Study the Rate of Deposition of Zinc Metal Ions on Metal by using Various Chemicals
Digambar Shelkeα, Pranav Chaudhariσ & Sagar Bhusalρ
The impact of corrosion on a system is usually a surface development. One of the key factors in any corrosion state of affairs is that the medium. This has found a wider influence on material strength and performance behavior. Environment is a variable that may modification with time and conditions, it affects a metal corresponds to the micro-environmental conditions. Zinc deposition is the phenomenon that uses an electric link to absorb dissolved metal cations form the solution so that they form a thin metal coating layer on an electrode. Zinc deposition is basically used to improve the surface properties of an electrode (such as abrasion and wear resistance, lubricity, corrosion protection, aesthetic qualities), but may also be help to build up coherent layer on undersized parts or to form objects by electroforming. After study of deposited zinc on the metal, various methods of deposition reviewed and identified best suitable method. Also based of various operation parameters the effects of operating parameters/ factors affecting on performance of deposition of zinc metal ions has been reviewed.
Keywords: Zinc Deposition, Metal ions, Anode, Cathode, Current.
Author ασρ: Department of Chemical Engineering Sir Visvesvaraya Institute of Technology, Chincholi Nashik, India.
The impact of corrosion on a system is usually a surface development. One in every of the key factors in any corrosion state of affairs is that the medium. This has found a wider influence on material strength and performance behavior. Environment is a variable that may modification change with time and conditions, it affects a metal corresponds to the micro-environmental conditions.
Zinc deposition is the phenomenon that uses an electric link to absorb dissolved metal cations form the solution so that they form a thin metal coating layer on an electrode. Zinc deposition is accustomed modification the surface properties of associate object (such as abrasion and wear resistance, lubricity, corrosion protection, aesthetic qualities), however may additionally be accustomed build up thickness on undersize elements or to make objects by electroforming.
The process employed in of zinc deposition termed electroplating or electro-deposition. It is primarily done by the action of zinc deposition. In one technique the cathode of circuit is the part which is going to be plated and in other technique the anode is made of the metal part which is to be plated. Both components are placed in a solution called an electrolyte solution of various chemicals which containing one or more dissolved metal ions as well as other ions that permit the flow of electricity. A power supply provides a direct current to the anode, oxidizing the metal atoms that it contains and permitting them to dissolve within the solution. At the cathode, the dissolved metal ions within the solution are reduced at the interface between the cathode and the solution, such that they "deposit out" onto the metal part. The speed at that the cathode is plated is capable that the rate at which the anode is dissolved. During this manner, the ions within the electrolyte bath are unchangingly renewed by the anode.
OBJECTIVES AND SCOPE
- To study the rate of depositions of zinc metal ions on metal by using various chemicals at various compositions
- To study the rate of depositions of zinc metal ions on metal by varying current
- To study the advantages of zinc deposition or electroplating over the other conventional processes like spraying, dipping or painting etc.
- To Performance evaluation of process parameters for the zinc-deposition of zinc on metal
- The importance of removing heavy zinc metals ions from particular industrial or domestic wastewater and chemicals
- Zinc deposition is frequently used to refurbish the various old metal parts
METHOD OF DEPOSITION
3.1 Electrochemical Deposition
Electrochemical deposition is usually used for the expansion of metals and conducting metal oxides attributable because of the following advantages: the thickness and morphology of the nanostructure will be exactly controlled by adjusting the electrochemical parameters; comparatively uniform and compact deposits will be synthesized in template-based structures; higher deposition rates are obtained; and the equipment is inexpensive due to the non-requirements of either a high vacuum or a high reaction temperature.
Figure 1: Electrochemical deposition
3.2 Pulse electroplating or pulse electro-deposition (PED)
A simple and closely connected method is pulse electroplating. This method involves the swift alternating of the potential or current between two different values leading to a series of pulses of equal amplitude, period and polarity, separated by zero current. By dynamical the heart beat amplitude and dimension; it’s doable to vary the deposited film's composition and thickness.
The experimental parameters of pulse electroplating sometimes accommodate peak potential, duty cycle, frequency and effective potential. Peak potential is that the most setting of electroplating current or potential. Duty cycle is that the most effective portion of your time in bound electroplating amount with the presenter potential applied. The effective potential is calculated by multiplying the duty cycle worth of peak value of current or potential. Pulse electroplating might facilitate to enhance the standard electroplated film and unharness the inner stress engineered up through quick deposition. Combination of the short duty cycle and high frequency could decrease the surface cracks. However, in order to maintain the constant effective current or potential, a high performance power supply may be required to provide high peak potential and fast switch. Another common problem of pulse electroplating is that the anode material could get plated and contaminated during the reverse electroplating, especially for the high cost, inert electrode like platinum.
3.3 Brush Electroplating
A closely related process is brush electroplating, in which localized areas or entire items are plated using a brush saturated with plating solution. The brush, typically a stainless steel body wrapped with an absorbent cloth material that both holds the plating solution and prevents direct contact with the item being plated, is connected to the anode of a low voltage direct current power source, and the item to be plated connected to the cathode. The operator dips the brush in plating solution then applies it to the item, moving the brush continually to get an even distribution of the plating material.
Figure 2: Brush Electroplating
Plating has several advantages over tank plating, including portability, ability to plate items that for some reason cannot be tank plated (one application was the plating of portions of very large decorative support columns in a building restoration), low or no masking requirements, and comparatively low plating solution volume requirements. Disadvantages compared to tank plating can include greater operator involvement (tank plating can frequently be done with minimal attention), and inability to achieve as great a plate thickness.
3.4 Electro-less Deposition
Usually an electrolytic cell (consisting of two electrodes, electrolyte, and external source of current) is used for electro-deposition. In contrast, electro less deposition uses only one electrode and no external source of electric current. However, the solution for electro less deposition needs to contain a reducing agent. In principle any hydrogen-based reducing agent can be used although the redox potential of the reducing half-cell must be high enough to overcome the energy barriers inherent in liquid chemist Electro less nickel plating uses hypophosphite as the reducer while plating of other metals like silver, gold and copper typically use low-molecular-weight aldehydes.
A major benefit of this approach over electroplating is that the power sources and plating baths are not needed, reducing the cost of production. This technique can also plate diverse shapes and types of surface. The downside is that plating is usually slower and cannot create thick plates of metal. As a consequence of these characteristics, electro less deposition is quite common in the decorative arts.
Figure 3: Electro-less Deposition
The rate of zinc deposition can be carried out by the some of the following methods like bath preparation, deposition of cathode current efficiency and deposit thickness, cathodic polarization studies, rate of zinc deposition which have been described below:
4.1 Bath Preparation
Zinc was electrodeposited from additive-free, aqueous solutions composed of standard laboratory reagents. Various types of chemicals was poured into a beaker and the reagent was added gradually with mild agitation initially and then more vigorously, to enhance dissolution. Measurements of pH were carried out using digital pH meter, and adjusted accordingly the concentration of the chemical solution. The solution was finally made up with respect to the size of the bath by adding more chemicals and size of the bath should be based on the scale of the production. The whole process was carried out at room temperature (approximately 220C).
4.2 Deposition of Cathode Current Efficiency and Deposit Thickness
Cathode current efficiency and deposit thickness were measured gravimetrically. Pre-weighed samples after plating were first rinsed immediately in running tap water, immersed in acetone, dried in a stream of warm air and then weighed again to determine the weight gain. Cathode current efficiency and deposit thickness were subsequently calculated using the following formulae:
Cathode Current efficiency (CCE) = ΔW/ WT * 100% (1)
CCE – Cathode current efficiency (%)
ΔW – Change in weight after plating (g)
WT - Theoretical weight of deposit (g)
WT = I * t * MZn / n* F (2)
Where, I = Current (A)
t = Time (second)
MZn = Molecular weight of zinc (g/mole)
F = Faradays constant (96,500 C/mole)
n = Number of electrons involved in the reaction
4.3 Cathodic Polorization studies
Cathode polarization studies were conducted for zinc using an ACM Instruments computer controlled potent ion stat, linked to a personal computer. Each test was carried out on a panel blanked off with chemically inert tape to expose an area of 10 cm2 (2.5 cm x 4 cm). The counter electrode material was platinum. Each of these different sets of polarization studies was conducted in order to obtain mechanistic data for metal deposition.
4.4 Rate of Zinc Deposition
Faraday’s law indicates that the weight of the zinc deposited in an electrolytic process is proportional to the current, plating time and its chemical equivalent.
W = Ite (3)
Where, W is the weight (in grams) of metal deposited,
I is the current (A),
t is time (secs) and
e is the chemical equivalent. The product of current and time (It), is the quantity of electricity passed.
For a given coulomb, the weight of an element discharged is proportional to its chemical equivalent. One Faraday (F) deposited a gram-equivalent of an element of atomic weight A.
W = ItA/nF (4)
F = Faraday (an electricity to deposit 1 gram equivalent of metal = 96500 coulomb or 26.8 ampere – hour),
C = Coulomb,
n = valence of the element,
V. FACTOR AFFECTING TO ZINC DEPOSITION
5.1 Effect of Current Density and Distribution
In the electro deposition process the uniform coating of specimen is depending upon the current distribution parameter. In general, the metal ions are attached to the cathode at certain favored sites. This condition will possibly result to the presence of discontinuities in the form of pores, cracks or in other irregularities. Thus, In Zinc deposition, current density and its distribution parameter play a centrally important role in determining the uniform coating of the final deposit. In the electro deposition process the current density over a cathode will vary from point to point. Current tends to concentrate at edges of the object.
In the Zinc deposition process cathode current density must be held within the proper interval with respect to bath composition and temperature. Insufficient current for given specimen will result in poor coating, while the presence of excessive current does not necessarily result in increased plating rate and is liable to create other difficulties. Low current densities tend to result higher impurity presence in the deposits. The reason for this is that once over the limiting current density for good deposition, hydrogen ions discharge occurs, that in turn; increase the pH level at cathode and- causing metal hydroxide ions to be included in the deposit coating.
To summarize, the optimum current density ranges for given plating bath is depending on composition of salt, operating conditions and the type of the plating sought. Anode current densities are also an important plating parameter and should be controlled properly. This can be done through the adjustment of the total anode area and the proportion of it made up of the metal being deposited.
5.2 Effect of pH
The value of pH is depending upon the composition of Bath. The pH value should be maintained for good result. The pH of the bath influences the hydrogen evolution voltage, the precipitation of basic inclusion, the decomposition of the complex or hydrate from which the metal is deposited, and the extent of adsorption of additives. In a complex bath, pH may influence equilibrium between various processes. When the anode is insoluble, oxygen evolution takes place at the anode
2H2O →O2 + 4H+ + e-
On the other hand, hydrogen evolution at the cathode is accompanied by the production of hydroxide ion:
2H2O+ 2e- →2OH- + H2
In a neutral bath, if the current efficiency is greater at the anode than at the cathode, the bath becomes more alkaline. If the electrode efficiencies are similar, the pH of the bath remains unchanged. Hence change in pH of a plating bath is a good indication of electrode efficiencies. In certain conditions precipitation of metal hydroxides may occur locally within the cathodic double layer, which get co-deposited with the plated metal and give defective deposit while increasing the pH due to hydrogen evolution. Thus buffers are necessary to minimize these pH changes. During Electro deposition of aqueous solution, hydrogen ions are discharged together with the ions of the metal being deposited. The hydrogen evolved not only has a detrimental influence on the plating rate and on the cathodic current efficiency, but it often also unfavorably affects the structure and properties of the metal being deposited by causing spongy or powdery deposits, pitting or other defects. In the Electro deposition, the metal of iron group or the-metal with ‘low hydrogen overvoltage are very sensitive to the Concentration of hydrogen ions in the electrolyte, a change in the pH value considerably affects both the cathodic current efficiency and the structure of the electrodeposits.
5.3 Effect of Temperature
In general, a rise in bath temperature causes a rise within the crystal size. Raise in bath temperature rise solubility and thereby the transport number, which in turn leads to increased conductivity of the solution. It also decreases the viciousness of the solution, thereby replenishing the double layer comparatively quicker. High bath temperature sometimes decreases less adsorption of hydrogen on the deposits and thereby reduces stress and tendency toward cracking.
By increasing the bath temperature from 45°C to 55°C, the grain size of deposit partial will be decreased, whereas additional increase of bath temperature resulted during a contrary result.
5.4 Effect of Bath Concentration
Generally, within the Electro deposition method, bath concentration obeying a crucial role to the plating performance. In traditional plating condition, the rise of bath concentration can increase the Concentration of metal ions in solution. Therefore, it will increase the deposition rate of the plating method.
5.5 Effect of Plating Time
In general, the plating thickness is increase directly proportionately to the plating time and current According to the Faraday's Laws, amount charge flow, Q within the solution is proportional to the current flow, l and also the Flow time, t as show in equation:
Q = I × T (5)
5.6 Nature of Metal
Supported on the magnitude of polarization, metals will be classified into three groups. Cluster I consists of metals like Ag, Pb, Cd, Sn etc., which are deposited at associate over-potential of a some milli volts and rough deposits are obtained with grain size bigger than 10-3 cm. Cluster III consists of metals like Ni, Co, Fe etc., which are related to an oversized electrochemical polarization and are deposited as dense deposits with the grain size of around 10-5 cm. Cu, Bi, and Zn constituting the II cluster are intermediate metals with relate to the over potential value and grain size of the deposit. The interaction of the substrates with the deposited metal differs and this have an effect on the kinetics of nucleation and hence the number of grains per unit area.
EQUIPMENT DESIGN AND EXPERIMENTAL PROCEDURE
6.1 Equipment Design
Figure 4: Experimental Setup of Zinc Deposition
The cell is graduated by using deposited thickness of the cathode panel and assuming appropriate current efficiencies. A formula could also be derived having the subsequent form
C = I (5.1- 5.25 log x) (6)
C = current density
I = current applied
x = distance to be measured on the panel
6.2 Experimenal Procedure Case study of Copper Plating
The cations go together with the anions in the solution. These cations are reduced at the cathode to deposit in the metallic, zero valence state. For example, for copper plating, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons. The Cu2+ associates with the anion SO2−4 in the solution to form copper (II) sulfate. At the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. The result’s the effective transfer of copper from the anode supply to a plate covering the cathode.
Many plating baths embody cyanides of different metals (such as potassium cyanide) in additionally to cyanides of the metal to be deposited. These free cyanides facilitate anode corrosion, facilitate to keep up a relentless metal particle level and contribute to conduction. In addition, non-metal chemicals such as carbonates and phosphates may be added extras to extend conduction.
Figure 5: Copper Plating
6.3 Support Equipment
pH meter: The pH of the bath was to be controlled accurately for good results. Measurements of pH were carried out using digital pH meter, and adjusted accordingly the concentration of the chemical solution.
Power supply: A DC power supply capable of delivering a ripple free constant current within the range of 2A was an associate applicable selection for electrodeposition of metal. A MIGHTY, regulated DC power offer will be use during this work.
Form this review we are able to analyze the performance of depositions of zinc metal ions on metals at varied chemicals by varying current. Shiny product will be obtained by the treatment of zinc deposition process as compare to different typical process. The procedure shows that current density is reciprocally proportional to time to get an equivalent deposit thickness. Increase in current density is in the middle of a decrease in deposition time to get thickness and contrariwise.
It is necessary to describe the exposure condition of every process before choosing the most effective zinc coating for that individual application, because as this aid points out, not all zinc coatings are created equally. Various methods of deposition reviewed and identified best suitable method. Also based of various operation parameters the effects of operating parameters affecting on performance of deposition of zinc metal ions has been reviewed. After study of deposited zinc on the metal, the rate of deposition and deposited thickness can calculate by using the formulae. The result of zinc deposited on metal under plating variable influence is reviewed.
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