Refractory Cores Research Articles

Carbon-rich icy moons and dwarf planets

Density and moment of inertia of icy moons and dwarf planets suggest the presence of a low-density carbonaceous component in their rocky cores. This hypothesis was tested using inner density structure and thermal models. Rocky core densities in dwarf planets and icy moons are found to consist of a mixture of chondritic silicate-sulfide rocks and carbonaceous matter. Carbonaceous matter was originally mixed with ice in a rock-free precursor. In a homogeneous accretion scenario where these components are mixed in solar proportions, ices then differentiated from the carbon-rich refractory core, while hydration of silicates could take place. Thermal models taking into account the presence of carbonaceous matter suggest that originally hydrated silicates are only partially dehydrated in the refractory cores of most moons. Viable scenarios point to a difference in formation or evolution between Ganymede and Titan in spite of their similar size and mass. Fully dehydrated mineralogies, inferred in Europa and possibly the densest dwarf planet Eris, require heterogeneous accretion near the water snow line of the solar or circumplanetary nebula. Progressive gas release from slowly warming carbonaceous matter-rich cores may sustain up to present-day the replenishment of ice-oceanic layers in organics and volatiles. It accounts for the observation of nitrogen, light hydrocarbons and complex organic molecules at the surface, in the atmospheres, or in plumes emanating from moons and dwarf planets. The formation of large carbon-rich bodies in the outer solar system suggests that carbon-rich planets could form at the outskirts of extrasolar systems.

Composition and structure of «core–shell» nanocrystalline particles based on titanium-molybdenum carbides obtained under the conditions of plasma-chemical synthesis

This paper provides the data on the composition and structure of nanocrystalline particles formed during the plasmachemical synthesis of mechanical mixtures containing TiC, Mo, and Co according to the plasma-induced Ostwald ripeningscheme. The paper was mainly intended to study the structural features and localizations of Mo0.42C0.58 carbide in TiC–Mo and TiC–Mo–Co nanocrystalline «core–shell» structures. As a result of X-ray diffraction and high resolution transmission electron microscopy (HRTEM) studies, it was found that the Mo0.42C0.58 carbide of orthorhombic modification is present in all fractions of TiC–Mo and TiC–Mo–Co mechanical mixtures after Ostwald ripening. Nanocrystalline TiC–Mo fractions and the TiC–Mo–Co mixture subjected to one-time Ostwald ripening from a baghouse filter were used in the electron microscopy study to illustrate the presence of «core–shell» structures where refractory cores are represented by Ti1–nMonCx titanium-molybdenum carbides, and high-contrast metal shells contain Mo, Mo0.42C0.58 and Co. Electron microscope images also showed the localization of orthorhombic Mo0.42C0.58. According to the results obtained, it can be concluded that «core–shell» structures are formed during the extreme exposure in the form of plasma-chemical synthesis of TiC–Mo and TiC–Mo–Co mechanical mixtures in a low-temperature nitrogen plasma. At the same time, it should be added that nanocrystalline compositions with the «core–shell» structure are crystallized in a tangential nitrogen flow at a cooling rate of 105 °C/s with the subsequent separation of products into ultra- and nanodispersed fractions in a vortex-type cyclone and a baghouse filter.

Characterizing the volatility and mixing state of ambient fine particles in the summer and winter of urban Beijing

Abstract. Understanding the volatility of atmospheric aerosols is important for elucidating the formation of fine particles and to help determine their effect on the environment and climate. In this study, the volatility of fine particles (40, 80, 110, 150, 200, and 300 nm) is characterized by the size-dependent volatility shrink factor (VSF) for summer and winter in the urban area of Beijing using measurements of a volatility tandem differential mobility analyzer (VTDMA). We show that there are two persistent aerosol volatility modes (one high-volatility and one less- or non-volatile mode) present both in the summer and winter. On average, the particles are more volatile in the summer (with a mean VSF of 0.3) than in the winter (with a mean VSF of 0.6). Although the new particle formation (NPF) process requires low-volatility vapors to form molecular clusters and nuclei, the significant high-volatility mode around noon on NPF days indicates partitioning of volatile substances into the growing particles during summer. We further retrieve the mixing state of the ambient fine particles from the size-resolved VSF and find that the non-black carbon (BC) particles that formed from nucleation processes accounted for 52 %–69 % of the total number concentration in the summer. On the other hand, particles containing a refractory core that is thought to be BC-containing particles dominate and contribute 67 %–77 % toward the total number concentration in the winter. The diurnal cycles of the retrieved aerosol mixing state for the summer further support the conclusion that the nucleation process is the main contributor to non-BC particles. In addition, the extent of aging of BC particles was characterized as the ratio of the BC diameter before and after heating at 300 ∘C (Dp/Dc), showing that the average ratio of ∼ 2.2 in the winter is higher than the average of ∼ 1.5 in the summer, which indicates that BC aging may be less efficient in summertime. This would result in differences in light absorption enhancement between the cold and warm seasons.

Three is the Magic Number: Techniques and Materials of the Prestigious Anne de Montmorency Bronze Virtues

ABSTRACT A technical study of the three exceptional figures adorning the Monument of the Heart of Duke Anne de Montmorency commissioned in 1571 and attributed to the sculptors Barthélémy Prieur and Martin Lefort was carried out. This study includes X-radiography, alloy analysis, characterisation of the refractory core, visual observation of the interior and the exterior of the sculptures, as well as endoscopic examination of the interior. The objective of this study was to fill in further details regarding the fabrication of the figures: where and by whom they were made and how they were cast. In particular, the question of whether the foundryman Nicolas Péron carried out the casting of all three bronzes is addressed here. The results show significant consistency between the three figures, which were cast using a technique commonly employed during the sixteenth century in France, known as the lasagna process. Yet, several specific details linked to the monument commission – the use of chaplets and a sandy-clay mixture defined by a specific grain size distribution – shed light on the working relationship between artist and founder. While the conclusions of this study confirm Prieur’s leadership over the technical aspects of his sculptures, Lefort seems to have been less involved in the casting process and to have relied on the expertise of both Prieur and Péron. Furthermore, the results contribute to a better understanding of the casting of large bronzes during the second half of the sixteenth century by providing key information on the relationship between artists and founders.

1.5 PHARMACOLOGICAL STRATEGIES IN ADHD

Increasingly complex cases of children with ADHD are presenting to child and adolescent psychiatrists requiring practitioners to learn new strategies for sequencing treatment, management of refractory core ADHD symptoms, and treatment of comorbidity(ies). Longer-term outcomes remain unclear.

Casting cores of French bronze statues of the 16th and 17th centuries: Identification of regional practices and artistic choices

What can the chemical and petrofabric study of casting cores of early modern large bronzes tell us about the practices of sculptors and foundry men? The technical study of 23 major large French bronzes dated from the 16th and 17th centuries provides some answers. These include three prestigious royal commissions, namely two of the six bronzes copied by Primaticcio from the marble models of the Belvedere for Francis I, two of the six statues from the funeral monument of Henry II and Catherine de Medicis, and the three bronzes from the heart monument of Constable Anne de Montmorency. Among the investigations carried out (alloy composition, X-ray radiography, and so on) [1], the chemical and petrographic analysis of the refractory cores sampled from inside the statues has proved to be crucial. Surprisingly, this approach is far from systematically applied in the field, despite some successful results [2] including the pioneering work of C. Reedy [3]. This paper introduces the new methodology of casting core analysis developed at the C2RMF. Results obtained from a large corpus of French bronze statues will be described, illustrating the complementary role of core analysis alongside the informative potential of metal analysis and the characterization of casting technique through multivariate technological studies. During the 16th and 17th centuries in France, casting cores were generally created from a sandy clay material with a variable addition of organic. The results of the study cast light on two aspects of the nature of the cores. On the one hand, the bulk chemical compositions of cores and mineralogical composition of added sand show a relatively good homogeneity within the region of Paris and its surroundings, thus testifying to a similar provenance of raw materials. Conversely, significant variations were evident in compositions from other regions. Consequently, the casting cores constitute an excellent regional marker. On the other hand, significant variations were observed in the size distributions of aplastic inclusions, thus witnessing local foundry know-how through the use of several sandy–clayey mixtures.

Partial Transient Liquid-Phase Bonding, Part I: A Novel Selection Procedure for Determining Ideal Interlayer Combinations, Validated Against Al2O3 PTLP Bonding Experience

Partial transient liquid-phase (PTLP) bonding is a bonding process that can bond hard-to-join materials, such as ceramics. The process uses a multi-layer interlayer composed of a thick refractory core and thin diffusant layers on each side. Upon heating, the diffusant material melts, and diffusion occurs until the liquid isothermally solidifies. Selecting interlayer materials is a key problem in producing strong, reliable PTLP bonds; materials are usually selected empirically or system by system. This article presents a novel selection procedure that provides a generalized, comprehensive, first-principles-based approach. Components of the selection procedure are linked directly to key characteristics of PTLP bonding. A filtering routine that provides structure for the selection procedure is summarized in this article and detailed in a companion article. Specific capabilities of the routine, such as non-symmetric bonds, add to its effectiveness in identifying additional PTLP bond candidates. By way of example, output from the selection procedure, in conjunction with sessile drop data, is used to analyze all Al2O3 PTLP bonds in the current literature. All analyzed bonds are included in various outputs from the selection procedure, validating its comprehensiveness. Also, Al2O3 PTLP bonds are analyzed as a whole, leading to the identification of important trends that result in increased bond strength. Finally, additional interlayer combinations for PTLP bonding of Al2O3 are presented based on output from the selection procedure and existing sessile drop data.

Overview of transient liquid phase and partial transient liquid phase bonding

AbstractTransient liquid phase (TLP) bonding is a relatively new bonding process that joins materials using an interlayer. On heating, the interlayer melts and the interlayer element (or a constituent of an alloy interlayer) diffuses into the substrate materials, causing isothermal solidification. The result of this process is a bond that has a higher melting point than the bonding temperature. This bonding process has found many applications, most notably the joining and repair of Ni-based superalloy components. This article reviews important aspects of TLP bonding, such as kinetics of the process, experimental details (bonding time, interlayer thickness and format, and optimal bonding temperature), and advantages and disadvantages of the process. A wide range of materials that TLP bonding has been applied to is also presented. Partial transient liquid phase (PTLP) bonding is a variant of TLP bonding that is typically used to join ceramics. PTLP bonding requires an interlayer composed of multiple layers; the most common bond setup consists of a thick refractory core sandwiched by thin, lower-melting layers on each side. This article explains how the experimental details and bonding kinetics of PTLP bonding differ from TLP bonding. Also, a range of materials that have been joined by PTLP bonding is presented.

Physical and chemical properties of the aerosol within the southeastern Pacific marine boundary layer

During the Stratus 2003 and 2004 cruises, a Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) was used to measure the size‐resolved concentration, hygroscopicity, and volatility of the submicron aerosol below the stratocumulus deck of the southeastern Pacific. The number size distributions were typically bimodal, although a nucleation event in 2003 skewed the relative importance of the two modes, while in 2004, influence from anthropogenic sources near the coast of Chile reduced the separation between the two modes. The average total aerosol number concentration was 398 ± 145 cm−3 and 301 ± 100 cm−3 for the 2003 and 2004 cruises, respectively. Measured size‐ and temperature‐dependent volatility suggested Aitken and accumulation mode particles were composed of refractory cores and acidic sulfate solutions having NH4/SO4 molar ratios of roughly 0.56 and 0.23, respectively. Cloud condensation nuclei (CCN) concentrations at the peak in‐cloud supersaturation and over a range in supersaturation were calculated using the collected data. The data were also used to quantify the number to volume concentration ratio of the accumulation mode aerosol.

Numerical simulations of the production of extinct short‐lived nuclides by magnetic flaring in the early solar system

Abstract Using the X‐ray flare observations of low‐mass protostars, we developed numerical simulations of thermal processing and irradiation of protoCAIs in the magnetic reconnection ring within the X‐wind formulation. Observed X‐ray flare luminosities have been used to model various simulation flare characteristics. Several approximations have been made regarding the thermal evolution that involve condensation, evaporation, and coagulation of protoCAIs. Ensembles of refractory cores with ferromagnesian mantles were evolved for irradiation production of the short‐lived nuclides 7Be, 10Be, 41Ca, 36Cl, 26Al, and 53Mn. Three distinct grain‐size distributions of protoCAIs with refractory cores in the ranges of 32μ m‐20 mm, 125 μ m‐16 mm, and 500 μ m‐13 mm were thermally evolved for irradiation. The latter two size distributions were found to result in the accumulation of protoCAIs in the reconnection ring during an X‐wind cycle, and hence can account for the total inventory of 26Al in the early solar system. The canonical value of ˜5 × 10‐5 for 26Al/27 Al can be inferred from the impulsive flare simulations by a suitable choice of simulation parameters. However, in most of the remaining simulations, the irradiation of protoCAIs by superflare(s) with Lx > 1032 ergs s‐1 subsequent to their thermal processing in the reconnection ring would be required to explain the experimental abundances of the short‐lived nuclides. These superflares have never been reliably observed in young stellar objects. If they are real, they would be extremely rare. The paucity of these superflares could impose stringent constraints on the validity of the X‐wind irradiation scenario as the source of the short‐lived nuclides.

Desorption of Molecules from Grain Mantles

As a prerequisite to returning their molecular inventory to the gas phase, icy grain mantles must desorb from the refractory core material of the grain. This desorption process can be instigated through interactions with photons or cosmic rays but can equally well be thermally driven. In this invited paper, the application of thermal desorption techniques borrowed from ultrahigh vacuum surface science to problems of astronomical interest will be discussed. The experimental methods employed by surface scientists to probe thermal desorption processes will be described and the analysis of the resulting empirical data outlined. The results of recent laboratory measurements from a number of groups will be highlighted.

Complex organic matter in Titan's atmospheric aerosols from in situ pyrolysis and analysis

Aerosols in Titan's atmosphere play an important role in determining its thermal structure. They also serve as sinks for organic vapours and can act as condensation nuclei for the formation of clouds, where the condensation efficiency will depend on the chemical composition of the aerosols. So far, however, no direct information has been available on the chemical composition of these particles. Here we report an in situ chemical analysis of Titan's aerosols by pyrolysis at 600 degrees C. Ammonia (NH3) and hydrogen cyanide (HCN) have been identified as the main pyrolysis products. This clearly shows that the aerosol particles include a solid organic refractory core. NH3 and HCN are gaseous chemical fingerprints of the complex organics that constitute this core, and their presence demonstrates that carbon and nitrogen are in the aerosols.

A model of the activity of comet wild 2

A numerical model of the thermal evolution and chemical differentiation of cometary nuclei was developed to help in the preparation of future comet missions. To better describe the microstructure of cometary matter we modified the way in which bulk thermal conductivity is expressed. The matter is now described as an aggregate of grains, formed by a refractory core and an ice mantle. In this way the evolution of the microstructure due to various physical processes, such as sintering, can be better simulated. With this kind of formulation, bulk conductivity could be very low, orders of magnitude lower than in our previous versions of the model. In order to test this expression and its consequences, we present here a simulation of the thermal evolution of comet Wild 2, the target of the STARDUST mission. We can see that a much lower conductivity changes the internal stratigraphy and the flux of low volatile gases, but does not affect surface properties and consequently water and dust fluxes.

The Origin of Chondrules and Refractory Inclusions in Chondritic Meteorites

Examples of calcium-aluminum-rich inclusions (CAIs) surrounded by thick chondrule mantles have been found in chondritic meteorites and cast doubt on the conventional belief that CAIs and chondrules possessed different spacetime origins in the primitive solar nebula. We study specific processes by which such objects, and the more common ordinary CAIs and chondrules, might have formed by flare heating of primitive rocks interior to the inner edge of a gaseous accretion disk that has been truncated by magnetized funnel flow onto the central proto-Sun. Motivated by the appearance of the chains of Herbig-Haro knots that define collimated optical jets from many young stellar objects (YSOs), we adopt the model of a fluctuating X-wind, where the inner edge of the solar nebula undergoes periodic radial excursions on a timescale of ~30 yr, perhaps in response to protosolar magnetic cycles. Flares induced by the stressing of magnetic fields threading both the star and the inner edge of the fluctuating disk melt or partially melt solids in the transition zone between the base of the funnel flow and the reconnection ring, and in the reconnection ring itself. The rock melts stick when they collide at low velocities. Surface tension pulls the melt aggregate into a quasi-spherical core/mantle structure, where the core consists mainly of refractories and the mantle mainly of moderate volatiles. Orbital drift of rocks past the inner edge of the disk or infall of large objects from the funnel flow replaces the steady loss of material by the plasma drag of the coronal gas that corotates with the stellar magnetosphere. In quasi-steady state, agglomeration of molten or heat-softened rocks leads to a differential size-distribution in radius R proportional to R-3e, where tL ~ 20 yr is the drift time of an object of fiducial radius L ≡ 1 cm and t is the time since the last inward excursion of the base of the funnel flow and X-wind. Thus, during the ~30 yr interval between successive flushing of the reconnection ring, flash-heated and irradiated rocks have a chance to grow to millimeter and centimeter sizes. The evaporation of the moderately volatile mantles above large refractory cores, or the dissolving of small refractory cores inside thick ferromagnesian mantles before launch, plus extended heating in the X-wind produce the CAIs or chondrules that end up at planetary distances in the parent bodies of chondritic meteorites.

Calcium‐aluminum‐rich inclusions in enstatite chondrites (I): Mineralogy and textures

Abstract— Like calcium‐aluminum‐rich inclusions (CAIs) from carbonaceous and ordinary chondrites, enstatite chondrite CAIs are composed of refractory minerals such as spinel, perovskite, Al, Ti‐diopside, melilite, hibonite, and anorthitic plagioclase, which may be partially to completely surrounded by halos of Na‐(±Cl)‐rich minerals. Porous, aggregate, and compact textures of the refractory cores in enstatite chondrite CAIs and rare Wark—Lovering rims are also similar to CAIs from other chondrite groups. However, the small size (<100μm), low abundance (<1% by mode in thin section), occurrence of only spinel or hibonite‐rich types, and presence of primary Ti‐(±V)‐oxides, and secondary geikelite and Ti, Fe‐sulfides distinguish the assemblage of enstatite chondrite CAIs from other groups.The primary mineral assemblage in enstatite chondrite CAIs is devoid of indicators (e.g., oldhamite, osbornite) of low O fugacities. Thus, high‐temperature processing of the CAIs did not occur under the reducing conditions characteristic of enstatite chondrites, implying that either (1) the CAIs are foreign to enstatite‐chondrite‐forming regions or (2) O fugacities fluctuated within the enstatite‐chondrite‐forming region. In contrast, secondary geikelite and Ti‐Fe‐sulfide, which replace perovskite, indicate that alteration of perovskite occurred under reducing conditions distinct from CAIs in the other chondrite groups. We have not ascertained whether the reduced alteration of enstatite chondrite CAIs occurred in a nebular or parent‐body setting. We conclude that each chondrite group is correlated with a unique assemblage of CAIs, indicating spatial or temporal variations in physical conditions during production or dispersal of CAIs.

The Physical and Chemical Effects of C-Shocks in Molecular Outflows

The bow shocks which are observed in jets associated with low-mass star formation probably have C-shock characteristics over at least part of their extent. We show that ion-neutral streaming in C-type shocks can give rise to the release of significant amounts of silicon from the refractory cores of dust grains and hence to the formation of SiO in the gas phase. The computed profiles of SiO emission lines are found to be qualitatively similar to those observed in molecular outflow regions such as L1448. The question of the validity of the stationary-state assumption, adopted in all previous studies of C-shocks in the interstellar medium, is addressed. Time-dependent calculations of the evolution of a C-type shock propagating in low-density gas suggests that steady state is unlikely to be attained under the dynamical conditions in outflows.

Shrinkage Reduction in Silica‐based Refractory Cores Infiltrated with Boehmite

Infiltration of silica‐based refractory cores with colloidal boehmite slurry has the effect of greatly reducing sintering shrinkage, as required for precision casting. Only 300 ppm of equivalent alumina is sufficient to decrease the shrinkage from RT to 1600°C more than three‐fold. Microstructural observations and XPS measures show that the silica grains are homogeneously coated with a reaction film which hinders viscous flow.

Thermal history of comets during residence in the Oort Cloud: Effect of radiogenic heating in combination with the very low thermal conductivity of amorphous ice

The thermal history of cometary nuclei during residence in the Oort cloud is studied with the use of the very low thermal conductivity of amorphous ice recently obtained by Kouchi et al. [1992a]. The heat sources included are (1) radioactive nuclides 40K, 232Th, 235U, and 238U with their chondritic abundances, and (2) latent heat released in transition from amorphous ice to crystalline ice. We model the cometary nucleus as a porous aggregate of grains with each individual grain being composed of a refractory core and an icy mantle. It is assumed that the ice is initially amorphous. The bulk thermal conductivity of a cometary nucleus is assumed to be expressed by the product of the thermal conductivity of individual grains and a reduction factor resulting from the porous structure of the nucleus. Numerical results of the thermal history are presented for various conditions including one case which includes heating by 26Al decay. It is shown that the thermal histories are clearly classified into two distinct types depending mainly on the nucleus thermal conductivity κ. (1) Comets with small κ experience a runaway increase in the internal temperature to higher than 120 K during residence in the Oort cloud, in which case most of the ice in the nucleus crystallizes. (2) Comets with a sufficiently large κ on the other hand, do not exhibit a runaway heating and the temperature is limited to < 100 K so that the initial amorphous ice is almost completely preserved. A criterion of nuclear ice crystallization is presented in an analytic expression derived from the analysis of the physical processes of the crystallization. A brief discussion is given on the implications of the results for the sources of volatile molecules observed in the coma.

Three-phase chemical models of dense interstellar clouds: gas, dust particle mantles and dust particle surfaces

Gas-grain models of the chemistry of dense interstellar clouds are presented in which two grain phases surrounding refractory cores are included. In addition to the actual grain surfaces, on which chemistry occurs, grain mantles, which are formed as adsorbed material trapped below new layers of such material, are considered. Material in grain mantles is assumed to be chemically inert, and therefore protected against destruction. The dust grain and gas temperatures are fixed at 10 K and the gas density |$n = n (\text H) + 2n(\text {H}_{2})$| remains at approximately |$2 \times {10}^{4} \text {cm}^{-3}$| in these models. Differences between the current three-phase (gas–mantle–surface) model results and those of previous two-phase (gas–surface) models for the overall grain abundances of individual species are small for inert species, but can be substantial for chemically reactive species, especially at late times ( ≥ 106 yr) after non-reactive, protected mantles have been built up. It is possible to obtain molecular abundances for different mantle layers deposited at different times; we find that all layers are dominated by water ice. The calculated condensed phase abundance of CO depends strongly on the surface abundance of atomic hydrogen.

The nature of zircon inheritance in two granite plutons

ABSTRACTUsing zircons taken from two granite plutons, Strontian (Caledonian, northwestern Scotland) and Kameruka (Bega Batholith, southeastern Australia), this study presents observations that have a bearing on refractory zircons as provenance indicators. Two broad textural types of refractory zircon were identified: (1) those which show simple two-stage growth histories; and (2) those which have apparently undergone repeated periods of growth, resorption, mechanical abrasion, fracturing and fracture-healing. SHRIMP U-Pb ages obtained from the Kameruka zircons indicate that the cores are the textural manifestation of inheritance. The shapes of refractory cores are not unambiguously indicative of their ultimate origin, since they may also be modified by processes that occur before and after incorporation into the magma. The cores within the two populations show a great diversity in types and styles of zoning, and in composition, implying that they have not chemically equilibrated internally, or externally with their host melt.