Papers by Keyword: Nanopowder

Abstract: Cr2O3 nano-powders were successfully fabricated with using chromium nitrate and aqueous ammonia as starting material and urea as dispersant agent by sol-gel method. The formation of crystalline phase during heat treatment of dry gel was characterized by differential thermogravimetry (DTG) and X-ray diffraction (XRD) techniques and the temperature of calcination was determined as 400°C. Scanning electron microscopy (SEM) was utilized to observe the morphology of the as-fabricated Cr2O3 particles. The results showed that Cr2O3 particles are spherical or square with little agglomeration and a diameter of about 30 nm. The specific surface area of Cr2O3 particles was measured as 44.23 m2/g by Brunauer-Emmett-Teller (BET).

Abstract: Wear resistance of Al2O3-8wt.%TiO2 coatings plasma-sprayed using nanopowders was investigated. Four types of nanostructured Al2O3-8wt.%TiO2 powders were plasma-sprayed on a low-carbon steel substrate by using different critical plasma spray parameters (CPSP). The coatings consisted of completely melted and partially melted regions. The hardness of the coatings increased with increasing CPSP, while the wear resistance was the highest for the coating sprayed with the lowest CPSP. The main wear mechanism was a delamination mode in the coating sprayed with the high CPSP, but was changed to an abrasive mode in the coating sprayed with the low CPSP. According to this change in the wear mechanism, the wear resistance was the best in the coating sprayed with lowest CPSP, while its hardness was lowest.

Abstract: Structural and microwave properties of Fe-based nanoalloy powders, mechanochemically synthesized with a composition corresponding to Finemet (Fe73.5Si13.5B9Nb3Cu1), were investigated. The nanopowders, dominated by bcc-Fe (Si), consist of nanocrystallites and display high magnetization with low-coercivity. The microwave measurements show that the nanocomposites comprising the nanopowders possess high, broadband magnetic permeability.

Abstract: Non-evaporable getters (NEGs) are characterized by two major properties i.e. the activation and gas sorption rate for specific gases. Most of the commercial getters are alloys composed of micron-size powders. There have been speculations on the advantage of using nanosize powders as getter material for the obvious increase in volume to surface area ratio and for effective reaction with gases on size reduced particles. In this study, titanium powders of about 80 nm were prepared by electrical wire explosion method and their gettering properties were measured in accordance to ASTM standard. The activation of nano-size titanium powders was completed at about 450oC and the sorption rate was over 4 times higher than those of the micron-size titanium powders.

Abstract: We report on a process in which CuO nanopowder was produced in a high yield by adopting ultrasonic in aqueous solution. In our experiment, CuCl2 solution was reacted with NaOH solution and NaNO2, at ambient conditions applying ultrasonic for 5 min. Precipitation was performed by varying the molar ratios of NaOH/CuCl2 and NaNO2/CuCl2. CuO nanoparticles of ~ 5 nm and spherical shape were obtained at the NaOH/CuCl2 of 2.0 and the NaNO2/CuCl2 of 0.097. Without ultrasonication, an amorphous phase was formed at these conditions. This indicates that sonochemical reaction facilitates direct formation of the nanosized CuO particles. In addition, the particle morphology varied from sphere through ellipsoid to needle forms depending on pH. In thick films prepared with the CuO powder for gas sensing, the maximum CO gas sensitivity reached 93 % at the temperature of 250 °C and depended linearly on CO concentration in log scale over the range of 10 ~ 104 ppm.

Abstract: Zirconia nanopowders (stabilized by 1.5 and 3 mol% Y2O3) with particle size below 10 nm were compacted by cold isostatic pressing. Pressureless sintering and hot isostatic pressing were applied to obtain dense nanocrystalline ceramics. The influence of the pore size in powder compacts on sintering behaviour was investigated. Green bodies pressed at 1000 MPa had a maximum pore size of 5 nm. These bodies were densified to a relative density of over 99.6% with an average grain size about 85 nm by pressureless sintering at 1100 °C. Indentation techniques were used to evaluate the hardness and fracture toughness of zirconia nanoceramics. The decrease in the yttria content from 3 to 1.5 mol% resulted in the toughness increasing from 5.3 to 11.1 MPa m1/2. The differences in fracture toughness of zirconia ceramics prepared with different yttria contents and by different sintering methods were discussed and their possible causes were proposed.

Abstract: Nano-particle hydroxyapatite (HAp) was directly prepared by a wet chemical precipitation method with the aid of ultrasonic irradiation in solution using Ca(NO3)2, NH4H2PO4 and NH2CONH2 as source materials. The nano-HAp formation rate at different preparation temperatures and under different ultrasonic irradiation powers was measured and the influence of ultrasonic irradiation power on the synthesis kinetics of the nano-hydroxyapatite was investigated. It was found that the nano-HAp content increased with the increase of ultrasonic irradiation power, preparation temperature and reaction time. Under different ultrasonic irradiation power, an Arrhenius relationship was found between the nano-HAp formation rate and preparation temperature. It showed that with the increase of ultrasonic irradiation power from 100W to 200W and 300W, the synthesis activation energy of nano-HAp crystallites decrease from 63.2 KJ/mol to 59.9 KJ/mol and 48.1 kJ/mol respectively by calculation.

Abstract: Non-aggregated nanoscale α-Al2O3 powders with average size ranging from 7 to 20 nm were prepared successfully at various conditions with the use of the hydrated aluminum sulfate extracted from kaolin by polyacrylamine (PAA) gel method. The calcination temperature was relatively lower about 100°C, compared to conventional solid-state reaction. It revealed that PAA worked as a chelating agent to disperse the Al3+ ions homogeneously, and the size of alumina nanoparticles could be controlled by varying the concentration of crosslinking agent.

Abstract: Nanosized Ce0.8Gd0.05Y0.15O1.9 powders were synthesized using glycine nitrate process for use as the electrolyte of intermediate temperature solid oxide fuel cells. The powders were characterized by simultaneous thermogravimetry analysis (TGA) and differential thermal analysis (DTA), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD pattern indicated that the powders exhibited a single phase with cubic fluorite structure. The TEM studies showed that the calcined powders exhibited an almost spherical morphology and the mean size of the particles was 30nm, which is in agreement with the calculated result of XRD.