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1 MINISTRY OF EDUCATION AND TRAINING VIET NAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ---------------------------- TRUONG THI NAM Thesis title: STUDYING THE EFFECTS OF SOME ADDITIVES ON THE ZINC PLATING PROCESS, ORIENTED APPLICATION FOR ALKALINE NON-CYANIDE ZINC PLATING BATH SUMMARY OF PHD DISSERTATION Major: Theoretical Chemistry and Physical Chemistry Code: 9.44.01.19 HA NOI 2021 This dissertation has been carried out at Graduate university of Science and Technology, hanoi. Viet Nam Academy of Science and Technology 2 Supervisors: Dr. Le Ba Thang Assoc. Prof. Dr. Nguyen Thi Cam Ha The thesis will be defended at the Board of Examiners of Graduate university of Science and Technology, hanoi. Viet Nam Academy of Science and Technology at …………………….. on ……………….. 1. Significance of the study 3 The problem of corrosion resistance for metal materials has become an urgent need for all countries in the world, especially for Vietnam which is located in the tropical monsoon climate: temperature, High air humidity [1]. Metal coating is one of the methods of corrosion protection that has been researched and used quite popularly in the world and in Vietnam. Among them, zinc is one of the most used metal coatings to protect components, parts, machine parts and carbon steel structures thanks to its low cost, cathodic protection for steel. . Galvanized coating can be obtained from a variety of methods such as electroplating, hot dipping, spray coating, where electroplating dominates with small details, is used in atmospheric conditions and does not require too much longevity. high. Some of the zinc plating solutions have been studied and used such as: zinc plating from sulfate solution, fluoride, cyanide, pyrophotphate, chloride and non-cyanide alkali. Among them, the solutions widely used in industry are cyanide, chloride and non-cyanide alkali. The world's cyanide alkali-plated solution was commercialized very early in the 1960s [3]. However, recently, thanks to the introduction of new polishing additive systems as well as due to environmental protection requirements, this plating tank is really interested, accepted and becomes the best solution to change. cyanide plating tank. The non-cyanide alkaline zinc plating solution has some outstanding advantages such as: more economical, non-toxic, good coating quality, easy to pass, especially suitable for passive solutions of Cr (III), good throwing power, especially easy to handle wastewater [2, 4]. The downside is more complex, which requires a good surface treatment. However, if the alkaline plating bath is free of cyanide without additives, the poor quality coating cannot be used in industry. Many organic and inorganic additives introduced at relatively low concentrations can alter zinc precipitation, coating structure, morphology, and properties. One added additive can affect many properties of the coating, but in reality many additives are still added at the same time because they need their synergy. They make the coating smooth, flat, increase throwing power, have a nice gloss, work at a wide current density [3, 5-24]. In fact, in Vietnam, to meet the additive requirements for the galvanizing process of automobile and motorcycle manufacturers, a number of additive systems have been introduced and put into production. Since the early 2000s, ENTHONE has introduced to the Vietnamese market the NCZ DIMENSION additive system, the COLOMBIA company introduced the COLZINC ACF2 system, etc. However, the applicability of these preparations is limited due to the cost. High quality has certain limitations. 4 In the country, the study of additive systems for zinc plating in general and alkali galvanizing in particular has not been given adequate attention. There is no official research result published on the effects of these factors on the zinc plating process in general and the non-cyanide alkali galvanizing process in particular, and no supplier has given an additive system. for non-cyanide alkaline galvanizing tanks. Stemming from the above domestic situation, the selection of the topic: " studying the effects of some additives on the alkaline non-cyanide galvanizing process, orienting the fabrication of the additive system for alkaline non-cyanide zinc plating bath, oriented to the fabrication of the additive system for the alkaline galvanized tank "Meeting the practical needs, the research direction can create a product oriented application for the domestic alkali galvanizing industry, and at the same time add insights to support the galvanizing businesses." 2. Research aims and objectives Determining the effect of the single additive being organic and inorganic substances such as poly alcohol, poly amines, sodium salt of various modules and the combination of additives on the properties of the zinc coating created in the solution. alkaline plating solution without cyanide, compare the chemical and physical properties of the coating obtained from the non cyanide alkaline plating bath and other plating baths. Since then, an additive system can be used in alkaline zinc-plated tanks without cyanide 3. Main research content 1. Investigate the effects of the single additive on the throwing power capacity, current efficiency, cathode polarization, working current density range, surface morphology, gloss of the zinc coating. 2. Investigate the effects of the combination of additives on the throwing power capacity, current efficiency, cathode polarization, working current density range, surface morphology, and gloss of the zinc coating from there. an additive system that can be used for alkaline non-cyanide zinc plating bath. 3. Determine the mechanism of action of the additives on zinc precipitation and some properties of the coating in the alkaline non-cyanid zinc plating bath CHAPTER 1. INTRODUCTION In 1973, Robert Leonard Adelman and Wilmington [30] used a combination of polyvinyl alcohol, vinyl alcohol products modified by periodic acid or sodium perionate salt as a polishing agent for non-cyanide alkaline galvanizing baths, improving the coating at low current density. Modified alcohols polyvinyls are also 5 used with other polishing agents especially heterocyclic nitrogen compounds with at least one substituent group to improve coating properties. In 1979, in their invention, Zehnder and Stevens [29] used polyamin sulpho with very different concentrations from 0.1 to 100g / liter, combined with pyrydin compounds or nicotine content of a few g. / liter to improve galvanizing properties, in alkali-free cyanide baths. However, pyrydin compounds are known to be very toxic volatiles, affecting the health of those working in the surrounding environment. In recent years, there are quite a few inventions and works published about additives for alkaline galvanized tanks [2-7,1221,23,26-32]. Substances used as additives for alkaline galvanizing tanks belong to such lines as: alcohol polymers, polymers of level 1 to 4 amines, heterocyclic compounds, surfactants, benzanaldehyde, poly alcohol or heterocyclic nitrogen compounds have a substituent group of sulfide, reducing sugars, sodium salts, and a number of complexing agents are used together, in each case, to improve the coating properties, to change precipitation properties, crystal smoothing, wetting agent, polishing agent. In general, commercial products are used well, the stability system is not much, the system composition is quite complex, often consisting of 4 components. In addition, a variety of other organic and inorganic additives added at relatively low concentrations can alter zinc precipitation, coating structure, morphology, and properties. One added additive can affect many properties of the coating, but in reality many additives are still added at the same time because they need their synergy. They make the coating smooth, flat, increase throwing power, have a nice gloss, work at a wide current density [3, 5-24] 6 CHAPTER 2. MATERIALS AND METHODS 2.1. Sample preparation, chemicals and equipment 2.1.1. Research materials Test sample: low carbon steel has different sizes depending on the test. Research steel equivalent to SPHC grade according to JIS G3131 standard. 2.1.2. Sample preparation Table 2.2. Types of test samples and intended use TT Size, shape 1 2 3 50 x 50 x 1,8 mm 40 x 40 x 1,8 mm 70 x 100 x 1 mm  10 mm; electric wire welding, epoxy coated 4 Uses SEM, XRD, IR, current efficiency determination Throwing power of determination Test of Hull Cathode polarization, CV Table 2.3. Sample creation process TT 1 2 3 4 5 step Conducting conditions Polished Sandpaper No 100 to No 600 Solution 60 g/L UDYPREP-110EC (ENTHONE), -temperature : Degreasing 50 ÷ 80 oC, time 5 ÷ 10 minute. Pickling of rust Activation plating Solution HCl 10% thể tích, urotropin 2-3 g/L, time 2 ÷ 5 minute Solution HCl 5% volume, time 10÷ 15 seconds Zinc plating solution 2.1.3. Test solution. - Alkaline non-cyanid zinc plating solution S0 have ingredients are as follows: NaOH: 140 g/L ZnO: 15 g/L - Other test solutions were based on S0 solution and added with polyamine (poliethyleneimin), polyvinyl alcohol, and natrisilicate with different concentrations. The chemical used is pure (China) and mixed with distilled water. 2.2. Equipment - Plating bath made of PP plastic, capacity 20 liters,- Electrolytic machine, 12V-30 A - Hulls cell, 250 ml, - Haring-Blum cell, 400 ml - Analytical balance, technical balance SHIMADZU AEG-220G with accuracy 0.1 mg And some other devices 7 2.3. Methods of analysis 2.3.1. Hull method. 2.3.2. Haring-Blum methob 2.3.3. Method of determining cathode current efficiency 2.3.4. Measure cathode polarization curve. 2.3.5. SEM –Scanning Electron Microscope. 2.3.6. Fourier FTIR transform infrared spectroscopy method 2.3.7. Measuring ring polarization CHAPTER 3. RESULTS AND DISCUSSION The polymers that can be used as additives to the non-cyanide alkaline zinc plating system must be soluble in the plating solution, depending on the molecular weight that the solubility in the alkali galvanizing solution changes or does not dissolve. After investigating the solubility of polymers it is found that polymers should only be studied at concentrations from 0.05 g / L to 1.0 g / L to ensure they are completely dissolved in the plating solutions. The insoluble additives in the plating solution can become impurities, causing precipitates to enter the coating, which can affect the coating quality. 3.1. Effects of Polivinyl ancol (PVA) to zinc plating process PVA has the ability to complex with metal ions and adsorb on metal surfaces when there is an electric current by the carbon-oxygen bonding polarization in the molecular structure, so PVA is used by many authors as auxiliary. surface leveling for plating systems. Quite a few publications mention the use of PVA as an additive to alkaline non-cyanide zinc plating bath 3.1.1. Effects of the molecular weight of PVA on cathodic polarization. To determine the additive effect on the plating process, the method of measuring the steel electrode cathode polarization curve at 250C, scanning from -1.2 to -1.8 V with a scanning rate of 2 mV / s in the capacities translation with and without PVA, results in figure 3.1, figure 3.2 and figure 3.5. 8 Fig 3.1. Effect of PVA - 05 on cathodic polarization, from -1.2 to 1.8 V, sweep speed 2 mV / s , 250C Fig 3.2. Effect of PVA - 16 on cathodic polarization, from -1.2 to 1.8 V, sweep speed 2 mV / s , 250C These plots were swept from the open current potential towards the negative direction at a scan rate of 2 mV/s. In all cases, the polarization curves were characterized by appearance of the first cathodic peak (I) followed by either rapid rise in current density for plating bath without PVA or the second cathodic peak (II) for plating baths containing PVA. There was little difference between PVA plating baths at concentrations of 1.0 and 1.5 g/L. For the plating bath without PVA, the cathodic polarization plot had a peak I followed by rapid growth in current density. It was assigned to the reduction of Zn2+ to Zn that is corresponding to the reaction below: Zn(OH)42- + 2e- ↔ Zn + 4OH(3.q) The following four step reaction path has been proposed for the deposition of zinc from zincate solution where reaction (iii) as the rate determining step [13]: Zn(OH)42↔ Zn(OH)3- + OH(3.2) Zn(OH)3 + e → Zn(OH)2 + OH (3.3) Zn(OH)2 ↔ ZnOH + OH (3.4) ZnOH + e → Zn + OH (v) 2+ Since Zn preferred to exist as a tetra or hexa-coordinate species, the coordinated Zn(OH)3- is more likely to exist as Zn(OH)3(H2O)-, thus step (3.3) became as (3.4) below: Zn(OH)3(H2O)- + e- → Zn(OH)2- + OH- + H2O (3.6) It was also possible that PVA replaced the presence of H2O in the complex Zn(OH)3(H2O)- as step (vii). Zn(OH)3(H2O)- + PVA ↔ Zn(OH)3(PVA)- + H2O (3.7) Hence, energy is needed to break the PVA complex to deposit zinc on steel surface. It might be the reason of appearance of the peak II. Moreover, PVA was able to adsorb on the peaks of substrate surface, which inhibited zinc deposition at peaks and promoted discharge of zinc ions at valleys, 9 because PVA owed to the polarity of the carbon-oxygen bond. Consequently, leveling effect was formed on surface. However, these hypotheses should be investigated by further studies. 3.1.2. Study the effect of the additives in the plating process by method cyclic voltammogram a. Study the effect of PVA in the plating process by method cyclic voltammogram Polarization curves were measured in PVA-containing and non-PVA zincplating solutions to study the effect of PVA on potential values and maximum currents.. Table 3.1. Potential values, excesses and currents at the pips of the plating in a solution with and without PVA So Sp2-4 ECo EI’c EI’c VAg/AgCl (V) VAg/AgCl (V) VAg/AgCl (V) -1,48 -1,48 -1,54 -1,65 Fig 3.3. Cyclic voltammogram of the steel electrode was measured in alkaline zinc plating solutions without additives from -1.2 to -1.65 V, with a scan rate of 2 mV/s, at 25°C ∆𝐸’c (V) ∆E”c (V) -0,06 -0,17 Ip(I’c) Ip(I”c) 2 (mA/cm ) (mA/cm2) -27,35 -30,90 Fig 3.4. Cyclic voltammogram of the steel electrode was measured in alkaline zinc plating solutions with and without PVA-16 from -1.2 to -1.65 V, with a scan rate of 2 mV/s, at 25°C The steel electrode ring polarization curves measured in alkaline galvanized solution give results, the peaks I'c and I ”c are equivalent to the peaks (I) and the peaks (II) of the plating process. The chemical reaction is shown later (Figs. 3.1 and Fig. 3.2), Ia is the anode current corresponding to the dissolution of the coating. b.Study on effects of PVA on diffusion process 10 Fig 3.5. Cyclic voltammogram of the steel Fig 3.6. Graph of the dependence of 1/2 electrode was measured in alkaline zinc i on v scan in alkaline zinc plating solutions (S0) plating solutions (S0) -1,2 to -1,65 V, tốc canning rate change, 250C Research results of the study on the effects of PVA on the galvanizing process in non-cyanide alkali galvanizing solutions by the ring polarization scanning method showed that the presence of PVA in the plating solution increases the potential in plating solution at the same time reducing the current density at the adsorption peaks. The results show that the presence of PVA in the plating solution makes the slope a (reflecting diffusion coefficient D) of the line i dependent on v 1/2, it can be said that PVA-05 and PVA- 16 both increase the diffusion potential in the plating solution. The ability of the additive to cover surface (Ꝋ) is calculated by the formula: Ꝋ= 𝑖−𝑖𝑠 𝑖 (3.8) Where i is the current density without additives, is the current density without additives. Impact level Ꝋ is determined at the potent at -1,65 for results Table 3.2. Table 3.2. Coverage of PVA Dung dịch Ꝋ Ꝋ1 Ꝋ2 D S0 2,446 Sp1-4 0,53 0,55 0,23 -112,9 Sp2-4 0,67 0,61 0,47 -128,9 The results showed that PVA adsorbs the cathode surface at convex peaks, this adsorption process prevents metal precipitation at the protrusion points, metal precipitates at the convex peaks decrease, the metal will precipitate at adjacent concave positions to level the surface. This adsorption process also reduces the rapid increase in particle size, when the metal precipitates at a point, that point will rise higher, and react (3.9): Zn2+ + 2e- = Zn (3.9) The electron density at that location will decrease compared to the surrounding positions, the precipitated zinc position will have a more positive charge than the