Chromic Acid Solution Research Articles

ABS 수지상의 도금층 형성을 위한 에칭 방법 연구

In the present study, we successfully developed an eco-friendly chemical etching solution and proper condition for plating on ABS material. The mechanism of forming Ni plating layer on ABS substrate is known as following. In general, the etching solution used for the etching process is a solution of chromic acid and sulfuric acid. The etching solution is given to the surface resulting in elution of butadiene group, so-called anchor effect. Such a rough surface can easily adsorb catalyst resulting in the increase of adhesion between ABS substrate and Ni plating layer. However a use of chromic acid is harmful to environment. It is, therefore, essential to develop a new alternative solution. In the present study, we proposed an eco-friendly etching solution composed of potassium permanganate, sulfuric acid and phosphoric acid. This solution was testified to observe the surface microstructure and the pore size of electrical Ni plating layer, and the adhesive correlation between deposited layers fabricated by electro Ni plating was confirmed. The result of the present study, the newly developed, eco-friendly etching solution, which is a mixture of potassium permanganate 25 g/L, sulfuric acid 650ml/L and phosphoric acid 250ml/L, has a similar etching effect and adhesion property, compared with the commercially used chromium acid solution in the condition at for 5 min.

PC/ABS 블렌드의 고속전단성형에 따른 모폴로지 변화에 관한 연구

본 연구에서는 PC/ABS 블렌드를 고속전단성형법을 사용하여 제조하였고 스크류 회전속도와 전단부하시간을 공정 변수로 하여 이에 따른 블렌드의 모폴로지 변화를 분석하였다. 블렌드의 모폴로지 및 ABS 분산상의 크기를 주사전자현미경으로 관찰하여 안정한 상 구조와 최적의 물성을 가지는 고속전단성형조건을 확립하였고, 전단응력에 의한 블렌드의 열화 현상을 알아보기 위해 기계적 물성의 변화를 측정하였다. 이 때, 스크류 회전속도는 500 rpm에서 3000 rpm까지 변화시켰으며 전단부하시간은 10초에서 40초까지 주었다. 고속전단성형법을 사용하여 제조한 PC/ABS 블렌드 및 고속전단성형을 가하지 않은PC/ABS 컴파운드의 분산상 크기를 명확하게 관찰하기 위하여 블렌드의 단면에 크롬산 수용액을 이용한 에칭공정을 시행하였고 공정 전후의 모폴로지를 비교 분석하였다. 에칭으로 생긴 블렌드 내의 ABS 홀을 이미지 측정 프로그램인 Image J를 이용하여 측정한 결과, 스크류 회전속도에 따라 그 크기가 감소하였으며 특히 1000 rpm 이상의 스크류 회전속도 하에서 제조된 PC/ABS 블렌드의 경우, 기계적 물성이 급격하게 감소하여 블렌드의 분해가 일어났음을 알 수 있었다. 결과적으로 PC/ABS 블렌드에 1000 rpm의 스크류 회전속도를 가한 경우, 나노미터 단위의 분산상을 가지며 가장 안정한 상구조를 관찰할 수 있었고 인장강도 및 신율도 상대적으로 높아서 PC/ABS 블렌드의 최적 고속전단성형조건이라 할 수 있다. The PC/ABS blends were manufactured with high shear rate processing. Changes of the blend morphology were analyzed according to the screw speed and processing time. To find optimal conditions of the high shear rate processing of the PC/ABS blend, blend morphology and size of the dispersed phase, ABS, were observed with a SEM. Also, tensile properties of the PC/ABS blends were measured to investigate the effect of the high shear rate process with the screw speed of 500 rpm to 3000 rpm for processing times of 10s to 40s. Especially, to observe the dispersed phase of the PC/ABS blend clearly, fracture surfaces of the PC/ABS blend were etched with chromic acid solution. As screw speed and processing time increase, dispersed phase size of the PC/ABS blend decreases and mechanical properties of the blend decrease as well. Especially, at screw speed over than 1000 rpm of high shear rate processing, mechanical properties of the PC/ABS blends decrease drastically due to the degradation of the blend during the high shear rate processing. Consequently, the optimal condition of screw speed of the high shear processing of the PC/ABS blend is set at 1000rpm, in this study. Under optimal condition, the PC/ABS blend has relatively high mechanical properties with the relatively stable micro-structure having nanometer scale dispersed phase.

Electropolishing of Kovar Alloy for Vacuum Applications

Kovar (53% Fe – 29%Ni - 17% Co) is one of the most commonly used materials in high vacuum applications which quite often require electrical isolation(s). Kovar has thermal expansion coefficient close to that of alumina over the range from brazing to cryogenic temperatures. Therefore, joining problems due to difference in thermal expansion coefficients can be minimized when alumina and Kovar alloy are used together. For the applications that require long vacuum life, Kovar parts should have smooth surfaces to minimize outgas from the surface due to inadequate cleaning. The surface modifications obtained by electropolishing, i.e., preferentially dissolving macroscopic and microscopic surface roughness without grain attack in the depressions, and surface metal oxide layer dissolution [1,2], are indispensable in high vacuum applications. Electropolishing has also long been proven to be a powerful tool for complex parts that are difficult to polish mechanically. Although it is widely used in the vacuum industry, there is very limited information about the Kovar electropolishing in the literature. There is no systematic study known by the authors that aims to reveal the optimum electropolishing conditions for the Kovar alloy.A two-electrode linear sweep voltammetry was conducted in a solution of acetic acid, chromic acid and water mixture, where a copper plate was used as the counter and reference electrode. A plot of current density versus applied potential given in Figure 1 was obtained at 9°C. In the light of almost constant current density, namely limiting current plateau region observed in this plot, some experiments were conducted at 30 V for durations of 30, 60, 90 and 120 seconds. Rectangular Kovar samples of 15x15 mm dimensions having about 0.50 μmRa initial surface roughness were electropolished to final surface roughness of about 0.25 μmRa. The surface roughness profiles and their microstructures before and after electropolishing process (EP) are given in Figures 2 and 3, respectively.Figure Captions:Figure 1: Current density vs. potential graph in acetic acid, chromic acid and water mixture.Figure 2: Surface profiles of samples, (a) before and (b) after EP. The horizontal and the vertical scales are embedded to left hand side.Figure 3: Microstructures of samples, (a) before and (b) after EP.

A comparative Study of Different Electrolytes for Obtaining Thick and Well-ordered nano-porous Anodic Aluminium Oxide (AAO) Films.

A comparative study has been carried out to find best electrolyte for obtaining thick and well-ordered nano-porous Anodic Aluminium Oxide (AAO) films using diluted Chromic, Oxalic, Phosphoric and Sulphuric acid solutions. The top view pore structure ordering and thickness of the AAO films have been determined from Field-emission Scanning Electron Microscopy. Extent of ordering is evaluated by comparing Fast Fourier Transforms (FFT) of the top view SEM images. It was found that films anodized in Oxalic acid are thickest and degree of pore ordering in this case is also highest.

Electrochemical characterization of chromate free conversion coatings on electrogalvanized steel

The chromate conversion treatment is widely used, but it requires highly toxic chromic acid solutions with the consequent effluent disposal and ecological problems. The removal of these toxic chemicals is considered a priority within European Union. The corrosion resistance of three alternative treatments applied on electrogalvanised steel, and immersed in aerated 0.3 M Na2SO4 solution, pH 10, at 25 °C, was investigated using electrochemical techniques. Their performance was compared with the obtained using the traditional Cr6+-based treatment in the same conditions. The achieved results show that the alternative coatings exhibited discrete protective properties in the sulphate solution. The nitro-cobalt chemical conversion treatment showed similar protective properties than the traditional Cr6+-based treatment, while with the Cr3+-based treatment those were very poor. The phosphate treatment initially performed acceptably but as the time elapsed, its protective properties decreased.

Experimental investigation of pool boiling heat transfer and critical heat flux of nanostructured surfaces

The present study aims to investigate the effect of pool boiling on nanostructured surfaces. For this purpose, nanocoating was performed on aluminum surface specimens by anodizing and their boiling heat transfer characteristics were compared with those of bare surface of aluminum. Also, the critical heat flux and boiling heat transfer coefficients were evaluated experimentally. Chromic acid and sulfuric acid solutions were utilized as the electrolytes. Prior to anodizing, sandblasting and etching were applied as mechanical and chemical treatments of the surfaces. The coating was performed over three different durations. The maximum critical heat flux was observed to occur in samples which had been weakly etched and anodized for 30min in the sulfuric acid solution. Critical heat flux increased by 8% compared with that of the untreated aluminum alloy surface. Also, boiling heat transfer coefficient increased by 159% in weakly etched samples. In order to investigate surface characteristics, contact angle and atomic force microscope (AFM) images were used. The surface roughness and real area were measured in six samples. The AFM images indicated that surface roughness increased with anodizing time. The change in roughness was more pronounced in surfaces treated in the chromic acid solution compared with those treated in the sulfuric acid solution.

Indirect Wafer Bonding and Epitaxial Transfer of GaSb-Based Materials

Results from a study of indirect wafer bonding and epitaxial transfer of GaSb-based materials are presented. Benzocyclobutene (BCB) was used as a bonding agent to bond GaSb and epitaxial structures lattice matched to GaSb onto Si, GaAs, and sapphire carrier substrates. To better understand sources of stress during the bonding process, which can result in cracking and subsurface damage of the GaSb-based materials, BCB’s hardness and reduced elastic modulus were measured at various stages during the curing process. Based on the results of curing experiments, a bonding and epitaxial transfer process for GaSb-based materials was then developed. Following bonding, using an experimentally determined low-stress cure cycle, GaSb substrates were removed from epitaxial layers of InAsSb using a combination of mechanical thinning and polishing followed by selective chemical etching using a hydrofluoric and chromic acid solution. Etch selectivity data are also presented where selectivity greater than 100:1 is achieved for GaSb:InAsSb.

Self-assembled nanostructured composites for solar absorber

Nanostructured composites designed for highly efficient solar energy absorption and conversion were studied. Self-assembled nanostructure was constructed on the Fe–Cr–Ni alloy surface directly through electrochemical treatment by applying potential of wave pulse in a mixed solution of sulfuric and chromic acid. The surface structure, featuring 2D quasi-periodic nano-needle array, was composed by a mixture of spinel oxides of the substrate elements. Film of this structure displays absorptivity of 99% over the solar spectrum (0.3–1.5μm), with low thermal emission in the IR region. The high selective absorption capability of nanostructured composites realizes efficient energy conversion and could be accepted in practice.

Study of the effects of the applied current regime and the concentration of chromic acid on the transport of Ni 2+ ions through Nafion 117 membranes

In the present work galvanostatic experiments are conducted with an electrodialysis cell in order to study the passage of Ni 2+ ions present in chromic acid solutions through a Nafion cation-exchange membrane. The competing transport between H + and Ni 2+ ions through the membranes has been studied under the imposition of under- and overlimiting currents. Results show an increasing competence between both ions when the concentration of protons exceeds that of the Ni 2+ ions. Increased nickel removal rates and current efficiency values were achieved with intensive current regimes due to the onset of electroconvection. However, at low values of the [Ni 2+]/[H +] ratio, this improved transfer through the membrane implies high values of specific energy consumption due to increased membrane voltage drops, thus decreasing the convenience of applying overlimiting currents. The obtained results are related to the values of plateau length calculated from the polarization curves of this membrane/electrolyte system and prove that Ni 2+ ions promote the arising of electroconvective vortices, whereas H + ions hamper electroconvection.

Determination of transport properties of Ni(II) through a Nafion cation-exchange membrane in chromic acid solutions

The transport properties of a cation-exchange membrane in the presence of nickel sulphate solutions were investigated by means of chronopotentiometry. The interest of this study relies on the application to the treatment of chromium plating rinse baths. The presence of chromic acid in the solutions and the initial concentration of nickel sulphate affect significantly the shape of the chronopotentiograms. The different shape of chronopotentiograms as well as the values of different parameters is thereby justified by the calculation of the speciation diagrams of Ni(II). Parameters like the limiting current density, resistance of the ohmic region, plateau length, and nickel transport numbers through the cation-exchange membrane were calculated from the chronopotentiometric and the current–voltage curves. The obtained results show an important competence between Ni 2+ and H + ions, with increases of the nickel transport numbers when the [Ni 2+]/[H +] ratio corresponding to the initial equilibrium exceeds the unity. The increase in the Ni 2+ concentration brings about a facilitated arising of electroconvection, which promotes overlimiting currents and additional mixing at the membrane surface.

Some considerations of conductivity and ion species for chromic acid electrodeposition solutions

Measurements of solution conductivity are reported for chromic acid solutions typical of those used in chromium electroplating. Optimum concentrations for conductivity are noted (450 g L−1) and the temperature ranges of ion dominance have been discussed including the use of ion colours in solution. It is concluded that practical solutions normally have trichromate and tetrachromate ions as dominant species.

Effect of surface treatment on the post-peak residual strength and toughness of polypropylene/polyethylene-blended fiber-reinforced concrete

This study involved an experimental investigation into the improvement of mechanical properties of fiber-reinforced concrete (FRC) utilizing chemically treated polypropylene/polyethylene fibers. Four types of chemical surface treatments were examined: two types of chromic acid (Types B and C), potassium permanganate (PP), and hydrogen peroxide solutions. Untreated and treated fibers were added at 0.32% by volume of concrete and also at 0.50% for the best treatment technique. Compressive and flexural strength were measured to quantify improvement. It was found that there were no significant differences in compressive strength. Type B chromic acid solution was found to be the most effective technique in improving the flexural strength of FRC resulting in average increases of 8.9% and 17.6% for peak and residual strengths, respectively, compared to nontreated fibers. While not as effective as plasma treatments, further research may be warranted for chemical treatments. Surface wettability of the treated fibers was measured by contact angle with water. The contact angle was found to have no correlation to the toughness. The higher volume of fibers, both treated and nontreated gave higher residual strength and toughness; however, surface treatment did not significantly enhance mechanical properties.

Nafion-117 Behavior during Cation Separation from Spent Chromium Plating Solutions

This study investigated the behavior of Nafion-117 ion-exchange membranes that are commonly used as the separator in electrolytic regeneration of spent chromium plating solutions. In the co-presence of Cu2+, Ni2+, and Fe3+ impurities (∼0.01−0.1 M) in ∼0.5−2.0 M H2CrO4, the exchange equivalents of Ni2+ by Nafion-117 was double that of Cu2+ (0.02 mmol of H+/(g of Nafion)) but smaller than that (∼0.03−0.15 mmol of H+/(g of Nafion)) of Fe3+, exhibiting the order Fe3+ ≥ Ni2+ ≥ Cu2+ in Nafion affinity. The water content (∼41%) of a Nafion-117 membrane soaked in 2 M H2CrO4 was greater than those (∼35−38%) in the contaminated 2 M chromic acid solutions, whereas the porosity (0.24) of the former was smaller than those (0.29−0.37) of the latter. For the Nafion-117 in 2 M chromic acid solutions with/without cation impurities, (1) the tortuosity coefficient of Fe3+ was about 1.8 times that of Cu2+ or Ni2+, (2) the calculated pore radius was 3.2 nm for a multiimpurity case (0.1 M Cu(II), Fe(III), Ni(II), and Cr(III) e...

Continuous electrodeionization for removal and recovery of Cr(VI) from wastewater

Continuous electrodeionization (CEDI) was investigated for removal and recovery of Cr(VI) from synthetic wastewater. Different anion exchange resins, including the gel strong-base resin, gel weak-base resin, macro-porous strong-base resin, and macro-porous weak-base resin, were examined. The gel strong-base resin was found to be the best one for use in CEDI. It was shown that CEDI could remove and recover Cr(VI) effectively from wastewater. After treatment, Cr(VI) concentration was reduced from initial 40–100 mg/L to 0.09–0.49 mg/L, and a pure chromic acid solution containing Cr(VI) as high as 6300 mg/L Cr(VI) was obtained. The current efficiency and energy consumption was 16.1–18.8%, and 4.1–7.3 kWh/mol Cr(VI), respectively.

Aging Time Effect on the Formation of Alumina Nanowires on AAO Templates

This article presents the fabrication of alumina nanowires by etching AAO templates using chromic acid solutions. Our work has shown that an aging process in the ambient atmosphere for a relatively long time is indispensable to obtain uniform, small diameter alumina nanowires, which may be due to the release/redistribution of internal stresses of AAO template. The study of the formation mechanism leads to the optimization of the fabrication procedure. Alumina nanowires with a diameter of 5–10 nm have been achieved with a very good uniformity, an excellent surface coverage, and a relatively large BET surface of ∼ 50 m 2 /g.

Interfacially polymerized thin film composite membranes on microporous polypropylene supports for solvent-resistant nanofiltration

Interfacial polymerization (IP) is a powerful technique for fabrication of thin film composite (TFC) membranes. The polymers used most often as support are polysulfone (PS) or polyethersulfone (PES). These supports have limited stability in organic solvents. In this work, microporous polypropylene (PP) flat film and hollow fiber membranes were used as a support to fabricate TFC membranes for nanofiltration by the IP technique. Porous polypropylene membranes can provide substantial chemical, pH, and solvent resistance and are therefore suitable as supports for fabricating TFC membranes functioning as solvent-stable nanofiltration membranes. The surface and the pore interior of polypropylene flat sheet and hollow fiber membranes were hydrophilized first by pre-wetting with acetone followed by oxidation with chromic acid solution. A standard procedure to successfully coat the hydrophilized flat film and hollow fiber membranes was developed next. The monomeric system chosen for IP was poly(ethyleneimine) and isophthaloyl dichloride. The TFC hollow fiber membranes were characterized by nanofiltration of safranin O (MW 351) and brilliant blue R (MW 826) dyes in methanol. Rejection values of 88% and 43% were achieved for brilliant blue R and safranin O, respectively at a transmembrane pressure of 413 kPa in the TFC hollow fiber membranes. Pressure dependences of the solvent flux and solute rejection of the TFC membranes were studied using the modified flat sheet membranes up to a pressure of 965–1241 kPa. Solvent flux increased linearly with an increase in the transmembrane pressure. Solute rejection also increased with an increase in the transmembrane pressure. All modified membranes were also characterized using scanning electron microscopy. Extended-term solvent stability of the fabricated membranes was studied in toluene; the membranes demonstrated substantial solvent stability in toluene.

Electrochemical Behavior of Chemical Conversion Coated Aluminum ASA6061 in Chromic Acid

The corrosion behavior of bare and chemical conversion coated (through anodizing) aluminum ASA 606 I in stagnant chromic acid solutions . Solutions of 2, 6 & J O wt. % Cr03 at 45°C, have been investigated using polarization technique. The anodizing experiments were conducted under fixed conditions of 35 minute exposure time and 30 volt supplied voltage. The most important feature achieved was the great difference in behavior between the anodic polarization curves for bare and anodized aluminum in different concentrations of chromic acid solutions.

Composition analysis of the plating on electrolytically treated steel sheets in chromic acid solution

The structure and composition of the chromium plating on Tin Free Steel (TFS) were investigated and analyzed with scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDS), X-ray photoelectron spectroscopy (XPS) and coulometric electrolysis method. The plating under investigation was manufactured by a two-step electrolytic reduction from a chromic acid solution. Experimental results showed that the plating on TFS had a two-layer structure. Moreover, two valences of chromium, three and zero, were detected in the plating and no hexavalent chromium was found in it. Correspondingly, all chromium in the outer layer was trivalent and existed as the form of Cr 2O 3 and Cr(OH) 3, the content of which was about 6.62 mg/m 2, while the pure metallic chromium was the only form of chromium found in the inner layer with the content of about 57.75 mg/m 2. In addition, the amount of O existed as M–OH was twice as that of M–O in the above-mentioned hydrated chromium oxide layer.

A study of direct- and pulse-current chromium electroplating on rotating cylinder electrode (RCE)

Direct- and pulse-current (DC and PC) chromium electroplating on Cr–Mo steel were performed in a sulfate-catalyzed chromic acid solution at 50°C using a rotating cylinder electrode (RCE). The electroplating cathodic current densities were at 30, 40, 50 and 60Adm−2, respectively. The relationship between electroplating current efficiency and the rotating speed of the RCE was studied. The cross-sectional microstructure of Cr-deposit was examined by transmission electron microscope (TEM). Results showed that DC-plating exhibited higher current efficiency than the PC-plating under the same conditions of electroplating current density and the rotating speed. We found the critical rotating speed of RCE used in the chromium electroplating, above this rotating speed the chromium deposition is prohibited. At the same plating current density, the critical rotating speed for DC-plating was higher than that for PC-plating. The higher plating current density is, the larger difference in critical rotating speeds appears between DC- and PC-electroplating. Equiaxed grains, in a nanoscale size with lower dislocation density, nucleate on the cathodic surface in both DC- and PC-electroplating. Adjacent to the equiaxed grains, textured grains were found in other portion of chromium deposit. Fine columnar grains were observed in the DC-electroplated deposit. On the other hand, very long slender grains with high degree of preferred orientation were detected in PC-electroplated deposit.

Alumina nanostructures prepared by two-step anodization process

Alumina nanostructures were obtained by two-step anodization process. The porous anodic aluminum oxide(AAO) membranes were anodized in oxalic acid, which was subsequently treated with chemical etching process with 1.0 mol/L sodium hydroxide solution, or mixed solution of phosphoric acid (6.0%) and chromic acid (1.8%), respectively. Field emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM) were employed to character the morphology and structure of the obtained alumina nanostructure. It is found that alumina nanowires are generated in the acidic chemical etching solution, while nanotube structures are formed in the alkaline solution. The influence of acid and alkaline solution on alumina morphologies in the chemical etching process was discussed.