Homogeneous Melt Research Articles

Особенности флюидных включений в минералах

Characteristics of new genetic type of inclusions being formed during boiling up of magma or hydrotherms is given. It is indicated that the form and sizes of inclusions of boiling up fluids have important role in studying the nature of minerals. Examples of analysis using the composition and temperature homogenous process of individual mineral groups’ inclusions from definite deposits of the world have been analyzed. Temperature analysis of individual inclusions homogenous process indicates that under certain conditions, separation of homogenous magmatic melt into two parts (silicate and sulphate) takes place. Comparison of microelement composition of kimberlites of various productivity indicated similarity of behavior spectra of light rare earth elements in commercially diamondiferous kimberlite bodies. Assessment of quantitative role of various mantle paragenesises in parent kimberlites with consideration of selective capture of depth material by proto-kimberlite melts, specific features of captured material transportation to the surface, and stability of diamonds in depth melts is of big interest. One should consider those parameters and processes, analysis of which may help in gaining better understanding of mechanisms of kimberlites’ productivity origination.

Photo-induced bond breaking during phase separation kinetics of block copolymer melts: a dissipative particle dynamics study.

Using a dissipative particle dynamics (DPD) simulation method, we study the phase separation dynamics in block copolymer (BCP) melts in d = 3, subjected to external stimuli such as light. An initial homogeneous BCP melt is rapidly quenched to a temperature T < Tc, where Tc is the critical temperature. We then allow the system to undergo alternate light "on" and "off" cycles. An on-cycle breaks the stimuli-sensitive bonds connecting both the blocks A and B in the BCP melt, and during the off-cycle, the broken bonds recombine. By simulating the effect of light, we isolate scenarios where phase separation begins with the light off (set 1); the cooperative interactions within the system allow it to undergo microphase separation. When the phase separation starts with the light on (set 2), the system undergoes macrophase separation due to bond breaking. Here, we report the role of alternate cycles on domain morphology by varying the bond-breaking probability for both set 1 and set 2, respectively. We observe that the scaling functions depend upon the conditions mentioned above that change the time scale of the evolving morphologies in various cycles. However, in all the cases, the average domain size respects the power-law growth: R(t) ∼tφ at late times, where φ is the dynamic growth exponent. After a short-lived diffusive growth (φ∼ 1/3) at early times, φ illustrates a crossover from the viscous hydrodynamic (φ∼ 1) to the inertial hydrodynamic (φ∼ 2/3) regimes at late times.

Learning Feedforward Control for Laser Powder Bed Fusion

Additive manufacturing is becoming increasingly important for industrial applications. Especially laser powder bed fusion processes play a decisive role. However, the technology often lacks in reliability and part quality due to complex process interactions and disturbing influences. To counteract these limitations, a flexible and high-dynamic control of relevant process parameters, taking into account the transient process conditions, is indispensable. Currently, the most process parameters are often kept constant, since the used control systems do not offer real-time capable interfaces for intervention. To enable the adjustment of parameters during the process, an open control architecture for galvanometer scanners and laser sources was developed. The architecture is based on an industrial control system in combination with a field-programmable gate array (FPGA) communicating via a real-time fieldbus. The novel control architecture is used to integrate a model-based feedforward control, adjusting the laser power, scan speed and scan strategy based on the current powder bed temperature calculated by a two-dimensional thermal model during run time. An integrated learning algorithm autonomously tunes the process parameters during the manufacturing process and determines the optimal combination of laser power, scan speed and powder bed temperature to achieve a homogeneous melt pool. On average, the standard deviation of the powder bed temperature along the scan path was reduced by 48% for the simulated test cases.

Influence of scan paths on flow dynamics and weld formations during oscillating laser welding of 5A06 aluminum alloy

Numerical simulations and experiments are conducted to investigate the influence of three different scan paths, namely straight, sine, and cycloid, on the flow dynamics and weld formation during the laser welding of 5A06 aluminum alloys. The cycloid scan path produced molten pools with the largest dimensions, most regular morphology, and lowest temperature gradients. And the shallowest keyhole with the highest stability and the lowest temperature is produced under this condition, which has the effect of reducing and homogenizing the distribution of the fluid velocity. The most complicated vortices are obtained when the cycloid scan path is used. Porosity ratios of 5.5, 4.9, and 0.59 are obtained when the scan paths are straight, sine, and cycloid, respectively. The large and stable molten pool, the shallow keyhole, as well as the low and highly homogeneous melt flow velocity and the complicated vortices, contribute to reduction in porosity formation.

Impact of Coseismic Frictional Melting on Particle Size, Shape Distribution and Chemistry of Experimentally-Generated Pseudotachylite

In natural friction melts, or pseudotachylites, clast textures and glass compositions can influence the frictional behavior of faults hosting pseudotachylites, and are, in turn, sensitive to the processes involved in pseudotachylite formation. Quantification of these parameters in situations where the host rock composition and formation conditions are well-constrained, such as analogue experiments, may yield calibrations that can be employed in analysis of natural pseudotachylites. In this paper, we experimentally-generated pseudotachylites in granitoid rocks (tonalite and Westerly granite) at Pconf= 40 MPa and slip rates of ∼0.1 m s−1, comparable to the conditions under which natural pseudotachylite is known to form in Earth’s upper crust. We find variations in both clast textures and glass compositions that reflect formation processes, and probably influence the frictional behavior of similar natural faults hosting pseudotachylite. Quantification of particle size and shape distribution with a semi-automatic image analysis method, combined with analysis of glass and host-rock composition of these experimentally generated pseudotachylites, reveals that the textures of pseudotachylite material evolved by combinations of 1) comminution, 2) heterogeneous frictional flash melting, and 3) homogeneous (diffusive) clast melting and/or marginal decrepitation. Fractal dimensions of pseudotachylite-hosted clasts (D ∼ 3) that are greater than those of marginal fragmented host rock particles (gouge, D ∼ 2.4), reflect an increase of the intensity of comminution by slip localisation during a pre-melting phase. Chemical analyses demonstrate that these pseudotachylite glasses were generated by frictional flash melting, where host rock phases melt individually. Biotite is the least resistant to melting, feldspar intermediate, and quartz is the most resistant. The peudotachylite glass generated in these experiments has an alkaline composition, is depleted in SiO2compared to the bulk host-rock, and shows heterogeneous compositions in a single sample related to proximity to host-rock minerals. The percentage contributions of host rock phases to the melt, calculated by a mixing model, shows that glass compositions are dominated by plagioclase and biotite. Within the melt, margins of clasts were dissolved uniformly by diffusion and/or affected by marginal decrepitation, resulting in convex and round shapes with convexities averaging ∼0.8 and circularities averaging ∼0.65.

Experimental Investigation of Diopside Melt Viscosity at High Pressure

This paper presents the experimental evaluation of viscosity of the diopside-based model composition conducted at high P-T parameters (at the pressure of 4 GPa and in the temperature range of 1750°C - 1800°C) in the presence of olivine crystals. The experiments are carried out using the multi-anvil high-pressure apparatus of the “split-sphere” type (Russian acronym — BARS) according to the falling sphere method. The traveling time of a platinum (Pt) sphere in a melt is one of the parameters measured in experiments. Measurement of this parameter starts when the given P-T values are attained and stops when the electric current is turned off. There are three main positions of the Pt sphere observed in the experiments. Viscosity is calculated using the Stokes’ Law. It is found out that the Pt sphere velocity decreases expectedly as the relative viscosity of such heterogeneous compositions (liquid + solid phase) increases (in contrast to homogeneous melts). Viscosity values remain low when there is up to 7-10 wt-% of solid phase crystals in magma. The increase of olivine xenocrysts in magma leads to the progressive increase of viscosity values of the melt: by 1.5-2 orders of magnitude at 20-25 wt-%, by 3-3.5 orders of magnitude at 35-40 wt-%. The obtained experimental results allow concluding that the amount of solid phase in magma should be sufficiently low (less than 20-30 wt-%), otherwise, melts of the investigated composition can be moved only by explosive processes.

Hybrid Nature of the Platinum Group Element Chromite-Rich Rocks of the Norilsk 1 Intrusion: Genetic Constraints from Cr Spinel and Spinel-Hosted Multiphase Inclusions

AbstractThe Norilsk 1 intrusion (Russia), renowned for its abundance of sulfide ores, contains an upper contact zone, which hosts sulfide-poor and Cr spinel and platinum group element (PGE)-rich discontinuous reefs with significant economic potential. Located within strongly inhomogeneous contact rocks of various compositions, the origin of these reefs is complex and debated. Enrichment in PGEs in these rocks is distributed heterogeneously, occasionally occurring in extremely dense disseminations of Cr spinel, which are unusual for other rocks of the Norilsk 1 intrusion. The compositions of Cr spinel vary significantly between individual samples, even within the same samples across clusters of several Cr spinel grains and single grains. Chromium spinel grains are broadly characterized by low Mg# (3–50 mol %), moderate to extremely high TiO2 content (1–18 wt %), diverse Fe2+/Fe3+ ratios, and elevated V and Zn. Multiphase silicate inclusions hosted by Cr spinel are dominated by orthopyroxene, alkali-feldspar, clinopyroxene, Na phlogopite, high-Al amphibole, chlorite, and albite, along with minor felsic glass, sulfide, apatite, baddeleyite, titanite, calcite, halite, and cordierite. Heating experiments (1,250°C) on the silicate inclusions failed to produce homogeneous glasses but showed evidence of partial melting and reactions with precursor minerals that crystallized new phases. The experimentally obtained glasses are characterized by compositions that strongly differ from any known igneous rock in the Norilsk region, and the assemblage of phases in these inclusions is not supportive of the entrapment of a homogeneous silicate melt. Trace element patterns of the glasses of the experimentally heated inclusions are compositionally distinct from the Norilsk trap basalts, and instead are closer to the sedimentary rocks of the Norilsk region. We suggest that an in situ interaction between the mafic melt and the sedimentary rocks was responsible for Cr spinel mineralization and the formation of the host rocks. The subsequent subsolidus modification of the initial rocks expanded the Cr spinel compositional range and formed muscovite-albite-chlorite assemblages, which replaced the original silicate minerals.

Features of basaltic melt-hydrogen interaction at hydrogen pressure 10–100 MPa and temperature 1100–1250 °C

New experimental data on interaction of basaltic melt with hydrogen at high temperature (1100–1250 °C) and hydrogen pressure (10–100 MPa) have been obtained to gain insight into the possible role of hydrogen in the processes occurring in basaltic melts in the earth's crust under reducing conditions (f(O2) = 10−13–10−15). The experiments were carried out in a unique in house built internally heated pressure vessel (IHPV). This apparatus is equipped with an internal device, which allows long-term experiments under hydrogen pressure at high temperatures without losing hydrogen. Two types of experiments were carried out: 1 - kinetic experiments with isobaric quenching, 2 - crystallization experiments with subsequent isobaric quenching. It was found that, despite the high reducing potential of the H2 - basaltic melt system, the hydrogen oxidation reactions and the Fe oxides reduction in the melt are not complete. Initially homogeneous basaltic melts become heterogeneous. H2O is formed in the fluid phase (initially consisted of pure hydrogen); H2O (0.34–0.9 wt%) also dissolves in the basaltic melts, and small metal blobs with an emulsion-like texture are formed in the melts at temperature significantly lower than the melting temperature of the metal phase (Fe). The texture and dimensions of the metal segregations resemble those reported from natural magmatic rocks. Some new features of the crystallization process of basaltic melt under very reducing conditions are also discussed. The assemblage of subliquidus minerals (olivine + clinopyroxene + plagioclase) formed in the crystallization experiment at T = 1100 °C, P(H2) = 10 MPa with run duration 2 h, and their chemical compositions match closely those described in natural lavas (e.g. Kamchatka volcanoes). This result can be considered as an experimental confirmation of the participation of hydrogen in the magmatic process, which also corroborates with the composition of volcanic gases.

Mechanisms of femtosecond laser ablation of Ni3Al: Molecular dynamics study

Detailed knowledge of the physical essence of femtosecond laser and Ni3Al interactions is of great significance for the effective processing of film-cooling holes in Ni3Al-based single crystal superalloy turbine blades. Although attempts have been made to understand the femtosecond laser processing of Ni3Al-based single crystal superalloys via experiments or mesoscopic simulation, several phenomena and material removal mechanisms at the atomic level remain obscure. The information obtained in previous studies cannot be directly related to the femtosecond laser processing of Ni3Al-based single crystal superalloys due to the differing intrinsic properties of materials. In this paper, using TTM-MD, three regimes of material response to femtosecond laser irradiation are identified in simulations with a single pulsed 500 fs laser: melting, photomechanical spallation and phase explosion. Several key physical parameters related to the thermodynamic and dynamic behaviour of Ni3Al are obtained at the atomic level, including the fluence threshold, crystal lattice thermal stability and thermodynamic critical temperature. At low fluence, the material behaviour is characterized by heterogeneous surface melting and homogeneous subsurface melting. Photomechanical spallation occurs at higher fluence, which can be interpreted as void nucleation and growth, microcrack formation and eventual large liquid layer ejection. Under extremely high laser fluence, the material behaviour follows the phase explosion mechanism, forming an ablation plume with a layered structure. The dominant driving force change under different fluences causes the mechanism change. Additionally, an integral visual picture is successfully created based on the key parameters obtained, through which the mechanisms throughout the laser spot are revealed.

Mid-infrared photoresponse of electrodeposited PbSe thin films by laser processing and sensitization

Thin films of PbSe semiconductors are important for mid-wave infrared imaging applications. There is a need for a low-cost large-area PbSe thin film deposition process to generate highly sensitive mid-infrared (mid-IR) responsive devices. Here, we report the mid-IR response in the 3 – 5 µm wavelength for PbSe thin films prepared by the electrodeposition process followed by laser processing for densification and sensitization. Scanning electron microscope imaging shows that electrodeposited films consisted of a porous structure having an interconnected particle network. A 1064 nm wavelength pulsed laser, with 50 nanosecond pulse width, was used for homogeneous melting and fast recrystallization of the porous films to convert into planar dense thin films. A comparison of XRD patterns of the as-deposited and laser processed films revealed improvement in PbSe crystallinity with the original crystal structure remaining intact. The electrical resistivity of the laser-sintered films was found to be around 0.027 Ω-cm. The two-step sensitization process of oxidation and iodization increased the final film resistivity to 10.77 Ω-cm and was highly sensitive to mid-IR radiation. The percentage change in film resistance between dark and due to mid-IR exposure of 18.5 mW/cm2 is reported to be 15.9% at an operating voltage of 10 V. Electrodeposition of thin films followed by laser processing can emerge as a viable tool to produce the large-area uniform film for PbSe thin film applications in electronics and photonics devices.

Key concepts in interpreting the concentrations of the rare earth elements in zircon

Because of the great potential for zircon to provide insights into crustal melting and evolution, much work has been done to develop tools to interpret its trace element concentrations. There are several complexities to zircon/melt partitioning that appear to be underappreciated, and these are illustrated using a combination of new and existing data. First, sector zoning causes significant dispersion in the population of zircon compositions even for those grown from a homogeneous melt. Second, many analyses of natural crystals contain trace elements at unrealistic concentrations: there are multiple potential sources for this apparent contamination. Third, new experimental data show that Henry's Law is obeyed by rare earth elements in zircon, despite recent suggestions to the contrary. Fourth, zircon/melt partition coefficients are functions of temperature, melt composition and in some cases oxygen fugacity, rather than being constants.

Experimental Continuous Casting of Nitinol

Commercially available nitinol is currently manufactured using classic casting methods that produce blocks, the processing of which is difficult and time consuming. By continuous casting, wherein molten metal solidifies directly into a semi-finished product, the casting and processing of ingots can be avoided, which saves time and expense. However, no reports on continuous casting of nitinol could be found in the literature. In this work, Φ 12 mm nitinol strands were continuously cast. Using a graphite crucible, smelting of pure Ni and Ti in a medium frequency induction furnace is difficult, because it is hard to prevent a stormy reaction between Ni and Ti and to reach a homogeneous melt without a prolonged long holding time. Using a clay-graphite crucible, the stormy reaction is easily controlled, while effective stirring assures a homogeneous melt within minutes. Strands of nearly equiatomic chemical compositions were obtained with acceptable surface quality. The microstructure of strands containing over 50 at. % Ni, consisted of Ti2Ni and cubic NiTi, whereas the microstructure of strands containing less than 50 at. % Ni consisted of TiNi3 and cubic NiTi. This is consonant with the results of some other authors, and indicates that the eutectoid decomposition NiTi → Ti2Ni + TiNi3 does not take place.

The effect of materials' rheology on process energy consumption and melt thermal quality in polymer extrusion

AbstractPolymer extrusion is an important but an energy intensive method of processing polymeric materials. The rapid increase in demand of polymeric products has forced manufactures to rethink their processing efficiencies to manufacture good quality products with low‐unit‐cost. Here, analyzing the operational conditions has become a key strategy to achieve both energy and thermal efficiencies simultaneously. This study aims to explore the effects of polymers' rheology on the energy consumption and melt thermal quality (ie, a thermally homogeneous melt flow in both radial and axil directions) of extruders. Six commodity grades of polymers (LDPE, LLDPE, PP, PET, PS, and PMMA) were processed at different conditions in two types of continuous screw extruders. Total power, motor power, and melt temperature profiles were analyzed in an industrial scale single‐screw extruder. Moreover, the active power (AP), mass throughput, torque, and power factor were measured in a laboratory scale twin‐screw extruder. The results confirmed that the specific energy consumption for both single and twin screw extruders tends to decrease with the processing speed. However, this action deteriorates the thermal stability of the melt regardless the nature of the polymer. Rheological characterization results showed that the viscosity of LDPE and PS exhibited a normal shear thinning behavior. However, PMMA presented a shear thickening behavior at moderate‐to‐high shear rates, indicating the possible formation of entanglements. Overall, the findings of this work confirm that the materials' rheology has an appreciable correlation with the energy consumption in polymer extrusion and also most of the findings are in agreement with the previously reported investigations. Therefore, further research should be useful for identifying possible correlations between key process parameters and hence to further understand the processing behavior for wide range of machines, polymers, and operating conditions.

Surface Formation Mechanisms in Selective Laser Melting of Cobalt-Chromium-Molybdenum Powder

Selective laser melting (SLM) is a manufacturing technology of metal parts of any shapes with target mechanical properties by means of laser melting. This paper discusses the effect of SLM parameters: laser output power, laser movement velocity, scanning pitch and preheating temperature of a powdered material on surface formation mechanism, namely, its physical configuration when melting cobalt-chromium-molybdenum powdered material Со28Cr3Mo. The study points at structural differences of melted surfaces even under identical process parameters. Several types of surface formation are identified, e.g. homogenous melt, coagulated particles, and shapeless particles. Vapor pressure, Marangoni effect, and heat effect of a melted powder are stated to be key reasons for rough surface. This research is of high importance for understanding the effect of SLM parameters on formation of a target quality surface, positive stability and repeatable accuracy of the process.

Heterogeneous melting kinetics in polycrystalline aluminum.

The heterogeneous melting kinetics of polycrystalline aluminum is investigated by a theoretical model which represents the overall melting rate as a functional of the Weibull grain-size-distribution. It is found that the melting process is strongly affected by the mean-grain-diameter, but is insensitive to the shape parameter of the Weibull distribution. The temperature-time-transformation (TTT) diagrams are calculated to probe dependence of the characteristic timescale of melting on the overheating temperature and the mean-grain-diameter. The model predicts that the heterogeneous melting time of polycrystalline aluminum exponentially depends on temperature in high temperature range and the exponent constant is an intrinsic material constant independent of the mean-grain-diameter. Comparisons between TTT diagrams of heterogeneous melting and homogenous melting are also provided.

Structural transition dynamics of the formation of warm dense gold: From an atomic scale view

With the highly optimized embedded-atom-method (EAM) potential and electron-phonon coupling factor obtained from experimental data, the dynamics of the formation of warm dense gold and the nuclear response of gold foils upon intense laser excitation were investigated using two-temperature molecular dynamics simulations. Considering laser energy densities ranging from 0.18 to 1.17 MJ/kg, we provide a microscopic picture of the formation of warm dense gold. A threshold (0.19 MJ/kg) for the laser energy density was determined, identifying two different melting mechanisms. For an energy density below 0.19 MJ/kg, the melting of the foil is controlled by the propagation of melt fronts from external surfaces, which results in heterogeneous melting on the time scale of hundreds of picoseconds. For an energy density above 0.19 MJ/kg, homogeneous nucleation and growth of liquid regions inside the foil play the leading role, and homogeneous melting occurs with several picoseconds. Compared with previous simulations and experimental measurements, the evaluated different threshold value indicates that the improvement in the electron heat capacity for the two-temperature model by including the kinetic information of electrons may predict better laser-matter interactions under such extreme non-equilibrium conditions.

Wear-resistant boride reinforced steel coatings produced by non-vacuum electron beam cladding

In this work, we present a wear-resistant coating fabricated by non-vacuum electron beam cladding of Fe62Cr10Nb12B16 at.% powder on a mild steel substrate. The protective coating was 1.3 mm thick, dense, and exhibited an α-(Fe,Cr) matrix reinforced by a significant fraction of hard borides formed upon solidification. Micrometric and nanometric borides homogeneously dispersed within the matrix were formed due to the homogeneous melting and the relatively fast cooling to suppress the excessive phase growth. An intimate metallurgically bonded interface between the coating and substrate was characterized by low compositional dilution and a fine eutectic-like transition zone microstructure anchoring the dissimilar materials. The coatings displayed a higher wear resistance compared to the mild steel substrate, showing specific wear rates, κ, about one order of magnitude lower (10−5 against 10−4 mm3/N.m, respectively). The abrasive wear mechanism was dominant for the coating sample when tested at low sliding velocity, 10 cm/s, due to the detachment of hard borides from the surface and their incorporation into the tribosystem. The adhesive wear mechanism was found to be dominant at higher sliding velocities of 20 and 40 cm/s. Dry sand/rubber wheel testing revealed the higher resistance of the coating against abrasive wear compared to the mild steel substrate. Regardless of the wear mechanism, the Fe62Cr10Nb12B16 at.% coatings showed a superior sliding and abrasive wear resistance and represented an interesting protective measure to extend the service of inexpensive mild steel components.

Study of local structure and ion dynamics in GdCl3 - Gd2O3 and KCl - GdCl3 - Gd2O3 melts: In situ Raman spectroscopy and ab initio molecular dynamics

The local structure and dynamics of ions in homogeneous GdCl3–Gd2O3 and KCl–GdCl3–Gd2O3 oxide-chloride melts with a gadolinium oxide concentration up to 6 mol% were studied using in situ Raman spectroscopy and ab initio molecular dynamics. Quantitative and qualitative changes in the spectral characteristics of homogeneous oxide-chloride melts compared with GdCl3 and GdCl3–KCl melts were observed. These comprised additional low-intensity vibrational bands appearing at 208, 371 and 202, 368 cm−1, respectively. No gadolinium oxide bands were detected, indicating dissociation in the chloride melt. Molecular dynamics simulations showed that oxygen in melts is adjacent to three gadolinium ions, with an inter-ionic OGd distance of 2.2 Å. The [Gd3O] associate, in turn, is incorporated into the network-like structure of the original chloride melt. As a result of this association, ion transport through the melt is hampered, as substantiated by the calculated self-diffusion coefficients.

Coupling of homogeneous and heterogeneous melting kinetics in overheated polycrystalline materials

Melting kinetics of overheated polycrystalline materials is analyzed on the basis of a new model which explicitly couples homogeneous and heterogeneous melting mechanisms. The distinct feature of this approach lies in its ability to evaluate not only grain-size-distribution effects on the overall melting kinetics but also competitions between the two melting mechanisms. For the first time, we reveal the three-part structure of temperature-time-transformation diagrams for melting of polycrystalline materials, through which it is possible to determine a critical temperature across which the dominant melting mechanism switches. The critical temperature increases as the mean-grain-diameter decreases following a negative power-law. The results are qualitatively consistent with experimental observations.

Experimental modeling of formation of native metals (Fe, Ni, Co) in the earth’s crust by the interaction of hydrogen with basaltic melts

In continuation of our early works, an experimental study of the kinetics and interaction mechanisms in the hydrogen-basalt melt system at a hydrogen pressure of 100 MPa and temperature of 1250C carried out. It was found in kinetic experiments that, despite the high reduction potential of the H2-melt system, the hydrogen oxidation reactions and the complete reduction of Fe oxides in the melt do not go to the end. As a result, initially homogeneous basalt melt becomes heterogeneous: H2O is formed in the fluid phase; H2O is dissolved in the basalt melts, and a small metal separation of the liquation structure formed at a temperature significantly lower than the melting temperature of the metal phases (Fe, FeNiCo alloy). The structure and dimensions of the experimentally established metal separations agree well with the natural data on the findings of small amounts of the metal phase, primarily iron and its alloys with nickel and cobalt, reported from magmatic rocks of various compositions and origins.