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[en] The effects of Nb and Sn on hydride embrittlement of Zr alloys were investigated. For this, experimental Zr alloys were prepared in a sheet shape and charged with hydrogen. The microstructure and hydride morphology were analyzed and the tensile properties were measured to understand the role of Nb and Sn on the hydride embrittlement of Zr alloy. With addition of Nb and Sn, recrystallization was retarded during the final annealing heat treatment. The retardation was mainly caused from β-Nb precipitates and Sn solute atoms, which was confirmed from texture analyses. Of the two, Sn was found to more effective in retarding recrystallization. When hydrogen was charged, hydride clusters with stacked hydride platelets were observed in unalloyed Zr. However, with addition of Nb and Sn, such hydride clusters were replaced with hydrides platelets which were more or less aligned with the rolling direction and linked up on the rolling plane, and hydride length and the spacing between hydrides were increased. This change in hydride morphology was caused by the retardation of recrystallization. Again, Sn was found to be more effective in in modifying the hydride morphology and aligning hydrides on the rolling plane. Both Nb and Sn contributed to the strengthening of Zr alloys, but Sn is more effective in strengthening than Nb. However, tensile strengths of the experimental alloys were nearly independent of the absorbed hydrogen contents. While ductility was reduced with increasing hydrogen contents, the degree of ductility loss was dependent on Nb and Sn contents which increased hydrogen solubility and retarded recrystallization. For alloys with 1%-Nb and/or 1%-Sn, increase in hydrogen solubility was the main contributor to increase in resistance to hydride embrittlement. On the other hand, for an alloy with 2%-Nb resulted in large amount of β-Nb precipitates, which in turn significantly retarded recrystallization. Therefore, the added contribution of retardation of recrystallization resulted in the largest resistance to hydrogen embrittlement
[en] The effects of hydrogen concentration on the axial fracture toughness of Zr-2.5 wt% Nb CANDU pressure tube material have been determined from room temperature to 300 .deg. C. The specimens was charged to 50, 100, 150, 200ppm of hydrogen. To observe hydride morphology and measure volume fraction, optical microscope was used. The crack growth during fracture toughness test was measured by direct current potential drop method. Fracture toughness characterized by J-R curve and dJ/da was discussed in terms of hydrogen concentration. As hydrogen concentration increased, hydride volume fraction, thickness and length increased. However, interhydride spacing remained nearly constant. At room temperature, fracture toughness decreased rapidly with increasing hydrogen concentration until hydrogen concentration was below 100ppm. However, fracture toughness remained at a similar level at above 100ppm. Ductile-brittle transition temperature increased slightly when hydrogen concentration increased. At high temperature, fracture toughness also decreased because yield stress increased by hydride volume fraction
[en] Nature has been providing us energy from the beginning of the world. However human has hardly used it wisely. Solar energy is a kind of renewable energy from the nature. This study has been carried out to study the use of solar energy as it is harnessed in the form of thermal energy. Solar energy is one of the most promising energy resources such as hydrogen, biomass, wind and geothermal energy, because it is clean and inexhaustible. Space heating in buildings can be provided from solar energy by systems that are similar in many respects to water heater systems. By tapping into solar energy, we can not only solve the problem of energy shortage, but also can protect the environment and benefit the human beings. There are currently two types of evacuated tube; a single glass tube and a double glass tube. The former consists of a single glass tube which contains a flat or curved aluminium plate attached to a copper heat pipe or water flow pipe. The latter consists of rows of parallel transparent glass tubes, each of which contains an absorber tube. Evacuated tube collectors introduced above, however, pose some problems as they break rather easily under mechanical stresses. This paper introduces some preliminary results in design and fabrication of a non-glass solar vacuum tube collector in which the thermosyphon(heat pipe)made of copper is used as a heat transfer device. A series of tests have been performed to assess the ability of a non-glass solar vacuum tube collector. The series of experiments are as follows: 1)Vacuum level inside a vacuum tube. 2)Effects of the air remaining inside a vacuum tube on the temperature on the absorber plate. 3)Comparison of a non-glass vacuum solar collector with a single glass evacuated tube(SEIDO 5). Different vacuum levels inside non-glass vacuum tubes were applied to check any leakage or unexpected physical or chemical developments with time. The vacuum level changed from 10-2torr to 5torr in 5 days due to air infiltration from the ambient and gas emissions from the materials they were made of. The effect of vacuum levels inside a vacuum tube on the absorber plate were investigated in different conditions. Due to less heat losses to the ambient, the non-glass vacuum tube at vacuum level 10-2 torr kept more heat at higher temperatures compared to the non-glass vacuum tube collectors whose vacuum levels were at 5 torr. However, the temperature was not linearly proportional to the vacuum level. Two types of solar collectors were used to investigate the ability of non-glass solar vacuum tube: one single glass evacuated tube and one non-glass vacuum tubes(10-2torr). The efficiency of a non-glass vacuum tube with 10-2torr was different from that of a single glass evacuated tube in which vacuum level is 10-4∼10-5torr due to the transmittance of ZnO. Unlike glass evacuated tubes, non-glass solar vacuum tubes generally require some measures to prevent air infiltration through invisible pores of the tube wall and gas emission from the materials. If the problems related with vacuum inside a tube are solved, the non-glass vacuum collector will work more efficiently
[en] Highlights: • Scrap tire rubber was successfully pyrolyzed in a two-stage pyrolyzer. • The two-stage pyrolyzer is composed of auger and fluidized bed reactors. • N_2 and temperatures of ∼500 °C were effective for a low-sulfur oil. • A pyrolysis oil contained only 0.55 wt.% of sulfur and 0.28 wt.% of nitrogen. • A pyrolysis oil from the auger reactor contained 50 wt.% DL-limonene. - Abstract: The aim of this work was to reduce the sulfur content of pyrolysis oil derived from the scrap tire pyrolysis. In this respect, a series of pyrolysis experiments was conducted in both a fluidized bed reactor (one-stage pyrolysis) and a newly developed two-stage pyrolyzer consisting of an auger reactor and a fluidized bed reactor in series (two-stage pyrolysis). The one-stage pyrolysis was carried out at ∼500 and 600 °C with different fluidizing gases (N_2 and product gas). In the experiments, the pyrolysis oil obtained at ∼500 °C had a lower sulfur content than that produced at ∼600 °C. N_2 was better at producing a low-sulfur pyrolysis oil than product gas. The sulfur contents of the oils obtained from the one-stage pyrolysis ranged from 0.75 to 0.92 wt.%. The two-stage pyrolysis was conducted using product gas as the fluidizing medium at different auger reactor temperatures (∼230–450 °C) and at a constant fluidized bed reactor temperature (∼510 °C). A pyrolysis oil containing only 0.55 wt.% of sulfur could be produced at the temperatures of the auger reactor of ∼330 °C and fluidized bed reactor of ∼510 °C. Moreover, the two-stage pyrolysis could produce an oil with a low nitrogen content (0.28 wt.%). A pyrolysis oil obtained from the auger reactor contained DL-limonene up to 50 wt.%.
[en] Scrap tire pyrolysis was performed using a two-stage pyrolyzer consisting of an auger reactor and a fluidized bed reactor to produce a low-sulfur pyrolysis oil. In the experiments, the effect of the residence time of the feed material in the auger reactor was investigated at ∼300 (auger reactor) and 500 °C (fluidized bed reactor). In addition, natural dolomite and olivine and calcined dolomite and olivine were used as the fluidized bed materials to examine their effects on reducing the sulfur content of pyrolysis oil. In the experiments, the yields of the oil from the auger reactor were 1.4–3.7 wt%, and it was enriched with DL-limonene whose content in the oil was 40–50 wt%. The yields of the oil from the fluidized bed reactor were 42–46 wt%. The optimum residence time of the feed material in the auger reactor turned out to be 3.5 min. Calcined dolomite and olivine significantly decreased the sulfur content of pyrolysis oil. Metal oxides of the additives appeared to react with H_2S to form metal sulfides. The sulfur content of pyrolysis oil obtained with calcined olivine was 0.45 wt%. - Highlights: • Scrap tires were successfully pyrolyzed in a new type two-stage pyrolyzer. • The two-stage pyrolyzer is composed of an auger and fluidized bed reactors. • Calcination of olivine and dolomite led to a strong decrease in sulfur. • The lowest sulfur content of pyrolysis oil was 0.45 wt%. • Pyrolysis oil yields from the fluidized bed reactor were 43–46 wt%.
[en] To produce a bio-oil having a high concentration of furfural, corn stover was fast-pyrolyzed using ZnCl_2 in a fluidized bed reactor at 330–430 °C. The effects of various parameters such as reaction temperature, water- and acid-washing prior to pyrolysis, and ZnCl_2 content on the product and furfural yields were investigated. Moreover, solvent extraction was conducted using toluene at different mass ratios of bio-oil/toluene to recover furfural from the obtained bio-oil. The maximum yield of bio-oil was 59 wt%. The bio-oil mainly comprised acetic acid, α-hydroxyketones, and furfural. The maximum furfural yield was 11.5 wt% when the feed material was water-washed, impregnated with 18.5 wt% ZnCl_2, and pyrolyzed. Although acid-washing removed alkali and alkaline earth metals much more efficiently than water-washing, water-washing was better than acid-washing for the furfural production. Toluene extraction was very effective to recover furfural from bio-oil. The maximum recovery rate (82%) was achieved at a bio-oil/toluene ratio of 1:4. - Highlights: • Corn stover pretreated and impregnated with ZnCl_2 was successfully pyrolyzed. • Furfural was recovered from bio-oil by extraction using toluene. • Water-washing was better than acid-washing for the furfural production. • The highest furfural yield was 11.5 wt% of the product. • The highest furfural recovery rate was 82%
[en] Pyrolysis of palm kernel shell was performed using a two-stage pyrolyzer consisting of an auger reactor and a fluidized bed reactor within the auger reactor temperature range of ∼290–380 °C at the fluidized bed reactor temperature of ∼520 °C, and with a variable residence time of the feed material in the auger reactor. The highest bio-oil yield of the two-stage pyrolysis was ∼56 wt%. The bio-oil derived from the auger reactor contained degradation products of the hemicelluloses of PKS, such as acetic acid, and furfural, whereas the fluidized bed reactor produced a bio-oil with high concentrations of acetic acid and phenol. The auger reactor temperature and the residence time of PKS in the auger reactor had an influence on the acetic acid concentration in the bio-oil, while their changes did not induce an observable trend on the phenol concentration in the bio-oil derived from the fluidized bed reactor. The maximum concentrations of acetic acid and phenol in bio-oil were ∼78 and 12 wt% dry basis, respectively. As a result, it was possible for the two-stage pyrolyzer to separately produce two different bio-oils in one operation without any costly fractionation process of bio-oils. - Highlights: • The two-stage pyrolyzer is composed of an auger and a fluidized bed reactor. • The two-stage pyrolyzer produced two different bio-oils in a single operation. • The maximum bio-oil yield of the two-stage pyrolysis was ∼56 wt%. • The maximum concentration of acetic acid in bio-oil was ∼78 wt% dry basis. • The maximum concentration of phenol in bio-oil was ∼12 wt% dry basis.
[en] A series of new alkali metal cadmium selenites, A2Cd(SeO3)2 (A = K, Rb, and Cs) and Li2Cd3(SeO3)4 have been synthesized in phase pure forms through hydrothermal and solid-state reactions. Structural analyses using single crystal X-ray diffraction indicate that while A2Cd(SeO3)2 and Li2Cd3(SeO3)4 reveal layered structures consisting of CdO6 and SeO3 polyhedra, their symmetry, bonding modes, and the orientation of lone pairs on Se4+ cations are different. A closer examination suggests that the observed structural variations found in the reported materials are attributed to the structure-directing effect of alkali metal cations with different sizes. Scanning electron microscopy/energy dispersive analysis by X-ray, thermogravimetric analysis, Infrared and UV–vis diffuse reflectance spectroscopy, transformation reactions under hydrothermal conditions, and local dipole moment calculations for the reported materials are also reported. - Graphical abstract: The size of alkali metal cations affects the direction of lone pairs on the Se4+ between the layers. Display Omitted - Highlights: • New selenites, A2Cd(SeO3)2 (A = K, Rb, and Cs) and Li2Cd3(SeO3)4, were synthesized. • Complete structural determinations and full characterizations have been performed. • The structural variations are due to the different size of alkali metal cations. • A2Cd(SeO3)2 transformed to Li2Cd3(SeO3)4 in aqueous LiNO3 under hydrothermal conditions.
[en] Five new alkali metal zinc selenites, A2Zn3(SeO3)4·xH2O (A = Na, Rb, and Cs; 0≤x≤1) and Cs2Zn2(SeO3)3·2H2O have been synthesized by heating a mixture of ZnO, SeO2 and A2CO3 (A = Na, Rb, and Cs), and characterized by X-ray diffraction (XRD) and spectroscopic analyses techniques. All of the reported materials revealed a rich structural chemistry with different frameworks and connection modes of Zn2+. While Rb2Zn3(SeO3)4 and Cs2Zn3(SeO3)4·H2O revealed three-dimensional frameworks consisting of isolated ZnO4 tetrahedra and SeO3 polyhedra, Na2Zn3(SeO3)4, Cs2Zn3(SeO3)4, and Cs2Zn2(SeO3)3·2H2O contained two-dimensional [Zn3(SeO3)4]2- layers. Specifically, whereas isolated ZnO4 tetrahedra and SeO3 polyhedra are arranged into two-dimensional [Zn3(SeO3)4]2- layers in two cesium compounds, circular [Zn3O10]14- chains and SeO3 linkers are formed in two-dimensional [Zn3(SeO3)4]2- layers in Na2Zn3(SeO3)4. Close structural examinations suggest that the size of alkali metal is significant in determining the framework geometry as well as connection modes of transition metal cations. - Graphical abstract: Variable dimensions and frameworks were found in a series of quaternary zinc selenites, A2Zn3(SeO3)4 (A = Na, Rb and Cs). - Highlights: • Five novel quaternary zinc selenites are synthesized. • All the selenites with different structures contain polarizable d10 and lone pair cations. • The size of alkali metal cations is significant in determining the framework geometry.
[en] Inspection and maintenance activities for air conditioning facilities within the plant are managed mainly for active facilities, and as the years of operation pass, a method for detecting in advance aging-related integrity problems of passive facilities and taking necessary measures against them is required. Therefore, this paper establishes a standard aging management guideline for air conditioning facilities by selecting systems for which those facilities are to be managed, analyzing degradation mechanisms and reviewing the current status of aging degradation management. According to the review of additional equipment-specific aging degradation mechanisms and the current status of management to apply the aging degradation program to air conditioning facilities, it has been found that internal and external visual inspection procedures for fans, dampers, coils, filters and housings have to be added. It has been confirmed that among additional equipment s, fire dampers, fan bearings and belts and air cleaning/conditioning units with charcoal filters do not require additional inspection as they are periodically inspected. It has been found, however, that air cleaning/conditioning units without charcoal filters are to be inspected along with fans, ducts and coils