Crack Self-Healing in SiC/Spinel Nanocomposite

Spinel is one of the best known and widely used ceramic materials. It has good thermal shock resistance, high chemical inertness in both acidic and basic environments, excellent optical and dielectric properties, high strength at both elevated and normal temperatures, and has no phase transition up to the melting temperature (2135°C). Spinel is used in the metallurgical, electrochemical, and chemical industrial fields. It has also found some applications in dentistry, catalyst supports, humidity sensors, reinforcing fibers, photoluminescent materials, etc. One of the limitations of spinel ceramic is its brittleness. Furthermore, at high temperature applications, a rapid heating or cooling can cause a high thermal gradient. Building up of such thermal stresses can lead to surface microcracking and crack growth, which finally can lead to a catastrophic failure of the component. In order to overcome this problem, it is highly desirable that the self-healing capability of spinel and spinel composites are investigated. In this research for the first time we studied the crack self-healing capability of nanostructure spinel. The results showed that grain growth and sintering phenomena are the two factors controlling the healing procedures. In the case of spinel ceramic, cracks can be completely healed after annealing the specimens at 1600°C for 100h with the strength recovery of 91%. On the other hand, it has been found that SiC can be used as a healing agent in many ceramics even in those ceramics without any crack healing ability. Therefore, first SiC/spinel nanocomposite was synthesized using talc, aluminum and graphite powders. The sintering behavior of the SiC/spinel nanocomposite was investigated and the best pellets from physical and mechanical properties point of views were selected to study the self-healing behavior of SiC/spinel nanocomposite. The results showed that SiC/spinel nanocomposite has an exceptional crack-healing ability as the surface cracks can be healed after sintering the specimens at 1550°C for 1 min in air with the strength recovery of 99%. Reaction of SiC with air and formation of SiO2 and subsequently formation of mullite and dissociation of enstatite are the possible mechanisms responsible for crack healing in SiC/spinel nanocomposite

PREPARATION OF BIOACTIVE NANOSTRUCTURE SCAFFOLD WITH IMPROVED COMPRESSIVE STRENGTH

Highly porous scaffolds with open structure are today the best candidates for bone substitution to ensure bone oxygenation and angiogenesis. In this study, we developed a new route to enhance the compressive strength of porous hydroxyapatite scaffold made of natural bone. Briefly, the spongy bone of an adult bovine was extracted, annealed, and coated by a nanostructure bioactive glass layer to be subsequently sintered at different temperatures. The apatite formation ability on the surfaces of the coated scaffolds was investigated by standard procedures. Our results showed that the scaffold and coating microstructure consisted of the grains smaller than 100 nm. These nanostructures improved the compressive strength and bioactivity of highly porous scaffold. The results showed that with increasing the sintering temperature, the compressive strength of scaffolds increased while their in vitro bioactivity decreased

Enhanced Mechanical Properties and Microstructure of Accumulative Roll-Bonded Co/Pb Nanocomposite.

Lead composites have been used as anode in electrowinning process to produce metals such as copper and zinc. Manufacturing of stable lead anodes with appropriate mechanical and chemical properties is required to improve the performance of the electrowinning processes. In this study, accumulative roll bonding (ARB) method was used to fabricate Co/Pb nanocomposite. Utilizing ARB method can help us to achieve a uniform structure with enhanced mechanical properties via sever plastic deformation. The results showed that suitable tensile properties were obtained in Pb-%0.5Co-10pass samples. The tensile strength and strain of these samples were 2.51 times higher and 83.7% lower than that of as-cast pure Pb. They also showed creep resistance and hardness up to 1.8 and 2.5 times more than that of as-cast pure Pb. ARB technique uniformly distributed Co par-ticles in the Pb matrix. The enhanced strength of Pb samples was observed in the composite in-cluding grain size less than 50 nm as a result of hindering the recovery phenomenon. The particle size of the Co distributed in the Pb matrix was 353 ± 259 nm. Compared to conventional methods, ARB process improved the mechanical properties of Co/Pb composites and can open a new horizon to fabricate this composite in metal industries

Acceptance and Use of E-Learning Based on Cloud Computing: The Role of Consumer Innovativeness

Cloud computing and E-learning are the inevitable trend of computational science in general, and information systems and technologies in specific.However, there are not many studies on the adoption of cloud-based E-learning systems. Moreover, while there are many papers on information system adoption as well as customer innovativeness, the innovativeness and adoption in the same model seems to be rare in the literature. The study combines the extended Unified Theory of Acceptance and Use of Technology (UTAUT2) and consumer innovativeness on the adoption of E-learning systems based on cloud computing. A survey was conducted among 282 cloud-based E-learning participants and analyzed by structural equation modeling (SEM). The findings indicate that the adoption of cloud-based E-learning is influenced by performance expectancy, social influence, hedonic motivation, and habit. Interestingly, although innovativeness is not significant to use intention, it has a positive effect on E-learning usage which is relatively new in Vietnam