The difference between borosilicate glass and ordinary glass?

The borosilicate glass is also called hard glass, and the coefficient of thermal expansion of the line is (3.3 ± 0.1) × 10 -6 / K, which is also called "borosilicate glass 3.3". It is characterized by small thermal expansion coefficient, good thermal stability, chemical stability, light transmission performance and electrical properties, so it has the advantages of chemical corrosion resistance, thermal shock resistance, good mechanical properties, high use temperature and high hardness. Also known as heat-resistant glass, heat-resistant impact glass, high temperature glass, but also a special fireproof glass. It is widely used in solar energy, chemical industry, pharmaceutical packaging, electric light source, craft jewelry and other industries. Its good performance has been widely recognized by all walks of life around the world, especially in the field of solar energy, and developed countries such as Germany and the United States have carried out more extensive promotion. I will introduce the difference between borosilicate glass and ordinary glass, the characteristics of high borosilicate glass, the composition of high borosilicate glass, the melting process of borosilicate glass, and the application of high borosilicate glass. I hope to deepen your understanding of borosilicate glass!

1. Characteristics of high borosilicate glass
Borosilicate glass has a very low coefficient of thermal expansion, about one-third that of ordinary glass. This will reduce the effects of temperature gradient stress and thus have stronger fracture resistance. Due to its very small shape deviation, this makes it an indispensable material in telescopes and mirrors. It can also be used to treat high-level nuclear waste. The borosilicate glass begins to soften at about 821 ° C (1510 ° F), at which temperature the 7740 viscosity borosilicate is 107.6 yoke.

2, borosilicate glass is lower than ordinary glass dense
1 Although more and more resistance is thermal shock than other types of glass, borosilicate glass can still be broken due to rapid or uneven temperature changes. When broken, borosilicate glass cracks tend to be larger rather than comminuted (it will unit, not split).

2 optics, borosilicate glass has low dispersion (about 65 Abbe number crown glasses) and relatively low refractive index (the entire visible range 1.51-1.54).
The linear expansion coefficient of 3G3.3 borosilicate glass is 3.3 ± 0.1 × 10 -6 / K, which is a kind of glass based on sodium oxide (Na2O), boron oxide (B2O2) and silicon dioxide (SIO2). The glass component has a high content of borosilicate, which is boron: 12.5 to 13.5%, and silicon: 78 to 80%, so that the glass is called borosilicate glass. It belongs to PYREX glass in borosilicate glass. It has acid and alkali resistance, water resistance, excellent corrosion resistance, good thermal stability, chemical stability and electrical properties. It has chemical corrosion resistance, thermal shock resistance, good mechanical properties and high temperature resistance.

Characteristics of borosilicate glass
First, thermal characteristics
Low thermal expansion coefficient, high thermal shock resistance and long-term withstand temperatures up to 450 °C make BOROFLOAT® 33 particularly suitable for applications requiring good temperature stability (eg, inner plates and high-power floodlights for pyrolysis self-cleaning ovens) Outer cover).

1. Linear thermal expansion coefficient;
2. Heat capacity 0.83 KJ x (kg x K)-1 thermal conductivity;
3, the highest working temperature short-term use of 500 ° C long-term use of 450 °;
4, the same piece of temperature difference (a piece of glass withstand the difference between the heating center and the cold edge temperature performance);
5, heat shock resistance (glass with temperature quenching performance) 5mm1

60k borosilicate glass viscosity softening point 820 °.

Second, chemical properties
1. The borosilicate glass contains little ferrous ions and is therefore a clear and transparent colorless glass.
2. High borosilicate glass is a clear and transparent colorless glass. Excellent transmission in the UV and visible near-infrared range makes borosilicate glass an ideal material for a wide range of floodlights, high-power spotlights and sunbeds (up to 450°C). The borosilicate glass glass has extremely low fluorescence, good surface quality and uniformity, and can be widely used in the fields of optics, optoelectronics, photonics, and analytical equipment.
Third, electrical characteristics

Due to its low alkali content, borosilicate glass can be used as a high insulator, so it is suitable for applications requiring high non-conductive properties at high temperatures (up to 450 ° C). Because of the unique structure of borosilicate glass, borosilicate glass has a neutron absorption effect.
Composition of borosilicate glass
The main raw materials are: quartz sand (SiO2), borax (Na2B4O7·10H2O), boric acid (H3BO3), sodium nitrate (NaNO3), aluminum hydroxide (Al(OH)3), sodium fluorosilicate (Na2SiF6), broken glass.

1. Quartz sand: mainly introduced silica (SiO2). Silica is an important glass-forming oxide in which an irregular continuous structure is formed by a structural unit of a silicon oxytetrahedron [SiO4] to constitute a skeleton of glass. Silica can reduce the thermal expansion coefficient of glass and improve the thermal stability, chemical stability, softening temperature, heat resistance, hardness, mechanical strength, transparency and viscosity of glass.

2. Borax: Na2O and B2O3 are simultaneously introduced during melting, and B2O3 is volatile. B2O3 can reduce the thermal expansion coefficient of glass, improve the thermal stability and chemical stability of glass, improve the gloss of glass, and improve the mechanical strength of glass. B2O3 lowers the viscosity of the glass at high temperatures and increases the viscosity of the glass at low temperatures. B2O3 also acts as a flux.
3. Boric acid: The high temperature is decomposed by heat to become molten B2O3. The role of B2O3 is as described in the above borax.
4, aluminum hydroxide: pyrolysis to form Al2O3, Al2O3 in glass can improve the chemical stability of the glass, increase the mechanical strength, and can reduce the crystallization tendency of the glass. Al2O3 can also reduce the thermal expansion coefficient of glass, improve the thermal stability of glass, and reduce the erosion of refractory by glass melt. However, the increase of Al2O3 content will greatly increase the viscosity of glass melt.
5. Sodium fluorosilicate: sodium fluorosilicate is used as clarification aid, cosolvent and opacification.

6. Sodium nitrate: NaNO3 has a lower melting point and lower decomposition temperature, and is decomposed into Na2O, N2 and O2 by heat, which can form a eutectic with silica (SiO2), and also has strong oxidation and clarification, thus accelerating the glass. Melt.
7, broken glass: the use of broken glass can not only use waste, but also under reasonable use, can also accelerate the glass melting process, reduce the heat consumption of melting, thereby reducing the production cost of glass and increase production.
High borosilicate glass melting process
Glass melting process
Melting is one of the important processes in the glass production process. It is a process in which the batch material is accelerated at a high temperature to form a uniform, bubble-free, and conforms to the glass required for molding. From the production practice, most of the defects of the glass product are mainly Glass products produced during the melting process are also closely related to fuel consumption and furnace life. Therefore, reasonable melting is an important guarantee for the smooth production of glass and the production of glass. Glass melting is a very complex process that involves a series of physical and chemical changes. These variations are generally the same for a variety of different batches. Only by fully understanding the various changes that occur in the glass melting process and the conditions required to complete these changes can a proper melting system be developed to smooth the glass melting process.

The specific process is as follows:
1. the formation stage of silicate
The silicate formation reaction is carried out in a solid state, and a series of physical changes and chemical changes occur in the components of the batch. The formation reaction temperature of silicate: 800~900 °C, the end of the reaction stage is the completion of the main solid phase reaction in the powder. A large amount of gaseous matter escapes. The batch material becomes an opaque sinter composed of silicate and silica.
2. the formation stage of glass
Upon continued heating, the silicate sinter begins to melt while the silicate and the remaining disiloxane dissolve. The reaction temperature of the glass formation is: 1200~1250 °C The end of the reaction stage is marked by the fact that the sinter becomes a transparent body and there is no unreacted batch. However, there are a lot of bubbles and streaks in the glass, and the chemical composition properties are not consistent.

3.the clarification stage of the glass
As the temperature continues to rise, the viscosity of the glass decreases, and the visible bubbles in the glass disappear, and the process of removing the bubbles is called the clarification process of the glass. The temperature of the clarification process is: 1400~1500 °C, and the way of eliminating bubbles during the clarification process:
1. Increase the volume of bubbles in the glass, accelerate it, and rupture after floating out of the glass surface. This method is mainly carried out in the melting section in the pool furnace, and is the main bubble elimination side.
formula. The determining factor for this process is the viscosity of the glass and the size of the bubbles themselves.
[Analysis of the time when a bubble of different diameter passes through a meter of glass at a specific temperature]
1φ1.0mm 14 hours;
2φ0.1mm 140 hours;
3φ0.01mm 1400 hours;
In the actual production process, a glass clarifying agent is added to the batch material, and a gas is generated at a high temperature to enter the bubble of the glass liquid to increase and rise to float out of the glass surface. This process is done at the location of the kiln.
2. The gas in the small bubbles is dissolved in the glass liquid, that is, absorbed by the glass liquid and disappears. During the cooling process of the glass liquid, the glass tension of the bubble surface increases, and the bubble shrinks under the action of the tension, and the bubble cooling volume is reduced, which makes the pressure increase in the small bubble facilitate the diffusion of the gas in the bubble into the glass liquid. Going, because the volume of the evolved gas is reduced, the pressure inside the bubble is further increased, and the gas is partially melted. This process until the end, the bubble completely disappears. In actual production, measures to accelerate the clarification of the glass:
1 Properly increase the temperature of the glass clarification stage to extend the clarification time so that the bubbles can fully escape the glass surface.
2 Add glass clarifying agent:
The mechanism of action of the glass clarifying agent: at high temperature, the clarifying agent itself releases the gas into the glass liquid, and brings out other gases in the glass liquid to eliminate the bubbles of the glass liquid.
3 Control the pressure inside the kiln to be slightly positive pressure and keep it stable, which is beneficial to the smooth discharge of gas in the glass liquid.
4 Ensure that the flame in the temperature zone is clarified.
5 The surface of the glass liquid clarifies the hot spot, and the furnace bottom bubbling system and the electric heating heat dam system are adjusted reasonably.

4. the homogenization of glass
The homogenization of the glass is to make the overall glass uniform in chemical composition, which is reflected in the product with uniform light transmission and no obvious stripe defects. The factors that promote the homogenization of the glass are:
1. The molten glass is at a high temperature for a long time, and the different parts of the molten glass are mixed with each other, and finally reach uniformity.
2. The stirring effect of the hot convection and bubble rise of the glass liquid is also an important factor to promote the homogenization of the glass liquid.
3. Controlling the proper temperature to reduce the viscosity of the glass liquid is beneficial to the homogenization process, which is lower than the clarification temperature.
4. Adjust the coverage of the flame in the homogenized area of the pool furnace to be uniform.
5. the cooling of the glass
The cooling of the molten glass is to cool the molten glass liquid to the temperature required by the molding process. During the cooling process, the fine bubbles are further melted and eliminated, and the homogenized glass liquid is in a stable state to form a stable undisturbed liquid flow. Enter the molding stage. At this stage the temperature of the glass solution should be controlled and stable. Actually, the setting and change of the temperature value are the main factors affecting the quality of the product. If the temperature of the homogenized glass liquid is increased again, small bubbles will be generated in the glass liquid, which is the gas which is dissolved in the glass liquid and precipitated again. The phenomenon. It is called a secondary bubble, so a strict temperature control system is implemented in the production process.

Application of borosilicate glass
1. Household appliances (glass panels inside the oven, microwave trays, stove panels, etc.);
2. Environmental engineering, chemical engineering (resistive lining, chemical reactor, safety mirror);
3. Lighting (protective glass for spotlights and high-power floodlights);
4. Solar power generation (solar cell substrate);
5. Precision instruments (optical filters);
6, semiconductor technology (wafer, display glass);
7. Medical technology and bioengineering;
8, security protection (bulletproof glass).

Editor：Eric from Rongdar Pharmaceutical Packing 

information in Blogspot