Influence of Small Amounts of Impurities on Copper Oxidation at 600–1050°C

In order to study the influence of small amount of impurities on the copper oxidation kinetics, the oxidation was examined at 600–1050°C in 0.1 MPa oxygen atmosphere using 99.5% (2N) and 99.9999% (6N) pure copper specimens. The influence of impurities has been discussed considering the roles of the nonprotective CuO layer, the impurity layer at the Cu₂O–Cu interface, and the diffusion of copper in the Cu₂O layer. The nonprotective CuO layer for 2N copper can greatly enhance copper oxidation. However, the impurities concentrated at the region near the Cu₂O–Cu interface for 2N copper can slow oxidation. Contrary to the presence of metallic impurities, such as Ni, Sb, and Pb, the nonmetallic elements As and Se dissolved in Cu₂O have a deleterious influence on the outward diffusion of copper. Grain-boundary diffusion in Cu₂O can somewhat contribute to 2N copper oxidation at 850–1050°C, but its effect in enhancing oxidation at 600–800°C is weaker than the effect of the impurity layer at the Cu₂O–Cu interface in impeding oxidation.     

Oxidation refining of iron using plasma-arc melting

Oxidation refining of Fe using plasma arc melting, by the addition of iron oxide as an oxidizing agent, has been carried out. In this refining process, an impurity element which has higher affinity for oxygen than iron was expected to be eliminated. As the result, decreases in Si, Mn, Al, Ca, Ga, and Zr were observed and 99.996 mass% of iron could be obtained from 99.93 mass% of electrolytic iron by plasma arc melting under oxidizing conditions followed by argon–hydrogen plasma arc melting. Specifically, the removal of Si was found to proceed by the distribution between in the liquid Fe phase and in the oxide phase. In addition, the relation of Si and oxygen concentration in liquid iron was consistent with the data in the literature.     

Purification of lanthanum and cerium by plasma arc zone melting

Purification of La and Ce by a horizontal plasma arc-zone melting (PZM) with Ar plasma arc heating under atmospheric pressure was examined. A stable molten zone of La and Ce on the water-cooled copper hearth could be maintained and, after zone passes, the segregation of impurities along the bars was recognized. Metallic impurities such as Fe, Cu, Al, and Si moved in the zone direction and decreased efficiently at the head side of the zone-melted bars. Especially, remarkable segregations of those impurities were observed on La. In addition, volatile impurities such as Ca, Mg, Zn, and Mn were reduced to further low levels by vaporization. For non-metallic impurities, O, N, C, and S in Ce, and O and N in La moved in the opposite direction of zoning, while C and S in La moved in the zone direction. Furthermore, nonmetallic impurities were reduced unexpectedly along the whole bar during PZM. Consequently, the purity around the head side of La and Ce bars could be sufficiently increased with PZM.     

Impurity behavior in Cu refined by Ar plasma-arc zone melting

Purification of a 4N grade Cu rod by argon plasma-arc zone melting (APZM) was carried out. Detailed impurity analysis of the Cu rod was performed using glow discharge mass spectrometry (GDMS). Three impurity behavior groups based on segregation and evaporation during APZM were discussed using the GDMS analysis. Although the impurities with segregation coefficient k_ℴ < 1 were theoretically expected to be segregated towards the end of the Cu rod, it was found that the segregation effect by APZM can occur when the equilibrium distribution coefficient (k_ℴ) is less than 0.4 due to the strong affinity of Cu for some metallic and non-metallic impurities. On the other hand, the impurities for which k_ℴ > 1 had no significant reduction in their impurity concentrations. Some impurities, like Mg, S, Cd and Zn, were reduced much faster than the others in Cu. This was ascribed to the removal by zone refining coupled with the evaporation of impurities for P_imp/P_Cu > 10².     

Efficacy of acidified sodium chlorite treatments in reducing Escherichia coli O157:H7 on Chinese cabbage

Efficacy of acidified sodium chlorite for reducing the population of Escherichia coli O157:H7 pathogens on Chinese cabbage leaves was evaluated. Washing leaves with distilled water could reduce the population of E. coli O157:H7 by approximately 1.0 log CFU/g, whereas treating with acidified chlorite solution could reduce the population by 3.0 log CFU/g without changing the leaf color. A similar level of reduction was achieved by washing with sodium chlorite solution containing various organic acids. However, acidified sodium chlorite in combination with a mild heat treatment reduced the population by approximately 4.0 log CFU/g without affecting the color, but it softened the leaves. Moreover, the efficacy of the washing treatment was similar at low (4 degrees C) and room (25 degrees C) temperatures, indicating that acidified sodium chloride solution could be useful as a sanitizer for surface washing of fresh produce.     

Effectiveness of irradiation treatments in inactivating Listeria monocytogenes on fresh vegetables at refrigeration temperature

Ionizing radiation can be effective in controlling the growth of food spoilage and foodborne pathogenic bacteria. This study reports on an investigation of the effectiveness of irradiation treatment to eliminate Listeria monocytogenes on laboratory-inoculated broccoli, cabbage, tomatoes, and mung bean sprouts. Irradiation of broccoli and mung bean sprouts at 1.0 kGy resulted in reductions of approximately 4.88 and 4.57 log CFU/g, respectively, of a five-strain cocktail of L. monocytogenes. Reductions of approximately 5.25 and 4.14 log CFU/g were found with cabbage and tomato, respectively, at a similar dose. The appearance, color, texture, taste, and overall acceptability did not undergo significant changes after 7 days of postirradiation storage at 4 degrees C, in comparison with control samples. Therefore, low-dose ionizing radiation treatment could be an effective method for eliminating L. monocytogenes on fresh and fresh-cut produce.     

Geiger mode operation of an In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode

Low-temperature photon counting with gated mode quenching is demonstrated with separate absorption, charge, and multiplication avalanche photodiodes that have an In/sub 0.52/Al/sub 0.48/As multiplication layer. A minimum of ten dark counts per second and single-photon detection efficiency of 16% were achieved at 130 K.     

Time series analysis of glottal airflow in normal and pathological phonation

Time series analysis of glottal airflow was carried out on 26 normal controls and 40 patients with voice disorders, using a modification of Isshiki's original technique which uses a hot-wire flowmeter, taking cycle-by-cycle fluctuations into consideration. The mean flow rate and mean AC/DC were shown to have significant differences among normal and patient groups. The standard deviations of AC/DC and AC/DC perturbation were calculated from the AC/DC value of 50 cycles and shown not to vary significantly among the normal and patient groups. The relationship between AC/DC and perceptual impression of voice was also studied among 20 selected patients with breathy voices. Using Spearman's rank correlation coefficient, this relationship was found to have statistical significance (P < .05).     

High-power 780 nm window diffusion stripe laser diodes fabricatedby an open-tube two-step diffusion technique

High-power and low-threshold-current GaAlAs lasers with a simple window structure fabricated by controllable open-tube two-step diffusion and single-step metalorganic chemical vapor deposition are discussed. The window structure and the waveguide with a narrow width around 2 μm are formed by diffusion of zinc, which just passes through an n-type active layer. CW output power up to 134 mW without catastrophic damage and a threshold current of 17 mA have been achieved. A maximum output power density of 16 MW/cm² is estimated. A stable fundamental transverse mode of up to 100 mV in the wavelength range of 780 nm is obtained. Excellent uniformity of device characteristics is confirmed