List of Titles

Effect of calcium lignosulphonate on the particulate processes during hydrogen reduction of nickel ammine sulphate solutions

- Iloy, R.A., Ntuli, F.

Authors: Iloy, R.A. , Ntuli, F.
Date: 2016
Subjects: Nickel reduction , Calcium lignosulphonate , Precipitation , Crystallization
Language: English
Type: Article
Identifier: http://hdl.handle.net/10210/93829 , uj:20396 , Citation: Iloy, R.A. & Ntuli, F. 2016. Effect of calcium lignosulphonate on the particulate processes during hydrogen reduction of nickel ammine sulphate solutions.
Description: Abstract: The use of additives in the precipitation of nickel with hydrogen is known to influence the particulate processes and by extension the powder properties such as morphology, microstructure and particle size distribution. Controlling these properties is crucial for some downstream processes. The present study assesses the effect of calcium lignosulphonate on the particulate processes taking place during the reduction of nickel ammine sulphate solutions by hydrogen gas. Reactions were carried out in an autoclave operated at 28 bar and 180°C under stirring conditions of 850 rpm. Particulate processes were studied by analysing the particle size distribution and the corresponding normalized moments. These were further validated by scanning electron microscopy and nitrogen physisorption analyses. The powder phase identification and purity were determined by means of X-ray diffraction and X-ray fluorescence respectively. Calcium lignosulphonate acted as a reduction catalyst, growth promoter and by extension agglomerating agent. At 2, 5 and 7 mg/L of calcium lignosulphonate, the system was found to be dominated by breakage while agglomeration was more pronounced at 10 mg/L, as validated by scanning electron micrographs. Furthermore the use of calcium lignosulphonate resulted in the increase of the reduction rate, indicating that this additive acted as a growth promoter.
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Polymorphism in long-chain n-alkylammonium halides.

- Rademeyer, Melanie

Authors: Rademeyer, Melanie
Date: 2008-05-16T07:43:17Z
Subjects: Crystallization , Halides , Polymorphism (Crystallography) , Organic compounds
Type: Thesis
Identifier: uj:1785 , http://hdl.handle.net/10210/414
Description: Long-chain molecules are widely used in many commercial products, including waxes, oils, fats and soaps. This study focuses on the primary n-alkylammonium chlorides that have applications as surfactants, detergents and as models for bio-membranes. The specific topic of this investigation is the polymorphism of three series of n-alkylammonium halides. Polymorphism is the ability of a substance to exist in more than one crystal form. Due to the conformational flexibility of the long alkyl chain and the forces (hydrogen bonding and van der Waals interactions) dictating the packing in these compounds, more than one type of molecular packing is possible, resulting in the crystallization of various polymorphs for each compound. Various investigations of the polymorphism of n-alkylammonium halides have been published in the scientific literature. This includes mainly studies on the polymorphism and structures of n-alkylammonium chlorides. Only a few reports on investigations of the polymorphism of n-alkylammonium bromides were found in the literature, but no investigation of the polymorphism of n-alkylammonium iodides could be located. This study is limited to the medium chain length primary n-alkylammonium halides, CnH2n+1N+H3X- where n = 11 to 18 (except 17) and X = Cl, Br and I. It is expected that in this chain length range, both packing forces (hydrogen bonding and van der Waals interactions) will play a role in dictating the molecular packing. It was attempted to crystallize the maximum number of polymorphs of each compound by extensive variation of the crystallization conditions. The parameters varied include crystallization temperature, solvent and crystallization method. Information regarding the polymorphism of a compound crystallized under specific conditions were collected by the complementary techniques of X-ray diffraction and thermal analysis. X-ray diffraction is the ideal technique to study polymorphism because the result of such an investigation is the three-dimensional packing in the crystal structure. Due to the wide scope of the investigation, only the polymorphic forms stable at room temperature were investigated. The single crystal X-ray technique allows the determination of the crystal structure of a polymorph, but due to the tendency of the compounds to crystallize in thin plates, very few single crystals of good diffraction quality were obtained. Nine crystal structures were, however, determined. Most polymorphic forms were available as polycrystalline powders. The new techniques for crystal structure determination from powder data were employed to determine two crystal structures from powder diffraction data, although at lower precision, and further refined them by the Rietveld technique. Conventional X-ray powder diffraction is well suited to the identification of polycrystalline materials. The technique does not give direct information regarding the structural nature of the polymorph, but gives a unique fingerprint for each polymorphic form. All polymorphs that were obtained by the various crystallization techniques were characterised by X-ray powder diffraction, and the unique long Summary iispacing of each polymorphic form was determined from the position of the low angle diffraction peaks in the diffraction pattern. Linear correlations between the chain lengths and long spacings were used to search for the presence of isostructural series amongst the phases. More than one isostructural series could be identified for each homologous series of compounds. Thermal analysis techniques were employed to determine the phase transition temperatures and enthalpies of phase transitions occurring at temperatures above room temperature. In this investigation the thermal behaviour of polymorphs were investigated by differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and hot stage microscopy (HSM). A stepwise melting behaviour that includes various solid-solid phase transitions was observed for all compounds studied. The sequence of phase transitions that occur with an increase in temperature were found to be unique to a specific polymorphic form. Thermogravimetric analysis provided information regarding the incorporation of solvent in the crystal lattice by monitoring the change of sample weight with increase in temperature. Hot stage microscopy allowed the visual observation of changes occurring in the morphology and texture of the sample with temperature. This investigation contributed a large amount of information to the pool of knowledge on the crystalline phases of the n-alkylammonium halides. Up to now, not much structural data on the crystal forms of these compounds were available in the literature. In this study, complex patterns of crystal packing and phase transitions were revealed. Six isostructural series of n-alkylammonium chlorides were identified, three of which have not been reported previously, and the crystal structure of one of the novel forms was determined. Four isostructural polymorphic forms of n-alkylammonium bromides were identified. Only two forms have been reported previously in the literature. Six crystal structures of compounds with a novel crystal form were determined. For the homologous series of n-alkylammonium iodides, four novel isostructural series were identified, and one structure was determined. Relationships between chain lengths and structural parameters like long spacings, unit cell parameters and phase transition temperatures were determined and expressed as mathematical functions. An analysis of all the known structures (structures reported in the literature and structures determined in this investigation) indicated that different molecular conformations and hydrogen bonds are responsible for differences in the packing, as expressed in the formation of polymorphs. A choice of anion for a specific compound (chloride, bromide or iodide) influenced not only the cell volume, as would be expected, but also dictated the preferential formation of pseudo-polymorphs and complex hydrogen bonding networks in the crystals themselves. Phase transition temperatures were found to be not simply a function of chain length, but to be significantly influenced by the anion and polymorphic form present. , Prof. G.J. Kruger
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Steric and electronic effects of phosphine and phosphite ligands in vaska-type complexes of rodium

- Muller, Alfred Johannes

Authors: Muller, Alfred Johannes
Date: 2008-10-14T11:38:32Z
Subjects: Phosphine , Organometallic compounds synthesis , Rhodium , Ligands , Crystallization , Complex compounds
Type: Thesis
Identifier: uj:12255 , http://hdl.handle.net/10210/1201
Description: Ph.D. , In order for any new useful complexes to be developed, whether of catalytic, biological or of other importance, it is very important that sufficient knowledge exists regarding the fundamental principles applying to the chemistry involved. In all chemical processes involving metal complexes, the coordinated ligands govern the reactions to a great extent. It is thus very important that the properties (solubility, reactivity, steric bulk, etc.) of various ligands of these complexes is clearly understood in order to enable intelligent adjustments to be made, inducing the effects of choice. In most catalytic cycles, basic chemical reactions like substitution, addition, oxidative addition and reductive elimination are of importance. Some of the methods used to quantify ligand properties include single crystal X-ray studies as well as investigating various reactions on model square planar complexes. Several problems are normally associated with this type of investigation and are summarized below along with the aims of this study to improve upon this. (i) Very often the Vaska type compounds crystallise on an inversion centre as is shown in a generalized structure in Figure 1.1. This creates several problems ranging from less accurate bond distances/angles to problematic refinement of single crystal data. As the disorder is ruled by symmetry, the occupancies of the disordered atoms are 50%. The example shown in Figure 1.1 is also a fortunate case where the disordered atoms do not have the same positions, making refinement of the data easier, but there are examples27 such as [Pt(Me)Cl(PCy3)2] where the disordered moieties (Me- and Cl-) occupy virtually the same positions. In examples such as these restraints have to be applied, i.e. fixing bond distances to average distances from literature. The important parameter of the ligand trans effect is then meaningless and cannot be reliably compared to data from solution studies. , Prof. A. Roodt
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The effect of poly (crylic acid) and poly (ethyleneco-maleic anhydride) on nickel powder precipitation

- Thandiswa Florence, Bodoza

Authors: Thandiswa Florence, Bodoza
Date: 2012-07-31
Subjects: Crystallization , Nickel powder precipitation
Type: Thesis
Identifier: uj:8886 , http://hdl.handle.net/10210/5357
Description: M.Tech. , The study into the effect of additives used in nickel powder precipitation by sodium hypophosphite has been carried out. Reduction experiments were conducted in a 10 L stainless steel batch reactor fitted with 3 baffles, 4-bladed axial impeller, heating element, thermocouple and thermostat. Nickel seed was used to initiate the reduction process, sodium hypophosphite was used as a reducing agent, and ammonia solution was used to adjust pH, poly(ethylene-comaleic anhydride) (EMA) was used as the first additive and poly(acrylic acid) (PA) as the second additive. Reduction experiments were conducted at a temperature between 60oC to 70oC, pH around 8 and a reaction time of 3 min. Synthetic nickel sulfate solution and sodium hypophosphite solutions at concentration of 0.5 g/L were used as nickel feed solution and reducing agent, respectively. Additives were investigated at high and low concentrations of 5 mg/L and 10 mg/L. The effect of additives on reduction behavior of nickel was investigated by studying the evolution of the volume distribution, moments, specific surface area, and rate of reduction and purity of the powder product. EMA was found to be a growth promoter and PA was found to be a growth inhibitor. The highest reduction rate was observed in the presence of EMA and the lowest in the presence of PA. The SEM micrographs of the powder obtained in the presence of EMA and PA showed that the powder was spherical shaped, open, dentritic and more porous compared with that of the seed particles. Both additives were found to increase the pore size of the powder particles. The presence of particle fragments observed in the scanning electron micrographs confirmed breakage as one of the major particulate process. The addition of additives significantly affected the volume distribution at lower concentrations of 5 mg/L. The extent of aggregation increased with increasing dosages of PA and decreased with increasing dosages of EMA. The highest specific surface area was obtained in the presence of 5 mg/L of EMA.
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