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Tuesday, 3 December 2013

Plastic deformation mechanisms in metals

The permanent changes in shape and dimensions of metals can be carried out by plastic deformation mechanisms. Crystal structure and lattice parameters remain unaltered during plastic deformation. Plastic deformation increases the number of imperfections in metals. The two main processes involved in plastic deformation are slip and twinning. In slip, atoms move over a number of interatomic distances relative to their initial positions. The displacement step magnitude is equal to full interatomic distance. The orientation of displaced region and undeformed region remains the same. Movement by an atom is a fraction of interatomic distance in twinning process. The orientation of twinned region and untwined regions are not same. Slip mechanism is preferred during high temperature and lower strain rate cases. At lower temperature, high strain rate cases, twinning is employed.

Monday, 7 October 2013


Nanotechnology has already become an important field in the medical field for diagnostic and drug delivery applications. Carbon-60 molecules which are also known as fullerene promises good appliance in medical field. Cylindrical fullerenes are known as carbon nanotubes. Carbon nanotubes can be synthesized in many forms. Single walled nanotubes and multi walled nanotubes are two important materials. A carbon nanotubes bent into a torus is known as nanotorus. Carbon nanobuds are latest member in Nanomaterials category which is created by the combination of carbon nanotubes and fullerenes. Fullerene in the form of buds is connected to carbon nanotubes by covalent bonding in nanobuds. Bonding is achieved between fullerene buds and sidewalls of carbon nanotubes. The main application of nanobuds is in field emission applications since they are excellent field emitters. Since the fullerene buds prevents slipping of nanotubes, nanobuds can be used as molecular anchors.

Thursday, 4 July 2013

Spool valves

Control valves are required in pneumatic and hydraulic systems to direct and regulate the flow of fluid from compressor or pump to the various load devices. Relief valves are infinite position valves. Finite position valves are used for passage or blocking of fluid flow. There can be either two or four parts for control valves. The three major types of control valves are poppet valves, rotary valves and spool valves. Simple discs, balls and cones are used in poppet valves. The two varieties of poppet valves are 2/2 simple valve and 3/2 valve. Poppet valves are economical but require large operating force. Rotary valves are used for hand operation in pneumatic systems. They are compact and have low operating forces. Spool valves are constructed with a spool moving horizontally within the valve body. The spool can be easily moved as there is no net force acting on the spool due to system pressure. There are two types of spool valves. They are two-way spool valve and four-way spool valve. Spools are shifted during the operation of spool valves. For this, a button, lever or a solenoid is used.

Friday, 24 May 2013

Microwave tunnel diodes

Tunnel diodes can be used in microwave applications. Quantum tunneling theory is used to explain the tunneling phenomenon that take place in tunnel diodes.  Tunneling phenomenon is actually a majority carrier effect. Some of the advantages of tunnel diodes are low cost, less weight, high speed, low noise, high peak current to valley current ratio and low power operations. These parameters make tunnel diodes ideal candidate in applications like microwave amplification and microwave oscillation. The tunnel diode is a p-n junction semiconductor diode with negative resistance. Tunnel effect is responsible for this negative resistance. Heavy doping is employed during the construction of tunnel diodes. In tunnel diodes, Fermi level lie inside the valence band in p-region and inside the conduction band in n-region. While using for amplifier applications, tunnel diodes are connected either in parallel or in series with a resistive load. Another common practice is connecting tunnel diode to a microwave circulator.

Monday, 20 May 2013

Leaf springs

A spring is the component of a vehicle which serves the purpose of absorbing the shock developed while it is in motion. There are two varieties here. They are tension spring and compression spring. In a tension spring load is connected to one end leading to tension (extension). In a compression spring, the loading results in compression. Leaf springs are specially designed springs which are mounted on vehicles for suspension purposes.  A number of leaf springs bound by a nut and bolt arrangement is widely preferred in vehicles. Commonly used configuration is semi elliptical. On the application of load, friction is developed between the leaf plates. A casing around the leaf plate prevents the accumulation of dust and grit materials. To reduce friction, a lubricant, preferably grease with graphite is applied between the plates. To facilitate bending and springing, one plate is allowed to slide against another.

Wednesday, 24 April 2013

Polyvinyl alcohol

Polyvinyl alcohol commonly known as PVA is an important material in materials science research and textile industry. It is used as a facilitator for speedy mixing of ceramic oxides. The hydrolysis of polyvinyl acetate in the presence of acids or alkalies yields polyvinyl alcohol. There is always a chance of retaining around 2 mole percentage of acetyl groups in the end product. Polyvinyl alcohol is easily soluble in water. When it is reacted with iodine, gives an intense blue colour. It can be used in the production of emulsions since it is a good protective colloid for aqueous emulsions. The other industries which use polyvinyl alcohol are suspension systems industry and adhesive industry. In textile industry, it is used only after the treatment with a concentrated aqueous solution of sodium sulphate containing calculated amounts of sulphuric acid and formaldehyde. Superlative water absorption property makes PVA fibers more attractive. Some other properties of PVA fibers are superior dimensional stability, quick washing and drying property, resistance to abrasion and outstanding tenacity.