Black Nickel Coatings Research Articles

Optical, structural and thermal performances of black nickel selective coatings for solar thermal collectors

In the present study, the possibility of devising efficient and durable black nickel selective coating based solar thermal collectors (STCs) at ambient temperature was explored. For this, NASA electrochemical bath initially formulated by Peterson and Lin [Final Report: NASA-CR-149928, 1976] was employed. Quality of the STCs were optimized by evaluating pH, temperature, electric current density (Id) and deposition time (Td) dependence of optical, structural and thermal performance of the black nickel coating on the copper sheets and tubes. The optical measurements in the UV–Vis–NIR and NIR-MIR ranges inferred us that at pH ≈ 5.8, temperature in the range 20–25 °C, 2 mA/cm2 ≤ Id ≤ 4 mA/cm2 and 5 min. ≤ Td ≤ 7 min. result in reasonably good black nickel coatings with optimal selectivity factor. Moreover, from the analysis of XRD spectra, for the first time we observed the significantly larger crystallites size of coatings on Cu sheets than that of the coating on tubes. Observed thermal performances (evaluated by measuring the collector efficiencies) indicate that the electro-deposited black nickel-based STCs were superior by more than 20% over black paint based STCs.

Physical and electrochemical behavior of black nickel coatings in presence of KNO3 and imidazole additives

As a unique type of nickel films, black nickel coatings possess remarkable optical and electrical properties but limited applications owing to their poor structure and corrosion resistance. In this study, black nickel coatings were electrodeposited on St37 steel and optimized utilizing nickel Watts bath modified with potassium nitrate. By investigating the coating structure and current efficiency (CE), optimum bath was determined as 190 g/L NiSO4, 25 g/L NiCl2, 30 g/L H3BO3, and 25 g/L KNO3 which resulted in CE of 79% and a compact structure. Next, cyclic voltammetry and chronoamperometric tests revealed that the dominant deposition mechanism was instantaneous nucleation. Besides studying the changes in CE and cathodic polarization, the improvement of properties with addition of imidazole was investigated by studying the surface morphology, phase structure, light absorption, and corrosion behavior using SEM, XRD, differential reflectance spectroscopy (DRS), potentiodynamic polarization, and electrochemical impedance spectroscopy tests, respectively. Adding imidazole to the deposition bath reduced the grain size and crack width from micro-scale to nano-scale, without affecting its nucleation mechanism or light absorption property. Also, imidazole enhanced the corrosion resistance of the black nickel coatings by 62% reduction of corrosion current density and increasing its polarization resistance by 58%.

Nanostructured Black Nickel Coating as Replacement for Black Cr(VI) Finish

This work compares different electrodeposition procedures to produce nickel black coatings as greener and less toxic alternatives to Cr(VI)-based coatings used in different applications. Nickel and nickel-plated brass served as substrates in studies with a Hull cell and polarization curves. After a set of comparative experiments, the best electrodeposition procedure was further studied and optimized. Optimal conditions were found with a bath consisting of 75 g/L NiCl2·6H2O + 30 g/L NaCl and a current density of 0.143 A dm−2 applied for 5 min at room temperature. Furthermore, a pre-treatment with 18.5 vol.% of hydrochloric acid in water was found to be necessary to warrant good coating adhesion to the substrate. The black color is attributed to the development of a nanostructured surface that absorbs the incident light. Corrosion testing was performed in 0.5 M NaCl aqueous solution using electrochemical impedance spectroscopy (EIS) and polarization tests.

Experimental Investigation on Properties of Surface Radiation of Solar Collector Receiver Tube Material with Black Nickel Coating

Experimental Investigation on Properties of Surface Radiation of Solar Collector Receiver Tube Material with Black Nickel Coating

Research of bi-nickel coatings obtaining process

Modern machine building industry can’t be without the use of special coatings, which allow increasing the physical and mechanical properties of the product. Nickel coatings are widely used, due to wear resistance and corrosion resistance. Black nickel coatings began to be used in solar power engineering, for efficient conversion of solar energy into thermal energy. Also nickel coatings are used in the manufacture of medical instruments. To improve the physical and mechanical properties of nickel coatings, the task was to study the possibility of creating a bi-nickel coating.

Effects of pH on the Nickel Coating Microstructure and Internal Stress from an Additive-Free Watts-Type Bath with Phytic Acid

The black nickel coatings were electro-deposited on Cu substrate in an additive-free Watts-type bath containing phytic acid. The function of phytic acid in the bath at different pH values on electrodeposition characteristics, surface morphology, microstructure, crystallographic orientation and grain size of nickel electrodeposits were systematically analyzed. In addition, the effects of phytic acid on deposit properties (microhardness, internal stress and plating color) were investigated. It is demonstrated that increasing pH promotes the preferred crystal orientation modification from (200) to (220) and refines grain size. With increasing the pH value, P element content increases. Under these circumstances, the internal stress reaches a minimum, the plating is the darkest and the microhardness is relatively high, when the pH is 4.5. The presence of phytic acid and appropriate pH value can lower the internal stress and get the dark nickel coatings.

Space qualification and characterization of high emittance black nickel coating on copper and stainless steel substrates

Black nickel coatings exhibiting high infrared emittance were developed on copper and stainless steel substrates by pulse electrodeposition using a modified Fishlock bath. The uniform jet black coating is intended to provide passive thermal control of spacecraft components. Space worthiness of the coating was evaluated by conducting a series of space environmental tests such as humidity, thermal stability, thermal cycling and thermo-vacuum performance tests. The thermo-optical properties namely solar absorptance (αS) and infrared emittance (εIR) of the coatings were measured before and after each environmental test. No significant change in thermo-optical properties was observed after environmental tests showing their high stability for spacecraft thermal control applications. The coatings were characterized by cross-sectional SEM and EDX, XRD, XPS, Nanoindentation and Nano Vision analysis. X-ray diffraction pattern reveals the amorphous nature of the coating with possible presence of ZnS. XPS analysis confirms the chemical and electronic state of the elements. Average modulus and hardness of the coating was recorded using Nanoindentation method and a high resolution 3D image of the surface was generated using Nano Vision scan.

Microstructure and properties of TiO2 sol-enhanced black nickel nanocomposite coating

Black nickel coatings are widely used in industries due to their shiny black color and other unique properties. However these coatings are normally soft, which limits their applications. In order to increase the mechanical properties of black nickel coatings, sol-enhanced technology has been applied to the plating process. TiO2 sol-enhanced black nickel nanocomposite coatings were electroplated on nickel-coated brass. A systematic study on the microstructure and properties of the black coatings were conducted. The effects of TiO2 concentration (TiO2 sol concentration in 0–20 mL/L) on the surface morphology, nanohardness and wear resistance have been studied. The results indicated that the nanohardness of the sol-enhanced black nickel coating was increased by [Formula: see text]20%. The mechanisms of improvement and surface morphology variation were also discussed.

Influence of a metallic nickel interlayer on the performance of solar absorber coatings based on black nickel electrodeposited onto copper

Black nickel is an interesting, economical, and abundant solar absorber material for low temperature solar-to-thermal energy conversion systems, and thin films can be prepared by electrodeposition. Critical parameters include the energy conversion efficiency and thermal stability, which depend on the design of the selective coating and the substrate material. In this work, we show that a metallic nickel interlayer is required in order to achieve thermal stability of black nickel coatings on copper, although the solar-to-thermal conversion efficiency for these multilayer coatings is slightly lower than for coatings of black nickel directly electrodeposited onto copper. The black nickel films were electrodeposited from a nickel chloride bath at pH 6.5 in order to avoid thermal stability issues related to the presence of sulfur. XPS and Raman spectroscopy illustrate that the composition of the black nickel film is complex, containing Ni(OH)2, NiO, NiOOH and metallic Ni. We show that the electrodeposition parameters strongly affect the performance of the selective coating.

High emittance black nickel coating on copper substrate for space applications

Black nickel, an alloy coating of zinc and nickel, is obtained on copper substrate by pulse electrodeposition from a modified Fishlock bath containing nickel sulphate, nickel ammonium sulphate, zinc sulphate and ammonium thiocyanate. A nickel undercoat of 4–5μm thickness is obtained using Watts bath to increase the corrosion resistance and adhesion of the black nickel coating. The effect of bath composition, temperature, solution pH, current density and plating time on the coating appearance and corresponding infra-red emittance of the coating is investigated systematically. Process parameters are optimized to develop a high emittance space worthy black nickel coating to improve the heat radiation characteristics. The effect of the chemistry of the plating bath on the coating composition was studied using energy dispersive X-ray analysis (EDAX) of the coatings. The 5–6μm thick uniform jet black zinc–nickel alloy coating obtained with optimized process exhibited an emittance of 0.83 and an absorbance of 0.92. The zinc to nickel ratio of black nickel coatings showing high emittance and appealing appearance was found to be in the range 2.3–2.4.

Electrodeposition of Selective Absorber Coatings Based on Black Nickel for Solar - Thermal Energy Conversion

Solar energy is the most abundant, renewable and clean energy source, and several systems exist to convert solar energy into a useful form for specific applications. One of them is the development of solar collectors based on selective coatings, with a high absorptivity in the visible and low emissivity in the near to mid infrared regions of the solar spectrum. The use of selective coatings has been widely established as an industrial practice to improve the efficiency in solar energy collection. For practical applications, a solar absorber coating with selective optical properties should be easily applicable with easy scale-up, low cost and short time of synthesis. These coatings can be applied to the collector substrate by various techniques including vacuum deposition, spray methods, sol-gel chemistry, and electrodeposition.In this work, bright and black nickel coatings were electrodeposited onto copper and stainless steel substrates with an area of 16 cm2. The experiments were performed at room temperature using electrolytes from nickel sulfate and nickel chloride salts. For the characterization of the coatings, several techniques were used, as profilometry, scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The optical properties of the coatings were measured by reflectance spectroscopy. For the evaluation of the energy conversion efficiency, the electrodeposited coatings were irradiated at 1 sun and the heating of an aqueous was measured as a function of film properties.

Black Nickel Coating and Color Anodized Layers for Solar Absorber

Solar selective absorbers are considered as an essential part of a thermal solar collector for which the optical properties are dependent upon their structure and surface morphology. In this paper, optical properties of Ni-pigmented anodized are compared with black electroless nickel coatings. The effect of heat treatment on optical properties of the coatings was also investigated. Anodized films were formed in 6 M phosphoric acid followed by a black coloration process. Scanning electron microscope was used to study the morphology, and X-ray diffraction was employed to identify the phases present. Evaluation of optical properties was carried out by spectral reflectance. Evaluation of the optical characteristics showed that Ni-pigmented anodized and black electroless samples, after heat treatment, had the highest absorption coefficient at about 0.98 as well as the lowest emission coefficient. The ξ factor reached about 6 in heat treated Ni-pigmented anodized layer and offered optimal properties in this research.

Electrodeposition and characterization of nano-structured black nickel thin films

The electrodeposition and characterization of nano-structured black nickel coatings were presented. The influences of bath pH, electrodeposition time, stirring speed, temperature and current density on the color and microstructure of the electrodeposited nickel film were investigated through naked eyes, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Meanwhile, the corrosion resistance of the optimized black nickel film was evaluated by the polarization measurement and electrochemical impedance spectroscopy (EIS) in the neutral 3.5% NaCl solution. The results show that the color of the electrodeposited nickel film was highly dependent on the above technological parameters. The operating parameters were optimized mainly according to the color. The optimized black nickel film possesses nano-structure with an average grain diameter of about 50 nm. It also exhibits enhanced corrosion resistance when compared with white nickel coatings electrdodeposited under the same condition except the variation of the electroplating current density.

Flat Absorber Phosphorous Black Nickel Coatings for Space Applications

A new process of flat absorber black nickel alloy coating was developed on stainless steel by electrodeposition from a bath containing nickel, zinc and ammonium sulphates; thiocyanate and sodium hypophosphite for space applications. Coating process was optimized by investigating the effects of plating parameters, viz concentration of bath constituents, current density, temperature, pH and plating time on the optical properties of the black deposits. Energy dispersive X-ray spectroscopy showed the inclusion of about 6% phosphorous in the coating. The scanning electron microscopy studies revealed the amorphous nature of the coating. The corrosion resistance of the coatings was evaluated by the electrochemical impedance spectroscopy (EIS) and linear polarization (LP) techniques. The results revealed that, phosphorous addition confers better corrosion resistance in comparison to conventional black nickel coatings. The black nickel coating obtained from hypophosphite bath provides high solar absorptance (αs) and infrared emittance (ɛIR) of the order of 0.93. Environmental stability to space applications was established by the humidity and thermal cycling tests.

Morphology, structure, and composition of coatings at electrodeposition of black nickel

We present the electrolyte composition and the conditions of the electrodeposition with the aim to produce black nickel coatings on the surface of a piece manufactured of steel alloy, including the inner surface of a small diameter hole (3.4–5.0 mm). The method used of the coating production involves the application of two regimes of electrodeposition from one bath containing salts of nickel and zinc, a complexing agent (ammonium thiocyanate), and boric acid. The first regime allows one to produce a fine-grained layer with a high concentration of nickel, and the second one (functional) includes a high concentration of zinc. The produced coatings also contain oxides and sulfides and are amorphous, as the X-ray analysis shows.

Electrochemical nano‐coating processes in solar energy systems

The efficiencies of electrochemically prepared nano‐thick CdS and black nickel coatings were investigated as a function of their preparation conditions in the application field of energy; such as, solar‐electricity conversion, solar cells, and solar‐thermal conversion, spectrally selective solar collectors.

Black nickel electrodeposition from a modified Watts bath

Black nickel coatings were electrodeposited on to steel substrates from a Watts bath containing potassium nitrate. The best operating conditions necessary to produce smooth and highly adherent black nickel were found to be NiSO4 · 6H2O 0.63 M, NiCl2 · 6H2O 0.09 M, H3BO3 0.3 M and KNO3 0.2 M at pH of 4.6, i=0.5 A dm−2, T=25 °C and t=10 min. The modified Watts bath has a throwing power (TP) of 61%, which is higher than that reported, not only for nickel, but also for many other metals electrodeposited from different baths. The potentiostatic current–time transients indicate instantaneous nucleation. X-ray diffraction (XRD) analysis shows that the black nickel deposit is pure metallic nickel with Ni(111) preferred orientation.

Electrocatalytic production of hydrogen on reticulated vitreous carbon

Reticulated vitreous carbon (RVC) was used as a porous cathode for the production of hydrogen gas from flowing alkaline solution. Polarization curves were measured to evaluate the overall performance of the RVC electrode. By an aid of a mathematical model, the kinetic parameters for HER at different conditions were estimated by fitting the experimental data with the model predictions. Black nickel coatings onto the RVC porous matrix reduced the potential and consequently the electric power needed for water electrolysis. The results showed also that operating the cell at high electrolyte concentrations and/or temperatures decreases the potential required to obtain a certain rate of hydrogen production. Stable current-transient and SEM micrographs were obtained after operation of the coated electrodes for a relatively long time at high rates of hydrogen evolution. This indicated that black Ni coatings did not flack off the surface after this period.

Characterization of black nickel solar absorber coatings electroplated in a nickel chlorine aqueous solution

Black nickel coatings electroplated in a nickel- and sodium chlorine aqueous solution have been prepared and parameters in the process have been optimized to achieve optimal solar selectivity. The best result is a solar absorptance of 0.96 and a thermal emittance of 0.10, as also has been obtained previously for the same type of coating [1]. Characterization by means of X-ray photo-electron spectroscopy (XPS), scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES), Rutherford backscattering (RBS) and 1H( 15N, αγ) 12C nuclear resonance reaction (NRR) have contributed with new information about surface chemical composition, morphology and atomic composition in depth profile. These investigations reveal that the coating is porous and contains mainly metallic nickel at the substrate–coating interface and mainly nickel hydroxide at the front surface. The stability of the coating has been tested regarding high-temperature and condensation at high humidity. It has been found that the solar absorptance changes initially, during the first hour of exposure at high temperature, but will then stabilize. Condensation causes a more severe attack on the coating by cracking it. This is contradictory to the results from previous tests at high temperature and humidity in which the black nickel coating was found to be resistant [1].

Electron Microscopic Investigations on the Morphology and Crystal Growth Characteristics of Black Nickel Thin Films

SummaryElectron microscopy studies were made on thin films of black nickel coatings during the initial stages of electrocrystallisation. Ni-Zn-S, Ni-Zn-Fe-S, Ni-Cd-Zn-Fe-S, and Ni-Mo-Fe-Mn were the four different types of black coatings examined. The coatings were electrocrystallised from sulphate baths with ammonium thiocyanate as the blackening agent in most experiments. Interesting morphological and crystal growth patterns were observed for the different types. Introduction of iron significantly alters the crystal growth characteristics. The mechanical and optical absorption properties of these films can be understood from the crystal growth behaviour.