Silica fume on the strength of high performance concrete

Although the application of pure cement can be made up to 100 MPa compressive strength of HPC, but will be much easier when using silica fume. For the preparation of the concrete strength exceeds 100 MPa, the use of silica fume is almost indispensable. Silica fume in concrete filler material and volcanic ash from the same material. Using silica fume, greatly reducing the hydration slurry pore size, pore size distribution improved, so that strength, permeability decreases.
For example, the study results show that (CEB2FIP1988), in order to obtain 70 MPa concrete strength, the application of pure cement needs water-cement ratio 0.35, and when plus 8% silica fume, the water-cement ratio can be 0.50. Since silica particles are very fine, they can occur within a few hours early pozzolanic reaction. According to Carette and Malhotra 1992) reports, the contribution of silica fume concrete strength mainly in the 28d before. So, the long-term strength of growth, generally considered as pure silica fume concrete cement concrete or fly ash concrete. Almad (1994) cited the development of silica fume on the NSC strength test results show that silica fume dosage increases the relative intensity of the early development of such reduction, Sandvik 1992 at 65 MPa concrete were also found in this phenomenon.
However, although the same water-cement ratio relative strength of silica fume concrete in the early development of slower than pure cement concrete, such as silica fume added strength greatly increased, the absolute strength of silica fume concrete is higher than that of pure cement concrete. On the other hand, experience has shown, HPC early strength development faster than the NSC, although HPC setting time may be slightly delayed hydration after its condensation due superplasticizer and silica fume greatly accelerated. The result is usually very fast strength development after condensation.
For some air drying or curing of low water-cement ratio of silicon carbide silica fume concrete specimens with compressive strength retraction reports (De Larrard and Aiticin 1993). This reduction in strength usually occurs after the age of 90 d, is generally considered by an internal self-drying and drying cracks caused. However, many other researchers in laboratory and field studies have shown that, HPC's late strength is not reduced. For example, from 6 different HPC obtained in three months to three years, all drill core samples of test results show that the intensity is growing. Of course, compared with the NSC, HPC's long-term growth potential of smaller intensity.

Black corundum corundum smelting method and the same

(1) A corundum
Corundum is bauxite, coal and iron as raw material in electric arc furnace at high temperature smelting. In the smelting process, the carbon anthracite in the silica alumina, iron oxide and titanium oxide is reduced to metallic impurities, the alloy of these metals taken together, due to its large specific gravity than the molten corundum to the bottom of settlement and corundum melt-liquid separation. Only a small amount of impurity inclusions in the corundum melting fast.
The main ingredients of mineral corundum corundum physics, trigonal system, a small amount of mineral impurities are: calcium silicate, calcium plagioclase, mullite (also known as mullite), titanium compounds, vitreous, and a small amount of iron alloy.
Corundum anti-crushing ability, anti-oxidation, corrosion resistance, good chemical stability, which is a widely used abrasive. Suitable for grinding high tensile strength of the metal materials, such as ordinary carbon steel, hard bronze, alloy steel grinding and grinding, thread and gear grinding, white fused alumina can be used for precision casting and high-grade refractory.
(2) black corundum BA
Black corundum corundum smelting methods and the same is Sanshui bauxite as raw material, add a small amount of reducing agent is made by smelting, its power consumption is about two-thirds of corundum. Black, the main chemical components: Al2O3 not less than 77%, SiO2 content of 10 ~ 12%, Fe2O3 content is 7 ~ 10%, TiO2 is about 3%, the proportion of not less than 3.61.
Black corundum with good self-sharpening, grinding, less heat, better finish machined parts for the bottom part before plating polished, aluminum and stainless steel polishing, can also be used to polish optical glass, processed timber. Due to its hydrophilic, can be used in the manufacture of sandpaper, emery cloth and resin abrasive, but also can be used for polishing paste and polishing powder. Black corundum due to iron content is high, and therefore should not be used in the manufacture of ceramic abrasive.
(3) White corundum WA
White fused alumina powder as raw materials in industry, in the arc by melting temperatures above 2000 degrees and then cooled steel. Aluminum oxide (Al2O3) content of 98%, and a small amount of iron oxide, silicon oxide and other ingredients, white.
Harder than corundum corundum, grit easily broken, sharp edges and corners, good cutting, grinding, heat a small and so on. For hard materials, heat-sensitive strong steel grinding. Such as hardened steel. High carbon steel, general high speed steel, alloy steel grinding. Mainly used for tools, cutting tools, dies, gears, threads, thin-walled parts grinding and profile grinding.

Green foreign polishing process using silicon carbide powder

Polishing process includes: Calibrating grinding, rough grinding, the grinding, fine grinding, polishing, edging and inverted corners and other processes. Abrasives and Abrasive used: Calibrating the above steps except use emery grinding, the rest are made of Green silicon carbide powder fineness ocean. Polishing is required for the cooling flush face to face away produce a lot of heat to prevent the products burst. After polishing needed for drying, waxing or other surface coatings to enhance its dirt capacity, improve the gloss, the current process is mainly used for polishing finishing ceramic tiles, and has developed a fully automatic polishing machine. The flexible abrasive polishing tools and polishing media particles or other modification of the surface of the workpiece processing.
Polishing can not improve the dimensional accuracy of the workpiece or geometric shape accuracy, but to obtain a smooth surface or specular gloss for the purpose, sometimes to eliminate gloss (extinction). Usually as a polishing buff polishing tool. Buff general use multi canvas, felt or leather crafted stacked on both sides with a metal circular plate clamped its rim coated abrasives and grease, etc. from the powder mixture evenly polish. Uniform fine polishing using material degreased thin wood or a special felts, its trajectory uniform dense mesh, the surface roughness after polishing is less than Ra0.01 microns, the enlarged 40 times under the microscope than any surface defects.

About corundum What is the main component and classification

Refers to the industrial alumina white fused alumina powder as raw material in the arc melting temperatures above 2000 degrees through steel. Corundum main chemical ingredient is AL2O3, its content in a 98.65% -99.37%, and the other a small amount of Fe, Si, Ti and so on. Corundum for the manufacture of ceramic, resin bonded abrasives and grinding, polishing, sandblasting, precision casting, etc., can also be used to manufacture advanced refractories.
Corundum behalf # "WA" on internationally accepted standards, national standards, most for export, there is a certain amount of supply domestic users.
Sandblasting grade corundum is divided into:
16 # 46 # 60 # 80 # 100 # 120 # 150 # 180 # 200 # 220 # 280 #
Particle size in accordance with international standards and national standards of production, processing granularity according to user requirements. Universal size # is F4 ~ F320, its chemical composition varies depending on the particle size. Prominent feature is the small crystal size impact resistance, due to a self-processing mill crushed particles are mostly spherical particles, dry surface cleaning, easy binding agent combination. Year the company provides silicon carbide, white fused alumina, corundum powder, green silicon carbide powder and sand grain size.

Silicon carbide in the three fields of application

Silicon carbide is also called moissanite, silicon carbide products can be divided into many categories, depending on the use of the environment, divided into different categories.
A general use to mechanically more. For example, using the mechanical seal, it can be called a silicon carbide seal ring, can be divided into static ring, ring, flat ring. Can also according to customer's special requirements, produce a variety of shapes silicon carbide products, such as silicon carbide shaped pieces, silicon carbide plates, carbide ring.
2 of one of silicon carbide SiC article has a high hardness, high corrosion resistance and high temperature strength characteristics, which makes silicon carbide has been widely used.
3 In the application of the sealing ring: SiC good chemical resistance, high strength, high hardness, wear resistance, low coefficient of friction and high temperature, so it is an ideal material for manufacturing sealing ring. It is paired with the graphite material composition, the friction coefficient smaller than that of alumina ceramic and carbide, which can be used for high PV values, in particular transport acid and alkali used in the working conditions. I produced the SIC-1-type silicon carbide Sintered products, with high density, high hardness, producing large quantities, can produce complex shapes products, suitable for use in high-performance seals, especially high PV value and resistant to acid and alkali conditions. And I produced the SIC-3-type silicon carbide ceramics containing graphite, silicon carbide material. Since the silicon carbide substrate contains a large number of fine graphite particles dispersed, when paired with other materials, the friction coefficient is very small, has good self-lubricating properties, especially for the production of dry gas seals or seal friction condition the use, so that the service life of the seal and the reliability improved.
SiC refractory Information superior function, as we all know already, has been widely used. Currently, high-performance silicon carbide refractory data is still in the research and development period, the outstanding features of silicon carbide from the forward, lower costs intentions to leave, with plenty of information to grasp the composition, microstructure and functional link between is produced to ensure future , followed by discussion deepening will gradually expand its use of the field, the market is extremely broad prospects.

Classification and the use of a variety of abrasive range

Abrasive grinding material is used, the general classification is now common abrasives, superhard abrasive types; ordinary abrasive including corundum (corundum, corundum, etc.), and its main chemical composition Al2O3 (aluminum oxide) , silicon carbide (black silicon carbide, green silicon carbide), and its main chemical components of SiC (silicon carbide). They are corundum hardness, microhardness 2000-2200 kgf / mm 2; corundum, microhardness 2200-2300 kgf / mm 2; black silicon carbide, microhardness 3100-3300 kgf / mm 2 ; green silicon carbide, microhardness 3200-3400 kgf / mm 2; grain size from 4 # - powder W0.5 (or finer), the hardness in the order that we can sort out the processing of granite is green silicon carbide, black carbonized silicon processing marble is corundum (soft), black, green silicon carbide (hard).The cost from the material in order to see the green silicon carbide, black silicon carbide, corundum, abrasives can be made around these, inorganic abrasive tool including magnesite, ceramics, etc.; organic grinding tools, including phenolic, unsaturated resins, and epoxy, etc. (This also includes emery cloth sandpaper), which constitute the common abrasive grinding tools, grinding tools.Superabrasive diamond abrasive belongs, and its processing history is a relatively long, but as more use is the last three decades a large number of industrial production, and its hardness 8000-10000 kgf / mm 2; hardness is the highest , processed materials are micro-cutting mechanism, so it is the preferred cutting tool, in recent years, there is a massive increase in the yield and reduction of industrial costs, high processing efficiency, (which is 5 times more than normal), the processing effect (may demanding material for polishing), and thus, it is a widely used.Diamond grinding tools are metal, resin, ceramics, etc. This is the type of binding agent according to the classification, metal grinding instruments mainly include iron-based, copper-based, these types of cobalt, it determine the different types of materials processing costs, as grinding tools, from the most coarse particle size (20 #), often to the fine grain size up to 400 # for use; which is characterized by long life, but the cost will be higher.Resin grinding tools, due to the production costs are relatively low, the application should be relatively more, it is now also used for rough grinding to polishing, grinding and polishing in the fine-grained aspects is its greatest advantage; ceramic diamond grinding tools are recent was the fastest growing tool, its processing performance in metalworking take long, to avoid resin processing short, is technically a good advantage, but because of cost reasons, have not seen used in stone renovation.

 

Green silicon carbide on the use and what are the characteristics

Green silicon carbide is quartz sand and coke for raw materials as a good thermal conductivity, high hardness of man-made materials. Green silicon carbide, white fused alumina even at high temperatures also have high strength, the elastic modulus when the temperature reaches 1600 ℃, began to decay. At a temperature of 2815 ° C begin to separate, but it does not melt at atmospheric pressure. Green silicon carbide suitable for use as super refractories, is also widely used for grinding areas.
Use
For 3-12 inch monocrystalline silicon, polycrystalline silicon, GaAs, quartz crystal wire cutting. Solar photovoltaic industry, the semiconductor industry, piezoelectric crystal engineering of industrial processing materials.
Feature
1, high-purity, large crystal silicon carbide material, the cutting of silicon carbide powder to ensure excellent cutting performance and stability of the physical condition.
2, plot size and shape of such a front edge, to ensure cutting edge material as silicon carbide powder balanced self-sharpening to ensure the material being cut TTV is minimized.
3, the particle size distribution is narrow and uniform.
4, a high thermal shock resistance and load softening temperature, which ensures that the cutting load of the small coefficient of linear expansion, thus ensuring the stability of the cutting; cutting machines and able to have a good adaptation of.
5, the surface is specially treated, powder with a large specific surface area and clean appearance, and polyethylene glycol coolant has good suitability.