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.

 

95 superhard materials in the field of polycrystalline diamond prospects

Polycrystalline diamond (collectively, polycrystalline diamond), is composed of many high-quality diamond powder at elevated temperature and pressure with (or without) the additive sintering conditions.
Synthetic polycrystalline diamond has the following characteristics because of its vitality shows: (1) crystal was disordered arrangement, and thus uniform hardness, non-directional; (2) has a high strength, especially impact strength and wear sex; (3) can be made into a specific shape; (4) can predict product design or performance characteristics necessary to give the product in order to adapt it for specific purposes.
Once you can replace other industrial diamond products, then you can get a huge market efficiency, which is a new development area of ??polycrystalline diamond. Previously, in oil well drilling, only two percent is the application of the cutting blade, tungsten carbide tips and the rest are occupied cone bit.
Now, the machinery industry, the tool commonly used material is high-speed steel, carbide, ceramics. These tools are made of a material difficult to effectively cutting hard, wear-resistant material difficult to machine.
Practice has proved that high cutting efficiency machining difficult materials ideal diamond tool should have as high hardness and wear resistance, CBN or ceramic as good thermal stability and chemical inertness, carbide as high strength and impact resistance, but even in the future can not find a material having all these desirable properties. Seen in this light, the development of a better tool materials the most promising approach is the combination of several known tool material to form a complex superhard material, so that it has a variety of excellent performance. U.S. GECo scientists back in the early 70s began to explore and research this composite material, they successfully developed PDC (Compax) and cubic boron nitride composite sheet (Compact), these two materials in the machining tool applications will be substantial growth, its fastest growing.
Drawing dies - drawing non-ferrous metals such as copper, zinc, nickel copper, aluminum, gold, etc., as well as hard-wire such as tungsten, molybdenum is better, especially drawing copper wire better. A drawing die before grinding can be drawn in 7000 t copper, equivalent carbide die 300 to 1,000 times, or natural diamond die 5 to 10 times.
Currently polycrystalline diamond drawing dies can be brushed diameter range of 8 to 0.1um. Because precision drilling technology can control a variety of profiled wires. As fine and ultrafine grain products emerge, polycrystalline can be used for drawing dies, but also for the finished mold.
Petroleum Geology Drilling - began in 1973, has had three series of polycrystalline diamond petroleum and geological drill mass production and application. GECo that: special geological drilling polycrystalline diamond - Geoset is synthetic diamond drilling applications in major developments.
Twist drill - the 1980s, the use of diamond drill holes on the extension to the general. One is the twist drill, drill blade inlaid with roof or gable-shaped sandwich formed PDC used in stone, concrete and other non-metallic materials, non-ferrous metals or alloys punch, is gaining popularity in the electronics industry.
Polycrystalline diamond mention the technical development of performance under the following aspects:
(1) the appearance of large polymer chips;
(2) Thermal Stability Product claim series;
(3) continue to refine the grain;
(4) the shape of structural diversification.

Three refractory materials

1) an acidic refractory silicon oxide as the main component, commonly used silica and clay. Silica is more than 93% silicon oxide-containing siliceous products, the raw materials used are silica, silica and other waste, and its acid resistance slag erosion ability, load softening temperature is high, the volume does not shrink after repeated firing, and even a slight swelling; but its vulnerability to erosion of basic slag, thermal shock resistance is poor.
2) neutral alumina refractory oxide, chromium oxide or carbon as a main component. Containing more than 95% of corundum alumina article is a wider use of high quality refractory material. Chromium oxide as the main component of chromium slag bricks for good corrosion resistance, thermal shock resistance, but poor heat load deformation temperature is lower.
3) alkaline refractory magnesium oxide, calcium oxide as the main component, is commonly used magnesia bricks. MgO containing 80% to 85% of the brick, the basic slag and iron slag has good resistance, high refractoriness than clay and silica.

Silicon carbide production process will produce harmful substances do

Silicon carbide production process will produce harmful substances, harmful substances, but what will it? I have a simple analysis of what, for reference only!
Harmful substances in the production process of silicon carbide are the following categories:
An atmospheric pollutants: dust, smoke, carbon monoxide (small), carbon dioxide (a lot), according to the impurities contained in the abrasive material used may also contain various sulfur dioxide, nitrogen oxides, etc.
2, water pollution: mainly salty higher if near farmland and lakes, while the outside row of the main plant in the form of sewage treatment, the contamination can be imagined.
3, light pollution: the production process requires ignition operations, open burning is the smelting furnace smelting, there is fire, if the neighborhood is a residential area it certainly will affect the residents' daily rest.
But mainly atmospheric pollution, harm far as to see how the wind plant location, this project is now disallowed smelting projects, the State restricted projects.

On the Development of silicon carbide industry

As we all know, silicon carbide has a very broad application areas, with high stability silicon carbide crystal is a good semiconductor materials, silicon carbide crystals used in China mainly relies on imported materials. However, the development of silicon carbide industry worries us, and in this I summed up 2011 silicon carbide industry status quo, from excess capacity, appearance and prosperity, and the prices swerved three aspects to elaborate, only represent their own suggestions!
First, excess capacity
In recent years, as the global voice of the yearly high energy saving, new energy photovoltaic enterprises to obtain a triumph of development, especially in the photovoltaic industry in 2010 experienced a spurt of development. With the rise of the photovoltaic industry, for important materials as silicon wire cutting silicon carbide fine powder to form a huge demand. 2010, the global installed capacity of 15.7GW, the demand for silicon carbide fine powder of about 260,000 tons (of green silicon carbide fine powder) is projected to be green silicon carbide materials known to block about 50 million tons. In the case of expectations and optimism, our green silicon carbide production capacity has reached 1.6 million tons, mainly distributed in Qinghai, Gansu, Xinjiang and other regions, serious excess capacity.
Second, the appearance of prosperity
Silicon carbide fine powder as a new multi-functional composite materials, in recent years, is widely used in high-end solar energy, cutting grinding semiconductor, LED, nonmetal ceramics, high-performance sealing rings and other fields. Especially in recent years, both domestic and foreign media and industrial policies are strongly boost the rapid development of this emerging industry. Strong development of photovoltaic industry expectations, resulting silicon carbide industry hot, attracting a large number of enterprises and social investors flocked to overcome the energy conservation and other multi-pressure silicon carbide production enterprises of all sizes can be described as everywhere, the burgeoning optimism .
Third, the market swerved
Into 2011, the photovoltaic industry experienced a 2005-2010 compound annual growth rate of more than 40% of high growth this year, from April to May, the most important by the European PV market policy changes, the PV installed capacity is almost stagnant state. Serious overcapacity photovoltaic industry chain inventory pressure makes drastic correction, prices have been falling, from integrated systems, components, into silicon, even to the higher threshold upstream polysilicon raw materials, industrial chain spared. Statistics show that since the start of April 1st polysilicon spot market prices fell 40% (by early April of 780,000 yuan / ton down to the current 350,000 yuan / ton), silicon prices fell more than 40%, component prices fell 27%.
The whole industry chain prices fell rapidly, so that all photovoltaic enterprises gross margins have fallen sharply, rapidly narrowing profit margins, some no-cost or even a loss advantage for SMEs, the operating rate fell below 50%. Tragic extent comparable to the 2008 financial crisis.
In this context, as part of its industrial chain on a ring, silicon carbide, can not escape the production enterprises, the products have no market price, business situation deteriorated sharply, the industry reshuffle is inevitable.

What corundum and corundum big difference

First, brown fused alumina and white fused alumina abrasives are used can be done. Corundum variety of colors, because it contains ions of different colors show different colors according to the color into brown fused alumina, white fused alumina, black corundum and so on.
Corundum are colorless, white, yellow (pigment ion Ni, Cr), yellow (pigment ion Ni), red (pigment ion Cr), and blue (pigment ion Ti, Fe), green (pigment ion Co, Ni, V), purple (Ti, Fe, Cr), brown, black (pigment ion Fe, Fe), incandescent violet, purple under fluorescent effect (pigment ion V).
In addition to color and itself contains pigment ion differences, corundum and corundum physicochemical characteristics and intended use also differ greatly.White fused alumina is high-quality aluminum oxide powder as raw material, corundum crystals formed by fused refined, high purity, good self-sharpening, acid corrosion, high temperature, thermal properties and stability. Slightly higher than corundum corundum hardness, toughness slightly lower, high purity, good self-sharpening, grinding ability, heat a small, high efficiency, acid and alkali resistance, high temperature resistance and good thermal stability. Made with corundum abrasive grain of sand, suitable for grinding high carbon steel, high speed steel and stainless steel fine-grained abrasive corundum can also be used for precision casting and high-grade refractory.
Corundum of sand :0-1mm 1-3mm 3-5mm 5-8mm white corundum Physical indicators: Al2O3 ≥ 99% Na2O ≤ 0.5% CaO ≤ 0.4% ≤ 0.003% magnetic material
Corundum is bauxite, anthracite, iron as the main raw material in electric arc furnace at high temperature smelting, brown color, good toughness, hardness 1800-2200Kg/mm2, bulk density ≥ 3.85g/cm3, resistance high temperature, high refractoriness 1850 ℃, do refractories, also used as an abrasive.

 

New calcium

The performance and characteristics of new calcium
1, through the depth of the molten steel deoxidation and improve the morphology of inclusions in molten steel, the molten steel to improve the fluidity, stability, chemical composition, to adapt to the needs of even the steel, so that the reduced oxygen content in the molten steel.
2, the cost is much lower than calcium alloy.
3, does not produce harmful gases, reduce environmental pollution.
4, the product floc continuous casting process in solving the slab pinhole outlet and has a unique role.

 

Green silicon carbide wheel Precautions during use

Side grinding problem grinders everyday use, we often find that some operators, regardless of the type of grinding machine, regardless of the type of wheel, casually on the side of the grinding wheel to use, this is a serious breach of security operations Statutes illegal operation behavior.
Procedures used by the peripheral surface should not be used to do the side face of the grinding wheel, this wheel radial strength greater axial strength is small, the operator excessive force will cause wheel broken, even wounding, in the actual The use of the process should prohibit such behavior.
Positive operational problems in daily use, many operators facing the wheel always used to operate because this direction can be put into effect, in fact, this behavior is grinding machine operation should specifically prohibited behavior.
Follow the rules, use the grinder grinding the workpiece, the operator should stand on the side of the wheel, the front wheel must not be operated in order to avoid wheel faulty, or the wheel broken wheel flying flying out.
Force operating problems when used in a grinding machine, some operations, especially the younger operators, for the sake of grinding speed, excessive force is too large, which is a very unsafe behavior. Any wheel flat body has a certain intensity, doing so may cause the wheel broken, and even flying out, but also a should be prohibited.
Common operational problems in the actual daily operations, there are also so happens, someone rush production tasks, grab the working time, the two share a grinding machine simultaneously, which is a serious violation operational behavior, should be strictly prohibited. A grinder is not enough time, can be used to add grinders solution, and definitely not at the same time share a grinder.