Extending the metal to insulator transitions of rare-earth nickelates towards low temperature ranges

Although the d-band correlated rare-earth nickelates (ReNiO₃) exhibit broadly adjustable metal to insulator transitions (MIT) that enables emerging correlated electronic applications, it is yet difficult to regulate their associated critical temperature (T_MIT) below 100 K. Herein, we extend the lower limit in T_MIT of ReNiO₃ down to 83 K while maintaining an abrupt switch in resistivity via partial La-substitution of PrNiO₃. The near edge X-ray fine structure analysis and density function theory calculations indicate the strengthening in the metallic orbital configuration and reduction in the ground state band gap via La-substitution of Re in NdNiO₃ and PrNiO₃. In contrast, analogous Ce substitution cannot reduce the T_MIT of ReNiO₃ owing to its valance variability toward +4, while La partial substitution of ReNiO₃ with middle or heavy rare-earth (e.g., Sm) easily disturb the co-occupation of the Re-site by the two rare-earths as one dispersive phase.     

Nonlinearity in regulating the metal to insulator transition of ReNiO3 towards low temperature range

Among the existing material family of the correlated oxides, the rare earth nickelates (ReNiO₃) exhibit broadly adjustable metal to insulator transition (MIT) properties that enables correlated electronic applications, such as thermistors, thermochromics, and logical devices. Nevertheless, how to accurately control the critical temperature (T_MIT) of ReNiO₃ via the co-occupation of the rare-earth elements is yet worthy to be further explored. Herein, we demonstrate the non-linearity in adjusting the T_MIT of ReNiO₃ towards lower temperatures via introducing Pr co-occupation within ReNiO₃ (e.g., Pr_xNd_1-xNiO₃ and Pr_xSm_1-xNiO₃) as synthesized by KCl molten-salt assisted high oxygen pressure reaction approach. Although the T_MIT is effectively reduced via Pr substitution, it does not strictly follow a linear relationship, in particular, when there is large difference in the ionic radius of the co-occupation rare-earth elements. Furthermore, the most significant deviation in T_MIT from the expected linear relationship appears at an equal co-occupation ratio of the two different rare-earth elements, while the abruption in the variation of resistivity across T_MIT is also reduced. The present work highlights the importance to use adjacent rare-earth elements with co-occupation ratio away from 1:1 for achieving more linear adjustment in designing the metal to insulator transition properties for ReNiO₃.     

Hot-surface ignition temperatures of dust layers

Minimum dust layer ignition temperatures on a hot surface were determined for several dusts, using a test procedure recommended by the National Academy of Sciences. The dusts included coal, three oil shales, lycopodium spores, corn starch, grain and brass powder. For a few of the dusts the effects of particle size and layer thickness on the minimum ignition temperatures were examined. Test results were repeatable and reliable for the fuels, the lycopodium and the brass powder. The minimum hot-surface ignition temperatures of 12.7-mm thick layers of these dusts ranged from 160°C for brass to 290°C for 20-gal ton⁻¹ oil shale. Flaming combustion was observed only with the brass powder. The minimum ignition temperatures decreased with thicker layers and with smaller particle sizes. Some difficulties were encountered with the corn starch and grain dusts. During heating, the starch charred and expanded; the grain dust swelled and distorted. The test was found acceptable for the purpose of determining the minimum layer ignition temperature of a variety of dusts. To prevent fire hazards due to smoldering or flaming dust layers the temperatures of surfaces on which combustible dusts accumulate should be lower than the minimum hot-surface ignition temperatures of the dusts.     

Metallurgy dusts as a pigment for glazes and engobes

This study is focused on using the dust from metallurgy as a pigment. The agglomerating dust is formed during metallurgical processes. This waste product is interesting for recycling process. The main mineralogical phase of dust is hematite α-Fe₂O₃. Both synthetic and natural iron oxides are commonly used as pigments in ceramic industry. In this experiment the metallurgy dusts were used as a pigment for preparation of glazes and engobes. Agglomerating dusts were used both precalcined thermally at 700 °C and 900 °C and in an original state. The prepared glazes were composed of a transparent glaze base with 10 wt% agglomerating dusts as pigment. The glazes calcined at 1060 °C were finally yellow colored and glazes calcined at 900 °C were brown colored. Engobes contained a ceramic clay base with 1, 5, 10 and 50 wt% of dust as pigment. Engobes calcined at 900 °C were red and grey colored. The pigments were characterized by X-ray diffraction (XRD), chemical (XRFS) analysis, granulometry (PSD), thermogravimetric (TG) and differential thermal (DTA) analysis, scanning electron microscopy (SEM) and CIELab values.     

Deflocculation and Classification of Electric Arc Furnace Dust in Aqueous Solution

Abstract

Electric arc furnace (EAF) flue dust is generated during EAF steelmaking from iron-containing scrap such as recycled automobile bodies. The relatively high level of Zn (20–30 wt%) in EAF dusts provides a potentially valuable resource, even though the zinc is present as oxide phases such as zincite (ZnO) and zinc ferrite (ZnFe₂O₄). In this work, a method to deflocculate and disperse ZnO and ZnFe₂O₄ particles in aqueous suspension of EAF dust is developed and the efficiency of Zn recovery by the classification method was evaluated. Major findings of this study indicate that citric acid, a tetradendate chelating agent, demonstrates the best liberation and dispersion efficiency for EAF dust. Elutriating at 0.01 cm/min fluid velocity we recover 10 wt% of EAF dust (mostly ZnO particles) at a grad of 70 wt% Zn from a well-liberated and dispersed suspension of EAF dust. About 30 wt% of Zn recovery may be achieved using only simple classification.     

Thin layer chromatographic analysis of possible aflatoxins within grain dusts

The National Institute for Occupational Safety and Health is interested in assessing the hazards to grain workers associated with respirable grain dusts of all types. One of these hazards could involve the occurrence of mycotoxin producing fungi either upon or within grains. Aflatoxins, types of mycotoxins produced by bothAspergillus flavus andA. parasiticus, are hepatocarcinogens, mutagens, teratogens and toxins. Here, we report an attempt to determine whether settled and/or airborne dusts from barley, corn, flax, oats and Durum as well as spring wheats contain aflatoxins. These dusts were collected at port grain terminals in the Superior-Duluth regions of the United States. The dusts were extracted with and chromatographed upon thin layer plates in a variety of solvents which have been approved for the separation of aflatoxins. Two acceptable aflatoxin B₁ confirmatory tests were employed to verify suspected aflatoxin B₁ within the extracts. Each dust contained a chloroform-soluble, blue fluorescent compound(s) which possessed an Rf similar to that of aflatoxin B₁ upon chromatography of chloroform extracts in chloroform/95% methanol. Methylene chloride/H₂O) extracted a blue fluorescent compound(s) from each dust, and the compound(s) possessed Rf intermediate between those of aflatoxin B₁ and B₂ upon chromatography in acetone/methylene chloride. The methylene chloride/H₂O extracted compounds failed to turn yellow upon spraying with 25% sulphuric acid in methanol and subsequent viewing with an ultraviolet source. Our results confirm those of Sorenson et al., who reported that aflatoxins were absent from airborne grain dusts collected from the Superior-Duluth areas of the United States in the fall of 1977. In conclusion, we stress the need for extracting, detecting, and identifying aflatoxins by a variety of analytical procedures including thin layer and high performance liquid chromatography and “approved” confirmatory tests.     

The effect of polydispersity on dust lifting behind shock waves

Knowledge-based modeling of dust lifting behind shock waves is a prerequisite for realistic simulation of dust explosions. Mostly numerical simulations of this process focus on dusts consisting of monodisperse particles, while real dusts are polydisperse. This article investigates the effect on the lifting process of the dust being polydisperse with a log–normal distribution of particle sizes. The spatial distribution of the various sizes in the rising layer is studied, and statistical results for the rise, the collision frequency and the particle kinetic energy are compared for polydisperse and monodisperse dusts. It is shown that a layer consisting of polydisperse particles rises significantly faster than a one consisting of monodisperse particles, all other parameters being the same.     

Utilization of rice-husk packed beds as fine dust collectors at heavy dust loadings

Typical rice mills generally generate tonnes of biomass which is rice husks and a significant quantity of coarse and fine dusts from the paddy, resulting in public health concern. Instead of normal air cyclones which are not efficient for collecting fine soft-hair (detached pubescence) particles smaller than a few microns, a new system using packed beds of rice husks was developed for collection fine dusts. It was found that the rice-husk packed beds could exhibit an effective performance in capturing fine dusts at various dust loadings with collection efficiency higher than 85% by mass. The filtrating phenomenon could be observed as an integrated effect of cake and deep-bed filtrations due to the heavy dust loads, agglomeration of dusts, and cohesion between the dusts and bed of irregularly shaped rice husks. Both the pressure drop across the bed and the overall filtration efficiency remarkably increased at the initial clean stage, then increased more slowly due to the recurrent fracture of the dust cake layer.     

Experimental investigation of jet-induced resuspension of indoor deposited particles

Particles deposited on indoor surfaces may be resuspended and become airborne when disturbed by intensive jets. Depending on the intended purpose, the resuspension of deposited particles may be minimized or promoted. This investigation experimentally measured the resuspension of Arizona test dusts (ATDs) after a jet impingement. The simulating pulsed jets were created by a tube using compressed nitrogen gas. The jets were released into the test section in a wind tunnel that was cleaned by high-efficiency particulate air (HEPA) filters. The particle resuspension was evaluated by the dust-removal zone shapes on particle-laden plates, total dust-removal mass, and the number of airborne particles. The effects of the jet impingement heights, surface dust loads, and particle-laden plate surface roughness on particle resuspension were examined. This study revealed that sparsely deposited dusts indoors are more difficult to resuspend by jets than are densely deposited dusts. The jet impingement to a surface whose roughness is comparable to the particle diameters may cause severer airborne particle exposure than to surfaces with extremely small or large roughness values. For a high surface dust load, there is an optimal jet impingement height that can resuspend the maximum amount of the deposited dusts.

Copyright © 2016 American Association for Aerosol Research     

Fortschritte bei der Abscheidung von Stäuben im Elektrofilter unter Berücksichtigung der Schadgas-Adsorption

Progress in dust collection by electrostatic precipitators with due attention to adsorption of noxious gases . It is shown on the basis of the present state of the art that the stipulations of the pollution control legislation for large boilers can be met by electrostatic precipitators and that fine dust and heavy metals are collected to a sufficiently high degree. Recent developments are dealt with which bring about a fundamental improvement of the collection in the precipitator. Noxious gases have to be separated together with the dust to an ever-increasing extent. With dry processes, fluidized beds are arranged upstream of the electrostatic precipitator for the adsorption of, for instance, HCl, HF, and SO₂. In these cases the dusts will be highly concentrated and of varying chemical composition. Dry gas cleaning in the expanded, circulating fluidized bed downstream of refuse incineration plants and defluorination of waste gases from aluminium electrolysis are considered as examples. The separation of dust under difficult conditions is then dealt with.     

Low metal–insulator transition temperature of Ni-doped vanadium oxide films

Elemental doping is the main means to regulate the phase transition of vanadium oxide (VO₂); however, the effects of low valence elemental (<4+) doping on the phase transition of VO₂ are still controversial. In the present work, Ni-doped VO₂ films were prepared on quartz glass by direct current reactive magnetron sputtering and subsequent annealing. With the increase of the Ni doping content, the phase transition temperature of heating (T_H) of the VO₂ films decreased from 73.4 °C to 52.4 °C. The temperature required for the occurrence of phase transition (T_b) was lower than T_MIT. Different from the undoped VO₂ film, the Ni-doped VO₂ films had a T_b of around 30 °C. XRD and Raman results revealed that some rutile VO₂ microcrystals appeared in the vanadium oxide films because of the lattice distortion by incorporated Ni. Hence, rutile VO₂ micro-crystallinities significantly facilitated the phase transition of monoclinic VO₂ to rutile one.     

Silica content of dusts from five texas cottonseed oil mills

Total dust samples, collected with high-volume samplers, were ashed and then analyzed for aluminum, silicon and silica (SiO₂). Ash and aluminum contents agreed with earlier reported data, but the silicon content was lower. The amounts of silica ranged from 2–7% in dusts from the cleaning rooms to 0.01–0.05% in dusts from the baling rooms. Agreement with silica contents determined by infrared (IR) spectrometry was good. IR spectra indicated silica particle diameters were in the range of 6–8 µm in the cleaning rooms and 10 µm or more in the delintering and baling rooms. Threshold limit values (TLV) calculated on the basis of total silica in the high-volume samples suggest silica values above the limit in 4 of the cleaning rooms, and possibly one at the delintering rooms. Calculation of respirable silica concentrations and TLV for respirable silica was precluded by the sampling method.     

Influence of dust particles on the hydrodynamic behavior and mass transfer in droplet column

Bubble columns are commonly used in industry for polluted gas treatment. Based on the same principle, the droplet column which is not widely known in the literature, uses much higher gas velocities, up to 14 m/s. This study concerns the hydrodynamics and mass transfer in this apparatus, in presence or absence of solid particles. Our results have demonstrated the impact of dusts on mass transfer performance giving rise to an increase in the k_L a_L coefficient with decreasing particle size. However, no influence of dust on the hydrodynamics of the column has been demonstrated within the studied particle size range. A study of liquid holdups obtained by three different methods is also carried out. Our results are comparable, thus validating the methods used.     

Models for minimum explosible concentration of organic dust clouds handled in industries

Dust explosion hazard exists in plants and facilities wherever combustible dusts are hardled. Minimum explosible concentration of dust clouds is an important factor requiring special attention for hazard evaluation if any technological equipment is to be protected by inertisation. The mathematical models available for prediction of this parameter have been analysed for their application to organic dust clouds. Solution of the most general mode for determination of minimum explosible concentration of dust clouds proposed by Mitsui and Tanaka is presented, together with the comparison with experimental data. It has been found that the model is not successful in predicting the minimum explosible concentration for organic dusts. Recommendations on requirement of development of a new model for prediction of minimum explosible concentration of an organic dust such as polyethylen have been given.     

粉尘对风电叶片涂层附着性能的影响

风电叶片在生产过程中,复合材料表面会由于各种原因粘附有粉尘.在叶片的涂装过程中,粉尘的存在会对漆膜在复合材料壳体上及漆膜层间的附着性能产生负面影响.该研究设计实验,使叶片壳体或涂层表面沉降粉尘后进行下道涂装,涂层固化后通过拉开法考察了涂装过程中粉尘对漆膜附着性能的影响.结果表明:粉尘的存在对涂层对复合材料壳体及涂层层间...     

硫磺粉尘爆炸特性研究

为研究硫磺粉尘爆炸危险性,采用哈特曼管式爆炸测试装置与20 L球爆炸测试装置对常温常压下不同粒径的硫磺粉尘爆炸特性参数进行了测试和评估,得到了不同粒径硫磺粉尘的最小点火能、爆炸下限质量浓度和爆炸指数,根据实验结果对硫磺粉尘危险性进行了分级。结果表明,70~850 μm不同粒径的硫磺粉尘最小点火能在0.144~125 mJ,且随着粒径的减小而降低;45~375 μm不同粒径的硫磺粉尘爆炸极限质量浓度在15~20 g/m3,且随着粉尘粒径的减小而降低;45~375 μm不同粒径的硫磺粉尘最大爆炸指数在34.46~39.87 MPa·m/s,且随着粒径的减小而增大,其粉尘爆炸危险性等级为St3。     

Characterization of filter media prepared from aligned nanofibers for fine dust screen

Nanofibers for fine dust filters of four structures (random, aligned, orthogonal, and nanofiber net) were prepared by electrospinning method using polymers such as PAN and PA6. While conventional electret filters experienced deterioration problems in fine dust(PM_1.0) capture as its surface charge decayed, the electrospun nanofibers prepared contributed to the removal capacity. The filters from aligned fibers showed high quality factors ( q _F : filter performance indicator) and filtration efficiency from 22 to 50% depending on particle size than simple electret media at a face velocity of 15.92 cm/s. The fiber structure of nanofiber net (NFN) presented almost absolute collection efficiency, particularly on dust particles smaller than 300 nm. Furthermore, the composite filters which are composed both of a commercial electret mask filters and nanofiber nets effectively enhanced the overall filtration efficiency by 59.46%, resulting in more than 99% for PM_1.0. Consequently, electrospun polymer nanofibers offer a promising plausible mask filter material with air permeability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48166.     

Minimum ignition temperature of polyethylene dust: a theoretical model

Dust explosion hazard exists in plants and facilities handling combustible dusts. The minimum ignition temperature of dust clouds is an important parameter requiring special attention to designing the explosion preventive measures. This paper presents a model developed for determining the minimum ignition temperature for an organic dust cloud, polyethylene, simulating the conditions in the Godbert-Greenwald furnace. The model correlates the particle size, as well as the dust concentration with the minimum ignition temperature. It is based on the two-stage oxidation mechanism involving devolatilization/decomposition of the solid particle and homogeneous oxidation of volatile combustible products. In the case of polyethylene, the main combustible gas responsible for ignition and flame propagation has been confirmed to be butylene. The results of the computations were compared with the experimental values and those predicted by Mitsui and Tanaka. The predicted values by the model developed are in close agreement with the experimental data which confirm the proposed ignition mechanism. The model can be used for the prediction of minimum ignition temperature of organic dusts having an autoignition mechanism similar to polyethylene dust. © 1997 John Wiley & Sons, Ltd.     

炭粒床高效工业除尘装置的设计与开发

The new dust removal technical route using the carbon-granular bed filter,packed of carbon particles with appropriate grade derive from an online-process vibration sieve,to replace the traditional baggy filter had been developed successfully for capturing the micro-carbon dusts produced from pulverization of petroleum coke,and the green close loop of carbon materials is thus completed in the combined pulverizing and classifying system and pulverized carbon dust removal process.The high dust removal efficiency greater than 99%,low outlet dust concentration less than 100 mg.m-3,low pressure drop through dust filtration chamber less than 980 Pa,simple and easy design,and flexible and stable operation were achieved also with the carbon-granular bed filter in both bench and industrial scale operations.