2. MATERIALS AND METHODS
Mg particles (800 nm, 99.9%, US Research Nanomaterials) and boric
acid powder (99.5%, Sigma Aldrich) were used in the synthesis.
Commercial MgB2 (−100 mesh, 99%, Sigma Aldrich) was purchased
to serve as a standard against which to compare the amount of energy
released. The synthesis method involves annealing the physical
mixture of the Mg and boric acid powders by a process similar to that
used to produce Mg/B solid solutions from Mg and B.10 Briefly, Mg
and boric acid were mixed in the weight ratio of 1:1 (excess Mg) by
dry powder-based magnetic mixing, and the mixture was spread on
the surface of the glass slide (Dot Scientific Inc.). After forming a layer
on the glass slide, the powder was compressed with another glass slide
from the top to maximize contact between particles in the powder and
minimize contact with air. Glass slides were packed using aluminum
foil and placed into a muffle furnace (model: FB1415M, Thermolyne)
for annealing. The temperature was increased to 550 °C at a rate of 30
°C/min and was maintained at 550 °C for 2 h. After processing, the
furnace was turned off, and the particles were left to cool inside for 3
h. Time and temperature conditions for the synthesis were optimized
by measuring the energy released from the oxidation of synthesized MgB2.
X-ray diffraction (XRD) was performed using Cu Kα X-rays on a
Malvern Panalytical XPert Pro MPD theta−theta diffractometer. X-
ray photoelectron spectroscopy (XPS) was carried out using a
Physical Electronics VersaProbe II instrument equipped with a
monochromatic Al Kα X-ray source. Scanning transmission electron
microscopy (STEM) with energy-dispersive spectroscopy (EDS) was
executed on a Talos F200X at 200 kV with an XFEG source and high-
angle annular dark-field (HAADF) imaging. Particle size analysis was
carried out using dynamic light scattering (DLS) on a Malvern
Zetasizer Nano ZS. Intensity fluctuations were analyzed, which gives
the velocity of the Brownian motion of the particles from which we
can measure the particle size using the Stokes−Einstein equation.
Thermal analysis was performed on a TA Instruments Model Q600
SDT, which provided simultaneous measurements of heat flow
(differential scanning calorimetry (DSC)) and weight change (TGA)
on the sample from ∼20 to 1000 °C. Analyses were conducted in air
at a volumetric flow rate of 100 mL/min. Alumina sample cups (90
μL, TA Instruments) were used in the analysis to hold the sample. A
heating rate of 20 °C/min was used till 1000 °C after maintaining
isothermal conditions for the first 10 min. To determine the storage
stability of the synthesized MgB2 and compare it with the stability of
Mg, accelerated aging tests were conducted. The Mg and MgB2
samples were placed in an oven for 120 min with temperature and
relative humidity of 100 °C and 70%, respectively. After this, both
samples were taken for DSC analysis to measure their oxidation
energy release. The changes in the energy release were noted and
compared before and after the aging tests to quantify the effect of
synthesizing MgB2 on Mg.
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. Thermite rxns are discussed far more often than they are performed.