I. D. Kashcheev, Professor, Ph. D., head of the Department "Chemical technology of ceramics and refractories", Ural Federal University;
E. N. Demin, LLC "Spetsogneuporkomplekt"
The article was published in the journal "New Ogneupory", No. 3 for the year 2012
Environmental security, currently, is one of the determining factors of the use of certain types of refractory materials and thermal insulation. And, combined with the best operational properties and economic expediency, no doubt, such materials should occupy the market the appropriate place.
Troubled materials from the point of view of ecology, have always been high temperature insulation materials and is primarily fibrous structure. Asbestos, as you know, no matter amphibolites or chrysotileasbestos, the world Health Organization recognized as particularly hazardous to human material. Although, from the point of view of biorastvorimogo, chrysotileasbestos much easier excreted from the body than refractory fiber. Chemical stability refractory fiber, which is often touted as one of the advantages of this type of fibers, actually is a huge disadvantage. This property of the ceramic fiber, and other fibers of aluminosilicate composition, in fact, allows us to speak about these materials as environmentally safe. In addition, a number of countries in Europe have started to ban the use of products from refractory fibre at its plants and thermal units.
In recent years, all major manufacturers ceramic fiber in the world, and these companies are not so much "Unifrax", "is your lovely choice" and "Morgan ceramics" engaged in the development of biosoluble fibres and, currently, judging by the publications, have mastered the production of such materials on the basis of oxides of magnesium, calcium and silicon.class="a-par-osn">We, in turn, also began to tackle the safety issue of artificial high-temperature fibrous materials, however, much later, just three years ago. However, during this short period, the algorithm was developed the manufacture of such fibers in the production of biosoluble ceramic fibers of the same ternary system oxides of magnesium, calcium and silicon. The main emphasis was made on magazinesonline raw materials with a wide range of contents of MgO and SiO2 . Currently, the ability to manufacture environmentally safe ceramic fibers (from the point of view of their biorastvorimogo) does not make any of labor. The MgO content in the material can range from 30 to 60%, the content of SiO2 , respectively, from 30 to 70% and iron oxide content from 0 to 15%. Essentially, it covers most of the natural minerals such as serpentine, olivine, talc, talcum magnesite, dunite and other varieties magnesioriebeckite raw materials.
Done a lot of research work in determining the optimal parameters of preparation furnace for the smelting, melting and other conditions providing Volochaevskaya with the necessary structure and physical properties.
We investigated the possibility of production of these textile fibers flame retardant fibers instead of asbestos. At a certain way of etching of the resulting ceramic fibers based on magneticresonance raw materials, it is possible to increase the specific surface area of these fibers is 6-8 times that allows to increase the mechanical grip of these fibers among themselves and to structure able to form strands without the use of organic fibers and without violating other physical properties magnesioriebeckite ceramic fiber.
The performance properties of materials and products from the new fiber is quite competitive compared with the refractory counterpartmi, in particular, the temperature stationary applications is in the range of 1000oC, the thermal conductivity at temperatures up to 6000S are also comparable, but at temperatures in the range 650-850onthe conductivity have magnetoelectricity fiber content of about 4% Fe2O3 is slightly lower than that of mullite. This allows you to provide higher insulation properties at such temperatures.
It should be noted that research work in this direction is not the end, although the production of materials of new fiber already mastered, mainly standard range of needle punched blankets, cardboard, plates. In the direction of the textile fibers research already completed and ongoing industrial development of this product.
The second direction in the field of high temperature insulation, our company, LLC "Spetsogneuporkomplekt", together with the Department "Chemical technology of ceramics and refractories", Ural Federal University, began to pay attention to is calcium silicate. Today, the insulation of calcium silicate along with diatomite insulation is the most effective and promising. The insulating properties of these materials far exceed the insulating properties of ceramic fibers materials. And calcium silicate and diatomite are inherently lightweight insulating materials with a microporous structure, the pore size of which is less than 40 microns. Unlike diatomite insulation calcium silicate has a higher operating temperature, in some cases, you can achieve maximum temperature and 1250oC.
It is very important in the process of manufacture and application of high temperature insulation materials, the structural properties of thermal insulation, and control these properties.
The thermal conductivity of a substance is the same chemical composition, but which is in crystalline or amorphous state different - crystalline materials thermal conductivity higher than amorphous.
The thermal conductivity decreases with every violation of the regularity of the crystal lattice, for example, a lower order of symmetry of the crystal lattice, with the defects of the structure of the grid, in places of introduction of extraneous ions on the groups of molecules in the crystal lattice at the grain boundaries, in amorphous portions in the microcracks and pores. The thermal conductivity as the transition from single crystal to polycrystal, a multiphase solid substance and further to a porous solid substance is reduced by one to two orders of magnitude.
Any body heated to a temperature different from absolute zero, sends in the space heat rays representing the electromagnetic waves, which differ from light only in wavelength.
Heat rays have the wavelength of 0.76 to 40 microns. The laws established for visible light fluxes of radiant energy, fair thermal. Therefore, insulation materials, whose predominant pore size is less than the wavelength of the heat ray insulating properties highest.
Microporous materials based on aluminates and calcium silicates produced by the hydrothermal technique, in addition to these qualities another important advantage over the life of the fiber materials, it is environmentally friendly. There are consumers who have faced problems arising Monttthe same life of the fiber materials, and some of them refuse to use ceramic fiber for this reason alone.
Given the high demand for products from the lungs of microporous materials, our experts have developed the technology of manufacturing these products by the hydrothermal technique entirely from domestic components; obtained and tested industrial designs and, at present, our company is the only one in Russia which mastered the production of the microporous calcium silicate.