Stabilization of 6H-Hexagonal SrMnO3 Polymorph by Al2O3 insertion

We demonstrate the structural evolution of polymorphic phases in Al₂O₃-inserted SrMnO₃ ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO₃ ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO₃ and the secondary hexagonal SrAl₂O₄ phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO₃ phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al₂O₃-inserted SrMnO₃ compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO₃.     

Structural transformation in Mn-substituted Sr2Bi2Ta2TiO12 Aurivillius phase synthesized by hydrothermal method: A comparative study and dielectric properties

In this study, a hydrothermal method was applied to synthesize the three-layer Aurivillius phase Sr₂Bi₂Ta₂TiO₁₂ (SBTTO) and Mn-substituted Sr_1·5Bi_2·5Ta₂Ti_0·5Mn_0·5O₁₂ (SBTTMO), with the use of NaOH as a mineralizer. The crystal structure, morphology, dielectric properties, and the correlation between the structural transformation and dielectric properties were investigated. The XRD data reveal that the SBTTO sample adopts a tetragonal crystal structure with the I4/mmm space group and is then transformed into an orthorhombic structure with the B2cb space group for SBTTMO. The morphology of both samples was observed by SEM, which showed anisotropic plate-like grains. With the Mn substitution, the ferroelectric transition temperature (T_c) significantly increases as the influence of the 6s² lone pair of Bi³⁺ increases, and this in turn further induces the relaxor-ferroelectric behavior. Consequently, the increase in T_c confirms the structural transformation from the paraelectric-tetragonal to the ferroelectric-orthorhombic phase.     

Designing optical glasses by machine learning coupled with a genetic algorithm

Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (T_g) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (n_d) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high n_d (1.7 or more) and low T_g (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses.     

聚酯/TGIC粉末涂料的贮存稳定性与性能退化

粉末涂料在贮存期间可发生物理及化学变化,高温贮存会造成粉末涂料因化学变化而产生不可逆的性能劣化.为找到粉末涂料的贮存稳定性与配方、生产以及贮存条件的关系,本研究通过分析粉末涂料的Tg、原材料、生产工艺等因素,发现粉末涂料的贮存稳定性以及性能劣化与粉末涂料的Tg、固化剂TGIC(异氰尿酸三缩水甘油酯)的品质、聚酯/TGI...     

Optical properties and magnetic properties of antisite-disordered Ni1–xCoxCr2O4 spinels

From the UV–Vis absorption spectra, the FT-IR absorption spectra and the Raman spectra, it is deduced that Co ions primarily occupy the tetrahedral (A) site, with a minor number of them entering into the octahedral (B) site in the Ni_1-xCo_xCr₂O₄ compounds. The origin of the position disorder of the Co ions is consistent with the similar ionic radii of the Co ion (0.65 Å) and the Cr ion (0.62 Å) at B site. The FT-IR peak at about 510 cm^?1 shifts towards high frequency side with the increasing cobalt content. It is resulted from the reduction of the cation–oxygen distance in the octahedron by the replacement of the Ni²⁺ with the Co²⁺ ions. The magnetic measurement shows that Curie temperatures (T_C) are 75 and 90 K for the compounds with x=0.2 and 0.8, respectively.     

热循环对Q890钢焊接热影响不同区域组织及性能的影响

采用热模拟技术和冲击试验研究经不同峰值温度热循环后Q890钢焊接热影响区的粗晶区、细晶区、不完全相变区和临界粗晶区的组织和韧性的变化规律.结果表明,细晶区冲击吸收功高达222.7 J,具有良好的冲击韧性;而粗晶区、临界区及临界粗晶区冲击吸收功分别为低至56、35.7和16.3 J;分析认为临界区和临界粗晶区中M-A组元主要沿晶界分布造成晶界弱化,晶界处应力集中形成微裂纹,降低其冲击韧性.细晶区中由于原奥氏体晶粒细化,并且大角度晶界取向角θ,在15°<θ<45°范围内的百分比最高为25.7%,能够提高冲击韧性.     

Molecular mobility and hydration properties of segmented polyurethanes with varying structure of soft‐ and hard‐chain segments

The molecular mobility and hydration properties of model segmented polyurethanes from either poly(propylene glycol) (PPG) or poly(butylene adipate) (PBAD), both of molecular weight 2000 (soft segments), and three different diisocyanates (all‐trans 4,4′‐dicyclohexylmethane diisocyanate, 100% t,t HMDI; HMDI with 20% of trans isomers, 20% t,t HMDI; and 4,4′‐diphenylmethane diisocyanate, MDI) (hard segments) were investigated using differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) measurements, ac dielectric relaxation spectroscopy (ac DRS), equilibrium water‐sorption isotherms (ESI), and dynamic water‐sorption isotherms (DSI). No effects of the structure and of the amount of the soft segments on the overall degree of microphase separation (DMS) into microphases rich in soft and hard segments, respectively, were observed. On the contrary, DMS depends on the composition of the diisocyanates used and systematically increases in the order MDI, 20% t,t HMDI, 100% t,t HMDI as indicated by DSC, TSDC, and ac DRS. The PPG‐based polyurethanes are characterized by larger values of water content at saturation, h, and smaller values of the diffusion coefficient of water, D. h increases with temperature, indicating that the sorption process is endothermic. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1209–1221, 1999     

Dynamic mechanical analysis on highly thermally stable polybenzoxazines with an acetylene functional group

Dynamic mechanical analysis is performed on polybenzoxazines from acetylene-terminated benzoxazine monomers, and glass transition temperatures of these polybenzoxazines are found in the range of 329–368°C. It has been identified that the high glass transition temperature and high thermal stability are due to polymerization of the acetylene terminal group, in addition to oxazine ring polymerization through a comparison study with analogous polybenzoxazines that are obtained from monomers without an acetylene functional group. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 857–862, 1999     

环氧化天然橡胶玻璃化转变温度与环氧化程度的关系

根据Ｖａｎ Ｋｒｅｖｅｌｅｎ 等提出的一些高聚物物理参数加合性原则,推导了环氧化天然橡胶（ＥＮＲ） 的玻璃化转变温度（Ｔｇ） 与环氧化程度（Ｂ） 的关系,并根据经验公式计算了不同环氧化程度ＥＮＲ 的Ｔｇ 。     

包覆红磷-氢氧化铝协效阻燃ABS的研究

探讨了包覆红磷对ABS的阻燃作用及其与氢氧化铝的协效阻燃作用。实验表明,包覆红磷用量约为9％,氢氧化铝用量约为20％时,可以得到阻燃性能和力学性能都比较优良的协效阻燃ABS制品。