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Dépôts électrochimiques d’argent, de palladium et d’alliages argent-palladium en solvants eutectiques profondsRayee, Quentin 13 March 2020 (has links) (PDF)
Le recours aux solvants eutectiques profonds se présente comme une alternative potentielle aux limitations rencontrées en milieux aqueux pour la réalisation de dépôts électrochimiques. La transposition des procédés électrochimiques des milieux conventionnels vers ces nouveaux milieux n’est pas immédiate et nécessite d’entreprendre des études fondamentales visant à comprendre l’impact de la nature des solvants eutectiques profonds sur différents processus survenant à l’interface électrochimique. Dans cette optique, le présent travail examine les mécanismes impliqués dans la formation de dépôts d’argent, de palladium et du mélange Ag-Pd en solvants eutectiques profonds à l’aide de plusieurs techniques voltampérométriques (voltampérométries cyclique, différentielle, alternative, hydrodynamique, à balayage linéaire) et de mesures chronoampérométriques. Le choix du dépôt d’argent a été retenu comme système modèle et a été étendu à la réalisation d’alliage Ag-Pd qui présente un intérêt plus appliqué. Les solvants eutectiques profonds sélectionnés pour cette recherche sont obtenus en mélangeant du chlorure de choline avec de l’urée (ChCl-U) ou avec de l’acide oxalique (ChCl-Ox). Le comportement électrochimique de AgCl en ChCl-U est fortement affecté par la nature de l’électrode. Sur carbone et platine, une importante surtension pour le dépôt à 3D est requise, alors qu’aucune surtension n’est nécessaire sur électrode d’or en raison d’un processus de dépôt à 2D (dépôt en soustension) de l’argent sur l’or. Ce mécanisme de dépôt en sous-tension est peu sensible à la nature du solvant eutectique profond et très similaire à celui obtenu en solution aqueuse avec une concentration équivalente en chlorures. Le recours à des monocristaux a permis d’examiner l’influence de la cristallographie sur le dépôt en sous-tension. Une attention particulière a été portée à la présence de thiourée en milieu ChCl-U et celle-ci affecte profondément les dépôts métalliques d’Ag en modifiant la coordination des espèces Ag(I) et l’adsorption des espèces constitutives du ChCl-U à la surface d’une électrode d’or. Les mesures voltampérométriques du PdCl2 en ChCl-U ont permis de distinguer quatre régions en potentiel où ont lieu respectivement (des potentiels les plus positifs vers les plus négatifs) un dépôt en sous-tension confirmé par des mesures de désorption oxydative de CO, un dépôt à 3D, la formation d’hydrure de palladium (PdHx) et, à des potentiels bien inférieurs, un processus d’inhibition du dépôt. L’utilisation du ChCl-Ox a mis en évidence que la formation de PdHx dépendait du pH apparent du solvant eutectique. L’étude du mélange de AgCl et de PdCl2 a révélé la coexistence de phases distinctes associées à des alliages de différentes compositions formés lors du dépôt électrochimique. Les proportions entre les différentes phases sont très sensibles aux conditions de température, potentiel de dépôt et concentration des précurseurs métalliques, et l’influence de ces différents paramètres est discutée en détail. De plus, un processus de remplacement galvanique de l’argent par le palladium a également été mis en évidence avec l’appui de mesures XPS. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished
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Dizajniranje, fizičko-hemijska karakterizacija, toksičnost i primena nove klase funkcionalizovanih jonskih tečnosti / Design, physico-chemical characterisation, toxicity and application of newly class of functionalized ionic liquidsAleksandar Tot 03 July 2019 (has links)
<p>U ovoj doktorskoj disertaciji sintetisane su dve različite klase jonskih tečnosti, na bazi imidazolijuma i holinijuma, sa ciljem snižavanja toksičnosti. Imidazolijumove jonske tečnosti su funkcionalizovane hidroksilnom i etarskom grupom u bočnom lancu. Uspešnost sinteza jonskih tečnosti potvrđena je snimanjem IC i NMR spektara. Izmerene su gustine, viskoznosti i provodljivosti čistih imidazolijumovih i holinijumskih jonskih tečnosti. Na osnovu dobijenih eksperimentalnih rezultata,potpomognutim računarskim simulacijama diskutovana je strukturna organizacija između katjona i anjona. Utvrđeno je da prisustvo hidroksilne grupe u bočnom lancu imidazolovog katjona, značajno utiče na lokaciju anjona i samim tim na makroskopska svojstva. U nastavku su izmerene gustine i viskoznosti vodenih rastvora sa ciljem dobijanja informacija o uticaju dodatka holinijumskih i imidazolijumovih jonskih tečnosti na strukturu vode. Na osnovu B koeficijenta iz<br />viskoznosti, ekspanzibilnosti i rezultata simulacija molekulske dinamike, utvrđeno je da sve jonske tečnosti imaju structure making osobine. Takođe, na osnovu izračunatih specifičnih molarnih zapremina i doking analize na receptoru za gorak ukus,<br />ustanovljeno je da vodeni rastvori holinijumskih jonskih tečnosti imaju gorak ukus.<br />Toksičnost funkcionalizovanih imidazolijumovih jonskih tečnosti ispitana je na nekoliko biljnih vrsta (pšenica, ječam i krastavac), kao i na larvama <em>A. salina</em> i ćelijskoj liniji MRC-5. Potvrđeno jeda uvođenje hidroksilne grupe u alkil niz najviše se redukuju<br />toksičnosti imidazolijumovih jonskih tečnosti, dok je uticaj etarske grupe na smanjenje toksičnosti značajno manji. Ispitivanje citotoksičnosti i antibakterijske aktivnosti ukazalo je da holinijumske jonske tečnosti se mogu smatrati netoksičnima, i<br />pokazuju beningnije dejstvo u poređenju sa njihovim polaznim komponentama (askorbinska kiselina, biotin i nikotinska kiselina).</p> / <p><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:TrackMoves/> <w:TrackFormatting/> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:DoNotPromoteQF/> <w:LidThemeOther>EN-US</w:LidThemeOther> <w:LidThemeAsian>X-NONE</w:LidThemeAsian> <w:LidThemeComplexScript>X-NONE</w:LidThemeComplexScript> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> <w:SplitPgBreakAndParaMark/> <w:DontVertAlignCellWithSp/> <w:DontBreakConstrainedForcedTables/> 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UnhideWhenUsed="false" Name="Colorful Grid Accent 6"/> <w:LsdException Locked="false" Priority="19" SemiHidden="false" UnhideWhenUsed="false" QFormat="true" Name="Subtle Emphasis"/> <w:LsdException Locked="false" Priority="21" SemiHidden="false" UnhideWhenUsed="false" QFormat="true" Name="Intense Emphasis"/> <w:LsdException Locked="false" Priority="31" SemiHidden="false" UnhideWhenUsed="false" QFormat="true" Name="Subtle Reference"/> <w:LsdException Locked="false" Priority="32" SemiHidden="false" UnhideWhenUsed="false" QFormat="true" Name="Intense Reference"/> <w:LsdException Locked="false" Priority="33" SemiHidden="false" UnhideWhenUsed="false" QFormat="true" Name="Book Title"/> <w:LsdException Locked="false" Priority="37" Name="Bibliography"/> <w:LsdException Locked="false" Priority="39" QFormat="true" Name="TOC Heading"/> </w:LatentStyles></xml><![endif]--><!--[if gte mso 10]><style> /* Style Definitions */ table.MsoNormalTable{mso-style-name:"Table Normal";mso-tstyle-rowband-size:0;mso-tstyle-colband-size:0;mso-style-noshow:yes;mso-style-priority:99;mso-style-qformat:yes;mso-style-parent:"";mso-padding-alt:0in 5.4pt 0in 5.4pt;mso-para-margin-top:0in;mso-para-margin-right:0in;mso-para-margin-bottom:10.0pt;mso-para-margin-left:0in;line-height:115%;mso-pagination:widow-orphan;font-size:11.0pt;font-family:"Calibri","sans-serif";mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:"Times New Roman";mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;}</style><![endif]--></p><p class="MsoNormal">In this doctoral thesis, ionic liquids based on imidazolium and cholinium cation were synthesized, in order to obtain new class of ILs with reduced toxicity. Imidazolium based ionic liquids were functionalized with hydroxyl and ether group in order to reduce their lipophilicity. All newly synthesized compounds were confirmed by measuring IR and NMR spectra. For pure ionic liquids, density, conductivity and viscosity were measured. Based on the obtained experimental results supported with results of molecular simulations, it was concluded that presence of oxygen in alkyl side chain of imidazolium ionic liquids significantly contribute to position of anion. Further, density and viscosity of diluted aqueous ILs solutions were measured with a purpose to investigate their influence on water structure. Based on obtained values for viscosicty B coefficient, expansibility and from MD simulations, all ionic liquids express structure making tendency. From calculated specific apparent molar volumes for cholinium ionic liquids it was noted bitter taste. The toxicity of functionalized imidazolium ionic liquids was investigated on different plant species (wheat , barley and cucumber), on larvae of <em><span style="font-family:"Calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi"> A. salina</span></em> and cell line MRC-5. From<br />obtained results it was concluded that introduction of hydroxyl group in alkyl side chain reduce toxicity significantly more than ether group. Experiments on cytotoxicicity and antibacterial effects allowed to conclude that those newly synthesized cholinium ionic liquids can be considered as non-toxic.</p>
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Caractérisations de matériaux pour la réalisation de supercondensateurs pour des applications automobiles / Characterization for materials for electrochemical capacitor and its further use in automotive applicationsLiu, Yinghui 03 May 2018 (has links)
Dans le cadre d’une Convention CIFRE, la thèse est financée par la société Renault, ce travail vise à développer un supercondensateur carbone-carbone dont le coût de fabrication est compatible avec le marché automobile ; c’est en effet leur coût élevé qui constitue encore à l’heure actuelle un frein à leur développement. Dans une première partie de ce travail, il a été montré que l’essentiel du coût repose en grande partie sur la purification de l’électrolyte utilisé mais surtout du carbone activé, qui est le matériau actif d’électrode. Notre travail s’est donc focalisé sur l’étude du vieillissement électrochimique de cellules de supercondensateurs de laboratoire assemblées avec différents carbones, afin d’essayer d’identifier les phénomènes responsables du vieillissement. Un autre objectif a été d’identifier les caractéristiques que doivent présenter les carbones alternatifs candidats au remplacement des carbones commerciaux. L’étude réalisée dans ce travail de thèse a permis de définir deux modes de vieillissement différents suivants les carbones utilisés. Un premier type de vieillissement entraîne l’augmentation conjointe de la résistance série équivalente et de la capacité, dû à une dégradation/oxydation du carbone à l’électrode positive. Un second mode de vieilissement mène à l’augmentation seule de la résistance série équivalente par la formation d’une couche d’interface solide conductrice ionique. Quelque soit le mode vieillissement, aucune corrélation directe n’a pu être établie avec les fonctions de surface des carbones activés. La piste la plus probable repose sur le taux et la nature des impuretés présentes dans le carbone activé, certaines étant électroactives, voire pouvant jouer un rôle catalytique. / In the context of a CIFRE Convention, the thesis is financed by Renault s.a.s., this work aims at developing a carbon-carbon supercapacitor whose manufacturing cost is compatible with the automotive market, which still hinders their development. In a first part of this work, it has been shown that the cost mainly depends on the purity of the materials used: electrolyte but also activated carbon, the electrode active material. Our work has therefore been focused on the study of the electrochemical aging of laboratory supercapacitor cells assembled with different carbons, to identify their ageing mechanisms and to define the key features alternative carbons must achieve to replace commercial carbons. This work has evidenced two different modes of aging, depending on the carbon used. A first ageing mode results in the joint increase of the equivalent series resistance as well as the capacity, due to a degradation / oxidation of the carbon at the positive electrode. A second mode leads to the sole increase in equivalent series resistance by the formation of an ionic conductive solid interface layer. Whatever the aging mode, no clear influence of the surface functions of activated carbons could be evidenced. The most likely assumption is based on the content and the nature of the impurities present in the activated carbon, some of which are electroactive and can even play a catalytic role.
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Approche physico-chimique de la formulation de bêta-lapachone complexée ou non à des cyclodextrines, dans des préparations liposomales / Physico-chemical approach to the formulation of beta-lapachone, and its complexes with cyclodextrins, in liposomesWu, Xiao 19 October 2018 (has links)
La bêta-lapachone (b-lap) est une substance active présentant des activités trypanocides, anti-infectieuses et anticancéreuses, avec une sélectivité thérapeutique. Cependant, en raison de sa faible hydrosolubilité et de sa toxicité, b-lap n'est pas encore appliquée en clinique. Nous avons étudié son encapsulation dans des vésicules phospholipidiques, complexée ou non par des cyclodextrines. Nous avons d'abord analysé l'interaction de b-lap avec des excipients lipidiques par des mesures de pression de surface, DSC et SAXS. Elles ont montré que blap est insérée dans les bicouches lipidiques, proche des têtes polaires avec une solubilité maximale d'environ 3,5 mol%. Les résultats expérimentaux ont été confirmés par des simulations de dynamique moléculaire. Le taux d'encapsulation (ER%) de b-lap dans les liposomes s’est avéré en accord avec sa solubilité maximale dans les lipides. Des complexes b-lap:cyclodextrines ont été formés et incorporés dans le coeur aqueux de liposomes déjà chargés en b-lap. Des ER% plus élevés ont été obtenus, mais avec une efficacité d'encapsulation plus faible. Des tests in vitro sur des lignées cellulaires épithéliales et tumorales de prostate ont démontré la cytotoxicité élevée de b-lap, sans différence toutefois entre b-lap libre et formulée, ni entre les cellules normales et les cellules cancéreuses. / Beta-lapachone (b-lap) is a potential drug with trypanocidal, anti-infectious and anticancer activities with reported selectivity of effects. However, due to its poor water solubility and toxicity, b-lap is not yet applied in therapeutics. We have studied the encapsulation of b-lap in conventional phospholipid vesicles and in-cyclodextrin-in-liposomes. We first analyzed the interaction of b-lap with lipid excipients by surface pressure measurements, DSC and SAXS. They showed that b-lap inserts in lipid bilayers close to polar head groups with a maximum solubility of about 3.5 mol%. The experimental results were supported by molecular dynamics simulations. Encapsulation rates (ER%) of b-lap in liposomes were consistent with b-lap maximal solubility in lipids. B-lap:cyclodextrin complexes were formed and entrapped in the aqueous core of blap-loaded liposomes. Higher ER% were obtained, but with lower encapsulation efficiency. In vitro tests on prostate epithelial and tumor cell lines demonstrated the high cytotoxicity of b-lap, however, without difference between formulated and free b-lap, nor between normal and cancer cells.
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Effect of haverst season and ripening duration on the physico-chemical properties of new 'fuerte-type' avocando fruit selections during ripeningMunzhedzi, Mukondeleli January 2016 (has links)
Thesis (MSc. Agriculture (Horticulture)) -- University of Limpopo, 2016 / The Agricultural Research Council-Institute for Tropical and Subtropical Crops (ARC-ITSC) is continuously developing new avocado selections, in order for the South African Avocado Industry (SAAI) to remain competitive in various international avocado markets. However, information on the response of some of these selections, including ‘Fuerte 2 and 4’, ‘BL1058’ and ‘H287’ to low temperature storage and ripening physiology, has not been investigated. Thus, the objective of this study was to evaluate the effect of harvest season and ripening duration on the physico-chemical properties of newly developed ‘Fuerte-type’ avocado fruit selections during ripening. ‘Fuerte-type’ avocado fruit were indexed for maturity using moisture content, thereafter harvested and stored at 5.5°C for 28 days during the 2014 and 2015 harvest seasons. The experiment comprised five treatments: control (commercial ‘Fuerte’), ‘Fuerte 2 and 4’, ‘BL1058’ and ‘H287’ arranged as a factorial in a completely randomised design (RCD) with 3 replicates. The treatment factors were: (i) 2 x harvest seasons, (ii) 5 x selections and (iii) 6 x ripening days. After withdrawal from low storage temperature, fruit were ripened at ambient temperature. During ripening, the following physico-chemical properties were evaluated; external chilling injury, electrolyte leakage, mass loss, firmness, respiration rate and peel colour. Results showed that selections and harvest seasons had no significant effect (P=0.668) on the moisture content of the evaluated ‘Fuerte-type’ avocado fruit. After withdrawal from low storage temperature, there was a significant interaction (P˂0.05) between selections and harvest seasons on external chilling injury and electrolyte leakage. Results further showed that external chilling injury correlated with electrolyte leakage during both harvest seasons. Treatment factors had no significant effect (P=0.997) on mass loss. Similarly, treatment factors had no significant effect (P=0.139) on firmness. However, selection ‘H287’ had hard skin with an average firmness of 83.44 densimeter units during ripening in both harvest seasons. Treatment factors were highly significant (P˂0.05) on respiration rate. Respiration rate followed a climacteric pattern and the magnitude of climacteric peak and day of occurrence varied amongst selections during both harvest seasons. Ripening percentage differed significantly (P˂0.05) amongst harvest seasons, selections and ripening days. Treatment factors had no significant effect on lightness (P=0.711), chroma (P=0.378) and hue angle (P=0.536) skin colour parameters,however, variations were recorded as a result of the cold damage black spots. The results indicated that the ‘Fuerte-type’ avocado selections had poor storage qualities. Further studies are required to evaluate physico-chemical properties during low storage temperature and the effect of season, production conditions and maturity level on development of chilling injury. In addition, studies on application of treatments to reduce chilling injury symptoms and analysis of bioactive compounds should be considered for conclusive recommendations. Thereafter, the selections can be planted in different production regions to assess and select the best producing and quality combinations for a given region as part of phase III of the project / Agricultural Sector Education Training Authority (AgriSeta) and National Research Foundation (NRF)
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Effects of irrigation, 1-methylcyclopropene (1-MCP) and cold storage temperature on quality of 'hass' avocado fruitMamila, Isaac Mareme January 2020 (has links)
Thesis (M.Sc. (Horticulture)) -- University of Limpopo, 2020 / The South African Agricultural Sector has a mandate to reduce water use so that water can be available for other economic sectors. Thus, various water saving techniques must be continuously investigated in agricultural production to find efficient water use technique that saves water without compromising fresh fruit quality. Therefore, combined effect of irrigation method, 1-methylcyclopropene (1-MCP) and cold storage temperature on postharvest quality of ‘Hass’ avocado fruit was evaluated. Postharvest attributes of fruit colour, flesh firmness, ripening percentage, respiration, weight loss, body rot, stem end-rot, vascular browning, chilling injury and electrolyte leakage were assessed for 2 x irrigation methods [Full irrigation (FI) and Partial root-zone drying (PRD)], 2 x 1-methylcyclopropene (300 ng/L 1-MCP and untreated) and 2 x storage temperature (2.0 and 5.5°C) treatments. An interaction between the three treatments did not significantly (P > 0.05) influence fruit colour, flesh firmness, ripening percentage, fruit weight loss, body rot, stem end-rot, vascular browning, chilling injury and electrolyte leakage. Their combined effect was only significant (P = 0.019) on ‘Hass’ fruit respiration rate. The combination of full and PRD irrigation, 1-MCP and low storage temperature (2.0°C) did not negatively affect fruit quality. However, fruit stored at 2.0°C without 1-MCP treatment were affected by chilling injury when compared with fruit stored at 5.5°C. In conclusion, due to the inconclusiveness of results obtained, further studies, on the effect of these treatments especially under 5.5°C storage temperature should be carried out prior recommending the combination treatment for export markets. / Agricultural Research Council-Tropical and Subtropical Crops (ARC-TSC) and Agricultural Sector Education Training Authority (AgriSeta)
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Synchoronised physical, chemical and microbial analysis of wastewater from University of Limpopo food- courtRapeta, Mokgadi Gladness January 2021 (has links)
Thesis (M.Sc. (Chemistry)) -- University of Limpopo, 2021 / The present research work deals with the study of some of the important physicochemical
parameters of restaurant wastewater effluents collected from Mankweng
business centre along the University of Limpopo road. Studies revealed that
restaurants, food preparation facilities, engineering, paper mill, fine chemical, dyes,
paint, pharmaceutical, petrochemical and textile industries are some of the major
industries responsible for polluting the aquatic environments. This research attempts
to review the physical, chemical, and microbial analysis of wastewater from food
service establishments (FSEs) and extraction of fats, oil, and grease (FOG) and its
characterization using different analytical techniques. The elemental analysis revealed
that the concentration of elements such as zinc, lead and manganese were 6.44 mg/L,
0.02 mg/L and 0.53 mg/L, respectively. The concentration of these elements was
above the required South African National Standards 241 (SANS241) limit, that is,
≤5mg/L, ≤0.01mg/L and ≤0.4mg/L for Zn, Pb and Mn, respectively. The elevated
concentrations may be due to corrosion, acidic pH found in some samples and high
organic load. High organic content in wastewater influenced the production of oxygen
by microorganisms in-order to degrade the amount of waste in the wastewater and
this has led to high chemical oxygen demand (COD) level ranging from 1784-7196
mg/L and biochemical oxygen demand (BOD5) from 1101.32 to 3222.32 mg/L. The
study has demonstrated that the wastewater samples are contaminated with faecal
coliforms because the concentration of microbes Escherichia Coli (E.coli) with a Most
Probable Number (MPN) >200.5 in most samples, P. aeruginosa, Pseudomonas spp.
were too numerous to count (TNC) and total coliforms at the highest concentration of
9.1x103 CFU/ml which was influenced by change in pH of the wastewater, the FOG
content consists of both triglycerides and acrolein. The overall results highlight the
discharge of highly polluted wastewater effluent, these FSE have resulted in pollution
of nearby rivers thereby affecting the growth of vegetation and aquatic life. The results
of the present investigation point out the need to implement common objectives,
compatible policies, and programmes for improvement in the FSEs wastewater
treatment methods. / National Research Foundation and
Sasol-Inzalo Foundation
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Příprava nesymetrických derivátů DOTA a studium jejich komplexů / Synthesis of unsymmetric DOTA derivatives and study of their complexesObuch, Jakub January 2021 (has links)
Lanthanide(III) complexes are compounds with both diagnostic and therapeutic applications. For diagnostic applications, they are used as contrast agents for imaging techniques such as MRI, PET or SPECT. In therapy, complexes of beta or alpha particle- emitting radionuclides are used. If the complexes contain protonable groups, their behaviour is dependent on pH of the solution. Protonation of these groups should occur close to the physiological pH. If the efficiency (relaxivity) of the MRI contrast agent is dependent on protonation state, this method can be used for determination of pH of tissues in vivo. For radiopharmaceuticals, fast complexation of short-lived metal radionuclides is important and protonation might significantly accelerate the complex formation. For therapeutic applications, possibility of labelling at low temperatures when heat-sensitive biovectors (e.g. antibodies) do not decompose. To assess the effect of protonation of amino group in the vicinity of the metal ion, amino-bis(phosphinate) pendant arm was proposed, where the dissociation constant of the amino group below the physiological pH can be expected. Three ligands containing this group and DO3A fragment were prepared and their complexes were studied to assess aforementioned possible uses in medicine. Their structure and...
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Structural studies of organic crystals of pharmaceutical relevance. Correlation of crystal structure analysis with recognised non-bonded structural motifs in the organic solid stateEssandoh, Ernest January 2009 (has links)
Pharmaceutical solids tend to exist in different physical forms termed as polymorphs. Issues about pharmaceutical systems are mainly concerned with the active ingredient's physico-chemical stability and bioavailability.
The main aim of this study is to investigate the non-bonded interactions in pharmaceutical solids that govern the physical pharmaceutics performance of such materials and through the use of structural techniques and correlation of these results with crystal structural database to establish the presence of physical motifs in selected systems. Structural motifs were identified by the use of single crystal and crystal packing analysis on diverse range of pharma-relevant materials including chalcones, cryptolepines, biguanides and xanthines. These selected systems were validated using functional group and molecular analysis and correlating them to the Cambridge Structural Database. Crystallization studies are done on these selected systems as well as exploiting those using synthetic analogues.
A total of 51 crystal structures were investigated including 16 new structure determinations. Addition synthesis of new xanthines to investigate novel intermolecular patterns was also undertaken. The understanding and exploitation of intermolecular interactions involving hydrogen bonds and coordination complexation during packing can be used in the design and synthesis of solid state molecular structures with desired physical and chemical properties.
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An investigation into the effect of physico-chemical factors affecting the extraction of calcium from iron and steel slagKohitlhetse, Itumeleng 02 1900 (has links)
M. Tech. (Department of Metallurgical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / During steel production, a large quantity of waste residue commonly known as slag is produced with a reasonable amount of metals such as calcium and magnesium. Iron and steel slags have various economically viable applications such as fertiliser production, cement production, road construction, land fill and soil reclamation. However, other applications respond to the issue of controlling and degrading high levels of anthropogenic carbon dioxide (CO2) gas emissions by carbonating calcium and magnesium leach solutions from iron and steel slags. One such technological method is the extraction of calcium by means of leaching from iron and steel slag whereby CO2 sequestration is a long-term goal. In contrast, calcium and magnesium leach solutions can produce precipitated carbonates for various uses when carbonated. In addition, it is a crucial step to study the leaching parameters and reliable solvents for the dissolution of calcium and magnesium owing to their contents in iron and steel slags.
The aim of this research project was to determine the physico-chemical factors affecting leaching of calcium from blast furnace slag and thereby improve the extent and kinetics of calcium extraction.
The chemical and mineralogical study by X-ray fluorescence (XRF) and X-ray diffraction (XRD) respectively, has shown that the blast furnace slag sample under study contained calcium in the form of aluminoakermanite ((Ca,Na)2(Al,Mg,Fe2+)). The minerals identified through XRD are classified as silicates with the host mineral being calcium in recoverable quantities. The initial XRF analysis showed that the slag contained 23.47% Ca, 5.21% Mg and 1.24% Fe with the rest being minor elements.
The slag was received at a particle size of 20 mm. Size reduction was conducted in a dry rod mill process to produce a size of 80% -75μm. Particle size distribution was analysed by a simple laboratory sieving method.
The leaching tests were conducted in an incubated orbital shaker by applying the one-factor-at-a-time method for a two-hour leaching test. Reaction temperature was controlled at 30, 50, 70 and 100˚C. Ionic strength varied at 0.5, 1.0, 1.5 and 2.0 molar (M). In addition, the solid/liquid ratio was observed in the range 200, 300, 400 and 600 gram/Litre (g/L). Acetic acid (CH3COOH), ammonium sulphate ((NH4)2SO4) and ammonium chloride (NH4Cl) were tested individually as lixiviants under varying temperatures, ionic strengths and solid/liquid ratio.
The results showed that extraction of calcium from ironmaking slag by leaching is feasible. 100% Ca was extracted using CH3COOH at 100˚C, 0.5 M, 200 g/L and 120 minutes. As the reaction temperature was increased from 50˚C up to 100˚C, silica gelling was observed, which hindered filtration of a leach liquor from a residue. Silica gelling did not compromise calcium recovery. The increase in lixiviant ionic strength and solid-liquid ratio did not influence calcium recovery. The role of anions during leaching by using ammonium sulphate, ammonium chloride and acetic acid as lixiviants was identified. Sulphate ions were found to have the least influence in the increase in calcium recovery. Acetate ions have a significant role on dissolution of calcium as well as chloride ions. Consequently, the findings showed that temperature is the critical operating parameter that yielded exceptionally high calcium extraction percentages. CH3COOH yielded 80%-90% of calcium extracted under high reaction temperatures.
The kinetic data for the effect of reaction temperature leaching data fitted one shrinking core model equation, which described diffusion-controlled leaching reactions. The diffusion controlled by a product layer model was fitted and the activation energy were calculated as 19.4930 kJ/mol for NH4Cl solvent. (NH4)2SO4 and CH3COOH did not fit into any model because of undefined kinetic data and formation of gelatinous silica layer during leaching process. The Arrhenius equation, confirmed that the leaching reaction by NH4Cl solvent fitted diffusion-controlled mechanism.
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