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Nanodiamond Thermal Conducting Fluid

April 23, 2014

The phrase, "the whole is greater than the sum of its parts," is often attributed to Aristotle (384 BC-322 BC), but there's nothing exactly like that in his works. Nonetheless, this statement is often true for composite materials. Epoxy wouldn't be quite as useful without the addition of glass fibers to form fiberglass.

The following is a formal definition of a composite found on Wikipedia.
"Composite materials... are materials made from two or more constituent materials with significantly different physical or chemical properties, that when combined, produce a material with characteristics different from the individual components."

Although we usually think of composites only as solids, the definition allows fluids, also. We have fluid-fluid mixtures, in which one of these fluids is usually called an additive. One example of these is motor oil, for which there are numerous additives. There are also liquid-in-solid composites, such as oil-impregnated bronze, used as a material for bearings; and solid-in-liquid composites, such as ink and paint sol colloids.

The easy production of nanoparticles has now allowed the development of much more useful sol colloids, principally since these particles can be suspended and dispersed in fluids (see, for example, refs. 1-2).[1-2]

Scientists from Rice University (Houston, Texas), the Council of Scientific and Industrial ResearchCentral Electrochemical Research Institute (CSIR-CECRI, Karaikudi, India), the Indian Institute of Science (Bangalore, India) and the University of Texas Pan American (Edinburg, Texas) have just published the results of their research on using nanodiamonds to enhance the thermal conductivity of mineral oil.[3-4]

Diamond is an excellent thermal conductor, having a room temperature thermal conductivity of 22 W/cm-K. This is five times greater than the thermal conductivity of copper, but if you form diamond from the isotope 12C, it has a theoretical thermal conductivity at 80 kelvin of about 2000 W/cm-K.[5]

Mineral oil has a thermal conductivity of just 0.00162 W/cm-K. This sounds small, but it compares favorably to ethylene glycol (0.00258 W/cm-K), one of the best thermally conducting liquids, although still a far second to water at 0.0058 W/cm-K. The Rice team investigated suspensions of nanodiamond in mineral oil, which is used as a standard transformer oil.

Suspension of nanodiamond in mineral oil

Suspension of nanodiamond in mineral oil.

The concentration of nanodiamond in mineral oil was tested up to 0.1 weight-percent.

(Image: Ajayan Group/Rice University.)[4)]

This work extended the team's previous work on addition of exfoliated layers of hexagonal boron nitride in mineral oil.[6] They were able to form stable nanosuspensions with high shelf life and a higher electrical resistivity than that of pure mineral oil. Just a small weight fraction of boron nitride nanoparticles (0.01 wt-%) enhanced the thermal conductivity by a factor of nearly two at higher temperatures.[6]

Nanoparticles of size less than 100 nanometers won't limit fluid flow if their concentration is low enough. The nanodiamond particles of the Rice research team were about six nanometers in diameter, and this produced mineral oil fluids with a higher thermal conductivity than those containing oxide, nitride or carbide ceramics, metals, semiconductors or carbon nanotubes.[3-4] Just a tenth weight-percent of nanodiamond increased the thermal conductivity of mineral oil by 70 percent at 373 kelvin, about 210 degrees Fahrenheit (see figure).[3-4]

Enhancement of thermal conductivity by nanodiamond addition

Enhancement of thermal conductivity by nanodiamond addition.

(Illustration by the author using Inkscape from Rice University data.)[3)]

An important consideration for most applications is the fluid viscosity. The nanodiamond-filled mineral oil had a viscosity that had an Arrhenius law behavior in which both the activation energy and the pre-exponential factor have an exponential dependence on the fraction of nanodiamonds.[3] says Taha-Tijerina, a coauthor of the paper and now a research scientist at Viakable Technology and Research Center in Monterrey, Mexico,
"The great properties of nanodiamond — lubricity, high thermal conductivity and electrical resistivity and stability, among others - are quite impressive... We found we could combine very small amounts with conventional fluids and get extraordinary thermal transport without significant problems in viscosity."[4]

It's thought that this large effect at such low concentration is achieved by a percolation mechanism combined with Brownian motion.[4]

Electron microscope image of nanodiamond in mineral oil

Electron microscope image of nanodiamond in mineral oil.

The inset is the electron diffraction pattern of the particles.

(Image: Ajayan Group/Rice University.)[4)]


  1. Virginia A. Davis, A. Nicholas G. Parra-Vasquez, Micah J. Green, Pradeep K. Rai, Natnael Behabtu, Valentin Prieto, Richard D. Booker, Judith Schmidt, Ellina Kesselman, Wei Zhou, Hua Fan, W. Wade Adams, Robert H. Hauge, John E. Fischer, Yachin Cohen, Yeshayahu Talmon, Richard E. Smalley and Matteo Pasquali, "True solutions of single-walled carbon nanotubes for assembly into macroscopic materials," Nature Nanotechnology, vol. 4, no. 12 (December, 2009), pp. 830-834.
  2. Olga Matarredona, Heather Rhoads, Zhongrui Li, Jeffrey H. Harwell, Leandro Balzano, and Daniel E. Resasco,, "Dispersion of Single-Walled Carbon Nanotubes in Aqueous Solutions of the Anionic Surfactant NaDDBS," J. Phys. Chem., vol. B 2003, no. 107, pp. 13357-13367 (PDF File).
  3. Jose Jaime Taha-Tijerina, Tharangattu Narayanan Narayanan, Chandra Sekhar Tiwary, Karen Lozano, Mircea Chipara and Pulickel M. Ajayan, "Nanodiamond-Based Thermal Fluids," ACS Applied Materials & Interfaces, Article ASAP, March 21, 2014, DOI: 10.1021/am405575t.
  4. Mike Williams, "Diamonds are an oil's best friend," Rice University Press Release, March 31, 2014.
  5. Lanhua Wei, P. K. Kuo, R. L. Thomas, T. R. Anthony and W. F. Banholzer, "Thermal conductivity of isotopically modified single crystal diamond," Physical Review Letters, vol. 70, no. 24 (June 14, 1993), pp. 3764-3767.
  6. Jaime Taha-Tijerina, Tharangattu N. Narayanan, Guanhui Gao, Matthew Rohde, Dmitri A. Tsentalovich, Matteo Pasquali and Pulickel M. Ajayan, "Electrically Insulating Thermal Nano-Oils Using 2D Fillers," ACS Nano, vol. 6, no. 2 (February 28, 2012), pp 1214-1220.
  7. Ajayan Research Group at Rice University.
  8. Rice Materials Science and NanoEngineering Department.

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