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Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024

Webmaster:

    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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Resistivity (ρ) & Conductivity (σ) of Metals, Alloys, Rocks, and Soils

Resistivity of Metals, Alloys, Rocks, and Soils - RF CafeResistivity, also referred to as specific resistance, is dependent on the nature of the material as well as its volume definition (shape and size). Resistivity is expressed in units that are the product of resistance and length; e.g., Ω·cm. The symbol most commonly used for resistivity is rho (ρ).

Conductivity (S/cm) - RF CafeConductivity is the reciprocal of resistivity. Conductivity is expressed in units that are the quotient of conductance (Siemens) and length; e.g., S/cm. The symbol most commonly used for resistivity is sigma (σ).

As an example of calculating a volume's resistance, consider the drawing to the left. Assume 12 AWG copper wire with a resistivity (from the table) of 1.72x10-6 Ω·cm, a cross-sectional area (A) of 0.03309 cm2, and a length of 1 meter. Per the given formula, its resistance is:

Resistance per kilometer of 12 AWG copper wire - RF Cafe,

which agrees well with typical specified Ω/km values published by wire manufacturers. Alpha claims 1.59 Ω/1000' or 5.22 Ω/km.

The table of resistivity values below are pulled from Reference Data for Radio Engineers, 1995, Sams Publishing. Please verify accuracy with a second source. See rocks and soils table at bottom. Interesting note: The nickel-silver compound actually contains no silver at all; its name is derived from a silver appearance.

 

Metal & Alloy Materials Form Resistivity

(x10-6 Ω·cm)

Temperature

(°C)

Temperature

Coefficient (°C-1)

Alumel solid 33.3 0 0.0012
Aluminum liquid

solid

20.3

2.62

670

20

.0039

Antimony liquid

solid

123

39.2

800

20

0.0036

Arsenic solid 35 0 0.0042
Beryllium solid 4.57 20  
Bismuth liquid

solid

128.9

115

300

20

0.004

Boron solid 1.8x1012 0  
Brass (66 Cu, 34 Zn) solid 3.9 20 0.002
Cadmium liquid

solid

34

7.5

400

20

0.0038

Carbon diamond

graphite

graphene

5x1020

1400

15

20

-0.0005

Cerium solid 78 20  
Cesium liquid

solid

36.6

20

30

20

 
Chromax (15 Cr, 35 Ni, balance Fe) solid 100 20 0.00031
Chromel solid 70-110 0 0.00011-0.000054
Chromium solid 2.6 0  
Cobalt solid 9.7 20 0.0033
Constantan (55 Cu, 45 Ni) solid 44.2 20 0.0002
Copper (annealed) liquid

solid

21.3

1.7241

1083

20

0.0039

Gallium solid

liquid

27

53

30

0

 
Gold liquid

solid

30.8

2.44

1063

20

0.0034

Granite solid 1x1013 - 1x1015    
Hafnium solid 32.1 20
Indium liquid

solid

29

9

157

20

0.00498

Iridium solid 5.3 20 0.0039
Iron solid 9.71 20 0.0052-0.0062
Kovar A (29, Ni, 17 Co, 0.3 Mn, balance Fe) solid 45-84 20  
Lava flow (basic)

Lava, fresh

liquid 1x1012 - 1x1013    
Lead liquid

solid

98

21.9

400

20

0.004

PbO2 solid 92    
Lithium liquid

solid

45

9.3

230

20

0.003

0.005

Magnesium solid 4.46 20 0.004
Manganese solid 5 20  
MnO2 solid 6000000 20  
Magnanin (84 Cu, 12 Mn, 4 Ni) solid 44 20 ±0.0002
Mercury liquid

solid

95.8

21.3

20

-50

0.00089
Molybdenum solid 5.17

4.77

0

20

0.0033

Monel metal (67 Ni, 30 Cu, 1.4 Fe) solid 42 20 0.002
Neodymium solid 79 18  
Nichrome (65 Ni, 12 Cr, 23 Fe) solid 100 20 0.00017
Nickel solid 6.9 20 0.0047
Nickel-Silver (64 Cu, 18 Zn, 18 Ni) solid 28 20 0.00026
Niobium solid 12.4 20  
Osmium solid 9 20 0.0042
Palladium solid 10.8 20 0.0033
Phosphor bronze (4 Sn, 0.5 P, balance Cu) solid 9.4 20 0.003
Platinum solid 10.5 20 0.003
Plutonium solid 150 20  
Potassium liquid

solid

13

7

62

20

0.006

Praseodymium solid 68 25  
Rhenium solid 19.8 20  
Rhodium solid 5.1 20 0.0046
Rubidium solid 12.5 20  
Ruthenium solid 10 20  
Selenium solid 1.2 20  
Silver solid 1.62 20 0.0038
Sodium liquid

solid

9.7

4.6

100

20

 
Steel (0.4-0.5 C, balance Fe) solid 13-22 20 0.003
Steel, manganese (13 Mn, 1 C, 86 Fe) solid 70 20 0.001
Steel, stainless (0.1 C, 18 Cr, 8 Ni, balance Fe) solid 90 20  
Strontium solid 23 20  
Sulfur solid 2x1023 20  
Tantalum solid 13.1 20 0.003
Thallium solid 18.1 20 0.004
Thorium solid 18 20 0.0021
Tin solid 11.4 20 0.0042
Titanium solid 47.8 25  
Tophet A (80 Ni, 20 Cr) solid 108 20 0.00014
Tungsten solid 5.48 20 0.0045
W2O5 solid 450 20  
WO3 solid 2x1011 20  
Uranium solid 29 0 0.0021
Zinc liquid

solid

35.3

6

420

20

0.0037

Zirconiumn solid 40 20 0.0044

 

Rock & Soil Materials Resistivity

(x10 Ω·cm)

Granite 107 - 109
Lava flow (basic)

Lava, fresh

106 - 107

3x105 - 106

Marble

Marble, white

Marble, yellow

4x108

1010

1010

Quartz, vein, massive >106
Schist, mica 107
Shale, bed

Shale, nonesuch

105

104

Limestone

Limestone, Cambrian

104

104 - 105

Sandstone

Sandstone, eastern

105

3x103 - 104

Clay, blue

Clay, fire

2x104

2x105

Clayey earth 104 - 4x104
Gravel 105
Sand, dry

Sand, moist

105 - 106

106 - 105

 

 

 

Posted July 13, 2018

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