Adhesion of tungsten particles on rough tungsten surfaces using Atomic Force Microscopy

Abstract

Adhesion forces between tungsten spherical microparticles and tungsten substrates with different roughnesses have been measured using the Atomic Force Microscopy (AFM) colloidal probe technique. Mean roughnesses of the tungsten substrates were measured by AFM and were ranked in three categories i.e. nanoscale, sub-microscale and microscale roughnesses. Experimental Hamaker constant of 37 ± 3.5 × 10 −20 J has been obtained using a spherical tungsten particle of 10.5 µm in radius and a tungsten substrate with nanoscale root-mean-square roughness of rms = 11.5 nm. It was shown that larger roughness of the order rms = 712 nm induces a two order of magnitude decrease on the adhesion of tungsten microparticles compared to a smooth tungsten surface with nanoscale roughness. Comparison with the van der Waals-based adhesion force model of Rabinovich which integrates the roughness of surfaces showed good agreement with experimental pull-off forces even when roughness of the substrate is close to the micrometer range. In such case, measurements have shown that dependency of adhesion force with particle size (in the micrometer range) has a secondary influence compared to the roughness of surfaces.

CFD modelling of particle resuspension in a toroidal geometry resulting from airflows during a loss of vacuum accident (LOVA)

“…The model can be used with a constant or a variable friction velocity according to the model formulation. It has to be noticed here that the Biasi correlation, which has been obtained with various experiments, could be replaced in a future work by real adhesion force distributions obtained by means of atomic force microscopy technique in the specific case of tungsten particles deposited on tungsten substrates [17].…”

“…For a particle to be resuspended, airflow forces have to be at least equal to the adhesion forces. In reality, the particles are not spherical and nor smooth and they are generally deposited on rough surfaces [17]. Hence, adhesion forces cannot be directly calculated by the expression in equation (3).…”

“…u* (17) ne = 0.00658 ( ) From the constant resuspension spécifie rate p(fa), the resuspension rate A(t), depending essentially on the particle diameter and the shear velocity, can be calculated according to airflow conditions: constant or variable.…”

“…The surface energy used for these calculations is equal to 4.4 J.m-, as preconized by Rondeau [27], from a fit of the Biasi correlation on its experimental data of resuspended fraction acquired in the AUG tokamak. However, Peillon [17] demonstrated from AFM measurements of tungsten spherical particles on a tungsten substrate that the adhesive forces can be very low, leading to surface energy lower than unity.…”

Current investigations on tritiated dust and its impact on tokamak safety

“…Fortunately, adhesion forces can be directly assessed using the Atomic Force Microscope (AFM) technique. Details on the technique and experimental procedure can be found in [12]. Adhesion force measurements have been realized with a Multimode 8 (Bruker) AFM in PeakForce Quantitative Nano-Mechanical mode (PF-QNM) in environmental conditions.…”