Glass Transitions in Viscous Monohydroxy Alcohols: Calorimetry Versus Dielectric Relaxation

An extensive comparison of the calorimetric and dielectric measurements of the glass transitions in both monohydroxy alcohols and other molecular liquids is presented, with only these alcohols displaying an additional pronounced dielectric Debye peaks. It is found that the calorimetric T _g’s of the non-Debye liquids with moderate cooling and heating rates (±20 K · min⁻¹, for example) are slightly higher than the kinetic ones which are determined as the temperatures at which the relaxation time is 100 s. As the difference does not exceed 3 K, this relation of calorimetric and kinetic T _g’s is used as ‘standard.’ Two kinetic glass transitions from the dielectric relaxation of Debye type monohydroxy alcohols are identified, and it is found that the Debye process is not the signature of the glass transition.     

Molecular dynamics investigations of structural changes accompanying with freezing a molten Cu135 cluster on cooling

We use molecular dynamics (MD) simulations within the framework of the embedded-atom method (EAM) to investigate structural changes during freezing a molten Cu cluster containing 135 atoms. The simulations show how the structural changes can strongly cause internal energy to change accordingly, and reveal that continuous interchange positions of atoms are the key in the formation of the icosahedral (Ih)-like Cu₁₃₅ cluster. By using visual inspection on atomic packing according to atomic density profiles, we analyze crystallization processes during freezing the molten cluster. At the initial stage of the freezing, one atom moves into the center of this cluster. Then the packing in interior atoms is changed into an ordered Ih structure, while outer atoms are becoming locally ordered with a fivefold Ih symmetry. Subsequently, nanocrystallization at lower temperatures propagates outward from the interior Ih structure, leading to the Ih-like cluster.     

二元系统分相区的定量预测方法——RO-B_2O_3(R=Mg、Ca、Sr、Ba)系统分相区的预测

本文对应用分相的普适性及定量计算方程来预测分相区进行了分析,认为,对二元系统的分相,只要知道临界点的实验值或临界点附近某两点以上的实验值,就可定量预测出临界点附近的分相区。并用此方法对已知分相区的硼酸盐碱土金属二元系 RO-B_2O_3(R=Mg、Ca、Sr、Ba)的分相区进行了预测验证。结果表明,用本文的方法来预测它们的分相区是可行的。本方法可望用于其它二元系统分相区的预测。     

Simultaneous Measurement of Thermophysical Properties and Dielectric Properties of PZT-Based Ferroelectric Ceramics by Thermal Radiation Calorimetry

Simultaneous measurements of thermophysical properties and dielectric properties have been performed for PZT-based ferroelectric ceramics. An apparatus based on thermal radiation calorimetry was used in the present measurements. Anomalies in the thermophysical properties were observed near the ferroelectric-to-paraelectric phase transition temperature. The anomalous peak was at almost the same temperature as the inflection point of the dielectric constant. It was found that modification of PZT with increasing Nb, Mg, Zn, and Sr causes a decrease of the Curie temperature and an increase of the hysteresis phenomena for the phase transition, and the values of the thermal conductivity increase with temperature similar to amorphous materials.     

现代连续相变理论在玻璃分相中的应用

玻璃分相区中存在一临界点,在此临界点的转变属于连续相变范畴。通过本文的讨论表明。对二组元玻璃系统的分相,可以用现代连续相变理论描述。在临界点附近区域内,其分相曲线为以临界点为界,以两曲线方程:(x~l-x_c)/x_c=A[(T_c-T)/T_c]~(1/3),(x~(l′)-x_c)/x_c=A′[(T_c-T)/T_c]~(1/3)来表达。这里 A、A′为二组元系统分相曲线的普适常数。本文中对 Li_2O-SiO_2,Na_2O-SiO_2,BaO-SiO_2系统分相实验值的拟合结果是 A=-1.8305;A′=2.3551。相应的计算曲线与实验值符合较好。     

Modification of bifunctional epoxy resin using CO2 fixation process and nanoclay

A bifunctional epoxy resin was modified by using a CO₂ fixation solution process in the presence of tetra n-butyl ammonium bromide (TBAB) as catalyst and the modified treated resin was treated by cloisite 30B as nano additive. The Unmodified epoxy resin (UME), CO₂ fixated modified epoxy resin (CFME), and CFME/clay nano composite (CFMEN), were cured by diethylenetriamine (DETA). A cycloaliphatic compound as a reactive diluent was used to control the viscosity of high viscose CFME. The exfoliation of organoclay in UME and CFME was investigated by X-ray diffraction and activation energy was computed using the advanced integral isoconversional method. The activation energy dependency demonstrated that the mechanism of UME curing did not change in the presence of nanoclay. In contrast, the CO₂ fixation results showed a significant change in the activation energy dependency. The Thermal stability parameters include the initial degradation temperature (IDT), the temperature at the maximum rate of weight loss (T_max), and the decomposition activation energy (E_d) were determined by thermal gravimetry analysis. Dynamic mechanical thermal analysis measurements showed that the presence of organoclay in CFME increases the T_g of nano composite in contrast to UME. The fracture roughness of UME, CFME and CFNE were determined by scanning electron microscope. The exfoliated UME/1%clay nanocomposite was confirmed by TEM image.     

Recent breakthroughs and perspectives of high-energy layered oxide cathode materials for lithium ion batteries

Ni-rich layered oxides (NRLOs) and Li-rich layered oxides (LRLOs) have been considered as promising next-generation cathode materials for lithium ion batteries (LIBs) due to their high energy density, low cost, and environmental friendliness. However, these two layered oxides suffer from similar problems like capacity fading and different obstacles such as thermal runaway for NRLOs and voltage decay for LRLOs. Understanding the similarities and differences of their challenges and strategies at multiple scales plays a paramount role in the cathode development of advanced LIBs. Herein, we provide a comprehensive review of state-of-the-art progress made in NRLOs and LRLOs based on multi-scale insights into electrons/ions, crystals, particles, electrodes and cells. For NRLOs, issues like structure disorder, cracks, interfacial degradation and thermal runaway are elaborately discussed. Superexchange interaction and magnetic frustration are blamed for structure disorder while strains induced by universal structural collapse result in issues like cracks. For LRLOs, we present an overview of the origin of high capacity followed by local crystal structure, and the root of voltage hysteresis/decay, which are ascribed to reduced valence of transition metal ions, phase transformation, strains, and microstructure degradation. We then discuss failure mechanism in full cells with NRLO cathode and commercial challenges of LRLOs. Moreover, strategies to improve the performance of NRLOs and LRLOs from different scales such as ion-doping, microstructure designs, particle modifications, and electrode/electrolyte interface engineering are summarized. Dopants like Na, Mg and Zr, delicate gradient concentration design, coatings like spinel LiNi_0.5Mn_1.5O₄ or Li₃PO₄ and novel electrolyte formulas are highly desired. Developing single crystals for NRLOs and new crystallographic structure or heterostructure for LRLOs are also emphasized. Finally, remaining challenges and perspectives are outlined for the development of NRLOs and LRLOs. This review offers fundamental understanding and future perspectives towards high-performance cathodes for next-generation LIBs.