Characterising the sintering behaviour of pulverised fuel ash using heating stage microscopy

Heating stage microscopy was used to investigate the sintering behaviour of pulverised fuel ash (PFA). The effect of chemical composition, heating rate, maximum temperature and metal inclusions on densification was studied. It was confirmed that dimensional changes of PFA powder compacts can be controlled by selecting appropriate conditions of sintering temperature and heating rate. It was also found that the sintering behaviour of PFA can be modified with the addition of metal inclusions. The results suggest that development of pores and microstructure of lightweight aggregates (LWA) manufactured from PFA can be controlled by changing the key sintering parameters such as temperature, time and heating rate.     

Fracture toughness (J1C) of electron beam welded AA2219 alloy

AA2219 (Al–6%Cu) was butt welded in T87 temper (solution heat-treated, cold worked and precipitation hardened) and T6 temper (solution heat-treated and precipitation hardened) using electron beam welding (EBW). Variables studied were base metal temper condition and mode of EBW. Mechanical properties of the weld joint and fracture toughness at fusion zone (FZ) and heat-affected zone (HAZ) were evaluated and compared with those of the base metal. Results showed that EB welds have higher joint efficiency and fracture toughness than that of gas tungsten arc welding (GTAW). Fracture toughness of T6 base metal was found to be higher than its T87 counterpart. When welded, FZ and HAZ in T87 showed higher fracture toughness than that of T6; HAZ was the toughest. Pulsed current (PC) EB weld showed marginal reduction in toughness compared to constant current (CC) weld. Toughness variation is analyzed with the help of tensile test, Charpy impact test and scanning electron microscopy (SEM) and transmission electron microscopy (TEM).     

Modeling of effective material properties of pyrolytic carbon with different texture degrees by homogenization method

The elastic properties of pyrolytic carbon material as a function of texture degree were calculated by means of a homogenization method. The material microstructure is modeled as a system of graphite crystals (inclusions) embedded in an infinite homogeneous matrix with unknown effective (overall) parameters. The texture degrees of carbon planes extracted from the experimental selected-area electron diffraction patterns as well as size of coherent domains extracted from high resolution transmission electron microscopy images have been used as reference points for modeling of material properties. The experimental diffraction curves exhibiting a good fitting with the Gauss density function have been used to simulate the spatial orientation of inclusions. After that the overall elasticity tensor is calculated and the influence of the texture degree of pyrolytic carbon material on the engineering elastic parameters is studied.     

Fracture behavior of HPHT synthetic diamond with micrometers metallic inclusions

The fracture behavior of the diamond single crystals with metallic inclusions was investigated in the present paper. Single diamond crystals with metallic inclusions were formed by a special process with high pressure and high temperature (HPHT). The inclusions trapped in the diamond were characterized mainly to be metallic carbide of (Fe,Ni)₂₃C₆ or Fe₃C and solid solution of γ-(Fe,Ni) by transmission electronic microscopy (TEM). The grain size of the inclusions is about micrometers. The fracture characteristics of the diamond single crystals, after compression and heating, were investigated by optical microscopy (OM) and scanning electron microscopy (SEM). The fracture sections of the compressed and heated diamonds were found to be parallel to the (111) plane. The interface of the inclusions and diamond is deduced to be the key factor and the original region of the fracture formation. Mechanisms of the fracture behavior of the HPHT synthesized diamonds are discussed.     

A new interpretation of temper embrittlement dynamics by non-equilibrium segregation of phosphor in steels

A new interpretation of temper embrittlement dynamics is proposed, which is based on the diffusion of phosphor atoms to grain boundaries by the complex of phosphor atom-vacancy. The dynamics of temper embrittlement in a medium-carbon Cr steel during 538°C tempering was carefully examined. The results show that the dependence of 50% fracture appearance transition temperature (FATT) on tempering time has a maximum, which can be satisfactorily elucidated by diffusion of the complex of phosphor atom-vacancy. However, the dependence of hardness on tempering duration decreases all the time. The fracture morphology was observed by scanning electron microscopy (SEM), the variation of intergranular fracture ratio also has a maximum during tempering treatment at 538°C, which is at the near same time as the one in the dynamic of temper embrittlement. The concentration of phosphor on grain boundary was measured by Auger electron microscopy (AES).     

Twilight polarization and optical depth of stratospheric aerosols over Beijing after the Pinatubo volcanic eruption

After the volcanic eruption of Mt. Pinatubo the degree of polarization of skylight during twilight over Beijing was monitored with a polarimeter aimed at the local zenith. We analyze the effect of changes in the scattering coefficient of atmospheric aerosols for the case of multiple scattering on skylight polarization at the zenith and then discuss the evolution of skylight polarization over Beijing during the posteruption period. As a reference and for comparison we also discuss the evolution of the aerosol optical depth retrieved from the combination of skylight polarization and backscattering ratio measured by the polarimeter and a lidar for the period beginning with the eruption of Mt. Pinatubo through the end of 1993. The contributions of atmospheric aerosols at different altitudes to the ground-observed twilight polarization depend on the solar zenith angle. For larger solar zenith angles, the skylight polarization is mostly sensitive to aerosol variations in the upper layer that range from 15 to 30 km. The twilight polarization at the zenith from June 1991 to mid-1994 shows different features for three periods: (1) From October 1991 to February 1992, volcanic dust traveled to mid-latitudes, and the degree of polarization decreased substantially. (2) From February 1992 to November 1993, volcanic dust was dispersed the minimum degree of polarization at the solar zenith angle of 93.5 degrees disappeared and the maximum increased. In addition, polarization for solar zenith angles less than 90 degrees also increased. (3) From November 1993 to May 1994, most of the volcanic dust had fallen off, the atmosphere was restored to the background state, and the skylight polarization approached the preeruption condition.     

Near-infrared spectroscopic determination of salinity and internal pressure of fluid inclusions in minerals

A near-infrared (NIR) spectroscopic method is proposed to achieve the simultaneous determination of salinity and internal pressure of fluid inclusions in natural minerals. A combination band between the anti-symmetric stretching and bending vibrations of molecular water at approximately 5180 cm-1 was observed for standard salt solutions and natural minerals containing fluid inclusions with known salinities. A curve-fitting procedure was used to analyze the change in the band shape of the combination. Justification of the calibration was confirmed by observation of fluid inclusions in natural minerals whose salinities had already been determined using microthermometry. The detection limit of the present method is 1 NaCl-eq wt. %. The minimum size of fluid inclusions that produced well-resolved spectra was approximately 30 microm. This method was applied to assess micro fluid inclusions in a natural diamond with cubic growth habit (cuboid). The salinity and residual pressure of those fluid inclusions were estimated respectively as 4.4 wt. % NaCl-eq and 0.6-0.8 GPa. The present method is complementary to Raman microscopy and microthermometry for the determination of salinity in fluid inclusions of geological samples.     

Extrusion Processing of High-Strength Al Alloy 7055

The effects of a combination of extrusion processing parameters and aging schedules on the microstructure and mechanical properties of the 7055 Al alloy were investigated. A safe extrusion processing zone is determined through a limit diagram constructed over the experimental initial billet temperature ranging from 380° to 420°C, extrusion ratio from 10:1 to 40:1, and the ram speed ranging from 1 to 15 mm s^-1. Microstructural characterization of as-extruded, solution-treated, and artificially-aged materials was carried out using polarized light microscopy (for grain structure) and transmission electron microscopy (for precipitate morphology). A combination of hardness and tensile tests was used to evaluate mechanical properties. It is shown that in 7055 Al alloy, the optimization of alloy composition, extrusion processing parameters, and peak aging treatment results in reproducible tensile properties of 0.2% P.S. = 725 MPa, UTS = 750 MPa, and % elongation = 12.9. In order to improve the stress-corrosion resistance of peak aged material, retrogression and reaging (RRA) temper was established. A strength-electrical conductivity relationship has been established for the RRA temper between 36% and 37% International Annealed Copper Standard (IACS) electrical conductivity to enable selection of suitable combination of properties.     

Entrapment of Inclusions in Diamond Crystals Grown from Fe—Ni—C System

Diamond single crystals grown from Fe-Ni-C system at high temperature-high pressure(HPHT) usually contain inclusions related to the metallic catalyst.During the diamond growth,the metallic inclusions are trapped by the growth front or are formed through reaction between the contaminants trapped in the diamond.In the present paper,the metallic inclusions related to the catalyst were systematically examined by transmission electron microscopy (TEM).The chemical composition and crystal structure of the metallic inclusions were for the first time determined by selected are electron diffraction pattern (SADP) combined with energy dispersive X-ray spectrometry(EDS).It is shown that the inclusions are mainly composed of orthorhomibic FeSi2,fcc(FeNi)23C6,and orthorhombic Fe3C,hexagonal Ni3C.     

Microstructure and mechanical properties of spray deposited and extruded 7000 series aluminium alloys

Abstract

The microstructure and mechanical properties of spray deposited 7000 series aluminium alloys were investigated. The 7000 type alloys were produced by the spray atomisation deposition method. These alloys were hot extruded and subsequently heat treated in the T6 and T7 temper conditions. Microstructural characterisation of the alloys was carried out by transmission electron microscopy (TEM). TEM studies revealed the presence of η′ and η(MgZn₂) hardening precipitates in both temper conditions. The mechanical properties were assessed through tensile and notched tensile tests using an Instron machine. It was observed that the 0.2% proof stress of these alloys after T7 temper decreased with increased elongation to fracture values.     

Use of 3D printing for biofuel production: efficient catalyst for sustainable biodiesel production from wastes

This work deals with the sustainable biodiesel production from low-cost renewable feedstock (waste and non-edible oils) using a heterogeneous catalyst constituted by potassium loaded on an amorphous aluminum silicate naturally occurring as volcanic material (pumice). The main challenge to biodiesel production from low-quality oils (used oils and greases) is the high percentage of free fatty acids (FFAs) and water in the feedstock that causes undesirable side reactions. The catalytic materials studied were tested in the transesterification reaction when using low-quality oils containing a high proportion of free fatty acids (FFAs) and water. Results indicated that the amount of acid and basic sites on the catalytic surface increases upon increasing potassium loading in the catalyst, displaying better performance for biodiesel production. Indeed, the modification of the aluminum silicate substrate upon potassium incorporation results in a catalytic material containing both acidic and basic sites, which are responsible for both triglycerides transesterification and FFA esterification reactions. The studied catalyst not only showed good performance in the biodiesel production reaction but also good tolerance to FFA and water contained in the feedstock for biodiesel production. The catalytic material was microstructured by 3D printing in order to design a catalytic stirring system with high mechanical strength, efficient and reusable. The use of 3D printing in biofuel production is a novelty that brings good solutions for catalyst production.     

Ni-Cu-P钢耐点蚀性能的机理研究

选择Ni-Cu-P钢和碳钢各两种,在pH=10的3%(质量分数)NaCl溶液中进行极化实验,比较钢的点蚀诱发敏感性;在3%海盐水中进行间浸挂片实验,评价钢的点蚀扩展速率;利用扫描电镜(SEM)、电子探针(EPMA)、X射线衍射(XRD)分析钢中夹杂物、腐蚀形貌和锈层的特征。结果表明:Ni-Cu-P钢比碳钢表现出更弱的点蚀诱发敏感性和更小的点蚀扩展速率。较弱的脱氧可降低碳钢的耐点蚀性能,但对Ni-Cu-P钢不产生明显影响。锈层分析结果发现,Ni-Cu-P钢和碳钢内锈层的主要成分接近,但Ni-Cu-P钢的内锈层明显比碳钢致密。Ni-Cu-P钢中Ni和P能有效降低酸化蚀坑内钢基体的腐蚀速率;Cu则有助于致密锈层的形成。     

Upper tropospheric temperature measurements with the use of a Raman lidar

Upper tropospheric temperature profiles were measured with the NASA Goddard Space Flight Center scanning Raman lidar five months after the eruption of Mt. Pinatubo. To derive temperatures in regions of high aerosol content, the aerosol transmission is calculated for the Raman N(2) return signals under cloud-free conditions. The lidar-derived aerosol backscattering ratio and an estimate of the aerosol extinction-to-backscatter ratio were used to compute the aerosol transmission. With a model reference temperature at 25 km, temperature profiles with a root-mean-square difference between the lidar and radiosonde temperatures of <2 K were obtained over an altitude range of 5-10 km for a 10-min integrated measurement with 300-m resolution.     

原板夹杂物诱发镀锡板点腐蚀缺陷分析

原板高强减薄和锡量降低是镀锡板发展的重要趋势,直接对原板夹杂物和镀锡板表面缺陷控制提出了更为严格的技术要求。通过对夹杂物含量异常的钢坯进行全流程加工得到的1.1/1.1 g/m2规格镀锡成品卷的研究,发现经过10 d在库测试,镀锡板表面产生点腐蚀缺陷。利用光学显微镜、扫描电镜和电子能谱等方法就镀锡板点腐蚀缺陷进行了深入分析,结果发现黄褐色腐蚀产物元素成分为O、Fe,源于基体腐蚀,并伴有原板夹杂物存在。通过金相切片确认典型点腐蚀缺陷样品夹杂物尺寸为96.82μm×50.00μm×8.86μm,属于原板表面嵌入型夹杂,其成分特征为主要含Al、O元素。夹杂物的存在改变了局部区域的原板轧制纹理和镀层形貌,产生近似椭圆白点缺陷,锡层沉积量由缺陷中心外延逐步增加,整体在11.02%～28.08%范围内波动。根据夹杂物伴随点腐蚀缺陷特征,其诱发镀锡板腐蚀行为与夹杂物形成的原板晶体结构缺陷、锡层差异沉积与夹杂物导电性和硬度直接相关。通过研究,清晰地描述了原板表面夹杂物对后续镀锡板成品的表面质量影响关系,为更好控制原板夹杂物提升镀锡板产品表面质量提供了实际数据支撑。     

钒-钛微合金化钢焊接热影响区晶内铁素体与夹杂物的界面关系

采用聚焦离子束方法制备试样,利用最高加速电压为1 300 kV的高分辨电镜观察钒-钛微合金化钢100 kJ/cm大线能量热模拟焊接热影响区,对作为晶内铁素体形核核心的夹杂物形貌与结构及夹杂物与晶内铁素体界面关系进行了研究.结果表明,晶内铁素体在MnS V(C,N)复合夹杂物相上形核析出,夹杂物和晶内铁素体存在确定的晶体学位向关系.     

Volcanic Bishop's ring: evidence for a sulfuric acid tetrahydrate particle aureole

Following the massive 1883 Krakatoa volcanic eruption, a new atmospheric optical phenomeon was identified by Rev. S. E. Bishop. This inconspicuous one-ringed corona, or aureole, was immediately linked to the global spread of volcanic debris injected into the stratosphere, but little refinement in the mechanisms responsible for Bishop's ring has since been made. On the basis of our combined studies of sulfuric acid droplet-freezing theory and polarization (0.694-μm) lidar measurements of Bishop's ring aerosols from the June 1991 Mt. Pinatubo eruption that show average linear depolarization ratios of ;~0.05, it appears that this solar diffraction phenomenon is caused by accumulations of nonspherical sulfuric acid tetrahydrate (SAT) particles. The diffraction-theory aureole-derived SAT particle radius of ~0.8 μm is consistent with the freezing of the large mode of volcanic acid droplets created by coagulation, which, according to theory, is necessary for concentrating a sufficient insoluble mass to promote het rogeneous drop freezing at temperatures below approximately -65 °C.     

STATISTICAL MODELLING OF INTERGRANULAR BRITTLE FRACTURE IN A LOW ALLOY STEEL

The intergranular brittle fracture (IBF) behaviour of a low alloy steel 16MND5 (A508 Cl. 3) was investigated. A temper embrittlement heat treatment was applied to the material to simulate the effect of local brittle zones (ghost lines) which can be found in the as-received material condition. An increase in the Charpy V toughness transition temperature and a significant decrease in the fracture toughness measured on CT-type specimens were observed in the embrittled material, as compared to the reference material which was submitted to the same austenitizing and tempering heat treatment, but which was not subjected to the temper embrittlement treatment. Tensile tests on notched specimens were carried out to measure the Weibull stress and scatter in the results. A statistical model, the Beremin model, originally proposed for brittle cleavage fracture was applied to IBF. It is shown that this model is not able to fully account for the results, in particular for the existence of two slopes in a Weibull plot. Systematic fractographic observations showed that the low slope regime in this representation was associated with the existence of MnS inclusions initiating brittle fracture, while the larger slope was related to microstructural defects. Initiation of IBF from MnS inclusions can occur when the material is still elastically deformed while the second population of microstructural defects is active in the plastic regime. A modified statistical model based on the Beremin model and taking into account these specific aspects is proposed in the framework of the weakest link theory. The parameters of this model are identified from test results on notched specimens. It is shown that this model is able to predict the temperature dependence of fracture toughness and the scatter in the experimental results.     

Investigation on defects in HPHT-grown diamond single crystals

In the diamond single crystals synthesized at high temperature and high pressure using FeNi as catalyst, there are usually supersaturated vacancies and inclusions formed during the diamond crystal growth and rapid cooling from high temperature. Some defects such as prismatic dislocation loops, stacking faults and array of dislocations are closely related to such supersaturated vacancies and inclusions. The supersaturated vacancies agglomerate into discs on the (111) close-packed planes, subsequent collapse of the discs forms the dislocation loops and stacking faults. The thermal internal stresses, which are caused by the difference of thermal contraction between the diamond and the inclusions due to the difference of thermal coefficients between them as the diamond is cooled from high temperature, may be relieved by the formation of array of dislocations. In the present paper, these defects in the diamond single crystals were directly examined by transmission electron microscopy (TEM). The characteristics and formation process of these defects were analyzed briefly.     

Cathodoluminescence characterization of defects in yttrium aluminum garnet doped with Nd

Nominally undoped and Nd-doped yttrium aluminum garnet (YAG) crystals were studied by scanning electron microscopy, electron probe x-ray microanalysis, and cathodoluminescence (CL) microscopy and spectroscopy techniques. The detection limit of CL for Nd in YAG was found to be 10^-6 wt %. The nature of inhomogeneities in the crystals with a high Nd concentration was established. The distribution of background Nd impurity over defect-rich YAG crystals was assessed. A method for the identification of solid-phase inclusions from x-ray microanalysis and CL data is proposed. The effect of the growth technique and impurity concentration on the CL spectrum of YAG is examined.     

Factors affecting corrosion behavior of inclusion containing stainless steels: A scanning electrochemical microscopic study

Stainless steels usually contain some amounts of sulfide type of inclusions which are known to affect their corrosion behavior in mild aqueous chloride solutions. The life of the stainless steel components is severely affected as the manganese sulfide inclusions dissolve and the reaction products at the site of inclusions lead to pitting corrosion. The pits so formed as well as manganese sulfide inclusions, being local heterogeneities were studied by a microprobing technique called scanning electrochemical microscopy. In order to demonstrate how this local probing technique can be optimally used to investigate the corrosion behavior of inclusion containing austenitic stainless steels, different experimental parameters were varied one by one. The effect of different factors such as substrate potential, rate of scanning and concentration of chloride was studied in detail. The study shows that a scan rate of 0.32 μm/s (3.2 μm step distance for 10 s hold time) for 50 μm by 50 μm scans and a scan rate of 0.1 μm/s (1 μm step distance for 10 s hold time) for 20 μm by 20 μm scans produced optimum results throughout the study.