Thermal Conductivity of Metal

Thermal Conductivity of Metal : Introduction

Metals represent a vast number of materials that have been the backbone of industrial development during the past two centuries. The importance of this development upon future technological progress is undiminished and unquestionable.

Whether in pure, elemental form or as new lightweight, high-strength alloys, metals are simply indispensable to modern industrial society. Metals are, of course, known for their lustrous and shiny appearance, for their malleability and ductility and, above all, for their ability to conduct electric current. Because of their myriad applications, it is highly desirable to be able to tailor the properties of metals to match and optimize their use for specific tasks. Often among the important criteria is how well a given metal or alloy conducts heat.

The physical parameter that characterizes and quantities the material’s ability to conduct heat is called thermal conductivity, often designated by k. Understanding the nature of heat conduction process in metals and being able to predict how well a particular alloy will conduct heat are issues of scientific and technological interest.

In this section we review the fundamental physical principles that underscore the phenomenon of heat conduction in metals, develop an understanding of why some metals are better than others in their ability to conduct heat, and illustrate the behavior of thermal conductivity on several specific examples encompassing pure metals and alloys.

Thermal Conductivity is a term analogous to electrical conductivity with a difference that it concerns with the flow of heat unlike current in the case of the latter. It points to the ability of a material to transport heat from one point to another without movement of the material as a whole, the more is the thermal conductivity the better it conducts the heat.

Let us consider a block of material with one end at temperature T₁ and other at T₂. For T₁>T₂, heat flows from T₁ end to T₂ end, and the heat flux(J) flowing across a unit area per unit time is given as-

Where, K is the thermal conductivity in Joule/meter-sec-K or Watts/meter-K.

Generally the heat transfer in solid has two components

Lattice conduction
Electronic conduction

Both types of heat conduction occur in solids but one is dominant over the other depending upon the type of material.

In case of insulating materials, lattice conduction contributes to heat conduction. This is mainly due to the fact that in insulators the electrons are tightly held by their parent atoms and free electrons do not exist. Hence the heat is transferred from one end to another by vibration of atoms held in the lattice structure. Obviously insulators are bad heat conductors since they do not posses enough heat transfer capability due to lack of free electrons.

However in case of metals we have large number of free electrons, and hence heat conduction is primarily due to electronic conduction. The free electrons of the metals can freely move throughout the solid and transfer the thermal energy at a rate very high as compared to insulators. It is due to this that the metals posses high thermal conductivity. It is also observed that among the metals the best electrical conductors also exhibits best thermal conductivity. Since both electrical as well as thermal conductivity is dependent on the free electrons, factors such as alloying effect both the properties.
Thermal conductivity of metals vary from 15 – 450 W/mK at 300K.

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Wiedemann Franz Law

Wiedemann Franz law basically relates the two conductivities of metals, i.e. thermal and electrical conductivity with temperature. It states that the ratio of thermal conductivity K and electrical conductivity

Metal, Metallic Element or Alloy	Temperature *– t –* *(^oC)*	Thermal Conductivity *– k –* *(W/m K)*
Aluminum	-73	237
Aluminum	0	236
Aluminum	127	240
Aluminum	327	232
Aluminum	527	220
Aluminum – Duralumin (94-96% Al, 3-5% Cu, trace Mg)	20	164
Aluminum – Silumin (87% Al, 13% Si)	20	164
Aluminum bronze	0 – 25	70
Aluminum alloy 3003, rolled	0 – 25	190
Aluminum alloy 2014. annealed	0 – 25	190
Aluminum alloy 360	0 – 25	150
Antimony	-73	30.2
Antimony	0	25.5
Antimony	127	21.2
Antimony	327	18.2
Antimony	527	16.8
Beryllium	-73	301
Beryllium	0	218
Beryllium	127	161
Beryllium	327	126
Beryllium	527	107
Beryllium	727	89
Beryllium	927	73
Beryllium copper 25	0 – 25	80
Bismuth	-73	9.7
Bismuth	0	8.2
Boron	-73	52.5
Boron	0	31.7
Boron	127	18.7
Boron	327	11.3
Boron	527	8.1
Boron	727	6.3
Boron	927	5.2
Cadmium	-73	99.3
Cadmium	0	97.5
Cadmium	127	94.7
Cesium	-73	36.8
Cesium	0	36.1
Chromium	-73	111
Chromium	0	94.8
Chromium	127	87.3
Chromium	327	80.5
Chromium	527	71.3
Chromium	727	65.3
Chromium	927	62.4
Cobalt	-73	122
Cobalt	0	104
Cobalt	127	84.8
Copper	-73	413
Copper	0	401
Copper	127	392
Copper	327	383
Copper	527	371
Copper	727	357
Copper	927	342
Copper, electrolytic (ETP)	0 – 25	390
Copper – Admiralty Brass	20	111
Copper – Aluminum Bronze (95% Cu, 5% Al)	20	83
Copper – Bronze (75% Cu, 25% Sn)	20	26
Copper – Brass (Yellow Brass) (70% Cu, 30% Zn)	20	111
Copper – Cartridge brass (UNS C26000)	20	120
Copper – Constantan (60% Cu, 40% Ni)	20	22.7
Copper – German Silver (62% Cu, 15% Ni, 22% Zn)	20	24.9
Copper – Phosphor bronze (10% Sn, UNS C52400)	20	50
Copper – Red Brass (85% Cu, 9% Sn, 6%Zn)	20	61
Cupronickel	20	29
Germanium	-73	96.8
Germanium	0	66.7
Germanium	127	43.2
Germanium	327	27.3
Germanium	527	19.8
Germanium	727	17.4
Germanium	927	17.4
Gold	-73	327
Gold	0	318
Gold	127	312
Gold	327	304
Gold	527	292
Gold	727	278
Gold	927	262
Hafnium	-73	24.4
Hafnium	0	23.3
Hafnium	127	22.3
Hafnium	327	21.3
Hafnium	527	20.8
Hafnium	727	20.7
Hafnium	927	20.9
Hastelloy C	0 – 25	12
Inconel	21 – 100	15
Incoloy	0 – 100	12
Indium	-73	89.7
Indium	0	83.7
Indium	127	75.5
Iridium	-73	153
Iridium	0	148
Iridium	127	144
Iridium	327	138
Iridium	527	132
Iridium	727	126
Iridium	927	120
Iron	-73	94
Iron	0	83.5
Iron	127	69.4
Iron	327	54.7
Iron	527	43.3
Iron	727	32.6
Iron	927	28.2
Iron – Cast	20	52
Iron – Nodular pearlitic	100	31
Iron – Wrought	20	59
Lead	-73	36.6
Lead	0	35.5
Lead	127	33.8
Lead	327	31.2
Chemical lead	0 – 25	35
Antimonial lead (hard lead)	0 – 25	30
Lithium	-73	88.1
Lithium	0	79.2
Lithium	127	72.1
Magnesium	-73	159
Magnesium	0	157
Magnesium	127	153
Magnesium	327	149
Magnesium	527	146
Magnesium alloy AZ31B	0 – 25	100
Manganese	-73	7.17
Manganese	0	7.68
Mercury	-73	28.9
Molybdenum	-73	143
Molybdenum	0	139
Molybdenum	127	134
Molybdenum	327	126
Molybdenum	527	118
Molybdenum	727	112
Molybdenum	927	105
Monel	0 – 100	26
Nickel	-73	106
Nickel	0	94
Nickel	127	80.1
Nickel	327	65.5
Nickel	527	67.4
Nickel	727	71.8
Nickel	927	76.1
Nickel – Wrought	0 – 100	61 – 90
Cupronickel 50 -45 (Constantan)	0 – 25	20
Niobium (Columbium)	-73	52.6
Niobium (Columbium)	0	53.3
Niobium (Columbium)	127	55.2
Niobium (Columbium)	327	58.2
Niobium (Columbium)	527	61.3
Niobium (Columbium)	727	64.4
Niobium (Columbium)	927	67.5
Osmium	20	61
Palladium		75.5
Platinum	-73	72.4
Platinum	0	71.5
Platinum	127	71.6
Platinum	327	73.0
Platinum	527	75.5
Platinum	727	78.6
Platinum	927	82.6
Plutonium	20	8.0
Potassium	-73	104
Potassium	0	104
Potassium	127	52
Red brass	0 – 25	160
Rhenium	-73	51
Rhenium	0	48.6
Rhenium	127	46.1
Rhenium	327	44.2
Rhenium	527	44.1
Rhenium	727	44.6
Rhenium	927	45.7
Rhodium	-73	154
Rhodium	0	151
Rhodium	127	146
Rhodium	327	136
Rhodium	527	127
Rhodium	727	121
Rhodium	927	115
Rubidium	-73	58.9
Rubidium	0	58.3
Selenium	20	0.52
Silicon	-73	264
Silicon	0	168
Silicon	127	98.9
Silicon	327	61.9
Silicon	527	42.2
Silicon	727	31.2
Silicon	927	25.7
Silver	-73	403
Silver	0	428
Silver	127	420
Silver	327	405
Silver	527	389
Silver	727	374
Silver	927	358
Sodium	-73	138
Sodium	0	135
Solder 50 – 50	0 – 25	50
Steel – Carbon, 0.5% C	20	54
Steel – Carbon, 1% C	20	43
Steel – Carbon, 1.5% C	20	36
Steel – Carbon, 1.5% C	400	36
Steel – Carbon, 1.5% C	122	33
Steel – Chrome, 1% Cr	20	61
Steel – Chrome, 5% Cr	20	40
Steel – Chrome, 10% Cr	20	31
Steel – Chrome Nickel, 15% Cr, 10% Ni	20	19
Steel – Chrome Nickel, 20% Cr, 15% Ni	20	15.1
Steel – Hastelloy B	20	10
Steel – Hastelloy C	21	8.7
Steel – Nickel, 10% Ni	20	26
Steel – Nickel, 20% Ni	20	19
Steel – Nickel, 40% Ni	20	10
Steel – Nickel, 60% Ni	20	19
Steel – Nickel Chrome, 80% Ni, 15% Ni	20	17
Steel – Nickel Chrome, 40% Ni, 15% Ni	20	11.6
Steel – Manganese, 1% Mn	20	50
Steel – Stainless, Type 304	20	14.4
Steel – Stainless, Type 347	20	14.3
Steel – Tungsten, 1% W	20	66
Steel – Wrought Carbon	0	59
Tantalum	-73	57.5
Tantalum	0	57.4
Tantalum	127	57.8
Tantalum	327	58.9
Tantalum	527	59.4
Tantalum	727	60.2
Tantalum	927	61
Thorium	20	42
Tin	-73	73.3
Tin	0	68.2
Tin	127	62.2
Titanium	-73	24.5
Titanium	0	22.4
Titanium	127	20.4
Titanium	327	19.4
Titanium	527	19.7
Titanium	727	20.7
Titanium	927	22
Tungsten	-73	197
Tungsten	0	182
Tungsten	127	162
Tungsten	327	139
Tungsten	527	128
Tungsten	727	121
Tungsten	927	115
Uranium	-73	25.1
Uranium	0	27
Uranium	127	29.6
Uranium	327	34
Uranium	527	38.8
Uranium	727	43.9
Uranium	927	49
Vanadium	-73	31.5
Vanadium	0	31.3
Vanadium	427	32.1
Vanadium	327	34.2
Vanadium	527	36.3
Vanadium	727	38.6
Vanadium	927	41.2
Zinc	-73	123
Zinc	0	122
Zinc	127	116
Zinc	327	105
Zirconium	-73	25.2
Zirconium	0	23.2
Zirconium	127	21.6
Zirconium	327	20.7
Zirconium	527	21.6
Zirconium	727	23.7
Zirconium	927	25.7

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