High-temperature Microscopy Research Articles

Lateral growth rate of δ phase during solidification of Fe-0.15wt%C-0.8wt%Mn steel

Taking Fe-0.15wt%C-0.8wt%Mn steel as the research object, in situ observations of the δ phase growth process during solidification were conducted by using a high-temperature confocal scanning laser microscope (HTCSLM). The effects of the solid/liquid (S/L) interface’s shape, temperature, and curvature radius on the lateral growth rate of δ phase were investigated in detail, and the relational expression among the lateral growth rate of δ phase, temperature, and curvature radius of column-shaped δ phase was deduced for the carbon steel during solidification. The results indicate the growth rate of the concave-shaped S/L interface is larger than that of the convex-shaped S/L interface during the beginning growth of δ phase, but these two kinds of growth rates gradually approach with proceeding in solidification. The calculated lateral growth rate of δ phase is consistent with the experimental result at a cooling rate of 0.045°C/s.

Combustion synthesis of Mg2Si

Magnesium silicide and its derivatives are perceived as light-weight eco-friendly materials for multiple applications, because of the advantageous combination of physical, mechanical and chemical properties. The principal components, silicon and magnesium, are abundant in nature and thus easily accessible. Manufacturing of Mg2Si-based materials is, however, challenging and a lot of efforts have been made to better control their composition and microstructure. In this work, magnesium silicide dense sinters were successfully produced by self-propagating reaction and hot pressing. The reaction was studied by DTA/TG and high-temperature microscopy. Composition and microstructure of reactants and products were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Property assessment comprised density, hardness, elastic modulus, specific heat, thermal diffusivity, and electrical conductivity.

Experimental Studies and Technology Process on Phosphor-Gypsum Decomposition for Producing Sulfuric Acid and Lime

Using phosphor-gypsum (PG) to produce sulfuric acid is one of the most effective ways of recycling sulfur resources. This paper studied the melting and decomposition behavior of PG with High Temperature Microscope and Infrared Sulfur Analyzer. Moreover, a new process of PG decomposition for producing sulfuric acid and lime is proposed and discussed. The result shows that the minimum communion point of PG is higher than 1200 °C, the desulphurization degree of PG at 1200 °C under reducing-oxidizing atmosphere can exceed 90%, and the decomposition products of PG have high hydration activity. This means that little liquid phase will occur if PG is decomposed at1200°C, so PG can be decomposed using a fluidizing furnace. The new process of PG decomposition for producing sulfuric acid and lime has many advantages over the traditional process of PG decomposition for producing sulfuric acid and cement, and has a broad application prospects.

Effect of Bi 2O 3 on structure and wetting studies of Bi 2O 3–ZnO–B 2O 3 glasses

Glasses with different Bi 2O 3 contents (37–42 mol%) have been prepared by conventional melt quench technique. The IR and Raman studies indicate that these glasses are made up of [BiO 6], [BiO 3], [BO 3] and [BO 4] basic structural units. The vibrations of [BiO 3] and [BO 3] become stronger as the content of Bi 2O 3 increases, which makes glass structure loosened. Viscosity of the glasses was measured by using a Rheotronic III paralleled plate rheometry, which shows that the viscosity of glass samples decreased when the content of Bi 2O 3 increased at the same temperature (400–460 °C). The temperature range which suits for glasses sealing was calculated by using the approximation of Arrhenian behaviour. The wetting performance of Bi 2O 3–ZnO–B 2O 3 glasses was described by using high-temperature microscope, which also proves that the structure of investigated Bi 2O 3–ZnO–B 2O 3 glasses become loosened due to the increasing of the content of Bi 2O 3.

The Influence of Carbonaceous Material on the Melting Behaviour of Mould Powder

AbstractThe melting behaviour of mould powder during continuous casting is an important consideration with respect to caster performance, production rate and steel quality. In this experimental study the effect of different carbonaceous materials on the melting characteristics of mould powders was evaluated. Using X‐ray diffraction, different types of carbon were quantitatively characterized in terms of their internal structure and reactivity experiments were conducted to investigate potential relationships between the structural morphology of carbons and their reactivity. High temperature microscopy and drip test experiments were then used to investigate the melting behaviour of mould powders containing different carbonaceous materials. From the results obtained, correlations were established between the structural factors, chemical reactivity and melting behaviour.

High-Temperature Stability of Lead Zinc Niobate: In Situ X-Ray Diffraction

The thermal stability of the relaxor ferroelectric Pb(Zn 1/3 Nb 2/3 ) 0 3 (PZN) upon heating was studied using high-temperature X-ray diffraction (XRD) and scanning electron microscopy. It was found that single-phase PZN is stable below 700°C, whereupon the first decomposition phase, the pyrochlore Pb 1.83 Nb 1 . 71 Zn 0 . 29 0 6 . 39 was observed. With the increasing temperature, the amount of pyrochlore increased until at 1100°C there is no PZN remaining. Pyrochlore formation was accompanied by the precipitation of ZnO above 800°C and after holding at 1100°C, the formation of Nb 2 Z H O 6 . Rietveld refinements based on the XRD patterns have allowed the relative phase proportions as well as the atomic site occupancies of the metal ions in PZN and the pyrochlore to be estimated. The Zn site occupancy within the perovskite PZN decreases upon heating in parallel with the pyrochlore formation. An elemental mass balance based on the XRD results shows that PZN decomposition is well under way before any Pb is lost from the sample. This indicates that Zn egress rather than Pb volatility is the determining factor in the instability of PZN, contrary to prior published work.

현무암의 용융특성과 연속섬유 방사 연구

제주도 표선리 현무암 원광을 이용하여 연속 방사에 의해 현무암 섬유를 제조하였다. 먼저 현무암의 용융특성을 확인하기 위하여 현무암 원광을 백금도가니에 넣고 <TEX>$1550^{\circ}C$</TEX>로 용융시킨 후, 물속에서 급냉하였다. 냉각한 후 X-선 회절, 열팽창, 고온 점도, 고온 전기전도도와 고온 현미경을 측정 분석하여 연속방사 조건을 조사하였다. 연속 섬유를 제조하기 위한 최적의 방사 온도와 고온 점도는 각각 <TEX>$1264^{\circ}C$</TEX>와 <TEX>$10^{2.8}$</TEX> poise이었다. 제조된 방사 섬유의 특성은 인장강도, 전자현미경 관찰, 내열시험 등으로 확인하였다. 부싱 온도 <TEX>$1240^{\circ}C$</TEX>와 와인더 속도 4600rpm의 방사 조건에서 제조된 섬유의 인장 강도는 3660MPa을 나타내었다. Basaltic fiber was prepared by continuous spinning process from Jeju Pyosun raw basalt materials. First, for confirming the melting characterization of basalt, basalt raw material put into Pt crucible and melted up to <TEX>$1550^{\circ}C$</TEX> then quenched by dropping it into water. After quenching, the optimum fiber spinning conditions were investigated by measurement and analysis of XRD, TMA, high temperature viscosity, high temperature conductivity and high temperature microscope. The optimum spinning temperature and viscosity for preparation of continuous filament fiber were <TEX>$1264^{\circ}C$</TEX> and <TEX>$10^{2.8}$</TEX> poise at <TEX>$1264^{\circ}C$</TEX>, respectively. Properties of prepared spinning fiber were confirmed by tensile strength, FE-SEM, heat resisting test and others. The tensile strength of fiber prepared by spinning conditions of the bushing temperature <TEX>$1240^{\circ}C$</TEX> and winder speed 4600rpm was 3660MPa.

In situ observation and simulation of growth process of faceted RE123 crystals

To clarify the growth mechanism of faceted REBa2Cu3O7−δ (RE123, RE=Sm, Y) crystals, the growth process of the crystals was observed in situ by using a high temperature microscope. The growth rate of each faceted interface of a crystal growing from the liquid+211 phases under an undercooling was obtained from the relationship between the position of each interface and growth time. It was observed that some of the faceted interfaces of a growing crystal stopped growing after a period of time, while other interfaces continued to grow with a growth rate approximated by a function of the undercooling. The above stoppage of the growth was observed in situ for the first time, and this fact could give powerful support to the mechanism for a similar phenomenon in REBCO films which were fabricated by the trifluoroacetates metal organic deposition method: growing microstructures of RE123 crystals in the film were revealed by transmission electron microscopy (TEM) for quenched specimens. Some very thin a-axis grains were formed by a change in c-axis growth rate. Furthermore, we showed the above growth and stop phenomena of faceted interfaces of REBCO crystal grains using numerical simulations.

In-situ investigation of oxidation behaviour in high-speed steel roll material under dry and humid atmospheres

The oxidation behaviour of a high-speed steel roll material has been investigated by a high temperature microscope in the temperatures ranging from 550 to 700 °C in both dry and humid atmospheres. In-situ observations indicate that the oxide scales of the high-speed steel first nucleate at the carbides/matrix interfaces, and then rapidly spread to cover the carbides and followed by continuous growth over the whole surface. Water vapour in oxidizing atmosphere significantly increases the oxidation rates of carbides and the matrix. With the increase in temperature, the roughness of oxidized surface becomes higher for both dry and humid atmospheres.

Aluminum-rich belite sulfoaluminate cements: Clinkering and early age hydration

Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO{sub 2} into the atmosphere when compared to ordinary Portland cements. Here, we discuss the laboratory production of three aluminum-rich BSA clinkers with nominal mineralogical compositions in the range C{sub 2}S (50-60%), C{sub 4}A{sub 3}$$ (20-30%), CA (10%) and C{sub 12}A{sub 7} (10%). Using thermogravimetry, differential thermal analysis, high temperature microscopy, and X-ray powder diffraction with Rietveld quantitative phase analysis, we found that burning for 15 min at 1350 deg. C was the optimal procedure, in these experimental conditions, for obtaining the highest amount of C{sub 4}A{sub 3}$$, i.e. a value as close as possible to the nominal composition. Under these experimental conditions, three different BSA clinkers, nominally with 20, 30 and 30 wt.% of C{sub 4}A{sub 3}$$, had 19.6, 27.1 and 27.7 wt.%, C{sub 4}A{sub 3}$$ respectively, as determined by Rietveld analysis. We also studied the complex hydration process of BSA cements prepared by mixing BSA clinkers and gypsum. We present a methodology to establish the phase assemblage evolution of BSA cement pastes with time, including amorphous phases and free water. The methodology is based on Rietveld quantitative phase analysis of synchrotron and laboratory X-ray powder diffraction data coupled with chemical constraints. A parallel calorimetric study is also reported. It is shown that the beta-C{sub 2}S phase is more reactive in aluminum-rich BSA cements than in standard belite cements. On the other hand, C{sub 4}A{sub 3}$ reacts faster than the belite phases. The gypsum ratio in the cement is also shown to be an important factor in the phase evolution.

Thermal stability of pure bcc Zr fabricated by high pressure torsion

Recently pure omega plus bcc Zr was fabricated for the first time through the simultaneous application of compression and shear to pure alpha Zr by high pressure torsion. This phase was found to be stable under ambient conditions after processing. Here the thermal stability of the pure bcc Zr thus fabricated is analyzed using differential scanning calorimetry (DSC), in-situ X-ray diffraction at high temperature and transmission electron microscopy (TEM). Our results show that the temperature of the reverse transformation of the bcc phase is close to that of the omega phase. The presence of a mixed structure formed by alternating nanolaminates of the omega and the bcc phases might play a key role in the retention of these two phases at ambient pressure and temperature.

Disintegration of Northern Cape iron ores under reducing conditions

Cracking occurs in the first step of gaseous reduction of hematite iron ore, to magnetite, and can lead to the formation of fine material, with deleterious effects on operation of shaft furnaces. To study this, samples of three ore types from the Northern Cape iron ore field in South Africa, and one blended ore from this region, were studied. The methods were high temperature microscopy (during reduction) and quantification of fines formation following reduction disintegration tests. The ore types do differ significantly with regards to their propensity to form fines. Although disintegration is clearly triggered by reduction, no direct correlation could be established between the degree of reduction and the amount of fines generated. Reduction disintegration increased with higher hydrogen percentages (>5%) in the reduction gas, and at higher temperatures (in the 500–700°C range). Disintegration of the samples decreased at temperatures >750°C. There was no correlation between the presence of gangue minerals and fines formation.

Warm deformation mechanism of hot-rolled Mg alloy

Tension attachment of high temperature microscopy was proposed to research the microstructure evolution and plastic behavior of AZ31 magnesium alloy in a temperature range of 473–523 K and a load range of 80–160 N. Transmission electron microscopy(TEM) was utilized to observe the morphology of twins after deformation process. The results show that as Zener-Hollomon parameter Z increases (temperature falls, strain rate rises), the peak stress obviously increases, while the ductility tends to become worse. A great amount of twins can be found at moderate temperatures. Therefore, basal slip, a +c non-basal slipping and twinning are considered the dominant mechanisms at moderate temperatures. Some DRXed grains can be observed in the twinned regions and grain boundaries, suggesting both twinning-induced DRX and continuous DRX occurs in the deformation process.

Kinetics of Spinel Formation and Growth during Dissolution of MgO in CaO-Al2O3-SiO2 Slag

The formation and growth of MgAl2O4 spinel crystals on a single-crystal MgO substrate submerged in a 40 pct CaO, 40 pct SiO2, and 20 pct Al2O3 slag were directly observed using high-temperature microscopy. This showed that the crystals initially form on the MgO surface, but may break off and be carried out into the liquid slag. Still pictures extracted from digitally recorded images were used to measure the size of these crystals at 1420 °C, 1440 °C, and 1460 °C as a function of time. Growth of the crystals was found to follow the parabolic rate law, with rates increasing with temperature. An activation energy of 564 kJ mol−1 was estimated from the experimental data. This was found to be comparable with previously published results from different types of experiments on spinel formation.

Predicting Polymer Flow during High-Temperature Atomic Force Microscope Nanoindentation

This paper reports predictions of nanometer-scale polymer deformation during nanoprobe indentation at elevated temperature. The simulations assume continuum polymer properties with modified boundar...

Atomically sharp 〈111〉 trihedral angle of a tungsten tip

The processes occuring in the course of heating of a tungsten tip in an electric field and resulting in the formation of the 〈111〉 trihedral angle at the intersection of three {011} closest packed planes in the crystal lattice of tungsten are investigated using field-emission microscopy, continuous-mode field-desorption microscopy, and high-temperature field evaporation microscopy. It is demonstrated that atomically sharp angles can be formed at temperatures above 2200 K in the absence of field evaporation. An atom forming the apex of the trihedral angle lies in the triangle of atoms arranged in the (111) plane. In the triangle, each atom is located at the intersection of the 〈111〉 close-packed atomic rows, which are the boundaries of the {011} planes forming the trihedral angle and the {112} planes forming the angle edges two rows in width.

Effect of Na2O/K2O substitution on thermophysical properties of PbO based phosphate glasses

PbO based phosphate glasses having composition 40P2O5·12Al2O3·6B2O3·9PbO·xNa2O·(33−x)K2O (x=0−33) [F=Na/(Na+K)] have been prepared using conventional melt quench technique. Density, morphology, thermal expansion coefficient (α) and glass transition temperature (Tg) were studied as a function of Na/(Na+K) ratio. Formation of transparent, bubble free and clear glass was observed up to x=18 mol%. Density was found to vary from 2.70 to 3.69 g cm−3. The significant changes were noticed in external morphologies at temperatures corresponding to softening, half ball and melting points under high temperature microscope for three compositions (x=0, 10 and 15 mol%). These glasses recorded the softening and half ball temperatures in the range 454–470°C and 523–576°C respectively and melting temperatures agree well with DTA studies within the experimental limits. Glass transition temperature showed a broad maxima while thermal expansion coefficient (TEC) a broad minima around Na/(Na+K)=0.54. This behaviour is explained on the basis of bond formation/phase separation.

High-Temperature Phase Transitions and Mechanical Properties in Steel of Peritectic Composition

Continuous casting of steels of peritectic composition has proven to be problematic mostly because of surface crack occurrence. We have studied in situ the peritectic reaction as well as the kinetics of the subsequent peritectic transformations using the so-called concentric solidification technique in a high-temperature laser-scanning confocal microscope. We have also assessed grain growth in reheated as well as in situ cast Fe-C specimens in a Gleeble 3500 thermo-mechanical simulator. Our findings will be discussed with reference to the observation in practice that so-called 'blown-out' grains are associated with oscillation marks in continuously cast slabs. Background It is generally accepted that the surface quality of continuously cast steel slabs is a strong function of events occurring during the early stages of solidification in the meniscus region of the mould. Brimacombe and Sorimachi [1] provided a comprehensive classification of the origin of cracks in the continuous caster and McPherson and McLean [2] followed by Wolf [3], summarised much of the work relating to transverse cracking. Peritectic steels are the most difficult to produce with respect to surface quality [2-5], most probably because of the volume change that accompanies this phase transition [5,6]. Ludlow et al [6], using a technique introduced by Hiebler, Bernard and Xia [7,8] , confirmed that the maximum crack susceptibility is encountered between 0.1% and 0.14% carbon equivalent.

In situ observations of early oxide formation in steel under hot‐rolling conditions

A technique was developed to study in situ the early stages of the reaction between iron and air. Using a high-temperature microscope, we observed at temperatures between 1000 degrees C and 1050 degrees C and within the first 30 s of reaction, the formation of iron-oxide layers on the surface of low-carbon steel. We observed the nucleation and growth of a first layer of iron oxide and the consecutive formation in sequence, of higher iron oxides sweeping over the surface of the former oxide. The grain boundaries of the steel substrate remain visible for quite some time following exposure to an oxidizing atmosphere indicating that diffusion through steel grain boundaries may have a determining influence on the formation of oxides. These findings emphasize the importance of conducting further studies to better understand the kinetics and mechanisms by which iron-oxide layers form in the early stages of oxidation.

Field desorption microscopy of the 〈111〉 trihedral angle of a reconstructed tungsten tip

The surface structure near the 〈111〉 trihedral angle, which forms in an electric-field-heated tungsten tip, is studied by field electron microscopy, continuous-mode field desorption microscopy, and high-temperature field evaporation microscopy. The shape and structure of the surface depend on the temperature, field, and time. The angle is formed by three {011} planes, with the (111) plane at its vertex being retained in the form of a triangle or a hexagon with randomly arranged atomic clusters. The edges between {011} faces represent long and narrow {112} planes having longitudinal or transverse steps. In the absence of field evaporation, the edges and angle sharpen, becoming monoatomic. Field evaporation from the angle or microprotrusions on the edges extends these edges and causes transverse steps to appear on them. The explanation of the changes in the shape and structure of the surface is based on considering the competition of surface diffusion, crystal growth in an electric field, and field evaporation.