With chromium concentration increase

It is clear from the data in Table 4.6 that the corrosion rates increase with increase in chromium in sulfuric acid solution. The presence of 10% Ni in the Fe-Cr alloy results in decreasing corrosion rate with chromium concentration. The corrosion rates of Fe-Cr alloys in ferric sulfate decrease with increasing concentration of chromium in the alloy. These observations are supported by the data on corrosion potentials of stainless steels in boiling acids and chlorides measured against a saturated calomel electrode. 

Alloying elements such as nickel, chromium, molybdenum, and copper, which may be introduced with scrap, can increase the hardenability, although only slightly, because the concentrations are ordinarily low. However, the heat-treating characteristics may change, and for appHcations in which ductihty is important, as in low carbon steels for deep drawing, the increased hardness and lower ductiHty imparted by these elements may be harmful. 

By monitoring the intensity of the carbonyl absorption it was observed that oxidation of methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexopyrano-side with chromium trioxide-pyridine at room temperature gave initially the hexopyranosid-3-ulose (2) in low concentration, but attempts to increase this yield resulted in elimination of methanol to give compound 3. However, when methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexo-pyranoside is oxidized by ruthenium tetroxide in either carbon tetrachloride or methylene dichloride it affords compound 2 without concomitant elimination. When compound 2 was heated for 30 minutes in pyridine which was 0.1 M in either perchloric acid or hydrochloric acid it afforded compound 3, but in pyridine alone it was recoverable unchanged (2). Another example of this type of elimination, leading to the introduction of unsaturation into a glycopyranoid ring, was observed... 

Two ions of the transition metal take part in this reaction. However, in the case of supported one-component catalysts the formation of the active bond seems to occur on the interaction of the monomer with isolated ions of the transition metal. That may be illustrated by the data showing that the activity of chromium oxide catalysts decreases linearly with decreasing chromium content (or even increases per chromium ion) to the rather low (0.01%) chromium concentrations on the catalyst surface (62, 69). In... 

The kinetics of chromium (III) oxide deposition from solution during the leaching of skeletal copper has been studied, and a linear rate was found that is not affected by chromate concentration but decreases with increasing hydroxide concentration [55], The total amount deposited was greater as the chromate concentration increased. 

Eischens and Selwood 176) have made a study of the activity of reduced chromia-on-alumina catalysts for the dehydrocyclization of n-heptane. The activity per unit weight of chromium was found to increase sharply at concentrations below about 5 wt. % Cr activities were measured down to 1.9 wt. % Cr concentration at which point the highest activity was observed. Selwood and Eischens concluded that this effect is due to the fact that the chromia is most dispersed at these low concentrations, in agreement with the present EPR data. However, if a two-site mechanism 177) is necessary for dehydrocyclization, the activity may drop at even lower chromium concentrations due to isolation of individual chiomium spins. 

The active site concentration on the organochromium catalysts may be higher than that of the oxide catalysts. The activity usually assumes a more linear increase with chromium loading than on the oxide catalysts, at least up to 2% Cr. Yermakov and Zakharov, studying allyl-Cr(III)/silica catalysts, stopped the polymerization with radioactive methanol, and found that the kill mechanism is different from that on the oxide catalysts (59). The proton of the methanol, and not the alkoxide, became attached to the polymer. This suggests a polarity opposite to that of the oxide catalysts, with the site being more positive than the chain. 

The submitters employed an aqueous 1.64Jtf solution of chromium(II) perchlorate which was prepared by stirring a mixture of 5.7 g. of pure chromium metal pellets (United Mineral and Chemical Corporation, 129 Hudson St., New York, 10013) with 60 ml. of aqueous 20% perchloric acid under a nitrogen atmosphere at 30° for 12 hours.2,3 The rate of dissolution of the chromium metal is increased if the metal is washed successively with concentrated hydrochloric acid and with water just before it is added to the perchloric acid. The checkers employed aqueous 0.519J/ chromium(II) perchlorate solution which was prepared in a comparable manner with chromium metal obtained from the Mining and Metals Division, Union Carbide Corporation. The deep blue solution of chro-mium(ll) perchlorate is transferred to a storage vessel with a... 

Autopsy studies in the United States indicate that chromium concentrations in the body are highest in kidney, liver, lung, aorta, heart, pancreas, and spleen at birth and tend to decrease with age. The levels in liver and kidney declined after the second decade of life. The aorta, heart, and spleen levels declined rapidly between the first 45 days of life and 10 years, with low levels persisting throughout life. The level in the lung declined early, but increased again from mid life to old age (Schroeder et al. 1962). 

Urine samples from six workers working in chromium plating factories were tested for the induction of unscheduled DNA synthesis (UDS) in pleural mesothelial cells (Pilliere et al. 1992). The mean chromium concentration in the urine samples was 11.7 8.8 pg/L. The urine from five of the workers showed a significant elevated in UDS over control subjects who were nonsmokers, with a trend toward increasing amounts of urine being tested. However, there was no correlation between UDS and chromium concentrations in urine. 

It is interesting to note the effect of chromium content on reaction rate at high pressures (,—500 p.s.i.g.). Experiments (5) were carried out with normal air-activated catalysts (Figure 4). Catalysts were used with chromium contents ranging from 0.7 to 0.0005 wt. % of the total catalyst. Results of one-hour ethylene polymerization tests at 132°C. and 450 p.s.i.g. with these catalysts, activated at 500°C., are given. As the concentration of chromium was decreased, catalyst charge was increased to compensate for poisoning of catalyst sites by trace impurities and to keep total rate of production about constant. 

Catalysts which have been heated for one hour at 250°C. with carbon monoxide at 100 mm., cooled to 35°C., and pumped to remove physically adsorbed gas have far greater activities than untreated catalysts at all chromium concentrations (7). At low pressures, CO treatment increases the activity by at least an order of magnitude. As described in a previous publication, on the basis of infrared evidence, it is believed that the CO-treated catalyst is characterized by the presence of a carbon monoxide-chromium complex. 

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