Reaction path in the magnesium thermite reaction to synthesize titanium diboride

Abstract

TiB2, along with MgO and Mg3B2O6, was formed by a thermite reaction between Mg, amorphous B2O3, and TiO2 powders in argon. The mixture 5Mg–TiO2–B2O3 along with binary mixtures and single components were analyzed using differential thermal analysis (DTA) and x-ray diffraction (XRD). Large (25 g) specimens were also ignited in bulk using a resistance-heated nichrome wire. The reaction path in forming TiB2 in the three component mixture was deduced. Mg reduces TiO2 and B2O3 to form Ti and MgB2, respectively, which in turn react to form TiB2. In an oxidizing atmosphere, the significant speed of the reaction permitted solid state reaction to form TiB2 before atmospheric oxygen could diffuse into the powder mass and react to form oxide phases. Thermite reactions in air have the advantage (over furnace heating in air) of not providing time at elevated temperatures for Mg and intermediate products to become consumed in the formation of oxides, nor time for oxidation degradation of TiB2.

A fast and low-cost room temperature process for TiB2 formation by mechanosynthesis

“…1 the XRD diffraction data for milled powders at different milling times are reported: it is evident that the reaction is near-instantaneous and takes place after about 1 h of milling. This trend, as reported in literature [12], is quite similar to that found for reaction of boron oxide and magnesium [14] or tungsten(VI) oxide and magnesium [15]. Further milling of the mixture results in a broadening of TiB 2 and MgO diffraction peaks (see Fig.…”

“…In the case of TiB 2 , another route to form the compound is by reaction of TiO 2 and B 2 O 3 with metallic magnesium during extend ball milling performed at room temperature in a tumbling mill for between 10 and 15 h in an inert atmosphere [11]: the final products are TiB 2 and MgO; the oxide can be easily removed by leaching in acid, leaving a fine powder composed of pure TiB 2 , as tested by X-ray diffraction (XRD) analysis [11]. This process is a combustive reaction [12] that takes place once the ignition temperature is reached during ball impacts-the conditions reported in literature allow for TiB 2 production only with long milling times (from 10 to 15 h, as reported above) due to the chosen conditions for ball milling and the relatively poor energy transfer during ball impacts due to the use of the tumbling mill.…”

Development of an effective modifier for hypereutectic Mg–Si alloys

“…It can be clearly seen that the changes in standard state Gibbs free energies of the three reactions are all negative, which indicates the above reactions are all favorable. This result is in agreement with that of Sundaram et al [15]. Based on thermodynamics calculation and the result of the sintering experiment ( Fig.…”

Effect of fine boron powders prepared with a self-propagating high temperature synthesis on flux pinning properties of the MgB2/Fe composite wires

“…Thus, the reaction is performed in a nonequilibrium manner. In addition to this, difference between Gibbs free energies for MgB 2 formation (4Mg + B 2 O 3 → 3MgO + MgB 2 , G(T) = −666,940 + 123.19T (J/mol)) and boron formation (3Mg + B 2 O 3 → 3MgO + 2B, G = −574,290 + 112.55T (J/mol)) are less than 100 kJ/mol which is much smaller than Gibbs free energy for either two reaction [13,15]. Thus, although the duration of high temperature reaction is very short (a few seconds), magnesium borides are inevitably incorporated in SHS processing of boron powders.…”

“…Since the maximum temperature available with adiabatic condition, an adiabatic combustion temperature for the SHS reaction in Eq. (1) is calculated to be about 2400 • C from thermodynamic data [13], the temperature rise during SHS reaction is very high even though heat flow should be considered. Thus, the reaction is performed in a nonequilibrium manner.…”