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### Transcript of Chapter 2 LITERATURE REVIEW - 2.pdf¢  Chapter 2 LITERATURE REVIEW Literature review...

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Chapter 2

LITERATURE REVIEW

Literature review relevant to the present study has been divided into three parts.

First part contains a comprehensive review of the existing literature on electro

conductive materials and their characteristics. In the second part, literature review

concerning the protective coatings and Cold spray (CS) process has been described.

The studies related to the behavior of the copper coatings have been reviewed in the

third part of this chapter.

PART-I

2.1 ELECTRO-CONDUCTIVE MATERIALS

Electrical resistivity (also known as resistivity, specific electrical resistance, or

volume resistivity) is a measure of how strongly a material opposes the flow of

electric current. A low resistivity indicates a material that readily allows the

movement of electric charge. It is commonly represented by the Greek letter ρ (rho)

and its SI unit is the ohm metre (Ω. m).

Electrical conductivity or specific conductance is the reciprocal quantity, and

measures a material's ability to conduct an electric current. It is commonly

represented by the Greek letter σ, and its SI unit is Siemens per metre (S·m −1

):

σ = 1/ ρ

2.1.1 Resistivity of various materials

The conductivity of a solution of water is highly dependent on its concentration of

dissolved salts, and other chemical species that ionize in the solution. Electrical

conductivity of water samples is used as an indicator of how salt-free, ion-free, or

impurity-free the sample is; the purer the water, the lower the conductivity (the higher

the resistivity). Conductivity measurements in water are often reported as specific

conductance, relative to the conductivity of pure water at 25 °C.

http://en.wikipedia.org/wiki/Electric_current http://en.wikipedia.org/wiki/Electric_charge http://en.wikipedia.org/wiki/Greek_alphabet http://en.wikipedia.org/wiki/Rho_(letter) http://en.wikipedia.org/wiki/SI http://en.wikipedia.org/wiki/Ohm http://en.wikipedia.org/wiki/Metre http://en.wikipedia.org/wiki/Electric_current http://en.wikipedia.org/wiki/Sigma_(letter) http://en.wikipedia.org/wiki/Siemens_(unit) http://en.wikipedia.org/wiki/Metre http://en.wikipedia.org/wiki/Solution_(chemistry) http://en.wikipedia.org/wiki/Water_(molecule) http://en.wikipedia.org/wiki/Concentration http://en.wikipedia.org/wiki/Salts http://en.wikipedia.org/wiki/Ionization

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The effective temperature coefficient varies with temperature and purity level of the

material. The 20 °C value is only an approximation when used at other temperatures.

For example, the coefficient becomes lower at higher temperatures for copper, and the

value 0.00427 is commonly specified at 0 °C.

The extremely low resistivity (high conductivity) of silver is characteristic of metals.

George Gamow (1947) tidily summed up the nature of the metals' dealings with

electrons in his science-popularizing book, One, Two, Three...Infinity: "The metallic

substances differ from all other materials by the fact that the outer shells of their

atoms are bound rather loosely, and often let one of their electrons go free. Thus the

interior of a metal is filled up with a large number of unattached electrons that travel

aimlessly around like a crowd of displaced persons. When a metal wire is subjected to

electric force applied on its opposite ends, these free electrons rush in the direction of

the force, thus forming what we call an electric current". Table 2.1 shows the

resistivity, conductivity and temperature coefficient of various materials at 20 °C (68

°F).

The cold spray process offers advantages to produce, with minimum thermal

exposure, coatings from functional materials such as thermoelectric, magneto-caloric,

photo-voltaic, piezo-electric, super-magnetic, and high-temperature superconductive

formulations.

Electrical resistivity of CS Al was higher than the bulk Al sample measured, and

anisotropic. These characteristics can be attributed to intrinsic defects within Al splats

(e.g. high dislocation density) and oxidized interfaces between splats. Anisotropy, on

initial approximation, could be attributed to the quasi-lamellar microstructure

containing more interfaces per unit length through the thickness of the coating versus

in-plane. Nevertheless, examining the data from Choi (2007) on the thickness

dependence of resistivity (as specimen thickness approaches splat size this effectively

confines electrons to a single interrupted conductive path). This concept was fully

explored in Sharma (2006); the imperfect interfaces between splats (interface normal

perpendicular to substrate normal) have a non-trivial effect on anisotropy. It could

further be argued that these interfaces are less well-bonded than those above and

below particles, but this assertion must be certified with direct measurements.

http://en.wikipedia.org/wiki/Electrical_conductivity http://en.wikipedia.org/wiki/George_Gamow http://en.wikipedia.org/wiki/Temperature_coefficient http://en.wikipedia.org/wiki/Celsius http://en.wikipedia.org/wiki/Fahrenheit

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Table 2.1: Resistivity, conductivity and temperature coefficient of various materials

Material ρ [Ω·m] at

20 °C

σ [S/m] at 20

°C

Temperat

ure

coefficient 1

[K −1

]

Reference

Silver 1.59×10−8 6.30×107 0.0038 Serway, 1998; Griffiths, 1999

Copper 1.68×10−8 5.96 × 107 0.0039 Griffiths, 1999

Annealed Copper2 5.80 × 107

Gold3 2.44×10−8 4.52 × 107 0.0034 Serway, 1998

Aluminium4 2.82×10−8 3.5 × 107 0.0039 Serway, 1998

Calcium 3.36x10−8 0.0041

Tungsten 5.60×10−8 0.0045 Serway, 1998

Zinc 5.90×10−8 0.0037 http://physics.mipt.ru/

Nickel 6.99×10−8 0.006

Lithium 9.28×10−8 0.006

Iron 1.0×10−7 0.005 Serway, 1998

Platinum 1.06×10−7 0.00392 Serway, 1998

Tin 1.09×10−7 0.0045

Titanium 4.20x10−7 X

Manganin 4.82×10−7 0.000002 Giancoli, 1995

Constantan 4.9×10−7 0.000008 O’Malley, 1992

Mercury 9.8×10−7 0.0009 Giancoli, 1995

Nichrome5 1.10×10−6 0.0004 Serway, 1998

Carbon (amorphous) 5-8×10−4 −0.0005 Serway, 1998; Pauleau, 1997

Carbon (graphite)6

2.5-5.0×10−6

⊥ basal plane

3.0×10−3 //

basal plane

Pierson, 1993

Germanium7 4.6×10−1 −0.048 Serway, 1998; Griffiths, 1999

Sea water7 2×10−1 4.8 Physical properties of sea

water

Drinking water8 0.0005 to 0.05

Deionized water9 5.5 × 10−6 Pashley et al., 2005

Silicon7 6.40×102 −0.075 Serway, 1998

Glass 1010 to 1014 ? Serway, 1998; Griffiths, 1999

Hard rubber approx. 1013 ? Serway, 1998

Sulphur 1015 ? Serway, 1998

Air 3 to 8 × 10−15 Pawar et al., 2009

Paraffin 1017 ?

Quartz (fused) 7.5×1017 ? Serway, 1998

PET 1020 ?

Teflon 1022 to 1024 ?

1 The numbers in this column increase or decrease the significant portion of the resistivity. For example, at 30 °C (303 K), the resistivity of silver is 1.65×10−8. This is calculated as Δρ = α ΔT ρo where ρo is the resistivity at 20 °C (in this case) and α is the

temperature coefficient. 2 Referred to as 100% IACS or International Annealed Copper Standard. The unit for expressing the conductivity of nonmagnetic

materials by testing using the eddy-current method. Generally used for temper and alloy verification of aluminium. 3 Gold is commonly used in electrical contacts because it does not easily corrode. 4 Commonly used for high voltage power lines 5 Nickel-Iron-Chromium alloy commonly used in heating elements. 6 Graphite is strongly anisotropic. 7 Corresponds to an average salinity of 35 g/kg at 20 °C. 8 This value range is typical of high quality drinking water and not an indicator of water quality. 9 Conductivity is lowest with mono-atomic gases present; changes to 1.2 × 10-4 upon complete de-gassing or to 7.5 × 10-5 upon

equilibration to the atmosphere due to dissolved CO2.

http://en.wikipedia.org/wiki/Silver http://en.wikipedia.org/wiki/Copper http://en.wikipedia.org/wiki/Annealing_(metallurgy) http://en.wikipedia.org/wiki/Copper http://en.wikipedia.org/wiki/Gold http://en.wikipedia.org/wiki/Aluminium http://en.wikipedia.org/wiki/Calcium http://en.wikipedia.org/wiki/Tungsten http://en.wikipedia.org/wiki/Zinc http://physics.mipt.ru/ http://en.wikipedia.org/wiki/Nickel http://en.wikipedia.org/wiki/Lithium http://en.wikipedia.org/wiki/Iron http://en.wikipedia.org/wiki/Platinum http://en.wikipedia.org/wiki/Tin http://en.wikipedia.org/wiki/Lead http://en.wikipedia.org/wiki/Titanium http://en.wikipedia.org/wiki/Manganin http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#cite_note-giancoli-7 http://en.wikipedia.org/wiki/Constantan http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#cite_note-8 http://en.wikipedia.org/wiki/Mercury_(element) http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#cite_note-giancoli-7 http://en.wikipedia.org/wiki/Nichrome htt