Thesis. 1977. Sc.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Vita. / Includes bibliographies. / Sc.D.

The knowledge of particle size and size distribution are important parameters for understanding the behavior of numerous colloid systems. These areas include for example, clays, viruses, paints and blood. Until recently this information could be obtained only by the use of expensive, slow and complex instrumentation. Hydrodynamic chromatography provides a means of investigating particles in the submicron and micron region. The separation mechanism of this method is based upon the flow parameters with which the solute particles interact as they pass through a packed column. In the past the interpretation of these chromatograms has been based upon the mathematical modeling of the column parameters. We have developed a new multiwavelength detector system to be used in conjunction with hydrodynamic chromatography which provides size and concentration information of the eluant directly. The result is a rugged system that provides size and size distribution information rapidly and at low cost. / Ph. D.

Conservation tillage tobacco production has gained little producer acceptance since introduction in the late 1960's. Yield reductions, tobacco quality issues, unacceptable weed control, and inadequate planting equipment limited practice adoption and substantiated the need for continued research. The recent developments of a Subsurface Tiller-TransplanterTM and the herbicide SpartanTM renewed producer interest in conservation tillage and led to an investigation with both flue-cured and Virginia dark-fired tobacco. Flue-cured tobacco was transplanted into rye mulch on bedded rows and subsequently cultivated at various timings. Conservation tillage significantly reduced soil erosion approximately 92 percent and tobacco yield approximately 23 percent when row cultivation was not applied. Row cultivation significantly increased tobacco yield without increasing soil erosion. The yield of conservation tillage tobacco receiving a minimum of two cultivations was similar to conventional tobacco. The second study evaluated wheat, rye, crimson clover, and mixtures of crimson clover with either wheat or rye as cover crop mulches for conservation tillage production of Virginia dark-fired tobacco. Conservation tillage, regardless of cover crop, reduced dark-fired tobacco yields approximately 779 and 488 pounds per acre in 1996 and 1997, respectively. The removal of cover crop residue for hay did not lower tobacco yield compared to leaving residue on the soil surface. Row cultivation increased conservation tillage tobacco yield approximately 247 pounds in 1997 regardless of cover crop. The nitrogen contribution of crimson clover was minimal in both years of the study and did not affect tobacco performance. / Master of Science

Yes / Mechanochemical synthesis has the potential to change the way in which chemistry is conducted, particularly with regard to removing or dramatically reducing the need for solvents. Recently, it has been demonstrated that mechanochemistry can be carried out continuously and on large scale through the use of twin-screw extrusion (TSE). TSE has successfully been applied to the synthesis of cocrystals, metal organic frameworks (MOFs), deep eutectic solvents (DESs), metal complexes, and organic condensation reactions. However, while TSE provides a route for mechanochemical synthesis to be developed into a continuous, high-volume manufacturing process, little is currently understood about how to best optimize the various process parameters involved. Herein, we investigate the use of a batch mixer that has been previously used in polymer processing, to optimize mechanochemical reactions performed by extrusion. In particular, reactions between 8-hydroxyquinoline (Hq) and metal acetate salts of zinc or aluminum to give quinolinate complexes Znq2·AcOH and Alq3·AcOH, which are of interest for organic light-emitting diode (OLED) applications, have been investigated. The manner in which the progress of the reaction correlates with the machine torque, temperature, and specific mechanical energy (SME) imparted by the batch mixer has been elucidated. Significantly, this knowledge enabled optimization of the mechanochemical reactions by TSE through the key parameters of screw speed, feed rate, temperature, and particle size. / EPSRC (EP/L019655/1).

Thesis: M.S., Massachusetts Institute of Technology, Department of Chemical Engineering, 1975 / Includes bibliographical references. / M.S. / M.S. Massachusetts Institute of Technology, Department of Chemical Engineering

Master of Science / Department of Grain Science and Industry / Keith C. Behnke / The effect of tracer particle size on the accuracy of measuring retention time inside the conditioner of a pellet mill was studied. Three experiments were conducted using tracers with different particle sizes. The control retention time was calculated using the hold-up capacity method, while retention times for treatments were calculated using the pulse-input method. In addition to the previously prepared tracers, crystalline salt and powder color dye were used as tracers in this study to represent small particle tracers. In experiment one, large, medium, and small tracers were used. The treatment with large particle size was closer to the control with differences around 1.5%. Conversely, using the tracer with small particle size resulted in larger differences, approximately 18%. Two tracers were used in experiment two, resulted in 33% difference between treatment and control using a small particle size tracer, and a 10% difference using a tracer with similar particle size to the main materials. A tracer similar in particle size to the materials flowing inside the conditioner was used in the third experiment in addition to the salt and dye. Statistical analyses for this experiment indicated that particle size affects the accuracy of retention time measurements. There was a significant difference (P<0.05) in the comparison between salt and red color dye in treatment two, while there was no significant difference (P>0.05) between them in treatment one (same particle size). Moreover, in another comparison of the differences between treatments and their related controls, there was significant difference (P<0.05). However, the P-value for the red dye comparison (0.0126) was higher than that of salt (0.0026), which adds density as another influential factor that affects retention time measurement.

Spray Polyurethane Foam insulation (SPF) kits are currently being marketed and sold to do-it-yourselfers to meet various insulating needs. Like commercial SPF systems, the primary health concern with SPF kits is user overexposure to the isocyanates during product application. The potential health risk associated with SPF applications is driven by several factors including (but not limited to): the toxicity of isocyanates; the potentially high exposure intensity; the quantity of isocyanates used in the process; the enclosed nature of the environment in which the product could be applied; the potentially high exposure duration/frequency; and the limited availability of control measures to reduce agent intensity (e.g., personal protective equipment, dilution ventilation). To better understand the potential hazards associated with the use of SPF kits, the current study was designed to provide an initial characterization of user exposure to airborne particulate during the application process. Specifically, the study would aim to answer the following: * What is the particle size distribution of the aerosol a SPF kit user is exposed to during application? * What is the airborne particle mass concentration a SPF kit user is exposed to during application? To answer these questions, a single commercially available SPF kit was selected for use and a mock residential environment was constructed to support repeated applications of SPF. Size-selective and total dust air sampling were conducted during the applications to determine the particle size distribution and mass concentration of aerosols generated by the selected kit. The particle size distributions developed from the size selective sampling results showed the presence of airborne particulate capable of penetration to the gas exchange regions of the respiratory tract. The average mass median diameter and geometric standard deviation of the particle size distributions were 4.6 µm and 2.7 respectively. The total dust sampling results showed mean airborne concentrations of 10.40 mg/m3. Based on the sampling results the study, personal air monitoring is needed to assess the degree of user exposure to methylene diphenyl diisocyanate (MDI) and to provide information for the selection of exposure control methods.

No description available.

Doctor of Philosophy / Department of Animal Sciences and Industry / Joe D. Hancock / A total of 2,840 1-d-old broiler chicks and 450 1-d-old layer chicks were used in three experiments to determine the nutritional value of corn- and sorghum-based diets in poultry reared in West Africa. In the broiler experiments, birds fed corn had greater average daily gain (P < 0.001) with similar carcass weight and yield for birds fed corn- vs sorghum-based diets (P > 0.18). Particle size treatments did not affect growth performance or carcass characteristics (P > 0.20). In the layer experiment, birds fed sorghum had greater body weight at d 126 (P < 0.001), started laying earlier (P < 0.01), ate more feed (P < 0.01), and produced more eggs (P < 0.01) than birds fed the corn-based diet. However, there was no difference in average egg weight among birds fed corn vs sorghum (P > 0.85). In conclusion, sorghums produced in West Africa are a good alternative to corn when fed to broiler chicks and laying hens.

Thesis (MSc)--Stellenbosch University, 2004 / ENGLISH ABSTRACT: The main aim of this study is to establish a standard procedure for all sedimentary particle size analysis methods specifically for clay minerals and mixtures thereof. Not only will it improve accuracy and reproducibility during clay size analysis, it will also secure comparability between different operators. As a start, all the apparatus-related parameters that can affect the accuracy and reproducibility were determined for the apparatus used, viz. the Sedigraph SOOOD. Thereafter, these parameters were kept constant, and the effects of potential material-related parameters were investigated one-by-one. First to be investigated were those parameters relating specifically to sample preparation. They were: grinding intensity, chemical dissolution of cementing materials, duration of prior soaking, salt content, centrifugal washing with polar organic liquids, deflocculant type and concentration, the effect of pH, ultrasonic time, and stirring during ultrasonic treatment. Then, the influence on accuracy and reproducibility of the physical and chemical parameters related to the suspension was determined. They were: the use of the viscosity and density of water to calibrate the apparatus in stead of those of the suspension liquid, hydrolysis of the deflocculant with suspension-ageing, and the effect of solid concentration on hindered settling. During this investigation a novel method was developed to enable faster and more accurate pycnometric density determinations. Next, the unique characteristics of clays, which can influence the results of sedimentary particle size analyses, were examined. Serious problems are encountered with the accuracy of the analyses of some clay types abundantly found in nature, viz. the smectites and mixed-layered clay minerals. Due to their swelling in water, and variations in the amounts of their crystal layers, they experience unpredictable changes in particle size. The latter is caused by the following external factors: clay type, humidity, type of exchange cation, electrolyte concentration, clay concentration, pH, deflocculant type and concentration, pressure history of the swell-clay suspension, and ageing of the suspension. The effect of each of them on the accuracy and reproducibility of the sedimentary particle size analysis of clays are investigated in detail. Another problem that influences the accuracy of the sedimentary methods is that owing to swelling, the densities of smectites and mixed-layered clays change by varying degrees when suspended in water. It is, however, impossible to pycnometrically determine the density of a swell-clay since it absorbs a part of the water used for its volume determination. To solve this problem, a novel method was devised to calculate swell-clay density. This method makes use of existing Monte Carlo simulations of the swelling mechanism of montmorillonite. During all sedimentary methods, an average clay density is normally used to calculate the particle size distribution of clay mixtures. However, if there is a large enough difference between the calculated average density and that of a component, then inaccurate results will be recorded. The magnitude of this effect was investigated for a few self-made clay mixtures, which consisted of different proportions of kaolinite, illite, and montmorillonite. Based on all the above results, a practical approach to, and a standard methodology for all the sedimentary methods of particle size analysis of clay minerals are presented. Additionally, a condensed summary is provided in table-form, which contains the magnitudes of the errors associated with each of the parameters that were examined. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie is om 'n standaard prosedure daar te stel vir alle sedimentêre metodes van partikelgrootte analise, spesifiek vir gebruik met kleiminerale en mengsels daarvan. So 'n standaard prosedure sal die akkuraatheid en herhaalbaarheid van klei-analises verbeter, en die vergelykbaarheid tussen verskillende operateurs verseker. Aanvanklik is slegs die parameters bepaal wat die akkuraatheid en herhaalbaarheid van die gekose apparaat (Sedigraph 5000D) kan beïnvloed. Daarna is al hierdie parameters konstant gehou, en is die potensiële effekte van die moontlike materiaal-verwante parameters een na die ander ondersoek. Eerstens is die invloed van monstervoorbereiding op akkuraatheid en herhaalbaarheid bepaal. Verskillende parameters nl. maal-intensiteit, chemiese oplossing van sementerende materiale, sentrifugale wassing met polêre organiese vloeistowwe, tipe ontvlokker en konsentrasie, die effek van pH, ultrasoniese tyd en die effek van roer tydens ultrasonikasie is ondersoek. Vervolgens is die invloed op die akkuraatheid en herhaalbaarheid van die fisiese en chemiese parameters verwant aan die suspensie bepaal. Hierdie parameters was nl. die gebruik van die viskositeit en digtheid van water in plaas van dié van die suspensievloeistof, hidrolise van die ontvlokker tydens suspensieveroudering, asook die effek van vastestof-konsentrasie op belemmerde uitsakking. Gedurende hierdie ondersoek is ook 'n nuwe metode ontwikkel wat vinniger, en meer akkurate piknometriese digtheidsbepalings moontlik maak. Die unieke eienskappe van kleie wat die resultate van sedimentêre metodes van partikelgrootte analises kan beïnvloed, is volgende ondersoek. Tydens die analises van party kleie wat baie volop in die natuur voorkom, nl. die smektiete en menglaag-kleie, word ernstige akkuraatheids-probleme ondervind. Hul swelling in water, tesame met variasies in hul aantal kristal-lagies, veroorsaak onvoorspelbare verandering van hul partikelgroottes. Laasgenoemde word deur die volgende eksterne faktore veroorsaak: klei tipe, humiditeit, tipe uitruil-katioon, elektrolietkonsentrasie, kleikonsentrasie, pH, ontvlokker-tipe en konsentrasie, drukgeskiedenis van 'n swelklei-suspensie, en veroudering van die suspensie. Die effek van elk op die akkuraatheid en herhaalbaarheid van die sedimentêre partikelgrootte analises van kleie word in detail bespreek. 'n Verdere probleem wat die akkuraatheid van sedimentêre metodes beïnvloed, is dat wanneer smektiete en menglaag-kleie in water gesuspendeer word, hulle digthede in verskillende mates weens swelling verander. Dit is egter onmoontlik om die digtheid van swelkleie in water piknometries te bepaal, omdat swelklei 'n gedeelte van die water absorbeer wat gebruik moet word om die kleivolume mee te bepaal. Om hierdie probleem op te los, is 'n nuwe metode ontwikkelom die digtheid van swelkleie mee te bereken. Die metode maak gebruik van reedsbestaande Monte Carlo simulasies van die swelling van montmorillonite. Tydens alle sedimentêre metodes word normaalweg van 'n gemiddelde kleidigtheid gebruik gemaak om die partikelgrootte-verspreiding van kleimengsels mee te bereken. Indien die berekende gemiddelde digtheid egter genoegsaam met dié van 'n kleikomponent verskil, sal onakkurate resultate verkry word. Hierdie effek is ondersoek vir 'n paar selfgemaakte kleimengsels wat uit verskillende hoeveelhede kaoliniet, illiet, en montmorilloniet bestaan het. Laastens word 'n praktiese benadering en 'n standaard metode vir alle sedimentêre metodes voorgestel, wat gebaseer is op al die bogenoemde resultate. 'n Verkorte opsomming, met die groottes van die foute geassosieer met elke parameter wat ondersoek is, word laastens in tabelvorm verskaf.