Self-propagating Reaction Research Articles

Confined space self-propagating room temperature synthesis of carbon-encapsulated Fe3O4 nanocrystals and its lithium storage performance

A self-propagating reaction between ferrocene and iron nitrate nonahydrate that is initiated at room temperature is discovered. Amorphous carbon-encapsulated Fe3O4 nanocrystals (Fe3O4@C) can be one-step prepared in an autoclave through this reaction. The equiaxed Fe3O4 nanocrystals have typical dimensions in the range of 5–60 nm with a median size of 24.1 nm, and their weight percent is up to 82.3%. The course of the reaction is recorded, and the formation mechanism of Fe3O4@C with the core–shell structure is proposed. The scaling-up synthesis is also achieved, and 52.1 g of the Fe3O4@C can be obtained in a single batch. The shock wave appeared in the fast gas release self-propagating reaction in confined space plays a decisive role in the preparation of homogeneous Fe3O4@C with a core–shell structure. The Fe3O4@C anode shows excellent capacity retention with a high specific capacity of 494 mAh g−1 at 1 A g−1 in the 200th cycle.

Characterization and Integrated Fabrication of Al Components with Thick TiCp/Al Composite Coatings via Self-Propagating Reaction

A novel and quick process combining self-propagating reaction with vacuum-expendable pattern casting is presented to accomplish integrated preparation of millimeter-thick TiCp/Al composite coatings on the Al substrate. Titanium and graphite powders were mixed with the polytetrafluoroethylene (PTFE) additive and pasted on the expendable polystyrene (EPS) followed by compaction. Al components with in situ TiCp/Al composite coating were simultaneously synthesized at a relatively low temperature of molten Al, which was poured into the assembly of EPS and powder compact inside the silica sands. Differential scanning calorimetry, x-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy and transmission electron microscopy were used to systematically investigate the thermodynamic characteristics of the reaction, the phase constituents, microstructure and tribological properties of the coatings. The infiltration model describing the densification of the reaction coatings was also developed for the critical wetting condition. The wear characteristics were assessed using a pin-on-disk tribometer with various loads. Results showed that uniform TiC particles stimulated by the PTFE-activated self-propagating reaction afforded superior mechanical properties and wear resistance.

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.

Kinetic role of Cu content in reaction process, behavior and their relationship among Cu-Zr-C system

The influence of Cu content on the reaction process, reaction behavior and obtained products in the Cu-Zr-C system, as well as their relationships, were investigated. The results showed that ZrC was synthesized through the diffusion and dissolution of C into a Cu-Zr liquid. Increasing the Cu content enhanced the amount of Cu-Zr liquid formed at the early stage but decreased the amount of C atoms dissolving into the melt at unit time. Consequently, the ignition time initially decreased and then increased. Conversely, with an increased Cu content, the energy required for igniting the neighboring unreacted powders increased, while the heat released by the reaction and the dwell time of the compact at high temperatures decreased. These effects then resulted in the reduction of combustion wave velocity, combustion temperature and ZrC particle size. Furthermore, the synthesis of ZrC is a multistage process, which provides a nonuniform distributed ZrC particle size. The sub-μm ZrC particle reinforced Cu matrix composite was fabricated by adding a ZrC-Cu master alloy prepared through a self-propagating high-temperature synthesis reaction into liquid Cu.

Self-propagating combustion of sputter-deposited Al/CuO nanolaminates

The complex Al/CuO self-propagating reaction involving multi-phase and multi-species dynamics was studied in order to investigate the very high flame temperature around the vaporization temperature of alumina, even under a neutral environment. Experiments were performed on different sputter-deposited Al/CuO multilayers coupling optical spectroscopy with high speed camera measurements. The clear presence of both AlO and Al signatures in gas phase suggests that the redox reaction starts in the bulk nanolaminate, which then rapidly tear off the substrate to continue burning in a heterogeneous (condensed and gas) phase in the environment. The flame temperature increases with the stoichiometry but is independent of the bilayer thickness. In addition to the confirmation of the effects of stoichiometry and the bilayer thickness on the characteristics of the self-propagating reaction, the predominant role of process-induced residual stress was highlighted for the first time; it can lead to an early disruption of the multilayer long before the completion of the redox reaction.

Laser-Ignited Self-Propagating Sintering of AlCrFeNiSi High-Entropy Alloys: An Improved Technique for Preparing High-Entropy Alloys

AlCrFeNiSi system porous high-entropy alloy material is manufactured by laser ignition and self-propagating sintering of natural chromite powder, which provides the idea of breaking the traditional synthesis procedure of high-entropy alloy compound material. The raw material powder obtained by ball milling is compacted into cylindrical compacts, and the self-propagating reaction comes from the ignition caused by the laser on the surface of compacts, the high-entropy alloy composite of chrome iron powder synthesized by laser sintering, is obtained as well. The raw material is prepared from Al, Cr, Fe, Ni and Si elements with similar effective components of natural chromite powder. The selected chromite powder is energy-saving and environment-friendly, so the preparation of high-entropy alloy by the low-cost short-process can be made for processing for pre-theoretical reserve and process design. The effect of Si content on microstructure and properties of AlCrFeNiSi high-entropy alloy is investigated.

Functionalization of silicene and silicane with benzaldehyde.

Organic functionalization of nanomaterials offers exceptional flexibility in materials design, and applications in molecular sensors and molecular electronics are expected. However, more studies should be conducted to understand the interaction between nanomaterials and organic molecules. In this work, we studied the functionalization of silicene and silicane with benzaldehyde, performing nudged elastic band calculations within density functional theory. We calculated the structural changes of the adsorption process, electronic properties of the main states, and the energetics. In silicene, the adsorption of benzaldehyde on the top site was found to be the most stable, with an adsorption energy of -0.55eV. For silicane, the functionalization proceeds through a self-propagating reaction on a highly reactive dangling bond generated by a hydrogen atom vacancy. Benzaldehyde adsorbed on this site depicts an adsorption energy of -1.39eV, which is larger than in bare silicene. Upon attaching, the double C=O bond breaks down turning the molecule into a highly reactive radical, which in this case, abstracts a neighboring H atom of the sheet. This process is highly achievable since the energy barrier to abstract the H atoms is 0.81eV, whereas the one needed to desorb the molecule is 1.39eV. After H abstraction, a new dangling bond is generated at the substrate, making a chain reaction possible to potentially form benzaldehyde monolayers. Organic functionalization is an excellent tool to engineer properties of 2D systems, and having a deeper understanding of the adsorption processes is the first step toward the development of new generation devices. Graphical abstract Benzaldehyde adsorbed on silicene and silicane.

Formaldehyde trapping by radical initiated reaction on hydrogenated boron nitride

Using density functional theory, we have studied the trapping of formaldehyde on hydrogenated boron nitride nanosheets. On the nitrogen terminated side, the formaldehyde molecule is physisorbed at a distance of ~3.1 Å on top of a N atom. A calculation of the adsorption energy, as function of vertical separation between the molecule and the substrate, shows that closer to the surface, there is a strong repulsion due to the electronegativity of the N and O atoms. On the other hand, the trapping of formaldehyde by the substrate on the boron terminated surface is very favorable. The reaction of a single molecule is described by calculating the minimum energy pathway. It begins with the formaldehyde molecule and the boron nitride substrate far away from each other. In the following state of the reaction, the molecule attaches to the boron side of the substrate, gaining a large amount of energy. Through this interaction, the double bond of the oxygen atom breaks down, turning the molecule into a highly reactive carbon centered radical. In the final state of the reaction, a neighbor hydrogen atom is abstracted. In this state, there is an additional energy gain of 0.06 eV. Once the stable molecule is formed by the abstraction of the hydrogen atom, a new dangling bond is created at a neighbor boron atom, which it may serve as a new site for the following molecule to attach. In this way, a chain reaction is possible. This self-propagating reaction is more viable for hydrogenated boron nitride than for graphane, opening an avenue to use hydrogenated h-BN in the indoor air pollution control. When there are two or more neighboring hydrogen vacancies in the substrate, the formaldehyde molecule prefers to attach forming OB and CB bonds with the substrate.

On the Dust Structures and Chain Reactions Induced over the Regolith by Gyrotron Radiation

Dust structures formed in exothermic chain plasma chemical processes initiated by pulsed gyrotron radiation in mixtures of metal and dielectric powders are studied. The composition of the powder mixture corresponds to the composition of the lunar regolith. Experiments at the energy of the gyrotron microwave pulse of 1–3 kJ and a pulse duration of 1.5–4 ms reveal an explosive process caused by the Coulomb repulsion of charged particles from the surface of the regolith into the reactor volume. The explosion is followed by the development of chain self-propagating high-temperature synthesis reactions. During these reactions lasting for tens of seconds, the suspension of dust particles rises tens of centimeters above the powder surface. The energy release is more than two orders of magnitude higher than the energy of initiation of a chain reaction. Regolith spheroids with diameters from 1 to 1000 µm precipitate on the side surfaces of the reactor. An analogy of the possible contribution of the Coulomb repulsion between charged particles and plasma exothermic processes to the dispersion of regolith dust when the Moon surface is bombarded by micrometeorites is considered.

Joining of Carbon Fiber Reinforced Plastic to Aluminum Alloy by Reactive Multilayer Films and Low Power Semiconductor Laser Heating

This study investigated the characteristics and strength of the dissimilar joints between carbon fiber reinforced plastic (CFRP) epoxy composites and aluminum alloys using two different heating methods, Ni/Al reactive multilayer films (RMF) and a low power continuous wave diode laser. To enhance the adhesion, the top resin layer of the CFRP and the surface of the aluminum alloy were patterned by femtosecond laser. Polycarbonate (PC) was used as a filler material during the joining processes. ANSYS simulation was applied to elucidate the thermal kinetics of the self-propagation reaction and the thermal profile, and evaluate the possibility of joining CFRP to aluminum using Ni/Al RMFs. The SEM image of the cross-section shows that melted PC flowed into the CFRP–aluminum alloy interface, suggesting strong mechanical bonding. A tensile strength of 9.5 MPa was reached using Ni/Al multilayers as heat sources, which provides a new way for joining CFRPs and aluminum alloys in space or under water.

Using reaction heat of laser-induced Al[sbnd]Ti[sbnd]C interlayer to connect CFRTP/aluminum

The carbon fiber reinforced thermoplastics (CFRTP) was successfully joined to aluminum using a laser-induced AlTiC powder interlayer. The selection principle of the composition and content of the interlayer was studied. We calculate the composition and content of the interlayer material is Al54Ti32C14. The influence of connection temperature and connection pressure on the mechanical properties of the joint is studied. The results show that the connection temperature is 1600 °C and the connection pressure is 30 N, the maximum shear strength of the joint can reach 5.2 MPa. This experiment uses exothermal reaction of AlTiC powder by laser induces self-propagating reaction to connect aluminum and CFRTP. In the aluminum side, the metallurgical reaction between interlayer and aluminum produces Al3Ti. In the CFRTP side, under the action of pressure, using the heat generated by the self-propagating reaction to melt the CFRTP, the molten CFRTP into the micro-hole of interlayer to form mechanical interlock. At the same time, element diffusion occurs at the interface, thus forming mechanical interlocking and diffusion connections.

Mathematical modeling of frontal polymerization

Frontal polymerization is way to convert liquid resin into a solid material with a self-propagating reaction. The reaction spreads like a flame from the heat of the reaction that diffuses into neighboring regions, starting more reaction. The frontal velocity has been accurately modeled for free-radical polymerization systems. The dynamics of fronts have been studied theoretically and experimentally. If the viscosity of the initial medium is low, then fronts can become unstable due to buoyancy-driven convection. A fascinating aspect of frontal polymerization is that fronts often do not propagate as a plane waves but exhibit complex modes such as “spin modes” and chaos. The kinetics of the polymerization significantly affects the onset of these modes. Multifunctional acrylates exhibit more complex dynamics than monoacrylates. Using multifunctional acrylates and inorganic fillers, 3P LLC created “cure-on demand” systems that do not require mixing before use, have a long shelf life and can be hardened in seconds to minutes. We consider two commercial products using frontal polymerization. The first is a wood filler that can be applied to a damaged section of wood and hardened in a few seconds by the application of heat to the surface. The second product is QuickCure Clay (QCC). QCC has an unlimited working time during which it can be sculpted. QCC is then cured by heating part of the object to 100 °C, setting off the propagating curing front. The modeling of frontal polymerization helped guide the development of these products.

Development of High-Sensitive Calorimeter for Small Amount of Pulverized Material with Self-Propagating Exothermic Reaction

Development of High-Sensitive Calorimeter for Small Amount of Pulverized Material with Self-Propagating Exothermic Reaction

Time of resolved X-ray analysis in Self-propagating exothermic reaction of Al/Ni multilayer films

Time of resolved X-ray analysis in Self-propagating exothermic reaction of Al/Ni multilayer films

A microscale explosive initiator integrated with a reactive thin-filmed metallic bridge of boron/titanium laminated layers

Aided by the advancement of microfabrication technologies, the electro-pyrotechnical initiators are being miniaturized into micron sizes to gain higher safety and reliability as well as lower mass manufacturing cost. One of the most important innovations proposed for the explosive initiator design in recent years would be the device integration with reactive thin-film metallic bridge which is composed of many laminated layers of different metals. The nanoscale boron and titanium (B/Ti) multilayers would be a feasible candidate for substantially improving the thermal initiation performance due to their fast reaction speed and high exothermic heat release. This study introduces the numerical modeling of ohmic heating in thin-film metallic bridge and the self-propagating intermetallic reaction in B/Ti laminated layers coupled with pulse-forming circuit in order to investigate the feasibility of such an initiator design. The computational results show that the ignition of intermetallic reaction and propagation of reaction wave in B/Ti multilayers of reactive initiator bridge are successfully modeled and simulated. The effects of several reactive bridge design parameters are investigated such as B/Ti layer thickness and its set number on bridge, electrical energy input in pulse form, and the existence of pre-mixing zone at bimetallic interface.

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.

Low-Temperature Cu-Cu Bonding Process Based on the Sn-Cu Multilayer and Self-Propagating Reaction Joining

Transient liquid phase bonding can be realized at a relatively low temperature through building an intermetallic interconnection. A self-propagating reaction joint can achieve a low temperature bond by confining the heat at the bonding interface and reduce the thermal effect on other components. In this work, a Sn-Cu alternating multilayer was combined with an Al-Ni self-propagating reaction joint to develop a highly efficient low-temperature Cu-Cu hybrid bonding process. The Sn-Cu alternating multilayer was directly prepared on the Cu substrates by an alternating electroplating process. The Al-Ni multilayer film was sandwiched between two Cu substrates under a pressure of 5 MPa and ignited with a 15-V spark at room temperature. Cu-Cu bonds with three different Sn/Cu thickness ratios were studied. It was found that the Cu6Sn5 layer within the three Sn layers had different thicknesses and decreased with increasing distance from the heat source of the Al-Ni nanofoil. The thickness difference between adjacent Cu6Sn5 layers at first decreased with the increasing Sn/Cu thickness ratio in these three groups and then remained constant. The shear strength of the bonds varied with the thickness of Cu6Sn5 layer and achieved a high shear strength with a Sn/Cu thickness ratio of 1.6 μm/1 μm, where fracture occurred within the Cu6Sn5 layer near the Cu substrate. The combination of the Sn-Cu multilayer and self-propagating reaction joining process can achieve a good low-temperature bond between Cu substrates with an optimized Sn/Cu thickness ratio, which has a strong influence on the quality of bonds, the Cu6Sn5 morphology, and shear strength.

Ignition in ternary Ru/Al-based reactive multilayers—Effects of chemistry and stacking sequence

While self-propagating reactions in metallic multilayers have been known since the early 1990s, the vast majority of research has been conducted on binary systems comprising either elemental or alloyed layers. The properties of reaction and ignition in these samples are, for a given composition, mainly determined by the bilayer thickness as main design parameter. Here, we present how the stacking sequence is established as an additional design parameter when going from binary to ternary layered systems. The basis for this study is reactive Ru/Al multilayers which are extended to ternary samples by introducing a third element (Ni, Pt, or Hf) as a third, individual component. It is shown that exothermic solid state reactions at the layer interfaces and grain boundaries control the ignition temperature. Furthermore, the stacking sequence determines the specific volume density of phase boundaries and, thus, the magnitude of contribution of these reactions to the process of ignition. While the addition of hafnium is found to have little to no effect on ignition, nickel and platinum lower the ignition temperatures by up to 150 °C (Ni) and 230 °C (Pt), respectively. This can be attributed to the exothermic formation of Ni2Al9, amorphous a-(Al,Pt), and Pt2Al3 which are formed at temperatures significantly lower than that of RuAl6 which is the driving reaction for ignition in binary Ru/Al multilayers.

Mechanical Synthesis of Tantalum Borides and Modeling of Solid Solutions of Boron in Tantalum

Two mechanisms of mechanochemical solid-phase reactions are observed when tantalum and boron powder mixtures are ground in the same conditions but at different contents of the starting components. The substitutional solid solution decomposes at 50 at.% B in the starting mixture and stimulates the self-propagating mechanochemical synthesis reaction to form the TaB phase. The supersaturated interstitial solid solution, whose formation is controlled by the diffusion of boron atoms into tantalum, shows up at a boron content of 66 at.% and gradually decomposes to form the TaB2 phase. Formalism is proposed for estimating the free Gibbs energy of the interstitial and substitutional solid solutions with the regular solution model. The use of this formalism shows that grinding of the tantalum and boron powders in a planetary-ball mill produces a combined interstitial and substitutional solid solution (two boron atoms substitute one tantalum atom) at the initial stage. Both the substitutional and interstitial mechanisms lead to decrease in the solution’s Gibbs energy. When the substitutional solid solution prevails over the interstitial solution, the Gibbs energy of the substitutional solution becomes minimal at 50 at.% B in tantalum and causes its disintegration.

Synthesis Mechanism and Material Characterization of C4AF Obtained by the Self-propagating Combustion Reaction Method

To investigate the influence of preparation process on the properties of synthesized C4AF, the powder was prepared via the self-propagating combustion reaction (SPCR) method using urea as fuel and metal nitrates as cation precursors. Synthesis mechanism of the SPCR method, calculation and adjusting principles of urea dosage were detailedly introduced. Material characterization of synthesized C4AF was performed with the aid of X-ray diffractometry, Fourier transform infrared spectrometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, 27Al nuclear magnetic resonance and isothermal microcalorimetric technique. Remaining content of transition phase of calcium carbonate in synthesized C4AF was determined by quantitative analysis of X-ray diffractometry. It was found that there was no difference in the hydration behavior of C4AF synthesized by the SPCR method and the traditional solid-state reaction (SSR) method. C3AH6 and amorphous iron (III) hydroxide (Fe(OH)3) would be formed during the hydration of C4AF while CH not. Crystallite size of synthesized C4AF was 16.1 A and the apparent activation energy was 36.2 kJ/mol. Coordinated condition of Al in C4AF can be detected by 27Al NMR technique, but the peaks were broadened and the intensities were relatively low, supporting the use of 27Al NMR for the quantitative analysis of C3A in Portland cements.