WCl_6－Al（i－Bu）_2Cl催化丁二烯－苯乙烯共聚合──丁苯共聚物的结构组成和竞聚率测定

对丁苯共聚物的~１Ｈ－ＮＭＲ谱图进行了归属，并建立了计算其４种结构单元含量的方程式。当Ａｌ（ｉ－Ｂｕ）_２Ｃｌ／ＷＣｌ_６＝６（摩尔比）时，苯乙烯（Ｓｔ）单元含量最低，丁二烯（Ｂｄ）单元含量最高；Ｂｄ单元含量随Ｂｄ／Ｓｔ值的增加而提高，总的Ｓｔ单元含量随Ｂｄ／Ｓｔ值的增加而降低；聚合时间对单元含量的影响与Ｂｄ／Ｓｔ值的影响相似；提高聚合温度，Ｓｔ单元含量降低。用微分法求得转化率低于１０时Ｓｔ的竞聚率为４．７０，Ｂｄ的竞聚率为０．２７。     

WCl6—Al（i—Bu）2Cl催化丁二烯—苯乙烯共聚合：丁苯共聚物的结构组…

对丁苯共聚物的＾１Ｈ－ＮＭＲ谱图进行了归属，并建立了计算其４种结构单元含量的方程式。当Ａｌ（ｉ－Ｂｕ）２Ｃｌ／ＷＣｌ６＝６（摩尔比）时，苯乙烯单元含量最低，丁二烯单元含量最高；Ｂｄ单元含量随Ｂｄ／Ｓｔ值的增加而提高，总的Ｓｔ单元含量随Ｂｄ／Ｓｔ值的增加而降低；聚合时间对单元含量的影响与Ｂｄ／Ｓｔ值的影响相似；提高聚合温度，Ｓｔ单元含量降低。用微分法求得转化率低于１０％时Ｓｔ的竞聚率为４．７０，Ｂｄ     

1,2—Bd对TMEDA体系丁二烯—苯乙烯共聚偶联反应的影响

在１,２－Ｂｄ／ＴＭＥＤＡ体系下丁二烯－苯乙烯负离子共聚反应中,加入ＳｎＣｌ４和ＤＥＡＰ进行偶联反应。结果表明,在ＴＭＥＤＡ／Ｌｉ摩尔比为０．１时,随着１,２－Ｂｄ的加入,偶联效率明显下降,这一进一步印证了１,２－Ｂｄ会引起ＴＭＥＤＡ调节的丁苯共聚体系活性链失活。     

Ni（naph）2—（i—Bu）6—nAl2Cln催化丁二烯聚合

为了合成低相对分子质量的顺丁橡胶，研究了Ｎｉ（ＮＡＰＨ）２－（ｉ－Ｂｕ）６－ｎＡｌ２Ｃｌｎ（Ｎｉ－Ａｌ）体系催化丁二烯取合中催化剂一和Ａｌ中氯／铝对催化活性的影响。结果表明，Ａｌ／Ｂｄ为（３－１０）×１０＾３时，增加Ｎｉ／Ｂｄ可提高转化率，Ｎｄ／Ｂｄ为５．０×１０＾－５，转化率趋于平稳，本体系催化效率为７２ｋｇ＝ｇ；     

镍催化体系合成低分子聚丁二烯

研究了Ｎｉ（ｎａｐｈ）２－Ａｌ（ｉ－Ｂｕ）３－ＢＦ３·ＯＥｔ２－Ｃ８Ｈ１７ＯＨ体系合成低分子聚丁二烯,考察了Ａｌ／Ｂ摩尔比、Ａｌ／Ｎｉ摩尔比、Ｎｉ／Ｂｄ摩尔比、Ｃ８Ｈ１７ＯＨ／Ｂ摩尔比等反应条件对聚合活性及聚合产物分子量的影响。实验结果表明,该体系在Ａｌ／Ｂ比于０１５～０３０之间时,随着Ａｌ／Ｂ比的降低,聚合活性下降,聚合物分子量也降低。由于辛醇的作用,聚丁二烯的特性粘数最低可降至０５ｄＬ／ｇ。Ａｌ／Ｂ比的变化对聚合活性及聚合物分子量的影响显著,Ａｌ／Ｂｄ比、Ｎｉ／Ｂｄ比、Ｃ８Ｈ１７ＯＨ／Ｂ比对其影响不大     

基于BP神经网络的水泥抗压强度预测研究

探讨应用ＢＰ（ｂａｃｋ－ｐｒｏｐａｇａｔｉｏｎ）神经网络进行经２８ｄ抗压强度预测的方法。利用ＢＰ网络很强的非线性映射功能,建立抗压强度相关因素与抗压强度之间的关系。通过对样本的学习,ＢＰ网络将这种非线性映射关系以分布并行的方式存储在网络的联结权矩阵中,从而达到对样本集的非逻辑归纳。本文提出了强度预测模型能够以较高的精度预测水泥２８ｄ抗压强度。作为对比,同时应用回归分析方法预测水泥２８ｄ抗压强度,两     

高性能数字记录用蒸镀带的实用可靠性

采用在Ｃｏ－Ｏ系斜蒸镀膜上加设一层金刚石状碳保护膜的方法，开发了一种电磁转换特性和实用可靠及保存可靠性都得到改善２的数字蒸镀带。在记录密度为１００ｋＢＰＩ条件下，与Ｈｉ－８ＭＥ带相比，其输出为＋５ｄＢ，载噪比为＋４ｄＢ。     

BS780系列电收尘大修介绍

ＢＳ７８０系列电收尘大修介绍关来庆，吕河龙河南省新乡水泥厂（４５３０１１）ＢＳ７８０系列电收尘器系联邦德国鲁奇公司８０年代的技术。其应用于新乡水泥厂１０００ｔ／ｄ窑外分解窑生产线的有两种型号：窑头：５０ｍ２、窑尾：９０ｍ２。我厂１０００ｔ／ｄ窑外分解...     

Ni(naph)_2—Al(i-Bu)_3—BF_3·OEt_2—ROR′体系催化丁二烯聚合

研究了Ｎｉ（ｎａｐｈ）２—Ａｌ（ｉ－Ｂｕ）３—ＢＦ３·ＯＥｔ２—ＲＯＲ′体系催化丁二烯聚合的特点,考察了Ａｌ／Ｂ摩尔比、Ａｌ／Ｎｉ摩尔比、Ｎｉ／Ｂｄ摩尔比、ＲＯＲ′／Ｂ摩尔比等反应条件对聚合活性及聚合产物分子量的影响,还考察了该体系的凝胶含量。实验结果表明,该体系中醚的加入不仅保持体系较高的聚合活性,较好地控制聚合物分子量,而且还能降低体系的凝胶含量。Ａｌ／Ｂ比的变化对聚合活性及聚合物分子量的影响显著,Ａｌ／Ｎｉ比、Ｎｉ／Ｂｄ比、ＲＯＲ′／Ｂ比对其影响不大。     

机械知识问答

１．减振合金的性质与用途？答：机械设备在运转中所产生的振动和噪声不仅破坏环境造成公害，而且还会引起机器零件的磨损和松动，严重影响机器的使用寿命。在正常环境下的噪声水平为５０ｄｂ左右，噪声达到１３０ｄＢ时就会使人感到头痛，１５０ｄＢ时就将令人难以忍受，...     

High extinction-ratio microstructure fiber based on chalcogenide glasses

Extinction ratio (ER) is one of the important parameters to characterize the polarization-maintaining (PM) performance of the fiber. In this paper, we report the preparation and properties of a novel chalcogenide microstructure fiber with a high ER. We fabricate a preform using a peeled-off extrusion method. The core and cladding material of the fiber are Ge₉As₂₃Se₆₈ and Ge₁₀As₂₂Se₆₈. The preform was drawn into a fiber with an average ER of −17.08 dB. The loss of the fiber is less than 2 dB over 5.20–8.55 μm, and the minimum loss of the fiber is 0.57 dB/m at 6.2 μm. Moreover, a flat mid-infrared supercontinuum spectrum spanning from 1.53 to 12.50 μm is generated by pumping an 18-cm-long PM fiber for the first time.     

Hybrid polyaniline/nanomagnetic particles composites: High performance materials for EMI shielding

In this work, two types of hybrid composite materials were elaborated. The first based on polyaniline (PANI) doped Camphor Sulfonic acid (CSA), Carbon‐Coated Cobalt (CCo), and FeNi nanoparticles dispersed in polyurethane. A value of 10⁴ S/m of conductivity and a 90 dB of shielding effectiveness in multilayer structure were obtained over the 8–18 GHz frequency band. The second type, based on PANI doped para‐toluene sulfonic acid (PTSA), dispersed in epoxy resin with FeNi nanoparticles. A thick material with moderate conductivity and high attenuation of electromagnetic waves was obtained. It was found that a PANI‐PTSA/FeNi/epoxy resin composite with thicknesses of 9.7 and 6.5 mm had, respectively, reflection loss values of ?22 dB at 9.52 GHz, and ?20.7 dB at 14.7 GHz. The electromagnetic properties of the elaborated structure hybrid materials can be optimized to increase the electromagnetic reflection–absorption properties. Thus, the obtained structure can be used in shielding and radar absorbing materials applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

High quality factor cold sintered LiF ceramics for microstrip patch antenna applications

Cold sintering is adopted to pre-densify LiF ceramics, where the relative density increases significantly from 72.1 % at 125 MPa to 88.9 % at 500 MPa. The following post-annealings at 800 °C lead to further optimizations of densification, and near-full densifications with relative densities of 95.6 % and 97.6 % are achieved at 375 and 500 MPa, respectively. Qf value increased with increasing uniaxial pressure until it reaches the maximum value of 134,050 GHz at 375 MPa, which is 1.82 times higher than that via conventional sintering (73,800 GHz). ε_r and τ_f are mainly determined by the relative density, and the optimum microwave dielectric properties are obtained as follows: ε_r = 8.45, Qf = 134,050 GHz, τ_f =–135 ppm/°C. A microstrip patch antenna is designed and fabricated using the LiF ceramic as the substrate, which gives an S11 of –20.3 dB, a simulated high efficiency of 90.5 %, and a gain of 4.25 dB at the resonant frequency of 6.81 GHz.     

High electromagnetic interference shielding effectiveness in MgO composites reinforced by aligned graphene platelets

Graphene has been considered as an excellent filler to reinforce ceramics with enhanced properties. However, the uniform dispersion and controlled orientation of graphene sheets in a ceramic matrix have become major challenges toward higher performance. In this paper, we prepared MgO matrix composites with parallel graphene layers through the intercalation of the precursor into expandable graphite. We obtained a high electromagnetic interference (EMI) shielding effectiveness of ~30 dB, due to the multiple reflections and absorptance of electromagnetic waves between the parallel graphene layers. The hardness and strength of the MgO composite were also increased by introducing parallel graphene layers. All these properties suggest that the graphene/MgO composite represents a promising electromagnetic shielding material.     

敏化316L不锈钢晶间腐蚀的声发射特性

采用沸腾硝酸法和声发射技术研究了敏化316L奥氏体不锈钢的晶间腐蚀特性。通过失重法对3个周期实验的腐蚀速率进行计算和评定,并利用金相显微镜观察了各周期实验后试样腐蚀形貌;同时利用声发射检测系统实时采集了实验过程中的晶间腐蚀声发射信号,通过对信号进行参数分析和小波分析探究了敏化316L不锈钢晶间腐蚀的声发射信号特征与规律。实验结果表明,敏化316L不锈钢的晶间腐蚀分为腐蚀萌生阶段、平稳腐蚀阶段和快速腐蚀阶段;对信号进行参数分析发现各腐蚀阶段的计数率先缓慢增大继而保持平稳不变,最后又迅速增大;信号幅值出现明显的分层现象:腐蚀萌生阶段为25²7dB,平稳腐蚀阶段为2727dB,平稳腐蚀阶段为27³0dB,快速腐蚀阶段为3130dB,快速腐蚀阶段为31³4 dB;最后对信号进行小波分析发现声发射信号主要由频率为200、280kHz的信号组成。     

High strength and microwave-absorbing polymer-derived SiCN honeycomb ceramic prepared by 3D printing

The combination of 3D printing technology and polymer-derived ceramic route provides an attractive strategy to construct microwave-absorbing honeycomb with fine structure through flexible process. However, preparation of honeycomb ceramics with both excellent mechanical and microwave-absorbing properties is still challenging. Herein, SiCN honeycomb ceramic was fabricated by stereolithography from UV curable polymeric precursor consisting of polysilazane and multifunctional acrylates. By optimizing the multifunctional acrylates and its ratio, the decomposition of organic moiety and the ceramization process of precursor are matched, rendering the achieved ceramic with high compactness. The hardness and specific compressive strength of SiCN honeycomb ceramic reach as high as 14.3 GPa and 333.3 MPa/(g·cm³), respectively. Meanwhile, at low pyrolysis temperature, the copolymerized acrylate and polysilazane that formed during curing process was converted to free-carbon nanodamins in-situ, which endows SiCN honeycomb ceramic with the minimum reflection loss of –49.0 dB, namely microwave absorption rate over 99.99%.     

声场高温流化床流化特性

在内径50 mm、高1000 mm的声场高温鼓泡流化床中,研究Geldart A, B两类颗粒的流化特性,考察了床层温度、声波频率及声压级对流化床最小流化速度的影响. 结果表明,引入声场后,颗粒的最小流化速度随温度升高而下降;固定温度及频率,最小流化速度随声压级增大而减小;固定声压级与温度,颗粒最小流化速度随声波频率增大先减小后增大,存在一个最佳频率范围. 对床内压力波动信号进行分析,得出声场影响高温流化床流化质量的判据：当声压大于110 dB、频率在100~200 Hz范围内时压力波动偏差与最小流化速度值最小.     

High temperature anti-oxidative and tunable wave absorbing SiC/Fe3Si/CNTs composite ceramic derived from a novel polysilyacetylene

With the rapid development of high power electromagnetic (EM) equipment and high-speed aircraft, the powerful and high oxidation-resistance absorbers are fundamentally desirable for the EM field. Herein, a novel high temperature anti-oxidative SiC/Fe₃Si/CNTs composite is synthesized by a facile polymer derived ceramic (PDC) route from a Fe-containing polysilyacetylene (PSA). The microstructure of as-prepared SiC/Fe₃Si/CNTs composite absorber is featured by micro-sized SiC ceramic grains with spherical Fe₃Si nanoparticles and carbon nanotubes (CNTs) attached to. The vector network analyzer tests show a tunable wave-absorbing performance by adjusting the thickness of layer, and the effective bandwidth (the reflection loss < −10 dB) is 3.3–16.8 GHz for the sample S-1400 (heat treatment at 1400 °C in nitrogen flow). The minimal RL value is −41.2 dB at 10.5 GHz at a thickness of 2 mm and an effective bandwidth is nearly 4 GHz (12.9–16.9 GHz) at the thickness of only 1.5 mm. Moreover, after the oxidation treatment at 800 °C in the air, this absorber maintains the main structure and shows a good high temperature oxidation resistance. This absorber still remains excellent wave absorption property, in view of a minimal RL value of −40 dB at the thickness of 3 mm and a bandwidth of 4.8 GHz (10.4–15.2 GHz) at the thickness of 2.5 mm. The mechanism of high EM wave absorption performance is studied and attributed to the impendence matching, polarization, and the magnetic properties. Thus, the SiC/Fe₃Si/CNTs composite is a promising EM absorber for high-temperature EM wave-absorbing applications.     

The influence of carbon materials on the absorption performance of polymer-derived SiCN ceramics in X-band

Carbon-containing polymer-derived SiCN ceramics (PDCs-SiCN-C) were successfully fabricated with multi-layer graphene (MLG) and multiwalled carbon nanotubes (MWCNTs) as additives at 1100?°C. The effects of MLG and MWCNTs on the microwave absorption properties of PDCs-SiCN-C ceramics were analyzed. The imaginary permittivity and loss tangent of SiCN-MLG and SiCN-MWCNTs were about 3.4, 0.67 at 11.2?GHz and 3.1, 0.57 at 10.6?GHz, respectively. The minimum reflection loss of SiCN-MLG and SiCN-MWCNTs at 3?mm was ??54?dB and ??48?dB with the effective absorption bandwidth (RL ≤ ?10?dB, >90% absorption) about 1.5?GHz and 0.9?GHz in X-band.     

A New Class of Glasses for Double-Crucible Optical Fibers with High Numerical Apertures

A series of boron- and germanium-free silicate glasses was developed for the core glass of high-numerical-aperture double-crucible optical fibers. When combined with a boro-silicate cladding glass from a series also investigated in this study, fibers with a numerical aperture in the range 0.3 to 0.5 can be produced. The relatively high refractive indices in the core glasses are achieved by including large mole fractions of BaO, CaO, and ZnO, accompanied in some cases by smaller additions of ZrO₂ and/or Y₂O₃ in the glass composition. Measurements of the refractive index, density, Rayleigh scattering coefficient, and viscosities and observations of the devitrification behavior and chemical durability of the glasses are presented. Attenuation spectra of suitable core glasses and of double-crucible optical fibers comprised of different core and cladding combinations yielding high numerical apertures are given. The fibers have attenuations near 10 dB/km at 850 nm.