Thermal Conductivity of Detonation Nanodiamond Hydrogels and Hydrosols by Direct Heat Flux Measurements

The methodology and results of thermal conductivity measurements by the heat-flow technique for the detonation nanodiamond suspension gels, sols, and powders of several brands in the range of nanoparticle concentrations of 2-100% w/w are discussed. The conditions of assessing the thermal conductivity of the fluids and gels (a FOX 50 heat-flow meter) with the reproducibility (relative standard deviation) of 1% are proposed. The maximum increase of 13% was recorded for the nanodiamond gels (140 mg mL(-1) or 4% v/v) of the RDDM brand, at 0.687 +/- 0.005 W m(-1) K-1. The thermal conductivity of the nanodiamond powders is estimated as 0.26 +/- 0.03 and 0.35 +/- 0.04 W m(-1) K-1 for the RUDDM and RDDM brands, respectively. The thermal conductivity for the aqueous pastes containing 26% v/v RUDDM is 0.85 +/- 0.04 W m(-1) K-1. The dignities, shortcomings, and limitations of this approach are discussed and compared with the determining of the thermal conductivity with photothermal-lens spectrometry.