熔盐辅助碳热还原氮化法制备氮化钽晶须

本文以五氧化二钽、活性炭为主要原料,氟化钾为熔盐介质,通过碳热还原氮化法在氨气气氛下成功制备了氮化钽(Ta5N6)晶须.运用X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)对合成产物的组成、结构和形貌进行了表征.研究了升温方式、氮化气氛、氮化时间和催化剂含量对产物形成的影响.当Ni与Ta2O5的摩尔比为0.1、氮化气氛为氨气(流量为300 mL/min)、氮化时间为6h时制备的晶须形貌最佳,晶须直径80～250 nm,长为1～5μm,晶须的生长机制为气-液-固(VLS)和气-固(VS)两种机理的混合机制.     

原位氮化法制备TiN纳米粉体

用溶胶凝胶法合成的纳米TiO2粉体作为原料,将该粉体在氨气中进行原位氮化制备了TiN纳米粉体.用XRD,TEM,化学分析等手段对合成的TiN纳米粉体的物相组成、形貌、成分进行了分析.实验分析表明:在1000℃和1100℃下分别氮化5h,可以制备粒径大约为40nm和80nm的TiN粉体,其TiN的含量分别为95.40;和98.37;;而在1000℃条件下氮化时间减少到2h时,TiN的含量仅为58.36;.氮化温度和氮化时间是合成纳米TiN的重要因素,提高合成温度和延长氮化时间均可形成纯度较高的TiN纳米粉体,但延长氮化时间更有利于获得粒径小的氮化钛粉体.     

直流电弧等离子体喷射法制备氮化碳薄膜研究

以H2、N2和CF4气体为前驱体,用直流电弧等离子体喷射设备在不同基底温度条件下于钼/金刚石过渡层基底上制备了氮化碳薄膜.利用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)对表面形貌和组织成分进行了表征.结果表明,当基底温度为900℃时,所沉积材料已初具晶型;所沉积材料含有α-C3N4和β-C3N4相成分.同时,提出在金刚石表面制备氮化碳时金刚石相刻蚀和氮化碳相生长同时进行的模型,较好地解释了不同基底温度条件下的膜材料沉积现象.     

热熔还原法制备超硬复合相氮化碳及其工艺探索

本文采用热熔还原法,以聚氯乙烯、氯化铵、氧化铁为原料制备复合超硬相氮化碳(α/β-C3 N4).采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)以及透射电子显微镜(TEM)对样品进行表征.在此基础上分析了不同温度和原料配比下合成复合相C3 N4的物相组成及形貌变化.结果表明样品形貌随着原料配比的不同在颗粒、棒状、纳米线之间转变.当C、N和Fe之间摩尔比为3:4:0.4时,所制备出的样品呈纳米线状,纳米线的直径约为15 nm,结晶性良好.而在其它配比下,只能获得棒状或颗粒状α/β复合相C3 N4.     

类石墨氮化碳薄膜的电化学沉积

用1:1.5的三聚氯氰和三聚氰胺的饱和乙腈溶液为沉积液,在Si(100)衬底上室温常压下电化学沉积了CNx薄膜.用X射线光电子能谱(XPS)、傅立叶转换红外光谱(FTIR)、X射线衍射图谱(XRD)对沉积的CNx薄膜进行了测试和分析.XRD的衍射峰的结构数据与文献计算的类石墨相氮化碳的结构数据较为吻合.XPS结果表明沉积的薄膜中主要元素为C、N,且N/C=0.81,C1s和N1s的结合能谱中287.84eV的碳和400.00eV的氮是样品中碳氮的主体,以C3N3杂环的形式存在.FTIR光谱中在800cm-1、1310cm-1和1610cm-1的吸收峰也表明薄膜中存在C3N3环,和XPS能谱的分析结果一致.Teter和Hemley预言的g-C3N4在结构形式上和三聚氰胺的完美脱胺缩聚物是一样的,红外光谱和X射线光电子能谱表明在样品中存在三嗪环(C3N3),支持XRD的实验结果.这说明CNx薄膜中有类石墨相的C3N4晶体存在.     

还原氮化对ZrO2薄膜SERS性能的影响研究

以八水氧氯化锆(ZrOCl2·8H2 O)为原料制备前驱体溶液,采用旋涂工艺制备ZrO2薄膜,并对其进行还原氮化.利用XRD、FE-SEM、UV-Vis-Nir和Raman测试薄膜结构、光学性能及SERS效应.结果表明,还原氮化后薄膜中出现了氮氧化合物,颗粒明显,薄膜厚度约为0.77μm.薄膜的紫外可见近红外光谱在350～650 nm附近展现出较强的吸收.利用R6G作为探针分子研究了薄膜的SERS效应,结果表明,还原氮化后的氧化锆薄膜拉曼增强效应显著提升,拉曼增强因子为2.479×102.     

用粉煤灰和高岭土混合原料合成β-Sialon粉体

以粉煤灰、高岭土混合物为原料,采用碳热还原氮化法制备了不同z值的β-Sialon粉体.研究了原料组成(Si/Al值)、活性炭配量以及反应温度对合成产物物相的影响.利用X射线衍射仪分析产物物相的组成,用扫描电子显微镜对产物的显微形貌进行分析.结果表明,当原料中Si/Al值为1.5,配炭量过量100;时,在1450℃保温6h条件下,可以合成主要物相为Si3Al3O3N5(β-Sialon,z=3)的粉体,粉体的显微形貌呈现纤维状;当原料中Si/Al值为1.7,配炭量过量150;时,在1450℃保温6h条件下,可以制备主要物相为Si4Al2O2N6(β-Sialon,z=2)的粉体,粉体的显微形貌呈现纤维状和板状.     

反应温度和锆英石添加量对石英碳热还原氮化产物的影响

本研究中选用石英和焦炭为原料、天然锆英石为添加剂,采用XRD、SEM和EDS等分析方法,研究了反应温度和锆英石添加量对石英碳热还原氮化产物影响.研究结果表明:在0.13 MPa的流动氮气气氛中,反应温度在1450～1550℃时,石英的碳热还原氮化产物中含有Si2N2O、β-SiC和β-Si3N4物相;当反应温度为1600℃时,石英的碳热等在1600℃条件下,石英碳热还原氮化产物主要含有柱状β-Si3N4和少量纤维状β-SiC物相;当添加10wt;的天然锆英石时,产物的主要成分为β-Si3N4 、ZrN以及少量βSiC物相;当锆英石添加量为20wt;到50wt;时,产物中不仅含有β-Si3N4和ZrN物相,还存在c-ZrO2,m-ZrO2,Si2N2O及β-SiC等物相.     

低温耦合固相氮化反应合成β-Sialon

本研究拟在氮化气氛下,以金属Al粉、Si粉、α-Al2O3为原料,添加Y2O3,耦合氮化反应制备β-Sialon.通过在不同温度下的氮化反应烧结试验,研究了Y3+对β-Sialon晶相组成、晶粒大小、晶格常数及显微结构的影响.采用XRD和SEM表征试样中的晶相和显微结构,利用X'Pert Plus软件对试样进行晶胞参数分析,通过Semi-quantification法对试样各晶相组成进行计算.结果表明:随着温度的升高,合成β-Sialon相的含量不断提高,在1550℃时达到最高;添加Y2O3可以在相对较低温度条件下合成β-Sialon相,y3+对Al3+的置换作用导致β-Sialon相结构畸变,且随耦合氮化反应烧成温度的升高,晶胞体积可由1350℃时的0.208448 nm3增大到1550℃时的0.236776 nm3,合成β-Sialon相呈现增加的趋势.同时在合成β-Sialon结构中,由于过量助烧结剂Y2O3易与原料中Al2O3形成针状YAG.     

微乳液静电纺丝制备多孔Nb4N5纤维及其电化学性能

以五氯化锯为原料,液体石蜡为分相剂,采用微乳液静电纺丝技术制备前驱体纤维,再经氨气还原氮化得到多孔氮化锯纤维.利用XRD、SEM、BET等进行物相及微观结构表征,结果表明合成的纤维为四方Nb4N5晶相,纤维连续,直径为260 nm,由于液体石蜡分相以及助纺剂PVP的分解作用,在纤维上形成较多孔道结构,其BET比表面积为125m2/g,孔径为2～5nm范围内的孔结构比例较高,同时在5～10 nm 范围也存在较多的孔道结构,平均孔径为7.3 nm.采用CV、GCD及EIS等测试其电化学性能发现,氮化锯纤维的储能主要受电极表面电荷传递过程控制的,外表面比电容贡献高,这得益于分布在纤维中的孔结构,其可为离子传输提供通道,并为电化学反应提供空间.当电流密度为5mA/g时,比电容为151 F/g,能量密度为7.73 Wh/kg时,功率密度为3.03 W/kg,其经2000次循环后其比电容保持在95;以上.     

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.     

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.     

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...     

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.