Tikalon Blog by Dev Gualtieri

Tikalon Header

Faux Palladium

January 14, 2011

There's been much press lately about potential problems with the supply of the rare earth elements . China is the principal supplier of these metals, which are important for manufacture of permanent magnets , catalysts and phosphors . China produces about 95 % of the world's rare earth elements, and the US imports most of its rare earth elements. In the period 2005-2008, the US imported 91% of its rare earths from China, 3% from France , 3% from Japan , and 3% from other sources.[1] China would like to allocate a larger share of this resource to its industries, which is causing price increases and supply problems in the rest of the world. I summarized this problem in a previous article (Rare Earth Shortage, June 21, 2010). It's been reported that rare earth exports from China will be cut 35%.[2]

Global rare earth element production (1 kt=10^6 kg) from 1950 through 2000

What happens when the government allows market forces to control its destiny. The US ceded rare earth production to China in the 1980s. (USGS data)

Some claim that there's a political component to the Chinese decision to keep more of its rare earths to itself. China stopped all exports of rare earth to Japan when a Chinese fisherman was detained by Japanese authorities for sailing into what Japan considers its sovereign waters around the Senkaku Islands , near Okinawa . China claims that these uninhabited islands are part of its territory.[2-3]

About thirty years ago, metallurgists were worried about shortages and increasing prices of another important metal, and that crisis had a political component as well. The metal was chromium , and the problem was that nearly half of the world's chromium is produced by South Africa . Although chromium has fallen out of favor for environmental reasons, each decade there's one material or another that appears crucial for advanced technology.

Palladium , which is considered as one of the six platinum group metals (the others are platinum , iridium , rhodium , ruthenium and osmium ) was an unknown metal outside of scientific circles until the early 1970s when it was used in automobile catalytic converters . It's a less expensive substitute for some, or all, of the platinum and rhodium for that application. There was additional press coverage of palladium in March, 1989, when "cold fusion " of hydrogen isotopes was suspected to have occurred in the palladium cathode of an electrochemical cell performing electrolysis of heavy water . Palladium is a well known hydrogen "sponge" material, so the deuterium produced from the electrolysis was sucked into the metal. When the physicists repeated these cold fusion experiments, the results did not confirm the electrochemist's theory of the process, and most cold fusion research stopped. It's pursued now mostly for curiosity's sake, which is something that scientists do. Because of palladium's affinity for hydrogen, it's used also in some types of fuel cells .

Palladium is a rare and expensive metal. Silver sells now for about $30 per troy ounce , and gold for about $1,375. The current palladium price is about $800/tr. oz., which makes it nearly as precious as gold. The figure below shows the palladium price trend through 1998.[4] The later linear extrapolation to today's value seems to be holding.

Palladium price from 1962 -1998 (USGS).

Palladium price from 1962 -1998 (United States Geological Survey, from Ref. 4.)

Although gold has some technical uses, palladium is unlike gold since it's valuable for what it does, not for what it is. A cheaper material that does all the nice things that palladium does would be welcome. Hiroshi Kitagawa , a professor of chemistry at Kyoto University , and his students have developed a palladium replacement using nanotechnology .[5-9]

Palladium is flanked in the periodic table by rhodium and silver. A chemist's first inclination, at least for transition metal elements , is to assume that a mixture of adjacent metals will give an alloy with an average property that approximates that of the middle element. The fundamental problem with rhodium and silver is that their liquids are immiscible , and the elements don't form solid solutions . Rhodium is insoluble in liquid silver, and the maximum solubility of silver in rhodium is about 10-15%.[10] This isn't good news when you want something like a 50-50 mixture. Although it's not clear from the press releases, what the Kyoto researchers appear to practice is a sol-gel type of process in which precursors of rhodium and silver metal were mixed, nebulized, and then reacted to form 10 nanometer particles of a rhodium-silver alloy. At this scale, the rhodium and silver atoms coexist in the same crystal lattice.[5-7]

As they say (or, at least, the older people say ), "The proof of the pudding is in the eating." Although hydrogen is essentially insoluble in rhodium and silver, this nano-alloy absorbs about half the hydrogen that palladium absorbs.[8] Chemists believe in molecular orbital theory , and Kitagawa is no exception. He's quoted as saying, "The orbits of the electrons in the rhodium and silver atoms probably got jumbled up and formed the same orbits as those of palladium."[5] Since patents are pending, the Kyoto team did not reveal the ratio of rhodium to silver.[9] Unfortunately, rhodium is about three times the price of palladium, so this may just have been an academic exercise, at least for palladium. The Kyoto team is using this technique for other materials.[8]

Japanese industry is especially sensitive to raw material prices and shortages. The Japanese government has spotlighted thirty one metals that are essential to its industry. Seventeen of these are rare metals, including the rare earths, for which they are heavily dependent on China. [11]

References: