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In this study, titanium dioxide (TiO2) and polyethylene (PE) fibers were employed to develop photocatalytic high-performance fiber-reinforced cement composites (HPFRCCs). To achieve high NOx removal capacity, it was necessary to confirm the dispersion of the TiO2 powder. For this purpose, various amounts of viscosity-modifying agent (VMA), ranging from 0% to 1% by weight to cement, were considered along with two types of white Portland cement: Union and Aalborg. Additionally, the PE fiber surface was modified via cold gas plasma and chromic acid treatment to improve the tensile performance of the HPFRCCs. The experimental results indicated that the plastic viscosity of the mortar increases with the addition of VMA. Optimum NOx removal capacities of 5.72 and 8.10 μmol were respectively achieved for the Aalborg and Union cement types in the mortar at a VMA content of 0.5%. The compressive strength of the tested photocatalytic HPFRCC was approximately 72.7–91.8 MPa. In the case of the hybrid argon (Ar) and oxygen (O2) gases being subjected to plasma treatment, optimum tensile performance—in terms of tensile strength, strain capacity, and g-value—was achieved, whereas the samples subjected to chromic acid treatment exhibited poorer tensile performance. Moreover, the single Ar–or O2-gas-based plasma treatment yielded an intermediate tensile performance. The cracking behavior showed trends similar to those of the g-value: the hybrid plasma treatment produced the most microcracks because of its high fiber bridging capacity.

Chromic acid oxidation of d,l-mandelic acid in the presence and absence of 1,10-phenanthroline (Phen) is studied in an aqueous micellar medium under kinetic conditions, [d,l-mandelic acid] >> [Phen]T >> [Cr(VI)]T at different temperatures. From studies on the effect of temperature on the rate constant (k), the activation parameters ∆H≠ (enthalpy of activation) and ∆S≠ (entropy of activation) are evaluated by using the Eyring equation [−ln (kh/kBT) = ∆H≠/RT − ∆S≠/R]. The high value of ∆H≠ indicates that the phen-catalysed path is favoured mainly due to very high negative value of ∆S≠. The negative value of ∆S≠ and the composite rate constant kcat support the suggested cyclic transition state. Both the catalysed and uncatalysed paths show a first-order dependence on [H+], and both also show a first-order dependence on [d,l-mandelic acid]T and [Cr(VI)]T. The Phen-catalysed path is first order in [Phen]T. These observations remain unaltered in the presence of externally added surfactants. The cationic surfactant N-cetylpyridinium chloride is found to retard the rate of the reaction.

Chromium layers applied by electroplating processes are widely used as coatings for piston rods in the hydraulics industry for improved wear resistance and corrosion resistance. Despite its advantages of beneficial tribological properties, availability, and established application, there are some drawbacks when using chromium plating, such as the well-known health hazards of Cr-VI precursors. Additionally, because of the introduction of mandatory registration of Cr-VI compounds according to REACH, including CrO3 and chromic acid, the plating industry has to deal with increased organizational expenses. We report on the usage of PACVD and heat treatment methods as potential alternatives for plated chromium as piston rod coatings. A comprehensive characterization of chromium coated and alternatively treated piston rod samples regarding corrosion resistance and tribological behavior showed that heat treated and DLC coated surfaces fulfill the requirements to piston rod coatings for certain application areas and can serve as a promising chromium-free alternatives.

Ozone, heating-in-air, and chromic acid treatments of polypropylene (PP) films and fibers were evaluated for their ability to promote ZnO nanoparticle (NP) adhesion. X-ray photoelectron spectroscop...

The paper examines the problem of the composition instability in the ready ground spice, turmeric. Analysis of the prevalent methods for turmeric adulteration and substances used for these purposes is given. The visual assessment of color tints of the turmeric root, spices containing it and chemical dyes based on chromium salts is presented. The studies on determination of the lead and chromium content were carried out to study the content of these metals and test the hypothesis of using lead chromate as a dye in adulteration of turmeric. Using the method of electrothermal atomic absorption spectroscopy, it was found that the lead content in the analyzed turmeric samples varied from 1.72 ± 0.58 to 5.03 ± 1.80 mg/kg, while the chromium content was in a range of 5.56 ± 0.85 to 16.15 ± 2.32 mg/kg. As a result of species specific PCR, wheat DNA was revealed in all purchased samples of ground turmeric. The levels of the main raw material replacement were established, which were 0.14% to 14.95% with the correlation coefficient close to 100%; efficiency of the reaction was 1.95, which was 97.5% when expressed as percentage. These levels of an undeclared allergen in the product composition can cause a serious allergic reaction. The authors tested the hypothesis of introduction of sodium and potassium salts for correction of the color spectrum in the ready spice and its correspondence to the natural color within the color spectrum of turmeric. As a result of the complex study of the spice composition, quite high values of chromium were found, presumably not only from the lead chromate compound but also from chromic acid salts, as the high level of potassium that significantly exceeded the native content of this element was found.

Piperonal is a key ingredient in the flavour and fragrance industry and a useful intermediate for the synthesis of fine chemicals. It is currently prepared by either ozonolysis or chromic acid oxidation of isosafrole, obtained upon isomerization of naturally abundant safrole. A chemo-enzymatic three-step procedure for the conversion of isosafrole into piperonal is herein described. Lipase-mediated perhydrolysis of EtOAc in the presence of H2O2 is employed to generate peracetic acid in situ and promote the epoxidation of isosafrole. The reaction mixture is submitted to methanolic KOH treatment to recover the corresponding mixture of vicinal diols. The latter is efficiently oxidized to piperonal using MnO2, periodically regenerated at the expense of tert-butylhydroperoxide (TBHP), which represents the terminal oxidant of this transformation. The use of continuous-flow conditions using a continuously-stirred tank reactor for the epoxidation, and a packed bed reactor for the final oxidation improves the productivity and stability of the whole method, with space–time yields of 75 mmol g−1 h−1 and 120 mmol g−1 h−1, calculated as amount of generated product per amount of catalyst per unit time.

The development of catalysts for dehydrogenation of light paraffin hydrocarbons in a fixed bed reactor is of great importance for the world petrochemical industry. The preparation of granules (~3 mm in diameter) of CrOx/Al2O3 catalysts is hindered by such problems as homogeneous distribution of active component and modifiers, high strength of granules, etc. In this paper, the alumina support dissolution in the impregnating solution containing chromic acid and the opportunity to apply vacuum impregnation to minimize this effect in the preparation of CrOx/Al2O3 catalysts are discussed. A series of catalysts is synthesized at different impregnation pressures (1, 0.85, and 0.7 atm), characterized by a complex of physical–chemical methods (low-temperature N2 adsorption, SEM, XRD, TPR-H2), and tested in isobutane dehydrogenation. The use of vacuum impregnation is shown to lead to the reduction of the specific surface area of the catalysts from to 91 to 56 m2/g and the growth of content of CrOx phases that decreases the catalytic activity in dehydrogenation. The isobutylene yield at 610 °C decreases from 68% to 54% for the catalyst prepared at P = 0.7 atm as compared with the one prepared at atmospheric pressure. The high activity and stability are connected with the hierarchical structure of the alumina support and homogeneous chromia distribution on its surface.

Different additives were added into the potassium fluorozirconate solution to prepare different nickel-free sealing reagents, with which the anodic oxidation film of aluminum alloy was sealed at room temperature. The phosphor chromic acid weight loss method was used to evaluate the sealing effects. Using electron scanning microscopy (SEM), the surface and cross-sectional micro-morphologies of the anodic oxidation films sealed by different fluorozirconate sealants were observed. The position and state of zirconium element distribution in the film hole were investigated by the further quantitative and distribution analysis of Zr element. This study provides an experimental evidence for the theoretical studies of fluorozirconate-sealed anodic oxidation films. It is shown that the fluorozirconate has good sealing effects and has a wide prospect for sealing the aluminum alloy samples. Its products were highly corrosion resistant, and were filled in the openings of the micropores in the oxide film.

The behavior of anodic porous alumina film formed on an aluminum surface by anodizing in chromic acid solutions was optimized using Box–Wilson experimental design. The film thickness was correlated as a function of temperature, acid concentration, applied voltage, and time. A mathematical model was suggested and optimized. Results of coating thickness indicate that both temperature and time play an important role in the anodizing process. The interaction effect of variables on the film thickness is less pronounced compared with the effect of the main variables. Optimum film thickness obtained during the anodizing process was 10.43 µm at the optimum value of temperature (45 °C) and time (68 min). The polarization measurement of anodized aluminum ASA 6061 in chromic acid shows a high corrosion resistance in the presence of coating. The results confirmed by using surface morphology investigations.

Chromic acid reagent as an alternative colorimetric method for the quantitative determination of reducing sugars and ascorbic acid in some selected fizzy drinks: Seven Up, Limca, Mirinda, Cocoa-Cola, Fanta, Pepsi Cola, Maltina, Guinness Malt, Hi-Malt and Maltonic) and fruits: pineapple (Ananas cosmoses), sweet orange (Cimifi sinensis), grape fruit (Dints paradise) and tangerine (Citrus reticulate) has been studied. Chromic method involves sugar solution of about 1% concentration. treated with an equal volume of concentrated nitric acid and a few drops of a 5% solution of potassium dichromate was added, a blue colour develops in less than a minute in the cold and the absorbance taken in a Spectronic 20D Spectrophotometer at 560 um. Results obtained from the simple chromic acid as test method compares well with those obtained from the titrimetric methods of Association of Official Analytical Chemists (AOAC, 2012) and Pearson (1991) as control, with negligible variations. Apart from being a very powerful oxidizing agent, its reaction with monosaccharide, disaccharides and ascorbic acid are less-time consuming, showed distinct colour development and its easy preparation, made chromic acid reagent a faster, better and suitable alternative method for the quantitative determination of reducing sugars and ascorbic acid in routine analyses of foods. Keywords: reducing sugar, ascorbic acid, chromic reagent.

The present study describes a novel green approach of waste to energy generation without use of any chemical in the pretreatment process. Lignocellulosic waste Rice Straw (RS) was taken as substrate and petha waste water (PWW) was used for the pretreatment of RS. Cow dung (CD) and soil were used as mixed microbial sources. Eight different batch reactors were set up with CD and soil as microbial sources separately. These reactors contained PWW pretreated RS which was ultrasonicated for 5, 10 and 15 min for three separate reactors and the fourth reactor was set up without ultrasonication. Methane was analysed by gas chromatograph (GC) equipped with thermal conductivity detector (TCD) and ethanol was analysed using chromic acid method by UV–Visible spectrophotometer (584 nm). Various physical parameters like COD degradation, pH, TS, TDS, TSS, VS were also analysed as per standard methods to check the feasibility of the process. Maximum methane yield was 47.8% with soil culture and maximum ethanol yield was 126.53 mg/L with CD, in the reactors with 15 min ultrasonication of RS and PWW. The methane and ethanol yields were about three times and two times more than that of reactors without ultrasonication with soil and CD respectively.

The surface modification of copolymer substrates of Acrylonitrile-Butadiene-Styrene (ABS) is significant for the electroplating industry. The sulfuric-chromic acid bath, used in the Electroless process, conditioning the ABS surface by selective oxidation of poly(butadiene) creating interconnected micro-holes, which allows an excellent mechanical adherence between the metallic film and the substrate. The chromium in its hexavalent form Cr(VI) is harmful to human beings and the environment being a carcinogenic element. This work shows a surface alteration effect with different types of chemical reagents on ABS surface and its treatment with the sulfuric-chromic acid bath in concentrations below those of the normal process, to analyze the possible application of the electroless process. The use of the different chemical reagents studied favored the alteration of the ABS surface causing various types of surface reactions, which could be shown spontaneously or during the conditioning step.

Under pseudo 1st order reaction condition cyclohexanol, an alicyclic alcohol produces cyclohexanone with a moderate rate of oxidation. Promoters and surfactants enhanced the rate of oxidation with chromic acid. The product is confirmed by melting point study; 2, 4 DNP test; IR and NMR study. Among the three micellar catalyst SDS shows higher rate where as phen promoted reaction shows smaller half life. Combination of SDS and bpy shows a 600 fold enhancement in the rate of the reaction. NMR study is also carried out to confirm the interaction between the surfactants and cyclohexanol.

The rate of fatigue crack propagation of the 7050-T7651 aircraft material subjected to automatic shot peening machine and chromic acid anodizing (CAA) has been studied and compared with previous research results. Shot peening is a surface treatment by firing shot material so that the dimple is formed and residual stress occurs on the surface of the working specimen in order to increase resistance to fatigue failure. Al 7050-T7651 is made into specimens according to ASTM E647 standard treated with automatic shot peening machine (with steel shot material, 0.017 inch diameter, shot flow 30%, 3 bar pressure, Almen intensity 0.0082 A with 100 mm shooting range and 90° angle of shot) and CAA (operating standard) in surface treatment area of Indonesian Aerospace. The fatigue cracking test with a load of about 200 kg, with a stress ratio of R = 0.1. The results of the fatigue crack growth test resulted in the constant of Paris A=3.654 × 10-9 and n = 1.67, indicating that the automatic shot peening machine and chromic acid anodizing treatment decreased the fatigue life and increased the fatigue crack growth rate compared to the automatic shot peening machine, manual machine with or without CAA, and without treatment.

Corrosion and passivation of tin at various pH have been investigated using different electrochemical techniques. Tin is a little active metal even if it is less than the hydrogen equilibrium compared to its domain stability set. Tin acts as Sn(II) via the active zone, so it corrodes with evolving H2 gas in an acidic medium. In passive areas, Sn(IV) is oxidized to produce an inclusive variety of passivity outstanding to the permanence of either Sn(OH)4 and/or SnO2 anodic surface of tin(IV), which is stable to lower pH. Tin's active dissolution requires one anodic peak and strengthens with rising acid electrolyte. The cathodic curve shows one cathodic peak consistent with passive tin layer reduction. Adding any polyethylene glycols to a solution of citric acid reduces the existing anodic peak density and changes its peak potential in the negative direction. Those changes depend on the added polyethylene glycol concentration and molecular weight. In an acidic environment comprised chromic, phosphoric, and hydrochloric acids, amorphous SnO nanotubes were manufactured using Sn nanowires (NW) electrodeposited to anodic aluminum oxide frameworks by a local degradation process. The phosphoric acid disintegrates the base initially, while also chromic acid generates an oxide layer of SnO at the NW level. Finally, Sn NWs with 10 μm in length and 30 nm in diameter are completely converted into the polycrystalline SnO form by crystallization of the amorphous nanotubes after heat treatment with rough morphology of the earth.

Anodizing was applied to improve the heat dissipation performance of aluminum (Al) alloys, by forming an oxide layer, such that they could be employed in aerospace applications. The methods employed were hard sulfuric acid (high hardness), soft sulfuric acid (low hardness), boric-sulfuric mixed acid, tin-sulfuric mixed acid, and chromic acid solutions. Each process was completed under optimized conditions. The surface morphology was observed using field emission scanning electron microscopy (FE-SEM) and a digital camera. For the determination of thermal performance, Fourier transform infrared spectroscopy (FT-IR) was used to measure the emissivity at 50 °C, and laser flash analysis (LFA) was utilized to analyze the thermal diffusivity at room temperature to 300 °C. The radiative property of metals is often ignored because of their low emissivity, however, in this research, the emissivity of the metal oxides was found to be higher than that of bare metal series. This study improved the heat dissipation properties by oxidization of Al via the anodizing process.

Chromic acid and chromates are oxyacids and oxyanions of hexavalent chromium, Cr(VI), and used widely in anodizing, electroplating, corrosion control, oxidation, wood treatment, and several other industrial applications. This chapter discusses recovery of chromates or oxyanions of Cr(VI) without changing their oxidation states. Chromate ions exist in the aqueous phase in different ionic forms, with total chromate concentration and pH dictating which particular chromate species will predominate. Brine in conjunction with caustic soda is used as a regenerant for strong-base anion exchangers, and the regeneration takes place in two consecutive steps, namely, deprotonation and chloride exchange. Alkali addition is required for the stoichiometric deprotonation of the chromate species. The chromate discharge limits are being subjected to more stringent regulatory control in every industrialized country.

Chromic acid anodizing (CAA) is still being used today for corrosion protection of fatigue-critical components in the aeronautic industry due to the lack of feasible alternatives. Ce-containing sulfuric acid anodizing (SAA) has been identified as a promising strategy for the development of alternatives to toxic CAA. This work explores thin sulfuric acid anodizing (TSAA) focusing on the following effects: (i) current density and voltage values; (ii) concentration of Ce(IV). Screening of the optimum combination in search of minimum thickness and the best corrosion resistance was performed using electrochemical impedance spectroscopy (EIS). Two Ce-containing anodic films were selected and further investigated in comparison with the inhibitor-free film in terms of morphology (FEG-SEM, TEM), composition (RBS), corrosion resistance (EIS, NSST), high-cycle fatigue and paint adhesion. The results indicate that the path to approach the CAA performance lies through thin (

Fibre metal laminates based on titanium and carbon fibre reinforced polyimide (TCP-FML) are designed and manufactured to meet the requirements of high temperature applications. In this work, the preparation technology of the TCP-FML was optimized through the investigation of prepreg manufacture as well as surface treatment of titanium. Prepreg were manufactured using a solution dip method. The effects of step width, fibre tension and translational speed on the performance of prepreg were studied. Surface treatments were performed on titanium using sandblasting, chromic acid (CAA) anodization and NaTESi anodization methods. SEM observation and contact angle were used to analyze the surface characteristics of titanium. The effects of surface treatment on the interlaminar properties of titanium/polyimide were investigated by single-lap shear test and double cantilever beam (DCB) tests. This careful surface preparation, to ensure a good interfacial strength, is crucial for good mechanical properties.

Isatin is an indole derivative firstly synthesized in the laboratory by Erdmann and Laurent by oxidation of indigo pigment having chromic acid. It is orange-red in color with freezing point 2000C...

Objectives Electroplating processes are widely used in metal industries to improve the resistance properties of manufactured metal parts. Workers in this industry are potentially exposed both to hexavalent chromium (Cr(VI)) and to other chromium compounds [mostly trivalent chromium (Cr(III))], due to the use of chromic acid baths. The goal of this study was to validate urinary chromium as a Cr(VI) exposure biomarker in the presence of exposure to other chromium compounds. Methods A biomonitoring study consisted in monitoring airborne chromium exposure and urinary chromium for one working week in 93 workers from nine electroplating companies. Chromium concentrations were measured in all urinations of each volunteer for the working week. Individual airborne soluble and insoluble Cr(VI) as well as Cr(III) concentrations were measured for all of the shifts of the week. The main statistical analysis consisted in modelling, in a Bayesian framework, the pre- and post-shift urinary chromium as a function of airborne Cr(III) and airborne Cr(VI), taking into account the day of the week and the time of collection of the urines (pre- or post-shift). Results Preliminary descriptions showed an increase in pre-shift urinary chromium during the working week. The model showed an increase in urinary chromium over the shift related to the shift-specific airborne Cr(VI) concentration as well as an increasing trend over the week and a relationship with the mean weekly Cr(VI) thought to reflect chronic exposure. Taking into account the Cr(VI) exposure, there was no evidence of an effect of Cr(III) exposure on urinary chromium. A biological limit value (BLV) was derived from the French occupational exposure limit for Cr(VI) of 1 µg m−3 and was estimated at between 1.9 and 2.6 µg g−1 creatinine for a urinary sample collected at the end of the shift on the last working day of the week. Conclusions In the present context of mixed exposure to Cr(III) and Cr(VI) in electroplating, this study showed that urinary chromium depended only on airborne Cr(VI) concentrations, which justifies using a BLV for assessing workers’ exposure. The estimated BLV was close to the recommended French BLV, which is 1.8 µg g−1 creatinine, in the electroplating industry.

Chromate conversion coating is an efficacious and fast means of protecting metal parts from corrosion, but problematic in that it uses the toxic and carcinogenic chromic acid as the reagent. This short report covers some key considerations and alternatives.

The hip joint is one of the most often used joints by humans in their activities. The hip joint can be impaired if an accident or an illness such as osteoarthritis-affected. It makes the patients need to get implants to restore their productivity. The implant must be biocompatible, bioactive, and have high strength and resilience to prevent damage. The implants in this study were made from 304 Stainless Steel. One of the stages in making implants is the electroplating process. The electroplating method implemented is hard chrome. Some operating conditions that are considered to affect the electroplating process and are used as independent variables are the concentration of chromic acid, electrical voltage, and length of coating time. This study aims to Optimization of Electroplating Thickness Quality at Hip Joint Implant. This study uses the Taguchi method to design the experiment and to obtain the optimum electroplating thickness results. ANOVA is used to obtain the influential prediction of the significance level. Process ANOVA was helped Minitab 16. Based on the ANOVA, it is known that the most significant factor for the electroplating thickness is the concentration of chromic acid, the voltage, and the least influential factor is the electroplating time.

Electrolytes for decorative chromium plating based on trivalent chromium salts are known since several decades. As the use of conventional, hexavalent chromium based plating baths is more and more restricted by governmental regulations, these electrolytes gain ground in electroplating industry. However, compared to hexavalent chromium electrolytes, trivalent chromium electrolytes cannot fully meet the requirements with regard to appearance of the electrodeposited chromium, and there is little knowledge about the influencing factors on the shade of color. In this paper, chromium plated from a solution of chromium(III) sulfate was characterized by colorimetry, SEM and AFM and compared to a sample plated from a chromic acid electrolyte in order to reveal correlations between visual appearance and surface morphology. A relation between an increase of grain size and a color shift from blueish to yellowish was observed. Unlike in hexavalent based systems, grain size, roughness and color depend on layer thickness as the grain growth mechanism appears to be different. A model based on the theory of light scattering at rough surfaces is provided that links roughness and reflection behavior of the chromium surface.

The improvement in the bonding strength of fiber metal laminate is proposed by the inclusion of multi walled carbon nanotubes (MWCNTs). The bonding strength of fiber metal laminate (FML) was studied using lap joint testing method. In the first stage the surface treatment of the aluminum sheets was carried out by varying the chromic acid bath temperature by 50, 60, 70 and 80 °C. The temperature of the bath at 50 °C has been resulted in superior surface texturing and higher bonding strength as verified by lap joint test of FML. The ratio of potassium dichromate in the chromic acid solution was also varied from 1.0 part to 2.5 part by 0.5. In the second stage, NH2 functionalized MWCNTs were used in 1.0, 2.0 and 3.0 wt% of the epoxy matrix of E-glass fiber composite to improve the bonding strength of the FML joint. The results have shown that the strength of the E-glass/epoxy and aluminum interface has been improved by the inclusion of NH2-MWCNTs, when the samples were cured under vacuum compression as compared to the similar samples when cured under atmospheric pressure.

ABS resin is widely used after the plating process. The traditional ABS resin surface etching process uses a chromic acid system, which is a great threat to environmental protection. This paper exa...

In the present investigation, a novel chromate-free Mn and V oxyanions sealed tartaric–sulfuric acid anodic oxide coating (TSA) was developed on airframe grade aluminum alloy (AA2024). The results obtained from field emission scanning electron microscopy and energy-dispersive x-ray analysis showed effective surface modification of TSA after Mn-V oxyanions sealing (TSAMnVO). Potentiodynamic polarization results showed no significant difference in corrosion current density value (0.01 µA/cm2) after 1 h and 336 h of immersion in 3.5% NaCl solution. EIS result exhibited barrier layer resistance (Rb) value of TSAMnVO > 106 kΩ cm2 even after 336 h of immersion in NaCl solution. The 3D profile and Raman analysis showed no significant difference in the topography and composition, respectively, on the surface of TSAMnVO even after 1000 h of salt spray test. TSAMnVO also showed excellent adhesion with aircraft grade epoxy primer as per the ASTM 3359. Tensile and constant amplitude fatigue test results of TSAMnVO exhibited ultimate tensile strength and number of cycles to failure comparable with chromic acid anodization (CAA) process. Hence, the developed novel TSAMnVO coating system eliminates the usage of chromate ions completely in anodization process since it provides comparable corrosion resistance and mechanical properties with CAA.

The use of the electromembrane method for the purification of chromium plating electrolytes from cationic impurities (iron, copper, etc.) by three approaches are described. The first variant is based on the removal of these ions during their migration from the solution to be purified into a catholyte through a cationexchange membrane. The second variant is a transfer of chromate anions from a contaminated solution into the anolyte through an anion-exchange membrane. In the third method for the recuperation of chromic acid, accumulated in a recovery bath, it is proposed to use the immersed electrochemical module, combining the processes of concentration and purification from impurities, instead of evaporation.

—A study of redox reaction kinetics in chromium-containing fixatives (mixtures of chromic acid, bichromate, formaldehyde, and acetic acid) showed that these fixatives were unstable chemical mixtures characterized by rapid kinetics of redox processes. Therefore, biological material fixation occurs in a non-stationary solution of a variable composition, including chromic acid, bichromates (chromium(VI)), formaldehyde, acetic acid, formic acid, and chromium(III) acetate. We propose the division of chemical fixation in these fixatives into two successive stages (“two-step fixation protocol”): the tissue is fixed in an acetic acid–formaldehyde mixture (a rapidly penetrating fixing mixture) at the first stage and washed thoroughly, and treated by the mordant for the staining at the second stage. Such a protocol will at least preserve the original composition of chromium-containing fixatives.

Metallization has been widely used to enhance the aesthetics and performance of injection molded plastic parts, but the techniques have not been widely extended to 3D printed parts due to intrinsic differences in surface chemistry and morphology. Here, we investigate direct metallization of acrylonitrile butadiene styrene (ABS) 3D printed thermoplastic parts using low cost environmentally benign surface preparations and physical vapor deposition (PVD) to avoid the use of preparation with toxic chromic acid. Fourier transform infrared (FTIR) spectra are gathered for each surface preparation method prior to metallization. The metallized parts are then characterized for thin film adhesion, electrical resistivity, and optical reflectivity. Additionally, each part is imaged using a scanning electron microscope (SEM) post-metallization. The results show that surface preparation with solvent results in a smooth and aesthetically pleasing surface, but metallic film adhesion is poor. Conversely, when 2000 grit sandpaper is used to mechanically prepare the surfaces, the resulting films have poor electrical conductivity and optical reflectance, but excellent adhesion. Atmospheric plasma treatment of the parts results in the highest overall performance, with superior adhesion strength and optical reflectivity and low electrical resistivity. Electron microscopy and FTIR reveal that the high adhesion resulting from atmospheric plasma is caused by modification surface morphology, but not surface chemical termination. The results indicate that direct metallization of 3D printed ABS is a viable method for creating metallized parts with high performance and an aesthetically pleasing appearance and that the use of chromic acid in surface preparation is not necessary.

The corrosion resistance is importantly influenced by the internal stress of the oxide film on lead-alloy anodes. In this article, pure lead anodes and Pb-Sn-Ag alloy anodes are taken as raw materials to study the effect of Sn-Ag addition on the internal stress change and electrochemical properties of oxide film in a chromic acid solution. The structural properties are researched by means of a metallurgical microscope, a Raman spectrometer and an X-ray diffractometer. The electrochemical properties are studied by electrochemical testing methods. During the oxidation process, both anodes behave as the compressive stress, while the internal stress of the Pb-Sn-Ag alloy anode exhibits fewer changes. PbO, which contributes to a compressive stress, is generated first and then turns into PbCrO4 that contributes to a tensile stress. Compared to pure lead anodes, Pb-Sn-Ag alloy anodes possess a better corrosion resistance, which can be maintained for a long time. PbCrO4 tends to weaken the corrosion resistance. The analysis shows that the more internal stresses accumulates, the poorer the corrosion resistance possessed by anodes. Moreover, an equation of σ OF = A ⋅ exp ( t / B ) + σ L is proposed to estimate the internal stress.

In chromium electroplating for decorative applications, trivalent chromium based electrolytes are recently used as alternatives for solutions of chromic acid. Since the use of hexavalent chromium is restricted in serval countries, the demand on chromium(III) electrolytes increases and there is a need for understanding the deposition kinetics in order to improve the performance of the plating process. Electrochemical quartz crystal microbalance (EQCM) was used to study the mass-charge balance of the cathodic processes in chromium(III)-sulfate based plating baths. Current efficiency and deposition rate were determined as a function of time, additive concentration and current density. The addition of benzoic sulfimide (BSI) facilitates the reduction to chromium metal, as an optimum current efficiency of 8.1% was observed at 2.5 A dm−2. pH changes near the cathode surface during electroplating were evaluated in-situ by combining a pH electrode with a metal mesh and correlated with the results obtained by EQCM.

International audience; Commercial zeolites with CHA, MFI, and LTL framework topology are subjected to acid treatment with chromic acid (H2CrO4) solutions with concentrations ranging between 0.1 and 10 w/%. As chromic acid forms polymeric species as a function of concentration, specific effects were obtained with these three zeolites, differing by their framework topology, pore size, Si/Al ratios and crystal size. The etched zeolites are characterized by X-ray diffraction, SEM, TEM, N 2 physisorption, ICP-AES, 27 Al and 29 Si MAS NMR, 29 Si{ 1 H} cross-polarization spectra, EDX. Their acidic properties are probed with pyridine and d 3-acetonitrile by in situ FTIR. Results indicate that the 8 MR (CHA) and 10 MR (MFI) zeolites are more resistant to acid treatment with chromic acid than the 12 MR (LTL) zeolite. This paves the way for rational control of zeolite dealumination since adjusting chromic acid concentration will generate anions appropriate for treating a particular zeolite.

The structural integrity of several structures could be determined by their joints strength. Over the years, adhesively bonded joints have been often chosen to achieve a compromise between mass reduction and higher mechanical strength. Among others, the reduction in stress concentrations, the ability of producing smooth surfaces with no discontinuities and the reduced weight penalties are some of the factors that make this type of joints so attractive. Normally, to increase the bond strength, the materials to be bonded must be subjected to a kind of surface treatment. For metals, and more specifically, for aluminium alloys, phosphoric acid anodizing and chromic acid anodizing have been the most used treatments worldwide. However, recent investigations show that these kinds of anodizing are detrimental to health due to the release of carcinogenic substances. With this in mind, it is of the utmost importance to find alternative surface treatments that can ensure an effective bond. In this paper, a vast experimental study was performed based in the single lap joint ASTM D 1002 standard method, with the objective of determining the best alternative surface treatment (Sulfuric Acid Anodizing and Boric-Sulfuric Acid Anodizing), for aluminium-to-aluminium joints, using two types of adhesives, namely the AF 163 and the EA 9658 AERO. Results show that the optimum surface treatment is different for each type of adhesive and this fact has a huge influence on mechanical behavior of this type of aeronautical adhesive joints. info:eu-repo/semantics/publishedVersion

Photoelectrochemical chromium ion oxidation from the trivalent to the hexavalent state has been demonstrated by using WO3 nanosponge photoanodes in sulfuric acid electrolytes under simulated sunlight. Faradaic efficiencies of almost 100% were achieved in electrolytes containing high Cr3+ (≥10 mM) and low SO42− (≤10 mM) concentrations at very low bias potential voltages below 1.1 VRHE. At the photoanode, the production of Cr6+ ions competed with the formation of S2O82− ions from HSO4−/SO42− ions. At the cathode, hydrogen evolution occurred with 100% faradaic efficiency. Additionally, Cr3+ recovery was also observed at the cathode upon switching the electrolytes of the anode and cathode cells after the Cr6+ production, demonstrating the complete cyclic photoelectrochemical reaction between Cr3+ and Cr6+ ions. Finally, we showed the applicability of chromic acid oxidation to quinone production by using the photoelectrochemically produced Cr6+ ions in the sulfuric acid solutions. p-Benzenediol was successfully converted into p-benzoquinone with high efficiency. Thus, we have demonstrated the production of high-value-added organic reagents via photoelectrochemically driven chromic acid oxidation with the recycling of Cr6+ from Cr3+ using solar energy.

Anodizing Al in chromic acid is a very useful surface finishing process for corrosion protection and nanoscale porous structure fabrication, whereas the self-ordering of porous anodic alumina (PAA) in chromic acid has never been found to date. Herein, we provide a self-ordered PAA film possessing numerous sub100-nm-scale characteristic bumps through anodizing in chromic acid at high temperature. Anodizing of high purity Al plates in a 0.3 M chromic acid solution at conventional low temperatures, such as 293 K, leads to the formation of a disordered PAA film, whereas anodizing at a high temperature of 348 K causes the self-ordering behavior of the pore structure. The PAA film grown in the initial stage possessed the highest regularity, and it decreased with anodizing time due to pore branching during anodizing. A highly ordered PAA film measuring approximately 340 nm in interpore distance can be fabricated by short-term, two-step anodizing in chromic acid at 348 K and 120 V. The ordered PAA film possesses a characteristic nanostructure consisting of hexagonally arranged 100-nm-scale pores and sub100-nm-scale disordered bumps on their pore walls without any electrolyte chromate anion.

Polyhydroxamic acid sorbent was synthesized by polymerization of acrylamide using N, N′-methylene-bis-acrylamide as crosslinker and ammonium per sulphate as a thermal initiator. The sorbent was characterized for composition, thermal stability, functional group and morphology by elemental analysis, thermal analysis, infrared spectroscopy and secondary electron microscopy respectively. The synthesized sorbent was evaluated for the removal of trivalent and hexavalent chromium ion from aqueous solution. Experimental parameters such as pH, equilibration time, solute concentration and temperature were optimized. It showed a sorption capacity of 322 mg g −1 for Cr (III) and 176 mg g −1 for Cr (VI) at pH 4. The sorbent reduces the more toxic Cr (VI) to relatively less toxic Cr (III) during the sorption process as confirmed by X-ray photoelectron spectroscopy. The sorption phenomena followed Langmuir model and the sorption reaction was found to be pseudo–second order confirming chemisorption.

Alumina is classified as an intermediate oxide that cannot form a glass and is industrially used as a multifunctional material. Intensive studies on the atomistic structure of amorphous alumina have been conducted because a fundamental understanding of its structure can be meaningful to the design of new materials and devices. Here we focused on anodic alumina as a model material for clarifying the atomistic structure of amorphous alumina and prepared anion-free and anion-incorporated porous-type amorphous alumina by anodization using chromic acid electrolyte and typical electrolytes (e.g., sulfuric acid, oxalic acid, and phosphoric acid), respectively. The local structure around aluminum atoms in the anodic alumina was investigated by nuclear magnetic resonance spectroscopy. We found that the structure of anodic amorphous alumina comprises AlO4, AlO5, and AlO6 units with predominant fractions of AlO5. We also observed that the fraction of each unit was 37.7, 54.3, and 8.0%, with an average coordination n...

Different spectroscopic methods have been applied to investigate the chromic acid oxidation of acetaldehyde in aqueous media, catalysed by surfactants. Three representative heteroaromatic nitrogen base promoters, 2-picolinic acid (PA), 2,2’-bipyridine (bpy) and 1,10-phenanthroline (phen), have been associated along with surfactants as promoters to the kinetic study. Comparative studies of unpromoted and promoted reactions invoked that 2,2’-bipyridine produced maximum rate enhancement. The mechanism of the reaction path has been proposed with the help of kinetic results and spectroscopic studies. The observed net enhancement of rate effects has been explained with scientific manipulations and data obtained. The combination of TX-100 and1,10-phenanthroline is found to be most effective for acetaldehyde oxidation. Chromium(VI) oxidation of acetaldehyde in aqueous micellar media has been carried out. Micellar catalysis by TX-100 in association with a ‘phen’ promoter increases the rate of the reaction almost 60 fold. The combination of TX-100 and ‘phen’ is the most suitable one for chromic acid oxidation of acetaldehyde to acetic acid in aqueous media.

An efficient, simple and practical protocol for one-pot sequential oxidative radical C–H/S–H cross-coupling of thiols with hydroquinones (HQs) and oxidation leading to the formation of quinonyl alkyl/aryl thioethers using H2CrO4 was developed. This cross-coupling of thiyl and aryl radicals offers mono thioethers in good to moderate yield and works well with a wide variety of thiols. Similarly, this method works well for coupling of 2-amino thiophenol and HQs to form phenothiazine-3-ones 5a–c. C–S bond formation via thioether synthesis was observed using a chromium reagent for the first time. Theoretical studies on the pharmacokinetic properties of compounds 5a–c revealed that due to drug-like properties, compound 5b strongly binds with Alzheimer's disease (AD) associated AChE target sites.

Aluminum alloys have a considerable appeal for mechanical and building designers. This characteristic lies in the mechanical and physicochemical properties of these alloys. Aluminum is often used in the anodized surface condition to impart pleasing aesthetics, higher corrosion resistance, better scratch and wear resistance, and thus an improved value of the product. Anodization is commonly produced by direct current (DC) that offers excellent protection against wear and corrosion. This work focuses on the surface condition of a 2030 aluminum alloy treated with chromium and sulfuric acid. Our goal is to understand what happens at the surface of the Al alloy after each treatment (chromic anodizing, sulfo-chromic anodizing) using a structural characterization (MEB) that will be followed by electrochemical characterization. The results obtained have shown the effectiveness of chromic anodizing, which gives rise to the formation of a thin layer and offers excellent protection against corrosion. Chromic anodic oxidation protects an aluminum part by creating a layer of alumina Al2O3, to give it anti-corrosion, decorative and heat resistance characteristics, as well as, any chromic acid residues do not attack the base material. This is the opposite of sulfuric acid, which makes it an excellent pretreatment for aerospace parts.

Electroless copper plating on Poly(methyl methacrylate) (PMMA) is a technology that is increasingly popular and widely used in practice. Poly (methyl methacrylate) (PMMA), also known as by the trade names, Plexiglas®, is a transparent thermoplastic often used in sheet form as a lightweight or shatter-resistant alternative to glass. Especially with the transparent plastic equipment requiring high aesthetic such as equipment in the automotive industry, toilet equipment, … coating a Copper layer on the material surface simply provides the device a high aesthetic ability, which prevents dust and also easy to be cleaned. However, most of the copper plating processes on plastics use Cr6+, which is toxic to the environment. This article presents a new approach, Copper plating on PMMA through organic covalent bonding, which is both safe and environmentally responsible.

Fat embolism is the mechanical blockage of blood vessels by circulating fat particles. It is frequently related to traumas involving soft tissues and fat-containing bones. Different techniques have been used for decades to demonstrate histologically fat emboli, being the extremely toxic post-fixation with osmium tetroxide one of the most used techniques in the last decades. In the present study, the osmium tetroxide technique was compared qualitatively and quantitatively, for the first time, with chromic acid and Oil Red O frozen techniques for histological fat emboli detection in the lungs of eight sperm whales that died due to ship strikes. This was also the first time that chromic acid technique was tested in cetaceans. Results showed that the three techniques were valuable for the histological detection of fat embolism in cetaceans, even when tissues presented advanced autolysis and had been stored in formaldehyde for years. Although quantitative differences could not be established, the Oil Red O frozen technique showed the lowest quality for fat emboli staining. On the contrary, the chromic acid technique was proven to be a good alternative to osmium tetroxide due to its slightly lower toxicity, its equivalent or even superior capacity of fat emboli detection, and its significantly lower economic cost.

A composite chromium coating has been potentiostatically electroplated on high-strength stainless steel substrates from a trivalent chromium bath. The electrolyte solvent consists of 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) to which water, hexadecyltrimethylammonium bromide (CTAB), poly(diallyldimethylammonium chloride) (PDDA), and Al2O3 particles (≈3–4 μm) were added to improve the ion transport properties, the wettability at the electrolyte–substrate interface, the metallic chromium content, and the microhardness of the coating, respectively. The X-ray photoelectron spectrum of the coating reveals 85% metallic chromium and 15% chromium oxides and chromium hydroxide. Characterization of the coating shows the existence of chromium carbide-type bonds, resulting from the incorporation of carbon atoms into the chromium crystal lattice, leading to a high degree of amorphization of the coating. Optimization of electroplating conditions yielded a uniform chromium composite coating with a Vicker's microhardness of 860 (±10) HV and a thickness of 42 μm (±4), which is comparable to a chromium coating obtained from conventional chromic acid baths. Keywords: Trivalent chromium, Electroplating, XPS, High-strength stainless steel, Ionic liquid

A simultaneous demonstration of scalability, mechanochemical robustness, self-healing and hot liquid repelling features is still a major challenge in fabricating superamphiphobic coatings. In this work, we developed a facile and effective silica-inorganic adhesive-based spray coating for the preparation of self-healing and hot liquid repelling superamphiphobic coatings that demonstrate good mechanical durability (under repeated adhesive tape-peeling tests, ultrasonic treatment, sandpaper abrasion and sand flow impact tests) and superstrong chemical robustness when exposed to highly corrosive media, such as 98% sulfuric acid and 5% chromic acid, for a long time. In addition, our superamphiphobic paints can be coated on large-sized substrates to create large robust coatings for real-world applications, which are still regarded as the tightest bottlenecks in the development of superamphiphobic materials. The large coatings also showed excellent liquid repellence when placed for a long time in the outdoor environment, and upon repeatable quartz sand abrasion and treading stepping test cycles. Moreover, the anti-smudge ability, semitransparency, repeated self-healing ability, self-cleaning behaviour both in air and oil, and hot liquid repelling behavior of the resultant coatings are also investigated. Taking multifaceted stability and scalability into consideration, our described coatings are promising for more vital applications such as windows, infrastructures, crude oil pipelines, in harsh chemical engineering, etc.

To improve the tensile performance and sustainability of high-strength strain-hardening cementitious composites (SHCC), waste cement kiln dust (CKD) was used, replacing 30% of ordinary Portland cement (PC), and polyethylene (PE) fibers were modified through chromic acid and plasma treatments. The chemical structure and morphology of the PE fiber surface were modified by exposure to chromic acid and plasma treatment with two gas types, argon (Ar) and oxygen (O2), at various power levels and frequencies. The effect of surface treatment method on enhancing the tensile performance of SHCC was investigated. The surface oxidation and increased roughness of the fibers were verified through X-ray photoelectron spectroscopy and atomic force microscopy analyses. The oxygen/carbon atomic ratio and surface roughness of the PE fibers increased by up to 5.3 and 2.4 times, respectively, by the O2 gas plasma treatment. With 30% of PC replaced by CKD, 12% higher energy absorption capacity prior to tension softening could be obtained. The tensile ductility and energy absorption capacity of SHCC were significantly enhanced by using PE fibers treated with chromic acid for 10 min, approximately 145% and 64%, respectively, although its tensile strength decreased. The Ar-gas plasma effectively improved the compressive strength and tensile performance of the SHCC relative to the O2-gas plasma given an identical power level and frequency. The SHCC containing O2-plasma-treated fibers under 300 W and 40 kHz exhibited the best tensile performance and absorbed the highest energy of 310 kJ/m3, approximately two to five times greater than those of ordinary SHCC materials.

The demand for C3-C5 olefins is constantly growing, that is why it is important to improve the performance of catalysts for dehydrogenation of light alkanes. The study regards the influence of the supports porous system, the contribution of α-Cr2O3 particles to the state of the active phase and the catalytic performance of the chromia-alumina catalysts in the isobutane dehydrogenation reaction. The catalysts were synthesized by impregnating the support with chromic acid. The supports and the catalysts were studied by the following techniques: low-temperature nitrogen adsorption, temperature-programmed desorption and reduction; UV-Vis- and Raman-spectroscopy, X-ray phase and X-ray fluorescence analyses. It was found that crystals of α-Cr2O3 are formed on a support with 56 m2/g specific surface area and 7.1% (m/m) chromium content, that contributes to stabilization of the particles of highly active phases of amorphous Cr2O3 and polychromates and catalytic performance. Meanwhile, no α-Cr2O3 particles are formed on a support with a 103 m2/g specific surface area and 7.4% (m/m) chromium content. Therefore, in the course of 54 regeneration reactions cycles, the rates of isobutylene formation and isobutylene selectivity are significantly reduced due to agglomeration of amorphous Cr2O3 particles, formation of di-, tri- chromates, and migration of part of chromium into the support structure.

In this study, we use advanced analysis techniques to examine the nanostructures of anodic films formed on aluminum in various electrolytes, including oxalic acid and sulfuric acid, in the original state (without being chemically dissolved) and reveal that pores grow with radially branched nanopores. Nanopores are generated in the main pores for the same reason that initial small pores are generated on the film surface: nanopores are created when the electric field is reduced due to the presence of a thick barrier layer. These radially branched nanopores appear in a form characteristic of a film formed in chromic acid, producing a feather-like pore wall. As a representative model, the atypical porous structures created in the film formed in chromic acid were classified into five categories: initial small pores, branched pores, side holes, spherical voids, and radially branched nanopores. We demonstrate that these structures are not unique to chromic acid films but are a universal phenomenon, particularly radial nanobranching, which occurs naturally during the anodizing of most electrolytes.