Results 1 - 10 of 83
Results 1 - 10 of 83. Search took: 0.018 seconds
|Sort by: date | relevance|
[en] Position estimation capability of an autonomous mobile robot is important for a correct path tracking as well as for a complete navigation in a given environment. This paper describes the system with which the robot can estimate the current position and orientation without perceiving its any outer environments or processing vision image which requires much computational load. The designed system is new and simple. It detects wheel slippage, the main cause of navigational error, and makes it possible to recover from its strayed position. The designed system is composed of an encoder on a non-driven castor, an encoded compass disc as an absolute reference frame, two laser-diodes units with photosensors, and some pertinent data processing hardware and software. An encoded compass disc has two-track codes along its outer perimeter, which give the information on the amount of rotation as well as the direction of rotation in case when slip occurs, and gives the information on the exact turning angles to a mobile robot. The experimental results show that the designed system detects wheel slippage and recovers the robot from its strayed position very well
[en] Beryllium–titanium intermetallic compounds (beryllides) are candidates for advanced neutron multipliers in water-cooled solid breeder demonstration (DEMO) reactor. In contrast to beryllium, which is highly reactive with water vapor above 873 K, the beryllide is considerably more stable with much lower hydrogen-gas-generation rates. To investigate the effect of phase compositions on the reactivity with water vapor, the beryllides were plasma-sintered for different times to produce different phase compositions. They were examined by thermogravimetric analysis and the H2-generation rate was measured at 1273 and 1473 K for 24 h under Ar gas containing 1% H2O. The resulting weight gain of the beryllides under 1% H2O was in good agreement with previous results showing that with an increase in the area fraction of Be, the oxidation resistance under Ar gas containing 1% H2O decreases. The result of the H2-generation rate at 1273 K demonstrates that the larger the fraction of Be, the higher the H2-generation rate. It is clear that the Be phase in the plasma-sintered beryllides attributes to an increase in H2-gas generation. We report here on the effect of phase compositions on reactivity with water vapor of the plasma-sintered beryllides
[en] Highlights: • We report the synthesis results of plasma-sintered Nb and V beryllides. • With increase of sintering time, area fraction of Be_1_2Nb and B_1_2V increased. • Nb beryllide indicates higher density and lower hardness than V beryllide. • Annealing at 1473 K for 5 h results in partial homogenization to Be_1_2Nb and Be_1_2V. - Abstract: Niobium and vanadium–beryllium intermetallic compounds (beryllides) were synthesized by plasma sintering under different sintering times at 1273 K. The beryllide with 7.7 at.% Nb mainly consisted of various phases of Be, Be_1_2Nb, Be_1_7Nb_2, and Be_2Nb, whereas that with 7.7 at.% V consisted of Be_1_2V, Be_2V, and V. As the sintering time increased, area fractions of the target compositions Be_1_2Nb and Be_1_2V increased while that of Be decreased. A comparative analysis demonstrated that the beryllide with 7.7 at.% Nb a showed higher density as well as a greater hardness than that with 7.7 at.% V, due to there being less difference between the sintering temperature and the melting point. In terms of thermal phase stability, the beryllide with 7.7 at.% Nb showed good thermal phase stability with fewer pores and a smaller unhomogenized area, because the beryllide contained a smaller area fraction of the Be phase, which may cause evaporation resulting in pore formation
[en] Highlights: • A new beryllide granulation process that combined process with a plasma sintering method for electrode fabrication and a rotating electrode method (REM) for granulation was suggested. • The beryllide electrode fabrication process was investigated for mass production. • As optimized beryllide electrode indicated higher ductility and was sintered at a lower temperature for a shorter time. • It appears to be more able to not only withstand the thermal shock from arc-discharge during granulation but also produce beryllide pebbles on a large scale. • These optimization results can reduce the time for electrode fabrication by 40%, they suggest the possibility of great reductions in time and cost for mass production of beryllide pebbles. - Abstract: Fusion reactors require advanced neutron multipliers with great stability at high temperatures. Beryllium intermetallic compounds, called beryllides such as Be12Ti, are the most promising materials for use as advanced neutron multipliers. However, few studies have been conducted on the development of mass production methods for beryllide pebbles. A granulation process for beryllide needs to have both low cost and high efficiency. To fabricate beryllide pebbles, a new granulation process is established in this research by combining a plasma sintering method for beryllide synthesis and a rotating electrode method using a plasma-sintered electrode for granulation. The fabrication process of the beryllide electrode is investigated and optimized for mass production. The optimized beryllide electrode exhibits higher ductility and can be sintered at a lower temperature for a shorter time, indicating that it is more suitable not only for withstanding the thermal shock from arc-discharge during granulation but also for producing the beryllide pebbles on a large scale. Accordingly, because these optimization results can reduce the time required for electrode fabrication by 40%, they suggest the possibility of great reductions in time and cost for mass production of beryllide pebbles
[en] Highlights: • Prototypic Be12V pebbles were successfully fabricated by a direct the rotating electrode granulation method. • Be12V pebbles were much more resistant to water vapor than pure Be. • A surface BeO layer on Be12V pebbles acted as a protective barrier preventing the hydrogen generation reaction. • The hydrogen generation rate was nearly reduced to background level via surface modification of Be12V pebbles. - Abstract: Prototypic pebbles composed of Be12V showing no peritectic reaction during cooling were successfully fabricated without homogenization. These Be12V prototypic pebbles were found to have a good oxidation resistance. BeO layer on the surface of Be12V pebbles was found to act as a protective barrier preventing the hydrogen generation reaction. Thus, the effect of BeO layer as a surface modification of beryllide was evaluated. Using surface-modified pebbles, hydrogen generation experiments were repetitively (3 times) carried out at 1273 K for 24 h. The hydrogen generation rate was nearly reduced to the background level by this surface modification. Thus, surface-modified Be12V pebbles showing no-hydrogen generation reaction were successfully fabricated.
[en] Density measurements and hydrogen generation test were carried out to investigate sinterability as well as reactivity of a plasma-sintered beryllium (PS-Be) at high temperatures for different grade beryllium. Density evaluation clarified that PS-Be was fabricated with high sintering density and low number of open pores, which was similar to the commercial beryllium fabricated by a hot-pressing method with different grades. Additionally, surface observation results implied that the PS-Be was fabricated not only with smaller grain sizes but also with less impurity. Regarding the reactivity for dry air as well as 10,000 ppm H2O/Ar, it showed that the PS-Be exhibited larger weight gains and higher H2 concentration at 1073 K, as compared to other beryllium specimens. However, at 1273 K all specimens indicated similar oxidation behaviour and H2 gas generation
[en] Highlights: • Ternary Be–Ti–V beryllide pebbles were fabricated by plasma sintering and rotating electrode method. • As V content increases in Be_1_2Ti_1_−_xV_x pebbles, the surface structure tends to become finer. • As V content increases, the area fraction of the Be phase decreases, whereas that of the Be_1_2V phase increases. • The higher V content of the pebbles has, the lower their weight gains and hydrogen generation rates are. - Abstract: A new combined plasma sintering and rotating electrode method for fabricating beryllide rods and pebbles has been suggested. Using these methods, preliminary synthesis of ternary beryllide pebbles with different chemical compositions, Be_1_2Ti_1_−_xV_x (x = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0), was successful. Scanning electron microscopy observations revealed that grain size on the surface decreased, whereas the area fraction of the Be phase in the cross-section decreased as the amount of V increased. These decreases may be attributed to the fact that the chemical composition of the pebble was closely varied to single-phase Be_1_2V, with no peritectic reaction as the amount of V increased, while the Be, Be_1_2Ti, and Be_1_7Ti_2 phases were formed with large grains caused by a peritecic reaction in Be_1_2Ti. This feature influenced the variation of reactivity with 1% water vapor at high temperatures. It was concluded that weight gain and H_2 generation decreased with decreases in grain size as well as Be phase on the surface, as the amount of V increased in Be_1_2Ti_1_−_xV_x. Based on cross-sectional observations after oxidation measurement for 24 h, we found that Be_1_2Ti_0_._3V_0_._7 and Be_1_2Ti_0_._1V_0_._9 pebbles showed high phase stability.
[en] Highlights: •The optimization of plasma sintering conditions was investigated. •Sinterability as well as mechanical property was evaluated. •Plasma-sintered Be-Ti intermetallic compounds are composed of four different phases. •Optimum sintering conditions for consolidation to Be12Ti phase were suggested. -- Abstract: Plasma sintering method has been newly suggested as a synthesis method for beryllium–titanium intermetallic compounds (beryllides) as an advanced neutron multiplier in a system of water cooled solid breeder demonstration fusion reactors. Not only synthesis of the beryllide but joining the beryllide could be successfully fabricated. We report on the optimization of the main sintering conditions, on the sinterability of the plasma-sintered beryllides in the light of sinterability, as well as consolidation to the Be12Ti phase. The optimum sintering temperature for consolidation to the Be12Ti phase was 1273 K and the area fraction of the Be12Ti phase obtained when sintering at 1273 K, was approximately 83%. To increase the fraction of the Be12Ti phase, increasing the sintering time was inevitable and this led to an increase in the Be12Ti phase corresponding to 97.5%. However, as the sintering time increased, variation in grain size of the beryllides was observed. With regard to the sintering pressure, the higher the sintering pressure applied, the higher the sinterability, even though lower pressure may lead to better consolidation with respect to the absence of the Be2Ti phase
[en] Highlights: • Beryllide pebbles with different Ti contents were successfully fabricated. • Mechanical properties are dependent to area fraction of Be phase in the pebbles. • Reactivity of beryllide pebbles is predominant to Be phase on the surface. - Abstract: A combinational process for the fabrication of beryllide pebbles, consisting of a plasma-sintering method and the rotating electrode method for fabrication of electrode rods and pebbles, respectively, is proposed. To investigate the effect of Ti content in titanium beryllide pebbles on the pebbles’ crush strength and oxidation resistance, beryllide pebbles with 3–10.5 at.% Ti were fabricated. Scanning electron microscopy (SEM) observations demonstrated that the surfaces of Be – 3 and 5 at.% Ti pebbles contained a Be phase, whereas the surfaces of Be – 7–10.5 at.% Ti pebbles did not. Moreover, according to cross-sectional SEM images, the area fraction of the Be phase decreased with increasing Ti content in beryllide pebbles with 3–9 at.% Ti, whereas the pebble with 10.5 at.% Ti consisted primarily of the Be_1_7Ti_2 phase. With regard to the mechanical properties of the pebbles, their strength and elongation decreased with increasing Ti content because of the brittleness of the Be phase. The weight gain and the amount of H_2 generated by the pebbles under reaction with 1% H_2O/Ar decreased with increasing Ti content, whereas the stability of the pebbles was strongly dependent on the presence of the Be phase on their surface.
[en] Highlights: • Single phase Be_1_2Ti pebbles were successfully fabricated by combination method. • Homogenized pebbles indicated larger surface area by ten times than as-granulated one. • Be phase in the homogenized pebbles contributes to increase of reactivity. • Single phase Be_1_7Ti_2 pebbles were successfully fabricated without homogenization. - Abstract: Advanced neutron multipliers such as beryllides with high stability at high temperatures are desired for demonstration power plant (DEMO) reactors. Prototypic pebbles 1 mm in diameter of single phase Be_1_2Ti beryllide were successfully fabricated by a combination process involving plasma sintering, a rotating electrode method, and a homogenization treatment. Relative to the non-treated, multi-phase pebbles, the homogenized Be_1_2Ti pebbles demonstrated an increased reactivity because the homogenization treatment caused an increase in the specific surface area of the treated pebbles. To prevent increased hydrogen generation, prototypic Be_1_7Ti_2 pebbles were successfully fabricated without homogenization. The Be_1_7Ti_2 prototypic pebbles where shown to have a good oxidation resistance.