Potassium Chromate Research Articles

De resíduo a insumo: a construção do caminho para uma química mais limpa através de um projeto de ensino

FROM RESIDUE TO INPUT: BUILDING A ROAD TO CLEAN CHEMISTRY THROUGH AN EDUCATIONAL PROJECT. The discussion among teachers, students, and technicians about the destination of residues from chemistry laboratories led to a research project whose results were incorporated into a course in its daily practices. The treatment of the residues from argentimetric practices allowed us to establish cognitive relations of technological basis and of those related to the rising of the level of awareness about environmental aspects and social responsibility of chemistry professionals. The techniques and the results, from the economic point of view, namely that of value aggregation (metallic silver) and the conversion of the residue into input (potassium chromate solution) are shown.

Preparation and Electrochemical Properties of Trivalent Chromium Coating on 6063 Aluminium Alloy

Chromium (Cr3+) conversion coating was prepared on 6063 aluminium alloy using chromic potassium sulfate and phosphoric acid. Tafel polarization curves and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of the coating formed under different conditions. The optimum conditions were obtained as following: temperature was 30-40 ℃, deposition time 9 min, the pH was adjusted to 2.0-3.0, the KCr(SO4)2 and H3PO4 concentrations were controlled within 15-25 g·L-1 and 10-20 g·L-1, respectively. The polarization result showed that the coating had more positive corrosion potential (Ecorr) and pitting corrosion potential (Epit), and lower corrosion current density (icorr), indicating that the coating formed under the optimum conditions had better corrosion resistance. To explain the electrochemical properties of the coating, a simple equivalent circuit was designed. Electrochemical parameters of EIS, such as the resistance (Rcoat) and capacitance (Ccoat), the charge transfer resistance (Rct) and double layer capacitance (Cdl), were obtained by fitting the EIS plots. The results of EIS were in good agreement with those of Tafel polarization curves.

Oxidation of thiols to disulfides using H2O2 catalyzed by recyclable chromic potassium sulphate at room temperature

Chromic potassium sulphate is found to be an efficient and recyclable catalyst for the selective oxidation of thiols to disulfides. The reaction was carried out in 60% methanol (v/v) using 30% H2O2 at room temperature. Cr(III) forms a complex with thiol which was then oxidized by H2O2 to produce disulfide in excellent yield after a simple workup procedure.

A study of significant variables and their effects on the analysis of hexavalent chromium

The recent reduction in the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for hexavalent chromium Cr(VI) will most certainly cause employers to perform more exposure determinations. The standard applies to Cr(VI) in both the soluble and insoluble form. The National Institute for Occupational Safety and Health (NIOSH) Method 7600, an analytical technique utilizing visible spectrophotometry, was examined. The new OSHA PEL of 5 micrograms per cubic meter (μg/m 3 ) mandated that the lowest possible method detection limit (MDL) be obtained. Also, the solubilities of the test samples were in most cases unknown. Accordingly, this study focused on the following: (1) removal of filter debris or other turbidity, (2) filter type, storage stability and (3) the alkaline extraction of the samples. Preliminary analysis of blank polyvinyl chloride (PVC) filters resulted in noticeable debris and turbidity. To test turbidity a blank PVC filter was placed in a centrifuge tube and extracted with sulfuric acid. Eight replicates yielded a MDL of 4 micrograms per liter (μg/L). The aliquots were then filtered using a Buchner funnel and yielded 2 μg/L MDL. Finally, the filtrates were centrifuged for 2 minutes further reducing the MDL to 0.7 μg/L. The use of the centrifuge to eliminate turbidity was significant enough to necessitate further investigation. To determine the effect of an alkaline extraction on soluble Cr(VI), a standard addition of 0.5 μg of potassium chromate was performed on a filter, allowed to dry and then extracted with the alkaline solution. Three replicates had a 109.4% recovery. Centrifuging the filters was useful in eliminating the CO 2 interference for the alkaline extraction. Also, the use of an alkaline extraction did not negatively impact the soluble Cr(VI). The positive result of the preliminary extractions resulted in further investigation of an alkaline extraction to incorporate the inclusion of both soluble and insoluble Cr(VI).

Potassium-Assisted Chromium Transport in Solid Oxide Fuel Cells

Chromium transport from stainless steel current collectors to the cathode can be a route for rapid performance degradation in solid oxide fuel cells. Typical volatile chromium species, such as , are manageable; however, volatile species with higher vapor pressures may play a significant role in chromium transport and deposition. One such species, , is readily formed by the chemical reaction between or and and electrochemically reduced along triple-phase boundaries. The vapor pressure and expected chromium deposition rate of potassium chromate and chromium oxyhydroxide phases are compared to the long-term electrical performance of anode-supported SOFCs. Experimental evidence supports the findings that potassium and chromium, in the presence of an applied electric field, greatly enhances the degradation of cell performance ( in ).

Polarization Studies on Inhibitory Effect of Chromates and Dichromates on Corrosion of Tin Coated Steel in 0.5M Monochloroacetic Acid

Chromates and Dichromates have been tested for its inhibitory effects towards tin coated steel in 0.5M monochloroacetic acid. The corrosion behaviour of potassium chromate, sodium chromate, potassium dichromate, sodium dichromate and ammonium dichromate was studied by polarization curves, Tafel parameters like Tafel slopes, extrapolation of cathodic Tafel line and intersection of cathodic and anodic line at open circuit potential in presence of inhibitors have been tabulated along with other electrochemical parameters and corrosion current have been calculated from Tafel lines. The efficiencies are calculated and compared reasonably well with those obtained from loss in weight data. All the inhibitors induce a significant increase of potential positive and direction accounts for cathodic polarization. The Icorr has also been calculated and that accounts well for cathodic reactions in presence of chromates and dichromates as inhibitors.

Investigation of Efficient Conditions for Oxidative Roasting of Chromite Ore to Produce Potassium Chromate with KOH Additive

A method of producing potassium chromate directly from chromite ore and KOH was investigated. The chromium recovery was >90% after roasting at 800 degrees C for 3 hours. The KOH-to-ore weight ratio was 1.2:1 and the ore-to-recycling residue weight ratio was 1:1. Production from the roasting process was easy to leach and about 100% of chromate could be recovered through a treatment at 30 degrees C for 30 similar to 40min with a water/solid ratio of 5:1. The obtained chromate solution was purified by addition of conventional compounds.

Synthesis of an Amide‐Linked Diporphyrin Xanthene as a Neutral Carrier for a Lead(II)‐Sensitive Electrode

The synthesis of a new compound, amide‐linked diporphyrin xanthene(ADPX), and its application for preparation of lead(II) ion selective electrodes are described. The electrode was prepared with a PVC membrane combining ADPX as a neutral carrier, 2‐nitrophenyl octyl ether (o‐NPOE) as a plasticizer and sodium tetraphenylborate (NaTPB) as an additive in the percentage ratio of 3:3:65:32 (ADPX: NaTPB: o‐NPOE: PVC, w:w). The electrode exhibited linear response with a near Nernstian slope of 28.2 mV per decade within the concentration range of 2.6×10−6 to 1.0×10−1 M lead ions, with a working pH range from 4.5 to 7.5, and a fast response time of less than 30 s. Selectivity coefficients for Pb(II) relative to a number of interfering ions were investigated. The electrode is highly selective for Pb2+ ions over a large number of cations. Several electroactive materials and solvent mediators have been compared and the experimental conditions were optimized. The sensor was applied as indicator electrode in titration of Pb(II) with potassium chromate solution with satisfied results.

Dietary chromium and nickel enhance UV-carcinogenesis in skin of hairless mice

The skin cancer enhancing effect of chromium (in male mice) and nickel in UVR-irradiated female Skh1 mice was investigated. The dietary vitamin E and selenomethionine were tested for prevention of chromium-enhanced skin carcinogenesis. The mice were exposed to UVR (1.0 kJ/m 2 3× weekly) for 26 weeks either alone, or combined with 2.5 or 5.0 ppm potassium chromate, or with 20, 100 or 500 ppm nickel chloride in drinking water. Vitamin E or selenomethionine was added to the lab chow for 29 weeks beginning 3 weeks before the start of UVR exposure. Both chromium and nickel significantly increased the UVR-induced skin cancer yield in mice. In male Skh1 mice, UVR alone induced 1.9 ± 0.4 cancers/mouse, and 2.5 or 5.0 ppm potassium chromate added to drinking water increased the yields to 5.9 ± 0.8 and 8.6 ± 0.9 cancers/mouse, respectively. In female Skh1 mice, UVR alone induced 1.7 ± 0.4 cancers/mouse, and the addition of 20, 100 or 500 ppm nickel chloride increased the yields to 2.8 ± 0.9, 5.6 ± 0.7 and 4.2 ± 1.0 cancers/mouse, respectively. Neither vitamin E nor selenomethionine reduced the cancer yield enhancement by chromium. These results confirm that chromium and nickel, while not good skin carcinogens per se, are enhancers of UVR-induced skin cancers in Skh1 mice. Data also suggest that the enhancement of UVR-induced skin cancers by chromate may not be oxidatively mediated since the antioxidant vitamin E as well as selenomethionine, found to prevent arsenite-enhanced skin carcinogenesis, failed to suppress enhancement by chromate.

Electrochemical behavior of membranes of ion-selective electrodes based on complex oxides

Lead-selective film electrodes with solid contact with membranes on the basis of niobates and vanadates of compositions Sr2.75Pb0.25La(VO4)3, Ba3.8Pb0.2Nb2O9, Ba3.5Pb0.5Nb2O9, Pb3NiNb2O9, and Pb2Nb2O7 are constructed and studied. Basic electrochemical characteristics of ion-selective electrodes, such as linearity region and steepness of the electrode function, working pH interval, type of electrode function, and reproducibility are determined. The electrode with a membrane on the basis of Pb3NiNb2O9 is tested and recommended as an indicator in the method of potentiostatic titration. The optimum titrant for assaying ions of lead(II) in solution is potassium chromate.

Determination of total and soluble chromium(VI) in compost by ion chromatography–inductively coupled plasma mass spectrometry

Ion chromatography coupled to inductively coupled plasma quadrupole mass spectrometry (IC-ICP-MS) was used for the specific determination of Cr(VI) in compost samples. Potential interferences from humic substances, carbon and chlorine species were avoided by chromatographic separation. Solution detection limits below 150 ng L−1 were obtained for injection volumes of 100 µL. Total Cr(VI) was determined by the previous alkaline digestion of the sample, following the method EPA3060A. Recoveries of pre- and post-digestion spikes (2.5 µg and 50 µg L−1 of Cr(VI) as potassium chromate, respectively) were better than 90%, indicating that the combined method can provide accurate results in spite of the high content of organic matter. Detection limits of 6 ng g−1 were obtained for the total Cr(VI) determination, the repeatability was better than 2% (at 30 µg L−1), and the reproducibility between extractions was around 6%. Soluble Cr(VI) was determined by the leaching of compost samples with water (liquid-to-solid ratio 10 : 1). A total Cr(VI) content of 1.2 µg g−1 was obtained for a compost from urban solid residues, whereas the soluble Cr(VI) in the pH range 4–10 was below the detection limit of the leaching method (1 ng g−1).

X-ray Absorption near Edge Structure and Extended X-ray Absorption Fine Structure Analysis of Standards and Biological Samples Containing Mixed Oxidation States of Chromium(III) and Chromium(VI)

For the first time a method has been developed for the extended X-ray absorption fine structure (EXAFS) data analyses of biological samples containing multiple oxidation states of chromium. In this study, the first shell coordination and interatomic distances based on the data analysis of known standards of potassium chromate (Cr(VI)) and chromium nitrate hexahydrate (Cr(III)) were investigated. The standards examined were mixtures of the following molar ratios of Cr(VI):Cr(III), 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25, and 1:0. It was determined from the calibration data that the fitting error associated with linear combination X-ray absorption near edge structure (LC-XANES) fittings was approximately +/-10% of the total fitting. The peak height of the Cr(VI) pre-edge feature after normalization of the X-ray absorption (XAS) spectra was used to prepare a calibration curve. The EXAFS fittings of the standards were also investigated and fittings to lechuguilla biomass samples laden with different ratios of Cr(III) and Cr(VI) were performed as well. An excellent agreement between the XANES data and the data presented in the EXAFS spectra was observed. The EXFAS data also presented mean coordination numbers directly related to the ratios of the different chromium oxidation states in the sample. The chromium oxygen interactions had two different bond lengths at approximately 1.68 and 1.98 A for the Cr(VI) and Cr(III) in the sample, respectively.

Validation of a capillary electrophoresis method for the analysis of ibandronate related impurities

A capillary zone electrophoretic (CZE) method has been developed for the determination of impurities (phosphyte and phosphate) in technical-grade ibandronate, which is a potent nitrogen-containing bisphosphonate. Successful separation of the drug from the impurities was achieved using 1 mM tetradecyl-trimethyl-ammonium bromide (TTAB) and 5 mM potassium chromate (pH 10.0) as background electrolyte with an indirect detection at 254 nm. The optimised method was validated for specificity, precision, linearity and accuracy. The limit of detection (LOD) was 2 μg/mL and the limit of quantification (LOQ) was 7 μg/mL for both phosphyte and phosphate. The developed CZE method used to determine phosphyte and phosphate as bisphosphonates impurities can be used to evaluate the quality of regular production samples of ibandronate.

Centrosymmetric Aliovalent KTP Isomorphs KMIII0.5Nb0.5OPO4 (M: Cr and Fe).

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Synthesis and characterization of nitrosylpseudohalochromium(I) complexes with morpholinomethyl urea and related ligands

Synthesis and characterization of nitrosylpseudohalochromiuni(I) complexes of the composition, [CrC(NO)X 2 L.H 2 O], where X = NCS- or NCO- and L = morpholinomethyl urea (MMU), morpholinomethyl thiourea (MMTU), piperidinomethyl urea (PMU) or piperidinomethyl thiourea (PMTU) is presented. These complexes have been prepared by treatment of potassium chromate with potassium thiocyanate/potassium cyanate and hydroxylamine hydrochloride followed by the addition of ligand (L). The complexes have been characterized by usual procedure.

High temperature interaction of Al/Si-modified Fe–Cr alloys with KCl

The corrosion behaviour of pure iron, pure chromium, and aluminium/silicon alloyed Fe–Cr materials was investigated at 650 °C in air accompanied by gaseous or solid KCl salt. The corrosion rates of these materials with KCl salt are high and they are strongly affected by the salt amount, the types of the alloying elements and the concentration of chromium. The dominant degradation mechanism for the chromia-forming alloys by KCl attack is the preferential formation of potassium chromate over the conventionally protective chromia, characterized by typical features of bubbles, cracks, volatility and severe spallation for the corrosion products. A detrimental effect of chromium is confirmed. Al-alloying addition to Fe–Cr alloys is beneficial by enhancing the corrosion resistance. Silicon is more effective in promoting the corrosion resistance of Fe–Cr alloys by forming a stable and dense oxide layer in the inner zone which suppresses the rapid growth of iron oxides.

Tripotassium Trichrome (III) Tetraphosphate K3Cr3(PO4)4: Synthèse, Étude Structurale, Caractérisation et Conductivité Ionique

The potassium chromium (III) phosphate K3Cr3(PO4)4 is prepared by a solid state reaction at 1173 K from a mixture of K2CO3, NH4H2PO4, and (NH4)Cr2O7. It is structurally characterized by single-crystal X-ray diffraction. It crystallizes in the Cmca (n°64) space group with a = 10.524(4) Åi, b = 20.466(6) Åi, c = 6.374(2) Åi, V = 1372.9(8) Åi3, Z = 4, R(F2) = 0.0452, and R W (F2) = 0.1184 for 790 reflections with I > 2σ(I). The structure consists of CrO6 octahedra and PO4 tetrahedra sharing corners and edges to form a two-dimensional framework. The K+ cations are located in the interlayer space. Conductivity measurement leads to σ = 47.32 10−5 Ω−1 m−1 at 729 K. K3Cr3(PO4)4 is a better ionic conductor than K3Cr3(AsO4)4 at the same temperature.

Centrosymmetric aliovalent KTP isomorphs KMIII0.5Nb0.5OPO4(M= Cr and Fe)

Aliovalent KTP isomorphic compounds potassium chromium niobium oxide phosphate, KCr0.5Nb0.5OPO4, and potassium iron niobium oxide phosphate, KFe0.5Nb0.5OPO4, exhibit structures that differ from that of the non-centrosymmetric KTiOPO4. There are two crystallographically independent octahedral sites, M1 and M2, statistically occupied by Nb and Cr (or Fe) atoms. The M1O6 and M2O6 octahedra are connected alternately to form a chain with a cis-trans arrangement. The Nb atoms prefer the M2 sites arranged in a cis-like configuration. Each PO4 tetrahedon has the P atom on a twofold axis. Site-splitting at the K-atom position is observed in both compounds. In the isomorphous structures, one Nb atom lies on an inversion centre and the other on a twofold axis. Similarly with the pairs of Fe/Cr sites, one is on an inversion centre and the other on a twofold axis.

Reductive conversion of hexavalent chromium in the preparation of ultra-fine chromia powder

By reducing potassium chromate with hydrogen and then calcining the obtained intermediate at high temperature, the ultra-fine chromia (Cr 2O 3) powder with a mean diameter of 0.3 μm was successfully prepared. Using scanning electron microscopy (SEM) and XRD, the chromia products were characterized. Through XPS, TG-DSC, FT-IR, XRD and chemical analysis, the reaction mechanism was explored. The results revealed that, the intermediate from reducing potassium chromate with hydrogen consists of Cr(OH) 3· nH 2O, CrOOH, KCrO 2 but the composition of the intermediate changes with the reduction temperature and time. Typically, the potassium content in the intermediate ranges approximately from 0.7% to 8% by weight and the chromium content from 50% to 57% by weight. It was also found that, just by calcining the intermediate in the presence of oxygen can the potassium in the intermediate be completely removed from the final chromia product.

Topography of the Prostaglandin Endoperoxide H2 Synthase-2 in Membranes

The topology of association of the monotopic protein cyclooxygenase-2 (COX-2) with membranes has been examined using EPR spectroscopy of spin-labeled recombinant human COX-2. Twenty-four mutants, each containing a single free cysteine substituted for an amino acid in the COX-2 membrane binding domain were expressed using the baculovirus system and purified, then conjugated with a nitroxide spin label and reconstituted into liposomes. Determining the relative accessibility of the nitroxide-tagged amino acid side chains for the solubilized COX-2 mutants, or COX-2 reconstituted into liposomes to nonpolar (oxygen) and polar (NiEDDA or CrOx) paramagnetic reagents allowed us to map the topology of COX-2 interaction with the lipid bilayer. When spin-labeled COX-2 was reconstituted into liposomes, EPR power saturation curves showed that side chains for all but two of the 24 mutants tested had limited accessibility to both polar and nonpolar paramagnetic relaxation agents, indicating that COX-2 associates primarily with the interfacial membrane region near the glycerol backbone and phospholipid head groups. Two amino acids, Phe(66) and Leu(67), were readily accessible to the non-polar relaxation agent oxygen, and thus likely inserted into the hydrophobic core of the lipid bilayer. However these residues are co-linear with amino acids in the interfacial region, so their extension into the hydrophobic core must be relatively shallow. EPR and structural data suggest that membrane interaction of COX-2 is also aided by partitioning of 4 aromatic amino acids, Phe(59), Phe(66), Tyr(76), and Phe(84) to the interfacial region, and by the electrostatic interactions of two basic amino acids, Arg(62) and Lys(64), with the phospholipid head groups.