion: this colored zirconia ceramic showed low cytotoxicity and elicited no allergic skin inflammation response, indicating good overall biological safety under these conditions.

Abstract: Minocycline, a semi-synthetic tetracycline antibiotic, was incorporated into gelatin- hydroxyapatite (HA) composite by using a biomimetic co-precipitation method, Firstly, a certain amount of acidic solution of hydroxyapatite was added into gelatin solution dropwise. After that, different amounts of minocycline (0mg, 50mg, 100mg, 200mg, 300mg) solution was added into the reaction system respectively , and obtain the hydroxyapatite - gelatin- minocycline composite. The results showed that the amount of the minocycline impacted the structure of the composite, and minocycline affects HA crystal growth by maybe bonding to 300 face. The approach described here may provide a basis for the preparation of an antibacterial biomaterial for bone regeneration.

Abstract: MCC-1 static short-term corrosion tests were performed to pyrochlore simulated waste forms in deionized water, at 90°C. Experimental results show that pyrochlore simulated waste forms has a good anti-leaching property. Both the normalized mass loss rate and the normalized mass loss of element Ce decrease with soaking time increasing in the short test. The corrosion process is co-dominated by the leaching agent and the corrosion temperature.

Abstract: A novel polyimide (PI) hybrid nanocomposite containing polyhedral oligomeric silsesquioxane (POSS) had been prepared by copolymerization of octa(aminophenyl)silsesquioxane (OAP-POSS), 4,4’ -oxydianiline (ODA), and pyromellitic dianhydride (PMDA). The AO resistance of these POSS/PI hybrid films was tested in the ground-based AO simulation facility. Exposed and unexposed surfaces have been characterized by X-ray photoelectron spectroscopy and FTIR. The XPS data indicate that the carbon content of the near-surface region is decreased from 63.6 to 19.3 at% after AO exposure. The oxygen and silicon concentrations in the near-surface region increase after AO exposure. The data reveal the formation of a passive inorganic SiO₂ layer on the POSS/PI hybrid films during the AO exposure, which serves as a protective barrier preventing further degradation of the underlying polymer with increased exposure to the AO flux. SEM images showed that the surface of the 10 wt% POSS/PI became much less rough than that of the pristine polyimide. The AO resistance of the POSS/PI hybrid films is up to several tenfold than that of the pristine polyimide.