纳米铝粉的性质及其对沉淀法制备纳米氧化铝粉体的作用

研究了纳米铝粉的氧化性质,并利用Al(NO3)3*9H2O、氨水和纳米铝粉为原料,采用液相沉淀法制备出Al(OH)3溶胶,经过真空抽滤和高温煅烧获得了纳米α-Al2O3粉体. 利用DSC/TG曲线分析了纳米铝粉和复合粉体不同温度下晶型和重量的变化,利用XRD分析了不同煅烧温度下复合粉体的成份变化、利用SEM观测了获得的α-Al2O3粉体形貌.研究表明纳米铝粉在相对较低的温度下氧化,这种氧化物籽晶的存在有利于α-Al2O3晶型的低温转化.     

喷雾燃烧法合成α-Al2O3微粉

以硝酸铝和无水乙醇为原料,采用喷雾燃烧法制备α-Al2O3微粉,研究了乙醇用量、α-Al2O3晶种、ZnF2、热处理温度等对合成α-Al2O3微粉的影响,采用XRD、SEM分析了微粉的结构与形貌.结果表明,增加乙醇的用量、引入α-Al2O3晶种都有利于α-Al2O3相的生成.     

氯化铵对AACH热分解制备纳米α-Al2O3的影响

以硫酸铝铵和碳酸氢铵为主要原料,采用沉淀法制备纳米碳酸铝铵(AACH)前驱体,通过碳酸铝铵热分解制备α-Al2O3,并利用X射线衍射(XRD),透射电镜(TEM)对前驱体及其煅烧产物的物相和形貌进行表征.研究表明通过添加氯化铵能够降低α-Al2O3的相变温度,并且随着加入量的增加,颗粒粒径减小,分散性改善.加入10;氯化铵的前驱体在1150 ℃下煅烧1 h后可以得到分散性较好的纳米α-Al2O3颗粒.     

铝纤维对Al2O3-Al-C材料高温机械性能和显微结构的影响

分别以板状刚玉、α-Al2O3微粉、金属铝(铝纤维和铝粉)、石墨为原料,以酚醛树脂为结合剂,制得Al2 O3-Al-C材料.借助XRD和SEM分析了试样的物相组成和显微结构,研究了铝纤维加入量对材料抗热震性、高温抗折强度的影响,结果表明:用铝纤维代替铝粉可提高材料的高温抗折强度和抗热震稳定性.保持金属铝的总加入量为6;,当铝纤维加量由0;增加到1;时,1400℃的高温抗折强度由26.5 MPa提高到34.7 MPa,热震后的残余强度保持率由62;增加到69;.高温时铝纤维转变为非氧化物晶须编织体或纤维束,与基质紧密结合,起桥接和强化作用,可改善材料的抗热震性并显著提高其高温抗折强度.     

Al2TiO5/Al2O3陶瓷复合材料的晶粒异向生长

通过机械激活法制备了Al2TiO5/Al2O3(nAl2TiO5: nAl2O3=1: 4)的陶瓷复合材料.利用X射线衍射(XRD)、扫描电镜(SEM)以及能谱(EDS)分析了不同的温度制度下Al2TiO5/Al2O3陶瓷复合材料的晶粒生长特性.X射线衍射谱图(XRD)显示烧结样品的主晶相为α-Al2O3和Al2TiO5.SEM和EDS分析显示,较低温度下烧结(1350 ℃)时Al2TiO5晶粒为等轴状.当温度升高到1450 ℃时,Al2TiO5开始异向长大,形成棒状晶粒.随着温度的升高(1500 ℃),棒状Al2TiO5的长径比继续增加.而Al2O3则始终为片状和等轴晶粒,且异向生长的Al2TiO5晶粒填充于Al2O3三角晶界处.研究表明,烧结温度的升高会促进晶体异向生长并增加其体积分数.Al2TiO5会阻碍Al2O3基体颗粒进一步生长,所以当Al2TiO5颗粒平均尺寸随着烧结温度增加而增大,Al2O3基体晶粒生长几乎停滞.     

溶胶凝胶法制备氧化石墨烯/氧化铝复合材料

将不同配比的异丙醇铝(AlIP)和氧化石墨烯(GO)水分散液,通过溶胶凝胶法制备了氧化石墨烯/氧化铝复合材料.通过SEM和TEM分析,氧化石墨烯被纳米颗粒包裹.XRD分析显示纳米颗粒的成分是Al2O3,通过原子力显微镜(AFM)分析,纳米颗粒的平均粒径为50 nm.复合材料的生长机理是:首先GO和AlIP分子结合,AlIP水解后在GO表面生成AlOOH的小颗粒,随着反应的继续进行颗粒逐渐长大,通过高温处理,AlOOH转变为Al2O3.     

颗粒级配对氧化铝多孔陶瓷膜支撑体孔径及抗折强度的影响

探讨了三种粒径的α-Al2O3(粗颗粒、中颗粒和细颗粒)的颗粒级配和工艺条件对多孔陶瓷膜支撑体的孔径、孔隙率及其抗折强度的影响.结果表明:粗α-Al2O3颗粒(d50＞29 μm)对多孔陶瓷的孔径分布起决定性作用,中、细颗粒的比例在一定程度上影响支撑体的孔隙率和抗折强度.SEM结果显示,经1650℃煅烧2h后,细α-Al2O3颗粒(d50＜1.6μm)迁移至粗α-Al2O3颗粒间的颈部而基本消失,在一定程度上提高了颈部连接.在合适的颗粒堆积条件下,细颗粒有助于提高多孔陶瓷的抗折强度.但是,团聚的细α-Al2O3颗粒间优先烧结,不利于细颗粒的助烧增强作用.     

AACH热分解法制备α-Al2O3超细粉末

以NH4Al(SO4)2与NH4HCO3为原料,采用共沉淀法制备出前驱物碳酸铝铵(AACH),并煅烧得到超细α-Al2O3粉末. 研究了pH值、滴加速度及醇水混合溶剂等因素对反应产物的影响,并对前驱物AACH的高温相变过程和α-Al2O3籽晶对θ-Al2O3→α-Al2O3相变的影响进行了分析.利用XRD、TEM和BET等对粉体的性能进行表征.结果表明:在醇水混合溶剂中控制反应体系的pH值为9～10,将硫酸铝铵溶液以＜18 mL/min的速度滴入碳酸氢铵溶液,可合成颗粒细小、粒度分布均匀且分散性优异的AACH前驱物.不含籽晶的AACH煅烧时α相完全转化温度为1150 ℃,获得α-Al2O3粒径约为100 nm,而α-Al2O3籽晶的加入可将完全转变温度降至1050 ℃,获得的α-Al2O3粒径约为70 nm.     

Ni-MoS2/γ-Al2O3催化剂的制备及其光催化性能研究

采用共沉淀结合水热合成方法,以γ-Al2O3为载体,制备出Ni-MoS2/γ-Al2O3复合催化剂.采用X射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)等方法对样品的结构与形貌进行表征.研究了MoS2负载量、煅烧温度对Ni-MoS2/γ-Al2O3复合催化剂光催化降解罗丹明B性能的影响,并考察了催化剂的循环使用性能.结果表明:负载量为30wt;,煅烧温度为300℃的复合催化剂Ni-MoS2/γ-Al2O3表面的MoS2纳米片兼具有良好的结晶度和均匀分散性,其纳米片尺寸约为200nm.可见光下,Ni-MoS2/γ-Al2O3(MoS2 30wt;/Ni 5wt;)复合催化剂对罗丹明B的降解效率能达到100;,且循环使用5次后,对罗丹明B的降解效率仍能够达到88.9;.     

添加锆英石、B4C和焦粉对铝碳质耐火材料抗氧化性能影响

在Al2O3-C质耐火材料中添加锆英石、B4C和焦炭,通过高温原位反应生成了ZrC-ZrB2-SiC复合非氧化物耐高温物相.采用XRD分析了不同锆英石、B4C和焦炭的添加量与不同烧成温度下反应产物的物相组成,并采用XRD与SEM进一步研究了含有ZrC-ZrB2-SiC复合非氧化物的铝碳质耐火材料的抗氧化性能及其抗氧化的机理.结果表明:当锆英石-焦炭-B4C混合粉体的加入量为20;,在1550 ℃保温3 h能在铝碳质耐火材料的基质中原位合成ZrC-ZrB2-SiC复合非氧化物,制备得到相应的铝碳质复合耐火材料.ZrC-ZrB2-SiC复合非氧化物在氧化条件下可生成玻璃相,形成致密保护层能够阻止其进一步氧化,从而显著提高铝碳质材料的抗氧化性能.     

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.     

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...     

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.     

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.     

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.