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Mr. Taylor's SCH4U IRP
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Pages and Files
Asmir, Tyler and Jake's Project. Trespassers will be prosecuted
Electroplating and Galvanizing
Hydrogen Fuel Cell
Semi- and Super-conductors
Wet Cell Batteries
Bio-Fuels (Jake, James and Zach)
Electroplating and Galvanizing
Electroplating And Galvanizing
What is Electroplating?
Metals are some of the most common elements that are around us. They all have their strengths and flaws. One of the biggest flaws that some metals can have is that eventually they
Electroplating puts a fine layer of metal onto less durable metals to prevent corrosion or make them shinier. (http://www.rosik.pl/historia-firmy,5.html?sLang=en)
corrode this change the way we look at these elements. But the good news is that chemist and metallurgists have figured out ways to alter them slightly and electroplating and galvanizing them. These processes change just a part of the metal at an affordable price. Electroplating has revolutionized the way metals are perceived by humans. Electroplating gives a cheap metal the look and the feel of an expensive metal at a very affordable cost. For example one can take iron (the most common element on this plane) and make it look and feel like gold (a rare and rather expensive element on this planet). There is also another process called Galvanizing which refers to iron or steel products to be coated by zinc (which is a rust resistant element). Galvanizing is also a very affordable process which basically make iron and steel the properties like rust resistance this makes a substance like steel rust proof which can be very helpful when that steel is used to make outdoor structures like bridges, buildings and machines.
History and Development
Electroplating has been in development for hundreds of years. It can be considered an industrial revolution due to its ability to make metal items less susceptible to corrosion. Though the methods and efficiency of the electroplating process may have improved over time, the basic chemical fundamentals in which the idea have sparked from remained the same.
The roots of the development of electroplating can be traced back to the early 19th century. An Italian physicist by the name of Alessandro Volta was studying electrochemical principles which lead him to invent the voltaic pile in 1800. A voltaic pile is a set of Galvanic cells in a series, and is considered to be the first electric battery. In 1805, a university professor named Luigi Brugnatelli, who was a friend of Volta, used this voltaic pile to experiment with different electrodeposition properties. He was able to use this power source as a means to move the metal ions from an anode to a cathode within a solution. Eventually in 1805, Brugnatelli had successfully completed the first refined electrodeposition, when he plated a layer of gold onto different silver objects. This is the first recorded process of electroplating. He then wrote in a letter to the Belgian Journal of Physics and Chemistry:
"I have lately gilt in a complete manner two large silver medals, by bringing them into communication by means of a steel wire, with a negative pole of a voltaic pile, and keeping them one after the other immersed in ammoniuret of gold newly made and well saturated".
Unfortunately, due to a fallout with the French Academy of Sciences (the leading scientific body in Europe), as well as scientific suppression by French dictator Napoleon Bonaparte, Brugnatelli was unable to make any more publications in scientific journals.
Although Brugnatelli’s known contributions in history had ended, in 1839 chemists in Britain as well as Russia had performed electrodeposition processes similar to Burgnatelli’s successfully for copper electroplating of printing press plates. During 1840, electroplating was further developed by Henry and George Elkington, as they expanded the idea for gold and silver plating. In Birmingham, England a surgeon named John Wright “first showed that items could be electroplated by immersing them in a tank of silver held in solution, through which an electric current was passed" (Birmingham Jewelry Quarter). He also found that potassium cyanide was a useful electrolyte for the reaction. Wright then patented this idea, but the patent was later purchased by George Elkington who held a monopoly in electroplating due to this cheap and efficient idea.
An early electroplating process. (http://www.sciencephoto.com/images/download_lo_res.html?id=862000126)
During the 1850’s many different electroplating methods including bright nickel, brass, tin, and zinc saw widespread usage and saw usage in both engineering and commercial purposes. This was also the time of the British industrial age, and electroplating processes began to spread throughout the world for the production of various goods. For the next several decades there were very little great technological leaps for electroplating other than a decrease in the use of batteries as an electricity source, and an increase in the usage of direct current power sources. Direct current power sources were recently invented by Thomas Edison, and are a much more effective means of electroplating, as electrons now only flow in one direction, rather than back and forth.
The earliest 20th century brought many new technological advances in the world, and with them brought new uses and needs for electroplating. Because of the dangers of corrosion for many different metal products, the electroplating industry became a massive market. Everything from automobiles, machinery, and airplanes requires some form of plating to make them more durable. In the 1940’s and 1950’s, gold became heavily used for plating for electronic components. Also, the use of cyanide potassium salt as an electrolyte decreased due to its potential health risks, and the use of more safe substitutes were used.
The last big breakthrough for electroplating was the ability to electroplate a metal onto plastic. This was very difficult to achieve because since plastic is not a conductor of electricity. An American physicist named Richard Feynman was the first to achieve this. It was done by creating ‘holes’ or notches in the plastic by placing it in a very strong acid solution. From you place the plastic in a palladium chloride solution, followed by coating it in copper. The palladium chloride places metal particles into the notches of the plastic substance, and then the copper is coated onto the palladium. Now the plastic is now coated in an electrically charged copper, and is now able to be plated with any desired metal finish.
History of Galvanization
Luigi Brugnatelli, the inventor of electroplating. (http://it.wikipedia.org/wiki/File:LVBrugnatelli.jpg)
Although galvanizing and electroplating may seem to go hand in hand, the developments of the two may be considered separate. A French chemist named Paul Jacque Malouin first demonstrated coating iron by submerging it in a molten zinc solution to the French Royal Academy of Sciences in 1742. In 1772, Luigi Galvani discovered several bioelectrical processes when he observed a frog’s leg twitched when it was touching an electric spark. Thus this became known as galvanization (although this is the classical term, and its meaning has since changed). Alessandro Volta then further researched Galvanization as he studied electropotential between two metals. For the next several decades many different scientists and engineers developed both galvanizing and electroplating properties unitl in1837, a French engineer Stanislas Sorel acquired a patent for coating iron in a zinc ‘galvanic paint’ using a method called ‘hot-dip galvanizing’, where the metals are simply submerged in a pool of zinc. From then on there was a massive increase in zinc consumption to galvanize mostly steel metal throughout Europe, and eventually the United States.
How does it work?
To understand electroplating we have to know the main reason electroplating is being done in the first place. The main purposes of electroplating are appearance, protection, and special surface properties of engineering or mechanical properties. Electroplating is a process through which a coating is added to a conductor using electricity via reduction reactions. The surface can be conductors like metals or it can be a nonconductor like plastic. The work piece that is getting plated is the cathode which is negatively charged. The anode on the other hand is capable of being one the two things which are: the sacrificial anode or the permanent anode. The Sacrificial anode is the anode that is made of metal and then end up deposited. The permanent anode can only complete the electrical circuit.
Copper is an excellent conductor of electricity so it is basic to such items as printed circuits and communications equipment. It does, however, quickly form tarnish films that interfere with joining operations such as soldering. To make soldering easier, coatings of tin or tin-lead alloys are often applied to copper, and for better contacts over plates of gold are frequently required. Other surface properties may call for modification; if light reflection is important, a silver or rhodium plate may be necessary. In wave guides for radar, high electrical conductivity is the most important criterion, so silver is the preferred metal.
Two materials are most commonly usually used within the anode reaction and they are platinum and carbon. One of the main important parts of electroplating is electrolysis. Electrolysis is the electrical conductor in which current is carried by ions rather than any free electrons. The main function of an electrolyte is that it completes the electric circuit between the cathode and the anode, so the electric current, which is the positive ions in the electrolyte, will move toward the cathode, and then the negative ions will move to the positive ions. This migration of ions through the electrolyte constitutes the electric current in that part of the circuit. The migration of electrons into the anode through the wiring and an electric generator and then back to the cathode constitutes the current in the external circuit.
This figure shows how plating works; it begins with plating copper from a solution of the metal salt copper sulfate. The cathode, which is the work piece, is to be plated, and is negatively charged. Some of the electrons from the cathode bar transfer to the positively charged copper ions. These copper atoms take their place on the cathode surface and copper plate it. The same number of sulfate ions SO4 is discharged on the copper anodes, thereby completing the electrical circuit. In so doing, they form a new quantity of copper sulfate that dissolves in the solution and restores it to its original composition. This procedure is typical of ordinary electroplating processes with sacriﬁcial anodes; the current deposits a given amount of metal on the cathode and the anode dissolves to the same extent of the same electrical charge, maintaining the solution more or less uniformly.
In general knowledge, all electron transfer reactions are considered oxidation and reductions. The substance gaining electrons (oxidizing agent) oxidizes the substance that is losing electrons (reducing agent). In the process, the oxidizing agent is reduced by the reducing agent. Moreover, the reduction process is sometimes called electronation, and the oxidation process is called deelectronation. Since a cathode is attached to the negative pole of the electric source, it supplies electrons to the electrolyte. On the contrary, an anode is connected to the positive pole of the electric source; therefore, it accepts electrons from electrolyte. Various reactions take place at the electrodes during electrolysis. In general reduction takes place at the cathode, and oxidation takes place at the anode.
Cu2+ + 2 e = Cu
Zn = Zn2+ + 2 e-.
One of the main laws used in this process is Faradays Laws of electrolysis which suggest the following:
The amount of any substance deposited, evolved, or dissolved at an electrode is directly proportional to the amount of electrical charge passing through the circuit
The mass of different substances produced by the same quantity of electricity are directly proportional to the molar masses of the substances concerned, and inversely proportional to the number of electrons in the relevant half-reaction
Main equations are Q=IT , M=Q/nF, and
Q = n(e) x F
Q= quantity of electricity or charge in coulombs(C)
I= current in amps (A)
n(e)= moles of electrons
Faraday constant = 96, 500 C mol-1
It is stated in Faraday’s laws that the amount of chemical charge at an electrode is exactly proportional to the total quantity of electricity passing. However, if several reactions take place simultaneously at the electrode, side reactions may consume the product. Therefore, inefficiencies may arise from the side reactions other than the intended reaction taking place at the electrodes. Current efficiency is a fraction, usually expressed as a percentage, of the current passing through an electrolytic cell or an electrode that accomplishes the desired chemical reaction. After the whole electroplating process done, the work pieces to be plated may be put through a variety of pre treating processes, including surface cleaning, surface modiﬁcation, and rinsing. The surface contamination can be extrinsic, composed of organic debris and mineral dust from the environment or preceding process the current divided by the apparent area yields an average figure. Except for the simplest geometries of a cell, such as when the anode and cathode are concentric, the current is not uniform over the surface of an electrode. In fact, the manner in which the current distributes itself over an electrode surface in any practical case is quite complicated, usually far too much so to be simply calculated from geometry. Current will tend to concentrate at edges and points, and unless the resistance of the solution is extremely low lower than in any practical case, it will flow more readily to parts near the opposite electrode than to more distant parts. Thus, except for the simplest parts subject to electroplating, the thickness of deposit, which depends on the current density, will not be uniform over the surface.
Applications & Future Applications
Electroplating is used in many manufacturing applications to coat a less expensive metal with an expensive or better looking finish for visual effect. Also, due to its rust preventing capabilities there are applications for electroplating and galvanizing in nearly everything that involves metals that need to withstand the elements.
Chrome plating is one of the most commonly used types of electroplating. Chromium is deposited onto a metal (usually steel or iron) which can then be finished into a shiny reflective coating. This coating also puts a physical barrier between a metal and the elements, so it is more resistant to wear. Chrome plating is used in automotive, furniture, and tools because of its resistance to wear and its shiny coating. Metals can also be plated with materials such as gold and silver for finish purposes, because plating a less expensive metal with an expensive metal costs less than making a whole product out of an expensive metal. Most applications of electroplating for finishing purposes are designed to create high quality looking goods without the entire cost of high quality materials. The Government also uses electroplating with our money. They plate zinc disks with copper to form pennies to keep the cost of manufacturing down.
Galvanization refers specifically to the plating of a metal with zinc to prevent rusting by cathodic prevention and a physical barrier. This is used heavily in construction and automotive applications because it is a low cost process that produces a long lasting, low maintenance product that will withstand weather, even if the coating is scratched. Nearly all structural metal in buildings is galvanized to prevent rust, and most hardware companies offer galvanized fasteners, such as nails and screws, which are for use outdoors. In the automotive industry car panels are galvanized to prevent rust from destroying vehicles. This is used more in areas where the weather conditions can cause rust to form very quickly such as Europe and North America. Most companies galvanize essential and external parts like the frame and doors and other areas that need rust protection, but some companies (ex/ Volkswagen) galvanize the whole body and all panels of their vehicles. This process is used once again to keep costs down. The cost of maintaining and operating a vehicle would be much higher if panels were not galvanized, due to rust damage. Galvanization also has uses in the marine industry. Boats and ships all have metal parts that are in constant contact with water, and would rust very quickly if they were not galvanized. Ships are completely made of galvanized steel, because it is cheaper to coat steel than to make such large ships out of a non reactive metal.
A structural frame being galvanized
Most of the applications of electroplating and galvanization are created by people and businesses trying to be cost effective, but there are applications of electroplating that are caused by a need for a metal to be introduced to a product. Gold is used in electroplating electrical conductors because it does not oxidize in air and keeps a constant conductivity. Palladium is also used for the same reasons, but is used on reactive conductors because it will not react, unlike gold that will eventually react with the conductor it is plated to. Electroplating is also needed in the food industry. Cans that food can be stored in are made from steel plated with tin. This is used because tin is too soft to make good cans but wont react with food. Steel will react with the contents of the can so it cannot be used on its own either.
There are already numerous applications for electroplating and galvanizing, and it is not an emerging technology, it is already established and useful in nearly every aspect of our lives. However, it can keep evolving as a technology as we find more uses for different metals, and could eventually lead to a way to make steel completely rust proof.
As amazing as electroplating is, it also has a dark side which is often overlooked by a lot of people (ignorance is bliss). Electroplating involves the deposition of a thin protective layer (usually metallic) onto a prepared metal surface, using electrochemical processes. The process involves pre-treatment (cleaning, degreasing, and other preparation steps), plating, rinsing, passivating, and drying. The cleaning and pre-treatment stages involve a variety of solvents (often chlorinated hydrocarbons, whose use is discouraged) and surface stripping agents, including caustic soda and a range of strong acids, depending on the metal surface to be plated. In the plating process, the object to be plated is usually used as the cathode in an electrolytic bath. Plating solutions are acid or alkaline and may contain complexing agents such as cyanides. Any or all of the substances used in electroplating (such as acidic solutions, toxic metals, solvents, and cyanides) can be found in wastewater, either via rinsing of the product or from spillage and dumping of process baths. The solvents and vapours from hot plating baths result in elevated levels of volatile organic compounds (VOCs) and, in some cases, volatile metal compounds, which may contain chromates. Approximately 30% of the solvents and degreasing agents used can be released as VOCs when baths are not regenerated. The mixing of cyanide and acidic wastewaters can generate lethal hydrogen cyanide gas, and this must be avoided. The overall wastewater stream is typically extremely variable (1 litre to 500 litres per square meter of surface plated) but is usually high in heavy metals, including cadmium, chrome, lead, copper, zinc, and nickel and in cyanides, fluorides and oil and grease. Electroplating on the large scale is done in big tanks. Cleaning or changing of process tanks and treatment of waste waters can generate substantial quantities of wet sludges containing high levels of toxic organics or metals.
In conclusion, Electroplating and galvanizing have definitely changed the way we perceive metals; not just the looks but also its properties. Science has pushed many frontiers and this one is definitely one of them. This technology which was developed during 1805 is still used in full fledged force. Today electroplating has its signature on every metallic object. The field of electrochemistry has really grown. Now even plastic is able to be electroplated. Then there is galvanizing which plating a metal with zinc to give a long lasting effect. Galvanizing was developed in 1772 and today it is used to rust proof most of the commonly used metals such as iron and steel. Most of the automobiles and their parts are either electroplated or galvanized, sometimes both to make it look good and work good.
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