机械合金化-低温烧结Ti3SiC2导电陶瓷材料

采用化学计量比为3Ti/Si/2C的单质粉体为反应原料,通过机械合金化工艺和热处理制备高纯度的Ti3SiC2陶瓷粉体,研究了热处理温度对提高机械合金化混合粉体中Ti3SiC2纯度的影响.研究表明:在球磨转速400 r/min,球磨时间10 h的条件下,合成以Ti3SiC2为主相的混合粉体,其中Ti3SiC2含量为75.5vol;,同时出现表面灰黑色且坚硬的不规则块体,成分与球磨粉体相似.在热处理温度为850～1000℃范围内,混合粉体中Ti3SiC2的含量随着热处理温度的升高而提高,当热处理温度为1000℃时,计算粉体中Ti3SiC2的含量高达98.5vol;..     

机械合金化-热处理制备Ti3AlC2导电陶瓷的研究

对Ti、Al、C单质混合粉体进行机械合金化加工,通过对所得混合粉体进行高温热处理以此获得高纯度的Ti3AlC2陶瓷粉体,研究了球磨时间和热处理温度对粉体中Ti3AlC2纯度的影响.研究表明:在球磨转速550 r/min,球磨时间3h的条件下,合成混合粉体中的Ti3AlC2的含量为83.5wt;.在850～1000℃范围内,粉体中Ti3AlC2的含量随着热处理温度的升高而提高,当热处理温度为1000℃时,计算粉体中Ti3AlC2的含量高达99.7wt;;将观察倍数扩大到60000倍,可以清晰观察到Ti3AlC2典型六方形状的晶粒.     

机械合金化-放电等离子烧结制备Ti_2SnC导电陶瓷

采用放电等离子烧结(SPS)技术对机械合金化合成的Ti2SnC粉体进行烧结,研究了烧结温度对机械合金化和SPS烧结Ti2SnC导电陶瓷块体相组成、显微组织及微结构的影响。结果表明:机械合金化合成Ti2SnC粉体在800~1000℃之间进行SPS烧结可以获得纯度较高的致密块体,在1000℃进行烧结时,孔隙率低于2%。在600~1000℃范围内,烧结块体中Ti2SnC的含量随烧结温度的提高逐渐增加;Ti2SnC的晶粒大小随温度升高逐渐长大。     

固相合成YAG微晶粉体的XRD研究

以高纯Al_2O_3和Y_2O_3超微粉为原料,通过高能球磨和固相反应法制备了Y_3Al_5O_(12)(YAG)微晶;采用X射线衍射法(XRD)研究了球磨时间、煅烧温度、保温时间等对合成YAG微晶相组成的影响.结果表明:原料粉体的粒度随研磨时间延长而降低;随煅烧温度的提高,产物的物相由Y_4Al_2O_9和YAlO_5 逐渐向YAG相转变;延长保温时间有利于Y~(3+)和Al~(3+)的扩散以及Al_2O_3和Y_2O_3的固相反应.当Al_2O_3和Y_2O_3的摩尔比为5 ∶ 3,混合粉体经过15 h的机械球磨并于1300 ℃煅烧40 min即可得到单一物相的YAG微晶粉末.     

Fe_3Al金属间化合物的机械合金化制备

采用钢球为研磨球,以单质Fe、Al为原料,对不同配比的Fe-Al混合粉体在无保护气氛和非真空条件下进行机械球磨,获得了Fe(Al)超饱和固溶体,对其进行真空退火制备了Fe3Al金属间化合物。XRD和DSC分析表明:在球磨大约10 h以后,粉体中单质Al的数量开始减少,且随着球磨时间的延长,这种趋势更加明显;球磨80 h后,粉体中单质Al已全部固溶于Fe中,形成了Fe(Al)超饱和固溶体。这说明在无保护气氛和非真空条件下机械合金化法可以制得较纯的Fe3Al金属间化合物。     

Ti3Al含量对TiC/(Ti3Al+ZrO2)陶瓷复合材料晶粒生长及性能的影响

采用机械合金化和热压烧结制备了TiC/(Ti3Al+ZrO2)复合材料.研究了1550℃烧结温度下,不同Ti3Al含量(10、15、20、25;质量分数)对复合材料烧结及力学性能的影响.结果表明:随着Ti3Al含量的增加,烧结体致密化程度提高,抗弯强度和硬度相应提高,但当Ti3Al超过一定量时,强度、硬度又有所降低.     

机械活化-放电等离子烧结制备Ti3AlC2块体材料

将Ti、Al、C单质粉体作为实验原料,利用机械合金化和放电等离子烧结技术制备Ti3AlC2块体材料.研究烧结温度和保温时间对块体相组成及性能的影响.研究表明:粉体经过机械活化作用,反应活性增加,Ti-Al-C体系的自由能得到提高,为后续的放电等离子烧结做了基础;在温度为1050℃(保温时间5 min)时进行块体烧结,所得块体中Ti3AlC2的含量为98.5wt;,随着保温时间的延长(10～20 min),块体中Ti3AlC2的纯度得到提升(＞99wt;),相对密度也随之增加,但显微硬度下降.     

用天然水镁石球磨法制备Mg-Al水滑石的实验研究

以水镁石、硝酸铝和碳酸氢钠为原料,利用球磨方法通过机械力化学作用合成了Mg-Al水滑石,考查了球磨速度、球磨时间对合成水滑石的影响.研究表明,提高球磨转速有利于水滑石的形成与晶化,同时也有利于Al2O3的析出.适当延长球磨时间有利于水滑石的形成和结晶,但球磨时间过长,水滑石结构破坏.在500 r/min转速下球磨3h制备的水滑石纯度最高、结晶最好.用该方法制备的水滑石粒径较大,结晶度较低,热学行为特殊,可能与结构中富镁、贫铝有关.     

光催化剂SnC2O4的合成及其可见光催化活性

以(NH4)2C2O4为沉淀剂,采用直接沉淀法合成了新型光催化剂SnC2O4粉末.通过X射线粉末衍射、扫描电镜、紫外-可见分光光度计及荧光分光光度计等手段对样品的物相结构、微观形貌以及光吸收性能等进行了分析表征.结果表明:所制备的样品为单斜白钨矿型SnC2O4,空间群为C2/C(15).样品的微观形貌为不规则多面体,其禁带宽度为3.44 eV.光致发光光谱表明样品内部可能有大量的氧空位和其它缺陷.以甲基橙为模拟染料废水对SnC2 O4样品的光催化活性进行了评价.当甲基橙染料的浓度为40 mg/L,SnC2 O4光催化剂的投加量为40 mg/50 mL时,在模拟可见光照射下,甲基橙降解率可达99.1;,且光催化降解反应符合一级动力学方程.此外,通过引入活性物种捕获剂证明·O2-在光催化降解甲基橙反应中起重要作用.     

超重力场自蔓延离心熔铸TiB2-(Ti,W)C复目陶瓷的研究

采用超重力场自蔓延离心熔铸技术在TiB2基体中引入不同质量分数的(Ti,w)C成功制得大体积复相陶瓷.陶瓷主要由片状TiB2晶、球状TiC晶及不规则(Ti,w)C晶粒组成.随着WO3+Al反应物料含量的提高,体系绝热燃烧温度首先保持不变,随后呈明显增加趋势;并且高温下液相停留时间的延长、产物Stock对流的加快导致产物陶瓷中夹杂减少、(Ti,w)C相含量增加.各相晶粒的均匀化、(Ti,w)C相含量的提高将陶瓷硬度由15.89 GPa提升至23.4 GPa.     

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...     

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.     

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.     

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...     

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.     

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.     

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.