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Chemical nickel plating additive effect and the mechanism of activation process

Time:2013-11-14     Klicks:4164

1. The influence of additives on chemical deposition rate and morphology

Explore the electroless Ni - P - P and Ni - W system of plating solution composition and the function of additives. Experiments have found that in the absence of the fluid of the additives of electroless Ni - P, Ni2 +, NaH2PO2 concentration and the increase of pH value, makes the chemical deposition rate is accelerated, and Ni2 + concentration and the increase of pH value is beneficial to the increased amount of Ni deposits, whereas NaH2PO2 significantly promote P deposit amount. Plating solution containing additives, discovered that thiourea (TU) helps Ni2 + reduction, but inhibit the oxidation of NaH2PO2; Propionic acid for Ni2 + reduction and oxidation has the promoting effect of NaH2PO2; And La2O3 is good for the oxidation of NaH2PO2.

TU is contained in the plating solution and does not contain TU coating morphology have bigger difference, the small particles on the surface of the latter, the cross section contains a lot of space, and particle size is big, the former section space less, attributed to TU suppress nucleation process and the reduction of H +. Large particles of Ni - P - W electroless plating is made up of many small particles, the small particles and contains the finer particles. LaCl3 by reducing plating W content and refine the particle size of coating.

Electroless Ni - P - W and Ni - P system, of LaCl3, lactic acid, Fe2 (SO4) 3, propionic acid, thiourea, La2O3 coupling pyridine and 2, 2 '- seven kinds of additives on a detailed study of the influence of deposition rate. Found their effect on the deposition rate showed a more consistent, namely with the increase of the concentration of additive has a maximum deposition rate, an adsorption model was built based on the experiment facts and theoretical formula of additives to accelerate the chemical deposition. Experimental results with theoretical formulas for curve fitting, get a fairly consistent results. According to the fitting results are adsorption equilibrium constant, results show that the adsorption equilibrium constant of the additive on the substrate (K1) is greater than on the adsorption of reductant adsorption equilibrium constant (K2), namely additive on the surface of the matrix, the stronger adsorption ability. LaCl3, thiourea, La2O3 and 2, 2 '- al pyridine K1, K2 values greater than the lactic acid, propionic acid and Fe2 (SO4) 3 K1, K2 values, which suggests that LaCl3, thiourea, La2O3 and 2, 2' - al pyridine adsorption ability is far stronger than the lactic acid, propionic acid and Fe2 (SO4) 3, therefore, LaCl3, thiourea, La2O3 and 2, 2 '- al pyridine deposition rate caused by the concentration of the peak is far less than lactic acid, propionic acid and Fe2 (SO4) 3.

2. The number of mechanism research of organic additives

The process of electroless plating is a conjugate, respectively the additive reduction of nickel ions and the impact of NaH2PO2 oxidation to understand the mechanism of the additives. The results showed that the additive mainly through surface effect, such as acrylic acid with Ni2 + and NaH2PO2 formed on the surface of complex to promote chemical deposition. Propionic acid and NaH2PO2 form intermolecular hydrogen bond, promoted the fracture of P - H keys, generates, PHO2 - intermediate; Propionic acid with "OCO -" functional groups and Ni2 + form bridge complexes, thus accelerate the deposition of Ni. Lactic acid and propionic acid on the similar structure, so in a similar mechanism to promote NaH2PO2 oxidation, but due to its alpha on a hydroxyl group more than propionic acid and lactic acid and Ni2 + may form chelate, that is not conducive to Ni deposits.

Although TU promoting effect to the Ni2 + deposit, but TU Ni2 + cathodic reduction on two aspects of influence. First, it prevent the formation of crystal nucleus to nickel, the greater the concentration of TU, the higher overpotential required for nucleation; Secondly, in the presence of nickel on the surface of the crystal nucleus, TU growth promoting effect of nickel particles, through which can also explain TU's influence on the chemical plating morphology. TU on the growth of the nucleation effect is related to the formation of a surface complex, but surface complex formation can accelerate the nickel deposition. Spectrum studies have shown that TU on the copper substrate in a S atomic adsorption, and when there are no Ni2 + in horizontal adsorption, adsorption when Ni2 + existed way to make the transition to vertical adsorption. In the formation of complex surface, TU and S atoms and Ni2 + coordination role.

3. The chemical plating high phosphorus alloy corrosion resistance and relationship with microscopic structure

Using polarization curve, ac impedance and differential scanning calorimetry respectively different P content was measured by chemical plating of Ni - P alloy corrosion resistance (in 5% NaCl solution) and the peak temperature of crystallization, found that the P content within the scope of the 21 ~ 22 at %, corrosion resistance and the temperature has a great value. XRD experiment shows that coating is amorphous structure, based on the amorphous alloy rhombohedron unit structure model (RUSM), with P and Ni formed by key number along with the change of P content, reasonably explained the electroless Ni - P alloy coating corrosion resistant performance and crystallization peak temperature of maximum phenomenon. At the same time by measuring the density of coating and compared with RUSM density formula of theoretical calculation value, proved the rationality of the RUSM structure model.

4. At the early stage of the chemical plating on metal substrates electrochemical detection

The experiment found that electroless Ni - P system of low carbon steel substrate mixed potential changes over time associated with pH and reduce over time. Measurement results show that under different pH pH will accelerate to reduce the chemical plating process induced. Concentration of sodium citrate mixed potential impact is not big, but sodium citrate concentration and pH caused mixed potential is moving can explain the phenomenon of chemical deposition rate slows.

In electroless Ni - W - P system, electrode pretreatment, plating solution composition, temperature, pH, and additives on the mixed potential shows that the influence of electrode without pickling will delay the cause of chemical plating process, appear on the mixed potential - time curve of three potential steps correspond to the oxide film and substrate and coating mixed potential; Improve the Na2WO4 and Na3C6H5O7 concentration, adding additives, reduce the pH will slow down the chemical plating time, difficult to trigger at low temperature electroless plating process.

In electroless Ni - P and Ni - Cu - W - P system, mixed potential steady potential to plating potential before the transition from the matrix, the matrix surface chemical plating process has occurred, the coating on the substrate after occupies certain proportion as 12% potential transition occurred.

The above experiments also show that the determination of mixed potential changes over time, although simple, but to understand the early stage of chemical plating process provides a quick and convenient useful information.

5. Carbon nanotubes and ceramic surface activation without using palladium salt chemical plating

Proposed carbon nanotubes and ceramic surface without palladium activation process of electroless plating nickel in the steps, and the substrate chemical changes before and after each process step for testing. Results show that the activation process step is put forward in this paper the essence of which is generated by carbon nanotubes and ceramic surface or introducing carboxyl (-cooh) group, carboxylic acid ion chemical adsorption in the Ni2 + ions, and then make the Ni2 + ions adsorption reduction, can be on the surface of the matrix of electroless plating nickel in the generation of the catalytic active center, which can trigger a chemical nickel plating process successfully. The graphite mesh structure of carbon nanotubes makes it formed on the surface of the carboxyl (-cooh) group - arrange evacuation such as functional groups, resulting in the distribution of active center is not close. Graphite mesh structure makes the horizontal direction and the loop direction radius of curvature difference is big, lead to grain growth speed is different, the "beads" and other different forms of sediments. And electroless plating on the surface of the ceramic is bright black, the phenomenon is generated on the surface of ceramic are dispersed, nanoscale particles. Using AFM and SEM observation of surface topography also shows that the ceramic surface has both 200 nm particles and 16 nm small particles.

6. The mechanism of electroless plating directly on monocrystalline silicon

In alkaline chemical nickel plating solution, monocrystalline silicon n - Si (100) without any activation treatment, can be directly caused by chemical plating process. Experiments show some mechanism existing in the literature is debatable, nickel ions as set out in this paper, based on the principle of the semiconductor electrochemical n - Si reduction and electroless plating on the surface of the trigger can be done through different channels, but the production of atomic hydrogen is the primary mechanism. In solid and solution shows that the level of species matching relation between H2O in pH10.0 solution can be in n - hydrogen evolution reaction on Si (100), nickel ions by capturing and reduction of nickel hydrogen atoms on the surface of the Si and deposition on the surface of the Si. Second, if the existence of localized electronic semiconductor surface level (surface), nickel ions may also be obtained by surface state electronics and reduction. Once the Si after the deposition of nickel on the surface, new changes have taken place in the n type solid surface. N - Si the work function of 4.0 eV, and the work function of ni is 4.5 eV, so metal nickel after contact with n-type Si nickel ion is also available on the nickel of negatively charged electron and reduction. Experiment also found that the change of temperature and solution pH can affect the chemical plating metal particle size, high temperature or pH hours coating particle size increases. EDS analysis that O elements in the chemical reduction of nickel layer mainly exists in silicon wafers of SiO2, the existence of these compounds to the chemical plating the electrical conductivity of the need to continue to study the influence of such performance.

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