Non-metallic Engineering Material

Ceramics

Ceramics are generally made by taking mixtures of clay, earthen elements, powders, and water and shaping them into desired forms. Ceramics are inorganic non-metallic materials that are processed and used at high temperatures. Common examples are earthenware, porcelain, and brick. The earliest ceramics made by humans were pottery objects (pots or vessels) or figurines made from clay, either by itself or mixed with other materials like silica, hardened and sintered in fire. Later, ceramics were glazed and fired to create smooth, coloured surfaces, decreasing porosity through the use of glassy, amorphous ceramic coatings on top of the crystalline ceramic substrates.

Properties of ceramic

Physical Properties

The physical properties of any ceramic substance are a direct result of its crystalline structure and chemical composition. Ceramics are physically hard and have resistivity towards wear and tear. Ceramics are opaque.

Chemical Properties

The components present in ceramics such as oxides, carbides, etc. give high chemical stability to ceramics. Most of the constituent oxides are usually resistant to highly oxidising and reducing atmospheres. Ceramics have high melting point.

Mechanical Properties

Ceramics are brittle solids. Ceramics are very resistant to compression. They have low thermal shock resistance. They also have low thermal expansion.

Electrical Properties

Oxide ceramics are generally bad conductors or insulators in their normal oxidation states. The non-oxide ceramics act as semiconductors.

 

Constituents of ceramics

Ceramics mainly constitute of three basic raw materials. They are clay, feldspar and sand.

Clay

Clays are generally used in the production of porcelain, earthen ware, etc. Clays are mouldable when finely pulverised and wet, rigid when dry and vitreous when fired at a higher temperature. Based on their structure, clays are classified into the following three major types of minerals:

Kaolinite (Al₂O₃.2SiO₂.2H₂O)

Montmorillonite (Mg.Ca)O.Al₂O₃.5SiO₂.nH₂O

Illite K₂O.MgO.SiO₂.H₂O

There are many types of clays available such as fire clay, ball clay, pottery clay, kaolin or China clay, bentonite, etc. Kaolin, pottery clay and ball clay are most important clays for ceramics.

Feldspars

Feldspars are widely spread in the earth’s crust. Feldspars do not occur in pure state in nature. Potash feldspar, sodium feldspar and lime feldspar are most commonly used in ceramic industry.

Silica

Silica is the third main constituent of ceramic material. Silica occurs in the form of quartz in volcanic rocks and consequently also in clays. Silica is used in ceramic industry in the form of sand or sandstone.

Engineering application of ceramic

Compared to metals and plastics, ceramics are hard, non-combustible and inert. Thus, they can be used in high temperature, corrosive and tribological applications.

Construction products: Tiles, bricks, etc.

Refractory Environments that have high-temperature applications such as crucibles, moulds, etc.

Concrete is also ceramic material is used in most buildings and other civil engineering applications.

Whiteware products: including pottery, stoneware, fine china, porcelain, and other tableware, etc.

Glass is also a type of ceramic.

Fibre glasses.

Ceramic insulation.

Types of ceramics

Structural ceramics: Structural ceramics are mainly used in constructing buildings and various other structures. For example: Building bricks, brick blocks, roof tile, ceramic slabs for floors, sewer pipes, etc.

Facing material: Articles used for internal and external facing of buildings and structures e.g. facing bricks and slabs and oven tiles.

Fine Ceramics: Porcelain wares and glazed pottery are included in this class. They are used domestically, electrically and in laboratories.

Special ceramics: A group of articles with specific properties utilised in radio industry, aviation instrument manufacture, etc.

In general, ceramics is also classified in following groups. They are as follows:

Terra cotta: Terra cotta includes all pottery ware made from common clays. Terra cotta comprises all porous pottery ware which are not covered with a glaze. It is not subjected to higher temperatures to allow the body of the ware to become impermeable to liquids. It can be scratched by a hard steel. Common bricks and tiles belong to this class.

Earthen ware: All properties that are porous made from red burning clays and white clays coated with a glaze are included in earthen ware. Earthenware is clay fired at relatively low temperatures of between 1,000 to 1,150 degrees. This results in a hardened but brittle material which is slightly porous (small holes through which liquid or air can go through), therefore cannot be used to contain water.

To remedy this, a glaze is used to cover the object before it is fired in the kiln for a second time and rendered waterproof.

Stone ware: Stoneware is made from a particular clay which is fired at a higher temperature of 1,200°C. This results in a more durable material, with a denser, stone-like quality. The finished product will be waterproof and unlike earthenware, does not need to be glazed.

Porcelain: Porcelain comes from a refined clay which is fired at very high temperatures of approximately 1,200^o–1,450°C. The result is an extremely hard, shiny material often white and translucent in appearance.

The earliest forms of porcelain originated in China around 1600BC and this association popularised the term 'fine China’, or bone China when the porcelain has had ground animal bone added to the clay, in order to create an even more durable material.

Refractories

Refractories are any material that has high melting point and that maintains its structural properties at very high temperatures. It can withstand high temperatures without softening or suffering a deformation in shape. Refractories are material which retain their mechanical properties even at 1,000°C. These are also used in making various parts of industrial furnaces, ovens and apparatus for operating at high temperatures.

Properties of refractories

Refractoriness: It is the property of refractory to resist high temperature and corrosion. It withstands the action of heat without appreciable deformation or softening under high temperatures.

Thermal spalling: Refractories are also resistant to thermal shock. Its expansion and contraction is not sudden. It is uniform with rise and fall of temperature.

Chemical inertness: It resist the scraping action of gases, molten metals and slags. It is chemically inert towards corrosive action of gases and molten metals.

Resistance to abrasion or erosion: Refractories are abraded by descending hard, charge, flue gases, particles of carbon, etc.

Thermal conductivity: Refractories are very good conductor of heat. This property is very important for designing of furnace.

Electrical conductivity: The refractory material should have low electrical conductivity.

Types of refractories

Based on the chemical properties of their constituent substances, refractories are classified into three categories:

Acid refractories: These refractories consist of acidic materials like alumina Al₂O₃ and silica SiO₂. They are not attacked by acidic materials, but mostly attacked by basic materials. Silica is the primary constituents of acid refractories. Example: alumina, silica and fire clay refractories

Basic refractories: It consist of basic materials like Cao, MgO etc and are especially resistant to basic slag. Example: Magnesite, dolomite refractories

Neutral refractories: Made from weakly basic/acidic materials like carbon zirconia (ZrO₂) and chromium (FeO.CrO₂). Example: zirconia, SiC(carborundum) refractories

Application

ü  Refractory materials are used in linings for furnaces, kilns, incinerators and reactors.

ü  They are also used to make crucibles and moulds for casting glass and metals and for surfacing flame deflector systems for rocket launch structures.

ü  Today, the iron- and steel industry uses approximately 70% of all refractories produced.

ü  Manufacturing of cement, glass, paper, metals.

Uses depending upon type of refractories

Fire clay bricks

A fire brick is a special type of brick made using fire clay and has a good resistance against high temperatures which are used in kilns, lining furnaces, fireplaces and fireboxes. These are made from finely ground soft plastic material fire clay (Al₂O₃.2SiO₂.2H₂O) with powdered calcined fire-clay called grog. Generally, composition of flag ranges from 53% SiO₂ and 35% Al₂O₃ (feebly acidic) to 55% Al₂O₃ and 40% SiO₂ (nearly neutral brick).

Properties of fire clay brick

ü  Fire-clay bricks are light yellow to reddish brown in colour depending on the contents of iron oxides.

ü  They are slightly acidic in character because of SiO₂ content.

ü  They possess low porosity and lower refractoriness than silica bricks.

ü  High crushing strength.

ü  Good resistance to thermal spalling and thermal shocks.

Uses

ü  Used in construction of blast furnace

ü  Stove, oven and crucible furnaces

ü  Boilers and charging doors

Silica bricks

Contains 90% to 95% SiO₂ and about 2% lime is added during grinding to furnish the bond. Basic materials used for their manufacturing are quartz, sand, sand stone, etc. Siliceous rock is crushed and about 2% lime is added. The thick paste so formed is then moulded into bricks by a mould. The bricks are then dried and burnt. The temperature is slowly raised during heating. Cooling of these bricks is a slow process which takes over a week.

Properties

ü  Silica bricks are yellowish in colour with brown speck.

ü  Silica bricks contains about 25% pores.  

ü  Silica bricks never contract when in use but have permanent expansion about 15% when reheated and then gets back to original size when cooled.

ü  Silica bricks must be heated at 1500⁰ C for 12 hours or it will expand to 17% during use which will collapse the refractory structure.

ü  Silica bricks have homogeneous structure.

ü  High load bearing capability even at higher temperatures

Uses

ü  Roofs of open-hearth furnaces

ü  Copper stoves

ü  Lining of acid converters

ü  Glass furnaces

Masonry bricks

There is various type of bricks used in masonry

ü  Common burnt clay

ü  Sand lime bricks

ü  Engineering bricks Concrete bricks

ü  Fly-ash clay bricks

Common burnt clay bricks: The common burnt clay bricks are constructed by pressing clay into moulds to make the shape, and then dried and fired in a kiln. They are often used in general constructions that don’t require any special aesthetic qualities – walls, for example. They have no distinctive qualities, and when used in walls, will require plastering and rendering.

Sand lime bricks: To make sand lime bricks, sand, fly ash and lime are mixed up, and then during wet mixing a chemical reaction takes place to bond the mixtures. The wet mix is then poured into a mould. Sand lime bricks offer a more uniform appearance and a smoother finish than common burnt clay bricks, which means that they don’t require plastering when used for walls. On top of this, sand lime bricks are immensely strong, so work well as load-bearing members. Rather than being red in colour, sand lime bricks offer a grey aesthetic.

Engineering bricks: Engineering bricks have an immensely high compressive strength, which when coupled with the brick’s low water absorption makes it immensely popular for use in areas that are likely to be exposed to the elements. These bricks are manufactured at high temperatures to form  a dense and strong brick that is damp-proof and has resistance to chemicals. Engineering bricks are often used for civil engineering, including for ground works, sewers, retaining walls and for damp-proof courses. Class A engineering bricks are the strongest, but Class B are the more commonly used. Engineering bricks vary in colour from red to blue.

Concrete bricks: Concrete common bricks have low compression strength and tend to be low quality. While these bricks can be used for facades, fences and internal brickwork thanks to their minimal maintenance requirements, noise reductions and heat resistance qualities. Generally speaking, common bricks shouldn’t be used below ground.

Fly ash brick: Fly ash clay bricks are manufactured, as the name suggests, with both clay and fly ash, and the construction process sees the temperature reaching 1,000 degrees Celsius. When these bricks come in contact with moisture, they have been known to expand, which can be problematic, but in general these bricks are less porous than clay bricks and are considerably more affordable. Fly ash clay bricks have a smooth surface and thin joints so don’t need to be plastered when used for walls.

Composite materials

composite material is a solid material that results when two or more different substances, each with its own characteristics, are combined to create a new substance whose properties are superior to those of the original components in a specific application. Each class of engineering materials has its own outstanding and distinct characteristics as well as limitations. For a specific requirement, technologist have developed a new class of material called composite.

Properties

High strength to weight ratio: Fibre composites are extremely strong for their weight.

Lightweight: Composite material are very lightweight.

Fire resistance: The ability for composites to withstand fire has been steadily improving over the years. There is two types of systems to be considered:

Fire Retardant: Are self extinguishing laminates, usually made with chlorinated resins and additives such as Antimony trioxide. These release CO₂ when burning so when the flame source is removed, the self extinguish.

Fire Resistant: More difficult and made with the likes of Phenolic Resins. These are difficult to use, are cured with formaldehyde, and require a hi degree of post curing to achieve true fire resistance.

Electrical properties: Composites are insulators and do not conduct electricity. This is a very important property of composite.

Stiffness: Composites have good ability to resist elastic deformation on loading. Composites have good resistance to corrosion and can withstand extreme temperature conditions.

Types of composites

The classification of the composite materials depends on the type of reinforcement they are using. These reinforcements are set into a matrix that holds them together.

Mud bricks for Construction: These are the examples of composite materials by the ancient humans in the early times. A brick made from only the mud is sturdy and resistant to the compression, but it has less flexibility, and it breaks when bent.

Fibreglass: Small glass shards make it up and resin and other components hold it together. It is important for making body kits in the automobile industries. The body shell of the car is made of different layers of fibre glasses. It is also a less expensive alternative when we compare it to other materials.

Particulate composites: Particulate composites are made by dispersing particles of varying size and shape of one materials in a matrix of another material.

Natural composites: Composites that are easily found in nature are natural composites. For example, wood. These fibres are found in cotton and thread, but the wood is much tougher because of the bonding power that it gets from the lignin. Many types of large rocks also fall under the category of natural composites.

Application of Composite Materials

ü  These materials basically come in use for the construction of the bridges, buildings, and many other structures.

ü  Such as swimming pool panels, boat hulls, bodies of some racing cars, stalls of the shower, bathtubs, cultured marble sinks, storage tanks, imitation granites, and countertops.

ü  The best examples perform routinely on the spacecraft and the aircraft in a demanding environment.

Adhesives

Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. Adhesive is a substance used for sticking two unlike bodies together, due to the molecular forces existing in the area of contact.

Adherends: The body held together by adhesive is known as adherends.

Bonding: The process of holding one adherent to another by adhesive is called bonding.

Bond: Final assembly of two adherends and adhesive is called bond or joint.

Properties of adhesive

Tackiness: A good adhesive should have a good degree of stickiness.

Rapidity of bonding: A good adhesive should create a bond between adherends rapidly.

Strength of bond: A good adhesive should form a strong bond between adherends.

Durability: A good adhesive should create a bond between adherends that last long.

Advantages

Adhesive can be applied to any materials.

ü  The structure formed by adhesives are free from residual stress.

ü  The bond formed by adhesive is durable

ü  Adhesive introduce electrical insulation between bonding surfaces.

ü  Adhesive formed quick bonds between adherends.

ü  Metal joined by adhesive can resist corrosion

ü  Adhesive joints are leak proof for gases and liquids.

Limitation of adhesive

ü  Most of the adhesive are organic materials, so the bond formed by adhesive weakens at high temperatures.

ü  Careful selection of adhesive for particular material is necessary

Examples of adhesive

Phenol-formaldehyde resin: Phenol formaldehyde is also known as phenolic resin. These resins are made by reacting phenol with formaldehyde. Phenol is nothing but an aromatic alcohol derived from benzene and formaldehyde is a reactive gas from methane.

Properties

ü  The bond formed by this adhesive is hard

ü  The bond formed by phenol formaldehyde is highly resistant to the action of insects, fungi, water, etc.

ü  They possess good moisture resistance.

Application

ü  Phenol-formaldehyde resins make excellent wood adhesives for plywood and particleboard because they form chemical bonds with the phenol-like lignin component of wood.

ü  They are especially desirable for exterior plywood, owing to their good moisture resistance.

ü  Phenolic resins, invariably reinforced with fibres or flakes, are also moulded into insulating and heat-resistant objects such as appliance handles, distributor caps, and brake linings.

Urea formaldehyde: Urea-formaldehyde resin is obtained by chemical combination of urea (a solid crystal obtained from ammonia) and formaldehyde (a highly reactive gas obtained from methane). Urea-formaldehyde resins are used mostly as adhesives for the bonding of plywood, particleboard, and other structured wood products. In industrial production, urea resins are made by the condensation of formaldehyde and urea in an aqueous solution, using ammonia as an alkaline catalyst. The condensation reaction gives a colourless, syrupy solution that can be spray-dried to a powder for later use in coatings or adhesives.

Properties

ü  Urea formaldehyde is a transparent syrup compound.

ü  The bond formed by urea formaldehyde is quite strong

ü  The bond formed by urea formaldehyde is resistant to moisture, insects and fungi.

ü  Action of acid or alkalis deteriorate the resin film after some time.

Application

ü  For bonding wooden surfaces

ü  For bonding ply-woods

ü  For bonding laminates

ü  Articles of aircraft and ship industries

Epoxy resin: Epoxy resins, also known as poly epoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. Epoxy compounds may be used in solid or liquid form. They are modified by adding some external compounds like unsaturated fatty acid or amine and some solvent. The solvent evaporates, leaving evaporates, leaving behind a very thin film which possess excellent adhesion.

Properties of epoxy resin

ü  Epoxy resin have ability of getting cured without the application of external heat

ü  Epoxy resin have good resistance to chemicals

ü  They have low shrinkage during curing

ü  They possess good electrical resistance

Application

ü  For bonding glass

ü  For bonding metallic articles

ü  For bonding ceramic articles

ü  Used in aircraft industry