Showing papers on "Chromium(III) oxide published in 2014"

Application of the zeta potential measurements to explanation of colloidal Cr2O3 stability mechanism in the presence of the ionic polyamino acids

Abstract: In the presented paper, the influence of the molecular weight and the type of polyamino acid functional groups on the electrokinetic properties and the stability of chromium (III) oxide suspension were examined. Analysis of the data obtained from the adsorption, potentiometric titration, zeta potential, and stability measurements allows to propose stabilization or destabilization mechanism of the studied systems. In the studies, there were used polyamino acids with different ionic characters: anionic polyaspartic acid and cationic polylysine. The measurements showed that the zeta potential depends on the concentration and molecular weight of the applied polymer. Stability of the chromium (III) oxide suspensions in the presence of ionic polyamino acids increases compared to the results obtained in the absence of polymers. The exception is LYS 4,900 at pH = 10. Under these conditions, the decrease in stability is observed due to formation of polymer bridges between the polymer chains adsorbed on different colloidal particles. Determination of the stabilization/destabilization mechanism of the polyamino acid/chromium (III) oxide system and examination of the effects of polymer molecular weight on the stabilization properties can contribute to a wider use of this group of compounds as potential stabilizers or flocculants in many industrial suspensions.

Sinorhizobium meliloti 1021 Exopolysaccharide as a Flocculant Improving Chromium(III) Oxide Removal from Aqueous Solutions

Abstract: Chromium(III) oxide is an amphoteric, dark green solid. This most stable dye is widely used in construction and ceramic industries as well as in painting. In this study, the attempt is made to determine flocculating properties of exopolysaccharide (EPS) synthesized by the bacteria Sinorhizobium meliloti 1021, which would increase the efficiency of chromium(III) oxide removal from sewages and wastewaters. The conditions under which EPS is the most effective destabilizing component of chromium(III) oxide suspension have been determined too. In order to characterize the structure of electric double layer formed at the solid/supporting electrolyte (EPS) solution interface, electrokinetic potential measurements and potentiometric titration were performed. The EPS amount adsorbed on the chromium(III) oxide surface as a solution pH function was also measured. Moreover, the stability of Cr2O3 suspension in the absence and presence of S. meliloti 1021 EPS was estimated. The pooled analysis of all obtained results showed that EPS causes chromium(III) oxide suspension destabilization in the whole examined pH range. The largest change in the system stability before and after the polymer addition was observed at pH 9. It is probable that under these conditions bridging flocculation occurs in the examined system.

Fabrication of Chromium (III) Oxide (Cr2O3) Coating by Electrophoretic Deposition

Abstract: Chromium (III) oxide has been widely used as a coating material for corrosion resistance. In this study, electrophoretic deposition (EPD) of nano chromium (III) oxide (Cr2O3) particle (60 nm) was investigated to develop coatings with potential applications of anticorrosive material. The stable suspension of Nano-Cr2O3 particles were obtained in the mixture of acetylacetone and ethanol containing 0.00025 M nitric acid. The coating growth rate was studied with using different deposition times in the range of 1–30 min at voltages of 50–150 V with various concentrations of suspension. The electrophoretic Cr2O3 coating was sintered at 1000°C and 1200°C for 2 h. The micro-morphology of coating was qualitatively characterized by focused ion beam scanning electron microscopy (FIB/SEM). The SEM micrographs obviously showed that the electrophoretic Cr2O3 coating has formed a uniform and dense ultrathin layer after sintering at 1200°C. We demonstrated that nano-Cr2O3 coating could be easily obtained by EPD for the surface modification of metallic materials for potential interest in hard wear-resistant and/or low-friction coatings.

Adsorption Properties of the Albumin–Chromium(III) Oxide System – Effect of Solution Ph and Ionic Strength

Abstract: The phenomenon of protein adsorption on solid surfaces is important in many scientific areas. It is a common process, but very complicated. In this paper, both the mechanism of BSA, HSA, and OVA adsorption on chromium(III) oxide and the structure of formed adsorption layers were determined. The adsorption process was examined as a function of solution pH and ionic strengths. Regardless of the protein type the highest adsorption level was observed when the pH value of the solution was close to the protein isoelectric point. Under these conditions the macromolecules have a compact and folded conformation that allows for the packing of a larger amount on the unit Cr2O3 surface. The minimum adsorption rate, regardless of the protein type, was observed at pH = 3. It can be related to the expanded conformation of macromolecules and the electrostatic repulsion between the positively charged Cr2O3 surface and the positively charged polymer segments. The obtained results may be very helpful in the development of r...

Kinetics of thermal transformations in nanosized chromium films

Abstract: The transformations in nanosized chromium layers at different layer thicknesses (d = 14–154 nm) and thermal treatment temperatures (T = 673–873 K) were studied by optical spectroscopy, microscopy, and gravimetry. The kinetic curves of conversion at different chromium film thicknesses and treatment temperatures are well approximated by the linear, inverse logarithmic, cubic, and logarithmic functions. The contact potential difference for Cr and Cr2O3 films and photo-emf for Cr-Cr2O3 systems were measured. An energy band diagram of Cr-Cr2O3 systems was constructed. A model of thermal transformation was constructed for Cr films that included the stages of oxygen adsorption, charge carrier redistribution in the contact field of Cr-Cr2O3, and chromium(III) oxide formation.

Effect of the nature of silicon oxide structures on the activity of an alumina-chromium catalyst in the reaction of iso -butane dehydrogenation

Abstract: The formation of silicon oxide structures in the composition of an alumina-chromium catalyst for the dehydrogenation of iso-butane is studied by means of nitrogen adsorption, XRD analysis, solid-state 29Si NMR spectroscopy, temperature-programmed desorption of ammonia, and UV-Vis and Raman spectroscopy. It is established that 0.5–1.2 wt % silicon was distributed on the catalyst surface in the form of Si(OSi)4 structures. As the silicon content was increased to 2.2–3.6 wt %, Si(OSi)3(O-) structural elements were present on the surface in addition to Si(OSi)4. The formation of silicon oxide structures on the catalyst surface was responsible for an increase in the concentration of Cr(III) ions and a decrease in the surface acidity; the activity and selectivity of the catalysts in the reaction of iso-butane dehydrogenation increased.