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 [r]
(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
(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 ………
(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]
(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 INTRODUCTION
(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 [2-7,12-21,23,26-32] Substances used as additives for alkaline galvanizing tanks belong to such lines as: alcohol polymers, polymers of level to 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 components
(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 Uses
1 50 x 50 x 1,8 mm SEM, XRD, IR, current efficiency determination 40 x 40 x 1,8 mm Throwing power of determination
3 70 x 100 x mm Test of Hull 10 mm; electric wire
welding, epoxy coated Cathode polarization, CV
Table 2.3 Sample creation process
TT step Conducting conditions
1 Polished Sandpaper No 100 to No 600
2 Degreasing Solution 60 g/L UDYPREP-110EC (ENTHONE), -temperature : 50 ÷ 80 oC, time ÷ 10 minute Pickling of
rust
Solution HCl 10% thể tích, urotropin 2-3 g/L, time ÷ minute Activation Solution HCl 5% volume, time 10÷ 15 seconds
5 plating 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
(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 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
(8)Fig 3.1 Effect of PVA - 05 on cathodic polarization, from 1.2 to
-1.8 V, sweep speed mV / s , 250C
Fig 3.2 Effect of PVA - 16 on
cathodic polarization, from 1.2 to
-1.8 V, sweep speed mV / s , 250C
These plots were swept from the open current potential towards the negative direction at a scan rate of 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)
Since Zn2+ 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
(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 zinc-plating 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
ECo
VAg/AgCl
(V)
EI’c
VAg/AgCl
(V)
EI’c
VAg/AgCl
(V)
∆𝐸’c
(V)
∆E”c
(V)
Ip(I’c)
(mA/cm2)
Ip(I”c)
(mA/cm2)
So -1,48
Sp2-4 -1,48 -1,54 -1,65 -0,06 -0,17 -27,35 -30,90
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
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 mV/s, at 25°C
(10)Fig 3.5 Cyclic voltammogram of the steel electrode was measured in alkaline zinc plating solutions (S0) -1,2 to -1,65 V, tốc
canning rate change, 250C
Fig 3.6 Graph of the dependence of
i on v1/2 scan in alkaline zinc plating
solutions (S0)
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 v1/2, 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)
(11)surrounding position, PVA molecule has negative polarized OH (OH -) will go to the surface adsorption to the surface to hinder the precipitation process, the particle size does not increase, but more new particles appear in the vicinity, this process produces seeded seeds with size Small smooth, coating surface more even
3.2.3 Effect of molecular weight PVA on the zinc plating process (Hull method) The Hull method shows that when adding PVA to plating solutions with different concentrations, it has the effect of smoothing crystals compared to coatings in solutions that not contain PVA
As the PVA concentration increases, the surface of the zinc precipitate becomes smoother, the gloss and gloss are enlarged It can be explained that in the presence of PVA, the reaction (3.6) was changed PVA can replace the presence of H2O in Zn (OH)3 (H2O-) and become Zn(OH)3(PVA)- as in reaction (3.7) above As a result, the reaction (3.6) becomes (3.10) below:
Zn(OH)3(PVA)- + e → Zn(OH)2- + OH- + PVA (3.10)
Assuming that the reaction (3.10) is much slower than (3.6) due to the energy required to break the PVA complex, will explain PVA's seed crystal smoothing properties in the plating solution [12] The results of the study on the influence of PVA on the plating process by Hull method, the results are consistent with the polarization curves If the PVA concentration increases, the Zn(OH)3 (PVA) complex - produces more and therefore the zinc precipitate requires more energy to break down the complex, leading to a decrease in the galvanic current density in the plating sample in the capacitance solution with high PVA concentration
Fig 3.14 Hull cell pattern obtained from alkaline non-cyanide bath containing
PVA-05 with various concentrations
Fig 3.15 Hull cell pattern obtained
from alkaline non-cyanide bath
(12)3.1.3. Effect of molecular weight PVA to SEM images of the sample plated in alkaline bath
Fig 3.16 SEM images of the sample plated in alkaline bath
PVA – 05, 0,5 A/dm2
The presence of PVA-16 and PVA-05 in the plating solution reduces the particle size, changes SEM images, semi bright
3.1.4. Effect of molecular weight PVA to throwing power and performance
a Effect of molecular weight PVA tothrowing power
Table 3.7 Throwing power
TT C (g/L) Throwing power(0,5 A/dm
2) Throwing powerở (2 A/dm2)
PVA-05 PVA - 16 PVA-05 PVA - 16
1 30,2 30,2 25,9 25,9
2 0,05 40,1 42,7 37,8 40,6
3 0,10 47,9 44,1 44,9 49,2
4 0,25 62,3 55,8 56,3 52,1
5 0,50 64 76,2 64,7 64,3
6 1,0 72,2 77,2 70,9 70,3
Table 3.9 results show that adding PVA in plating solution increases the throwing power of the plating process The distribution increase is highly dependent on the PVA concentration in the plating solution, while less dependent on the working current density
PVA-16 has greater molecular mass than PVA-05, and also has a greater impact on throwing power than PVA-05
(13)Table 3.10 Performance of plating system with and without PVA
TT C (g/L) performance (0,5 A/dm
2) performance (2A/dm2)
PVA -05 PVA - 1600 PVA-05 PVA - 1600
1 80,7 80,7 79,2 79,2
2 0,05 72,7 73,9 39,91 56,65
3 0,10 67,1 69,3 23,53 41,8
4 0,25 49,08 55,8 11,59 19,89
5 0,50 34,92 36,2 7,56 9,15
6 1,0 15,93 15,2 7,18 7,43
The presence of PVA reduces plating efficiency
3.2. Effect of BT on the galvanizing process
3.2.1. Effect of BT on cathodic polarization
The polarization lines are measured in alkakine on-cyanide zinc plating solution with and without BT variable molecular and concentration to evaluate of BT on plating process
Fig 3.20 Effect of BT on cathodic polarization, -1,2 to -1,8V, 2mV/s, 250C
The results showed that, the BT with different molecular weights, added to the plating solution at the same concentration, the BT has a higher molecular weight than BT-200, BT-700, has less effect on polarization cathode than BT with low molecular weight BT-12, BT-18 (Fig 3.21) Due to the same concentration, the low molecular weight exercises contain more molecules, participating in the reaction at more locations
(14)Table 3.9 Peak values of
galvanizing process in solution with and without BT-18
solution ECo
VAg/AgCl (V) EI’c VAg/AgCl (V) EI’c VAg/AgCl (V) ȠI’c (V) ȠI”c (V) Ip(I’c) mA/cm2 Ip(I”c) mA/cm2
S0 -1,48
SB2-1 -1,48 -1,52 -1,59 -0,04 -0,11 27,70 40,7 SB2-2 -1,48 -1,52 -1,56 -0,04 -0,08 18,60 43,18 SB2-3 -1,48 -1,53 -1,59 -0,05 -0,05 32,70 39,76
SB2-4 -1,48 -1,53 -1,6 -0,05 -0,05 30,90 41,58
SB2-5 -1,48 -1,52 -1,65 -0,04 -0,04 18,50 43,10
Fig 3.23 Cyclic voltammogram of the steel electrode was measured in alkaline
zinc plating solutions (S0)+ BT-700, -0,5 đến -1,65 V, mV/s, 250C
Table 3.10 Peak values of
galvanizing process in solution with and without BT-700
Solution ECo
VAg/AgCl (V) EI’c VAg/AgCl (V) EI’c VAg/AgCl (V) ȠI’c (V) ȠI”c (V) Ip(I’c) mA/cm2 Ip(I”c) mA/cm2
S0 -1,48
(15)Fig 3.26 Cyclic voltammogram of the steel electrode was measured in alkaline zinc plating solutions (S0)+ BT-700 -1,2 to -1,65 V, tốc canning
rate change, 250C
Fig 3.27 Graph of the dependence of
i on v1/2 scan in alkaline zinc plating
solutions (S0)+ BT-700
Table 3.11 Values on the graph of the dependence of i on v1/2 scan in alkaline
zinc plating solutions (S0)+ BT-700
R2 Coefficient a (reflects diffusion coefficient D)
b
S0 0,9942 244,6 -6,3
SB2-4 0,9499 -181,3 0,045
SB4-4 0,9678 -77,7 5,63
The results show that the presence of BT in the plating solution makes the slope a (reflecting coefficient D) of the dependent line of i in v1 / 2, it can be said that BT-18 and BT 700 both increase the diffusion potential in the plating solution
Table 3.12 Coverage of BT
Solution Ꝋ Ꝋ1 Ꝋ2 D
S0 244,6
SB2-4 0,49 0,37 0,25 -181,3
SB4-4 0,61 0,56 0,43 -77,7
Table 3.12 shows that BT adsorb the cathode surface at convex peaks, this adsorption process prevents metal precipitation at the protruding points, the metal precipitates at the convex peaks is reduced, the metal will precipitate at adjacent concave positions to level the surface
This adsorption process also prevents the rapid increase in particle size, when the metal precipitates at a point, the point will rise higher, and the reaction occurs(3.9):
(16)At the current density at that location lower than the surrounding locations, the precipitated zinc position will have a more positive charge than the surrounding positions, the BT molecule has the function group -N = has double Free electrons will go to, adsorbed on the surface to hinder precipitation, the particle size does not increase, but more new particles appear in the vicinity, this process creates seed plated with small size smooth, coating surface more even
BT with larger molecular weight has higher coverage than BT with smaller molecular weight
Studying the stability of the plating process in a solution containing polyamide additive
Measurement of the 10-sweep polarization curve in the plating solution containing BT, the results show that from round to round the peak height decreases, this shows that in the first scan the coating still has convex peaks, Convex vertices are leveled after sweep rings After the 5th round of scanning, the rings from 6, 7, 8, 9, 10 have the same peak heights, this shows that the coating surface has become flat after rounds of scanning
3.3.4 Effect of molecular weght BT to brightness and bright range (Hull)
Fig 3.29 Hull cell pattern obtained from BS containing BT-12
(17)Table 3.13 Effect of the number of substituents and molecular weight of polyamines on brightness and bright ranges of zinc deposits in non-cyanide
alkaline plating bath
TT
Additive content
(g/L)
Semi-bright ranges (A/dm2) The highest brightness of
samples at 60°
BT-700 BT20 BT-18 BT-12 BT-700 BT20 BT-18 BT-12
1 0,00 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
2 0,05 0,0 < 6,0 < 2,0 < 1,0 0,0 2,6 2,1 1,4
3 0,1 0,0 < 6,5 < 5,5 < 3,0 0,0 4,3 4,0 3,7
4 0,25 <5 <5,0 < 5,5 < 4,0 11,6 7,2 8,3 5,4
5 0,5 0,7÷10 <7,0 < 4,0 < 5,0 51,4 39 15,7 9,5
6 ,00 <10 Cả < 3,0 <10,0 56,7 38,0 14,0 6,1
The BT is added to the alkali galvanizing solution at a concentration of 0.05 g / L for a smoother coating, which looks more uniform at variable current densities, a better coating distribution on the Hull plate than coating in alkaline zinc solution without BT When increasing the BT concentration in the plating solution to 0.1; 0.25; 0.5; 1.0 g / L coating on the Hull plate has a wider semi-gloss, in the gloss semi-gloss area increases BT with low molecular weight BT-12, BT-18 affects the surface leveling process, the crystal smoothing is less than BT with high molecular weight BT-200, BT-700
BT-200 is added to the plating solution at a concentration of g / L semi-gloss over the entire Hull plate However, the measured glossiness is reduced compared to the 0.5 g / L sample
Effect of BT on coating glossiness of: BT-700, BT-200> BT-18, BT-12
(18)the area of flow density where these additives are most effective Select current density of 0.50 A / dm2 and 5.0 A / dm2 for further studies
3.3.5. Effect of BT to SEM images
Fig 3.40 SEM images of the sample plated in alkaline bath
BT – 700, 0,5 A/dm2
The results show that the high molecular weight polyamide BT-12 and BT-18 affect the surface morphology, the larger, the low molecular weight polymins BT-200 and BT-700 Image Figs of the coating in an additive-free solution at current densities of 0.5 A / dm2 and 5.0 A / dm2 (M0) show that, when plating in an additive-free solution, the image current density greatly affects the seedling size
3.3.6. Effect of molecular and concentration BT to performance and Throwing
power
a Effect of molecular and concentration BT to performance
Table 3.14 Effect of molecular and concentration BT to performance
TT
Additive content
(g/L)
performance (0,5 A/dm2) performance (5 A/dm2) BT-12 BT-18 BT-200 BT-700 BT-12 BT-18 BT-200 BT-700
1 0,0 80,7 80,7 80,7 80,7 79,2 79,2 79,2 79,2
2 0,05 25,5 23,8 81,8 59,8 28,1 27,8 39,3 70,9
3 0,1 19,2 19,1 79,4 57,4 25,3 27,2 35,3 47,1
4 0,25 18,1 18,3 63,6 53,3 21,1 22,4 31,1 31,4
5 0,50 17,2 18,3 58,2 46,3 17,6 17,2 25,9 22,2
6 1,0 14,1 16,7 46,1 36,7 17,1 16,9 22,1 21,9
The presence of BT in the plating solution, it reduces the plating performance compared to the plating sample in a polyamide-free plating solution
(19)Table 3.15 Effect of molecular weight and concentration BT to throwing power
TT Additive
content (g/L)
Throwing power(0, 5A/dm2)
(%)
Throwing power (5 A/dm2)
(%)
BT-12 BT-18 BT-200 BT-700 BT-12 BT-18 BT-200
BT-700
1 0,0 80,7 80,7 30,2 30,2 25,9 25,9 25,9 25,9
2 0,05 38,2 38,9 37,5 48,4 38,6 41 37,2 41,8
3 0,10 39 39,2 38,8 49,5 39,8 42,9 39 42,4
4 0,25 44,9 45 42,5 58,3 45,3 45,6 43,1 43,6
5 0,50 51 50,5 49,6 60,8 53,7 51,2 52,6 46,3
6 1,0 58,7 60,1 60 66,6 62,1 59,3 61,3 49,1
Table 3.15 It was shown that when poliamin was added to plating solution with different concentrations and molecular weights increased distribution compared to plating in non-BT plating solutions
The increase in distribution depends much on the concentration, molecular weight and on the BT working current density in the plating solution When plating at a high working current density, the distribution is inferior to that of a seedling at a low working current density
3.4. Effect of natrisilicate and polyamide - natrisilicate system on zinc plating process
3.4.1. Effect of natrisilicate and polyamide - natrisilicate on cathodic polarization
After researching, the effect of molecular weight and polyamide concentration on zinc plating in alkaline plating bath without cyanide, BT-700 concentration 0.5 g / L was selected as the base additive Poliamin BT-700 crystal smooth, for semi-gloss coating, high measured gloss, about 0.8 to over 10.2 A/dm2 semi-gloss However, the coating surface is not uniform, the test should be conducted very carefully because it is very sensitive and difficult to use in industry Plating in the plating solution contains only additive BT-700 for low cathode efficiency, at a current density range <0.8 A /dm2 the dark coating, so it is necessary to combine with a second additive to increase stability of the base additive in the plating system, increasing the plating efficiency and extending the semi-gloss towards the low current density
(20)not change the zinc precipitation substitution, while the polyamide shifts the precipitation potential of zinc to a more negative side, từ -1.48 lên -1.62 V (Fig 3.43a)
Fig 3.43 Effect of natri silicate and polyamide – natri silicate on cathodic
polarization -1,2 đến -1,8 V, tốc độ quét mV/s, 250C
The results showed that when the concentration of natrisilicate in the plating solution increases, the cathode polarization increases Measurement in a plating solution with a natrisilicate concentration of maximum g / L for maximum polarity The addition of g / L natrisilicate to the alkaline galvanizing solution showed that cathode polarity increased as the natrisilicate modulus increased The polarization lines measured in alkaline zinc solutions with poliamin and natrisilicate of different modules have an adsorption peak, the absorption peak shifts to a more negative direction when the natrisilicate modulus is increased
3.4.3 Ảnh hưởng poliamin natrisilicat đến độ bóng khoảng bóng lớp
mạ kẽm bể mạ kiềm không xyanua theo phương pháp Hull
(21)Row 1: Hull sample plated in corresponding solutions, (b) S0: NaOH solution 14 g / L + ZnO 15 g / L, (a) SB4-4 solution S0 + 0.51 g / L BT- 700, (c) Solution S0 + g / L natrisilicate,
Row 2: Hull samples plated in the respective solutions, (d) Mn1-1: S0 + g / L modulus natrisilicate (e) Mn1-2: S0 + g / L modulus natrisilicate 1, (f) Mn1 -3: S0 + 16 g / L modulus natrisilicate 1,
Row 3: Hull samples plated in the corresponding solutions, (d) Mn2-1: S0 + g / L modulus natrisilicate 2,5 (e) Mn2-2: S0 + g / L modulus natrisilicate 2,5, (f) Mn2-3: S0 + 16 g / L modulus natrisilicate 2,5,
Row 4: Hull samples plated in the corresponding solutions, (d) Mn3-1: S0 + g / L modulus natrisilicate (e) Mn3-2: S0 + g / L modulus natrisilicate 3, (f) Mn3 -3: S0 + 16 g / L modulus natrisilicate 3,
The research results show that poliamin acts on all research properties, for the galvanizing process in alkaline plating baths without cyanide While natrisilicate only affects some properties of the plating process
Poliamin increases cathode polarization and shifts the precipitation potential of zinc to a more negative side from -1.48 to -1.62 V Natrisilicate affects only cathode polarization but does not change the zinc precipitation potential
The Hull method shows the presence of polyamide in crystal smoothing solution, semi-gloss coating on almost the entire Hull sheet Adding natrisilicate creates a brighter and more uniform coating
The study of surface morphology showed that adding more poliamin, the particle size decreased sharply and there was no grain The particle size is about to µm in the plating sample in a solution not contained in polyamide to a flat surface with no visible particles in the plating sample in the polymer addition solution Adding only natrisilicate did not significantly reduce the size of the particles However, more uniform particles were found The addition of natrisilicate and in the plating solution containing polyamide more uniformity is observed on the coating surface
The addition of natrisilicate has little effect on the plating efficiency but significantly increases the coating throwing power
After the study, the 2-component additive system was selected as follows:
Table 3.20 Thesis additive system and parameters of the system
poliamin Natrisilicat Khoảng
bóng Độ bóng
Hiệu suất (%)
Phân bố (%)
BT-700
0,5 g/L Modun 3/8 g/L
0,06÷trên10 A/dm2
109.9 139.5 117
(22)3.4. Studying effects processes of additives on the plating process
3.5.1. Studying on the coating composition of additives by infrared spectrum
Additives and coatings in the alkaline galvanizing solution and the alkaline plating solution contain additives, captured by infrared spectroscopy, to study the participation of additives in the coating composition
Infrared spectrum results show that PVA does not participate in membrane composition
3.5.2. Studying the effects of additives on zinc crystals by XRD
Effects of the additives on zinc crystals were studied by XRD
Research according to the XRD method shows the results: zinc crystals change proportions in different planes, combined with surface morphology studies, the Hull study shows the change in this rate for layers The seedlings are arranged tighter, the surface of the coating is smoother, creating better gloss and adhesion Analysis results of the XRD (Table 2.21) schematic analysis of crystals in solutions containing and without additives showed that: the zinc coating in the alkaline plating solution contains and does not contain PVA and BT additives in both The research current density is for hexagonal zinc crystal The most obvious change is the FIG to 100 in both study additives This result has also been shown in the study of Aparicio [17] Besides, the analysis of the seed crystal size in the plating solutions shows that when adding additives to the plating solution, the crystal size of the seedlings changes 3.6 Compare the coating properties to that of commercial alkali galvanizing
and other plating systems.
The alkaline galvanizing system of the thesis, commercial systems, with added additives, with the optimal and upper and lower bound, according to technical data, is called medium concentration, high concentration, concentration low electrolysis according to different research methods, to compare the properties of the coating and the plating system
3.6.1. Ảnh hưởng nồng độ chất phụ gia hệ mạ kẽm tới độ bóng
của lớp mạ dải mật độ dịng thích hợp, phương pháp Hull
(23)Fig 3.51 Hull cell pattern obtained from plating systems
Row 1: The plating sample in plating systems does not contain additives
Row 2: Galvanizing samples in the non-cyanide alkaline galvanizing system of the thesis Row 3: Sample plated in a commercial non-cyanide alkaline zinc-plated system Row 4: Galvanized sample in commercial ammonium-chloride galvanizing system In addition, the coating needs to improve the gloss gap in the low current density area The zinc chloride system has good gloss and gloss, but the disadvantage is that it causes environmental pollution, ammonium ion-containing waste is difficult to handle
Table 3.22 Brightness and bright ranges of zinc deposits in non-cyanide alkaline plating bath
TT Solution for
plating bright ranges
Brightness at 600 High
density
Average density
Low density
1 Mo 0,0 0,0 0,0 0,0
2 Ma-1 0,8÷10,2 A/dm2 96,7 98,8 91,1
3 Ma-2 0,4÷10,2 A/dm2 107,4 113,9 109,3
4 Ma-3 0,4÷ 10,2 A/dm2 109,9 139,5 117
5 Mt-1 0÷ 10,2 A/dm2 83,5 87,4 83,7
6 Mt-2 0÷ 10,2 A/dm2 86,1 87,0 98,9
7 Mt-3 0÷ 10,2 A/dm2 105 103,2 120
8 Mc 0 0
9 Mc-1 0÷ 10,2 A/dm2 164 163 155
10 Mc-2 0÷ 10,2 A/dm2 384 380 348
(24)Effect of additives to Throwing power and cathodic current efficiencies
Table 3.23 Throwing power and cathodic current efficiencies of the plating process in solution contains various additives
solution efficiencies (%) Throwing power(%)
S0 79,2 25,2
Sa-1 52,616 61,246
Sa-2 45,1 66,2
Sa-3 35,560 77,384
St-1 51,02 73,31
St-2 47,692 80,282
St-3 44,836 86,228
Sc 98,176 26,225
Sc-1 87,353 32,132
Sc-2 78,077 38,372
Sc-3 95,393 32,92
The study comparing the advantages and disadvantages of the zinc plating process from the proposed two-component additive system with the galvanizing process from other methods gives the results Table 3.23: When using the proposed additive system at the concentration the low level for the plating process has the galvanizing efficiency equivalent to that of commercial alkali galvanized additive system, throwing power is higher than that of zinc ammonium chloride
In addition, the plating process also needs to improve the plating efficiency and distribution when using the additive system at high concentrations, this is because the proposed 2-component additive system is incomplete, so studies are needed next to combine the right ingredients
CONCLUSION
1- Investigated the effect of additives of different molecular weight polymin and polivinyl alcohol group on properties of zinc coating formed from alkali plating process The results of investigating the effects of the additives with molecular weight, concentration used on coating properties showed that polyamide BT-700 at 0.5 g / L concentration gives the best coating quality
(25)and desorption process, change the precipitate, diffusion potential, change the crystal structure, increase throwing power and decrease cathode flow efficiency 3- Study on the effects of a combination of two additives including poliamin and natrisilicate shows that the coating quality is significantly improved, the gloss and gloss, the ability to distribute increases, the coating is more uniform than when only using an additive From the obtained survey results, a suitable 2-component additive system is proposed, including: Poliamin BT-700 - 0.5 g / L + modulus natrisilicate -8 g / L
4- Conducted research to compare the advantages and disadvantages of the zinc coating made up of the proposed 2-component additive system with those made from other methods with the following results: zinc plating made up of the proposed 2-component additive system is quite high compared to that made up of a commercial alkaline galvanizing system
NEW CONTRIBUTIONS OF THESIS
1 Effect of sodium silicate on electrodeposited process and properties of electrodeposited coatings was studied Obtained results showed that sodium silicate almost had not effect on electroplating process and electrodeposited coatings’ properties while sodium silicate combined with polyamine BT700 significantly affected on electroplating coatings such dispersion capacity of electroplating solution improvement, electroplating coating had high gloss and better uniform throwing power in coating thickness, which only shows uniformity coefficient on the surface of plating workpiece
(26)LIST OF PUBLISHED
Qualy reinforcement of electroplating zinc coatingselectrodeposited from cyanide free alkaline solution by poliamine 70.000 and Polivinyl alcohol 16.000 “Truong Thi Nam, Le Ba Thang, Nguyen Thi Cam Ha, Hoang Thi Huong Thuy, Hoang Van Hung” Vietnam Journal of Science and Technology, 55 (5B), 18-26 (2017)
2 The effect of poliamine 70000 (BT-700) on the zinc plating process in the non-cyanide alkaline plating bath Truong Thi Nam, Le Ba Thang, Nguyen Thi Thanh Huong, Nguyen Van Khuong, Nguyen Van Chien, Le Duc Bao Do Ngoc Bich Tạp chí hóa học, 55 (4), 400-405 (2017)
3 The effect of sodium silicate and poliamine – sodium silicate system on the alkaline non-cyanide zinc plating process “Truong Thi Nam, Le Ba Thang, Le Duc Bao, Nguyen Thi Thanh Huong, Nguyen Van Khuong, Nguyen Van Chien, Nguyen Thi Cam Ha” Vietnam Journal of chemistry, 55 (5e12), 425-429 (2017)
4 Effects of molecular weight of poliamine on the alkaline non-cyanide zinc plating process “Truong Thi Nam, Le Ba Thang, Nguyen Thi Cam Ha, Nguyen Quoc Dung, Hoang Thi Huong Thuy Processdings Asam – 6, 616-621(2017)