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Material characterization studies on the laser beam formed AISI 1008 mild steel

  • Authors: Kumpaty, Subha , Brossard, Bradley , Kamara, Sheku , Akinlabi, Stephen A. , Akinlabi, Esther Titilayo , Raju, Govinda , Panda, Nirmal , Balasubramanian, K.
  • Date: 2013
  • Subjects: Metal-work , Metals , Thermal stresses , Steel - Heat treatment
  • Type: Article
  • Identifier: uj:5097 , http://hdl.handle.net/10210/13713
  • Description: Laser Beam Forming is a new non-contact method without the use of a die, to achieve deformation in metals, which traditionally involved the application of mechanical forces to change the shape and form of the material permanently. Laser forming causes deformation by introducing thermal stresses from an external heat source as opposed to the simple application of forces in mechanical forming. In this study, samples were formed mechanically by using a dynamic press brake machine, whereby, a punch and die apply the force. A 4.4 kW Nd:YAG laser system was used to form a second set of samples made from cold rolled AISI 1008 mild steel using laser forming. In this collaborative work involving researchers from the USA, South Africa and India, the mechanical and metallurgical properties of the unformed, mechanically formed and laser formed samples were experimentally investigated. The objective is to compare these properties amongst the different samples in order to analyze the impact of the varying methodologies especially the laser energy effects on the samples. The conclusions from these tests have provided valuable information on the applicability of laser forming to attain the appropriate surface modifications yielding the desired mechanical and metallurgical properties of the metal.
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Repair of cracks in metals : a review

Method development on sample preparation for trace metals in petroleum products prior to their determination using inductively coupled plasma-spectrometric techniques

  • Authors: Nomngongo, Philiswa Nosizo
  • Date: 2014-07-15
  • Subjects: Petroleum products - Analysis , Plasma spectrometry , Trace elements , Metals
  • Type: Thesis
  • Identifier: uj:11689 , http://hdl.handle.net/10210/11411
  • Description: Ph.D. (Chemistry) , The main objective of this study was to develop sample preparation methods based on separation and preconcentration of trace metals in organic matrices (alcohols, diesel and gasoline). The presence of metals in organic matrices is undesirable, unless they are used as additives. Therefore, it is important to control and monitor their concentrations in fuel and petrochemical products as they tend to affect the quality of these products. Solid phase extraction (SPE), solid phase microextraction (SPME) and hollow fiber-liquid phase microextraction (HF-LPME were used for separation and preconcentration of Ag, Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Ti, V and Zn prior to their inductively coupled plasma optical emission/mass spectrometric (ICP OES/-MS) determination. For solid phase extraction, the exchange efficiencies of different commercial ion exchange resins, namely Dowex 50W-x8, Dowex 1-x8, Dowex MAC-3 and Chelex 100, for preconcentration of metal ions in alcohol and fuel samples, were investigated. The results obtained indicated that Dowex 50W-x8 was suitable for simultaneous preconcentration of cations such as Cd, Co, Ni, Cu, Fe, Mn and Zn, among other metals while Dowex 1-x8 was suitable for metal ions that exists in more than one oxidation states, namely, As, Cr, Mo, Sb and V. Chelex-100 and Dowex MAC-3 were found to be selective to a limited number of target metal analytes. For further applications, Dowex 50W-x8 and Dowex 1-x8 were employed. Furthermore, the applicability of synthetic adsorbents such as nanometer-sized alumina and functionalized cellulose nanofibers for preconcentration of trace metals in gasoline samples, was investigated. Nanometer-sized alumina sorbent was found to be suitable for simultaneous separation and preconcentration of Co, Cr, Mn, Ni and Ti. Functionalized cellulose nanofibers on the hand, were suitable for simultaneous preconcentration of Cd, Cu, Fe, Pb and Zn. The optimization of the experimental parameters was achieved by both univariate and multivariate procedure. The second preconcentration technique was solid phase microextraction which was also used for extraction and enrichment of metal ions in diesel samples using two approaches of the SPME method. The first approach was hollow fiber-solid phase microextraction (HF–SPME) method using fiber-supported sol-gel combined with a cation exchange resin (Dowex 50W-x8). This method showed satisfactory results for the preconcentration of Cd, Cu, Fe, Pb and Zn in diesel and gasoline samples. The second approach was based on membrane solid phase microextraction (MSPME) using titania-alumina hollow fiber. The MSPME method applied was used for extraction and preconcentration of trace amounts of Co, Cr, Mo, Ni, Sb and V in liquid fuel samples. Multivariate techniques were used for optimization of experimental parameters for both approaches. The last preconcentration technique that was developed was hollow fiber- liquid phase microextraction (HF-LPME). In this method fuel samples were first digested before being subjected to HF-LPME system. Ammonium pyrrolidine dithiocarbamate (APDC) and [C6MIM][PF6] ionic liquid were both used as chelating agent and acceptor phase, respectively. Two level factorial and central composite designs were used for multivariate optimization of experimental parameters. Satisfactory results were obtained for extraction and preconcentration of Ag, Al, As, Mn and Ti.
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Tribocorrosion behaviours of AISI 310 and AISI 316 austenitic stainless steels in 3.5% NaCl solution

The impact of capital structure on the profitability of the industrial metals and mining sector on the JSE

  • Authors: Sibanda, Mthokozisi
  • Date: 2019
  • Subjects: Capital investments , Corporations - Finance , Mineral industries - South Africa , Metals
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/402989 , uj:33749
  • Description: Abstract : The study seeks to investigate the relationship between company capital structure and profitability with special reference to the industrial metals and mining industry of South Africa. Out of the 22 companies listed on the Johannesburg Stock Exchange under the industrial metals and mining industry, 14 companies were selected to be analysed in this study. Secondary data in the form of published financial statements relating to the period 1994 to 2017 of the selected companies was used. The study used return on equity (ROE), net profit margin (NPM), and return on assets (ROA) as proxies for profitability (dependent variables), while short-term to total debt (STDTA) ratio, long term as a ratio of total assets (LTDTA), and the total debt as a ratio of total assets (TTDTA) were used as proxies for capital structure (independent variables). The study employed panel data regression with pooled, random effects and fixed effects regression; however, the fixed effects regression was found to be the most appropriate. The results indicate that short-term debt is statistically insignificant as an independent variable of company profitability. Long-term debt was found to be more significant as a determinant of profitability for companies listed in the industrial metals and mining industry on the JSE. The results of the study show that the profitability of companies listed in the industrial metals and mining industry on the JSE is negatively related to the use of long-term debt over the period 1994 to 2017, implying that an increase in the company’s long-term debt would adversely affect the return of shareholders. , M.Com. (Finance)
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