Unit-5 notes in the topic of smart materials.pdf
- 3. Methods of production of Metallic Glasses Metallic glasses are manufactured by the following methods. They are, 1. Twin roller technique 2. Melt extraction technique 3. Melt spinning technique Melt spinning technique Principle Quenching is a technique used to form metallic glasses. Quenching means Rapid Cooling. Due to rapid cooling, atoms are arranged irregularly and from metallic glasses.
- 4. Melt spinning Technique A melt spinner consists of a copper roller over which a refractory tube with fine nozzle is placed. The metal alloy is melted by induction heating under inert gas atmosphere (helium or argon). The properly super heated molten alloy is ejected through the fine nozzle at the bottom of the refractory tube. The molten alloy falls on the copper roller which is rotated at high speed. Thus, the alloy is suddenly cooled to form metallic glass. In this method a continuous ribbon of metallic glass can be obtained. By increasing the disc speed and making ejection pressure constant, increases the width of the ribbon and decreases the thickness of the ribbon.
- 5. Glass transition temperature It is an important parameter for the preparation of metallic glasses. It is defined as a temperature at which the liquid like atomic structure is obtained into a solid. The value of glass transition temperature for metallic alloys is about 200C to 300C.
- 6. Structural Properties 1. They do not have any crystal defects such as grain boundaries and dislocations. 2. They have tetrahedral packed structure. These materials do not passes long range anisotropy Mechanical Properties 1. Metallic glasses are stronger than metals and alloys because they are free from defects and dislocations. 2. They have high corrosion resistance due to random ordering. 3. They have high elasticity and ductility. Properties
- 7. Electrical Properties 1. Electrical resistivity of metallic glasses is high and it does not vary with temperature. 2. Eddy current loss is very small due to high resistivity. 3. The Hall co-efficient of metallic glasses is found to have both positive and negative signs. Magnetic Properties 1. It obeys both soft and hard magnetic properties. 2. The core losses of metallic glasses are very small. Chemical Properties 1. They have high corrosion resistance. 2. They have catalytic properties. 3. They are highly reactive and stable
- 8. APPLICATIONS OF METALLIC GLASSES Metallic glasses have found wide applications in different fields because of their low coercivity and high permeability. Structural application They posses high physical and tensile strength. They are superior to common steels and thus they are very useful as reinforcing elements in concrete, plastic and rubber. Strong ribbons of metallic glasses are used for simple filament winding to reinforce pressure vessels and to construct large fly wheels for energy storage. Due to their good strength, high ductility, rollability and good corrosion resistance, they are used to make razor blades and different kinds of springs.
- 9. Electrical and Electronics It have soft magnetic properties, they used in tape recorder heads, cores of high- power transformers and magnetic shields. Used in motors can reduce core loss very much when compared with conventional crystalline magnets. Superconducting metallic glasses(Zr75Rh25) are used to produce high magnetic fields and magnetic levitation effect. It have high electrical resistance, they are used to make accurate standard resistance, computer memories and magneto resistance sensors. Metallic glasses have excellent magnetic properties. When they are used as transformer core.
- 11. Definition The ability of the metallic alloys to retain their original shape when heating or cooling is called as Shape Memory Alloys (SMA). These metallic alloys exhibit plastic nature when they are cooled to very low temperature and they return to their original nature when they are heated. This effect is known as Shape Memory Effect. It is also called as smart materials or intelligent materials or Active materials.
- 12. Share memory alloys (SMA’s) are metals, which exhibit two very unique properties, pseudo-elasticity and the shape memory effect. Arne Olander first observed these unusual properties in 1938 (Oksuta and Wayman 1998), but not until the 1960’s were any serious research advances made in the field of shape memory alloys. The most effective and widely used alloys include NiTi (Nickel – Titanium), CuZnAl and CuAlNi.
- 13. Phase of shape memory alloys Martensite and Austenite are two solid phases in SMA Martensite is relatively soft and it is easily deformable phase which exists at low temperature (monoclinic) Austenite is a phase that occurs at high temperature having a crystal structure and high degree of symmetry (cubic)
- 14. Types of SMA 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. Examples of shape memory alloys Generally, shape memory alloys are intermetallic compounds having super lattice structures and metallic- ionic-covalent characteristics. Thus, they have the properties of both metals and ceramics. Ni –Ti alloy (Nitinol) Cu –Al –Ni alloy Cu –Zn –Al alloy Au –Cd alloy Ni –Mn –Ga and Fe based alloys
- 15. CHARACTERISTICS OF SMA 1. Shape memory effect The change of shape of a material at low temperature by loading and regaining of original shape by heating it, is known as shape memory effect. The shape memory effect occurs in alloys due to the change in their crystalline structure with the change in temperature and stress.
- 16. 2.SMAs exhibit changes in electrical resistance, volume and length during the transformation with temperature. 3.The mechanism involved in SMA is reversible (austenite to martensite and vice versa.) 4. Stress and temperature have a great influence on martensite transformation. 2. Pseudo elasticity Pseudoelasticity occurs in shape memory alloys when it is completely in austenite phase. With no change in temperature, when the load on SMA is increased, it transforms to martensite from austenite. When the load is removed, it regains its original shape. Pseudoelasticity is also called as super-elasticity. It is non- linear.
- 17. Load induced phase change –Constant temperature
- 18. 3. Hysteresis The temperature range for the martensite to austenite transformation which takes place upon heating is somewhat higher than that for the reverse transformation upon cooling. The difference between the transition temperature upon heating and cooling is called hysteresis. The difference of temperature is found to be 10-50oC.
- 19. 4. Training shape memory alloys There are two types of training, One way trained shape memory alloy – It recovers its shape only when heating Two way trained shape memory alloy – It recovers its shape on both heating and Cooling.
- 20. ADVANTAGES OF SHAPE MEMORY ALLOYS They are simple, compact and high safe. They have good bio –compatibility. They have diverse applications and offer clean, silent and spark-free working condition. They have good mechanical properties and are strong corrosion-resistant. DISADVANTAGES OF SHAPE MEMORY ALLOYS They have poor fatigue properties. They are expensive. They have low energy efficiency.
- 21. APPLICATIONS OF SHAPE MEMORY ALLOYS 1. Microvalve (Actuators): One of the most common applications of SMAs is microvalves. Actuator is a microsensor that can trigger the operation of a device. The electrical signal initiates an action. 2. Toys and novelties: Shape memory alloys are used to make toys and ornamental goods. A butterfly using SMA moves its wings in response to pulses of electricity.
- 22. 3. Medical field: SMAs must not be vulnerable to degradation, decomposition, dissolution or corrosion in the organism and must be biocompatible. (i) Blood clot filters - When the SMA is in contact with the clot at a lower temperature, it expands and stops the clot and blood passes through the veins. (ii) Teeth braces - NiTi wire holds the teeth tight with a constant stress irrespective of the strain produced by the teeth movement. It resists permanent deformation even if it is bent. NiTi is non-toxic and non-corrosive with body fluid. (iii) They are used in artificial hearts, artificial hip joints, connecting broken bones and artificial muscles. (iv) They are employed for bone plates and marrow pins for healing bone fractures. (v) SMAs (NiTi) are used to make eye glass frames and medical tools. Sun-glasses made from superelastic Ni-Ti frames provide good comfort and durability.
- 23. 4. Antenna wires: The flexibility of super elastic Ni –Ti wire makes it ideal to use as retractable antennas. 5. Thermostats: SMAs are used as thermostat to open and close the valves at required temperature. 6. Cryofit hydraulic couplings: SMAs are used as couplings for metal pipes. 7. Stepping motors: Digital SMA stepping motors are used for robotic control. 8. Aircraft industry: Titanium-aluminium shape memory alloys offer excellent strength with less weight and dominate in the aircraft industry. They are high temperature SMAs, for possible use in aircraft engines and other high temperature environments.
- 25. DIFFERENT FORMS OF CARBON Allotropes of carbon a) Diamond b) Graphite c) C60 (Buckminsterfullerene or bucky ball) d) C36, C70, C76 and C84 – new carbon molecule e) Fullerenes- S.Lijima 1991- Carbon nanotube (CNT)
- 26. DIFFERENT FORMS OF CARBON
- 27. TWO WELL KNOWN FORMS OF CARBON
- 28. CARBON – GRAPHENE The hexagonal lattice of carbon - graphite Graphene- single sheet of graphite
- 29. CARBON NANO TUBES CNT – sheet of graphene is rolled up into a cylindrical shape
- 32. TYPES CARBON NANO TUBES (Based on structure)
- 33. • Zigzag- The angle Ө = 0 , by folding CNT parallel to x-axis • Armchair- The angle Ө = π/6 , by folding CNT perpendicularly. • Chiral - The angle Ө is anywhere between 0 and π/6 , by folding CNT tilted.
- 34. TYPES CARBON NANO TUBES (Based on number of walls)
- 35. PREPARATION OF CARBON NANO TUBES Laser ablation method • Graphite target placed inside the oven. • Oven filled with He or Ne gas with 500 torr pressure. • Nickel or cobalt added as catalyst. • Temp of oven – 1200oC • Laser evaporates carbon atom & it reaches copper cooled collector. • 10-20 nm diameter nanotubes formed. • Vary temp, process parameters, the nanotube diameter and size varied.
- 36. PROPERTIES OF CARBON NANO TUBES
- 37. Tensile strength is greater than steel. So they are elastic High thermal and electrical conductivity. Youngs modulus value is higher. Smaller carbon nanotube diameter results in increased chemical reactivity. They are very strong structures. They possess high melting point. PROPERTIES OF CARBON NANO TUBES
- 38. APPLICATIONS OF CARBON NANO TUBES They are used in energy storage devices because of their small dimension. CNT is used to store hydrogen They are used in creation of artificial muscle tissues. Alternative to tungsten filament in incandescent bulbs. Certain nanotubes exhibit superconducting effect. Multiwalled nanotubes with magnetite can generate strong magnetic fields. Nanotube films show promise for use in displays for computers, cell phones and automated teller machines(ATM)
- 39. APPLICATIONS OF CARBON NANO TUBES
- 40. APPLICATIONS OF CARBON NANO TUBES