Crystal Fragments Research Articles

Modelling freckles and spurious grain formation in directionally solidified superalloy castings

Segregation channels with misoriented spurious grains, known as freckles, are an unacceptable casting defect in superalloy turbine blades. A digital-twin method to predict segregation channels was proposed in our previous studies; however, the formation of spurious grains was ignored. Here, we extend the digital twin methodology by incorporating dendrite fragmentation, which is recognized as the predominant mechanism in the formation of spurious grains. The flow-induced fragmentation process has been refined to account for the timing of dendrite pinch-off. A three-phase mixed columnar-equiaxed solidification model was used to track the motion of the crystal fragments. Directional solidification experiments for superalloy casting were conducted in an industrial-scale Bridgman furnace, and the distribution of spurious grains in the freckles was metallographically analysed. Excellent simulation-experiment-agreement was achieved. Based on this study, the formation of spurious grains within the segregation channels is mainly caused by the flow-driven fragmentation mechanism. Experimentally measured freckles can be reproduced only if the timing of the dendrite pinch-off is considered.

Developing a novel toffee-type soft candy process by sonocrystallization: A preliminary study

This study aimed to evaluate the applicability of sonocrystallization, an innovative process, as a low-cost and time-efficient alternative for the crystallization of confectionery dough, which is a crucial step in the production of conventional toffee-type soft candy. In this regard, according to the design plan, sonocrystallization time and current were selected as independent variables. The samples (36 run) nucleated by sonocrystallization using the optimum conditions (1600 and 2400 mA, 20 min) were allowed to aging under different times (0, 2, 4, 6, 8, and 10 min) and temperatures (60, 65, and 70 °C) in order to determine crystal growth. According to the texture profile analysis results, all parameters except for cohesiveness were significantly affected by both the sonocrystallization and aging conditions (p < 0.05), and dramatically higher hardness values were obtained for samples sonocrystallized at 2400 mA. Micrographs showed the formation of a crystalline network with more crystals of smaller size, fragmentation of larger crystals, and a more homogenous crystallization, especially in the samples sonocrystallized at 2400 mA and allowed to aging at >65 °C for durations of >6 min. The targets of the study were achieved by subjecting the samples to sonocrystallization at 2400 mA and aging at 70 °C for 8 min for crystal growth.

The Evolution of Dilatant Shear Bands in High-Pressure Die Casting for Al-Si Alloys

Bands of interdendritic porosity and positive macrosegregation are commonly observed in pressure die castings, with previous studies demonstrating their close relation to dilatant shear bands in granular materials. Despite recent technological developments, the micromechanism governing dilatancy in the high-pressure die casting (HPDC) process for alloys between liquid and solid temperature regions is still not fully understood. To investigate the influence of fluid flow and the size of externally solidified crystals (ESCs) on the evolution of dilatant shear bands in HPDC, various filling velocities were trialled to produce HPDC samples of Al8SiMnMg alloys. This study demonstrates that crystal fragmentation is accompanied by a decrease in dilatational concentration, producing an indistinct shear band. Once crystal fragmentation stagnates, the enhanced deformation rate associated with a further increase in filling velocity (from 2.2 ms−1 to 4.6 ms−1) localizes dilatancy into a highly concentrated shear band. The optimal piston velocity is 3.6 ms−1, under which the average ESC size reaches the minimum, and the average yield stress and overall product of strength and elongation reach the maximum values of 144.6 MPa and 3.664 GPa%, respectively. By adopting the concept of force chain buckling in granular media, the evolution of dilatant shear bands in equiaxed solidifying alloys can be adequately explained based on further verification with DEM-type modeling in OpenFOAM. Three mechanisms for ESC-enhanced dilation are presented, elucidating previous reports relating the presence of ESCs to the subsequent shear band characteristics. By applying the physics of granular materials to equiaxed solidifying alloys, unique opportunities are presented for process optimization and microstructural modeling in HPDC.

Effect of single/multi-particle grinding parameters on surface properties of bearing steel GCr15

Grinding surface residual stress (RS) has an important influence on the service life of parts. In this study, the mathematical model of grinding force (GF) and grinding temperature (GT) of single particle was established. The relationship between grinding parameters, grinding force-thermal coupling and residual stress of single particle was analyzed by numerical simulation. Meanwhile, aiming at the multi-grain grinding of aviation precision high-speed bearing rings, the experimental analysis of crystal fragmentation, element content and residual stress of service and non-service bearing rings were carried out. Based on the above, the following results were obtained: in the simulation, the residual stress in the Y direction > the residual stress in the X direction > the residual stress in the Z direction at the same grinding force and grinding temperature. In the experiment, (1) The grain size of bearing raceway before service was about 24 μm, and the grain size of bearing raceway after service was about 3 times smaller than that before service. (2) C, Si, Cr and Fe decreased by 0.83 %, 0.07 %, 1.09 % and 32.75 % respectively after crushing (after service). On the contrary, it increased 0.66 % O and 34.08 % Pr. The Pr element was mainly distributed in the broken grain boundaries. (3) After service, the tangential residual compressive stress decreased by 169.3 MPa, while the axial residual stress increased by 172.6 MPa.

Dynamic behavior of fractured gabbro treated by high temperatures

Rock masses in deep engineering are often subjected to high geothermal effect, and blasting is a key technique for deep rock excavation. It is crucial to study the dynamic characteristics of fractured rock masses under high geothermal conditions and blasting excavation. This paper focuses on fractured gabbro, examining the effects of high temperatures on its surface chromaticity and mass. Dynamic splitting tests were conducted using a Split Hopkinson Pressure Bar (SHPB) apparatus, and the microstructure was analyzed with scanning electron microscopy (SEM). The results indicate that: (1) High temperatures significantly affect the surface chromaticity and mass of gabbro samples. (2) Elevated temperatures lead to the progression from a microstructure with no noticeable microcracks to the development of extensive microcracks and mineral particle fragmentation. (3) The impacts of high temperatures on the splitting strength, peak strain, and dynamic elastic modulus of gabbro samples reach a critical point around 500 °C. At this temperature, the strengthening effect of high temperature is evident, whereas at 800 °C, these properties significantly decrease due to extensive mineral crystal fragmentation and microcrack expansion, weakening the sample's strength, stiffness, and deformation resistance. (4) From 25 °C to 600 °C, the fissure angle significantly influences the splitting strength, peak strain, and dynamic elastic modulus of gabbro. Although the fissure angle still impacts these properties at 800 °C, the overall effect of high temperature is more pronounced. (5) The failure of fractured gabbro samples is primarily characterized by tensile and shear failures, with the crack initiation angle closely related to the fissure angle.

Poly(ethylene 2,5-furandicarboxylate) pole figures to determine the microstructural scheme upon uniaxial stretching: Link between orientation and crystallisation

The emergent biobased polymer poly (ethylene 2,5-furandicarboxylate), PEF, has been studied through an innovative approach based on pole figures and orientation factor calculation. PEF uniaxial stretching was performed with different mechanical conditions (different equivalent strain rates), up to several levels of strain and while considering different post-stretching cooling conditions (interrupted, unloaded and ruptured samples). Samples were stretched and interrupted before and after the Natural Draw Ratio (NDR), the deformation for which the material starts strain-hardening. When PEF strain-hardens, it reveals both an increase of the crystalline orientation and crystallinity ratio with the deformation imposed. Unloading the material at temperature tends to decrease partially crystalline orientation, especially regarding the aliphatic part of the chains. Moreover, stretching PEF up to high strains, superior to the NDR, leads to crystal fragmentation. After all, all experimental results were compared to a texture model. It appears that a texture can be developed upon stretching that is close to a fibre texture, as the furan cycles tend to be parallel to the specimen plane.

High-performance lithium-ion full-cell batteries based on transition metal oxides: Towards energy density of ∼ 1300 Wh kg−1

Half-cell structure including sufficient lithium ions for theoretical studies exhibits different electrochemical performance with commercial full-cell rechargeable lithium ion batteries (LIBs) featuring moderate lithium ions. So, understanding the property correlation between half-cell and full-cell LIBs is imperative, but remains a big challenge. Herein, a series of full-cells are assembled with transition metal oxide (TMO) nanowires as cathodes and silicon/graphite (Si/G) anode via electrochemical pre-lithiation, to figure out the key determinants in comparison to their corresponding half-cells. It is found that eletrochemical performances of half-cell and full-cell batteries are basically consistent by using insertion-type cathodes of V2O5, MoO3 and MnO2, but different in the cases of conversion-type cathodes of Fe2O3 and Co3O4 due to their high polarization relieved crystal fragmentation. In addition, compared with the other five materials, V2O5 nanowire exhibits the lowest charge transfer resistance (240.2 Ω), highest lithium ion diffusion rate (10-13 ∼ 10-11 cm2 s−1) and discharge midpoint voltage (1.6 V). Thus, V2O5||PL-Si/G achieves the state-of-the-art gravimetric energy density, discharge midpoint voltage and cycle performance, giving rise to the record-high 1288 Wh kg−1 at 0.1 A g-1 in potential range of 0.3 ∼ 4.0 V. These results indicate the significance of rational material selection and effective pre-lithiation for developing high-performance full-cell LIBs.

Hydrochromic and piezochromic dual-responsive optical film derived from poloxamer and ethyl cellulose for visual fingerprints identification

Developing new materials that could identify fingerprint using the naked eye and observe the level 3 microscopic details is challenging. Here, we designed a novel hydrochromic and piezochromic dual-responsive optical film, which achieved the visual transparency transition. The performances of hydrochromic and piezochromic responses from high transparency to opaque whiteness were attributed to the introduction of poloxamer. The hygroscopic swelling of the disordered micelles led to light scattering, causing the hydrochromic response. The piezochromic response may be ascribed to the microcracks in the fragments of poloxamer crystals, which changed the refractive index of light. The fascinating combination of hydrochromic and piezochromic response was effectively applied in fingerprint identification. Hydrochromic response accurately recognized sweat pores, and piezochromic response could gradually reveal the ridges and valleys according to the different color of imprinted fingerprints. The film could identify fake fingerprints based on the differences in sweat pores between fake fingerprints and living fingers. More importantly, the film could easily detected not only the clear ridges but also the detailed sweat pores using the naked eye, indicating that the film has profound research significance in fingerprint analysis and liveness fingerprint detection.

Resilient Si@C architecture fabricated by mechanochemical conjugation and thermal reduction for lithium storage: Simulation on interfacial state evolution

Synchronal comminution via high-energy bead milling not only efficiently pulverizes Si particles and exfoliates graphene oxide (GO) sheets but also facilitates Si surface functionalization and intensify Si-C conjugation. After a thermal reduction, a well-wrapped Si@C anode material can be fabricated for lithium storage. The discharge specific capacities of this Si@C composite sustain at 1110.3 mAh g−1 after 300 cycles at 1 A g−1 and 316.4 mAh g−1 for 800 cycles at 5 A g−1, which are respectively 1.35 and 2.07 times that of its random blended Si/C counterpart. By employing molecular dynamics (MD) simulations with ReaxFF reactive force field to investigate the mechanochemical reactions between Si and GO amidst high-energy milling, an atomic scale portrayal of Si crystal fragmentation and Si-C bonding can be depicted. Analyses focusing on the differential forces exerted on various Si crystal planes, coupled with potential energy (PE) trends, reveal a higher propensity for cleavage in (111) plane, with (311) plane followed. Radial distribution function (RDF) outcomes indicate that ball milling leads to substantial disruption of crystalline order in Si particles, generating a plethora of Si dangling bonds. This disruption stimulates the formation of SiOOC, SiOC and SiC bonds at the Si/C interface, thus enhancing the integration of GO with Si substrate. Subsequent thermal reduction processes not only restore the structural order of Si and GO but also consolidate Si/C bonding.

Uncovering crystal growth and regeneration mechanism to control crystal morphology: The case study of aceclofenac

The study of crystal growth and regeneration mechanisms is of great significance for controlling the morphology of crystals. Through the investigation of the recovery and regrowth processes of crystals, we have revealed the regeneration mechanism of aceclofenac (ACF) crystals and the influence of hydroxypropyl methylcellulose (HPMC) on the regeneration of ACF crystals. Firstly, ACF crystal regeneration experiments were conducted in acetone (ACT) and methyl acetate (MA), and it was found that the broken crystals could be successfully regenerated and restored to their original morphology, the regenerated ACF crystals in MA exhibited a larger aspect ratio. Secondly, the crystals obtained from the two solvents were placed in different solvents for regrowth, and it was shown that solvent was a key factor influencing the aspect ratio of ACF crystals. Additionally, HPMC was used to regulate the crystal morphology, it was found that the best effect was achieved when the mass fraction of HPMC was 0.5%, resulting in a regenerated crystal with an aspect ratio of only 2.19. Molecular simulation results indicated that the interaction between the radial (110) crystal facet and the solvent was weaker than that with the axial (1 0 -1) crystal facet, leading to a higher radial growth rate and a larger aspect ratio of the crystal. However, after adding HPMC, the interaction between HPMC and the radial (1 1 -1) and (110) crystal facets became stronger. HPMC selectively adsorbed on these two crystal facets, ultimately resulting in crystals with a smaller aspect ratio. The research findings of this study will provide theoretical basis for solving the problem of difficult morphology control due to crystal fragmentation in the pharmaceutical industry production process.

The Emergence of the Hexagonal Lattice in Two-Dimensional Wigner Fragments.

At very low density, the electrons in a uniform electron gas spontaneously break symmetry and form a crystalline lattice called a Wigner crystal. But which type of crystal will the electrons form? We report a numerical study of the density profiles of fragments of Wigner crystals from first principles. To simulate Wigner fragments, we use Clifford periodic boundary conditions and a renormalized distance in the Coulomb potential. Moreover, we show that high-spin restricted open-shell Hartree-Fock theory becomes exact in the low-density limit. We are thus able to accurately capture the localization in two-dimensional Wigner fragments with many electrons. No assumptions about the positions where the electrons will localize are made. The density profiles we obtain emerge naturally when we minimize the total energy of the system. We clearly observe the emergence of the hexagonal crystal structure, which has been predicted to be the ground-state structure of the two-dimensional Wigner crystal.

VCD spectra of chiral naphthalene-1-carboxamides in the solid-state

The VCD spectra of chiral 2,3-dihydro-1H-benzo[de]isoquinolin-1-one (8-substituted naphthalene-1-carboxamide, BIQ) were studied in KBr pellets. The X-ray diffractometry revealed that the Me, Ph, and pClPh BIQs crystalize in the monoclinic P21, while nBu, pMePh, and oMeOPh BIQs in the orthorhombic P212121 space group. Only the Me-BIQ crystal exhibits the presence of cyclic amide dimers, while the others contain chains of the amid group hydrogen bonds. For all BIQs, except pMePh, the most intense IR band in the 1750–1550 cm−1 region is located at ca. 1680 cm−1 and is accompanied by two weak ones at ca. 1618 and 1590 cm−1. For the pMePh derivative, four almost equally intense IR bands at 1662, 1639, 1614, and 1588 cm−1 are observed. This region of the IR spectra of BIQs, but pMePh, is well reproduced by calculations based on BIQ monomers. On the other hand, the complex IR pattern of pMePh is computationally reproduced when larger crystal fragments, like octamers, are considered. Registration of the VCD spectra enabled recognizing the complexity of IR contours at ca. 1680 cm−1 by the corresponding VCD motives. For (i) Me, Ph and pClPh (R)-enantiomers, two (+)(–) bands were distinguished and for (ii) nBu and pMePh ones, one VCD band with right-side asymmetry was found. For (iii) oMeOPh the VCD pattern cannot be unambiguously assigned. Thus, the VCD spectra in the ν(C=O) range diverse the studied compounds. Among the set of molecules, pMePh has exceptional crystal geometry. Therefore, its most intense ν(C=O) band position and shape can be connected with the geometry of the hydrogen bonds, interactions, and crystal packing. Interpretation of the VCD spectra is based on linear and packed BIQ octamers. This cluster model can reproduce the main features of the solid-state VCD of BIQs.

Ultrahigh-Pressure Orange Garnets from the Sedimentary Deposits of the Upper Bug Area (Ukrainian Shield)

The article is dedicated to the investigation of orange garnets from Miocene-Pliocene deposits of the Balta suite and the Sarmatian stage in the Vinnytsia area. The Vinnytsia area is located on the southwestern slope of the Ukrainian Shield. The crystalline basement on most of the area is represented by granitoids of the Berdychiv complex of Paleoproterozoic age, and to a lesser extent by enderbites and charnockites of the Lityn complex of Neoarchean age. Among these, there are mafic and ultramafic bodies ranging from 0.5 to 2 meters in thickness. The sedimentary cover with a total thickness of up to 20 m is represented by sands and clays of the middle Sarmatian, Balta and Quaternary sediments. These deposits are enriched with mantle minerals, predominantly pyrope, and four diamond crystals have also been discovered. We studied the chemical composition (253 crystals) and morphology (278 crystals) of the orange garnets. The studied samples are mostly represented by garnets of pyrope and pyrope-almandine composition, a small part is represented by grossulars. Most of the garnets are unrounded crystal fragments ranging in size from 0.2 to 0.6 mm, exhibiting signs of intense hypergene changes. These are evident in the development of positive (block) and negative relief features, appearing as drop-shaped, cone-shaped, small hilly microrelief and various forms of etching channels. The morphological features suggest that these garnets were probably relocated a short distance from their primary sources and had been present in the weathering crust for an extended period. The original sources of garnets are most likely Precambrian and located on active tectonic zones, which led to their destruction. According to chemical composition data, among orange garnets low-chromium websterite and low-calcium eclogite varieties, as well as garnets of high-iron mantle pyroxenites are dominated. The presence of titanium impurities in many garnets indicates the possible diamond-bearing nature of some primary sources.

Structural evolution of biodegradable polyglycolide fibers under stress-temperature coupled field and its impact on properties

The properties of polyglycolide (PGA) fibers used as surgical sutures depend on their aggregated state structure. The study investigated the relationship between the structural evolution and macroscopic properties of PGA fibers with low-crystallinity under coupled stress-temperature fields by conducting in-situ WAXD/SAXS, DSC and SEM measurements. The WAXD and SAXS results indicated that the structural evolution during the low-temperature stretching stage primarily relied on stress-induced amorphous molecular chain orientation and the formation of small crystals. The DSC results confirmed that uniaxial stretching enhanced the orientation of amorphous molecular chains, leading to cold crystallization of PGA fibers at lower temperatures. During the heating stretching stage at temperatures of 60–90 °C, numerous crystals were generated through a lamellar insertion mechanism and underwent lateral growth. This is reflected by the crystallinity, crystal orientation, and crystallite sizes increased significantly, while the long period decreased rapidly. The high-temperature stretching stage resulted in fragmentation and recrystallization of lamellar crystals, forming fibrous crystals. Stretching at 110 °C exhibited higher Iq2/Iq1 values than other temperatures, which means that 110 °C is more favorable for the formation of fibrous crystals. Additionally, PGA fibers stretched at 150 °C exhibited the highest crystallinity and crystal orientation, which led to a 440 % increase in tensile strength. Its resistance to degradation has also been significantly improved compared to the original fibers.

Syuzevskoye diamond placer: A new stage in studying the diamond potential of Western Urals

Research subject. Geological features of the structure and composition of the Syuzevskoye diamond placer in the Aleksandrovsky region of the Perm Krai. The placer was found in the border zone of two regional tectonic structures of the Urals: the Western Ural outer folding zone and the Central Ural uplift. This placer was developed within the erosion-karst (?), erosion-structural or tectonically determined Chikman-Nyarskaya depression. Materials and methods. The placer was identified in the period from 2017 to 2022 during a geological study of the subsoil area “Glubokiy” (License PEM 02687 KP LLC “Almining”). Mining and enrichment works were carried out according to the original enrichment scheme using the clamshell sampling method, heavy media and electromagnetic separation. The morphometric characteristics of several hundred diamonds were identified and described; reports were prepared; and reserves were assessed. Results. In the section of the Syuzevskoye placer, two diamond-bearing strata are clearly distinguished, separated by poor- and non-diamond-bearing deposits; anomalously high seam thickness for the Ural placers (up to 14-16 m) was established; high areal productivity of the placer (up to 0.7-1.2 ct/m2) and high diamond content (up to 0.5 ct/m3 per sample and an average of 0.09 ct/m3 for the placer). The placer is attributed to the type of placers of tectonic scarp zones. Reserves of alluvial diamonds weighing 430.5 thousand ct of the Syuzevskoye deposit are estimated at C1 + C2 categories in the area limited by the area between exploration lines 107-116 (size 1000 x 750 m); approved by the Minutes of the GKZ Rosnedra No. 7139 dated November 18, 2022 and will be increased. Certificate No. PEM 23 DRK 10147 confirming the discovery of a mineral deposit, issued by the Federal Agency for Subsoil Use of the Russian Federation to LLC Almining on March 29, 2023. Over 90% of diamonds are of gem quality. The average mass of crystals in the reserve calculation loop is 87 mg, and behind the loops is 29 mg. The leading size classes by mass -8 + 4 and -4 + 2 mm are 93.9% and 72.3% in quantity with an average mass of a diamond crystal of 99.9 mg. The shape is dominated by dodecahedroids (66.9%), less fragments of crystals with an unpreserved shape (14.9%) and fragments of crystals (13.1%); octahedrons (2.4%) and tetrahedroids (2.2%) are rare, rhombic dodecahedroids (0.4%) are rare. The preservation of crystals is good: full crystals make up 63.7%, fragments of crystals - 16.3%, fragments - 12.9%. Most of the crystals do not have wear (42.4%), or have weak wear of the tops and ribs (43.0%), medium and strong wear was noted only in 13.7% of the crystals. The average cost of diamonds is estimated at 361.59 USD per 1 ct. Conclusions. A unique deep-seated diamond deposit has been discovered, which is considered as a new type of deep-seated diamond-bearing placers in tectonic ledge zones. The geological criteria for identifying such diamond deposits in the Urals were determined. A new technological scheme for prospecting and exploration of deep-seated diamond placers within erosion-karst and tectonically determined depressions was developed, which is applicable for prospecting for precious metal placers.

The Beacon Heights “Tinguaite” (Phonolite): A recrystallised agpaitic ignimbrite in the Mesoproterozoic Pilanesberg alkaline complex, South Africa

AbstractAn extrusive rock unit in the Mesoproterozoic Pilanesberg alkaline complex that has been referred to as the “Beacon Heights Tinguaite” since the work of Shand (1928) has been reexamined in the field and studied by petrographic microscopy, scanning electron microscopy, and whole-rock major and trace element analysis. The new observations indicate that the unit (here informally renamed the “Beacon Heights Phonolite” to comply with current petrographical nomenclature) is a laminated, volcanic rock in which mafic layers rich in sodic pyroxene alternate on any scale with discontinous, felsic layers consisting of alkali feldspar, nepheline, sodalite and their alteration products natrolite and analcime. Highly strontian apatite, fluorite, a manganiferous pectolite-group mineral, sphalerite and pyrrhotite are minor to accessory minerals. In addition, the rock carries indicator minerals typical of agpaitic rocks (including lamprophyllite and eudialyte-group minerals and their replacement products). The rock contains abundant crystal fragments of felsic minerals (alkali feldspar, nepheline and sodalite), fragments and elongated lenses of nepheline syenite, some of which contain primary magmatic lamprophyllite, and rare armoured lapilli. The overall structure of the rock is that of a welded ashflow tuff (igmimbrite) affected by post-magmatic recrystallisation processes. Whole-rock major and trace element compositions suggest a compositional affinity with members of the agpaitic, intrusive Green Foyaite Suite of the Pilanesberg Complex, and probably also a genetic relationship. The Beacon Heights Phonolite is a rare, possibly unique, example of an ashflow deposit of agpaitic, highly silica-undersaturated composition.

In-situ observation of falling-weight impact damage in isotactic polypropylene sheet

Isotactic polypropylene (iPP) sheets were subjected to low-energy falling-weight impacts under various conditions. The elastic energy recovered during unloading gradually increases with increasing impact energy and reaches a fixed value, while the dissipated energy during the impact test increases monotonically. Whereas higher impact energy and repeated impacts result in enhanced whitening in an iPP sheet, the load–displacement curve is unaffected by impact repetition. The stress–strain curves of the impact-damaged iPP specimens indicate that these specimens retain high ductility irrespective of the impact energy and number of impacts. In addition, the striker impact did not affect the crystalline lattice of the original iPP. The impact damage solely induces the decrease in yield stress, suggesting impact in the crystalline phase. The yield stress gradually decreases with increasing impact energy and number of repetitions owing to accumulation of impact damage in the crystalline phase. The yield stress reaches a constant value after several repeated impacts, where the asymptotic value decreases with the impact energy. Because the drop of the yield stress increases with the impact energy, it is suggested that preferential fracture in the lamellar crystals takes place owing to fluctuation in the strength. Impact-induced voids with a size of approximately twice the long period are found by in-situ small-angle X-ray scattering. Partial fragmentation of the lamellar crystal into lamellar cluster units is suggested to be the microscopic origin of the impact damage.

Solidification Principle in Large Vertical Steel Casting Under the EMS Effect

The surging demand for large high-quality rotor shafts or similar steel components in heavy industries (energy sector) poses new challenges to steelmakers. Based on the experience of conventional ingot and continuous casting, several new process concepts have been proposed, e.g., vertical continuous casting (VCC), semi-continuous casting (SCC), and segment casting (SC), but none of them are optimally put in operation. The main problems include the control of the as-cast structure and macrosegregation. Electromagnetic stirring (EMS) is necessary to obtain the center equiaxed zone, but EMS-induced multiphase flow can cause severe macrosegregation and uneven distribution of the as-cast structure between equiaxed and columnar. In this study, an advanced mixed columnar-equiaxed solidification model was used to investigate the formation of the as-cast structure and macrosegregation in an example of SCC with a large format (diameter 1 m). The main role of EMS is to create crystal fragments by fragmentation, which is regarded in this work as the only origin of equiaxed grains. The created equiaxed grains are brought by the EMS-induced (primary and secondary) flow and gravity-induced sedimentation to the central/lower part of the casting. The main goal of this study was to understand the solidification principle of SCC. In addition, a numerical parameter study by varying the EMS parameters was also performed to demonstrate the model capability towards the process optimization of SCC.

Recycling of waste gypsum from αlpha-hemihydrate phosphogypsum: Based on the atmospheric hydrothermal process

Phosphogypsum (PG) is a typical solid waste in the phosphorus chemical industry, which restricts the sustainable development of the phosphorus chemical industry. From the perspective of green manufacturing in the whole life cycle, this paper puts forward the hydrothermal recycling and utilization of waste gypsum (WG) from αlpha-hemihydrate phosphogypsum (α-PGHH). It is revealed that the raw material characteristics of WG will lead to the crystal fine fragmentation of the product, which will lead to the significant deterioration of the strength and filtration performance of the hardened paste. The increase of the acidity of the reaction medium is proposed to weaken the negative effect of the crystal modifier on crystal phase transition, so as to obtain recycled αlpha-hemihydrate gypsum (α-HH) with better crystal integrity and macroscopic performance. It was proved that when the pH value was controlled at 4.5, the comprehensive properties of the product were good, and the 2 h bending strength and 3 d compressive strength were 4.1 MPa and 29.2 MPa, respectively. The preparation of recycled α-HH from WG produced by α-PGHH can be achieved through the atmospheric hydrothermal process.

Revised stratigraphy and first geochronology of the Miocene submarine volcanic succession at Kennaook/Cape Grim, northwestern Tasmania

Kennaook/Cape Grim in far northwestern Tasmania, Australia, was a site of submarine intraplate basaltic volcanism during the Miocene. The succession is exceptionally well preserved and is dominated by pillow lava, massive lava and pillow fragment breccia. The total volume of volcanic products (1.1 km3) is relatively small on a global scale, but the preservation is world class. The oldest unit, the Woolnorth Tuff lies unconformably on the Neoproterozoic Rocky Cape Group. The first 40Ar/39Ar dating of the volcanic rocks reveals an early Miocene (24.5–23 Ma) age for the entire sequence. The Woolnorth Tuff is composed almost entirely of devitrified basaltic glass shards and olivine crystal fragments. The Woolnorth Tuff is overlain by the Slaughter Bluff Volcanic Breccia (23.12 ± 0.19 Ma) at Kennaook/Cape Grim. The Slaughter Bluff Volcanic Breccia is dominated by diffusely bedded pillow fragment breccia. North of Kennaook/Cape Grim, the Little Trefoil Basalt (ca 24 Ma) intrudes the Woolnorth Tuff. To the south of Kennaook/Cape Grim, the Woolnorth Tuff is overlain by the Studland Bay Basalts (23.73 ± 0.08 Ma) and intruded by a newly recognised unit, the Hippo Basalt (24.52 ± 0.12 Ma). The Studland Bay Basalts comprise mounds of basaltic pillow lavas followed by a succession of diffusely bedded, matrix-dominated, pillow fragment breccia and basaltic breccia. Detailed field mapping and sampling have revealed that the environment of deposition of all Kennaook/Cape Grim units was submarine and that they were emplaced in relatively rapid succession. KEY POINTS First 40Ar/39Ar geochronology for the Kennaook/Cape Grim volcanic succession. Little Trefoil Basalt has been re-interpreted from a subaerial extrusive unit to a submarine intrusive unit. A new intrusive unit, the Hippo Basalt, has been recognised. The stratigraphy of the Kennaook/Cape Grim volcanic succession has been revised.