Advances in the study of ceramic materials have brought about a number of new products for industrial use. Two of the most important novelties in this area recently came out of the Electrochemical and Ceramic Interdisciplinary Laboratory (Liec), of the Federal University of São Carlos (UFSCar), where researchers, under the coordination of Professor Elson Longo, have managed to discover, with innovative advantages and the registration of a patent as well, the technology employed by international companies to make devices that protect electrical networks from overloads caused by lightning. They also made some modifications to the refractory ceramics used by steel companies to produce steel, which has resulted in significant savings for Companhia Siderúrgica Nacional (CSN), of Volta Redonda (RJ). The company is now saving US$ 6 million a year with the changes made to the wagon – called a torpedo car – used to transport the pig iron, the molten iron that will be transformed into steel.
These two novelties are part of the various lines of research carried out by Liec, makes up the Multidisciplinary Center for the Development of Ceramic Materials (CMDMC), in which other participants are the Nuclear and Energy Research Institute (The Nuclear and Energy Research Institute – IPEN), the São Carlos Institute of Physics, of the University of São Paulo (USP), and the Araraquara Institute of Chemistry, of the São Paulo State University (Unesp). The CMDMC is one of the ten Centers for Research, Innovation and Dissemination (Cepids) selected by FAPESP in 2000. The Foundation sets aside R$ 15 million a year for this program.
One of the Cepids’ objectives is to foster innovative research, developing products like the ceramic device developed at Liec that is able to protect the electricity transmission network. Called a varistor, it has a dual function: it is an insulator and a conductor of electricity. When it receives the electrical discharge from lightning, the device, installed in a lighting rod between the wires (which distribute electricity) and the earth, is brought into action. He variation in voltage detected makes the ceramic become a conductor. The unwanted current is then discharged to earth by the ceramic varistor, preventing damage to the transmission line.
When the effect of the lightning ceases, after a few thousandths of a second, the ceramic material reverts to acting as an insulator. There are several kinds of varistors on the world market, and there are four companies that have mastered this technology: Matsushita, in Japan; Asea Brown Boveri and Siemens, in Europe; and General Electric, in the United States. “The varistor is a complex system, with at least eight components made up of different oxides and a heat treatment sequence, which are kept under lock and key as a trade secret”, says Professor Edson Leite, one of Liec’s researchers.
Japanese invention
Developed in Japan in the 70’s to protect low voltage equipment, the device was adapted by the Americans to work with high voltage. The varistors available on the market are based on zinc oxide (ZnO), a technology deciphered by Liec, which has also now patented a new proposal for the manufacture of these devices, using stannic oxide (SnO2), a raw material found in great quantity in Brazil.
According to Professor Longo, who is also the coordinator of the Cepid for Ceramic materials, the one made with stannic oxide is more resistant against aggressive chemical environments, besides having greater thermal conductivity of heat. At the moment when lightning falls where the varistor is installed, the temperature rises close to 200° Celsius. The electrical discharge leaves the clouds for the ground, and on its course causes the air to ionize, which may generate the formation of nitrates. These nitrates can attack the zinc oxide and destroy the varistor. Longo points out that stannic oxide does not have this problem. “This is a 100% Brazilian invention. All the international articles that have been published in the world about stannic oxide are ours”, he says.
In Brazil, the risk of blackouts caused by strikes of lightning is very great. According to data from the National Institute for Space Research (Inpe), about 100 million lightning discharges hit Brazilian territory every year. In March 1999, ten Brazilian states remained in the dark for four hours, as a consequence of lightning hitting a substation in the city of Bauru.
Leite points out that the electricity generating and distributing companies have been trying, more and more, to protect their equipment from the electrical discharges caused by lightning. This potential market has motivated two companies from Minas Gerais and one from São Paulo to make zinc oxide varistors with the technology developed by Liec. Negotiations are already under way. The product made with stannic oxide has attracted attention, but is still depends on interested parties to put it into a production line.
There are a few companies making lightning conductors in Brazil, but most of the blocks are imported, and, according to Longo, there is no quality standard. “Only an advanced knowledge of basic science can foster the generation of this kind of technology”, he says. “This is the big gamble.” He recalls that a technology developed to improve ceramic items (wall tiles, floors), was essential for getting to varistors. “We discovered that oxygen was fundamental for eliminating black heart (a defect in the middle of the item originated during the firing process) from ceramic surface items. This project was developed in partnership with White Martins and is being used by Cerâmica Gerbi”.
Rapid transport
Technological research is also a factor for competitiveness for the steel industries. But, as in other sectors, innovations incorporated into the production of steel can only mange to be kept secret for ashort period of time. Whenever there is a congress, the novelties are announced, and the technicians, in turn, set about adapting them. Being a step ahead of the competition, however, makes all the difference, as CSN was able to prove.
The novelty that led the steel company to save US$ 6 million a year was the development of a ceramic insulator, put between the car’s metal body and its refractory ceramics, and a lid, also a ceramic one, that brought about a gain of 40° Celsius, which used to be lost in the course of transport between the blast furnaces and the converter (the equipment used to transform the pig iron into steel, by the addition of oxygen, which reacts with the carbon, making carbon dioxide). This means that the pig iron can be made at a lower temperature. “In this way, less coke is used, which means an economic gain, albeit a small one, because this fuel is cheap. The real gain lies in the fact that the torpedo car can be moved more quickly, because there is no loss of temperature”, says Longo.
CSN has also achieved steel of a better quality, with less sulfur, without making any changes in the system for production, as a result of a process developed two years ago by Liec’s researchers. Silicon, phosphorus and sulfur are three undesirable elements that get incorporated into the molten iron. The first two are easier to get rid of. The last one, though, interferes with the quality of the steel, making it more brittle, and it needs a more complex process to remove it.
The new method, at the stage of industrial tests at the steelworks, allows the gradual removal of the sulfur with four different agents (calcium carbonate, calcium carbide, aluminum-magnesium, and aluminum sediment), injected while the pig iron is being transported in the torpedo cars. The processes in current use all over the world use calcium carbonate to remove the unwanted sulfur. “In the first stage, we put calcium carbide with calcium carbonate, and then we add the sediment that comes from the manufacturing of aluminum, to raise the temperature of the desulfurization”, says Longo. The research that led to this innovative process is part of the thesis for a doctorate by Sérgio Murilo Justus, who is supervised by Longo and by researcher Sidney Nascimento Silva, from CSN. The steel company invested R$ 150,000 in this project, and FAPESP also paid a grant for the doctorate.
“In addition, we developed a system for CSN to produce pig iron à la carte, to a standard of quality for the steel defined by the purchaser”, says Longo. The percentages of sulfur and the mixtures are done by the computer. Before this system was put into effect, depending on the purchase, the steel mill would have to stop the production in order to make steel with, for example, a lower percentage of sulfur. The lower the level of this substance, the better the steel.
Longo says that Brazilian steel is reaching the United States 30% cheaper than the steel made there, as a result of the innovations to the system of production. “When we started to work with CSN, 12 years ago, production came to 2 million tons a year. Today, it is almost 5 million tons a year, with the same equipment. The process is the same, we have only changed the refractories.” Optimizing the equipment, which works 350 days a year, has cut out the halts in production.
Single stage
Leic researches are not just restricted to products with an immediate application. Nanostructured materials (scaled in millionths of millimeters) are being studied in the laboratory and should be available in the next few years, for the development of several pieces of equipment in the areas of optics and electronics. Also called nanocompounds, they are a result of mixing two different materials, on a nanometric scale.
One of these compounds, with promising properties tested in the laboratory, may be applied in electronic nanocircuits for computers, with a 30 to 40 times reduction in their current size and an increase in their processing speed; they may also be used in catalysts (substances that accelerate chemical reactions), used mainly by the pharmaceutical and petrochemical industries, and to generate hydrogen, with the objective of getting clean energy.
To achieve this nanocompound, made up by a matrix of silica, or amorphous silicon dioxide and metallic particles of nickel, a way of synthesizing was developed – based on a polymer obtained from citric acid -, a process called sol-gel, which uses chemical reagents in processing and just one stage of heat treatment, while the others require at least two. “That is what we are patenting”, says Leite. This process also solves two of the problems with metallic nanoparticles: agglomeration and the formation of oxides on the surface of this material. “As metallic nanoparticles carry magnetic information, knowing how this material is processed and organized is an enormous advantage, as we can apply the technology to other materials”, says Leite. Among these applications are a photocatalyst (a light-activated catalyst), intended to clean up polluted waters.
The studies to avoid the growth of particles during the preparation of the material began in 1999 with stannic oxide, when Liec’s team started to work with nanostructured semiconductors. “We used a dope in which one atom of rare earth is put into the structure of the stannic oxide. While being heated up, the stannic oxide expels these undesirable neighbors, the contaminants, to the surface, and this operation stanches growth”, Leite sums it up.
Technological advantage
The researchers from Liec have also synthesized nanowires and nanotapes for the stannic oxide semiconductor by a simpler and cheaper process than the one presented by the Americans Zheng Wei Pan and Zu Rong Dai, in an article published last year in Science magazine. The Americans obtained these materials, which have a potential application in nanoelectronics, using a vacuum furnace, which makes the procedure more expensive and practically out of the question for industry. The Brazilians, though, reached the same results using a common tube-shaped furnace. The patent for the process has now been requested and the results published in this April’s issue of the Journal of Nanoscience and Nanotechnology.
Liec’s lines of research extend to other materials and applications, such as the study of photoluminescence in amorphous compounds. Like glass, these materials do not have a defined internal atomic organization, unlike crystals, in which atoms or molecules are distributed in an organized and regular manner. Photoluminescence is characterized by the emission of light by a few substances and by the action of radioactivity on them. This property has been known since the 60’s, but only in crystalline materials.
“We ended up discovering a new class of luminescent material”, says Professor Paulo Sérgio Pizani, from the Physics Department at UFSCar. In the experiments carried out at the laboratory, photoluminescence was found in titanates of barium, calcium, strontium and lead, compounds in an amorphous state, without the need for special conditions and for synthesis. The emission of light in these amorphous compounds was achieved at room temperature and the form of powder and of nanostructured materials (thin films), allowing it to be applied to several kinds of surface.
Longo points out that the great gain for science is the contribution it makes to people’s daily lives. And he recalls the role played by the Brazilian Agricultural Research Corporation (Embrapa). The technology developed for soya and sugarcane, for example, was fundamental for increasing the productivity and the competitiveness of these products, which has a significant weight in the agricultural balance of trade. Liec follows this precept to the letter. The results can be corroborated in the products developed in partnership with industry and in materials that, if they are today very distant from the common citizen, will certainly have implications in changing his daily life.
The project
Multidisciplinary Center for the Development of Ceramic Materials – Cepid; Coordinator Elson Longo – UFSCar; Investment R$ 1,204,888.02 (annual average)
