Search

Alumina-TiB 2 is a hard ceramic composite with applications in aviation, aerospace and wear resistant tools. It can be manufactured in-situ through a highly exothermic aluminothermic self-sustaining reaction from the starting materials of Al, TiO 2 and B 2 O 3. In this paper, the effect of vibration ball milling on the particle size reduction and the reactivity enhancement of the Al–TiO 2 –B 2 O 3 powder mixture is examined by XRD, SEM, EDS, DTA and particle analysis techniques. Measures for combating the stoichiometric inconsistencies deriving from the tendency of B 2 O 3 to absorb atmospheric water, giving boric acid H 3 BO 3 , are implemented. Characterisation of the milled samples display Al microparticles with d(0.9) below 64 μm, coated with nano-particles of TiO 2 and B 2 O 3 , with particle sizes up to 600 nm. Differential thermal analysis reveals that ignition is feasible for all of the milled mixtures, unlike the un-milled one. It also presents that extensive milling results in a reduction in the ignition temperature of the reactant mixture to 925 °C for the 5 h-30Hz milled sample, from the previous 982 °C recorded for the 1 h–20Hz milled sample. The in-situ synthesised Al 2 O 3 –TiB 2 matrix deriving from the 5 h-30Hz milled sample, gives less of the unwanted Al 5 BO 9 phase and improved skeletal and bulk densities, by 0.15 g/cc and 0.1 g/cc respectively, compared to the respective composite deriving from un-milled reactants powder mixture. [ABSTRACT FROM AUTHOR]

[Display omitted] • VBSS contains above 40% CaO which poses difficulty in recovering vanadium, hence parametric ball-milling was used. • Above 80% vanadium was effectively recovered with the low-temperature Na 2 CO 3(aq) MA-Leaching. • The MA parametric modeling integrated the chemical concentration into derivation for effective reactivity prediction. • The process is simple, low-temperature leaching, cost-effective, and eco-friendly. Powder formation using a ball mill has found applications in various industries such as extractive metallurgy, nanomaterials, chemicals, materials science, and pharmaceuticals, but the particle size reduction rate, speed, and milling/ignition time required for each industrial application are very crucial. A novel environmentally-friendly parametric modeling of wet ball-milling- Na 2 CO 3 (aq) leaching at low temperature without roasting operation was carried out to recover vanadium from vanadium-bearing steel slag (VBSS). The paradigm shift in the source of strategic metals (SMs) globally validates the fact that the gangue of today is the valuable mineral of tomorrow. Due to the depletion of primary resources, the world has shifted focus towards recovering SMs from secondary resources to cater to its upsurge demands and sustainability worldwide satisfactorily. VBSS has proven to be a promising secondary resource from which SMs especially vanadium can be recovered more economically and environmentally via mechanical activation-assisted leaching. In previous research works, a rigorous process (high temperature, high stirring speed pressure MA- leaching with/without roasting) has been used to recover vanadium from VBSS. This present research work investigated the effective processing of VBSS by paying meticulous attention to the processing parameters via particle size reduction (reactivity) equation derivation considering the chemical solution. A vanadium recovery efficiency above 80 % was achieved from VBSS at a reaction/milling time of 30 min, ball size 10 mm, BPR 7.8, speed 140 rpm, leaching time 2hrs, leaching temperature 80 °C–90 °C, and stirring speed 300 rpm. Generally, the experimental and derived theoretical model results follow the same trend in perfect agreement. [ABSTRACT FROM AUTHOR]

Energy-intensive industries are one of the key greenhouse gas emitters, and decarbonization of such industries is a top priority to promote global sustainability. As one of the top energy-intensive industries, ceramic manufacturing industries are urged to boost energy efficiency in ceramic structure production. In this paper, we present a rapid and low carbon footprint strategy for freeform manufacturing spatial ceramic composites. Our approach integrates layer-by-layer deposition, photothermal in-situ solidification, and self-sustaining ceramization, enabling consolidation using only 1920 J energy. Compared to state-of-the-art processes, energy consumption can be reduced by over 100-fold, resulting in an estimated 1000-fold decrease in CO 2 emissions. This energy-efficient process also demonstrates the rapid fabrication of ceramic gyroid heat exchangers, capable of withstanding extreme environments. • Design ceramic powders-mixed feedstocks for both printability and capability of self-sustaining consolidation. • Identify the process window for low porosity and low energy consumption. • Consolidation at high temperatures with neglectable external energy. • Reduce energy consumption by over 100-fold and CO 2 emissions by 1000-fold. • Manufacturing heat exchanger with heat transfer coefficient improved by 13-fold. [ABSTRACT FROM AUTHOR]

Several new compounds, with desirable properties of ion mobility and working voltage, have been recently proposed using a density functional theory (DFT) computational approach as potential electrode materials for beyond-lithium battery systems. After evaluation of the 'energy above hull', thiospinel MgCr2S4 has been suggested as interesting multivalent battery cathode candidate, even though the synthesis of its exact stoichiometry poses serious challenges. In this work, MgCr2S4 is prepared using an innovative mechanochemical route starting from magnesium or magnesium hydride, chromium, and sulfur powders. The progress of such mechanically induced reaction as a function of processing time is carefully monitored by XRD with Rietveld refinement, evidencing the occurrence of a mechanically induced self-propagating reaction (MSR). The effect of parameters associated with the milling apparatus (impact energy) on the products composition are also investigated. To our knowledge, this work represents the first report of the scalable and simple mechanical alloying synthesis of thiospinel MgCr2S4 (space group Fd-3 m, a = 10.09 Å) and opens up interesting possibilities for the exploitation of such material in next-generation post-lithium batteries. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) provides an effective way to fabricate geometrically tailored structures. Existing metal AM technologies depend on external heat-induced phase transformation or consolidation to fabricate structures, showing limited energy efficiency and low manufacturing rate. Here, we report an energy-efficient and rapid strategy for metal AM by uniting self-sustaining metallic reactions with the AM process. Multilayer reactive nickel (Ni) and aluminum (Al) foils are compressed into a hybrid rod with compact bi-continuous Ni and Al phases as feedstock. A transient heat initiated the automatically propagating exothermic reaction among the reactive components, then synchronized with layer-by-layer deposition, forming 3D dense structures without expensive power equipment. The reactive feedstock structural configurations were found to be critical for controlling the deposition rate and mechanical strength of the printed part. The as-printed structure achieves a flexural strength of 170.1 MPa, which can be further improved by post-treatment. Among all metal AM processes, our method realizes the fastest AM rate of 30.0 kg/h, and the lowest AM energy consumption of 3 × 10 − 4 kWh/kg, representing over a three-order-of-magnitude reduction in energy consumption compared to the least energy-consuming current metal AM process. Throughout the entire lifecycle of our approach, it is also energy-efficient and economically viable when compared to traditional AM processes. This technology provides a cost-effective, energy-efficient, rapid AM approach to fabricating mechanically robust metallic structures. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Here, we report on a size-controlled synthesis of highly crystalline germanium particles, via the self-sustained reaction of GeO 2 with Zn, Mg, and NaBH 4. The thermodynamic analysis suggests that the GeO 2 + 2Zn and GeO 2 + NaBH 4 systems are characterized by moderate heats of reaction (−121 and −204 kJ per mole of Ge, respectively), while GeO 2 + 2Mg exhibits a much higher reaction enthalpy (−623 kJ). Magnesium reduction has been found not to be suitable for the preparation of germanium crystals due to the high reaction temperature, which exceeds 2000 °C. The partial substitution of Zn by Mg, however, enables increasing the overall reaction temperature in the low caloric GeO 2 +Zn system. By using different reducers and their mixtures, the reaction temperature was optimized to be in the 600–1100 °C range. Such temperature modifications allow for control of the germanium particle sizes, ranging from 200 nm to 2 mm. Thermal analysis of the reacting mixtures and electron microscopy examination of the products indicates that dissolution-precipitation is the dominant formation mechanism of the germanium crystals in the GeO 2 + Zn system. The higher reaction temperatures in the GeO 2 + Zn + Mg and GeO 2 + NaBH 4 systems cause melting, and subsequent coalescence of the primarily precipitated germanium resulting in much larger particles. Graphical abstract Size-tunable germanium particles. fx1 [ABSTRACT FROM AUTHOR]

Several new compounds, with desirable properties of ion mobility and working voltage, have been recently proposed using a density functional theory (DFT) computational approach as potential electrode materials for beyond-lithium battery systems. After evaluation of the ‘energy above hull’, thiospinel MgCr2S4 has been suggested as interesting multivalent battery cathode candidate, even though the synthesis of its exact stoichiometry poses serious challenges. In this work, MgCr2S4 is prepared using an innovative mechanochemical route starting from magnesium or magnesium hydride, chromium, and sulfur powders. The progress of such mechanically induced reaction as a function of processing time is carefully monitored by XRD with Rietveld refinement, evidencing the occurrence of a mechanically induced self-propagating reaction (MSR). The effect of parameters associated with the milling apparatus (impact energy) on the products composition are also investigated. To our knowledge, this work represents the first report of the scalable and simple mechanical alloying synthesis of thiospinel MgCr2S4 (space group Fd-3 m, a = 10.09 Å) and opens up interesting possibilities for the exploitation of such material in next-generation post-lithium batteries.

Abstract: The formation of ZnSe via a mechanically-induced self-sustaining reaction (MSR) from a Zn/Se mixture showed that only size reduction and mixing of the reactants without product formation occurred during the induction period prior to ignition. Therefore, all mechanical energy supplied by the planetary mill during this time, called the ignition time (t ig), was used exclusively in the activation of the reactants. This system was chosen to study the dependence of t ig on the main parameters characterising the milling intensity of planetary mills. The variation of the ignition time with the process conditions reflected changes in the mechanical dose rate of the planetary mill. A direct relationship between the inverse of the ignition time and the power of the planetary mill was established, which allows the validation of theoretical models proposed in the literature for the energy transfer in milling devices and the comparison of milling equipment efficiencies. [Copyright &y& Elsevier]