Electroplating
Electroplating is a process that us electric current to reduce dissolved metal cations so that they form a coherent metal coating on an electrode. The term is also ud for electrical oxidation of anions onto a solid substrate, as in the formation silver chloride on silver wire to make silver/silver-chloride electrodes. Electroplating is primarily ud to change the surface properties of an object (e.g. abrasion and wear resistance, corrosion protection, 如何做好社区工作lubricity, aesthetic qualities, etc.), but may also be ud to build up thickness on undersized parts or to form objects by 浙江南浔古镇electroforming.
The process ud in electroplating is called electrodeposition. It is analogous to a galvanic cell acting in rever. The part to be plated is the cathode of the circuit. In one technique, the anode is made of the metal to be plated on the part. Both components are immerd in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that it compris and allowing them to dissolve in th
e solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they "plate out" onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, vis-a-vis the current through the circuit. In this manner, the ions in the electrolyte bath are continuously replenished by the anode.[1]
Other electroplating process may u a non-consumable anode such as lead or carbon. In the techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution.[2] The most common form of electroplating is ud for creating coins such as pennies, which are small zinc plates covered in a layer of copper.
Process
活龙虾怎么保存
Electroplating of a metal (Me) with copper in a copper sulfate bath
See also: Electrotyping and 画猫头鹰Electroforming
The cations associate with the anions in the solution. The cations are reduced at the cathode to deposit in the metallic, zero valence state. For example, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons. The Cu2+ associates with the anion SO42− in the solution to form copper sulfate. At the cathode, the Cu2+ is r芦荟胶的正确用法
新加香薷饮educed to metallic copper by gaining two electrons. The result is the effective transfer of copper from the anode source to a plate covering the cathode.
The plating is most commonly a single metallic element, not an alloy. However, some alloys can be electrodeposited, notably brass and solder关于学习的歌.
Many plating baths include cyanides of other metals (e.g., potassium cyanide) in addition to cyanides of the metal to be deposited. The free cyanides facilitate anode corrosion, help to maintain a constant metal ion level and contribute to conductivity. Additionally, non-metal chemicals such as carbonates and phosphates may be added to increa 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, lacquers, and waxes.[4]
Strike
Initially, a special plating deposit called a "strike" or "flash" may be ud to form a very thin (typically less than 0.1 micrometer thick) plating with high quality and good adherence to the substrate. This rves as a foundation for subquent plating process. A strike us a high current density and a bath with a low ion concentration. The process is slow, so more efficient plating process are ud once the desired strike thickness is obtained.
nfl超级碗
The striking method is also ud 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, 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 ca a copper strike is ud, which has good adherence to both.[2]
Electrochemical deposition
Electrochemical deposition is generally ud for the growth of metals and conducting met
al oxides becau of the following advantages: (i) the thickness and morphology of the nanostructure can be precily controlled by adjusting the electrochemical parameters, (ii) relatively uniform and compact deposits can be synthesized in template-bad structures, (iii) higher deposition rates are obtained, and (iv) the equipment is inexpensive due to the non-requirements of either a high vacuum or a high reaction temperature.[5][6][7]
Pul electroplating or pul electrodeposition (PED)
A simple modification in the electroplating process is the pul electroplating. This process involves the swift alternating of the potential or current between two different values resulting in a ries of puls of equal amplitude, duration and polarity, parated by zero current. By changing the pul amplitude and width, it is possible to change the deposited film's composition and thickness.[8]
Brush electroplating
A cloly 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 a cloth material that both holds the plating solution and prevents direct contact with the item being plated, is connected to the positive side of a low voltage direct-current power source, and the item to be plated connected to the negative. 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. Brush electroplating has veral 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.
