Bath Constituents Research Articles

Ammonia Borane Oxidation at Gold Microelectrodes in Alkaline Solutions

Borane-based electroless plating baths are of interest in many microelectronics applications such as barrier and capping layers for copper integrated circuit interconnect. To optimize the plating baths a thorough understanding of the role of the bath constituents is required. To this end we have employed microelectrodes to investigate the oxidation mechanism of boranes in alkaline solutions. In this paper we present data for the simpler ammonia borane (AB) oxidation and compare it with the previous analysis of dimethylamine borane (DMAB) oxidation. Both AB and DMAB are shown to oxidize in two steady-state mass transport-controlled oxidation waves for specific concentration ranges. Particular emphasis is placed on the analysis of the second oxidation wave observed at less negative potentials and the differences observed in the analysis of AB and DMAB in this potential region. The potential range for oxidation, the optimum concentration, and a suggested mechanism for oxidation are shown.

DMAB Oxidation for Electroless Deposition from Alkaline Solutions

Dimethylamine borane (DMAB) has been used as a reducing agent in electroless baths for many years. There has been an increased interest in DMAB-based electroless baths recently for applications in microelectronics such as barrier/capping layers for copper IC interconnect. To optimise the plating baths a thorough understanding of the role of each of the bath constituents is required. To this end we have employed microelectrodes to investigate the oxidation mechanism of boranes in alkaline solutions. In this paper we present data for DMAB and the simpler ammonia borane (AB) to assist in the analysis of borane oxidation in alkaline solutions. Both DMAB and AB are shown to oxidise in two steady state mass transport- controlled oxidation waves for specific concentration ranges. The potential range for oxidation, the optimum concentration and a suggested mechanism for oxidation are shown.

A new condensation product for zinc plating from non-cyanide alkaline bath

Zinc electroplating from non-cyanide alkaline solution is carried out in the presence of condensation product formed between DL-alanine (DLA) and glutaraldehyde. The bath constituents and bath variables are optimized through standard Hull cell experiments. The current efficiency and the throwing power are measured. High shift of potential towards more cathodic direction was observed in presence of addition agents. Corrosion resistance test reveals good protection of base metal by zinc coating obtained from the developed electrolyte. SEM photomicrographs show fine-grained deposit in the presence of condensation product. IR spectrum of the scraped deposit shows the inclusion of the condensation product in the deposit during plating. The consumption of brightener in the lab-scale is 6 mLL-1 for 1000 amp-hour.

Formation and characterization of borohydride reduced electroless nickel deposits

The present work aims to study the formation of electroless Ni-B deposits and evaluation of their characteristic properties. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless Ni-B deposits. The influence of variation in bath constituents as well as operating conditions on the plating rate, and, the nickel and boron content, of the resultant Ni-B deposits were studied. Selected deposits were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), evolved gas analysis (EGA), vibrating sample magnetometer (VSM) and transmission electron microscope (TEM), respectively, for assessing the phase content, phase transformation behaviour, liberation of hydrogen during crystallization, saturation magnetic moment and micro-structural features. The corrosion resistance of Ni-B deposits, in 3.5% sodium chloride solution, both in as-plated and heat-treated (450 °C/1 h) conditions, was also evaluated by potentiostatic polarization and electrochemical impedance studies. XRD patterns reveal that Ni-B deposits of the present study are amorphous in as-plated condition and undergo phase transformation to crystalline nickel and nickel borides upon heat-treatment. DSC traces exhibit two exothermic peaks at 306 and 427 °C, corresponding to the phase transformation of amorphous Ni-B to crystalline nickel and Ni 3B phases and the transformation of a higher phase compound to Ni 3B and Ni 2B, respectively. TEM microstructures and EGA strongly support the occurrence of phase transitions at 306 and 427 °C. Electroless Ni-B deposits demonstrate a moderate corrosion resistance in 3.5% sodium chloride solution. The extent of corrosion resistance offered by electroless Ni-B deposits is relatively less compared to electroless Ni-9 wt.% P deposit.

Solution Grotwh, Characterization and Possible Applications of Beryllium Fluoride (BeF2) Thin Films Deposited at 320K and at pH of 7 - 12

Solution growth technique (SGT) was successfully used to deposit good quality BeF2 thin films on glass slides at 320K for 3 hours and at pH of 7 – 12. The bath constituents were beryllium nitrate-4-water, and sodium fluoride as starting materials, sodium hydroxide as complexing agent and ethelemediamine tetra-acetate to vary the pH values. Effects of pH and bath constitutions were also investigated. Our numerous investigations reveal that beryllium fluoride thin films were produced only in alkaline medium. The deposited thin films modify the optical properties of the glass substrates at various wavelength regions. Average transmittance (T) values ranges from 0.615 – 0.904, reflectance (R) from 0.052 – 0.175, coefficient of absorption (a) (0.106 – 0.486) x10-4 cm-1 and refractive index (n) from 1.59 – 2.43. Values of solid-state properties such as band gap (Eg) range from 2.22-2.66 eV, electrical conductivity (s) from 0.73 – 1.26) X10-5 (W-cm)-1 and film thickness (t) from 465 - 214Å. Films with refractive index (n) lower than 1.8 have high transmittance (T) and low reflectance (R) while those with refractive index (n) greater than 1.8 have low transmittance (T) and high reflectance (R). The possible applications of the deposited beryllium fluoride (BeF2) thin film in optical, architectural, agricultural and electronics industries were also discussed. (Nigeria Journal of Pure and Applied Physics: 2003 2 (1): 21-27)

Ozonation of Exhausted Reactive Dye-Bath Analogues: the Use of Atrazine as an OH* Probe Compound

Ozonation and O3/H2O2 treatment of a spent reactive dye–bath analogue containing aminofluorotriazine type reactive dyestuffs were examined in semi–batch experiments at different pH (2, 7 and 12), bicarbonate (0.18 M at pH7) and carbonate (0.19 M at pHl2) alkalinity. Atrazine (23.2 µM) was added as an OH* – sensitive probe compound to the reactive dye–bath analogue to evaluate the individual contributions of both direct molecular (O3) and indirect radical (OH*) type reaction pathways for the treatment of spent dye–bath ingredients. From the obtained results it was evident that particularly de–aromatization (expressed in terms of UV254 and UV270 removal) kinetics were significantly retarded in the presence of HCO3, CO3 2‐ and particularly H2O2. O3 decomposition and consumption increased appreciably when H2O2 (0.125 mM at pH7) was added as compared in the presence of carbonate/bicarbonate alkalinity when H2O2 was added indicating that H2O2 and alkalinity could act as radical chain reaction promoters (carriers) and inhibitors, respectively. Atrazine degradation and UV270 abatement rates paralleled each other revealing that particularly de–aromatization of the spent dye–bath constituents mainly involves the action of OH*. Nitrate formation was distinctly higher at pH7 than at pH 12 as a consequence of the stronger OH* scavenging effect of carbonate alkalinity at pH12.

Autodeposition of organic coatings

Autodeposition of organic coatings refers to a chemical process for depositing paint coatings onto metal surfaces. This process resembles electrodeposition in that the objects to be coated are submerged in an aqueous bathcontaining ionized organic materials; however, in autodeposition, the coating is produced by a chemical reaction between the metal surface and the bath constituents as opposed to electrodeposition where the coating is produced by the electrolysis of water due to an imposed electric current. After autodeposition, the wet film is water rinsed and cured by application of heat to produce an inert, corrosion-resistant coating.

Treatability of textile dye-bath effluents by advanced oxidation: preparation for reuse

Treatability of textile dye-bath effluents by advanced oxidation with Fenton and Fenton-like reagents (FeII/H2O2 and FeIII/H2O2), in the presence and absence of UV light was investigated, using a reactive azo-dye (Procion Red HE7B), and typical dye bath constituents. Under the experimental conditions employed, it was found that with 20 min UV irradiation, complete color removal and 79% total organic carbon degradation is possible, when the system is operated at pH=3, and with a H2O2/Fe(II) molar ratio of 20:1. The increased dissolved solids content of the treated solution implies the necessity of an appropriate membrane system to make the effluent reusable in the dye/wash processes.

Treatability of textile dye-bath effluents by advanced oxidation: preparation for reuse

Treatability of textile dye-bath effluents by advanced oxidation with Fenton and Fenton-like reagents (FeII/H 2 O 2 and FeIII/H 2 O 2 ), in the presence and absence of UV light was investigated, using a reactive azo-dye (Procion Red HE7B), and typical dye bath constituents. Under the experimental conditions employed, it was found that with 20 min UV irradiation, complete color removal and 79% total organic carbon degradation is possible, when the system is operated at pH=3, and with a H 2 O 2 /Fe(II) molar ratio of 20:1. The increased dissolved solids content of the treated solution implies the necessity of an appropriate membrane system to make the effluent reusable in the dye/wash processes.

Stability and transport characteristics of reverse osmosis membranes using cyanide rinse waters

The recovery of cyanide rinse water using commercially available membranes (DESAL 3, MS10, SW30HR) is the objective of this work. Accordingly, flux, rejection, pretreatment and stability studies were carried out with these thin-film, composite, reverse osmosis membranes. The transport properties of membrane sections were tested using both cyanide rinse waters and NaCl solutions for flux and rejection on a flat-sheet test module after long term exposure to copper cyanide solutions. While SW30HR exhibited good chemical stability, DESAL3 and MS10 were not stable after exposure to high pH solutions for up to 6 months. Pretreatment studies were carried out on SW30HR membranes for flux enhancement in order to improve the recovery of the reverse osmosis system. SW30HR pretreated with ethanol exhibited a five-fold increase in water flux accompanied by an increase in ion rejection. Similar high fluxes and high rejection of principal bath constituents were exhibited by the SW30HR membrane when copper cyanide rinse water solutions were employed as the feed. These results indicate that this type of pretreated reverse osmosis membranes may have significant utility for reprocessing of copper cyanide rinse waters.

Morphology and Impedance Characteristics of Nickel Electroplating from Watts Bath

The electroplating of bright nickel from Watts bath with stepwise additives of gelatin, benzene sulphonic acid and its sodium salt was investigated. Electroplating of fine dispersed nickel layer from the same bath with inclusions of gelatin, benzene sulphinic acid sodium salt, Al 2 (SO 4 ) 3 and SiO 2 was also examined. The effects of bath constituents on the cathodic polarization and the interfacial impedance response during deposition of both forms of nickel was discussed. The surface morphology of the deposits was examined by scanning electron microscopy (SEM) and the crystal structure was elucidated by X-ray diffraction.

Process analysis of electroless nickel deposition baths using optical spectroscopies

The analytical techniques of Vis-spectrophotometry and FTIR spectroscopy have been applied to the quantitative determination of important plating bath constituents of an electroless nickel-phosphorus electrolyte under realistic bath operation conditions. In combination with multivariate calibration methods (partial-least squares (PLS)- and principal component (PCR) regression) Ni2+, the reducing agent H2PO2−and its oxidation product HPO3−could be directly determined even in the presence of other bath constituents like malic, lactic and adipic acids. For Ni2+, absorbance spectra in the 500–900 nm wavelength range were used to develop a PLS calibration model that allows to compensate matrix influences on the Ni2+ spectrum. PLS regression was carried out in the concentration range 0.5–6 g l−1 Ni2+ with independently varying bath parameters (concentration of other bath constituents, pH and temperature). Evaluation of the model by predicting the concentrations of test samples which had been drawn from real process solutions of a Ni plating bath yielded a root-mean-squared error of 0.06 g l−1. The metal concentration of the nickel electrolyte in a compact electroplating unit was monitored in-line by measuring spectra by means of a Vis-spectrometer adapted to the process via quartz glass fiber optical cables of 50 m length. A comparison of the in-line data with potentiometric off-line reference analyses showed good agreement of both data sets with a root mean-squared error of 0.15 g l−1. The potential of FTIR spectroscopy for process analysis of plating bath solutions could be demonstrated by measuring off-line the concentrations of H2PO2−and HPO3−. For these two components calibration samples containing all other main bath constituents were used to set up a PCR calibration model with IR spectra measured in the range from 850 to 1800 cm−1 with an ATR trough technique. The data showed — within the error of the method of about 10% — generally a good accordance with the stoichiometry of the Ni2+/H2PO2−reduction process. The correlation of both parameters which was confirmed in these experiments could allow effective bath control with minimum analytical instrumentation, e.g. only a Vis-spectrophotometer.

Influence of Bath Compositions and Some Operating Conditions on the Electroplating of Cobalt from Aqueous Sulphate Baths

SUMMARYA systematic study has been made of the influence of aqueous sulphate bath constituents on the cathodic polarization curves during cobalt electrodeposition. The optimum bath composition has been established and it contains: 0.30 mol l−1 CoSO4.7 H30, 0.30 mol−1 H3BO3. 0.05 mol l−1 (NH4)2SO4 and 0.10 mole l−1 Na2SO4.10 H2o. Cobalt electroplating from the optimized bath has been performed under a variety of conditions viz: pH, 1.5 to 5.3; current density, 0.2 to 2.0 A dm−2 and temperature 25 to 53°C. Under the most suitable conditions, the optimum bath is characterized by a high cathodic efficiency (~ 99%), moderate throwing power (21.6%) and throwing index (1.47). The bath produced smooth, adherent and semibright plates characterized by a high microhardness (411.4 kgf mm−2) and their morphologies, as revealed by scanning electron microscopy, showed a dependence on the plating variables.

Electroplating of bright cadmium from an optimized acetate bath under the influence of superimposed alternating current

A systematic study of the electroplating of bright cadmium from an acetate bath is described. The process was carried out in electrolytes containing cadmium acetate with inclusion of boric acid, acetic acid and sodium acetate, in addition to gelatin and toluene-4-sulphonic acid as organic additives. The effects of the bath constituents on the cathodic polarization and the current efficiency of cadmium deposition from each bath as well as on the surface morphology of the as-formed cadmium electroplates is discussed. The optimum acetate bath composition is suggested. The influence of a superimposed sinusoidal a.c. with the d.c. on the above-mentioned characteristics of cadmium electroplating from the optimum bath was also examined.

Effect of bath constituents and superimposed sinusoidal A.C. on nickel electroplating from acidic acetate solutions

The electroplating of nickel from acidic acetate solutions containing 0.25 mol (CH 3COO) 2Ni·4H 2O l -1 with the stepwise inclusion of 0.3 mol H 3BO 3 l -1, 0.2 mol CH 3COOH l -1 and 0.1 mol CH 3COONa·3H 2O l -1 was investigated. Electroplating in the presence of 1 g gelatin l -1 and/or 1 g toluene-4-sulphonic acid l -1 as organic additives was also examined. The cathodic polarization and current efficiency for nickel electroplating were affected to different extents by the bath constituents. Structural studies with a scanning electron microscope proved that the most regular and coherent nickel plate was that obtained from the solution containing both of the organic additives. The operating conditions to obtain a mirror-bright nickel plate from this solution were j = 2 A dm -2, t = 10 min and pH 5.25 at 25 °C. It was found that sinusoidal a.c. superimposed on the direct plating current decreases both the cathodic polarization and current efficiency, but increases the brightness of the nickel plate.

Some characteristics of Ni-Co alloy powders electrodeposited from dilute sulphate baths

Electrodeposition of Ni-Co alloy powder was carried out utilizing dilute sulphate electrolytes containing concentrations of Ni 2+ and Co 2+ ions within the range found in some industrial effluents. The electrolytes examined had the composition 0.0125 – 0.0750 mol l -1 NiSO 4·6H 2O, 0.0125 – 0.0500 mol l -1 CoSO 4·7H 2O, 0.23 – 1.00 mol l -1 (NH 4) 2SO 4, 0.2 – 0.4 mol l -1 H 3BO 3 and 0.07 mol l -1 Na 2SO 4·10H 2O. The effects of the bath constituents, pH and current density on some characteristics of the alloy were investigated. Increased concentration of NH + 4 ion in the bath was found to increase both the cathode potential and current efficiency and decrease the nickel content of the alloy. The cathode potential decreased with increasing concentration of either of the metal ions in the bath; a corresponding increase in the current efficiency and the metal content in the alloy were also observed. An increase in pH increased the cathode potential and current efficiency without appreciably affecting the alloy composition. The catalytic activity of the alloy powder towards the decomposition of 0.4% H 2O 2 solution increased with increase in the concentrations of NH + 4 and/or CO 2+ ions in the bath and with raising the pH. The surface morphology of the alloy powder was greatly influenced by the above-mentioned variables. The structure of the alloy, as revealed by X-ray diffraction studies, was dependent on its composition.

Electrodeposition of cobalt‐nickel alloys from ammoniacal single‐complex baths

AbstractThe electrodeposition of cobalt‐nickel alloys has been studied from ammoniacal single‐complex baths containing 5–50 CoSo4·7H2O, 5–50 NiCl2·46H2O, 20–50 g dm−3 (NH4)2SO4 and 250–350 cm3 dm−3 NH4OH (20.5% solution). The effects of the plating current density and the concentrations of the bath constituents on the cathodic polarisation, current efficiency and composition of the alloy were investigated. A wide range of alloy compositions with a current efficiency of 60–80% could be obtained from the main baths examined. The alloy plating system interchanged between the normal and the anomalous types depending upon the plating current density and the concentration of NH+4 ion in the bath. Electron microscopic and X‐ray diffraction studies proved that the structure of the electrodeposited alloy was controlled by the alloy composition.

Electrodeposition of catalytically active nickel powders from sulphate baths. I. Effect of bath constituents

A detailed study was made of the influence of the sulphate bath constituents: 0.3 - 0.0125 NiSO 4·7H 2O (I), 0.05 – 0.23 (NH 4) 2SO 4 (II), 0.1 – 0.4 H 3BO 3 (III) and 0.07 – 0.35 mol l −1 Na 2SO 4·10H 2O (IV) on the electrodeposition of nickel powder. The cathodic polarization, current efficiency, growth morphology, crystallite size and catalytic activity of the electrodeposited nickel powders were affected to different extents by the bath constituents. A highly pure nickel powder characterized by a small crystallite size (776 Å) and moderate catalytic activity was obtained from a bath containing: 0.0125 (I), 0.23 (II), 0.1 (III) and 0.07 mol l −1 (IV) at a current density of 10 A dm −2 and electrolysis time 60 min. at 25 °C. Structural studies with a scanning electron microscope are given and a reaction mechanism for the electrolytic powder deposition is discussed.

Effect of bath constituents and some plating variables on the electrodeposition of cadmium from acidic chloride baths

The electrodeposition of cadmium from acidic chloride electrolytes containing 0.3 M CdCl 2·(5/2)H 2O, 0.1 M HC1, 0.4 M H 3BO 3 and 2.0 M NH 4Cl (bath I) was investigated. Electrodeposition in the presence of 0.5 M sodium potassium tartrate and 5 g gelatin 1 −1 as organic additives (bath II) was also studied. The effects of the bath constituents, the plating current density i, the duration t and the pH on the cathodic polarization, the efficiency and the throwing power of cadmium electroplating from each bath, as well as on the morphology and the microhardness of the as-plated cadmium electrodeposits, are discussed. It was found that the additive-containing bath II yields more compact finer-grained brighter and harder plates than the additive-free bath I. The optimum conditions for cadmium electroplating from bath II at 25 °C are as follows: i, 1.0–1.6 A dm −2 5–15 min; pH 3.8–4.5.

Black chrome solar selective coatings optimized for high temperature applications

A statistical design approach has been used on a specified set of plating parameters to optimize the thermal stability of electrodeposited black chrome solar coatings. Plating parameters studied included the bath composition (chromic acid, acetic acid, trivalent chromium and iron), current density, plating time, substrate and bath temperature. The optimization procedure consisted of maximizing the solar absorptance values after thermal aging at high temperatures (up to 450°C in air). The estimated functional dependence of the thermally aged solar absorptance values on the four bath constituents was determined in the region of most stable coatings. This relationship was used to specify a range of bath compositions that provide coatings with optimum thermal stability. It was also found that chloride ion contamination of the black chrome plating solution significantly degraded the thermal stability of plated coatings. Fortunately, the chloride ions could be effectively removed through the addition of silver oxide, which precipitates silver chloride. When the plating variables were properly controlled, electrodeposited black chrome coatings were obtained which should maintain solar absorptance values of 0.96 or higher during years of operation at 300°C in air.