Showing papers on "Sodium dichromate published in 2003"

Influence of Dichromate Ions on Corrosion Processes on Pure Magnesium

Abstract: The corrosion behavior of Mg is of interest because of its growing use as an alloy in the transportation industry and also because it is a major component of some intermetallic phases in Al alloys, such as the deleterious S (Al 2 CoMg)-phase found in AA2024-T3. Pure Mg corrodes rapidly in a chloride-containing solution and even dissolves in water if the surface hydroxide is damaged by scratching the surface, for example. Uniform dissolution is drastically reduced in NaCl solutions (from 0.01 to 0.5 M) with the addition of very dilute concentrations of dichromate (10 -4 M). However, it is replaced by a strong localized attack in the form of fast filiform-like attack. On a large-grained sample with a defined defect structure, the attack can be seen to propagate at twin boundaries. Orientation imaging microscopy analysis found that corrosion was limited to planes near {0001} orientations with propagation being in prismatic directions. Auger electron spectroscopy analysis shows that interaction of chromate with the Mg hydroxide results in incorporation of reduced chromium ions in the hydroxide surface layer. Formation of a more resistant surface film could explain the very local nature of the corrosion in this case. The interaction between dichromate ions and Mg hydroxide can also explain the higher corrosion resistance of S-phase particles in chloride solutions containing dilute dichromate, although differences in the surface film formed compared to pure Mg are observed. Sputter-etching of the surface in order to assess the depth of the attack revealed that very hard or isolating corrosion products difficult to sputter are produced along the filiform path and that chromium compounds are not integrated in the corrosion products. Focused ion beam sectioning followed by scanning electron microscopy investigation of the sectioned area, demonstrates the presence of a continuous protective surface film. Adhesion between the Mg hydroxide and the metal is lost at the location of the corrosion filament, suggesting that the mechanism of propagation is similar to filiform corrosion under a coating. The depth of attack is a couple of micrometers with large cracks present within the corroded area that could induce severe surface damage.

Aqueous oxidative chemical polymerization of N-methylaniline in acid medium and characterization of the obtained polymer

Abstract: The oxidative chemical polymerization of N-methylaniline was studied in hydrochloric acid solution using sodium dichromate as oxidant at 5°C under nitrogen atmosphere The effect of hydrochloric acid, sodium dichromate and monomer concentration on the polymerization reaction was investigated The order of reaction with respect to hydrochloric acid, sodium dichromate and monomer concentration was 0816, 0735 and −083 respectively Also, the effect of temperature on the polymerization rate was studied and the apparent activation energy of this polymerization reaction was found to be 1999×104 J/mol The characterization of the obtained polymer sample at the optimum conditions was carried out by IR, UV-visible, 1H-NMR, X-ray diffraction, electron microscope and thermogravimetric analysis The ac conductivity of the obtained polymer samples was measured and the highest values were found for the samples prepared at hydrochloric acid, sodium dichromate and monomer concentrations of 0200, 00094 and 01869 mo

Silica Sulfuric Acid/Sodium Dichromate Dihydrate as an Efficient Heterogeneous Method for the Oxidation of Alcohols Under Mild Conditions

Abstract: A combination of silica sulfuric acid and sodium dichromate dihydrate in the presence of wet SiO 2 were used as an effective oxidizing agent for the oxidation of alcohols to their corresponding aldehyde or ketone derivatives in dichloromethane or toluene with excellent yields.

Process for the utilization of vanadium bound in chromium ore as vanadium(V) oxide by electrolysis

Abstract: Process for recovering the vanadium present in the chromium ore chromite, as vanadium pentoxide, as a by-product from the vanadium-containing sodium chromate solution produced in the process of preparing sodium chromate and sodium dichromate from said ore, by precipitation of calcium vanadate from the sodium chromate solution, treatment of the precipitate with water and sodium carbonate, sodium bicarbonate, carbon dioxide or sodium carbonate and carbon dioxide, to precipitate calcium carbonate and electrolysis of the solution remaining after separation of the calcium carbonate precipitate, to produce vanadium pentoxide.

Process for the utilization of vanadium from chromium ore as vanadium (V) oxide

Abstract: Process wherein the vanadium present in the chromium ore chromite is recovered as vanadium pentoxide during the course of the fusion of the chromium ore with alkali and its work-up to produce sodium chromate solution and sodium dichromate.

Chloric Acid and Chlorates

Abstract: Sodium chlorate is the primary raw material for the manufacture of chlorine dioxide, a bleaching agent in the pulp and paper industry. Chlorine dioxide substitutes for chlorine in pulp bleaching, most ore of the sodium chlorate produced is used in the bleaching process. Sodium chlorate is prepared electrolytically. The modern technology described minimizes sodium chloride and sodium dichromate impurities. Chlorates are powerful oxidizers, and they are also used in perchloric salt and uranium production. They are strong irritants. Chloric acid technologies have been developed which allow the generation of chlorine dioxide directly from the acid, without the formation of sodium salts in the generator. Keywords: Chloric acid; sodium chlorate Potassium Chlorate Chlorates Bleaching agent; pulp; paper; Roch palt; chlorine dioxide

New 6-Arylsulfonyl-1,2-benzoisothiazol-3(2H)-one 1,1-Dioxides Derived from Diphenyl Sulfone Monosulfonyl Chlorides

Abstract: Various methods were studied for the oxidation of 2-methyl-5-(phenylsulfonyl)benzenesulfamide and its derivatives. The oxidation by sodium dichromate in sulfuric acid was found most efficient. The effects of temperature, concentration, reagent ratio, and time of the oxidation reaction on the yield of the desired product were investigated. Conditions were proposed for obtaining the desired product in yields up to 95%. A synthesis was developed for a series of new saccharin derivatives.

Process for the utilization of vanadium in chromium ore as ammonium metavanadate

Abstract: A process for recovering the vanadium present in the chromium ore chromite. as ammonium metavanadate, as a by-product of the fusion of the chromium ore with alkali and its work-up to produce sodium chromate solution and sodium dichromate.

Sodium Dichromate Dihydrate

Abstract: Precautionary Statement(s): Wear eye protection/face protection. Wear protective gloves. Do not breathe dust/fume/gas/mist/vapours/spray. Avoid release to the environment. Wash hands and skin thoroughly after handling. Use only outdoors or in a well-ventilated area. Wear respiratory protection (powered air-purifying respirator with an appropriate cartridge). IF ON SKIN: Wash with plenty of water. IF INHALED: Remove person to fresh air and keep comfortable for breathing. IF SWALLOWED: Immediately call a POISON CENTRE/doctor/ IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. Classification

New 6‐Arylsulfonyl‐1,2‐benzoisothiazol‐3(2H)‐one 1,1‐Dioxides Derived from Diphenyl Sulfone Monosulfonyl Chlorides.

Abstract: Various methods were studied for the oxidation of 2-methyl-5-(phenylsulfonyl)benzenesulfamide and its derivatives. The oxidation by sodium dichromate in sulfuric acid was found most efficient. The effects of temperature, concentration, reagent ratio, and time of the oxidation reaction on the yield of the desired product were investigated. Conditions were proposed for obtaining the desired product in yields up to 95%. A synthesis was developed for a series of new saccharin derivatives.

Synthesis and thermal swelling of residual graphite hydrosulfates obtained using the Na2Cr2O7-H2SO4 system

Abstract: The influence exerted by the conditions of synthesis of residual graphite hydrosulfate in a system constituted by concentrated sulfuric acid and saturated aqueous solution of sodium dichromate on the properties of the final product was studied in a wide range of reagent consumptions. The swelling coefficient and the loss of the product were analyzed as functions of the intercalate content in the product.