Glass refers to all amorphous bodies obtained by supercooling melts, regardless of their chemical composition and temperature range of solidification, which, as a result of a gradual increase in viscosity, have the mechanical properties of solids, and the transition from liquid to glassy should be reversible. Glasses are divided into natural and artificial. To natural include glass formed during the activity of volcanoes (magma eruption), such as obsidian glass. Artificial glass includes other melted materials created from mineral silicate melts. They are divided into the following groups: glass, stone, slag, sitalls and slagositalls.
Composition, structure and condition of glass
Glass does not have a specific structural chemical formula, unlike crystalline bodies. The composition of the glasses is expressed by the sum of the oxides. Depending on the type and purpose, the building glass contains oxides SiO2, Na2O3; K2O; CaO; MgO; Al2O3; Fe2O3; SO3; B2O3. Each of the oxides in the process of cooking plays a role in the formation of the properties of glass.
Since glass has zero porosity, its average density is equal to true and, depending on the chemical composition, varies from 2.2 to 7.5 g / cm3. Most industrial building glass (window, polished, profile) has a density of 2.5 ... 2.7 g / cm3, in particular window glass - 2.55 g / cm3. The average density of heat insulating glass products ranges from 15 to 600 kg / m3.
Glass properties
The thermal conductivity of ordinary glass varies from 0.5 to 1.0 W / (m · ° C), and the insulating glassware is 0.032 ... 0.14 W / (m · ° C). The heat capacity of the glasses at room temperature is 0.63 ... 1.05 kJ / (kg ° C). Due to the high coefficient of thermal expansion (910-6 ... 1510-6), ordinary glass has a relatively low temperature resistance.
Optical properties of glasses are their important properties and are characterized by light transmittance (transparency), light refraction, reflection and scattering. Ordinary silicate glasses transmit the entire visible part of the spectrum and practically do not transmit ultraviolet and infrared rays. The coefficient of directional transmission of light glasses reaches 0.89.
The sound insulation capacity of glass is relatively high. According to this indicator, 1 cm thick glass corresponds to a brick wall with a half-brick - 12 cm.
Deformative properties . Glass has no plastic deformations, that is, its destruction is absolutely fragile, unlike all other building materials. Fragility is the main drawback of glass, which is poorly resistant to impact. The strength of ordinary glass with impact bending is only 0.2 MPa. The modulus of elasticity of glasses of different composition ranges from 45,000 to 98,000 MPa (71 400 MPa for quartz glass) .
The compressive strength for various types of glass ranges from 500 to 2000 MPa, for example, the strength of window glass 900 ... 1000 MPa. Glass is tensile working 15 ... 20 times worse than compressing, therefore tensile strength of glasses is one of their most important mechanical properties. In this case, the calculated theoretical tensile strength of glass is 12 000 MPa, and the real (technical) - 30 ... 100 MPa. This is explained by the presence of micro-inhomogeneities, microcracks, internal stresses, foreign inclusions, etc. in the glass. Damage and scratches on the glass surface are especially dangerous, since these defects result in concentration and reinforcement of stresses that destroy the structure. The tensile strength of the glass under tension can be increased by chemical etching of the surface layer, its melting, polishing, and quenching.
Chemical resistance of glass depends on its composition. Silicate glass has a high chemical resistance to most aggressive media with the exception of hydrofluoric and phosphoric acids.
About technological properties . Important is the property of the glass in a plastic state to take any shape, including stretching into the thinnest threads, which is impossible for materials that are heterogeneous in structure. In construction, fiberglass with a diameter of 5 ... 15 μm is used, the tensile strength of which reaches 4000 MPa.
In general, materials from glass and melts have high durability, excellent decorative properties. Studies are being conducted in the direction of a fundamental change in the properties of glass, in particular the elimination of brittleness, as well as a significant increase in strength properties.
Basics of glass production
The main raw materials are quartz sand SiO2, soda Na2CO3, dolomite CaCO3MgCO3, limestone CaCO3, potash K2CO3, sodium sulfate Na2SO4, blast furnace slag, quartz-containing materials, calcium tetraborite, broken glass, etc. In addition, brighteners are also introduced, which contribute to disposal from glass melt of gas bubbles (sodium and aluminum sulphates, potassium nitrate, arsenic anhydride); silencers that make the glass opaque (cryolite, fluorspar, double superphosphate); dyes for imparting a given color (cobalt - blue, chrome - green, manganese - purple, iron - brown and blue-green tones, etc.).
Production of building glass consists of the following main operations: preparation of raw materials; batch preparation; glass cooking in bath or pot furnaces; molding products; their annealing and quenching if necessary.
The mixing of the crushed components in strictly dosed quantities (an error of no more than 1%) is carried out in drum or disc type mixers. The finished mixture is loaded into a bathroom oven - a pool made of refractory materials, or in a pot furnace. The fuel is natural gas. When the mixture is heated to 600 ... 900 ° C, its components melt and decompose to form oxides of sodium, potassium, calcium, magnesium and release a large amount of carbon dioxide.
When the mixture is heated to 1100 ... 1150 ° C, the formation of silicates occurs, first in solid form, and then in the melt. With further increase in temperature, the most refractory components of SiO2 and Al2O3 completely dissolve in this melt - glass melt is formed. This mass is heterogeneous in composition and is so saturated with gas bubbles that it is called cooking foam. For clarification and homogenization, the glass melt temperature is raised to 1500 ... 1600 ° C. At the same time, the melt viscosity decreases, facilitating the removal of gas inclusions and obtaining a homogeneous melt. Glassmaking is completed by cooling (a stud) of the glass mass to a temperature at which it acquires the viscosity required for making glassware.
Molding products produced by extrusion, casting, rolling, pressing and blowing. Sheet glass shaping is performed by vertical or horizontal stretching of the ribbon from the melt, by rolling or by floating-strip method (float method).
Annealing - a mandatory operation in the manufacture of products. During rapid cooling, large internal stresses arise in order to fix the shape of the products in them, which can even lead to spontaneous destruction of glassware. Hardening - this operation is used to obtain glass with increased 4-6 times in compression and 5-8 times in bending strength compared with ordinary glass. Hardening is carried out by bringing the glass to a plastic state and then by sharp cooling of the surface. Final processing of products includes the operations of grinding, polishing, decorative processing.
Glass product range
1. Sheet glass . Used for glazing of window and door openings, shop windows and interior decoration of buildings. Sheet glass is divided into: window; shop window; patterned; reinforced; tempered; multilayer (triplex); uviol; heat absorbing and heat reflecting; electrically conductive; absorbing x-rays and radioactive rays.
2. Architectural and building glass
a) Translucent building products and product designs are effective
transparent translucent building material for exterior and interior fences in residential, public and industrial buildings and for glazing window openings. In the construction are used: glass blocks, stekloprofilit, double-glazed windows, glass-concrete structures and glass tiles.
b) Glass cladding is used for cladding the walls of many buildings. TO
They include: colored sheet glass, sterealite, marblit, glass marble, glass tiles, enamel tiles, carpet mosaic tiles, smalt, glass chips, foam decorator, porous clay, sigran, glass-crystallite, glass ceramite, glass silicon.
3. Foam glass
It is obtained by swelling at the softening temperature of ground glass mixed with a blowing agent (charcoal, limestone, etc.). Foam glass is well processed, glued, tacked, breathable and non-absorbent. Foamglass density is 15 ... 700 kg / m3, thermal conductivity coefficient is 04.04-0.15 W / (m · ° C), compressive strength is 0.1-15 MPa. It is made in the form of blocks of 475-400-120 mm for thermal insulation of building structures, industrial equipment, refrigerators, and granules as a particularly light (bulk density - 100-150 kg / m3) aggregate in light concrete.
4. Glass fiber and products from it - continuous filaments (obtained by melt pulling) for the manufacture of fiberglass pipes and tanks by winding onto appropriate mandrels; fiberglass for the manufacture of fiberglass on the polymer binder, as well as in the construction of pipe insulation; fiberglass canvas (thin sheet material of interwoven continuous fibers bonded with a synthetic binder) for the manufacture of waterproofing and roofing materials, in particular, glass-reinforced; chopped glass fiber (as a reinforcing element in concrete and mortars) and glass wool (made from aluminosilicate melts with an Al2O3 content of at least 45%).
5. Glass pipes
6. Technical glass (heat-resistant, chemical-laboratory, medical, lighting, quartz, etc.) and enamel.
Sitally, shlakositalla and sitalloplasta
Sitalls are glass-ceramic materials obtained from glass melts by their complete or partial crystallization. According to the structure, the cellars are composite materials with a vitreous amorphous continuous phase - a matrix filled with small (1-2 μm) crystals. The thickness of the layers of the glass phase does not exceed a few tenths of a micron. The volume of the crystalline phase in the cellals reaches 9095%. Possessing a polycrystalline structure (an analogue of metal), the sitalls, while maintaining the positive properties of glass, are devoid of its drawbacks: brittleness, low flexural strength, low heat resistance. According to their physico-technical properties, sitalls are comparable with metals.
The hardness of the glass is close to the hardness of hardened steel. The heat resistance of products from sitalla reaches 1100 ° C. Sitalls are highly resistant to strong acids (except hydrofluoric acid) and alkalis. Certain types of sitalls are heat resistant and the ability to braze with steel. Compressive strength of sitals is up to 500 MPa. In appearance, the sitalls can be dark, gray, brown, cream, light colors, deaf and transparent. The raw materials for the production of sitalls are the same natural materials as for glass, but very high demands are placed on the purity of the raw materials. In addition, additives that catalyze crystallization during the subsequent heat treatment are introduced into the melt. Alkali and alkaline-earth metal fluoride or phosphate compounds are used as crystallization catalysts. The technology of production of products from the glass does not differ from the technology of production of glass products. Only additional heat treatment of the glass in the crystallizer is required.
In the construction of sitalls are used for the device floors of industrial plants, in which there may be spills of acids, alkalis, molten metals, as well as the movement of heavy machinery.
Shlakositalla are a type of sitalum, the production of which has received the most extensive development. These are glass-ceramic materials obtained by controlled crystallization of glass obtained on the basis of metallurgical slags, silica sand, and some additives. Shlakositalla much cheaper than technical sitalalls.
Sittoplastic materials - materials manufactured on the basis of fluoroplastics and sitalls, are distinguished by higher chemical resistance and wear resistance than each of the components separately. Used for the manufacture of products operating in conditions where neither the sitalls nor the fluoroplast satisfy the durability to chemical resistance.
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