裂解型高聚物的共混辐射交联

本文对聚甲基丙烯酸甲酯（PMMA）和聚异丁烯（PIB）两种典型的辐射裂解型高聚物的共混体系聚甲基丙烯酸甲酯-聚氧化乙烯（PEO），聚甲基丙烯酸甲酯-聚偏氟乙烯（PVDF），和聚异丁烯-乙丙共聚物（EPR）进行了较为详细的研究，结果表明：1、PMMA-PVDF共混体系溶胶抽提发现，在此共混体系中，PMMA发生裂解，且随辐照剂量增加，体系可被抽出量增加，符合关系（D_o-D_R) = KR + b k，b是常数，R为剂量，D是归一后的PMMA的相对剩余量，PMMA在共混体系（PMMA-PVDF）中的辐射裂解遵守无规降解规则，适合1/((M-bar)_n) = K (R_o + R)关系。PMMA的裂解程度可直接由溶胶抽提决定。机械性能测定表明，PVDF的存在，对PMMA的机械性能的辐射损伤有保护作用，少量PVDF的加入，不影响材料的透明性，抗冲击强度大为增加，且经一定剂量辐照后，抗张强度和断裂伸长无显下降。结晶分析发现，PVDF不论在共混体系或均聚物中，经辐照到一定高的剂量，其DSC曲线上的结晶熔峰分裂为双重。和国外文献报道的结果正相反。由此得出PVDF中多种晶型的存在，及晶型在一定温度发生转化。2、PMMA-PEO共混体系 凝胶抽提，热形变测定，付立叶变换红外光谱和动态力学粘弹谱测定都证明，PMMA和PEO共混以后，无论是在真空，还是在空气中辐照，PMMA发生了交联。并且交联是在一定的PEO-PMMA混合配比和一定辐照剂量范围内进行的。在某一配比时，交联率达最高。用扫描电镜和透射电镜对共混体系的相结构形态进行研究表明。交联最好的组成比是在PMMA-PEO共混体系的相倒转点附近。溶液共混时，PMMA-PEO体系的互溶程度与共混的温度条件有关，温度高于PEO的熔点时，共混体系的互溶性要比常温时共混要好，这和理论预测的结果一致。红外分析的结果说明，PMMA的交联主要是通过残基结合的方式进行的。3、PIB-EPR共混体系 采用低温DSC对PIB-EPR共混体系的互溶性进行了研究，发现PIB-EPR的互溶性较好，其Tg转变为-拓宽的单峰。凝胶抽提指出，聚异丁烯经与乙丙共聚物共混以后，在一定配比和一定辐照剂量范围内，聚异丁烯发生了交联，且在一定配比时交联率达到最高。交联是否发生，还与共混的方式有关，溶液共混时不发生交联。低温DSC研究显示，溶液共混时，其互溶性不如机械共混时PIB与EPR的互溶性好，前者的Tg转变呈现出分裂的双峰。4、裂解型高聚物与交联型高聚物共混以后，是否可以发生交联，首要的是体系的互溶程度，体系越均匀，交联的可能性越大（但不是充分条件）。由于互溶性不好，PMMA和很多橡胶共混合不产生交联，PIB与1，2-PBD以及和其它一些不饱和橡胶共混合不产生交联。在PIB，1，2-PBD共混体系的DSC分析曲线上，Tg转变是两独立的双峰，对应于PIB和1，2-PBD的Tg转变。交联的可能性能否实现，还与交联聚合物的链结构，柔顺性，及两种分子链间的相互作用有关。PMMA与PEO和PVDF两者的共溶性都很好（分子水平上），但前者可交联，而同后者共混后则裂解。

CaS:M (M=Ce~(3+), Dy~(3+), Eu~(2+), Cu)和Cas:Ce~(3+), M (M=Dy~(3+), Cu)的合成及其光致发光和热释发光性质研究

本文研究了Ce~(3+), Dy~(3+), Eu~(3+), Cu离子以及它们的共掺杂在硫化钙基质中的光致发光和热释发光性质，并用顺磁共振方法研究了磷光体中缺陷的性质及其对磷光体光致发光的影响。在CaS:Ce~(3＋)磷光体的稳定性影响因素，并经包膜后稳定性有所提高。计算了新的热释发光峰的陷阱参数。确定了热释发光的动力学级数。在Cas: Dy~(3+)磷光体中，研究了合成条件对磷光体发光性质的影响，讨论了新的热释发光峰的陷阱参数，确定了热释发光的动力学级数。在CaS:Dy~(3+)磷光体中，发现基质对Dy~(3+)离子具有敏化作用，讨论了黄兰比随Dy~(3+)离子浓度变化出现最大值的原因。计算了热释发光峰的陷阱参数，确定了热释发光的动力学级数。在CaS:Ce~(3+)，Dy~(3+)磷光体中，研究了Ce~(3+)离子的发光随Dy~(3+)离子浓度的变化，可能具有Dy~(3+) → Ce~(3+)的能量传递。计算了热释发光峰的陷阱参数，确定了热释发光的动力学级数。在CaS:Cu磷光体中，确定了不同Cu~+离子格位所产生的发射峰。根据磷光体中缺陷的转化过程解释了光致发光和热释发光性质随Cu离子浓度增加所呈现的规律性变化。通过实验证明磷光体有可能用作紫外剂量材料。本文还首次研究了CaS:Cu磷光体在UV（3bb nm)辐照下，发生Cu~+→Cu~(2+)的光氧化反应，通过EPR实验证明在Cu'_(Ca)→Cu_i~+处发生光氧化反应。在CaS:Ce~(3+),Cu磷光体中，观察到了Cu离子对Ce~(3+)离子的能量传递现象。在CaS:Eu~(2+)光体中，发光强度随Eu~(2+)离子浓度变化，显示浓度猝灭特性。本文还研究了CaS:Ce~(3+), CaS:Dy~(3+), CaS:Cu以及CaS:Ce~(3+), Cu磷光体中缺陷的性质，在CaS:Ce~(3+)中存在V_S~(2+)空位，并根据这一空位的性质，解释了发光光谱，并且选择适当的助熔剂使发光效率提高。在CaS:Dy~(3+)磷光体中，存在V_S~(2+)-V_(Ca)~(2-)空位对；在CaS:Cu和CaS:Ce~(3+), Cu磷光体中，存在V_S~(2+)空位和Cu'_(Ca)缺陷。

高Tc超导体R_1Ba_2Cu_3O_(2-x)(R-rare earth)的磁性和超异电性研究

本论文合成了R_1Ba_2Cu_3O_(2-x) (R = La、Nd、Sm、Eu、Gd、Dr、Ho、Er、Tm、Yb)、Y_2Ba_2Cu_3O_(2-x) (x = 0.10～1.17)和Y_1Ba_2Cu_3O_(7-x)S_x (x = 0～2)，并对磁性和超导电性进行了较为系统的研究。R_1Ba_2Cu_3O_(2-x)的磁化率在T > Tc的很宽的温度范围内服从Curic-Weiss定律，求得的有效磁矩略大于理论值，差值与Y_1Ba_2Cu_3O_(2-x)中Cu~(2+)磁矩相近，说明Cu~(2+)的磁矩对体系磁性有额外贡献，这贡献随R~(3+)离子中自旋平行的电子权的增多而增大。其高温下的磁化率CT > 700K)相对Curic-Weiss定律发生较大偏离，这偏离可能的来源有三个：高温下稀土离子发生较大的能级反转效应，高温下结构相变对磁性的影响，高温下氧含量减少造成Cu~(2+)磁矩增大。R_1Ba_2Cu_3O_(2-x)磁化率在T < Tc时也服从Curic-Weiss定律，R~(3+)磁矩是定域的，表明超导与磁性相互独立。互不相关，稀土磁矩与传导电子间无相互作用。用Sr取代R_1Ba_2Cu_3O_(2-x)中的Ba，没能使体系产生磁有序的变化，但却使有效磁矩增大，并完全破坏了样品的超导电性。Sm~(3+)磁化率不服从Curic-Weiss定律，在Sm_1Ba_2Cu_3O_(2-x)中Sm~(3+)显示了典型Van VlccK离子的特性。Y_1Ba_2Cu_3O_(2-x)随氧含量减少发生超导体一半导体一绝缘体的转化，当氧含量由6.90减小至6.49时发生由正交到四方的结构相变。当(7-x) = 5.83时有较多杂质相出现，123相开始分解。样品磁化率均服从Curic-Weiss定律，并随氧含量增大磁化率－温度曲线越来越趋于平缓（直线），当(7-x) = 6.90时磁化率基本不随温度变化，这时Pauli顺磁性占主导地位，这说明氧含量增加定域磁矩减少，求得的有效磁矩Peff随氧含量增大总趋势减小。提出了电子“巡游”的观点，较好地解释了上述现象，并推测出Cu(2)的d电子是离域的，对样品磁矩没有贡献，样品Peff来源于部分Cu(1)的定域Cu~(2+)的磁矩，上述推测被EPR结果证实。正交相Y_1Ba_2Cu_3O_(2-x)的EPR谱显示了中心对称成准立方晶场中Cu~(2+)(d~9, S = 1/2, I = 3/2)的EPR物性。而四方相样品的EPR谱却出现了明显的各向异性，说明观察到的为Cu(1)的EPR信号，由Cu(1)~(2+)的写域磁矩产生。Y_1Ba_2Cu_3O_(2-x)的EPR信号束源于本体相，而非Y_2Cu_2O_5、BaCuO_2、Y_2BaCuO_5等杂质相。各样品EPR信号的自旋浓度远小于1spin/cu，并随氧含量减小而增大，当(7-x) = 6.49、6.40时自旋浓度出现陡增，这时伴随由正交到四方的转化，证明了电子“巡游”观点的正确。用硫部分取代Y_1Ba_2Cu_3O_2g中的氧，当Y_1Ba_2Cu_3O_(2-x)Sx中x = 0.11时Tc = 92.6K，比Y_1Ba_2Cu_3O_(7-x)升高2K，但由于杂质相的存在，ΔTc加宽。其他样品多为半导体和绝缘体。硫取代0，当x = 0.04，0.06，0.11和1.20时磁化率服从Curic-Weiss定律，并且x = 0.87，1.2时分别在230K、240K出现反铁磁有序。其他样品由于Cu被还原为＋1价而变成抗磁性。x = 0.11 (Tc = 92.6K)，EPR谱为正交场中Cu~(2+)的信号。自旋浓度与温度无关。当所有Cu均为Cu~(1+)时，测问的是-s-的EPR信号，而Cu为混合价态(+1和+2时)测问是上述两种信号的叠加。

丙烯－乙烯分段共聚物的研究

本工作用核磁共振(~(13C-NMR)、示差扫描量热技术（DSC）、动态力学分析（DMA）、付里叶红外光谱（FTIR）、扫描电子显微镜（SEM）等手段系统地研究了丙烯、乙烯两步分段共聚、预期为聚丙烯－聚乙烯两嵌段共聚物（PP－B-PE）的合成物（简称丙烯－乙烯分段共聚物）的分子结构，热性能，形态及其分散相的坛韧作用。结果表明，将丙烯、乙烯分段共聚并不能得到预想的PP－b－PE两嵌段共聚物。由于残存丙烯单体和催化剂活性中心链转移反应的影响，丙烯－乙烯分段共聚物事实上是由PP、PE、EPR组成的共混物，从催化剂的催化机理推测合成物中可能含有一定量的PP-b-EPR两嵌段共聚物，但没有证据能证实它的存在。DSC的结果表明分段共聚物的热性能不同于PP／PE二元共混物，但绝不可能以此作为判别PP－B-PE嵌段共聚物存在的证据。形态的结果表明了分段共聚物为两相结构，EPR和PE组成聚集体以球形无规分布于PP基体中，并且在断裂过程中，分散相以多种方式起到坛韧的作用。在丙烯－乙烯分段共聚物／EPDM共混物的研究中，本工作系统地研究了共混物的热性能、结晶结构、结晶形态、转变行为、形态及其力学性能，发现在共混物中，PEDM对分段共聚物的热性能有一定的影响并与形态的变化有关。EPDM不改变分段共聚物的结晶结构，但使其结晶形态有很大变化，表现在球晶尺寸变小，球晶结构变得不完善等。EPDM能使共混物的韧性有较大提高，但却使共混物的模量和屈服强度有所下降。在共混物坛韧机理的研究中发现，EPDM通过以下几种方式起到坛韧的作用：1．EPDM改变了分段共聚物的结晶形态，如减小球晶尺寸，使球晶边界不明显并使其不完善。2．PEDM和分段共聚物中的分散相组成聚集体，形成类似于高抗冲聚苯乙烯的蜂窝状分散相，且随EPDM含量的坛加，分散相尺寸坛大，分散相之间的距离减小，改变应力场在分散相同围的分布，有利于共混物实现脆一韧转变。3．EPDM的加入，降低了分散相在低温下的模量，使分散相在低温下引发基体产生大量的银纹。4．分散相在断裂过程中被拉伸，在断面间形成桥一样的结构，阻止裂纹生长，减轻应力在裂纹尖端的集中。

A mechanism for enhanced photocatalytic activity of silver-loaded titanium dioxide

In this paper, silver-loaded TiO2 photocatalyst was prepared by photochemical impregnation method and characterized by transmission electron microscopy (TEM), diffuse reflectance spectra (DRS), photooxidation of phenol and photoreduction of Cr(VI). Electron paramagnetic resonance (EPR) was used to detect photoproduced paramagnetic radicals. The correlation of photocatalytic activity and photogenerated reactive species was discussed, and the mechanism of silver-loaded TiO2 for enhancement of photocatalytic activity was elucidated. The results show that deposited silver on TiO2 Surface acts as a site where electrons accumulate. The better separation between electrons and holes on the modified TiO2 surface allowed more efficiency for the oxidation and reduction reactions. The enhanced photocatalytic activity was mainly attributed to the increased amounts of O-2(.-) reactive species and surface Ti3+ reactive center on silver-loaded TiO2 photocatalyst. (C) 2004 Published by Elsevier B.V.

Effect of support on chromium based catalysts for the oxidative dehydrogenation of C2H6 with CO2 to C2H4

The oxidative dehydrogenation of ethane (ODE) with CO2 to C2H4 has been studied over a series of Cr-based catalysts using SiO2, Al2O3, (MCM-41 zeolite) MCM-41, MgO and Silicate-2 (Si-2) as the supports. TPR, NH3-TPD, and EPR characterizations of catalysts were carried out to investigate the reduction property of Cr species on different supports, the acidities of catalysts and Cr species of 6Cr/SiO2 catalysts, respectively.

The enhancement of TiO2 photocatalytic activity by hydrogen thermal treatment

In this study, conventional TiO2 powder was heated in hydrogen (H-2) gas at a high temperature as pretreatment. The photoactivity of the treated TiO2 samples was evaluated in the photodegradation of sulfosalicylic acid (SSA) in aqueous suspension. The experimental results demonstrated that the photodegradation rates of SSA were significantly enhanced by using the H-2-treated TiO2 catalysts and an optimum temperature for the H-2 treatment was found to be of 500-600 degreesC. The in situ electron paramagnetic resonance (EPR) signal intensity of oxygen vacancies (OV) and trivalent titanium (Ti3+) associated with the photocatalytic activity was studied. The results proved the presence of OV and Ti3+ in the lattice of the H2-treated TiO2 and indicated that both were contributed to the enhancement of photocatalytic activity. Moreover, the experimental results presented that the EPR signal intensity of OV and Ti3+ in the H-2-treated TiO2 samples after 10 months storage was still significant higher than that in the untreated TiO2 catalyst. The experiment also demonstrated that the significant enhancement occurred in the photodegradation of phenol using the H-2-treated TiO2. (C) 2002 Elsevier Science Ltd. All rights reserved.

Mass transfer resistance in the production of high impact polypropylene

Mass transfer resistance in the production of high impact polypropylene (hiPP) produced by a two-stage slurry/gas polymerization was investigated by field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. It is found that the formation of ethylene-propylene copolymer (EPR) phases in polypropylene (iPP) particle produced in the first stage slurry polymerization exhibits a developing process from exterior to interior

Blends of Polypropylene and Syndiotactic 1,2-Polybutadiene: Morphology, Crystallization Behaviors and Mechanical Properties

Morphologies, crystallization behavior and mechanical properties of polypropylene(PP)/syndiotactic 1,2-polybutadiene(s-1,2 PB) blends were investigated. Morphology observation shows the well dispersed domains of s-1,2 PB in PP matrix with the rather small domain sizes from 0.1 to 0.5 mu m when the s-1,2 PB content increases from 5% to 20% (mass fraction) in the blends, and the phase structure tends to become co-continuous as s-1,2 PB content further increases.

Bluish-white emission from radical carbonyl impurities in amorphous Al2O3 prepared via the Pechini-type sol-gel process

Many efforts have been devoted to exploring novel luminescent materials that do not contain expensive or toxic elements, or do not need mercury vapor plasma as the excitation source. In this paper, amorphous Al2O3 powder samples were prepared via the Pechini-type sol-gel process. The resulting samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), photoluminescence (PL) excitation and emission spectra, kinetic decay, and electron paramagnetic resonance (EPR).

Effect of Copolymerization Time on the Microstructure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-Reactor Alloys

Three Polypropylene/Poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys produced by a two-stage slurry/gas polymerization had different ethylene contents and mechanical properties, which were achieved by controlling the copolymerization time. The three alloys were fractionated into five fractions via temperature rising dissolution fractionation (TRDF), respectively. The chain structures of the whole samples and their fractions were analyzed using high-temperature gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), C-13 nuclear magnetic resonance (C-13 NMR), and differential scanning calorimetry (DSC) techniques. These three in-reactor alloys mainly contained four portions: ethylenepropylene random copolymer (EPR), ethylene-propylene (EP) segmented and block copolymers, and propylene homopolymer. The increased copolymerization time caused the increased ethylene content of the sample. The weight percent of EPR, EP segmented and block copolymer also became higher.

Hydroxyapatite Nano- and Microcrystals with Multiform Morphologies: Controllable Synthesis and Luminescence Properties

Hydroxyapatite (Ca-5(PO4)(3)OH) nano- and microcrystals with multiform morphologies (separated nanowires, nanorods, microspheres, microflowers, and microsheets) have been successfully synthesized by a facile hydrothermal process. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra, kinetic decay, and electron paramagnetic resonance (EPR) were used to characterize the samples. The experimental results indicate that the obtained Ca-5(PO4)(3)OH samples show an intense and bright blue emission under long-wavelength UV light excitation. This blue emission might result from the CO2 center dot- radical impurities in the crystal lattice.

Phase transformation and photoluminescence properties of nanocrystalline ZrO2 powders prepared via the Pechini-type sol-gel process

Nanocrystalline ZrO2 fine powders were prepared via the Pechini-type sol-gel process followed by annealing from 500 to 1000 degrees C. The obtained ZrO2 samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), and photoluminescence spectra (PL), respectively. The phase transition process from tetragonal (T) to monoclinic (M) was observed for the nanocrystalline ZrO2 powders in the annealing process, accompanied by the change of their photoluminescence properties. The 500 degrees C annealed ZrO2, powder with tetragonal structure shows an intense whitish blue emission (lambda(max) = 425 nm) with a wide range of excitation (230-400 nm). This emission decreased in intensity after being annealed at 600 degrees C (T + M-ZrO2) and disappeared at 700 (T + M-ZrO2), 800 (T + M-ZrO2), and 900 degrees C (M-ZrO2). After further annealing at 1000 degrees C (M-ZrO2), a strong blue-green emission appeared again (lambda(max) = 470 nm).

Two-Step Spin-Transition Iron(III) Compound with a Wide [High Spin-Low Spin] Plateau

A new iron(III) coordination compound exhibiting a two-step spin-transition behavior with a remarkably wide [HS-LS] plateau of about 45 K has been synthesized from a hydrazino Schiff-base ligand with an N,N,O donor set, namely 2-methoxy-6-(pyridine-2-ylhydrazonomethyl) phenol (Hmph). The single-crystal X-ray structure of the coordination compound {[Fe(mph)(2)](ClO4)(MeOH)(0.5)(H2O)(0.5)}(2) (1) determined at 150 K reveals the presence of two slightly different iron(III) centers in pseudo-octahedral environments generated by two deprotonated tridentate mph ligands. The presence of hydrogen bonding interactions, instigated by the well-designed ligand, may justify the occurrence of the abrupt transitions. 1 has been characterized by temperature-dependent magnetic susceptibility measurements, EPR spectroscopy, differential scanning calorimetry, and Fe-51 Mossbauer spectroscopy, which all confirm the occurrence of a two-step transition. In addition, the iron(III) species in the high-spin state has been trapped and characterized by rapid cooling EPR studies.