Discussion Examples for Plating Experiments | Deposition Amount, Film Thickness, and Adhesion

What Is a Plating Experiment?

A plating experiment is an experiment in which a thin layer of another metal is deposited on the surface of a metal or conductive material to change its surface properties.
In electroplating, the object to be plated is used as the cathode and current is passed through a solution containing metal ions.
At the cathode surface, the metal ions accept electrons and are deposited as metal.

Plating can change the appearance, corrosion resistance, hardness, electrical conductivity, solderability, and other surface properties.
However, to obtain a clean plating layer with good adhesion, it is necessary to appropriately control the metal-ion concentration, current density, temperature, pH, substrate pretreatment, energization time, and other conditions.
Plating is not merely a surface change but an experiment involving electrochemical reactions and the properties of material surfaces.

Main Items to Include in the Results

In the results of a plating experiment, organize the plating metal, substrate to be plated, type of plating solution, current, voltage, energization time, electrode area, mass before and after energization, deposition amount, film thickness, surface condition, adhesion, and other information.
When using Faraday’s law, the current value and energization time are important.

Main Items to Include in the Results

• Type of plating metal
• Type of substrate
• Type of plating solution
• Metal-ion concentration
• Anode material
• Cathode material
• Electrode area
• Current
• Voltage
• Energization time
• Cathode mass before energization
• Cathode mass after energization
• Measured deposition amount
• Theoretical deposition amount
• Current efficiency
• Film thickness
• Surface color and luster
• Uniformity of plating
• Evaluation of adhesion
• Causes of error and points for improvement

Reference Experimental Values and Calculation Examples for Electroplating Experiments

Here, using a copper-plating experiment as an example, the energization conditions, deposition amount, film thickness, current density, and evaluation of adhesion are organized using reference experimental values.

In electroplating, current is passed through an electrolyte containing metal ions to deposit metal on the cathode surface.
The thickness and adhesion of the plating film are affected by the current, energization time, current density, pretreatment of the electrode surface, electrolyte concentration, stirring conditions, and other factors.

Reference Experimental Conditions

Measurement Results When the Energization Conditions Are Changed

The following is an example in which copper plating was performed while changing the current and energization time, and the deposition amount was determined from the difference in mass before and after plating.
The greater the electric charge passed through the system, the greater the amount of copper deposited.

Example Calculation of Electric Charge

Electric charge is determined from the product of current and energization time.

Electric charge Q = Current I × Time t

For sample C, the current is 0.20 A and the energization time is 600 s, so the electric charge is calculated as follows.

Q = 0.20 A × 600 s = 120 C

Therefore, 120 C of electric charge was passed through sample C.

Example Calculation of Measured Deposition Amount

The measured deposition amount is determined by subtracting the mass before plating from the mass after plating.

Measured deposition amount = Mass after plating − Mass before plating

For sample C, the mass before plating is 12.441 g and the mass after plating is 12.478 g.

Measured deposition amount = 12.478 − 12.441 = 0.037 g

From this result, 0.037 g of copper was considered to have been deposited on the electrode surface in sample C.

Example Calculation of Film Thickness

The average thickness of a plating film can be determined by dividing the volume of deposited metal by the plating area.
The volume of the metal can be determined by dividing its mass by its density.

Deposition volume = Deposition amount ÷ Density

Film thickness = Deposition volume ÷ Plating area

For sample C, the deposition amount is 0.037 g, the density of copper is 8.96 g/cm³, and the plating area is 10.0 cm².

Deposition volume = 0.037 g ÷ 8.96 g/cm³ = 0.00413 cm³

Film thickness = 0.00413 cm³ ÷ 10.0 cm² = 0.000413 cm

Since 1 cm = 10000 μm,

0.000413 cm × 10000 = 4.13 μm

Therefore, the average film thickness of sample C is approximately 4.1 μm.

Example Calculation of Current Density

Current density represents the current flowing per unit electrode area.
It is an important condition when considering the appearance and adhesion of the plating film.

Current density = Current ÷ Plating area

For sample C, the current is 0.20 A and the plating area is 10.0 cm².

Current density = 0.20 A ÷ 10.0 cm² = 0.020 A/cm²

In other words, the current density of sample C is 20 mA/cm².

Relationship Between Current Density and Plating Appearance

If the current density is too low, the deposition rate is slow and the film thickness becomes small.
On the other hand, if the current density is too high, the surface may become rough, and burning, powdery deposition, or poor adhesion may occur.

In this reference example, a relatively uniform plating film was obtained near 20 mA/cm².
On the other hand, at 30 mA/cm², although the deposition amount increased, some roughness was observed.

Example of an Adhesion Test

The quality of a plating film depends not only on film thickness but also on adhesion.
Here, an example of a simple evaluation of adhesion using a tape test and bending test is shown.

In samples that were sufficiently pretreated, the plating film was uniform and adhesion was also good.
On the other hand, in samples that were not pretreated, oil, oxide films, and dirt remained, making it difficult for the plating film to adhere to the substrate.

Comparison with the Theoretical Deposition Amount

In electroplating, the theoretical deposition amount can be determined from Faraday’s law and compared with the measured deposition amount.
In the copper-deposition reaction, 2 mol of electrons are required to deposit 1 mol of copper.

Theoretical deposition amount m = Q × M ÷ (n × F)

Here, Q is the electric charge, M is the molar mass of copper, 63.5 g/mol, n is the number of electrons, 2, and F is the Faraday constant, 96500 C/mol.

For sample C, Q = 120 C, so the theoretical deposition amount is calculated as follows.

m = 120 × 63.5 ÷ (2 × 96500) = 0.0395 g

Since the measured deposition amount is 0.037 g, the current efficiency is calculated as follows.

Current efficiency = 0.037 ÷ 0.0395 × 100 = 93.7%

The measured value being smaller than the theoretical value is considered to have resulted from the effects of side reactions such as hydrogen evolution, loss of deposits, and losses during washing and drying.

Relationship Between Plating Time and Film Thickness

At the same current density, the longer the plating time, the greater the deposition amount and the greater the film thickness.
However, during long plating times, deposition may become concentrated at the edges or the film may become rough.

Increasing the plating time increases the film thickness, but it does not always improve the appearance or adhesion.
To obtain a uniform plating film, it is necessary to adjust the current density, plating time, stirring, and pretreatment conditions together.

Example of How to Write the Results

Copper plating was performed using a copper sulfate aqueous solution.
Under conditions of a current of 0.20 A and an energization time of 600 s, the mass before plating was 12.441 g and the mass after plating was 12.478 g, giving a measured deposition amount of 0.037 g.
When the average film thickness was calculated using a plating area of 10.0 cm² and a copper density of 8.96 g/cm³, it was approximately 4.1 μm.

When the current density was increased from 10 mA/cm² to 30 mA/cm², the deposition amount and film thickness increased.
On the other hand, under the 30 mA/cm² condition, some roughness was observed and the appearance of the plating film became somewhat coarse.
This suggests that although an excessively high current density increases the deposition rate, it may reduce uniformity and adhesion.

In addition, in the sample that was polished and degreased, no peeling of the plating film was observed in either the tape test or the bending test.
On the other hand, in the sample that was not pretreated, the plating film peeled over a wide area.
From this result, the cleanliness of the substrate surface was considered to have a major effect on the adhesion of the plating film.

Points for Connecting the Results to the Discussion

In a discussion of an electroplating experiment, it is important to explain not only the deposition amount and film thickness but also the appearance of the plating film, adhesion, current density, and the effects of pretreatment in relation to one another.

• Did the deposition amount and film thickness increase when the energization time or current increased?
• Was the film thickness calculated from the deposition amount, density, and plating area?
• Did roughness or burning occur under conditions with excessively high current density?
• Did an excessively low current density result in a small deposition amount and thin film?
• Was there a difference in adhesion depending on the presence or absence of pretreatment?
• Could insufficient polishing, insufficient degreasing, oxide films, oil, or dirt have caused poor adhesion?
• If the measured deposition amount was smaller than the theoretical value, could side reactions or loss of deposits have occurred?

Example Discussion

In this experiment, the current and energization time were varied in copper plating, and the deposition amount and film thickness were compared.
Under conditions of a current of 0.20 A and an energization time of 600 s, the measured deposition amount was 0.037 g and the average film thickness was approximately 4.1 μm.
Because the deposition amount increased and the film thickness also increased as the energization time became longer, the thickness of the plating film was considered to depend strongly on the electric charge passed through the system.

On the other hand, under conditions with high current density, the deposition amount increased, but some roughness was observed.
This was considered to result from the supply of copper ions to the electrode surface failing to keep up, causing locally nonuniform deposition.
In addition, at high current density, side reactions such as hydrogen evolution are more likely to occur, potentially reducing the appearance and adhesion of the plating film.

Regarding adhesion, good results were obtained for the sample that was polished and degreased.
In the sample that was not pretreated, the plating film readily peeled in the tape test and bending test.
This was considered to result from oil, oxide films, and dirt remaining on the substrate surface, preventing the deposited copper from adhering sufficiently to the substrate surface.

Comparison of the theoretical and measured deposition amounts showed that for sample C, the theoretical deposition amount was 0.0395 g whereas the measured deposition amount was 0.037 g, giving a current efficiency of 93.7%.
Possible reasons why the measured value was smaller than the theoretical value include side reactions other than copper deposition, loss of deposits, and losses during washing and drying.
Therefore, when evaluating plating conditions, it is necessary to make a comprehensive judgment based not only on film thickness but also on current efficiency, appearance, and adhesion.

Summary

In an electroplating experiment, metal is deposited according to the electric charge passed through the system, and the thickness of the plating film increases.
The average film thickness can be calculated using the deposition amount, density, and plating area.

In this reference example, increasing the current or energization time increased the film thickness, but surface roughness was observed under conditions with high current density.
In addition, samples that were sufficiently pretreated showed good adhesion.
In a report, it is useful to discuss the deposition amount, film thickness, current density, pretreatment, adhesion, and difference from the theoretical value in relation to one another.

Principle of Plating

The basic principle of electroplating is the reduction reaction of metal ions.
When the object to be plated is used as the cathode, electrons are supplied from an external power source.
Metal ions in the solution accept electrons at the cathode surface and are deposited as metal atoms.

For example, in copper plating, Cu2+ accepts two electrons and is deposited as metallic copper, Cu.
In nickel plating, Ni2+ is reduced to Ni.
For any metal, checking the number of electrons using the electrode-reaction equation makes it possible to calculate the deposition amount.

Cu2+ + 2e- → Cu

Ni2+ + 2e- → Ni

Zn2+ + 2e- → Zn

Reactions Occurring at the Cathode

The object to be plated is usually connected to the cathode.
Because electrons are supplied at the cathode, a reduction reaction of metal ions occurs.
Through this reaction, metal is deposited on the substrate surface and forms a plating film.

For the intended metal to be deposited at the cathode, metal ions must be sufficiently supplied to the cathode surface.
If the current density is too high, the reduction at the surface proceeds too rapidly for the ion supply to keep up, and rough deposition or hydrogen evolution may occur.
Therefore, the cathodic reaction is related not only to the deposition amount but also to the quality of the film.

Reactions Occurring at the Anode

In plating experiments, the same metal as the plating metal may be used as the anode.
In this case, the metal is oxidized at the anode and dissolves into the solution as metal ions.
This makes it possible to replenish the metal ions consumed at the cathode.

On the other hand, when an inert electrode is used as the anode, the anode itself is difficult to dissolve, and oxidation of water or another oxidation reaction may occur.
In this case, the metal-ion concentration in the plating solution decreases as the metal is deposited at the cathode.
In a plating experiment, it is important to discuss whether the anode material participates in the reaction.

Copper anode: Cu → Cu2+ + 2e-

Inert anode: 2H2O → O2 + 4H+ + 4e-

Deposition Amount and Faraday’s Law

The amount of metal deposited by plating is basically proportional to the electric charge passed through the system.
This can be explained by Faraday’s law.
The electric charge Q is determined from the product of current I and energization time t.
The electric charge carried by 1 mol of electrons is the Faraday constant F, approximately 96500 C/mol.

The number of electrons a metal ion must accept to become a metal can be determined from the electrode-reaction equation.
For example, 2 mol of electrons are required to convert Cu2+ or Ni2+ into the metal.
Therefore, the theoretical deposition amount can be determined by dividing the amount of electrons passed through the system by the number of electrons required for the reaction.

Q = I × t

Amount of electrons = Q ÷ F

Amount of deposited metal = Amount of electrons ÷ Number of electrons required for the reaction

How to Determine Film Thickness

The thickness of a plating film can be estimated from the mass of the deposited metal, the plated area, and the density of the metal.
Assuming that the deposited metal spreads as a uniform film, its volume can be determined by dividing the mass by the density.
Dividing this volume by the plating area gives the average film thickness.

However, the actual plating film is not necessarily completely uniform.
Deposition may be thicker at the edges, the surface may become rough, or deposition may fail to occur in some areas.
Therefore, the film thickness determined from mass is an average film thickness and may differ from the local film thickness.

Volume of plating film = Mass of deposited metal ÷ Density of metal

Average film thickness = Volume of plating film ÷ Plating area

Factors Affecting Film Thickness

Plating-film thickness is affected by energization time, current, electrode area, current efficiency, metal-ion concentration, and other factors.
At the same current, the longer the energization time, the greater the deposition amount and the greater the film thickness.
Even with the same deposition amount, the film becomes thinner when the plating area is larger and thicker when the area is smaller.

In addition, when the current does not flow uniformly over the electrode surface, the film thickness becomes nonuniform.
Current tends to concentrate at corners and edges, where deposition may become thicker.
Flat areas or regions that are difficult for current to reach may become thinner.
When discussing film thickness, it is important to consider not only the simple average value but also the uniformity of the plating.

What Is Adhesion?

Plating adhesion is a property indicating how firmly the plating film adheres to the substrate surface.
A plating film with high adhesion is difficult to peel off even when rubbed or bent.
In contrast, a plating film with low adhesion peels off easily or falls off in a powdery form.

Adhesion is affected by dirt, oxide films, oil, surface roughness, pretreatment, current density, deposition rate, and other factors on the substrate surface.
Because the plating film forms directly on the substrate surface, it is extremely important for the substrate surface to be clean.
Adhesion is an important observation item for evaluating the practical usefulness of plating.

Effect of Substrate Pretreatment

Pretreatment of the substrate before plating greatly affects the adhesion and appearance of the plating.
If oil, fingerprints, oxide films, or dirt remain on the substrate surface, reduction and deposition of metal ions do not occur uniformly.
As a result, the plating may fail to adhere in some areas or may peel off easily.

Substrate pretreatment includes cleaning, degreasing, acid pickling, and polishing.
Cleaning the surface and, when necessary, giving it an appropriate degree of roughness makes it easier for the plating film to adhere.
If the plating peeled off in the experiment, insufficient substrate pretreatment can be discussed as an important cause of error.

Effect of Current Density

Current density is the magnitude of current flowing per unit area.
In plating, current density greatly affects the condition of the film.
At an appropriate current density, a relatively uniform plating film with good adhesion can be obtained.

If the current density is too high, the supply of metal ions cannot keep up and the deposit may become rough, dendritic, or powdery.
In addition, side reactions such as hydrogen evolution become more likely and adhesion may decrease.
If the current density is too low, the deposition rate is slow and it takes longer to obtain sufficient film thickness.

Effect of Hydrogen Evolution

During plating, hydrogen evolution may occur at the same time as deposition of the intended metal.
In acidic solutions, H+ is reduced and hydrogen, H2, is generated.
Even under neutral or basic conditions, water may be reduced and hydrogen generated.

When hydrogen evolution occurs, part of the electric charge passed through the system is used for hydrogen generation instead of metal deposition, so the current efficiency decreases.
In addition, if bubbles adhere to the substrate surface, metal becomes difficult to deposit in those areas, causing pinholes and unevenness.
Hydrogen evolution affects the deposition amount, film thickness, and adhesion.

2H+ + 2e- → H2

2H2O + 2e- → H2 + 2OH-

Role of the Plating Bath

The plating bath not only supplies metal ions but also makes it easier for current to flow and adjusts the deposition condition.
The concentration of metal salts, pH, additives, temperature, and other factors greatly affect the quality of the plating film.
If the metal-ion concentration is too low, metal ions become insufficient at the cathode surface, making rough deposition and hydrogen evolution more likely.

Acids and salts contained in the plating bath increase electrical conductivity and stabilize the state of metal ions.
When additives are used, they may affect luster, smoothness, crystal growth, and other properties.
In an experimental report, it is useful to consider how the composition of the plating bath is related to the deposition condition.

Effect of Stirring

Moderate stirring of the solution during plating makes it easier to supply metal ions to the cathode surface.
If stirring is insufficient, the metal-ion concentration near the cathode decreases and deposition may become nonuniform.
Insufficient ion supply is particularly likely to become a problem under high-current-density conditions.

However, if stirring is too strong, the deposit may peel off or the film may become nonuniform because of bubbles or liquid flow.
Stirring assists the supply of metal ions while also affecting the stability of the film.
It is important to compare samples under consistent conditions.

Effect of Temperature

The temperature of the plating bath affects the migration rate of metal ions, reaction rate, solution viscosity, and crystal growth.
As the temperature increases, metal ions move faster and deposition may proceed more readily.
On the other hand, if the temperature is too high, side reactions may increase or the film may become rough.

If the temperature is too low, ion movement becomes slower and the deposition rate may decrease.
To compare samples under the same conditions, it is important to keep the plating-bath temperature constant.
If the temperature changes greatly, it can be discussed as a cause of variation in deposition amount and film quality.

Discussion of Surface Luster and Color

The color and luster of the surface after plating reflect the type of deposited metal and the condition of the film.
In copper plating, a reddish-brown color may be observed, while nickel plating may show a silvery-white luster.
When the surface is formed uniformly from fine crystals, the film tends to be relatively smooth and lustrous.

On the other hand, if the surface is blackish, powdery, mottled, or rough, possible causes include excessively high current density, insufficient substrate pretreatment, hydrogen evolution, or insufficient metal-ion concentration.
Visual observation is important information for discussing film quality.

Causes of Uneven Plating

Causes of uneven plating include uneven current density, dirt on the substrate surface, nonuniform electrode arrangement, bubble adhesion, nonuniform concentration of the plating solution, and insufficient stirring.
Current tends to concentrate particularly at corners and edges, making the plating thicker there.
In contrast, plating may become thinner in recessed areas or regions that are difficult for current to reach.

In addition, in areas where oil or an oxide film remains on the substrate, metal may fail to deposit properly and the plating may appear to be repelled.
Unevenness affects not only appearance but also film thickness, adhesion, and corrosion resistance.
Electrode arrangement and substrate pretreatment are important for obtaining uniform plating.

Discussion of Current Efficiency

Current efficiency is the proportion of the electric charge passed through the system that was actually used for deposition of the intended metal.
It can be determined by comparing the theoretical deposition amount with the measured deposition amount.
When the current efficiency is close to 100%, most of the electric charge is considered to have been used for the intended plating reaction.

When the current efficiency is low, possible causes include side reactions such as hydrogen evolution, peeling of deposits, contamination of the electrode surface, insufficient metal ions, and fluctuations in current.
Conversely, when the current efficiency exceeds 100%, insufficient drying, adhesion of plating solution, weighing errors, and other factors may have caused the measured mass to appear larger.

Current efficiency = Measured deposition amount ÷ Theoretical deposition amount × 100

Reasons Why the Theoretical Deposition Amount and Measured Value Differ

The theoretical deposition amount is calculated using Faraday’s law under the assumption that all of the electric charge passed through the system is used for deposition of the intended metal.
However, in practice, the measured value may differ from the theoretical value because of side reactions such as hydrogen evolution, loss of deposits, fluctuations in current, insufficient metal-ion concentration, and the condition of the substrate surface.

If the measured value is smaller than the theoretical value, a decrease in current efficiency or loss of the deposited material can be considered.
If the measured value is larger than the theoretical value, insufficient drying, plating solution remaining on the surface, or errors during weighing can be considered.
Checking the direction of the deviation and organizing the possible causes makes the discussion easier to write.

Discussion When the Plating Film Peels Off

When the plating film peels off, possible causes include dirt, oxide films, oil, insufficient surface roughness, rapid deposition, and internal stress on the substrate surface.
If the metal film cannot directly adhere to the substrate, it remains merely resting on the surface and peels off when rubbed or washed.

In addition, if the current density is too high, deposition proceeds rapidly, the crystals become coarse, and the film may become brittle.
Bubbles caused by hydrogen evolution also reduce adhesion.
If the plating film peels off, both substrate pretreatment and current conditions must be reviewed.

Discussion When the Plating Film Is Thin

When the plating film is thin, possible causes include a short energization time, small current, low current efficiency, insufficient metal-ion concentration, and a large plating area.
According to Faraday’s law, the smaller the electric charge passed through the system, the smaller the deposition amount, so the film thickness becomes smaller.

In addition, when the plating is concentrated only on part of the surface, the observed region may appear thin even if the average film thickness is constant.
When considering film thickness, it is necessary to check not only the deposition amount but also the area, uniformity, and current distribution.

Discussion When the Plating Film Is Rough

When the plating film is rough, possible causes include excessively high current density, insufficient metal-ion supply, insufficient stirring, inappropriate bath temperature or pH, and a rough substrate surface.
When metal is deposited rapidly, crystal growth becomes nonuniform and the film is more likely to become rough.

A rough film not only has a poor appearance but also affects adhesion and corrosion resistance.
If the surface becomes porous or gaps are formed, the substrate becomes more likely to be exposed.
The roughness of the plating film provides a clue for determining whether the deposition conditions were appropriate.

Causes of Error in Plating Experiments

Causes of error in plating experiments include fluctuations in current, errors in energization time, errors in electrode-area measurement, peeling of deposits, insufficient drying, adhesion of plating solution, dirt on the substrate surface, uneven current density, hydrogen evolution, changes in metal-ion concentration, differences in stirring conditions, and temperature changes.
When determining deposition amount and film thickness from mass, weighing procedures are also important.

Causes that make the measured deposition amount smaller include peeling of deposits, losses during washing, and reduced current efficiency because of side reactions.
Causes that make the measured deposition amount larger include insufficient drying, adhesion of electrolyte solution, and adhesion of impurities to the substrate surface.
Organizing the causes into overestimation and underestimation makes the discussion easier.

When the Results Can Be Considered Good

A plating experiment can be considered to have produced good results when the intended metal is uniformly deposited on the substrate surface, the color and luster correspond to the characteristics of the metal, the film is difficult to peel off, and the increase in mass does not greatly contradict the theoretical deposition amount.
In addition, if there is little unevenness or powdery deposition on the surface and the current remained stable, the conditions can be considered relatively appropriate.

When the film thickness is calculated, if it changes according to differences in energization time or current, the result is consistent with Faraday’s law.
If the film was difficult to peel off in an adhesion test, the substrate pretreatment and current conditions can be considered appropriate.

Example Discussion When the Experiment Did Not Go Well

When a plating experiment does not go well, possible causes are considered from results such as the plating not adhering, the film peeling, the surface becoming black, powdery deposition, unevenness, a small increase in mass, or disagreement with the theoretical value.
Organizing the causes according to substrate pretreatment, current density, plating bath, stirring, temperature, washing and drying, and weighing makes the discussion easier.

How to Write Points for Improvement

In a discussion of a plating experiment, writing not only the causes of error but also points for improvement makes the report easier to organize.
Points for improvement can be organized according to substrate pretreatment, electrolysis conditions, plating bath, measurement procedure, and film evaluation.

Improvements to Substrate Pretreatment

• Degrease the substrate surface
• Remove the oxide film
• Lightly polish the surface
• Do not touch the surface by hand after treatment
• Perform plating promptly after washing
• Do not leave moisture or dirt on the surface

Improvements to Electrolysis Conditions

• Keep the current constant
• Set the current density appropriately
• Measure the energization time accurately
• Keep the distance between the electrodes constant
• Measure the electrode area accurately
• Avoid excessively high voltage
• Review the conditions if a large amount of hydrogen is generated

Improvements to the Plating Bath and Measurement

• Prepare the concentration of the plating solution accurately
• Keep the bath temperature constant
• Stir moderately
• Wash carefully so that the deposit does not peel off
• Measure the mass after drying
• Perform multiple measurements and calculate the average value
• Calculate film thickness from the area and density

Difference Between a Superficial Discussion and a Good Discussion

In a discussion of a plating experiment, simply writing that “metal adhered” or “the film was thin” results in a superficial discussion.
A good discussion relates reduction of metal ions, electric charge and deposition amount, film thickness, current density, substrate pretreatment, adhesion, and current efficiency.

Examples of Expressions That Can Be Used in Reports

The following expressions can be used when writing the results and discussion of plating experiments.
Adjust the necessary parts according to your own experimental results.

• In plating, metal ions are reduced at the cathode surface and deposited as metal.
• The deposition amount is proportional to the electric charge passed through the system.
• According to Faraday’s law, the theoretical deposition amount can be determined from the current and energization time.
• Film thickness can be determined as an average value from the deposited mass, plating area, and metal density.
• Film thickness is affected by energization time, current density, current efficiency, and plating area.
• If dirt or an oxide film is present on the substrate surface, the adhesion of the plating film decreases.
• If the current density is too high, rough deposition and hydrogen evolution are more likely to occur.
• Hydrogen evolution reduces current efficiency and causes unevenness and pinholes in the film.
• If the measured value is smaller than the theoretical value, peeling of deposits or side reactions may be considered.
• If the measured value is larger than the theoretical value, insufficient drying or adhesion of plating solution may be considered.

Points to Check When Discussing Plating Experiments

Checking the following points before writing the report makes the discussion easier to write.

• Is the principle of plating explained?
• Is it stated that metal ions are reduced at the cathode?
• Is the effect of the anode material considered?
• Is the deposition amount discussed using Faraday’s law?
• Is the method for determining film thickness explained?
• Is it understood that film thickness is an average value?
• Is the relationship between adhesion and substrate pretreatment described?
• Is the relationship between current density and film quality considered?
• Are side reactions such as hydrogen evolution considered?
• Are surface luster, unevenness, and roughness included in the observations?
• Is the difference between the theoretical and measured deposition amounts discussed?
• Do the points for improvement correspond to the causes of error?

Summary

A plating experiment is an experiment in which current is passed through a solution containing metal ions and metal is reduced and deposited on the cathode surface.
The deposition amount is proportional to the electric charge passed through the system, and the theoretical deposition amount can be calculated using Faraday’s law.
By comparing the measured deposition amount with the theoretical value, the effects of current efficiency and side reactions can be discussed.

The thickness of a plating film can be determined as an average film thickness from the deposited mass, plating area, and metal density.
However, the actual film thickness may be nonuniform because of current distribution, edge effects, and surface condition.
Therefore, not only the calculated film thickness but also the surface color, luster, unevenness, and roughness are important observation items.

In a report, rather than simply writing that “metal adhered,” organize and discuss the reduction reaction at the cathode, anodic reaction, deposition amount, film thickness, substrate pretreatment, adhesion, current density, hydrogen evolution, current efficiency, causes of error, and points for improvement.
Plating experiments are important experiments for understanding the relationship between electrochemical reactions and the properties of material surfaces.