Thermal conductivity of high porosity alumina refractory bricks made by a slurry gelation and foaming method

Alumina has high heat resistance and corrosion resistance compared to other ceramics such as silica or mullite. However, for its application to refractory bricks, its high thermal conductivity must be reduced. To reduce this thermal conductivity by increasing the porosity, a GS (gelation of slurry) method that can produce high porosity solid foam was applied here to produce the alumina refractory brick. This method was successfully applied to produce alumina foam with high porosity and thermal conductivity of the foam is evaluated. At room temperature, the thermal conductivity was about 0.12 W/mK when the foam density was 0.1 g/cm³. At elevated temperature above 783 K, thermal conductivity of the foam was strongly affected by heat radiation and increased with increasing temperature, in contrast to the thermal conductivity of alumina itself, which decreased with increasing temperature. The alumina foams developed here achieved sufficient thermal insulating properties for use in refractory bricks.     

Defect sizing of small inclined cracks on a free surface using multi-tip waves

The most effective method of ultrasonic defect sizing is recognized to be the tip echo method. However, tip waves have very weak intensities, and require skill and experience by the operator. Recently, low noise fully digital flaw detectors have been developed, which make it easy to capture several tip echoes simultaneously. Experiments were carried out using a fully digital detector for the reflection by an artificial inclined crack of 1.5 mm height on a free surface, and numerical simulations were also performed to distinguish each tip echo. Crack height, inclination angle, and crack width were estimated using the tip echo distances of the experimental data from one side. The results show good agreement with actual values. The method is stable for changes in probe position. An experiment on fatigue cracks was also performed. Automatic inspection will be possible using the results of this method in the near future. Many tip waves are generated by the deflection of ultrasound from crack tips and corners, and the evaluation of defect size can be accomplished by full use of the tip waves.     

Multiple melting behavior of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) investigated by differential scanning calorimetry and infrared spectroscopy

The multiple melting behavior of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(HB-co-HHx)) (HHx = 12 mol%) isothermally crystallized from the melt state has been characterized by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The influence of different experimental variables (such as crystallization temperature, time, and heating rate) on the multiple melting behavior of P(HB-co-HHx) was investigated by using DSC. Moreover, it has been further examined by monitoring intensity changes of the characteristic IR bands during the subsequent heating process. For the isothermally crystallized P(HB-co-HHx) samples, triple melting peaks were observed upon heating. The weak lowest-temperature DSC endotherm I always appears at the position just above the crystallization temperature, and shifts to a higher temperature linearly with the logarithm of the crystallization time. The combination of DSC and IR results suggested that the occurrence of peak I was a result of the melting of crystals formed upon long-time annealing. As for the other two main melting endothermic peaks, endotherm II corresponds to the melting of crystals formed during the primary crystallization, and endotherm III is ascribed to the melting peak of the crystals formed by recrystallization during the heating process.     

The removal of estrogenic activity and control of brominated by-products during ozonation of secondary effluents

The purposes of this study were to investigate the behavior of brominated by-products, such as bromate ion and total organic bromide, formed during ozonation for the removal of estrogenic activity in sewage effluents and to propose operation parameters for the ozonation process. It is necessary to reduce the E(2) equivalent concentration of estrogenic activity in secondary effluent treated by 90% of the initial one. To do so, ozonation until dissolved ozone concentration increased to 0.1mg/L (which corresponds to approximately 1mg O(3)/mg DOC(0) [consumed ozone per initial DOC] of consumed ozone for the effluent in this study) is proposed as an operation parameter for ozonation without the formation of brominated by-products.     

The Control of Brominated By-products and the Removal of Organic Pollutants during the Ozone/Hydrogen Peroxide Treatment of Secondary Effluent

This study aims to establish appropriate conditions to control the formation of bromate ion and brominated organic compounds during the O₃/H₂O₂ treatment of the secondary effluents of sewage. When the H₂O₂/O₃ mole ratio of injection was above 0.5 and the dissolved ozone concentration was below 0.1 mg/L, bromate ion formation was controlled, and treatment purposes such as the reduction of estrogenic activity or organic matter were completed. The formation of TOBr and individual brominated organic compounds during O₃/H₂O₂ treatment was also completely controlled.     

Centrifugal Sintering of a Barium Titanate Thick Film

A highly packed barium titanate film with a thickness of 30 μm was prepared under 1000 g _n ( g _n , standard acceleration of free fall) via centrifugal sintering. Here, BaTiO₃ particles were used as the source material, and LiF flux was co-added as a grain growth enhancer. The film was originally printed on a substrate by screen printing, and subsequently sintered. As the amount of flux increased, the film density also increased with remarkable grain growth. However, it was difficult to remove pores in conventional sintering even by the heavy addition of flux such as 20 wt%. In contrast, centrifugal sintering successfully compacted films (90% of theoretical density). The centrifugally sintered film possessed a relatively smooth surface and showed no flux segregation. These features of a centrifugally sintered film are thought to be attributed to the enhancement of particles' rearrangement at an elevated temperature by a centrifugal force.     

Grain-Boundary Diffusion of Strontium in (La,Ca)CrO3 Perovskite-Type Oxide by SIMS

The grain-boundary-diffusion coefficient ( D _gb) of strontium in La_0.9Ca_0.13CrO_3-δ was determined by secondary-ion mass spectrometry (SIMS), using two different measurement modes: depth profiling from the surface and line scanning on the fracture surface. The depth profiles that were sputtered by an O₂⁺-primary-ion beam gave two slopes of strontium concentration profiles, which corresponded to grain (bulk) and grain-boundary diffusion. The depth profiles were fitted to an appropriate equation that gave the grain- (bulk-) and grain-boundary-diffusion coefficients ( D _bulk= 6.5 × 10^-20 m²/s and D _gb= 1.6 × 10^-15 m²/s in air at 1273 K, respectively). Initially, to obtain the D _gb value via the SIMS line-scanning measurement, the fracture surface of La_0.9Ca_0.13CrO_3-delta was measured by a low-energy O₂⁺-primary-ion beam. The line-scanning measurement enabled us to successfully determine the strontium concentration profiles around the grain boundary. However, the D _gb value that was obtained via the line-scanning mode was 6.0 10⁻¹³ m²/s, which was a factor of 100 greater than that which was obtained by the depth-profile mode. Comparison between the depth-profile and line-scanning modes will require additional careful examination.     

Fabrication and Sintering of Fine Yttria-Doped Ceria Powder

Yttria–doped ceria powder was prepared from oxalate precursors. The oxalate coprecipitation bath parameters were closely monitored and found to influence the sintering behavior of the subsequently obtained oxide powders strongly. The use of concentrated (Ce,Y) metal nitrate solutions and dilute neutralized oxalic acid for coprecipitation were identified as the most–important parameters. Following calcination at 700°C, compacts of such powders were sintered to high density (98%) at 1400°C (4 h). Ball milling of the powder further reduced the sintering temperature. Dry milling, for tape–casting applications of the powder in particular, was more effective than wet milling. Tape–cast membranes were fired at 1400°C (2 h), with resulting densities of 98%.     

Removal Characteristics of Organic Pollutants in Sewage Treatment by a Pre-Coagulation,Ozonation and Ozone/Hydrogen Peroxide Process

The applicability of a sequential process of ozonation and ozone/hydrogen peroxide process for the removal of soluble organic compounds from a pre-coagulated municipal sewage was examined. 6–25% of initial T-COD_Cr was removed at the early stage of ozonation before the ratio of consumed ozone to removed T-COD_Cr dramatically increased. Until dissolved ozone was detected, 0.3 mgO₃/mgTOC₀ (Initial TOC) of ozone was consumed. When an ozone/hydrogen peroxide process was applied, additional COD_Cr was removed. And we elucidated that two following findings are important for the better performance of ozone/hydrogen peroxide process; those are to remove readily reactive organic compounds with ozone before the application of ozone/hydrogen peroxide process and to avoid the excess addition of hydrogen peroxide. Based on these two findings, we proposed a sequential process of ozonation and multi-stage ozone/hydrogen peroxide process and the appropriate addition of hydrogen peroxide. T-COD_Cr, TOC and ATU-BOD₅ were reduced to less than 7 mg/L, 6 mgC/L and 5 mg/L, respectively after total treatment time of 79 min. Furthermore, we discussed the transformation of organic compounds and the removal of organic compounds. The removal amount of COD_Cr and UV₂₅₄ had good linear relationship until the removal amounts of COD_Cr and UV₂₅₄ were 30 mg/L and 0.11 cm^?1, respectively. Therefore UV₂₅₄ would be useful for an indicator for COD_Cr removal at the beginning of the treatment. The accumulation of carboxylic acids (formic acid, acetic acid and oxalic acid) was observed. The ratio of carbon concentration of carboxylic acids to TOC remaining was getting higher and reached around 0.5 finally. Removal of TOC was observed with the accumulation of carboxylic acids. When unknown organic compounds (organic compounds except for carboxylic acids) were oxidized, 70% was apparently removed as carbon dioxide and 30% was accumulated as carboxylic acids. A portion of biodegradable organic compounds to whole organic compounds was enhanced as shown by the increase ratio of BOD/COD_Cr.