Hydrogenated Electrochemical Combined Mechanism of Electroless Ni-P Alloy Plating

Electroless Ni-P alloy plating reaction system is complex. At present, there are many controversies about the mechanism of electroless plating of NP alloys. Different researchers adopt different research methods and put forward some mechanism theories or opinions according to their experimental results. However, from the conditions of plating and the plating process From the facts of the changes and plating results, people basically reached a consensus on the following points: (1) The reaction must be carried out on a surface that is catalytically active (or made active); 2) The reaction produces bubbles, That is, there is a ratio generation, and it is known from isotope experiments that H in H2 is derived from H2 and H2PO respectively. (3) The positive value of plating solution continuously decreases, indicating that hydrogen ions are generated in the reaction; 4) When the pH value increases At this time, the plating rate is accelerated and the P content in the coating is reduced. The above provides a basis for exploring the mechanism of electroless plating of NP alloys, and at the same time, it also establishes objective criteria for detecting the correctness of the reaction process.

2 Experiments and research methods 2.1 Quantum chemistry research methods The electroless plating reaction must pay attention to the activity of the substrate surface, and the active surface will only be generated from the chemical deposition of the project funded by the Director of the Institute of Chemical Materials of the Chinese Academy of Engineering Physics, forming a coating. Surface activity is closely related to its own structure, and it is also closely related to such reactants or reaction intermediates as H2PO7. In fact, it is the interaction between the surface and such substances that determines the activity of the surface. So far, most of the electroless nickel-phosphorus alloys are produced in a solution system using sodium hypophosphite as a reducing agent. The adsorption and decomposition of HPCOT on the surface of the substrate to be plated is the initial step and key step of the process, so the matrix The size and manner of interaction between the surface and H2POT is a concrete manifestation of the surface activation ability. For this purpose, the relevant characteristics of the HPOT were first calculated at the Gaussian series level, and then a nickel atom (mainly considering the limitation of the calculation ability and the convenience of solving the problem, see the figure) simulates the nickel activation surface to calculate the HPCOT and the nickel surface. The purpose of the interaction is to look at the role that the nickel surface can play in the dehydrogenation process of HROT, so the selection of the coordinates requires that nickel and a H atom of HPOT are close (ie the H2 atom in the figure) to form a NiH-HROT transition state.

In the electroless nickel plating test of Lu's induced copper sheet, two tests were performed in the plating bath around °C: (1) Using intact Ni-P alloy as the induced material, copper electroless nickel plating was induced by direct contact and wire connection; (2) Take a copper sheet, and first half of the surface is plated with NP alloy by means of active metal contact induction, and the other half is still copper. Observe whether the reaction under the following conditions can occur: Immerse one half of the surface of the copper in the bath (note that the bath should not be in contact with the other half) Immerse one half of the surface of the NP alloy in the bath; Dip the entire copper piece. Bath solution.

3 Results and analysis Quantum chemistry study Table 1 Geometric configuration of H2P2 Po bond angle P-H bond length 10 bond length Table 2 Day 2 [2] Settlement number and atom net charge Atomic net charge Set number An atomic electron set The number of dwellings reflects the ability of the atom to attract or repel electrons in a specific chemical environment, and it can also be used as the relative magnitude of atomic electronegativity in a molecule. Table 2 lists the number of sites, the net charge, and the number of overlaps between each atom in the H2ROT. It can be seen that the hydrogen atom has 0.8984 negative charges, and the P-H overlaps the settling number 0.20602. We know that PH3 is a strong reducing agent. To understand the properties of H2PO7, we compared the characteristics of H and P-H in H2POT and PH3, and calculated the net charge of hydrogen atoms in PH3 to be 0.00894 negative charges in the same basis group ( Less than the net negative charge carried by hydrogen atoms in H2PO7.) P-H has an overlapping population of 0.34847 (greater than the P-H overlap in H2PO7). Because of the Pauling electronegativity of P atoms and H atoms, 2.1, the above data shows that the electron pair in the P-H bond is basically distributed in the middle of two atoms, forming a covalent bond with small polarity and weak stability. However, for HPOs that also have P—H bonds—there are two P—O bonds in the molecule at the same time, the number of electrons on the P atom is significantly reduced (1,405,167, about 1 electron), and on the H atom, The number of electron populations has increased (from 1.18984 to about 20%). These data indicate that the polarity of the P–H bond in O is significantly stronger than that of PH3 and the shared electron pair is slightly biased toward H, so the P of H2PO7 ―H may be more easily reacted with polar solvents and is more easily broken than the P―H bonds in PH3. This leads to the following conditions: H2PO7 can exhibit extremely strong reduction; when P―H is broken in H2ROT The hydrogen in the dissociation product may appear in the form of H atom or H-ion, ie the effect of H2PO7 2 solvent on the properties of H2POT The electroless nickel plating reaction is carried out in solution, the conformation, electronic structure and chemical reaction of the solvent on the molecule. There are important influences on the behavior of the solvent in the solvent and the behavior of the gaseous molecule.This article uses the special SCRF (self-consistent reaction field) method for calculating the solvation and calculates the characteristics of the HPCOT in the SCRF. Energy, due to H2PO The radius of T is larger and the charge is less, so the polarization energy of H2PO7 is smaller and has little effect on the reaction; in geometry, the HH bond length in SCRF is 0. 14157Pm, which is the ratio of non-reaction field. The length of the bond is 0. 0.00028 Pm longer than the 0.14893 Pm non-reaction field. This indicates that the H2HOT has been deformed due to solvation but the degree of deformation is very small; in terms of the number of sets, the number of P—H is 0.20602. It changed to 0.21223, an increase of 3%, and the net charge of H atoms changed from 0.198984 to 0.17262, which was a decrease of about 9%. Overall, the effect of the solvent on the properties of H2PO7 was negligible. 3.1.3 The effect of H2POT on the surface of nickel Table 3 and Table 4 show that the shape of H2PCOT has changed due to the effect of the nickel surface. The H-P-H bond angle becomes smaller, the O-P-O bond angle becomes larger, and the P-H2 bond length increases. Obviously longer, this indicates that the nickel surface makes the P-H2 bond weaker; from the population number point of view, the number of P-H overlap sets significantly and sharply decreases, while the Ni-H2 population number is 0.25519; Both Ni and H2 have a relatively large amount of negative charges.The above shows that nickel has a strong hydrogen bonding effect, which is consistent with the strong hydrogen absorption of nickel. By calculation, it was found that when the temperature rises, P-H in H2PO7 ruptures, the H atom or H-ion energy in the dissociation product forms a stable hydride with nickel metal. Table 3 Ni:HPO-Geometry Table 4 Overlapping population and atomic net charge overlap. Atomic net charge. 3. Induced copper electroless nickel plating test. Test found: Test (1) with intact Ni-P alloy as induced material, through direct contact and wire connected two This method induced copper electroless nickel plating reactions to be successful.

In the test (2), no reaction occurs when half of the surface is copper immersed in the plating solution; when the surface is half of the Ni-P alloy is immersed in the plating solution, the reaction occurs only in the portion that is in contact with the plating liquid. When the entire copper sheet is immersed in the bath, the reaction can take place over the entire surface of the copper sheet. This shows that the evoked response is most likely to be accomplished by the formation of a chemical battery in the solution with both electrodes. Induced metal - Ni-P alloy electroless nickel plating reaction occurs in the plating solution, the electrons flow through the contact induced surface of the metal (copper), so that the adsorption of Ni2 + electrons deposited, followed by a continuous reaction, so that It plays an inductive role. At the same time, the electrons that play an inductive role here come from the role of the NP alloy and the plating solution. This effect is the electroless nickel plating reaction itself. This just shows that there is an electrochemical step in the electroless nickel plating reaction. 14.4 Hydride-electrochemistry The mechanism of HPOT oxidation is considered as the key and entry point for studying the history of electroless NP alloys. Through the quantum chemical calculation and analysis of NiH-HPO7 system, it is recognized that nickel has strong hydrogen absorption ability and can form stable Ni. ―H bond 13′51, combined with the experimental fact of electrochemical step in the electroless nickel plating reaction, formulates the mechanism of chemical deposition of NP alloy as hydride-electrochemical combined mechanism.

4.1 Formation of Chemically Adsorbed H2P2 and Nickel Hydride In the bath, HPOT is adsorbed on the active nickel surface and undergoes a chemical adsorption process that generates a transition state: when the temperature rises, it will further react and form a hydride: see from the induction experiment. There are electrochemical steps in the electroless nickel plating reaction. They are expressed by the formula: 4.3Ni-P alloy deposition and hydrogen generation. Of course, the following reactions are not excluded (ads with the labeled “ads” indicates the adsorption of these substances. The hydride formed on the nickel surface or formed with nickel. 5 Conclusions Electroless nickel plating of copper sheets induced by quantum chemistry calculations and NP alloys has found that H2HT can be strongly chemisorbed by the nickel surface. This adsorption is effected by nickel on hydrogen. The key cooperation is used to realize that when the temperature rises, the P―H bond breaks, H or H forms a hydride with nickel, and the electrons that induce the electroless nickel plating of the copper plate come from the Ni-P alloy and the plating solution. The role - the electroless nickel plating reaction itself, which just shows that there are electrochemical steps in the electroless nickel reaction. For this reason, the hydride-electrochemical combined mechanism of electroless nickel plating proposed by the author of this paper can explain the phenomenon in electroless plating NP alloy reasonably.