Mr. A. R. Jundle

Dehydration reaction is a chemical reaction that involves the loss of water from the reacting molecule or ion.

PRINCIPLE OF WORKING OF TEM

• Electrons possess a wave like character.
• Electrons emitted into vacuum from a heated filament with increased accelerating potential will have small wavelength.
• Such higher-energy electrons can penetrate distances of several microns into a solid.
• If these transmitted electrons could be focused -images with much better resolution.
• Focusing relies on the fact that, electrons also behave as negatively charged particles and are therefore deflected by electric or magnetic fields.

WORKING OF TEM

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• Specimen is bombarded by a beam of electrons, the primary electrons. The bombarding electrons are focused onto a bundle of object.
• In areas in the object where these electrons encounter atoms with a heavy atomic nucleus, they rebound.
• In regions where the material consists of lighter atoms, the electron is able to pass through.
• The fine pattern of electrons leaving the object, and reaching the objective lens forms the image.
• It is then greatly enlarged by the projector lens.
• Eventually, the traversing electrons (transmission) reach the scintillator plate at the base of the column of the microscope.
• The scintillator contains phosphor compounds that can absorb the energy of the striking electrons and convert it to light flashes.
• Thus a contrasted image is formed on this plate.

ADVANTAGES & DISADVANTAGES OF TEM

• TEMs offer very powerful magnification and resolution.
• TEMs have a wide range of applications and can be utilized in a variety of different scientific, educational and industrial fields.
• TEMs provide information on element and compound structure .
• Images are high-quality and detailed.
• TEMs are large and very expensive.
• Laborious sample preparation.
• Operation and analysis requires special training.
• Samples are limited to those that are electron transparent.
• TEMs require special housing and maintenance.
• Images are black and white .

X-ray diffraction (XRD) is a powerful method for the study of nanomaterials (materials with structural features of at least one dimension in the range of 1-100 nm).

D-Spacing - This is the distance between successive, parallel planes of atoms. 

What is Ceramics?

Traditional ceramics include materials like glass, refractories, abrasives, and enamels. Some of them are metal oxides, carbides, borides, nitrides, and silicates. Tungsten carbide, Silicon carbide, Beryllia, Zirconia, Alumina, and magnesium are a few of their examples. Ionic atomic bonding typically exists between them.

Ceramics Definition

The name "ceramics" comes from the Greek word "potter's clay," Keramos. But today, many substances that are categorized as ceramics don't even include clay. Compounds of metals and non-metals are what modern ceramics are defined as.

Although different types of ceramics have very different properties, such as corrosion-resistant, hard, and brittle. The majority of ceramics are also excellent insulators and can withstand high temperatures. Because of these properties, they are used in almost every aspect of modern life. Ceramic materials can be found as single crystals or as polycrystalline materials (polycrystals). These polycrystals are oriented more or less randomly with respect to one another. They are also known as "grains." When the composition of the grains varies, the ceramic material is multiphase. The grains in monolithic material are all of the same phases.

Ceramics Processing

Types of Ceramics

There are different material categories into which ceramics can be divided. Ceramics are mainly divided into two categories:

• Traditional
• Advanced

These categories can all be evolved into distinctive material features. Let us see each of these categories in detail.

Traditional Ceramics

Objects made of clay and cement hardened by high-temperature heating are examples of traditional ceramics. Dishes, crockery, flowerpots, and roof and wall tiles are all made from traditional ceramics. Earthenware, stoneware, and porcelain pottery are the types of pottery displayed here.

• Structure clay product
• Whitewares

Advanced Ceramics

Carbides, such as silicon carbide, SiC; oxides, such as aluminium oxide, Al2O3; nitrides, such as silicon nitride, Si3N4; and many other materials, including mixed oxide ceramics that can act as superconductors, are examples of advanced ceramics. Modern processing techniques are required for advanced ceramics, and developing these techniques has led to advances in medicine and engineering. There are two types of advanced ceramics:

• Non-silicate oxide ceramics
• Non-oxide ceramics

Semiconductors are a type of ceramic; they are covalently bonded solids that include, in addition to the well-known Si and Ge, GaAs, CdTe ...etc. Outside of electronic materials, other semiconductors include SiC, TiO2, ZnO, and others. Atoms in solids, in general, and ceramics in particular, will be arranged in long-range order, short-range order, or a combination of both. Solids with long-range order are known as crystalline solids, while those without that periodicity are known as amorphous, glassy, or non-crystalline solids.

Advantages of Ceramics

There are numerous materials available to create a wide range of items. Every substance, from glass to metal, has advantages. Here, we'll list a few significant benefits of working with ceramic materials and using final ceramic products:

• Because they have high hardness, they are commonly used as abrasive powder and cutting tools.
• Because of their high melting point, they are excellent refractory materials.
• They are also good thermal insulators, which is why they are used as a refractory material.
• They have high electric resistivity, making them suitable for use as an insulator.
• Due to their low mass density, they produce lightweight components.
• They are generally chemically inert, making them long-lasting.

Disadvantages of Ceramics

Ceramic materials have a lot of high installation and transportation requirements, and their main drawback is fragility. It is easy for them to break when hard objects strike ceramic art. The following drawbacks are listed below:

• They have a brittle nature.
• They have a low degree of ductility.
• Their tensile strength is low.
• Even for identical specimens, there is a wide range of variation in strength.
• They are challenging to shape and machine.

Applications of Ceramics

Ceramics are harder, non-combustible, and inert than metals and plastics. As a result, they are suitable for use in high-temperature, corrosive, and tribological applications.

• Because of their lightweight, they are used in the space industry.
• They serve as cutting instruments.
• They serve as refractory substances.
• As electrical insulators and thermal insulators, they are utilized.
• Photoelectrochemical devices or cells PEC are solar cells that produce electrical energy or hydrogen through a process similar to water electrolysis.

Polymer Materials

Classification of Polymers

Polymers cannot be classified under one category because of their complex structures, different behaviours and vast applications. We can, therefore, classify polymers based on the following norms.

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Classification of Polymers Based on the Source of Availability

There are three types of classification under this category, namely, natural, synthetic, and semi-synthetic polymers.

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Natural Polymers

They occur naturally and are found in plants and animals. For example, proteins, starch, cellulose and rubber. To add up, we also have biodegradable polymers called biopolymers.

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Semi-synthetic Polymers

They are derived from naturally occurring polymers and undergo further chemical modification. For example, cellulose nitrate and cellulose acetate.

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Synthetic Polymers

These are human-made polymers. Plastic is the most common and widely used synthetic polymer. It is used in industries and various dairy products. For example, nylon-6, 6, polyether, etc.

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Also Read: Natural Polymers vs Synthetic Polymers

Classification of Polymers Based on the Structure of the Monomer Chain

This category has the following classifications:

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Linear Polymers

The structure of polymers containing long and straight chains falls into this category. PVC, i.e., polyvinyl chloride, is largely used for making pipes, and an electric cable is an example of a linear polymer.

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Branched-chain Polymers

When linear chains of a polymer form branches, then such polymers are categorised as branched chain polymers. For example, low-density polythene.

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Cross-linked Polymers

They are composed of bifunctional and trifunctional monomers. They have a stronger covalent bond in comparison to other linear polymers. Bakelite and melamine are examples of cross-linked polymers.

Other Ways to Classify Polymers

Classification Based on Polymerization

Addition Polymerization: For example, poly ethane, Teflon, polyvinyl chloride (PVC), etc.

Condensation Polymerization: Examples include nylon -6, 6, perylene, polyesters, etc.

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Classification Based on Monomers

Homomer: In this type, a single type of monomer unit is present. For example, polyethene.

Heteropolymer or co-polymer: It consists of different types of monomer units. For example, nylon -6, 6.

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Classification Based on Molecular Forces

Elastomers: These are rubber-like solids, and weak interaction forces are present in them. For example, rubber.

Fibres: Strong, tough, high tensile strength and strong forces of interaction are present. For example, nylon -6, 6.

Thermoplastics: These have intermediate forces of attraction. For example, polyvinyl chloride.

Thermosetting polymers: These polymers greatly improve the material’s mechanical properties. It provides enhanced chemical and heat resistance. For example, phenolics, epoxies and silicones.

Important properties and applications of commercial polymers-polyethylene

01. Polyethylene, also known as polyethylene or polyethylene, is one of the most commonly used plastics in the world. Polyethylenes usually have a linear structure and are known to be addition polymers. The primary application of these synthetic polymers is in packaging. Polyethelyne is often used to make plastic bags, bottles, plastic films, containers, and geomembranes. It can be noted that over 100 million tonnes of polyethylene is produced on an annual basis for commercial and industrial purposes.

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The general formula of polyethylene can be written as (C2H4)n. The primary constituent of polyethylene is ethylene For the production of polyethylene, the typical specifications involve less than 5 parts per million of oxygen, water, and other alkenes. However, other compounds can be present during the polymerization reaction as contaminants. Some commonly accepted contaminants during the production of polythene include nitrogen, methane, and ethane.

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Since ethene is a relatively stable molecule, its polymerization requires suitable catalysts. It is important to note that the conversion of ethylene into polyethylene is highly exothermic in nature.

Physical properties of Polyethylene:

• The mechanical strength of polyethylene is relatively lower than other plastics. The rigidity and the hardness of these polymers are also relatively low.
• Polyethylene is known to be highly ductile. Furthermore, this plastic is known to possess very high impact strength.
• This synthetic polymer exhibits strong creep when placed under a persistent force.
• Polyethylenes usually have a waxy texture.
• The melting points of commercial grades of high-density polyethylene (HDPE) and medium-density polyethylene (MDPE) lie in the range of 120 – 180 degrees Celsius.
• The melting point of the commercially available low-density polyethylene (LDPE) usually lies in the range of 105 – 115 degrees Celsius.
• Polyethylene is known to be a very good insulator of electric current since it offers high electrical treeing resistance.

Applications of Polyethylene:

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• The most important application of polyethylene is in packaging products. This plastic is often employed for the production of plastic bags, plastic films, bottles, geomembranes, and containers.
• Polyethylene is also used in crates, trays, jugs that carry milk or fruit juices, and other food packaging products.
• High-density polyethylene is used in toys, garbage containers, ice trays, and other houseware. The versatility of this plastic makes it ideal for a wide spectrum of applications.
• HDPE is also used in ropes, fishing nets, agricultural nets, and industrial fabrics. It is not uncommon for this plastic to be used in wirings and cables as well.
• Low-density polyethylene (LDPE) is widely used in the production of squeeze bottles, garbage bags, laminations, and food packaging due to its high flexibility and low cost.
• LDPE is also used in pipes and fittings. It is ideal for such applications due to its low water absorption and also due to its plasticity.
• Polyethylene is also used for cable jacketing since it is a good insulator of electric current.

02. Polyvinylchloride, also known as PVC is the third most extensively produced synthetic polymer globally, with around 40 million tonnes produced yearly.

It is widely used to produce pipes, wire and cable insulation, medical devices, etc.

Polyvinyl Chloride is a white, brittle solid material available in form of powder or granules.

It is lightweight, durable, low-cost, and can easily be processed.

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The general formula of polyethylene can be written as (C2H4)n. The primary constituent of polyethylene is ethylene For the production of polyethylene, the typical specifications involve less than 5 parts per million of oxygen, water, and other alkenes. However, other compounds can be present during the polymerization reaction as contaminants. Some commonly accepted contaminants during the production of polythene include nitrogen, methane, and ethane.

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Since ethene is a relatively stable molecule, its polymerization requires suitable catalysts. It is important to note that the conversion of ethylene into polyethylene is highly exothermic in nature.

Physical properties of PVC:

• PVC is a lightweight, durable, and abrasion-resistant material by nature.
• All inorganic chemicals have no effect on this flexible thermoplastic polymer.
• Due to its high dielectric strength and vapor barrier capacity, PVC is an excellent insulation material.
• It is resistant to adverse weather conditions, stress, and corrosion.
• PVC materials have an inherent flame-retardant property.
• It has high tensile strength and is naturally stiff.
• It is a cost-effective option.
• It requires less maintenance and is resistant to grease and oil.
• Because the durability is higher, the product will last longer.
• Because of the high chlorine concentration, PVC goods self-extinguish.
• PVC can be made more flexible and softer by adding plasticizers such as phthalate, and it can be bent to meet the user's needs.

Applications of PVC:

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• Plasticized PVC is utilized in flooring, while unplasticized PVC (PVC-U) is used to make window frames.
• PVC is used to make sewage pipes and other pipe applications where the usage of metal is prohibitively expensive or vulnerable to corrosion.
• It is utilized in various industries, including construction, electronics, electrical cables, automotive, medical, and packaging.
• Aprons, shower curtains, raincoats, jackets, and sports bags are all made from PVC fabric.
• It is utilized in garden hoses and faux leather upholstery.
• PVC is used in the construction industry for electrical wire insulation or flooring in hospitals, schools, houses, and other sectors where a hygienic atmosphere is necessary.

03. Polystyrene, also known as PS is (C8H8)n is a synthetic aromatic hydrocarbon polymer with the chemical name Polystyrene.

Polystyrene is a hard, brilliantly transparent, stiff resin. It is produced by the polymerization of styrene and is the most widely used plastic. At room temperature, the thermoplastic polymer is a solid but when heated above 100 °C it flows. It becomes rigid again when it cools down. Polystyrene is insoluble in water.

Applications of PS:

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• Medically it is used for sterilizing test tubes, diagnostic components, and other medical devices.
• It is used to manufacture car parts which include knobs, instrument panels, sound dampening foam, etc.
• Polystyrene foodservice packaging keeps the food fresh for a longer period of time and is less expensive than alternatives.
• It is used in packaging consumer goods such as DVD cases, and egg cartons, to protect against spoilage or damage.
• It provides thermal insulation and is used in refrigerators, freezers, etc.
• Used in housing in all IT equipment such as Television, computer, etc.

04. Nylon

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Nylon is the most useful synthetic material with applications varying from daily life activities to industries. It is a plastic which can be drawn into fibres or moulded into daily products for making amenities. We can live our entire life with nylon on our side. You hop across the nylon carpet to the kitchen, eat your breakfast on a nylon bowl after cleaning your teeth with a toothbrush whose bristles are made of nylon. A nylon umbrella over your head is used to move out of the house in heavy sunlight or to keep out of the rain.

Properties of Nylon:

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• Lustrous - तेजस्वी
• Elastic
• Very strong
• Damage resistant to oil and many chemicals
• Resilient - लवचिक
• Does not absorb water
• Dries quickly

Applications of Nylon:

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• Clothing – Shirts, Foundation garments, lingerie, raincoats, underwear, swimwear, and cycle wear.
• Industrial uses – Conveyer and seat belts, parachutes, airbags, nets and ropes, tarpaulins, thread, and tents.
• It is used to make a fishnet.
• It is used as plastic in manufacturing machine parts.

05. Polyesters

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Polyester is a class of polymer.

Polyester in its primary chain contains polymers.

The fibres of polyester in a combination with natural fibres are used for clothing purposes.

Natural polyesters and a few synthetic polyesters are biodegradable.

The softness and texture of fibre depend upon the synthetic materials.

Polyesters are made in India, Korea, Taiwan, Japan and Indonesia.

Properties of Polyesters :

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• Polyester retains its shape
• Polyester is durable
• Polyester can be coarse
• Polyester is non-biodegradable
• Polyester is moisture resistant

Applications of Polyesters:

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• Polyesters are majorly used in clothing fabrics.
• Polyester is required for manufacturing types of car tyre reinforcements.
• Polyester utilized in the manufacturing of home furnishing materials.
• Polyesters are also used in the manufacture of dielectric films and film insulation
• Polyester is also used in upholstered furniture.

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06. Silicones

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Silicones are polymers that are also known by the name polysiloxanes.

These are the polymers that involve any inert, synthetic compound made up of iterative units of siloxane.

It is a chain of alternating oxygen and silicon atoms that are frequently combined with hydrogen and carbon.

The general formula of silicone is (R2SiO)x, where R belongs to any one of the organic groups.

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Properties of Silicones :

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• Silicones have low thermal conductivity and chemical reactivity.
• Their toxicity is also low.
• It can repel water and form watertight seals.
• It has high resistance to oxygen, ozone, and ultraviolet (UV) light.
• It has both electrically insulative and conductive properties.
• It has high gas permeability and high thermal stability
• They are superior solvents for organic compounds.

Applications of Silicones:

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• Personal Care Products - Silicones are used in cosmetics, shampoos and conditioners to retain the color and luster of the compound. Silicones have been said to offer better shine, and skincare products can be made with stronger SPF.

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• Construction Materials - Silicones are used extensively as a construction material for erecting commercial and residential buildings. They are said to prevent damage from moisture and bacteria build-up.

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• Electronics - Silicones can be found in keypads, keyboards and copier rollers. Many other components of computers, mobile electronics and home entertainment equipment make use of silicones. LED lighting technology is made possible by silicones. It has high thermal stability and excellent dielectric properties. So, it is used in a variety of electrical transmission applications.

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• Solar Panels and Photovoltaic Devices - Silicones are ideal materials that are used to improve the efficiency, durability and performance of solar panels and photovoltaic devices. They can basically withstand the sun for years.

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• Aviation Industry - Due to its high stress and temperature resistivity, silicone adhesives and sealants are practically used to seal and protect many parts of an aeroplane. It is used as a sealant in windows, doors, overhead bins, fuel tanks, engine gaskets, hydraulic switches, wings, wing edges, landing gear, electrical devices, vent ducts and even in black boxes.
• Kitchenware - Silicone bakeware and cookware are available widely and used in the kitchen to prepare different dishes. These utensils do not affect food taste or quality.
• Paints and Coatings - Today, there are silicone-enhanced paints available in the market. These types of paints help to keep the exterior coatings of houses, bridges and railway cars flexible, so they can withstand different temperature cycles or weather conditions and especially prevent cracking. Silicone coatings are less likely to corrode.
• Sporting Apparels and Goods - Silicones are used in goggles and diving masks. Silicones are a lightweight, durable, water repellent and high-performing material. With such properties, silicones can be used to design new sportswear and goods.
• Toys - Silicones are used in making different types of toys.