1. What are metallic glasses?
Metallic glasses are amorphous metals [Glassy metals]. It is a non-crystalline alloys with molten liquid state. It has the short range of atomic order.
Metallic glasses share the properties of both glasses and metals. These are strong, ductile, malleable, opaque and brittle.
2. Define Glass transition temperature.
It is the temperature at which liquid like structure is frozen into the solid. The glass transition temperature for metallic alloys is about 20°C to 30°C.
3. How the metallic glasses are prepared? Mention the different methods.
Metallic glasses are usually prepared by rapid quenching, ie., cooling a metallic liquid so rapidly such that there is no enough time for ordered crystalline structure to develop. By this way we retained the liquid like structure into the solid. The cooling rate is in the order of 2×106 Kelvin per second.
Methods of preparation
- Twin roller system
- Melt spinning system
- Melt Extraction system
Melt spinning system is the most commonly used method.
4. What are the types of metallic glasses?
Metallic glasses are classified into two types:
1.Metal – Metal metallic glasses
2. Metal – Metalloid metallic glasses
Fe, Co, Ni and B, Si ,C, P
5. What are the properties of metallic glasses?
- Amorphous phase
- Absence of grain boundaries
- Absence of dislocations
- Tetrahedral close packing [TCP] structure
Mechanical Properties
- Very high corrosion resistance
- High strength
- High workability
- Highly ductility
Electrical Properties
- High resistivity.
- No variation of resistance with temperature.
- The temperature coefficient may be zero or negative.
- Eddy current loss is very small.
- Soft and hard magnetic properties.
- Easy magnetization and demagnetization.
- High saturation magnetization.
- Low hysteresis loss.
- High corrosion resistant
- Reactive and stable
- Act as Catalyst
6. What is the advantages of the metallic glasses used as core material?
The reasons for choosing metallic glasses as transformer core
- Transformer core is used to get maximum magnetic flux (energy). Transformer core should have low hysteresis loss and low eddy current loss.
- Metallic glasses are available in thin sheets there fore the size and weight of the transformer is reduced.
- Hysteresis loss is directly proportional to the area of the hysteresis loop. The loop area of the metallic glasses is very small and also have high initial permeability. So, the hysteresis loss is almost zero.
- The eddy current in the core inversely proportional to the resistivity of the core material and directly proportional to the thickness of the lamination of the core. Since the resistivity of the metallic glasses is high and the thickness of the core laminated core is less. Therefore the eddy current loss is very less.
- Thus metallic glasses used as core material due to small thickness, smaller area, less weight high resistivity soft magnetic with low hysteresis and eddy current losses.
7. What are the applications of metallic glasses?
- Reinforcing elements in concrete, plastic, rubber
- Reinforcing filament in pressure vessels
- Construction of flywheels for energy storage
- Razar blades and different kinds of springs
- Tape recorder heads
- Cores of transformer
- Magnetic shields
- Generating Harmonics
- Motors
- Heavy magnetic fields
- Magnetic levitation effect
8. What are SMAs or Shape Memory Alloys? What are its Types?
The ability of some metallic alloys to retain their original shape when heating or cooling is called as Shape Memory Alloys (SMA). It is also called as smart materials or Intelligent materials or Active materials. There are two types of shape memory alloys,
- One way shape memory : It returns to its memory only when heating
- Two way shape memory: It returns to its memory on both heating and Cooling.
9. How the SMAs are Classified ? Give Examples of SMAs.
- Piezo electric SMA materials.
- Electrostrictive SMA materials.
- Magnetostrictive SMA materials.
- Thermoelastic SMA materials.
Examples: Ni−Ti alloy, Cu−Zn−Al alloy, Cu−Al−Ni alloy, etc.,
10. Give the principle of Shape memory Alloys.
The shape memory effect occurs between two temperature states. ie, Martensite and Austenite.
The SMA in the Martensite is attained the temporary deformed shape when cooling. But when heating the martensite state is changed into Austenite state. During deformation the resistivity, thermal conductivity, Youngs modulus and yield strength are decreased by more than 40%.
11. What are martensite and austenite phase?
Martensite, is the relatively soft and easily deformed phase of shape memory alloys, which exists at lower temperatures. It has two molecular structures
- Twinned martensite and
- Deformed martensite
Austenite is the stronger phase of shape memory alloys, occurs at higher temperatures. The shape of the Austenite structure is cubic.
12. Define shape Memory Effect?
Some metallic alloys exhibit plastic nature when they are cooled to very low temperature and they return to their original nature when it is heated. This effect is known as Shape Memory Effect.
13. Name the materials exhibit Shape memory effect?
Most effective and widely used alloys are:
- Ni Ti (Nickel-Titanium)
- Cu Zn Al
- Cu Al Ni
- Au−Cd
- Ni-Mn-Ga and
- Fe based alloys
14. What is pseudo elasticity?
When a metallic material is cooled from a temperature T2 to a lower temperature T1, it deforms and changes its shape. On reheating the material to Temperature T2, the shape change is recovered so that the material returns to its original state. This effect is known as pseudo elasticity or thermo elastic property.
15. Define Hysteresis of a SMA?
Hysteresis of a SMA is defined as the difference between the temperature at which the material is 50% transformed to austenite when heating and 50% transformed to martensite when cooling.
16. What is Super elasticity?
Super elasticity is a property of SMA. When a material is deformed at a temperature slightly greater than its transformation temperature super elasticity property appears.(Rubber like property).
17. What are the advantages and disadvantages of SMA?
Advantages
- SMAs are Simple, compactness and safety.
- SMAs have Good biocompatibility.
- SMAs are Strong and have high corrosion resistance.
- They have High power to weight ratio.
Disadvantages
- SMAs have Poor fatigue
- They are Expensive
- SMAs have Low energy efficiency
- SMAs have Complex control
- They Limited bandwidth.
18. What are the applications of Shape memory alloys?
- It is used as a thermostat valve in cooling system.
- It is used as a fire safety valve.
- It is used for cryofit hydraulic couplings.
- It is used for eye glass frame, toys, liquid safety valve.
- It is used to make microsurgical instruments, orthopedic implants.
- It is used as blood clot filter and for fracture pulling.
- It is used as antenna wires in cell phones.
19. What is Nano Technology or Nano Science?
Nanotechnology is a field of applied science and technology which deals with the matter on the atomic and molecular scale, normally 1 to 100 nanometers.
20. What are Nanomaterials?
Nanomaterials are the materials with atoms arranged in nanosized clusters which become the building block of the material. Any Material with a size between 1 and 100 nm[10-9 m to 10-7 m] is called nanomaterial.
21. What is Top-down approach? Give its Methods.
Top-down approach: The removal or division of bulk material or the miniaturization of bulk fabrication processes to produce the desired nanostructure is known as top- down approach. It is the process of breaking down bulk material to Nanosize.
Top – down Methods: Milling, Lithographics and Machining
22. What is Bottom-up approach? Give its Methods.
Bottom-up approach: Molecules and even nanoparticles can be used as the building block for producing complex nanostructures. This is known as Bottom-up approach. The Nano particles are made by building atom by atom.
Bottom up Methods: Vapour phase deposition, Molecular Beam epitaxy, Plasma assisted deposition, Metal Organic vapour phase epitaxy (MOVPE), Liquid phase process [Colloidal method and Sol-Gel method]
23. Mention the methods used to fabricate nanostructures?
- Milling
- Lithographics
- Machining
Bottom up Methods
- Vapour phase deposition
- Molecular Beam epitaxy
- Plasma assisted deposition
- Metal Organic vapour phase epitaxy [MOVPE]
- Liquid phase process [Colloidal method and Sol-Gel method]
24. What is milling ?
Large grained materials [metals, ceramics and polymers] in the form of powders are crushed mechanically in rotating drums by hard steel or tungsten carbide balls to produce nano grains is called milling. It is also called ball milling or mechanical alloying or mechanical attrition.
25. What are importance steps to be carried out in milling?
- Milling should be done in inert gas atmosphere to prevent from oxidation
- Milling should be carried out at room temperature for upto 150 hours.
26. What is chemical vapour deposition?
It is a method in which the reaction or thermal decomposition of gas phase species at elevated temperatures {500−1000°C} and subsequent deposition on to a substrate. In CVD method carbon nanotubes are grown from the decomposition of hydrocarbons at temperature range of 500 to 1200°C.
27. Define pyrolysis.
Pyrolysis is the chemical decomposition of organic materials by heating in the absence of oxygen or any other reagents particles separation due to heat.
Thin films of GaAs, InP and group III and V elements can be manufactured.
28. What is nonlinear optics?
Nonlinear optics (NLO) is the branch of optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light.
29. Give Some of the nonlinear optics phenomena.
Second harmonic generation (SHG), Third harmonic generation (THG), High harmonic generation (HHG),Sum frequency generation (SFG), Difference frequency generation (DFG), Optical parametric amplification (OPA).
30. What are the various nonlinear optics Processes?
Optical Kerr effect, Self-focusing, Kerr-lens modelocking (KLM), Self-phase modulation(SPM), Optical solitons, Optical phase conjugation and Multi-photon absorption.
31. Give examples of nonlinear optical materials.
Barium borate BaB2O4, calcite CaCO3, lithium niobate LiNbO3, magnesium fluoride MgF2, quartz SiO2, ruby Al2O3.
32. What is Birefringence?
Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. Birefringence is responsible for the phenomenon of double refraction whereby a ray of light, when incident upon a birefringent material, is split by polarization into two rays taking slightly different paths.
33. Define double refraction.
When a beam of ordinary un polarized light is passed through a calcite crystal, the refracted light is split up into two refracted race. The one which always obeys the ordinary laws of refraction and having vibrations perpendicular to the principal section is known as ordinary ray. The other, in general, does not obey the laws of refraction and having vibration in the principal section is called as extra-ordinary ray. Both the rays are plane polarized. This phenomenon is known as double refraction. the crystal showing this phenomenon are known as doubly refracting crystal.
34. What are the types doubly refracting crystals?
-
uniaxial and
-
biaxial
In uniaxial crystals there is only one direction(optics axis)along which the two refracted rays travel with the same velocity (examples are calcite, tourmaline and quartz.)
In biaxial crystals: there are two such direction along which the velocity’s are they same (Examples are topaz, aragonite etc.)
35. Give the name of optical devices which uses Birefringence.
Liquid crystal displays, Light modulators, Lyoț filter and Wave plates.
36. What is Kerr Effect?
- The Kerr effect was discovered by John Kerr in 1875.
- He discovered that some transparent substances (like nitrobenzene) which are otherwise isotropic, become doubly refracting under a strong electric field. Thus they rotate they plane of polarization of light passing them. This effect is known as Kerr effect.
- It is the changes in the refractive index linearly with the value of the applied electrical field. i.e., the change in the refractive index is proportional to the square of the applied electric field.
37. Define Kerr cell.
Kerr cell is a small container having two parallel electrodes immersed in a suitable insulating liquid (like nitrobenzene) with a high potential difference applied between them. The cell behaves as an uniaxial crystal with optic axis parallel to the line of force. The cell is placed between two crossed Nicol prisms N1 and N2. When a plane polarized light from Nicol prism N1 is passed through Kerr cell, it is broken up into two components.
| Read More Topics |
| Magnetic materials – Questions and Answers |
| Semiconducting material – Questions and Answers |
| Quantum physics – Questions and Answers |
