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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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