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41.
When fresh shell-on tails of penaeid shrimp were treated with sodium bisulfite according to current good manufacturing practices, residual sulfite (SO2) on the edible portion varied from a high of 92.7 to a low of 60.9 ppm with an average of 80.2 ppm. During freezing and a short period of frozen storage, there was an average loss of 17% in residual sulfite. For shrimp held on ice storage, on the other hand, there was a rapid decrease in residual sulfite to below 10 ppm after six days of storage. The residual levels found on treated shrimp were consistent with action levels set by USFDA for shrimp treated according to good manufacturing practices. 相似文献
42.
Membrane-electrode assemblies (MEAs) for direct methanol fuel cells (DMFC) have been prepared by depositing platinum on the
surface of solid polymer electrolytes (SPE). Chemical and electrochemical depositions were used to achieve good adhesion between
platinum particles and the SPE and for reducing the contact resistance. Platinum particle structure and composition were investigated
by means of SEM and EDX. Cyclic voltammetry (CV) and methanol oxidation tests were used to determine the electrochemical characteristics
of the Pt-SPE electrodes which can be applied in DMFC. Overall the electrodes produced by chemical and electrochemical deposition
of Pt onto the membranes are not as active as those produced by hot pressing carbon supported Pt catalyst layers onto the
membrane. 相似文献
43.
The phase equilibrium relations in the systems Y2 O3 -Al2 O3 and Gd2 O3 -Fe2 O3 were examined. Each system has two stable binary compounds. A 3:s molar ratio garnet-type compound exists in both systems. The 1:1 distorted perovskite structure is stable in the system Gd2 O3 -Fe2 O3 but only metastable in the system Y2 O3 -AI2 O3 . This interesting example of metastable formation and persistence of a compound with ions of high Z/r values explains the discrepancies in the literature on the structure of the composition YA1O3 . A new 2:1 molar ratio cubic phase has been found in the system Y2 O3 -A12 O3 . Since silicon can be completely substituted for aluminum in this compound, the aluminum ions are presumably in fourfold coordination. 相似文献
44.
Glasses containing up to several percent of Ar, N2 , and CO2 were prepared at 2000 to 150,000 psi and up to 950°C and retained under ambient conditions. The solubilities are presented as a function of pressure, temperature, and composition of glass. Solubilities of O, He, and H2 O were also investigated in various glass compositions, especially K2 O–4SiO2 and B2 O3 . The evolution of the gases at atmospheric pressure was followed by electron microscopy and density measurements. 相似文献
45.
Crystallization kinetics of calcium tungstate from unstirred supersaturated solutions in sodium tungstate melts was studied by continuous cooling from initial crystallization temperature T O =1000° to 800°C to room temperature at cooling rates RT =0.67° to 3.3°C min−1 . Crystals were examined by optical microscopy and analyzed by various methods. The main crystal growth was diffusion-rate-controlled. The final crystal growth was rate-controlled by the development rate of excess solute concentration. Diffusion rate constant ( kD ) values were estimated. These values increased with cooling rate and initial crystallization temperatures but they are very much smaller than the rate constants for diffusion-controlled growth of calcium tungstate from lithium chloride melts. 相似文献
46.
OLAF MULLER RUSTUM ROY WILLIAM B. WHITE 《Journal of the American Ceramic Society》1968,51(12):693-699
Phase equilibria were determined for the systems NiO-Cr2 O3 −O2 , MgO-Cr2 O3 ,-O2 , and CdO-Cr2 O3 −O2 from 450° to above 850° C and at oxygen pressures of from 2 to 3500 atm. Only two intermediate phases were found in the nickel system: NiCrO., (CrVO4 structure) and the spinel NiCr2 O4 . The magnesium and cadmium systems are similar in that they have three analogous phases: the low-temperature α-MgCrO4 and α-CdCrO4 (both with the CrVO4 structure), the high-temperature β-MgCrO4 and β-CdCrO4 (both with the α-MnMoO4 structure), and the spinels MgCr2 O4 and CdCr2 O4 . The cadmium system contains an additional phase, Cd2 CrO5 , which is primitive monoclinic. 相似文献
47.
LiAl5 O8 exists in many forms. The equilibrium high-temperature form (I) has a spinel structure. It undergoes a first-order reconstructive transformation at 1295°× 5°C to an equilibrium low-temperature form (II) with primitive cubic symmetry, the unit edge changing from a 0 = 7.921 A (I) to a 0 = 7.907 A (II). In addition, a whole series of phases (II-metastable) exist with the same symmetry as II but with a disorder different from I → II disorder. 相似文献
48.
On the basis of 190 runs made up to 1860°C in sealed noble-metal containers the following revisions have been made in the equilibrium diagram for the system A12 O3 –SiO2 . Mullite melts congruently at 1850°C. The extent of equilibrium solid solution in mullite at solidus temperature is from approximately 60 mole % Al2 O3 (3/2 ratio) to 63 mole % A12 O3 . Metastable solid solutions can be prepared up to about 67 mole % Al2 O3 . There is no evidence for stable solubility of excess SiO2 beyond the 3/2 composition at pressures below 3 kbars. Refractive indices are presented for glasses containing up to 60 mole % Al2 O3 and from them the composition of the eutectic is confirmed at 5 mole % SiO2 . The variation in lattice constants of the mullite solid solution is not an unequivocal guide to composition since mullites at one composition produced at different temperatures show differences in spacing, no doubt reflecting Al-Si ordering phenomena. The possibility of quartz and corundum being the stable assemblage at some low temperatures and pressures cannot be ruled out. A new anhydrous phase in the system is described, which was previously thought to be synthetic andalusite; it is probably a new polymorph of the Al2 SiO5 composition with ortho-rhombic unit-cell dimensions a =7.55 A, b =8.27 A, and c = 5.66 A. 相似文献
49.
The liquidus-solidus relations along the join Ca2 SiO4 -Ca(OH), in the system CaO-SiO2 -H2 O have been determined at 1000 atm up to 1110°C. This join is binary and contains the calcium silicate hydrate, calciochondrodite, Ca5-(SiO4 (OH)2 . Calciochondrodite melts incongruently to Ca2 SiO2 + liquid (composition 23 wt% Ca2 Si04 ) at 955°C. The eutectic between calcium hydroxide and calciochondrodite lies at 13% Ca2 Si04 and 822°C. Preliminary experiments, also at 1000 atm, in the ternary system CaO-Ca2 Si04 -Ca(OH), indicate that the eutectic at which the fields of primary Ca(OH)2 , CaO, and Ca2 (Si04 )2 (OH)2 meet is close to the CaO-Ca. (OH), side of the triangle at approximately 805° C. The ternary reaction point Ca2 SiOl + liquid ⇌Ca5 (SiO4 )2 (OH)2 + CaO + liquid is believed to lie in the low-CaO (<5%) high-Ca(OH)2 (>70%) part of the system. 相似文献
50.
On heat treatment in air the solubility of MgO or TiO2 , in Al2 3 is too small to detect by lattice parameter shifts. The solubility of MgTiO3 in Al2 O3 in air increased to the measured values, expressed as atomic fractions Mg:A1or Ti:A1of0.82 × lo-2 , 1.43 × 10-2 , and 1.75 × 10-2 at 1250°, 1650°, and 1850°C, respectively. In 1 atm hydrogen the TiO2 solubility expressed as the atomic fraction Ti:A1 is 0.55 × lo-2 , 0.75 × 10W2 , 1.15 × 10-2 , and 1.50 × 10p2 at 1400°, 1500°, 1600°, and 1700°C, respectively. The increased solubility in H2 was attributed to reduction of the titanium ion. The solubility of MgO in A12 O3 in vacuum (0.3μ) expressed as the atomic fraction Mg:A1 was measured as 1.10 × loW4 , 3.00 × 10"4 , 6.80 × 10–4 , and 1.40 × 10-3 at 1530°, 1630°, 1730°, and 183O°C, respectively. These contents did not cause an observable change in lattice parameter, but a slight change was observed when MgO was dissolved in A12 O3 in a hydrogen atmosphere. 相似文献