Volatility Of Pb Research Articles

Recycling of flotation residual carbon from coal gasification fine slag through thermal combustion reaction: Insight into the spatial and temporal multi-scale evolution of typical heavy metals

The necessity for a fundamental comprehension of the migration and transformation patterns of heavy metals in the combustion reaction process is paramount to ensure the effective and targeted prevention and control of heavy metal pollution in the context of large-scale energy utilization of waste coal gasification fine slag. This study aims to reveal the fate of typical heavy metals during the combustion reaction of coal gasification fine slag to provide valuable insight for its clean secondary use. In this work, the thermal combustion reactivity of coal gasification fine slag was initially enhanced through froth flotation, and then the spatial and temporal multi-scale evolution of heavy metals in the flotation carbon-rich fraction was investigated by a series of analytical experiments. The results demonstrate a strong correlation between the volatility of typical heavy metals and the combustion reaction process of the flotation carbon-rich fraction. The volatility of V, Ni, Cu, Zn, and Pb is consistently high, of which the volatility of Zn and Pb is consistently above 50%, while the volatility of Cr, Mn, and Ba exhibits greater temperature sensitivity. As the reaction proceeds, the specific surface area of the solid residue expands, and then the smooth and dense mineral particles dissolve into each other to form a cluster structure simultaneously with the collapse of the pore structure, resulting in the volatility of the heavy metals firstly increasing and then decreasing. Furthermore, alkali metals and alkaline earth metal compounds are effective carriers of Cr, Mn, and Ba in the bottom residual. Additionally, the type and number of crystalline minerals in the bottom residual gradually increase as the reaction progresses. This results in the gradual conversion of the heavy metals bound to unstable carbonate minerals and sulphones into more stable chemical forms. The findings provide novel theoretical support and technical guidance for the environmentally sound and efficient utilization of residual carbon in the waste coal gasification fine slag.

Emission of nitrogen/sulfur pollutants and migration of heavy metals during combustion of oily sludge from the oil refining process in fluidized bed

Oily sludge is a kind of hazardous waste due to the enrichment of nitrogen, sulfur, and heavy metals. In this work, the combustion of oily sludge from an oil refining factory in a fluidized bed reactor at 850–1050 °C and 0.8–1.2 excess air ratios were studied, with a focus on emission of nitrogen and sulfur pollutants and migration of Cr, Ni, Cu, Zn, Cd, Pb. The emission characteristics of nitrogen and sulfur pollutants were exhibited through monitoring the flue gas. The migration characteristics of heavy metals were clarified by analyzing their retention in bottom and fly ash. Moreover, the BCR (European Community Bureau of Reference) sequential extraction of the heavy metals in bottom ash was also carried out to obtain the migration of heavy metals in different forms. The contents of NOx and SO2 in the flue gas increased with temperature and excess air ratio increasing. High temperature led to less heavy metal retention in the bottom ash. The strong oxidizing atmosphere can weaken the volatilization of heavy metals. The stabilities of the heavy metal in different forms were in the following order: F4 (residual fraction) > F3 (oxidizable fraction) > F2 (reducible fraction) > F1 (exchangeable and acid soluble fraction). F4 was the dominant fraction of heavy metals in the bottom ash. The >60 % content of F3 and F4 led to the high stability of Cu and Ni while the >57 % content of F1 and F2 led to the high volatility of Cd and Pb in bottom ash. The differences in the component map of F1-F4 for the six heavy metals gave rise to their different migration characteristics during combustion.

Measurement and modeling of heavy metal behaviors during the incineration of RDF in a pilot-scale kiln incinerator-Part 1: Modeling using multizonal thermodynamic equilibrium calculation

Multizonal thermodynamic equilibrium calculation is one of the methods used in estimating or explaining the fate of elements such as heavy metals during waste incinerations and probably only one method that can estimate the fate of trace elements, but the ability of the calculation as a fate-estimation tool was not fully examined. This study examines the performance of multizonal thermodynamic equilibrium calculation applied to waste incineration by comparing the calculated results with the results from the incineration test and literature information. High temperature behaviors of the heavy metals were also reviewed to correctly understand their gas phase speciation in the incinerator, and the thermodynamic data of gaseous Cd species were modified to better reproduce the high temperature vaporization behavior. The calculation represented the high volatility of Hg, Cd, Pb, and low volatility of Cr in the incineration, whereas the measured high volatility of Zn and As could not be obtained by the calculation. The calculation succeeded in reproducing the possible gas phase chemical speciation of heavy metals in the incinerator expected from the review on the high temperature properties, whereas the calculated fly ash speciation does not match with the measured speciation. Possible reasons for these inconsistencies were considered.

Thermal treatment of municipal solid waste incineration fly ash: Impact of gas atmosphere on the volatility of major, minor, and trace elements

Development of thermal processes for selective recovery of Zn and other valuable elements from municipal solid waste incineration (MSWI) fly ash requires comprehensive knowledge of the impact of gas atmosphere on the volatile behaviour of the element constituents of the ash at different reaction temperatures. This study assesses the partitioning of 18 elements (Al, As, Bi, C, Ca, Cd, Cl, Cu, K, Mg, Na, P, Pb, S, Sb, Sn, Ti, and Zn) between condensed and gaseous phases during thermal treatment of MSWI fly ash in both oxidising gas and reducing gas atmospheres, at different temperatures spanning the range 200–1050 °C. The operating atmosphere had major impacts on the partitioning of the following elements: As, Bi, C, Cd, Cu, Na, Pb, S, Sb, Sn, and Zn. The partitioning of these elements cannot be accurately predicted over the full range of investigated operating conditions with global thermodynamic equilibrium calculations alone, i.e. without also considering chemical kinetics and mass transfer. In oxidising conditions, the following elements were predominately retained in condensed phases, even at high temperatures: As, Bi, Sb, Sn, and Zn. All these elements, except As, were largely released to the gas phase (>70%) at high temperatures in reducing conditions. The impact of gas atmosphere on the volatility of Cd and Pb was greatest at low reaction temperatures (below ~750 °C). Results for volatile matrix elements, specifically C, Cl, K, Na, and S, are interpreted in terms of the mechanisms governing the release of these elements to the gas phase.

Thermal separation of zinc and other valuable elements from municipal solid waste incineration fly ash

Municipal solid waste incineration fly ashes can contain high concentrations of Zn and other valuable elements including Cu, Pb, Sn, and Sb. These elements can potentially be separated from fly ashes by selectively volatilising and condensing them in thermal processes. This study presents a thermal process for production of zinc concentrates from fly ashes and assesses the impact of the reducing gas atmosphere used in the process on the volatility of Zn, Pb, and Cu. Concentrates were produced by heating samples of municipal solid waste incineration fly ash in a reducing atmosphere, consisting of 10% H2 and 90% N2, and selectively condensing elements which volatilised from the ash at 900 and 1100 °C. Thermodynamic equilibrium calculations were used to predict the volatile behaviour of Zn, Pb, and Cu in the reducing atmosphere and in an oxidising atmosphere (air). The extent of volatilisation of these elements was also determined experimentally for both the reducing atmosphere and the oxidising atmosphere by means of mass balances based on elemental analyses of untreated and heat-treated ashes. The concentrate produced at 900 °C contained high concentrations of Zn (55.9 ± 12.5% w/w) and Pb (4.7 ± 1.1% w/w). These metals and other higher value elements, specifically, Sn, Sb, and Bi, were greatly enriched in the concentrates when compared with the untreated fly ash, showing a high potential for the developed process to separate multiple valuable elements from ashes. However, several deleterious impurities, particularly K, Na, and Cd, also reported to the concentrates in significant concentrations. Further refinements to the process are needed to separate these elements from Zn. The reducing gas atmosphere substantially increased the volatility of Zn, but suppressed the volatility of Cu and, to a lesser extent, the volatility of Pb. The equilibrium calculations overestimated the release of Cu in oxidising conditions and the release of Zn and Pb in both oxidising and reducing conditions.

Volatility and partitioning of Cd and Pb during sewage sludge thermal conversion

In this paper, the thermal characteristics of sewage sludge and the transformation behavior of Pb and Cd during the thermal conversion process were addressed. The incineration process and pyrolysis process of the sewage sludge were investigated by thermogravimetric analysis. The results indicated that the thermal conversion process of the sewage sludge could be divided into three stages and the presence of oxygen could accelerate the decomposition of the sewage sludge. Furthermore, the effects of thermal conditions on the concentration ratio of Cd and Pb and their species partitioning in the residual char and ash were investigated. For the pyrolysis process, the maximum concentration ratio of Cd reached 41.64% at 500 °C and the lowest one 2.92% at 700 °C. Contrary, the concentration ratio of Pb remained above 93% as the temperature increased. Thus, the suitable temperature for the sewage sludge pyrolysis was below 500 °C. For the incineration process, the incineration temperature had great influence on the concentration ratio of Cd and Pb. When the incineration temperature increased from 700 °C to 900 °C, the concentration ratio of Cd decreased drastically from 99.32% to 10.96%. The maximum concentration ratio for Pb (95.31%) was reached at 800 °C. Besides, the lowest concentration ratio of Cd and Pb were obtained at a residence time of 30 min. The partitioning analyses of the Cd and Pb contained in the ash showed that the residence time had little effect on the partitioning of Cd and Pb, and the residual fractions of Cd and Pb were both above 90%. It was concluded that Cd and Pb were properly stabilized in the ash. Thus, Cd and Pb in the ash were difficult to be released into the environment and to cause secondary pollution.

Environmentally-friendly, Pb-free Cu front electrode for Si-based solar cell applications

In this study, a double glass system with PbO base and ZnO base of Cu paste is designed, prepared and printed with narrow line screen printing process on polycrystalline Si solar cell which has already finished the back Al printing and deposition of double anti-reflection coatings (DARCs). And then, a two-step firing process is applied to sinter the front electrode and obtain the ohmic contact between front electrode and solar cell. The first step of firing is conducted in air atmosphere. In this process, PbO-based glass frit etched the DARCs and Ag recrystallized at the surface of Si, constructing the preliminary contact. The second step of firing is conducted in a reducing atmosphere (H2/N2 = 5/95). In this process, the CuO is reduced into Cu which is sintered with ZnO based-glass. Ag nanoparticles recrystallized in the glass layer at interface due to the interactions between H2, Ag and PbO-based glass frit and the volatility of Pb, improve the Ohmic contact between electrode and solar cell.According to our investigation, a model of the reaction mechanisms in the double glass system of Cu paste in each sintering stage is proposed. And we have shown that Ohmic contact and good sheet resistance for the Cu front electrode with Pb-free could both be obtained by applying the newly-invented Cu paste and two steps of firing process. The lowest sheet resistance and contact resistance for such a Cu front electrode measured are 0.090 Ω/□ and 0.0040 Ω/□, respectively.

Study on the behavior of heavy metals during thermal treatment of municipal solid waste (MSW) components.

Laboratory experiments were conducted to investigate the volatilization behavior of heavy metals during pyrolysis and combustion of municipal solid waste (MSW) components at different heating rates and temperatures. The waste fractions comprised waste paper (Paper), disposable chopstick (DC), garbage bag (GB), PVC plastic (PVC), and waste tire (Tire). Generally, the release trend of heavy metals from all MSW fractions in rapid-heating combustion was superior to that in low-heating combustion. Due to the different characteristics of MSW fractions, the behavior of heavy metals varied. Cd exhibited higher volatility than the rest of heavy metals. For Paper, DC, and PVC, the vaporization of Cd can reach as high as 75% at 500 °C in the rapid-heating combustion due to violent combustion, whereas a gradual increase was observed for Tire and GB. Zn and Pb showed a moderate volatilization in rapid-heating combustion, but their volatilities were depressed in slow-heating combustion. During thermal treatment, the additives such as kaolin and calcium can react or adsorb Pb and Zn forming stable metal compounds, thus decreasing their volatilities. The formation of stable compounds can be strengthened in slow-heating combustion. The volatility of Cu was comparatively low in both high and slow-heating combustion partially due to the existence of Al, Si, or Fe in residuals. Generally, in the reducing atmosphere, the volatility of Cd, Pb, and Zn was accelerated for Paper, DC, GB, and Tire due to the formation of elemental metal vapor. TG analysis also showed the reduction of metal oxides by chars forming elemental metal vapor. Cu2S was the dominant Cu species in reducing atmosphere below 900 °C, which was responsible for the low volatility of Cu. The addition of PVC in wastes may enhance the release of heavy metals, while GB and Tire may play an opposite effect. In controlling heavy metal emission, aluminosilicate- and calcium-based sorbents can be co-treated with fuels. Moreover, pyrolysis can be a better choice for treatment of solid waster in terms of controlling heavy metals. PVC and Tire should be separated and treated individually due to high possibility of heavy metal emission. This information may then serve as a guideline for the design of the subsequent gas cleaning plant, necessary to reduce the final emissions to the atmosphere to an acceptable level.

An experimental and thermodynamic equilibrium investigation of the Pb, Zn, Cr, Cu, Mn and Ni partitioning during sewage sludge incineration

The effects of different chlorides and operational conditions on the distribution and speciation of six heavy metals (Pb, Zn, Cr, Cu, Mn and Ni) during sludge incineration were investigated using a simulated laboratory tubular-furnace reactor. A thermodynamic equilibrium investigation using the FactSage software was performed to compare the experimental results. The results indicate that the volatility of the target metals was enhanced as the chlorine concentration increased. Inorganic-Cl influenced the volatilization of heavy metals in the order of Pb>Zn>Cr>Cu>Mn>Ni. However, the effects of organic-Cl on the volatility of Mn, Pb and Cu were greater than the effects on Zn, Cr and Ni. With increasing combustion temperature, the presence of organic-Cl (PVC) and inorganic-Cl (NaCl) improved the transfer of Pb and Zn from bottom ash to fly ash or fuse gas. However, the presence of chloride had no obvious influence on Mn, Cu and Ni. Increased retention time could increase the volatilization rate of heavy metals; however, this effect was insignificant. During the incineration process, Pb readily formed PbSiO4 and remained in the bottom ash. Different Pb compounds, primarily the volatile PbCl2, were found in the gas phase after the addition of NaCl; the dominant Pb compounds in the gas phase after the addition of PVC were PbCl2, Pb(ClO4)2 and PbCl2O4.

Role of dual-laser ablation in controlling the Pb depletion in epitaxial growth of Pb(Zr0.52Ti0.48)O3 thin films with enhanced surface quality and ferroelectric properties

Pb depletion in Pb(Zr0.52Ti0.48)O3 (PZT) thin films has remained as a major setback in the growth of defect-free PZT thin films by pulsed laser ablation techniques. At low excimer (KrF) laser fluences, the high volatility of Pb in PZT leads to non-congruent target ablation and, consequently, non-stoichiometric films, whereas, at high laser fluences, the inherent ejection of molten droplets from the target leads to particulate laden films, which is undesirable in heterostructure growth. To overcome these issues, a dual-laser ablation (PLDDL) process that combines an excimer (KrF) laser and CO2 laser pulses was used to grow epitaxial PZT films on SrTiO3 (100) and MgO (100) substrates. Intensified-charge-coupled-detector (ICCD) images and optical emission spectroscopy of the laser-ablated plumes in PLDDL revealed a broader angular expansion and enhanced excitation of the ablated species as compared to those for single-laser ablation (PLDSL). This led to the growth of particulate-free PZT films with higher Pb content, better crystallinity, and lower surface roughness as compared to those deposited using PLDSL. For FE measurements, PZT capacitors were fabricated in situ using the latticed-matched metallic oxide, La0.7Sr0.3MnO3, as the top and bottom electrodes. PZT films deposited using PLDDL exhibited enhanced polarization for all driving voltages as compared to those deposited using PLDSL. A highest remanent polarization (Pr) of ∼91 μC/cm2 and low coercive field of ∼40 kV/cm was recorded at 9 V driving voltage. Fatigue characterization revealed that PZT films deposited using PLDDL showed unchanging polarization, even after 109 switching cycles.

Trace elements in co-combustion of solid recovered fuel and coal

Trace element partitioning in co-combustion of a bituminous coal and a solid recovered fuel (SRF) was studied in an entrained flow reactor. The experiments were carried out at conditions similar to pulverized coal combustion, with SRF shares of 7.9wt.% (wet basis), 14.8wt.% and 25.0wt.%. In addition, the effect of additives such as NaCl, PVC, ammonium sulphate, and kaolinite on trace element partitioning was investigated. The trace elements studied were As, Cd, Cr, Pb, Sb and Zn, since these elements were significantly enriched in SRF as compared to coal. During the experiments, bottom ash was collected in a chamber, large fly ash particles were collected by a cyclone with a cut-off diameter of ~2.5μm, and the remaining fly ash particles were gathered in a filter. It was found that when coal was co-fired with SRF, the As, Cd, Pb, Sb and Zn content in filter ash/cyclone ash increased almost linearly with their content in fuel ash. This linear tendency was affected when the fuels were mixed with additives. The volatility of trace elements during combustion was assessed by applying a relative enrichment (RE) factor, and TEM–EDS analysis was conducted to provide qualitative interpretations. The results indicated that As, Cd, Pb, Sb and Zn were highly volatile when co-firing coal and SRF, whereas the volatility of Cr was relatively low. Compared with coal combustion, co-firing of coal and SRF slightly enhanced the volatility of Cd, Pb and Zn, but reduced the volatility of Cr and Sb. The Cl-based additives increased the volatility of Cd, Pb and As, whereas addition of ammonium sulphate generally decreased the volatility of trace elements. Addition of kaolinite reduced the volatility of Pb, while the influence on other trace elements was insignificant. The results from the present work imply that trace element emission would be significantly increased when coal is co-fired with SRF, which may greatly enhance the toxicity of the dusts from coal-fired power plant. In order to minimize trace element emission in co-combustion, in addition to lowering the trace element content in SRF, utilizing SRF with low Cl content and coal with high S and aluminosilicates content would be desirable.

Investigation of heavy metal partitioning influenced by flue gas moisture and chlorine content during waste incineration

The impact of moisture on the partitioning of the heavy metals including Pb, Zn, Cu and Cd in municipal solid waste (MSW) was studied in a laboratory tubular furnace. A thermodynamic investigation using CHEMKIN software was performed to compare the experimental results. Simulated waste, representative of typical MSW with and without chlorine compounds, was burned at the background temperature of 700 and 950°C, respectively. In the absence of chlorine, the moisture content has no evident effect on the volatility of Pb, Zn and Cu at either 700 or 950°C, however, as flue gas moisture increasing the Cd distribution in the bottom ash increased at 700°C and reduced at 950°C, respectively. In the presence of chlorine, the flue gas moisture reduced the volatility of Pb, Zn and Cu due to the transformation of the more volatile metal chlorides into less volatile metal oxides, and the reduction became significant as chlorine content increase. For Cd, the chlorine promotes its volatility through the formation of more volatile CdCl 2. As a result, the increased moisture content increases the Pb, Zn, Cu and Cd concentrations in the bottom ash, which limits the utilization of the bottom ash as a construction material. Therefore, in order to accumulate heavy metals into the fly ash, MSW should be dried before incineration.

Direct Growth of Single-Walled Carbon Nanotubes without Metallic Residues by Using Lead as a Catalyst

The IVA group metal Pb was found to be an efficient catalyst for the chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWCNTs) under suitable conditions. Especially the volatility of Pb made it feasible to realize the direct growth of SWCNTs with no metallic catalyst residues. Three methods including a low gas flow process, a fast-heating process, and a polymer-assisted process were used to control the volatility of lead at a suitable level. Both random SWCNT networks and horizontally aligned SWCNT arrays were efficiently grown on silicon wafers. The density of the SWCNT arrays can be altered by the CVD conditions. The electrical transport measurements for single tubes show that the produced SWCNTs are of high quality. These directly prepared SWCNTs with no metallic impurities will greatly benefit the study of the intrinsic properties of SWCNTs and are very important for making use of SWCNTs in nanodevices and in biological systems.

The fate of trace elements in fluidised bed combustion of sewage sludge and wood

Combustion tests have been carried out in a fluidised bed boiler to investigate the fate of trace elements during co-combustion of wood and municipal sewage sludge. The approach was to collect fuel and ash samples and to perform thermodynamic equilibrium calculations for gasification (reducing) and combustion (oxidising) conditions. Trace elements are found in the ash. Even most of the highly volatile Hg is captured in the bag filter ash. The bag filter ash offers higher surface area than the secondary cyclone ash and enhances the capture of Hg. There is no obvious correlation between capture and parameters investigated (sludge precipitation agent and lime addition). As, Cd, Hg, Pb, Se, Sb and Tl are predicted by equilibrium calculations to be volatile in the combustion chamber under oxidising conditions and Hg even at the filter temperature (150 °C). Reducing conditions promote, in some case more than others, the volatility of As, Cd, Pb, Sb, Se, Tl and Zn. The opposite effect was observed for Cu and Ni. Data points to the necessity of including bag filter in the gas cleaning system in order to achieve good removal of toxic trace elements.

Investigation of Pb-free Bi-2223 high temperature sintering

The Bi-2223 performance could be significantly improved by melt processing. However, it is a very difficult task, partly due to the volatility of Pb, its main dopant. On the other hand, it is also a hard task to obtain high Pb-free 2223 amounts, even by sinterization using a primary phase field composition (Bi/sub 2.5/Sr/sub 1.9/Ca/sub 2.1/Cu/sub 3/O/sub x/). In the present work, we investigate the sinterization of Pb-free 2223 in the presence of appreciable liquid fractions. The samples were analyzed by XRD, SEM/EDS and Magnetic Susceptibility. The results show significant Pb-free 2223 amounts after sintering at temperatures close to the melting. Such investigation represents an additional step toward the elucidation of the Pb-free 2223/melt equilibrium.

レーザーアブレーション-誘導結合プラズマ質量分析法による地球化学試料の微量元素分析

This paper describes advances in elemental and isotopic ratio measurements that have been made with inductively coupled plasma mass spectrometry (ICP-MS) coupled with a laser-ablation sample introduction technique. Laser ablation utilizing UV light (frequency quadrupled to 266 nm or quintupled to 213 nm by a Nd-YAG laser, or an ArF Excimer 193 nm laser) is now the most widely used system because of its higher analytical precision and analytical capability to most of solid samples. However, even with UV lasers, serious elemental fractionation may occur during laser ablation, mainly due to differences in the element volatility. Therefore, the reduc- tion of elemental fractionation during ablation is necessary for further precise and accurate ele- mental and isotopic analyses of trace elements. This is particularly the case for high quality-iso- tope data for age determination. In the field of geochemistry, great efforts have been made to obtain accurate Pb/U ratios, because 206 Pb/ 238 U ratios provide chronological information. The basic problem is that Pb/U results using conventional LA-ICPMS techniques show serious frac- tionations of the ratio over a prolonged measurement. The observed Pb/U ratio increases dur- ing the measurement because of the greater volatility of Pb. The Pb/U elemental fractionation is successfully reduced by an active focus technique, chemically assisted-laser ablation technique, or by soft-ablation technique. Moreover, recently developed techniques including signal sta- biliser, a correction for the slow response of a Faraday amplifier and removal of isobaric interfer- ence by cool plasma conditions, will also expand the application fields and analytical accuracies of the LA-ICPMS technique. Outlines of these techniques are introduced.

Occurrence and volatilization behavior of Pb, Cd, Cr in Yima coal during fluidized-bed pyrolysis ☆

The volatilization behavior of Pb, Cd, Cr and the influence of coexisting mineral matters were investigated during pyrolysis of Yima coal in a fluidized-bed reactor at temperatures ranging from 500 to 900 °C. The modes of occurrence of Pb, Cd, Cr in Yima raw coal and two char samples were determined using density fractionation, demineralization and sequential chemical extraction methods. Lead in Yima coal is mostly associated with mineral matter in various forms, mainly pyrite, sulfates and monosulfides. Large part of cadmium is associated with pyrite. Chromium in Yima coal is mainly associated with organic matter. Different trends are observed for various forms of trace metals during pyrolysis. Lead associated with pyrite, sulfates and carbonates, lead in water soluble and ion exchangeable forms, and cadmium associated with pyrite are all unstable under pyrolysis conditions. During Yima coal pyrolysis, the volatilities of lead and cadmium vary greatly with pyrolysis temperature, while chromium volatility in Yima raw coal only has slight changes over the temperature range (500–900 °C) studied. The volatility of Pb, Cd, Cr in demineralized Yima coal (YimaD) is much higher than that of Yima coal during pyrolysis. New thermally stable forms of Pb, Cd and Cr are formed during pyrolysis of Yima, whereas the sources of them are different. The interactions between chromium and its coexisting mineral matters in Yima coal retard its vaporization during pyrolysis.

Electrical and Structural Properities of PZT Films Deposited by MOCVD Using Ultrasonic Nebulization

Pb(Zr x Ti 1-x )O 3 [PZT] thin films were deposited on Pt/MgO/Si and MgO/Si substrates by MOCVD using the ultrasonic nebulization and their structural and electrical properties were investigated. At the substrate temperatures between 500C ∼ 550C, PZT thin films grew with single perovskite phase. However, Pb contents of PZT thin films were very low compared to those in the source solution, which was due to large volatility of Pb at those temperatures. To obtain a stoichiometric PZT thin films, therefore, composition ratio of [Pb]/[Zr+Ti]=2 in the source solution was used in this experiment. The remanent polarization of PZT films was about 17 w C/cm 2 at - 5Voltage. Leakage-current density of PZT thin films was about 9.6 2 10 m 5 A/cm 2 at +10V and 1.4 2 10 m 5 A/cm 2 at m 10V. Fatigue test of this PZT thin film shows stable behavior and no degradation characteristic after 10 10 cycle.

Microstructure of PbTi03/SrTi03 Superlattice Grown by MBE

Abstract Ferroelectric superlattices have been actively and intensively studied in recent years for their great scientific and technological interest. Superlattice containing Pb-based ferroelectric layers are important among ferroelectric superlattice systems, however, it is difficult to grow such superlattice due to the high volatility of Pb. Recently, great progress has been made in fabricating superlattice structure of PbZrO3/PbTiO3 by multi-ion-beam sputtering’ and molecular beam epitaxy (MBE). In this paper, we report the microstructural investigations of PbTiO3/SrTiO3 superlattice films, which were epitaxially grown on the SrTi03 substrate by MBE, using transmission electron microscopy (TEM). [(PbTiO3)l0/(SrTiO3)l0]15 superlattice films were stacked on (100) SrTiO3 substrate alternately by MBE. Before growing the superlattice structure, a baffle layer including the 1000Å La-doped SrTi03 and the subsequent 500 Å PbTiO3 thin films was grown on the substrate. Above the PbTi03/SrTi03 superlattices, another PbTi03 thin film (1000 Å) was grown. Cross-section TEM specimens were prepared by standard methods.

Radionuclides in fly ash and bottom ash: improved characterization based on radiography and low energy gamma-ray spectrometry

Two radiation-based techniques for determining the distribution and relative abundance of radionuclides are described, and applied to a suite of fly ash and bottom ash samples from a Kentucky power plant. The technique of fission-track radiography provides new observations of the variety of uranium hosts and of uranium distribution in individual particles of fly ash, and thus aids prediction of the leachability of uranium during long-term disposal or utilization of fly ash. Uranium is largely dispersed within glassy components of fly ash particles and shows little evidence for obvious surface enrichment that could be attributed to secondary adsorption. The technique of low energy gamma-ray spectrometry provides simultaneous, non-destructive determination of the relative abundance of 238U, 226Ra, 228Ra and 210Pb in representative 150–250 g samples. The measurements provide a means for screening samples to determine if the combustion process causes significant preferential redistribution of radionuclides that could affect their subsequent mobility. Results indicate that radium isotopes are not significantly (within 10–15%) fractionated from parent 238U and 232Th during coal combustion. In contrast, 210Pb appears to be preferentially enriched in some samples of fly ash, and depleted in bottom ash relative to 238U and 226Ra. In this application 210Pb acts as a tracer for elemental lead, and confirms the expected greater volatility of Pb compared to more refractory elements during coal combustion.