One type of multimodal (comprised of nanometer and sub-micrometer WC particles) and two types of conventional (comprised of nanometer and sub-micrometer WC particles, respectively) WC/Co powders were deposited on AISI 304L stainless steel substrates by using high velocity oxygen fuel spraying. The use of multimodal WC particles was indicated to have a beneficial effect on the solar absorptance (α) of the WC/Co coatings. The α of the multimodal WC coating reached 0.87, which was much higher than what can be achieved by either fine (0.82) or coarse powders (0.80) alone. By microstructural analysis, the enhancement in solar absorptance of the multimodal WC/Co coating was ascribed to the layer of distributed WC particles. During the thermal spraying, the nanostructured WC particles underwent rapid melting for the large specific surface area while the aggregated powders were heated, but not necessarily melted. The molten nano-WC would fill the available pores between the softened and heated aggregates, providing a layered distribution of WC particles for the spray-deposited coating. In this condition, the light-trapping in the multimodal coating will be enhanced due to the efficient light reflection among the multimodal WC particles, which contributes to the enhancement of solar absorptance.

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A dynamic magnetic field (DMF) with different angular frequencies (50, 100, and 150 π rad/s) was introduced during diamond growth via hot filament chemical vapor deposition (HFCVD). The effects of the dynamic magnetic field on the growth rate, diamond quality, growth orientation, and deposition uniformity of large-area diamond films were investigated with scanning electron microscopy (SEM), X-ray diffractometry (XRD), and Raman spectroscopy. The correlation between diamond growth and angular frequency was discussed. The results showed that a faster growth rate (about 2.5 times) and higher diamond quality were obtained by increasing the angular frequency of the DMF. A (100) textured polycrystalline diamond film was achieved, and the preferential orientation was found to evolve from (110) to (100), while the expected uniform deposition of a large-area diamond film under DMF was not achieved. The enhancement effect of the DMF was ascribed to the activation of more gas molecules, which participated in CVD diamond growth.

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