quasicrystal.pptx

Seminar

1. A Seminar On “ Quasicrystals ” Presented By: Premananda Marndi B.Sc. Chemistry 3 rd yr. Class Roll No : BS19-808 Exam Roll No: IB2219066 Under the supervision of: Dr. Gobinda Ch. Behera MPC Auto. College Takhatpur , Bpd., Mbj .

2. Contents Introduction Discovery Structure Properties Preparation Application

3. Introduction Classical view of solid-state Two types of solid states Crystalline Amorphous Structure

4. According to Crystallography Crystals occur with Long range order Holding a lattice which contains the atoms, ions or molecules with translational periodicity 1,2,3,4 and 6-fold rotational symmetries 5 ,7 and higher fold symmetries are forbidden

5. Discovery of quasicrystal Dan Shechtman , Philip Tobias Prof. Nobel prize, Chemistry 2011 In 1984, he first discovered a regular dodecahedron pattern, but was not allowed in crystallography and many crystallographers were not convinced. Prof. Psai prepared an alloy of Al and Mn ; (Al6Mn) with this pattern .

6. ‘Quasi’- resembling /pretending to be Quasicrystal: resembling or pretending to be crystal Quasicrystals are materials with long range order, but with no 3D translation symmetry They are typically binary or tertiary metallic aloys Some of their properties are similar to crystal and some have similarities with amorphous It is also called quasiperiodic crystal .

7. Structure Prof. Dan Shechtman claimed that he has observed an dodecahedron single grain with 5-fold symmetry The ratio of distances between the central and other spots is the Fibonacci no . known as golden mean Atomic positions are ordered, but with rotational symmetries e.g. 5,8,10 or 12-fold which are forbidden in crystal

8. Physical properties Properties are intermediate between crystalline and amorphous alloys. The alloys are harder than the individual components, are brittle. Have a very low co-efficient of friction (non-stick ) -> They have a very low surface tension Low electrical and thermal conductivity Resistant to oxidation and corrosion

9. Preparation Rapid solidification (Melt spinning) Conventional Casting Multi-layer deposition Mechanical alloying (Ball milling) Laser and electron melting method

10. Applications Surface non-stick coating and thin film -> C oatings of AlCuFe is deposited at high tempr . Surgical instruments Hydrogen storage -> TiZrNi can store a prodigious amount of hydgen . Heat insulation Protection against corrosion and oxidation Catalysis

11. New definition for crystal “…….By crystal we mean any solid having an essentially discrete diffraction diagram, and by aperiodic crystal we mean any crystal in which three- dimentional lattice periodicity can be considered to be absent.” Solid state: Crystalline Quasicrystal Amorphous Material Ordered Periodic Crystal   Quasicrystal  ꭓ Amorphous ꭓ ꭓ