Effects of temperature on fracture behavior of Al-based in-situ composites reinforced with Mg_2Si and Si particles fabricated by centrifugal casting

An aluminum-based in-situ composites reinforced with Mg2Si and Si particles were produced by centrifugal casting A1-20Si-5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on fracture behavior of the composite were investigated. The results show that the average fraction of primary Si and Mg2Si particles in the composites is as high as 38%, and ultimate tensile strengths （UTS） of the composites first increase then decrease with the increase of test temperature. Microstructures of broken specimens show that both the particle fracture and the interface debonding affect the fracture behavior of the composites, and the interface debonding becomes the dominant fracture mechanism with increasing test temperature. Comparative results indicate that rich particles in the composites and excellent interface strength play great roles in enhancing tensile property by preventing the movement of dislocations.

In-situ Formation of MgAl_(2)O_(4):A Method of Tailoring Microstructure and Properties for Development of High-performance Refractories

The in-situ formation mechanism of MgAl_(2)O_(4) was introduced,focusing on the formation process by solid phase reaction and gas phase reaction as well as the phenomenon of secondary spinelization.The influencing factors of the in-situ MgAl_(2)O_(4) formation and its effect on the microstructure and the properties of materials were systematically summarized for the Al2O3-MgO-MgAl_(2)O_(4) system and the carbon-containing refractories systems.It was pointed out that the in-situ formation of MgAl_(2)O_(4),including secondary spinelization,can regulate the microstructure and the service performance of materials.Its expansion effect can not only offset the shrinkage caused by sintering to improve the corrosion resistance of refractories,but also seriously restrict the reliability of functional refractories.The composition,the particle size,the atmosphere,and the temperature are important factors affecting the in-situ formation of MgAl_(2)O_(4).In the carbon-containing materials systems,the solid-solid reaction and the gas-solid reaction coexist to produce MgAl_(2)O_(4),which provides an effective way to further regulate the microstructure and the properties of materials through the reaction process.

In-situ ultrasonic calibrations of pressure and temperature in a hinge-type double-stage cubic large volume press

Here,simultaneous in-situ calibration of pressures and temperatures was performed in a hinge-type second-stage cubic large volume press(LVP)up to 15 GPa and 1400 K by an acoustic travel-time approach.Based on the recently reported P-tSand P-T-tP-tSequations for Al2O3buffer rod,the cell pressures and temperatures in the chamber of LVP were insitu determined,in comparison with those by conventional off-line(or fixed-points)pressure calibration method and direct thermocouple measurement,respectively.It is found that the cell pressures of the LVP chamber are significantly reduced after annealing at simultaneous high pressures and high temperatures,owing to the stress relaxation as accumulate in the LVP chamber.This acoustic travel-time method is verified to be a good way for precise determination of thermal(cell)pressures at high temperature conditions,and is of great importance and necessity to conduct in-situ physical property measurements under extreme high P-T conditions,especially when the precious synchrotron x-ray/neutron diffraction beams are not available.

High temperature X-ray diffraction study of the formation of Na_(2)Ti_(3)O_(7) from a mixture of sodium carbonate and titanium oxide

Na2Ti3O7 has attracted much attention in the field of anode materials for Na-ion batteries thanks to its non-toxicity and very low working potential of 0.3 V vs Na0/Na+.Building a clearer picture of its formation from cheap Na_(2)CO_(3) and TiO_(2) starting materials is therefore of obvious interest.Here,we report new insights from an in-situ high temperature X-ray diffraction study conducted from room temperature to 800°C,complemented by ex-situ characterizations.We were thereby able to position the previously reported Na_(4)Ti_(5)O_(12) and Na_(2)Ti_(6)O_(13) intermediate phases in a reaction scheme involving three successive steps and temperature ranges.Shifts and/or broadening of a subset of the Na_(2)Ti_(6)O_(13) reflections suggested a combination of intra-layer disorder with the well-established ordering of successive layers.This in-situ study was carried out on reproducible mixtures of Na_(2)CO_(3) and TiO_(2) in 1:3 molar ratio prepared by spraydrying of mixed aqueous suspensions.Single-phase Na_(2)Ti_(3)O_(7) was obtained after only 8 h at 800°C in air,instead of a minimum of 20 h for a conventional solid-state route using the same precursors.Microstructure analysis revealed~15 mm diameter granules made up from rectangular rods of a fewmm length presenting electrochemical properties in line with expectations.In the absence of grinding or formation of intimate composites with conductive carbon,the specific capacity of 137 m Ah/g at C/5 decreased at higher rates.

In situ high temperature X-ray diffraction studies of ZnO thin film

An epitaxial ZnO thin film was entirely fabricated by pulsed laser deposition. Both the orientation and the size of the crystallites were studied. The X-ray diffraction （XRD） patterns of the film show strong c-axis oriented crystal structure with preferred （002） orientation. The Phi-sca~ XRD pattern confirms that the epitaxiM ZnO exhibits a single- domain wurtzite structure with hexagonal symmetry. In situ high-temperature XRD studies of ZnO thin film show that the crystallite size increases with increasing temperature, and （002） peaks shift systematically toward lower 20 values due to the change of lattice parameters. The lattice parameters show linear increase in their values with increasing temperature.

High temperature mechanical properties of low carbon silicon-bearing steel by twin-roll strip casting

The tensile equipment of the advanced confocal scanning laser microscope （CSLM） was used to research the high temperature mechanical properties of low carbon silicon-bearing steel by twin-roll strip casting. The results show that, at the strain rate of 0. 000 5 s ^-1, the strip clearly shows signs of brittleness at around 600 ℃ and its plasticity falls considerably between 750 ℃ and 600 ℃. This is because during the transformation from austenite to ferrite, the low strength ferrite at the austenite grain boundaries greatly reduces the steel＇ s high temperature plasticity. The subsequent strip coiling process should be controlled at less than the brittle temperature of approximately 600 ℃, so cracks at the coiling stage can be prevented.

A high-pressure study of Cr3C2 by XRD and DFT

The equation of state(EOS)of Cr3C2 at high pressure is studied by the synchrotron radiation x-ray diffraction(XRD)in a diamond anvil cell(DAC)at ambient temperature,and density functional theory(DFT).The XRD analysis shows that the orthorhombic structure is maintained to a maximum pressure of 44.5 GPa.The XRD data show that the bulk modulus is K0=292(18)GPa with K0'=3.25(0.85).In addition,the high-pressure compression behavior of Cr3C2 is studied by first principles calculations.The obtained bulk modulus of Cr3C2 is 323(1)GPa.

蓝宝石高温弹性模量的理论计算和实验测量

蓝宝石因其良好的透光性和高温稳定性而成为光纤式高温压力传感器的理想结构材料。蓝宝石在高温下弹性模量的变化与其高温压力测量的准确性密切相关,因此获取高温条件下蓝宝石的弹性模量是设计和制备高温压力传感器的必要前提条件。基于高温原位XRD测试得到不同温度下蓝宝石的晶胞参数,然后利用第一性原理对蓝宝石的弹性性能进行了理论计算,得到蓝宝石高温情况下的弹性刚度矩阵和柔度矩阵。同时基于脉冲激振法,测量了室温至1200℃范围内不同取向蓝宝石样品的弹性模量,验证了理论计算结果的准确性。理论计算及实验结果均表明:随着温度的升高,蓝宝石的弹性模量减小,并且不同晶向之间存在显著差异。所获取蓝宝石的高温弹性模量数据可为相关高温压力传感器的设计提供基础数据参考。

高温热处理木材的FTIR和XRD分析

该文采用傅立叶变换红外光谱(FTIR)仪和X射线衍射(XRD)仪较系统地研究了高温热处理对马尾松木材FTIR和XRD特征的影响规律。结果表明:随着热处理温度的升高和处理时间的延长,木材红外吸收光谱中羟基吸收峰的强度明显降低,羰基吸收峰的强度略呈降低趋势,有利于木材尺寸稳定性的增加;在160~220℃的热处理范围内,马尾松木材纤维素结晶度随着温度的增加呈现出先增加、后减小、再增加的变化规律;当热处理温度为200℃时,随着时间的延长,马尾松木材的结晶度整体呈现降低趋势,但处理时间为2 h时,木材的结晶度略有增加;除220℃热处理4 h外,其他高温热处理工艺对马尾松木材纤维素结晶区宽度的影响不明显,其变化幅度均在3%以内。

Cu纳米线的高温原位加热XRD研究

采用电化学沉积方法,在孔径约50nm的阳极氧化铝模板中生长Cu纳米线,经过高温原位加热XRD实验,证实了其热膨胀系数约2.6×10-5K-1,稍大于块体Cu,与文献中Cu纳米线近似为零的热膨胀系数有明显的区别。对这一现象进行了简要的讨论后得出结论认为:基于模板生长的Cu纳米线,其晶格完整程度是决定热膨胀的重要因素。

MC尼龙6/纳米ZnO复合材料热稳定性的原位XRD法研究

采用原位聚合反应制备MC尼龙6/纳米ZnO复合材料．动态高温XRD(20～210℃)分析表明,随着温度的升高,MC尼龙6的α_1(200)晶面和α_2(002+202)晶面分别发生了收缩和膨胀,纯MC尼龙6和MC尼龙6/纳米ZnO复合材料的α_1和α_2晶面热膨胀系数分别为α_T^(α_1)=-8．8×10^(-5)℃^(-1),α_T^(α_2)=1．6×10^(-4)℃^(-1)和α_T^(α_1)=-1．7×10^(-4)℃^(-1),α_T^(α_2)=3．4×10^(-4)℃^(-1)．随着温度的升高,MC尼龙6/纳米ZnO复合材料相对结晶度逐渐降低,在熔融温度附近结晶结构基本被破坏,在达到升温高点后的降温过程中产生了重结晶,在20～210℃之间的结构变化基本是可逆的．加入纳米ZnO提高了MC尼龙6的热稳定性,随着纳米材料含量的增加,复合材料的热稳定性呈上升趋势,分散得越好,热稳定性越强;加入纳米ZnO使MC尼龙6的起始降解温度提高1～9℃,最大失重速率时的温度提高．

A_2W_3O_(12)(A=Y,Er,Ho,Yb)型稀土钨酸盐的高温XRD研究及结构精修

用高温固相反应法制备出A2W3O12型稀土钨酸盐材料(A=Y,Er,Ho,Yb),用室温及高温XRD测定其在不同温度下的结构、晶胞参数及晶胞体积,并用TOPSA软件对其结构进行精修。发现除Ho2W3O12外,都具有较大的负热膨胀系数。据A.W.Sleight预测,Ho2W3O12具有较大的负热膨胀特性,但本实验却发现它并没有负热膨胀性,反而具有非常大的正热膨胀系数。

原位XRD研究合成尖晶石LiMn_2O_4的相变机理

采用高温原位XRD方法对合成尖晶石LiMn2O4的相变机理进行研究,确定了合成尖晶石L iMn2O4的适宜温度区间。对不同温度点得到的尖晶石LiMn2O4的晶胞参数进行计算,发现晶胞参数a与热处理温度基本呈线性关系。

电解铝炭渣高温焙烧熔融试验与物相分析研究

炭渣是电解铝生产过程中产生的一种危险固体废弃物,含有较多电解质。某公司通过高温焙烧法处理炭渣并回收其中的电解质。本文研究了工业化高温焙烧处理电解铝炭渣的工艺条件,并采用X射线衍射分析法研究高温焙烧处理电解铝炭渣过程中各环节主要产物的物相组成。结果表明,采用高温焙烧法,炉内整体温度达到1200℃以上时,炭渣中的电解质完全熔融且流动性良好,无固化状态,炭渣中的电解质和碳质组分得到有效分离,高温焙烧后形成新的物相。其中电解质主要由Na3AlF_(6)、CaF_(2)、Al_(2)O_(3)、K_(2)NaAlF_(6)、LiNa_(2)AlF_(6)、Li_(3)N、LiF、Mg_(3)Al_(2)(SiO_(4))_(3)和NaAl_(11)O_(17)等组成;尾渣主要由Na_(3)AlF_(6)、CaF_(2)、Al_(2)O_(3)、K_(2)NaAlF_(6)、LiNa_(2)AlF_(6)、Li_(3)N和C等组成;收尘灰主要由Na_(5)Al_(3)F_(14)、Na_(3)AlF_(6)、LiNa_(2)AlF_(6)、AlF_(3)、NaAlF_(4)和KAl_(11)O_(17)等物相组成;炭渣中的钙盐始终以游离的CaF_(2)形式存在,一部分夹杂在回收的电解质中,另一部分存在于尾渣中。

(La_(0.75)Sm_(0.25))_2Zr_2O_7纳米粉体的高温动态XRD研究

采用化学共沉淀-高温煅烧技术制备的具有烧绿石结构的(La0.75Sm0.25)2Zr2O7纳米粉体,其平均晶粒尺寸约为47 nm,其晶体结构为等轴晶系,空间群为F d-3m,晶胞参数a0=1.075 nm。采用高温动态XRD技术研究了(La0.75Sm0.25)2Zr2O7纳米粉体的热稳定性、热膨胀性及抗烧结性能。结果表明:(La0.75Sm0.25)2Zr2O7纳米粉体具有良好的热稳定性,高温下晶体结构仍保持稳定,1 400℃的热膨胀系数为9.7×10-6K-1;具有优异的抗高温烧结性能,1 250℃以上纳米晶粒才开始快速生长,1 400℃时,晶粒尺寸为132 nm。

Mixing processes and patterns of fluids in alkane-CO_(2)-water systems under high temperature and high pressure——Microscopic visual physical thermal simulations and molecular dynamics simulations

Various types of geofluids exist in deep and ultra-deep layers in petroliferous basins.The geofluids are much more active under high-temperature and high-pressure(HTHP)conditions,but their properties are unclear.We simulated the mixing of different fluids in CH_(4)/C_(3)H_(8)/C_(6)H_(14)/C_(8)H_(18)-water systems and C_(6)H_(14)/C_(8)H_(18)-CO_(2)-H_(2)O systems at temperatures of 25℃ to 425℃ and pressures of 5 MPa to 105 MPa,using an in-situ micron quartz capillary tube thermal simulation system and molecular dynamics numerical simulation software.The mixing processes,patterns,and mechanisms of various fluids were analyzed at microscale under increasing temperature and pressure conditions.The results show that the miscibility of fluids in the different alkane-H_(2)O and alkane-CO_(2)-H_(2)O systems is not instantaneous,but the miscibility degree between different fluid phases increases as the temperature and pressure rise during the experiments.The physical thermal experiments(PTEs)show that the mixing process can be divided into three stages:initial miscibility,segmented dynamic miscibility,and complete miscibility.The molecular dynamics numerical simulations(MDNSs)indicate that the mixing process of fluids in the alkane-H_(2)O and alkane CO_(2)-H_(2)O systems can be divided into seven and eight stages,respectively.The carbon number affects the miscibility of alkanes and water,and the temperature and pressure required to reach the same miscibility stage with water increase with the carbon number(C_(3)H_(8),C_(6)H_(14),CH_(4),C_(8)H_(18)).CO_(2) has a critical bridge role in the miscibility of alkanes and water,and its presence significantly reduces the temperatures required to reach the initial,dynamic,and complete miscibility of alkanes and water.The results are of great significance for analyzing and understanding the miscibility of geofluids in deep and ultra-deep HTHP systems.

基于XRD对高强混凝土高温后力学试验研究

通过对掺与不掺聚丙烯纤维的高强混凝土进行不同高温作用后的劈裂抗拉强度、抗压强度试验研究,探讨高强混凝土劈裂抗拉强度、拉压比随温度变化的规律。研究结果表明,随着温度的升高,混凝土中的凝胶体不断分解,内部结构不断破坏,高温后高强混凝土脆性增大,劈裂抗拉强度降低;与未掺纤维的高强混凝土相比,相同温度作用后掺有聚丙烯纤维的高强混凝土劈裂抗拉强度略有提高,并借助X射线衍射(XRD)试验,分析高温作用前后高强混凝土内部成分的变化,初步揭示高温对混凝土力学性能影响的机理。

Entropy-driven phase regulation of high-entropy transition metal oxide and its enhanced high-temperature microwave absorption by in-situ dual phases

High-temperature microwave absorbers are significant for military equipment which experiences severe aerodynamic heat.In this work,high-entropy oxide(HEO)(FexCoNiCrMn)mOn with excellent high-temperature microwave absorption is studied.Driven by the effect of entropy,the composition of the oxide can be transformed from spinel-type phase(FexCoNiCrMn)_(3)O_(4) to corundum-type phase(FexCoNiCrMn)2O3 with the increasing content of iron.Only spinel-type or corundum-type structure composes the oxide when x≤3 or x≥5.But in-situ dual phases can coexist when x equals 4 during phase transition.Interestingly,obliged to abundant heterogeneous interfaces and crystal defects in the dual-phase HEO,magnetic property,dielectric polarization,and microwave loss ability are all well enhanced.The Smith chart analysis demonstrates the impedance matching condition is well improved due to the enhanced loss ability.These findings pave a new way for the adjustment of electromagnetic properties of HEO by entropy-driven phase regulation.Meanwhile,the dual-phase absorber can achieve better than 90%absorption in 9.6-12.4 GHz at 800℃ with a thickness of 2.6 mm,a low thermal diffusivity of 0.0038 cm^(2)/s at 900℃,and excellent high-temperature stability,which indicates it’s promising as a high-temperature microwave absorber.

In-situ imaging the electrochemical reactions of Li-CO_(2) nanobatteries at high temperatures in an aberration corrected environmental transmission electron microscope

Rechargeable lithium-carbon dioxide(Li-CO_(2))batteries have attracted much attention due to their high theoretical energy densities and capture of C0_(2).However,the electrochemical reaction mechanisms of rechargeable Lo-CO_(2) batteries,particularly the decomposition mechanisms of the discharge product Li_(2)CO_(3) are still unclear,impeding their practical applications.Exploring electrochemistry of Li_(2)CO_(3) is critical for improving the performance of Li-C0_(2) batteries.Herein,in-situ environmental transmission electron microscopy(ETEM)technique was used to study electrochemistry of Li_(2)CO_(3) in Li-C0_(2) batteries during discharge and charge processes.During discharge,Li_(2)CO_(3) was nucleated and accumulated on the surface of the cathode media such as carbon nanotubes(CNTs)and Ag nanowires(Ag NWs),but it was hard to decompose during charging at room temperature.To promote the decomposition of Li2C03,the charge reactions were conducted at high temperatures,during which Li_(2)CO_(3) was decomposed to lithium with release of gases.Density functional theory(DFT)calculations revealed that the synergistic effect of temperature and biasing facilitates the decomposition of Li_(2)CO_(3).This study not only provides a fundamental understanding to the high temperature Li-C0_(2) nanobatteries,but also offers a valid technique,i.e.,discharging/charging at high temperatures,to improve the cyclability of Li-CO_(2) batteries for energy storage applications.

Investigation the improvement of high voltage spinel LiNi_(0.5)Mn_(1.5)O_(4) cathode material by anneal process for lithium ion batteries

The spinel LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)has been attracted great attention as lithium ion cathode material due to its high voltage and large energy density.However,the practical application of LNMO is still limited by poor cycling stability.Herein,to improve the cycling stability of spinel LNMO,it was treated with anneal process at 900℃for 2 h after prepared by traditional solid-state method(LNMO-A).LNMO-A sample presented better electrochemical property especially under high rate,with capacity of 91.2 mAhg^(-1) after 1000 cycles under 10 C.Its superior electrochemical property was ascribed to the anneal process,resulting a stable crystal structure,indicated by XRD and Raman results of electrodes after 1000 cycles under 10 C and the longer solid-solution reaction,revealed by in-situ XRD.In addition,the optimized particle size,micro morphology and the larger BET area surface induced by the recrystallization in anneal process also contributes to its superior electrochemical property.What's more,the thin layer,which interacted LNMO-A particles with each other,induced by particles remelting in anneal process is also beneficial for its excellent electrochemical property.This study not only improved the electrochemical properties by anneal process,but also revealed the origins and mechanisms for its improvement.