Boron carbide is produced in a heat resistance furnace using boric oxide and petroleum coke as the raw materials. In this process, a large current is passed through the graphite rod located at the center of the cylindrical furnace, which is surrounded by the coke and boron oxide mixture. Heat generated due to resistance heating is responsible for the reaction of boron oxide with coke which results in the formation of boron carbide. The whole process is highly energy intensive and inefficient in terms of the production of boron carbide. Only 15% charge gets converted into boron carbide. The aim of the present work is to develop a mathematical model for this batch process and validate the model with experiments and to optimize the operating parameters to increase the productivity. To mathematically model the process and understand the influence of various operating parameters on the productivity, existing simple one-dimensional (1-D) mathematical model in radial direction is modified first. Two-dimensional (2-D) model can represent the process better; therefore in second stage of the project a 2-D mathematical model is also developed. For both, 1-D and 2-D models, coupled heat and mass balance equations are solved using finite volume technique. Both the models have been tested for time step and grid size independency. The kinetics of the reaction is represented using nucleation growth mechanism. Conduction, convection and radiation terms are considered in the formulation of heat transfer equation. Fraction of boron carbide formed and temperature profiles in the radial direction are obtained computationally. Experiments were conducted on a previously developed experimental setup consisting of heat resistance furnace, a power supply unit and electrode cooling device. The heating furnace is made of stainless steel body with high temperature ceramic wool insulation. In order to validate the mathematical model, experiments are performed in various conditions. Temperatures are measured at various locations in the furnace and samples are collected from the various locations (both in radial and angular directions) in the furnace for chemical analysis. Also, many experimental data are used from the previous work to validate the computed results. For temperatures measurement, pyrometer, C, B and K type thermocouple were used. It is observed that results obtained from both the models (1-D and 2-D) are in reasonable agreement with the experimental results. Once the models are validated with the experiments, sensitivity analysis of various parameters such as power supply, initial percentage of B4C in the charge, composition of the charge, and various modes of power supply, on the process is performed. It is found that linear power supply mode, presence of B4C in the initial mixture and increase in power supply give better productivity (fraction reacted). In order to have more confidence in the developed models, the parameters of one the computed results in the sensitivity analysis parameters are chosen (in present case, linear power supply is chosen) to perform the experiment. Results obtained from the experiment performed under the same simulated conditions as computed results are found in excellent match with each other.

Call number: LD2668 .T4 1961 N37

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Thesis (MScAgric)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: In South Africa tomato production in greenhouses normally occurs out of season when conditions are unfavourable for production and for the pollination process. Pollination is of special importance and the backbone of production. High temperatures contribute to the formation of abnormalities in flower morphology such as splitting of the anther cone and style exsertion. Low temperatures inhibit growth of the anther cone and therefore the style is uncovered. The movement of pollen from the anther to the style is inhibited by the higher style position in relation to the anther cone. Under humid conditions the pollen tends to stick to the anther surface. Another factor contributing to the problem is the banning of European bumble bees in South Africa. Alternative methods of pollen transport have to be found. Truss vibration, honey bees and plant growth regulators (PGR) are the most popular alternatives. Truss vibration and the use of PGR's are labour intensive and honey bees tend to get disorientated inside a plastic greenhouse. During the first part of this study pollen from plants, grown at four different B-levels (0.02; 0.16; 0.32 and 0.64 mg rl) was germinated in vitro. It was kept at different temperatures and periods before incubating on different growth media. No proof was found that pollen from B-deficient plants germinated poorly. Germination of pollen decreased significantly after one week storage. Deterioration of pollen viability could be lowered by storage at 5°C. At least 10% sucrose is needed in the growth medium for in vitro germination but addition ofB had no positive effect. In a second phase of the study, the influence of the mentioned B application rates were tested. The experiment was done in a glasshouse where temperatures were mechanically regulated (22°C and 10°C day/night). Seedlings of the greenhouse tomato cultivar, Abigail, were planted in acid washed river sand. Plants were grown with the main stem trellised vertically and the side shoots removed weekly. Only the first, third and fourth cluster were used for this part of the study. The uptake of all the essential nutrient elements, fruit set, the relation of larger to smaller fruits, physical and chemical quality and fruit shelf life were evaluated. The application of B at higher rates increased the uptake of Ca and decreased K-uptake. Fruit set, fruit development, fruit color and shelf life were the best at a B-Ievel of 0.16 mg r'. At this rate the abortion of flowers was the least. The same plants were used for the second part of the study, using the third cluster. The influence of the same four B-Ievels, the relative humidity (RH) of the truss atmosphere and truss vibrations were tested. The second cluster was covered with a plastic bag. Dry {<I 0% relative humidity (RH)}, normal {60-7S% RH} and moist {8S-97% RH} air were constantly applied to the bags at ± 50 ml min-I. As a third factor, truss vibration was applied daily by means of an electric vibrator (polli-bee), The amount of flowers per cluster, fruits per cluster, fruit set, weight of the cluster (yield), fruit weight, seed production, fruit weight per amount of seeds formed and fruits with blossom-end-rot (BER) were evaluated. The application of higher B-Ievels, air with the normal RH and the vibration of the clusters positively affected fruit weight, weight of the cluster and fruit set. High RH increased the occurrence of BER, probably due to a lack of transpiration from the fruit surface and therefor a lack in Ca translocation. / AFRIKAANSE OPSOMMING: Die verbouing van kweekhuistamaties in Suid-Afrika geskied meestalonder toestande wat ongunstig is vir produksieprosesse en veral die bestuiwingsproses wat die basis van produksie is. Onder toestande van hoë temperature is die voorkoms van afwykings in die blommorfologie (gesplete meeldraadbuis en verlengde styl) algemeen. Net so, onder toestande van lae temperature, sal gebrekkige groei van die meeldraadkrans ook tot die blootstelling van die stempel lei. Die oordraging van die stuifmeel vanaf die helmknop na die stempel word hierdeur benadeel. Tydens humiede toestande mag vasklewing van stuifmeel aan die helmknoppe ook die beweging van stuifmeel belemmer. 'n Verdere faktor wat tot die probleem bydra is die verbod op die invoer van hommelbye uit Europa. Alternatiewe metodes vir oordraging van stuifmeel moet dus gevind word. Trosvibrasie, heuningbye en die gebruik van plantgroeireguleerders (PGR's) is die mees populêre alternatiewe. Trosvibrasie met 'n 'polli-bee' en die aanwending van PGR's is arbeidsintensief. Heuningbye ondervind navigasieprobleme in plastiek kweekhuise en is nie so effektief as hommelbye nie. Tydens die eerste fase van die ondersoek is stuifmeel vanaf plante, wat by vier verskillende Bvoedingspeile (0.02; 0.16; 0.32 en 0.64 mg rl) verbou is, versamel en in vitro ontkiem. Dit is by verskillende temperature en periodes opgeberg en op verskillende media vir ontkieming geïnkubeer. Geen bewyse kon gevind word dat stuifmeel vanaf B-gebrekkige plante swak ontkiem nie. Kiemkrag van stuifmeel het na sewe dae opberging betekenisvol verswak. Verswakking in kiemkrag kon beperk word deur die stuifmeel by SoC op te berg. 'n Ontkiemingsmedium met ten minste 10% sukrose is vir goeie in vitro ontkieming van stuifmeelkorrels nodig terwyl die byvoeging van B geen voordelige effek getoon het nie. Tydens die tweede gedeelte van hierdie ondersoek is die invloed van die genoemde vier B-voedingspeile ondersoek. Die ondersoek is in 'n glashuis, waarvan die temperature meganies beheer is (22°C en 10°C dag/nag), uitgevoer. Plantmateriaal van die kweekhuistamatiekultivar, Abigail, is in suurgewasde riviersand geplant. Hoofstamme is vertikaalopgelei en die sylote is een maal per week uitgebreek. Die eerste, derde en vierde bloeiwyses is vir die ondersoek gebruik. Die opname van al die essensiële voedingselemente (blaarontledings), vrugset, die verhouding van groot vrugte tot kleiner vrugte, fisiese en chemiese kwaliteite van die vrugte en die raklewe daarvan is ge-evalueer. Die toediening van B teen hoër peile het die opname van Ca ten koste van K bevoordeel. Die beste resultate ten opsigte van vrugset, vrugontwikkeling, vrugkleur en die houvermoë (raklewe) van die vrugte is verkry teen 'n B-toedieningspeil van 0.16 mg.l'. Vir die derde gedeelte van die ondersoek is die tweede tros van dieselfde aanplanting gebruik. Die invloed van die vier B-voedingspeile, relatiewe humiditeit (RH) van die omgewing rondom die tros en trosvibrasie is ondersoek. Die tweede bloeiwyse is met 'n deursigtige plastieksakkie bedek. Droë {dO% relatiewe humiditeit (RH)}, normale {60-75% RH} en vogtige {85-97% RH} lug is teen 50 ml min-1 oor die tros gestuur. Trosvibrasie is as derde faktor teen twee peile gebruik deur trosse daagliks met 'n elekriese vibreerder ("polli-bee') te vibreer. Die aantal blomme per tros, vrugte per tros, vrugset, trosmassa (opbrengs), vrugmassa, aantal sade, vrugmassa per saad en blom-end-verrotting (BER) is ge-evalueer. Die toediening van hoër B-voedingspeile, 60-75% RH lug en trosvibrasies het vrugmassa, trosmassa en vrugset bevoordeel. Hoë lugvog het die omvang van BER verhoog, waarskynlik weens 'n gebrek aan transpirasie vanaf die vrugoppervlakke wat aanleiding tot 'n beperking in translokasie van Ca kon gee.

The stable isotopes of the conservative element boron, 11B and 1°B, have been employed as co- migrating isotopic tracers to determine the origin of nitrate observed in groundwater from a large capacity (2500 gpm) irrigation well in the Avra Valley of southeastern Arizona. The isotopic ratios of the conservative element, boron, provided an identifying signature for various nitrate rich source waters. Additional chemical parameters were also examined to corroborate the isotopic indications. Findings of this investigation indicate that most of the nitrate observed in groundwater from well CMID 18 at the beginning of the 1993 irrigation season was due to municipal wastewater contamination. As the irrigation season progressed, an increasing proportion of nitrate was contributed by irrigation return flow from neighboring agricultural fields.

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Submitted in fulfillment of the requirements for the award of the Degree of Master of Applied Science in Chemistry, Durban University of Technology, Durban, South Africa, 2016. / The 𝛼-aminophosphonates (APs) and dihydropyrimidinones (DHPMs) exhibit a wide range of important biological activities. The great potential of these compounds in biological applications prompted an increased interest in the development of efficient synthetic methods for their preparation. A novel rhodium supported boron nitride (RhBNT) material was synthesized by simply mixing boron nitride in a solution of rhodium acetate, under inert atmosphere for 7 days followed by filtration; the yield was 95 %. It exhibited excellent catalytic properties for the synthesis of 13 novel APs and 5 DHPMs. Characterization of RhBNT was performed by several techniques: the crystalline nature of RhBNT and nano size was confirmed by SEM spectroscopy, EDX pattern for RhBNT showed signals for rhodium metal, the Brumnauer-Emmett-Teller (BET) analysis showed the specific surface area of RhBNT to be 28.12 m2/g, pore volume 0.23cm3/g and pore size of 199.8Aº thereby suggesting RhBNT as a potentially effective catalyst for organic reactions; the mesoporous nature of the material was established by a type- IV adsorption isotherm; the DSC-TGA Profile indicates that RhBNT has good thermal stability and can be used adequately for catalysis. The DSC curve showed evidence of a broad exothermic peak. The RhBNT was subsequently used in the Kabachnik-Fields and Biginelli reaction in order to assess its catalytic potential. Herein Vilsmeier-Haack reagent was used to synthesize 4-oxo-chromene-3-carbaldehyde and 4-oxo-4H-benzo[h]chromene-3- carbaldehyde from 2-hydroxyacetophenone and 1-hydroxy-2-acetonaphthone, respectively. These two carbaldehydes were subsequently used to synthesize thirteen novels APs and five DHMPs using RhBNT as the catalyst The antimicrobial activities of the synthesized compounds were assessed against Escherichia coli, Bacillus cereus, Micrococcus luteus, Staphylococcus aureus and Candida albicans using the disc diffusion method. It was found that none of the compounds inhibited growth of bacteria or fungus. The assessment of toxicity was evaluated by using the brine shrimp lethal test. It was found that six of the novel compounds exhibited more than 50% brine shrimp death and were considered toxic against Artemia sp. and hence unsuitable as a potential drug whilst four compounds were found to be less toxic, exhibiting a brine shrimp death of less than 50%. Molecular docking studies were carried out for 13 APs to estimate their binding interactions with HIV-1 reverse transcriptase. Four APs showed good potential for the inhibition of HIV-1 reverse transcriptase. / M

Thesis advisor: James P. Morken / This dissertation will discuss in depth four main projects pertaining to the synthesis and utility of organoboronates for the construction of enantioenriched small molecules. First, reaction optimization and substrate scope expansion of the platinum-catalyzed enantioselective diboration of alkenes are reported. Based on extensive experimental and computational mechanistic analysis, a preliminary stereochemical model is also proposed. A practical boron-Wittig reaction is presented in which synthetically challenging di- and trisubstituted vinyl boronates can be accessed in a highly stereoselective fashion from readily available starting materials. The enantioselective diboration of cis- and trans-vinyl boronates furnished novel 1,1,2-tris(boronate) esters in up to 95:5 er. The intermediate tris(boronate) esters were employed successfully in deborylative alkylations to furnish enantioenriched internal vicinal bis(boronates) in excellent diasteoselectivity. In the final chapter, an enantioselective palladium-catalyzed intramolecular Suzuki-Miyaura coupling between allyl boronates and aryl electrophiles is disclosed. The newly developed transformation provides enantioenriched 5, 6, and 7-membered carbocycles in up to 93:7 er. / Thesis (PhD) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.