High‐Strength Sub‐Micrometer Spherical Particles Fabricated by Pulsed Laser Melting in Liquid

Abstract

nanostructures. However, these nanostructures have strongly anisotropic mechanical properties originated from their shapes. Furthermore, various nanocomposites using nanoparticles [3] or nanosheets [4] as fillers have been extensively studied because of their designable mechanical properties. However, direct studies on the mechanical properties of smaller 0D nanoparticles have been quite limited so far.Sub-micrometer spherical particles can be synthesized by applying pulsed laser irradiation onto raw colloidal nanoparticles dispersed in a liquid medium as a new type of 0D nanoparticles. This technique is referred to as pulsed laser melting in liquid (PLML). [5][6][7][8] In this process, raw nanoparticles are selectively heated and melted by unfocused pulsed laser irradiation to form droplets due to the temperature increase over the melting point. Raw nanoparticles are generally aggregated in liquid, and therefore aggregates merge into large sub-micrometersized droplets during instantaneous laser heating. Subsequently, generated droplets are quenched by the surrounding liquid to become highly crystalline nonporous sub-micrometer spherical particles. Sub-micrometer-sized particles are obtained due to the balance between the size-dependent optical absorption efficiency of particles and the heat capacity of the material to reach the melting point. [9,10] Using this technique, sub-micrometer spherical particles can be fabricated for various materials, such as metals, [11,12] oxides, [13,14] semiconductors, [15] and even carbides. [7,16] As commercially available sub-micrometer spherical particles are Sub-micrometer spherical particles that are obtained by pulsed laser melting in liquid (PLML) are usually observed to be single crystalline, and it is suggested that they are mechanically very strong. In this study, fracture tests of various sub-micrometer spherical particles are performed by compressive force application. The results indicate that B 4 C and TiO 2 sub-micrometer spherical particles exhibit brittle fracture behavior under tensile fracture mode at the center of the particles. The fracture strength of the sub-micrometer spherical particles is larger than that of the bulk material reported in the literature by about one order of magnitude. TiO 2 sub-micrometer spherical particles obtained by PLML are stronger than the commercially available TiO x sub-micrometer spherical particles with a porous structure. In addition, due to the single crystallinity of particles, smaller particles have larger fracture strength, becoming up to 10-40% of ideal tensile fracture strength calculated based on density functional theory. Thus, these results demonstrate that sub-micrometer spherical particles obtained using PLML exhibit fairly strong and unique mechanical properties, and therefore they are very promising for various mechanical applications at the sub-micrometer size scale. Fracture Strength AnalysisThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/ppsc.2018...

Determining the Composite Structure of Au-Fe-Based Submicrometre Spherical Particles Fabricated by Pulsed-Laser Melting in Liquid

“…PLML can produce submicrometre spherical particles of various materials, such as metals [ 7 , 8 ], oxides [ 5 , 6 , 9 ], semiconductors [ 10 , 11 ] and carbides [ 3 , 4 ]. Given the unique features of submicrometre spherical particles—including their dispersibility, stability, crystallinity and sphericity—applications utilizing optical [ 5 , 12 ], medical [ 13 ], mechanical [ 14 , 15 ] and magnetic [ 16 ] functionality have been examined.…”

Fracture and Embedment Behavior of Brittle Submicrometer Spherical Particles Fabricated by Pulsed Laser Melting in Liquid Using a Scanning Electron Microscope Nanoindenter

“…An indentation device (Hysitron PI SEM PicoIndenter) installed 4600 F) was utilized for compressive fracture and embedment tests denter speed for all compression tests was fixed at 12.5 nm s −1 . Fur mental conditions and the typical arrangement of the particles, subst were the same as those described in a previous report [4]. The diam flattened to a 1 μm square, using a focused ion beam installed on th operation and observation of the particles during mechanical tests.…”

“…Spherical SMPs composed of NP aggregates have also been reported for TiO 2 [ 3 ]. However, these SMPs are polycrystalline or porous, and, therefore, their mechanical properties are not good, owing to the high density of grain boundaries or nanopores, which act as defect sources [ 4 ].…”

“…However, only a few studies on mechanical properties of hard, brittle, crystalline SMPs have been reported so far [ 4 , 17 ]. In our previous report, brittle non-porous SMPs of B 4 C and TiO 2 were fabricated via PLML, and their mechanical properties were measured using a nanoindenter equipped in a SEM [ 4 ]. In that experiment, the particles were placed on a hard SiC substrate and pressed using a diamond indenter.…”

Guided Slow Continuous Suspension Film Flow for Mass Production of Submicrometer Spherical Particles by Pulsed Laser Melting in Liquid

“…Our group extended this technique to be more powerful by increasing the yield using unfocused laser beam and by developing a method to estimate the size range of produced particle size at specific laser energy density for various materials (not only metals but ceramics and semiconductors) 12 , 24 – 27 . To exploit the unique features of particles obtained by PLML (submicrometer size, crystalline, and spherical) 24 , 28 , 29 in practical applications, a mass-production PLML technique is also demanded. In our previous PLML particle synthesis for batch type irradiation, the production rate reached 7 mg h −1 under typical conditions 24 , 25 .…”