ELEMENT - SMALLEST DIVISIBLE PART OF A SUBSTANCE METAL IDENTIFIATION TESTS - TO SEPARATE COMMON...
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Transcript of ELEMENT - SMALLEST DIVISIBLE PART OF A SUBSTANCE METAL IDENTIFIATION TESTS - TO SEPARATE COMMON...
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ELEMENT
- SMALLEST DIVISIBLE PART OF A SUBSTANCE
METAL IDENTIFIATION TESTS
- TO SEPARATE COMMON METALS– MAGNETIC TEST– VISUAL OBSERVATION TEST– HARDNESS TEST– SURFACE REFLECTIVITY TEST– WEIGHT PER VOLUME TEST– CHEMICAL REACTION TEST– SPARK TEST
ASTM, ASM, Al. Assn., ASME, Society of Automotive Engineers, AWS, ANSI, Aerospace Materials Specification, Federal Specification (WW) etc.
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MAGNETIC TEST Simple
Steel, Ni, Co, - magneticCu, Al, Tin, Zn, Cr, Mn- nonmagnetic
Exceptions too eg: Stainless steel
Corrosion resistant poor corrosion resistance.
No magnetic attraction highly magnetic
316 410
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VISUAL OBSERVATION TEST
o Compare with standards
o COLOUR,
o SURFACE,
o SECTION AFTER FRACTURE etc.
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HARDNESS TEST
FILE HARDNESS TEST- WITH FILE
USE SAMPLE AND COMPARE
OBSERVE SCRATCHES ON SURFACE
(eg: deep file scratches on structural steel, shallow on high carbon steel)
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SURFACE REFLECTIVITY TEST
A VISUAL TEST
Compare ability to reflect light.
(eg: Al & Mg.- Al more than Mg.
Lead-tin: more tin- more reflectivity
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WEIGHT PER VOLUME TEST
Small sample in a graduated container
Wt of metal/volume of water displaced
Compare with known samples
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CHEMICAL REACTION TEST
Test reaction with certain acids
–simple / complex
METALS HAND BOOK, VOL 11. by American Society for Metals
Eg: carbon content of carbon steel, test for Mn,
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SPARK TEST
To separate alloys containing known alloying elements
Eg: MS, carbon tool steel, Mn, S, Ni content steels etc.
Manganese Sulphur Nickel
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REFER DATA BOOK FOR STANDARDS-
SYMBOLS FOR DIFFERENT CLASSES
UNIFIED NUMBERING SYSTEMS FOR METALS AND ALLOYS-
SAE 1975
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STRUCTURE OF SOLID MATERIALSCLASSIFICATION OF SOLIDS
• SOLIDS CLASSIFIED AS CRYSTALLINE, AMORPHOUS OR A COMBINATION OF THE TWO.
• CRYSTALLINE- BUILT UP OF CRYSTALS OF SIMILAR/VARYING SIZES
• CRYSTAL AS LARGE TO FORM A COMPLETE BODY- SINGLE CRYSTAL
• AMORPHOUS- MOLECULES AS BASIC STRUCTURAL UNIT; PRINCIPAL CHARACTERISTIC MORE OR LESS DISORDERED; NO REGULARITY OF ARRANGEMENT- LOWER IN DENSITY
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CRYSTALLINE SOLIDS• During solidification, atoms arrange
themselves into ordered, repeating,
3 – dimensional pattern• Such structures called Crystals.
• Or, Crystal is said to have formed whenever atoms arrange themselves in an orderly 3- D pattern
• Rows can be identified – in various directions- along which atoms are regularly spaced.
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SCHEMATIC REPRESENTATION OF CRYSTAL LATTICE
Eg: all metals, salts, many oxides &
certain plastics
• Axes of this lattice are three lines at right angles to one another
• Lines that make up the lattice are parallel to the axes and equally spaced along them
• Atoms of a single cubic crystal occupy the lattice points- at intersections of the lines
• Atoms oscillate about fixed locations and are in dynamic equilibrium, rather than statically fixed.
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Three dimensional network of
imaginary lines connecting the
atoms called SPACE
LATTICE
Smallest unit having the full symmetry of the
crystal called- UNIT CELLLATTICE PARAMETERS- edges of unit cell and angles
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14 possible different networks of lattice points
All crystals based on these possible space lattices
BRAVAIS LATTICES
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Body Centered Cubic (BCC)
Face Centered Cubic(FCC)
Hexagonal Close Packed
(HCP/CPH)
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BODY CENTERED CUBIC• Atoms at corners,
one at geometric centre of volume, total-9 atoms
• Each corner atoms shared by 8 adjacent cubes
No. of atoms/cell= 2
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FACE CENTERED CUBIC• Atoms at corners, one
atom at centre of each face
• Each face atom shared by one adjoining cube
No. of atoms/ cell = 4
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HEXAGONAL CLOSE PACKED• Basic unit cell is
hexagonal prism• Three atoms in the form
of triangle midway between the two basal planes. When 6 equilateral triangles considered, 3 atoms on alternate triangles Total 17 atoms
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COORINATION NUMBERNo. of equally spaced nearest neighbours that each atom has in a
given crystal structure
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ATOMIC PACKING FACTORRatio of volume of atoms to volume of unit cell
no. of atoms /unit cell X volume of atom
Volume of unit cell Centre and corner atoms touch one another along cube diagonal. a and R are related through a = 4R/√3
Thus,in BCC, a = 4R/√3 and APF = 0.68
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For FCC, a = 2R√2
APF = 0.74
Similarly,
For HCP, APF = 0.74
4R a
a
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CRYSTAL STRUCTURE- EXAMPLES
STRUCTURE METALS
BCC Molybdenum, Tantalum, Tungsten, Chromium, alpha iron
FCC Copper, Aluminum, Silver, gold
HCP Cadmium, Cobalt, Titanium (α), Zinc
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HCPHCP
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Knowledge of crystal structure
For computing theoretical density ρ
AcNV
nA
Where n = number of atoms associated with each unit cellA = Atomic weightVc= volume of the unit cellNA= Avogadro’s number (6.023 X 1023 atoms/mol)
Eg: Copper- FCC - atomic radius = 0.128nm (1.28A0) Atomic weight= 63.5g/mol
Here, n = 4, A= 63.5 ; for FCC, Vc = a3 ; a = 2R √2,
ρ = 8.89 g/cm3
The value from tables is 8.94 g/cm3
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CRYSTALLOGRAPHIC DIRECTIONS A LINE BETWEEN TWO POINTS, OR A VECTOR.
STEPS IN DETERMINING THE 3 DIRECTIONAL INDICES:1. A vector of convenient length is positioned such that it passes
through the origin of the coordinate system. Any vector can be translated without alteration, if parallelism maintained.
2. The length of the vector projection – on each of 3 axes- is determined, measured in terms of unit cell dimensions
3. These 3 nos. are multiplied/divided by common factor to reduce to smallest integer values
4. 3 indices- not separated by commas, are enclosed in square brackets– each corresponds to reduced projections along x, y and z axes. Both +ve and -ve coordinates can exist. –ve represented by a bar over index
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X
Y
Z
X Y ZPROJ. a/2 b 0ca=b=c 1/2 1 0reduction 1 2 0
Crys. Direction: [1 2 0]
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• 1 [1 0 0]
• 2 [1 1 0]
• 3 [1 1 1]
3
12
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INDICES: [1 1 1]
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INDICES: [ 2 0 1 ]
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INDICES: [1 0 1]
NOT as [ 1 0 -1]
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INDICES: [1 1 1 ]NOT as [ 1 -1 1]
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INDICES: [1 0 1 ] NOT as [ 1 0 -1]
INDICES: [1 1 1 ] NOT as [ 1 -1 1]
SIMILARLY, THE CRYSTALLOGRAPHIC PLANES ARE ALSO INDICATED .
Eg: (2 0 1)