Materials and Technologies for Sustainable Development

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Authors: Nadia H. Tsao, Karen A. Malatesta, Nicolas E. Anuku, Winston O. Soboyejo
Abstract: The consumption of microbially - and virally - contaminated water is a pressing health issue in developing nations. The concentration of surface and underground water is often responsible for a high incidence of diarrheal diseases, especially among children under the age of five years [1]. Ceramic water filters (CWFs) have been proposed as a household water treatment solution. However, despite their high bacterial filtration efficiency [2], existing CWFs cannot yet effectively remove viruses from water. Using MS2 bacteriophage as a model for human enteric viruses, this work explores the effect of doping CWFs with goethite (FeOOH) on the removal of viruses from contaminated waters. Fe-CWFs were found to remove bacteriophage from challenged water at significantly higher efficiencies than the control CWF. Filters composed of 60:40 ceramic:sawdust volume ratios and doped with different amounts of FeOOH were studied. A Fe-CWF containing 24.9 wt% Fe2O3 removed a mean of 1.93 log (98.83%) of MS2. The efficiency of viral filtration decreased significantly when the pH of the challenged water deviated from neutral (pH 5.9, 8.7 and 10.2). In addition, all Fe-CWFs tested removed more than 3 log (99.9%) of bacteria.
Authors: F.O. Kolawole, A.M. Rees, G.A. Etuk-Udo, Shola Odusunya, W.O. Soboyejo
Abstract: Conversion of lignocellulosic biomass from bamboo (Bambusa vulgaris) to butanol is an important alternative energy source. In this work, bamboo was used as biomass feedstock for the production of butanol by the fermentation of sugars. Mechanical grinding was carried out, followed by pre-treatment with dilute sulfuric acid concentration of 0.5 and 1.0 (%v/v). This was done at temperatures of 25, 110, 120, 150 and 200°C at time intervals of 2 and 4 hours. Pre-hydrolysate was later analyzed for total sugars by the use of UV-Visible Spectrophotometer. For the conditions considered, the maximum glucose yields were obtained at 200°C. The yields after pre-treatment were 244.80 mg/g, at pre-treatment conditions of 200°C and acid concentrations of 1% for 4 hours. Water insoluble solids obtained were subsequently hydrolysed with Celluclast (Trichoderma reesi) and β-glucosidase (Novozyme 188) for 72 hrs. Bacteria (Clostridium acetobutylicum) were then used to ferment the solubilized sugar into butanol. Raman spectroscopy was used to determine the butanol yield. Optical Microscope images of bamboo samples were obtained at various stages of pre-treatment and enzymatic hydrolysis. These revealed the morphological changes that occur in the cellular structure of the bamboo during exposure to acid and enzymatic hydrolysis. The results show that, increasing temperature, time and acid concentration are associated with higher total sugar yields and cellulose conversion rates. 10.4mg/mL of butanol was produced in sample treated at 1% H2SO4 for 110°C.
Authors: E.K. Arthur, E. Ampaw, K.J. Akinluwade, A.R. Adetunji, O.O. Adewoye, Winston O. Soboyejo
Abstract: Cassava-leaf-enhanced carbonitriding is a surface hardening procedure that utilizes the high cyanide content that is present in processed cassava leaves to thermochemically diffuse carbon and/or nitrogen into the interstitial sites of steel. This paper presents analytical models for the prediction of carbon and nitrogen concentration profiles, as well as the total case depths associated with the diffusion of carbon and nitrogen during the cassava-leaf-enhanced carbonitriding of low carbon steel. Using Fick's second law of diffusion and approximate initial and boundary conditions, two separate analytical models were presented for intermediate and high temperature cassava-leaf-enhanced carbonitriding processes. The trends in the total case depths are shown to be qualitatively similar to experimental measurements of case depths. The implications of the results are discussed for the surface hardening of steels by carbonitriding processes.
Authors: E.K. Ampaw, E.K. Arthur, O.O. Adewoye, A.R. Adetunji, S.O.O. Olusunle, Winston O. Soboyejo
Abstract: In this paper, ductile iron was produced using a rotary furnace. The microstructures of the ductile iron (with and without cyanided coatings) were then characterized using optical microscopy, scanning electron microscopy (SEM) and energy diffraction X-ray spectroscopy (EDS). The surfaces of the ductile iron were then subjected to high temperature carbonitriding using a pack cementation process in which carbon and nitrogen were diffused into the ductile iron from powder mixtures consisting of ground cassava leaves and barium carbonate (BaCO3) energizers. The wear behavior of the coated and uncoated ductile iron was studied using the pin-on-disk method. The wear mechanisms were also elucidated using a combination of SEM and EDS. The mechanisms of wear were also studied using nanoscratch experiments. The resulting wear rates are then compared with those from micron-scale wear tracks obtained from pin-on-disk experiments. The implications of the results are then discussed for the design of wear resistant ductile irons.
Authors: S.K. Kolawole, F.O. Kolawole, O.P. Enegela, O.O. Adewoye, A.B.O. Soboyejo, W.O. Soboyejo
Abstract: This paper presents the results of the combined study of experiments and modeling of the pitting corrosion behavior of low carbon steel. The effects of pH are elucidated via experiments on low carbon steel exposed to various corrosive media. The corrosion rates for the steel samples immersed in various corrosive media were determined by polarization experiments via a gamry potentiostat. The microscopic observations of the surfaces reveal clear evidence of corrosion pits that increase in size with increasing exposure duration. The observed pit size distribution and the evolution of pit size are modeled using statistical models. The implications of the results are used for the application of low carbon steels in corrosive environment.
Authors: Ngasoh Fayen Odette, Wole Soboyejo
Abstract: This paper presents the result of an experimental study of the corrosion behavior of epoxy-coated steel specimens. The spray-coated X65 steel samples were immersed in HCL solutions with varying pH levels. The effects of water adsorption and corrosion were studied via weight gain measurements and microscopic studies. The initial adsorption of fluid resulted in increasing weight gain prior to the weight loss that followed the onset of film delamination/debonding. The underlying mechanisms of corrosion are also elucidated for the steel substrate at different stages of exposure. The delamination is modeled using fracture mechanics concepts and discussing the implication of the current work for robust pipeline design.
Authors: Winston O. Soboyejo, J.D. Obayemi, E. Annan, E.K. Ampaw, L. Daniels, N. Rahbar
Abstract: This paper presents a review of high temperature ceramics research for aerospace applications. Following a brief historical perspective, the paper reviews the effort to toughen ceramics for high temperature structural applications. These include: efforts to toughen zirconia-based ceramics, aluminum oxide, silicon carbide, silicon nitride, molybdenum disilicide and zirconium diborides and carbon-based composites. The development of thermal protection systems is also reviewed within the context of thermal barrier coatings (TBCs) and thermal protection systems for space vehicles. The paper concludes with a final section in which the implications of the results are then discussed for the thermostructural applications of ceramics in aerospace structures.

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