Low-temperature Stage Research Articles

The characterization of free radical reaction in coal low-temperature oxidation with different oxygen concentration

To explore the mechanism of low-temperature oxidation of residual coal at different depths in goaf, the oxygen concentration of airflow was dynamically adjusted to simulate the natural oxidation of coal at different depths in goaf with the aid of a self-built simulation experiment system of low-temperature coal oxidation. Based on electron spin resonance (ESR), analyses were made on the variation of free radicals during coal oxidation at low temperatures in different concentrations (volume fraction) of O2. Besides, an industrial analyzer and a gas chromatograph were also applied to the determination of the change of volatile matter and the emission of gaseous products. The results show that line height, the free radical concentration, volatile matter, and CO concentration change in stages with the increase of oxidation temperature. At about 130 °C, they shift from slow-varying to rapid-changing, reflecting that the coal steps out of a slow oxidation stage and enters a rapid one. The variation trend of line height and free radical concentration is basically the same, and g values are always in the range of 2.00141–2.002034, with little change. As O2 concentration rises, the tendency of each parameter with the oxidation temperature remains unchanged, but the overall variation gradually increases. When O2 concentration is lower than or equal to 9%, free radicals undergo reaction at a low speed and CO generation delays in the low-temperature stage. When it is higher than 9%, there is a growing possibility of coal-oxygen reaction. The increase in temperature improves the excitation of free radical reaction, so that CO concentration rises exponentially. Since different O2 concentrations have varying effects on coal oxidation, it is of great importance to adopt prediction and prevention technology in different-depth areas of goaf to ensure the safe mining of coal seam.

Thermal behavior of chitosan as a carbon material precursor under IR radiation

An effective accelerated synthesis procedure of a carbon material based on chitosan via infrared pyrolysis was developed. Infrared radiation heating allows to shorten preparation time significantly. It takes only 2 min of the residence time at 800 °C for complete carbonization of the polymer. The chemical transformations in chitosan during infrared pyrolysis depended on temperature were studied. The formation of C=C–C=N and C=C–C=C conjugated bonds at a low-temperature stage of the carbonization process was demonstrated. It was revealed that the main product of the chitosan pyrolysis at 600-800 °C represents a graphite-like carbon material in the form of carbocyclic structures.

Sulfide Mineralization in the Carbonatites and Phoscorites of the Guli Massif, Polar Siberia, and Their Noble-Metal Potential

We report the first combined investigation (neutron activation, X-ray fluorescence, and electron microprobe analysis) of mineral forms of Au and Ag and noble metal distribution in the sulfide-bearing phoscorites and carbonatites of the Guli alkaline ultrabasic massif (Polar Siberia) and magnetite and sulfide separates from these rocks. The highest noble metal contents were observed in the sulfide separates from the carbonatites: up to 2.93 Pt, 61.6 Au, and 3.61 ppm Ag. Pyrrhotite, djerfisherite, chalcopyrite, and pyrite are the most abundant sulfides and the main hosts for Au and Ag. The latest assemblage of chalcopyrite, Ag-rich djerfisherite, lenaite, sternbergite, and native silver shows significant Ag concentrations. The wide occurrence of K sulfides and presence of multiphase inclusions in pyrrhotite consisting of rasvumite, K‒Na–Ca carbonate, carbocernaite, strontianite, galena, chalcopyrite, sternbergite, lenaite, and native silver suggest that the sulfides were formed at high activities of K, Na, Sr, LREE, F, Cl, and S. Chlorine shows high complex-forming capacity to Ag and could be an agent of noble metal transport in the carbonatites. Crystallization of the early djerfisherite–pyrrhotite assemblages of the phoscorites and carbonatites began at a temperature not lower than 500°C and continued up to the formation of late Ag-bearing sulfides at temperatures not higher than 150°C. The carbonatite-series rocks could be enriched in Au and Ag during late low-temperature stages and serve as a source for Au placers.

High selectivity humidity sensors of functionalized graphite oxide with more epoxy groups

With large amounts of functional groups, graphene oxide (GO) is a promising sensing material for detecting gas molecules. Due to the different binding abilities between different oxygen-containing functional groups and target gas molecules, the selective response of the target gas can be realized through the regulation of functional groups in the GO structure. Herein, a new kind of GO with abundant epoxy groups was prepared by adding water as the activator in the low-temperature stage. The structure, spectral characteristics, and humidity sensitivity were systematically investigated by the XRD, FT-IR, XPS and sensitivity curves. The results showed that epoxy groups in GO structures could be effectively controlled with the addition of activator. Besides, the GO with more epoxy groups exhibited excellent selective sensitivity for humidity. At a 32.8% RH environment, the sensitivity of this kind of GO could reach 40.1%, and the response and recovery curves almost kept the same during five response and recovery cycles.

A numerical investigation of the effect of natural gas substitution ratio (NGSR) on the in-cylinder chemical reaction and emissions formation process in natural gas (NG)-diesel dual fuel engine

Abstract In this research, a newly proposed method combining Chemkin with CONVERGE was used to study the transient in-cylinder chemical reaction process in NG-diesel dual fuel engine. The selected mechanism was verified by comparing the results of CONVERGE with experimental data, and then the calibrated model of CONVERGE was used to provide boundary conditions for Chemkin. On this basis, the detailed combustion process was simulated at different natural gas substitution ratio (NGSR). The results show that, the chain branching reaction, long-chain to short-chain reaction, and reactions associated with OH radicals have significant impacts on temperature. It can also be found that the combustion of fuel shows a distinct two-stage reaction process. During the low temperature stage, both the CO and NO emissions are little. While at the high temperature stage, the CO emissions first rapidly increase and then decrease due to the consumption reaction, and the NO emissions also have a quick increase. When the NGSR is reduced, a new path for CO generation occurs at low temperature stage, resulting in minor increase (up to 0.0019 mol fraction) of CO concentration. Meanwhile, the ignition delay is reduced significantly (by 88.5%), but the increase of diesel species does not alter the formation mechanism of emissions. All these provide guidance for improving combustion and emission performance of NG-diesel dual fuel engine.

Comparative study of aromatic hydrocarbons in bitumens and expelled oils generated by hydrous pyrolysis of coal

An immature humic coal sample from the Yaojie Formation of the Muli coal field is pyrolysed in a hydrous closed system. The differences in aromatic hydrocarbon compositon between bitumens and expelled oils are investigated with the simulation temperature ranging from 250 to 500 °C. The absolute concentrations of the main aromatic classes in bitumens and expelled oils initially increase and thereafter decrease with increasing maturity. The absolute concentrations of naphthalene are always higher in expelled oils than in the corresponding bitumens; however, the absolute concentrations of alkyl-naphthalenes, phenanthrene, and alkyl-phenanthrenes are higher in bitumens than in expelled oils at the lower-maturity stage, and reversals occur with continuous increase in RO. Most of the common parameters—MNR, MPI1, MPR, F1, and F2—exhibit regular differences in bitumen–expelled oil pairs. The ratios of different alkylation degrees of naphthalenes and phenanthrenes (such as N/C1–5-N, C1-N/C1–5-N, C1-N/C5-N, P/C1–3-P, and C1-P/C3-P) and the ratios of aromatic components (such as naphthalene/phenanthrene, phenanthrene/fluoranthene, and phenanthrene/pyrene) that have different numbers of aromatic rings exhibit regular differences in bitumen–expelled oil pairs. These ratios of expelled oils are always higher than those of corresponding bitumens; reversals may occur at a high maturity stage. The systematic differences between the compositions of the main aromatic hydrocarbons in bitumens and expelled oils could be predominantly controlled by the fractionation effect at a lower-temperature stage and differentiated decomposition at a higher-temperature stage during the hydrous pyrolysis of coal.

The origin, age and duration of hydrothermal alteration associated with iron skarn mineralization determined from clay/phyllosilicate minerals, Bizmişen-Erzincan, East-Central Turkey

The Bizmişen skarn-type iron deposit is one of the major operating mines in east-central Turkey. Middle Eocene (46.3–42.0 Ma) plutonic rocks (quartz diorite) were intruded into Triassic-Cretaceous limestones and Upper Cretaceous ophiolites forming skarns (garnet, diopside, epidote, scapolite and tremolite), iron mineralization and clay-bearing alteration zones (argillic alteration). Clay-rich rocks of the argillic zone, contain mainly quartz, calcite, dolomite, feldspar and clay/phyllosilicate minerals comprising dioctahedral smectite, kaolinite, mixed-layered illite-smectite (I-S) and illite, and trioctahedral vermiculite, serpentine/chrysotile, talc, chlorite and mixed-layered chlorite-smectite (C-S). Na-Ca smectite, I-S, illite and kaolinite are developed at both the quartz diorite-limestone contact and within the quartz diorite body. However, phlogopite, vermiculite, serpentine/chrysotile, talc and chlorite occur at the quartz diorite-ophiolite contacts, indicating the distributions of clay/phyllosilicate minerals are influenced primarily by the host-rock composition. Chlorite geothermometry data suggest ~300 °C for the retrograde stage of skarn formation and ~120 °C for the late argillic alteration overprint, and the formation of low-temperature clays (smectite, vermiculite, C-S) in areas of skarn formation. Kaolinite 1 M (one-layer monoclinic) and I-S (I75-S25, R1 ordering) are indicative of low-temperature (<200 °C) argillic alteration conditions. Optical and electron microscopy studies of kaolinite, smectite and I-S indicate a completely hydrothermal (neo-formation) origin, with the absence of any detrital input. The major and trace/REE whole-rock analyses of clays show they have a composition between the analyses of quartz diorite and ophiolite rocks (i.e., serpentinite and serpentinized peridotite). However, the analyses are closest to those of the quartz diorite. The calculated δ18O and δD values of fluids in equilibrium with the clays (using the average values of the fluid inclusion homogenization temperatures) indicate a pre-dominantly magmatic water source. Assuming the clay-forming fluids originated from magmatic water, the δ18OV-SMOW and δDV-SMOW compositions indicate <200 °C for smectite during the supergene or low-temperature argillic stage, but in excess of 200 °C for I-S and kaolinite during the hypogene or high-temperature argillic stage. 40Ar/39Ar age data of illite and I-S (37.5–25.5 Ma) indicate alteration started during the late Eocene, ~4 Ma after intrusion of the pluton at 42 Ma, and continued to the late Oligocene, with a duration of ~12 Ma. The age data imply a long period of cooling at depth, without exhumation, during epithermal alteration after the retrograde skarn stage. The data show that hydrothermal clays formed from magmatic fluids in a hydrothermal system that persisted well after the intrusion of the igneous body and are indicative of how long hydrothermal systems can persist in areas of mineralization.

Effect of Igneous Intrusions on Low-temperature Oxidation Characteristics of Coal in Daxing Mine, China

ABSTRACT In order to investigate the effect of igneous intrusions on low-temperature oxidation characteristics of coal, metamorphic coal samples affected by igneous intrusions and normal coal samples were collected from Daxing Mine. The thermal effect of coal at a low temperature was studied by Thermogravimetric analysis and Differential scanning calorimetry (TG-DSC). The oxidation kinetics experiment was used to analyze the oxygen consumption, the index gas, the crossing point temperature (CPT) and apparent activation energy of coal. Compared with normal coal, the metamorphic coal had lower weight loss rate and higher oxygen absorption rate due to igneous intrusions. At the same time, the metamorphic coal absorbed less heat at low-temperature stage and entered the exothermic stage first, and the total heat release in the whole stage was larger. The author also found that the initial exothermic temperature of coal decreased obviously due to igneous intrusions. In addition, metamorphic coal had lower apparent activation energy because of igneous intrusions, which indicated that the molecular structure of coal became easy to be activated, and the energy needed for activation became lower. Fourier transform infrared spectroscopy (FTIR) analysis suggested igneous intrusions changed the chemical structure of coal and increased the branching degree and short aliphatic chains. Moreover, metamorphic coal consumed more oxygen and produced more carbon monoxide, ethylene and ethane, with lower crossing point temperatures, which concluded that the igneous intrusions accelerated the oxidation reaction of coal at low-temperature stage and increased the spontaneous combustion risk of Daxing coal.

Effect of Mono-, Di-, and Triethylene Glycol on the Sulfidation Behavior of NiMo(P)/Al2O3 Hydrotreating Catalysts

The effect of ethylene glycol (EG), diethylene glycol (DEG), and triethylene glycol (TEG) on the sulfidation behavior of phosphate-doped NiMo/Al2O3 hydrotreating catalysts has been investigated. The catalyst prepared with DEG shows a higher activity in the hydrodesulphurization of straight-run gas oil than other catalysts due to more efficient sulfidation at the low-temperature stage.

Thermal Transformation of Carbon and Oxygen-Containing Organic Compounds in Sewage Sludge During Pyrolysis Treatment

Organic carbon (C) and oxygen (O) contained in sewage sludge strongly impact its thermal behavior during pyrolysis treatment. This study was aimed at getting an insight into the decomposition mechanism of organic compounds containing C and O during sludge pyrolysis using thermo-gravimetric Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis-gas-chromatography/mass spectrometry (Py-GC/MS) and helpfully improving energy conversion of sewage sludge. The temperature domains of transformation were determined and indications of the main compounds produced during each stage were obtained. Results showed that the volatile compounds that evolved after sludge pyrolysis were mainly distributed into six groups: alkenes, aromatic hydrocarbons, alcohols, aldehydes, phenols and carboxylic acids. Comparison in thermal behavior and composition of the evolved volatile compounds were observed. In the low temperature stage (&lt;350 °C), compounds containing O–C=O accounted for the highest proportion in the evolved gas (55%). Over 350 °C, the production of C=C, –OH, and –C6H5 compounds gradually increased; but little was found of compounds containing O–C=O. Above 550 °C, as thermal chemical reaction involving oxygen-containing groups enhanced, compounds containing O–C=O and –OH tended to disappear, and an increasing amount of macromolecular polycyclic aromatic hydrocarbon was formed. Finally, the thermal transformation pathways of the oxygen and carbon-containing compounds were proposed.

A field study of polychlorinated dibenzo-p-dioxins and dibenzofurans formation mechanism in a hazardous waste incinerator: Emission reduction strategies

To clarify the dominant formation mechanism of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and reduce PCDD/F emissions in full-scale hazardous waste incinerators (HWIs), three tests were designed by adding different PCDD/F precursors in phenol-containing raw material. Flue gas from three stages of the incineration facility, as well as bottom ash and fly ash were collected to investigate formation pathways, emission characteristics and mass balance of PCDD/Fs. The results showed that in tests A and C, the PCDD/F emission levels were 0.02 and 0.83 ng I-TEQ Nm−3, with adding naphthalene and p-dichlorobenzene, respectively. Test B, the control group, only incinerated raw materials, resulting in 0.72 ng I-TEQ Nm−3 PCDD/F emissions. PCDD/F formation mechanism analysis suggested that high-temperature radical-molecule reaction was the dominate pathway in test A, while for test B, memory effect in the air pollution control devices (APCDs) led to high PCDD/F emissions. With the addition of p-dichlorobenzene in test C, PCDD/F levels at the quenching tower outlet were one order of magnitude higher than those observed at the inlet, indicating that the quenching tower failed to suppress the formation of PCDD/Fs. The PCDD/PCDF ratios indicate that with the abundance of PCDD/F precursors, surface-mediated precursor reaction is the dominant formation mechanism in low-temperature stages. These finding raise the following strategies for industry to control PCDD/F emissions: (1) strict regulation of the organochlorine content in feed material; (2) frequent and thorough cleaning the APCDs; (3) optimizing the injection rate of activated carbon.

Platinum metals on the Bam gold ore deposit of the Upper Amur region

The problems of complex extraction of noble metals (Ru, Rh, Pd, Ag, Os, Ir, Pt, Au) during the development of gold-silver deposits have recently acquired increasing practical importance and relevance, due to the clear tendency to exhaust the base of available ores, their concentration of useful components and deterioration of mining processing conditions. The aim of the work was an additional study of platinum mineralization in ore objects at the large Bam gold ore deposit of the Upper Amur region and obtaining estimates of noble metal contents by atomic absorption, electrochemistry and chemical analyzes. It is shown that industrial concentrations for mining are gold and silver, and platinum metals are present at concomitant concentrations and do not reach the values required for cost-effective industrial processing. The revealed peculiarities of the Bam deposit are superposition of high-temperature and low-temperature stages of mineralization of precious metals within the ore columns, which leads to averaging of general geochemical regularities and leveling of characteristic local differences. It is noted that platinum mineralization increases with depth and proximity to the source of volcanic heat, just like the relative sample of gold.

Experimental research on a 4 K hybrid refrigerator combining GM gas refrigeration effect with magnetic refrigeration effect

A hybrid cryogenic refrigerator that combines the magnetic refrigeration effect with the GM refrigeration effect has been experimentally studied. ErNi and TmCuAl, which have large magnetocaloric effects, are used to fill the second (low-temperature) stage regenerator of a GM refrigerator and put in a magnetic field varying from 0 to 1.1 T. A phase angle α is defined as the phase between the varying magnetic field and displacer movement and can be tuned in order to find the best timing between the magnetic refrigeration and the GM refrigeration cycle. Efforts have also been made to suppress eddy current losses induced due to the varying magnetic field through the cold head. A phase angle of 60° was found to generate best cooling performance through experiments. A minimal no-load temperature of 3.5 K was obtained at 0.5 Hz while the GM refrigeration alone can only generate a no-load temperature of 4.2 K.

ОЦІНКА ЕФЕКТИВНОСТІ ГЛИБОКОГО ОХОЛОДЖЕННЯ ПОВІТРЯ НА ВХОДІ ГАЗОТУРБІННИХ УСТАНОВОК В РІЗНИХ КЛІМАТИЧНИХ УМОВАХ

The efficiency of deep air cooling at the inlet of gas turbine units of a simple scheme has been investigated for changed climatic conditions of operation during the month. For air cooling, the application of waste heat recovery chiller has been proposed, which transform the heat of exhaust gases of gas turbine units into the cold. The efficiency of air cooling at the inlet of gas turbine units to different temperatures has been analyzed: to 15°C – an absorption lithium-bromide chiller, which is used as the first high-temperature pre-cooling stage of ambient air and down to 10°C – a combined absorption-ejector chiller, which acts as the second low-temperature stage. The air cooling efficiency is compared for different climatic conditions using the example of Yuzhnoukrainsk (Ukraine) and Shanghai (China). The climate peculiarity of Shanghai is the high relative humidity of the air, respectively, and its moisture contents at the same time its high temperatures. As indicators for assessing the effectiveness of air cooling at the inlet of gas turbine units down to 15°C in an absorption lithium-bromide chiller and deep air cooling to 10ºС, in a combined absorption-ejector chiller used an increase in useful power and a reduction in specific fuel consumption. It is shown that, through extremely different thermal and humidity parameters of ambient air, it is cooling at the inlet of gas turbine units for the climatic conditions of Ukraine provides the current increase in useful power by 10...15%, and for the climatic conditions of China – 18…22%. However, it should be noted that deeper air cooling at the inlet of the gas turbine unite to a temperature of 10°C in a combined absorption-ejector chiller compared to its traditional cooling to 15°C in an absorption lithium-bromide chiller provides an increase in useful power for a temperate climate of Ukraine (for example, Yuzhnoukrainsk) by 70...90%, whereas for tropical climatic conditions of China (Shanghai) – by 30...35%.

On the removal behavior of aluminum paste for silicon solar cell

The removal behavior of the aluminum paste was investigated using thermogravimetric analyzer, and it was found that the mass loss curve could be divided into two main stages including low-temperature and high-temperature stages and a complex transition between them. The pre-exponential factors of the two main stages were calculated by Kissinger method. And the activation energies were determined using different methods named as Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sinose (KAS) and Kissinger. The dependence of the activation energy on the conversion has been analyzed in detail. The activation energy of the low-temperature stage keeps approximately constant, and the average value is 38.74 kJ mol−1 of FWO method and 33.86 kJ mol−1 of KAS method. According to KAS method, the activation energy for the high-temperature stage decreases from 157.03 to 94.65 kJ mol−1 with the temperature increasing from 596 to 675 K. The variation range of the activation energies indicates the existence of a complicated reaction mechanism during the high-temperature stage. Though high removal rate during the low-temperature stage is beneficial to reducing the processing time of silicon solar cells, the heating rate should be controlled when the temperature is close to the value resulting in the maximum mass loss rate to avoid causing defects in the aluminum back electrode.

A new approach to increasing the efficiency of the ship main engine air waste heat recovery cooling system

The efficiency of integrated cooling air at the intake of Turbocharger and Scavenge air at the inlet of working cylinders of the main diesel engine of dry-cargo ship by transforming the waste heat into a cold by an Refrigerant Ejector Chiller (ECh) as the most simple in design and reliable in operation and by complex in design but more efficient Absorption Lithium-Bromide Chiller (ACh) was analyzed. A ship power plant of cogeneration type using the relatively low-grade heat of water of a heat supply system with a temperature of about 90 °C, that significantly complicates the problem of its conversion into cold were considered. Because of the insufficiently high efficiency of transformation of the heat of hot water (low coefficient of performance) as compared with steam, the resulting cooling capacity may not be enough for cooling intake air of the turbocharger and scavenge air, that raises the problem of the rational distribution of heat loads between the Turbocharger Intake Air cooling circuit (subsystem) and Scavenge air cooling circuit and the need to use chillers of various types. This takes into account the rational parameters of cooling processes of the scavenge air in the cogeneration high-temperature stage of scavenge air cooler, in the intermediate stage of traditional cooling air with seawater, and in the low-temperature stage for deep cooling of the scavenge air by using a chiller. A new approach is proposed to improve the efficiency of integrated cooling Intake Air of the turbocharger and Scavenge Air at the inlet of the working cylinders of the ship main engine of a transport ship, which consists in comparing the required cooling capacity and the corresponding heat needs during the trade route with the available heat of exhaust gases and scavenge air of the cogeneration power plant, determining the deficit and excess cooling capacity of heat utilizing cooling machines of various types, that allows to identify and realize the reserves of improving the efficiency of cooling intake air of the turbocharger and the scavenge air of the main diesel engine through the joint use of chillers of various types.

Analyzing the efficiency of moderate and deep cooling of air at the inlet of gas turbine in various climatic conditions

The efficiency of deep cooling air at the inlet of gas turbine unite to the temperature of 10 °С by waste heat recovery combined absorption-ejector chiller was analyzed in climatic conditions at Kharkov site, Ukraine, and Beijing site, China, and compared with the moderate cooling to the temperature of 15°C in traditional absorption lithium-bromide chiller. The refrigerant ejector chiller is chosen as the most simple and reliable in operation chiller. It was used as the low-temperature stage for subcooling the air precooled in absorption lithium-bromide chiller to the temperature about 15 °C. Both waste heat recovery absorption lithium-bromide chiller and ejector chiller use the heat of gas turbine unite exhaust gas to produce a cooling capacity. Air cooling at the inlet of gas turbine unite was investigated for varying climatic conditions during the year. The current values of temperature depression with cooling ambient air to different temperatures of 10 °C and 15 °C and corresponding cooling capacities required were calculated. The comparison of the effect due to gas turbine unite inlet air cooling was performed by annual fuel saving and power production growth. With this the current values of turbine power output increase and specific fuel consumption decrease due to cooling inlet air from current varying ambient temperatures to the temperatures of 10 °C and 15 °C were calculated. It was shown that annual fuel saving and power production growth have increased by 1,8 times for Kharkov (Ukraine) site climatic conditions and by 1,6 times for Beijing (China) site due to deep cooling air to the temperature of 10 °C by absorption-ejector chiller as compared with cooling inlet air to the temperature of 15 °C by absorption lithium-bromide chiller.

Study on supercritical water oxidation of o-dichlorobenzene in a quartz micro-reactor with in situ microscope and Raman spectroscopy

The supercritical water oxidation (SCWO) of o-dichlorobenzene (o-DCB) in a fused quartz capillary reactor was studied by in situ microscope combined with Raman spectroscopy. The influence of oxidant dosage, reaction temperature and time on the o-DCB degradation efficiency was investigated and the reaction kinetics for CO2 yield was explored as well. The obvious phase change of o-DCB-H2O/H2O2 system was observed during the heating and cooling process. The increase in H2O2 dosage, temperature and time enhanced the o-DCB degradation efficiency. The degradation of o-DCB could be attributed to the simultaneous oxidation induced by HO· and O2. The effect of temperature on the o-DCB degradation efficiency and the CO2 yield was not significant at the lower temperature stage but turned to be important at the higher temperature stage. When the oxidant dosage was twice that of chemometry and the temperature and time were 440.0 °C and 4 min, respectively, the o-DCB degradation efficiency reached approximately 100%. Under the same conditions, the CO2 yield was lower than the o-DCB degradation efficiency, indicating that the degradation of o-DCB was a multi-step reaction. The reaction kinetics showed that the kinetics of CO2 production in SCWO followed the pseudo-first order and the apparent activation energy was 172.4 kJ mol−1.

Martensite to austenite reversion in a high-Mn steel: Partitioning-dependent two-stage kinetics revealed by atom probe tomography, in-situ magnetic measurements and simulation

Austenite (γ) reversion in a cold-rolled 17.6 wt.% Mn steel was tracked by means of dilatometry and in-situ magnetic measurements during slow continuous annealing. A splitting of the γ-reversion into two stages was observed to be a result of strong elemental partitioning between γ and α′-martensite during the low temperature stage between 390 and 575 °C. Atom probe tomography (APT) results enable the characterization of the Mn-enriched reversed-γ and the Mn-depleted remaining α′-martensite. Because of its lower Mn content, the reversion of the remaining α′-martensite into austenite takes place at a higher temperature range between 600 and 685 °C. APT results agree with partitioning predictions made by thermo-kinetic simulations of the continuous annealing process. The critical composition for γ-nucleation was predicted by thermodynamic calculations (Thermo-Calc) and a good agreement was found with the APT data. Additional thermo-kinetic simulations were conducted to evaluate partitioning-governed γ-growth during isothermal annealing at 500 °C and 600 °C. Si partitioning to γ was predicted by DICTRA and confirmed by APT. Si accumulates near the moving interface during γ-growth and homogenizes over time. We used the chemical composition of the remaining α′-martensite from APT data to calculate its Curie temperature (TCurie) and found good agreement with magnetic measurements. These results indicate that elemental partitioning strongly influences not only γ-reversion but also the TCurie of this steel. The results are important to better understand the thermodynamics and kinetics of austenite reversion for a wide range of Mn containing steels and its effect on magnetic properties.

The common origin and alteration history of the hypabyssal and volcanic phases of the Wadi Tarr albitite complex, southern Sinai, Egypt

New data and interpretations are presented for the igneous albitites of the Wadi Tarr area, southern Sinai, Egypt. The albitite masses are isolated in outcrop from any granitic intrusions and have intrusive contacts against the country rocks without any structural control. They have marginal zones of breccias with jigsaw-fit angular clasts suggesting explosive, in-situ formation. The albitites are of two types: the western, medium-grained, hypabyssal albitite and the eastern, fine-grained porphyritic albitite. The field relations suggest emplacement at different levels in a magmatic cupola: the hypabyssal texture and steeply dipping slope of the upper contact of the western albitite imply deeper emplacement whereas the gently dipping contacts and porphyritic texture of the eastern albitite masses indicate that they define the probable location of the cupola apex. Both types of albitites consist of albite (92–97%) with minor amounts of quartz, K-feldspar and biotite. The accessory minerals include Fe-oxides, augite, sulphides, zircon, rutile, xenotime, titanite, allanite and monazite. The whole-rock compositions of the hypabyssal and porphyritic albitites are closely related, but the porphyritic type has lower abundances of Sr, Ba, Y, Nb, Th and Zr. We show that the hypabyssal and porphyritic albitites have a common petrogenetic origin, most likely as late-stage cumulates from a fractionating, strongly alkaline A-type magma, consistent with the compositions of the mafic minerals. The source magma was probably a tephritic liquid; we use MELTS models to show that only a sufficiently alkaline magma follows a differentiation path that both avoids quartz saturation and encounters the alkali feldspar solvus, reaching a residual liquid in equilibrium with highly sodic feldspar. Although the MELTS results show a chemically consistent means of forming igneous albitite, they are incomplete in that physical segregation mechanisms are still required to isolate the albite from mafic minerals and or a low-temperature aqueous alteration stage is needed to leach K from the feldspar. Alteration surrounding the Wadi Tarr albitites is extensive and dominated by alkali metasomatism similar to fenitization. Alteration in the marginal breccia zone of the albitite is dominated by precipitation of amphibole and carbonate in veins and in the breccia matrix, whereas the volcanic country rocks show replacement of feldspars by sericite, carbonate and epidote as well as vein carbonate. The altered volcanic country rocks show lower concentrations of Fe2O3, Sr, Cu, Pb, Ba and Ce, accompanied by higher concentrations of Na2O and MgO compared to unaltered equivalent samples.