Abstract
Pulsed laser melting in liquid (PLML) is a technique to fabricate submicrometer crystalline spherical particles of various materials by laser irradiation of suspended raw particles with random shapes. To fully exploit the unique features of PLML-fabricated particles (crystalline and spherical) in practice, a mass-production PLML technique is required. To this end, the present study develops a new slit nozzle that guides the suspension film flow into a non-droplet continuous stream with a low flow rate. These two incompatible flow properties (continuity and slowness) are difficult to be realized for a liquid jet to free space. The suspension film flow was irradiated with a typical laboratory scale-flash lamp pumping laser at 30 Hz pulse frequency. Only a single flow passage of the slit nozzle with a few laser pulse irradiation transformed 95% of the raw particles into spherical particles. This spheroidizing ratio exceeded those of low-rate drip flow and high-rate cylindrical laminar flow directly jetted into free space through a Pasteur pipette nozzle. Extrapolating the data obtained from a 20-ml suspension, the average production rate was determined as 195 mg h−1. The high spheroidizing ratio and yield through the slit nozzle is attributable to the uniquely slow but continuous liquid film flow. The structure of the slit nozzle also prevents particles from adhering to the slit wall during continuous laser irradiation. Thus, the suspension film flow through the newly developed slit nozzle can potentially scale up the PLML technique to mass production.
Highlights
Metal and titanium oxide[16,17,18,19,20,21,22,23]
The suspension flow rate in a transparent tube is controlled, the particles in the irradiated suspension immediately adhere to the inner tube wall, which is fatal for successive mass productions
The present study proposes a new slit nozzle for a suspension film flow, which is suitable for a laser with high pulse energy and a pulse repetition rate of several tens of Hz
Summary
Metal and titanium oxide[16,17,18,19,20,21,22,23]. 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 ( metals but ceramics and semiconductors)[12,24,25,26,27]. To achieve a high spheroidizing ratio of irradiated particles in the vessel, the PLML batch process requires a long irradiation time to compensate the extinction by suspended particles (which limits the effective irradiated space in suspension)[30,31]. Laser irradiation on a suspension of raw particles flowing at an adequate rate should continuously produce submicrometer spherical particles with a high spheroidizing ratio. The present study proposes a new slit nozzle for a suspension film flow, which is suitable for a laser with high pulse energy and a pulse repetition rate of several tens of Hz. After single-flow-passage irradiation of an adequately slow and continuous suspension flow through this new nozzle, high spheroidizing ratio exceeding 90% and high spherical particle yield 195 mg h−1 of the product are confirmed using boron nanoparticles as raw particles
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