Glass is inorganic material, amorphic structures of high performance. Glass is a uniform, transparent material, which is obtained in a complex technological process. The basis of this process is two phases: melting of glass stone and shattered glass, in the first and cooling of liquids with continuous increase of viscosity before finished cooling, in the second phase. Glass features depend on:
- Chemical composition (Relationships and types of components)
- Process of obtaining
- Methods of processing
- Additional processing
All glass features can appear in different shapes and combinations that result in a large number of glass products. Depending on the chemical composition, the glass can be creal and leaded. Creal (usually) glass has the primary significance for application in architecture. The basic raw materials produced by the glass are quartz sand (SiO2) from 69% to 74%. The composition of the Lime Glass also includes:
- Calcium oxide (CaO) 5%-12%
- Sodium oxide (Na2O) 12%-16%
- Magnesium oxide (MgO) 0%-6%
- Aluminum oxide (Al2O3) 0%-3%
Borosilikat Glass is a glass that is composed of pine trees (B2O3) in the following relation to other components in addition to quartz sand:
- Quartz Sand (SiO2) 70%-87%
- Bor-Osid (B2О3) 7%-15%
- Sodium oxide (Na2O) 1%-8%
- Potassium oxide (K2O) 1%-8%
- Aluminum oxide (Al2O3) 1%-8%
Lead Glass (crystal) is obtained when the limestone is replaced with a lead oxin (PbO)
- Chromium-oxide (Cr2O3)-Green
- Cobalt oxide (CoO)-Blue
- Copper oxide (Cu2O)-Red
- Selenium (Se)-Purple
- Uranium oxide (U2O3)-Yellow
For the application of glass in architecture, the following groups of traits are most likely:
- Physical characteristics of glass
-Optical and energy transmission (missed) light-light wrapping index-thermal characteristics-resistance in fire-acoustic characteristics-porosity
- Mechanical characteristics of glass: strength, hardness and resistance to wear
- Chemical: Chemical Durability
- Visual: transparency, color and surface character.
PHYSICAL TRAITS of the GLASS
Under the physical properties of the material include those properties that are not changed (i.e., that are changed only while the samples that change are caused), which are characterized by no matter the amount and shape or product Is.
OPTICAL and ENERGETIC CHARACTERISTICS of GLASS
Part of the spectrum of electromagnetic solar radiation that reaches the surface of the earth is a part of optical radiation, which moves in waveform from 290 to 2,100 nm and includes visible, ultravioi and infrared radiation. The visible part of the spectrum is between 400 and 780nm is Ultravioi radiation, while from 780 to 2.110 nm zone of infrared (thermal radiation. The distribution of optical radiation could be expressed by the following ratio: Ultravioi 3%, visible 53%, infrared 44%. For architecture, the lack of light is of great importance given the significance of light as a phenomenon for perceprciju in space. Optical characteristics include all material characteristics in relation to optical electromagnetic radiation, especially in relation to the visible part of the spectrum and depend on the type of glass. In glass and other tranparent materials, the photons in the visible part of the spectrum are not absorbed. When light falls on usually untainted flat glass, 6mm thick, part is reflected (about 4%), part absorbed (1.6%-2.5%), and the rest missed (maximum 91-92%).
In terms of the passing of sunlight and energy, the basic characteristics of glass: transmission (permissibility) of light, total energy transmission and solar factor can be defined. Light Transmission (Eng. Light transmission-LT) is a measure of the release of solar radiation within the visible part of the spectrum, i.e. with waveways of 400 780nm. It represents the ratio of the missed light and the total amount of light that falls onto the glass at an angle of 90 °. Expressed in percentages (%). Direct Energy transmission (Eng. Direct Transmission Energy-DET) represents the missed energy in the inner space within the Wavelengand from 320 to 2,500 nm. Expressed in percentages (%). The solar factor (g) is the ratio of the amount of heat energy that passes through the glass (directly as thermal and the one that is absorbed first) and the total energy that reaches the glass. Adding glass to certain chemical ingredients and by applying special layers (eng. (alumil), different types of glass, specific light and thermal traits are obtained.
THERMAL CHARACTERISTICS of GLASS
For architectural objects are of the utmost importance are the following thermal characteristics:
The specific thermal capacity (C) indicates the speed of heating or cooling of material, i.e. the amount of heat that needs to be brought to the mass unit to temperature changed by 1K; For usually glass 0.85-1kJ/kg °.
The Heat gateway coefficient [U (k)]-reflects the amount of heat that passes in the unit of time, through the single surface, at the scale of the temperature of 1K. For the glass, 4mm is 5.81 W/m2K.
The coefficient of the thermal spread – measures to spread material, determines the behavior of material in temperature changes, which is of great importance, especially for contact with other materials in construction. Thermical coefficient of thermal exteration depends on the chemical composition of the glass: for calcium-Silicate glass is 9 * 10-6, and for Borosilikat 3-6 * 10-6. For glass plates, more significant information is information about surface expansion and has the value of double-coefficient of linear exalation.
Changing the length of the glass element due to heat effects, can be expressed: ΔL = α · ΔT · L (α-linear-prolonged coefficient, ΔT – Temperature change, L – initial element length).
Thermic fatigue occurs when material is exposed to temperature changes for a long time. It is a consequence of reducing mechanical strength and damage to material. The thermo-tenidity of the glass in heated warming is higher than cooling, since the resistance of glass pressure is about ten times larger than the resilience of the glass to the tension. By increasing the thickness of the glass, it decreases the value of the temperature difference that glass can handle. When choosing a glass for construction elements, it must be particularly careful in its resilience to temperature shocks. The temtic shock arises due to the sudden change in temperature (e.g., or fire extinguishing).
Thermal conductivity coefficients [λ] for certain materials:
• Water 0, 56W/mK
• Glass 1W/mK
• Aluminum 230W/mK
• Steel 70W/mK
• Plastic 0.16-0, 25W/mK
• Wood 0.14-0, 17W/mK
• Opeka 0.8-1, 2W/mK.
GLASS RESISTANCE IN THE FIRE
In the fires of fire, as well as for other materials, glass are the most important characteristics: flammable and resistance in fire. Usually glass is in non-inflammatory materials (class A1). In the fire, usually the glass shoots rapidly due to thermal shock and cannot be considered fire material. However, by applying Borosilitar and multi-layer glass with high-temperature interlock, the behavior of the glass in the fire has been significantly altered, hence the glass has become one of the materials that can be used as a fire barrier.
The resistance in the fire is a time interval in which the elements are capable of performing their function in the conditions of standard fire, glass resistance class is 30, 60, 90, 120 and 180 minutes.
ACOUSTIC FEATURES of GLASS
Under acoustic characteristics are considered a set of qualities that relate to the behavior of the material in the sound of audio. In a narrow sense, this is the ratio of applied material and noise protection. Large density of glass is affordable to acoustic traits, but taking into account small thickness, values are unsatisfactory. Multi-layer glass can provide a certain level of sound weakening, as well as thermal insulation glass, which in addition to its basic functions, increasing the gap between the glass gives good results in reducing noise levels. Sound protection depends on the thickness of the glass, and for a 3mm glass of 24dB, for a glass of 9mm – 30dB.
POROSITY of GLASS
Porosity is an important feature of material in architecture and is a degree of material compact. At glass porosity is zero, glass is not leaking fluid or gas.
MECHANICAL FEATURES of GLASS
Mechanical traits are characterized by the behavior of material in the effects of external (mechanical) forces, in which there is a certain voltage condition (strain), until the change of matter, or breaking of material.
STRENGTH GLASS (E)
This feature includes several aspects of glass behavior: the ability to withstand pressure, tightening and bending. The behavior of the glass in the conditions of strain is largely determined by its usability, since the material is projected and performed by these constructive elements. According to the way it deforms, the glass falls into the stern materials, where the breakdown comes sharply, without prior warnings. The krta nature of the glass will not allow redistribution of the load or energy absorption. Glass is amorphic structures and its mechanical properties are the same in all directions. The glass is strong in pressure, but low on tension. To the breaking of the glass due to bending, it comes to the part of the glass exerted for tension, not pressure. The resistance of glass in the strain depends on the length of the strain (long or short term), the thickness of the glass, the temperature and very much of the integrity of the glass surface (edge, hole in the glass, etc.). Theoretical values are more than practical, mainly due to the imperfections of glass povine, so-called. Griffith’s Napr’s. Strength glass under pressure for one of the same kind of glass moves in wide boundaries and depends on the form being examined and the conditions in which the examination is performed. For the usual construction glass is 20,000 – 45,000 N/cm2. . Strength of tension and bending is up to ten times smaller and for the usual construction glass is 4,000 N/cm2. The measure indirectly expresses the strength of the material in pressure is the Jungov module which is equal to the volume between strain and deformations. For example, the diamond is 1.200.000 MN/m2, aluminum 73.000 MN/m2, and for glass 70,000 MN/m2. It is a very important measure of glass resilience, as material, in which the requirements of the maximum use of materials will be harmonised, without endangering the safety. The safety is expressed by the security of a safety fee [x], which represents the ratio between the maximum allowed and actual voltage, which material can withstand. The improvement of the glass features in the strain can be achieved by the process of caling, thermal or chemical processing.
HARDNESS of the GLASS
Hardness is a quality that refers to resistance to local effect of force and implies the resilience of material according to: mating, notation and penetration of other material. Hardness depends on the composition and manner of glass processing. The glass is very hard material, comparable to steel. It is one of its most important qualities, significant for the processing and duranost of materials. According to Moss, a scale of 1 to 10 glass has a value of 5-7.
The RESISTANCE OF GLASS
Wearing wear is the occurrence of the touching surfaces of materials with other materials, when the consequence of friction occurs to the discharge or turning. For Glass, this is a very important quality, especially for those elements of the construction that runs, where dust and dirt can be an abrazive tool. In glass the wear process affects, primarily, to change visual quality, and not to a significant change of mass. For homogenous materials such as glass, wear is evenly and manifested by losing the glow, becomes semi-transparent and matricular. Surface processes can increase the wear resistance.
CHEMICAL CHARACTERISTICS of GLASS
Chemical consistency of glass – durability of glass is a reflection of chemical consistency and great hardness. The glass is resistant to acid, salt and their dissolve and short-lasting effect of bases at lower temperatures. Moisture and water when inappropriate storage can cause corrosion from 8 μm annually, after which the surface becomes crude. The first gray is formed on the surfaces, and then the white layer, which is hard to remove. Borosilicative Glass has increased resistance to acids and alkaline soles.
VISUAL FEATURES OF GLASS
Transparency in relation to all other materials, a very significant feature of glass, related to its application in architecture in terms of visual comfort, is transparency (transparency). This feature in direct connection with the transmission of light and according to European norms is defined in the standard EN 572 – 1, where for certain thickness of the glass is given the minimum value of light transmission (measured according to EN 410) for transparent and semi-transparently Glass. The most transparent glass, no color, are glass with a small amount of ferooxide (Fe2O3). This quality, certain processing procedures, can be changed and ranges from fully transparent, through semi-transparent (airy) to solid types of glass. The transparency effect can also depend on the angle that is viewed through the glass. Holographic foil glasses are transparent only when viewed in a straight glass.
Adding additives in the molten mass of glass are provided with glass of different colours for decorative reasons or for obtaining specific types of glass in terms of missing visible or infrared radiation. These glass absorb a higher amount of thermal radiation, but they have a significant flaw – change the quality of color perceptions in space, because they change colors. Colored glass can be later processed – cutting, grinding, drilling, baking, shaping. The most widespread are the windows of green, blue, gray and brown in all shades.
The SURFACE CHARACTER of the GLASS
When it comes to the appearance of glass surface, it is in plain glass, shiny and smooth. Extra glass is possible to get glass surfaces of modified look, without brightness or with a embossable invoice. Changing the surface character also changes the transparency level.
Under glass dimensions include its width, length and thickness. Dimensions are conditioned by manufacturers ‘ production processes and depend on the type and thickness of the glass. Limitations exist for all types of glass, and the value manufacturers express through the minimum/maximum possible values in the MM and the permitted tolerance of the same. In architecture, it is often desirable as the larger size of the glass, due to reducing the number of connections and due to aesthetic criteria, although at the same time it involves a great weight for the individual panel, which in particular makes the overall construction. The most obvious advantage of glass is a simple chemical structure and transparency that defines the visual aspect of this material. Glass has positive qualities, but should be emphasized that they are not without limit. The features of the glass vary greatly depending on the type. For the constructive application of glass in architecture, it is of utmost importance mechanical characteristics of glass and behavior in fire conditions. Glass is a cross material and problems of hardness of regular glass and low resistance under the effect of the strength of the forces cause easy and fast breaking. Behavior in the fire (except for expensive composite products) is weak. In addition to the good and desirable transmission of light, the glass has a problem with heat conductability.