1. CHAPTER 3 Imperfection in Solids
Dr. Syafiqah Saidin
CHAPTER 3 Imperfection in Solids
SMBE3313
2017/2018 Semester 1

2. Solidification & Crystallisation Bonding Energy / Potential Energy
Dr. Syafiqah Saidin
OUTLINE
Defects in Solids
Solidification & Crystallisation
Bonding Energy / Potential Energy
Ionic Bonding
Covalent Bonding
Metallic Bonding
Secondary Bonding

3. Imperfection or faulty or deficiencies in crystalline solid materials.
Dr. Syafiqah Saidin
Defects in Solids
Defects in Solids
Imperfection or faulty or deficiencies in crystalline solid materials.
Crystal defect
Discontinuity in the lattice of a crystal caused by missing or introduction of extra atoms or ions, or by dislocations.
Defect types and amounts depend on composition, temperature, pressure, and processing history.

4. Solidification & Crystallisation
Dr. Syafiqah Saidin
Solidification & Crystallisation
Solidification
Hardening of materials from the casting of molten liquid/gels (metals and alloys).
Size and shape of the materials structure depend on its cooling rate.
Solidification process involves the formation of nuclei and the growth of nuclei to form grain and crystal structures.
nuclei
crystals growth
grain structure
liquid

5. Solidification & Crystallisation
Dr. Syafiqah Saidin
Solidification & Crystallisation

6. Solidification & Crystallisation
Dr. Syafiqah Saidin
Solidification & Crystallisation
Equiaxed grains
(Roughly same grain size
in all directions)
Columnar grains
(Elongated grains)
Fine grain is more strong than the coarse grain
Grain refiner is added to improve the uniformity of grains and to produces more equiaxed grains
Y. Yang et al., “Nanostructured ceramic composite coating prepared by reactive plasma spraying micro-sized Al-Fe2O3 composite powders”, Journal of Alloys and Compounds, vol. 509, pp. L90-L94, 2011

7. Polycrystalline Materials
Dr. Syafiqah Saidin
Polycrystalline Materials
Grain Boundaries
Interfaces between two grains or crystallites
Disadvantage : Site for the onset of corrosion and precipitation of impurities
Advantage : Prevent dislocation
Grain boundaries can be clearly seen through polishing and etching. Grain boundary atoms have higher energy than the bulks, resulting in more chemically reactive site
Grain boundaries
Crystallites

8. Polycrystalline Materials
Dr. Syafiqah Saidin
Polycrystalline Materials
Grain boundaries : Ti6Al4V
Grain boundaries : SS316L
Grain boundaries : graphene
Grain boundaries : diamond
H. Najar et al., “Increased thermal conductivity polycrystalline diamond for low-dissipation micromechanical resonators”, Micro Electro Mechanical Systems (MEMS), 2014 IEEE 27th International Conference, 2014
S. Saidin et al., “Polydopamine as an intermediate layer for silver and hydroxyapatite immobilisation on metallic biomaterials surface”, Materials Science & Engineering C, vol. 33, pp , 2013
A. Edrisy and K. Farokhzadeh, “Plasma nitriding of titanium alloys” in Plasma Science and Technology - Progress in Physical States and Chemical Reactions, editor: T. Mieno, 2016
L. P. BirÓ and P. Lambin, “Grain boundaries in graphene grown by chemical vapor deposition”, New Journal of Physics, vol. 15, 2013

9. Classification of defects
Dr. Syafiqah Saidin
Types of Defects
Classification of defects
Point defects (0D)
Line defects (1D)
Surface defects (2D)
Volume defects (3D)
Dimensionality
Vacancy atom
Interstitial atom
Impurities defect
Edge dislocation
Screw dislocation
Mixed dislocation
External surfaces
Grain boundaries
Twin boundaries
Stacking fault
Anti phase boundaries
Pores
Cracks
Foreign inclusions
Voids
Precipitates

10. Higher temperature Higher distortion Greater imperfection
Dr. Syafiqah Saidin
Point Defects 1
Vacancy : Empty lattice space due to missing of atom that cause plane distortion 2
Self interstitial : Squeezing of extra atom within interstitial lattice site that cause plane distortion
Substitutional
Higher temperature Higher distortion Greater imperfection

11. Dr. Syafiqah Saidin
Point Defects
Impurities defects : Interstitial impurity and substitution impurity 3
Interstitial impurity : Squeezing of extra impurity atom within interstitial lattice site that cause plane distortion
(e.g., C in Fe) 4
Substitution impurity : Substitution of impurity atom into crystal lattice that cause plane distortion
(e.g., Cu in Ni)

12. Line Defects Line Defects : Dislocations
Dr. Syafiqah Saidin
Line Defects
Line Defects : Dislocations
Misalignment of atoms due to application of stress/force that cause slip between crystal planes
Produces permanent (plastic) deformation
Burger’s vector, b is used to measure lattice distortion
Little dislocation: Lower the materials strength
More dislocation that entangle: Higher strentgh
Edge dislocation
Screw dislocation

13. Line Defects Edge dislocation
Dr. Syafiqah Saidin
Line Defects 1
Edge dislocation
Extra half-plane of atoms is inserted in a crystal structure b  to dislocation line

14. Dr. Syafiqah Saidin
Line Defects 2
Screw dislocation : Spiral planar ramp resulting from shear deformation b  to dislocation line

15. Line Defects Mixed Edge Screw
Dr. Syafiqah Saidin
Line Defects
Mixed
Edge
Screw 3
Mixed dislocation : The combination of both screw and edge dislocations

16. Discontinuity in structure of interfaces or grain boundaries, etc
Dr. Syafiqah Saidin
Surface/Planar Defects
Discontinuity in structure of interfaces or grain boundaries, etc 1
External surfaces : Obvious boundaries, along which the crystal structure terminates.
Surface atoms are not bonded to maximum number of nearest neighbors which lead to higher energy state than bulk atoms.
Surface atoms tend to minimize its surface area to reduce surface energy.
Two or more crystal mismatch
External surface defects

17. Visualization of grain boundaries under SEM
Dr. Syafiqah Saidin
Surface/Planar Defects 2
Grain boundaries : Disorientation of adjacent grain boundaries.
Usually occurs when two crystals begin growing separately and then meet.
Common defect in low density grain boundaries that cause high mobility, high diffusivity and high chemical reactivity.
Grain boundaries
Crystallites
Grain boundary: Region between crystal
Visualization of grain boundaries under SEM
M. O. Orlandi et al., “Nonohmic behavior of SnO2.MnO2-Based Ceramics”, Materials Research, vol. 6, 2003

18. Surface/Planar Defects
Dr. Syafiqah Saidin
Surface/Planar Defects 3
Twin boundaries : A reflection of atom positions across the twin plane.
Atomic displacement cause by shear forces which one side of a plane mirror the other side.

19. Surface/Planar Defects4
Stacking fault: Interruption in regular sequence of stacking.
Common example is in close-packed structures. Eg: FCC stacking structure is differ from HCP stacking structure.
Eg: For FCC metals, an error in ABCABC packing sequence arise when the stacking sequence become ABCBCABC.
Stacking fault

20. Surface/Planar Defects
Dr. Syafiqah Saidin
Surface/Planar Defects 5
Anti phase boundaries: Each side of boundary has an opposite phase while the crystallographic direction remains the same.
Eg: Normal stacking order is ABABABAB but for anti phase boundaries defect, the sequence will be ABABBABA.
Anti phase boundaries

21. Dr. Syafiqah Saidin
Volume Defects
Volume defects include pores, cracks, foreign inclusions and other phases.
Pores : Affect optical, thermal and mechanical properties
Cracks : Affect mechanical properties
Foreign inclusion: Affect electrical, optical and mechanical properties
Normally occurs during processing and fabrication processes.
Foreign inclusion
Pores
Crack
K. Sato et al., “Novel characterization procedure of large defect in ceramics,” The AZO Journals of Materials Online, vol. 2, 2006

22. Voids : Combination of several vacancies cause cluster void.
Dr. Syafiqah Saidin
Volume Defects
Voids : Combination of several vacancies cause cluster void.
Precipitates : Combination of impurities to form small region of different phase.
Precipitates
Impurity
Vacancy
Voids
B. A. Gurovich et al., “Investigation of high temperature annealing effectiveness for recovery of radiation-induced structural changes and properties of 18Cre10NieTi austenitic stainless steels,” Journal of Nuclear Materials, vol. 465, pp , 2015
Y. C. Lee et al., “Removal of malachite green by adsorption and precipitation using aminopropyl functionalized magnesium phyllosilicate,” Journal of Hazard Materials, vol. 192, 2011

23. Depends on type of microscope and size of defect
Dr. Syafiqah Saidin
All these defects are visible under microscopy examination !!!
Depends on type of microscope and size of defect

24. Microscopic Examination
Dr. Syafiqah Saidin
Microscopic Examination
To predict properties and composition of materials based on its morphology
To visualise structure of materials / morphology
PURPOSE
To design composite with new combination property
To understood association between properties and structure
To visualize defects and mechanical failure

25. Confocal laser scanning microscope
Dr. Syafiqah Saidin
Microscopic Examination
Light / Optical microscope :
Use visible light to magnify morphology.
Up to 1000x magnification depends on types of optical microscope.
Optical microscope
Compound microscope
Stereo microscope
Confocal laser scanning microscope
Build up of two lenses system for better magnification
Provides 3D images and common used in visualizing opaque object
Able to scan in depth parameter and stained elements

26. Microscopic Examination
Dr. Syafiqah Saidin
Microscopic Examination
Compound microscope Stereo microscope CLSM
H. Bugger et al., “Proteomic remodelling of mitochondrial oxidative pathways in pressure overload-induced heart failure”, Cardiovascular Research, 2vol. 85, pp , 2010
H. N. Ho et al., “Optimization and characterization of artesunate-loaded chitosan-decorated poly(D,L-lactide-co-glycolide) acid nanoparticles”, pp.1-12, 2015
heart failure

27. Microscopic Examination
Dr. Syafiqah Saidin
Microscopic Examination
Fluorescence microscope :
Use UV light to magnify morphology.
When UV light hits an object, it excites the electrons of the object, and they give off light in various shades of color.
S. Saidin et al., “Polydopamine as an intermediate layer for silver and hydroxyapatite immobilisation on metallic biomaterials surface”, Materials Science & Engineering C, vol. 33, pp , 2013

28. Microscopic Examination
Dr. Syafiqah Saidin
Microscopic Examination
Electron microscope :
Use beam of electrons to magnify morphology.
The beam strikes most objects in its path and increases the resolution for brighter intensity image. 
The electrons must travel in vacuum.
Electron microscope
Scanning electron microscope
Transmission electron microscope
High magnification and high resolution
The sample is coated with gold/platinum coating for better image resolution
High magnification and high resolution
The sample is cut into thin slice before the visualization process

29. Microscopic Examination
Dr. Syafiqah Saidin
Microscopic Examination
SEM TEM