Thermoelectrics: Roughing it

(Nanowerk News) Thermoelectric materials convert a temperature gradient into a voltage. Most thermoelectrics, however, are too inefficient for widespread practical application. Still, the possibility that these materials could usefully harness heat waste, such as that generated by combustion engines, makes improving their efficiency an important pursuit in materials science. A team of scientists led by Wooyoung Lee at Yonsei University in Korea has now shown that interface roughening may be an effective way to enhance the thermoelectric properties of core/shell nanowires (“Reduction of Lattice Thermal Conductivity in Single Bi-Te Core/Shell Nanowires with Rough Interface”).

In the ideal thermoelectric, the charge conducts easily from a hot point to a cold one, while heat conduction is low. The ratio between these quantities is contained in the thermoelectric ‘figure of merit’.

As both electrons and vibrational waves in the lattice, known as phonons, contribute to a material’s thermal conductivity, Lee and his colleagues attempted to raise a material’s thermoelectric figure of merit by suppressing the conductivity of phonons without impairing electrical conductivity. This can be achieved by adding defects or nanostructuring a material to make it smaller than the phonon mean-free path — the typical distance a phonon travels before it scatters.

Lee and his team combined both of these tricks to reduce the thermal conductivity of a promising thermoelectric material consisting of a bismuth nanowire core coated with a tellurium shell. The team synthesized the wires by cooling just-prepared bismuth nanowires with liquid nitrogen and then coating them with tellurium using a sputtering technique, giving a core/shell structure with a smooth interface. They also prepared the wires without the cooling step, resulting in a rough interface.

After examining a series of the core/shell nanowires of 160–460 nm in diameter in both the smooth and rough versions, the researchers noticed two trends: the narrowest wires had the lowest thermal conductivity, and wires with rough interfaces had lower thermal conductivity than those with smooth interfaces — in some cases by as much as a factor of five.

According to Lee, roughening of the interface between the bismuth and tellurium reduces the thermal conductivity of phonons more significantly than electron thermal conductivity (see image). “The overall effect is to increase the thermoelectric figure of merit,” says Lee.

Source: Tokyo Institute of Technology 

Bismuth, Stepping Out of Leads Shadow

Today we hear much about the demise of lead and its uses because of its toxicity.  This will have a huge impact on the value of the rare industrial metal we will discuss today.  Enter bismuth, the brittle white metal an element symbol of Bi and atomic number 83.  Bismuth was discovered in 1783 by Claude Geoffroy the Younger.  This rare industrial metal is mined as a by-product of lead, silver, copper, molybdenum, tin and gold.  The element is 86% as dense as lead.  Bismuth is the most naturally diamagnetic metal meaning it is the most resistant to being magnetized.  Mercury is the only metal that has a lower thermal conductivity.  It also has a high electrical resistance.  Bismuth has been classified as the heaviest naturally occurring element.

One of the most interesting aspects of bismuth is its crystalline structure that forms a spiral stair step structure.  It is caused by a higher growth rate around the outside edges than on the inside edges of cooling bismuth.  The beautiful colorations of the crystals are caused by variations in the thickness of the oxide layer that forms on the crystal surface which causes wavelengths of light to interfere upon reflection.  When bismuth burns with oxygen present it burns with a blue flame.

Bismuths uses are growing all the time.  Some of its largest uses are in cosmetics, pharmaceuticals, catalysts, metallurgical additives, galvanizing, solders, ammunition and fusible alloys.  The one most people associate with bismuth is, Pepto Bismol.  Lead-Bismuth Coolant is also used as a coolant for nuclear reactors.

There are a few issues that are causing alarm within the industries that use bismuth.  The first is that China is implementing export controls over all rare earth elements and rare industrial metals.  China produces about 80% of all the world´s refined bismuth.  The second issue is lead acid batteries will soon be replaced by nickel-cadmium and lithium-ion.  Lead mining is the main source of bismuth mining worldwide.  Crude lead bullion contains approximately 10% bismuth which is taken out when lead is refined further using the Kroll-Betterton or the Betts process.  This leaves us with 99% pure bismuth.  The long-term sustainability is in jeopardy because of the lead storage battery.  There is a distinct possibility that we will soon see this battery replaced.  Overnight 80-90% of the lead market would be gone.  This will be catastrophic for bismuth industries.  The mining of bismuth would then have to rely on its other sources which provide much less metal.  Recycling would have to be a major source of bismuth in the future.  The problem with recycling bismuth is that many of its uses, almost 60% in pharmaceutical and cosmetic uses, would make it very difficult to meet the demand.

Once again we have the story about a rare industrial metal that is used in so many products that we use every day.  How will this affect the end prices of these products?  History tells us not much initially, but in the future the story could be much different.  Bismuth with its many uses may be worth enough that mines open exclusively for this metal.  Recently the British Geological Survey 2011 put bismuth on its list of at risk metals.  Countries like Bolivia, Canada, Peru, Mexico and China will no doubt profit greatly if we have a significant rise in the value of bismuth.  How will you profit?

By: Randy Hilarski - The Rare Metals Guy

Sources Discuss Bismuth Price Increase in China

BEIJING (Asian Metal) 21 Apr 11 - Bismuth price rises very quickly in China with demand improving from end users. “We still have some stocks at hand, in no hurry to sell while bismuth price may rise further in the near term,” said the source, with an estimated output of about 90 metric tons monthly.

A Hunan-based producer reported to Asian Metal that there are many inquiries from end users these days and bismuth price rises very quickly. According to the source, there is one major consumer of bismuth coming to them for bismuth, but as their bid is too low, they are reluctant to make a long term contract.

 Another Guangdong-based trader confirmed that bismuth price rises further and the price has reached record highs.

Tellurium Nerds Gold

Tellurium, used in both photovoltaic and thermoelectric technologies, has become a recent topic of debate in cleantech and materials science because of its rarity. With massive recent commodity price increases in rare earths and precious metals, I attempt to make some sense of the tellurium demand picture and whether we might expect a similar rush for the inconspicuous chalcogen element.


Tellurium (Te) is an element, number 52 on the periodic table, whose rarity on earth rivals only that of a handful of other elements, including gold. It is the namesake of the Telluride Film Festival and Telluride, Colorado, a mining town where gold telluride was thought to be found in the late 1800s.

The chart above shows the natural abundance of elements on Earth. For all practical purposes, this picture is static: it is the result only of world-formative events like the big bang and major asteroid impacts (despite any attempt at alchemy, black magic old or particle accelerator new). The fact that gold and tellurium have similar abundances on earth is merely a coincidence, but they are nonetheless found together in alloys of tellurium, or tellurides. Tellurides like calaverite were initially foolishly discarded during the first gold rush of 1849 and the subsequent discovery of gold in them spawned a second gold rush a few years later. Mining and metallurgy, an often high-tech profession at the time, was probably the only field that had tellurium in its vernacular.

Unlike tellurium, gold is the element of basilicas and twenty twos not because of its rarity, but because of its (anti) corrosive properties. Technically speaking, gold’€™s chemical reduction potential is positive, meaning it requires extra energy to become oxidized and therefore it never loses its luster while adorning our teeth and bathroom door handles. Tellurium, on the other hand, was not blessed with the pretty gene. Its current spot price on metals markets (~$200/kg, 200x cheaper than gold) reflects this.

Any engineer will tell you that looks aren’€™t everything. Tellurium, in the throws of its own fifteen minutes, has the potential to become similarly priced in the long term due to its increasing use in the highest tech applications. Tellurium has a rich history, if anything, having played a role in every stage of mining and materials science since 1849. During the space race, mining and metallurgy eventually became materials science, an interdisciplinary field of science and engineering incorporating physics and chemistry. With the discovery/invention of quantum mechanics in the 1910s and 20s, solid state physics was born and so was the modern notion of a semiconductor material. It would be thirty years before a semiconductor was applied to computation through microchips, and it would be silicon that proved ideal for this application. Initially, however, an alloy of tellurium, bismuth telluride, was the star of the solid state physics community for its fantastic Peltier, or thermoelectric, properties. A Soviet physicist who published much of the seminal work on solid state physics named Abram Ioffe believed that the commercial application of semiconductors would come in refrigeration through something known as the Peltier effect. The Peltier effect is when a semiconductor material pumps heat when electricity is made to flow through it. Any material that does this efficiently is called a thermoelectric.

Clearly, bismuth telluride and thermoelectric technology lost to the common compressor refrigerator, but one can nonetheless find these semiconductor coolers in a few places. If you have a quiet wine fridge in your living room, a climate controlled seat that cools you down in your Ford F150, or night vision goggles, then you’€™ll find a Peltier cooler inside.

Today tellurium is seeing its first real growth in use in a different application: solar cells. First Solar (FSLR), darling of all solar startups, uses a thin-film of cadmium telluride (CdTe, or €œcad-tell€) as one of the functional layers in its cells that helps collect sunlight. The company is increasing production quickly. Raw cadmium and tellurium demand is increasing and alas, tellurium could finally have its day. The question is whether Te, currently priced at ~$200/kg on the spot market and with the same supply constraints as gold, will ever have the type of demand that has gold currently trading two hundred times higher at ~$40,000/kg.


Tellurium supply has historically never been much of a concern to anyone. Today tellurium is produced from the refining of copper in the same way gold is produced, as the byproduct of an electrolytic refining process that manifests itself in nasty resultant anode sludges. Tellurium is produced primarily by a Canadian company named 5N Plus which extracts it from these sludges. According to the US Geological Survey, 200 metric tonnes of tellurium were mined in 2009 worldwide and the world can sustain 1,600 metric tonnes of production per year maximum (but these estimations are hard to make accurately“ see Jack Lifton’s piece on tellurium supply here). In comparison, there were about 2,500 tonnes of gold mined in 2009, and 165,000 tonnes of gold have been mined, ever. Gold production peaked in 1999 at 2,600 tonnes. Let’s assume that tellurium could be produced at similar levels to gold going forward.

Gold demand currently comes from three areas: jewelry (~2,750 tonnes/year), reserve assets (~350 tonnes/year), and the electronics industry (~350 tonnes/year). Adding this up we get 3,450 tonnes/year demand, well over the amount produced. The difference is made up from both recycling of jewelry and the selling of reserve assets.

Gold, however, as an element that is also tied to the world economy through federal reserves and currencies, is not truly a commodity because its price is not generally close to its marginal cost of production. For that reason, let’€™s consider an element that might be slightly more similar to gold (Au) in that sense: platinum (Pt) or palladium (Pd). Both of these elements currently trade at $60,000/kg and $25,000/kg, respectively. The order of magnitude of these spot prices are the same as that of gold’€™s; while these elements tend to follow gold and are therefore somewhat subject to price swings that may not be concomitant with economic fundamentals, tellurium’€™s price can still be expected to rise significantly, albeit perhaps not quite by 200x, if demand for it was also >2,000 tonnes/year.

So how could tellurium demand increase by a factor of ten? Should First Solar be worried? Should producers of bismuth telluride thermoelectric devices be worried?

Tellurium Demand

First, let’€™s examine how much tellurium First Solar uses, and what this costs as a fraction of their total cost to produce a CdTe photovoltaic cell.

The density of CdTe is 5.8 g/cc. This gives 3.08 g/cc of Te in CdTe.

The efficiency of FSLR’€™s modules is ~11%. At a solar irradiance of ~1100 W/m^2, their cells will have a maximum power density of ~121 W/m^2.

At a CdTe film thickness of 3 µm, and at a 2.7 GW target production in 2012, they will be using roughly 71 m^3 of tellurium per year in the cells alone.

This would mean using 218 metric tonnes of tellurium per year in their cells. As described earlier, global production is currently estimated at 200 metric tonnes/year and could go as high as 2,500 if we do a straight comparison to gold.

This means FSLR would have to be producing somewhere near 27 GW per year of solar panels to ever be truly supply constrained by tellurium. Considering 20 GW of new power plants were built in the US in 2009, and that 550 GW of new capacity is expected to be installed in China between 2010 and 2020, 27 GW of PV production per year is somewhat plausible many years out and by no means likely.

To understand whether First Solar is shielded from volatility in the price of tellurium, let’€™s look at what the cost of tellurium is within their cells. From our analysis above it takes 80 metric tonnes of tellurium to manufacture a gigawatt of cell, assuming FSLR’€™s CdTe deposition is 100% efficient in that no tellurium is wasted or lost (not the case, but we’€™ll stick with this assumption). At $200/kg, 80 metric tonnes costs $16 million, or 1.6¢/Watt. At an overall production cost of $1.00/Watt, the price of tellurium would have to increase by at least 10x before FSLR would feel significant pain. It is safe to say that they are not going to affect the tellurium market nor be sensitive to much volatility in it with business as usual.

Now let’€™s look at thermoelectrics and their application for something converse to refrigeration: power generation. Bismuth telluride and a similar alloy, lead telluride, have been studied for a long time for their ability to generate electricity from an applied temperature gradient such as a waste heat source. The automotive industry, in particular, has big plans to incorporate thermoelectric waste heat recovery technology into engine tailpipes to turn wasted heat in exhaust back into electricity. These systems require roughly 1 kg of bismuth or lead telluride per car typically, roughly half of which is tellurium.

Will adoption of automotive thermoelectric generators cause a tellurium shortage? About 60 million motor vehicles were produced in 2009, only a tiny fraction of them not with an internal combustion engine. If each had a thermoelectric generator on them with 0.5 kg of tellurium within, over 30,000 metric tonnes of tellurium would be required per year€“ over 10x more production than what is thought to be possible, and over 100x more than what is currently produced annually. Modestly, if only 7 million cars per year had thermoelectric generators (all of GM’€™s and BMW’€™s autos, for instance) we would expect tellurium demand to be 3,500 metric tonnes/year. Even if we assume this tellurium usage could come down by a factor of ten through going to more power dense configurations and by using thin film materials, the long term picture is still bleak. Surely a problem for anyone expecting to scale this technology€“ and for FSLR for that matter! (Note FSLR’€™s relationship with the largest tellurium supplier 5N Plus.)

More importantly, however, is that it currently costs $100 for just the tellurium in an automotive thermoelectric waste heat recovery generator, and these systems typically produce no more than 500 W of power. In the low margin automotive industry, $0.20/Watt will never cut it; the question of whether the automotive industry will ever impose a tellurium shortage practically moot.

Gold, platinum, palladium, and rare earth elements have all seen their values skyrocket in recent months. While there is nothing immediately suggesting tellurium will follow suit, it will surely be an interesting metal to follow over the next decade – and an analysis like this hopefully helps guide technologists away from the use of telluride materials in all but the niche-est of applications.

Matthew L. Scullin is CEO of Alphabet Energy, Inc., a producer of thermoelectric materials that use no tellurium. This article was previously published on his Scullin blog.

Rare Earth Elements and Rare Industrial Metals

Swiss Metal Assets offers packages or “baskets” with the following metals that will secure and protect your wealth and inflation because these metals are in High Demand by different manufacturers and used in 80% of industry today.

Hafnium is a heavy metal of high density (13.31 g/cm3), a lustrous, silvery gray, tetravalent transition metal. Hafnium is found neither dignified nor in their own minerals.

Hafnium is used in nuclear power plants. China already decided to start to construct many nuclear power plants. The demand for hafnium will increase even more because of this fundamental decision. In the nuclear industry such as in aircraft hafnium is in strong demand.

The hafnium we are offering has the big quality of not more than 1% of zirconium in it. It is difficult to buy this quality it in the market. But we do have it. So our hafnium really can be resold, the demand for that quality is high.

Indium has a great future ahead. The main application is in solar technology. A hot new economic use will be the coating of screens / windshields of cars with indium. Ice is then without any chance - even at -0.4° Fahrenheit (-18 ° C). Before the economic crisis indium was already three times as expensive as today.

Gallium can be alloyed with numerous other metals. Due to its ideal attributes high-purity Gallium is mainly used as semiconductor material. The chips so produced are faster than others. Furthermore, it is used in the optoelectronic area, i.e. for the production of LEDs, in thermometers as eutectic consisting of Gallium-Indium-Tin, and others.

Bismuth is a rare, reddish-white semi-metal. Bismuth is used for the production of alloys and in medicine it is applied in field of chemotherapy.

Tantalum is used in alloys. Tantalum is very hard and can be applied for the production of surgical instruments, electronic elements and fast turning steels.

Tellurium is used as a pigment for glass and in alloys. Furthermore, Tellurium compounds are applied in the semi-conductor electronic area.

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