Reactive Fragments Research Articles

Numerical Simulation Study on Impact Initiation on Shielded Charge Using Hypervelocity Composite-Structure Reactive Fragments.

In order to study the impact initiation process and mechanism of hypervelocity PTFE/Al composite structure reactive fragments on a shielded charge, first, an existing PTFE/Al reactive fragment hypervelocity collision experiment was numerically simulated using the SPH algorithm in ANSYS/AUTODYN 17.0 software. Then, the Lee-Tarver model was verified to describe the detonation reaction behavior and explosion damage effect of reactive materials. A numerical simulation analysis of the impact of two kinds of ultra-high-speed PTFE/Al composite-structure reactive fragments on a shielded charge was carried out using the SPH algorithm. These were steel-coated PTFE/Al and steel-semi-coated PTFE/Al fragments, and they were compared with the impact of steel fragments. The results indicate that the threshold velocities of the impact initiation of the two composite-structure reactive fragments on the shielded charge were both 2.6 km/s, while the threshold velocity of the steel fragment was 2.7 km/s. Under the threshold velocity condition, the two composite-structure reactive fragments increase the time and intensity of the compressed shock wave pulse in the explosive due to the impact energy release effect of the reactive materials, causing the shielded charge to detonate under the continuous long-term pulse loads. However, the mechanism of the steel fragment on the shielded charge belongs to the shock-detonation transition. The research results can provide scientific references for the design of hypervelocity reactive fragments and the study of their damage mechanism.

Physico-chemical alteration of pyroxene in coastal environments: Empirical constraints from New Zealand and the Azores

Developing approaches to determine the modes of transport and weathering of mafic detrital minerals in natural sedimentary environments is critical to our understanding of sediment production, dispersal and provenance, as well as carbon capture under natural and enhanced weathering regimes. We integrated the characterisation of morphological and surface textures with the surface composition of recent detrital clinopyroxene grains concentrated in a sandy coastal area from the western North Island of New Zealand and a rocky shore area of Santa Maria Island in the Azores Archipelago. Using the compactness shape descriptor, 341 grains were subdivided into elongated, elongated angular, euhedral, angular and subangular groups, with each group further characterised using morphological and microtextural indicators of abrasion, breakage and dissolution/chemical weathering. In both studied environments, the clinopyroxenes are dominated by elongated to angular shapes with flat cleavage surfaces and conchoidal fractures. This is consistent with dominant subaqueous transport by rivers and longshore currents for New Zealand, and dominant wave action with limited sediment supply by rivers along the rocky shore of Santa Maria. More abundant subabraded and abraded shapes with bulbous and elongated depression microtextures are observed in New Zealand, which indicates additional effects by aeolian transport that are not seen in Santa Maria. Consistent with semi-quantitative EDS spot analyses that document fresh clinopyroxenes surfaces, chemical weathering textures are very rare to absent. In Santa Maria, sampling of recent beach sand was complemented by ∼125 kyr-old palaeobeach clinopyroxenes, but these yielded similar textural results without evidence for chemical weathering. However, the surface of these older clinopyroxenes includes small adhering smectite (typically <50 μm in width and a few μm in thickness) interpreted to reflect incipient cementation with buffering of acidic fluids by more reactive lithic fragments in the deposits. The lack of chemical weathering but pervasive evidence for mechanical breakage of clinopyroxenes indicate that, at the sand size, these minerals break faster than they dissolve due to frequent subaqueous and/or aeolian reworking in the studied high-energy environments and temperate climatic conditions.

An approach to distinguish chemical and kinetic energy of reactive materials: PTFE/LiF as an inert substitute to PTFE/Al

AbstractTo distinguish between the kinetic and chemical contributions in the impact of PTFE/Al, this study explores the feasibility of introducing an inert substitute for PTFE/Al by substituting aluminum (Al) with inert materials. Three specimens were fabricated through a process involving mixing, compression, and sintering of raw materials The mechanical properties of these specimens were assessed. Dynamic fragmentation tests of PTFE/Al and PTFE/LiF specimens were performed. These results further substantiate the potential of PTFE/LiF as an inert alternative to PTFE/Al, the two materials exhibit comparable fragmentation distribution characteristics. A preliminary exploration of the energy release in both materials was conducted via vented chamber calorimetry tests. The findings reveal that, at an impact velocity of roughly 650 m/s, only 66.9 % of the materials were deposited into the chamber, with a mere 17.8 % being initiated, about 88.9 % of the total deposited energy results from the chemical reaction energy within the PTFE/Al materials. Importantly, this method demonstrates promise for further application in energy release analysis experiments for various PTFE/Al‐based reactive materials. These findings are beneficial for evaluating the energy release characteristics of reactive fragments on typical targets and lay the foundation for refining energy release models of such materials in future research.

Nitro-functionalized analogues of 1,3-Butadiene: An overview of characteristic, synthesis, chemical transformations and biological activity

The nitrovinyl moiety is surely one of the most reactive fragments in organic chemistry, continuously employed to explore original pathways and reach new targets. One of the most important classes of chemicals containing this fragment are nitro-functionalised analogues of 1,3-butadiene. In this paper a comprehensive review study of these compounds is performed. The manuscript includes an analysis of physicochemical properties, spectral characteristic, synthesis, biological activity, and possible transformations of nitro substituted analogues of 1,3-butadiene. The analysis was divided into several parts, depending on the number of nitro groups included in the structure of a 1,3-butadiene analogue. In addition, the work includes information about hazards and safety principles when working with nitro compounds. Based on the analysis of the literature, it can be concluded that nitro-functionalised analogues of 1,3-butadiene exhibit diversified profile of properties, and an outstanding potential as valuable reagents in organic synthesis useful to obtain heterocycles that can be applied in medicine.

Bond breaking and making in mixed clusters of fullerene and coronene molecules induced by keV-ion impact.

We have performed classical molecular dynamics simulations of 3 keV Ar + (C24H12)n(C60)m collisions where (n,m) = (3,2),(1,4),(9,4) and (2,11). The simulated mass spectra of covalently bound reaction products reproduce the main features of the corresponding experimental results reported by Domaracka et al., Phys. Chem. Chem. Phys., 2018, 20, 15052-15060. The present results support their conclusion that molecular growth is mainly driven by knockout where individual atoms are promptly removed in Rutherford type scattering processes. The so formed highly reactive fragments may then bind with neighboring molecules in the clusters producing a rich variety of growth products extending up to sizes containing several hundreds of atoms, and here we show examples of such structures. In addition, knocked out atoms may be absorbed such that e.g. hydrogenated coronene and fullerene molecules are formed.

Mechanism of inhibitory action of fruit cake extracts as a new environmentally inhibitors of carbon steel corrosion

In this study the firstly study reported on the use of plum, cherry, nectarine and apple pomace extract as corrosion inhibitors of steel in water solution. Potentiodynamic polarization study showed that extracts act as a mixed type inhibitors with dominant cathodic effect. Linear polarization resistance method (LRP) assesses the time-related effect of inhibitors during open circuit potential corrosion. The results show that the inhibitory efficiency of our extract increases with increasing time formation protective film to reach 99 % in a concentration of 500 ppm. LC - MS and FTIR spectroscopy techniques can be concluded that several water-soluble interaction products of chemical reaction in NaCl are identified namely flavanol–anthocyanin and flavanol-aldehyde adducts. Subsequently, the iron-mediated complexation and oxidation of the extract components (flvonoids) in the aqueous solution were explored using UV-spectrophotometric and HPLC methods. With the passage of time, iron-mediated oxidative degradation and coupling reactions occurred, resulting in the production of hydroxybenzoic acid derivatives. Consequently, the inhibition decreased after 24 h. The chemisorption type of interaction of the product formed in the inhibited solution forming the adsorption-polymerization layer with the steel surface is established. Based on the quantum-chemically calculated parameters of the electronic structure of flavanol–anthocyanin and flavanol-aldehyde adducts, it was established for the first time that the combination of reactive fragments in them, which are spatially located in different planes with a higher quantity of hydroxyl groups, increases their adsorption activity and, as a result, their inhibitory capacity.

Furan and benzene ring formation in cellulose char: the roles of 5-HMF and reducing ends.

The authors previously proposed that 5-hydroxymethylfurfural (5-HMF) can be produced from the reducing ends of cellulose as a key intermediate during carbonization. The present work investigated the mechanisms by which furan and benzene rings are formed in cellulose char based on carbonization at 280 °C using 13C-labeled 5-HMF together with 13C-labeled glucose (as a model for the cellulose reducing ends). Glycerol was added to the 5-HMF to prevent the formation of stable glassy polymers. The resulting char was subjected to pyrolysis gas chromatography/mass spectrometry (764 °C, 5 s hold time) and the incorporation of 13C in furan-, phenol-, benzofuran- and benzene-type fragments was assessed. The apparent formation mechanisms include a direct rearrangement of the six carbons of 5-HMF to phenols, Diels-Alder reactions of furan rings with double bonds to give benzofurans and a more random process involving reactive fragments producing benzene rings. On the basis of these results, the roles of 5-HMF and reducing ends during cellulose carbonization are discussed herein.

Perforation Characteristics of Three-Layer Steel Plates Subjected to Impact with Different Shapes and Velocities of Reactive Fragments

In this paper, the AUTODYN/Smoothed Particle Hydrodynamics (SPH) method was used to study the impact of reactive fragments on three-layer equidistant steel plates. The perforation characteristics of equidistant three-layer steel plates were investigated along with the parameters of combustion energy release from reactive fragments under varied impact velocities and shape conditions. The modification of the steel plates’ perforation diameter was investigated using the dimensional analysis approach. The shock wave pressure and chemical reaction characteristics were examined using the shock wave theory. The results show that within the examined impact velocity range, the perforation diameter initially increased and then decreased as the impact velocity of the reactive fragment rose. In addition, the perforation diameter was approximately 1.5–3 times the diameter of the reactive fragment. As the impact speed increased, the active reaction generated by the reactive fragments became more sufficient. The energy released contributed to the impact’s pressure rise; in addition, the temperature of the steel plate was raised in part by the reactive fragment impact, making the steel plate more prone to melting. The results of this investigation provide important support for a detailed understanding of the rules governing the failure of steel plates under the impact of reactive fragments as well as the combustion of reactive fragments under impact.

Study on the effect of grain size on the microstructure evolution of Q345 steel plate under high-speed impact

This study used a two-stage light gas gun to launch reactive fragments at high speeds into steel plates with different grain sizes (large and small). In addition, utilizing material characterization technologies like SEM, EBSD, and TEM, the microstructure evolution of steel plates with varying grain sizes was measured and analyzed both before and after impact. The results indicate that small-grain steel plates are more prone to intergranular or transgranular crack propagation, and they produce more macroscopic and microscopic cracks on the perforated surface under high-speed impact than large-grain steel plates. At the grain boundaries of both large and small grains of steel plate, as well as high-density dislocations, the impact process produces a significant number of minor angles with local misorientation ranging from 2 to 10°. A small-grain steel plate has an obvious grain boundary-strengthening effect. Small grains are more likely than large grains to cause changes in the crystal structure of BCC-HCP close to the perforation, and some grains form a lot of nanoscale elongated structures with the same crystal structure as the matrix. The interaction between dislocations or the emission of a large number of dislocation cells from grain boundaries may occur within some of the larger grains. The study's findings, which are illustrated in this article, can be used as a reference to understand how grain size influences the steel plates' microstructure changes after impacts.

Accessing Ta/Cu Architectures via Metal‐Metal Salt Metatheses: Heterobimetallic C−H Bond Activation Affords μ‐Hydrides

AbstractWe employ a metal‐metal salt metathesis strategy to access low‐valent tantalum‐copper heterometallic architectures (Ta−μ2‐H2−Cu and Ta−μ3‐H2−Cu3) that emulate structural elements proposed for surface alloyed nanomaterials. Whereas cluster assembly with carbonylmetalates is well precedented, the use of the corresponding polyarene transition metal anions is underexplored, despite recognition of these highly reactive fragments as storable sources of atomic Mn−. Our application of this strategy provides structurally unique early‐late bimetallic species. These complexes incorporate bridging hydride ligands during their syntheses, the origin of which is elucidated via detailed isotopic labelling studies. Modification of ancillary ligand sterics and electronics alters the mechanism of bimetallic assembly; a trinuclear complex resulting from dinuclear C−H activation is demonstrated as an intermediate en route to formation of the bimetallic. Further validating the promise of this rational, bottom‐up approach, a unique tetranuclear species was synthesized, featuring a Ta centre bearing three Ta−Cu interactions.

Accessing Ta/Cu Architectures via Metal-Metal Salt Metatheses: Heterobimetallic C-H Bond Activation Affords μ-Hydrides.

We employ a metal-metal salt metathesis strategy to access low-valent tantalum-copper heterometallic architectures (Ta-μ2 -H2 -Cu and Ta-μ3 -H2 -Cu3 ) that emulate structural elements proposed for surface alloyed nanomaterials. Whereas cluster assembly with carbonylmetalates is well precedented, the use of the corresponding polyarene transition metal anions is underexplored, despite recognition of these highly reactive fragments as storable sources of atomic Mn- . Our application of this strategy provides structurally unique early-late bimetallic species. These complexes incorporate bridging hydride ligands during their syntheses, the origin of which is elucidated via detailed isotopic labelling studies. Modification of ancillary ligand sterics and electronics alters the mechanism of bimetallic assembly; a trinuclear complex resulting from dinuclear C-H activation is demonstrated as an intermediate en route to formation of the bimetallic. Further validating the promise of this rational, bottom-up approach, a unique tetranuclear species was synthesized, featuring a Ta centre bearing three Ta-Cu interactions.

Frustrated Lewis Pair Chelation in the p-Block.

Frustrated Lewis pairs (FLPs) have been the subject of considerable study since the field's inception. While much of the research into FLPs has centered around small molecule activation for diverse stoichiometric and catalytic transformations, intramolecular FLPs also show promise as chelating ligands. The cooperative action of Lewis basic and acidic moieties enables intramolecular FLPs to stabilize low oxidation state centers and (consequently) reactive molecular fragments through a donor-acceptor approach, making them an attractive ligand class in main group element chemistry. This review outlines the state of FLP chelation to date throughout the p-block, encompassing primarily groups 13-16.

Tracking the transformation pathway of dissolved organic matters (DOMs) in biochars under sludge pyrolysis via reactomics and molecular network analysis

This work examined the transformation pathways of sludge biochar-derived dissolved organic matters (SBC-derived DOMs) under sludge pyrolysis via FT-ICR-MS-based reactomics and molecular network analysis. Lignin/carboxylic-rich alicyclic molecules, proteins/aliphatic, and lipids of SBC-derived DOMs did not contribute equally to the overall pyrolytic reactions. Reactomics suggested that the pyrolysis reactions of SBC-derived DOMs consist of multiple cascade reactions involving the elimination of assemblages of reactive fragments during each pyrolysis reaction region, and the overall pyrolysis process was divided into three stages according to cascade reaction variations. Especially, cascade reactions at 400–500 °C produced potential environmental risk substances of N-containing, carbonyl-containing, and phenolic compounds. Besides, network analysis unraveled the complexity and number of molecular reaction pairs of SBC-derived DOMs decreased with the increase in pyrolytic temperatures. Keystone molecules and pathways results indicated that the pyrolytic temperature of the sludge pyrolysis process should be controlled at temperatures above 500 °C according to the harmful substances generation pattern in reaction products. Overall, the possible transformation pathways of SBC-derived DOMs during sludge pyrolysis treatment were proposed. This study elucidated the underlying mechanisms in generating SBC-derived DOMs and provided theoretical support for process optimization and harmful substances control of sludge pyrolysis.

Block Chemistry for Accurate Modeling of Epoxy Resins.

Accurate molecular modeling of the physical and chemical behavior of highly cross-linked epoxy resins at the atomistic scale is important for the design of new property-optimized materials. However, a systematic approach to parametrizing and characterizing these systems in molecular dynamics is missing. We therefore present a unified scheme to derive atomic charges for amine-based epoxy resins, in agreement with the AMBER force field, based on defining reactive fragments─blocks─building the network. The approach is applicable to all stages of curing from pure liquid to gelation to fully cured glass. We utilize this approach to study DGEBA/DDS epoxy systems, incorporating dynamic topology changes into atomistic molecular dynamics simulations of the curing reaction with 127,000 atoms. We study size effects in our simulations and predict the gel point utilizing a rigorous percolation theory to recover accurately the experimental data. Furthermore, we observe excellent agreement between the estimated and the experimentally determined glass transition temperatures as a function of curing rate. Finally, we demonstrate the quality of our model by the prediction of the elastic modulus based on uniaxial tensile tests. The presented scheme paves the way for a broadly consistent approach for modeling and characterizing all amine-based epoxy resins.

Enhancement of explosive effect of thermobaric explosive by metal reactive material

AbstractReactive materials have mechanical properties comparable to metal materials and also have the reaction‐release energy characteristics of energetic materials. The calorific value of reactive materials is even higher than that of explosives. They can react under high pressure/high temperature and release a large amount of chemical energy. Therefore, reactive materials have a wide range of potential applications in aviation and national defense fields. This study examines the energy release characteristics of the metal reactive material casing (MRMC) under thermobaric explosives and compares them to traditional steel casing. The test specimens had the same casing‐charge mass ratio and size, with the only difference being the casing material: reactive material (with reactive elements Zr and Al) and AISI 1020 steel. The physical and chemical properties of the reactive materials were tested and analyzed using ICP‐MS, oxygen bomb calorimeter, and SHPB. Through explosion tests, the characteristic parameters of explosion fireball and ground shock wave overpressure were measured. And the reactive fragments recovered from the experiment were subjected to XRD testing. The results show that MRMC can significantly increase the diameter, duration, and temperature of the explosion fireball compared to steel casing data. The maximum fireball diameter of the MRMC specimen increased by 31.9 %, while the duration before attenuation increased by 47.3 %. MRMC can increase the area ratio of high‐temperature areas (greater than 1300 °C) in the fireball. MRMC increases the overall temperature of the fireball, not just in specific local areas. Additionally, MRMC significantly enhances far‐field shock waves. At a scaled distance of 2.54, the peak overpressure and positive impulse of the MRMC specimen were 50 % and 52 % higher than those of the steel specimen, respectively. This study provides new insights into the application, design, and energy release research of MRMC.

Surfactants facilitated glycerol organosolv pretreatment of lignocellulosic biomass by structural modification for co-production of fermentable sugars and highly reactive lignin

This study reported that surfactants could facilitate the organosolv pretreatment of lignocellulosic biomass (LCB) to produce fermentable sugars and highly active lignin. Under the optimized conditions, the surfactant-assisted glycerol organosolv (saGO) pretreatment achieved 80.7% delignification with a retention of 93.4% cellulose and 83.0% hemicellulose. The saGO pretreated substrate exhibited an excellent enzymatic hydrolyzability, achieving 93% of glucose yield from the enzymatic hydrolysis at 48 h. Structural analysis showed that the saGO lignin contained rich β–O–4 bondings with less repolymerization and lower phenolic hydroxyl groups, thus forming highly reactive lignin fragments. The analysis evidenced that the surfactant graft the lignin by structural modification, which was responsible for the excellent substrate hydrolyzability. The co-production of fermentable sugars and organosolv lignin almost recovered a gross energy (87.2%) from LCB. Overall, the saGO pretreatment holds a lot of promise for launching a novel pathway towards lignocellulosic fractionation and lignin valorization.

Experimental Study on the Effect of Buffer Layer on the Explosive Drive of Reactive Fragment

In order to study the influence of the buffer layer on the explosive drive of the reactive fragment, for the reactive fragment warhead of the same structure, the warhead static explosion test and the break-through target test method were used to test the fragment integrity and the fragment integrity of the reactive fragment warhead of the reactive fragment warhead with several different thickness silicone rubber buffer layers. The initial velocity of the fragment was measured, and its integrity and the variation law of the initial velocity were analyzed. The results show that with the increase of the thickness of the buffer layer, the integrity of the reactive fragments increases. When the thickness of the buffer layer is 2 mm, the fragment integrity rate is zero, and when the thickness of the buffer layer is greater than 8 mm, the integrity rate is greater than 0.85. The difference in the initial velocity of the warhead of the same reactive fragment is small, mainly because with the increase of the thickness of the buffer layer, the initial velocity of the fragment decreases mainly because the loading ratio of the warhead decreases; the buffer layer has a significant effect on reducing the initial velocity of the reactive fragment, and k=0.83 can be used The modified Gurney formula was used to estimate the initial velocity of the reactive fragments of the silicone rubber buffer layer.

Efficient Ligand Discovery Using Sulfur(VI) Fluoride Reactive Fragments.

Sulfur(VI) fluorides (SFs) have emerged as valuable electrophiles for the design of "beyond-cysteine" covalent inhibitors and offer potential for expansion of the liganded proteome. Since SFs target a broad range of nucleophilic amino acids, they deliver an approach for the covalent modification of proteins without requirement for a proximal cysteine residue. Further to this, libraries of reactive fragments present an innovative approach for the discovery of ligands and tools for proteins of interest by leveraging a breadth of mass spectrometry analytical approaches. Herein, we report a screening approach that exploits the unique properties of SFs for this purpose. Libraries of SF-containing reactive fragments were synthesized, and a direct-to-biology workflow was taken to efficiently identify hit compounds for CAII and BCL6. The most promising hits were further characterized to establish the site(s) of covalent modification, modification kinetics, and target engagement in cells. Crystallography was used to gain a detailed molecular understanding of how these reactive fragments bind to their target. It is anticipated that this screening protocol can be used for the accelerated discovery of "beyond-cysteine" covalent inhibitors.

Damage Effect of Titanium Alloy by Reactive Fragment Oblique Penetration

The damage effect of reactive fragments on titanium alloy plates is studied through experiment and theoretical analysis. The oblique penetration process and the damage effects of the target influenced by the incident angle and velocity were analyzed. The results show that: Under the condition of 30° incidence angle, the perforation formation modes are extrusion and warping/tearing at 734m/s and 704m/s, respectively, which result to the perforation dimension at 704m/s is 1.56 times of 734m/s; The bulge is formed under the velocity of 1040m/s, at 60° and the reaction ratio of reactive fragments is insufficient. According to the damage morphology of the plate, the damage area in front of the plate can be described as five regions, and the energy density effect on the plate decreases with the increase of the incident Angle.

Study on damage of reactive fragment impacting partially-filled fuel tank

The damage effect of PTFE/Al/W reactive fragment impacting partially-filled fuel tank is investigated by combining the ballistic gun experiment and theoretical analysis. The experimental results show that, with the impact velocity ranging from 806m/s to 1331m/s, the reactive fragments successfully perforate the front plate of fuel tank and cause the flash-ignition of fuel/air mixture, but the fuel tank does not fail obviously. Based on the experimental results, a temperature analysis model of reactive debris is developed by combining the energy release characteristic of reactive material and the convective heat transfer model. The model result shows that the high-temperature reactive debris can effectively ignite fuel/air mixture, which is in good agreement with the experimental results.