Nanoscale silica coating of porous stainless steel and its impact on water wettability
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Nanoscale silica coating of porous stainless steel and its impact on water wettability Chiemi Oka , Kimihide Odagiri, Hosei Nagano
Received: 10 January 2020 / Revised: 18 August 2020 / Accepted: 23 August 2020 Ó American Coatings Association 2020
Abstract The water wettability of porous stainless steel specimens was enhanced via a nanoscaled silica coating for application to passive two-phase heat transfer devices. A combination of porous stainless steel and water has attracted attention in the area of the heat transfer devices. However, the water wettability of stainless steel is poor, limiting the performance of the devices. In the present study, the silica coating of the specimens was conducted via a reaction of tetraethyl orthosilicate (TEOS) after pretreatment using NaOH aq. or HCl aq. Energy-dispersive X-ray spectrometry revealed that the amount of silica deposited on the surface was dependent on the pretreatment conditions and the composition of the silica-coating solutions. Measurement of porous properties indicated that the silica coating did not affect pore diameter and gas permeability since the coating was in nanoscale. Microscale contact angles were directly evaluated using an environmental SEM. The specimens showed excellent water wettability when they were covered with numerous tiny silica bumps. When the specimen was pretreated with 2 M NaOH aq. and coated in weak alkaline TEOS solution, the Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11998-020-00417-1) contains supplementary material, which is available to authorized users. C. Oka (&) Department of Micro-nano Mechanical Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan e-mail: [email protected] K. Odagiri Department of Aerospace Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan H. Nagano Department of Mechanical System Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
contact angle of the porous stainless steel decreased from 87° to 54° after silica coating. The excellent water wettability originated from the relatively smooth surface and a sufficient coverage ratio, which resulted from the moderate strength of chemical etching of the NaOH aq. and the mild silica-coating condition in the weak alkaline solution. Keywords Silica coating, Porous material, Stainless steel, Wettability
Introduction Stainless steels are widely used for various applications because of their higher corrosion resistance and lower manufacturing costs.1–3 Applications include heat transport, fluid transport, fluid filtration, and orthodontic applications.4–6 The present study focuses specifically on heat transport applications of stainless steels. We have investigated stainless steel SUS316L as a key material in heat transfer devices.7–9 A loop heat pipe (LHP) is a passive two-phase heat transfer device utilizing the capillary force of a porous medium to disturb the backward flow of a working fluid.10–12 LHPs are expec
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