Acid Leaching of SHS Produced MgO/TiB2
Lok, Jonathan Y.
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The stoichiometric Self-propagating High-temperature Synthesis (SHS) thermite reaction involving magnesium oxide (MgO), titanium dioxide (TiO2), and boron oxide (B2O3) forms titanium diboride (TiB2) and MgO as final products. Selective acid leaching is used to remove the MgO leaving high purity TiB2 powder. The SHS method to produce TiB2 is attractive because of the relatively low temperature required to initiate the reaction, fast reaction time, and product purity. This study investigates the acid leaching of SHS produced MgO/TiB2 and a stoichiometric mixture of commercial MgO and TiB2 powders. Leaching was conducted at 90Â° C, 60Â° C, and 30Â° C at pH levels of 4.0, 2.5, and 1.0 by introduction of concentrated aliquots of HNO3. This method maintains a minimum pH target throughout the leaching process, thereby sustaining a dynamic concentration to remove the oxide. The optimal leaching conditions were determined to be at 90Â° C at a minimum pH target of 2.5 for the SHS produced product. At these conditions, conversion percentages of 83%-84% of MgO were measured with only trace amounts of TiB2 measured in the solution (less than 100 ppm). Conversion percentages for each leaching condition and dissolution mass of solid MgO and TiB2 at each pH are also reported. Results from powder XRD confirm the removal of MgO and minimal dissolution of TiB2, and indicate the formation of unidentified compounds. Inductively coupled plasma mass spectrometry (ICP) was used to analyze the ionic composition and extent of leaching. Scanning electron microscopy (SEM) was used to observe the particle morphology of the leached powders.
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