Currently, a lack of accurate emission data exits for particulate matter (PM) in agricultural air quality studies (USDA-AAQTF, 2000). PM samplers, however, tend to over estimate the concentration of most agricultural dusts because of the interaction of the particle size distribution (PSD) and performance characteristics of the sampler (Buser, 2004). This research attempts to find a practical method to characterize and correct this error for the Federal Reference Method (FRM) PM10 sampler. First, a new dust wind tunnel testing facility that satisfies the USEPA’s requirement of testing PM10 samplers was designed, built, and evaluated. Second, the wind tunnel testing protocol using poly-dispersed aerosol as the test dust was proved to be able to provide results consistent with mono-dispersed dusts. Third, this study quantified the variation of over sampling ratios for the various cut point and slopes of FRM PM10 samplers and proposed an averaged over sampling ratio as a correction factor for various ranges of PSD. Finally, a method of using total suspended particle (TSP) samplers as a field reference for determining PM10 concentrations and aerosol PSD was explored computationally. Overall, this dissertation developed successfully the methodology to correct the sampling error associated with the FRM PM10 sampler: (1) wind tunnel testing facilities and protocol for experimental evaluation of samplers; (2) the variation of the oversampling ratios of FRM PM10 samplers for computational evaluation of samplers; (3) the evaluation of TSP sampler effectiveness as a potential field reference for field evaluation of samplers.

The objective of this research was to investigate the retention of arsenate (iAsV), arsenite (iAsIII), monomethyl arsenate (MMAsV) and dimethyl arsenate (DMAsV) by calcite and assess the impact of dissolved Ca2+, Mg2+, phosphate and sulfate on arsenic solubility, adsorption and precipitation phenomena. Adsorption kinetics of iAsV, evaluated at a low and high concentration, was a relatively rapid process, with a fast initial reaction rate within the first few minutes and a subsequent slower reaction rate as equilibrium was approached. The relative adsorption of arsenicals decreased in the following order: iAsV > iAsIII > DMAV > MMAV. In no case was a clear adsorption maximum observed with increasing dissolved arsenic concentration. Dissolved 0.01 M Ca2+ resulted in an increase in iAsV adsorption; however, in the presence of 0.1 M Ca2+ adsorption of iAsV was decreased. The presence of Mg2+ as 0.01 M Mg(NO3)2 resulted in decreased iAsV adsorption probably the result of a lower iAsV affinity for adsorbed Mg2+ as compared to Ca2+. Phosphate and sulfate were highly competitive with iAsV in adsorption to calcite and both resulted in decreased iAsV adsorption. The total prevention of iAsV adsorption at initial equimolar arsenic/phosphate concentrations > 88 µM each could be from the consumption of available calcite surface sites by the specific adsorption of phosphate. Equilibrium modeling, using the geochemical and mineral speciation of equilibrium model (MINTEQA2), indicated that at low concentrations of arsenate or phosphate solid-phase precipitation was not likely and adsorption processes likely controlled solubility. At high concentrations of arsenate Ca3(AsO4)2 · 3 2/3 H2O and Ca3(AsO4)2 · 4 1/4 H2O solid phases could be controlling arsenate solubility. This study indicates that arsenic adsorption response by calcite was different than that of phosphate suggesting that arsenic may not be specifically adsorbed to calcium at the calcite surface. Reduction and biomethylation of arsenic decreased adsorption, suggesting that processes which could affect the speciation of arsenic in the environment, could increase arsenic mobility in environmental systems where calcite and dissolved aqueous calcium play a predominant role in controlling arsenic solubility. Dissolved aqueous concentrations of magnesium, phosphate and sulfate generally reduced the ability of arsenic to be adsorbed to calcite.

Hexagonal boron nitride (h-BN) formation by carbothermic reduction of B2O3 under nitrogen atmosphere at 1500&deg / C and effect of CaO addition into the initial B2O3 &amp / #8211 / active C mixture were investigated during this study. Reaction products were characterized by powder X-ray diffraction, scanning electron microscopy (SEM) and quantitative chemical analysis. Main aim of this study was to investigate the presence of a second reaction mechanism that catalytically affects h-BN formation during CaO or CaCO3 addition into the initial mixture. It was found that similar to CaCO3 addition, CaO addition has a catalytic effect on carbothermic formation h-BN. In order to investigate the reaction mechanism experiments with B2O3 &amp / #8211 / CaO mixtures without active carbon addition into the mixture were conducted. Furthermore nucleation of h-BN from calcium borate melts had been investigated and experiments were conducted with h-BN addition into CaO &amp / #8211 / B2O3 mixtures. It was concluded that nucleation of h-BN in calcium borate slags under experimental conditions is not possible. Hexagonal BN should be present in the system in order to activate the second nitrogen dissolution followed by h-BN precipitation mechanism. Highest efficiency was achieved in the experiment conducted with CaCO3 addition and largest particle size was observed during the experiment conducted to investigate the effect of nucleation.

Effect of Na2CO3 on formation of hexagonal boron nitride (h-BN) by carbothermic method has been studied by subjecting B2O3-C and Na2CO3-added B2O3-C mixtures to N2 (g) atmosphere. Na2CO3 amount in the mixtures was changed in the range of 0-40 wt. %. Time and temperature were used as experimental variables. Reaction products were analyzed by XRD and scanning electron microscope. Na2CO3 was found to increase both the amount and the particle size of h-BN similar to CaCO3 [1]. Na2CO3 was found to be less effective than CaCO3 in increasing the amount while it was more effective than CaCO3 in increasing the particle size of h-BN forming.

Carbothermic production of hexagonal BN by using boric acid and ground colemanite mined from Bigadi&ccedil / Region in Turkey was investigated by subjecting pellets prepared from B2O3, activated carbon and colemanite mixtures to nitrogen gas at 1500&deg / C. Similar to CaCO3 addition, colemanite addition to the B2O3-C mixtures resulted in higher amounts of h-BN in the final products. As a result of the experiments conducted with colemanite and CaCO3 additions providing the same quantity of CaO to the initial mixtures, similar amounts of hexagonal BN in the reaction products were observed. As a result of the experiments conducted with different compositions of colemanite- B2O3- C mixtures, 5 wt % colemanite addition was determined to be the optimum composition giving the highest amount of hexagonal BN in the reaction products. Increasing duration of the experiments increased the amount and particle size of h-BN formed in the products. Optimum amount of colemanite addition resulted in higher amounts and coarser particles of h-BN in the products than the optimum amounts of CaCO3 addition.

No description available.

Abstract In order to understand the source, transport pathway and sink of settling particulates off northeast Taiwan, time-series sediment traps (PPS-3/3) were deployed on the north slope of Ilan ridge (T18) and in the Okinawa trough (T15 and T16) to collect settling particulates. The trapped particulate samples were determined for apparent mass flux (T18), particle size distribution, and contents of lithogenic portion, metals (Al, Mg, Ca, Fe, Mn, Cu), opal, OC (organic carbon) and IC (inorganic carbon). The results show that mass flux in winter is higher than in summer except for typhoon or rainstorm in summer which may cause high particulate flux. At mooring T11 and T17, only 2 cups had collected particulates but with rapid decrease, and the remaining cups were empty. It is not clear whether Kuroshio plays a role and further investigation is needed. The trapped particulates were mainly clay and silt in the north slope of Ilan ridge and south Okinawa trough, and were sand and silt in the Mien-Hwa canyon. The portion of coarse silt and larger particles (>31 mm) decreases with an increase of distance from the land (from T11 to T18). The grain size distribution of particulate at T18 is similar to that at T15 and T16, but the mass flux in the north slope of Ilan ridge is an order of magnitude higher than in the south Okinawa trough. The size distribution pattern below 600m water depth is very similar at both T15 and T16, but the coarse fraction (> 31 mm) is more at the upper than lower traps, presumably due to lateral transport. The Mn content of the trapped particulates in the south Okinawa trough is twice as hign as that in the north slope of Ilan ridge. High Mn/Al ratio in the trough suggests that Mn is supplied by hydrothermal activities. Lithogenic portions occupy about 84~88.5% at T18, T16 and T15. Relative to other marginal seas biogenic contributions are clearly lower.

Abstract This study investigated the optimal operating parameters on road dust removal by a flusher. It aimed at enhancing road flushing efficiency, analyzing particle size range, and establishing a flushing model. This study explored main roads by collecting road dusts in Kaohsiung metropolitan area in October 2001. The roads were classified by road dust loading (RDL) as follows: level A (minor, RDL<1g/m2), level B (normal, RDL=1~5g/m2), level C (abnormal, RDL=5~11g/m2), and level D (serious, RDL= 11~25g/m2). The frequency of road flushing was recommended as follows: Level D roads were flushed every day to maintain RDL≤20g/m2. Level C roads were flushed every day, while level B roads were flushed every two days, to keep RDL≤10g/m2. Level A roads were flushed every week to maintain RDL≤5g/m2. A pilot-scale road-flush testing field was designed for this particular study to investigate the influence of operating parameters on road flushing efficiency. The findings indicated that flat-fan type nozzle demonstrated higher flushing efficiency than hollow-cone type nozzle, and that the flushing speed and the distance of the nozzle away from the ground were correlated negatively with the road flushing efficiency, whereas the pressure of nozzle and RDL was correlated with the road flushing efficiency. The results suggested that, in the condition of eighty percent of flushing efficiency, the optimal operating parameters were flushing speed of 15km/hr, the pressure of nozzle of 2.0kg/cm2, the distance away from the ground of 30cm, the angle of 40o, and the particle size less than 150£gm. The results showed that particle size was correlated negatively with the road flushing efficiency under various operating parameters of flushing for different road levels. Beside, the road flushing efficiency was above 80% for silt with particle size less than 75£gm. However, for particle size larger than 850£gm, the road flushing efficiency was up to 40%. It concluded that the road flushing efficiency of fine particles was better than that of coarse particles. After conducting dimensionless analysis and multiple regression analysis, the model of road flushing efficiency can be shown as follows, ¡]R¡×0.8276¡^ where £b is the road flushing efficiency, U is the flusher speed (m/s), P is the water injecting pressure (N/m2), W is the road dust loading (kg/cm2), H is the distance of nozzle away from the ground (m), q is the amount of water per square meter (m3/m2), and £c is the angle of nozzle spread. In this model, RDL is negatively correlated with U, W and H. Moreover, the road flushing efficiency increases with water injection pressure and flow rate. On the basis of the above model, the average percentage of error was approximately 0.28%. In this study, the optimal operating parameters of a flusher were that the flushing speed of 10km/hr, water injecting pressure of 2.0kg/cm2, the distance of nozzle away from the ground of 20cm, and the water injecting angle of 45o. However, depending upon the road cleanness levels, the optimal operating parameters could be varied. For instance, the distance of the nozzle away from the ground should be increased up to 30cm in order to prevent the damage from uneven roads or cavities. The experiments showed that 30cm of the height was a better option due to the road flushing efficiency was only 2% lower while compared with that of 20cm. After the analysis of experimental data, the results can serve as the operation condition for road flushing practice as authorities concerned. The operating parameters proposed in this study could be useful for basic design of a high-efficiency flusher. Moreover, the model of road flushing efficiency can be further applied to predict the road flushing efficiency.

Die Charakterisierung von Nanopartikeln erfordert eine Messung des Dispersitätszustandes bei allen Schritten der Herstellung - von der Synthese bis zum fertigen Produkt. Dafür ist eine leistungsfähige Partikelmesstechnik notwendig, deren Methoden bei der Beschreibung des komplexen Materialverhaltens helfen können. Die Ultraschalldämpfungsspektroskopie ist eine Messmethode, die zur prozessbegleitenden Charakterisierung hochdisperser Pulver und Suspensionen geeignet ist. Mit Vergleichen von Messungen und Modellrechungen wurde festgestellt, dass für die Ultraschalldämpfungs-Modellierung in Dispersionen homogener Partikel ein auf dem Phänomen der elastischen Streuung basierendes Modell praktisch relevant ist. Dies betrifft sowohl die Anwendung zur Messung in Suspensionen als auch in Emulsionen homogener Partikel. Bei einem Vergleich von Modellrechungen und Messungen für ein System poröser Partikel bzw. Aggregate wurde das Modell der Streuung an poroelastischen Kugeln als geeignet zur Beschreibung der Dämpfung disperser Systeme identifiziert. Bei Vorhandensein grober Partikel in Suspensionen nanoskaliger Systeme ist somit eine korrekte Auswertung der Partikelgröße möglich; der bislang übliche Messbereich wurde erweitert. Sekundärer Schwerpunkt der Arbeit ist die Diskussion der numerischen Modellanwendung. Es werden weiterhin Lösungsmöglichkeiten zur Dämpfungsberechnung und zur Berechnung der Größenverteilungen beschrieben. Des Weiteren wurden Anregungen für Entwickler von Ultraschallspektrometern abgeleitet.

<p>Denna licensiatavhandling behandlar oxidativ upplösning av UO2. Upplösning av UO2 studeras huvudsakligen då UO2-matrisen hos använt kärnbränsle förväntas fungera som en barriär mot frigörande av radionuklider i ett framtida djupförvar. Lösligheten av U(IV) är mycket låg under i djupförvaret rådande förhållanden emedan U(VI) har betydligt högre löslighet. Oxidation av UO2-matrisen kommer därför att påverka dess löslighet och därmed dess funktion som barriär. I denna avhandling studeras den relativa effektiviteten av en- och två-elektronoxidanter för upplösning av UO2. Vid låga oxidantkoncentrationer är utbytet för upplösningen för en-elektronoxidanter signifikant lägre än för två-elektronoxidanter. För en-elektronoxidanter ökar dock utbytet med ökande oxidanthalt, vilket kan förklaras av den ökade sannolikheten för två konsekutiva en-elektronoxidationer av samma reaktionssite och den ökade möjligheten till disproportionering.</p><p>Radikaler och molekylära radiolysprodukters relativa inverkan på oxidativ upplösning av UO2 studeras också i denna avhandling genom mätning av mängden upplöst U(VI) i γ-bestrålade system som dominerades av olika oxidanter. Dessa studier visade att upplösningshastigheten av UO2 kan uppskattas från oxidantkoncentrationer framtagna genom simuleringar av radiolys i motsvarande homogena system och hastighetskonstanterna för ytreaktionerna. Simuleringarna visar att de molekylära oxidanterna kommer vara de viktigaste oxidanterna i alla system i denna studie vid långa bestrålningstider (>10 timmar). Vid liknande simuleringar av α-bestrålade system fanns att vid förhållanden relevanta för ett djupförvar för använt kärnbränsle, är det endast de molekylära oxidanterna (i huvudsak H2O2) som är av betydelse för upplösningen av bränslematrisen.</p><p>Då använt kärnbränsle innehåller en mängd radionuklider som utsätter UO2-matrisen för kontinuerlig bestrålning, är det av vikt att undersöka hur bestrålning påverkar reaktiviteten av UO2. Bestrålningseffekten på reaktionen mellan UO2 och MnO4- studerades. Dessa försök visade att bestrålning av UO2 vid doser >40 kGy leder till att reaktiviteten ökar upp till 1.3 gånger reaktiviteten av obestrålad UO2. Den ökade reaktiviteten kvarstår efter bestrålningen och effekten kan därför möjligen tillskrivas permanenta förändringar i materialet. Vid uppskattning av reaktiviteten hos använt kärnbränsle måste hänsyn tas till denna effekt då bränslet redan efter ett par dagar i reaktor blivit utsatt för doser >40 kGy.</p><p>Det har tidigare föreslagits att hastigheten för en heterogen västka/fast-fas reaktion är beroende av partikelstorleken hos det fasta materialet, vilket har studerats för UO2-partiklar i denna avhandling. Experimentellt bestämda kinetiska parametrar jämförs med de föreslagna ekvationerna för fyra storleksfraktioner av UO2-pulver och en UO2-pellet. Studien visade partikelstorleksberoendet av andra ordningens hastighetskonstant och aktiveringsenergin för oxidation av UO2 med MnO4- beskrivs relativt väl av de föreslagna ekvationerna.</p> / <p>The general subject of this thesis is oxidative dissolution of UO₂. The dissolution of UO₂ is mainly investigated because of the importance of the UO₂ matrix of spent nuclear fuel as a barrier against radionuclide release in a future deep repository. U(IV) is extremely insoluble under the reducing conditions prevalent in a deep repository, whereas U(VI) is more soluble. Hence, oxidation of the UO₂-matrix will affect its solubility and thereby its function as a barrier. In this thesis the relative efficiency of one- and two electron oxidants in dissolving UO₂is studied. The oxidative dissolution yield of UO₂was found to differ between one- and two-electron oxidants. At low oxidant concentrations the dissolution yields for one-electron oxidants are significantly lower than for two-electron oxidants. However, the dissolution yield for one-electron oxidants increases with increasing oxidant concentration, which could be rationalized by the increased probability for two consecutive one-electron oxidations at the same site and the increased possibility for disproportionation.</p><p>Furthermore, the relative impact of radical and molecular radiolysis products on oxidative dissolution of UO₂is investigated. Experiments were performed where the amount of dissolved U(VI) was measured in γ-irradiated systems dominated by different oxidants. We have found that the UO₂dissolution rate in systems exposed to γ-irradiation can be estimated from oxidant concentrations derived from simulations of radiolysis in the corresponding homogeneous systems and rate constants for the surface reactions. These simulations show that for all systems studied in this work, the molecular oxidants will be the most important oxidants for long irradiation times (>10 hours). Similar simulations of α-irradiated systems show that in systems relevant for a deep repository for spent nuclear fuel, only the molecular oxidants (mainly H₂O₂) are of importance for the dissolution of the fuel matrix.</p><p>The effect on UO₂ reactivity by irradiation of the material is of importance when predicting the spent fuel dissolution rate since the fuel, due to its content of radionuclides, is exposed to continuous self-irradiation. The effect of irradiation on the reaction between solid UO₂and MnO₄^- in aqueous solutions was studied. It was found that irradiation of UO2 at doses >40 kGy increases the reactivity of the material up to ~1.3 times the reactivity of unirradiated UO₂. The increased reactivity remains after the irradiation and can possibly be attributed to permanent changes in the material. This issue must be taken into account when predicting the reactivity of spent nuclear fuel since the fuel is exposed to doses >40 kGy after only a few days in the reactor.</p><p>It has earlier been suggested that the rate of a heterogeneous liquid-solid reaction depends on the size of the solid particles. This was investigated for UO₂particles in this thesis. Experimental kinetic parameters are compared to the previously proposed equations for UO₂ powder of four size fractions and a UO₂ pellet. We have found that the particle size dependence of the second order rate constant and activation energy for oxidation of UO₂ by MnO₄^- is described quite well by the proposed equations.</p>