MeCeOx(Me=In,Zr)固溶催化剂制备及催化合成碳酸二甲酯研究

采用液相共沉淀法制备了MeCeOx(Me=In,Zr)双金属氧化物固溶催化剂.借助X射线衍射(XRD)、X射线光电子能谱(XPS)、程序升温还原(H2-TPR)、程序升温脱附(CO2-TPD、CH3OH-TPD)及漫反射傅里叶变换红外光谱(DRIFTS)等手段对催化剂物化性质进行了分析表征.在系统考察不同金属氧化物种类...     

SAPO-34提升铁钒基催化剂抗碱性能研究

采用浸渍法制备Fe-VO_x/SAPO-34和Fe-VO_x/TiO₂脱硝催化剂,探究SAPO-34分子筛与TiO₂两种载体负载铁钒基氧化物催化活性及抗碱性能的差异。借助X射线衍射(XRD)、X射线光电子能谱(XPS)、氨气程序升温脱附(NH₃-TPD)、氢气程序升温还原(H₂-TPR)、原位红外漫反射(in-situ DRIFTs)等表征手段对催化剂的骨架结构、表面物化性质、氧化还原能力以及对反应气体的吸脱附情况进行分析。结果表明:SAPO-34分子筛内部特定的孔道结构和稳定的骨架,有利于活性组分在载体上均匀分散,降低碱金属对表面活性中心的物理覆盖作用;同时其表面丰富的酸位点能够作为碱金属捕获位,保护催化剂表面的活性中心,保证催化剂的吸附-反应过程能够正常进行,从而使Fe-VO_x/SAPO-34表现出良好的抗碱金属能力。     

MnOx/TiO2低温SCR脱硝催化材料热失活原因研究

针对锰钛选择性催化还原(SCR)脱硝催化材料运行失活问题,采用X射线衍射(XRD)、N2吸附-脱附(BET)、程序升温还原(H2-TPR)、程序升温脱附(NH3-TPD)、X射线光电子能谱分析(XPS)等表征手段,以及催化活性评价装置,对比分析了使用前后SCR脱硝催化材料催化活性以及物化性质的差异,综合分析SCR催化材料的失活原因.结果表明,催化材料在200℃下运行100h后脱硝效率由98;下降到50;,催化活性降低是多种因素共同作用的结果,其中结晶度提高、活性成分分散性降低、表面酸性位点数量减少导致催化材料无法吸附足够的NH3去参与反应,是催化活性降低的主要原因;而活性成分MnOx中Mn3含量下降,品格氧所占比例增加,也在一定程度上促进了催化材料的失活.     

ZnO-SiO2的制备及其光催化降解罗丹明B

采用溶胶-凝胶法制备负载型ZnO-SiO2光催化材料,研究升温速率及负载量对ZnO结构、形貌及光催化活性的影响.通过X射线衍射、N2物理吸附-脱附、扫描电子显微镜、光致发光光谱和紫外-可见漫反射光谱等手段对催化剂进行表征,并以罗丹明B为模拟污染物,紫外光为光源,评价催化剂活性.结果表明,升温速率对ZnO-SiO2光催化剂结晶度和光催化活性影响显著.当ZnO与SiO2的质量比为1∶1时,ZnO-SiO2具有均匀、平滑的球形形貌,并且ZnO光催化活性明显改善.     

钒改性对铁基脱硝催化剂活性及抗碱性能的影响

通过引入V物种对二氧化钛负载的铁基催化剂进行改性,制备出了FeV/TiO₂催化剂,并与未改性的铁基催化剂进行比较,通过X射线衍射(XRD)、拉曼光谱测试(Raman)、比表面积测试(BET)、紫外-可见-近红外漫反射光谱测试(UV-Vis-NIR)、氨气程序升温脱附(NH₃-TPD)以及氢气程序升温还原(H₂-TPR)等一系列测试对催化剂进行了表征。结果表明,引入V后的催化剂呈现出以FeVO₄为主相的状态,并存在大量的酸性位点而具有较强的表面酸性,Fe、V物种间的强相互作用大大提升了氧化还原性,因此催化剂低温活性得以显著提升且温度窗口大大拓宽。此外,催化剂的结构几乎不受碱中毒的影响,且在K中毒后仍能维持较强的表面酸性,具有良好的抗碱金属中毒性能。     

不同厚度TS-1空心球分子筛的制备及表征

以四丙基氢氧化铵(TPAOH)为模板剂,正硅酸乙酯(TEOS)为硅源,低成本硫酸钛(Ti(SO4)2)为钛源,在传统碱处理的基础上通过溶解-再结晶的后处理方法,制备得到了形貌规整且大小均匀的球形TS-1空心纳米颗粒,其颗粒尺寸约为200 nm.采用X射线衍射(XRD),N2吸脱附测试,扫描电镜(SEM),透射电镜(TEM)以及红外可见光谱(FTIR)等手段对不同后处理条件所得空心材料进行表征,结果表明,再结晶时间对空心材料的壁厚有明显的影响,且所得样品中Ti物种主要是以骨架内四配位形式存在的.同母体分子筛相比,空心材料在丙烯环氧化反应中体现出更好的催化活性.     

化学沉淀法制备纳米Fe/TiO2及其光催化活性的研究

以TiCl4为钛前驱体,氨水为沉淀剂,氯化铁为掺杂离子给体,采用化学沉淀法,制备了纯的与铁掺杂的TiO2纳米光催化剂.采用XRD、差热-热重等分析方法对产物进行了表征.通过苯酚水溶液的光催化降解实验研究了样品的光催化性能,考察了Fe3+掺杂量、苯酚溶液的pH值对光催化活性的影响.结果表明:Fe3+掺杂抑制了晶粒长大,细化了晶粒.Fe3+取代晶格中Ti4+的位置或进入间隙位置,引起晶格畸变.适量的Fe3+掺杂能减少光生电子与空穴的复合,提高光催化剂的光催化性能.在本实验条件下,Fe3+掺杂量为0.1 mol;,苯酚溶液的pH为9时,纳米TiO2具有最佳的光催化性能,在20 W 紫外灯照射下降解16 h,降解率达到89.3;.     

Ti3Al/HAP复合材料的制备与性能研究

采用化学沉淀法在模拟体液中制备了纳米羟基磷灰石(HAPs)粉体,用金属钛粉和铝粉经过机械合金法,制备了金属间化合物Ti3 Al;将制备的HAP粉体作为基体材料加入第二相Ti3Al粉体,经过球磨分散得到Ti3Al/HAP复合粉体,经过热压烧结,得到羟基磷灰石与金属间化合物Ti3Al的复合材料.通过XRD、SEM及TEM等测试方法,分析了用普通化学沉淀法制备的羟基磷灰石(HAPc)和在模拟体液中生成的羟基磷灰石(HAPs)的区别及Ti3Al对羟基磷灰石结构和性能的影响.测试结果显示:在模拟体液中生成的羟基磷灰石颗粒均匀细小,纯度较高,结晶度较低;羟基磷灰石掺入一定量的Ti3Al后,弯曲强度和断裂韧性有所降低,X射线衍射显示复合材料中只有Ti3 Al和HAP两种物质,没有新物质生成.     

Mn含量对Ba(Ti0.7-xMnxFe0.3)O3陶瓷的磁性能及交换机制的影响

通过固相反应法制备Ba(Ti0.7-xMnxFe0.3)O3(0.05≤ x≤0.2)陶瓷,并利用X射线衍射、穆斯堡尔谱和振动样品磁强计研究其微结构、磁性能及交换机制随Mn含量的变化规律.结果表明:所有样品都具有6H-BaTiO3型六方钙钛矿单相结构.在Mn含量较低时,分布在四面体Ti位和八面体Ti位上的Fe3+间的超交换相互作用使样品表现出顺磁性;随着Mn含量的增加,除了Mn7+外还出现了Mn4+,Mn4+-O2--Fe3+ 铁磁超交换机制使样品逐渐转变为室温铁磁性.与相同Fe含量及制备条件下的Ba(Ti0.7Fe0.3)O3相比,Mn的共掺杂可使饱和磁化强度提高近19倍.     

炭吸附纳米氧化铁的制备及其可见光催化性能

采用炭吸附共沉淀法制备了氧化铁(Fe2O3)纳米粉体,通过热重分析仪(TG-DTA)、X射线衍射仪(XRD)、紫外可见分光光度计(UV-Vis)和透射电镜(TEM)等手段对催化剂的热稳定性、物相结构、吸光性能、形貌进行表征;以甲基橙(MO)为目标降解物,镝灯为可见光源,研究了Fe2 O3纳米粉体的光催化性能.结果表明,炭吸附共沉淀法制得的Fe2O3粉体粒径小、分布均匀、团聚较少;Fe2O3的吸收波长发生红移且在紫外光、可见光区域的吸收能力增强.光催化降解甲基橙结果显示,炭吸附共沉淀法制得的Fe2O3粉体在60 min内降解率达到74;,是沉淀法制备的Fe2O3粉体降解率的2.2倍.     

Modelling of mechanism of agglomeration of KCl crystallization

The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

Mechanism of spatial ordering of dislocations during plastic deformation of crystals

Mechanisms of spatial ordering of dislocations during plastic deformation of crystals are considered. The system of evolution equations, which take into account the effects of elastic and correlated interactions of screw dislocations, is derived. The study is performed with due regard for the dynamics of spatial fluctuations of the dislocation density.