Wonder materials for 21st century
by Pravin Kumar
IN the last 10 years, a group of new materials has been emerging from the laboratories of the world to cope with the demands of industries.

Magnetic refrigeration
by S.S. Verma
HEAT is transferred naturally from a hot place to a cold place, as demonstrated by the cooling down of a hot cup of tea in a room with time.

Wonder materials for 21st century
by Pravin Kumar

IN the last 10 years, a group of new materials has been emerging from the laboratories of the world to cope with the demands of industries. These new materials will greatly impact the quality of life in the next century. Among them are high-performance plastics, smart materials and intelligent materials.

New materials have always influenced the quality of life greatly. Iron, which began replacing copper about 1,200 BC, helped the farmer get more out of his land by providing him with more durable tools. Iron allowed new methods of forging in dies and stamping and punching of coins and, later, in the drawing of wires and the rolling of sheets and rods.

Iron and steel made the first Industrial Revolution possible. We are now in the age of silicon, which has made possible the transistor and its progeny, the integrated circuit and the microprocessor. The silicon age also marks the Second Industrial Revolution — the electronics and micro-electronics revolution — which is freeing man from routine mental tasks.

A new material may signal the birth and death of products, of entire industries. Bakelite made possible 78 rpm gramophone records; polyvinyl chloride enabled the production of long-playing records which gave the death-blow to 78 rpm records and record changers; LPs themselves were displaced by audio-cassettes which use magnetic film; and audio cassettes are being replaced by the compact disc.

In electronics, silicon chips replaced vacuum tubes in the 1950s. In telecommunications, optical fibers are now displacing copper wires. However, even electronic material materials like silicon are giving way to multi-functional materials which mimic the efficient and economic materials used by Nature.

In most industrialised countries, the electronics revolution occurred overnight. They are the engines of growth in developing countries today. Success in the electronics industry does not depend on petroleum and other natural resources. Taiwan, Hongkong, South Korea and Thailand have modernised themselves through electronics and the exploitation of electronic materials.

Typically, there is a 20-year lag between the invention of a new material and its widespread adoption. Hence, many companies prefer to sell the invention after 10 years or allow another company to pick it up gratis. The 20-year time frame also means that, by the time a material comes to the market, the patent protection covering the original lapses, and the proprietary advantage is lost. Today, products based on new materials have life-cycles too short for a company to recoup its investment, e.g., the life-span of the gramophone was 70 years, that of magnetic tape, 30 years, while the compact disc may become obsolete after 20 years.

The new materials which have gained prominence in the last few years are composites, ceramics, surface engineering materials, high-performance plastics and neo-magnets. However, the difference between these classes of materials is breaking down, thanks to novel process technologies. We can now obtain metallic glasses, plastics that conduct electricity and ceramics that conduct heat.

Ceramics are non-metallic minerals (like porcelain) used in electronics for their low electrical conductivity. The new generation of fine ceramics include aluminium oxide, silicon nitrite and silicon carbide. These are manufactured as extremely pure, fine powders which, after consolidation, yield a durable, dense structure. The new-generation ceramics are expected to aid in the development of superior computer chains, photonic devices, capacitors, at cetera, which will trigger the evolution; of the optical computer, that is, a computer in which information pulses will travel at the speed of light.

Since the 1950s, the widespread use of semi-conductors in electronics has been spurred by their preparation in an extremely high degree of purity. Silicon has long ruled the semiconductor roost, but the new semi-conductor, gallium arsenide, scores over silicon: it moves electrons three to six times faster than silicon. It also operates at higher temperatures than silicon. It also operates at higher temperatures than silicon, hence the cooling requirements for computers and other electronic systems are less.

Gallium arsenide should enable the production of supercomputers with hitherto-undreamt-of capabilities. They would help develop wrist-watch radio-telephones that would communicate via orbiting satellites. Gallium arsenide chips are considered vital to the success of direct broadcast satellites that beam television programmes to small, roof-top dish antennas.

Gallium arsenide emits light when a current of a specific frequency is passed through it. Hence, gallium arsenide lasers have found a use in the digital audio-disc players and laser-disc data-recording systems which use tiny lasers to inscribe and read information.

Among other important compound semiconductors is indium antimonide, which is used for thermistors (that is, heat-sensitive resistors used for controlling temperature or liquid flows). Another is Indium phosphide, which when subjected to radiation, returns to its original condition, unlike standard semi-conductors, which suffer irreversible damage.

The search is also on for new superconducting materials. Superconductivity is zero resistance to electricity, which is attained by some materials at temperatures near absolute zero. Superconducting materials, on account of their low power consumption, will be favoured for power transmission over long distances. However, the ultra-low temperatures needed for superconductivity call for bulky and costly refrigeration. Since nitrogen is easier to liquefy than helium — becoming liquid at 77 degrees Kelvin, — what are needed are materials that will become superconductive at this temperature and above. The Indian Institute of Technology, Chennai, is reported to have developed superconducting alloys based on rare-earth elements which show zero resistance at 95 degrees Kelvin.

Plastics, or polymers, have been with us for some time, but the new, high-performance plastics (also called engineering resins) are taking the place of steel in machinery and in electronics, too. In electronic chips, plastics called polyimides are taking the place of glass and quartz for insulation. Glass and quartz often harden with tiny bumps on top, increasing the possibility of short circuits between the layers. Polyimides promise a comfortably flat surface when deposited, in addition to good heat resistance and insulation; these qualities become important as electronic circuits become packed ever more densely.

Lately, electrically conductive plastics have been coming to the fore. One such is polyacetylane, which can be produced as a film with a smooth metallic-looking outer surface and a rough, black inner surface. This can be used in photo-voltaic devices and as electrode materials for batteries.

We now come to piezo-electric materials. In these materials, applying a mechanical force generates an electrical charge, or applying an electric field creates a change in their shape. Traditionally, they have been used in microphones and sonar devices, but a variety of new piezo-electric materials like lead zirconium titanate have been used in gas stove lighters to generate a spark, as well as in new products like vibrators, oscillators, filters and ultrasonic humidifiers.

Magnets are not exactly new. Up to 1930, steel magnets were the best magnets. They were followed by alnico magnets (that is, iron-based magnets containing aluminium, nickel and cobalt) and by hard ferrites or iron oxides containing metals like barium or strontium. The year 1983 was the year of the neo-magnets based on a compound of iron, neodymium and boron. Neo-magnets which are 10 times more powerful than ferrite magnets, have made possible high-quality sound and improved hearing-aids, not to mention the tiny magnetic sensors in automobiles to detach engine “knock”, throttle choke position and tyre pressure.

Magnetic recording materials represent the fastest growth segment of the magnetics industry. Metal particles are increasingly used in high-density recordings such as 8 millimetre videotapes and in the emerging digital audiotape and videotape technologies. Video discs for instant replay are made by electroplating a thin film of cobalt-phosphorus or cobalt-nickel-phosphorus onto an aluminium substrata.

In 1985, scientists discovered a new form of elemental carbon — ‘Buckminster fullerene’ or ‘buckyballs’, for short. Buckyballs have 60 atoms in each baseball-like molecule. By including an atom of a metal such as potassium or rubidium inside the buckyball molecule, superconductive compounds called metallo-fulleranes can be made. Scientists of the Indian Institute of Science, Bangalore, and the Indira Gandhi Centre for Atomic Research, Kalpakkam (Tamil Nadu) have also made metallo-fullerenes with iron and lead. Metallo-fullerenes could be useful in assembling ultratiny structures called nano-structures.

Even the traditional materials like silicon are giving way to multi-functional or smart materials which mimic Nature’s own materials. A helicopter rotor with a microprocessor embedded in its blades would monitor and process environmental changes in temperature and humidity and use shape-memory actuators to alter the chamber of the rotor blades; while elector-rheological fluids and magneto-strictive materials would control vibrations. The International Space Station, Freedom, may use smart skins to control vibrations following meteorite hits.

In conventional aircraft, smart skins containing embedded sensors and computer networks would alert the pilot on internal defects or if the ice build-up on the wings exceeds a specified threshold.

In the coming decades, research and development will focus on “intelligent” materials, which will be of a magnitude more sophisticated than smart materials. For instance, environmental concerns in the USA and Europe will focus on intelligent material harmonising with the environment , while developing innate properties of homeostasis or equilibrium. To create intelligent materials, scientists will have to draw upon fields as diverse as physics, chemistry and biology.

Magnetic refrigeration
by S.S. Verma

HEAT is transferred naturally from a hot place to a cold place, as demonstrated by the cooling down of a hot cup of tea in a room with time. There is never any “natural” net transfer in the other direction. Thus, it is not possible for heat to be transferred from one body to another body that is at a higher temperature with no other change taking place (i.e., 2nd law of thermodynamics). A device that transfers energy as heat from a cold place to a warm place is called a refrigerator. Figure shows the schematic diagram of a refrigeration system.

In our household refrigerator, the low-temperature (evaporator) reservoir is the cold chamber (inside box) of the refrigerator in which the food is stored, the high-temperature reservoir (condenser) is the room in which the unit is housed. Work done to extract heat from the food and rejecting it in the room is done by the motor (compressor) that derives the unit. Refrigeration units are rated with their coefficient of performance (COP). Design engineers and the users want the COP of a refrigerator to be as high as possible. A value of 5 is typical for a household refrigerator. It is very difficult to go for refrigeration units with higher COPs. The development of equipments/auxiliaries of a refrigeration e.g. compressor, evaporator, condenser, throttling valve have attained a level of maximum expertise in terms of increasing the COP of the system and there is no new development in these since a long time. Refrigerators are becoming indispensable with the modern life-style. Presently, efforts are only in order to design these systems with variable capacity, outlook and cost effective tips, but no progress is towards improving their efficiency.

The miracle of taking heat from the cold space and rejecting it into the hot space is performed by a liquid known as refrigerant. Refrigerant is a liquid satisfying some particular thermophysical properties. There is a large list of such liquids. In the present environmentally conscious age, it has been pointed out that production, leakage, disposal etc. of these refrigerants put lots of adverse effects on our environment viz., ozone layer depletion, green house gas effect etc. Though, efforts are being to replace these refrigerants with better environmental friendly refrigerants but again the chemicals will have one or the other effect on the environment.

Thus, due to a saturation in improving of efficiency and concern about the use of refrigerants efforts are being directed to find the alternative ways of refrigeration. (i.e. refrigerant-free refrigeration systems). In this regard present breakthrough has been achieved by making the use of “Magnetocaloric effect”.

The newly proposed magnetic refrigerator is not based on the standard gas-compression cooling system. On the contrary, it has two cylinders of powdered gadolinium compound — a dense, gray, rare-earth metal — and a superconducting magnet. This type of refrigerator is reported to work at near-room temperature to produce substantial amounts of cooling power-more than 500 watts, three times the power of a large conventional household refrigerator.

This refrigeration effect relies on the magnetocaloric effect, the ability of ferromagnetic materials to heat up in the presence of a magnetic field and cool down when the magnetic field is removed. At a fixed temperature, the entropy of a magnetic system is lowered as the spin align with an applied magnetic field. When a ferromagnet, such as Gadolinium, is placed in a magnetic field, the magnetic moments of its atoms become aligned, making the material more ordered. But, the amount of entropy in the magnet must be conserved. This magnetocaloric effect typically produces a temperature drop of 0.5-2K for a field change of 1 tesla. It is found that combining gadolinium with silicon and germanium increased the effect to 3-4K/tesla.

Such refrigeration systems with cooling effect of several thousands of a degree above absolute zero have been in use in scientific applications (e.g., liquifying hydrogen and natural gas) for a long time. But, commercial applications have been limited by the fact that the “magnetocaloric effect” is relatively weak in most of ferromagnetic materials at room temperature. However, gadolinium is an exception. Each atom of gadolinium has seven unpaired electrons in an intermediate shell, giving the element a strong magnetic moment. Moreover, the magnetocaloric effect reaches its maximum at the Curie temperature (i.e., the transition point above which a material is no longer a ferromagnetic) and that point for gadolinium is 20 °C. Even under ideal conditions, the magnetocaloric effect is not huge. With a powerful superconducting magnet, the magnetic refrigerator reported so far, produces a maximum temperature change of only 14 °C in the cylinder of gadolinium. Besides, the machine uses an ingenious refrigeration system to increase the cooling power of the machine, in which, water is pumped into one of the cylinders of gadolinium immediately after it moves out of the magnetic field. The water, thus, cools as it moves through the porous bed of demagnetised gadolinium, then flows through a heat exchanger. Next, the water passes through the cylinder of gadolinium that is inside the magnetic field. The water heats up and flows through another exchanger, providing ample refrigeration power by continually heating one exchanger and cooling the other. After a present interval, the two cylinders of gadolinium switch places, and the flow of water is reversed. Besides, antifreeze can be added to the water to allow the machine to cool below zero degree Celsius.

This type of refrigeration system is very efficient because very little energy is lost during the magnetic warming and cooling. The experimental prototype system has the 30 per cent efficiency of the Carnot limit-the maximum possible efficiency for a refrigerator — which is comparable with the efficiency of most household units. Moreover, with the help of recent developments and future prospects in superconducting magnetic materials as well as the materials exhibiting high level of magnetocaloric effect, a magnetic refrigerator for household with enough temperature change will be possible in near time.

The writer is from the Department of Physics, Sant Longowal Institute of Engineering and Technology, Longowal.

1. A British mathematician has authored the best selling book “A Brief History of Time” and has developed a new theory about the origin of the universe. Whom are we talking about?

2. The study of the jawbone fossil of an animal found in Himachal Pradesh has revealed that this animal lived 3.5 million years earlier than what was accepted till now and that this species gradually developed from a land animal to a sea mammal. Name this animal.

3. Latest advances in chemistry now allow the testing of hundreds and thousands of new compounds in a very short time. The technique can be used to produce new industrial compounds and drugs. What is this type of chemistry called?

4. The work done by a force in moving an object between two points is independent of the shape of the path along which the object is moved. What is the general name given to such a force?

5. Light waves that can travel long distances without any distortion in shape or size have great potential for communication. What are such waves called?

6. ATP, found in all living cells, is a chemical compound that stores and releases energy for the performance of the activities of the cells. What is the chemical name of ATP?

7. “Giraffes with longer necks have better chances of survival than those with shorter necks”. Which underlying theory does this statement refer to? Who proposed this theory?

8. What does GIGO stand for in computer technology and what does it mean?

9. What is the science of classification of organisms according to their resemblances and differences called?

10. Complete the limerick:

There was a young lady named Bright

Who travelled much faster than light

She departed one day

In an Einsteinian way.

Answers:

1. Stephan Hawking 2. Whale 3. Combinatorial chemistry 4. Conservative force 5. Light or optical solitons 6. Adenosine triphosphate 7. Theory of natural selection; British naturalist Charles Robert Darwin 8. Garbage-In, Garbage-Out; feeding wrong data will give wrong results. 9. Taxonomy 10. And returned on the previous night.

Sun-lit offices on the cards

In order to use solar energy in its purest form, scientists at the Fraunhofer Institute for Solar Energy System (ISE) in Freiburg, Germany, are developing concepts of how offices can make best use of sunlight — even if people are working at a computer.

According to the scientists, natural light is the ideal form of illumination. Making more use of it would have two positive effects: it would save electricity and people would work more effectively as it has a positive influence on human beings.

To find out the best way of natural lighting German scientists are using simulations to test various configurations of the working environment, according to a report in Fraunhofer Gesellschaft Research News.

Different light levels, sizes of room, glazing and colour combinations are tried out in the computer to determine the quality of the working environment.

Besides developing this virtual place of work, the ISE scientists are measuring and testing the optical properties of new materials.

The simulation can test, for example, what proportion of a window should be of glass in order to deliver natural light to bordering offices, without resulting in a increase in temperature.

Even on an overcast or a rainy day, a properly planned office can run without artificial light with properly shaped venetian blinds and other reflecting elements incorporated in the windows, to deflect daylight into the building.

Smog discriminates between the sexes

A study on smog undertaken for the California Air Resources Board has fond that while both boys and girls suffer from common air pollutants, they suffer differently, reports Reuters.

The results, reported in the Sacramento Bee, based on an ongoing 14-million-dollar, 10-year investigation of 5,000 children in southern California which is scheduled to end in 2003.

The study by researchers at the University of Southern California tracks respiratory symptoms, breathing capacity and school absenteeism among children in the fourth, seventh and tenth grades — aged 9 to 18 — in a dozen California cities.

Investigators reported they had found distinct general differences in the way that boys and girls react to high levels of nitrogen oxides, or (NOx), ozone and particle pollution.

The report found that boys were more likely to be affected by high levels of ozone gas while girls were more affected by high levels of particle pollutants like dust and NOx, a smog forming contaminant that comes mainly from vehicle exhaust.

The investigators did not offer any explanation for the difference in health effects between boys and girls, saying that more testing and analysis was needed.

Scratch-resistant plastic lenses

By coating plastic lenses with a new curing material, German scientists have developed a new class of scratch-resistent plastic lenses for magnifying glasses and spectacles, according to a report in Fraunhofer Gesellschaft Research News.

Lenses, made of polymethyl methacrylate (PMMA) are just as transparent as glass ones, and have the advantage of being virtually unbreakable.

Normally plastic lenses are coated with a hard surface layer to make them scratch proof.

The new coating material developed by at colleagues at Fraunhofer Institute for Silicate Research (ISC) in Wurzburg cures without heat and can be used in hand held magnifying glasses.

This new class of materials combines vitreous and polymer components — is almost as hard as glass, yet behaves like plastics and is cured by ultra-violet light.

The method is considerably faster than the previous system which took an hour, compared to only seconds under ultra-violet light.

The material is also suitable for new application like furnitures and other equipment.

High-resolution LCD

By using single crystal silicon technology, British scientists have come up with a new high-resolution miniature colour liquid crystal display (LCD) unit which can be used in a number of industrial and military devices.

The new display unit can be used in helmet-mounted display systems, medical imaging, telepresence, portable data access and in personal 3-dimensional display systems, reports GEC Journal of Technology.

Other applications of the unit include compact projection and direct-view simulator systems, where colour and high resolution are essential requirements.

Devices of this type are also required for use in optical processing systems like optical correlation telecommunication switching, holographic beam manipulation and adaptive optics.

New “restaurant” for bacteria

By making pollutants as the feed for hungry bacteria, Canadian researchers have come up with a new bioreactor to clean toxic organic chemicals.

The clean up takes place in two liquid phases. The first uses a solvent that readily dissolves high concentrations of toxic chemicals such as benzene, toluene, and para-xylene (collectively referred to as BTX). These man-made chemicals are components of gasoline and are used extensively in industrial processes.

In the second phase, the BTX is fed to a Pseudomonas bacteria cultivated in water.

The new bioreactor has been developed by researchers of Queen’s University, according to a report of the American Chemical Society (ACS).

Since the pollutants are much more soluble in the solvent than in water, a large amount of BTX can dissolve in the solvent phase of the two-phase bioreactor without leading to high concentrations in the water phase. This is beneficial because too much of the BTX can kill the bacteria.

Origin of life breakthrough

A team of Japanese researchers has announced that they have managed to recreate the conditions from which life itself may have sprung, Reuters reports, quoting a report.

In a major breakthrough in the never-ending debate about how life started, Koichiro Matsuno and colleagues at the Nagaoka University of Technology built an artificial system simulating the environment at undersea thermal vents, where water heated deep below erupts through the seabed into cooler ocean water.

By this they were able to produce some of the elementary building blocks from which proteins essential to life are formed.

“For ten years, underwater hydrothermal vents have been thought to be the place where life began — and we were able to prove it”, Matsuno said.

Writing in the journal Science, Matsuno described how his team simulated a process called polymerisation, in which complex molecules — in this case oligopeptides, one of the elements that make up proteins — are formed from simpler amino acids.

This process was likely to be repeated numerous times, possibly aided by “heating in dry and wet conditions, day-and-night cycles”, tidal waves and dry-wet conditions in lagoons”, the authors wrote.

The chemical products, synthesised in hot hydrothermal vents in the sea, could re-enter the vents after being quenched in the surrounding cold water and undergo further reactions.

Matsuno and his team built a flow reactor that mimicked the cooling and heating parts of the cycle.

The two-chambered flow reactor circulated materials from hot to cold environments in roughly one-minute cycles. When they added the amino acid glycine, they found that this formed more complex oligopeptide molecules in a stepwise process.

Key to the process was the addition of bivalent copper ions, one of many minerals present on the sea floor — an addition which Matsuno said, was serendipitous.