Foam ceramic is a kind of porous material. It is the third generation of porous ceramic products developed after the first generation of ordinary porous ceramics and the second generation of honeycomb porous ceramics. Its pore size ranges from nanometer to micrometer, and it has three-dimensional network structure and high porosity material characteristics, and the porosity can reach up to 90%. It has the advantages of light weight, high porosity, large specific surface area, thermal shock resistance, corrosion resistance, high temperature resistance, long service life and good filter adsorption.
The development of the third generation of foam ceramic materials began in the 1970s. As a new type of inorganic non-metallic filter material, it mainly uses raw ore powder, kaolin, or ceramic industry waste residue, fly ash, coal gangue, and marble tailings. , Slag and other inorganic materials as raw materials, mixed with a certain proportion of foaming agent, co-solvent, etc. to make water-based ceramic slurry, immersed in foam plastic to form a ceramic film coating, and then fired. According to the liquid metal object to be filtered, common materials are silicon carbide, alumina, zirconia, magnesia, etc.
At present, foam ceramics have been widely used in many fields. In addition to purifying molten metal in the metallurgical industry, they are also used in thermal insulation materials, chemical catalyst carriers and other applications. For example, Jiangxi Longfa Industry has recently recycled and reused waste ceramics as raw materials to make ceramic permeable bricks, thereby achieving the sustainable development and reuse of local ceramic waste.
1: Purify metallurgical industry to filter molten metal
The foam ceramic filter is mainly used in the casting process to purify the liquid casting alloy and reduce or eliminate various non-metallic inclusions and exhaust problems during casting. Due to defects in casting problems such as non-metallic inclusions, casting waste accounts for 50% -60% of the total waste. At the same time that various costs increase, the outflow of excess waste can be expected to damage the external environment, and the inclusion defects are not only Seriously dragged down the mechanical properties and casting performance of the casting, but also had a harmful effect on the cutting processing and appearance of the casting.
In order to solve this problem, people initially used wire mesh, perforated steel plates, etc., to make simple filters inserted into the pouring system to remove inclusions; to two-dimensional structure filters such as silicate pin fibers, boron nitride fibers. Nowadays, foam ceramic filters use pore size to mechanically intercept large particles of mixed oxides and filter cake to filter small particles of mixed oxides. And with the adsorption and rectification capabilities, the production line of foam ceramic filters has significantly improved the yield of castings. For example, after using the foam ceramic filter in Dongfeng No. 2 Casting Factory, the production rate increased from 65.3% to 71.5%, and the molten iron was saved by 6% only from the weight of the riser. The hardness of the filtered casting is also significantly improved, which in turn extends the life of the cutting tool.
Foam ceramic filters generally use polyurethane foam as a carrier, immersed in ceramic slurry made of refractory aggregate sintering aids, binders and other fine powders and water, and then squeeze out excess slurry, leaving the remaining coated The ceramic material around the foam fiber is then dried, fired and sintered at high temperature, and finally the foam-like ceramic product is left. Due to the different casting temperature of the casting alloy, the foam ceramic filter of the refractory material should be selected for the casting. In recent decades, according to the performance of alloys of different materials, foam ceramic filters of various materials have been developed at home and abroad.
2: Thermal insulation and sound insulation materials on environmentally friendly buildings
As a brand-new low-cost green energy-saving and environmentally friendly product, energy-saving thermal insulation foam ceramics mainly use waste fly ash, slag, waste glass, ceramic flakes, clay, feldspar tailings, etc. as raw materials. Metal material, with excellent characteristics such as fire prevention, waterproof, anti-freezing, mothproof, anti-magnetic wave static electricity, sound insulation and noise reduction, small thermal conductivity, and good adhesion to various types of mud. The foam ceramic light-weight partition board is compared with the traditional light-weight Building wall materials such as blocks, lime sand bricks, and red bricks have high-quality heat insulation and waterproof performance, and have fast construction speed, low difficulty, moderate cost, and low working hours.
2.1 Foam ceramic sound-absorbing and noise-reducing materials
The complicated living environment of big 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, which can be used as sound absorption and noise reduction materials, are soundproofed in cities It has a great role in construction. Foam ceramics have a large number of pores in a three-dimensional spatial network structure. When sound waves are introduced into the porous interior, they will cause the air in the pores to vibrate and friction at the ribs in the foam ceramics. Due to the effect of paper sticking, the sound waves are converted into heat and disappear. So as to achieve the effect of sound absorption and noise reduction.
The use of foam ceramics as a sound-absorbing and noise-reducing material has the following advantages:
1. Light weight, high strength, excellent mid-to-low frequency sound absorption performance, durable, safe and reliable, flexible structure, easy construction and installation;
2. At the same time, it is suitable for use in high temperature and humid environments. Even if it is subjected to wind, sunshine and rain all the year round, it will not change its own mesh structure and sound absorption performance;
3. Ability to absorb reverberation sounds due to reflection;
4. Has good fire resistance and high cost performance.
The current applications of foam ceramics as sound-absorbing materials include installation in the middle of automobile exhaust pipes to reduce noise there. Some new green buildings also use foam ceramics as wall materials, thereby achieving excellent sound insulation. Some developed countries such as the United States, Japan and Germany have adopted new foam ceramics to construct viaducts and highways as noise and sound barriers.
2.2 Foam ceramic insulation materials
The high porosity of the foam ceramic and the low thermal conductivity of the matrix make it have the characteristics of low thermal conductivity and good thermal shock resistance, which can be used in various occasions to prevent heat radiation, heat preservation and energy saving. Building materials made of foamed ceramics can make the house have excellent thermal insulation effect, so that the air conditioning in summer and the heating in winter can be well kept indoors and not easy to spread out. In the fire protection function of the building, the foam ceramic does not burn, and its expansion coefficient is similar to that of the metal material, and the difference in expansion and contraction is relatively small. This can avoid the danger of the shell of the insulation material and the wall material being caused by the difference in expansion and contraction, ensuring the tightness of the insulation structure .
At present, several advanced building materials have been applied in some newly built residential quarters and office buildings in China. In addition, foam ceramic materials in the aerospace field play an important role. For example, this material is widely used in the thermal protection system of spacecraft.