Mechanically Induced Self-sustaining Reaction Research Articles

Hafnium-Zirconium Carbonitride (Hf,Zr)(C,N) by One Step Mechanically Induced Self-Sustaining Reaction: Powder Synthesis and Spark Plasma Sintering

Nanostructured single-phase hafnium-zirconium carbonitride powders were synthesized using a simple and fast mechanochemical synthesis approach. The critical milling duration, after which a (Hf,Zr)(C,N) solid solution formation inside a jar occurred via mechanically induced self-sustained reaction (MSR), was 10 min. After 30 min of treatment, a solid-gas reaction was completed, and as a result, a homogeneous (Hf,Zr)(C,N) powder consisting of 10–500 nm submicron particles was obtained. The phase and structure evolution of the powders after different treatment durations allowed for the establishment of possible reaction mechanisms, which included the formation of Hf/Zr/C-layered composite particles, their interaction via MSR, and further grinding and nitridization. Spark plasma sintering (SPS) was used to produce bulk hafnium-zirconium carbonitride ceramics from nanostructured powder. The sample had higher values of relative density, hardness, and fracture toughness than those for binary compounds of a similar composition.

In situ observation of a mechanically induced self-sustaining reaction for synthesis of silver

We revealed the processes for the activation, mechanically induced self-sustaining reaction (MSR) and crystal growth of Ag in the mechanochemical reduction of AgCl with Al by in situ synchrotron X-ray diffraction.

Tuning the excitation wavelength of luminescent Mn2+-doped ZnSxSe1-x obtained by mechanically induced self-sustaining reaction

Mn2+-doped ZnSxSe1–x solid solution samples (Mn:ZnSxSe1-x) were synthesized by the mechanochemical process denoted as mechanically-induced self-sustaining reaction from Mn/Zn/S/Se powder elemental mixtures. The samples were characterized by X-ray diffraction, scanning electron microscopy, diffuse reflectance UV–Vis spectroscopy and emission and excitation photoluminescence measurements. The band-gap energy of samples was controlled by changing the stoichiometry, x, of the solid solution. All samples showed the characteristic Mn2+ 4T1-6A1 emission at ~588 nm when exciting the host material, so it was possible to tune the excitation wavelength from 349 nm to 467 nm. However, an efficiency loss was observed with increasing Se content, probably due to the overlap between the absorption and emission spectra that induced self-absorption and emission quenching.

Nickel Nanoparticles by Mechanical Synthesis in the NiO–Mg System

Ni nanopowder was synthesized from NiO through mechanically induced magnesiothermic NiO–Mg reaction that can also be regarded as a kind of progressive synthesis, or Mechanically induced Self-sustaining Reaction (MSR). The obtained powder was characterized by XRD, FESEM, and TEM. After 8 min of milling, the mixture ignited in the mill vial to yield Ni and MgO. The latter was removed by leaching with 18% HCl. The mean crystallite size of resultant Ni was found to have a value of 45–50 nm.

Effects of the speed ratio on the efficiency of planetary mills

The ignition time (tig) of the mechanically induced self-sustaining reaction (MSR) process involving the formation of TiB2 from Ti/2B elemental mixtures was used to study the influence of the ratio (k = -ωv/ωd) between the rotational speed of the supporting disc (ωd) and vials (ωv) on the milling efficiency of a Pulverisette 4 planetary mill. The variation of the inverse of the ignition time (1/tig), which is directly related to the milling power provided by the planetary mill, with the process conditions has shown that it is not possible to find a single k value as optimal independently of the experimental conditions used (ωd and the ball-to-powder ratio, BPR). Moreover, it was observed that the lowest milling efficiency (longer tig values) was found for k = 1, which is the usual value employed in routine laboratory works. The best efficiencies were found for the larger k values (2.5 or 3). At lower ωd, the shortest tig was obtained for k = 2.5 and at higher ωd for k = 3, independently of BPR.

Synthesis of a cubic Ti(BCN) advanced ceramic by a solid-gas mechanochemical reaction

In this work, a titanium boron carbonitride advanced ceramic was successfully synthesised by a solid-gas mechanochemical reaction in a planetary ball mill from a mixture of elemental Ti, B, and C under nitrogen atmosphere. This material, with a general formula of Ti(BCN), exhibits a face-centred cubic structure (NaCl type) that is analogous to Ti(CN). This phase was gradually formed with sufficient milling time as a result of diffusional processes, which were permitted by the reduction of the energy in the system caused by the decrease in the spinning rate of the planetary ball mill. In contrast, under more energetic milling conditions, a mechanically induced self-sustaining reaction (MSR) took place, leading to the formation of a TiB2-Ti(CN) ceramic composite. The microstructural characterisation revealed that Ti(BCN) was composed of ceramic particles constituted of misoriented nanocrystalline domains. B, C and N were optimally distributed in the Ti(BCN) phase. The TiB2-Ti(CN) ceramic composite was composed of micrometric and nanometric particles homogeneously distributed. Additionally, the nitrogen content obtained for Ti(BCN) was higher than for the Ti(CN) phase in the composite material.

Mechanically induced combustion synthesis of niobium carbonitride nanoparticles

Niobium carbonitride [Nb(C,N)] nanoparticles were synthesized by a combustive mechanochemical reaction in the Mg/Nb2O5/C3H6N6 system. High-energy ball milling was used to promote a mechanically induced self-sustaining reaction (MSR). Combustion occurred after a very short milling period of 5 min. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) analyses revealed that the nature of the product is an intermixed carbonitride material. The formation mechanism of Nb(C,N) resulted from the magnesiothermic reduction of niobium oxide to generate elemental Nb, which then reacted with the species generated from the melamine decomposition.

Effects of additives on the synthesis of TiCxN1−x by a solid-gas mechanically induced self-sustaining reaction

The synthesis of TiCxN1−x from Ti/C mixtures in a N2 atmosphere performed in a high-energy planetary mill was used as example to study the influence of the use of additives in mechanically induced self-sustaining reaction (MSR) processes. In particular, the effect of the addition of TiN, TiC, Si3N4 and SiC was analyzed. The self-sustaining reaction was extinguished when additive contents of 50, 40, 40 and 30 wt% for TiN, TiC, Si3N4 and SiC, respectively, were employed. These additives cannot be regarded as real inert since they served as an extra solid source for nitrogen and carbon, modifying the final stoichiometry of the TiCxN1−x phase. The adiabatic temperature (Tad) determined for the mixtures with no MSR effect was well above the empirical limit value of 1800 K adopted as criterion for the occurrence of the self-propagating high-temperature synthesis (SHS) process. The ignition time (tig) of the MSR process was practically invariant for low additive contents (approximately 50 min) and tended to increase up to maximum values of 85–95 min for the larger additive contents.

Self‐propagating mechanosynthesis of HfB2 nanoparticles by a magnesiothermic reaction

AbstractA mechanically induced self‐sustaining reaction (MSR) was used to synthesize hafnium diboride nanoparticles. Along this route, magnesium was selected as a robust reducing agent for co‐reduction in boron and hafnium oxides in a combustive manner. Combustion occurred after a short milling period of 12 minutes. The hafnium diboride nanoparticles had a polygonal faceted morphology and were 50‐250 nm in diameter. The assessment of the processing mechanism revealed that the initial combustive reduction in B2O3 to elemental B by Mg was the major step for progressing the overall reaction. After that, HfO2 can be reduced to elemental Hf, followed by the synthesis of HfB2 phase.

A new combustion route for synthesis of TaB2 nanoparticles

Tantalum diboride (TaB2) nanoparticles were synthesized through a mechanically induced self-sustaining reaction (MSR). In this method, the ternary system of Mg/Ta2O5/B was employed in which, magnesium was used as a reducing agent for reduction of tantalum oxides in a combustive regime. The processing route of TaB2 by the solid-state combustion was very short-term and the product purification was extremely easy and rapid. The synthesis mechanism was studied and revealed that magnesiothermic reduction of tantalum oxide is the initiator of the total reaction, while borothermic reduction of the oxide may occur in parallel.

Influence of milling parameters on the solid-gas synthesis of TiCxN1 − x by mechanically induced self-sustaining reaction

The synthesis of a titanium carbonitride solid solution (TiCxN1−x) performed in a high-energy planetary mill by a solid-gas Mechanically induced Self-sustaining Reaction (MSR) was used to study the influence of a full set of experimental milling parameters on the ignition time (tig) as a measure of the mechanical dose rate provided by the mill. The highly exothermic Ti-C-N mixture was selected to ensure no competitiveness between MSR and diffusion-controlled routes under the milling conditions employed. The results showed that the dependence of tig on the spinning rate followed a potential function, with a potential factor higher than the value of 3 that would be obtained if a perfect collision model is assumed. The scalability of milling processes performed using planetary mills was confirmed. The results suggested that to define a milling experiment, it is necessary to provide not only the Ball-to-Powder mass Ratio (BPR) and spinning rate values, as is usually performed, but also the full set of milling parameters including the nature of the milling media (vial and balls), the number and size of balls, the mass of the powder charge, the pressure of the reactive gas and even the volume of the vial.

A novel, simple and rapid route to the synthesis of boron cabonitride nanosheets: combustive gaseous unfolding

The ternary compound boron carbonitride (BCN) was synthesized in the form of few-layer nanosheets through a mechanically induced self-sustaining reaction (MSR). Magnesium was used to reduce boron trioxide in the presence of melamine in a combustive manner. The process to form the nanostructured material was very rapid (less than 40 min). The prepared powder was investigated by various techniques such as X-ray diffraction (XRD), Fourier Transform infrared (FTIR), Micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS). The thermal stability and the optical behavior of the BCN nanosheets were also studied by thermal analysis and UV-vis spectroscopy, respectively. The formation mechanism of the nanosheet morphology was described in detail.

Effect of the impact energy on the chemical homogeneity of a (Ti,Ta,Nb)(C,N) solid solution obtained via a mechanically induced self-sustaining reaction

Abstract A titanium-tantalum-niobium carbonitride solid solution, (Ti,Ta,Nb)(C,N), was synthesised in a planetary mill via a mechanochemical process that involves a mechanically induced self-sustaining reaction (MSR) from stoichiometric Ti/Ta/Nb/C mixtures that are milled under a nitrogen atmosphere. The influence of the spinning rate of the planetary mill, which determines the impact energy of the milling process, on the ignition time (t ig ) of the MSR process as well as the chemical homogeneity of the final product was analysed. The results indicated that the dependence of t ig on the spinning rate followed a potential function with a potential factor of 4.85, implying a remarkable reduction in the milling time required to induce the self-sustaining reaction at increasing spinning rates (i.e., from 4200 min at 200 rpm to 15 min at 800 rpm). However, the chemical and structural characterisation of the obtained products at ignition without any extra milling treatment indicated that a single solid solution phase was only obtained at the lowest spinning rates (i.e., less than 300 rpm). At increasing rates, the relative amount of the intended solid solution phase continuously decreased, and new undesirable secondary phases were formed. Despite the long milling times required for the milling experiments that were performed at the slowest spinning rates, iron contamination from the milling media was negligible due to the low intensity milling regime.

Wear damage of TiTaCN-Co cermets at room and elevated temperatures

The work is focused on microstructure, mechanical and tribological properties of TiTaCN-Co based complex solid solution cermets with different graphite addition (0, 1.8, 2.2 %) with the typical use as cutting tools. The materials were prepared by the way of mechanochemical MSR (mechanically induced self-sustaining reaction), using a high energy milling of the starting constituents - Ti, Ta, C, and Co in nitrogen atmosphere. Then they were compacted by cold isostatic pressing and sintered at 1500 °C. Microstructure of the obtained materials was studied by SEM/EDX and assessed by image analysis. Hardness and indentation toughness were evaluated using Vickers indentation. Tribological tests were carried out on the high temperature tribometer THT Tribometer (CSM Instruments) to obtain friction coefficient. Ball-on-disc method was used. Wear testing was carried out under following conditions: normal load 5N, sliding distance 300 m, linear sliding velocity 0.1 m/s, atmosphere: air, temperatures: 25 °C, 200 °C, 400 °C, tribological static partners were WC-Co ball and steel ball with 6mm diameter. Created wear track was observed using scanning electron microscopy to identify wear mechanisms. Area of the wear track cross-section was measured using 3D optical profiler (SENSOFAR Plu neox) and the specific wear rate in terms of the volume loss was calculated according to the international standard ISO 20808.

A new family of cermets: Chemically complex but microstructurally simple

Cermets based on Ti(C,N) have interesting properties, such as high wear resistance, high chemical stability and good mechanical strength at high temperature, but to become a viable alternative to cemented carbides, the fracture toughness and damage tolerance must be significantly improved. Complete solid-solution cermets (CSCs) have been proposed to further improve the mechanical properties of these materials. However, to develop this family of cermets with a high level of quality and reliability, using pre-fabricated complex carbonitrides is necessary instead of unalloyed mixtures as the raw ceramic material. A mechanochemical process called mechanically induced self-sustaining reaction (MSR) is suitable to obtain these complex carbonitrides with high stoichiometric control. On the other hand, high entropy alloys (HEAs), which can also be obtained by mechanochemical processes, are a good candidate to replace the current binder phase in cermets because they exhibit high strength and ductility at high temperature and good resistance to both wear and corrosion. In this work, a new family of CSCs based on (Ti,Ta,Nb)CxN1−x with HEAs belonging to the Fe-Co-Ni-Cr-Mn-V system as the binder phase is developed by mechanochemical processes. With only two constituent phases, these cermets have a simple microstructure but a high compositional complexity because both the ceramic and binder phases are complex solid solutions with at least five components.

Mechanochemical Synthesis of High Crystalline Cerium Hexaboride Nanoparticles from CeO2‐B2O3‐Mg Ternary System

AbstractHigh crystalline cerium hexaboride (CeB6) nanoparticles (NPs) were synthesized using mixture of mag‐ nesium (Mg), cerium oxide (CeO2) and boron oxide (B2O3) via the mechanochemical process at room tem‐ perature. Based on the results, magnesiothermic reduction of B2O3 occurred after about 2 h of milling in a mechanically induced self‐sustaining reaction (MSR). The significant amount of heat produced by the reduction reaction resulted in CeO2 reduction to elemental Ce which finally reacted with elemental B and formed CeB6 compound. According to XRD analyses, the degree of crystallinity and lattice parameter of the product was calculated about 93 % and 4.1458 Å, respectively. The morphology observations revealed that the synthesized CeB6 had semi‐cubic shape with the range of size 25–60 nm. The synthesis of CeB6 during the thermal treatment was studied by simultaneous thermal analysis (STA) technique. It was found that the reduction of B2O3 took place after melting of Mg meanwhile, no CeB6 phase achieved even up to 1100 °C.

Hot-pressing of (Ti, Mt)(C, N)–Co–Mo2C (Mt = Ta, Nb) powdered cermets synthesized by a mechanically induced self-sustaining reaction

A mechanically induced self-sustaining reaction (MSR) has been successfully employed for manufacturing powdered cermets based on Ti, Ti–Ta and Ti–Nb carbonitrides using Co as the binder phase and Mo2C as the sintering additive. The powders were sintered by hot-pressing, and complete chemical, microstructural and mechanical characterizations were performed on the densified cermets. When elemental Ta, Nb and/or Mo2C were added to the initial raw mixture submitted to the MSR process, smaller ceramic grains were observed after sintering, which suggested that ceramic particle growth was hindered by the presence of Ta, Nb and/or Mo in the host titanium carbonitride structure. Nanoindentation measurements enabled the determination of the hardness of the ceramic and binder phases, and values in the range of 26–29GPa and 14–16GPa were found, respectively. The high hardness values of the binder were related to the formation of intermetallic phases.

Mechanochemical behavior of magnesium–boron oxide–melamine ternary system in the synthesis of h-BN nanopowder

Hexagonal boron nitride (h-BN) nanopowder was synthesized by the mechanochemical method using mixtures of magnesium, boron oxide and pure melamine as raw materials. X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the synthesized powder. According to the results, the reaction starts with the magnesiothermic reduction of boron oxide after about 3.5h of milling in a mechanically induced Self-sustaining Reaction (MSR). The significant amount of heat generated from reduction reaction caused to decompose melamine to nitrogen-based active radicals, which reacted with elemental B to form h-BN compound. The formation of BN during the thermal treatment was also investigated by simultaneous thermal analysis (STA) technique. It was found that melamine decomposition took place at a temperature around 350°C; meanwhile, no boron nitride phase was achieved even up to 1100°C. Based on the morphological evolutions, it is evident that the mechanosynthesized BN is made up of nanometric particles.

Investigation on mechanochemical behavior of the TiO2–Mg–C system reactive mixtures in the synthesis of titanium carbide

TiC–MgO composite was synthesized using mixtures of TiO2, Mg, and wood dust via a mechanochemical process. The influence of various Mg values (0–2.4mol) on the titanium carbide formation and the mechanism of reactions during the milling of TiO2–Mg–C mixture were investigated. Phase transformations, grain size, strain, lattice parameters, and morphology of the powders during the milling process were examined using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Thermodynamic calculations revealed that the Mg value played a main role. Consequently, the overall reaction enthalpy and adiabatic temperature (Tad) changed with variation of the magnesium content. Experimentally, after 10h of milling, TiC was synthesized in the mixture powder with stoichiometric ratio (Mg=2mol). The type of reactions was mechanically induced self-sustaining reaction (MSR). In addition, at lower Mg content (Mg=1.5), the heat resulted from magnesiothermic reaction also activated the carbothermal reduction. Further decrease in the Mg value (Mg=0.5 and 1mol) resulted in formation of MgTiO3 as a major phase. Using the excess Mg value (Mg=2.2 and 2.4molMg) as a diluent agent led to formation of Mg2TiO4 besides the MgO and TiC phases.

Investigation on mechanochemical behavior of Al/Mg–B2O3–Nb system reactive mixtures to synthesize niobium diboride

Aluminum and magnesium were used in the M–B2O3–Nb (M=Al, Mg) system to synthesize niobium diboride (NbB2) via a mechanochemical process. The phase transformation and structural evaluation were investigated by means of X-ray diffractometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential thermal analysis techniques (DTA). Unlike thermodynamic possibility and DTA results, negligible aluminothermic reaction was occurred in the system and AlNb2 intermediate phase was formed during milling. On the other hand, nanostructure NbB2 was mechanosynthesized by the magnesiothermic reduction after 2.4h of milling and the type of reactions was mechanically induced self-sustaining reaction (MSR). DTA results revealed that Mg3(BO3)2 was largely formed during the thermal process, while the quantity of this by-product extremely decreased during the mechanochemical synthesis and completely eliminated after 5h of milling. Scanning and transmission electron microscopy observations confirmed that the range of particle size was within 100nm.