scholarly journals The formation of impact coesite

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
F. Campanale ◽  
E. Mugnaioli ◽  
M. Gemmi ◽  
L. Folco
Keyword(s):  
Shock Wave ◽  
Amorphous Phase ◽  
Formation Mechanism ◽  
Nucleation And Growth ◽  
Transformation Model ◽  
Porous Rocks ◽  
Formation Pathway ◽  
Crystallographic Study ◽  
Impact Ejecta ◽  
Topotactic Transformation

AbstractCoesite in impact rocks is traditionally considered a retrograde product formed during pressure release by the crystallisation of an amorphous phase (either silica melt or diaplectic glass). Recently, the detailed microscopic and crystallographic study of impact ejecta from Kamil crater and the Australasian tektite strewn field pointed in turn to a different coesite formation pathway, through subsolidus quartz-to-coesite transformation. We report here further evidence documenting the formation of coesite directly from quartz. In Kamil ejecta we found sub-micrometric single-coesite-crystals that represent the first crystallization seeds of coesite. Coesite in Australasian samples show instead well-developed subeuhedral crystals, growing at the expenses of hosting quartz and postdating PDF deformation. Coesite (010) plane is most often parallel to quartz {10–11} plane family, supporting the formation of coesite through a topotactic transformation. Such reaction is facilitated by the presence of pre-existing and shock-induced discontinuities in the target. Shock wave reverberations can provide pressure and time conditions for coesite nucleation and growth. Because discontinuities occur in both porous and non-porous rocks and the coesite formation mechanism appears similar for small and large impacts, we infer that the proposed subsolidus transformation model is valid for all types of quartz-bearing target rocks.

The Kinetics of Austenization Process of T91 Ferritic Heat-Resistant Steel

2011 ◽  
Vol 317-319 ◽  
pp. 42-47
Author(s):  
Li Fang Zhang ◽  
Yong Chang Liu
Keyword(s):  
Experimental Data ◽  
Phase Transformation ◽  
Kinetic Parameters ◽  
Nucleation And Growth ◽  
Transformation Model ◽  
Resistant Steel ◽  
Kinetic Characteristics ◽  
Heat Resistant Steel ◽  
Austenite Grain ◽  
Kinetics Of

By fitting the calculated transformed fraction according to developed phase-transformation model to the experimental data obtained by differential dilatometry, the kinetic characteristics of the austenitization process in T91 steels have been investigated. According to the kinetic parameters fitted, we recognize that the nucleation and growth of austenite grain are mainly controlled by the diffusion of carbon in ferritic and austenite respectively. In addition, by increasing the diffusion active energy of carbon in austenite, carbides hinder the motion of interface and thus refine austenite grain.

scholarly journals Research on Formation Mechanism of Dynamic Response and Residual Stress of Sheet Metal Induced by Laser Shock Wave

2018 ◽  
Vol 167 ◽  
pp. 05007
Author(s):  
Aixin Feng ◽  
Yupeng Cao ◽  
Heng Wang ◽  
Zhengang Zhang
Keyword(s):  
Shock Wave ◽  
Residual Stress ◽  
Dynamic Response ◽  
Formation Mechanism ◽  
Experimental Studies ◽  
Material Surface ◽  
Propagation Mechanism ◽  
Laser Shock ◽  
Surface Residual Stress ◽  
Laser Shock Wave

In order to reveal the quantitative control of the residual stress on the surface of metal materials, the relevant theoretical and experimental studies were carried out to investigate the dynamic response of metal thin plates and the formation mechanism of residual stress induced by laser shock wave. In this paper, the latest research trends on the surface residual stress of laser shock processing technology were elaborated. The main progress of laser shock wave propagation mechanism and dynamic response, laser shock, and surface residual stress were discussed. It is pointed out that the multi-scale characterization of laser and material, surface residual stress and microstructure change is a new hotspot in laser shock strengthening technology.

An experimental study of reflected liquefaction shock waves with near-critical downstream states in a test fluid of large molar heat capacity

1994 ◽  
Vol 277 ◽  
pp. 163-196 ◽  
Author(s):  
Seyfettin C. Gülen ◽  
Philip A. Thompson ◽  
Hung-Jai Cho
Keyword(s):  
Shock Wave ◽  
Heat Capacity ◽  
Phase Change ◽  
Molar Heat Capacity ◽  
Continuous Process ◽  
Nucleation And Growth ◽  
Test Fluid ◽  
Average Lifetime ◽  
Wave System ◽  
Two Phase

Near-critical states have been achieved downstream of a liquefaction shock wave, which is a shock reflected from the endwall of a shock tube. Photographs of the shocked test fluid (iso-octane) reveal a rich variety of phase-change phenomena. In addition to the existence of two-phase toroidal rings which have been previously reported, two-phase structures with a striking resemblance to dandelions and orange slices have been frequently observed. A model coupling the flow and nucleation dynamics is introduced to study the two-wave system of shock-induced condensation and the liquefaction shock wave in fluids of large molar heat capacity. In analogy to the one-dimensional Zeldovich–von Neumann–Döring (ZND) model of detonation waves, the leading part of the liquefaction shock wave is a gasdynamic pressure discontinuity (Δ ≈ 0.1 μm, τ ≈ 1 ns) which supersaturates the test fluid, and the phase transition takes place in the condensation relaxation zone (Δ ≈ 1–103 μm, τ ≈ 0.1–100 μs) via dropwise condensation. At weak to moderate shock strengths, the average lifetime of the metastable state, τ ∞ 1/J, is long such that the reaction zone is spatially decoupled from the forerunner shock wave, and J is the homogeneous nucleation rate. With increasing shock strength, a transition in the phase-change mechanism from nucleation and growth to spinodal decomposition is anticipated based on statistical mechanical arguments. In particular, within a complete liquefaction shock the metastable region is entirely bypassed, and the vapour decomposes inside the unstable region. This mechanism of unmixing in which nucleation and growth become one continuous process provides a consistent framework within which the observed irregularities can be explained.

The Metastable Micro-Nanocrystals and Formation Mechanism of Rapidly Solidified Al-21Si Multi-Alloys

2014 ◽  
Vol 636 ◽  
pp. 97-100 ◽  
Author(s):  
Ai Qin Wang ◽  
Hui Hui Han ◽  
Jing Pei Xie ◽  
Ji Wen Li
Keyword(s):  
Formation Mechanism ◽  
Melt Spinning ◽  
Primary Silicon ◽  
Nucleation And Growth ◽  
Microstructure Formation ◽  
Microstructure Morphology ◽  
Alloy Microstructure ◽  
Rapidly Solidified ◽  
Melt Spinning Technique ◽  
Scanning Electron

In the present work, rapidly solidified Al-21Si-0.8Mg-1.5Cu-0.5Mn alloys strips was prepared by melt-spinning technique. The microstructure morphology and phase structures of experimental alloy were characterized by means of scanning electron microscopy (SEM), transmission electric microscopy (TEM) and XRD technique. The results show that the grains were refined and the micro-nanocomposite structural were formed under rapid solidification. The nucleation and growth of primary silicon were suppressed and primary silicon could not deposited, meanwhile, α-Al phase was nucleated which prior to eutectic. The microstructure of the Al-21Si alloy was composed of micro-nanostructured α-Al phase and feather-needles-like eutectic α-Al+β-Si phase. The hypereutectic Al-21Si alloy showed the hypoeutectic microstructure. The rapidly solidified Al-21Si alloy microstructure formation mechanism has also been discussed.

Shock Wave Synthesis of Diamond and other Phases

1995 ◽  
Vol 383 ◽  
Author(s):  
Paul S. Decarli
Keyword(s):  
Shock Wave ◽  
Growth Process ◽  
Impact Crater ◽  
Nucleation And Growth ◽  
Unexpected Result ◽  
Subsequent Work ◽  
Thermally Activated ◽  
Thermal Equilibration ◽  
Axis Compression ◽  
Wave Synthesis

ABSTRACTShock wave synthesis of diamond was an unexpected result of experiments designed to explore the effects of shock waves on a variety of materials. The initial announcement in 1959 was controversial; shock synthesis of diamond had been shown to be unlikely, on the basis of kinetic arguments. Jamieson confirmed the identification and suggested a diffusionless mechanism, c-axis compression of rhombohedral graphite. Subsequent work has provided strong evidence that shock wave synthesis of cubic diamond is a conventional thermally activated nucleation and growth process. Thermal inhomogeneities provide the requisite high temperatures; quenching via thermal equilibration is implicit in the process. Shock synthesis of adamantine BN phases appears to be quasi-martensitic; a martensitic mechanism may partially account for the Lonsdaleite (hexagonal diamond) observed in some meteorites and in some artificial shock products. Diamond is also formed as a detonation product in oxygen-deficient explosives. The polycrystalline product of shock synthesis is similar to natural carbonado. The association of carbonado with an ancient giant impact crater is noted.

Phase Separation in Shock Consolidated Amorphous Powder

1985 ◽  
Vol 43 ◽  
pp. 38-39
Author(s):  
Naresh Thadhani ◽  
Andrew H. Mutz ◽  
T. Vreeland
Keyword(s):  
Shock Wave ◽  
Phase Separation ◽  
Heat Flow ◽  
Amorphous Phase ◽  
Amorphous Matrix ◽  
Amorphous Powder ◽  
Stereo Pair ◽  
Powder Specimen ◽  
Shock Energy ◽  
Melt Spun

During shock-wave consolidation of irregularly shaped (≌50 μm diameter) Marko-met 1064 powder (Ni55.8Mo25.7Cr9.7B8.8), obtained from melt-spun ribbon, the shock energy is preferentially input at particle surfaces. Heat flow to particle interiors is sufficiently rapid to quench melted regions and form the amorphous phase at shock energies less than about 400 kJ/kg.Amorphous powder was rolled between two 100 μm thick sheets. Discs cut from the composite strip and sections of a consolidated sample (shock energy ≌325 kJ/kg) were electrolytically jet thinned (at -25°C and -50°C) for TEM examination in a Philips EM 420 TEM/STEM.Figure 1 is a stereo pair taken at an interparticle melted and resolidified region in the compacted powder specimen. The microstructure exhibits a dispersion of fine amorphous spherical phase (diameter ≌0.01 to 0.08 μm), randomly distributed in a continuous amorphous matrix.

Recent Advances on the Modeling of Phase Change Materials and Devices

2008 ◽  
Vol 1072 ◽  
Author(s):  
Andrea Leonardo Lacaita ◽  
Ugo Russo ◽  
Daniele Ielmini
Keyword(s):  
Phase Change ◽  
Amorphous Phase ◽  
Electrode Materials ◽  
New Technologies ◽  
Nucleation And Growth ◽  
Amorphous Chalcogenide ◽  
Recent Advances ◽  
Chalcogenide Material ◽  
Wide Range ◽  
The Impact

ABSTRACTAs non-volatile memory technology is approaching the 45nm generation node and in view of severe scaling limitations of conventional Flash, phase-change memory (PCM) is gaining momentum as a reference emerging memory. The high applicative interest in this new technologies asks not only for progress in the integration issues of the new storage concept, but, most importantly, for a significant improvement of the physical understanding of programming, reliability mechanisms and scalability of the new technology. This can only be possible by a detail study of microscopic processes in the chalcogenide material covering a wide range of physics, from electron transport in disordered media to self-heating effects, from solid-state nucleation and growth processes at the nanoscale.The presentation will review the most recent advances in the understanding and modeling of the programming and reliability mechanisms in chalcogenide-based PCM devices. Electro-thermal simulations of the programming behavior allows to understand the impact of cell geometry and active/electrode materials on the programming current, and to benchmark different scaling rules for future technology nodes. Cell reliability will be discussed with emphasis on the spontaneous crystallization kinetics in the amorphous chalcogenide material, on the acceleration laws to predict retention time at low temperature, and on the possible scaling limitations due to fast phase transition in amorphous chalcogenide nanoclusters/nanowires. An analytical model for nucleation and growth in the amorphous phase will be shown, allowing to draw guidelines for material engineering and reliability improvement. Other scaling-related reliability issues, such as statistical spread of crystallization times and structural relaxation of the amorphous phase, will be discussed.

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