Papers by Keyword: Oxide

Abstract: We report synthesis of nanosized oxide materials using a novel water assisted solid state reaction (WASSR) method. This novel soft chemical synthesis method is very simple and can synthesize nanoparticle materials just by storing or mixing raw materials added a small amount (typically 10wt%) of water in a reactor at low temperature below 373 K. Combinations of raw materials have a significant influence on the reaction rate.

Abstract: The actuality of the topic chosen by us lies in the fact that the effect of oxygen on the properties of semiconductors has not been studied sufficiently well, mainly because of the imperfections of methods for controlling the oxygen content in semiconductor materials. Almost in all such materials, oxygen is present either as an uncontrolled impurity or as a doping additive, or, in the case of oxide semiconductors, as in our case with a semiconductor film of vanadium dioxide, is part of the compound. The oxygen contained in the semiconductor film significantly affects the property of the material: in the first two cases, this influence is determined by the amount and state of the impurity, in the third - by the composition, or by the stoichiometry of the oxide compound. We set a goal to develop a technique for obtaining a semiconductor film of vanadium dioxide in a controlled atmosphere of oxygen. The semiconductor film thus obtained is used in holography to record and store optical information. For the production of VO₂ films by oxidation in a controlled atmosphere, an apparatus including an oxygen pump based on stabilized zirconia dioxide has been developed. The principle of operation and the main characteristics of such an oxygen pump is the unique application of the property of the superionics - to carry through itself exclusively oxygen ions under the influence of a constant current field and a high temperature. The technique developed by us for obtaining a semiconductor film of vanadium dioxide in a controlled atmosphere of oxygen has no analog.

Abstract: Melt-SHS (Self-propagating High-temperature Synthesis) was used for the preparation of Al–5Ti–1B master alloy. The quality ratio of Ti powder/TiO₂ in initial powder mixture was varied from 0:1 to 1:0. The AES, XRD and SEM were applied to evaluate the microstructure and phase componet. The results showed that the Al-5Ti-1B master alloy could be successful produced by the reaction of Al powder, TiO₂ and H₃BO₃ in Al melt, while the reaction rate was slow. The microstructure mainly presents the TiAl₃ particles with long strip shape. A significant improvement was noted both in reaction rate and in the grain refining efficiency when Ti powder was added to the reactants and the optimized ratio of Ti powder/TiO₂ was 2:3. The TiAl₃ particles were reduced and the grain refining efficiency turned bad when Ti powder was totally used to supply Ti

Abstract: The Brazilian reserves of rare earths were updated. Brazil is among the countries with the largest reserves of rare earths in the world. Rare earths present a series of applications in the high technology industry. Magnet production is one of the applications requesting largest volumes of rare earths. Another relevant application is catalysis and Petrobras needs 1000 tons/year of La₂O₃ for petroleum refining. CBMM mine has a pilot plant able to produce tons of separated rare earth oxides, notably didymium (a mixing of Nd and Pr oxides) used in magnet manufacture. Serra Verde mine in Goiás also produced separated rare earth oxides. The magnet production in Brazil can be important for the high efficiency electrical motors industry and also for the automotive industry.

Abstract: Simultaneous thermal oxidation and nitridation technique was utilized to transform sputtered Zr to stoichiometric ZrO₂ thin films on Si substrate. The stoichiometry of this type of oxide has high dielectric constant value of ~25 may be applied as dielectric in metal-oxide-semiconductor-based power devices. Through nitrous oxide gas environment, the oxidation/nitridation process was performed at 700°C for a set of time of 5–20 min. Chemical properties of the fabricated films have been characterized by angle-resolved x-ray photoelectron spectrometer. From the characterization, it was found that stoichiometric Zr-O (ZrO₂) was formed. Nitrogen content in the samples was investigated. It was identified that sample oxidized/nitrided for 15 min gives the highest atomic percentage of nitrogen of 2.64 at% in the interfacial layer. This nitrogen content in the near interface region may help to passivate the Si dangling bonds, which may thus enhance the interface quality of oxide-semiconductor.

Abstract: Cermets with four different compositions of lanthanum and cerium oxide in Cu-Ni-Ag alloy as metallic matrix were fabricated by powder metallurgy and characterized by their structural and physical properties. It was detected the formation of intermetallic compounds as a consequence of diffusion processes. The powder metallurgy allowed to obtain samples with high electrical conductivities and interesting structural characteristics with potential technological applications.

Abstract: In this paper, we present surprising MOS capacitor C–V bias instability observed in NO-grown oxides, with distinctly different behavior compared to that of conventional NO-annealed oxides on 4H-SiC. Using sequential back-and-forth and bias-temperature stress C–V measurements, it was demonstrated that the C–V shift direction of NO-grown oxides was opposite to that of NO-annealed oxides. A model based on bias-temperature stress orientated near-interfacial dipoles is proposed to explain this unique behavior of NO-grown oxides.

Abstract: A sessile drop experiment involving slow heating and cooling of lead-free solder alloys under inert gas revealed segregation of trace elements to the sample surface. Addition of germanium or gallium to Sn-0.7Cu-0.05Ni alloys promoted a metallic lustre in samples, in contrast with the blue/purple colour of the parent alloy. Alloys with Ge or Ga additions showed oxidation resistance. Depth profiling of surfaces of sample alloys with Ge or Ga showed a significant concentration of these elements within the oxide film, which may be responsible for oxidation resistance of these alloys.

Abstract: Phosphorus (P) is often added to wave-solder baths as an anti-oxidation agent for older generation eutectic Sn-37wt%Pb solders. For Pb-free solder alloys trace amounts of germanium (Ge) have been added successfully in Sn-0.7wt%Cu-0.05wt%Ni for anti-oxidation purposes during the wave soldering process. Despite this practice, there is little information on how P and Ge distribute in solder alloys and dross in this alloy system. In this paper, the effects of combinations of trace levels of Ge (< 100ppm) and P (< 100ppm) in Sn-Cu-Ni solder alloys and their dross has been investigated by XRD and SEM/EDS. It was found that the weight fraction of tin oxides in the dross is increased with an addition of less than 100ppm P. The dross consists on SnO oxide with Sn in samples containing Ge and no P, while SnO and SnO₂ oxide are both present when P and Ge additions are made. In samples containing P, (Cu,Ni)₆Sn₅ and Ni-P and/or Ni-Sn-P intermetallics particles were found.

Abstract: In this study, grain refinement efficiency of a new oxide master alloy based on MgAl₂O₄ was demonstrated in Al alloys. The grain size of the reference alloy was reduced by 50-60% with the addition of the master alloy and introduction of ultrasonic cavitation. While cooling rate has an influence on the grain size reduction, higher levels of addition of master alloy was found to be not effective in further reducing the grain size.