Hard glass, also known as high borosilicate glass, 95 glass: SiO2 (about 80%), sodium borate (12%). High temperature resistance, high pressure, corrosion resistance, high mechanical strength, high thermal conductivity, temperature difference change, operating temperature <783K, annealing temperature 778-833K, can be heated to 873K in a short time, but need to be evenly slow during cooling annealing. To reduce stress. Has good flame processing properties. Used in the manufacture of beakers, flasks, pressure tubes and complete sets of experimental equipment. It is a good material for anti-corrosion and anti-ion pollution, such as domestic GG-17, 95 glass material belongs to this category.
Soft glass, also known as ordinary glass, 17 glass: according to the composition can be divided into soda lime glass (SiO2, CaO, Na2O) and potassium glass (SiO2, CaO, K2O, Al2O3, B2O3).
Potassium glass is better than soda glass in terms of corrosion resistance, hardness, transparency and devitrification, but it is inferior in thermal stability. Low softening temperature, strong alkali resistance, not easy to devitrify, suitable for lamp flame processing, but because it can not withstand excessive temperature difference, it is often used to manufacture instruments that are not directly heated. Such as burette, pipette, measuring cylinder, etc., because its expansion coefficient is close to Pt, it can be sealed with Pt wire.
Identification method of glass tube material:
1. Tube end color: soft glass is blue-green, hard glass is yellow or white, the lighter the color, the harder the material and the lighter the weight.
2, heating: soft glass: soften soon after heating. If it is aluminum glass, it will turn black at the same time, and the soda glass flame will be yellowish; hard glass: it will not soften for a short time, it will soften when heated for a long time, and it will become hard after leaving the flame.
3, volumetric flask: soft glass, medical penicillin bottle: hard glass.
4, performance characteristics: soft glass contains soluble silicate, chemical corrosion resistance is poor, has a strong adsorption, large thermal expansion coefficient, temperature mutation is easy to break. Therefore, the vessel made of ordinary glass is generally only used for diluting the acid-base solution and titrating.
Hard glass contains less soluble impurities and has a small coefficient of thermal expansion, which is convenient for heat treatment. Hard glassware should be used for general chemical element analysis. Commonly used are borosilicate glass.
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