What Are the Metals with Low Thermal Conductivity

In materials science, the property of thermal conductivity characterizes how readily heat flows through a metal or alloy.

While pure metals such as copper and aluminum exhibit high conductivity, alloys with low conductivity confer advantages in applications requiring thermal resistance or insulation. Several metal groups stand out for their inherently poor conductive properties.

The conductivity values for these materials range between 10-30 W/mK, compared to the most thermally conductive metals which exceed 100 W/mK. Let’s see the metals with low thermal conductivity, their advantages, and what are the challenges that come with them.

What is Thermal Conductivity?

Thermal conductivity is a property of materials that describes their ability to transfer heat from one region to another. It specifically refers to the rate at which heat flows across a temperature gradient under steady-state conditions.

Thermal conductivity is an intrinsic characteristic of a metal or alloy and depends strongly on its composition and microstructural features.

This important property is quantified using the units of watts per meter-Kelvin (W/mK). It specifies the quantity of heat in watts that passes through a thickness of 1 meter in material for each 1-degree temperature difference between the two sides.

Metals with high thermal conductivity like silver, copper, and aluminum have values above 100 W/mK. This enables them to rapidly conduct heat away from concentrated sources and distribute it over large volumes.

Such heat dispersion is critical in applications like electronics cooling, heat exchangers, and cooking surfaces.

Thermal Conductivity Is a Property That Indicates How Well a Metal Conducts Heat

Thermal Conductivity Is a Property That Indicates How Well a Metal Conducts Heat

On the other hand, some metals have thermal conductivities below 30 W/mK, classifying them as thermally insulating materials. Examples include stainless steel compositions, titanium alloys, and tungsten metals.

Their low conductivities impede heat flow and resist the spread of thermal energy. This heat localization is advantageous for applications like furnace linings, steam turbine blades, and spacecraft skin that require insulation from extreme temperatures.

A metal’s thermal conductivity is determined by how efficiently heat is transferred by the free electrons in its crystal lattice structure. Factors like alloying additions, precipitates, defects, grain boundaries, and plastic deformation all impact the electron flow.

Processing approaches including work hardening, annealing, and control of second phases allow careful tuning of thermal properties alongside mechanical performance.

 

What is the Thermal Conductivity of Metal?

A metal’s thermal conductivity depends on its alloy composition, microstructure, and processing history. While pure metals like copper and aluminum have high intrinsic conductivities, alloying elements can significantly reduce heat transfer.

Impurities and defects impede the flow of free electrons that carry thermal energy.

Grain boundaries also inhibit conductivity, since heat must cross from one grain to another. Refining the grain size and reducing the grain boundary area can therefore raise conductivity.

Precipitation-hardening alloys tend to have lower conductivity due to dispersed second-phase particles at grain boundaries.

Plastic deformation from cold working decreases conductivity as it introduces dislocations in the crystal structure. Annealing restores a more ordered structure and higher conductivity. Porosity from gas entrapment or cracking provides insulation and further reduces thermal transfer.

Metals Thermal Conductivity Depends on a Lot of Factors

Metal’s Thermal Conductivity Depends on a Lot of Factors

Measurement techniques like laser flash analysis are used to quantify thermal conductivity. ASTM and other standards exist to ensure consistent, repeatable test methods that control for factors like specimen geometry, temperature, and measurement uncertainty.

Understanding how microstructure and processing influence thermal conductivity allows materials engineers to optimize metal alloys.

Which Metals Have Low Thermal Conductivity?

Several metals and alloys stand out for their relatively low thermal conductivity compared to highly conductive metals like copper and aluminum. Three of the most common are stainless steel, titanium, and tungsten.

Stainless Steel

Stainless steel has a thermal conductivity ranging from 10-30 W/mK depending on the alloy grade. The most common 304 and 316 grades have conductivity around 15 W/mK.

Stainless steels contain chromium which oxidizes to form an insulating oxide layer on the surface. The alloying elements also limit conductivity by scattering free electrons. The austenitic crystal structure further reduces transfer compared to ferritic steel.

Stainless is valued for applications like cookware, bolts, and valves where its low conductivity prevents burning and reduces heat loss.

Titanium

Commercially pure titanium has a thermal conductivity of around 22 W/mK. When alloyed with elements like aluminum and vanadium, this drops to 15-18 W/mK for workhorse titanium alloys.

The hexagonal close packed crystal structure coupled with interstitial elements that block electron movement are key factors behind titanium’s resistivity to heat flow. This makes titanium invaluable for aircraft skin, pressure vessels, and medical implants where limiting heat transfer protects components and personnel.

Tungsten possesses the lowest conductivity among pure metals at 180 W/mK. Alloying with elements like rhenium and molybdenum that solubilize in the crystal lattice creates solid solution strengthening while further reducing conductivity down to 25-100 W/mK.

Pure Titanium Has Low Thermal Conductivity

Pure Titanium Has Low Thermal Conductivity

Tungsten alloys have the highest melting point among metals along with low thermal expansion and conductivity. This enables applications in rocket nozzles, radiation shielding, turbine blades, and lamp filaments operating at extreme temperatures.

Low Carbon Steel

Low-carbon steel has a conductivity of around 50 W/mK. The addition of nickel, chromium, and molybdenum during alloying continuously decreases conductivity in grades of stainless steel.

Engineers balance composition to achieve target strength, corrosion resistance, weldability, and thermal behavior. Similarly, titanium and tungsten alloys control precipitation and solid solution effects to tailor a broad range of mechanical and thermal properties.

Advantages of Low Thermal Conductivity

Metals with low thermal conductivity have distinct advantages for many applications where limiting heat transfer is beneficial. Some of the main benefits of low thermally conductive metals include:

Slowing Heat Transfer and Insulation

Low-conductivity metals impede heat flow, allowing them to act as thermal insulators and barriers. This helps preserve heat in applications like furnace linings, engine exhaust components, and heating elements.

It also reduces unwanted heat transfer into adjacent temperature-sensitive materials. Insulation protects personnel and components.

Heat Concentration/Localization

Since heat is constrained locally, low conductivity creates thermal resistance that enables heat concentration and localization. This facilitates heating up a small zone rapidly without dissipating energy elsewhere.

Applications like soldering iron tips and sputtering targets for metal coating rely on localized heat input.

Thermal Shock Resistance

Sudden temperature changes can create damaging thermal stresses between hot and cold regions. Low thermal conduction helps mitigate this by slowing the thermal response.

Titanium alloys withstand thermal shock in aerospace engines. Ceramic coating layers on metals also lower conductivity.

Energy Savings

Limited heat flow reduces energy expenditures for heating or cooling. Stainless steel and aluminum alloys need less energy input for processing thanks to lower heat losses. Insulated cryogenic piping and storage vessels also conserve energy.

High Temperature Use

Materials like tungsten alloys withstand extreme temperatures above 1000°C partially thanks to low thermal conductivity. This reduces the heat transferred internally between hot and cold sections. Thermal shielding allows positioning adjacent to high heat.

Limited Heat Flow Reduces Energy Expenditures for Heating or Cooling

Limited Heat Flow Reduces Energy Expenditures for Heating or Cooling

Burn Protection

Lower heat transfer to exterior surfaces reduces the risks of burns to users. Cookware, firefighting apparel, and steam turbine casings all leverage this benefit. Gradual, uniform heating is safer.

What Are the Main Challenges in Working With Metals With Low Thermal Conductivity?

While metals with low thermal conductivity confer advantages in many applications, their poor heat transfer ability also poses some unique challenges during materials processing and end use:

Difficulties in Heating/Cooling

The same insulating properties that help these metals maintain heat also make it harder to heat up or cool down the material uniformly. Longer times are required to reach thermal equilibrium.

This could reduce productivity in manufacturing. Special heating methods may be needed.

Thermal Stress and Cracking

Localized hot spots can still develop despite the low conductivity. Combined with constraints on heat dissipation, this leads to large thermal gradients in the material, resulting in thermal stress.

Cracking may occur if the strain is excessive. Careful design and controlled heating/cooling are necessary.

Oxidation Sensitivity

Some low-conductivity alloys rely on the formation of insulating surface oxide layers to maintain low transfer. If these oxides are damaged during use in harsh environments, the conductivity will increase. The material may then experience excessive heat input and fail prematurely.

Thermal Fatigue

Continuous heating/cooling cycles soften and reharden areas of the metal differently depending on heat flux. This causes thermal fatigue over time, limiting component life. Low conductivity exacerbates the cyclic stress problems.

Warping and Distortion

Without free heat flow, uncontrolled expansion and contraction occur as temperatures change. This can lead to warpage or distortion problems. Parts may no longer fit together properly or lose functionality if dimensions shift.

Joining Challenges

Standard fusion welding is difficult since heat gets trapped in the weld zone. This requires special joining techniques like diffusion bonding or brazing. Even if welds are sound, the uneven heating can still cause distortion.

Applications of Low Thermal Conductivity Metals

Metals with low thermal conductivity find use across many industries where their insulating properties offer performance advantages and safety benefits. Some examples include:

Cookware

Stainless steel and aluminum alloys heat up gradually and evenly while also resisting hot spots that burn food. Handles and knobs stay cooler for safe handling.

Low Thermal Conductivity Metals Are Used in Cookware

Low Thermal Conductivity Metals Are Used in Cookware

Nuclear Reactors

Zirconium alloys contain nuclear fuel rods, resisting heat transfer to the surroundings. This enables higher operating temperatures and thermal efficiencies.

Aerospace

Titanium alloys withstand extreme fluctuating temperatures in jet engine components. The low conductivity resists cracking from thermal shock.

Automotive

Exhaust system components such as manifolds and mufflers utilize stainless steel to contain high-temperature gases while limiting heat transfer to surroundings.

Electrical

Tungsten wire in power lamp filaments operates at over 2400°C. Its low conductivity confines heating to the filament without melting the supports.

Medical

Implants made from titanium alloys transfer minimal body heat to surrounding tissue. This protects cells from damage during temperature changes.

Gas Turbines

Thermal barrier coatings applied to turbine blades create an insulating layer to reduce heat flow and allow higher combustion temperatures.

Electronics

Heat sinks made of aluminum alloys with compositional gradients optimize heat dissipation from key areas while keeping adjacent components cooler.

Cryogenics

Stainless steel allows low-temperature storage and transport of gases like liquid nitrogen with minimal heat gain. This reduces losses.

Frequently Asked Questions

1. Which Material Has Lowest Thermal Conductivity?

Diamond has the lowest thermal conductivity of any bulk material at around 2000 W/mK. Other very low-conductivity materials include aerogels, polymers like polyethylene, and ceramics.

2. Why Would I Want a Metal With Lower vs. Higher Thermal Conductivity?

Lower conductivity provides insulation while higher conductivity enables heat dissipation. The ideal choice depends on the application and whether resisting or spreading heat flow is preferred.

3. Can the Thermal Conductivity of a Metal Be Altered or Controlled?

Yes, thermal conductivity can be controlled in metals through alloy composition, heat treatment, microstructure, and cold working. Elements are added to impede heat transfer or precipitation strength. Grain size, dislocations, and annealing alter results.

4. How Can I Lower the Thermal Conductivity in a Metal Alloy?

Alloying elements, precipitates, plastic deformation, porosity, and insulating surface films can effectively reduce thermal conductivity. Refining grain size and optimizing heat treatment also lowers conductivity. This allows customization of thermal properties.

Conclusion

Metals like stainless steel, titanium, and tungsten provide low thermal conductivity that resists heat flow for applications requiring insulation or thermal barriers.

Careful engineering of the alloy composition, microstructure, and processing tailors the thermal properties to ideally balance strength, workability, and resistivity to heat transfer.

As a leading PCB manufacturer, PCBMay helps customers select and design with low thermal conductivity metals like aluminum, copper-invar-copper, and chromium-copper alloys.

Our expertise in materials science and thermal processing enables optimized fabrication. With robust quality control and testing, we produce exceptional circuit boards using metals with thermal conductivities aligned to the application requirements.

Contact us anytime to explore your thermal conductivity needs.

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