Cr/MSU-1催化剂中Cr含量对CO2氧化丙烷脱氢反应催化性能的影响

研究了CO2氧化丙烷脱氢制丙烯高效wCr/MSU-1 (w＝2, 4, 6, 8, 10, 质量分数, 以Cr2O3计算)催化剂中Cr含量对催化剂结构和催化活性的影响. 催化剂活性评价结果表明, 随Cr含量的增加, 催化剂的活性呈现先提高后降低的变化趋势. 在600 ℃条件下, 6.0Cr/MSU-1表现出最佳的催化反应活性, 其中丙烷、CO2转化率分别达到62.6%和22.1%. 为明确Cr含量对催化剂结构的具体影响, 对催化剂样品进行了XRD, UV-Vis和XPS表征: 催化剂样品的XRD表征发现Cr/MSU-1催化剂不仅能够保持良好的MSU-1分子筛的孔道结构, 而且活性金属Cr在载体表面具有很高的分散度, 随着Cr含量的增加催化剂表面形成明显的Cr2O3晶相; UV-Vis表征结果证实低Cr含量催化剂表面主要以Cr6＋的形式存在, 高Cr含量催化剂表面有明显的Cr3＋出现; 反应前后的催化剂XPS表征结果进一步证实催化剂表面的Cr6＋与催化反应活性具有良好对应关系. 基于上述结果, 我们认为Cr6＋是该催化剂重要的活性中心.     

Nd2Fe14.5Cr2.5化合物的结构和相变

通过X射线衍射、差热分析及磁测量等手段对电弧炉熔炼的Nd2Fe14.5Cr2.5化合物的结构和相变进行了研究,研究结果表明,950℃下退火的样品具有Th2Zn17型结构,其居里温度为375 K.1100℃下退火的样品具有Nd3(Fe.Ti)29型结构,其居里温度为445 K.Nd2Fe14 5Cr2.5化合物在1100℃左右发生结构相变,山菱方相的Th2Zn17型结构转变成单斜相的Nd3(Fe,Ti)29型结构.具有Th2Zn17型相结构的Nd2Fe14.5Cr2.5化合物在约300℃左右可以发生有效的吸氮反应.     

Ca改性钛酸铅纳米晶的制备及结构研究

用溶胶-凝胶工艺制备了Pb_1-xCa_xTiO₃(0≤x≤0.3)纳米晶,在不同焙烧条件下研究其粉体晶相结构的变化.研究结果表明,升温速度和焙烧温度对纳米粉的晶相、晶胞参数和晶粒尺寸有显著影响.讨论了晶胞参数、四方畸变度和晶胞体积与Ca含量的关系.     

NdxEr5-xSi3系列化合物晶体结构和磁性研究

利用电弧熔炼制备了NdxEr5-xSi3(x=0~5)系列化合物样品。通过X射线粉末衍射分析和磁性测量研究了Nd替代Er对Er5Si3化合物结构和磁性的影响。研究结果表明:随着Nd替代量的增加,其晶体结构、相组成及磁性能发生了明显变化。低Nd含量时(x≤3),样品具有Mn5Si3型六角结构,空间群为P63/mcm,样品具有反铁磁性。虽然奈尔温度不遵循De Gennes定律,但能被RKKY理论完美解释。高Nd含量时(x=5),样品具有Cr5B3型四方结构,空间群为I4/mcm,对外显示铁磁性。Nd含量为x=4时,两种结构共存,Rietveld精修表明Mn5Si3型结构占58(1)%,Cr5B3型结构占42(1)%。其磁化率温度曲线在50~100 K具有铁磁性特征,但随着温度的进一步下降,又显示出反铁磁性的特征,暗示其内部存在着铁磁相和反铁磁相的耦合。     

2H NMR和DSC法研究十二烷基磺酸钠-正戊醇-水三元体系的溶致液晶

测定了十二烷基磺酸钠/正戊醇/水体系的相平衡,在相图中的液晶区选取样品点,采用²H NMR和差示扫描量热方法,并结合其液晶纹理,研究了该体系液晶相的结构特点。结果表明,在一定温度下,整个液晶区均为层状液晶,其相结构不随水含量和醇含量的变化而变化。在组成固定的情况下,该体系液晶的相结构随温度的升高而发生变化。     

^2H NMR和DSC法研究十二烷基磺酸钠—正戊醇—水三元体系的…

测定了十二烷基磺酸钠／正戊醇／水体系的相平衡，在相图中的液晶区选取样品点，采用＾２Ｈ ＮＭＲ和差示扫描量热方法，并结合其液晶纹理，研究了该体系液晶相的结构。结果表明，在一定温度下，整个液晶区均为层状液晶，其相结构不随水含量和醇含量的变化而变化。在组成固定的情况下，该体系液晶的相结构随温度的升高而发生变化。     

乙烯含量对抗冲丙烯共聚物等温结晶行为的影响

利用DSC研究了乙烯含量不同的4种抗冲丙烯共聚物的等温结晶动力学.结果表明4种样品在考察的温度范围内(126~130℃)的等温结晶动力学完全符合Avrami方程,并得到了不同结晶温度下Avrami方程的结晶动力学参数k,n和t1/2,随着样品中乙烯含量的增加,Avrami指数(n)随温度变化不大,样品的结晶过程可能属于三维扩散控制的成核增长,4种样品的结晶活化能ΔE在279.5~343.1 kJ/mol范围内,且随乙烯含量增加,结晶活化能增大,充分说明样品中的乙烯含量是影响其结晶活化能的主要因素.结晶分级分析测试结果显示,随着乙烯含量的增加,聚丙烯均聚物部分链结构规整性提高,结构规整、可结晶的长序列含量在减少,可见乙烯含量的变化规律直接决定上述参数的变化规律.     

丙烯酰胺双水相聚合体系稳定性研究

通过浊点滴定法测定了不同温度下PAAmPEGH2O双水相体系相图,发现分相浓度随着温度的升高先增后降,55℃时分相浓度最低.双水相聚合体系微观结构显示,分散相以砾状液滴形式均匀分散在连续相中.研究了聚合过程中聚合体系粘度的变化,以及聚合温度、分散介质、单体、引发剂及乳化剂等对聚合体系最终粘度的影响,聚合体系最终粘度在一定范围内随分散介质和单体浓度增加变化不大,但是超过某一浓度后聚合体系粘度急剧增加;聚合体系中加入少量乳化剂对体系粘度影响不大,但加入大量乳化剂后体系稳定性变差,聚合体系粘度急剧增加;聚合体系最终粘度随着聚合温度升高先降后增,与相图的预测结果一致.     

CaO杂质对铝型材厂工业污泥合成堇青石材料晶相结构及其含量影响

探讨原料组成对铝型材厂工业污泥合成堇青石材料的影响是非常重要的。研究目的有助于确定不同杂质在原料中允许的存在量,为选择其他原料提供可靠的依据。采用XRD法和SEM法分析各试样的晶相结构:用半定量分析方法确定各晶相的含量:用philipsX抪ertplus软件确定试样中各晶相结构参数。实验结果表明:CaO杂质含量从1.2~2.5%对合成堇青石有利:从2.5~2.8%堇青石含量开始下降:确定2.5%为CaO杂质最佳存在量,其对应的堇青石含量为91%。经plus软件确定结果:CaO杂质含量为1.2%时,其结构与单晶相同,晶胞参数变化很小:CaO含量从1.2~2.8%,其晶系由六方转变为四方结构,晶胞参数发生较大变化。镁铝尖晶石结构与晶胞参数变化较大,由单晶的立方结构转变为四方结构。     

反应温度与时间对铝型材厂工业污泥合成堇青石材料的得率与晶相结构影响

本研究主要探讨反应温度和反应时间对铝型材厂工业污泥合成堇青石材料的得率和晶相结构的影响。该污泥系由铝型材表面处理时产生的大量废液, 经沉淀过滤所得。主要成分是一种超细的γ-AlOOH, 其中部分是晶体, 部分是无定形体, 活性很高, 有利于堇青石晶相的形成, 能降低反应温度。 实验结果表明: 堇青石含量随着反应温度升高而增加; 晶相结构和晶胞参数与反应温度有关; 确定1350℃为最佳的反应温度; 反应时间在 2~5 h的试样中,堇青石含量增加, 在5~6 h含量降低. 5 h为最佳的反应时间。     

Thermodynamics and defect structure of intermetallic phases with the B2 (CsCl) structure

Available theoretical models that describe the thermodynamic properties and the defect structures of intermetallic phases with the B2 structure are reviewed. The experimental methods for the determination of the Gibbs energy of alloys are briefly discussed and a summary of experimental data of lattice parameters, densities, activities, and enthalpies for nearly 30 B2 phases is given. It is shown that the data can be expressed in terms of a few simple model parameters. The importance of theoretical models for an understanding of the structural stability of intermetallic phases and for the evaluation and eventual prediction of binary and ternary phase diagrams is discussed.     

Ordered binary crystal phases of Lennard-Jones mixtures

The lattice energies at zero temperature are calculated, using Lennard-Jones interactions, for a large number of crystal structures associated with ordered binary compounds. In units of the AA interaction length and strength (i.e., sigmaAA= epsilonAA= 1.0) we examine the lowest energy structures, including coexisting phases, across the space of cross-species interactions 0.6< or = sigmaAB< or = 1.1 and 1.0< or = epsilonAB< or = 2.0. The remaining parameters sigmaBB= 0.88 and epsilonBB= 0.5 are chosen so that the parameter space studied includes the space of binary glass-forming alloys. In addition to some large unit cell structures such as Ni3P and PuBr3 appearing among the lowest lattice energies, a number of low-energy structures based on close-packed lattices are found that do not correspond to any experimentally observed crystals. The prevalence and stability of metastable crystal phases at the compositions AB, A2B, and A3B is examined.     

Phase equilibria in the Al-Cu-Fe system at a temperature of 853 K in the aluminum enriched region

The phase equilibria in the Al-Cu-Fe system at 853 K in the aluminum enriched region are studied using the methods of scanning and transmission electron microscopy, X-ray phase analysis, and electron probe microanalysis. An isothermal cross section of the system is constructed. Crystal lattice parameters of the phases based on binary and ternary compounds are determined. Approximant phases are not found to form in the quasicrystalline i-phase region.     

亚稳态Fe0.5-xCoxCu0.5纳米晶粉末的微观结构研究

利用机械合金化方法制备了Fe0.5-xCoxCu0.5(x=0,0.1,0.2,0.3,0.4,0.5)系列合金材料,采用X射线衍射和DSC方法对不同组分的样品进行了测试和分析,将XRD的分析结果与DSC测量结果进行了比较,并从γ相转变温度的角度对微观结构进行了研究.结果表明,球磨60h后可以得到以Cu为基的fcc的均相结构,合金粉末的晶粒尺寸、均方根内应力和均缺陷密度与组分的关系不大,晶格常数与组分的关系很大,Co0.5Cu0.5样品的晶格常数比纯Cu的小.合金样品的组分和微观结构对γ相的转变温度和放热焓有很大影响.     

Influence of a Second Cation (M = Ca2+, Mg2+) on the Phase Evolution of (BaxM1–x)F2 Starting from Amorphous Deposits

A second type of cation (Mg²⁺, Ca²⁺) was introduced into BaF₂ by low‐temperature atomic beam deposition. The structure evolution from low‐temperature (–150 °C) amorphous deposits to high‐temperature (< 1000 °C) annealed crystalline phases was studied by in‐situ transmission electron microscopy and X‐ray diffraction. Amorphous (Ba_0.5, Ca_0.5)F₂ crystallizes in a first step to metastable solid solution phase (fluorite‐type), which then decomposes into the pure phases of CaF₂ and BaF₂ at higher temperature. The crystallization behavior of amorphous (Ba_xMg_1–x)F₂ is completely different. When the Mg/Ba atomic ratio is around 1:1, the mixture transforms to the ternary compound BaMgF₄ at annealing, and no decomposition occurs by further heating up to 1000 °C. When the Ba concentration is below 15 % in atomic ratio (x < 0.15), the mixture forms a solid solution phase (rutile type) with the lattice expanded by +1 % compared to rutile type MgF₂. The difference between the phase evolutions of the two mixture systems is discussed.     

MB25镁合金中的准晶体与晶体相的研究

利用透射电子显微术（ＴＥＭ）及能谱仪微区成分分析（ＥＤＳ）技术，对含有稀土元素的铸态Ｍｇ－Ｚｎ－Ｚｒ－Ｙ系高强镁合金ＭＢ２５中的稀土相鉴定发现，在铸态合金的晶界上存在准晶相，其电子衍射谱显示出５－３－２次对称的特点，为二十面体准晶相。在与准晶相连区域发现一种ＭｇＺｎ＿２型的Ｌａｖｅｓ相，其点阵常数为ａ＝０．５４２ｎｍ，Ｃ＝０．８７３ｎｍ。     

Investigations of the tin-antimony-oxygen system by high-resolution electron microscopy

A range of tin-antimony oxides, prepared by the calcination of precipitates, were examined by high-resolution electron microscopy. Products formed at 600°C contain small crystals of a rutile-type material and, depending on antimony concentration, varying amounts of disordered and/or amorphous phases. The observations are consistent with a resistivity to bulk phase equilibrium under conditions of low temperature and high antimony concentrations. Heating of the tin-antimony oxides to 1000°C for prolonged periods is accompanied by an increase in the crystallinity and particle size of the rutile-type material as a result of the thermally induced aggregation of tin(IV) oxide units. The observations are consistent with limited antimony incorporation in the bulk tin(IV) oxide lattice and a migration of antimony to surface sites. There was no evidence for any discrete, readily identifiable, antimony oxide phases, although a nonrutile-type material was observed at higher antimony concentration. The rutile-type phases often contained planar faults which were identified in some instances as twin boundaries; the possibility that these might provide a means of accommodating antimony within the tin oxide lattice is briefly considered. The relationship between our observations and the information available from other techniques is discussed.     

The compounds and the phase diagram of MoO3-Rich Bi2O3MoO3 system

The equilibrium phase diagram between 0 and slightly above 50 mole% Bi₂O₃ in the Bi₂O₃MoO₃ system has been studied by differential thermogravimetric analysis (DTA) and X-ray diffraction measurements on fused mixtures and single crystals. The results confirm the existence of the four compounds α (Bi₂O₃·3MoO₃), β (Bi₂O₃·2MoO₃), γ (Bi₂O₃·MoO)₃ and ? (～1.3Bi₂O₃·MoO₃) in the system. However, the phase diagram as well as the nature of melting of the α and γ were found disagreed with previous results. The γ compound melts incongruently at 947°C, whereas the α compound melts congruently at 662°C. The crystal class and lattice parameters of the compounds were determined based on the single crystal as well as powder pattern techniques. The results show that all four compounds have the monoclinic structure. The unit cell parameter of the β, γ, and ? compounds were found to be quite different from previously reported data. The lattice parameters obtained from X-ray analysis were also verified by density measurements of the single crystals. The polymorphism of the compounds was also investigated with single crystal samples. No polymorphic transformations for the α, β, and γ phases were detected in the work.     

Phase Equilibria in the Ni–Al–W System at 900°C

Summary. Multicomponent Ni-base alloys exhibit good mechanical properties even at elevated temperatures and they are widely used for industrial production of exertion-resistive parts of engines. These properties are mainly determined by the coexistence of a disordered γ matrix with a face centred cubic lattice and cuboidal domains of its ordered γ′ structure. Therefore it is useful to study phase equilibria in Ni-base systems, namely in the regions involving both mentioned phases. One of the conclusions of our recent work on Ni–Al–Cr–W system was a necessity of modification of selected thermodynamic parameters of the ternary Ni–Al–W subsystem in order to achieve a better agreement of our experimental observations with theoretical modelling. This involves new measurements of the microstructure of selected samples of the Ni–Al–W system at 900°C and the comparison of the results with existing literature data in order to confirm our conclusions on higher order system investigated before. It is a first step on the way to an assessment of the Ni–Al–W system, which has not been done before.