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

Resistivity of Metals, Alloys, Rocks, and Soils - RF Cafe Resistivity, 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 Cafe Conductivity 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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