晶种法制备高长径比纳米银线的研究

利用AgNO3和NaCl反应生成的AgCl颗粒作为晶种合成纳米银线.详细研究了纳米银线在溶液中的生长过程,探讨了AgCl晶种与银源AgNO3物质的量的比和反应时间对纳米银线形貌的影响.通过SEM、TEM、XRD、紫外可见光光谱等测试方法,对纳米银线的生长过程和不同条件下制备的纳米银线的微观形貌和晶体结构进行表征.实验表明,纳米银线是在AgCl颗粒表面上定向生长,AgCl与AgNO3物质的量的比和反应时间影响纳米银线的长度和直径大小.当AgCl与AgNO3的物质的量比为1:5,反应时间4 min时,制备的纳米银线平均直径52 nm,长径比超过了1000.     

反向微乳液法合成ZnO纳米棒及其生长机理研究

采用对比实验法,利用表面活性剂CTAB、正己烷、异丙醇和Zn2水溶液组成的反向微乳液体系制备了ZnO纳米棒,探讨了组成及工艺因素对纳米棒形貌影响,采用XRD和SEM分析技术对实验产物物相结构及形貌进行了表征.结果表明,通过调控Zn2+水溶液的浓度、水相含量与表面活性剂加入量的物质的量比(W)能更有效的控制ZnO纳米棒的长径比.     

PVP的混合分子量体系对AgNWs生长包覆的影响研究

近年来,AgNWs(Ag Nanowires)透明电极由于良好的导电性、优秀的韧性,作为氧化铟锡(ITO)的替代材料受到了广泛的关注,可以用于多种电子设备,如触摸屏、有机太阳能电池和显示器等.但是,在近年的透明电极应用中,低长径比所带来的雾度过高、导电性较差的缺陷使AgNWs不能广泛地推广,所以提高长径比是迫在眉睫的.本文采用一步多元醇法制备AgNWs,探究不同分子量的混合PVP体系参与反应对包覆效果及生长过程的影响.研究结果表明,与单一分子量PVP体系相比,PVP混合体系在生长过程中的再次形核点减少,AgNWs的长径比更高;分子量为1 300 000与分子量为58 000的PVP按2∶1的比例混合,AgNWs宽度最小,长径比最高可达到1 200以上.     

长径比可控的CdS纳米棒制备及光催化性能研究

采用溶剂热法制备了长径比可控的纤锌矿CdS纳米棒;以3CdSO4·8H2O、CH4 N2S为原料在180℃、24 h溶剂热反应条件下,通过改变Cd/S物质的量比和保温时间等因素来调节CdS纳米棒的长径比.利用扫描电镜(SEM)、X射线衍射(XRD)、紫外可见吸收光谱(UV-Vis)、光催化分别对其形貌、结构和光催化性能进行了表征和分析.结果表明:Cd/S摩尔比对CdS棒的生长起到关键作用,随着镉硫比的减小,CdS纳米棒的长径比逐渐增大.当Cd/S摩尔比为1∶6时,制备的CdS为长径比较大且表面光滑的纳米棒,纳米棒的尺寸大约为长800 nm、直径70nm.通过降解亚甲基蓝溶液测试了CdS纳米材料的可见光照射下的光催化性能,结果表明具有大长径比的CdS纳米棒表现出优异的光催化活性.     

银纳米棒的醇热法合成与性能表征

采用醇热法在多元醇体系下加入微量氯化钠,以硝酸银为银源,聚乙烯吡咯烷酮(PVP)为分散剂成功合成了银纳米棒.采用X射线衍射仪(XRD),透射电子显微镜(TEM),X射线能量色散分析仪(XEDS)和紫外-可见吸收光谱仪对所制备的样品进行了表征.结果表明,所制备的银纳米棒为结晶良好的面心立方结构,没有杂峰出现,晶格畸变表现为晶格收缩.样品为一维棒状结构,直径大约在几十纳米至200 nm之间,长度分布在几个微米至十几微米范围,分散性良好,长径比较高.样品的纯度比较高,在397 nm和350 nm处出现了两个表面等离子体共振吸收峰.并分析了银纳米棒的形成机理.     

有机熔盐(OMS)法制备AgInS2纳米针

本文以AgNO3、INCl3·4H2O和硫代尿素为原料,尿素和氯化胆碱为有机熔剂,用有机熔盐法(OMS)在200℃制备出纯度较高的黄铜矿结构AgInS2纳米针.使用X射线衍射(XRD)、扫描电镜(SEM)、X射线能谱(EDS)等对纳米针的物相、形貌和化学配比进行了定性和定量表征.XRD测试结果表明,实验获得产物确为黄铜矿结构AgInS2.使用Scherrer公式估算了AgInS2产物的晶粒平均粒度大小约为50 ～ 80 nm,表明所得确为AgInS2纳米晶.SEM观测到的纳米晶形貌外形均匀呈针状,纳米针的几何尺寸基于60 ～80 nm×1000～1500 nm.EDS测试结果显示AgInS2纳米针中Ag、In和S三元素的原子相对百分含量为26.66;、24.82;和50.52;,其化学计量比几近于1:1∶2物质的量比.通过紫外可见透过光谱得到截止波长为661 nm,禁带宽度为1.88 eV.以上结果充分表明OMS法是一种制备AgInS2纳米针的有效方式.     

水热条件下黄磷炉渣废料制备碳酸钙晶须

本文采用黄磷炉渣制备白炭黑后的残留废液为原料,尿素作为沉淀剂制备碳酸钙晶须,系统研究了晶型控制剂(MgCl2)的浓度、反应温度、反应时间、尿素和残留废液的体积比等因素对碳酸钙晶须形貌和物相组成的影响,所得产品通过X射线衍射、扫描电镜进行了分析与表征.研究结果表明,反应温度140℃,反应时间3 h,(NH2)2CO:CaCl2体积比为1:3,晶型控制剂为0.3 mol/L的条件之下,可获得平均长度在50 p.m,长径比为10左右的碳酸钙晶须.     

超细长银纳米线的制备及其导电薄膜性能优化

以硝酸银为银源、聚乙烯吡咯烷酮(PVP)为形貌导向剂、硫酸铁为诱导剂、葡萄糖为还原剂,采用高效便捷的水热法制备银纳米线(AgNWs),通过调控PVP用量和热处理时间致使其长径比大于1000;将异丙醇与乙醇按照一定比例混合,配制出分散性良好的AgNWs墨水,并采用变速旋涂法在玻璃衬底上制备透明导电薄膜;通过低温低压烧结和聚乙烯醇(PVA)固化处理优化薄膜的光学及导电性能,制得方块电阻为(19±2)Ω·sq-1、透过率大于86;透明导电薄膜.     

微波水热法制备ZnO纳米晶

采用微波水热(microwave hydrothermal,M-H)法在MDS-6型温压双控微波水热反应仪中成功地制备出平均晶粒尺寸为30 nm且呈现棒状形貌的ZnO纳米晶.并在一定的水热温度和反应时间下系统研究了微波水热反应过程中[Zn2+]离子浓度、反应釜填充比、反应物浓度比[Zn2+]/[OH]等工艺因素对ZnO纳米晶的晶粒尺寸及形貌的影响.采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)和透射电子显微镜(TEM)对所制备的ZnO纳米晶进行表征.结果表明:所制备ZnO的平均晶粒尺寸约为30 nm,ZnO纳米晶呈现棒状形貌.随着[Zn2+]离子浓度的增加,ZnO纳米晶的晶粒尺寸先减小后增大;随着反应釜填充比和反应物浓度比[Zn2+]/[OH]的增大,ZnO纳米晶的晶粒尺寸先减小后增大,并逐渐趋于稳定.制备ZnO纳米晶的最佳反应条件为:[Zn2+]=1.6 mol·L-1;反应釜填充比=70;;[Zn2+]/[OH]=1/2.     

多元醇法制备一维Ag纳米线

以硝酸银为前驱物,乙二醇为还原剂,聚乙烯吡咯烷酮为表面活性剂,在金晶种存在条件下成功制备出一维银纳米线.对所得样品进行了X射线衍射,场发射扫描电镜,透射电子显微镜以及EDS分析.结果表明,制备的银纳米线为面心立方结构,长度在2～8μm范围,直径约为75～150 nm,产率较高.不同反应时间以及不同PVP(单体)与银离子摩尔比值均对最终纳米形貌产生影响.反应所得银纳米线为五重孪晶结构,最后对纳米线的生长机制进行了详细讨论.     

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.     

A SAXS study of kinetics of aggregation of silica sols

SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process.     

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.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...     

Study of the possibility of interactive control of the surface profile of X-ray optical elements

We investigate the possibility of controlling the curvature parameters of parabolic mirrors that are modular elements of two types consisting of a base and thin inserts placed at the opposite side of the work surface. In the first type of modular elements, bending is controlled by the difference in the coefficients of the thermal expansion of the base and inserts. In the second type of elements, the profile is changed by the piezoelectric straining of the inserts under an electric field. A correlation is established between the parameters of modular elements and their surface curvature profile.     

Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn₂V₂O₇ are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn₂V₂O₇ unit cell in the temperature range of 300–600°С, α _V =–17.94 × 10^–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn₂V₂O₇ is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.     

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.