Quanta 450 sem

Micrographs of the base metal and the heat-affected zone (HAZ) of the two welded joints were made using an SEM. The SEM analysis was necessary because optical microscopy does not allow a precise microstructure identification. The sample preparation followed the conventional gridding procedure, with mesh SiC paper of 100, 220, 320, 400, and 600 grit sizes and diamond polishing to 1 μm. The samples were chemically etched with Nital 2% (a solution of 2% nitric acid with 98% alcohol) for 10 s.
For a complementary result, the weld metals of the two joints were analyzed via an Quanta 450 SEM (FEI, OR, USA) equipped with a Quantax electron backscatter diffraction (EBSD) system (Bruker, Billerica, MA, USA). The analyses were performed in the center of the weld metals in the region of filler passes to avoid the influence of epitaxial grain growth close to the fusion line. The regions analyzed by the EBSD were welded with a heat input of 1.7 to 2.0 kJ/mm for the GMAW process and 1.2 to 1.5 kJ/mm for the SMAW process, as seen in Figure 3. The step size, the work distance, and the arc voltage were 2.39 μm, 15.7 mm, and 20 kV, respectively. The samples for EBSD were prepared by mechanized polishing to 0.04 μm for 1 h, using colloidal silica and no chemical etching.

The microstructure of surimi gels was determined using scanning electron microscopy (SEM). Briefly, the surimi gels were prepared by cutting them into 3 mm × 3 mm × 2 mm cuboids. The cuboids were then fixed with 2.5% (v/v) glutaraldehyde in 0.2 M phosphate buffer solution (pH 7.2). The samples were rinsed for 1 h in distilled water and then dehydrated with serial concentrations in ethanol: 50%, 70%, 80%, 90%, and 100% (v/v). The dried samples were put on the aluminum stub using carbon tape, and the samples were coated with gold for approximately 60 s. The specimens were observed using a SEM (Quanta 450 SEM, FEI Company, Hillsboro, America).

The MVL morphology was examined using both optical microscopy (BX-53, Olympus, Tokyo, Japan) and cryogenic-scanning electron microscopy (cryo-SEM; Quanta 450, FEI, Hillsboro, OR, USA). The cross-section of MVLs could be observed by cryo-SEM. Briefly, conductive carbon adhesive was put on the sample table, and the diluted MVLs were placed on the conductive carbon adhesive. Then, the sample table with MVLs was rapidly frozen in liquid nitrogen for 30 s and transferred to the preparation chamber in a vacuum state for sublimation gold-coating. Finally, the sample was fractured and an approximately 5 nm of gold layer was sputter-coated on the exposed surface. The sample was imaged in the pre-cooled (~ −140) FEI Quanta450 SEM (FEI, Hillsboro, OR, USA) operated at 5 kV. The particle size distribution and average particle size of the MVLs were measured using a laser particle size analyzer (Bettersize2600, Better, Dandong, China).

Optical microscope images were captured in a reflective bright-field mode (Axio Imager M2m, Carl Zeiss, Germany). E-SEM images (at 4 °C sample temperature, and 100% relative humidity) were obtained using FEI quanta 450 SEM (FEI, OR) by increasing water vapor pressure to or above saturation pressure during E-SEM imaging. Raman spectra were obtained with the laser excitation wavelength of 633 nm, 1800 l/mm grating, 10 seconds of accumulation (Renishaw Raman/PL Micro-spectroscopy, Gloucestershire, UK). Water contact angles were measured by a goniometer KSV CAM200 (KSV Instruments Ltd., Helsinki, Finland).