1. Composite silicate insulation material
Composite silicate refractory insulation material is a closed-pore network structure material connected by a solid matrix. It is mainly based on special non-metallic minerals of aluminum magnesium silicate, mixed with quantitative auxiliary materials and filling materials, and then added Materials prepared with suitable chemical additives. The reason why it has thermal insulation properties is that it has a closed microporous network structure, which is generally prepared from mineral raw materials such as basalt and white jade by electrostatic principles and wet processes. Its main chemical components are SiO2 and MgO, and a small amount of Fe2O3, CaO, Al2O3, MnO2, etc.; the thermal conductivity at room temperature is 0.031W/(m K), and the thermal conductivity at 350°C is 0.117W/(m K). Composite silicate material is flame-retardant and heat-insulating, and has certain tensile and impact resistance properties in mechanics. It is often used in metallurgy, electric power, chemical industry and other industries; mixing, stirring, gelling, filtration and forming dried products are not only for heat preservation of general thermal equipment, but also for heat preservation of general thermal equipment. Special-shaped equipment and some non-standard equipment also play an important role and are the preferred products for thermal insulation materials. In recent years, composite silicate thermal insulation coatings have also developed rapidly and been widely used, such as rare earth composite thermal insulation materials.
FBT (rare earth) series composite thermal insulation material is a national patent product. It is a white or off-white viscous paste made of minerals and various chemical reagents through a special process; it can be constructed under normal temperature or high temperature. It is suitable for various thermal equipment such as pipelines and heating furnaces, as well as special-shaped valves, indoor special-shaped pipes and variable diameter pipes that are difficult to solve with traditional insulation materials. The construction is simple, and it is tightly combined with the equipment itself after drying. And gaps, long service life, and can play a good heat insulation effect, the maximum operating temperature can reach 1200 ℃.
Sepiolite-type thermal insulation materials are the outstanding results of the recently researched composite silicate thermal insulation materials. With thermal insulation, high temperature volume stability, corrosion resistance and many other excellent performance conditions, they occupy a place in the refractory and thermal insulation material industry. , has a wide range of application markets. Other composite silicate series products are also widely used in the thermal insulation industry, usually at a temperature of about 600°C to 700°C.
2. Closed-cell perlite insulation material
Closed-cell perlite is made from natural perlite ore through a series of complex processes. The process is: raw perlite ore→crushing and screening into perlite ore sand→preheating→multi-stage heating→expansion vitrification→cooling treatment→finished product.
After expansion and sintering of closed-cell perlite, it is vitrified spherical and the interior is a closed hollow structure. That is, by precisely controlling the heating temperature and time, the ore sand expands rapidly in a short time, forming a honeycomb structure inside, and superficially melts and forms The pores are closed, and the surface vitrifies into micro-spherical particles. Compared with the expanded perlite with irregular shape and porous surface, closed-cell perlite has the advantages of low water absorption and high strength, and its thermal conductivity is 0.047W/(m·K) to 0.054W/(m K); in addition, it has the advantages of environmental protection and no pollution, sound absorption and sound insulation, heat preservation and non-combustibility, light weight and porous, good fluidity, high compressive strength, etc., making it can be used as heat preservation of refractory bricks Aggregate and filling materials for furnace insulation layer, etc. The refractoriness is as high as 1360°C, and the use temperature of perlite products is about 800°C.
Closed-cell expanded perlite is mainly used as thermal insulation aggregate and added to refractory materials to make new thermal insulation materials, such as perlite thermal insulation refractory bricks, thermal insulation mortar and thermal insulation concrete. Perlite thermal insulation bricks are made of closed-cell perlite and refractory aggregates, adding suitable binders, stabilizers and curing agents to make lightweight thermal insulation bricks. This kind of refractory bricks has excellent performance and good practical application. A new type of industrial wall material. Insulation mortar is an insulation material made by adding an appropriate amount of closed-cell expanded perlite to mortar. It has the advantages of light weight and heat insulation, flame retardant and high temperature resistance, and short setting time. At present, closed-cell perlite insulation mortar has achieved outstanding results in this regard best results. For example, in the patent of lightweight thermal insulation castable (patent number: CN102503467A), closed-cell perlite is used as thermal insulation aggregate (content 10% to 30%), and mullite hollow balls, high alumina cement, solid water glass, Aluminum-silica sol, etc. are made of thermal insulation castables, which are simple in construction and have good thermal insulation properties. In the foundry production, the closed-cell perlite and refractory aggregate are mixed in a certain proportion to make insulation risers and insulation subsidies, which can improve the quality of castings and reduce production processes. Adding spherical closed-cell expanded perlite and water reducer to the concrete can play a role in heat insulation and noise reduction without affecting the mechanical properties of the material itself such as flexural resistance and compression resistance.
6. Floating beads refractory insulation materials
Floating beads are when fly ash is burned in a power plant boiler, it is dehydrated and melted into micro-droplets in a high-temperature environment, and forms a round sphere under the action of air; after a variety of physical and chemical reactions, the generated gas expands in the sphere, and then cooperates Under the action of surface tension, the sphere turns into a hollow glass bubble, then rapidly cools and hardens, and finally forms a high-vacuum glassy hollow floating bead. The main components are SiO2 and Al2O3, and also contain Fe2O3, CaO, MgO, TiO2, K2O and Na2O, among which silicon aluminum oxide accounts for more than 80%. The substance content and color of floating beads in different origins are slightly different. Most of them are off-white, thin-walled and hollow, with closed and smooth surface, spherical particles with transparent translucent white pearl luster, and their thermal conductivity is 0.065W/(m · K). Fly ash floating beads have the characteristics of small bulk density, high refractoriness, flame retardancy, corrosion resistance, high strength, thermal insulation, etc., and are one of the widely used refractory raw materials, especially in industries such as metallurgy, petroleum, machinery, heat treatment, etc. Insulation subsidies in kiln and foundry production. Under normal circumstances, the working temperature of floating bead insulation materials is not higher than 1000°C.
Foreign research on the development and research of floating beads products began in the middle of the last century, mainly studying the formation mechanism, chemical and physical properties, and heat insulation mechanism of fly ash floating beads [26] and floating pearl bricks with floating beads as the main thermal insulation aggregate. and other refractory materials. Domestic research on floating beads is relatively backward compared to foreign countries. Many aspects of theoretical knowledge are based on foreign literature. However, after years of research and development, many achievements have been made. Floating bead thermal insulation coatings have been successfully developed one after another. For example, the thermal conductivity of floating bead refractory insulation bricks in some patented products can be around 0.18W/(m K), the compressive strength at room temperature can reach 5MPa, and the thermal shock stability can reach 30 times for 10 minutes of air cooling at 800°C; Chu Lin [27] In the study of aluminophosphate floating beads, aluminum dihydrogen phosphate was used as a binder and aluminum hydroxide was used as a curing agent to prepare a floating bead insulation material. The compressive strength of the material can reach 4.346MPa, and the bulk density is 0.517g/ cm3, thermal conductivity 0.069W/(m K); Li Wendan et al. used fly ash floating beads as the substrate to prepare high thermal reflectivity exterior wall thermal insulation coatings by heterogeneous precipitation method.
3. Nanoporous silicon insulation material
The heat conduction and heat convection of gas and the heat conduction of solid materials are the main ways for materials to transfer heat. Therefore, it is the key to explore a new material that can hinder various heat transfer methods of materials. Through the continuous efforts of researchers, nanopores are finally Silicon insulation materials come into people’s field of vision.
Although the thermal conductivity of air and most gases is very small in a static state, the existence of heat convection increases the range of heat transfer, while the micropore size of SiO2 airgel in nanoporous silicon thermal insulation materials is less than 50nm, and the micropores The size is small enough and smaller than the mean free path of gas molecules, so that there is no collision or a small probability of collision between gas molecules, and convective heat transfer is basically impossible, thus blocking the heat conduction of gas molecules; the ideal of silicon airgel The microporous structure makes its thermal conductivity at room temperature between 0.03 and 0.05W/(m K), which is lower than that of air; and it also has good light transmission at room temperature, and The function of shielding infrared rays. Therefore, amorphous SiO2 has become the main material for the preparation of nano-microporous thermal insulation materials due to its unique structural characteristics and its own performance advantages. The nanoporous carrier of nano-thermal insulation materials currently in practical use is SiO2 airgel. Airgel is called the most advanced and most promising thermal insulation material together with vacuum insulation panel (VIP). Compared with SiO2 airgel nanoporous thermal insulation materials, gas phase SiO2 is another research direction for the preparation of nanoporous thermal insulation materials; AbeH.Y. et al. use gas phase SiO2 as the main raw material, SiC as opacifying agent, and alkali-free glass fiber as reinforcement. Agent, nano-SiO2 porous thermal insulation material was prepared by dry molding process, the fracture stress of the product reached 1.58MPa, the thermal conductivity was 0.0282W/m·K at 400°C, and the porosity was 80.1%. There are also great achievements in the preparation of nano-SiO2 thermal insulation materials by the gas phase method in China. Feng Jinpeng et al. made nano-SiO2 porous thermal insulation materials from nano-SiO2 powder, SiC and other materials by steam curing method. Nanoporous silicon thermal insulation materials have become the research target of many researchers due to their light weight, porosity, and good thermal insulation performance; There is a lot of room for development. Such materials can be used for a long time in a high temperature environment of 950°C, and the higher temperature can reach 1025°C, and even some optimized materials can work in a high temperature environment of 1200°C for a period of time.
