Structural (in)stability and spontaneous cracking of Li-La-zirconate cubic garnet upon exposure to ambient atmosphere

Among the Li-ion conducting inorganic materials, lithium lanthanum zirconate (LLZO) is believed to possess good chemical stability against Li metal and hence considered to be a promising solid electrolyte for Li-ion batteries. However, systematic sets of studies conducted here at regular intervals during storage of Al-doped LLZO (cubic garnet) sintered pellets in ambient atmosphere have raised serious concerns over their structural/mechanical stability/integrity upon exposure to air. Spontaneous cracking/disintegration/pulverization of LLZO pellets takes place after about three weeks of exposure, primarily due to formation of La₂Zr₂O₇ in the LLZO bulk; as found to be thermodynamically feasible at room temperature upon reaction with CO₂/moisture. Steep increase in La₂Zr₂O₇ content coincides with the spontaneous cracking/disintegration. Estimation suggests that internal stresses associated with the formation of La₂Zr₂O₇ from LLZO can be high enough to cause spontaneous fracture. This mandates the development/fabrication/usage of solid-state cells using LLZO under stringent controls against exposure to atmospheric species.     

An efficient solid phase extraction of Pb2+ using tannic acid-coated cerium oxide nanoparticles followed by electrothermal atomic absorption spectrometry

Cerium oxide-Tannic acid (CeO₂-TA) nanocomposite were used for preconcentration of Pb²⁺ followed by electrothermal atomic absorption spectrometry. Cerium oxide nanoparticles were synthesized by microwave method and modified by tannic acid to produce CeO₂-TA nanocomposite. In order to optimize the experimental conditions, Response surface methodology based on central composite design was used. The obtained results show that the calibration curve was linear in the range of 0.025–1.5 µg L^?1 Pb²⁺. Also, the accuracy of the method was validated by the analysis of certified referenced material. Finally, the proposed method was applied for determination of Pb²⁺ in different real samples.     

钢渣的膨胀相及其对水泥体积稳定性的影响

借助XRD、DTG和SEM分析了钢渣中石灰相和RO相的结构形态、化学组成和水化条件,并讨论了二者与水泥体积稳定性的关系。分析结果表明：石灰相和RO相与水反应的总体能力偏低,且二者的微晶与水反应的能力有强有弱,具有不均一性;石灰相在沸煮条件下就可以水化,RO相在压蒸条件下才能水化,因此,石灰相是影响水泥的沸煮安定性和压蒸安定性的主要原因,RO相只影响水泥的压蒸安定性,且不是引起水泥压蒸安定性不良的主要原因;钢渣水泥的体积安定性不仅与钢渣中石灰相和RO相的化学组成有关,而且还和钢渣的掺量有关。     

Recover of C3N4 nanoparticles under high-pressure by shock wave loading

Theory predicts that β-C₃N₄ with its dense structure is a superhard material. In order to synthesize this material, light-gas gun loading and shock recovery technology were used to perform experiments. The amorphous nitrogen-enriched g-C3N4, produced by the thermal decomposition of melamine, was used as a precursor. The shock synthesis experiment was completed under the pressure of 50?GPa. A high-density phase with a β-C₃N₄ structure was detected only in the desired product. It is suspected that the elemental composition and synthetic pressure of precursors may be the main factors affecting the phase composition of products. This has significant potential for the synthesis of pure superhard carbonitride compounds.     

Shock compressibility and shock-induced phase transitions of C60 fullerite

Shock compressibility of C₆₀ fullerite and sound velocities in shock-compressed fullerite were experimentally studied at the pressures range up to 50 GPa. In our experiments, we used polycrystalline C₆₀ specimens with a density of 1.64 g/cc. The Hugoniot of C₆₀ fullerite had a set of peculiarities, which may be attributed to a series of polymorphic phase transitions. The jump of sound velocity in shocked C₆₀ at pressure 9 GPa indicates the formation of a rather hard carbon phase. It is possible to assume that it is a polymerized C₆₀ phase. In the region of pressures 9–25 GPa, destruction of this phase and formation of a graphite-like carbon occurs. With further growth of shock pressure, phase transition of the graphite-like carbon to a diamond-like phase is observed with a transition onset pressure 25 GPa. If shock pressures are higher than 33 GPa, Hugoniot of C₆₀ fullerite is determined by the thermodynamic properties of the diamond-like phase.     

High temperature crystallographic and low temperature magnetic phase transitions in Fe doped Sr2RuMnO6

Fe doped Sr₂RuMnO₆ (SRMO) double perovskites (Sr₂RuMn_1-xFe_xO₆, x = 0, 0.1, 0.2 and 0.3) were prepared by solid-state route. Both x-ray diffraction and Raman spectroscopy were performed to investigate the crystal structure of the synthesized double perovskites. Rietveld refinement of the x-ray diffraction patterns confirmed a phase transition from tetragonal to cubic space group as a function of doping concentration of iron. Raman spectroscopy at room temperature and group theory analysis revealed the phonon modes associated with the space group of the samples. The temperature dependent Raman spectroscopy showed an anharmonic behaviour of the phonon modes of the Fe doped SRMO samples. The temperature evolution of the phononic modes in the range of 300 K–620 K is predominantly influenced by the lattice degrees of freedom. The presence of several oxidation states Mn (2⁺, 3⁺ and 4⁺) and Fe (3⁺ and 4⁺) was confirmed by an X-ray photoemission spectroscopy analysis of the highest doped sample (x = 0.3). The magnetic properties measurements showed that the samples were completely paramagnetic at room temperature. The samples exhibit antiferromagnetism at very low temperatures and we conclude that they exhibit ferrimagnetic ground state in the mid temperature region.     

无机盐对乳状液稳定性和转相的影响

在进行化学驱油尤其是表面活性剂驱油的过程中,油藏地层水中含有的无机盐离子会对表面活性剂的乳化等性能产生影响。使用0.4%（质量分数）的十二烷基苯磺酸钠（SDBS）作为乳化剂与原油制备了水包油型乳状液,通过向SDBS溶液中加入不同浓度的共13种无机盐,考察了这些无机盐对水包油型乳状液稳定性和转相的影响。实验结果表明：钠盐和钾盐均存在最佳盐质量浓度,在此质量浓度下乳状液稳定性增强,没有引发乳状液转相;二价和三价无机盐不利于乳状液的稳定,其引发乳状液发生转相的能力依次为氧化铝＞氯化铁＞氯化钡＞氯化锶＞氯化钙＞氯化镁;处于最佳盐质量浓度时,弱碱性钠盐可与SDBS产生协同效应,有利于乳状液的稳定。     

Assessment of thermodynamic stability of sapphire in eutectic molten chloride environment

The continued development of molten salt reactors and concentrated solar power plants requires highly efficient and stable instruments that can efficiently monitor the chemical conditions of the molten salt during long-term operation in both the fuel and coolant/heat transfer fluid loops. Sapphire (Al₂O₃) fibers have shown tremendous potential due to inherent radiation resistance and a broader operational range of temperature. In this work, computational thermodynamic modeling (CALPHAD) using the ThermoCalc software in conjunction with the SGTE (Scientific Group Thermodata Europe) Molten Salts (SALT1) and Pure Substances (Pure5) databases is applied to understand the compatibility of Al₂O₃ fibers with NaCl-MgCl₂ eutectic molten salt in the temperature range of 1500–2500 K. The thermodynamic calculations show that sapphire fibers are not expected to be stable over the long-term when exposed to molten chloride salts at these temperatures. To improve the stability of these diagnostic fibers in molten salt environments, various pure metallic elements were evaluated as potential cladding materials for Al₂O₃ fibers. Based on the thermodynamic analysis, molybdenum (Mo) and nickel (Ni) could be effective cladding materials to enhance the stability of Al₂O₃ in NaCl-MgCl₂ chloride salt molten bath in the desired temperature range. Thus, the presence of Mo and Ni cladding can provide a protective coating against the corrosive molten salts, thus improving the stability of Al₂O₃. Additionally, it is also shown that Al₂O₃ remains stable up to 2400 K in the presence of preexisting Al₂MgO₄ and Al₂NiO₄ in the eutectic molten chloride bath environment.     

乙醇酸酯对甲醇汽油体系相稳定性及蒸发性的影响

合成了系列乙醇酸酯,考察其对不同甲醇汽油无水体系的相稳定性以及蒸发性的影响规律,并对不同碳链乙醇酸酯的影响效果进行了考察。结果显示:对于不同比例的甲醇汽油体系,乙醇酸酯类助剂均具有良好的相稳定作用;随着乙醇酸酯中碳原子数的增加,其相稳定温度降低,相稳定效果增强,助溶效果增加。乙醇酸酯的加量增大,其体系的饱和蒸气压先减小后略有增大。其中乙醇酸甲酯的量增加,甲醇汽油M15体系饱和蒸气压呈现减小的趋势。随着乙醇酸酯中碳链的增长,甲醇汽油体系饱和蒸气压的降低效果增强;碳链继续增长,乙醇酸庚酯、乙醇酸辛酯、乙醇酸癸酯呈现出特殊性,对体系饱和蒸气压的降低效果减弱。     

Enhancing temperature stability in potassium-sodium niobate ceramics through phase boundary and composition design

Phase boundaries and composition design were explored to achieve both high piezoelectricity and favorable temperature stability in potassium-sodium niobate ceramics, using (1-x)(K,Na)(Nb,Sb)O₃-xBi(Na,K)(Zr,Sn,Hf)O₃ ceramics. A rhombohedral-tetragonal (R-T) phase boundary was constructed at x=0.035–0.04 by co-doping with Sb⁵⁺ and Bi(Na,K)(Zr,Sn,Hf)O₃. More importantly, a superior temperature stability was observed in the ceramics with x=0.035, accompanying with a stable unipolar strain at room temperature to 100 °C. The ceramics with x=0.035 also exhibited improved piezoelectric properties (e.g., piezoelectric coefficient d₃₃∼465 pC/N and electromechanical coupling factor k_p=0.47) and Curie temperature (T_c∼240 °C). The Rietveld refinement and in-situ temperature-dependent piezoresponse force microscopy (PFM) results indicated that the enhancement of the piezoelectric properties was caused by the easy domain switching, high tetragonal fraction, and tetragonality, while the improved temperature stability mainly originated from the stable domain structures.     

Superior phase stability of high entropy oxide ceramic in a wide temperature range

A high entropy fluorite oxide (Hf_0.2Zr_0.2Ce_0.2Y_0.2Yb_0.2)O_2-δ (HEFO) was investigated to reveal its ultra-wide-temperature phase stability in air. The HEFO exhibited a single-phase fluorite structure, and its lattice constant, a, was evaluated to be 0.527 ± 0.02 nm from room temperature (RT) to > 2573 K. No precipitation of single-component oxides, such as HfO₂, ZrO₂, Y₂O₃ and CeO₂, was experimentally observed. Since both Gibbs free energy (G) change of possible precipitation reactions and the second derivative of G_HEFO with respect to all single-component oxides were positive, the HEFO exhibits no precipitation and decomposition at temperatures above 1700 K. The sluggish dynamics, which was verified by a long-term annealing experiment at 1473 K for 175 h showing a few Yb₂O₃ precipitation, contributed to the single-phase solution nature of HEFO below 1700 K. Such a superior phase stability in ultrawide temperature range help accelerate the engineering application of HEFO to be thermal structural components.     

Effects of Re addition on phase stability and mechanical properties of hexagonal OsB2

ReB₂‐type hexagonal Osmium diboride (OsB₂) has been predicted to exhibit higher hardness than its orthorhombic phase, but hexagonal‐orthorhombic phase transformation occurs at temperature higher than 600°C, resulting in the decrease in its hardness. Therefore, ReB₂‐type hexagonal OsB₂ samples with Re addition were produced by a combination of mechanochemical method and pressureless sintering technique, and the effects of Rhenium (Re) addition on phase composition, thermal stability and mechanical properties of OsB₂ were investigated in this study. X‐ray diffraction (XRD) analysis of the as‐synthesized powders by high‐energy ball milling indicates the formation of hexagonal Os_1‐xRe_xB₂ solid solution with Re concentration of 5 and 10 at.% without forming a second phase. After being sintered at 1700°C, part of the hexagonal phase in OsB₂ transformed to orthorhombic structure, while Os_0.95Re_0.05B₂ and Os_0.9Re_0.1B₂ maintained their hexagonal structure. This suggests that the thermal stability of the hexagonal OsB₂ was significantly improved with the addition of Re. Scanning electron microscopy (SEM) photographs show that all of the as‐sintered samples exhibit a homogeneous microstructure with some pores and cracks formed throughout the samples with the relative density >90%. The measurements of micro‐hardness, nano‐hardness, and Young's modulus of the OsB₂ increased with Re addition, and these properties of the sample with 5 at.% addition of Re is higher than that with 10 at.% Re.     

提高水相法氯化聚乙烯弹性体热稳定性的实验

对水相法氯化聚乙烯(CPE)弹性体的氯化浆料进行了实验室研究,找出了导致CPE弹性体热稳定性较差、热分解温度偏低的原因,通过改造使CPE的热分解温度稳定在170℃以上。     

空调用纳米有机复合相变蓄冷材料分散稳定性

纳米材料在有机相变蓄能材料中的分散稳定性对其整体性能的保持具有决定性作用.本文将具有高导热性的纳米材料(MWNTs、Al₂O₃、Fe₂O₃)添加到热导率较低的空调用有机相变材料(质量比为73.7:26.3的辛酸/肉豆蔻醇)中,制备了纳米复合蓄冷材料;利用测量热导率的高低来间接反映分散稳定性的好坏,研究了分散剂种类、分散剂浓度和超声分散时间对纳米复合有机相变材料分散稳定性的影响.实验证明:分散剂十二烷基苯磺酸钠(SDBS)对纳米复合材料的分散稳定效果最好;当添加的分散剂SDBS与不同纳米材料MWNTs、Al₂O₃和Fe₂O₃质量比分别为2:1、3:1和3:1时,所对应的分散稳定性能最好;超声分散时间为90min时纳米复合材料的分散稳定性能最优.为获得性能良好、稳定的纳米有机复合材料提供了新的评价方法和指导.     

Meticulously tailoring phase boundary in KNN-based ceramics to enhance piezoelectricity and temperature stability

Although KNN-based ceramics with high electrical properties are obtained through a variety of strategies, the temperature sensitivity is still one of the key technical bottlenecks hindering practical applications. Here, we use a new strategy, meticulously tailoring phase boundary, to refine the ferroelectric boundary of KNN-based ceramics, leading to high piezoelectricity companied with improving temperature stability. The highest d₃₃ value in this system reaches 501 pC/N with a T_C ∼ 240°C, whereas a large strain of ∼0.134% can be kept with 10% lower deterioration until 100°C. The origin of high piezoelectricity is mainly attributed to the well-preserved multiphase coexistence and the appearance of nanodomains, which greatly facilitate the polarization rotation. Instead of the changed intrinsic thermal insensitivity, the precision phase boundary engineering plays an important role in strengthening the temperature stability of electric-induced strain. This work provides a simple and effective method to obtain both high electrical properties and excellent thermal stability in KNN-based ceramics, which is expected to promote the practical applications in the future.     

含钙三元氯化物体系相图计算与熔盐热稳定性

为寻求太阳能热利用高温传热储热材料,以盐湖资源为原料,提出分支/分区相图计算方法,设计NaCl-CaCl₂-KCl和KCl-CaCl₂-MgCl₂熔盐传热储热材料。基于正规溶液模型,以不同分支不同相互作用系数,计算了5个边界体系相图,实现用正规溶液模型计算含化合物体系复杂相图。含化合物KCl-CaCl₂和KCl-MgCl₂体系及3个不含化合物二元体系的计算相图与实验相图十分吻合。以分区域方法计算三元体系相图,预测出5个低共熔点来指导熔盐制备。采用差示扫描量热法测试并验证熔盐最低共熔点,确定其工作温度下限;以质量损失实验,确定其工作温度上限。结果表明,钠钾钙和钾镁钙氯化物熔盐能在550~850℃和480~700℃内稳定运行,可用作高温传热储热流体。     

Composition-driven broad phase boundary for optimizing properties and stability in lead-free barium titanate ceramics

A new piezoelectric system of (1−x−y)BaTiO₃-yCaZrO₃-xBaSnO₃ (BT-yCZ-xBS) was designed to achieve enhanced piezoelectric/strain properties and temperature stability. First, the relationships between composition, phase, and electrical properties are systematically investigated. The broad phase boundary with successive rhombohedral-orthorhombic (R-O) and orthorhombic-tetragonal (O-T) was obtained in 0.04 ≤ x ≤ 0.05 and 0.04 ≤ y ≤ 0.07 by tailoring the relationship of composition and phase structure, confirmed by X-ray diffraction, temperature-dependent dielectric constants, and Raman spectra. The optimized piezoelectric coefficient of d₃₃ = 560 pC/N, high strain of >0.20%, and large converse piezoelectric coefficient of d₃₃* = 1170 pm/V were realized. Second, the optimized piezoelectricity both demonstrate a stable performance with fluctuation <8% for d₃₃* and 20% for d₃₃ between 22 and 60°C since the broad phase boundary is exhibited in this temperature range. We believe that this work is a successful example to optimize piezoelectric properties and enhance the stability for piezoceramics.     

Investigation into the phase structures and temperature stability of BiScO3-PbTiO3-based piezoelectric ceramics

Phase structure has a strong influence on the temperature stability of ceramics; however, their influence on BiScO₃-xPbTiO₃ has been neglected. To meet the requirements for practical applications, (0.98-x)BiScO₃-xPbTiO₃-0.02Bi(Sn_1/3Nb_2/3)O₃ (BS-xPT-BSN, 0.59 ≤ x ≤ 0.65) polycrystalline ferroelectrics with rhombohedral phase, morphotropic phase boundary (Cm and P4mm coexisting), and tetragonal phase has been prepared and studied. The relationship between the phase structures and temperature stability is established from the macro properties as well as the underlying domain behaviors. The results show that the tetragonal phase is not sensitive to temperature because of its stable domains, which is a positive motivator for improving the temperature stability of ceramics. This work provides a new strategy for the design of high-temperature piezoelectric ceramics in the future.     

High thermal stability in PLZST anti-ferroelectric energy storage ceramics with the coexistence of tetragonal and orthorhombic phase

The orthorhombic phase Pb_0.97La_0.02(Zr_0.93Sn_0.05Ti_0.02)O₃ (PLZST) and the tetragonal phase (Pb_0.93Ba_0.04La_0.02)(Zr_0.65Sn_0.3Ti_0.05)O₃ (PBLZST) were composited by the conventional solid state method to acquire high energy storage density and high thermal stability. X-ray diffraction spectra revealed the coexistence of orthorhombic and tetragonal structure, indicating that the ceramics were successfully composited. The component ratio of PLZST/PBLZST significantly influenced the thermal stability as well as the energy storage density due to the opposite energy storage performance-temperature trend of PLZST and PBLZST. The phase composition, microstructure and electric properties were discussed to explain the performance in the ceramic composites. High energy storage density of 3.20?±?0.02?J/cm³ at 20?°C with a variation <15% over a temperature range from 20?°C to 150?°C were found in the ceramic composite with a PLZST/PBLZST ratio of 55:45. This work provide an effective method to broaden applications of energy storage ceramics in high temperature.     

Optimized piezoelectric properties and temperature stability in PSN-PMN-PT by adjusting the phase structure and grain size

For relaxor ferroelectric materials, improving the piezoelectric properties and temperature stability simultaneously is still a great challenge up to now. In this work, the structure, electric properties, and thermal stability of xPSN-(1 − x)PMN-0.4PT (x = 0.15, 0.29, 0.43, and 0.5) ceramics were studied systematically by experiment and phase field simulation. A high Curie temperature T_c of 255℃ and good longitudinal electricmechanical coupling factor k₃₃ of 0.75 and piezoelectric constant d₃₃ of 650 pC/N are achieved in x = 0.43 ceramics with monoclinic C and tetragonal phases coexistence at room temperature. At 30℃, this composition ceramics sintered at 1260℃ shows the remnant polarization P_r and coercive field E_c are about 36.8 µC/cm² and 8.2 kV/cm respectively. Moreover, as the temperature increases to 150℃, these values remain as high as 22.6 µC/cm² and 5.7 kV/cm. In the temperature range of 30–230℃, the variation of k₃₃ and d₃₃ is about 24% and 25%. These high piezoelectric performance and superior temperature stability are related to the more complex domain structures caused by phase coexistence and larger grains with more stable domain structure due to internal stress. The former is beneficial in improving the piezoelectric properties, and the latter dominates the enhanced temperature stability.