Primary Fragmentation Processes Research Articles

Fragmentation and atomization characteristics of near-orifice liquid jet under transverse gas film

In order to understand the fragmentation and atomization characteristics of the liquid jet in transverse gas film, a pintle injection element using air and water as simulants is designed. The two-phase flow large eddy simulation and backlight imaging are used to study the liquid-jet breakup process and spray-field dynamic characteristics in the nearorifice area of pinte injection element under the atmospheric environment. The primary fragmentation process of the liquid jet dominated by surface wave is obtained by large eddy simulation, which reveals the establishment process of the spray field in near-orifice area of the gas-liquid pintle injector. After the subsonic airflow leaves the slit, it expands and accelerates into supersonic state. Then the deceleration and pressurization phenomenon occurs once the supersonic airflow passes through the detached bow shock upstream of the liquid jet. The liquid jet bends downstream due to the difference in pressure between upstream and downstream, and the Rayleigh-Taylor (R-T) unstable surface wave appears on the jet windward surface. As the surface wave develops, the penetration of the wave trough by airflow causes the continuous liquid jet to fragment. Proper orthogonal decomposition (POD) method can effectively reconstruct spray snapshot. The POD mode shows that the low-frequency spray oscillation in near-orifice area is caused by the overall expansion/contraction process of the spray field, while the high-frequency one is due to the “impact wave” movement of the liquid block or liquid mist group on the windward side. The latter is produced by the R-T unstable surface wave before the jet breakup, and can be categorized as traveling wave structure. The dimensionless traveling wave wavelength has a power-law relationship with Weber number.

Standardized analysis of juvenile pyroclasts in comparative studies of primary magma fragmentation; 1. Overview and workflow

Juvenile pyroclasts, especially in the ash size range, provide important information on primary fragmentation processes, i.e., initial explosive magma fragmentation, and on the state of the magma both prior to and at the point of fragmentation and quenching. There exists an extensive body of literature focusing on the quantification of juvenile particle morphology (shape), internal textures, and surface features spanning several decades; however, a standardized method has yet to emerge for comparative studies. No community-wide consensus currently exists (i) regarding the most representative size fraction(s) to be examined, (ii) on sample preparation procedures (such as whether to use whole-particle silhouettes or 2D cross-sections), (iii) on imaging techniques and image acquisition parameters, or (iv) on the optimal morphometric parameters to measure. Lack of a standardized method precludes robust comparison between different studies and laboratories. We propose here a preliminary “best practices” and workflow for characterization of juvenile pyroclasts, for comparative studies of primary fragmentation. If the community follows such a standardized method, it will become possible to accumulate a large volume of consistent data on juvenile pyroclasts from a range of eruption styles, fragmentation mechanisms, and magma compositions. This will ultimately allow deeper insights into the full panoply of magma-to-pyroclast processes that drive particle-producing volcanic eruptions. One or more “fragmentation diagrams” may eventually be developed to allow different types of magmatic and phreatomagmatic explosive eruptions to be distinguished based on their products.

Primary Fragmentation Characteristics in the Process of Coal Slime Combustion

ABSTRACT As a by-product of coal washing, coal slime has a high moisture content and it will fragment during combustion. To explore the primary fragmentation characteristics of coal slime, tests on a single pellet of different coal types with different water contents are carried out on a visual weighing test bench. The primary fragmentation process of the pellets is recorded by a camera and analyzed in combination with a weighing device to investigate the influence of moisture and temperature on the fragmentation characteristics of coal slime. The results show that water in coal slime is the factor that drives fragmenting of coal slime, and there is only a little volatile release from the slime during the primary fragmentation. The fragmenting form of coal slime pellets is intermittently “broken off layer by layer.” The fragmenting process is caused by internal stress produced by water that is rapidly released under high temperature and acts on the outer dry shell of pellets. The initial time required for primary fragmentation of coal slime is shortened with increasing temperature and is prolonged with the increase in the water content. There is a critical water content value for primary fragmentation, and when the water content of coal slime is lower than this value, it will not fragment; different types of coal slime have different critical values.

Molecular structure, spectroscopy and photochemistry of alprazolam

In this article, a comprehensive study of the molecular structure, spectroscopy, and photochemistry of alprazolam (Xanax®; 8-chloro-1-methyl-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine) is reported. The structure of the isolated molecule of the compound was investigated using density functional theory (DFT), revealing that the molecule exists in a single conformer, which is associated with 12 equivalent-by-symmetry minima. The molecules of the compound were trapped from the gas phase into a low temperature (10 K) argon matrix, and the infrared (IR) spectrum of the matrix-isolated monomers was obtained and assigned. The matrix-isolated molecules were then subjected to in situ ultraviolet (UV) irradiation. It was concluded that alprazolam is photostable under these experimental conditions, contrarily to what is known to happen for the compound in solution or in solid state in the presence of excipients used in the pharmaceutical formulations. An explanation for the photostability of the matrix-isolated compound is provided, based on rapid recombinations of the biradical formed from the UV-induced diazepine ring cleavage or the chlorine atom and the complementary radical resulting from the scissoring of the C–Cl bond, which are favored by the cage confinement of the matrix-isolated molecules. The major fragmentation channels of the alprazolam molecule upon electron bombardment (70 eV) were determined by analysis of its electron ionization mass spectrum, which reveals that the major primary fragmentation processes lead to formation of cyanobenzene, N2, HCl (Cl2), and benzene.The compound was also investigated in solution by multinuclear (1H, 13C and 15N) nuclear magnetic resonance (NMR) and ultraviolet (UV) spectroscopies, and in crystalline phase (P-1 polymorph) through IR and Raman spectroscopies. In addition, the structure of the crystal, previously reported in the literature [M. R. Caira, B. Easter, S. Honiball, A. Horne and L. R. Nassimbeni, Structure and Thermal Stability of Alprazolam and Selected Solvates, J. Pharm. Sci., 1995, 84, 1379–1384], was revisited in order to evaluate the relative importance of the different types of intermolecular interactions, using Hirshfeld surface analysis, the CE-B3LYP energy decomposition model, and the harmonic oscillator model of aromaticity (HOMA) index. Finally, the enthalpy of sublimation of the crystal was estimated from the CE-B3LYP calculated lattice energy.

The products of primary magma fragmentation finally revealed by pumice agglomerates

Abstract Following rapid decompression in the conduit of a volcano, magma breaks into ash- to block-sized fragments, powering explosive sub-Plinian and Plinian eruptions that may generate destructive pyroclastic falls and flows. It is thus crucial to assess how magma breaks up into fragments. This task is difficult, however, because of the subterranean nature of the entire process and because the original size of pristine fragments is modified by secondary fragmentation and expansion. New textural observations of sub-Plinian and Plinian pumice lapilli reveal that some primary products of magma fragmentation survive by sintering together within seconds of magma break-up. Their size distributions reflect the energetics of fragmentation, consistent with products of rapid decompression experiments. Pumice aggregates thus offer a unique window into the previously inaccessible primary fragmentation process and could be used to determine the potential energy of fragmentation.

Peculiarities in breakup and transport process of shock-induced ejecta with surrounding gas

The interaction of shock-induced ejecta with gas beyond the free surface is a critical unsolved issue and being investigated broadly. Using models containing micrometer-sized gas environments, we perform molecular dynamics simulations to investigate the coupling interactions of surrounding gases with ejecta from shock-loaded tin surface. Ejected microjets experience progressively aggravated deceleration with increasing gas density, and particle flows ahead of jet tips are suppressed. Despite the drag effect, the primary fragmentation process is yet intrinsically dominated by a velocity gradient. The continuous interaction between ejecta and gas leads to the progressive formation of transmitted shock waves in background gases, which is jointly determined by ejecta velocity and thermophysical properties of gas. Meanwhile, a mixing layer between ejecta and gas is directly observed, leading to discrepant mass distributions of ejecta along shock direction. With increasing gas density, the volume density tends to rise in the mixing zone while the zone thickness decreases. Further, with the presence of gases, the size distribution of ejected particles is altered with an outstanding feature of enhanced formation of atomic particles. It is found that the stripping effect of gas dominates the growth of ejecta clusters in the transport process. The stripped particles strongly couple and flow with compressed gas, accompanied by recombination into subsequent clusters. As the gas density increases, both formation and annihilation of atomic particles are promoted. The revealed peculiarities provide microscopic views of ejecta interaction with ambient gas, which would further the understanding of gas effects on the breakup and transport of ejected particles.

Modern State and Topical Issues of Studying Solid Fuel Particle Primary Fragmentation Processes as Applied to Biomass Combustion and Gasification in Fluidized and Dense Bed (Review)

It is shown that it is important to take into account the variation of particle sizes due to their fragmentation in fluidized bed biomass combustion. The present state of investigations into the fragmentation process is analyzed. It is shown that primary fragmentation, a process involving cracking and disintegration of initial fuel particles into two or more parts due to thermal stresses and growth of pressure in the particles during their rapid heating at the drying and devolatization stages is the most essential issue. Factors causing the cracking of fuel particles and the nature of this process are considered. The particle fragmentation quantitative characteristics and criteria are analyzed. It is shown that the particle critical diameter is the simplest criterion for estimating the susceptibility of different fuels to fragmentation. The main factors influencing the occurrence of primary fragmentation, namely, particle size, heating rate, bed temperature, and fuel characteristics, are considered. The list of fuel’s main characteristics affecting its primary fragmentation includes the volatiles content, porosity, moisture and ash content, susceptibility of particles to swelling or shrinking, and the organic part composition. Matters concerned with predicting primary fragmentation of fuels are considered. Information about the interrelation between the main characteristics of fuels, their susceptibility to primary fragmentation, and its nature is presented. In view of biomass properties and its combustion conditions, both of the primary fragmentation mechanisms, namely due to devolatization induced stresses and thermal stresses, are supposed to take place. It can be expected that the domination of one or another mechanism will depend on the combination of particle size and heating temperature. The lines of and methods for studying the nature of biomass particles primary fragmentation and its quantitative characteristics under different conditions are outlined. The data obtained as a result of such fundamental investigations will form the basis for elaborating methods for designing furnace devices and gasifiers operating on biomass taking into account the effect of particle fragmentation on the combustion, gasification, carryover, and heating surface contamination processes.

Primary and secondary fragmentation of crystal-bearing intermediate magma

Crystal-rich intermediate magmas are subjected to both primary and secondary fragmentation processes, each of which may produce texturally distinct tephra. Of particular interest for volcanic hazards is the extent to which each process contributes ash to volcanic plumes. One way to address this question is by fragmenting pyroclasts under controlled conditions. We fragmented pumice samples from Soufriere Hills Volcano (SHV), Montserrat, by three methods: rapid decompression in a shock tube-like apparatus, impact by a falling piston, and milling in a ball mill. Grain size distributions of the products reveal that all three mechanisms produce fractal breakage patterns, and that the fractal dimension increases from a minimum of ~2.1 for decompression fragmentation (primary fragmentation) to a maximum of ~2.7 by repeated impact (secondary fragmentation). To assess the details of the fragmentation process, we quantified the shape, texture and components of constituent ash particles. Ash shape analysis shows that the axial ratio increases during milling and that particle convexity increases with repeated impacts. We also quantify the extent to which the matrix is separated from the crystals, which shows that secondary processes efficiently remove adhering matrix from crystals, particularly during milling (abrasion). Furthermore, measurements of crystal size distributions before (using x-ray computed tomography) and after (by componentry of individual grain size classes) decompression-driven fragmentation show not only that crystals influence particular size fractions across the total grain size distribution, but also that free crystals are smaller in the fragmented material than in the original pumice clast. Taken together, our results confirm previous work showing both the control of initial texture on the primary fragmentation process and the contributions of secondary processes to ash formation. Critically, however, our extension of previous analyses to characterisation of shape, texture and componentry provides new analytical tools that can be used to assess contributions of secondary processes to ash deposits of uncertain or mixed origin. We illustrate this application with examples from SHV deposits.

Dynamic fragmentation of powders in spherical geometry

Experimental evidence from a wide range of sources shows that the expanding cloud of explosively disseminated material comprises of “particles” or fragments which have different dimensions from those associated with the original material. Photographic evidence shows jets or fingers behind these expanding fragments. Powders and liquids have often been used to surround explosives to act as blast mitigants; this is the main driver for our research. Other examples of areas where these features are observed include fuel air explosives and enhanced blast explosives as well as quasi-static pressure mitigation systems. In this paper, we consider the processes occurring when an explosive interacts with a surrounding layer of powder in spherical geometry. Results from explosive experiments designed to investigate the effects of powder grain size and powder fill-to-burster charge mass ratio (\(F\)/\(B\)) are presented and compared with results from numerical modelling to explore what determines the primary fragment size distribution resulting from explosive dissemination of a layer of material and when this process begins. The evidence clearly shows that the process starts during the first wave transit period of the powder material and, despite the surrounding material initially being a loose powder, shows the characteristics of a brittle fracture mechanism. Later time video evidence shows the same number of jets or fingers as are identified by X-rays of the early, primary fragmentation process. The number of fragments is only a very weak function of the initial grain size of the powder.

Three-dimensional lithofacies variations in hyaloclastite deposits

Analysis of the spatial lithofacies variability within lava-fed delta formations in southern Iceland has revealed complex three-dimensional volcanic architectures in hyaloclastite deposits in non-glacial settings. Two depositional environments are studied, (a) lava entering a marine embayment (Stóri-Nupur) and; (b) lava advancing into a body of water of the flanks of a Surtseyan cone (Hjörleifshöfði). Interaction between environmental factors such as shoreline geomorphology, water depth, wave energy levels, the nature of the lava transport system, lava supply rate all affect the resulting lava deltas creating complex lithofacies arrangements and stacking patterns. Recognised here are two types of hyaloclastite deltas. One of syn-sedimentary origin (Hjörleifshöfði) and one derived from primary fragmentation processes (Stóri-Nupur). Syn-sedimentary systems are dominated by destabilisation of the hyaloclastite pile leading to reworking downslope and share similarities to alluvial delta systems. Conversely, primary fragmented systems are controlled by waxing and waning cycles in volcanic effusivity whereby the hyaloclastite unit recorded is not the product of one lava flow rather than one eruptive event.

Statistical vs. non-statistical deactivation pathways in the UV photo-fragmentation of protonated tryptophan–leucinedipeptide

The excited state dynamics of protonated tryptophan-leucine ions WLH+, generated in an electrospray source, is investigated by photo-induced fragmentation in the gas phase, using femtosecond laser pulses. Two main features arise from the experiment. Firstly, the initially excited pipi* state decays very quickly with 2 time constants of 1 and 10 ps. Secondly, the transient signals recorded on different fragments are not the same which indicates two competing primary fragmentation processes. One involves a direct dissociation from the excited state that gives evidence for a non-statistical deactivation path. The other is attributed to a statistical decay following internal conversion to the ground electronic surface.

Molecular cloning and structural characterization of the hagfish proteinase inhibitor of the alpha-2-macroglobulin family.

The "most primitive" living vertebrate the hagfish has a dimeric proteinase inhibitor, a protein homologous to human alpha2-macroglobulin, in its plasma at high concentration. Although the hagfish proteinase inhibitor has been isolated and its function and quaternary structure studied, its primary structure, subunit composition and fragmentation process remain unclear. In this study, hagfish proteinase inhibitor cDNA was cloned, sequenced and cDNA-deduced amino acid sequence was analyzed. A large fraction of homosubunits in the dimeric structure of the protein has undergone a cleavage at a specific arginyl residue (Arg833) while the rest retained their chain integrity without being processed. Thus random combinations of processed and nonprocessed subunits in the dimeric structure of this protein result in different molecular conformers and generate a complicated multiband pattern in SDS-PAGE. It was further demonstrated by proteolytic analysis that the hagfish inhibitor has no susceptible arginyl residues within its bait region and thus incapable of trapping arginine specific proteinases. This implies that the specific subunit cleavage at Arg833 was caused by an unknown arginine specific proteinase which escaped from the entrapment by the hagfish inhibitor.

Modified Evans–Polanyi–Semenov relationship in the study of chemical micromechanism governing detonation initiation of individual energetic materials

The paper deals with basic problems of the study of the thermal reactivity of individual energetic materials with special attention on the compatibility of results obtained using different methods. It is shown that the activation energies for thermal decomposition of these materials, obtained under comparable conditions, correlate with the respective detonation heats through a modified Evans–Polanyi–Semenov equation. These correlation relationships apply within groups of molecules with closely related structures and underline the importance of the bond that is primarily split in the molecule for the detonation of a given material. They also indicate that the primary fragmentation processes during low-temperature thermal decomposition are the same as those controlling the detonation reaction. It is shown that the correlation relationships found are also valid in the case of electric spark initiation.

Thermal decomposition of 2,2-bis(difluoroamino) propane studied by FTIR spectrometry and quantum chemical calculations: the primary dissociation kinetics and the mechanism for decomposition of the (CH 3) 2CNF 2 radical

The kinetics of the thermal decomposition of 2,2-bis(difluoroamino) propane (BDFP) has been studied by pyrolysis/FTIR spectrometry at temperatures between 528 and 553 K using toluene as radical scavenger. The disappearance of BDFP was found to follow the first-order kinetics with the rate constant, k 1=10 16.0±0.7 exp[−(24200±840)/T] s −1, which agrees closely with the expression obtained by Fokin et al. [Dokl. Akad. Nauk. 332 (1993) 735], k 1=10 15.60 exp(−23600/T) s −1. The measured large A-factor supports the earlier conclusion that the primary fragmentation process corresponds to the breaking of one of the two NF 2 groups. The measured activation energy is also consistent with the predicted first CN bond dissociation energy, 44–48 kcal/mol, by the hybrid density-functional theory and that evaluated by variational RRKM calculations fitting the observed rate constant, 47.9 kcal/mol. The 2-difluoroamino propyl radical, (CH 3) 2CNF 2, was predicted to be thermally unstable, producing readily F atoms and HF molecules via the (CH 3) 2CFNF intermediate. The quantum-chemically predicted mechanisms for the fragmentation of (CH 3) 2C(NF 2) 2 and (CH 3) 2CNF 2 agree with the product distribution reported by Ross and coworkers [J. Am. Chem. Soc. 94 (1972) 8776].

Volcaniclastic aggradation in a semiarid environment, northwestern Vulcano Island, Italy

Most studies of volcaniclastic facies and aggradation cycles have been conducted in regions with humid climates, and on regional scales. Here we document a volcaniclastic succession that formed in a semiarid climate characterized by rare, heavy rains onto a relatively barren volcanic landscape on Vulcano Island, Italy. The deposits, which we informally call the Cuesta succession, occur in a small valley between two rhyolite domes, and consist of a sequence of pyroclastic surge and fallout deposits interbedded with their reworked equivalents. A phase of eruptive activity characterized by sporadic hydrovolcanic explosions supplied ash to the valley and its flanks. Runoff events during the eruptive phase continually washed ash down to the valley floor in the form of hyperconcentrated flows. The inferred transport mechanism and depositional facies of these beds reflect the control of primary volcanic fragmentation processes on sedimentation; the abundant, medium-to-coarse ash supplied by eruption was incorporated sufficiently easily into the runoff to hyperconcentrate the flows, but not sufficiently fine grained to make the flows cohesive. These flows moved out onto the floor, merged, and transported ash down the valley axis, depositing the ash as a monotonous succession of massive to faintly laminated beds. The combination of primary deposits and the deposits washed off the valley flanks led to aggradation of the valley floor. As eruptions waned, ash was eroded off the flanks faster than it was replenished, leading to a stratigraphic upward increase in lithic clasts derived from the underlying lavas and a wider range of sedimentary facies as the ash load became more variable. After eruptions ceased and all remaining ash was removed from the flanks, aggradation gave way to degradation to form small canyons that expose the succession.

1] New photoprotecting groups: Desyl and p-hydroxyphenacyl phosphate and carboxylate esters

This chapter introduces two new phototriggers for caging nucleotides, amino acids, peptides, and related functional group derivatives, potentially including higher-order homologs. These new phototriggers have several advantages that favor them over the conventional o-nitrobenzyl derivatives, including a more rapid release of the substrate by a primary photochemical fragmentation process; adequate to excellent aqueous solubility; and stable, benign photoproducts. Added attractive features for the p-hydroxyphenacyl phototrigger include its rearrangement to a phenylacetic acid, thus shifting the chromophore absorption to a shorter wavelength, eliminating its interference with the incident radiation. Finally, the absence of a chiral center eliminates diastereomeric mixtures during synthesis. It is anticipated that these features will result in added demand for use of α-keto phototriggers for many new applications in biochemistry and physiological studies.

Tandem Mass Spectrometry of Large Biomolecule Ions by Blackbody Infrared Radiative Dissociation

A new method for the dissociation of large ions formed by electrospray ionization is demonstrated. Ions trapped in a Fourier transform mass spectrometer at pressures below 10(-)(8) Torr are dissociated by elevating the vacuum chamber to temperatures up to 215 °C. Rate constants for dissociation are measured and found to be independent of pressure below 10(-)(7) Torr. This indicates that the ions are activated by absorption of blackbody radiation emitted from the chamber walls. Dissociation efficiencies as high as 100% are obtained. There is no apparent mass limit to this method; ions as large as ubiquitin (8.6 kDa) are readily dissociated. Thermally stable ions, such as melittin 3+ (2.8 kDa), did not dissociate at temperatures up to 200 °C. This method is highly selective for low-energy fragmentation, from which limited sequence information can be obtained. From the temperature dependence of the dissociation rate constants, Arrhenius activation energies in the low-pressure limit are obtained. The lowest energy dissociation processes for the singly and doubly protonated ions of bradykinin are loss of NH(3) and formation of the b(2)/y(7) complementary pair, with activation energies of 1.3 and 0.8 eV, respectively. No loss of NH(3) is observed for the doubly protonated ion; some loss of H(2)O occurs. These results show that charge-charge interactions not only lower the activation energy for dissociation but also can dramatically change the fragmentation, most likely through changes in the gas-phase conformation of the ion. Dissociation of ubiquitin ions produces fragmentation similar to that obtained by IRMPD and SORI-CAD. Higher charge state ions dissociate to produce y and b ions; the primary fragmentation process for low charge state ions is loss of H(2)O.

Mass spectrometry of some C6F13‐compounds and their C6H13‐analogs

AbstractThe 70 eV electron ionization mass spectrometric behaviour of some C6F13‐compounds has been studied in detail by means of mass‐analyzed ion kinetic energy spectroscopy and compared with that of the C6H13‐analogs. As a general trend, the incorporation of fluorine leads to a strengthening of the alkyl chain; in fact the extensive primary fragmentation processes related to the chain cleavages observed for hydrocarbon derivatives are strongly suppressed in the case of the corresponding fluorocarbons. Moreover, the interaction of fluorine with functional groups leads to unexpected decomposition processes. The CH2CF2 bond, often considered in condensed‐phase chemistry as a weak point in the molecule, never undergoes fragmentation.

Use of bond orders and valences for the description and prediction of primary fragmentation processes

AbstractSome approaches and examples are shown to demonstrate the usefulness of inherently ‘classical’ parameters, such as bond orders and valences derivable from quantum mechanical wavefunctions, in the description and prediction of mass spectral primary fragmentation processes.

GC-MS investigation of α-polyfluoroalkylbenzyl phosphorus esters

The stereochemistry of some α-polyfluoroalkylbenzyl phosphorus esters has been studied by capillary gas chromatography (CGC). The compounds are mixtures of two or three diastereomers, depending on the number of asymmetric centers and the molecular symmetry. The primary fragmentation processes in the mass spectra of the phosphorus esters and their deuterated analogous have also been studied.