Materials Science and Engineering Commons^™

Defects In Reinforced Concrete Due To Environmental Conditions And Concrete Treatment: A Case Study At The University Of Dar Es Salaam, A. Rubaratuka

Tanzania Journal of Engineering and Technology (TJET)

Concrete is produced by mixing together cement, water and aggregates (i. e. sand and coarse aggregates) in specified proportions. It can do well with compressive forces but it is very weak under tensile forces. To overcome this problem, steel reinforcement are normally added to produce reinforced concrete which can also withstand tensile forces. Experience shows that environmental conditions may have a negative impact on the durability of reinforced concrete structures resulting in development of defects if not properly assessed and appropriate measures adopted to arrest the same at the design and construction stages.

The severity of damages for the investigated …

Behavior Of Gamma Tial Subjected To Impact Damage And Elevated Temperature Fatigue, Trevor S. Harding, J. Wayne Jones

Materials Engineering

Gamma titanium aluminide has received significant attention in recent years as a candidate material for use in aerospace and industrial gas turbine engine applications. In particular, these materials offer significant weight reductions (densities are less than half that of nickel-based superalloys), high specific strength retention at elevated temperature and high specific stiffness which is particularly important in vibrating components such as blades. This combination of weight savings and good mechanical properties has led to the possibility that γ-TiAl may be a suitable replacement for nickel-based alloys, such as Inconel 718, in low pressure turbine blades without significant redesign of the …

The Behaviour Of Reinforced Block-Work Walls In Axial Tension, Laurent Shirima

Tanzania Journal of Engineering and Technology (TJET)

Reinforced blockwork with horizontally laid reinforcing bars is used for walls in liquid retaining structures in developing countries. This is the case where, the level of technology in terms of skills and equipment is not in a position to allow successful construction of reinforced concrete walls. Blockwork walls are very sensitive to cracking which cannot be prevented by reinforcement. The major problem for designers is the behaviour of such walls in tension caused by hydrostatic pressure of the stored liquid. This paper reports results of a research work to study the behaviour of reinforced blockwork walls in tension. It was …

Application Of Vibrational Techniques In Determination Of Dynamic Properties Of Agricultural Products-State Of The Arton Of Vibrational Techniques In Determination Of Dynamic Properties Of Agricultural Products-State Of The Art, Silas Kajuna

Tanzania Journal of Engineering and Technology (TJET)

Vibration is one of the techniques employed in the determination of dynamic properties of fruits and vegetables. It entails generation of a mechanical or acoustic vibrational signal which is propagated through the flesh of the agricultural material. A transducer is either attached or held close to the specimen to monitor the propagation of the signal through the specimen. The manner in which the signal is transmitted through the material is analyzed, and the dynamic properties of the specimen which relate to its firmness or its internal being are derived. The technique has been around for the past 30 years or …

The Effect Of System And Oxygen Partial Pressure On Single Coal Particle Heterogeneous Ignition Temperature Under Conditions Of Negligible Convection; Experimental Observation, H. Katalambula

Tanzania Journal of Engineering and Technology (TJET)

Abstract Under conditions of high volatile concentrations, the influence of oxygen concentration on single coal particle ignition becomes more significant. The high volatile concentration conditions have been simulated by employing a microgravity environment. Results show that under these conditions, the heterogeneous ignition temperature decreases faster with increasing oxygen concentration than under normal conditions. The ignition temperature also decreases with increasing system and oxygen partial pressure under both conditions. Generally, the system and oxygen partial pressure show similar and complimenting effects on ignition temperature.

Estimation Of Volatile Cloud Density For Single Coal Particles Using Microgravity Condition, H. Katalambula

Tanzania Journal of Engineering and Technology (TJET)

Single coal particle’s volatile cloud density has been estimated by employing a microgravity condition. The volatile yield was found to decrease with pressure while the density was found to increase, indicating that volatiles occupies less space when under pressure and hence causing some volatiles to be retained within the particle. The volatile cloud density was also found to increase with volatile yield suggesting volatile composition changes with yield. The effect of heating rate on volatile yield was found to be the same as reported by other investigators where the yield increased with heating rate.

Concrete Cracking In Coastal Areas, S. R. Mpinzire

Tanzania Journal of Engineering and Technology (TJET)

The paper discusses cracking and corrosion of reinforced concrete (RC) structures in coastal zones where aggressive action of salt burdened air is the primary cause of concrete deterioration. Case studies are presented, along with discussion of possible remedies including local demolition, reconstruction and epoxy injection as well as concrete treatment.

Effects Of Foreign Object Damage From Small Hard Particles On The High-Cycle Fatigue Life Of Ti-6a1-4v, Joseph L. Hamrick Ii

Theses and Dissertations

Thin rectangular samples of Ti-6Al-4V were damaged by four methods to represent foreign object damage found in turbine engine blades: 1) impact with 2 mm and 5 mm diameter glass spheres at 305 m/s, 2) impact with 2 mm and 4 mm diameter steel spheres at 305 m/s, 3) quasi-static displacement controlled indentation using steel chisels with 1 mm, 2 mm and 5 mm diameter tips and 4) shearing notches with a 2 mm diameter chisel point under a quasi-static loading condition. Finite element analysis was used to study the relationship between the stress state created by the plastic damage …

Electrical And Optical Characterization Of Intrinsic And Ion-Implantation Induced Defects In 6h- And 4h-Sic, Michael B. Scott

Theses and Dissertations

Deep level transient spectroscopy (DLTS), Hall effect, and cathodolummescence (CL) measurements are used to characterize the intrinsic and ion-implantation induced defects in high-temperature (475 and 500 °C) ion-implanted epitaxial n-type 6H- and 4H-SiC, ion-implanted with Cr, Mg, Ar, N, and P atoms. Comparison of room-temperature and high-temperature ion-implanted 6H-SiC:Mg and :Cr indicate the significance of high-temperature ion implantation on the activation of the ion-implanted atoms and damage-recovery of the crystalline lattice. The effects of high-temperature annealing on both damage-recovery and implanted ion activation are detected and analyzed, from 1200 to 1800 °C. Trap parameters of both damage-related and species-related defects …

Studies On Methods Of Fuel Cells Electrodes Preparation, Jun Gu, Sheng Sui, Guang-Qiang Li, Zhitong Sui

Journal of Electrochemistry

In fuel cells, the structure of electrodes is an important factor which effect the cell performance. To improve the structure and the performance of electrodes, a new method of providing fuel cell electrodes is proposed in this paper. PTFE (polytetrafluoroethylene) and ethyne black was ground for about half an hour in a high-speed grinder, then the catalyst was added into the grinder and milled for an hour. This milled catalyst was transferred into a mixer followed by the addition of surface-active agent. After a suspension was formed, it was filtered under vacuum condition.Then a thin uniform filter-cake of the catalyst …

A Novel Reaction Region Moving Electrode System For Electrochemical Power Sources, Jin-Kua You, Que Tu, Zheng-Jian Wang, Jie Sun, Zu-Geng Lin

Journal of Electrochemistry

In most of practical rechargeable batteries, charging/discharging process is always concerned with phase-transformation in the solid state. Due to the irreversibility of the phase-transformation, the cyclic performance of the rechargeable batteries are limited. In this paper, a novel reaction-region moving counter electrode system is constructed in our laboratory. The electrode system is operated at room temperature and cycled in solid-liquid phase during charging/discharging processes. With this electrode, the metal-complexes are firstly deposited (i.e. charging process) on the nearest working electrode and gradually extended to those another working electrodes several centimeters away from the counter electrode. The deposite is dissolved again …

The Electrochemical Behaviors Of Superoxide Dismutase At Promoter Modified Gold Electrode, Xia-Qin Wu, Xiao-Yun Meng, Zhe-Su Wang, Zong-Rang Zhang

Journal of Electrochemistry

The electron-transfer process of superoxide dismutase was investigated by cyclic voltammetry at the 4,4'-dithiodipyridine, L-cysteine, histidine and arginine modified gold wire electrodes repectively. The quasi-reversible behavior was observed at L-cysteine modified gold electrode. An irreversible electrochemical behavior has been observed at hisdinine modified gold wire electrode.

Electro-Oxidation Of Phenol On Sno2/Ti Electrodes Prepared By Thermal Oxidation, Qing-Song Zhang, Hui-Huang Wu

Journal of Electrochemistry

A SnO₂/Ti electrode prepared by thermal oxidation was used as the anode for galvanostatic electrolysis in acidic solution containing phenol, the time-dependances of phenol concentration, chemical oxygen demand in solution(COD) and instantaneous current efficiency were determined during electrolysis. The results show that with the SnO₂/Ti anode instead of Pt, the COD significantly decreases at the same charge passage, and average current efficiency of oxidation increases by three times. The mechanism for phenol oxidation at two electrodes was discussed.

Study On Electrochemical Reduction Properties Of Nitrobenzene, Chu-Na Ma, Wen-Kui Zhang, Hui Huang, Yong-Ping Gan

Journal of Electrochemistry

The electrochemical reduction characteristics of nitrobenzene was extensively investigated by using the techniques such as quasi-steady-state polarization, cyclic voltammetry, fast linear potential sweep method and chronoamperometry in this paper. The electroanalytic properties of Cu, Cu-Hg and Cu-Ni electrodes were evaluated. Based on the study of the transient steping behaviour of nitrobenzene to PAP, the reduction mechanism was discussed. The results showed that the transition steps existed on the electrochemical reduction of nitrobenzene in acidic solution, the reactant is also absorbed on electrodes surface. The control step in the reduction of nitrobenzene was ascribed to the diffusion of nitrobenzene and its …

High Performance Proton Exchange Membrane Fuel Cells, Jing-Rong Yu, Bao-Lian Yi, Ming Han, Xiao-Liang Cheng, Zhi-Gang Shao, Jing-Xin Zhang

Journal of Electrochemistry

Proton-exchange membrane fuel cells(PEMFC) using a perfluorosulfonic acid proton exchange membrane as an electrolyte can simplify water and electrolyte management. In this paper, the effects of thickness of PEM on the performance of PEMFC were studied. The Nafion-112 PEM and low platinum loading E-TEK electrode yielded very high power density, of the order of 0.95 W/cm². The energy-conversion efficiency, the degree of platinum utilization and stability for PEMFC using Nafion 112 and E-TEK electrode were also investigated.

Photoelectrochemical Studies On The Tio2 Nanostructured Porous Film Sensitized By Cyanine Dye, Li Zhang, Mai-Zhi Yang, Xue-Bin Qiao, Yan-Zhong Hao, En-Qing Gao, Sheng-Min Cai

Journal of Electrochemistry

The photoelectrochemical behaviors of the TiO₂ nanostructured porous film sensitized by cyanine dye were investigated in this paper. The results showed that the excitaed state level matched the conduction band edge of TiO₂ nanoparticle. Therefore the sensitization of the dye can increase the photocurrent intensity of the TiO₂ nanostructured electrode obviously and results in a red-shift of optical absorption from the ultra-violet region to the visible. As a result, the light-to-electricity conversion efficiency was improved evidently, the maximum value of IPCE has reached 12.1%.

Investigation Of Sodium Hypophosphite Anodic Oxidizing Behavior In The Process Of Acid Electroless Nickel Deposition, Mei-Yuan Wang, Ya-Fei Kuang, Yan Xu

Journal of Electrochemistry

The anodic oxidizing behavior of sodium hypophosphite in the process of electroless nickle deposition (pH=5.5) was investigated with the linear potential sweep method and alternating current impedance. The results indicated that, the oxidation of NaH₂PO₂ was a complicated electrochemical process and affected by the concentration of NaH₂PO₂, the temperature of the bath, the sweep rate and the existence of nickel ion. The NaH₂PO₂ electrooxidation reaction was very likely preceded by heterogeneous interface transformation process, which might be the control step of the whole anodic process.

The Preparation Of Flexible Polymeric Anode And The Measurement Of Its Protective Ability For Cathodic Protection, Ai-Ling Du, He-Ming Zhang, Ming-Zong Zhang, Shi-De Ma

Journal of Electrochemistry

The flexible electrode, whose shape can be changed freely, was made of ethenyl copolymer and conductive component and proper amount of additive for cathodic protection. The resistance of electrode was measured.In low concentration of H₂SO₄, the flexible electrode can be used as auxiliary anode to protect the carbon steel. The protection ability of the flexible auxiliary anode was measured too.

Studies Of The Electrode Preparation Of Electrode From Lead Carbonate For Lead Acid Batteryⅰ. The Activation Of The Pme, Zhong-Xu Dai, Di-Hua Wang, Jun-Wei Jiang, Yun-Hong Zhou, Jin-Yun Zou

Journal of Electrochemistry

Lead carbonate which was an intermediate product in lead hydrometallurgy without pollution of lead vapor and sulfur dioxide was selected as electrode material of lead-acid batteries. In the present work, the performances of PbO₂/PbSO₄ or PbSO₄/Pb electrode transformed from PbCO₃ have been investigated by powder microelectrode technique combined with cyclic voltammetry. The results show that the CV characteristics of either negative or positive electrode prepared from PbCO₃ is as good as that of both electrodes made from lead oxide produced by mill machine,when a powder microelectrode with PbCO₃ transformed into PbSO 4 …

The Studies Of The (Photo) Electrochemical Character On The Electrodeposited Silver Indium Selenium Thin Films, Shao-Ai Xie, Xun-Nan Deng, You-Jin Kua

Journal of Electrochemistry

A photoelectrochemical cell (PEC) is constructed, using an AgInSe₂ film photoanode made from electrodeposition and a platinium electrode in aqueous polyiodide or polysufide electrolyte. The V_oc and I_sc of PEC have been tested and measured, and the effect of chemical decoration on the photoanodes also studied.

Method Of Destroying Hazardous Organic Compounds, Dibakar Bhattacharyya, Susan Mawhinney

Chemical and Materials Engineering Faculty Patents

The present invention relates to a method of destroying hazardous vapor phase or aqueous phase organic compound(s) by providing a polymeric siloxane based solvent in a vessel and adding the hazardous organic compound(s) and ozone to the solvent. The solvent may also comprise a mixture of polymeric siloxane based solvent and fluorinated hydrocarbon solvent.

Structural Disorder And The Origin Of High-Tc Suppression In La1.875ba0.125cuo4, Daniel Haskel, Edward A. Stern, Fatih Dogan, Arnie R. Moodenbaugh

Materials Science and Engineering Faculty Research & Creative Works

Polarized x-ray absorption fine structure (XAFS) measurements at all La, Pa and Cu sites were used to study local structural features that accompany the strong T_c suppression at x similar to 1/8 in La_2-xBa_xCuO₆. Two critical parameters regulating the strength of hole-lattice coupling in this material were determined, i.e., the direction and magnitude of CuO₆ octahedra local tilts. Our findings include the existence of large disorder in the magnitude of the tilt angle about its average value {theta}, with an rms {radical}{delta} {theta}{sup 2}] {approx_equal} 2{theta}. We suggest that this large disorder …

Reactive Infiltration Of Silicon Melt Through Microporous Amorphous Carbon Preforms, P. Sangsuwan, Surendra N. Tewari, Jorge E. Gatica, M. Singh, R. Dickerson

Chemical & Biomedical Engineering Faculty Publications

The kinetics of unidirectional capillary infiltration of silicon melt into microporous carbon preforms has been investigated as a function of the pore morphology and melt temperature. The infiltrated specimens showed alternating bands of dark and bright regions, which corresponded to the unreacted free carbon and free silicon regions, respectively. The decrease in the infiltration front velocity for increasing infiltration distances is in qualitative agreement with the closed-form solution of capillarity-driven fluid flow through constant-cross-section cylindrical pores. However, drastic changes in the thermal response and infiltration front morphologies were observed for minute differences in the preform's microstructure. This suggests the need …

Effect Of Interfacial Mobility On Flexural Strength And Fracture Toughness Of Glass/Epoxy Laminates, T. W. H. Wang, Frank D. Blum, Lokeswarappa R. Dharani

Chemistry Faculty Research & Creative Works

Mechanical testing and surface fractography were used to characterize the fracture of E-glass fiber reinforced epoxy composites as a function of the silane coupling agent used. gamma-Aminopropyltriethoxysilane (APS) and delta-aminobutyltriethoxysilane (ABS) were used because these have been shown to have different interfacial mobilities at multilayer coverage. The values of the properties studied generally increased from untreated c, as determined from a Mode I translaminar fracture toughness tests, for the untreated composites (10.5 ± 0.4 kJ/m2) was lower than that for the ABS-treated composites (14.3 ± 2.1 kJ/m2) which was lower than that for the APS-treated composites (17.1 ± 2.4 kJ/m2). …

Evaluation Of The Transport Properties Of Gasb For Bipolar Applications Through Monte Carlo Simulations, Damayanthi Palaniappan

Electrical & Computer Engineering Theses & Dissertations

GaAs is currently the semiconductor material of choice for high speed, low power applications. Its electronic transport properties are superior to almost all other semiconductors. It is also used in a variety of bipolar applications such as photodetectors and photo-mixers. However, as is well known, the hole mobility and related transport parameters of GaAs are not very good. This is a serious drawback, and poses a potential problem for all applications involving bipolar conductivity. In order to increase the high :frequency limits and high-speed capability of bipolar devices, the choice of an alternative material, therefore, becomes necessary. An important first …

Optical Spray Painting Practice And Training System, Richard J. Klein Ii

Patents (University of Northern Iowa)

An optical spray painting practice gun emits a shaped optical beam onto a practice surface to simulate an actual paint spray on the surface. The gun preferably uses a class 2 diode laser to generate a laser beam which is reshaped by a collimating lens into a diverging beam that illuminates the practice surface. The collimating lens creates an elongated image on the practice surface having a length corresponding linearly to the distance of the practice gun nozzle to the practice surface as with a conventional spray gun. The illuminated image distorts when the practice gun is not perpendicular to …

Charge Fluctuations In Yba2cu3o7-X High-Temperature Superconductors, Herbert A. Mook, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Understanding the behavior of the electrons in the high-temperature copper oxide superconductors remains a challenging problem. An important class of models1,2,3,4,5 argues that the distribution of electronic charge and spin is not homogeneous: rather, spin and charge adopt a dynamic arrangement in which the spins on the copper form antiferromagnetic stripes, separated by domain walls containing the charge1,2,3,4,5. The dynamic behavior of the spins has been extensively studied by neutron scattering, and recent results have shown that the low-frequency fluctuations for different classes of materials display a universal spatial behavior that is consistent with the stripe picture. But arguments for …

Theoretical And Experimental Investigation On The Low Temperature Properties Of The Nbcr2 Laves Phase, Dan J. Thoma, Chu Fuming, Katherine C. Chen, Paul G. Kotula, Terence E. Mitchell, John M. Wills, Alim Ormeci, Shao Ping Chen, Robert C. Albers

Materials Engineering

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The goal of the project was to develop methodologies in which to define and improve the properties of NbCr₂ so that the high temperature structural applications of alloys based upon this would not be limited by the low-temperature brittle behavior of the intermetallic. We accomplished this task by (1) understanding the defect structure and deformation mechanisms in Laves phases, (2) electronic and geometric contributions to phase stability and alloying behavior, and (3) novel processing of dual phase (Laves/bcc) …

The Weights Of Various Features In The Magnetic Spectra Of Cuprates, G. Aeppli, S. M. Hayden, Pengcheng Dai, Herbert A. Mook, R. D. Hunt, T. G. Perring, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

We review briefly the magnetic fluctuation spectra, obtained by neutron scattering, of the high temperature superconductor YBa₂Cu₃O_6.6 (T_c = 62.7 K). The resonance at 34 meV is the most prominent spectral feature in the superconducting state. Even so, its net weight accounts for a mere 1% of the total squared moment expected for planar Cu₂₊ ions. For context, we also provide a discussion of the spectral weights associated with the magnetic order and spin waves in two-dimensional S = 1/2 Heisenberg antiferromagnets.

Cellular/Dendritic Array Tip Morphology During Directional Solidification Of Pb-5.8 Wt Pct Sb Alloy, L. Yu, G. L. Ding, J. Reye, S. N. Ojha, Surendra N. Tewari

Chemical & Biomedical Engineering Faculty Publications

Cellular/dendritic array tip morphology has been examined in directionally solidified and quenched Pb-5.8 wt pet Sb alloy by a serial sectioning and three-dimensional image reconstruction technique. There is a large scatter in the tip radius, the nearest neighbor spacing, and the mushy zone length, even among the immediately neighboring cells and dendrites. This scatter may be caused by the natural convection (in the mushy zone and in the bulk melt at the array tip), which also produces macrosegregation along the length of the directionally solidified samples. Even in the presence of convection, however, the tip radii are observed to be …