Shock Melting Research Articles

Melting of Titanium by a Shock Wave Generated by an Intense Femtosecond Laser Pulse

Laser shock peening with ultrashort laser pulses has been studied by hydrodynamic and atomistic simulations, as well as experimentally. It has been shown that, in contrast to traditional nanosecond pulses, ultrashort laser pulses allow one to increase the produced pressures by two or three orders of magnitude from 1–10 GPa to 1000 GPa (1 TPa). The physics of phenomena changes fundamentally because shock waves generating pressures exceeding the bulk modulus of a metal melt it. It has been shown for the first time that the shock melting depth at pressures about 1 TPa is an order of magnitude larger than the thickness of the melt layer caused by heat conduction. The appearance, propagation, and damping of a melting shock wave in titanium have been studied. The damping of the shock wave makes it possible to modify the surface layer, where the melting regime changes from a fast one in the shock jump to a slow propagation of the melting front in the unloading tail behind the shock wave. It has been shown experimentally that the ultrafast crystallization of the melt forms a solid layer with a structure strongly different from that before the action. The measured depth of this layer is in good agreement with the calculation.

Unique evidence of fluid alteration in the Kakowa (L6) ordinary chondrite

Meteorites preserve evidence of processes on their parent bodies, including alteration, metamorphism, and shock events. Here we show that the Kakowa (L6) ordinary chondrite (OC) preserves both shock-melt veins and pockets of detrital grains from a brecciated and altered object, including corundum, albite, silica, fayalite, forsterite, and margarite in a Pb- and Fe-rich matrix. Preservation of the observed mineralogy and texture requires a sequence of at least two impacts: first, a high-velocity collision formed the shock melt veins containing the high-pressure minerals ringwoodite, wadsleyite, majorite, and albitic jadeite; later, a low-velocity impact formed fractures and filled them with the detrital material. Oxygen and Pb isotope ratios suggest an OC origin for these detrital minerals. Although fluid alteration is common in carbonaceous chondrites, the discovery of margarite with an OC oxygen isotopic signature is novel. Kakowa extends both the impact and alteration history of L6 ordinary chondrites in general.

Shock temperatures and melting curve of an Fe–Ni–Cr alloy up to 304 GPa

The melting temperatures of Fe–Ni alloys and their densities in the liquid state at relevant pressure–temperature (P–T) conditions present in the core are of great importance for understanding the composition and thermal structure of the Earth's core. We measured shock temperatures of the Fe–11Ni–18Cr (wt. %) alloy up to ∼304 GPa using a special target configuration, a quasi-spectral pyrometer, and velocimeter diagnostics in a two-stage light-gas gun. The present results show that Fe–11Ni–18Cr starts to melt at the pressure of 210 (8) GPa and 4700 (300) K and completes at the pressure of 280 (10) GPa and 5250 (350) K under shock loading, which is ∼1000 K lower than some previous shock temperature measurements. The melting temperatures of the Fe–11Ni–18Cr alloy are 4100 (250) K and 5500 (450) K at the pressures present at the core-mantle boundary (∼136 GPa) and inner-core boundary (∼330 GPa), respectively, which are slightly lower than that of pure iron. Combined with the previous results of the pressure–density measurements at Hugoniot states, our results indicate that the presence of limited amounts of Ni and Cr into Fe has a minor effect on its melting curve and density in the liquid state, suggesting that sufficient light elements are required in the outer core to satisfy both the core density deficit and the reduced melting temperature.

<i>In situ</i> X-ray diffraction measurement of shock melting in vanadium

The solid-liquid phase transition under shock wave loading in materials is called shock melting. Shock melting is important not only in fields like high pressure EOS or material dynamic response, but also in applications like device protection in modern industry and national defense construction. The obtaining of precise melting curve is more than understanding the high pressure melting behavior, and it can provide the reliable evidence for the theoretical model of melting mechanism. So the solid-liquid phase transition under extreme conditions is a research hotspot, and a lot of researches have been carried out. But, the enormous discrepancy between the melting curve of dynamic loading and hydrostatic loading in transition metals, especially, the vanadium has been unclear for decades. The difference in melting temperature under 200 GPa between dynamic loading and hydrostatic loadirng is as large as twice (about 4000 K). Recently, Errandonea and Zhang’s experiments present a new insight into this discrepancy, indicating that the new shock melting curve is consistent with the extrapolated melting curve contained by LH-DAC. But all the dynamic loading experimental data are measured by macroscopic quantities; they can determine the occurrence of the phase transition, but cannot provide the microscopic structure of the material under extreme conditions. So, as the technic of in situ X-ray diffraction has developed well in recent years, we use the high power laser driving technic combining with in situ X-ray diffraction measurement to explore the structure of vanadium near the melting line. We measure the micro structure of vanadium at up to 200 GPa in shock experiment for the first time. We find that the bcc phase transition is not observed at around 60 GPa, which is different from previous experiments in DAC or gas gun loading experiments, but consistent with Chen’s leaser driving experiment. The result confirms that when the impact pressure is 155 GPa, vanadium still remains solid BCC phase. It becomes liquid at about 190 GPa. In contract to Zhang’s results, the DXRD melting point is consistent with the new melting line. This work provides the evidence of the consistency of shock and hydrostatic melting curve, confirming the phase boundary of vanadium under 200 GPa. This work has important scientific significance in understanding the pressure melting behavior of transition metals. The method in this work can be applied to the research of melting properties of other materials.

Petrography and shock-metamorphic features of impact breccias from the Xiuyan impact crater

撞击角砾岩是陨石撞击过程形成的特有岩石种类，是研究撞击成坑过程、陨石坑定年、矿物岩石冲击变质的理想对象。岫岩陨石坑是一个直径1800m的简单陨石坑，坑内有大量松散堆积的撞击角砾岩。本研究通过光学显微镜、费氏台、电子探针、X射线荧光光谱仪、电感耦合等离子质谱仪等分析测试手段，主要研究了岫岩陨石坑撞击角砾岩的岩相学和冲击变质特征，并在此基础上讨论了撞击角砾岩的形成过程和陨石坑的形貌特征。岫岩陨石坑内产出有三种撞击角砾岩，分别是来自上部的玄武质角砾岩和复成分岩屑角砾岩，以及底部的含熔体角砾岩。组成玄武质角砾岩和复成分岩屑角砾岩的碎屑受到的冲击程度较低，仅有少量石英发育面状变形页理，指示不超过20GPa的冲击压力。而组成含熔体角砾岩的碎屑受到了很强的冲击，发育了熔融硅酸盐玻璃、石英面状变形页理、柯石英、二氧化硅玻璃、击变长石玻璃、莱氏石等冲击变质特征，指示的峰值压力超过50GPa。本研究证实了含熔体角砾岩通常产出在简单陨石坑底部，由瞬间坑的坑缘和坑壁垮塌的岩石碎屑与坑底的冲击熔体混合形成。岫岩坑的真实深度是495m，真实深度与直径的比值为0.275，符合简单陨石坑的尺寸特征。陨石坑内的撞击角砾岩中心厚度为188m，与直径之比为0.104，略低于其它简单坑，可能是受丘陵地貌影响导致改造阶段垮塌到坑内的岩石角砾偏少。;Impact breccia is a unique rock type that formed during the meteorite impact process and it is an ideal sample for the studies on the formation process of impact crater, dating impact craters, and shock effects in minerals and rocks. The Xiuyan impact crater is a simple crater with a diameter of 1800m and large amount of impact breccia in it. Here we mainly document the petrology and shock metamorphism of impact breccias from the Xiuyan impact crater through optical microscope, universal-stage microscope, electron probe microanalysis, X-ray fluorescence, and inductively coupled plasma mass spectrometry and then discuss their formation process and the morphology of impact crater. There are three types of impact breccia in the Xiuyan impact crater, which are the basaltic breccia and the polymict lithic breccia from the upper part of impact breccia lens, and the melt-bearing breccia at the bottom. The clasts in the basaltic breccia and the polymict lithic breccia are weakly shocked and only some quartz grains display planar deformation features which indicate shock pressures less than 20GPa. In contrast, the clasts in the melt-bearing breccia are strongly shocked, in which silicate glass, quartz planar deformation features, coesite, silica glass, diaplectic feldspar glass, reidite are observed, which indicate a shock pressure >50GPa. This study confirms that the melt-bearing breccia is usually produced at the bottom of simple impact craters and is formed by mixing rock clasts collapsed from the transient crater rim and wall with shock melt at the bottom. The true depth of Xiuyan impact crater is 495m, and the true depth/diameter ration is 0.275, which is consist with other simple impact craters. The central thickness of impact breccia lens is 188m and the thickness/diameter ration is 0.104, slightly lower than that of other simple impact craters, which may be due to less rock clasts collapsed into the crater in the modification stage that caused by hilly terrain.

Northwest Africa 6486: Record of large impact events and fluid alteration on the L chondrite asteroid

AbstractWe report the results of petrological, geochemical, and geochronological investigations of the unusual K‐rich L chondrite melt rock Northwest Africa 6486 (NWA 6486). The rock has slightly fractionated siderophile elements and a mostly unfractionated L chondrite pattern of lithophile elements with the exceptions of enrichments in K and Rb and chondritic Sr abundance similar to the K‐rich inclusions found in the ordinary chondrites and indicating a fractionation of alkaline elements through the vapor. We suggest that NWA 6486 and related K‐rich chondritic inclusions were formed in situ on the OC parent bodies and that K and Rb enrichment of these rock most probably is a result of the selective impact evaporation of volatile alkali elements followed by the reaction of a vapor with shock melt. NWA 6486 recorded a breakup event of the L chondrite parent asteroid at 470 Ma during which it was formed. Unusual veins, depleted in K, Na, Ca, and Al relative to the host rock were found in NWA 6486. We suggest that NWA 6486 was affected by aqueous fluids that produced alteration zones depleted in a feldspar component on the walls of opened fractures. The melt veins could be formed during a subsequent impact event by in situ melting of the fracture walls or due to decomposition of an injected supercritical aqueous silicate fluid. The aqueous alteration and the second impact event had no detectable effect on Ar and oxygen isotopic systems. Cosmic ray exposure ages indicate that NWA 6486 was ejected from its parent asteroid ~3–4 Ma ago.

Shock-induced H loss from pyroxene and maskelynite in a Martian meteorite and the mantle source δD of enriched shergottites

Assessing the water abundance and hydrogen isotopic signature (δD) of the Martian interior dictates our understanding of the formation of inner solar-system planets, the origin of their volatiles, Martian volcanic history, and the potential for life-bearing environments on the surface of the red planet. Although several Martian meteorites, representing the planet's crust, have been analyzed before for this assessment, little is known about the effect of shock on recorded hydrogen (H) in their mineral phases. Here, hydrogen contents and isotopes are measured by secondary ion mass spectrometry (SIMS) in an enriched olivine-phyric shergottite, Larkman Nunatak (LAR) 06319, containing impact-melted zones. Systematic 100 μm-long traverses in pyroxene and maskelynite grains reveal decreases of hundreds of µg/g H2O and increases in δD of thousands of ‰ towards the contact with impact-melted zones, which is interpreted as H diffusive loss during shock-melting. Diffusion modeling reveals that temperatures high enough to permit H diffusion following shock were maintained near the impact-melted zone for a few minutes. By comparison, the interior of pyroxenes > 200 μm away from impact-melted zones have some of the highest H content with 170–480 µg/g H2O and the lowest δD with ∼ 300‰. The latter values, obtained on the most Mg-rich, i.e. earliest crystallized pyroxenes, are used to estimate that the enriched shergottite mantle source contains 300–1000 µg/g H2O and has a δD of ∼ 300‰. This δD is similar to that of depleted shergottite and nakhlite mantle sources, but higher than Earth’s upper mantle, suggesting slightly different water source materials for the two planets. The enriched shergottite mantle source has ∼ 10 times more water than that inferred for the depleted shergottite source and for Earth’s upper mantle. The high water content and wide range of δD in olivine (from 90 µg/g H2O and 2700‰ to 1350 µg/g H2O and −14‰) is interpreted as overprinting by a combination of Martian and terrestrial surface alteration. Finally, the high δD recorded in the impact-melt produced glass (3350–4700‰), its moderate water content (100–230 µg/g H2O), and the presence of vesicles, are likely the result of incorporation of Martian surficial material (ice and atmospheric gases) and degassing during shock melting. This study shows that shock can induce H loss from minerals, accompanied by > 1000‰ δD increases. Additionally, although it confirms that the Martian mantle may be heterogeneous in its water content, it implies that the Martian mantle is homogeneous within uncertainties for δD.

Shock melting and the hcp-bcc phase boundary of Mg under dynamic loading

The high-temperature and high-pressure response of magnesium has been investigated through shock-release experiments performed up to shock melting. The longitudinal and bulk sound speeds of Mg are reported along the Hugoniot from 25 to 56 GPa and used to determine the elastic properties and Gr\"uneisen parameter. The hexagonal close-packed (hcp)--body-centered cubic (bcc) phase transition is marked by a reduction in the determined shear wave speed. Thermal softening is observed to begin between 40 and 44 GPa, with incipient melt at 55.5 GPa, in close agreement with previous diffraction measurements under laser shock loading. Examination of the release profiles showed that two different responses were observed, depending on the peak stress. When plotted in a stress-energy phase diagram, the two responses are observed to form separate lines that intersect the static hcp-bcc phase transition and incipient melt. The results indicate that the hcp-bcc transition occurs on the Hugoniot at 28.4 GPa and place the hcp-bcc-liquid triple point \ensuremath{\sim}20 GPa. A multiphase equation of state is developed which places the melt boundary below the previously reported static measurements.

Spallation Characteristics of Single Crystal Aluminum with Copper Nanoparticles Based on Atomistic Simulations.

In this study, the effects of Cu nanoparticle inclusion on the dynamic responses of single crystal Al during shockwave loading and subsequent spallation processes have been explored by molecular dynamics simulations. At specific impact velocities, the ideal single crystal Al will not produce dislocation and stacking fault structure during shock compression, while Cu inclusion in an Al–Cu nanocomposite will lead to the formation of a regular stacking fault structure. The significant difference of a shock-induced microstructure makes the spall strength of the Al–Cu nanocomposite lower than that of ideal single crystal Al at these specific impact velocities. The analysis of the damage evolution process shows that when piston velocity up ≤ 2.0 km/s, due to the dense defects and high potential energy at the interface between inclusions and matrix, voids will nucleate preferentially at the inclusion interface, and then grow along the interface at a rate of five times faster than other voids in the Al matrix. When up ≥ 2.5 km/s, the Al matrix will shock melt or unloading melt, and micro-spallation occurs; Cu inclusions have no effect on spallation strength, but when Cu inclusions and the Al matrix are not fully diffused, the voids tend to grow and coalescence along the inclusion interface to form a large void.

On the role of shock melting and anatexis in breccia formation: Southern Sudbury impact structure, Canada

The ca. 1.85 Ga Sudbury Igneous Complex (SIC) in Ontario, Canada, represents the partially eroded remnant of an impact melt sheet that overlies brecciated target rocks. At Crean Hill, along its southwest margin, it is underlain by contact metamorphosed basement rocks cut by breccias of various compositions. The breccias formed as melts with contact-parallel flow textures, which are defined by elongate wispy clasts that wrap around basalt clasts. The presence of melts in the footwall of large impact melt sheets may be due to shock melting during propagation of the shock wave, frictional melting along superfaults during modification of the crater, injections from the impact melt sheet, or anatexis during cooling of the impact melt sheet. The absence of nearby superfaults at Crean Hill precludes the formation of the breccia by frictional melting. Modeling of partial melt compositions during contact metamorphism produces chemical melts that are generally enriched in Zr and more felsic than the breccia matrices, negating the possibility of their formation by anatexis during contact metamorphism. The breccia matrices have significantly lower SiO2 and higher TiO2 than the SIC original melt composition, suggesting that they could not have formed by the injection of SIC melt into the fractured target rocks. Because the composition of the breccias mirrors that of their host rocks, the breccias are interpreted as pockets and dikes of locally-derived shock melt that formed during shock compression and were trapped in the basement rocks during cooling of the SIC. Thus, the breccias formed by shock melting during impact and were subsequently modified by contact metamorphism (T ≥ 750 °C) during cooling of the SIC, and by later syn-tectonic regional metamorphism at upper greenschist to amphibolite conditions.

Petrology and mineralogy of an igneous clast in the Northwest Africa 1685 (LL4) chondrite: Comparison with alkali‐rich igneous clasts in LL‐chondritic breccias

AbstractWe have conducted petrological and mineralogical studies on an igneous clast in the Northwest Africa (NWA) 1685 (LL4) chondrite. This meteorite was described in the Meteoritical Bulletin as containing clasts similar to alkali‐rich clasts in LL chondritic breccias Yamato (Y)‐74442 (LL4), Bhola (LL3‐6), and Krähenberg (LL5). We carefully compared the textures, as well as mineral and matrix compositions, of the NWA 1685 clast with those of the previously described alkali‐rich clasts in the LL chondritic breccias. Olivine grains are embedded in glassy matrix and have no chemical zoning. Shock melt veins and fractures were observed only in olivine grains and did not continue into matrix. Potassium abundance of matrix glasses of the NWA 1685 clast is lower than those of alkali‐rich igneous clasts in Y‐74442, Bhola, and Krähenberg, indicating that the igneous clasts in NWA 1685 are different from the alkali‐rich clasts previously reported in the LL chondritic breccias. The NWA 1685 clast might have formed during an impact melting and quenching event on the LL‐chondrite parent body, and then been incorporated into a breccia.

Spall damage in single crystal tin under shock wave loading: A molecular dynamics simulation

Using molecular dynamics methods, we investigated the spall damage in single crystal tin under different shock pressures. The results show that release melting and shock melting occur when the shock velocities increase in the metallic tin. The spall strengths in the molten tin are ~1.5–2.0 GPa lower than that in solid. When release melting occurs, the spall strength drops rapidly, whereas the downtrend of the spall strength becomes gentle during shock melting. The results also show that the spall strength is affected by not only the shock pressure and phase state, but also the temperature and strain rate. By visualizing the development of spall damage, we find that it forms a spall layer in the solid. In molten tin, a cavitation region with a large volume is formed. The maximum number of voids increases with an increase in the shock pressure. The growth rate of the void volume fraction slows down after reaching the initial time of void growth at different impact pressures. We elucidated the variation trend of spall strength between solid and molten tin under different shock pressures. The relevant results can provide a reference for future studies on spall damage investigations.

The classification of Parauapebas Meteorite: Petrological, mineralogical and elemental compositions and physical properties

The Parauapebas meteorite, an ordinary chondrite, was investigated through a systematic classification method, applying non-destructive analytical techniques: Electron Microprobe Micro-Analyzer (EPMA), X-Ray Fluorescence (XRF), Proton-Induced X-Ray Emission (PIXE), Cathodoluminescence (CL), and Optical Microscopy (OM). The goal was to achieve a complete and detailed chemical and petrological description of the official Parauapebas meteorite (MB 107). Additionally an inter-technique comparison was included for the bulk chemical composition obtained by means of the X-ray fluorescence PIXE and XRF techniques. The measured elemental compositions were compared to XRF and INAA average values reported in previous works on chondrites. The physical properties, such as density and magnetic susceptibility, of Parauapebas meteorite were also included as a tool for the chemical group classification. The meteorite is rich in iron metal, except into the silicates, thus Parauapebas is an H chemical group chondrite. Nevertheless some elemental compositions were found within the range of L chemical group chondrites. It presents two different lithologies with homogeneous chemistry observed in the analyzed thin sections, which point the meteorite as a genomict breccia (indicated by shock melt veins) formed by petrologic type 4 and 5. A shock stage S3/S4 is indicated by the olivine crystals with undulatory extinction, irregular and some planar fractures and a weak mosaicism, Neumann lines in iron-nickel, in addition to the presence of shock melt veins and pockets. The weathering degree is the lowest (W0), since the fragment was recovered soon after the fall.

Shock-ramp analysis test problem

Quasi-isentropic (ramp) compression is now a well-established experimental method and so are the analysis techniques to give Lagrangian sound speed, pressure, and density along the sample material's isentrope. A shock followed by ramp compression is a natural extension to investigate, for example, shock melt and refreeze on compression, or isentropes of states off the Hugoniot or principal isentrope. In practice, graded-density impactors produce initial shocks, compression by shaped laser pulses may be unable to produce a smooth pressure increase from zero, and incidental perturbations on the drive pulse may also give rise to shocks, so robust shock-ramp analysis methods will be needed. Appropriate analysis methods are needed for shock-ramp experiments, based on those for quasi-isentropic compression, and these require validation. This paper describes three different analyses of a shock-ramp test problem, including an assessment of their estimated errors. The methods tested were based on hydrodynamic characteristics or integration backward in space. All methods gave the known Lagrangian sound speed to within ∼1%, and pressure and volume to within less than 2% and 1%, demonstrating that the analysis methods of isentropic compression experiments can be confidently extended to the analysis of shock and ramp compression.

Petrology and mineralogy of the Viñales meteorite, the latest fall in Cuba.

The new Cuban chondrite, Viñales, fell on February first, 2019 at Pinar del Rio, northwest of Cuba (22°37'10″N, 83°44'34″W). A total of about 50-100 kg of the meteorite were collected and the masses of individual samples are in a range 2-1100 g. Two polished thin sections were studied by optical microscope, Raman spectroscopy and electron microprobe analysis in this study. The meteorite mainly consists of olivine (Fa24.6), low-Ca pyroxene (Fs20.5), and troilite and Fe-Ni metal, with minor amounts of feldspar (Ab82.4-84.7). Three poorly metamorphosed porphyritic olivine-pyroxene and barred olivine chondrules are observed. The homogeneous chemical compositions and petrographic textures indicate that Viñales is a L6 chondrite. The Viñales has fresh black fusion crust with layered structure, indicating it experienced a high temperature of ∼1650°C during atmospheric entry. Black shock melt veins with width of 100-600 μm are pervasive in the Viñales and olivine, bronzite, and metal phases are dominate minerals of the shock melt vein. The shock features of major silicate minerals suggest a shock stage S3, partly S4, and the shock pressure could be >10 GPa.

Microtextures in the Chelyabinsk impact breccia reveal the history of Phosphorus‐Olivine‐Assemblages in chondrites

AbstractThe geochemistry and textures of phosphate minerals can provide insights into the geological histories of parental asteroids, but the processes governing their formation and deformation remain poorly constrained. We assessed phosphorus‐bearing minerals in the three lithologies (light, dark, and melt) of the Chelyabinsk (LL5) ordinary chondrite using scanning electron microscope, electron microprobe, cathodoluminescence, and electron backscatter diffraction techniques. The majority of studied phosphate grains appear intergrown with olivine. However, microtextures of phosphates (apatite [Ca5(PO4)3(OH,Cl,F)] and merrillite [Ca9NaMg(PO4)7]) are extremely variable within and between the differently shocked lithologies investigated. We observe continuously strained as well as recrystallized strain‐free merrillite populations. Grains with strain‐free subdomains are present only in the more intensely shocked dark lithology, indicating that phosphate growth predates the development of primary shock‐metamorphic features. Complete melting of portions of the meteorite is recorded by the shock‐melt lithology, which contains a population of phosphorus‐rich olivine grains. The response of phosphorus‐bearing minerals to shock is therefore hugely variable throughout this monomict impact breccia. We propose a paragenetic history for P‐bearing phases in Chelyabinsk involving initial phosphate growth via P‐rich olivine replacement, followed by phosphate deformation during an early impact event. This event was also responsible for the local development of shock melt that lacks phosphate grains and instead contains P‐enriched olivine. We generalize our findings to propose a new classification scheme for Phosphorus‐Olivine‐Assemblages (Type I–III POAs). We highlight how POAs can be used to trace radiogenic metamorphism and shock metamorphic events that together span the entire geological history of chondritic asteroids.

Molecular dynamics simulations of shock melting in single crystal Al and Cu along the principle Hugoniot

Shock melting in single crystal Al and Cu along the principle Hugoniot was investigated through molecular dynamics simulations. First, the GRAY equation of state (EOS) was employed to reproduce the melting curve, which aimed at obtaining the Simon melting equation. The accuracy and validity of Simon melting curve are evaluated by the first-order derivative of melting temperature with respect to pressure at zero pressure, initial and complete melting temperatures and pressures, which are in good agreement with the available data. Next, the specific melting volume and latent heat calculated by the Clausius-Clapeyron equation present a descending and ascending trend as pressure increases, respectively. Then it is assumed that the liquid fraction is a power law function of pressure, whose nonlinear increasing is featured by the symmetry. More importantly, the expression of second-order derivative of melting temperature with respect to pressure is deduced by the Clausius-Clapeyron relation and Simon melting equation, respectively. Specifically for the Clausius-Clapeyron relation, its application to solid-liquid phase transformation for Al and Cu is quite effective and the result of the second-order derivative at zero pressure is reasonably compatible with that calculated from the Simon melting equation, which manifests that this two methods can be verified mutually. Moreover, it further discusses that the change characteristics of Simon melting equation by virtue of its first- and second-order derivatives.

Heat diffusion in numerically shocked ordinary chondrites and its contribution to shock melting

High pressure shock metamorphism in ordinary chondrites involves heating and melting of individual phases from shock entropy, pore collapse, frictional heating, and heat transfer. Numerical models using shock physics codes have recently been used to comprehend the mechanism of shock heating and melting in multiphase mesoscale models. Such models suggest that the formation of sulfide and metal melt veins in ordinary chondrites (shock-darkening) can be explained by preferential heating and melting of iron and iron sulfides during shock. However, those models usually dismissed heat transfer between heterogeneously shock heated phases. This leads to an underestimation of the degree of melting in phases that experienced low degrees of shock heating (e.g. iron metal) but are in direct contact with strongly shock heated phases (e.g. iron sulfides). In our study, we implemented a finite difference 2-D heat diffusion code to model heat diffusion among neighboring grains in shock heated multiphase meshes that represent typical textural relations of silicate, sulfide and metal grains in ordinary chondrites. Post-shock temperature maps for each textural model were calculated using the iSALE shock physics code and used as input for the diffusion code. We find that heat diffusion, not initial shock heating, is the principal cause for heating and melting of metals in eutectic contact with iron sulfides at ~50 GPa of pressure. In addition we study the effects of iron and troilite grain sizes, shock pressures and pre-shock porosities of the silicate matrix, and discuss the preservation of melt allowing melt migration in shock-darkened meteorites and the observation of metal-silicate intermixed melting. With our work, we demonstrate that the consideration of heat diffusion during and after shock is crucial for a better understanding of melting features in both experimentally and naturally shocked ordinary chondrites.

Hydrodynamic computations of high-power laser drives generating metal ejecta jets from surface grooves

Understanding dynamic fragmentation in shock-loaded metals and predicting properties of the resulting ejecta are of considerable importance for both basic and applied science. The nature of material ejection has been shown to change drastically when the free surface melts on compression or release. In this work, we present hydrodynamic simulations of laser-driven microjetting from micron-scale grooves on a tin surface. We study microjet formation across a range of shock strengths from drives that leave the target solid after release to drives that induce shock melting in the target. The shock-state particle velocity (Up) varies from 0.3 to 3 km/s and the shock breakout pressure is 3–120 GPa. The microjet tip velocity is 1–8 km/s and the free-surface velocity varies from 0.1 to 5 km/s. Two tin equations of state are examined: a “soft” model (LEOS 501) where the target melts for Up>1 km/s and a more detailed multiphase model (SESAME 2161) that melts for Up>1.4 km/s. We use these two models to examine the influence of phase change and the choice of the material model on microjet formation and evolution. We observe in our computational results that jet formation can be classified into three regimes: a low-energy regime where material strength affects jet formation, a moderate-energy regime dominated by the changing phase of tin material, and a high-energy regime where results are insensitive to the material model and jet formation is described by an idealized steady-jet theory. Using an ensemble of 2D simulations, we show that these trends hold across a wide range of drive energies and groove angles.

Examining the high-pressure response and shock melting in cerium using optical pyrometry

The ability to measure temperature in shock wave experiments has been a long-standing scientific challenge complicated by the short timescales involved ($l1$ microsecond) and the presence of nonthermal or external light sources that pollute measured radiances using optical pyrometry methods. In the current work, we present the first experimental data on cerium metal designed to measure the temperature on-Hugoniot from the low-pressure $\ensuremath{\alpha}$ phase well into the high-pressure liquid phase. Radiance data obtained in this work were used to determine the Hugoniot curves for solid ($\ensuremath{\alpha}$-Ce) and liquid cerium by measuring the longitudinal stress and temperature simultaneously in the shocked state. These data were used to estimate the temperature for incipient shock melting and complete melting, and to further constrain a multiphase equation of state developed to describe the dynamic response of cerium at high pressures.