Borosilicate glass has good thermal and chemical stability and has been widely used in instrument glass, vessel glass, etc.; with the development of the glass melting process and refractory materials, borosilicate glass will be used in more fields.
Borosilicate glass is a glass whose basic composition is SiO2: B2O3, Na2O.
The basic composition range ：
ω(SiO2) = 70% ~ 80%, ω(B2O3) = 6% ~ 15%, ω(Na2O) = 4% ~ 10%, ω(Al2O3) = 0 ~ 5%, ω(BaO) = 0 ~ 2%, ω(CaO) = 0 ~ 2%.
A few typical representative components are as follows：
Where Na2O provides free oxygen to transform the boron oxygen triangle [BO3] into boron oxygen tetrahedra [BO4], and the structure of boron is transformed from lamellar to shelf-like, creating conditions for B2O3 to form a uniform and consistent glass with SiO2.
B2O3 enters the glass structure with [BO3] or [BO4], especially when it forms a structural network with [BO4] and [SiO4] together, which increases the network integrity and compactness, so borosilicate glass has many excellent properties: Such as good thermal and chemical stability, good mechanical properties and process properties, excellent optical properties, etc.
(1) Thermal properties
Borosilicate glass has excellent thermal properties due to its high content of SiO2: and B2O3, which makes its network integrity and density better than ordinary soda-lime-silica glass. Such as, its coefficient of thermal expansion is generally less than 6 × 10-7 / ℃, while ordinary soda-lime-silica glass is about (9 ~ 100) × 10-7 / ℃; borosilicate glass heat impact △ T is generally greater than 150 ℃, known as hard glass or extra hard glass, ordinary soda-lime-silica glass is less than 100 ℃. Therefore, borosilicate glass has good thermal stability and can be used in utensils and cookware, architectural fire protection, etc.
(2)Optical properties
Pure raw materials, uniform mixing, and processing precision, combined with their excellent performance, result in a high light transmission of borosilicate glass. Better light transmittance, higher surface flatness, and lower fluorescence properties enable borosilicate glass to be used in electrophoresis, optics, photonics, and optoelectronics. Since the borosilicate system is more soluble for rare earth oxides than the silicate system and has a relatively wide range of glass formation, the rare earth borosilicate system has become the main system for people to study rare earth optical glasses. Studies have shown [3] that the lanthanum-containing borosilicate glass system can be expected as a system for developing high-density glasses.
(3) Mechanical properties
Borosilicate glass not only has a high thermal shock strength but also has a high surface hardness that can prevent scratches; at the same time, its density is about 12% lower than that of ordinary soda-lime-silica glass (borosilicate glass is generally 2.3 g / cm3, soda-lime-silica glass is generally 2.5 g / cm3). These significant advantages mean that borosilicate glass will be used for many important applications, such as glass for construction, especially high-rise buildings, which will greatly reduce the weight of the overall building, which is also in line with the development of modern architecture in the direction of lightweight and high strength; can also be used as bullet-proof glass and armored car glass. In addition, its high strength, lightweight, and high bond strength will greatly reduce the cost, volume, and weight if used in fields that require lamination and sandwiching.
(4) Chemical properties
In addition to its good resistance to acid and alkali, borosilicate glass has fairly good resistance to hydrolysis, two grades higher than soda-lime-silica glass. It can resist water vapor in the air and even water containing liquid acid or alkali. Unlike soda-lime-silica glass, it is subject to significant erosion. Especially for micro-cracks on the glass surface, borosilicate glass does not exhibit better water stability due to crack expansion caused by the action of water molecules in moist air, unlike soda-lime-silica glass.
As mentioned earlier, due to borosilicate glass's many unique and excellent properties, the glass system has been widely used and developed and can be divided by application areas.
Instrument glass manufactures chemical, biological, laboratory vessels, tubes, and devices. Instrument glass has been widely used in scientific research, culture and education, the chemical industry, medicine and health, industrial production and astronautics, lasers, biological engineering, nuclear engineering, and other high-tech fields.
Its requirements for instrument glass are good chemical stability, thermal stability, high mechanical strength, good process performance, etc... And borosilicate glass has exactly these properties.
There are many types of instrument glass. Its performance, use, and process can be divided into.
① chemical vessels: such as beakers, flasks, flasks with curved necks, evaporation dishes, etc.
② physical and chemical instruments: micro-distillation flasks, micro-distillation tubes, fractionation tubes, test tubes, etc.
③ thick-walled products: alcohol lamps, bellows, desiccators, sinks, etc.
④Measurements: sedimentation tubes,
measuring cylinder, measuring cup, burette, etc.
⑤ Thermometer products: such as thermometers, specific gravity meters, alcohol meters, etc.
Glassware is an important branch of the glass industry, basically belonging to the pressed and blown glass products; its output is second only to flat glass and glass bottles, and glass jars and ranked third. Its characteristics are high transparency, color, lustrous, good thermal and chemical stability, and high mechanical strength. Among them, glass cookware requires good thermal shock resistance, generally above 150 ℃, to heat with an open flame directly. The glass used for glass cookware is mainly borosilicate glass and microcrystalline glass, two categories. They are characterized by a low coefficient of thermal expansion (generally below 4 × 10-6 / ℃) and high thermal shock strength (generally above 150 ℃). In addition to cookware, it is also used for electric stove panels and microwave heaters, such as the top plate of the kitchen with heating components.
Pharmaceutical glass is a major branch of the pharmaceutical packaging industry and an important part of the entire pharmaceutical industry. Pharmaceutical glass usually refers to the higher chemical stability of neutral glass. It requires high chemical stability, good sealing, and mechanical properties, such as strong, mainly borosilicate glass. Several major types of pharmaceutical glass are.
(1) ampoule glass. It refers to thin-walled glass vials for filling injections or powders. The most important thing about ampoule glass is its chemical stability, and the basic composition of this glass is borosilicate glass. Water injection is mainly ampoule glass. The current annual demand of the domestic market is 29 billion, and the annual growth rate of China's pharmaceutical injection will be 5% and reach 37.5 billion in 2010. 10%-15% of the injections need ampoules resistant to strong acids, and alkalis, and light-proof.
(2) Infusion bottles, also known as saline bottles. Its chemical composition is mainly aluminum borosilicate or low borosilicate glass. It mainly contains saline, glucose, and other medicinal solutions, which require good neutrality, certain thermal shock resistance, and mechanical strength.
(3) syringe glass. Usually made of aluminum, borosilicate glass must be sterilized by autoclaving before use to prevent bacterial infection. Therefore, syringe glass must have good heat-resistant properties and good chemical stability.
Photochromic glass is generally divided into two categories: homogeneous and heterogeneous; heterogeneous photochromic glass formation system is very extensive, and its composition is mainly borosilicate glass. Photochromic glass is most commonly used as eyeglass glass; it can also be used for automotive protective glass, laser protection, window materials for spacecraft, switches for new instruments, etc. Industrial glass sight glass is used under certain temperature and pressure conditions of the see-through window glass, with high transparency, temperature and pressure resistance, chemical stability, and other characteristics. Currently developed and produced glass sight glass "alkali-free aluminosilicate glass sight glass," "borosilicate glass sight glass," and "quartz glass sight glass" three series, several varieties. Industrial glass sight glass is widely used in petroleum, chemical, and pharmaceutical industries, such as pipelines, valves, cracking furnaces, storage tanks, and other pressure vessels and instruments.
The production of glass fiber with glass is different from other glass products. At present, the international commercialization of fiber with the glass composition of the main four kinds: E a glass, also known as alkali-free glass; C a glass, also known as alkali glass; A ~ glass, also known as high alkali glass; E-CR glass, is an improved boron-free alkali-free glass. Currently, the most widely used glass fiber is known as E, a glass borosilicate glass; it has good electrical insulation and mechanical properties, is widely used in the production of electrical insulation with glass fiber, but also a large number of glass fiber for the production of glass fiber, its disadvantage is easy to be eroded by inorganic acids, so it is not suitable for use in acidic environments.
The use of glass scales made of heavy anti-corrosion coatings in the 1960s abroad on the use of major anti-corrosion projects received good anti-corrosion effect and has attracted the extensive attention of coating experts around the world. Glass scale American Owens - Corning company (Owens Corning) invented, in 1957 obtained the first patent of glass scale and its coating. According to the relevant information, the glass used for scale-making is generally borosilicate. Borosilicate glass is chosen because of its good chemical stability, especially good acid and alkali resistance.
Domestic has an annual output of 2 million solar vacuum collector manufacturers; it is through first-class high-tech equipment, high borosilicate glass 3.3 (special hard material) as the material, using an internationally advanced level of sputtering selective absorption coating process, the product has a high absorption rate, good strength, hail impact resistance, acid and alkali resistance, good insulation performance, etc., the technical indicators and performance are among the leading domestic level. The service life is more than 15 years. Solar water heater products developed with all-glass vacuum solar collector tubes as heat-absorbing elements have a very high absorption rate of sunlight (more than 93%) and a very low thermal emission rate (less than 6%), and the heat conduction and heat loss rate are reduced to a minimum.
Borosilicate glass has many excellent properties, but when melting borosilicate glass in an ordinary pool furnace, there are some problems: high melting temperature, high viscosity, long clarification time, boron is easy to volatilize, layering and dividing, etc... In particular, the high melting temperature, viscosity, and corrosiveness lead to difficulties in meeting the float forming process, and these problems greatly limit the full play of its excellent performance and large-scale application; at the same time, it also puts forward higher requirements for refractory materials and heating elements. With the improvement of refractory material performance, the development of glass electric kiln technology and the progress of glass processing technology will enable the rapid development of float production borosilicate glass technology so that its excellent performance gives full play to become possible, its application areas will be greatly broadened and in-depth.
3.1 Display glass
Flat-panel displays have become part of people's daily lives. It is difficult to imagine what our information exchange and technical operation will be and how to achieve if there is no display. From watch dials, temperature meters and indicators, and communication terminal equipment, such as fax machines, and cell phones, to desktop computers and television equipment, borosilicate glass has been or will be widely used.
In particular, liquid crystal displays (LCD) are now the new favorite among flat panel displays and have become a trend. All These displays have one thing in common: the glass substrate used must be high quality, the thin thickness of special glass, and in this glass, the sheet can be stored in precision. The requirements for this glass substrate are high, strict standards, almost defect-free (<50 "m) and high surface flatness; coefficient of thermal expansion to match the functional layer of the crystal, the absence of alkali metals; excellent chemical stability, and most importantly, thermal stability. With the development of glass processing technology, display glass will develop in the direction of large size and thin thickness; these requirements can only be achieved through float technology. A liquid crystal display (LCD) device is a flat panel display (FPD) device that does not emit light. Since liquid crystals do not emit light, LCD devices must be transmitted or reflected by an external light source to achieve the display. In the development of LCD with organic LED (OLED) backlighting mouth ..., Oxford University, England, A. Mo.stey and others to borosilicate glass as a substrate glass developed a green, two blue OLED backlighting devices for LCD, with a fast response time, impact resistance, high brightness, wide operating temperature range, and other advantages.
3.2 Fireproof glass for construction
Architectural fire glass Germany is one of the first countries in Europe to develop and produce fire glass, known for its production of float borosilicate transparent tempered fire glass in the world. Germany's Schott Pyrans fire glass products manufactured by the company, are the world's only single borosilicate fire glass produced by float process, which combines excellent thermal shock resistance and excellent optical properties of float glass in one, providing nearly perfect visual effects, not only in the domestic market but also in European countries have been welcomed. The use of glass substrates characterizes the product as transparent borosilicate glass after tempering treatment. For this reason, unlike other types of fire glass, fire glass has a lower coefficient of thermal expansion; its fire resistance can generally reach 60 ~ 120 min or more, and even under high-temperature radiation at 1000 ° C, can still fire mouth¨. Its product specifications are more, there are 5 mm, 6.5 mm, 7.5 mm, 10 mm, 12 mm, etc., and passed the British standard BS6206, that is, with a 45kg bag from 457 mm high vertical fall on the glass surface without breaking, which is to ensure the safety of people in the impact glass. With the improvement of modern buildings on the safety and fire requirements, single borosilicate fire glass will be more widely used and developed worldwide.
3.3 Photovoltaic cells
Resources and energy problems have become a highly important issue today; photovoltaic cells as renewable energy will become a key technology in the 21st century. At present, silicon wafers still occupy a dominant position in photovoltaic materials. However, its price is very expensive, and in the long run, it is impossible to produce on a large scale and large size. Therefore, the trend of photovoltaic cells will be high-efficiency thin-film solar cells, reducing the number of layers and thickness to reduce costs. In other words, a layer of substrate and cover glass will be used. This substrate glass must withstand a considerable degree of thermal load (550 ~ 630 ℃), resist chemical attack, and meet the mechanical strength requirements. And the good thermal expansion and thermal stability of borosilicate glass can be matched with amorphous silicon wafers.
The application of borosilicate glass has just started, and its huge development prospects are incomparable to ordinary soda lime silica glass. In the future, borosilicate glass will develop in the direction of multiple specifications, large size, multi-function, high quality, and large scale. Science and technology workers worldwide have already paid great attention to borosilicate glass, along with the rising requirements and needs of people for glass; borosilicate glass will play an important role in the glass industry.
