Black Chromium Plating Research Articles

Facile preparation of high-performance hydrochar/TiO2 heterojunction visible light photocatalyst for treating Cr(VI)-polluted water

In order to remedy the shortcomings of narrow absorption wavelength range and low photogenerated carrier separation efficiency of TiO2 photocatalyst, hydrochar (HC) was chosen to modify TiO2 by constructing HC/TiO2 heterojunction composite. HC/TiO2 composites were synthesized from glucose, tetrabutyl titanate and deionized water by a simple one-pot hydrothermal way, and their photocatalytic Cr(VI) reduction properties were studied. The results indicated that HC/TiO2 composites had tremendously improved photocatalytic Cr(VI) reduction activity, in comparison with TiO2, HC and a number of newly reported TiO2-based visible light photocatalysts. When the mass percentage of glucose to tetrabutyl titanate was 14, the obtained HC/TiO2-2 possessed the maximal photocatalytic activity, which was 19 times that of TiO2 and 14.3 times that of HC under visible light (wavelength > 420 nm) irradiation, and 3.2 times that of TiO2 under ultraviolet-visible light (Xenon lamp) irradiation. Furthermore, the photocatalytic stability of HC/TiO2-2 was also excellent. Additionally, proper choice of the photocatalysis experiment parameters could further raise the photocatalytic Cr(VI) reduction efficiency of HC/TiO2-2. The exceptionally elevated photocatalytic activity of HC/TiO2-2 was found to be due to its type-II heterojunction structure, which drastically heightened the separation and transfer efficiencies of photogenerated electrons and holes. Besides, HC/TiO2-2 also showed great potential for practical application in photocatalytic treatment of the Cr(VI) effluents discharged from freezing brine and black chromium plating industries.

Synthesis and application of Fe3O4/FeWO4 composite as an efficient and magnetically recoverable visible light-driven photocatalyst for the reduction of Cr(VI)

Fe3O4/FeWO4 composites with different compositions were synthesized via hydrothermal way, and characterized by many compositional and structural analysis techniques. 20% Fe3O4/FeWO4 showed the highest efficiency in photocatalytic reduction of aqueous Cr(VI) under visible light (λ > 420 nm) irradiation. Its photocatalytic rate is about 4.4 times as that of Fe3O4 and 1.5 times as that of FeWO4. Moreover, its photocatalytic stability was also good. According to the photoelectrochemical test results, the photocatalytic improvement mechanism of 20% Fe3O4/FeWO4 was proposed. Results from photocatalytic treatment of diluted black chromium plating solution (DBCPS) indicated that 20% Fe3O4/FeWO4 had noteworthy activity in visible light-driven photocatalytic reduction of DBCPS over a wide range of pH (3–11), but its photocatalytic efficiency was higher at lower pH. Besides, 20% Fe3O4/FeWO4 had fairly strong magnetism and could be recovered efficiently using a magnet. Hence, Fe3O4/FeWO4 composite photocatalyst holds potential for application in the treatment of Cr(VI) wastewater.

An experimental study on the effect of salt spray testing on the optical properties of solar selective absorber coatings produced with different manufacturing technologies

Solar selective absorber coating (SSAC) is one of the key components of a solar collector, with its optical properties having a significant impact on the collector’s thermal performance. The key parameters characterizing the optical properties of an SSAC are the solar absorptance (absorptance of solar radiation) and the thermal emittance (emittance for long-wave radiation). However, some of high-performing SSACs suffer from some drawbacks, such as lower durability, lower resistance to corrosion and abrasion, which is particularly harmful for SSACs, as, for example, chlorides in the atmosphere have become a main contributor to corrosion in coastal areas with the increasing trend of global warming. In this paper, salt spray tests have been conducted on the SSACs manufactured by three common manufacturing technologies, i.e., the anode oxidation (AO) technology, the vacuum magnetron sputtering (VMS) technology, and the black chromium plating (BCP) technology, over the testing durations of 12 h, 24 h, 36 h, and 48 h, respectively, to examine the effect of the salt spray testing on the optical properties of SSACs manufactured by different manufacturing technologies. The salt spray testing is an accelerated aging testing method for evaluating the SSAC’s resistance to corrosion when it is under an extended exposure to a saline, or salted, spray (fog). The experimental results show that, in general, the SSACs manufactured by the BCP technology have excellent resistance to salt spray (i.e., to corrosion) and those manufactured by the AO technology have only reasonable resistance to corrosion, whereas the SSACs manufactured by the VMS technology have very poor resistance to corrosion. The results also demonstrate that there are noticeable differences in the optical properties of the SSAC samples even manufactured by the same technology but by different manufacturers, with some having significant differences. The causes for the differences have been further examined through the inspection of the physical appearance of the selected SSAC samples and the experimentally measured distributions of the monochromatic reflectance of solar radiation of the samples over the solar spectrum before and after the salt spray testing over different durations.

The use of trivalent chromium bath to obtain a solar selective black chromium coating

Abstract Black chromium coatings were electrodeposited from a trivalent chromium bath using a ZnO additive as a second main component. Black chromium was electrodeposited on steel and copper plates and substrates plated with bright nickel prior to black chromium electrodeposition. The black chromium coatings were characterized by XRD and SEM. The XRD data suggest that the phase structure of black chromium may be defined as a zinc solid solution in chromium or a chromium solid solution in zinc depending on the chromium/zinc ratio in the deposit. The role of substrate finish was evaluated through the corrosion resistance and reflectance of black chromium. According to corrosion tests the samples plated with bright nickel prior to black chromium deposition have shown the highest corrosion resistance. The electrodeposited black chromium possesses good optical properties for the absorption of solar energy. The absorption coefficient of black chromium was found to be over 0.99 for the samples obtained without the Ni undercoat and below 0.99 for those obtained with the use of Ni undercoat. However, the use of nickel undercoat before black chromium plating is recommended because it remarkably improves the corrosion resistance of samples.

Chromium electrodeposition from [BMIm][BF4] ionic liquid

The electrodeposition of black chromium coatings from ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate with chromium chloride, and the chemical composition of the deposits are discussed in this article. The UV–Vis spectra recorded for chromium(III) species in 1-butyl-3-methylimidazolium tetrafluoroborate suggest that along with the chromium(III) complexes containing three ligands, there are some amounts of chromium species containing four ligands in the bath employed. The cathodic process of chromium electrodeposition in the employed ionic liquid is complicated by the electrochemical reduction of water molecules, which is followed by chemical disintegration of tetrafluoroborate ions. The surface morphology of black chromium films deposited potentiostatically (–1.5 to −2.0 V) at 85 °C shows nodules and microcracks increasing in size with cathodic potential. Analysis of the X-ray photoelectron spectra recorded from surface to depth of the deposit has shown that the black oxide-rich chromium coating consists of chromium in both oxide and metallic states with small impurities of other elements (fluorine, boron, carbon and nitrogen) and the surface is covered with a thin layer of organic substances. The results of this study show that 1-butyl-3-methylimidazolium tetrafluoroborate may be considered as a promising substitute of toxic Cr(VI) baths for black chromium plating.

Investigation of the structure and the physical properties of nickel-phosphorus ultra-black surfaces

Ultra-black materials with low reflectivity can be applied in many fields of science and technology. We deposited nickel-phosphorus alloys (Ni-P) on copper substrate with the electroless plating method and etched the electroless plating with nitric acid in order to build ultra-black surface. On the one hand, the components of the Ni-P ultra-black surface layer were investigated by XRF and XPS. SEM represented that there are innumerable conical holes with the different diameters on the surface. XRD showed that the whole surface has become amorphous. On the other hand, compared to electroless blackening film by oxidation and black chromium plating materials, the Ni-P ultra-black surface showed lower wavelength dependence and lower reflectance in the range of 380–780 nm. In addition, the temperature of the sample with the Ni-P ultra-black surface increased more highly and quickly compared to the black chromium plating film after exposure in an IR laser for about half an hour.

表面処理による黒色化技術 １ 黒色クロムめっきの原理と応用

表面処理による黒色化技術 １ 黒色クロムめっきの原理と応用

The present status of black chromium plating

Black coatings, and particularly black chromium coatings, have many applications in various fields, e.g. as non-reflecting coatings, decorative coatings and solar-selective coatings. Most of the studies on black chromium plating that have been reported to date are reviewed in this paper. Both the bath compositions and the process details for obtaining various black chromium finishes are given. The nature of the black chromium deposit is discussed with particular reference to its thermal, optical, structural and physical properties. The applications of black chromium coatings are indicated.

定電位法によるクロム酸溶液の分極特性

Polarization characteristics of the solution of chromic acid were examined by current-time curves determined by potentiostatic method. The following results were obtained:1) The electrodeposition of black chromium plating gradually proceeded in the aqueous solution of single chromic acid, but the deposition was remarkably promoted by addition of a small amount of fluorides.2) In the solution containing fluorides, the tendency to deposit black chromium plating was greater with the drop of the bath temperature and that to deposit metallic chromium plating was greater with the rise of the bath temperature.3) In the solution containing sulfuric acid, the electrode reaction for electrodeposition of chromium was more promoted with the drop of the bath temperature.

純クロム酸溶液中での陰極分極特性

The cathodic polarization characteristics of pure chromic acid solution were measured by potentiostatic method for the investigation of its chathodic reaction.The following results were obtained:1) Electro-deposition of metallic chromium appeared in the chromic acid solution to which anions had been added in the potential range of the 4th branch on the polarization curve; whereas, in pure chromic acid solution, deposition of hydrated chromium oxide film appeared at first, and subsequently black chromium plating occurred.2) Significant hysteresis was observed in pure chromic acid solution when in was polarized to the potential range of the 4th branch.

黒色クロムメッキの研究

In an attempt to carry out the electrodeposition of black chromium from chromic acid-oxalic acid bath, several investigations were made by means of Hull cell test and plating test.The results obtained were summarized as follows.(1) The electrolyte was prepared by dissolving one or more of sulfuric acid, sodium fluosilicate, ammonium persulfate, sodium thiosulfate, ete. in chromic acid-oxalic acid solution and further dissolving nitric acid and its salts in the above bath. Black chromium plating having excelent throwing power and uniform color tone was obtained from the above electrolyte. It was important under these conditions that the concentrations of both chromic and oxalic acids in the bath should be kept constant during the electrolysis.(2) When the temperature of electrolyte for obtaining black chromium plating was lower, the available range of current density was wider. The optimum current density was found in the range of 10-30amp./dm2.

ケイフッ酸系黒色クロムメッキ浴による黒色クロムメッキの結晶構造

There have been no complete researches on the crystal structure of black chromium deposit from the plating bath containing hydrogen silicofluoride. The authors studied these crystal structures by microstructures and electron diffraction pattterns for explaining relationship between physical properties and structures of the deposits.As the results, it was found that the black chromium plating layer consisted of laminated structure, in which the upper layer was peeled off from the lower one. The upper layer was a black deposit consisting of Cr2O3 which contains Cr (body-centered cubic). However, these crystallizations depended upon plating conditions; when the bath temperature and current density were higher, the crystallization was more accelerated and the growth of single crystals (Cr2O3) was also more developed. In these conditions, deposits were likely to be more easily cracked owing to the growth of other complicated chromium oxides or metastable hexagonal chromium crystals on the boundaries of these Cr2O3 single crystals.The lower layer was a grayish black thin layer, consisting of Cr2O3 of body-centered cubic lattice or hexagonal system which contains various other chromium oxides.Cr2O3 had crystal structure of hexagonal system and was cleaved along (100) plane and peeled off on (001) base plane.Hardness and abrasion resistance of the black chromium deposit depended upon composition and structure of these crystals, and the cracks of the deposit were formed along the cleavage planes of Cr2O3 single crystals.

ケイフッ酸系黒色クロムメッキ浴の改良

Addition of nitric ions to the black chromium plating bath containing hydrogen silicofluoride was most effective for blackness of platings as described in the previous report (Part 2). Then, platings from the bath containing hydrogen silicofluoride and nitric ions were studied and it was observed that the bath was very stable and gave platings, having extremely good characteristics.The results obtained were as follows.(1) Thermal resistance: Resistant at 500°C for 5hr. on nickel plated substrate.(2) Adhesion: Satisfactory results in tape-test and 180° bending test.(3) Wear resistance: Lower than that of nickel platings, and much lower than that of chromium platings (equivalent to a few divisions of the latter).(4) Hardness: Lower than that of nickel platings.(5) Adhesion of paints: Satisfactory results for some kinds of paints.(6) Corrosion resistance: No rust was observed in continuous salt-spray test for 64hr.

ケイフッ酸系黒色クロムメッキ浴の検討

Various kinds of black chromium plating baths have hitherto been reported in literatures. However, the bath composition is not yet established in actual practice at present. Physical and chemical properties of these deposits and the mechanism of their coloration are not also thoroughly researched.The authors examined black chromium plating baths in the literatures and found out that the bath containing hydrogen silicofluoride gave the plating with least powdery deposit and strongest adhesion; but its unevenness in color was most enormous among the platings from these kinds of baths.Plating conditions for the most even black color were researched and the following results were obtained.(1) The optimum composition of bath and plating conditions were as follows:CrO3 300g/l Bath temperature above 10°CH2SiF6 above 1g/l DK 30-50amp./dm2(2) Sulfuric acid should completely by removed, because its presence limited the range of black color. Hydrogen silicofluoride should be supplied to the bath according to its electrolytic comsumption.(3) Higher throwing power was obtained by coating the substrate with copper or nickel, and then, immediately plating black chromium on that coating.

ケイフッ酸系黒色クロムメッキ浴の添加剤

Bath composition and plating conditions of black chromium plating bath containing hydrogen silicofluoride were given in the previous report (Part 1). The addition of hydrogen silicofluoride to this bath was intended to give higher blackness and evenness in coloration but these effects were not com- plete in the results.Then, effects of further addition agents to the above bath were studied and found that the addition of nitric and formic ions among acid radicals and barium ion among metallic ions was most effective for color in platings; and no other agents were effective.Bath composition and plating conditions for giving the most even and black coloration were as follows:Cr2O3……300g/lH2SiF6……1g/lAddition agents……3-5g/lBath temperature……above 10°CDk……30-50amp./dm2