Crystal Structure of Monohydrate of γ-Modification of Rubidium Uranoniobate

The compound γ-RbNbUO₆·H₂O was prepared for the first time as single crystals, which were studied by X-ray diffraction. Crystal data: rhombic system, space group Pcab, a = 7.614(2), b = 11.219(2), c = 16.510(3) Å, Z = 8. The crystal structure is built from uranium-containing layers of the composition [NbUO₆] _2∝ ^δ? , infinite in two directions. The water molecules and rubidium atoms distributed over two randomly occupied positions are accommodated between the layers.     

Investigation of the Dynamics of Evaporation of Condensed Bodies on the Basis of the Law of Spectral‐Radiation Intensity of Particles

The fundamentals of radiation theory and the mechanism of evaporation of condensed bodies are presented. The distribution functions of particles of a body by energies and by the intensity of their transition from one energy level to another in the process of evaporation have been obtained based on the law of spectralradiation intensity of the body particles. The temperature dependence of the resulting vapor flow on the outer surface of a massive condensed body and a thin layer in equilibrium and nonequilibrium states, which, in the limit, transforms to the known Hertz–Knudsen formula, has been found.     

Magnetothermal Analysis of Nanocrystallization of Amorphous and Relaxations of Nanocrystalline Materials

For a few years it has been realized that nanocrystalline phases can be formed during crystallization of amorphous alloys annealed isothermally below the crystallization temperature of usual heating experiments. Data of this transformation monitored by the measurement of magnetic susceptibility are presented. A method using a magnetic balance with electronic stabilisation and combined computer facilities is applied. Constant heating and cooling rates as well as isothermal heat treatments are used. Magnetic measurements are able to detect the onset of the transformation of amorphous Ni-P alloys much earlier than was possible with differential scanning calorimetry. The transformation kinetics can be analyzed by means of the Avrami plot based on the Johnson-Mehl-Avrami equation.The kinetics of solid state reactions in the nanostructured material can be investigated similarly. Formation of a Ni-phase in a nanostructured Hf-Ni alloy could be detected in a very early stage, where calorimetric methods are not sensitive. Segregation phenomena could be detected from the experiments even after long time. The sensitivity of the applied method is not dependent on the heating rate as the sensitivity of scanning calorimetry is     

Brief Outline of the Metallurgy Department of Kunming Institute of Technology

The metallurgy department of Kunm-ing Institute of Technology,with its empha-sis on nonferrous metallurgy,is one of themajor academic and technical centres underthe China National Nonferrous Metals In-dustry Corporation(CNNC).The province of Yunnan,of whichKunming is the capital city,is very rich withresources of nonferrous metals,such as     

Analysis of clusters and uniformity of distribution of states of polarization on the Poincaré sphere

An analysis of the clusters and the uniformity of distribution of states of polarization on the surface of a Poincaré sphere generated by rotating wave plates is given. The analysis of clusters of the states of polarization is based on a spherical radial distribution function. For uniform analysis of the distribution, two methods are proposed. The first method is based on calculation of the correlation coefficient; the second method is based on calculation of the angles between pairs of the states of polarization on the Poincaré sphere. For polarization scramblers consisting of eight or more rotating wave plates, nonclustered and near-uniform distribution of states of polarization is obtained.     

Influence of Temperature‐Time Parameters of Heat Treatment on the Process of Planarization of the Surface Relief of Microelectron Structures

The authors consider the process of fusion of phosphorosilicate and borophosphorosilicate glasses in planarization of the surface of integrated microcircuits under the conditions of both isothermal and pulse heat treatment. An expression for calculating the angle of fusion of the relief step as a function of the concentration of doping impurities in a glass and the time and temperature of heat treatment is obtained.     

Measurement of the activity of individual subunits of single molecules of the tetrameric enzyme β-galactosidase

Escherichia coli β-galactosidase was incubated in the presence of the slow-release inhibitor D-galactal for 30 min at a concentration of 70 times its K(i). The sample was then diluted 20000-fold into buffer containing the fluorogenic substrate 9H-(1,3-dichloro-9,9-dimethylacridin-2-on-7-yl) β-D-galactoside, reducing the inhibitor concentration to K(i)/280. The sample was subjected to a capillary electrophoresis continuous flow single enzyme molecule assay. As the inhibitor dissociated while the enzyme traveled the length of the capillary, a fraction of molecules showed stepwise increases in activity. This was due to the activation of individual subunits within single molecules. The changes in activity can be largely explained in terms of each molecule containing subunits of indistinguishable activity.     

Inhomogeneity of Grain Boundaries of ZnO Varistor

The zinc oxide varistor with a low threshold voltage and large grain size was derived with ZnO crystalline seeds from a molten salt process The chemical composition and I-V characteristics of single grains and single grain boundaries were determined by means of energy dispersive spectrum (EDS) and microcontact measurement respectively. Temperatu re dependence of dielectric loss at various frequencies and voltage dependence of capacitance were carefully measured. Based on these experimental data. the barrier heights of giain boundaries are estimated to be 0.2. 0.5 and 0.6 eV respectively corresponding to thick, th in and direct contact grain boundaries. In addition. a computerized electrical circuit simufation is employed in simulating I-V characteristics of single grain boundary within ZnO varistor. By adjustjng parameters of resistor and diode, a general agreement between the measured data and simulated curves is achieved     

The Establishment of National TC of Superconduction

National standardization technical committee of superconduction was established on Aug 26th, 2003. Tmittee contains 22 experts, of which the percentage of professors and researchers reaches up to 77.3%mention there are four academician consultants, Gan Zizhao, Zhao Zhongxian and Yang Guozhen fromAcademy of Sciences, and Zhou Lian from China Academy of Engineering. The four academicians had ed earlier in the 7th Academic Seminar of Superconduction in April that the high-tech superconduct…     

Effect of carbon content and microalloying on martensitic hardenability of austenite of dual-phase steel

Abstract

Microstructure maps were constructed for a C–Mn steel and microalloyed steels of the same base composition, after intercritical annealing to produce 23 and 50% of austenite. The critical cooling rates for the transformation to martensite of 90 and 50% of the austenite present were thus determined as functions of the carbon content of the austenite. At the 90% martensite level, the hardenability of the austenite was very similar to that of fully austenitized steel of the same composition, and varied identically with carbon content. At the 50% martensite level, the hardenability of the austenite was considerably greater than that of fully austenitized steel of the same composition. The presence of niobium and vanadium had no effect on the martensitic hardenability of the austenites: by forming carbides they simply altered the carbon content of the austenite at a fixed volume fraction of austenite. It is proposed that the martensitic hardenability of austenite of dual-phase steel depends on the size of the austenite volumes as well as on their carbon content. In the present study, the size of the austenite volumes was large enough to make them more hardenable than would be predicted on the basis of standard hardenability data for fully austenitized steels.

MST/548     

Carbon composition and temperature dependence of relative change in length during isothermal decomposition of Fe–C austenite

Abstract

The carbon composition and temperature dependence of the relative change in length during isothermal decompos ition of Fe–C austenite has been modelled. Decomposition of austenite above and below the A₁ temperature has been considered, as well as a two-step procedure where a specimen decomposes into ferrite and carbon enriched austenite at a temperature above A₁ and is subsequently subjected to transformation below A₁ leading to ferrite and cementite. Analytical expressions have been given for the relative change in length as a function of carbon composition, isothermal decomposition temperature, and degree of transformation. Predicted changes in length have been compared with experimental results.     

Simulation and characterisation of the microstructure of ultra-fast heated dual-phase steel

The current study focuses on the composition of the constituents that are obtained from ultra-fast heating and the composition of the parent austenite that was achieved at the peak temperature. In order to analyse the content and distribution of important elements such as carbon, manganese, chromium and molybdenum in the microstructure, simulation software was used. It is also found that the content of these elements shows a gradient in the microstructure in relation to the distance from the undissolved cementite. This leads to carbon-rich areas in the vicinity of cementite and carbon-depleted areas as the distance from the cementite grows. The former creates ideal conditions for the retainment of austenite due to the higher carbon content while the latter creates conditions that enable the formation of bainite in the microstructure.     

Formation of austenite in steels during heating: analysis of dilatation data

A novel method has been presented to estimate the volume fraction of the phases along with their linear thermal expansion coefficients and carbon concentration of austenite directly from the experimental dilatation data of a low alloy (LA) steel. The unusual expansion associated with austenite formation in the LA steel has been investigated. It has been shown that the relative contribution of (i) the variation of the amount and composition of phases with temperatures and (ii) thermal expansion coefficient of the phases have significant effect on the dilatation behaviour. It is also shown that the present method, rather than the ‘lever rule’ approach, is more appropriate for estimating the amount of austenite from the dilatation curve when it shows unusual expansion.     

Investigation of the evolution of retained austenite in Fe–13%Cr–4%Ni martensitic stainless steel during intercritical tempering

The microstructure and amount of retained austenite (the austenite remained at room temperature) evolved in Fe–13%Cr–4%Ni martensitic stainless steel during intercritical tempering at 620 °C have been investigated. The amount of retained austenite showed a parabolic trend with increase in tempering time, which can be attributed to the gradual decrease in the thermal stability of the reversed austenite (the austenite formed at high temperature). The influences of chemical composition, morphology of reversed austenite, and mechanical constraints originating from tempered martensite matrix on the thermal stability have been discussed. The precipitation and growth of M₂₃C₆ in reversed austenite dilute the carbon concentration in reversed austenite. The spheroidization of lathy reversed austenite during tempering decreases the interfacial energy barrier to the phase transformation of reversed austenite to martensite. Furthermore, the decrease in the strength of martensite matrix lowers the strain energy associated with the transformation of reversed austenite to martensite. All these factors during tempering weaken the thermal stability of reversed austenite and facilitate the phase transformation of reversed austenite to martensite during the cooling step of intercritical tempering.     

Effect of intercritical annealing on retained austenite characterization in textured TRIP-assisted steel sheet

Optimization of high strength and high formability of multiphase cold rolled sheet TRIP-aided steels is based on the composition and the austempering conditions. The effect of intercritical annealing temperature on the volume fraction and carbon concentration of the retained austenite was investigated in two different TRIP-aided steels. Experimental results show that the optimum annealing temperatures are 860 °C for Al-containing and 810 °C for Si-containing TRIP steels. It was demonstrated that the measurement of retained austenite can be successfully performed for textured TRIP steels by XRD.     

High-Pressure Processing and Characterization of Fe–High-C/N Alloys

A new process has been developed that results in (i) enhanced nitrogen addition to ferritic iron–carbon alloys and (ii) melt-casting in a single operation. This new processing technique enables Fe–C alloys to retain high nitrogen interstitial concentrations and to reduce significantly, and possibly eliminate, carbide formation. In this study two commercial-grade, steel alloys were cast under elevated nitrogen pressures, resulting in solid solution (austenite, ferrite, and martensite) high-carbon and high-nitrogen iron alloys that were, within detection limits, carbide- and nitride-free. These alloys were subsequently thermally processed to transform part of the retained austenite to martensite. The microstructure and mechanical properties of the alloys were studied as a function of carbon and nitrogen composition and as a function of thermal processing. The retain high nitrogen concentrations in these cast and processed iron–carbon alloys resulted in a substantial improvement in compression strengths.     

The kinetics of low-pressure carburizing of alloy steels

In the article the author analyzed the kinetics of low-pressure carburizing of alloy steels, based on steel 16MnCr5 and CSB 50NIL. It was found that an active radical-carbon layer (carbon deposit) deposits on the surface of austenite grains or austenite and carbides during boost steps. This layer mediates in moving the carbon deeper into the austenite grains. During the diffusion steps the layer deposited on the carbide surfaces transfers into the austenite grains. Both this layer and the one previously deposited on the austenite grains surface now undergo another catalytic decomposition into atomic carbon and hydrogen, other types of radicals and fine-crystalline graphite. The resulting carbon atoms are absorbed by surface austenite grains and next diffuse deeper into the austenite grains, and, alternatively, into the carbide surface, making the carbides grow and contributing to the increase in the carburized layer thickness.     

The kinetics of low-pressure carburizing of alloy steels

In the article the author analyzed the kinetics of low-pressure carburizing of alloy steels, based on steel 16MnCr5 and CSB 50NIL. It was found that an active radical-carbon layer (carbon deposit) deposits on the surface of austenite grains or austenite and carbides during boost steps. This layer mediates in moving the carbon deeper into the austenite grains. During the diffusion steps the layer deposited on the carbide surfaces transfers into the austenite grains. Both this layer and the one previously deposited on the austenite grains surface now undergo another catalytic decomposition into atomic carbon and hydrogen, other types of radicals and fine-crystalline graphite. The resulting carbon atoms are absorbed by surface austenite grains and next diffuse deeper into the austenite grains, and, alternatively, into the carbide surface, making the carbides grow and contributing to the increase in the carburized layer thickness.     

The morphology of martensite in Fe-C,Fe-Ni-C and Fe-Cr-C alloys

The morphology of martensite in widely varying series of Fe-C, Fe-Ni-C and Fe-Cr-C alloys was investigated using optical microscopy. The effects of formation temperature and alloying elements on the martensite morphology were studied in detail. It was found that in Fe-C alloys, lath martensite forms in alloys with less than 0.8wt% carbon, butterfly martensite forms in alloys with between 0.98 and 1.42wt% carbon and lenticular martensite forms in alloys with more than 1.56wt% carbon. In Fe-Ni-C alloys, four different martensite morphologies form depending upon the formation temperature and composition, and for alloys of a fixed carbon content the martensite morphology changes from lath to butterfly to lenticular to thin plate as the formation temperature is decreased. In Fe-Cr-C alloys, lath martensite forms at high temperature, and below the lath formation temperature mainly {2 2 5}_f plate martensite is formed. Based on the results obtained, the importance of the strength of austenite, and the austenite stacking fault energy to the martensite morphology was discussed.