Does political upheaval in the Congo threaten Technology Industries?
Harry Dutton
March 28th, 2010
Recently my attention was drawn to a “Wikipedia” article on “Coltan” (http://en.wikipedia.org/wiki/Coltan). Coltan is an ore containing the metals Niobium and Tantalum. The article reports that there is significant concern that the money generated from Coltan is fueling the civil wars in Africa and especially in the Congo. It is suggested that 80% of the world’s Coltan exists in the Congo and that the micro-electronics industry is critically dependent on Coltan as the raw material in making Tantalum Capacitors. This raises the question of whether the electronics industry is in danger of being “held to ransom” by current rebel gangs or even a future Congolese Government. On studying the issue it seems that the fears are unfounded but nevertheless it raises some interesting issues.
Capacitors are extremely simple devices and the number of potential ways of making them is in all practical terms, infinite! All you need is two materials that conduct electricity (usually metal plates but even a liquid will do) separated by an insulator. When you connect a voltage across them a stable charge is built up between them due to electrostatic attraction. But as with most things, the devil is in the detail.
If we consider two hypothetical metal plates separated by an insulator the amount of charge that can be stored (the “Capacitance”) is determined by three things.
1. The Surface Area of the plates. The larger the area the more charge can be stored.
2. The distance between them. The closer the plates are to one another the more charge can be stored. Of course the plates must be insulated from one another.
3. The characteristics of the insulating material which separates the plates. This insulating material (which could even be air or a vacuum) is called the “dielectric” and the important characteristic for capacitors is called the “dielectric constant”.
It seems obvious that to make a capacitor of any given value, the closer we can put the plates to one another the smaller the device will be. Also, if we can do something to the surface of the plates to increase their area (such as corrugation or scoring) this will also make the device smaller. If our “dielectric” (separating insulator) has a high “dielectric constant” then again the resulting device will be smaller. Tantalum is a wonderful material for making capacitors because it lends itself to a unique construction method. You take a fine powder of pure Tantalum and compress it into a small
“slug” around a piece of Tantalum wire. Then you “sinter” it by heating to about 1800 deg C (very hot but below the melting point of Tantalum). The material forms a “sponge” with Tantalum particles stuck together but with plenty of space in-between. The slug is then immersed in a liquid bath and a current passed through it. This forms a uniform coating of Tantalum Oxide on the surface throughout the sponge. Tantalum Oxide is an excellent insulator AND it has a high dielectric constant (24). All that needs to happen now is fill the spaces in the Tantalum “sponge” with a conductive material (usually manganese dioxide), seal it in a package, and you are done.
The “sponge-like” configuration of the Tantalum produces an enormous surface area. The tantalum Dioxide dielectric is very thin, a good insulator, and has a high dielectric constant. Thus in terms of capacitance per unit volume (i.e. efficiency), Tantalum is the material of choice. In addition Tantalum capacitors are extremely tolerant of high-temperatures and thus can be used on circuit boards that are immersed in a bath of molten solder during the manufacturing process. In addition, being completely solid-state they are extremely tolerant of mechanical shock and vibration and seem to last forever (some alternative capacitor types do not).
Of course there are negatives:
1. The TaO coated Ta will conduct current very well indeed in one direction (as will all electrolytic capacitors) but the capacitors are absolutely intolerant of reversed voltage polarity (they can explode). Thus you have to be very careful with circuit design to ensure that they never see reverse current.
2. Even used as designed, Ta capacitors can only be used at relatively low voltages (maximum 35 volts today).
3. You don’t get too much benefit from Tantalum versus other capacitor designs at low capacitance values (below about 1 micro-farad). “Ceramic” capacitors are lower in cost and not much bigger.
4. They can cost a lot more than competitive devices.
In the consumer electronics world of today there are three major uses for capacitors:
1. Coupling high-frequency signals in Radio-Frequency transceivers. Capacitors used here will typically be quite small and usually NOT a candidate for Tantalum devices.
2. “De-coupling” digital chips as they mount on a circuit board. Every large chip on a modern circuit board requires external capacitors to “short-circuit” unwanted high-frequency components to ground and to smooth power supply currents. A quick examination of one modern circuit design shows a large ASIC (Application Specific Integrated Circuit) requiring 10 decoupling capacitors. Based on the required values, four of these could be Ta devices.
3. “Smoothing” to output of “chopper” power supplies. These are the small, light power supplies used for mobile telephones, laptop computers and similar things. This applies especially where size and weight is a factor, such as where a power supply is integrated within a portable device itself. You often need quite large capacitance values here.
However, the use of capacitors in general in computer devices is reducing quite quickly. If we remember any old computer circuit board (PC mother board etc) of the 1980’s, it had lots of large components on the top surface - but if you turn it over you find dozens - even sometimes approaching 100 “small components” connected to the underside of the board. These were almost always very small capacitors and resistors used to smooth and distribute power and to “decouple” unwanted high-frequency noise. NOW - as technology has progressed, many of the functions that were once performed by several interconnected chips, have been bundled up onto a single chip - these days a modern laptop has far fewer major chips - thus fewer interconnections and fewer points that require “decoupling”.
Of course there are critical applications where reliability is of critical importance. Implanted medical devices (such as pacemakers) are one example. The spacecraft designed by NASA for the mission to Pluto uses tantalum capacitors exclusively. Also, there are many military applications were ruggedness and reliability outweigh all other considerations.
So what if the world supply of Tantalum ran out or became unavailable. In the short term some products would need to be re-designed to use other capacitor types. This might result in these devices becoming a bit larger and/or heavier. In the longer term there is an infinity of possible capacitor designs. Niobium is a lot more plentiful than Tantalum and it looks promising as an almost direct replacement. (Of course Coltan contains niobium too).
However, there are other minerals that contain Tantalum and many of them have not been exploited. We are told that (in theory at least) tantalum should be plentiful. In addition it seems questionable that the electronics industry is even the largest user of Tantalum. Because of its very high melting point and its other metallic characteristics, tantalum is in heavy demand for use in heat-shields. It would be surprising if Ta were not used in at least some parts of modern jet engines and rocket motors.
Throughout history human conflict has been fueled by the desire for resources. Today there is a continuing insurrection on the island of Bougainville (part of Papua New Guinea). Bougainville has a very large and profitable Copper mine. Many local Bougainville people want the money for themselves rather than see it go to the wider Papua New Guinea government. Gold and diamonds were the root causes of South Africa’s problems over the years. The Japanese involvement in WW2 was primarily motivated by a quest for resources. The list goes on - today many believe that the “troubles” in the Middle-East are caused by the desire for oil and consequent profits. But you can make a case against almost anything! Last week a newsletter arrived in the mail suggesting that I shouldn’t buy soap that contained palm oil (most do). This is said to be because people are cutting down the Amazon forest to plant Palm trees for oil!
Many “rare earth” elements used in current electronics. Some people feel that continued technological development is threatened by shortages in supply. As recently as this week a bill has been introduced into the US Congress aimed at ensuring continuing supply in the face of shortage and monopoly suppliers. Currently 95% of rare earth supplies come from China but the Chinese Government has stated that when their domestic demand becomes great enough to use all of the available supply then they will ban exports! They could potentially “take over” the world technology industry by controlling the supply of essential raw materials! In many applications it seems possible to replace rare earths with other, less scarce, materials. Indeed there is a big race on to find a replacement for the rare-earth metals used in large screen TVs. Change of this nature of course takes time.
In the immediate future I would think that the supply of Tantalum and of the ore Coltan is not our greatest concern. After all. Tantalum is NOT a “rare earth”.


Francis Turner 

