Granular Crystals Research Articles

Controlled growth of ruthenium dioxide nanostructures in borosilicate glass melts

Ruthenium, a fission product generated during the fission of uranium oxide fuel in a reactor, interacts with alkali metals such as sodium in the upper layer of the cold cap, forming a sodium ruthenate intermediate (NaxRuyOz), which promotes the crystallization of acicular RuO2 within the glass melt. During vitrification, RuO2 predominantly settles at the bottom of the melt owing to its high density and low solubility, significantly increasing both the conductivity and viscosity of the glass melt. Herein, the formation of NaxRuyOz, along with the chemical reactions promoting the crystallization of RuO2 in the waste glass, was comprehensively investigated. The results of X-ray diffraction and X-ray spectroscopy indicate that lamellar and granular Na3RuO4 do not form directly through the reaction between NaNO3 and RuO2 but rather through an intermediate stage from Na2RuO4. This reaction critically affects the morphology of RuO2 within the waste glass. The uncalcined mixture of NaNO3 and RuO2 was found to interact with the glass melt, forming granular RuO2 crystals, whereas the reaction of Na3RuO4 with the glass melt was found to lead to the formation of acicular RuO2 crystals. The results of X-ray absorption fine structure analysis indicate that the valence state of Ru in NaRu-BSG is slightly higher than that in reference RuO2, which was attributed to the presence of trace amounts of Na3RuO4 in the glass.

Uncovering Pattern-Transformable Soft Granular Crystals Induced by Microscopic Instability

Abstract Upon compression, some soft granular crystals undergo pattern transformation. Recent studies have unveiled that the underlying mechanism of this transformation is closely tied to microscopic instability, resulting in symmetry breaking. This intriguing phenomenon gives rise to unconventional mechanical properties in the granular crystals, paving the way for potential metamaterial application. However, no consistent approach has been reported for studying other unexplored transformable granular crystals. In this study, we present a systematic approach to identify a new set of pattern-transformable diatomic granular crystals induced by microscopic instability. After identifying the kinematic constraints for diatomic soft granular crystals, we have generated a list of feasible particle arrangements for instability-induced pattern transformation under compression. Instead of computationally intensive finite element models (FEMs) with continuum elements, we adopt a simplified mass-spring model derived from granular contact networks to efficiently evaluate these feasible particle arrangements for pattern transformation. Our numerical analysis encompasses quasi-static analysis and microscopic/macroscopic instability analyses within the framework of linear perturbation. Subsequently, the pattern transformation of the identified particle arrangements is confirmed through quasi-static analyses employing detailed finite element (FE) simulations with continuum elements. Additional numerical simulations with continuum elements reveal that the pattern transformations of particle arrangements are significantly influenced by the initial void volume and some transformed granular crystals may exhibit strong low-frequency directional phononic band-gaps, which were not observed in the initial granular crystals.

Anomalous flocking in nonpolar granular Brownian vibrators

Using Brownian vibrators, we investigated the structures and dynamics of quasi-2d granular materials, with packing fractions (ϕ) ranging from 0.111 to 0.832. Our observations revealed a remarkable large-scale flocking behavior in hard granular disk systems, encompassing four distinct phases: granular fluid, flocking fluid, poly-crystal, and crystal. Anomalous flocking emerges at ϕ = 0.317, coinciding with a peak in local density fluctuations, and ceased at ϕ = 0.713 as the system transitioned into a poly-crystal state. The poly-crystal and crystal phases resembled equilibrium hard disks, while the granular and flocking fluids differed significantly from equilibrium systems and previous experiments involving uniformly driven spheres. This disparity suggests that collective motion arises from a competition controlled by volume fraction, involving an active force and an effective attractive interaction resulting from inelastic particle collisions. Remarkably, these findings align with recent theoretical research on the flocking motion of spherical active particles without alignment mechanisms.

Integrable approximations of dispersive shock waves of the granular chain

In the present work we revisit the shock wave dynamics in a granular chain with precompression. By approximating the model by an α-Fermi–Pasta–Ulam–Tsingou chain, we leverage the connection of the latter in the strain variable formulation to two separate integrable models, one continuum, namely the KdV equation, and one discrete, namely the Toda lattice. We bring to bear the Whitham modulation theory analysis of such integrable systems and the analytical approximation of their dispersive shock waves in order to provide, through the lens of the reductive connection to the granular crystal, an approximation to the shock wave of the granular problem. A detailed numerical comparison of the original granular chain and its approximate integrable-system-based dispersive shocks proves very favorable in a wide parametric range. The gradual deviations between (approximate) theory and numerical computation, as amplitude parameters of the solution increase are quantified and discussed.

Physicochemical properties and in vitro digestibility of ginseng starches under citric acid-autoclaving treatment

In this study, the effects of citric acid-autoclaving (CA-A) treatment on physicochemical and digestive properties of the native ginseng starches were investigated. The results showed that ginseng starch exhibited a B-type crystal structure with a low onset pasting temperature of 44.23 ± 0.80 °C, but high peak viscosity and setback viscosity of 5897.34 ± 53.72 cP and 692.00 ± 32.36 cP, respectively. The granular morphology, crystal and short-range ordered structure of ginseng starches were destroyed after CA-A treatment. The more short-chain starches were produced, resulting in the ginseng starches solubility increased. In addition, autoclaving, citric acid (CA) and CA-A treatment promoted polymerization and recrystallization of starch molecules, increased the proportion of amylopectin B1, and B3 chains, and improved molecular weight and resistant starch (RS) content of ginseng starches. The most significant multi-scale structural change was induced by CA-A treatment, which reduced the relative crystallinity of ginseng starch from 28.26 ± 0.24 % to 2.75 ± 0.08 %, and increased the content of RS to 54.30 ± 0.14 %. These findings provided a better understanding of the structure and properties of Chinese ginseng starches and offered new ideas for the deep processing of ginseng foods.

Olive Pomace Oil Structuring for the Development of Healthy Puff Pastry Laminating Fats: The Effect of Chilling Storage on the Quality of Baked Products.

Developing puff pastry (PP) laminating fats (LFs) with sustainable structured olive pomace oil (OPO) could contribute to its increased valorization. This study evaluated the physicochemical stability of four OPO-based LFs or margarines and the performance of their baked PP counterparts during two months of chilling storage at 4 °C. LF samples, developed at the laboratory scale, contained 41% (LF1 and LF2) OPO and 31% (LF3 and LF4) OPO together with 10% cocoa butter when using two static initial crystallization conditions (room temperature for LF1 and LF3, freezer for LF2 and LF4) before storage. During the storage period, the proximate composition, thermal and dynamic rheological properties, firmness and spreadability, oil-binding capacity, color, and lipid oxidation of the four LF samples were examined, along with the baking performance and textural properties of the PP counterparts. The initial cooling rate had minimal significance. Cocoa butter negatively influenced post-crystallization processes occurring in OPO-based LF3 and LF4, resulting in increased hardness and reduced performance after 18 days of storage, attributed, at least partially, to a high amount of 1,3-dipalmitoyl-2-oleoyl-glycerol (POP), mainly from cocoa butter. Conversely, OPO-based LF1 and LF2 maintained their quality and were stable for two months without apparent granular crystal formation.

Evaluation of Pharmacognostical and Phytochemical Studies for the Development of Quality Control Parameters for Stem Bark of Ximenia americana Linn. (Olacaceae)

Abstract Background: Plants are extremely useful to humankind as medicine, and hence the properties of medicinal plants have to be scientifically evaluated. Aim: The aim of this study is to establish pharmacognostical and phytochemical parameters for stem bark of Ximenia americana Linn. (Olacaceae). Materials and Methods: Macroscopical, microscopical evaluation, powder microscopical studies, quantitative microscopy, physicochemical evaluation, fluorescence analysis, analysis of inorganic elements, and determination of heavy metal contamination were performed as per the World Health Organization guidelines and standard methods. To evaluate various phytoconstituents, phytochemical investigations such as preliminary phytochemical screening, high-performance thin-layer chromatography, and high-performance liquid chromatography were performed. Results: Microscopical studies showed the presence of thick cortex, periderm cells, phloem parenchyma, phloem fibers, sieve elements, prismatic and granular calcium oxalate crystals, and resinous cells. The length and width of fibers, stone cells, and diameter of starch grains were measured. Physicochemical evaluation like ash values has shown total ash – 8.01% ± 0.02% w/w, acid-insoluble ash – 1.53% ± 0.02% w/w, water-soluble ash – 1.54% ± 0.01% w/w, sulfated ash – 12.02% ± 0.07% w/w, water-soluble hot extraction – 26.48 ± 0.02% w/w, cold maceration – 11.76% ± 0.04% w/w, alcohol soluble – 15.69% ± 0.03%w/w, ether soluble – 2.06% ± 0.03% w/w, and loss on drying – 4.88% ± 0.01% w/w. Conclusion: Pharmacognostical study on the stem bark of Ximenia americana may be reported as first. The results of pharmacognostical and phytochemical studies will be helpful for authentication and provide quality control parameters for the stem bark of this plant.

Genesis and Geological Significance of Siderite in the First Member of the Nantun Formation of Dongming Sag, Hailar Basin

Multiple siderite beds developed in the first member of the Lower Cretaceous Nantun Formation (K1n1) in the basin. The results show that the siderites in K1n1 of the study area are mostly stratiform or massive, with three micromorphological features (dense micronized crystals, bands, and paragenesis with quartz and calcite). The siderite beds are mainly composed of siderite, clay, quartz, calcite, and feldspar. Under the microscope, charcoal, algal fossils, granular pyrite crystals, vein-like siliceous bands, etc., were observed. The oxides in the siderite beds include Fe2O3, SiO2, Al2O3, etc. The trace elements are typically characterized by high Mn and Be contents; low Sr/Ba, Th/U, and Al/Ti ratios; and high V/Cr ratios. These indicate weakly reducing, freshwater depositional paleoenvironments. The δ13Cv-PDB and δ18Ov-PDB values of siderite are −0.20–1.11‰ (mean: 0.62‰) and −18.22‰ to −10.14‰ (mean: −14.23‰), respectively, which shows that the carbon in siderite came mainly from carbonate dissolution. The Fe-bearing rocks in the source area migrated to the basin after undergoing physical and chemical weathering, and when the resultant Fe2+ concentration reached saturation, Fe2+ combined with CO32− in the water bodies to form authigenic siderite.

Phases and morphology of CuFeTe2 films prepared by electrodeposition

This work reports one low-priced way for the production of CuFeTe2 films on the conductive glass surface. CuFeTe2 films were prepared by electrodeposition and treatment at 220 °C for 20 h in N2 atmosphere for the first time. The effect of different deposition potentials on the CuFeTe2 phase was studied. CuFeTe2 films were prepared by electrodeposition using copper sulfate, ammonium ferrous sulfate, tellurium dioxide, and sodium citrate as raw materials. When the deposition potential is −1.0 V and the deposition time is 20 min, CuFeTe2 thin films with good phrase formation can be obtained at 25 °C. The phase of samples was characterized using x-ray diffraction (XRD). The morphology of samples was characterized via scanning electron microscopy (SEM). The crystallinity of CuFeTe2 thin films prepared under these conditions is relatively good. The microcosmic morphology of the samples is granular crystals. The lattice constants of CuFeTe2 are also calculated.

Sound characteristics of disordered granular disks: effects of contact damping

We investigate numerically the sound properties of disordered dense granular packings in two dimensions. Employing linear equations of motion and excluding contact changes from our simulations, we demonstrate time evolution of sinusoidal standing waves of granular disks. We varied the strength of normal and tangential viscous forces between the disks in contact to explore the dependence of sound characteristics such as dispersion relations, attenuation coefficients, and sound speeds on the contact damping. For small wave numbers, the dispersion relations and sound speeds of acoustic modes are quite insensitive to the damping. However, a small dip in the phase speed of the transverse mode decreases as the viscous force in normal direction increases. In addition, the dispersion relation of the rotational mode differs qualitatively from the theoretical prediction for granular crystals. Therefore, disordered configurations with energy dissipation play a prominent role in sound properties of granular materials. Furthermore, we report how attenuation coefficients depend on the contact damping and quantify how they differ from the prediction of lattice theory. These improved relations, based on our numerical results, can in future be compared to advanced theories and experiments.

Mesoscopic evolution and kinetic properties of dense granular flow crystallization under continuous shear induction

The influence of spatial structure on the kinetic response of discrete soft matter is critical. The exploration is not limited to structural evolution, jamming point, phase transition, etc. However, the mesoscopic response under continuous loading has always been difficult to make progress in experiments. In this study, we explored the mesoscopic evolution and properties of the ordered structure in dense granular flow under continuous shear by experiments and simulations. It shows that the crystal structure of the particles develops simultaneously inward from the boundary of the shearing cell. Two morphological clusters formed one after another within a 2D cylindrical layer parallel to the boundary. At the single-particle level, continuous strain is found to make the crystallization process within the cylindrical layers an evolution of chain-like polycrystalline to monocrystal structures. Compared to oscillatory shear, splicing or fusion is the way to reach the final state from the transition state under continuous shear rather than epitaxial growth. Due to continuous shear, the symmetry of the crystal switches between hexagonal close-packed (HCP) and face-centered cubic (FCC) and is dynamically balanced in the flow. We also describe the switching path. The results show that HCP in flow is more favored by the environment than FCC.

Crystallization behavior and mechanical properties of mica-diopside based glass-ceramics from granite wastes with different SiO2/MgO ratio

Mica-Diopside based glass-ceramics were generated by melting method from granite wastes. The effects of SiO2/MgO (S/M) molar ratios on crystallization behavior, microstructure and mechanical characteristics of glass-ceramics were investigated. The analysis indicated that with the increase of S/M, the glass transition temperature (Tg) increased. The higher heat treatment temperature facilitated the formation of Forsterite than Nepheline. With S/M ratio rising, diopside turned into the main crystal phase instead of Forsterite along with Tainiolite as the minor phase at 850 °C and 900 °C respectively. At 900 °C, the crystallinity of glass-ceramics dropped with S/M ratio increasing. Meanwhile, there were some columnar crystals interleaving with granular crystals, and the average size of crystals obviously decreased. After heated at 900 °C, their Vickers-hardness fell dramatically with S/M rising, while the fracture toughness increased initially followed by a decrease, reaching the largest value of 1.97 MPa·m1/2 with the S/M ratio of 2.82.

Geochemical Characterization of Laminated Crystalline Crust Travertines Formed by Ca2+-Deficient Hot Springs at Sobcha (China)

Travertines formed of crystalline crust have been widely reported, but there has not been focus on their geochemical characteristics. We therefore carefully conducted a series of geochemical investigations and U-Th dating on a travertine mound mainly composed of crystalline crust from Sobcha (southwest China) to determine their geochemical features and geological implications. The Sobcha travertines dominantly consist of granular crystals and fan crystals and show δ13C from 3.4‰ to 4.9‰ V-PDB, δ18O from −26.7‰ to −23.7‰ V-PDB, and 87Sr/86Sr from 0.712458 to 0.712951. When normalized to PASS, the Sobcha travertines exhibit MREE enrichment relative to HREE and LREE, HREE enrichment relative to LREE, and positive Eu anomalies. The δ13C signatures and mother CO2 evaluation of the Sobcha travertines show that the Sobcha travertines were thermogene travertines largely receiving mother CO2 from (upper) mantle (i.e., magmatic CO2) or a mixture of soil-derived CO2 and CO2 related to carbonate decarbonation. The 87Sr/86Sr of the Sobcha travertines is out of the 87Sr/86Sr ranges of local deposits exposed at Sobcha and surrounding areas but is well matched with the mean 87Sr/86Sr of Nadi Kangri volcanic rocks which cropped out to the northeast of the studied travertines (over 20 km away). This might indicate the important role of the Nadi Kangri volcanic rocks in suppling Sr to the studied travertines, but more studies are required. The LREE depletion compared to MREE and HREE in the Sobcha travertines was interpreted to be caused by the difference in geochemical mobility between LREEs and HREEs during water–rock interaction at depth, while the MREE enrichment compared to HREE was considered to be most likely inherited from reservoir/aquifer rocks. The positive Eu anomalies of the Sobcha travertines may result from very high reservoir temperatures and/or preferential dissolution of Eu-rich minerals/rocks (especially plagioclase). The Sobcha travertine mounds displays no or very slight vertical variations in δ13C, 87Sr/86Sr, and REE patterns, indicating the compositional stability of mother CO2 and paleo-fluids. However, a significant vertical increase in δ18O was observed and was explained as the result of gradual water temperature decrease related to climate cooling, self-closure of the vents, or mound vertical growth. The findings in this study might help us better understand the deposition of crystalline crust in Ca2+-deficient hot spring systems.

Influence of Aspect Ratio on Wave Propagation in Granular Crystals Consisting of Ellipse-Shaped Particles

The behavior of waves in granular materials is very complex and closely related to the macro-micro properties such as particle shape, packing, and particle size distribution. In this study, the influence of the aspect ratio (AR) and confining stress on wave propagation in 2D granular crystals consisting of ellipse-shaped particles is investigated based on discrete element method. The energy attenuation, wave velocity, wavefront shape, and frequency dispersion are mainly focused. The results show that the energy attenuation exhibits an increasing trend with bigger confining stress and smaller AR in the direction of wave propagation. The wave velocities increase with increasing AR, and the relation between compressive wave velocities and the confining stress and AR is obtained. Wavefront has the elliptical shape which has the same AR as elliptical particles of specimen, and its analytical expression is also obtained. The dispersion is affected by AR, which is mainly reflected in the modified particle spacing in sine fitted frequency dispersion curve. Larger confining stress allows a larger maximum frequency, and produces stronger dispersion. The above conclusion can provide a reference for wave-guided granular crystals design.

Granular crystals as strong and fully dense architectured materials

Dense topologically interlocked panels are made of well-ordered, stiff building blocks interacting mainly by frictional contact. Under mechanical loads, the deformation of the individual blocks is small, but they can slide and rotate collectively, generating high strength, toughness, impact resistance, and damage tolerance. Here, we expand this construction strategy to fully dense, 3D architectured materials made of space filling building blocks or "grains." We used mechanical vibrations to assemble 3D printed rhombic dodecahedral and truncated octahedral grains into fully dense face-centered cubicand body-centered cubic"granular crystals." Triaxial compression tests revealed that these granular crystals are up to 25 times stronger than randomly packed spheres and that after testing, the grains can be recycled into new samples with no loss of strength. They also displayed a rich set of mechanisms: nonlinear deformations, crystal plasticity reminiscent of atomistic mechanisms, geometrical hardening, cross-slip, shear-induced dilatancy, and microbuckling. A most intriguing mechanism involved a pressure-dependent "granular crystal plasticity" with interlocked slip planes that completely forbid slip along certain loading directions. We captured these phenomena using a three-length scale theoretical model which agreed well with the experiments. Once fully understood and harnessed, we envision that these mechanisms will lead to 3D architectured materials with unusual and attractive combinations of mechanical performances as well as capabilities for repair, reshaping, on-site alterations, and recycling of the building blocks. In addition, these granular crystals could serve as "model materials" to explore unusual atomic scale deformation mechanisms, for example, non-Schmid plasticity.

Development of adaptive granular metamaterials for impact mitigation

Granular crystals exhibit highly nonlinear impulse responses and are therefore excellent candidate materials for applications such as vibration absorption, impact mitigation, and shock protection. This work presents a new class of adaptive metamaterials in the form of granular crystals immersed in MR fluids which offer the unique ability to reversibly generate rheological defects at any spatial location using external magnetic fields. To demonstrate the utility and efficacy of these tunable metamaterials, a novel experimental methodology was developed to visualize the wave propagation through granular crystals immersed in opaque fluids subjected to low-speed impact loading. This experimental approach relied on a drop-tower-based setup to subject the granular crystals immersed in MR fluids to low-speed impact loading. The kinematic and strain fields in each grain at any instant during impact loading were calculated using a combination of high-speed imaging and digital image correlation. The experimental methodology was employed to illustrate the influence of “point” defects generated by using an external magnetic field on the wave propagation in granular immersed granular crystals. In this letter, a single rheological “point” defect was introduced in the center of the granular crystals using external magnetic fields of varying magnitudes, and the influence of the strength of the magnetic field on the wave dynamics was quantified. The experimental measurements demonstrated that the strength of the magnetic field has a significant influence on the wave propagation process, and it is possible to control the spatial kinetic and strain energy distribution by varying the magnetic field.

Gysinite-(La), PbLa(CO3)2(OH)⋅H2O, a new rare earth mineral of the ancylite group from the Saima alkaline complex, Liaoning Province, China

AbstractThe new mineral, gysinite-(La), with the ideal formula PbLa(CO3)2(OH)⋅H2O, has been discovered in lujavrite from the Saima alkaline complex, Liaoning Province, China. It commonly occurs as subhedral to anhedral, granular and platy crystals of 5 to 50 μm in size, in interstices or enclosed in microcline, aegirine and nepheline. Associated minerals include nepheline, aegirine, microcline, natrolite, eudialyte, lamprophyllite, bastnäsite-(Ce), parasite-(Ce), ancylite-(La), ancylite-(Ce), bobtraillite, britholite-(Ce), thorite, calcite and galena. The crystallisation of gysinite-(La) may be related to the post-magmatic carbonation event. Gysinite-(La) crystals are generally transparent, colourless, or pale yellow, with a vitreous lustre and white streak. It is brittle with an uneven fracture, and the estimated Mohs hardness is 3½ to 4. The calculated density is 5.007 g/cm3. Optically, gysinite-(La) is biaxial (–), α= 1.832(2), β= 1.849(4), γ = 1.862(5) in white light and 2Vmeas = 81.6°. The empirical formula of gysinite-(La) is (La0.93Pb0.61Nd0.23Pr0.14Sr0.04Gd0.02Sm0.01Eu0.01Ca0.01)Σ2(CO3)2(OH)1.34⋅0.66H2O, which is calculated on the basis of general formula (REExM2+2–x)(CO3)2(OH)x⋅(2–x)H2O. The strongest eight lines of its powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 5.596 (21) (011), 4.349 (100) (110), 3.732 (68) (111), 2.984 (61) (121), 2.667 (21) (031), 2.363 (48) (131), 2.090 (29) (221) and 2.028 (21) (212). Gysinite-(La) is orthorhombic, in the space group Pmcn, and unit-cell parameters refined from single-crystal X-ray diffraction data are: a = 5.0655(2) Å, b = 8.5990(3) Å, c = 7.3901(4) Å, V = 321.90(2) Å3 and Z = 2. It is a new member of the ancylite group and isostructural with gysinite-(Nd), but with La and Pb dominant in the metal cation sites in the structure.

Gardner-like crossover from variable to persistent force contacts in granular crystals.

We report experimental evidence of a Gardner-like crossover from variable to persistent force contacts in a two-dimensional bidisperse granular crystal by analyzing the variability of both particle positions and force networks formed under uniaxial compression. Starting from densities just above the freezing transition and for variable amounts of additional compression, we compare configurations to both their own initial state and to an ensemble of equivalent reinitialized states. This protocol shows that force contacts are largely undetermined when the density is below a Gardner-like crossover, after which they gradually transition to being persistent, being fully so only above the jamming point. We associate the disorder that underlies this effect with the size of the microscopic asperities of the photoelastic disks used, by analogy to other mechanisms that have been previously predicted theoretically.

Occurrence of Iron in the Minerals of Carboniferous Coal Gangue of the Pingshuo Open-pit Mine, North China

AbstractThe state of iron in coal gangue minerals is an important factor in determining the potential for value-added utilization of this solid waste; this is especially true for the coal gangue coming from the Pingshuo open-pit mine in China. The objective of the present study was to characterize the petrological, mineralogical, and chemical states of Fe in the coal gangue from the Carboniferous Taiyuan Formation. Methods used included polarizing microscopy, X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS), X-ray fluorescence, micro-Fourier-transform infrared (micro-FTIR) spectroscopy, and Mössbauer spectroscopy. The coal gangues are mudstones, silty mudstones, and pelitic siltstones, which are composed primarily of kaolinite, quartz, feldspar, pyrite, illite, and magnesite. In coal gangue, the Fe was found to occur in ferruginous minerals, in crystal-lattice substitutions, or in a colloidal state. The ferruginous minerals in the coal gangue are pyrite and marcasite, and the pyrite morphologies are framboidal, euhedral octahedral crystals, subhedral granular crystals, and irregular crystals. The results of SEM–EDS and micro-FTIR confirmed that the lattice substitution of Fe in the coal gangue minerals occurred mainly in kaolinite, resulting in two types of kaolinite: iron-containing and iron-free kaolinite. The former may be transformed from volcanic biotite and the latter from volcanic feldspar. The Mössbauer spectra of kaolinite showed intense doublets with isomer shift and quadrupole splitting values consistent with tetrahedrally coordinated Fe3+ and ocahedrally coordinated Fe2+, suggesting the presence of two types of substitution sites: (1) Fe2+ replacing Al3+ in the octahedral sheet; and (2) Fe3+ replacing Si4+ in the tetrahedral sheet. This study has important theoretical significance for the high-value utilization of coal gangue.

In situ growth of Ca-Zn-P coatings on the Zn-pretreated WE43 Mg alloy to mitigate corrosion and enhance cytocompatibility

Magnesium (Mg) alloys are potential materials for orthopedic fixation devices but rapid degradation of the materials restricts wider clinical applications. Herein, zinc-incorporated calcium phosphate (Ca-Zn-P) coatings are prepared on the Zn-pretreated WE43 Mg alloy by a hydrothermal technique under relatively stable and favorable conditions. The hydrothermal coating consists of a compact bottom layer of CaZn2(PO4)2∙2 H2O and ZnO granular crystals and a jagged upper layer of CaHPO4. The Zn coating reduces the corrosion current density of WE43 to (3.49 ± 1.60) × 10−5 A cm−2, whereas the Ca-Zn-P/Zn composite coating further reduces it by 3 orders of magnitude in the simulated body fluid (SBF). The charge transfer resistances of the Zn-coated and Ca-Zn-P/Zn-coated alloys increase by 49 and 7176 times to 835 and 1.22 × 105 Ω cm2, respectively. The 7-day immersion results reveal that the Zn coating cannot provide long-term protection to WE43 in SBF because of the formation of galvanic couples between the Zn coating and WE43. In contrast, Ca-Zn-P/Zn-coated WE43 remains intact after soaking for 7 days and furthermore, the Ca-Zn-P coating self-repairs and continues to grow despite dissolution. The compact and adherent Ca-Zn-P bottom layer plays a major role in mitigating corrosion of WE43 by hindering penetration of the aggressive medium and charge transfer of the corrosion reactions resulting in only slight corrosion of the Zn layer. Biologically, the Zn coating reduces attachment and proliferation of MC3T3-E1 pre-osteoblasts on WE43, but the composite coating fosters cell adhesion and proliferation which stems from the good biocompatibility of the hydrothermal layer and relatively stable surface conditions avoiding severe corrosion.