Chemistry of ceramics, glass, adhesives and sealants
Every day in our homes we are using smooth, beautiful designed coffee cups, tea cups, plates and bowls. These should be handled carefully and proper maintenance required. Even in laboratories mortar and pestles lab ware manufactured by using special kind of material. All these kind of utensils and lab ware are made up of ceramic.
Ceramic materials are non-metallic, inorganic compounds-primarily compounds of oxygen, carbon, nitrogen, boron, and silicon. Ceramics includes the manufacture of earthenware, porcelain, bricks, sewer pipe and electrical insulators.
Ceramics was started using in time of Neolithic time. In this 20th centaury their uses reached to bowls to semiconductors. Some kind of advanced ceramics include alumina ceramics are using in missiles and rocket nose cones. Other advanced usage includes uranium dioxide (UO2) ceramics used in nuclear power plant elements, laser materials, ceramic capacitors, piezoelectric materials.
Ceramics making process
Ceramics is made up of clay, talc, silica, feldspar, organometallic compounds, silicon carbide, alumina, and barium titanate.
First natural material like clay is required to be heated to high temperatures. Clay consists of a large number of very tiny flat plates, stacked together by thin layers of water. The water allows the plates to attach together and allowing the plates to slide past one another. As a result, clay is easily molded into various shapes.
High temperatures make drying water inside the clay and allow bonds to form between plates, holding and promoting the formation of a hard solid. Binders such as bone ash are sometimes added to the clay to promote sturdy bond formation, which makes the ceramic resistant to breakage.
Ceramic is also made by mixing clay and cements and hardening it by heating it to high temperatures. Advanced technique of making of ceramics used sol-gel process.
Ceramics contain following properties
- Chemical properties
- Mechanical properties
- Physical properties
- Thermal properties
- Electrical properties
- Magnetic properties
Industrial ceramics are made up of compounds of oxygen, heavy metals, carbon, boron, nitrogen, silicon. Ceramics do not react with most liquids, gases, alkalies, and acids.
Ceramics are smooth, lighter in weight, hard and resistance to abrasions.
Ceramics are also used as insulators. Certain ceramics, such as porcelain, act as insulators at lower temperatures but in contrast they will conduct electricity at higher temperatures.
Ceramics used for making strong, hard, and abrasion-resistant materials.
In textile industry ceramics resist the cutting action of fibers traveling through these guides at high speed.
Scientists discovered a family of superconductive copper-oxide-based ceramics.
Besides to usage of ceramics in laboratories glass [glassware] also used in the different laboratories. Other places where glass is used include windscreens of cars, windows in houses, furniture, television sets, soft drink bottles, water drinking glass, and spectacles
Glass is an amorphous solid material that exhibits a glass transition. It is a state of matter in which the atoms and molecules are locked into place, but instead of forming neat, orderly crystals, they arrange themselves randomly.
Glass is having similarity with ceramics in terms of their properties like durability, strength and brittleness, high electrical and thermal resistance, and lack of chemical reactivity.
Glass is made up of silica (SiO2). Following are the other components of silica
History of glass
First true glass was made in coastal north Syria
The story of glass dates back to ancient Egypt where glass-making became popular during the late Bronze Age.
Anglo-Saxon period glass was a luxury material across England
In 10th centaury stained glass came to usage
In 1330 crown glass was produced in Rouen
In 14th and 19th centauries stained glass employed in building purposes
In 1843 Henry Bessemer invented float glass
In 120th centaury reinforced glass and glass bricks came to usage
Colored glasses are due to inclusion of ions of chemical elements like iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), chromium (Cr), and manganese (Mn)
The main constituent of flat Glass is SiO2. This has a high melting temperature in the region of 1700 degrees C. The basic building block of silica has a tetrahedral pyramid shape with silicon at its centre linked symmetrically to four oxygen atoms at its corners.
On cooling molten silica quickly, a random organised network of these tetrahedra is formed, linked at their corners, to give an amorphous material known as vitreous silica.
High melting point and viscosity of silica can be reduced by the addition of sodium oxide. Here sodium oxide works as flux. Sodium oxide used in the form of a carbonate and the sodium-oxygen atoms enter the silicon-oxygen network.
These network modifiers make the structures more complex so that when the components are melted together. In the glass making process, the cooling rate is arranged such that viscosity increases and the mobility of the atoms are hindered thus preventing arrangements and crystallization from occurring.
Flat glass is used in glazing in buildings, to car windscreens, doors and mirrors.
Container glass extensively used in beer, wine, spirits, juices, food, cosmetics.
Borosilicate glass possesses good chemical and thermal shock resistance which make it ideal for laboratory equipment and various forms of ovenware.
Adhesives & Sealants
An adhesive is a material used for holding two surfaces together. An adhesive must wet the surfaces, adhere to the surfaces, and by surface attachment that resists separation. Inorganic substances such as portland cement also can be considered adhesives. Natural adhesives have been known since antiquity. In the performance of adhesive joints, the physical and chemical properties of the adhesive are the most important factors.
Types of adhesive raw materials
- Cellulose nitrate
- Cellulose acetate
- Methyl cellulose
- Ethyl cellulose
- Polyvinyl acetate
- Polyvinyl alcohol
- Polyvinyl butyral
- Polyvinyl ether
- Polyvinyl chloride
Mechanism of adhesion process
The main mechanism of adhesion is explained by the adsorption theory.
Adsorption theory can be defined as substances stick because of intimate intermolecular contact. In adhesive joints this contact is attained by intermolecular or valence forces exerted by molecules in the surface layers of the adhesive and adherend.
In addition to adsorption, four other mechanisms of adhesion have been proposed.
It occurs when adhesive flows into pores in the adherend surface or around projections on the surface.
Interdiffusion results when liquid adhesive dissolves and diffuses into adherend materials.
Adsorption & Surface Reaction
In this process bonding occurs when adhesive molecules adsorb onto a solid surface and chemically react with it.
This theory suggests that electrostatic forces develop at an interface between materials with differing electronic band structures
A sealant is the viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary action.
The main difference between adhesives and sealants is that sealants typically have lower strength and higher elongation than do adhesives.
Sealants fall between higher-strength adhesives at one end and extremely low-strength putties and caulks at the other. Sealants fill a gap between two or more substrates. It forms a barrier through the physical properties of the sealant itself and by adhesion to the substrate. Sealants maintain sealing properties for the expected lifetime, service conditions and environments.
Dental sealants are a dental treatment consisting of applying a plastic material to one or more teeth, for the purpose of preventing dental caries (cavities) or other forms of tooth decay.
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