Mechanically Induced Self-propagating Reaction Research Articles

Solvent-Free Mechanochemical Approach towards Thiospinel MgCr2S4 as a Potential Electrode for Post-Lithium Ion Batteries

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.

Fast and efficient approach to synthesis of ultra-fine TiC powder

A fast and large scalable process to produce TiC powder was obtained using a horizontal rotary ball mill within 60 min via a mechanically induced self-propagating reaction (MSR). The as-synthesized TiC particles have well-defined crystals structure and the median diameter of ∼1 μm with less impurity due to short duration of milling. The mechanism for the acceleration of MSR was investigated in detail. The graphene nano-platelets are exfoliated from graphite by ultra-high-energy of the horizontal rotary ball mill after less than 30 min of milling, which plays a crucial role in formation of leaf-like nanoplatelets with Ti lamella by ball collision. At the same time, the ultra-high-energy of ball milling can boost self-prorogating reaction in a short duration of milling.

Mechanochemical synthesis of CeB6 nanopowder

Abstract Mechanochemical synthesis of CeB6 nanopowder was performed using a mixture of CeCl3, CeO2, B2O3 and either Mg or MgH2. The reaction for the CeO2-3B2O3-11MgH2 mixture to form CeB6 and MgO gradually proceeds during ball milling, while the mechanically induced self-propagating reaction (MSR) behavior is observed during ball milling of the CeO2-3B2O3-11 Mg mixture. X-ray diffraction patterns of the CeO2-3B2O3-11MgH2 mixture indicate that CeH2+x exists as an intermediate phase during the reaction. Scanning electron microscopy indicates that the particle size of CeB6 powder from the CeO2-3B2O3-11MgH2 mixture is much smaller than that from the CeO2-3B2O3-11 Mg mixture. Transmission electron microscopy revealed that CeB6 particles 10–30 nm in size from the CeO2-3B2O3-11MgH2 mixture are highly agglomerated with surface oxide layers. The mechanochemical reaction of the 2CeCl3-6B2O3-21MgH2 mixture produces CeB6 instead of Ce(BH4)3.

A discussion on the formation mechanism of tungsten carbides during mechanical milling of CaWO4[sbnd]Mg[sbnd]C mixtures

Synthesis mechanism of tungsten carbides via mechanically-induced self-propagating reaction (MSR) was investigated. Scheelite (CaWO4) is the main ore of tungsten and was used as precursor of tungsten in this study. To investigate the effect of magnesium and carbon contents on the milling products various mixtures were prepared according to the following equation: CaWO4 +x Mg + (4 - x) C = WC + x MgO + (3 - x) CO (g) + CaO. The value of x was varied from 0.5 to 3. It was seen that the reaction is gradual when x≤2 while the reaction occurred in MSR mode at higher x values. CO gas was detected in vial for samples in MSR mode that was due to participation of carbon in reduction reaction of scheelite. Therefore W2C phase was formed because of carbon deficiency. WC was not formed because of high reaction temperature and carbon deficiency. In the second group of experiments milling of CaWO4 - 3 Mg - (1 + y) C mixtures were investigated. The elimination of carbon deficiency was the aim of these experiments. It was seen that metallic tungsten was converted to W2C. Addition of more carbon lead to the formation of WC at y=0.8−1. WC disappeared by addition of more carbon due to decrease of adiabatic temperature and interruption of atomic diffusion.

Study of reaction sequences during MSR synthesis of TiC by controlled ball milling of titanium and graphite

During reactive ball milling of Ti and C, mechanically induced self-propagating reaction (MSR) synthesis of TiC is reported to occur via a process including initial formation of small amounts of TiC prior to exothermic ignition, followed by MSR and the formation of stiochiometric TiC (Dorofeev et al., 2011; Oghenevweta et al., 2016 [1, 2]). However, both the chemical evolution and mechanisms of reaction and growth of TiC both prior to, during and after ignition are not fully understood. This research focuses on fundamental understanding of the reaction sequences during MSR synthesis of TiC from elemental Ti and C (graphite).Magnetically controlled ball milling of stoichiometric (1:1) powder mixtures of titanium (Ti) and graphite (C) was performed under He gas with the exothermic ignition point by determined via in-situ temperature measurement. X-ray diffraction, Scanning Transmission Electron Microscopy (STEM) with electron energy loss spectroscopy (EELS), Raman Spectroscopy and X-ray Photoelectron Spectroscopy (XPS) were employed to interpret the reaction sequences.The reaction sequence involved the following: During milling prior to ignition, severely deformed Ti, spheriodised graphite and amorphous carbon forms, and minor amounts of off-stiochiometric nano-TiC1−x crystals. In addition to the formation of TiC1−x, XPS revealed the formation of oxide skins coating the surface regions of the milled powders. There is also an evolution towards stiochiometric TiC with increasing milling time. Immediately after ignition, a reacted product comprising a mixture of multi-layer stacks of thin TiC plates form, in addition to a matrix comprising large TiC particles which have been liquid phase sintered under the high local heat of reaction by thin layers of unreacted Ti. MSR occurs via a dual mechanism involving rapid growth of existing TiC, plus nucleation and growth of new TiC. High spatially resolved EELS combined with STEM revealed additional information about the inhomogeneous chemical environment of the milled powders.

An investigation on the mechanism and reaction sequence of scheelite-magnesium mixtures during mechanical milling

The mechanism of mechanically-induced self-propagating reaction (MSR) of scheelite with magnesium during reactive ball milling was investigated using in-situ monitoring of the vial temperature, X-ray diffraction analysis and field emission scanning electron microscopy. Temperature variations of the vial versus milling time curves showed unusual behaviors in comparison to the reported patterns in literature. It is found that the main reason for these exceptional temperature behaviors is sublimation-deposition of magnesium. X-ray diffraction patterns of milled scheelite-magnesium mixtures revealed the formation of intermediate phases during MSR. The sequence of scheelite-magnesium reaction appeared as CaWO4→ Ca3WO6 → Ca2MgWO6 → WO3-x → W. Atomic force microscopy showed that the final product contains nanosize particles that are smaller than 50nm.

Investigating mechanochemical behavior of Cr2O3–B2O3–Mg–C quaternary system

Fundamental aspects of reaction behavior and formation path in the Cr2O3–B2O3–Mg–C quaternary system have been studied to synthesize chromium boride–chromium carbide nanocomposite. In order to find the influence of simultaneous presence of magnesium and carbon on final products, various powder mixtures were chosen according to following reaction: B2O3+Cr2O3+(9− x) Mg+x C. The value of x varied from 0 to 4. In the absence of carbon (x=0), CrB2 was synthesize through mechanically induced self-propagating reaction (MSR). In the presence of 8molMg and 1mol C (x=1), the dominant boride phase was CrB while no chromium carbide was detected. By increasing C content (x=2), the magnesiothermic reduction occurred in MSR mode; whereas, the synthesis of Cr3C2 initiated after combustion reaction and completed gradually during milling for 6h. Further increase in C amount (x=3) resulted in formation of Mg3(BO3)2 as unwanted phases as well as CrB and Cr3C2. In the presence of 6molMg and 4mol (x=4), no mechanical reaction was observed even after 8h of milling. Optimum value of x for the formation of CrB–Cr3C2 nanocomposite was 2. Based on the morphological evolutions, it is evident that the mechanosynthesized powder is made up of nanometric particles.

Mechanochemical synthesis mechanism of Ti3AlC2 MAX phase from elemental powders of Ti, Al and C

In this study, the synthesis of Ti3AlC2 MAX phase in Ti–Al–C system was investigated by high-energy ball milling. To this aim, mixtures of Ti, Al and C with stoichiometric ratios were milled by a planetary ball mill for different milling times up to 10h. The structural evaluation of powder particles, after different milling times, was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) and measurement of vial temperature. Thermodynamic investigations showed that direct reactions among elemental powders of titanium, aluminum, and carbon were strongly exothermic and the product phases were formed in a self-sustaining regime. The experimental result showed that after 10h milling the elemental powders reacted together through a rapid combustion reaction process resulting in the formation of Ti3AlC2 and TiC. It was proved that mechanically induced self-propagating reaction (MSR) is dominant mechanism.

Early stages of phase formation before the ignition peak during mechanically induced self-propagating reactions (MSRs) of titanium and graphite

The mechanism of mechanically induced self-propagating reaction (MSR) of titanium with graphite to produce TiC during reactive ball milling of elemental powders was investigated using high resolution electron microscopy, and Raman and X-ray photoelectron spectroscopies. Prior to the exothermic ignition, off-stoichiometric Ti(1+x)C(1−x) nuclei are formed by reaction at the interface between the severely deformed Ti particles and graphite milling debris. After ignition, both rapid growth of existing nuclei, and nucleation and growth of additional off-stoichiometric Ti(1+x)C(1−x) occurs. Local product morphologies after the ignition varied, depending local restrictions on the rate of diffusion of carbon into the TiC as it grows.

Mechanochemical reduction of natural pyrite by aluminum and magnesium

Abstract Mechanochemical reaction of pyrite with aluminum and magnesium were carried out for pyrite reduction using a planetary ball mill in an inert atmosphere. Thermodynamic studies indicated that the mechanochemical reactions are mechanically-induced self-propagating reaction (MSR). The XRD patterns of pyrite and magnesium mechanochemical reaction proved the reaction could not be complete after 280 min milling under the test conditions. On the other hand, the mechanochemical reaction between aluminum and pyrite completed after 120 min under similar milling conditions. The results confirm that in the primary MSR reactions troilite (FeS) phase was formed as an evidence for non-stoichiometric mechanochemical reaction. Thus, the mechanochemical reaction primary test of pyrite and aluminum was corrected with addition of more aluminum. The XRD results verified the troilite could be completely eliminated from the final product and the iron and aluminum phases contained main constituents of the obtained powder. The FE-SEM images indicated that the particles are about 100 nm to less than 1 μm in size. Finally, from SEM/EDS and XRF results, the zero-valent iron (ZVI) particles were surrounded by aluminum sulfide phase comparing.

Pre-milling Effects on Self-propagating Reactions in Mechanochemical Synthesis of CdSe and ZnSe

Abstract CdSe was synthesized from an elemental mixture via a mechanically-induced self-propagating reaction (MSR). No reaction was observed in the induction period. When each elemental powder was separately pre-milled for 15 min, the elemental mixture formed CdSe after 5 s of milling, which is much shorter than that for MSR without the pre-milling process. It was thus deduced, that in the induction period, the mechanical energy supplied by the ball-milling process was employed primarily for activation of the particles. ZnSe was also formed via MSR from a pre-milled elemental mixture after 5 s of milling. The pre-milled Zn and Se powders showed lattice expansion, suggesting that the strain energy accumulated in the particles.

Synthesis of mullite–MoSi2 nano-composite through a mechanochemical processing

Nano-composite mullite–MoSi2 with 40wt.% MoSi2 was produced from the raw materials of MoO3, Al and Si by mechanochemical processing. Different Al amounts (stoichiometric amounts of 1, 1.5 and 2mol) and milling times (15, 23, 30, 60, 180, 300min) were applied to obtain this composite. A planetary ball mill with a rotation speed of 250rpm and a ball-to-powder ratio (BPR) of 40:1 was employed. The composite was formed using 1.5mol of Al and occurrence of mechanically induced self-propagating reaction (MSR) in 23–30min. The evolutions of phases and their microstructure were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDX). By means of transmission electron microscopy (TEM) the particle size and morphology of the obtained powders were examined. The mean crystallite size of the composite changed from 60nm in 30min to 20nm in 5h; the average particle size was about 155nm in 5h.

Mechanochemical synthesis and spark plasma sintering of the cerium silicides

The cerium silicides, Ce5Si3, Ce3Si2, CeSi, CeSi2−y, and CeSi2−x, have been prepared from the elements by mechanochemical processing in a planetary ball mill. Preparation of the cerium silicide Ce5Si4 was unsuccessfully attempted and potential reasons for this are discussed. Temperature and pressure of the milling vial were monitored in situ to gain insight into the mechanochemical reaction kinetics, which include a mechanically-induced self-propagating reaction (MSR). Some prepared powders were consolidated by spark plasma sintering to high density. Starting materials, as-milled powders, and consolidated samples were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The results obtained help elucidate key questions in mechanochemical processing of intermetallics, showing first phase formation similar to thin films, MSR ignition times that are composition- and milling speed-dependent, and sensitivity of stable compound formation on the impact pressure. The results demonstrate mechanochemical synthesis as a viable technique for rare earth silicides.

Effect of Mo-Si Molar Ratio on the Synthesis of MoSi2 Through Mechanical Alloying

In this work, mechanical alloying (MA) technique, which involves repeated cold welding, fracturing and re-cold welding of powder particles, was used to produce molybdenum disilicide (MoSi2) starting from elemental powder mixtures of Mo and Si. The effects of composition of starting materials on the formation mechanism and phase formation were investigated. Two different molar ratios of Mo:3Si and Mo:4Si were prepared in addition to the stoichiometric powder mixture Mo:2Si. Intermittent sampling was done from 4 to 20 h. Samples were characterized by using X-ray diffraction (XRD)/scanning electron microscopy analyses and crystallite size calculated was based on the conventional Scherrer method. With stoichiometric powder mixture, MoSi2 was synthesized based on the mechanism of mechanically induced self-propagating reaction (MSR). Increasing Si content clearly delayed the MSR and the reactants were gradually converted to both α-MoSi2 and β-MoSi2 phases over a relatively long time. Agglomeration was noticed in samples, even though with different extents. The samples were then heat treated at 900°C. The phase transformation and crystallite size evolutions of the heat-treated powders were characterized by XRD. Final product of Mo:2Si mixture included Mo5Si3 compound, while for other compositions with extra Si the final product was α-MoSi2 and the excess Si.

Mechano-chemical sulfidization of zinc oxide by grinding with sulfur and reductive additives

A novel process for sulfidation of ZnO by co-grinding with sulfur and reductive additives (P, Fe, Al, and Mg) was developed. The sulfidation extent of ZnO with the addition of P, Fe, Al or Mg can reach 85.2%, 81.6%, 96.7% and 92.6% after grinding for 4, 6, 1 and 1 h, respectively. Based on the chemical phase composition analysis and morphological characteristics of sulfidized products by XRD, SEM and TEM, a possible reaction mechanism, mechanically induced self-propagating reaction (MSR), was proposed to explain the sulfidization reaction. In addition, the floatability of sulfidized products was investigated for the recovery of metal sulfide and ZnS can be concentrated with a high concentration ratio and concentrate grade. By using the sulfidizing process, it is expected that the recovery of zinc from the wastes or purification of heavy-metal-containing hazardous residues is technically feasible.

Synthesis of nano-structure molybdenum disilicide from primary mixture of MoO3 + Si + Al through mechanochemical reactions

The formation of nanocrystalline molybdenum disilicide intermetallic compound from the primary mixture of MoO3+Si+Al by mechanochemical synthesis (MS) method via mechanical milling was investigated. The mechanochemical processes were designed based on thermodynamic calculations and with the aim of studying the effects of changing the Al amount of the primary mixture. An MSR (mechanically induced self-propagating reaction) process was done using a high-energy planetary ball mill. The experiments were optimized to increase the amount of low temperature α-MoSi2 phase and convert the unstable β-MoSi2 phase to the stable α-MoSi2 phase. With the aid of XRD (X-ray diffraction) experiments, phases and their microstructure were analyzed. EDX (energy dispersive X-ray) experiments were carried out in order to investigate the composition of the products and TEM (transmission electron microscopy) was used to study powder particles. The crystallite size and the particle size of the obtained α-MoSi2 phase were around 18.2 and 179nm, respectively. The mass fraction of each obtained phase was determined employing the semi-quantitative analysis of X-ray diffraction patterns.

Effect of the aluminum content on the mechanochemical behavior in ternary system Al–B2O3–C

The effect of aluminum content on the mechanochemical behavior of ternary system Al–B2O3–C to fabricate Al2O3/B4C composite was investigated. A mixture of boron oxide powders along with different amounts of aluminum and graphite was activated in a ball mill. The value of Al content varied from 2mol to 7mol compared to the stoichiometric mole ratios (4mol). Thermodynamics evaluation indicates that the value of Al content in the mixture plays a key role and overall reaction enthalpy and adiabatic temperature altered by variation of aluminum and carbon content. Experimental findings revealed that at low aluminum content (2mol Al), aluminothermic reaction proceeded in gradual mode and no carbothermal reduction took place. Increase in Al content up to 3mol led to a change in the mode of aluminothermic reaction to MSR (mechanically induced self-propagating reaction) and gradual occurrence of carbothermic reaction. By increasing the amount of Al (10/3–4mol Al), aluminothermic reaction provided sufficient heat for activating endothermic carbothermic reduction; hence, both reducing reactions happened simultaneously. Further increase in Al content (7mol Al) led to gradual aluminothermic reaction and excess Al acted as inert matrix.

Obtaining NiAl intermetallic compound using different milling devices

NiAl intermetallic compound was synthesized by mechanical alloying technique in planetary and attritor mills. The starting powders consisted of elemental mixtures of Ni and Al at Ni50Al50 (at%) composition. In the planetary mill, compound formation occurred gradually during mechanical alloying, while the occurrence of a mechanically induced self-propagating reaction (MSR) can be suggested in the attritor mill. The NiAl obtained in both mill types was partially disordered with long-range order parameter not inferior to 0.66. Quantitative phase analysis using the Rietveld method was performed in as-milled samples, and this method was also employed to estimate changes in crystallite size and lattice strain of the NiAl produced during mechanical alloying.

Effect of milling variables on the synthesis of NiAl intermetallic compound by mechanical alloying

NiAl intermetallic compound was synthesized by mechanical alloying of elemental mixtures of Ni and Al powders in a Spex mill. The compound formation took place according to a mechanically induced self-propagating reaction (MSR), and the influence of milling variables on its ignition time was determined using a factorial design. Results indicated ignition time as a function of initial particle size of Ni, process control agent, and ball-to-powder ratio. Also, an interaction between ball-to-powder ratio, process control agent, and a set of balls was found to control the average particle size of as-milled powders.

Kinetics and Formation Mechanisms of a Nanostructured Fe-Y<sub>2</sub>O<sub>3</sub> Powder Prepared by Reactive Ball Milling

Reactive high energy ball-milling has known a growing interest from both fundamental and applied point of view. We focus here on the specific system Fe-Y2O3 metal-oxide nanocomposite because of its potential application to the synthesis of oxide dispersion strengthened steels, which are promising materials for nuclear applications. YFe3 and Fe2O3 were ball-milled during different milling durations in the stoichiometric proportions defined by the chemical reaction 2 YFe3 + Fe2O3 → 8 Fe + Y2O3. The obtained milled powder was characterized by XRD, SEM, TEM and their thermal behaviour was investigated by DTA. Through those characterizations, a Mechanically induced Self-propagating Reaction (MSR) was observed and several steps in the ball-milling process were identified: mixing of reactants, chemical reaction propagation, amorphization and refinement of the microstructure. The role of the milling intensity was also examined.