Tracking explosions with toughened-up tracers PNNLab
Agglomerated silica particles made by the Stöber method have received far less attention until recentlywhen their specific porous properties have been sought. One of the methods to make agglomerated silica particles is by the iterative stepwise addition of reagents. Iterative synthesis of the particles allows for control of both the smaller silica shell around the quantum dots and their overall agglomerated microparticle size.
Two methods to create luminescent silica-covered quantum dots were employed in this work. For particles less than one micron in diameter, multiple shells of silica were grown around the quantum dots to make particles with known size ranges. As luminescent intensity was diminished for single silica shell particles larger than 1 µm, an iterative reagent addition method was employed to make agglomerated microscale particles that maintain their luminescent intensity.
In this work, the synthesis of 0.1–4-µm-diameter silica-covered ZnS:Mn-based tracers is presented and their response to environmental pH is examined. Specifically, the authors hypothesize that the luminescence intensity of 3-mg/mL-concentration, 1-µm-diameter microagglomerates will be above the detection threshold of an Ocean Insight HDX detector after 40 days of pH 3 or higher exposure.
Particle sizing was performed by three methods, depending on the particle size. Scanning electron microscope images were taken on a Helios 600 for particle diameters below 1 µm. The bias was set to 10 kV and a working distance of 4–8 mm. Dynamic light scattering was performed with a NanoBrook from Brookhaven Instruments, at ambient temperature for all diameters.
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