Mechanically Induced Self-propagating Reaction Research Articles

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.

Synthesis of Ti<sub>2</sub>AlC and Ti<sub>3</sub>AlC<sub>2</sub> by Mechano-Chemical Reaction and Hot Pressing Process

The mechanically induced self-propagating reaction (MSR) and hot-pressing consolidation were adapted to synthesize Ti2AlC and Ti3AlC2 using Ti, C and Al powder mixtures. The effects of Al content on the microstructure and mechanical properties of fully dense Ti2AlC and Ti3AlC2 were investigated. The results reveal that the Ti3AlC2, TiC and TiAlx transitional phases were formed by mechanically alloying according to the mechanically induced self-propagating reactions (MSR). Through hot pressing the as-milled powders with initial composition of 2Ti/1.5Al/C and 2Ti/Al/C, respectively, at 1100°C for 1 h, the desired high purity Ti2AlC and Ti3AlC2 were produced. SEM images confirmed that the as-fabricated Ti2AlC and Ti3AlC2 grains are plate-like with nanoscale layered structure and dispersed uniformly.

High Purity Ti<sub>2</sub>AlC Powder Prepared by a Novel Method

Ti2AlC powders with high purity were successfully synthesized via high energy milling and heat treatment of Ti, C and Al powders. The effects of composition and thermal treatment on the formation and purity of Ti2AlC were examined in detail. The results shown a mechanically induced self-propagating reaction (MSR) was triggered to form Ti3AlC2, TiC and TiAlx during the high energy milling. When the as-milled powders were heat treated, Ti2AlC was initially formed by the reaction between TiAl and TiC. With continuously increasing temperature, Ti2AlC was also produced by the reaction between TiAl and Ti3AlC2.

Effect of diluent on the synthesis of molybdenum disilicide by mechanically-induced self-propagating reaction

The effect of the addition of diluent to Mo–Si system on the formation of MoSi 2 by mechanically-induced self-propagating reaction was investigated in a high-energy ball mill. MoSi 2 intermetallic was added as diluent to Mo–Si powder mixture. The structure and morphology of the reaction product was analyzed by X-ray diffraction and scanning electron microscope. The diluent decreased the adiabatic temperature, increased the ignition temperature and modified the Mo/Si reactants interface. Therefore, the incubation period of mechanically-induced self-propagating reaction was extended from 90 min to 140 min with the addition of diluent from 0 wt% to 10 wt% to Mo–Si powder mixture. The extended milling time reduced the size of agglomerated particles and fine MoSi 2 product was obtained.

Effects of stearic acid on synthesis of nanocomposite WC–MgO powders by mechanical alloying

The effects of stearic acid as a process control agent (PCA) on the synthesis of WC–MgO by mechanical alloying have been investigated. 0–2.0 wt% of stearic acid is added into the mixture of WO3, Mg, and graphite powders in high-energy planetary ball milling experiments, and the as-milled powders are characterized by XRD and TEM. Results show that the mechanochemical reaction among WO3, Mg, and graphite to form WC–MgO can be changed from a mechanically induced self-propagating reaction (MSR) to a gradual reaction by the addition of stearic acid in the range from 1.2 to 1.8 wt%, when other milling parameters are maintained at the same level. It has also been found that with the addition of stearic acid, the crystallite and particle size of WC–MgO powders can be refined, the homogeneity of particle size can be improved and the powder yield can be increased.

Effects of tungsten and aluminum additions on the formation of molybdenum disilicide by mechanically-induced self-propagating reaction

Abstract The effects of tungsten and aluminum additions to Mo–Si system on the formation of MoSi 2 by mechanically-induced self-propagating reaction in a high-energy ball mill were investigated by X-ray diffraction. The incubation time for mechanically-induced self-propagating reaction to form MoSi 2 was 90 min in Mo–Si system. With the addition of tungsten to Mo–Si system, the incubation time of mechanically-induced self-propagating reaction of (W x ,Mo 1− x )Si 2 system was prolonged. It was due to the decrease of adiabatic temperature with increase in x , and the mechanically-induced self-propagating reaction was not observed until 150 min of high-energy milling in (W x ,Mo 1− x )Si 2 powder sample with x equals to 0.4. Conversely, the minor aluminum ( y 1− y ,Al y ) 2 system) substituting for silicon had shorten the incubation period and accelerated the reaction. When tungsten and aluminium were added simultaneously to Mo–Si system, the mechanically-induced self-propagating reaction was observed in (W 0.1 ,Mo 0.9 )(Si 0.9 ,Al 0.1 ) 2 sample, but it was not observed in (W 0.2 ,Mo 0.8 )(Si 0.8 ,Al 0.2 ) 2 and (W 0.3 ,Mo 0.7 )(Si 0.7 ,Al 0.3 ) 2 samples.

Control of carbon loss during synthesis of WC powder through ball milling of WO 3–C–2Al mixture

WC–Al 2O 3 composite powder potentially could be synthesized through milling of WO 3–C–2Al mixture. High temperature resulted from reduction of WO 3 by Al, activates the reduction reaction of WO 3 by C and brings about carbon deficiency in the system which consequently causes the formation of undesirable W 2C phase. Hence, addition of excess amounts of C becomes necessary. The aim of the present study has been to find out some appropriate routes for the fabrication of WC–Al 2O 3 composite powder from WO 3–2Al–C mixtures in such a way that the formation of W 2C is prevented. Results of high energy milling showed that the mode of reaction in WO 3–2Al–C mixture is MSR (mechanically induced self-propagating reaction). In this system, evolution of CO gas and high value of C loss were evidences for the need of excess C. For samples produced via suggested routes, no CO evolution was observed and the amounts of total carbon were constant. These observations showed that the proposed routes have been capable of producing WC phase without the presence of W 2C. Mechanism of the reactions in each route has been discussed.

Effect of the aluminum content on the behavior of mechanochemical reactions in the WO 3–C–Al system

In order to produce tungsten carbide from its oxide through mechanochemical process, a mixture of tungsten oxide, carbon and aluminum powders was subjected to high energy milling. Excess carbon addition was made in expense of aluminum, so that carbon acts not only as a carbide former agent but also as a reductant. Aluminum and carbon contents of the mixture were altered according to the following reaction: WO 3 + (4 − 1.5 x)C + xAl = WC + ( x/2)Al 2O 3 + (3 − 1.5 x)CO(g). The value of x varied from 0.5 to 1.9 and the effect of Al content on the mechanism of tungsten carbide formation was investigated. Thermodynamic calculations revealed that the amount of Al in the mixture plays a key role. Experimental results showed that at lower Al content in the WO 3–Al–C mixture ( x = 0.5–1.2), reactions proceed through a gradual mode. By increasing Al content ( x = 1.3–1.6), type of reactions changed to mechanically induced self-propagating reaction (MSR) with no carbothermic reduction reaction of WO 3. Further increase of Al content ( x = 1.7–1.9) resulted in MSR mode reactions consisting of both aluminothermic and carbothermic reactions. Optimum value of x which yields maximum amount of WC was found to be around 1.7. Discussion has been made to elucidate the phase formation types in accordance with the above three reaction modes.

Structural evolution of Si-50%C powder during mechanical alloying and heat treatment

The nanocrystalline β-SiC powder was successfully synthesized by ball milling the Si-50%C elemental powder. During ball milling, a solid solution of C in Si, Si(C), firstly forms, followed by SiC. The formation of SiC is controlled by the mixing mechanism of the gradual diffusion reaction(GDR) and the mechanically induced self-propagating reaction(MSR). The amount of β-SiC increases with milling time increasing. After 40 h milling, there exists only β-SiC in the milled powder. The grain size of β-SiC is about 6.4 nm after the powder is milled for 60 h. After the 60 h-milled Si-50%C elemental powder is heat treated at 1 100 °C for 1 h, the grain size of β-SiC does not change, but the lattice ordering degree of β-SiC increases.

Synthesis of Ti 3AlC 2 ceramic by high-energy ball milling of elemental powders of Ti, Al and C

Synthesis of the ternary carbide Ti 3AlC 2 by high-energy ball milling of elemental Ti, Al and C powders with a stoichiometric composition was tentatively investigated. The results show that high content Ti 3AlC 2 was successfully obtained after ball milling of powder mixture only for 3 h. The milled products consist of powder and a coarse granule with 8 mm in diameter, and both are mainly composed of Ti 3AlC 2 with TiC as impurity based on X-ray diffractometer (XRD) and energy-dispersive spectroscopy (EDS) characterization. It is believed that a mechanically induced self-propagating reaction (MSR) was triggered to form Ti 3AlC 2 and TiC during high-energy ball milling process.

Mechanosynthesis of molybdenum carbides by ball milling at room temperature

β-Mo2C and high temperature phase η-Mo3C2 were mechanosynthesised by ball milling mixtures (MoO3+2Al+xC) with different molar graphite contents (x=0.5, 1.0, 1.25, 1.5, 1.75, 2.0) at room temperature. The experimental results and thermodynamic calculations reveal that the mechanosynthesis reactions were mechanically induced self-propagating reaction (MSR). The effects of graphite content on the phase constitution of the resultants were discussed. The structure and thermal stability of the molybdenum carbides were also studied.

Synthesis of TiC by controlled ball milling of titanium and carbon

Titanium and carbon powder mixtures with compositions of Ti100−xCx (x = 50, 40, 30) were milled under a helium atmosphere using a magneto ball mill. Controlled ball milling was performed in a higher energy impact mode and a lower energy shearing mode. For Ti50C50 and Ti60C40 powder mixtures milled in impact mode, TiC was formed via a mechanically-induced self-propagating reaction (MSR). When milling Ti70C30 in impact mode, the reaction to form TiC proceeded gradually as milling progressed; indicating that, for milling conditions that lead to the formation of TiC via MSR, a minimum carbon content is required to sustain the self-propagating reaction to form TiC. Milling in shearing mode resulted in the gradual formation of TiC during milling. This study found that increasing the carbon content of the starting powder mixture slowed the milling process. Replacing the activated carbon starting powder with high purity graphite was found to have little effect on the ignition time; indicating that the slowing of the milling process is not due to graphite acting as a lubricant during milling. Rather, this slowing of the milling process is most likely due to an increased carbon content resulting in an increase in the volume of the powder mixture. This would have a similar effect during milling to decreasing the ball:powder weight ratio (BPR), which is known to slow the milling process.

Synthesis of MoSi 2–Al 2O 3 nanocomposite by mechanical alloying

MoSi 2–Al 2O 3 nanocomposite was synthesized by mechanical alloying (MA) of MoO 3, SiO 2 and Al powder mixture. The structural evolution of the powders was studied by X-ray diffraction (XRD). Both β-MoSi 2 and α-MoSi 2 were obtained after 3 h of milling. The spontaneous formation of β-MoSi 2 during milling proceeded by a mechanically induced self propagating reaction (MSR), analogous to that of the self propagating high temperature synthesis (SHS). After 70 h of milling the β-phase transformed to α-phase. The crystallite size of α-MoSi 2 and Al 2O 3 after milling for 100 h was 12 and 17 nm, respectively. Residual Mo and Si in the 3 and 70 h milled samples formed β-MoSi 2 and Mo 5Si 3 during heating at 1000 °C, respectively.

Formation of Ti3AlC2 by mechanically induced self-propagating reaction in Ti–Al–C system at room temperature

The formation of Ti3AlC2 was first investigated by mechanically induced self-propagating reaction (MSR) in Ti–Al–C system at room temperature. The effects of the milling parameters on the formation of Ti3AlC2 were discussed. The phase composition and microstructure were analysed and observed by using X-ray diffraction and scanning electron microscopy, respectively. The formation mechanism of Ti3AlC2 was analysed. An MSR was ignited during mechanical alloying of Ti, Al and C powders after a short time. An exothermic reaction between Ti and Al in the Ti–Al–C system first occurred after a certain milling time. Then, Ti–C reaction was induced at high temperature. All of the above reactions were exothermic that resulted in Ti–Al liquid formation. The previously formed TiC dissolved into and nucleated in the Ti–Al liquid. At last, Ti3AlC2 formed between the Ti–Al melt and the TiC. The final products consist of Ti3AlC2, TiC and Al3Ti.

Synthesis of Ti 3SiC 2 powders by mechanically activated sintering of elemental powders of Ti, Si and C

Mechanically activated sintering process has been employed to fabricate titanium silicon carbide (Ti 3SiC 2) powders by using the elemental powders of Ti, Si and C. Superfine powders were obtained after milling of both the powder mixtures with a stoichiometric composition and with an excess of 20 mol.% Si for only 1.5 h. The milled powders comprised TiC, Ti 3SiC 2 and silicides because a mechanically induced self-propagating reaction (MSR) was triggered during mechanical alloying. The aim of the extra-Si introduced to the starting composition is to study its effect on the formation of Ti 3SiC 2. High content of Ti 3SiC 2 has been obtained after sintering the milled powders at relatively low temperature of 1250 °C. Ti 3SiC 2 grains exhibit a fast growth behavior and various features in shape. A large amount of Ti 3SiC 2 whiskers have been found after sintering the milled powders with excess of Si at 1350 °C. The formation of Ti 3SiC 2 whiskers has relation to the appearance of eutectic liquid phases at that temperature.

Effect of starting composition on the synthesis of nanocrystalline TiC during milling of titanium and carbon

Titanium and carbon powder mixtures with compositions of Ti 100− x C x ( x = 50, 40, 30) were milled under a helium atmosphere using a magneto ball mill. For Ti 50C 50 and Ti 60C 40 powder mixtures, nanocrystalline TiC was formed via a mechanically induced self-propagating reaction (MSR), indicated by an abrupt increase in the temperature of the milling vial that corresponded to the formation of TiC. The sudden temperature increase occurred after milling for approximately 70 h for Ti 50C 50 and after approximately 40 h for Ti 60C 40. No such abrupt temperature increase was detected when milling Ti 70C 30 and XRD analysis indicated that, for Ti 70C 30, the reaction to form TiC proceeded gradually as milling progressed. These results demonstrate that, for milling conditions that lead to the formation of TiC via MSR, a minimum carbon content is required to sustain the self-propagating reaction to form TiC, below which TiC is formed via a gradual reaction.

Effect of Moisture on the Synthesis of TiC by Mechanically-Induced Self-Propagating Reaction

Effect of Moisture on the Synthesis of TiC by Mechanically-Induced Self-Propagating Reaction

Quantitative comparison of the efficiency of mechanochemical reactors

A simple method is proposed for the comparison of the mechanical dose rates of different mills, based on measuring the ignition time of a mechanically-induced self-propagating reaction (MSR). Specifically, a SPEX 8000 Mixer Mill with round-ended and flat-ended milling vials and a Fritsch Pulverisette-6 planetary mill are compared, using the ignition of MSR between Zn and S powders as the test reaction. The method facilitates the comparison of reaction kinetics data obtained by using different milling equipment.

Influence of stearic acid on mechanochemical reaction between Ti and BN powders

The influence of stearic acid as a process control agent on the mechanochemical reaction between Ti and BN to form TiN/TiB 2 nanocomposite powder by high energy ball milling has been investigated. A powder mixture of pure Ti and hexagonal BN powders with a molar ratio of 3:2 was milled for up to 40 h with up to 1.75 wt.% of stearic acid. The XRD analysis shows that an intimate mixture of TiN and TiB 2 crystalline powders was formed during milling by a displacement reaction. It has been observed by monitoring the temperature of the vial surface during the milling process that the addition of over 1.5 wt.% of stearic acid changed the reaction mode from a mechanically induced self-propagating reaction (MSR) to a gradual reaction. It has also been found by XRD and TEM analyses that the MSR produces TiN and TiB 2 particles initially of sub-micron size, which are reduced gradually by further milling. However, there still remain some coarse TiB 2 particles larger than a few hundred nanometers even after 16-h milling due to their extremely high hardness. On the other hand, the gradual reaction induced by stearic acid successfully inhibits the formation of coarse TiB 2 particles and eventually decreases the crystallite size of the products below 40 nm after 16 h of milling.

고에너지볼밀링을 이용한 MnFeP1-xAsx나노분말의 합성

Nanocrystalline powders of <TEX>$MnFeP_{1-x}As_x$</TEX>(x=0.45-0.6) have been synthesized by mechanochemical reaction at room temperature using high-energy ball milling from mixtures of Mn, Fe, P, and As Powders. It has been found that a mechanically induced self-propagating reaction (MSR) occurs within 2 hours of milling and it produces very fine polycrystalline powder having a hexagonal <TEX>$Fe_2P$</TEX> structure. Further milling up to 24 hours did not change the crystalline and average particle sizes or the phase composition of the milling product. When x is 0.65, no reaction among the reactants has been observed even after 24 hours of milling. As the P content decreases in <TEX>$MnFeP_{1-x}As_x$</TEX>, the incubation time for the MSR has increased and the lattice constants in both a and c axes have changed.