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How Inorganic Glasses are Made

written by: Asheesh • edited by: Lamar Stonecypher • updated: 6/1/2011

Inorganic or fundamental glass is an important material that is used for various applications worldwide. This article describes the fundamental facts of the various types of inorganic glasses.

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    Inorganic glass is an amorphous, hard, brittle, transparent, and super-cooled liquid of infinite viscosity. It is manufactured by fusing a mixture of number of metallic silicates.

    The term Inorganic is added with glass because a glass is a mixture of inorganic compounds such as silicates of sodium, potassium, calcium, and lead. Only a few metallic carbonates are used for manufacturing. Although carbonates have only a little amount of carbon, carbonates of metals are studied in inorganic science. Organic compounds are not used for manufacturing any type of glass; therefore, it is called inorganic glass.

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    Structure of Fundamental Inorganic Glasses

    The structure fundamental inorganic glass is xR2O.yMO.6SiO2, where R is an atom of monovalent alkali metals such as Na, K, etc. and M is an atom of a bivalent metal such as Ca, Pb, Zn etc., and x and y are whole numbers.

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    General Properties of Inorganic Glass

    • It is amorphous in nature.
    • It has no definite melting point.
    • It can absorb, reflect, and transmit light.
    • It can take a high polish.
    • It is a good electrical insulator.
    • It is affected by alkalis.
    • It is not affected by air, water, or acids or chemical reagents except HF. When it reacts with HF, the silicate component of inorganic glass converts to SiF4.
    • It can be formed into different articles; even it can be formed in complex shapes.
    • It is brittle in nature.
    • It is softened by heating.
    • It is light in weight with respect to the volume or size. This is because it has a homogeneous internal structure.
    • It does not have a crystal structure; due to this, it has a high compressive strength.
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    Different Steps of Manufacturing Inorganic Glass

    Different types of inorganic glasses are manufactured by four steps described below:

    • Melting

    This is the process of melting raw material in proper proportions. First of all, raw materials are mixed with cullets for powdering. The powdered mixture is then sent for fusing. For fusing the mixture, different chambers are used regarding different purposes such as fireclay pots used for making high-grade glass, and tanks (a part of open- hearth furnaces) are used for low-grade glasses. The mixture melts and fuses at high temperature, about 1800 0C.

    • Forming and Shaping

    Molten glass is then converted into desired shape either by molding or by pressing between rollers.

    • Annealing

    Glass articles are then allowed to pass through different chambers having different temperatures, but the chambers are placed in descending order of temperature. This is designed to cool glass articles nearly to room temperature.

    The glass article cannot cool rapidly because inorganic glass is a bad conductor of heat. When the article is rapidly cooled, then the superficial layer cools down first and the interior part gets high strain and the article breaks into pieces.

    • Finishing

    After the annealing process all glass articles are subjected to perform different finishing processes such as cleaning, grinding, polishing, cutting, and sand-blasting.

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    Reference: Engineering Chemistry-Jain.Jain
    Image: Salva Del Saz -The Glassy Prow
    Image: flyingsourcers- Glass Pane
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    Types of Inorganic Glasses- Composition, Properties, and Uses

    The fundamental types of glasses are given below

    • Soda-lime or Soft Glass

    Composition- Na2O.CaO.6SiO2

    Properties- They are low in cost, resistant to water, and can melt easily.

    Uses- Used as windows glass, plate glasses, electric bulbs, bottles, jars, and building materials.

    • Potash-lime or Hard Glass

    Composition- K2O.CaO.6SiO2

    Properties-They have high melting point, fuse with difficulty, and are less affected by acids, alkalis and other solvents.

    Uses- Used for chemical apparatus and combustion tubes.

    • Lead Glass or Flint Glass

    Composition- K2O.PbO.6SiO2

    Properties- They are more expensive than lime-soda glass but easier to shape and work with.

    Uses- Used for high quality tableware and optical purposes.

    Glass Pane 

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    Other Inorganic Glasses Based on Fundamental Glasses

    The above glasses are the fundamental glasses. The types of glasses given below are manufactured using these fundamental glasses.

    • Pyrex Glass or Jean Glass

    Composition- These glasses contain virtually only silica and boron, with a small amount of aluminum and some alkali oxides.

    Properties- They have low thermal coefficient of expansion, high chemical resistance very high softening point and high resistivity.

    Uses- Used in industries of pipe lines, gauge glasses, superior laboratory glasses, kitchenware, chemical plants, and television tubes.

    • Aluminosilicate Glass

    Composition- they are made up of mainly aluminum and silica, with a small amount of boron and alkalis oxides.

    Properties- They have comparatively high softening temperature.

    Uses- Used for high mercury discharge tubes, chemical combustion tubes, domestic equipment.

    • 99.5% Silica or Vitreosil

    Composition- It is produced by heating pure sand, i.e. SiO2 (quartz)

    Properties- They have high viscosity, shaping is difficult, and the thermal expansion is low.

    Uses- Used for chemical plants, chemical laboratory wares, electrical insulating materials in electric heaters, furnaces.

    • Optical or Crooks Glass

    Composition- It contains phosphorous and lead silicate, together with cerium oxide.

    Properties- They are capable of absorbing ultraviolet rays, have low melting point, and are relatively soft.

    Uses- Used for making lenses.

    • Insulating Glass

    Composition- They are made by using two or more plates of glass separated by 6 to 13 mm thick gap, filled up with dehydrated air.

    Properties- They are transparent units and provide high insulation against heat.

    Uses- Used for separating apartments.

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    Inorganic Glasses manufactured by adding organic Components

    There are also some new types of glasses those are manufactured by adding organic components. A few of them are as follows:

    • Laminated Glass

    Composition- They are made by bonding together two or more sheets of glass with one or more alternate layer of bonding material such as plastic resin, asphalt, or synthetic rubber.

    Properties- This glass is shatter proof and shock proof.

    Uses- Used as safety glasses for automobiles, airplanes, helicopters, and submarines.

    • Safety Glass

    Composition- Made by taking 2 or 3 glass sheets and adding alternate thin layer of vinyl plastic.

    Properties- It is tougher than any other glass.

    Uses- Used for automobile and airplane industries as wind shields.

    • Toughened Glass

    Composition- They are made by dipping the hot article in an oil tank. This process makes the outer layer of article shrink and acquire a state of compression, while the inner layer remains tensioned.

    Properties- They are more elastic and they can absorb for mechanical and thermal shock.

    Uses- Used for window shields for fast moving vehicles, window shields for furnaces, automatic doors, and large show-cases

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    Reference: Engineering Chemistry-Jain.Jain
    Image: Salva Del Saz -The Glassy Prow
    Image: flyingsourcers- Glass Pane

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