Palladium has a history that is sealed with that of platinum, with which it is found, and with which it is also associated as a member of the platinum metals group, also known as the nobel metals. “Native platinum” refers to the natively occuring platinum which is not actually pure platinum at all, but rather a natively alloyed mix of platinum group metals including palladium. Palladium was not separated from platinum for quite some time after the discovery of native platinum, so the early history is a shared one.

Despite being worked with some skill by South American Indians over 1,000 years ago, not until the Spanish conquest of the New World during the fifteenth and sixteenth centuries did news reach Europe of a new white metal with unusual properties. The Spanish first considered the metal a nuisance because it interfered with their gold mining activities. In fact, since native platinum was considered of little value, it was soon being used by forgers to adulterate Spanish gold coins. The coins were struck in native platinum then guilded with gold to look like genuine gold coins. Platinum’s extraordinary properties did interest European scientists where platinum was noted as a substance that could not “melt by fire or by any of the Spanish arts.” It was heavier than gold and virtually impossible to corrode with gases or chemicals and, in 1751, recognized as a newly discovered element.

From the Greek name “Pallas”, goddess of wisdom, Palladium was discovered by the British chemist William Hyde Wollaston in 1804. It took nearly two centuries for palladium’s significance to be recognized, and the fight against global pollution owes a lot to this unique metal.

Following the perfection of his technique to obtain pure samples of platinum in 1801, William Hyde Wollaston went on to isolate palladium from platinum two years later by dissolving native platinum in aqua regia (a mixture of hydrochloric and nitric acid). He named it after Pallas, the ancient Greek goddess of wisdom whose name had also been recently lent to the second asteroid ever discovered.

In an attempt to keep his techniques a secret, Wollaston offered samples of palladium for sale anonymously and his peers were cynical about the new metal’s provenance, suspecting that it was an alloy of platinum. This forced him to publish details of his findings in 1805.

The use of palladium really took off in the 1970s when demand for catalytic converters - in which its remarkable properties play a key role increased as automobile emission standards were introduced in the developed world. As these standards were tightened and applied globally in the 90s, demand for palladium expanded exponentially.

Palladium Uses:

Autocatalysts

Softer than platinum, ductile and resistant to oxidation and high temperature corrosion, palladium is useful in eliminating harmful emissions produced by internal combustion engines. Autocatalysts are by far the largest user of palladium; autocatalysts convert over 90 percent of hydrocarbons, carbon monoxide and oxides of nitrogen produced in the exhaust from gasoline engines into carbon dioxide, nitrogen and water vapor.

By far the largest use of palladium today is for automobile catalytic converters. Based upon some estimates the 450 million automobiles in the world today is projected to more than double in the next 30 years requiring a growing use of palladium. And, while some forecasters suggest palladium recycled from scraped automobiles will become a large factor in the supply/demand price equation for palladium in coming years, other factors will mitigate these projections.

First, as mentioned, the growth in the number of cars in the world is expected to continue unabated with an increasing number of cars each year, each required to meet increasing environmental standards. Second, many of the cars reaching the end of their useful life in developed countries of the world are increasingly finding their way to less developed countries as used cars. Some used cars simply gravitate there; others are even being refurbished and then freighted.

This will delay and may eliminate the recovery of metals in many of these cars. Working against some of these gains will be increasing fuel economy and improved engine and catalytic technology, both of which will reduce the level of PGM consumption in cars.

Diesel engines operate at lower temperatures than gasoline engines and, to date, platinum is better suited as a catalyst in converting CO, NOx and hydrocarbons to harmless emissions at the lower temperatures. However, when it comes to reducing or eliminating DPM, which is essentially carbon, temperatures must be increased in order for the carbon to be oxidized before being exhausted. At the higher temperatures palladium may be important, as it not only reacts well at higher temperatures, but it can tolerate higher temperatures better than platinum. Further, with palladium currently at a steep discount to platinum there is an economic incentive to develop technology using palladium.

In this regard, a large European automobile manufacturer recently mandated a research and development effort to examine and advance palladium-based technology for diesel catalytic converters. The reason is apparent. In Europe, 44 percent of the cars built in 2003 were equipped with diesel engines and recent CAFÉ (fuel economy) standards announced by China, will ultimately result in a similar percentage of cars built by China’s surging car industry to be diesel. Thus, a growing concern over insufficient supplies of platinum to meet this growing diesel demand, placing urgency in finding a way to use palladium for this application.

One remaining obstacle to perfecting this palladium technology is the sulfur content of diesel fuel. Sulfur tends to collect on palladium more than on platinum. And at higher temperatures the sulfur tends to generate sulfates that are then exhausted. Sulfur will be sharply reduced in diesel fuel in the U.S. in 2006 enhancing the opportunity for palladium technology for cleaning diesel emissions. Knowing this, Stillwater Mining Company is currently having a palladium catalytic converter and DPM filter fabricated using palladium to test with low sulfur fuel in our mine operations.

Electronics

Palladium has a number of electronic applications. For example, palladium’s chemical stability and electrical conductivity make it an effective and durable alternative to gold for plating in electronic components.

Electronic Uses of Palladium

Palladium-containing components are used in virtually every type of electronic device, from basic consumer products to complex military hardware.  Although each component contains only a fraction of a gram of metal, the sheer volume of units produced results in significant consumption of palladium.

The largest area of palladium use in the electronics sector is in multi-layer ceramic (chip) capacitors (MLCC). Smaller amounts of palladium are used in conductive tracks in hybrid integrated circuits (HIC) and for plating connectors and lead frames.

MLCC

Capacitors are components that help to control the flow of an electric current through the various parts of a circuit by storing a charge of electricity until it is required.  They consist of layers of conductive electrode material (usually palladium or palladium-silver) sandwiched between insulating ceramic wafers.

In the early 1990s MLCC manufacturers responded to the drive towards miniaturisation of consumer goods by producing ever smaller capacitors using less palladium per unit. Soon afterwards came the development of technology to substitute palladium with nickel. This was not significant until 1997, when the increasing palladium price encouraged manufacturing of nickel-based capacitors on a much larger scale.

HIC

A hybrid integrated circuit consists of a ceramic substrate on which are mounted a number of different electronic components, including integrated circuits and capacitors. They are linked by conductive silver-palladium tracks. The function of the palladium is to hold the silver in place, without which it would migrate. The automotive industry is the largest market for HIC.

Plating

Components inside computers are linked by connectors plated with a conductive layer of precious metal. Palladium is used as an alternative plating material to gold for connectors as it has a lower density and so less weight of metal is required for a coating of similar thickness.

Lead frames are used to connect integrated circuits to other electronic devices. Some manufacturers use palladium to plate the frames as an environmentally preferable alternative to tin-lead solder.

Source: Johnson Matthey

Dentistry

Palladium-based alloys are used in dentistry for dental crowns and bridges. And palladium metal is also compatible with human tissue and is used, in a radioactive form, in the medical industry for the treatment of cancer.

Dentists have used gold alloys containing platinum for many decades but the use of palladium in dentistry is relatively recent.

Dating from the 1980s, a rising gold price then encouraged palladium to be introduced as a lower-cost alternative. When the price of palladium increased sharply a few years ago this trend reversed. However, at the moment the price of palladium is lower by far than either gold or platinum and consumption of palladium in dental alloys has again increased.

Palladium is usually mixed with gold or silver as well as copper and zinc in varying ratios to produce alloys suitable for dental inlays, crowns and bridges. Small amounts of ruthenium or iridium are sometimes added. The most common application is in crowns, where the alloy forms the core onto which porcelain is bonded to build up an artificial tooth. The aim of using platinum group metals in dental alloys is to provide strength, stiffness and durability whilst the other alloyed metals provide malleability.

In Japan, the government operates a specific mandate stating that all government-subsidized dental alloys have to include a palladium content of at least 20 percent. This alloy is known as the “kinpala” alloy and is used in around 90 percent of all Japanese dental treatment. Hence, Japan is the largest palladium-consuming region for dental applications, followed by North America and then Europe.

Jewelry

Palladium is lighter than platinum having about the same density as silver, thus, palladium is a jewelry metal as well. Palladium in jewelry is primarily used as an alloy with platinum to optimize platinum’s working characteristics and wear properties. Palladium is also used as an alloy in producing white gold.

Palladium versus other jewelry metals
Alone or alloyed with silver or gold, palladium offers some of the same metal working properties as other jewelry metals, and remains tarnish free. It also offers jewelers a sharply different pricing point than either gold, white gold or platinum. It is more precious than silver and whiter than platinum. Because it is also lighter than platinum, nearly half the weight, more intricate necklaces and bracelets can be made capable of bearing larger gemstones with no gain in overall weight. For the same reason, Palladium can be an especially good choice in earrings. With the price of platinum and gold reaching recent highs, use of palladium for jewelry has seen renewed interest domestically and abroad. Palladium is an excellent material for electroplating, and sees significant use in the plating of jewelry and watches, such as the timepiece here from Morpier Firenze.

950 Palladium
Palladium, a platinum group metal, was first used for jewelry when platinum was declared a strategic metal and reserved for military use in 1939. Palladium alloys developed for jewelry typically contain 95% palladium and about 5% ruthenium and have trace amounts of other metals proprietary to their developers. These 950 palladium alloys are white, noble, malleable, lightweight, hypoallergenic, easy to finish and polish, furthermore they do not require rhodium plating, and have desirable, platinum-like setting and forming characteristics.

White Gold
Palladium is the standard for alloying with gold for producing white gold in Europe. Palladium’s use is mandated to avoid allergic reactions such as skin rashes, dermatitis, and eczema that may otherwise result from wearing white gold jewelry made with nickel. A white gold alloy content is typically 75 percent gold and 15 percent palladium for an 18-carat gold piece of jewelry. While traditionally other metals including nickel and zinc have been used as the whitening agent for white gold, the least skin sensitive gold alloy is made with palladium.

In the table below you can find some commonly available white gold compositions, with metal content displayed in percent:

	Gold	Palladium	Silver	Copper	Zinc	Nickel
18k	75	20	5
	75	15	10
	75	10	15
	75	10	10.5	3.5	0.1	0.9
	75	6.4	9.9	5.1	3.5	1.1
	75	15		3.0		7.0
14k	58.3	20	6	3	1
	58.5	5	32.5	20.5	1.4

The addition of palladium to gold:
  •  Increases its melting point
  •  Increases its modulus of elasticity
  •  Increases its strength
  •  Increases its hardness
  •  Turns yellow gold white (depending on the amount added)

Platinum alloyed with palladium
Platinum is typically alloyed with small amounts of other metals to increase its hardness and is typically produced at 85 to 95 per cent purity. Purity or “fineness” is nearly always measured in parts per thousand (ppt). Platinum-palladium alloys are widely used in Japan and China. The most common alloys are Pt900/Pd (100 ppt palladium) Pt850/Pd and Pt950/Pd. Pt900/Pd is the general purpose alloy of choice in Japan, offering a good combination of hardness, workability, and suitability for casting, welding and soldering. Chain manufacturers prefer Pt850 because its softness and ductility minimize tool wear and are also very well suited to the chain making process.

Pd/Pt	Melt	Hardness Hv	Applications	Countries
50/950	1,765	60, 68(c)	Castings, delicate settings	Japan
100/900	1,755	80, 72(c)	General purpose	China, Japan
150/850	1,750	90, 64(c)	Chain making	Japan

platinum source: Johnson Matthey, Platinum Jewellery Alloys 2002

Precium
Precium is a palladium - silver alloy developed for jewelers by Handy & Harman, and is used both as a casting alloy and a wrought alloy. As a casting alloy it is widely used by manufacturers of class rings. Precium is 25% palladium and 62 - 75% silver, the rest unnamed.

Sources of jewelry grade palladium
Jewelry grade palladium is not widely available, though a few suppliers stock it. Palladium white gold is more commonly available.

Hoover & Strong

Hauser and Miller
These folks produce a .955 palladium alloyed with .045 ruthenium and available in a number of wire sizes. Can be used in settings.

Surepure Chemetals
Surepure manufactures a palladium alloy with .05 ruthenium.

Chemical

With the fall in palladium prices and the rise in platinum prices palladium’s cost-effectiveness in chemical applications has become apparent. Various chemical applications use palladium, including the manufacture of paints, adhesives, fibers and coatings. Palladium is used in the production of purified terephthalic acid, which is a precursor to polyesters and to polyethylene terephthalate a plastic resin used in packaging of film and glass laminates.

PGM catalysts for nitric acid production take the form of a gauze made out of fine wire. Palladium is used in the production of catchment gauze used in the making of nitric acid for the manufacture of nitrogen fertilizers.

When nitric acid was first produced commercially in 1904, a platinum-only catalyst was used. Rhodium was later added for strength and to reduce the amount of platinum lost during conversion of the gas. Palladium-based “catchment” or “getter” gauze was introduced in 1968 to further reduce losses of platinum and rhodium, which can be as high as 300 mg per ton of acid produced. The catchment sits downstream of the gas flow and collects pgm vaporized from the catalyst.

Ethanol is produced using palladium catalysts through the “Wacker Process”. This process manufactures ethanol by oxidizing ethane, yielding 95% acetaldehyde which is converted to the ethanol. The process has good economics due to the abundance of ethylene.

The reaction is catalyzed by PdCl₂ and CuCl₂. It involves the reaction of ethylene with palladium chloride in water. Palladium is thereby reduced to palladium black. To make the reaction catalytic, palladium is reoxidized by reaction with copper chloride and oxygen. The process is run in one vessel at slightly elevated temperatures and pressures (50-130 °C and 3-10 atm).

		[Pd(0)/Cu(II)]
C2H4 + 1/2 O2				CH3CHO

Palladium is also used in chemical processes that require hydrogen exchange between two reactants, such as that which produces butadiene and cyclohexane, the raw materials for synthetic rubber and nylon.

Another important use as a catalyst is in the manufacture of polyester.

 

 

                                                                                          Fuel Cells

With the fall in palladium prices and the rise in platinum prices palladium’s cost-effectiveness in chemical applications has become apparent. Various chemical applications use palladium, including the manufacture of paints, adhesives, fibers and coatings. Palladium is used in the production of purified terephthalic acid, which is a precursor to polyesters and to polyethylene terephthalate a plastic resin used in packaging of film and glass laminates.

PGM catalysts for nitric acid production take the form of a gauze made out of fine wire. Palladium is used in the production of catchment gauze used in the making of nitric acid for the manufacture of nitrogen fertilizers.

When nitric acid was first produced commercially in 1904, a platinum-only catalyst was used. Rhodium was later added for strength and to reduce the amount of platinum lost during conversion of the gas. Palladium-based “catchment” or “getter” gauze was introduced in 1968 to further reduce losses of platinum and rhodium, which can be as high as 300 mg per ton of acid produced. The catchment sits downstream of the gas flow and collects pgm vaporized from the catalyst.

Ethanol is produced using palladium catalysts through the “Wacker Process”. This process manufactures ethanol by oxidizing ethane, yielding 95% acetaldehyde which is converted to the ethanol. The process has good economics due to the abundance of ethylene.

The reaction is catalyzed by PdCl₂ and CuCl₂. It involves the reaction of ethylene with palladium chloride in water. Palladium is thereby reduced to palladium black. To make the reaction catalytic, palladium is reoxidized by reaction with copper chloride and oxygen. The process is run in one vessel at slightly elevated temperatures and pressures (50-130 °C and 3-10 atm).

		[Pd(0)/Cu(II)]
C2H4 + 1/2 O2				CH3CHO

Palladium is also used in chemical processes that require hydrogen exchange between two reactants, such as that which produces butadiene and cyclohexane, the raw materials for synthetic rubber and nylon.

Another important use as a catalyst is in the manufacture of polyester.

Oil Refining

Petroleum refining is an important use for palladium and the other platinum group metals as catalysts for a number of different refining processes. Johnson Matthey includes this use within their catchall category “other uses”.

Distillation is the first step in the process, and alone can separate the heavy crude into its primary fractions of gasoline, jet fuel, diesel, heating oil, and fuel oil. Because the natural ratio of these fractions does not match the demands for the various fuels, additional steps are required to reform some of the products into products that are in demand. This is particularly true for high demand automobile gasoline.

These additional processes are as follows:

 • Catalytic Reforming
 • Alkylation
 • Catalytic Cracking
 • Hydroprocessing

Catalytic Reforming produces high octane gasoline for today’s automobiles. Gasoline and naphtha feedstocks are heated to 500 degrees Celsius and flow through a series of fixed-bed catalytic reactors. Because the reactions absorb heat additional heaters are installed between reactors to keep the reactants at the proper temperature. The catalysts are palladium or other platinum group metal on an alumina base. While catalysts are never consumed in chemical reactions, they can be fouled, making them less effective over time. The series of reactors used in Catalytic Reforming are therefore designed to allow the catalyst can be regenerated.

Alkylation is another process for producing high octane gasoline. The reaction requires an acid catalyst of sulfuric acid or hydrofluoric acid at low temperatures (1-40 degrees Celsius) and low pressures (1-10 atmospheres). Neither palladium nor other platinum group metals are typically involved in this process.

Catalytic Cracking takes long molecules and breaks them into much smaller molecules and in so doing, converts heavy distillate to compounds with lower boiling points (e.g., naphthas), which are fractionated. Cracking is typically conducted in a fluidized bed reactor with a regenerator to continuously reactivate the catalyst. Cracking catalysts are typically zeolites comprised of alumina and silica. Platinum group metals are typically not involved.

Hydroprocessing includes both hydrocracking and hydrotreating techniques. Hydrotreating involves the addition of hydrogen atoms to molecules without actually breaking the molecule into smaller pieces and improves the quality of various products (e.g., by removing sulfur, nitrogen, oxygen, metals, and waxes and by converting olefins to saturated compounds). Palladium, among a number of other catalysts, can be used. Hydrocracking breaks longer molecules into smaller ones. Hydrocracking is a more severe operation than hydrotreating, using higher temperature and longer contact time, resulting in significant reduction in feed molecular size. Typically, Hydrocracking reactors contain fixed, multiple catalyst beds. The catalyst pellets are shaped similarly to Hydrotreating catalysts, the active metals impregnated in the silica-alumina catalyst base are typically palladium, platinum, or nickel, depending on the catalyst licensor.

Polyester
Palladium is a critical catalyst in the manufacture of polyester. 

Photography

Platinum and palladium processes for producing photographic prints have been known since the mid 1800s and the early days of photography. As a process descended from the Cyanotype, it was known as Platinotype. Both metals are still used as an alternative process today in producing archival and museum suitable prints. In this form, palladium and platinum are very nearly interchangeable.

In the late 1800s, palladium was more expensive than platinum, and so saw less use in the printing process, but seemed to be viewed as a finer alternative. The book Platinotype by Captain Pizzighelli and Baron Von Hubl was released in 1886, translated by J.F. Iselin, MA. and edited by W. DE W. The forward:

“The growing popularity of the Platinotype process has induced the Council of the Photographic Society of Great Britain to authorize a reprint of the translation of the brochure by Captain Pizzighelli and Baron Von Hubl, which appeared in the Photographic Journal in 1883”

- W. DE W. Abney

Palladium prints produced warmer tones than platinum, which some preferred, and a heated developer was not required. Nevertheless, palladium printing did not see widespread use until 1910s. Both platinum and palladium prints have the reputation of being permanent due to the stability of the metal that constitutes the final image. In 1917 William Willis introduced his Palladiotype paper, the first commercially available palladium based photographic paper. In the 1930s, the Platinotype declined in favor of the mass production of gelatin silver papers and steep rise in the price of platinum, which had then become a strategic metal vital in the defense industry. A number of photographers continued to use the process, however.

Although platinum was again obtainable after World War I, its price remained extremely high. The war thus also stimulated experimentation with palladium photography. Some rather renowned photographers used the process. Alfred Stieglitz, printed mostly on platinum and palladium papers. Platinum was also preferred by his young protégés Paul Strand and Clarence White. Edward Weston used platinum and palladium papers throughout his early, greatest period; Edward S. Curtis, Irving Penn, Manuel Alvarez Bravo and most of the greats in the history of photography have all produced perfect, beautiful images in platinum or palladium.

After the Second World War, commercially available platinum paper was no longer available, forcing photographers to hand coat their paper, and eroding its popularity.

In the 1970s, the Platinotype saw renewed interest as a beautiful art medium more permanent than the commercially available silver based papers. Palladium differs from platinum to produce a slightly more “warm” image, with a bit more contrast. Some photographers learned to mix platinum and palladium together in varying proportions, to achieve even finer results than with either substance used alone. Today platinum and palladium prints are widely considered the princes of the photographic medium, and the greatest expressions of fine art photography.

Water Treatment

Palladium is a very promising catalyst for a process of purifying groundwater contaminated by certain toxic substances that have previously been difficult to remove. The contaminents in question are termed halogenated volatile organic compounds (VOCs). VOCs are some of the most pervasive groundwater pollutants in the United States. These tend to be hydrocarbons that are used as solvents, degreasers, and used in the production of paints and adhesives. The United States Geological Survey indicated that in a 2002 study of 1500 drinking water wells, 44% contained at least one VOC.

Trichloroethylene (TCE) and tetrachloroethylene (PCE) are common groundwater contaminants with adverse affects on human health. They are widely used for dry cleaning and degreasing purposes. After leakage from storage or disposal sites, they can leach into aquifers and then become long-lasting groundwater contaminants.

Numerous studies are now underway to pioneer techniques to use palladium as a catalyst to promote the chemical conversion of the contaminants into benign end products in the presence of added hydrogen gas. The reaction essentially replaces the chlorine atoms in the contaminant with hydrogen.

Advantages over existing treatment methods are many.

• Existing technologies do not destroy the contaminates outright, but rather entrap them in another medium where disposal is still an issue.
• The palladium catalytic action is extremely fast; allowing the water to be treated with in-well reactors and eliminating the need to pump to the surface for treatment.
• The technology can be applied where conventional treatment is not currently even feasible, such as deep aquifers with high contaminant concentrations.

Ongoing studies can be found as follows:

Environmental Security Technology Certification Program
A list of current palladium research projects most of which are involved with groundwater treatment.

Western Region Hazardous Substance Research Center (WRHSRC)
One of five university-based hazardous substance research centers in the United States, this page details several studies underway. The Centers are funded by grants from the US EPA Office of Research and Development and Office of Solid Waste and Emergency Response

Hydrogen Purification

Medicine