Foam ceramic is a kind of porous material, following the first generation of common porous ceramic, the second generation of honeycomb porous ceramic developed after the third generation of porous ceramic products. Its pore size varies from nanometer to micron, and it has the characteristics of three-dimensional network structure and elevated porosity, with the highest porosity of more than 90%. It has the advantages of light weight, elevated porosity, large specific surface area, thermal shock resistance, corrosion resistance, elevated temperature resistance, long service life and excellent filtration adsorption.
The third generation of foam ceramics product development began in the 1970 s, as a different kind of inorganic nonmetal filtering material, mainly in ore powder, kaolin, or ceramic industrial slag, fly ash, coal gangue, marble tailings, slag and other inorganic materials as raw materials, adding a certain proportion of foaming agent and cosolvent, water-based ceramic slurry, It is impregnated onto styrofoam to form a ceramic film coating and then fired. According to the metal liquid object to be filtered, the common material is silicon carbide, aluminum oxide, zirconia, magnesium oxide and so on.
At present, foam ceramics have been widely used in various fields, in addition to purifying metallurgical industry and filtering molten metal, but also used in heat insulation and sound insulation materials, chemical catalyst support and other applications. For example, recently, Jiangxi Longfa Industry has recycled and reused discarded ceramics as raw materials to make ceramic permeable bricks, so as to realize the sustainable development and reuse of local ceramic waste.
One: purification of metallurgical industry filter molten metal
Ceramic foam filter is mainly used in the casting process, purify liquid casting alloy, reduce or eliminate all kinds of non-metallic inclusions and exhaust problems in casting. Because the casting problems such as non-metallic inclusion defects caused by the casting scrap ratio as high as 50% - 60% of the total number of scrap, along with the increase of the costs, unnecessary waste of outflow can want to predict the destruction of the environment, and the inclusion defects not only serious drag on the mechanical properties and casting properties of the casting, but also for the castings and appearance of machining process on the harmful effects.
In order to solve this problem, a simple filter made of barbed wire and steel plate with holes was inserted into the gating system to remove inclusions. To silicic acid pin fiber, boron nitride fiber and additional two-dimensional structures inside the filter. Nowadays, ceramic foam filters use pore size to mechanically intercept large particles of oxide inclusion, and filter tiny particles of oxide inclusion using filter cake. The casting yield of the production line with adsorption and rectifying capacity and using ceramic foam filter is improved markedly. For EXAMPLE, THE PRODUCTION RATE increased FROM 65.3% TO 71.5% AFTER the use of foam ceramic filter in DONGFENG Motor Casting Plant No. 2, and 6% of molten iron was saved only in terms of pouring riser weight. The hardness of the filtered casting is also significantly improved, thus extending the service life of the cutting tool.
Foam ceramic filter is commonly used in carbamic acid ethyl ester foam as the carrier, refractory aggregate immersed by sintering additives, such as adhesive powder ceramic slurry made of water, and then squeeze out excess slurry, the remaining wrap around the bubble fiber ceramic material, after drying, roasting sintered at elevated temperature, finally left the foamy ceramic products. Due to the different pouring temperature of the casting alloy, the foam ceramic filter of the refractory material should be selected. In recent decades, a variety of foam ceramic filters have been developed at home and abroad according to the properties of different alloy materials.
Two: HEAT INSULATION and sound insulation materials for ENVIRONMENTALLY friendly buildings
As a current low-cost, green, energy saving and environmental protection product, energy saving and thermal insulation foam ceramics are mainly made of porous inorganic non-metallic materials formed by elevated temperature foaming with waste fly ash, slag, waste glass, ceramic sheets, clay and feldspar tailings as raw materials. Have fire prevention, waterproof, antifreeze, moth-proofing, magnetic wave electrostatic prevention, sound insulation, noise reduction, tiny coefficient of thermal conductivity and good bonding effect with all kinds of mud excellent properties, such as foam ceramic lightweight partition board compared to traditional light block, lime-sand brick, red brick building wall materials have excellent heat preservation and heat insulation and waterproof performance, and construction speed is quick, moderate difficulty, low cost, low working hours.
2.1 Ceramic foam sound absorption and noise reduction materials
The jumble living environment in large cities brings a series of noise problems, which will cause great impact and harm to people from hearing, sleep, physiological and psychological aspects. Therefore, foam ceramics can be used as sound absorption and noise reduction materials in the construction of urban sound insulation has a great role. Foam ceramic has a large number of pores in the three-dimensional space network structure. After acoustic waves are introduced into the porous interior, the air in the pores will vibrate and friction will occur at the tendons in the foam ceramic. Due to the effect of adhesive paper, the sound waves will turn into heat and disappear, so as to achieve the effect of sound absorption and noise reduction.
Foam ceramic used as sound absorption and noise reduction materials has the following advantages:
1. Light weight, extreme strength, excellent sound absorption performance in low and medium frequency, durable, safe and reliable, flexible structure, easy construction and installation;
2 at the same time suitable for use in elevated temperature, humid environment, even if the perennial wind, sun, rain will not alter their network mechanism and sound absorption performance;
3. It can absorb the reverberation sound caused by reflection;
4. It has excellent fire resistance and high cost performance.
Current applications of ceramic foam as a sound absorbing material include installation in the middle of a car exhaust pipe to reduce noise there, and some modern green buildings also use ceramic foam as a wall material to achieve excellent sound insulation. Some developed countries, such as the United States, Japan and Germany, use modern foam ceramics to build viaducts and expressways as noise barriers.
2.2 Foam ceramic thermal insulation material
The steep porosity and low thermal conductivity of the matrix make the foam ceramics have the characteristics of low thermal conductivity and excellent thermal shock resistance, which can be used in various occasions to prevent thermal radiation, heat preservation and energy saving. The use of foam ceramic building materials can make the house with excellent heat insulation effect, so that the summer air conditioning and winter heating can be well preserved indoors, not easy to disperse. In the building fire protection function, the foam ceramic does not burn, its expansion coefficient is close to the metal material, the expansion and contraction difference is relatively tiny, so as to avoid the expansion and contraction difference caused by the danger of insulation materials and wall materials, to ensure the insulation structure of the airtight.
At present, several advanced building materials have been applied in some newly built residential communities and office buildings in China. In addition, ceramic foam materials play an essential role in the aerospace field. For example, the thermal protection system of spacecraft is widely used in this material.
