Dehydration and phase transformation in chrysotile asbestos—A radial distribution analysis study

Radial distribution analysis of x-ray intensities diffracted by chrysotile samples untreated and treated at different temperatures upto 900°C has been carried out. Interatomic distances, coordination numbers, mean square displacements and the interatomic coupling constants for different pairs of atoms have been calculated from the radial distribution curves. The interatomic distances and octahedral co-ordination number is found to decrease marginally upto 640°C and thereafter decrease steadily upto 800°C. The hydroxyl water is completely expelled from the structure and the original chrysotile structure breaks down. The entire process of dehydration has been interpreted in terms of RDF data.     

铁磁性Cr3+掺杂纤蛇纹石纳米管的制备与表征

研究了在水热条件下,通过离子替代的方法制备Cr3+掺杂纤蛇纹石纳米管.采用X射线衍射、扫描电子显微镜、高分辨透射电子显微镜、红外光谱和磁性测试等手段对样品进行了表征.结果表明,掺杂Cr3+后的纤蛇纹石样品其晶胞参数6值增大,内外径分别为6～8nm和30～40nm,长度为50～300nm;掺杂样品中,Cr3+部分替代了Mg2+进入纤蛇纹石的八面体结构单元层中,使得其具有室温铁磁性和磁滞回线特性.     

合成纤蛇纹石纳米管的CdS组装实验研究

采用超声化学法在合成纤蛇纹石纳米管内进行了组装CdS量子点的研究.利用X射线衍射仪、透射电子显微镜及紫外-可见光谱仪对组装样品进行了分析表征.透射电镜观察发现在纤蛇纹石纳米管中组装的CdS量子点呈分散的球形粒子,直径约3～6nm;X射线衍射分析表明在纤蛇纹石纳米管中所组装的CdS量子点为β-CdS型结构,其平均晶粒度约为4.1nm;紫外-可见吸收光谱研究表明CdS量子点的吸收边蓝移了约10nm.     

天然纳米管纤蛇纹石的结构性能和应用研究

纤蛇纹石是一种独特的天然硅酸盐矿物纤维,具有纳米中空管状结构,以及表面化学活性和生物活性高等特点,在环境治理、纳米材料制备等领域得到广泛的关注和研究。以纤蛇纹石纳米管为模板,可组装一维量子点和量子线;酸蚀得到的一维氧化硅纳米线也可作为载体合成一维纳米复合材料,在催化、光电等方面有广泛的应用。针对纤蛇纹石独特的纳米管和物理化学性质进行应用研究,发挥其管状结构均一、稳定的优势,对于天然纳米材料的发展具有十分重要的现实意义。     

密封垫片中石棉的检测方法研究

针对国内没有密封垫片中石棉检测方法的现状,开展了关于样品前处理、定性、定量的研究。结果表明:密封垫片前处理的最佳灰化温度450℃,灰化时间为4h;偏光显微镜(PLM)和X射线衍射仪(XRD)联合使用对样品定性分析,快速准确;XRD法定量的标准曲线线性良好,仪器检出限为0.4mg,回收率在75.45%～102.89%之间,标准偏差为8.85%,满足日常检测需要。     

温石棉尾矿活化产物制备纳米SiO_2实验研究

为了减少温石棉尾矿的大量丢弃而造成环境污染与资源浪费,以青海芒崖温石棉尾矿的活化产物为原料,采用碳化法制备纳米二氧化硅,研究Na2SiO3溶液浓度、碳化时间、碳化温度、碳化终点pH值及表面改性剂用量对纳米SiO2形成的影响。采用X射线衍射、X射线荧光光谱分析及扫描电镜对制备的纳米SiO2样品的物相、化学成分及颗粒形貌进行表征。结果表明:当Na2SiO3溶液浓度为0.6 mol/L、碳化时间50 min、反应温度为70℃、碳化终点pH值为8.5左右、表面改性剂质量分数为0.6%时,可制备出粒度为50 nm左右的球状无定形纳米SiO2,且w(SiO2)=99%,同时,纳米SiO2的转化率达77%以上。     

Strain-induced phase transformation in a cobalt-based superalloy during different loading modes

The strain-induced face-centered cubic (FCC) → hexagonal-close packed (HCP) phase transformation in a cobalt-based superalloy was investigated with four in situ loading neutron-diffraction experiments: monotonic tension, monotonic compression, high-cycle fatigue, and low-cycle fatigue. The transformation onsets for the four respective cases were 685 MPa, 698 MPa, 1 cycle, and 3 cycles, respectively. The HCP phase accumulated at rates of 0.1 wt.%-MPa⁻¹ and 0.05 wt.%-MPa⁻¹ for the tension and compression cases, respectively. For the cyclic-loading cases, the accumulation rates were found to be inversely proportional to the number of fatigue cycles. The results under the different loading modes suggest that the phase transformation occurs according to a tensile plastic-work criterion.     

隔热手套中石棉的检测方法研究

采用X射线衍射仪(XRD)、扫描电子显微镜-能谱仪(SEM-EDS)、偏光显微镜(PLM)种分析手段,通过对样品形貌以及元素的定性定量分析,可完整有序、快速、准确地测定手套中石棉含量,克服单独使用某种检测手段的局限性,对手套中石棉的检测具有一定指导意义.     

In situ ESEM study of the thermal decomposition of chrysotile asbestos in view of safe recycling of the transformation product

The thermal transformation of asbestos into non-hazardous crystalline phases and their recycling is a promising solution for the "asbestos problem". The most common asbestos-containing industrial material produced worldwide is cement-asbestos. Knowledge of the kinetics of thermal transformation of asbestos fibers in cement-asbestos is of paramount importance for the optimization of the firing process at industrial scale. Here, environmental scanning electron microscopy (ESEM) was used for the first time to follow in situ the thermal transformation of chrysotile fibers present in cement-asbestos. It was found that the reaction kinetics of thermal transformation of chrysotile was highly slowed down in the presence of water vapor in the experimental chamber with respect to He. This was explained by chemisorbed water on the surface of the fibers which affected the dehydroxylation reaction and consequently the recrystallization into Mg-silicates. In the attempt to investigate alternative and faster firing routes for the decomposition of asbestos, a low melting glass was mixed with cement-asbestos and studied in situ to assess to which extent the decomposition of asbestos is favored. It was found that the addition of a low melting glass to cement-asbestos greatly improved the decomposition reaction and decreased the transformation temperatures.     

In situ synchrotron X-ray study of bainite transformation kinetics in a low-carbon Si-containing steel

The bainite transformation in a low-carbon Si-containing steel has been studied in situ by synchrotron X-rays. While the austenite is homogeneous prior to transformation, the carbon distribution becomes nonuniform as bainite plates form. This is because of the different degrees of physical isolation of films and blocks of residual austenite. The method for converting dilatational strain into bainite volume fraction, using lattice strain as a reference, during isothermal transformation was found to overestimate it. The bainitic and martensitic ferrite did not exhibit a tetragonal unit cell due to the low-carbon content of the steel and the high transformation temperature.     

Structural studies of copper sulfide films: effect of ambient atmosphere

Abstract

We examined the structural properties of copper sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and covellite phases were formed with increasing sulfurization time. To evaluate the structural stability of various films, all the films were exposed to the ambient atmosphere for the same amount of time. Although the phase structure and stoichiometry of the films were maintained at a greater depth, the near-surface region of the films was oxidized and covered with overlayers of oxide, hydroxide, and/or sulfate species due to the exposure and reaction with the ambient atmosphere. The oxygen uptake and its reactivity with the copper sulfide film surfaces were enhanced with increasing sulfur content of the films. In addition, the type of divalent state of copper formed on the film surfaces depended on the phase structure, composition, and stoichiometry of the films.     

Structural studies of copper sulfide films: effect of ambient atmosphere

We examined the structural properties of copper sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and covellite phases were formed with increasing sulfurization time. To evaluate the structural stability of various films, all the films were exposed to the ambient atmosphere for the same amount of time. Although the phase structure and stoichiometry of the films were maintained at a greater depth, the near-surface region of the films was oxidized and covered with overlayers of oxide, hydroxide, and/or sulfate species due to the exposure and reaction with the ambient atmosphere. The oxygen uptake and its reactivity with the copper sulfide film surfaces were enhanced with increasing sulfur content of the films. In addition, the type of divalent state of copper formed on the film surfaces depended on the phase structure, composition, and stoichiometry of the films.     

The influence of temperature on deformation-induced martensitic transformation in 301 stainless steel

Deformation-induced martensitic transformations are increasingly being used to create desirable mechanical properties in steels. Here, the kinetics of the deformation-induced martensitic transformation is investigated at 300, 263, 223, 173 and 100 K using in situ neutron diffraction during tensile loading. The results from these experiments show a distinct change in the transformation behaviour between 300 K and the tests conducted at 263 K and below, causing a difference in martensite structure. The difference in transformation kinetics is correlated to the suppression of slip at low temperatures, as evidenced using diffraction peak intensity analysis for different grain families and corroborated using transmission electron microscopy. A direct correlation between the deformation-induced martensite fraction and the work-hardening rate is shown.     

Sophisticated equipment developed for growth and evaluation of perfection of nearly perfect crystals

This paper reviews four major equipment developed at the National Physical Laboratory for growth and perfection evaluation of single crystals, namely (i) a crystal puller for growth of nearly perfect crystals by the Czochralski method; (ii) a microfocus x-ray generator; (iii) an x-ray diffraction topography camera; and (iv) a triple crystal x-ray diffractometer. The crystal puller can provide smooth, uniform and variable pulling rates. The maximum length of pull is nearly 60cm. Efforts have been made to isolate vibrations. Nearly perfect single crystals of KCl, KBr and NaCl with maximum diameter of ∼ 60 mm have been grown. The crystals give diffraction curves with half width in the range of 10–30 sec of arc. In the projection topographs, dislocations can be resolved and characterized. The microfocus x-ray generator is a demountable continuously evacuated system with specially designed electron gun and anode assembly. The vacuum is continuously monitored for ease of maintenance. In the point focus mode the spot size is 40 μm on the anode. X-ray topography system is a versatile equipment used for projection and section topography. It can provide 360° rotations to the specimen disc around an axis perpendicular to it. Rotations of a few sec of arc can be given to the specimen around a vertical axis. Typical diffraction curves of a dislocation-free crystal and a crystal with boundaries are shown. Well-resolved images of dislocations are shown in a topograph as an illustration. In the triple crystal x-ray diffractometer a highly collimated and monochromated Kα₁ exploring x-ray beam is obtained by combining microfocus source, a special collimator and crystal monochromators of Bonse-Hart type. With this beam very narrow diffraction curves with half width of about 5 sec of arc can be recorded. Typical results of measurement of diffuse x-ray scattering (dxs) on nearly perfect silicon single crystals are discussed. It has been observed that the contribution of phonons to thedxs is negligible. Thedxs is mainly due to point defect aggregates.     

Characterization of phase transformation behaviour and microstructural development of electroless Ni-B coating

Phase transformation behaviour of amorphous electroless Ni-B coating with a targeted composition of Ni-6 wt% B is characterized in conjunction with microstructural development and hardness. Microscopic observations of the as-deposited coating display a novel microstructure which is already phase separated at multiple length scales. Spherical colonies of ∼5 μm consist of 2-3 μm nodular regions which are surrounded by ∼2-3 μm region that contains fine bands ranging from 10 to 70 nm in width. The appearance of three crystalline phases in this binary system at different stages of heat treatment and the concomitant variation in hardness are shown to arise from nanoscale fluctuations in the as-deposited boron content from 4 to 8 wt%. High temperature annealing reveals continuous crystallization up to 430 °C, overlapping with the domain of B loss due to diffusion into the substrate. The implications of such a microstructure for optimal heat treatment procedures are discussed.     

Grain growth and structural transformation in ZnS nanocrystalline thin films

Fabrication of ZnS thin films having similar stoichiometry at different substrate temperatures (T_S) e.g. 200 °C, 300 °C and 400 °C by means of RF magnetron sputtering method is presented. The films grown at T_S of 200 °C are in cubic zinc-blende phase and textured along (111) plane. The films deposited at T_S of 300 °C and 400 °C are in hexagonal wurtzite phase. The surface roughness and grain size of the films increase with increasing T_S. The ultra-violet and visible absorption studies show that the bandgap of films can be tailored by varying T_S, taking advantage of the structural transformation.     

Emerging methods and opportunities in nanoscale materials characterization

The emergence of powerful nanomaterials characterization techniques promises to underpin a new range of advances in materials research. There have been significant developments in the characterization of the phase, structure, composition, and dynamics of materials at the nanoscale. Articles in this issue report recent advances in three areas: atom probe tomography, x-ray nanobeam scattering and diffraction, and x-ray photon correlation spectroscopy. Each of these provides three-dimensional insight into hard materials in ways that have been previously unavailable. Taken together, these emerging methods have the potential to provide new tests for materials theory and computation and to extend significantly the range of questions that can be answered in materials research.     

Thermal stress-focusing effect in a cylinder with phase transformation

Summary When a cylinder is suddenly subjected to an impact cooling, thermal stress waves occur at the surface of the cylinder the moment the thermal impact is applied. The stress waves in a cylinder with a focusing point proceed radially inward to the center of the cylinder. The wave may accumulate at the focusing point and give rise to very large stress magnitudes, even though the initial stresses may be relatively small. This phenomenon is called the stress-focusing effect. When the cooling process passes through the phase transformation point of metal, a phase transformation may occur. The eigenstrains of phase transformation also cause the stress-focusing effects at the center of a cylinder. In this paper, we analyze the stress-focusing effects induced by the thermal and phase transformational stresses caused by the thermal shock in a cylinder theoretically. The results give a clear indication of the mechanism of stress-focusing effects and clarify the orders of singularities of the stress-focusing effects in a cylinder. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday     

Estimating a transformation and its effect on Box-CoxT-ratio

This article concernsi) the stochastic behavior of the Box-Cox transformation estimator andii) the effect of estimating a transformation on the Box-CoxT-ratio used for the post-transformation analysis. It is shown that the transformation estimator depends on three factors: the model structure, the mean-spread and the error standard deviation σ₀. In general, a structured model is able to estimate the transformation very well; an unstructured model can do well also unless the mean-spread and σ₀ are both small; and a one-mean mode can give a poor-estimate if σ₀ is small. When the sample is not large, it is shown that the unconditional effect of estimating a transformation on the Box-CoxT-ratio is generally small, and the “conditional” effect is also negligible in most of the situations except the case of one-way ANOVA with small σ₀. Extensive Monte Carlo simulations are performed to support the theoretical findings.