Synthesis of zinc ferrite nanopowders in an RF thermal plasma

Nanosized zinc ferrite spinel powders of various compositions were produced in an RF thermal plasma from oxide mixtures and from co-precipitated hydroxides. The products were characterised for bulk chemical (ICP-AES), and phase composition (XRD). In spite of the short residence time of the reagents in the plasma reactor considerable extent of spinel formation was achieved. Magnetization and Curie point measurements indicated that the spinel phases exhibited ferrimagnetic behaviour. Ferrites synthetized in the RF plasma reactor were compared to that produced by the conventional ceramic route

Atmospheric ageing of nanosized silicon nitride powders

Ambient oxidation of nanosized silicon nitride powder produced by the vapour phase reaction of silicon tetrachloride and ammonia has been studied in this work. Aliquots of the powder were stored in argon gas, in dry air and in air of 80% humidity, and changes in the bulk and surface properties were investigated against the ageing time. The powder samples were characterised by wet chemical analysis, XPS, TG-MS, FTIR, XRD and TEM methods. No significant changes were detected on storage in argon gas for 90 days. However, in samples stored in dry air and humid air, remarkable oxidation and formation of N-H species were found. The particulate powder tends to agglomerate in both dry and humid air, and this results in changes in the particle size and morphology. The nanosized silicon nitride powders therefore should be processed by excluding their contact with the oxygen and moisture containing ambient atmosphere

Synthesis of Zinc Ferrites in RF Thermal Plasma Reactor

Formation of nanosized zinc ferrite spinels was studied from iron- and zinc oxide powders and corresponding nitrate solutions, respectively in a radiofrequency thermal plasma reactor. From the viewpoint of applications, the research was motivated by the potential use of these materials in advanced magnetic devices on the one hand, and by their biomedical applications such as drug carriers or agents for cancer treatment by hyperthermia on the other. In this work effects of synthesis conditions on properties of products were studied in details. The products were characterised for chemical composition, phase conditions, particle size distribution, morphologies and saturation magnetisation. Most products exhibited ferrimagnetic behaviour. Correlations among domain- and particle sizes were also investigated. Conditions for the synthesis of nanosized, inverse zinc ferrites of high saturation magnetisation were established. It was proved that in thermal plasma conditions normal and inverse ferrites could be produced in a single step process

Synthesis of Spinel Ferrites in Radiofrequency Thermal Plasma Reactor

Formation of nanosized zinc-ferrites and nickel-zinc ferrites from iron- and zinc oxide powders and corresponding nitrate solutions, respectively, was studied in RF thermal plasma conditions. The products were characterized for chemical composition, phase conditions, particle size distribution, morphologies and saturation magnetization. Effects of synthesis conditions on properties of products were studied in details

Crystallite size distribution and dislocation density in nanocrystalline silicon nitride powders produced by two different procedures

Két különböző eljárással készült nanokristályos szilicium-nitrid por mikroszerkezetét vizsgáltuk röntgen vonalprofil analízissel. Az egyik mintát termikus plazmában SiCl(4) és NH(3) gőzfázisú szintézisével majd kristályosításával készítettük, míg a másik egy a kereskedelmi forgalomban kapható por, amit szilicium nitridálásával majd őrlésével állítottak elő. A porok szemcseméreteloszlását és diszlokációsűrűségét röntgen vonalprofil analízissel határoztuk meg. Megállapítottuk, hogy a nitridálással és őrléssel előállított por szemcséinek átlagos mérete kisebb, míg eloszlásuk szélesebb mint a plazmában előállított mintáé. Mindkét por diszlokációsűrűsége 10(14) és 10(15) m(-2) között volt. A röntgen diffrakciós mérésből meghatározott szemcseméret jól egyezik a fajlagos felületből számolt értékkel és az elektronmikroszkópos megfigyelésekkel. | Two silicon nitride powders were investigated by high resolution X-ray diffraction. The first sample was crystallized from the powder prepared by the vapor phase reaction of silicon tetrachloride and ammonia in thermal plasma while the second was a commercial powder produced by the direct nitridation of silicon and milling. Their crystallite size and dislocation density were obtained by the recently developed procedure of diffraction profile analysis. In this procedure assuming spherical shape and log-normal size distribution of crystallites, the Fourier coefficients of the measured physical profiles are fitted by the Fourier coefficients of well established ab initio functions of size and strain peak profiles. The anisotropic broadening of peak profiles is accounted for by the dislocation model of the mean square strain in terms of average dislocation contrast factors. The area-weighted average particle size calculated from nitrogen adsorption isotherms was in good agreement with that obtained from X-rays. The powder produced by silicon nitridation and milling has a wider crystallite size distribution with a smaller average size than the powder prepared by vapor phase reaction in thermal plasma and subsequent crystallization. The dislocation densities were found to be between 10(14) and 10(15) m(-2)

Historical Context and Hazardous Waste Facility Siting: Understanding Temporal Patterns in Michigan

This article tests the proposition that, beginning in the 1970s, historic growth of public environmental concern and opposition to waste facilities, as well as changes in the policy environment increasingly encouraged hazardous waste facilities siting to follow the path of least (political) resistance and resulted in environmental inequities. Our longitudinal analysis of sitings in the State of Michigan from 1950 to 1990 reveals a distinct temporal pattern supporting our hypotheses. Whereas significant racial, socioeconomic, and housing disparities at the time of siting were not in evidence for facilities sited prior to 1970, patterns of disparate siting were found for facilities sited after 1970. Thus, we call for environmental justice studies employing longitudinal methods to understand the processes and factors contributing to environmental inequalities with greater consideration to changes in historical context

Racial Inequality in the Distribution of Hazardous Waste: A National-Level Reassessment

National-level studies examining racial disparities around hazardous waste treatment, storage, and disposal facilities have been very influential in defining the academic and political debates about the existence and importance of environmental injustice. However, these studies tend to employ methods that fail to adequately control for proximity between environmentally hazardous sites and nearby residential populations. By using GIS and applying methods increasingly used in environmental inequality research that better control for proximity, we conduct a comprehensive reassessment of racial inequality in the distribution of the nation \u27s hazardous waste facilities. We compare the magnitude of racial disparities found with those of prior studies and test competing racial, economic, and sociopolitical explanations for why such disparities exist. We find that the magnitude of racial disparities around hazardous waste facilities is much greater than what previous national studies have reported. We also find these disparities persist even when controlling for economic and sociopolitical variables, suggesting that factors uniquely associated with race, such as racial targeting, housing discrimination, or other race-related factors are associated with the location of the nation\u27s hazardous waste facilities. We further conclude that the more recent methods for controlling for proximity yield more consistent and definitive results than those used previously, and therefore argue for their wider utilization in environmental inequality research. Keywords: environmental justice, environmental inequality, environmental racism, racial inequality, hazardous waste, GIS

Which came first, people or pollution? Assessing the disparate siting and post-siting demographic change hypotheses of environmental injustice

Although a large body of quantitative environmental justice research exists, only a handful of studies have examined the processes by which racial and socioeconomic disparities in the location of polluting industrial facilities can occur. These studies have had mixed results, we contend, principally because of methodological differences, that is, the use of the unit-hazard coincidence method as compared to distance-based methods. This study is the first national-level environmental justice study to conduct longitudinal analyses using distance-based methods. Our purposes are to: (1) determine whether disparate siting, post-siting demographic change, or a combination of the two created present-day disparities; (2) test related explanations; and (3) determine whether the application of distance-based methods helps resolve the inconsistent findings of previous research. We used a national database of commercial hazardous waste facilities sited from 1966 to 1995 and examined the demographic composition of host neighborhoods around the time of siting and demographic changes that occurred after siting. We found strong evidence of disparate siting for facilities sited in all time periods. Although we found some evidence of post-siting demographic changes, they were mostly a continuation of changes that occurred in the decade or two prior to siting, suggesting that neighborhood transition serves to attract noxious facilities rather than the facilities themselves attracting people of color and low income populations. Our findings help resolve inconsistencies among the longitudinal studies and builds on the evidence from other subnational studies that used distance-based methods. We conclude that racial discrimination and sociopolitical explanations (i.e., the proposition that siting decisions follow the \u27path of least resistance\u27) best explain present-day inequities

Which came first, people or pollution? A review of theory and evidence from longitudinal environmental justice studies

A considerable number of quantitative analyses have been conducted in the past several decades that demonstrate the existence of racial and socioeconomic disparities in the distribution of a wide variety of environmental hazards. The vast majority of these have been cross-sectional, snapshot studies employing data on hazardous facilities and population characteristics at only one point in time. Although some limited hypotheses can be tested with cross-sectional data, fully understanding how present-day disparities come about requires longitudinal analyses that examine the demographic characteristics of sites at the time of facility siting and track demographic changes after siting. Relatively few such studies exist and those that do exist have often led to confusing and contradictory findings. In this paper we review the theoretical arguments, methods, findings, and conclusions drawn from existing longitudinal environmental justice studies. Our goal is to make sense of this literature and to identify the direction future research should take in order to resolve confusion and arrive at a clearer understanding of the processes and contributory factors by which present-day racial and socioeconomic disparities in the distribution of environmental hazards have come about. Such understandings also serve as an important step in identifying appropriate and effective societal responses to ameliorate environmental disparities