Abstract: Dental impression is a source of cross infection and transmission of diseases. Conventional disinfection may lead to a change in physical properties. Self-disinfectant irreversible hydrocolloid is an alternative to the disinfection and can prevent microbial cross contamination. The present study evaluates the physical properties of irreversible hydrocolloid impression material incorporated with 0.5%, 1.0% and 1.5% w/w silver nanoparticles (AgZrPO4, Sunshine Factory Co.,Ltd, China). The working time and detail reproduction were tested according to ISO 21563:2013 with some modification. The result showed that AgZrPO4 did not significantly affect the physical properties of the impression material. Based on this in vitro study, AgZrPO4 can be added to the impression material for its antimicrobial benefit without significant changes in the physical properties of the material.
Abstract: Irreversible hydrocolloid impressions are easily contaminated with saliva and blood that are potentially capable of cross-infection. Disinfection with addition of Silver (Ag) nanoparticles into the impression material has been explored recently. This research aims to evaluate the in-vitro efficacy of Ag nanoparticle-incorporated irreversible hydrocolloid impression material. Ag nanoparticles (AgZrPO4, National Direct Network Company, Thailand) at concentrations of 0.50%, 1.00% and 1.50% w/w were added to powder of impression material (Kromopan, Lascod, Italy). Impression material samples were prepared on sterile plate in accordance with manufacturer’s instruction. After setting, a 100 microliter of P. aeruginosa ATCC 6538 and C. albicans ATCC 13803 suspension (106 cells/mL) were inoculated on the surface of the impression sample and left for 10 minutes. The amount of the P. aeruginosa and C. albicans on the surface was quantified using imprint technique on the individual culture media respectively. Impression materials incorporated with AgZrPO4 showed antimicrobial property against microbes compared with control (impression material without AgZrPO4). This beneficial effect can be used to reduce cross contamination. However, further investigations are required to study the physical properties of the Ag nanoparticle-incorporated impression material.
Abstract: Bio-materials which would interact with human cells are chosen based on the issues of compatibility. The materials preferred in bone repair or replacements at load bearing sites require particular attention to strength and rigidity, which should match the native tissue. Any kind of mismatch between native bone and implant would lead to adverse results such as improper bone growth leading to reoperation. Further, the bone has varied mechanical properties at different sections and is anisotropic. Present work is a manifestation of Polyetheretherketone (PEEK) and Hydroxyapatite (HAp) bio-composite mechanical properties. The composites are prepared by mixing in a ball mill followed by compression moulding, sintering and heat treatment.
Abstract: Ti-6Al-7Nb (Ti67) alloy has recently been developed to replace the commercial Ti6Al4V (Ti64) alloy because of the reported cytoxicity of vanadium. Surface modification by thermal oxidation is used to enhance the hardness and wear resistance of such titanium alloys. Since Ti67 alloy contains Nb as β phase stabilizer instead of V in Ti64, it is expected to behave differently upon processing by thermal oxidation. Therefore, it is of interest to compare the response of the two alloys to thermal oxidation in terms of hardness and wear resistance. Forged and cast samples were used to study the influence of the microstructure on the surface properties after oxidation. The forged samples with their equiaxed microstructure showed a well developed sub-surface hard layer (α-case) compared to the cast structure for the two alloys. The thickness of this case in Ti64 after oxidation at (900-1100 °C) was greater than in Ti67. This resulted in higher wear resistance of the Ti64 alloy relative to Ti67. These results are worth considering when designing implants for joints replacement.
Abstract: The paper adopts modified carbon fiber with Meldrum's acid and silane coupling agent (KH-550), then add the modified carbon fiber to the paper based friction materials. The paper aims to explore the changes of modified carbon fiber in its surface structure and properties by electron microscopy and infrared spectral analysis, and the effect of anionic microparticle forming retention aid system comprised of lithium soapstone-cationic polyacrylamide (CPAM) on mechanical properties and retention of paper based friction materials. Compared with the addition of unmodified carbon fiber to paper based friction materials, the addition of modified carbon fiber with Meldrum's acid, silane coupling agent, Meldrum's acid and silane coupling agent enhance the tensile strength of paper based friction materials. The tensile index of paper based friction materials was separately enhanced by 64.87 %, 91.38 % and 28.88 %. Compared with the paper based friction materials without the anionic microparticle forming retention aid system, the basis weight of paper based friction materials increased by 13.97 %.
Abstract: We have prepared nondoped and Cu-doped NiO thin films by sol-gel method on SiO2 substrate using nickel acetate and copper acetate as precursors. Thin films of NiO were formed by thermal annealing of gel films at 500 - 900°C for 10 h in air. X-ray diffraction (XRD) peaks of NiO have been observed at higher annealing temperature than 500°C, and intensity of the peaks increased with annealing temperature until 800°C. On the other hand, the dependency of XRD signal intensity on annealing temperature becomes less significant by Cu-doping. Nondoped NiO films show high transparency at lower annealing temperatures than 800°C. The result means that the film with high crystalline volume ratio is not consistent with the films with high transparency. Cu-doping decreases the transmittance of the films with low crystalline volume ratio. It is considered that the doped Cu atoms exist in amorphous fraction make the transmittance lower. Conductivity of the films is increased with Cu-doping only in the films annealed at 500 - 700°C. The highest conductivity obtained in the Cu-doped film is around 10-6 W-1cm-1 at 600°C. On the other hand, the Cu-doped films show similar conductivity to nondoped films at high annealing temperature, 800 or 900°C.
Abstract: One of the main processes in metal products is heat treatment. However, existing regimes of heat treatment are not suitable for the new gradient metals. This article presents a method of obtaining gradient metallic materials and heat treatment development. Also presents the studies results of heat treatment effect on mechanical properties and metal structure.
Abstract: The aim of this work is to investigate the synthesis of reduced graphene oxide (rGO) aqueous suspension by a conventional heating method using vitamin C as a reducing agent. The influences of reaction temperatures (70, 90 and 100 °C) and heating times (30, 45 and 60 min) on the chemical reduction of graphene oxide (GO) were studied. Then, the obtained rGO samples were characterized by FT-IR, Raman and UV-Vis spectroscopy. The FT-IR and Raman results showed that the reduction degree of GO to rGO was increased with the rising of the reaction temperature and time. Moreover, the UV-Vis spectra demonstrated that the absorption band at around 230 nm (π-π*) of pristine GO had shift to the longer wavelength upon the chemical reduction, indicating that GO is reduced to rGO. The optimal condition of the chemical reduction of GO to achievable rGO was the temperature of 90 °C with the 45 min of heating time. This condition yielded the rGO black aqueous suspension with the high quality and stability. Thus, this method of synthesis has an advantage of the rGO dispersion which led to many potential applications.
Abstract: To use solar energy effectively and as a standalone source, the performance of thermal energy storage device is crucial. The quantity and quality of energy stored using these devices play an important role in the efficient operation of thermal engineering equipment in the area of Heating Ventilation and Air Conditioning (HVAC), Refrigeration and many other. The selection of storage system depends mainly on application considering quality of energy and cost of storage. Phase change materials (PCM) have played a vital role in the storage of thermal energy in various applications. Out of the various types of phase change materials, organic compounds have a distinct advantage of high latent heat per unit volume, high thermal conductivity, non-flammability and low cost compared to inorganic compounds. The present study compares the performance of two of the most commonly used phase change materials like Paraffin wax and Fatty acids which are organic. They are highly chemically stable, melt congruently and super-cooling does not pose as a significant problem. Moreover, they have been found to be compatible with various kinds of materials of common use. The various performance parameters like temperature variation during charging and discharging, heat absorbed and rejected and overall system efficiency are evaluated for these two materials and also for the combination of these two materials. From the experimental results it is concluded that fatty acids show better performance characteristics than paraffin wax under the same operating conditions. Combination of the two PCM does not give much advantage in terms of operating efficiency.
Abstract: Acid-functionalized carbon nanotube (fCNT)-poly (vinylidene fluoride) (PVDF) composite films with different CNT contents (0-0.5wt%) were prepared by melt-blending followed by compression molding. The electrical resistance (R) of the composite films under tensile loading was measured by a two-probe method using a custom made equipment connected to digital multimeter. The films (0.35 and 0.5wt% fCNT composites) showed exponential increases in R with displacement after attaining the elastic strain. Further, the change in resistance divided by resistance (ΔR/R) showed a linear increase with strain (ε). The slope of the linear region is found to be higher for 0.35wt% fCNT composite (5.4) as compared to 0.5wt% fCNT composite (3.4), indicating a better sensitivity in the former case. This may be due to less number of electrical conducting paths in case of 0.35fCNT composite. On account of the results obtained, the composites promise as potential candidates for strain sensing in health monitoring.