Electrodeposition of Gold

Abstract

While all that glitters may not be gold, it is the most beautiful of all the elements in their pure form. The name gold comes from the Old English Anglo-Saxon word for geolo meaning "yellow" while the symbol, Au, comes from the Latin word aurum, meaning "glowing dawn." Historically gold was one of the first metals known. Gold has been valuable throughout the ages chiefly because of its physical properties of softness, ductility, corrosion resistance, density, and scarcity. The first gold coin dates back to about 560 BC. Gold cups and jewelry predating 3500 BC have been found in Iraq. The ancient Egyptians knew how to hammer gold into leaf as thin as 66 nm. The importance of gold as a form of currency was at a high point in the 1900s when most countries were on the gold standard. The bullion price of gold over the past 21 years is shown in Figure 4.1.There have been about 160 metric kilotons of gold mined since it was first discovered, and it occupies about 0.005 ppm of the earth's crust. The world demand for gold in 2007 was approximately 80,000,000 troy ounces. Figure 4.2 shows the breakdown of the gold usage by industry. Jewelry comprises the largest fraction of the usage; however, much of that is not electroplated. For jewelry applications, gold is commonly alloyed with group IB or IIB metals, particularly copper, silver, platinum, and palladium, principally to improve its strength and wear resistance.The electrodeposition of gold is a relatively new process; it has been traced to the early work of Brugnatelli in 1805 [1]. The motives behind the use of electroplated gold changed dramatically in the mid-twentieth century when the emerging electronics industry required special-purpose electrical connections. The electronics industry consumed 5,330,000 troy ounces in 1994. Figure 4.3 shows the growth in the use of gold in the electronics industry by year. The use of electroplated gold in a variety of different functions in the electronics industry has led to (1) many advances in our fundamental understanding of the electrodeposition process and (2) new electroplating technologies over the past 25 years.Electrochemically deposited gold has satisfied many of the demands of the electronics industry. Gold has the third best electrical and thermal conductivity of all metals at room temperature. Also it has high ductility and excellent wear resistance, which are important for electrical contacts. The inertness of gold prevents the formation of insulating surface oxides (as compared to metals like aluminum). Group IIB metals (e.g., gold) are not good catalysts for other reactions, thus avoiding certain problems. For example, group IB metals (particularly platinum and palladium) can catalyze the polymerization of organic molecules forming insulating layers. In addition, gold is an excellent metal for wire bonding integrated circuits (ICs). Gold wires can be bonded to pure, soft gold pads by thermocompression bonding (300-400 C at high pressure to form a weld) or thermosonic bonding (150-200 C with ultrasonic energy to fo...

Amberlite XAD Resins Impregnated with Ionic Liquids for Au(III) Recovery

“…The leachates are generally containing low concentrations of precious metals their recovery and separation from base metals is then an economical challenge . Several processes can be used including solvent extraction, electrochemical deposition and membranes processes . However, these processes are generally poorly competitive for low‐concentration effluents and ion‐exchange and chelating resins or biosorbents may be more competitive.…”

Encapsulation of Cyanex 302 with Alginate for Palladium Recovery

“…Metal recovery is becoming an important challenge for the Industry due to the tightening of regulations regarding the discharge of metals (accumulative toxic effects on biotope) but also to the necessity of recycling precious and strategic metals. Different processes are commonly used for the treatment of metal‐bearing solutions including precipitation, membrane processes, electrodeposition, liquid–liquid extraction or ion‐exchange/chelating resins . The choice of the process is actually controlled by the characteristics of the effluents, the value of the metal, its concentration, the regulations concerning its discharge into the environment, etc.…”

Soft gold electroplating from a non-cyanide bath for electronic applications

“…[1] Cyanide based electrolytes are the most extensively used in the industry. The gold (I) cyanide complex Au(CN) 2 has a stability constant of 10 39 , which makes the solution very stable, and shifts the standard reduction potential of gold (I) from 1.71V to -0.61V (SHE). [2,3] However, in recent years, the health and safety concerns regarding the use of cyanide have overwhelmed the benefits it brings.…”

“…The gold (I) cyanide complex Au(CN) 2 has a stability constant of 10 39 , which makes the solution very stable, and shifts the standard reduction potential of gold (I) from 1.71V to -0.61V (SHE). [2,3] However, in recent years, the health and safety concerns regarding the use of cyanide have overwhelmed the benefits it brings. In addition, free cyanide containing solutions can be incompatible with positive photoresists used in the microelectronics industry because they attack the interface between the resist film and the substrate, lifting the resist and depositing extraneous gold under the resist.…”

“…[6] Therefore, stability is always an issue for sulfite-based gold electroplating solutions, and stabilizing additives are usually necessary. [7][8][9] Gold (I) thiosulfate complex Au(S 2 O 3 ) 2 3is another alternative to cyanide. Its stability constant (10 28 ) is between cyanide and sulfite complexes and it is stable in weakly acidic solutions.…”