SYNTHESIS AND THERMAL PROPERTIES OF POLYBENZOXAZOLE FROM SOLUBLE PRECURSOR WITH HYDROXY-SUBSTITUTED POLYENAMINONITRILE

Aromatic polybenzoxazole (PBO) precursor, hydroxy-substituted polyenaminonitrile, was prepared by direct polycondensation of 1,4-bis(l-chloro-2,2-dicyanovinyl)benzene (CCB) and 4,6-diaminoresorcinol dihydrochloride (DAR) using pyridine and N,N-dimethylacetamide as condensing agent and solvent. The precursor has good solubility in polar aprotic solvent which is due to the strong dipolar nature of the main chain. The soluble precursor was subjected to thermal cyclization in an inert atmosphere to convert it into the corresponding PBO, which has its 5% weight loss temperature at 540℃ The fully cyclized PBO were characterized by FT-IR and TGA. The introduction of 10% mol 1,3,5-benzenetricarboxylic chloride (BTC) into the main chain not only has little effect on the solubility of PBO precursor but also raises its 5% weight loss temperature to 552℃ and char yield at 700℃ for the cyclized PBO with BTC.     

紫外拉曼光谱研究焙烧气氛对氧化锆相变的影响

 以紫外拉曼光谱技术研究了在不同焙烧气氛中氧化锆样品的表面晶相结构及其转变过程．结果表明，在有氧气氛中焙烧的氧化锆样品易转变为单斜相，而在惰性气氛中焙烧可以有效地稳定样品体相和表面的四方相结构．在缺氧气氛中焙烧的样品暴露于空气中后，表面极易转变为单斜相，而其体相仍为四方相结构，这表明四方相氧化锆在样品表面是极不稳定的．     

Li2B4O7坩埚内预氧化熔融铸片XRF法测定含还原物耐火材料中主量和次量组分

在四硼酸锂坩埚中,以碳酸锂和硝酸铵为氧化剂,在铂金坩埚外对含还原物耐火材料进行预氧化和烧结。在高温氧化过程中,由于样品表面包裹有含氧化剂为主的烧结物,在继续熔融氧化产生的气体浮力作用下,样品在未被氧化前,不与铂金坩埚接触。因此,避免了熔融过程中铂金坩埚腐蚀问题。实验结果表明,氧化温度控制在730℃以下,时间15min内,含还原物耐火材料样品与氧化剂发生氧化烧结反应,四硼酸锂坩埚不会熔穿。确定的预氧化温度为720℃,时间为5~15min。结合现有的报道,确定了熔融铸片所需氧化剂和脱模剂的用量、熔融温度和时间。按拟定的方法,用国家和行业标准样品绘制工作曲线,对含还原物耐火材料样品进行了测定。与湿法分析结果进行比较表明,准确度与湿法分析相当。     

部分相干电磁光束在湍流介质中传输的偏振变化

 从推广的惠更斯-菲涅尔原理出发,推导出了部分相干电磁光束的偏振态在湍流介质中传输的表达式。并以电磁高斯-谢尔模型(EGSM)光束为例,研究了湍流对电磁高斯-谢尔模型光束偏振态的影响。研究结果表明,对于轴上点,湍流介质的折射率结构常数越大,偏振度趋于最大值的速度越快,达到的最大值越小;光斑越大,偏振度达到最大值的位置离光源越远,在光斑增大的过程中,偏振度所达到的极大值会先增大后减小,最后保持与光源相同的偏振度不变。对于轴外点,一个固定的z,光的偏振度随着离轴距离的增大而逐渐下降,并最终等于零。折射率结构常数越大,偏振度随离轴距离的增大而下降得越缓慢;光斑越大,偏振度随离轴距离的增大下降得越快。     

大气消光特性与机载激光雷达眼睛安全关系的研究

依据美国ANSI标准，定量分析了气溶胶、卷云和沙尘的垂直消光特性对机载激光雷达激光脉冲眼睛安全最大阈值能量的影响；以地基激光雷达探测得到的合肥上空沙尘暴为例，定量给出了大气中各成分消光特性对飞机眼睛安全最低高度的影响；模拟计算了各种大气成分的消光特性对激光脉冲眼睛安全系数的影响随高度的变化规律。计算结果表明：沙尘层对激光脉冲眼睛安全最大阈值能量的影响幅度可达几十毫焦。该结果为我国第一台机载大气探测激光雷达激光脉冲能量设置提供了基本依据。     

蒙特卡罗模拟光通过大气后的时间分布

采用蒙特卡罗方法模拟了光通过光学特性参数不同的大气后透射光时间分布.分析了大气的散射系数、吸收系数、不对称因子及折射率对透射光时间分布的影响.结果表明:透射光时间分布曲线存在两个峰,分别对应子弹光与漫射光.各光学参数界定了子弹光、蛇形光、漫射光的大小和时间范围,并从统计模拟的角度解释了折射率大的大气中难以成像的因为.     

减压氩气下基体对激光微等离子体电子温度的影响

以激光微区发射光谱分析仪结合CCD光栅光谱仪为装置，采用二谱线法，以FeⅠ356.54nm和FeⅠ358.12 nm为分析线，在减压氩气下，测量了镁基体、铝基体、硅基体和低碳钢标样6-0中的激光微等离子体的电子温度及其空间分布，给出了相同基体中微等子体电子温度的空间变化趋势和不同基体中相同空间位置处的电子温度的差异并进行了分析.利用测量的结果，以CuⅠ324.75 nm和ZnⅠ334.50 nm为分析线，从电子温度角度探索了两分析谱线相对强度的基体效应，给出了合理的解释. 关键词： 激光微等离子体 电子温度 减压氩气 基体     

Valence control of cobalt oxide thin films by annealing atmosphere

The cobalt oxide (CoO and Co₃O₄) thin films were successfully prepared using a spin-coating technique by a chemical solution method with CH₃OCH₂CH₂OH and Co(NO₃)₂·6H₂O as starting materials. The grayish cobalt oxide films had uniform crystalline grains with less than 50 nm in diameter. The phase structure is able to tailor by controlling the annealing atmosphere and temperature, in which Co₃O₄ thin film was obtained by annealing in air at 300-600, and N₂ at 300, and transferred to CoO thin film by raising annealing temperature in N₂. The fitted X-ray photoelectron spectroscopy (XPS) spectra of the Co2p electrons are distinguishable from different valence states of cobalt oxide especially for their satellite structure. The valence control of cobalt oxide thin films by annealing atmosphere contributes to the tailored optical absorption property.     

Rainfalls during great Forbush decreases

Summary The changes of rainfall values during great Forbush decreases recorded by the low-latitudinal neutron monitor of Huancayo (47 events from 1956 through 1992) were examined. The data on precipitations were taken from the State of S?o Paulo and from the Amazonian region, Brazil. As a rule, the data from more than 50 meteorological stations were used for each events. The main result is the following: during strong decreases of cosmic-ray flux in the atmosphere (great Forbush decreases) the precipitation value is decreased. The effect of rainfall changes is seen more distinctly if wet seasons are considered.     

Radical polymerization in the presence of peroxide and reducing agent monomer for branched polymers

In this article, we report the radical polymerization in the presence of peroxide and commercially available or designed reducing agent monomer (RAM) for the preparation of branched poly(methyl methacrylate)s (PMMAs). The reaction behavior of the RAM was studied by NMR. Triple‐detection SEC (TD‐SEC) analysis was used to confirm the branching structure of the prepared PMMAs and to investigate the influence of peroxide concentration and RAM concentration on molecular weight and branched structure. The obtained branched PMMAs exhibited high molecular weights and relatively narrow polydispersities at high conversion of MMA. Interestingly, a significant increase in molecular weight and degree of branching of the obtained polymers are observed in higher BPO concentration, these results are quite different from that reported in the literature. The unique radical polymerization mechanism in the RAM/BPO redox‐initiated radical polymerization system resulted in branched PMMAs with high molecular weights at relatively high RAM and BPO concentrations. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 833–840