Explosion Process Research Articles

Investigation on structural feature and bonding performance of Hastelloy foil/steel explosive welding composites under different explosive loads

Hastelloy foil/steel composite is of most interest in many industrial fields, as it has competitive advantages of excellent corrosion resistance and low cost. Due to the low thermal conductivity and thermal hardening property, traditional fusion-based connection methods fail to provide high-quality Hastelloy/steel composites. Here an improved explosive welding was introduced to prepare this composite, and the effect of the explosive amount was carefully investigated. The characterizations (including optical microscopy (OM), electron backscatter diffraction (EBSD), bending, nanoindentation, and electrochemical corrosion) were conducted to understand the bonding properties, and Smoothed Particle Hydrodynamics (SPH) simulation was used to investigate transient interface behavior. It was found that the self-developed explosive welding was a suitable method to produce superior Hastelloy/steel composites. Under reasonable welding parameters, both the surfaces of Hastelloy and Hastelloy/steel interface exhibited ideal welding patterns without defects, and the composite remained intact under 90° bending loading. The explosive load is a crucial factor determining bonding properties, and the undesirable features like wrinkles and melting area were found to be positively correlated with the explosive load, which reduced the corrosion resistance. This comprehensive research enabled to provide a new perspective for Hastelloy/steel preparation and improve the understanding of explosive welding process behavior.

Simulating carbon dioxide diffusion during airflow merging in Y-shaped bifurcated tunnels after blasting operations

This research aims to evaluate the dilution and discharge effects of noxious gas produced by the drilling and blasting method under the merging of airflows during the ventilation of Y-shaped bifurcated tunnels. A finite volume model was utilized to simulate the overall diffusion process of explosion and noxious gas in the tunnel after blasting, taking into account various parameters of bifurcated structures. The flow field characteristics and the temporal and spatial evolution of the CO concentration field was analyzed under parameters including the bifurcating angle θ and cross-sectional area ratio F, as well as air supply ratio Q. The results show that the CO concentration decreases in a negative exponential manner with the ventilation time and it reaches the concentration limit within 480–610 s. By comparing conditions under different bifurcating angles θ of the main transverse tunnel, the dilution effect of CO is optimal when θ is 90° and the CO concentration reaches the safety threshold after ventilation for 489 s. Considering the influence of the cross-sectional area ratio (F) of the main transverse tunnel, the CO concentration reduces most rapidly when F is 0.7 and it reaches the safety threshold after ventilation for 476 s. Upon estimating the influence of the air supply ratio (Q) on the CO diffusion process, it is found that Q of 0.4 is most conducive to the dilution and discharge of CO and the CO concentration reaches the safety threshold after ventilation for 485 s. The results provide technical and theoretical support for the ventilation and smoke discharge during the construction of a Y-shaped bifurcated tunnel.

Study on pyroshock response of micro-satellite pyrotechnic cutter

When the micro-satellite panel is deployed in orbit, it needs to be unlocked by the pyrotechnic device. The high-amplitude pyroshock environment generated in the unlocking process is fatal to the sensitive components on the satellite. Therefore, accurate and quantitative analysis of the structural response caused by the explosion can better understood the transmission characteristics of pyroshock, so that effective isolation methods can be carried out. In this paper, the finite element model of the pyrotechnic cutter is established in LS-Dyna, and the explosive unlocking process of the pyrotechnic cutter is simulated by the Particle Blast Method (PBM). The whole motion process of the cutter from unlocking to cutting off the pretightening rod is obtained, the distribution of stress and the propagation law of pyroshock wave are extracted. The results show that before unlocking, the explosion shock is the main part of the pyroshock, while after unlocking, it is mainly caused by the prestress release of the pretightening rod and the impact of the cutter hitting the cutting board. Explosive shock is the main factor affecting the near-field pyroshock, while the far-field pyroshock is mainly affected by the impact. To verify the accuracy of the simulation, a unlock test of pyrotechnic cutter are performed, the acceleration response values of the main reference points are obtained, and the results show that the two results are in good agreement in time domain and frequency domain. Based on the study of the separation characteristics, some suggestions on the optimization of damping buffer are proposed here.

Experimental Study on the Characteristics of Camellia oleifera Fruit Shell Explosion by Hot Air Drying

The shell explosion by hot air drying is a critical step in the processing of Camellia oleifera fruit (COF), which directly affects the degree of the shell explosion, and the separation effect of Camellia oleifera seed and Camellia oleifera shell after the shell explosion of COF. To reveal the characteristics of the COF shell explosion, a hot air drying device was designed based on mass conservation and drying principles. The physical characteristics of COF and the evolution of drying parameters were thoroughly analyzed with a combination method of drying analysis and experimental. Moreover, under the conditions of air temperature 50–70 °C, relative humidity 20–50%, and air velocity 1.3–1.9 m/s, the internal relationship between COF shell explosion formation through hot air drying and the hot air drying medium was systematically investigated by response surface methodology, and a prediction model for the shell explosion rate of COF by hot air drying was constructed using statistical methods. Results demonstrated that decreasing the relative humidity and increasing the temperature and air velocity of the drying medium could reduce the dehydration time of COF. The moisture content of Camellia oleifera shell was found to be 177.45% d.b. (dry basis) at the initial cracking stage of COF. Furthermore, at temperatures ranging from 50 to 70 °C Deff values of COF were estimated to be within the range of 0.915 × 10−9 to 1.782 × 10−9 m2/s. Similarly, at relative humidity levels of 20 to 50%, Deff values ranged from 1.226 × 10−9 to 1.501 × 10−9 m2/s. At an air velocity of 1.3 to 1.9 m/s, Deff values ranged from 0.956 × 10−9 to 1.501 × 10−9 m2/s. The measured values of the shell explosion rate were in close agreement with that calculated using the fitted model, with a correlation coefficient of 0.997 and a root mean square error of 0.9743. This study will provide a theoretical basis for optimizing the shell explosion process and improving shell explosion rate of COF by hot air drying.

Study on the thermodynamic mechanism of external magnetic field on gas explosion characteristics

To investigate the thermodynamic mechanism of the magnetic field on the explosion characteristics of gases, experiments were carried out to study the influence of the applied magnetic field of 300 mT on the explosion characteristics of 5.7 % C2H6, 6.5 % C2H4 and 7.7 % C2H2 by volume. CHEMKIN-PRO software was used to simulate the three kinds of gas explosion chain reaction process. The chemical bond strength, stability and bond energy of the three gases were calculated and analyzed by Materials Studio software to derive the strength of chemical bond stability of the three gas molecules in the explosion process. The results show that the magnetic field weakened the breaking rate of CC, CC, and CC, the maximum explosion pressures of C2H6, C2H4, and C2H2 were reduced by 12.14 %, 16.47 %, and 18.71 %. The three gases carbon–carbon bond strength was weaker than the strength of the carbon-hydrogen bond, carbon-hydrogen bond was not easy to break, which in turn reduced the rate of generation of ·H in the chain initiation stage of the cleavage reaction, thus presenting a significant inhibitory effect of the magnetic field on C2H6, C2H4, and C2H2 explosions. The COOP of CC is 0.377 Ha, and the bond energy is 839 KJ/mol, which was greater than CC and CC, so the number of free radicals generated in the C2H2 cleavage reaction was lower, leading to a slower chain reaction rate which led to a stronger inhibitory effect of the magnetic field on C2H2 explosions than that on C2H6 and C2H4.

Experimental and numerical simulation of the attenuation effect of blast shock waves in tunnels at different altitudes

Traffic engineering such as tunnels in various altitudinal gradient zone are at risk of accidental explosion, which can damage personnel and equipment. Accurate prediction of the distribution pattern of explosive loads and shock wave propagation process in semi-enclosed structures at various altitude environment is key research focus in the fields of explosion shock and fluid dynamics. The effect of altitude on the propagation of shock waves in tunnels was investigated by conducting explosion test and numerical simulation. Based on the experimental and numerical simulation results, a prediction model for the attenuation of the peak overpressure of tunnel shock waves at different altitudes was established. The results showed that the peak overpressure decreased at the same measurement points in the tunnel entrance under the high altitude condition. In contrast, an increase in altitude accelerated the propagation speed of the shock wave in the tunnel. The average error between the peak shock wave overpressure obtained using the overpressure prediction formula and the measured test data was less than 15%, the average error between the propagation velocity of shock waves predicted values and the test data is less than 10%. The method can effectively predict the overpressure attenuation of blast wave in tunnel at various altitudes.

Wettability and reactivity of liquid aluminium and highly deformed steel

The high-temperature liquid Al - solid S355J2N steel interaction was studied using a modified wettability test. A sessile drop method with a capillary purification procedure was employed for the first time, involving non-contact aluminium isothermal heating followed by the dropping of a pure liquid Al drop onto the severely deformed steel substrate and isothermal contact heating of Al with steel. The calculated contact angles and wetting kinetics curves demonstrated a good spreading and wetting of the investigated system. Scanning electron microscopy investigations played an important role in interpretation of the microstructural characteristics of the specimen, especially those located at the drop/substrate interface. The electron backscattered diffraction measurements allowed to characterize the microstructure of the interface zone to obtain more detailed information about the grain size, type of the intermetallic phases: θ-Al13Fe4, Fe2Al5, FCC Al and ferrite and their distribution in the neighborhood of the interface zone. These intermetallics were also confirmed via transmission electron microscopy studies coupled with energy-dispersive X-ray spectroscopy analysis of the drop/substrate interface. Research findings provide valuable insights into the liquid Al and steel interaction during the explosive welding process, where the local melting of metal takes place at the interface of colliding plates, strongly deformed due to the collision.

Geopolymer composites reinforced with silverskin fibers from the coffee industry waste

This paper aims to develop sustainable geopolymer composites reinforced with silverskin fibers derived from coffee industry waste. Geopolymer and geopolymer composites were synthesized from blast furnace slags (BFS) with a solid/liquid (alkaline solution) ratio of 1.4. A sodium metasilicate/sodium hydroxide (Na2SiO3/NaOH) mixture at a mass ratio of 2.5 served as the alkaline activator in the geopolymerization process. The composites were evaluated by incorporating 2%, 3%, and 5% by weight of silverskin fibers, which were used in their natural form (SGCn), after treatment with sodium hydroxide (SGCNaOH), and after treatment with sodium hydroxide followed by a steam explosion process (SGCSE).Characterizations of the geopolymer composites included X-ray fluorescence analysis (XRF) for elemental oxide identification, Fourier transform infrared spectroscopy (FTIR) for functional group detection, and thermogravimetric analysis (TGA) for thermal stability assessment. The influence of fibers on the hardness of the geopolymer materials was evaluated using hardness scale measurements. Morphologies, microstructures, and elemental compositions were analyzed through field emission gun scanning electron microscopy with energy dispersive X-ray spectroscopy (FEG-SEM/EDS).The results demonstrate that the incorporation of silverskin fibers, especially those treated with NaOH and subjected to steam explosion, significantly enhances the thermal stability of geopolymer composites. The 5% NaOH-treated fiber composite exhibited the highest Tmax and Tend, indicating superior thermal stability. Additionally, the 5% SGCNaOH composite showed the highest residual mass, further supporting the enhanced thermal stability of these composites.Unlike other fibers, which showed a decrease in hardness, the addition of SGCSE fibers maintains a relatively high hardness in the geopolymer composites. The 2% SGCSE composite exhibited an average hardness equal to that of the pure geopolymer at 66 Shore D.These findings underscore the potential of using treated silverskin fibers to develop more thermally stable, cost-effective, and sustainable geopolymer materials. By utilizing industrial residues and waste, these advanced materials can be applied in the production of construction and building materials, contributing to both environmental sustainability and economic efficiency.

Experimental and numerical research on the debris bed formation in severe accidents of nuclear reactors

The formation and coolability of the debris bed play a crucial role in the core meltdown process in nuclear reactors. Previous studies mainly focused on experiments involving interactions between small masses of molten material and water, with emphasis on the steam explosion process, lacking analytical data on debris beds and fragments. Therefore, the formation of the debris bed is studied by visual experiments, along with the relevant models are established and applied in this study. In the experiments, a large mass of zirconium dioxide is heated to a molten state in the crucible and then released into a water tank through the release device. The water tank is equipped with four glass windows and high-speed cameras to capture snapshots.Firstly, experiments on the formation of hundred-kilogram-scale debris beds were conducted using the prototype material, zirconium dioxide. The molten material temperature was 3000 K, the molten material mass ranged from 50 to 100 kg, the jet diameter varied from 10 to 20 mm, the water pool depth ranged from 0.55 to 1 m, and the water subcooling varied from 10 to 80 K. Visualized images of the debris bed formation were obtained, and an experimental database of debris bed formation was established, primarily including key parameters such as debris morphology, debris size, debris bed accumulation form, and debris bed porosity. The results indicate that the rise in the mass of molten material and the decrease in water subcooling increase the proportion of large-sized fragments. The experiments did not form a “cake” debris bed but instead achieved loose debris beds due to the small jet diameter. With an increase in the jet diameter and a decrease in water subcooling, the porosity of the debris bed will also increase. Subsequently, computational analysis codes were developed for the processes of jet break-up, debris bed accumulation, and formation, and finally, the deviation of the predicted accumulation morphology was less than 20 %. The results reveal that the influence of the jet diameter and mass of the molten debris on the deposition characteristics of the debris bed is very pronounced. Experimental research and code development hold significant reference value for the formulation of preventive and mitigative measures for severe accidents in nuclear power plants.

Modelling the growth of the network value

We investigate the evolution of network effects, specifically focusing on the emerging paradigm of third-generation networks known as group-forming networks (GFNs). In contrast to traditional views where network value adheres to Metcalfe’s quadratic growth or Sarnoff’s linear growth, GFNs, such as social networks and community-centric platforms like Apple, Microsoft, and Google, exhibit a distinct exponential growth pattern in network value as postulated by Reed’s hypothesis.Unlike conventional network science, economic perspectives on network effects do not necessitate precise knowledge of the network topology. Instead, they often align with mean-field models akin to those found in statistical physics. Recent empirical studies challenge earlier assumptions, revealing that many GFNs have undergone exponential or notably superquadratic growth, deviating significantly from established models based solely on user and link counts.This paper introduces a simplified model aimed at capturing the growth dynamics of marketable groups within a network comprising n users. The model explores various hypothetical mechanisms governing the expansion of these groups, and through rigorous analysis and simulation, we uncover compelling evidence that the observed growth in GFNs surpasses traditional quadratic models. Our findings challenge existing notions, suggesting a new framework for understanding the intricacies of network growth dynamics, and providing solid analytical and conceptual foundations for the recent explosive processes of economic and financial value growth of networks that exploit the formation of groups.

Research on the Explosion Reaction Mechanism of Volatile Gases from Coal Dust Pyrolysis

ABSTRACT It is imperative to have an in-depth understanding of the coal dust explosion reaction mechanism to control and prevent coal explosions in the coal mining industry and promote the safe and efficient utilization of coal resources. The volatile gases are the primary components involved in coal dust explosion reactions. Therefore, studying the explosion reaction mechanism of volatile gases in coal dust is of great significance for revealing the process of coal dust explosion. This study conducted a thermogravimetric mass spectrometry (TG-MS) experiment to analyze the mass loss characteristics and volatile gas components during coal dust pyrolysis. Experimental results showed that the pyrolysis process of coal dust is mainly divided into three stages. The main components of volatile gases escaping from coal dust pyrolysis are CO, CH4, CO2, and H2O. Then, the Chemkin-Pro numerical simulation method was also introduced to analyze the mixture explosion reaction process of coal dust pyrolysis volatile gas. The sensitivity analysis and the rates of production analysis (ROP) of reactants, products, and intermediate products during the volatile gas explosion reaction were conducted. Furthermore, 14 components and 27 key elementary reactions involved in the reaction process were simplified and extracted. A simplified reaction pathway for the mixture explosion of coal dust pyrolysis volatile gas was constructed. This study introduces a novel approach to investigate the mechanism of homogeneous combustion of volatile gases in coal dust explosion reactions.

Catalyst-recirculating system in steam explosion pretreatment for producing high-yield of xylooligosaccharides from oat husk

We propose a closed-loop pretreatment process, wherein volatiles produced during steam explosion pretreatment were recovered and reintroduced as acid catalysts into the pretreatment system. The volatiles were separated through a drastic decompression process followed by a steam explosion process and recovered as a liquified catalyst (LFC) through a heat exchanger. The LFC effectively served as an acid catalyst for hemicellulose hydrolysis, significantly decreasing residence time from 90 min to 30 min to achieve 80 % conversion yield at 170 °C. Hydrolysates with high content of lower molecular weight oligomeric sugars were obtained using LFC, and were considered advantageous for application as prebiotics. These results are attributed to the complementary features of acetic acid and furfural contained within the LFC. Computational simulation using Aspen Plus was used to investigate the effects of recycling on LFC, and it demonstrated the feasibility of the catalyst-recirculating system. A validation study was conducted based on simulation results to predict the actual performance of the proposed pretreatment system. Based on these results, the recirculating system was predicted to improve the conversion yield and low-molecular weight oligomers yield by 1.5-fold and 1.6-fold, respectively.

Explosion quenching characteristics of corrugated plate microchannels in ethanol-gasoline/air mixtures

The flame quenching characteristics of ethanol gasoline are investigated under different thicknesses and porosities of corrugated plate arrester. The results indicate that increasing the flame arrester thickness or reducing porosity leads to a significant decrease in overpressure and flame velocity during ethanol gasoline explosions. The analysis of the time difference collected by the photoelectric sensor before and after the corrugated plate reveals that convective heat transfer between the ethanol gasoline flame and the corrugated plate contributes to two-thirds of the entire explosion process. The duration lengthens with the increase in corrugated plate thickness and the decrease in porosity. This observation demonstrates that increasing the corrugated plate thickness and decreasing the porosity can enhance the heat transfer between the ethanol gasoline flame and the solid microchannel. The flow resistance and Nusselt number are calculated for different porosities, and the mechanism of convective heat transfer in microchannels is analyzed in detail. It can be demonstrated that an increase in the diameter of the microchannel and the velocity of the flame will result in an increase in the Nusselt number and the promotion of convective heat transfer. In conclusion, the corrugated microchannel exhibits superior heat transfer and pressure drop capabilities, which can effectively mitigate the explosion risk associated with ethanol gasoline.

Study on interface characteristics of TC4/7075 explosive welding based on molecular dynamics algorithm

The preparation of TC4/7075 composites for ultra-thin flyer plates is a significant challenge in the field of explosive welding. A weldability window for multi-layer metal explosive welding and a configuration for ultra-thin flyer plate explosive welding were established in this study. TC4/7075 composite materials were successfully prepared with a flyer plate thickness of only 0.3 mm. An analysis was conducted on the material bonding ability, element diffusion, crystal evolution, and microscopic morphology during the explosive welding process of TC4/7075, utilizing the weldability window, molecular dynamics algorithm, and electron backscattered diffraction testing. The results show that various dislocations are present at the interface, predominantly 1/6 ⟨112⟩ dislocations. Element diffusion primarily occurs during the unloading stage at high temperature and zero external pressure; the interface has the best bonding ability when titanium exhibits FCC lattice structure. The prepared composite material demonstrates high intra-grain and grain boundary stresses; the rolling texture is observed on the aluminum side while an equiaxed twin structure forms on the titanium side due to interactions between stacking faults, Stair-rod dislocations, and Hirth immovable dislocations.

Quantitative analysis of flame luminance and explosion pressure in liquefied petroleum gas explosion and inerting: Grey relation analysis and kinetic mechanisms

To evaluate the explosion intensity by flame luminance, a series of explosive and inerting tests on LPG in a 20-L spherical chamber were taken. A quantitative assessment of flame luminance was performed using the grey level theory, and the association between explosion pressure parameters and flame luminance parameters was examined through grey relation analysis. Furthermore, the intrinsic relationship and mechanism between these two variables were explored based on heat-chain reaction kinetics and energy conversion. The findings revealed a synchronous trend between flame luminance and explosion pressure during the LPG explosion process. Notably, a significant positive correlation between explosion pressure and flame luminance was established. Flame luminance emerged as a valuable indicator of explosion intensity, akin to explosion pressure. The grey relational grade between flame luminance and explosion pressure remained remarkably consistent under varying volume fractions of both LPG and CO2. The addition of CO2 exerted a comprehensive influence on factors such as reaction rate, heat release rate, and the concentration of key radicals. This collective impact resulted in reduced explosion pressure and flame luminance. This study offers a theoretical foundation for assessing explosion risks and enhancing energy safety management within the domains of chemical, petroleum, and natural gas industries.

Flame propagation dynamic characteristics and mechanisms of methane–syngas–air mixtures in a semi-enclosed duct

The composition of syngas is complex, often leading to the generation of methane, which impacts the explosive characteristics of syngas. The analysis focused on the kinetic characteristics and mechanisms of flame propagation in methane–syngas–air mixtures in a semi-enclosed duct under various equivalence ratios (φ = 0.8–1.4) and methane volume ratios (R = 0 %–70 %) under ambient temperature and pressure. The results indicated that the flame speed and pressure propagation of methane–syngas–air mixtures could be divided into three stages: a stable stage, an oscillatory increase stage, and an oscillatory decrease stage. In the stable stage, as the methane proportion in the premixed gas increased, the oscillations in the flame and pressure decreased. Turbulent flow of the mixed gas was observed due to restrictions and obstructions within the duct. This led to an increase in the peak pressure and flame speed of the mixed gas, thereby resulting in an oscillatory increase stage. Distorted tulip-shaped flames were also formed in the semi-enclosed duct. The flame of the pure syngas/air mixture exhibited a hemispherical shape and a finger-shaped and slope-shaped propagation structure. When 30 %, 50 %, or 70 % of the methane in the methane–syngas–air mixtures was added, the flame exhibited a propagation structure characterized by a hemispherical shape, finger shape, slope shape, flat shape, tulip shape, or distorted tulip shape. The flame front evolved with time from a linear growth stage to a nonlinear growth stage. The flame front speed of the methane–syngas–air mixtures was closely related to the pressure and flame structure. With the increase in the methane proportion in the methane–syngas–air mixtures, the concentration of key radicals and the rate of OH* generation and consumption gradually decreased. Sensitivity analysis revealed that with increasing methane proportion in the premixed gas, the most important reaction dominating OH* consumption changed from R15 (H + O2(+M) <=> HO2(+M)) to R138 (CH4 + OH <=> CH3 + H2O) and then to R112 (2CH3(+M) <=> C2H6(+M)); moreover, the most important reaction dominating OH* generation remained R1 (H + O2 <=> O + OH). The addition of methane interrupted the hydrogen–oxygen chain reaction of the methane–syngas–air explosion process.

Impact of Intermediate Species in Simulating Oblique Detonation with Pre-Vaporized N-Decane/air Mixtures Substituting for Kerosene/Air Mixtures

ABSTRACT A renewed two-step n-decane mechanism is presented to improve reliable and robust simulation results, substituting for kerosene. This mechanism demonstrates that effective control of ignition delay time and heat release, based on the Chapman – Jouguet condition, enables successful simulation of oblique detonation waves. Chain reactions influence the overall reaction heat and explosion temperature, especially in simplified mechanisms with few steps. Therefore, carbon monoxide (CO) generation is crucial for balancing the overall reaction heat and reducing species sensitivity to pressure, a factor previously not discussed in simplified models. The computational time for solving detailed chemical kinetics increases exponentially with species count, driving the pursuit for further reduction in kinetic mechanism size. The sensitive interaction between density and temperature during the fuel/air mixture explosion process affects initiation zone formation and cellular structure. Analyzing the distribution of CO can provide insights into structural details. The study considers applying the Rankine – Hugoniot curve to confirm detonation speeds, temperatures, and kinetic energy changes induced by chemical reactions.

Research on the hazards of gas leakage and explosion in a full-scale residential building

The gas explosion in residential building has always been a highly concerned problem. Explosions in homogeneous mixtures have been extensively studied. However, mixtures are often inhomogeneous in the practical scenarios due to the differences in the densities of methane and air. In order to investigate the effects of gas explosions in inhomogeneous mixtures, experimental studies involving gas leakage and explosion are conducted in a full-scale residential building to reproduce the process of gas explosion. By fitting the dimensionless buoyancy as a function of dimensionless height and dimensionless time, a distribution model of gas in large-scale spaces is established, and the mechanism of inhomogeneous distribution of methane is also be revealed. Furthermore, the stratified reconstruction method (SRM) is introduced for efficiently setting up inhomogeneous concentration fields in FLACS. The simulation results highlight that for the internal overpressure, the distribution of methane has no effect on the first overpressure peak (ΔP1), while it significantly influences the subsequent overpressure peak (ΔP2), and the maximum difference between the overpressure of homogeneous and inhomogeneous distribution is 174.3%. Moreover, the initial concentration distribution also has a certain impact on the external overpressure.

Microstructure evolution mechanisms of vortex region at explosive welding interface based on Mo/Ta model system

The vortexes at explosive welding interface are the key structures affecting the bonding properties, due to their complex microstructures and tendency to form defects. Here, using Mo/Ta clad as a model system, the various structural characteristics and underlying evolution mechanisms associated with the vortexes were carefully investigated by advanced characterizations and quantitative simulations. It was found that the impact-induced heat energy plays a dominant role in determining the geometries and metallurgical structures of the vortex region. The formations of different types of microdefects were governed by a variety of mechanisms, and the revealed grain information provided strong supports for the microstructure evolution mechanisms developed. The insights gathered here are helpful to further understand explosive welding process and promote performance optimization of the composite materials.

INFLUENCE OF THE NANOSTRUCTURE OF TANTALUM OXIDE ON THE FLARE CHARACTER OF ITS ELECTROLUMINESCENCEWITH ANODIC-ELECTROLYSIS FORMATION IN CHEMICALLY PURE WATER

Theoretical and experimental studies were carried out to identify the reasons for the flash nature of the combustion of electroluminescence (EL) of tantalum oxide (Ta2O5), formed in chemically pure (distilled) water during high-voltage anodization of 1700 s. Nonlinear growth of the Ta2O5 film during this time was established, and a polychrome effect was discovered for its thicknesses from 150 ± 28 nm to 820 ± 80 nm. At the same time, EL ignition begins at an oxide thickness of 390 ± 74 nm, which corresponds to an anodization time of 78 ± 15 s, and from 968 ± 185 s until the end of this process, bright EL flashes are observed. Their luminosity can reach 2.8·10–3 lm/m2. It is shown that the cause of the outbreaks is explosive processes in dynamically changing Ta2O5 pores ranging in size from tens of nanometers to several micrometers and containing gas-discharge plasma from various products of electro- and plasma-chemical reactions with a temperature of the order of 12000 K, created due to Joule heating by the flowing current. It has been established that the formation of the plasma itself occurs as a result of electrical breakdown in pores, the field strength in which can reach the order of 3·108 V/m or more.