Acid Leaching of SHS Produced Magnesium Oxide/Titanium Diboride

Abstract

The stoichiometric self-propagating high-temperature synthesis (SHS) thermite reaction involving magnesium (Mg), titanium dioxide (TiO 2 ), and boron oxide (B 2 O 3 ) forms MgO and titanium diboride (TiB 2 ) as final products. Selective acid leaching is used to remove the MgO leaving TiB 2 powder. This study investigates the acid leaching of SHS-produced MgO/TiB 2 powders and a stoichiometric mixture of commercially obtained MgO and TiB 2 powders. Leaching was conducted at pH levels of 4.0, 2.5, and 1.0 by the introduction of concentrated aliquots of HNO 3 . 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 901C 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 TiB 2 measured in the solution (o100 lg/L). Conversion percentages for each leaching condition and dissolution mass of solid MgO and TiB 2 at each pH are also reported. Results from powder X-ray diffraction confirm the removal of MgO and minimal dissolution of TiB 2 , 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 was used to observe the particle morphology of the leached powders.

Synthesis and characterization of nano-structured TiB2 processed by milling assisted SHS route

“…Although some TiB 2 particles have grown in hexagonal morphology, as MgO has irregular shaped particles it acts as cement, binding TiB 2 particles together to form large agglomerates. A similar type of microstructure in the as synthesized samples was also reported in the literature [25]. SEM micrograph of N-5H-SHS sample indicates non-uniform agglomerated particles of TiB 2 phase with a mean particle size of 350 nm together with some irregular shaped particles (Fig.…”

“…It is widely used as cutting tool composites, wear resistance parts, metal melting crucibles, gaskets, electrode materials and cathodes for electro-chemical processing of aluminum in Hall-Heroults process [1][2][3][4][5]. TiB 2 can be synthesized by different methods like carbothermic/borothermic reduction of titanium oxide with boron carbide, solid state reduction of TiCl 4 , Mg and MgB 2 , sol-gel, ball milling and self-propagating high-temperature synthesis (SHS) followed by acid leaching technique [5][6][7][8][9][10][11][12].Mechanical alloying is a well known method for the extension of solid solubility limits through the formation of meta-stable solid solution with crystalline or amorphous structure. In fact, mechanical alloying induces high energy impacts on the initial powder by collision between balls and particles causing severe plastic deformation, repeated fracturing and cold welding of the particles leading to nanocrystalline materials [13].…”

Production of TiB2 by SHS and HCl leaching at different temperatures: Characterization and investigation of sintering behavior by SPS

“…During SHS, a highly exothermic combustion reaction occurs which is initiated by an electrical/chemical calorific device or a torch and the reaction becomes self-sustaining by utilizing the thermal energy released from the combustion reaction [19][20]. SHS technique has been reported in current literature as an economical and a novel route for the preparation of TiB2 and TiB2-based ceramic powders [5,[16][17][18][19][20][21][22][23]: The typical combustion synthesis system is TiO2-B2O3-Mg, where the chemical reaction processes affect the resultant phases [19][20]. The effects of combustion process parameters such as compositions, particle size and shapes of the reactant mixtures or type and amounts of the diluent additives (KCl, NaCl etc.)…”

Aluminothermal Reaction Approach for Micro‐/Nanofabrications: Syntheses of In2O3 Micro‐/Nanostructures and InN Octahedral Nanoshells

“…The ATR approach can be particularly useful in fabricating various functional ceramic, semi-conducting, and superhard materials by using high-melting oxides as precursors. Thermite reactions involving Mg, [26,27] Zr, [28] and Si [29] have been studied and reported in the literature. Therefore, one may rationally anticipate that a whole family of exothermic reactions involving a reducing metal and metallic or nonmetallic oxides can be utilized.…”