Composition Of Grains Research Articles

CORRELATIONS AND VARIATION STRUCTURE OF GRAIN QUALITY TRAITS AND YIELD OF WHEAT LINES WITH FOREIGN GENETIC MATERIAL

We studied variation structure and correlations between the traits of grain quality and yield in the sample consisting of T. aestivum cultivars, related common wheat species and introgression lines obtained on their basis. In the grain of wheat relatives, two-year average grain macronutrients, micronutrients and protein content were higher than in T. aestivum (1.02 to 2.13 times, depending on the element; 1.4 — for protein). The genetic diversity of mineral composition traits was wider for the lines containing foreign genetic material than for their parental forms, and as a rule, the introgression lines exceeded the original common wheat varieties in the microelements accumulation. The greatest possible number of statistically significant correlations (at least 7) was found for N, P, Zn and Fe content. Protein content was associated with grain's Mg, P, Fe, Zn, Cu. Thousand-kernel weight (TKW) is was negatively correlated with some traits of mineral composition and seed protein content. But the only significant (p = 0.05) association was
 between TKW and seed nitrogen. We identified lines with optimal mineral composition and high grain productivity, which are of interest for wheat breeding programs.

Elementary Composite Binary and Grain Alignment Locked in Dust Growth

Abstract Planets are known to grow out of a star-encircling disk of the gas and dust inherited from an interstellar cloud; their formation is thought to begin with coagulation of submicron dust grains into aggregates, the first foundational stage of planet formation. However, with nanoscale and submicron solids unobservable directly in the interstellar medium (ISM) and protoplanetary disks, how dust grains grow is unclear, as are the morphology and structure of interstellar grains and the whereabouts and form of “missing iron.” Here we show an elementary composite binary in 3D sub-10 nm detail—and the alignments of its two subunits and nanoinclusions and a population of elongated composite grains locked in a primitive cosmic dust particle—noninvasively uncovered with phase-contrast X-ray nanotomography. The binary comprises a pair of oblate, quasi-spheroidal grains whose alignment and shape meet the astrophysical constraints on polarizing interstellar grains. Each member of the pair contains a high-density core of octahedral nanocrystals whose twin relationship is consistent with the magnetite’s diagnostic property at low temperatures, with a mantle exhibiting nanoscale heterogeneities, rounded edges, and pitted surfaces. This elongated binary evidently formed from an axially aligned collision of the two similar composite grains whose core–mantle structure and density gradients are consistent with interstellar processes and astronomical evidence for differential depletion. Our findings suggest that the ISM is threaded with dust grains containing preferentially oriented iron-rich magnetic nanocrystals that hold answers to astronomical problems from dust evolution, grain alignment, and the structure of magnetic fields to planetesimal growth.

Multi-scale study of diffusion in composite grain–pore systems based on particles random walk

Multi-scale study of diffusion in composite grain–pore systems based on particles random walk

The Use of ZrO2 Waste for the Electrolytic Production of Composite Ni-P-ZrO2 Powder.

Ni–P–ZrO2 composite powder was obtained from a galvanic nickel bath with ZrO2 powder. Production was conducted under galvanostatic conditions. The Ni–P–ZrO2 composite powder was characterized by the presence of ZrO2 particles covered with electrolytical nanocrystalline Ni–P coating. The chemical composition (XRF method), phase structure (XRD method) and morphology (SEM) of Ni–P–ZrO2 and the distribution of elements in the powder were all investigated. Based on the analyses, it was found that the obtained powder contained about 50 weight % Zr and 40 weight % Ni. Phase structure analysis showed that the basic crystalline component of the tested powder is a mixed oxide of zirconium and yttrium Zr0.92Y0.08O1.96. In addition, the sample contains very large amounts of amorphous compounds (Ni–P). The mechanism to produce the composite powder particles is explained on the basis of Ni2+ ions adsorption process on the metal oxide particles. Current flow through the cell forces the movement of particles in the bath. Oxide grains with adsorbed nickel ions were transported to the cathode surface. Ni2+ ions were discharged. The oxide particles were covered with a Ni–P layer and the heavy composite grains of Ni–P–ZrO2 flowed down to the bottom of the cell.

Modeling Grain Rotational Disruption by Radiative Torques and Extinction of Active Galactic Nuclei

Abstract Extinction curves observed toward individual Active Galactic Nuclei (AGN) usually show a steep rise toward far-ultraviolet (FUV) wavelengths and can be described by the Small Magellanic Cloud (SMC)-like dust model. This feature suggests the dominance of small dust grains of size a ≤ 0.1 μm in the local environment of AGN, but the origin of such small grains is unclear. In this paper, we aim to explain this observed feature by applying the RAdiative Torque Disruption (RATD) to model the extinction of AGN radiation from FUV to mid-infrared (MIR) wavelengths. We find that in the intense radiation field of AGN, large composite grains of size a ≥ 0.1 μm are significantly disrupted to smaller sizes by RATD up to d RATD > 100 pc in the polar direction and d RATD ∼ 10 pc in the torus region. Consequently, optical–MIR extinction decreases, whereas FUV-near-ultraviolet extinction increases, producing a steep far-UV rise extinction curve. The resulting total-to-selective visual extinction ratio thus significantly drops to R V < 3.1 with decreasing distances to AGN center due to the enhancement of small grains. The dependence of R V with the efficiency of RATD will help us to study the dust properties in the AGN environment via photometric observations. In addition, we suggest that the combination of the strength between RATD and other dust destruction mechanisms that are responsible for destroying very small grains of a ≤ 0.05 μm is the key for explaining the dichotomy observed “SMC” and “gray” extinction curve toward many AGN.

Aging behavior and mechanical properties of ultra-fine grained Al2024-2TiN composite prepared by spark plasma sintering

2 wt%TiN nanoparticles reinforced ultra-fined grain Al2024 composite (Al2024-2TiN) and ultra-fined grain Al2024 alloy were prepared by high-energy ball milling, spark plasma sintering (SPS), and hot compression deformation. The effect of TiN nanoparticles on aging behavior and mechanical properties of Al2024-2TiN composite was investigated. The results show that, with the introduction of TiN nanoparticles, the tensile strength of as-aged Al2024-2TiN composite increased from 568 MPa of Al2024 alloy to 783 MPa, while the yield strength and elongation decreased from 376.5 MPa and 12.7% to 359.1 MPa and 9.4%, respectively. The average grain size of as-aged Al2024-2TiN composite was 452.4 nm, smaller than 3.2 μm of Al2024 alloy. TiN nanoparticles reduced the dissolution of the second phases during solution treatment, and decreased the number of age precipitating phases which resulted in the yield strength of Al2024-2TiN composite being lower than that of Al2024 alloy. Nevertheless, TiN nanoparticles promoted the aging kinetics of Al2024-2TiN composite. The peak aging time of 6 h for Al2024-2TiN composite was 2 h earlier than that of Al2024 alloy. The thermal diffusion activation energies of phase S′ precipitated in Al2024-2TiN composite and Al2024 alloy were 78.98 kJ/mol and 82.06 kJ/mol, respectively. Phase S′ precipitation in Al2024-TiN composite became easier.

High grade ores of the Onverwacht platinum pipe, eastern Bushveld, South Africa

ABSTRACT The platiniferous dunite pipes are discordant orebodies in the Bushveld Complex. The Onverwacht pipe is a large body (>300 m in diameter) of magnesian dunite (Fo80–83) that crosscuts a sequence of cumulates in the Lower Critical Zone of the Bushveld Complex. In a pipe-in-pipe configuration, the main dunite pipe at Onverwacht hosts a carrot-shaped inner pipe of Fe-rich dunite pegmatite (Fo46–62) which comprises the platinum-bearing orebody. The latter was ca. 18 m in diameter and a mining depth of about 320 m was reached. In the present work, a variety of ore samples were studied by whole-rock geochemistry, including analyses of platinum group elements, ore microscopy, and electron probe microanalysis. Olivine of the ore zone displays considerable chemical variation (range 46–62 mol.% Fo) and may represent either a continuum, or different batches of magma, or vertical or horizontal zonation within the ore zone. Chromite is principally regarded to be a consanguineous component of the pipe magma that crystallized in situ and simultaneously with olivine. The Onverwacht mineralization is Pt-dominated (>95% of the platinum group elements) and the ore is virtually devoid of sulfides. Platinum-dominated platinum group minerals predominate, followed by Rh-, Pd-, and Ru-species. Pt-Fe alloys are most frequent, followed by Pt-Rh-Ru-arsenides and -sulfarsenides, platinum group element antimonides, and platinum group element sulfides. Our hypothesis on the genesis of the Onverwacht pipe and its mineralization is as follows: After near-consolidation of the layered series of the Critical Zone, the magnesian dunite pipe of Onverwacht was formed by upward penetration of magmas that replaced the existing cumulates initially by infiltration, followed by the development of a central channel where large volumes of magma flowed through. Fractional crystallization of olivine within the deeper magma chamber and/or during ascent of the melt resulted in the formation of a consanguineous, residual, more iron-rich melt. This melt also contained highly mobile, supercritical, water-bearing fluids and was continuously enriched in platinum group elements and other incompatible elements. In several closing pulses, the platinum group element-enriched residual melts crystallized and sealed the inner ore pipe. Crystallization of the melt resulted in the coeval formation of Fe-rich olivine, chromite, and platinum group minerals. The non-sulfide platinum group element mineralization was introduced in the form of nanoparticles and small droplets of platinum group minerals, which coagulated to form larger grains during evolution of the mineralizing system. The suspended platinum group minerals acted as collectors of other platinum group elements and incompatible elements during generation and ascent of the melt. With decreasing temperature, the platinum group mineral grains annealed and recrystallized, leading to the formation of composite platinum group mineral grains, complex intergrowths, or lamellar exsolution bodies. On further cooling, platinum group minerals overgrowing Pt-Fe alloys formed by reaction of leached elements and ligands like Sb, As, and S mobilized by supercritical magmatic/hydrothermal fluids. Redistribution of platinum group elements/platinum group minerals apparently only occurred on the scale of millimeters to centimeters. Finally, surface weathering led to the local formation of platinum group element oxides/hydroxides by oxidation of reactive precursor platinum group minerals.

A simulated study of surface morphological evolution on coarse-textured soils under intermittent rainfall events

The evolution of slope surface morphology directly affects the hydrological process and forms a dynamic feedback loop with the runoff and sediment production. However, the unique erosion processes and feedback mechanism for the surface morphological changes of coarse-textured granite soils have been rarely studied previously. Here, a series of rainfall simulation experiments (intensity of 90 mm h−1) were conducted under continual intermittent rainfall conditions (duration of 20 h) on a 0.8 m by 3.0 m soil flume packed with the four coarse-textured granite soils (sieved soils from the counties of Tongcheng, Ganxian, Changting, and Wuhua, China, defined as TCA, GXA, CTA and WHA, respectively) to measure the surface roughness, coarse grain coverage, soil erosion rate, stream power and sediment sorting. The results showed: 1) the coarse grain coverage of the four soils gradually increased with rainfall duration, with the final maximum (74.89%) for CTA soil, which corresponded to the enrichment of fine particles in the sediments; 2) the mean soil erosion rate of the four soils ranged from 0.090 to 0.76 kg m−2 min−1 with the decrease of clay content from 24.19% to 13.60% in the original soils, coinciding with the surface roughness controlled by rill erosion around the coarse grains; 3) the coarse grain cover provided a protective layer to reduce further soil loss in inter-rill areas; 4) the model of soil clay content and stream power was shown to be suitable for soil erosion prediction of coarse-textured soils (R2 = 0.93). The results highlighted soil mechanical composition and coarse grain coverage on the surface as the key factors affecting the coarse-textured soil erosion. This study facilitates our understanding of the unique erosion processes and the erosion feedback mechanism of coarse-textured soils.

Laser Heating Study of the High-Temperature Interactions in Nanograined Uranium Carbides.

Nanograined nuclear materials are expected to have a better performance as spallation targets and nuclear fuels than conventional materials, but many basic properties of these materials are still unknown. The present work aims to contribute to their better understanding by studying the effect of grain size on the melting and solid–solid transitions of nanograined UC2−y. We laser-heated 4 nm–10 nm grain size samples with UC2−y as the main phase (but containing graphite and UO2 as impurities) under inert gas to temperatures above 3000 K, and their behavior was studied by thermal radiance spectroscopy. The UC2−y solidification point (2713(30) K) and α-UC2 to β-UC2 solid–solid transition temperature (2038(10) K) were observed to remain unchanged when compared to bulk crystalline materials with micrometer grain sizes. After melting, the composite grain size persisted at the nanoscale, from around 10 nm to 20 nm, pointing to an effective role of carbon in preventing the rapid diffusion of uranium and grain growth.

On the microstructure, texture and mechanical properties through heat treatment in Al–CuO nanocomposite fabricated by Accumulative Roll Bonding (ARB)

This study focuses on the Al-0.5 vol% CuO composite creation. Therefore, the researchers used the accumulative roll bonding (ARB) process to establish the Al-0.5 vol% CuO composites. The composites were created in three ARB methods; the usual way, with rapid annealing and preheating between ARB cycles. Heat treatment was adjusted at 190 ᵒC and lasted for 5 min. This study used a small amount of reinforcing particles, which resulted in the absence of any porosity in the composite. The ARB process resulted in the average size of the created composite grain in the usual way, with the rapid annealing and preheating to be 219.19 nm, 306.54 nm, and 355.65 nm, respectively. The composite creation through the ARB process increased the tensile strength by more than 2.5 times. The ARB with preheating, causes dynamic recovery, dramatically reducing the metal matrix hardness. In this way, the particles were swept instead of getting spread. Therefore, the tensile strength and elongation of the sample were lowered.

Effect of Grain Size on the Corrosion Behavior of Fe-3wt.%Si-1wt.%Al Electrical Steels in Pure Water Saturated with CO2.

The corrosion behavior of two silicon steels with the same chemical composition but different grains sizes (i.e., average grain area of 115.6 and 4265.9 µm2) was investigated by metallographic microscope, gravimetric, electrochemical and surface analysis techniques. The gravimetric and electrochemical results showed that the corrosion rate increased with decreasing the grain size. The scanning electron microscopy/energy dispersive x-ray spectroscopy and X-ray photoelectron spectroscopyanalyses revealed formation of a more homogeneous and compact corrosion product layer on the coarse-grained steel compared to fine-grained material. The Volta potential analysis, carried out on both steels, revealed formation of micro-galvanic sites at the grain boundaries and triple junctions. The results indicated that the decrease in corrosion resistance in the fine-grained steel could be attributed to the higher density of grain boundaries (e.g., a higher number of active sites and defects) brought by the refinement. The higher density of active sites at grain boundaries promote the metal dissolution of the and decreased the stability of the corrosion product layerformed on the metal surface.

A reliable technique to fabricate superconducting joints between single grain, Y–Ba–Cu–O bulk superconductors

The production of large (RE)Ba–Cu–O single grains ((RE)BCO), where RE = Y, Gd or Sm, of complex geometries is presently limited by the intrinsic slowness of the grain growth process. Additionally, the shapes achievable using established melt processing are constrained by the small number of post-processing techniques available. These materials are brittle and hard, which makes machining a difficult task and largely eliminates the possibility of producing highly intricate shapes. An alternative to this slow and inflexible growth process would be to join many small single grains to form one large composite grain, connected by high-performance superconducting joints. A reliable joining technique would also overcome the need for the careful and time-consuming post-growth machining processes. In this work we report on the use of single grain YBCO–Ag as an interface medium to achieve superconducting joints between (RE)BCO bulks. This joining technique is relatively quick and does not require tight process parameter control as there is no need to re-grow the interface joining material. We report on six joints produced from samples cut and joined in a variety of orientations. In addition, a joint was produced using bulk YBCO from two independent single grains. The trapped field properties of the resulting joined sample were measured and the microstructure at the joint was examined. We show that this simple but effective joining technique makes it possible to produce multiple composite grains with comparable superconducting properties to those of a single grain of the same size.

Drifting inwards in protoplanetary discs

In previous laboratory experiments, we measured the temperature dependence of sticking forces between micrometer grains of chondritic composition. The data showed a decrease in surface energy by a factor ~5 with increasing temperature. Here, we focus on the effect of surface water on grains. Under ambient conditions in the laboratory, multiple water layers are present. At the low pressure of protoplanetary discs and for moderate temperatures, grains likely only hold a monolayer. As dust drifts inwards, even this monolayer eventually evaporates completely in higher temperature regions. To account for this, we measured the tensile strength for the same chondritic material as was prepared and measured under normal laboratory conditions in our previous work, but now introducing two new preparation methods: drying dust cylinders in air (dry samples), and heating dust pressed into cylinders in vacuum (super-dry samples). For all temperatures up to 1000 K, the data of the dry samples are consistent with a simple increase in the sticking force by a factor of ~10 over wet samples. Up to 900 K super-dry samples behave like dry samples. However, the sticking forces then exponentially increase up to another factor ~100 at about 1200 K. The increase in sticking from wet to dry extends a trend that is known for amorphous silicates to multimineral mixtures. The findings for super-dry dust imply that aggregate growth is boosted in a small spatial high-temperature region around 1200 K, which might be a sweet spot for planetesimal formation.

Heavy mineral record from the east China sea inner shelf: Implications for provenance and climate changes over the past 1500 years

The heavy mineral composition and sensitive grain size changes from core SS4 retrieved from the mud wedge on the East China Sea inner shelf have been studied for better understanding provenance variations in the sediment and climate changes during the last ~1500 yr. High dolomite content and occurrence of ubiquitous polysynthetic mica indicate that the sediments in core SS4 were mainly derived from the Yangtze River, while the relatively high epidote content represent the contribution of small local rivers from Zhejiang and Fujian provinces. The substantial decrease in the epidote/hornblende ratio since ~730 yr BP manifests a decline in the relative contribution of sediment from the small local rivers to the core. We propose that the changes in drought/flood conditions in response to the East Asian winter monsoon (EAWM) and human activities might have been mainly responsible for changes in sedimentary characteristics. During 1400–730 yr BP, the core sediments were characterized by relatively finer sensitive grain size and high epidote/hornblende ratio, due to a possibly weaker EAWM (i.e., less Yangtze River-derived sediment transported by the southward coast current). This time interval coincides with the Sui-Tang Warm Period (1400–1130 yr BP) in China and the Medieval Warm Period (1000–730 yr BP) on a broader regional scale. The prolonged warm periods were, however, interrupted by three short cold phases at 1350–1280 yr BP, 1130–1000 yr BP and 870–750 yr BP, characterized by coarse sensitive grain size and decreased epidote/hornblende ratio. Between 360 and 150 yr BP, the sensitive grain size significantly coarsened, which corresponded to the Little Ice Age. Our new findings suggest that sedimentation processes of mud wedge formation are responsive to natural environmental change and human activity.

Genetic control of kernel compositional variation in a maize diversity panel.

Maize (Zea mays L.) is a multi-purpose row crop grown worldwide, which, over time, has often been bred for increased yield at the detriment of lower composition grain quality. Some knowledge of the genetic factors that affect quality traits has been discovered through the study of classical maize mutants; however, much of the underlying genetic control of these traits and the interaction between these traits remains unknown. To better understand variation that exists for grain compositional traits in maize, we evaluated 501 diverse temperate maize inbred lines in five unique environments and predicted 16 compositional traits (e.g., carbohydrates, protein, and starch) based on the output of near-infrared (NIR) spectroscopy. Phenotypic analysis found substantial variation for compositional traits and the majority of variation was explained by genetic and environmental factors. Correlations and trade-offs among traits in different maize types (e.g., dent, sweetcorn, and popcorn) were explored, and significant differences and meaningful correlations were detected. In total, 22.9-71.0% of the phenotypic variation across these traits could be explained using 2,386,666 single nucleotide polymorphism (SNP) markers generated from whole-genome resequencing data. A genome-wide association study (GWAS) was conducted using these same markers and found 72 statistically significant SNPs for 11 compositional traits. This study provides valuable insights in the phenotypic variation and genetic control underlying compositional traits that can be used in breeding programs for improving maize grain quality.

Platinum and gold placer from Tugidak Island, Alaska: Platinum-group minerals and their inclusions, gold, and chromite mineralogy

ABSTRACT Black sand beach placers from Kodiak, Sitkinak, and Tugidak Islands, Alaska, have been mined intermittently for gold and minor platinum-group alloys for more than 100 years. High-grade platinum-rich magnetic separate and accompanying black sand from the southern beach placer of Tugidak Island were studied using electron microprobe WDS and scanning electron microscope EDS; mineral classification and identification were based on these techniques. The major platinum mineral is isoferroplatinum, followed by minor tetraferroplatinum and tulameenite, and rare ferronickelplatinum. Two types of alteration were identified in about 3–4% of the alloy grains: rim formation involving Pt loss and increased Fe, Ni, and/or Cu, and fracturing and vein filling by Cu-rich alloy. Ruthenium-Ir-Os-Pt alloys occur as inclusions and veins as well as form part of composite grains. Ten percent of the alloy grains contain a large variety of platinum-group minerals (PGM). Inclusions of cuprorhodsite, malanite, cuproiridsite, laurite, erlichmanite, cooperite, braggite, bowieite, kashinite, miassite, hollingworthite, irarsite, sperrylite, stillwaterite, genkinite, stibiopalladinite, keithconnite, zvyagintsevite, and probable palladodymite and vincentite were identified. Two unidentified inclusion phases also occur. Most of the PGM inclusions are primary and were trapped by a growing crystal from a melt; some inclusions exhibit textures that suggest trapping of an As,Te,S-rich immiscible melt. Secondary inclusions and evidence of deformation were observed in a few alloy grains. Associated with PGM inclusions or as separate inclusions are various base-metal sulfides. Two silicate-melt inclusions in one isoferroplatinum grain have an andesite–shoshonite composition. Minor gold and Ag-rich gold in the high-grade magnetic separate contain magnetite, pyrrhotite, and chromite inclusions. The gold composition suggests that their sources are the numerous quartz veins and apophyses related to granitoids on Kodiak Island. The composition of the placer chromite is similar to chromite from the Border Ranges mélange fault system and suggests that the Uyak Complex ultramafic and mafic rocks are part of a supra-subduction-zone ophiolite and are the source of the platinum-group minerals.

Telluride Mineralogy of the Deer Horn Au-Ag-Te-(Bi-Pb-W) Deposit, British Columbia: Implications for the Generation of Tellurides

ABSTRACTThe Deer Horn deposit, located 150 km south of Smithers in west-central British Columbia, is an Eocene polymetallic system enriched in Au-Ag-Te with lesser amounts of Bi-Pb-W; the Au and Ag are hosted in Te-bearing minerals and Ag-rich gold (Au-Ag alloy). A quartz-sulfide vein system containing the main zones of Au-Ag-Te mineralization and attendant sericite alteration occurs in the hanging wall of a local, spatially related thrust fault and is genetically related to the nearby Eocene Nanika granodiorite intrusive suite. Tellurium-bearing minerals commonly form isolated euhedral to subhedral grains or composite grains (up to 525 μm in size) of Ag-, Bi-, Pb-, and Au-rich tellurium-bearing minerals (e.g., hessite, tellurobismuthite, volynskite, altaite, and petzite). Panchromatic cathodoluminescence imaging revealed four generations of quartz. Within remnant cores of quartz I, local oscillatory zoning occurs in quartz II. Fine-grained veinlets of quartz III and IV crosscut quartz I and II, showing evidence of at least two deformation events; late-forming veinlets of calcite crosscut all generations of quartz. The tellurides and Ag-rich gold occur in stage III quartz. Three types of fluid inclusions were observed in stage III and IV quartz: (1) aqueous liquid and vapor inclusions (L-V); (2) aqueous carbonic inclusions (L-L-V); and (3) carbonic inclusions (vapor-rich). Primary fluid inclusions related to the telluride mineralization within quartz III were tested with microthermometry, along with a few primary inclusions from quartz IV. Homogenization temperatures are 130.0–240.5 °C for L-V inclusions and 268.0–336.4 °C for L-L-V inclusions. Aqueous carbonic inclusions had solid CO2 melting temperatures from –62.1 to –56.8 °C, indicating the presence of ≈1 to 30 mol.% dissolved methane in these inclusions.The Deer Horn Au-Ag-Te-(Bi-Pb-W) deposit is a reduced intrusion-related gold system characterized by sheeted veins, metal zoning, low salinity aqueous-carbonic fluids, and a genetic relationship to an Eocene granodiorite. Values of δ34S of pyrite vary from –1.6 to 1.6 per mil and are compatible with a magmatic source of sulfur.

Testing Trace-Element Distribution and the Zr-Based Thermometry of Accessory Rutile from Chromitite

Trace element distribution and Zr-in-rutile temperature have been investigated in accessory rutile from stratiform (UG2, Merensky Reef, Jacurici), podiform (Loma Peguera), and metamorphic chromitites in cratonic shields (Cedrolina, Nuasahi). Rutile from chromitite has typical finger-print of Cr-V-Nb-W-Zr, whose relative abundance distinguishes magmatic from metamorphic chromitite. In magmatic deposits, rutile precipitates as an intercumulus phase, or forms by exsolution from chromite, between 870 °C and 540 °C. The Cr-V in rutile reflects the composition of chromite, both Nb and Zr are moderately enriched, and W is depleted, except for in Jacurici, where moderate W excess was a result of crustal contamination of the mafic magma. In metamorphic deposits, rutile forms by removal of Ti-Cr-V from chromite during metamorphism between 650 °C and 400 °C, consistent with greenschist-amphibolite facies, and displays variable Cr-Nb, low V-Zr, and anomalous enrichment in W caused by reaction with felsic fluids emanating from granitoid intrusions. All deposits, except Cedrolina, contain Rutile+PGM composite grains (<10 µm) locked in chromite, possibly representing relics of orthomagmatic assemblages. The high Cr-V content and the distinctive W-Nb-Zr signature that typifies accessory rutile in chromitite provide a new pathfinder to trace the provenance of detrital rutile in placer deposits.

Synthesis and characterisation of lead free BaFe12O19 –(K0.5Na0.5)NbO3 magnetoelectric composites, and the comparison of various synthetic routes

Polycrystalline lead-free (1-x)BaFe12O19–x(K0.5Na0.5)NbO3 magnetoelectric ceramic composites (x = 10, 20 and 30 wt%) were fabricated for the first time, comparing various synthesis techniques, namely solid state reaction, sol-gel, co-precipitation and citrate combustion methods for the synthesis of the ferrite phase. As well as the four synthesis routes, comparisons were made between uniaxial pressing and cold isostatic pressing of the samples prior to sintering at 1200 °C/2 h. Formation of separate magnetic hexaferrite BaFe12O19 (BaM) and ferroelectric (K0.5Na0.5)NbO3 (KNN) phases in the composites was confirmed using x-ray diffraction. The microstructural features revealed distribution of BaM and KNN grains in all the composite systems. Piezoresponse (PFM) and magnetic force (MFM) modes of scanning probe microscopy (SPM) were utilised to assess responses from piezoelectric and magnetic grains. Localised piezoelectric hysteresis loops were measured on KNN grains in composites made by all four methods. Typical hard magnetic hysteresis loops for BaM were observed exhibiting high coercivity values (up to 281 kA m−1 or 3530 Oe), and those composites made using solid state reaction and citrate combustion methods, which contained no impurity phases, had close to maximum magnetisation values (equivalent to ~70 A m2 kg−1 for the BaM phase). SEM, MFM and magnetisation measurements all suggested that the grain size of the BaM in the composites made using solid state reaction, co-precipitation and citrate combustion methods was around 1 µm, and consisting of single magnetic domains. As a result, it is likely that these samples will exhibit a high degree of magnetoelectric coupling.

Pengaruh Kecepatan Pengadukan pada Proses Stircasting terhadap Sifat Mekanik pada Paduan Aluminium

<p class="Abstract">The composite material is a material composed of a mixture or combination of two or more of the major elements that macro differ in shape and material composition that basically can not be separated. In this research, the aluminum used was the outcome of production cesspool with the addition of volcanic dust from Mount Kelud by 2% as reinforcement. The stir casting process is the casting process by adding a material (powder form) in pure metal (aluminum), which has been melted and then stirring constantly. After that, the composite materials (the volcanic dust from Mount Kelud) were mixed slowly into the stirred liquid material. In this research, the variations of stirring speed were 0,200,300,400,500 and 600 rpm. The stirring each time for 4 minutes. In this study, the stirring speed in the casting process was 0, 200, 300, 400, 500, and 600 rpm. Tensile test, Impact test, and microstructure observations were carried out on the casting results. From these tests, the highest modulus of elasticity and impact value was obtained at the 600rpm stirring process. It may due to globular grains are more evenly distributed. And the result of metallographic testing was stirring speed could affect the amount and density of composite grain structure. The faster the stirring, the grain structure was getting smaller and close.</p>