Crystals In Regime Research Articles

Light Non-Magnetic Steels Based on the Fe–25 Mn–5 Ni–Al–C System

The influence of aluminum (5–10%) and carbon (0.04–1.7%) contents on phase transformations, structure formation processes and mechanical properties of Fe–25 Mn–5 Ni–Al–C steels was studied theoretically and experimentally. The authors have estimated intervals of optimal crystallization regimes and subsequent deformation-thermal effects for obtaining austenitic steels with high specific strength. Hardness measurements on the sample section and mechanical tests in a wide interval of temperatures of cold, warm and hot deformation were performed, as well as the phase structure assessment of steels (alloys) on the basis of Fe–25 Mn–5 Ni–Al–C. In a cast state, an alloy with 5% of Al was non-magnetic, i.e., it had austenitic structure; alloys with 10–15% of Al were magnetic with two-phase structure (γ + α). Aluminum considerably increases deformation resistance. At the same time, values σ1 and σmax grow, i.e., also deformation hardening grows and softening processes are slowed down. With deformation rate growth, the Al influence becomes stronger. Austenitic high-manganese alloys with 5% of Al, both with low and high carbon content, have rather high plasticity and durability, and differ in high austenite stability. Alloying with nickel increases plasticity. Alloys with Al less than 10% are rather plastic also in a cast state. High-manganese (from 25% of Mn) alloys with Al content to 5–7% can be considered as high-strength cold-resistant and heat-resistant with thermally and mechanically stable austenite up to carbon content ~1.5%.

Approaching the melting temperature: There regimes in the non-isothermal crystallization of Ce68Al10Cu20Co2 bulk metallic glass revealed by nanocalorimetry

Nanocalorimetry is an ideal candidate for revealing the crystallization of metallic glass in a wide temperature range attributing to its ultrafast heating rate and ultrahigh sensitivity. In this study, in situ preparation of Ce68Al10Cu20Co2 (at.%) metallic glass was realized by the nanocalorimetry. By the subsequent reheating at the rates from 500 to 40,000 K/s, the crystallization in a wide temperature range was demonstrated. The crystallization activation energy and Avrami exponent are calculated with the aid of the Kissinger and Johnson-Mehl-Avrami (JMA) equations to reveal the temperature-dependent nucleation and crystal growth behavior in the undercooled liquid, where three crystallization regimes are identified. At low temperature, the crystallization occurs with constant activation energy. In an intermediate temperature range, the crystallization is controlled by crystal growth with a reduction of activation energy. At temperatures approaching Tm, an increased activation energy resulting from the thermodynamic driving force dominates the nucleation-controlled crystallization. This study provides a novel strategy to reveal the crystallization behavior in the undercooled liquid from Tg to Tm and to demonstrate the transition from growth-controlled crystallization to nucleation-controlled one with the decrease of undercooling.

Crystallization and Cooling of the Noril’sk Intrusions According to the Pyroxen’s Geothermometry Data

Composition of clinopyroxenes in vertical sections of some ore-bearing basic intrusions in the Noril’sk area has been studied by EPMA. These data formed the basis for the calculation of the pyroxene crystallization temperatures using the El Negro monopyroxene geothermometer (Fe-Mg exchange between M1-M2 positions). The results of the calculations allowed estimating the variations of temperature crystallization within the magmatic chambers from early to the late stages. The temperature varies from 1200 for idiomorphic crystals in equilibrium to liquid and up to 400 degrees (in solid intra exchange) for xenomorphic grains and marginal zones of pyroxenes. We reconstructed the regimes of crystallization of the magmatic chamber by this data. The vertical distribution of paleotemperatures of the intrusive chamber there is the evidence of absence vertical move crystals into such magmatic chambers.

The Origins of Enhanced and Retarded Crystallization in Nanocomposite Polymers.

Controlling the crystallinity of hybrid polymeric systems has an important impact on their properties and is essential for developing novel functional materials. The crystallization of nanocomposite polymers with gold nanoparticles is shown to be determined by free space between nanoparticles. Results of large-scale molecular dynamics simulations reveal while crystallinity is affected by the nanoparticle size and its volume fraction, their combined effects can only be measured by interparticle free space and characteristic size of the crystals. When interparticle free space becomes smaller than the characteristic extended length of the polymer molecule, nanoparticles impede the crystallization because of the confinement effects. Based on the findings from this work, equations for critical particle size or volume fraction that lead to this confinement-induced retardation of crystallization are proposed. The findings based on these equations are demonstrated to agree with the results reported in experiments for nanocomposite systems. The results of simulations also explain the origin of a two-tier crystallization regime observed in some of the hybrid polymeric systems with planar surfaces where the crystallization is initially enhanced and then retarded by the presence of nanoparticles.

Manipulation of Chain Entanglement and Crystal Networks of Biodegradable Poly(butylene adipate-co-butylene terephthalate) During Film Blowing through the Addition of a Chain Extender: An In Situ Synchrotron Radiation X-ray Scattering Study

One prerequisite for the large-scale application of biodegradable polymers is the manipulation of macroscopic performances of commercially available biopolymers during processing according to different real service requirements. Herein, the microstructural evolution of poly(butylene adipate-co-butylene terephthalate) (PBAT) modified by chain extender during film blowing was investigated by in situ synchrotron radiation X-ray scattering to unveil the origin of different performances. The chain dynamics difference induced by the chain extender was first characterized by the rheological measurement and 1H Multiple Quantum (MQ) NMR. It shows that the terminal relaxation is significantly slowed down, while the locally segmental dynamics is not apparently changed. With the assistance of the custom-built film blowing apparatus, the microstructure right above the die exit (D = 13-165 mm) was in situ, simultaneously captured by small- and wide-angle scattering (SAXS/WAXS), where four distinct regimes can be defined. Only the PBAT melt signals are found in regime I, whereas the formation of the mesomorphic domains as shown by the SAXS streaks appearing in regime II. The crystal shows up in regime III, where the WAXS signal appears. A dramatic increment of the crystallinity is found in regime III, which contributes to the continuous increasing bubble modulus with the formation of the crystal-based network. Such a crystal-based network is filled with crystals in regime IV, where the diameter of the PBAT bubble remains constant. The addition of the chain extender is found to significantly influence the structural evolution within different regimes. These dynamics and structure information could supply general guidance for bubble stability improvement and modification of macroscopic performances of biodegradable polymer products.

Structure Diagnostic of Iron-Based Out-of-Peritectic Alloys during Nonequilibrium Crystallization

The effect of the contribution of basic components (silicon, manganese, chromium, and nickel) in multicomponent iron-based alloys on critical point position of the peritectic reaction was studied by using the POLYTHERM software package. Obtained temperature and concentration values of critical points of peritectic transformation, depending on the content of iron-based alloy components (Si, Mn, Cr, Ni) were used to build summary equations, represented the change in temperature and concentration of critical points by variation of binary, ternary and quaternary alloy composition. Investigation of nonequilibrium crystallization of out-of-peritectic casting steels was performed by using a system of computer models describing thermodynamic, thermophysical, diffusion and capillary processes during solidification under coalescence of dendritic branches. The nonequilibrium crystallization regime was specified by suppression of diffusion in the solid phase, reflected by adding the inverse diffusion parameter to the system of the computer model. The application of these computer models not only allows to make calculations of the temperature course, the solid phase fraction and the composition of the components in the liquid phase but also the calculation of secondary arm spacing during crystallization with taking into account the coalescence process.

Differentiation in impact melt sheets as a mechanism to produce evolved magmas on Mars

Asteroid bombardment contributed to extensive melting and resurfacing of ancient (>3.5 Ga) Mars. Evidence from the largest impact structures on Earth and the Moon suggests that vertically thick impact melt sheets experience chemical differentiation. Recently observed materials in Gale crater are enriched in alkalis (up to 14 wt% Na2O + K2O) and silica (up to 67 wt% SiO2) with low MgO (<5 wt%). This differentiation trend has previously been attributed to fractional crystallization of mantle-derived magmas. The influence of impact melting on Mars' crustal petrology, however, has not been explored in depth. In this study, we investigate differentiation of impact-generated melts as a mechanism for petrogenesis of evolved rocks on Mars. We scale melt volumes for multiple impact magnitudes and employ the MELTS algorithm to model mineral phase equilibria in those melts as they crystallize. We consider a range of possible melt geometries, oxidation states (IW to QFM), crystallization regimes (equilibrium and fractional), and water contents (anhydrous to water-saturated). Moderate pressure and dissolved volatiles are required to produce alkaline differentiation trends in mafic melts. Large impacts that melt a water-bearing early basaltic crust provide a mechanism to generate wet magmas on Mars, consistent with some modeled Martian differentiation trends. Low-degree partial melting and/or an alkali-enriched source are needed to generate observed highly alkaline compositions, motivating future work to further assess whether these conditions can be achieved in impact-generated melts.

Isothermal Crystallization Kinetics of Poly(4-hydroxybutyrate) Biopolymer.

Thermal properties and crystallization kinetics of poly(4-hydroxybutyrate) (P4HB) have been studied. The polymer shows the typical complex melting behavior associated to different lamellar populations. Annealing processes had great repercussions on properties and the morphology of constitutive lamellae as verified by X-ray scattering data. Kinetics of isothermal crystallization was evaluated by both polarizing optical microscopy (POM) and calorimetric (DSC) measurements, which indicated a single crystallization regime. P4HB rendered banded spherulites with a negative birefringence when crystallized from the melt. Infrared microspectroscopy was applied to determine differences on the molecular orientation inside a specific ring according to the spherulite sectorization or between different rings along a determined spherulitic radius. Primary nucleation was increased during crystallization and when temperature decreased. Similar crystallization parameters were deduced from DSC and POM analyses (e.g., secondary nucleation parameters of 1.69 × 105 K2 and 1.58 × 105 K2, respectively). The effect of a sporadic nucleation was therefore minimized in the experimental crystallization temperature range and a good proportionality between overall crystallization rate (k) and crystal growth rate (G) was inferred. Similar bell-shaped curves were postulated to express the temperature dependence of both k and G rates, corresponding to the maximum of these curves close to a crystallization temperature of 14–15 °C.

Non-Isothermal Crystallization Kinetics of Poly(4-Hydroxybutyrate) Biopolymer.

The non-isothermal crystallization of the biodegradable poly(4-hydroxybutyrate) (P4HB) has been studied by means of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). In the first case, Avrami, Ozawa, Mo, Cazé, and Friedman methodologies were applied. The isoconversional approach developed by Vyazovkin allowed also the determination of a secondary nucleation parameter of 2.10 × 105 K2 and estimating a temperature close to 10 °C for the maximum crystal growth rate. Similar values (i.e., 2.22 × 105 K2 and 9 °C) were evaluated from non-isothermal Avrami parameters. All experimental data corresponded to a limited region where the polymer crystallized according to a single regime. Negative and ringed spherulites were always obtained from the non-isothermal crystallization of P4HB from the melt. The texture of spherulites was dependent on the crystallization temperature, and specifically, the interring spacing decreased with the decrease of the crystallization temperature (Tc). Synchrotron data indicated that the thickness of the constitutive lamellae varied with the cooling rate, being deduced as a lamellar insertion mechanism that became more relevant when the cooling rate increased. POM non-isothermal measurements were also consistent with a single crystallization regime and provided direct measurements of the crystallization growth rate (G). Analysis of the POM data gave a secondary nucleation constant and a bell-shaped G-Tc dependence that was in relative agreement with DSC analysis. All non-isothermal data were finally compared with information derived from previous isothermal analyses.

Pressureless Crystallization of Glass for Transparent Nanoceramics.

Transparent nanoceramics embedded with highly dense crystalline domains are promising for applications in missile guidance, infrared night vision, and laser and nuclear radiation detection. Unfortunately, current nanoceramics are strictly constrained by the stringent construction procedures such as super‐high pressure and containerless processing. Here, a pressureless crystallization engineering strategy in glass for elaboration of transparent nanoceramics and fibers is proposed and experimentally demonstrated. By intentional creation of a sharp contrast between nucleation and growth rates, the crystal growth rate during glass crystallization can be significantly suppressed. Importantly, this unique phase‐transition habit enables the achievement of transparent nanoceramics and even smooth fibers with extremely tiny crystalline size (≈20 nm) and high crystallinity (≈97%) under atmospheric pressure. This allows the generation of an attractive nonlinear optical response such as dynamic optical filtering and luminescence in the mid‐infrared waveband of 4300–4950 nm. These findings highlight that the strategy to switch the phase‐transition habit of glass into the unconventional crystallization regime may provide new opportunities for the creation of next‐generation nanoceramics and fibers.

A Dual-Wavelength Pulsed Laser Processing Platform for a-Si Thin Film Crystallization

Interest in laser crystallization (LC) of silicon (Si) thin films has been on the rise in fabrication of polycrystalline silicon (pc-Si) based thin/ultrathin photovoltaic solar cells and Si based thin film transistors (TFT). Laser based fabrication of device quality pc-Si thin films at room temperature is expected to be a key enabling technology because of its low energy, material and process time budget. Fabrication of high-quality pc-Si thin films without pre-/post-treatment at large is a disruptive technology which has the potential to revolutionize the Si thin film industry. We hereby describe in detail a multi-wavelength laser processing platform specially developed for crystallization of amorphous silicon (a-Si) thin films into pc-Si thin films. The platform has three main stages. The first stage consists of a nanosecond pulsed ytterbium (Yt3+) doped fibre-laser with a master oscillator power amplifier architecture, operating at a wavelength of 1064 nm with an adjustable repetition rate between 80 kHz–300 kHz. The output beam has a maximum power of 18 W with a pulse energy of 90 µJ. The pulse durations can be set to values between 15 ns–40 ns. The second stage has free-space optical elements for second harmonic generation (SHG) which produces an emission at a wavelength of 532 nm. Conversion efficiency of the SHG is 25% with an output pulse energy of 20 µJ. The platform provides two wavelengths at either 1064 nm or 532 nm in crystallization of a-Si films for different crystallization regimes. The last stage of the platform has a sample processing assembly with a line-focus, which has an x-y motorized stage on a vibration isolated table. Speed of the motorized stage can be set between 1 mm/s–100 mm/s. Stage speed and repetition rate adjustments help to adjust overlap of successive pulses between 97.22–99.99%. Our platform has variety of tune parameters that make it a uniquely flexible system for delicate Si thin film crystallization. A large selection of operational parameter combinations, the wavelength selection and simultaneous x-y scanning capability allow users to crystallize Si films on various substrates optimally. The operation wavelength choice can be done by considering optical absorption and thickness of a-Si films on different types of substrates. Hence, delivering precise amount of absorbed energy in the line-focus irradiation is useful in increasing the average size of crystalline domains; moreover, nucleation of crystallites can be initiated either from the top or bottom interface of the film. Continuous and simultaneous motion of the stage in two dimensions allows to process arbitrary continuous pc-Si geometries in a-Si film. In summary, our multi-wavelength laser processing platform offers all-in-one LC utility for intricate LC-Si processing.

Isotope Effects on the Crystallization Kinetics of Selectively Deuterated Poly(ε‐Caprolactone)

ABSTRACTDeuterium labeling of semi‐crystalline polymers can dramatically affect their crystallization behaviors. However, the influence of different labeled positions in a partially deuterated polymer on its crystallization is still far from understood. Here, we synthesized a series of selectively deuterated poly(ε‐caprolactones) (PCLs) through ring‐opening polymerization of ε‐caprolactone with controlled deuteration sites, including fully protiated (D0), fully deuterated (D10), tetra deuteration at the 3‐ and 7‐ caprolactone ring positions (D4) and hexa deuteration at the 4‐, 5‐, and 6‐ caprolactone ring positions (D6). All the PCLs showed a similar lamellar structure and parameters. Differential scanning calorimetry (DSC) analysis revealed that the equilibrium melting temperature , melting temperature Tm, crystallization temperature Tc, and crystallization kinetics changed systemically with the deuterium content except for D4, which indicates that the presence of CD2 moieties on either side of ester group in the polymer chain combined with isotopic inhomogeneity could influence the chain packing. The nonmonotonic trend of Tm as a function of deuterium content could be attributed to the difference in a hydrogen‐bond like intermolecular interaction between different PCLs. Partially deuterated PCLs (D4 and D6) showed an Avrami index near 2. After analyzing the parameters at the same supercooling temperature ΔTc, the existence of two crystallization regimes of PCLs were detected. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 771–779

Microstructural evidence for crystallization regimes in mafic intrusions: a case study from the Little Minch Sill Complex, Scotland

The magma forming the 20 m thick crinanitic/picrodoleritic Dun Raisburgh sill, part of the Little Minch Sill Complex of NW Scotland, comprised a mafic carrier liquid with a crystal cargo of plagioclase and olivine (1 vol%). The olivine component of the cargo settled on the floor of the intrusion while the more buoyant plagioclase component remained suspended during solidification, resulting in a relatively high plagioclase content in the centre of the sill. The settled olivine grains form a lower fining-upwards sequence overlain by a poorly sorted accumulation formed of grains that grew within the convecting magma. The accumulation of olivine on the sill floor occurred over 5–10 weeks, synchronous with the upwards-propagation of a solidification front comprising a porous (~ 70 vol% interstitial liquid) plagioclase-rich crystal mush.

Impulsive Supply of Volatile-Rich Magmas in the Shallow Plumbing System of Mt. Etna Volcano

Magma dynamics at Mt. Etna volcano are frequently recognized as the result of complex crystallization regimes that, at shallow crustal levels, unexpectedly change from H2O-undersaturated to H2O-saturated conditions, due to the impulsive and irregular arrival of volatile-rich magmas from mantle depths. On this basis, we have performed hydrous crystallization experiments for a quantitative understanding of the role of H2O in the differentiation of deep-seated trachybasaltic magmas at the key pressure of the Moho transition zone. For H2O = 2.1–3.2 wt %, the original trachybasaltic composition shifts towards phonotephritic magmas never erupted during the entire volcanic activity of Mt. Etna. Conversely, for H2O = 3.8–8.2 wt %, the obtained trachybasalts and basaltic trachyandesites reproduce most of the pre-historic and historic eruptions. The comparison with previous low pressure experimental data and natural compositions from Mt. Etna provides explanation for (1) the abundant release of H2O throughout the plumbing system of the volcano during impulsive ascent of deep-seated magmas; (2) the upward acceleration of magmas feeding gas-dominated, sustained explosive eruptions; (3) the physicochemical changes of gas-fluxed magmas ponding at shallow crustal levels; and (4) the huge gas emissions measured at the summit craters and flank vents which result in a persistent volcanic gas plume.

Flow-Induced Crystallization of Polyamide-6

Abstract Flow-induced crystallization has been widely studied for a variety of polymers with the main focus on polyolefins. In this work, research has been conducted on the flow-induced crystallization of another important class of polymers, namely polyamides. Different polyamides-6 with varying molecular weight have been studied. At relatively modest values of shear rate, rheology has been used to study the kinetics of flow-induced crystallization. Typical scaling relations based on the longest relaxation time and the Rouse time – usually obtained for polyolefins – are tested for the polyamides under investigation in order to identify the different regimes of flow-induced crystallization. At high shear rates, a correct rheological signal was impossible to collect. However, the rheometer was used in this case to prepare the sample to be studied ex-situ by Wide Angle X-ray Scattering experiments to determine the onset shear rate for the formation of highly oriented shish-kebab structures.

Crystallization Behaviors and Regime Kinetics Analysis of Poly(L-lactide)-poly(butylene adipate)-poly(L-lactide) Based Multiblock Thermoplastic Polyurethanes

Poly(L-lactide)-based (PLLA) poly(ester-urethane)s are particularly relevant and gain significant attention due to their environment-friendly degradability and elastomeric shape memory capability. The tensile properties, resilience and degradation are strongly affected by their crystallization. This work was to investigate crystallization behaviors of the poly(L-lactide)-poly(butylene adipate)-poly(L-lactide) (PLLA-PBAPLLA) based thermoplastic polyurethane elastomers (PLAEUs) we synthesized previously. Dynamic scanning calorimetry (DSC) and polarized optical microscopy (POM) in combination with Avrami, Jezioney and Hoffman-Weeks models were used to analyze the impact of the PLLA block length on the crystallization temperature Tc, degree of crystallinity Xc, nucleation and spherulite growth mode and crystallization regime kinetics of the PLAEUs. The results indicate the low melting point poly(butylene adipate) (PBA) block resides in the amorphous domains while the PLLA block resides in both crystalline and amorphous phases. The Xc of the PLAEUs increase with the increased length of the PLLA block (i.e. higher content of PLLA block). The analyses with Avrami and Jezioney models show the PLAEU copolymers follow a disc-like spherulite growth. The covalently bonded PBA block decreases both nucleation velocity and spherulite growth rate in the isothermal crystallization. Such an impact is lessened as PLLA block length increases. The PLLA homopolymers demonstrate crystallization regime transition from II to III at a certain Tc of isothermal crystallization, while the crystallization regime kinetics of PLLA block in the PLAEUs are explained by a single regime III at low molecular weights of PLLA and the transition is restored as the PLLA block length increases (i.e. regime II to III).

Calorimetric and rheokinetic analyses merged to capture crystallization kinetics in polyamide/clay nanocomposites: Revisiting predictability of models

ABSTRACTCrystallization kinetics of polymer/clay systems was the subject of numerous investigations, but still there are some ambiguities in understanding thermal behavior of such systems under isothermal and nonisothermal circumstances. In this work, isothermal rheokinetic and nonisothermal calorimetric analyses are combined to demonstrate crystallization kinetics of polyamide6/nanoclay (PA6/NC) nanocomposites. As the main outcome of this work, we detected different regimes of crystallization and compared them by both isothermal dynamic rheometry and nonisothermal differential scanning calorimetry (DSC), which has not been simultaneously addressed yet. A novel analysis, somehow different from the common ones, is used to convert the storage modulus data to crystallinity values leading to more reasonable Avrami parameters in isothermal crystallization. It was found based on isothermal rheokinetic studies that increase of NC content and shear rate are responsible for erratic behavior of Avrami exponent and crystallization rates. Optimistically, however, isothermal crystallization by rheometer was confirmed by DSC. Nonisothermal calorimetric evaluations suggested an accelerated crystallization of PA6 upon increasing NC content and cooling rate. The crystallization behavior was quantified applying Ozawa (r2 between 0.070 and 0.975), and combinatorial Avrami–Ozawa (r2 between 0.984 and 0.998) models, where the latter appeared more appropriate for demonstration of nonisothermal crystallization of PA6/NC nanocomposites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46364.

Evaluation of thermal transitions in Poly (butylene terephthalate)/15A MMT nanocomposites: Nonisothermal experiments and modelling using isoconversional methods

Friedman’s differential isoconversional approach is applied to obtain effective activation energy (Eα) for Poly (butylene terephthalate) and PBT/15AMMT nanocomposites. The presence of 15AMMT content has largely affected Eα values. Further Vyazovkin and Sbirrazzuoli’s approach is used to determine Hoffman-Lauritzen parameters (Kg &U*). The crystallization regime transition (II–III) occurs for neat PBT at 189 °C and its nanocomposites is at 189–192 °C. Kg(III)/Kg(II) ratios are closer to theoretical value of 2. However the corresponding value of U* is inappropriately too low with negative sign (Correlation coefficient R2 = 0.9–0.99) and which is however highly anomalous when compared to other polymers. Setting U* to 6300 J/mol, 4300 J/mol and 0 J/mol, resulted in poor Kg(III)/Kg(II) ratios and R2. This imply that there is a considerable chain mobility during regime II crystallization which is explained in terms of rapid extraction of PBT chain segments by the force of crystallization, following the tube-reptation postulate.

Iron snow in the Martian core?

The decline of Mars' global magnetic field some 3.8–4.1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core. The dynamo was probably powered by planetary cooling and so its termination is intimately tied to the thermochemical evolution and present-day physical state of the Martian core. Bottom-up growth of a solid inner core, the crystallization regime for Earth's core, has been found to produce a long-lived dynamo leading to the suggestion that the Martian core remains entirely liquid to this day. Motivated by the experimentally-determined increase in the Fe–S liquidus temperature with decreasing pressure at Martian core conditions, we investigate whether Mars' core could crystallize from the top down. We focus on the “iron snow” regime, where newly-formed solid consists of pure Fe and is therefore heavier than the liquid. We derive global energy and entropy equations that describe the long-timescale thermal and magnetic history of the core from a general theory for two-phase, two-component liquid mixtures, assuming that the snow zone is in phase equilibrium and that all solid falls out of the layer and remelts at each timestep. Formation of snow zones occurs for a wide range of interior and thermal properties and depends critically on the initial sulfur concentration, ξ0. Release of gravitational energy and latent heat during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies at least 400 km of the core. Snow zones can be 1.5–2 Gyrs old, though thermal stratification of the uppermost core, not included in our model, likely delays onset. Models that match the available magnetic and geodetic constraints have ξ0≈10% and snow zones that occupy approximately the top 100 km of the present-day Martian core.

Influence of doping and crystallization regimes on forming of structure, casting and mechanical properties of a Cu – Ni – Zn system alloy

Influence of doping and crystallization regimes on forming of structure, casting and mechanical properties of a Cu – Ni – Zn system alloy