Change in the Microstructure of Ferritic Stainless Steel with Surface Roughness and the Number of Thermal Cycles

One of the candidates for metallic interconnects of solid oxide fuel cells is ferritic stainless steel, Crofer 22 APU. Ferritic stainless steel Crofer 22 APU specimens with different surface roughness were prepared by grinding with SiC powder papers of various grits and then thermally cycled in air. Variation in the microstructure of the samples having different roughness with thermal cycling was investigated. Polished Crofer 22 APU specimens after three and five thermal cycles had relatively flat oxide layers with thicknesses of about 13.8 and 17.9 μm, respectively. Micrographs of a trench made by milling with FIB (focused ion beam) for a Crofer 22 APU specimen ground with grit 80 SiC powder paper after 8 thermal cycles (total oxygen exposure time of 200 h at 1073 K), captured by ESB (energy selective back-scattering) and SE2 (type II secondary electrons), showed that the surface of the sample was very coarse and its oxide layer was undulated. In the oxide layer, the phase of the sublayer was Cr2O3, and that of the top layer was (Cr, Mn)3O4 spinel. The surface of the sample ground with grit 80 SiC powder paper was very rough after 60 thermal cycles (total oxygen exposure time of 1500 h at 1073 K). The polished Crofer 22 APU is a better applicant to an interconnect of SOFC than those with rougher surfaces.

Microalgae: A promising bioresource for a sustainable future

Microalgae are highly diverse unicellular photosynthetic organisms found in aquatic environments. Microalgae produce oxygen during their proliferation, contributing to nearly 50% of the total oxygen production in the world. Concurrently, microalgae consume carbon dioxide in the atmosphere, thereby serving as carbon sinks to alleviate the effects of global warming. In comparison to terrestrial plants, microalgae exhibit rapid growth rates, higher photosynthetic efficiency, shorter harvesting time and higher biomass productivities. Moreover, they do not require arable land or potable water to facilitate their growth, hence becoming a more sustainable feedstock as compared to conventional crops. Altogether, microalgae have been identified as a bioresource with great industrial potential due to their ability to accumulate commercially valuable metabolites that can be extracted and subsequently processed into diverse bioproducts such as biofuels, pharmaceuticals/nutraceuticals, biofertilizer and animal feed.

Study of Soft/Hard Bimagnetic CoFe2/CoFe2O4 Nanocomposite

We report an experimental study of the bimagnetic nanocomposites CoFe2/CoFe2O4. The precursor material, CoFe2O4 was prepared using the conventional stoichiometric combustion method. The nano-structured material CoFe2/CoFe2O4 was obtained by total oxygen reduction of CoFe2O4 using a thermal treatment at 350 °C in H2 atmospheres following the partial oxidation in O2 atmospheres at 380 °C during 120; 30; 15, 10, and 5 min. The X-ray diffraction, Mössbauer spectroscopy and transmission electronic microscopy images confirmed the formation of the material CoFe2/CoFe2O4. The magnetic hysteresis for the nanocomposite with different saturation magnetization (from 87 to 108 emu/g) also confirms the formation of the CoFe2/CoFe2O4 with different content of CoFe2O4. Furthermore, the magnetic hysteresis curves for all samples presented a single magnetic behavior, suggesting the magnetic coupling between the phases of the nanocomposite. The effects of high energy milling on the magnetic properties of the precursor material and nanocomposites samples were evaluated.

Study on the Variation in Microstructure of a Ferritic Stainless Steel with Surface Roughness and Thermal Cycling in Air

A ferritic stainless steel, Crofer 22 APU, is one of candidates for metallic interconnects of solid oxide fuel cells. Ferritic stainless steel Crofer 22 APU specimens with different surface roughnesses were prepared by grinding with SiC powder papers of various grits and were then thermally cycled. Polished Crofer 22 APU specimens after one thermal cycle and five thermal cycles had relatively straight oxide layers with similar thicknesses of 30 μm, suggesting that after one cycle (total oxygen exposure time of 100 h at 1073 K), the oxidation does not progress. Micrographs of a trench made by milling with the FIB (focused ion beam) for a Crofer 22 APU specimen rubbed with grit 80 SiC powder paper after 8 thermal cycles (total oxygen exposure time of 200 h at 1073 K), captured by ESB, InLens, and SE2, showed that the surface of the sample was very coarse and its oxide layer was undulated. In the oxide layer, the phase of the sublayer was Cr2O3, and that of the top layer was (Cr, Mn)3O4 spinel. The sample ground with grit 80 SiC powder paper after 60 thermal cycles (total oxygen exposure time of 1500 h at 1073 K) was very coarse. Some ridges were quite straight and continuous. After 20 and 40 thermal cycles, ASR (area specific resistance) decreased as the number of grit of the SiC powder paper increased, suggesting that the polished Crofer 22 APU is better than those with rougher surfaces for application as an interconnect of SOFC.

Modeling of Azadirachta indica leaves powder efficiency for the remediation of soil contaminated with crude oil

A regression analysis model was developed to examine the reliability and the acceptability of the sun-dried and room-dried Azadirachta indica leaves for the remediation crude oil contaminated soil in Niger Deltal, Nigeria. An experimental approach was used to monitor the concentration of the total petroleum hydrocarbon (TPH) degradation that was enhanced in the presence of the microbes in the reactor. A regression analysis was performed to evaluate the reaction behavior microbes in reactor for the remediation of the TPH in the presence of sun-dried and room-dried A. indica leaves in sandy and loamy soils contaminated with 100 ml of crude oil. The physicochemical properties of control loamy soil was as; pH (6.75), electric conductivity (10.36 μS/cm), total oxygen (2.99%), total Nitrogen (0.091%), potassium (36.82942%), phosphorus (15.36%) and total bacteria (2.15×102 cfu/g). Whereas, these values were as pH (6.82), electric conductivity (21.48 μS/cm), total oxygen content (1.18%), total nitrogen (0.036%), potassium (24.03681%), phosphorus (5.18%) and total bacteria count (1.86×102 cfu/g) for sandy soil. The inoculant was prepared by blending sun-dried and room-dried A. indica leaves. The blended A. indica leaves in 50 to 100 g range were applied on the polluted soils for 35 days and significant reduction in contaminating agents was observed. The highest remediation was observed in soils treated with 100 g room dried A. indica leaves. A 96% remediation recorded in sandy soil treated with 100 g room dried A. indica leaves as TPH depleted from 35818.69 mg/kg to 1349.109 mg/kg and 92% reduction was observed in loamy soil treated with 100 g dried A. indica leaves and TPH depleted from 48508.92 mg/kg to 3977.739 mg/kg. The regression model developed was successfully employed to predict TPH remediation behavior, which can be applied to monitor remediation of contaminated soil.

THE PERCENTAGE OF OXYGEN ABSORPTION BY VANNAMEI SHRIMP (LITOPENAEUS VANNAMEI) WHICH IS SUPPORTED BY THE PADDLEWHEEL

<p>A dynamic model was used to obtain optimal value or amount in the application of paddlewheel. Stella 9.1.4 software programing was employed to find relationships among parameters. The aims of this reasearch was to determine the percentage of oxygen uptake by vannamei shrimp (Litopenaeus vannamei) which is supported by 1 paddlewheel. The result showed that the optimal number of paddlewheel was 1 paddlewheel with Standart Aeration Efficiency was 1,31 kgO2/kWh. The percentage of oxygen absorption on vannamei shrimp until final cultivation was 24% during the cultivation, the percentage of oxygen absorption on vannamei shrimp had increased. In this research, total oxygen demand was 567 ppm, shrimp production was 1054,88 kg, the amount of feed was 2278,1 kg with a pond area was 600 m2, stocking density was 133 PL/m2 during a cultivation period of 98 days.<br />Keyword : Paddlewheel, Oxygen, Vannamei shrimp (Litopenaeus vannamei)</p>

Study on the utilization of supersaturation degree in Al deoxidation to improve cleanliness and control of Al2O3 inclusions in ultra-low carbon steel

Effects of supersaturation degree (S) in Al deoxidation on cleanliness and alumina inclusions in steel were studied. If enough Al was added to steel, higher initial dissolve oxygen before Al deoxidation resulted in higher steel cleanliness. In the experiments, with the rise of [mass% O] from 102 ppm to 340 ppm and 931 ppm, logS in steel melts were increased from 4.8, to 7.0 and 8.8, respectively. As a result, total oxygen (T.O) was decreased to 25 ppm, 22 ppm and 21 ppm, respectively. Based on the results, important influence of supersaturation degree on the formation of Al2O3 was revealed. At lower S, Al2O3 would be singular and smaller particles ≤ 5 µm that was difficult to be removed. However, Al2O3 would exist as large clusters in steel at higher S, which can be efficiently removed. By utilizing the findings in laboratory, RH refining of ultra-low-carbon steel was optimized. Steel cleanness and control of inclusions were improved. As a result, surface defects in cold rolling sheets caused by Al2O3 inclusions were effectively minimized.

Influence of Parameters on the Pre-Reduction Process of Vanadium-Titanium Magnetite Carbon-Containing Composite Pellets in Rotary Kiln

A novel smelting reduction process called pre-reduction in rotary kiln and total oxygen melting pool is a promising route to reduce environmental pollution from the ironmaking industry. In this paper, the process parameters and appropriate efficiency of reduction in the pre-reduction process of the rotary kiln were investigated via the detection of the metallization rate, phase composition, and internal morphology of the product combining with the analysis of the off-gas. The results indicated that the parameters of reduction temperature, reduction holding time, and coal ratio have a remarkable influence on the metallization rate. The reduction temperature has the most significant effect, followed by the reduction time and the coal ratio. Furthermore, under the condition of reduction temperature 1000 °C, holding time 30 min, coal ratio = 1, a product with a metallization rate of more than 70% can be obtained, which meets the requirements of the rotary kiln process, and its CO2/CO value of the pre-reduction endpoint is appropriate. Continue to increase the temperature, holding time, and coal ratio can raise the metallization rate of the pellets, but only a little improvement and may cause reoxidation of the product.