Mixed phase bioceramics in the CaMgSi2O6 – MoO3 system: Mechanical properties and in-vitro bioactivity

Mixed phase materials in the quasi binary diopside (CaMgSi₂O₆) – molybdite (MoO₃) system were synthesized by a precipitation method. Materials were fabricated with diopside to molybdite ratios of 1:0, 10:1, 5:1, 2:1 and 1:1. XRD, SEM and EDS results show that alongside the initial diopside phase, phases such as calcium molybdate CaMoO₄, rod-like enstatite MgSiO₃ and cristobalite SiO₂ formed as the molybdite content increased, and diopside was entirely absent at the highest molybdite content. At lower Mo content, mixed phase materials showed higher hardness and slower biodegradation in SBF relative to pristine diopside, while maintaining reasonable hydroxyapatite (HAp) formation capability. In contrast, materials with higher molybdite content exhibited lower hardness and bioactivity. The variation in the mechanical and bioactive performance could be attributed to the presence of bulk CaMoO₄, acting as a reinforcement, and rod-like MgSiO₃ with a highly porous and fragile structure. The trend of hardness is not consistent to the proportion of the component phases could be attributed to morphologies, interfaces, and densities of the samples. Both of secondary phases had poorer HAp deposition compared to pure diopside, indicating the MoO₃ addition lowered mixed phase CaMgSi₂O₆ – MoO₃ bioceramics’ ability to form Hap. The results suggest that moderate addition of molybdite to diopside would be an effective pathway towards crystalline bioceramics with enhanced performance.     

基于三种干旱指标的朝阳市干旱特征分析

旱灾具有出现频率高、持续时间长、波及范围广等特点，本文运用降水距平百分率、Z指数、SPI标准化降水指数，对朝阳地区50a（1969～2018）干旱特征进行分析。结果表明：Z指数与SPI标准化降水指标得到的朝阳地区干旱特征情况基本一致，能较好地反映出该地区的干旱特征，朝阳地区1969～2018年自然灾害频繁发生，严重干旱年份主要集中在1980、1981、1982 年，与实际相符。     

Facile high yield synthesis of MgCo2O4 and investigation of its role as anode material for lithium ion batteries

In this article, we have reported a one-step scalable synthesis of MgCo₂O₄ nanostructures as efficient anode material for Li-ion batteries and investigated the role of post-synthesis calcination temperature (400, 600 and 800 °C) on its physiochemical properties and electrochemical performances. The XRD pattern of the calcinated sample at 400 °C (MC 400) indicates a pure phase of MgCo₂O₄. However, on increasing the calcination temperature to 600 °C (MC 600), an additional phase corresponding to MgO was detected and the corresponding XRD peak intensity further increased on increasing the calcination temperature to 800 °C (MC 800 °C). This was accompanied by a morphological transformation from flake and rod-like nanostructures, to an agglomerated dense flake-like morphology. Electrochemical studies revealed that the calcination temperature plays an important role in determining the electrochemical performance of the MgCo₂O₄ as anode material. In a half cell, the MC 600 showed the best electrochemical performance with high discharge capacity of 980 mA h g⁻¹ (2nd discharge at 60 mA g⁻¹) and a reversible discharge capacity of 886 mA h g⁻¹ at the end of 50 cycles with high coulombic efficiency of 98%. Long term stability was carried out at 0.5C which showed a capacity retention of 358 mA h g⁻¹ at the end of 500 cycles. The superior electrochemical performance of the MC600 can be attributed to the presence of the small amount of MgO, which is believed to provide the anode materials better structural stability during cycling. The claim was further supported by ex-situ TEM analysis of the anode material of a cycled cell (50 cycles).     

Formation mechanism of hydride precipitation in commercially pure titanium

Since titanium has high affinity for hydrogen and reacts reversibly with hydrogen,the precipitation of titanium hydrides in titanium and its alloys cannot be ignored.Two most common hydride precipitates in α-Ti matrix are γ-hydride and δ-hydride,however their mechanisms for precipitation are still unclear.In the present study,we find that both γ-hydride and δ-hydride phases with different specific orienta-tions were randomly precipitated in the as-received hot forged commercially pure Ti.In addition,a large amount of the titanium hydrides can be introduced into Ti matrix with selective precipitation by using electrochemical treatment.Cs-corrected scanning transmission electron microscopy is used to study the precipitation mechanisms of the two hydrides.It is revealed that the γ-hydride and δ-hydride precipita-tions are both formed through slip + shuffle mechanisms involving a unit of two layers of titanium atoms,but the difference is that the γ-hydride is formed by prismatic slip corresponding to hydrogen occupy-ing the octahedral sites of α-Ti,while the δ-hydride is formed by basal slip corresponding to hydrogen occupying the tetrahedral sites of cα-Ti.     

Soft-Magnetic High-Entropy AlCoFeMnNi Alloys with Dual-Phase Microstructures Induced by Annealing

The simultaneous enhancement of magnetic and mechanical properties is desirable but challenging for soft-magnetic materials.A fabrication strategy to meet this requirement is therefore in high demand.Herein,bulk equiatomic dual-phase AlCoFeMnNi high-entropy alloys were fabricated via a magnetic levitation induction melting and casting process followed by annealing at 700-1000℃,and their microstructures as well as mechanical and magnetic properties were investigated.The as-cast alloy possessed a single metastable B2-ordered solid solution that decomposed upon annealing into a dual-phase structure comprising an Al-and Ni-rich body-centered cubic(BCC) matrix and Fe-and Mn-rich face-centered cubic(FCC)precipitates both in the grain interior and along the grain boundaries.The magnetic and mechanical properties were closely related to the relative volume fraction of FCC in the alloy.The FCC volume fraction could be increased by increasing the annealing temperature,thereby offering tunable properties.The optimal annealing temperature for balanced magnetic and mechanical properties was found to be 800℃.The alloy annealed at this temperature had an average BCC grain size of 12±3μm and FCC volume fraction of 41±4%.Correspondingly,the s aturation magnetization and coercivity reached 82.57 Am~2/kg and 433 A/m,respectively.The compressive yield strength and fracture strength were 1022 and 2539 MPa,respectively,and the plasticity was 33%.Owing to its adjustable microstructure and properties,the AlCoFeMnNi alloy has potential for use as a multi-functional soft-magnetic material.     

Synthesis conditions effect on the of photocatalytic properties of MnWO4 for hydrogen production by water splitting

This work aims to study the synthesis conditions effect on the photocatalytic properties of manganese tungstate (MnWO₄) for H₂ production by the water splitting reaction under visible light irradiation. This is achieved by relating the materials characterization and photocatalytic evaluation of MnWO₄ at different synthesis conditions. MnWO₄ was synthesized through a precipitation reaction between Mn²⁺ and (WO₄)^2- ionic species, while adding oleic acid (OA) as surfactant at two concentrations (0.1% and 1% V) and using three different stirring methods: magnetic stirring (AM), ultrasound (US) and high-shear stirring (UT). Characterization was carried out by TGA, XRD, BET surface area, UV–Vis spectroscopy and FESEM. XRD patterns confirm the wolframite structure of MnWO₄. BET surface area increased by using UT stirring. UV–Vis spectroscopy results revealed indirect transition Eg values of ≈2 eV, favorable for the MnWO₄ photoactivation under visible light irradiation. During the photocatalytic evaluation, sample 1%-UT produced the highest H₂ amount among all samples with a value of 72 μmolH₂g⁻¹, which was far higher compared to WO₃, which was taken as a reference photocatalyst.     

Microstructural evolution and corresponding property changes after deep cryotreatment of tool steel

The microstructural evolution and structure–property correlation subjected to deep cryotreatment of tool steel were studied. The results show that the retained austenite continues to transform into martensite almost but not complete at low temperature. The topography of retained austenite exhibits as a nanoscale thin film with a thickness range of 20–60?nm between the martensite laths. The changes of internal friction peaks have been explained well by the coupling model, which indicates that deep cryotreatment is not only removing retained austenite but also promoting the interstitial carbon atoms segregated to nearby dislocations under the shrinking strain energy. In addition, more carbides precipitated from the matrix during tempering in cryotreated samples and were verified by analyses of transmission electron microscopy.     

Effect of Mn doping on hydrolysis of low-temperature synthesized metastable alpha-tricalcium phosphate

In the present work, effect of Mn doping on hydrolysis rate of low-temperature synthesized metastable α-tricalcium phosphate (α-TCP) was investigated. α-TCP powders containing different amount of Mn²⁺ ions (0, 0.5 and 1 mol%) were synthesized by wet co-precipitation process, followed by annealing and crystallization of as-precipitated amorphous calcium phosphate at 700 °C. It was demonstrated that the presence of Mn²⁺ ions significantly retards hydrolysis rate of α-TCP. While pristine α-TCP fully hydrolyzed with a conversion to calcium-deficient hydroxyapatite in 10 h, complete hydrolysis of α-TCP doped with 0.5 and 1 mol% of Mn occurred only after 20 and 35 h, respectively. Initial and final products were characterized by X-ray diffraction (XRD) analysis, infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Chemical composition of starting and fully hydrolyzed α-TCP powders was determined by inductively coupled plasma optical emission spectrometry (ICP-OES).     

Investigation of precipitation selectivity and particle size concentration dependences in supercritical antisolvent method via online supercritical fluid chromatography

Supercritical antisolvent (SAS) precipitation technique, although being versatile and ecologically friendly, suffers from the lack of convenient methods for necessary thermodynamic parameters measurement. Recently we have proposed a method for solubility measurement in binary fluids based on an online hyphenation of supercritical antisolvent method and supercritical fluid chromatography (SAS-SFC). In this paper, we demonstrate the applicability of this method to the investigation of both selective precipitation from solution and particle size tuning in SAS using lower dicarboxylic acids as model objects. Measured solubility values adequately reflect selective crystallization from solution. SAS precipitation was observed only for those components, which concentration was above solubility in CO₂-solvent mixture as predicted by SAS-SFC method. Also, concentration dependences of particle size plotted in supersaturation coordinates instead of direct concentration in initial solution give additional insight into crystallization behaviour in SAS.