Plating Solution Research Articles

Quantitative analysis of organic additives in acid copper plating solution

Due to the decomposition, condensation, and invalidation of organic additives in acid copper plating solution, it is hard to identify the effective concentration of additives, which causes difficulties in the prediction and grasping of the electroplating effect. To solve this problem, this paper established the linear relationship between absorbency and the concentration of organic additives based on the principle of ultraviolet spectrophotometry and the luminescence mechanism of the chromogenic agent and three organic additives after eliminating the interference of copper and hydrogen ions in the plating solution. The concentrations of polyethylene glycol (PEG), bis-(sodium sulfopropyl)-disulfide(SPS), and gelatin in the solution were analyzed quantitatively according to Law of Lambert-Beer. According to the results, the linear relationship between PEG’s mass concentration and absorbency can be described as y = 0.01057 + 0.01372x, with a linear correlation of 0.9982, a relative error of about 0.56%-3.7%, and a minimum detection limit of 1 mg/L. The method adopted for detecting the SPS content records a relative error of around 0.817%-4.202% with the minimum detection limit of 2 μmol/L. The linear relationship between gelatin concentration and absorbancy is expressed as y = 0.02165x + 0.00932, in which the linear correlation r = 0.9906.

DEVELOPMENT OF RECYCLING TECHNOLOGY FOR SPENT CHEMICAL NICKEL PLATING SOLUTION

Currently, the chemical nickel plating process is one of the most popular electroplating methods compared to others due to a number of advantages. However, the production process generates a significant amount of spent chemical nickel plating solutions, which poses a threat of environmental pollution. To solve this problem, the possibility of regenerating the spent solution of chemical nickel plating from one of the industrial enterprises of Udmurtia by the reagent method was studied. Sodium carbonate was chosen as the precipitant for nickel ions, the amount of which was determined from potentiometric titration curves; the most complete precipitation of nickel ions occurs at pH 10. It has been established by IR spectroscopy that nickel hydroxide salts are formed as a result of the interaction of the spent electrolyte with the precipitant. The results of thermogravimetric and differential thermal analysis of the precipitate showed three endothermic effects: at temperatures up to 100 °C, it corresponds to dehydration; at 280±10 °C - to the removal of a part of chemisorbed water and carbonates; at 420 °C - to the final removal of water. As a result of heat treatment of the hydroxocarbonate precipitate, a black fine powder of nickel(II) oxide is obtained, the IR spectrum of which has a set of bands characteristic of this compound. Two variants of the technological scheme for the regeneration of spent electrolytes for the preparation of initial working solutions for chemical nickel plating from nickel(II) hydroxocarbonate and nickel oxide are proposed. The quality of the obtained solutions was checked by applying a nickel coating on brass products. The thickness of the coating was measured by scanning electron microscopy. It has been established that the highest quality coating is obtained using an electrolyte prepared from nickel hydroxocarbonate.

Preparation of a Ni-P-nanoPTFE Composite Coating on the Surface of GCr15 Steel for Spinning Rings via a Defoamer and Transition Layer and Its Wear and Corrosion Resistance.

In this study, a method of preparing a Ni-P-nanoPTFE composite coating on the surface of GCr15 steel for spinning rings is proposed. The method incorporates a defoamer into the plating solution to inhibit the agglomeration of nano-PTFE particles and pre-deposits a Ni-P transition layer to reduce the possibility of leakage coating. Meanwhile, the effect of varying the PTFE emulsion content in the bath on the micromorphology, hardness, deposition rate, crystal structure, and PTFE content of the composite coatings was investigated. The wear and corrosion resistances of the GCr15 substrate, Ni-P coating, and Ni-P-nanoPTFE composite coating are compared. The results show that the composite coating prepared at a PTFE emulsion concentration of 8 mL/L has the highest concentration of PTFE particles (up to 2.16 wt%). Additionally, its wear resistance and corrosion resistance are improved compared with Ni-P coating. The friction and wear study shows that the nano-PTFE particles with low dynamic friction coefficient are mixed in the grinding chip, which gives the composite coating self-lubricating characteristics, and the friction coefficient decreases to 0.3 compared with 0.4 of Ni-P coating. The corrosion study shows that the corrosion potential of the composite coating has increased by 7.6% compared with that of the Ni-P coating, which shifts from -456 mV to a more positive value of -421 mV. The corrosion current reduces from 6.71 μA to 1.54 μA, which is a 77% reduction. Meanwhile, the impedance increased from 5504 Ω·cm2 to 36,440 Ω·cm2, which is an increase of 562%.

Electrochemical performance analysis based on chromium mist inhibitors

In this paper, the stability of the fog suppression effect of 20 different domestic chrome fog inhibitors and their effect on the thickness and corrosion resistance of the plated layer were studied by formulating the basic chrome plating solution with a common chrome plating solution formulation. The stability of the fog suppression effect of the 20 different chromium fog inhibitors was analysed by measuring the variation of the thickness of the chromium fog inhibitor foam layer with time. It was found that the thickness of the foam layer produced by the TDFS chromium mist inhibitor during the plating process changed least significantly at 30 min after plating, and the stability of the fog inhibiting effect was the best; compared with the thickness of the layer obtained from a common chromium plating solution without the addition of chromium mist inhibitor, it was found that the thickness of the layer obtained from the plating solution with the addition of PALDOTMV-400 chromium mist inhibitor was the thickest. The experimental results show that the chromium plating solution with the addition of WH-883 chromium mist inhibitor has the best electrochemical corrosion resistance, because its impedance value is the largest and the corrosion current is smaller.

Incorporation of TiO2 nanoparticles in CoWP coating for improved wear and corrosion resistance via electrodeposition

The CoWP/TiO2 composite coating is prepared by electrodeposition by adding TiO2 nanoparticles in the plating solution. The influence of TiO2 nanoparticles on the composition, thickness, roughness, surface morphology, mechanical performance and corrosion resistance of CoWP/TiO2 composite coating is investigated. It is found that adding proper amount of TiO2 nanoparticles in the plating solution can improve the deposition rate, increase the coating thickness, and enhance the wear resistance and corrosion resistance of composite coating. TiO2 nanoparticles in the plating solution can enter the crystal lattice of CoWP alloy and induce heterogeneous nucleation during electrodeposition, which plays the role of refining grain, so as to obtain compact surface morphology with smaller surface roughness. The CoWP/TiO2 composite coating electrodeposited from the plating solution with 15 g/L TiO2 nanoparticles has the best wear resistance and corrosion resistance with the smallest wear scar depth (17.04 µm) and minimum corrosion current density (12.92 μA/cm2). When the TiO2 nanoparticles in the solution are up to 20 g/L, the agglomeration phenomenon of TiO2 nanoparticles inhibits the electrodeposition, resulting in the decline of deposition rate, the increase of alloy surface roughness, and the decrease of wear and corrosion resistance performance.

Effects of suppressors on the incorporation of impurities and microstructural evolution of electrodeposited Cu solder joints

BackgroundCopper (Cu) electrodeposition is a cost-effective and scalable technology commonly used to fabricate interconnects and heat sinks in microelectronic devices. Adding organic functional additives, such as suppressors, to plating solutions is crucial to achieve conformal microvia filling by Cu electroplating. However, codeposition of organic additives is inevitable and leads to reliability concerns regarding impurity residues in the Cu electrodeposited layer. MethodsIn this study, polyethylene glycol (PEG) at 8,000 g mol−1 and a triblock copolymer EPE (polyethylene oxide-polypropylene oxide-polyethylene oxide) at 2,900 g mol−1 are applied as suppressors and individually added to plating solutions to compare their suppression strength toward Cu deposition using galvanostatic measurements. Their adsorption/desorption behaviors on the Cu surface are theoretically analyzed based on the electronic distribution properties of the two suppressor molecules calculated by quantum chemical calculations. The impurity residues in the Cu layers are measured by a time-of-flight secondary ion mass spectrometer, and their effects on the joining reactions between tin (Sn) solder and Cu are investigated by observing the microstructural evolution in the Sn/Cu joints subjected to isothermal aging. Significant findingsEPE2900 outperforms PEG8000 in the suppression strength toward Cu deposition. Unlike PEG8000, which causes a high level of impurity incorporation, the impurity residues in the Cu layer constructed by EPE2900 are negligible. As a result, the Sn/Cu solder joint constructed by EPE2900 exhibits high microstructural stability free of the propagation of detrimental voids during isothermal aging at 200 °C. The better suppression efficacy and negligible impurity residues of EPE2900 can be rationalized based on quantum chemical calculations.

Nanocomposite Co-nSiC coatings electrodeposited from cobalt-gluconate bath via pulse reverse plating technique with anionic surfactant

The co-deposition of silicon carbide nanoparticles (50 ± 5 nm diameter) in an electrodeposited metallic cobalt matrix has been investigated under pulse reverse plating (PRP) conditions with the inclusion of an anionic surfactant. The effect of variable anionic surfactant content in the plating solution with a particle content of 5 g L−1 was evaluated using both direct current (DC) plating and PRP. The particle content of the coatings was investigated by varying the cathodic cycle during PRP by varying the cathodic cycle time between 30 and 240 s per pulse whilst maintaining a fixed anodic charge. The coatings were assessed by SEM and EDX in cross section to determine the effect of PRP parameters and anionic surfactant content on the particle content of. With no anionic surfactant, all coatings produced contained a similar particle content. Addition of anionic surfactant affected the SiC content of DC and PRP coatings. PRP combined with anionic surfactant to produce an electrophoretic nanoparticle delivery mechanism increasing the SiC content of coatings compared to DC coatings. Higher SiC content was observed at shorter cathodic cycle times.

Investigation of electroless copper plating with high plating coverage in small BVH for next generation fine pattern SAP

Printed wiring board (PWB) used for package substrates are required to have higher circuit densities. We anticipate that PWB circuit patterns and blind via hole (BVH) will continue to be miniaturized due to higher density requirements. The electroless copper plating solution generally used has less chemical material supply to the inside of the BVH than the surface of the substrate. As a result, the copper thickness at the bottom of the BVH tends to be thinner than that on the surface of the substrate. It is difficult to uniformly deposit the electroless copper plating in the BVH on the package substrate by the semi-additive process (SAP), especially when the BVH are becoming smaller. Therefore, we investigated additives that suppress the electroless copper plating deposition on the surface of the substrate and additives that improve the permeability of the plating solution into the BVH. Two additives have been discovered that dramatically improve the plating uniformity in the small BVH compared to the conventional bath. In addition, we used this plating solution with the new additives to evaluate the internal stress and peel strength of the electroless copper plating film. As a result, it was confirmed that both internal stress and peel strength were improved compared to the conventional bath.

A Novel Analytical Method of Thallium Determination in Gold Electrodeposition

Thallium is used in both cyanide and sulfite-based gold plating bath solutions as an additive that modulates how gold deposits on the target substrate. The level of Tl in the plating solutions has a large effect on the properties of the gold being deposited, including its microstructure and hardness. Thus, especially in commercial process applications, it is critical to be able to measure the Tl content of plating solutions accurately, quickly, and facilely in order to ensure proper quality of the products being manufactured. The cyclic voltametric behavior of Tl-containing gold plating bath solutions has been investigated, but quantification of its Tl content is unsatisfactory, either expensive and time consuming, or not accurate in complexed matrices. Here, we present a proprietary, electroanalytical method of Tl measurement that is fast and gives excellent accuracy and sensitivity, even in the presence of common bath breakdown products.

Mixed reaction gold as versatile plating solution for ENIG, ENEPIG and EPAG plating

The surface finish on a printed circuit board (PCB) or substrate serves as surface protection and at the same time enables a variety of assembly techniques. Depending on which final finish is selected it allows for e.g. soldering connections or wire bonding by Al, Au or even Cu-wires. Surface finishes are typically characterized by different metal layers, including tin, nickel, palladium or gold. In this context the electroless or immersion plating of gold has a long history in the electronics industry. The gold plating represents a key step in different finish systems such as electroless nickel/immersion gold (ENIG), electroless nickel/electroless palladium/immersion gold (ENEPIG) and electroless palladium/autocatalytic gold (EPAG). ENIG, ENEPIG and EPAG finishes are characterized by their capabilities to be used as solderable and wire-bondable finish with specific benefits for ENEPIG and EPAG such as enhanced solder joint reliability and gold-wire bondability. In this paper an overview is given on the different types of electroless gold plating electrolytes from fully immersion type and autocatalytic type to mixed reaction type gold electrolytes. The details of the various plating mechanisms are presented, and the different properties and capabilities of these electrolytes are compared and explained based on the respective mechanisms. The presented study investigates the performance of a gold electrolyte of a mixed reaction type looking into the layer properties as well as the soldering and bonding capabilities. The results show that a mixed reaction gold electrolyte can be capable for versatile application- ENIG, ENEPIG and EPAG. The capability of the process was tested with respect to the solder wetting performance, solder joint reliability, wire bonding performance, corrosive attack to the nickel and thickness distribution. It can be shown that this gold process passes or exceeds all related industry standards and target requirements for ENIG, ENEPIG and EPAG final finishes.

Life Cycle Environmental Analysis of Valuable Metal (Ag) Recovery Process in Plating Waste Water

In 2018, the demand for silver (referred to as Ag) in the electrical and electronics sector was 249 million tons. The demand stood at 81 million tons in the solar module production sector. Currently, due to the rapid increase in solar module installation, the demand for silver is increasing drastically in Korea. However, Korea’s natural metal resources and reserves are insufficient in comparison to their consumption, and the domestic silver ore self-sufficiency rate was as low as 2.2% as of 2021. This implies that a recycling technology is necessary to recover valuable metal resources contained in the waste plating solution generated in the metal industry. Therefore, this study compared and analyzed, the results of the impact evaluation through life cycle assessment according to an improvement in the process of recovery of valuable metals in the waste plating solution. The process improvement resulted in reducing GWP (Global Warming Potential) and ADP(Abiotic Depletion Potential) by 50% and 67%, respectively. The GWP of electricity and industrial water was reduced by 98% and 93%, respectively, which significantly contributed to the minimization of energy and water consumption. Thus, the improvement in recycling technology has a high potential to reduce chemical and energy use and improve resource productivity in the urban mining industry.

Role of cationic surfactants in palladium adsorption of commercial ion exchange resins using electroless plating solutions

AbstractThis work investigates the role of cationic surfactants in the adsorption of palladium ions from synthetic electroless plating solutions using a commercial resin, Lewatit TP-214. This would also help us in determining the batch adsorption experiments elaborated on the optimal parameters such as surfactant concentration, pH, dosage, initial metal ion concentration for the development of an ion-exchange resin with high metal removal efficiency. Critical micelle concentration (CMC) appears to be an important parameter in determining the adsorption behavior of ion-exchange resins with palladium ions. Equilibrium models were measured for their fitness with the obtained Pd (II) batch adsorption characteristics and Freundlich isotherm confirms the heterogeneous Pd (II) adsorption on Lewatit TP-214. FTIR analysis confirmed that the Pd (II) metal uptake of Lewatit TP-214 resin largely depends on amine groups (-NH2+ and -NH+) and the donor atoms attached to cationic surfactant. The optimized choice of adsorption parameters (pH of 8, dosage of 1 g/L, and contact time of 300 min) of Lewatit TP-214 adsorbent provided the highest metal uptake and removal efficiency as 201.7 mg/g and 90.16%, respectively, for the lowest Pd concentration of 300 mg/L.

Electrodeposition and corrosion performance of Ni-Co alloys with different cobalt contents

The deposition mechanism of Ni-Co alloys with different cobalt compositions plays an important role in the preparation and application of Ni-Co alloys by electrodeposition. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were used to study the effect of the Co content on the electrodeposition mechanism of the plating. The surface morphology and crystal structure of the plated layers were studied by scanning electron microscopy and X-ray diffraction. The corrosion performance of nickel-cobalt alloys with different Co contents was analyzed by anodic polarization curves and electrochemical impedance spectroscopy. The results showed that during the early stage of electrocrystallization, increasing the CoSO4 content in the plating solution decreased the charge transfer resistance during nucleation and decreased the activation energy of nucleation/growth. Nucleation occurred via a three-dimensional transient nucleation mechanism, which was controlled by both diffusion and electrochemical factors. Compared with pure nickel, the Ni-Co alloy had a more pronounced (1 1 1) orientation and superior corrosion resistance. Plating with 10 wt% Co provided the best corrosion resistance.

Study on magnetic performance and corrosion resistance of CoPtWP coating prepared by electrodeposition

Electrodeposition is used to prepare the Co, CoPt, CoPtW, and CoPtWP coatings on the surface of pure copper. The association between magnetic performance, corrosion resistance, surface morphology, roughness, thickness, and electrodeposition process is investigated by contrasting the four electrodeposited coatings. The deposition of cobalt and tungsten is discovered to be a type of induced codeposition. The chloroplatinate and hypophosphate ions receive electrons to reduce to the CoPtWP alloy at the surface of the CoPt coating. The adding of WO42- and H2PO2- ions in the plating solution is beneficial to promote the electrochemical reaction near cathode surface. The surface of Co coating shows leaf-like and loose morphology with largest surface roughness leading to poor magnetic performance and corrosion resistance. However, the surface morphology of the CoPt coating, CoPtW coating, and CoPtWP coating is all compact with nodular structures. With the least surface roughness and greatest thickness, the CoPtWP electrodeposited coating exhibits superior magnetic performance and enhanced corrosion resistance.

Effect of SiO2 nanoparticles on the hardness and corrosion resistance of NiW/SiO2 nano composite coating prepared by electrodeposition

In this paper, NiW/SiO2 composite coatings were prepared on Q235B steel using the electrodeposition technique. The relationship between the concentration of SiO2 nanoparticles in the plating solution and the properties of NiW/SiO2 composite coating was investigated. The results show that the addition of an appropriate amount of SiO2 nanoparticles in the plating solution can enhance the cathode current, increase the surface hardness, improve the corrosion resistance, and reduce the roughness of the composite coating. The SiO2 nanoparticles covered on the coating surface can penetrate the lattice of NiW alloy to induce heterogeneous nucleation, and play a role in refining grain. However, when the SiO2 nanoparticles in the plating solution reaches 8 g/L, the agglomeration phenomenon occurs due to excessive nanoparticles, which will increase the roughness and decrease the compactness, resulting in the decrease of hardness and corrosion resistance. The NiW/SiO2 composite coating electrodeposited from the solution containing 6 g/L SiO2 nanoparticles exhibits the best hardness (643.23 HV) and the greatest corrosion resistance with the smallest corrosion current density (9.7 μA/cm2).

A study of Ni–P electroless coating modified by rare earth oxide (La2O3, Y2O3 and Ce2O3) on pre-phosphorized zirconium alloy

Electroless Ni–P coatings are successfully deposited on the surface of pre-phosphorized zirconium alloy from plating baths containing various concentrations of rare earth oxide (Re Y2O3, Ce2O3 and La2O3). The surface morphology, elementary composition, and structure of coatings are characterized by scanning electron microscopy, energy dispersive X-ray spectrometer and X-ray diffraction, respectively. Gravimetrical method is used to calculate the deposition rate. Electrochemical corrosion resistance of coatings is analyzed using electrochemical workstation. Results revealed that a small amount addition of rare earth oxides does not change the original cauliflower-like morphology and amorphous structure of coatings. When the amount of addition is moderate, the deposition rate and microhardness increase with the increment of the amount of addition, while P content decreases. However, excessive addition can lead to poisoning of the plating bath. Electrochemical corrosion data indicates that the addition of rare earth oxide in the plating solution has little influence on the corrosion resistance of the coating.

Microstructure and properties of graphene oxide reinforced copper-matrix composite foils fabricated by ultrasonic assisted electrodeposition

In this paper, graphene oxide (GO)/Cu composite (GO/Cu) foils with high thermal and mechanical properties were prepared by ultrasonic-assisted direct current electrodeposition. The effect of ultrasonic power and graphene concentration on the microstructure and properties of the composite foils was systematically investigated. It was found that the average grain size can be refined by both the addition of GO reinforcement and ultrasonic treatment. Under the optimized preparation condition with 120 W ultrasonic power and GO concentration of 0.8 g/L GO in plating solution, the average grain size was about 0.26 μm and illustrated strong crystallographic orientation of (220). In addition, the GO content in the composites was increased from 0.67 wt% without ultrasonic treatment to 1.72 wt%, and it was uniformly dispersed in the composite foil with ultrasonic effect. Compared with pure copper foil, the hardness value of the GO/Cu composite foil nearly doubled to 74.6 HV0.1, the average friction coefficient was decreased from 0.87 to 0.72 and the tensile strength of the composite foil was improved to 239 MPa with an elongation of 17%. Meanwhile, the thermal conductivity with optimized condition increased 39.8% to 556.57 W m−1 K−1. The improved mechanical and thermal properties of the GO/Cu composite foil were mainly ascribed to the grain refinement, change of preferred orientation and the presence of reduced GO reinforcement as a network in the composite foil.

Effect of Process Parameters on Electrodeposition Process of Co-Mo Alloy Coatings

Plating bath composition, temperature, current density, and pH have a great influence on the properties of a Co-Mo alloy coating. However, these conclusions are obtained from the perspective of test results. Most of the factors that affect the properties of the coating operate by interfering with the electrodeposition process. Therefore, it is of great significance to study the kinetics of the electrodeposition process. To further study the influence of process parameters on the deposition process of Co-Mo alloy coatings, cyclic voltammetry (CV), scanning linear voltammetry (LSV), and electrochemical impedance testing (EIS) were used to study the deposition kinetics of Co-Mo alloy coatings. The results show that with the increase in sodium molybdate content in the plating solution, more Mo elements are involved in the deposition process. At the same time, a higher Mo element content can reduce the dissolution of the coating as the anode and improve the service life of the coating, but too high a Mo element content will lead to cracks on the surface of the coating. The deposition temperature will affect the processes of reduction deposition and oxidation dissolution of the coating. The pH of the plating bath will directly affect the reduction reaction process of MoO42− ions in the plating bath. With the increase in the pH value, the reduction reaction rate of MoO42− ions decreases, and the cathodic reduction reaction current density decreases. At the same time, the peak current density of anodizing decreases with the decrease in the pH value of the plating solution, indicating that the alkaline plating solution has an inhibitory effect on the plating dissolution process.

A transfer-adsorption model for forward understanding the synergistic effects of additives in through-hole uniform copper thickening

The additives in acidic copper electronic plating solution are of crucial importance in uniform thickening of through-hole (TH) for printed circuit board (PCB) fabrication. In this present study, we set up a transfer-adsorption model to forward understanding the synergistic effects of additives on TH uniform thickening based on the experimental facts of galvanostatic measurements, density functional theory calculations and chronocoulometric measurements. According to this model, during copper electronic plating, the suppressor of polyethylene glycol (PEG) adsorbs more at the mouth because of the replacement of PEG by the accelerator of bis-(sodium sulfopropyl)-disulfide (SPS) at the center of TH, the leveler of Janus Green B (JGB) adsorbs uniformly both at the mouth (where it works with PEG to weaken the adsorption of SPS) and center of TH (where it cooperates with SPS to promote the cupric ions electro-reduction), resulting in the copper layer thickness decreasing at mouth and increasing at center. Such complicated but effective synergistic effects of the three additives result in uniform thickening of TH. Copper electronic plating results further confirmed the reliability of the transfer-adsorption model in synergistic effects of copper electronic plating additives, and unveiled the interaction mechanism of additives for TH uniform thickening.

Directly preparing well-dispersed ultra-hydrophilic NiFeP nanoparticle/Mxene complexes from spent electroless Ni plating solution as efficient hydrogen evolution catalysts

A novel approach is proposed to prepare well-dispersed ultra-hydrophilic NiFeP nanoparticle/Mxene complex by recovering Ni, P, and organic acid from spent electroless Ni-plating solution. The mechanism of NiP-based nanoparticle formation and size regulation during the hydrothermal process is analyzed. Ni2+ chelated with sodium citrate in the electroless Ni plating effluent anchors on the Ti3C2 surface with -OH functional groups by chemical reaction and charge adsorption owing to Mxene surface negativity. The as-prepared ultrafine NiFeP nanodots are connected with alkali-induced Ti3C2 Mxene nanosheets, which possess ultra-hydrophilic performance and rapid H2 bubble desorption behavior. The introduction of alkali-induced Ti3C2 MXene as a substrate controls particle agglomeration in the hydrothermal crystallization process and achieves perfect dispersed distribution of NiFeP nanoparticles to further increase the specific surface area of catalyst. Consequently, the NiFeP/Ti3C2 nanohybrid catalyst exhibits outstanding hydrogen evolution reaction (HER) electrocatalyst performance as a result, with an overpotential of 122 mV at 10 mA cm−2, quick reaction kinetics of 68 mV dec−1, and strong long-term stability over 24 h in 1 M KOH. This research develops a strategy for directly preparing high-value catalyst materialization from spent electroless Ni-plating solution.