Editing Electroplating (section)

==Process==
[[File:Copper electroplating principle (multilingual).svg|thumb|upright|Simplified diagram for electroplating copper (orange) on a conductive object (the cathode, "Me", gray). The electrolyte is a solution of copper sulfate, {{chem|CuSO|4}} in [[sulfuric acid]]. A copper anode is used to replenish the electrolyte with copper cations {{chem|Cu|2+}} as they are plated out at the cathode.]]
{{See also|Electrotyping|Electroforming}}

The electrolyte in the electrolytic plating cell should contain positive ions (cations) of the metal to be deposited. These cations are reduced at the cathode to the metal in the zero valence state. For example, the electrolyte for [[copper electroplating]] can be a solution of [[copper(II) sulfate]], which dissociates into Cu<sup>2+</sup> cations and {{chem|SO|4|2-}} anions. At the cathode, the Cu<sup>2+</sup> is reduced to metallic copper by gaining two electrons.

When the anode is made of the metal that is intended for coating onto the cathode, the opposite reaction may occur at the anode, turning it into dissolved cations.  For example, [[copper]] would be oxidized at the anode to Cu<sup>2+</sup> by losing two electrons. In this case, the rate at which the anode is dissolved will equal the rate at which the cathode is plated, and thus the ions in the electrolyte bath are continuously replenished by the anode. The net result is the effective transfer of metal from the anode to the cathode.{{sfn|Dufour|2006|p=IX-1}}

The anode may instead be made of a material that resists electrochemical oxidation, such as [[lead]] or [[carbon]]. [[Oxygen]], [[hydrogen peroxide]], and some other byproducts are then produced at the anode instead. In this case, ions of the metal to be plated must be replenished (continuously or periodically) in the bath as they are drawn out of the solution.<ref name="Dufour, IX-2">{{harvnb|Dufour|2006|p=IX-2}}</ref>

The plating is most commonly a single metallic [[chemical element|element]], not an [[alloy]]. However, some alloys can be electrodeposited, notably [[brass]] and [[solder]]. Plated "alloys" are not "true alloys" (solid solutions), but rather they are tiny crystals of the elemental metals being plated. In the case of plated solder, it is sometimes deemed necessary to have a true alloy, and the plated solder is melted to allow the tin and lead to combine into a true alloy. The true alloy is more corrosion-resistant than the as-plated mixture.

Many plating baths include [[cyanide]]s of other metals (such as [[potassium cyanide]]) in addition to cyanides of the metal to be deposited. These free cyanides facilitate anode corrosion, help to maintain a constant metal ion level, and contribute to conductivity. Additionally, non-metal chemicals such as [[carbonate]]s and [[phosphate]]s may be added to increase conductivity.

When plating is not desired on certain areas of the substrate, ''stop-offs'' are applied to prevent the bath from coming in contact with the substrate. Typical stop-offs include tape, foil, [[lacquer]]s, and [[wax]]es.<ref name="dufour3">{{harvnb|Dufour |2006|p=IX-3}}</ref>

===Strike===
Initially, a special plating deposit called a ''strike'' or ''flash'' may be used to form a very thin (typically less than 0.1&nbsp;μm thick) plating with high quality and good adherence to the substrate. This serves as a foundation for subsequent plating processes. A strike uses a high current density and a bath with a low ion concentration. The process is slow, so more efficient plating processes are used once the desired strike thickness is obtained.

The striking method is also used in combination with the plating of different metals. If it is desirable to plate one type of deposit onto a metal to improve corrosion resistance but this metal has inherently poor adhesion to the substrate, then a strike can be first deposited that is compatible with both. One example of this situation is the poor adhesion of electrolytic [[nickel]] on [[zinc]] alloys, in which case a copper strike is used, which has good adherence to both.<ref name="Dufour, IX-2"/>

===Pulse electroplating===
{{See also|Pulse electrolysis}}
The pulse electroplating or pulse electrodeposition (PED) process involves the swift alternating of the [[electrical potential]] or [[Electric current|current]] between two different values, resulting in a series of pulses of equal amplitude, duration, and polarity, separated by zero current. By changing the pulse amplitude and width, it is possible to change the deposited film's composition and thickness.<ref>{{cite journal|last1=kunji durai|first1=M. S.|first2=Mathy|last2=chaala|title=Pulse and pulse reverse plating—Conceptual, advantages and applications|journal=Electrochimica Acta|volume=53|issue=8|year=2008|pages=3313–3322|doi=10.1016/j.electacta.2007.11.054}}</ref>

The experimental parameters of pulse electroplating usually consist of peak current/potential, duty cycle, frequency, and effective current/potential. Peak current/potential is the maximum setting of electroplating current or potential. Duty cycle is the effective portion of time in a certain electroplating period with the current or potential applied. The effective current/potential is calculated by multiplying the duty cycle and peak value of the current or potential. Pulse electroplating could help to improve the quality of electroplated film and release the internal stress built up during fast deposition. A combination of the short duty cycle and high frequency could decrease surface cracks. However, in order to maintain the constant effective current or potential, a high-performance power supply may be required to provide high current/potential and a fast switch. Another common problem of pulse electroplating is that the anode material could get plated and contaminated during the reverse electroplating, especially for a high-cost, inert electrode such as [[platinum]].

Other factors that affect the pulse electroplating include temperature, anode-to-cathode gap, and stirring. Sometimes, pulse electroplating can be performed in a heated electroplating bath to increase the deposition rate, since the rate of most chemical reactions increases exponentially with temperature per the [[Arrhenius equation|Arrhenius law]]. The anode-to-cathode gap is related to the current distribution between anode and cathode. A small gap-to-sample-area ratio may cause uneven distribution of current and affect the surface topology of the plated sample. Stirring may increase the transfer/diffusion rate of metal ions from the bulk solution to the electrode surface. The ideal stirring setting varies for different metal electroplating processes. 

===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 [[graphite]] 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 and 3-4 ampere [[direct current|direct-current]] power source, and the item to be plated (the [[cathode]]) is grounded. The operator dips the brush in plating solution and then applies it to the item, moving the brush continually to get an even distribution of the plating material.

Brush electroplating has several advantages over tank plating, including portability, the 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. Mainly used industrially for part repair, worn bearing surfaces getting a nickel or silver deposit. With technological advancement deposits up to .025" have been achieved and retained uniformity. Disadvantages compared to tank plating can include greater operator involvement (tank plating can frequently be done with minimal attention and the solutions used are often toxic), and the inconsistency in achieving as great a plate thickness.

===Barrel plating===
{{main article|Barrel plating}}
This technique of electroplating is one of the most common used in the industry for large numbers of small objects. The objects are placed in a barrel-shaped non-conductive cage and then immersed in a chemical bath containing dissolved ions of the metal that is to be plated onto them.  The barrel is then rotated, and electrical currents are run through the various pieces in the barrel, which complete circuits as they touch one another. The result is a very uniform and efficient plating process, though the finish on the end products will likely suffer from abrasion during the plating process. It is unsuitable for highly ornamental or precisely engineered items.<ref name="Tan1992">{{cite book|author=A.C. Tan|title=Tin and Solder Plating in the Semiconductor Industry|url=https://books.google.com/books?id=DyrohYlFCiYC&pg=PA122|date=30 November 1992|publisher=Springer Science & Business Media|isbn=978-0-412-48240-3|page=122|access-date=16 May 2019|archive-date=1 August 2020|archive-url=https://web.archive.org/web/20200801074731/https://books.google.com/books?id=DyrohYlFCiYC&pg=PA122|url-status=live}}</ref>

=== Cleanliness ===
[[Parts cleaning|Cleanliness]] is essential to successful electroplating, since molecular layers of [[oil]] can prevent adhesion of the coating. [[ASTM]] B322 is a standard guide for cleaning metals prior to electroplating. Cleaning includes solvent cleaning, hot alkaline detergent cleaning, electrocleaning, [[ultrasonic cleaning]] and acid treatment. The most common industrial test for cleanliness is the waterbreak test, in which the surface is thoroughly rinsed and held vertical. [[Hydrophobic]] contaminants such as oils cause the water to bead and break up, allowing the water to drain rapidly. Perfectly clean metal surfaces are [[hydrophilic]] and will retain an unbroken sheet of water that does not bead up or drain off. ASTM F22 describes a version of this test. This test does not detect hydrophilic contaminants, but electroplating can displace these easily, since the solutions are water-based. [[Surfactant]]s such as [[soap]] reduce the sensitivity of the test and must be thoroughly rinsed off.