Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

Browse

Filters

2002 - 200932010 - 20193

Settings

Subject: search.filters.subject.Boron

Search Results

Now showing 1 - 6 of 6
  • Master Thesis
    Optimization of Oxide Additives in Boron Carbide Powders Using Precipitation Method
    (Izmir Institute of Technology, 2019) Elçi, Caner; Toksoy, Muhammet Fatih
    This study aims to precipitate oxides to boron carbide powders to achieve homogeneous dispersion of additive which is essential for sintering. Fine boron carbide powders were suspended in distilled water, then nitrate salts were solved in alcohol. Solved nitrate salts were fed to mixture in high pH levels. Mixing stage of the precipitation was done with both magnetic stirrer and ultrasonic treatment to investigate the effect of the mixing method. After the precipitation, synthesized powders were calcined under various atmospheres to eliminate the inorganic residues from the precipitation process. The examination of the XRD graphs showed that the calcination atmosphere is important for the oxide layer of the boron carbide powders. Inert atmosphere restrained the formation of the boron oxide layer due to the lack of oxygen. Methanol washing also eliminated the boron oxide layer. According to the zeta potential analysis, surface characteristics were obtained better when the ultrasonic treatment was applied during the precipitation. Ultrasonic treatment increased the dispersion of the additives between the particles during the suspension stage of the precipitation. Calcination time also affected the dispersion of the yttrium oxide at the sintered compacts when the SEM images were observed. When the calcination time increased, dispersion of the yttria was getting more agglomerated.
  • Master Thesis
    Synthesis and Characterization of Boron Composite Nanoparticles for Wear and Friction Reduction
    (Izmir Institute of Technology, 2019) Gökmen, Esin; Polat, Mehmet
    Since most of the conventional lubricants reach their performance limits, new antiwear and extreme pressure (EP) additives are designed so that lubricants can minimize friction and wear when used in high temperature and pressure conditions. There is growing interest in the use of nanoparticles as an additive in lubricants. Due to its outstanding chemical properties, boron is frequently involved in the design of nanoparticles. Especially borate derivatives and hexagonal boron nitride (h-BN) have already taken their places in many lubricant formulations. The aim of this study was the production of silica-boron composite nanoparticles that can replace the phosphate-derived additives used in lubricant formulations and to provide the extreme pressure, antiwear and friction-regulating properties at the same time. For this purpose, the Stöber method that is used for silica production was modified to produce Si/Na-Borate nanoparticles. It was found that the synthesis of composite nanoparticles in desired size distribution and morphology as well as composite structures composed of Si and Na-Borate, was possible changing the amounts of ingredients and modes of addition. It was observed that the morphology and the chemical structure of these particles depend on the amount of Na-Borate (1, 3, and 5% w/w) and the addition type of Na-Borate (Direct, 500 �����L/min, 5�����L/min). Then composite nanoparticles were characterized using SEM, FTIR and ICP-MS and some tests were conducted to examine the structure of particles. The tribological performance of these particles tested using Four Ball Test method have shown that there is a significant improvement in the presence of these particles.
  • Master Thesis
    B and Se Transport Modeling in Saturated/Unsaturated Zones
    (Izmir Institute of Technology, 2002) Yüreklitürk, O. Emin; Tayfur, Gökmen
    There has been renewed interest in the application of models to the transport of non-point source pollutants. However, very little work has been done to evaluate the performance of a functional transient-state model for the transport of a reactive solute over an extensive study period. This research consists of mathematical modeling to simulate water flow, boron and selenium transport through soil in tile-drained croplands.For Boron part a mathematical model was developed to simulate non-conservative boron transport. The dynamic two-dimensional finite element model simulates water flow and boron transport in saturated-unsaturated soil system, including boron sorption and boron uptake by root-water extraction. Two different models have been employed for the sorption of boron. Similarly, for selenium part a finite element model is developed to simulate species of selenium transport in two dimensions in saturated/unsaturated zones. The model considers water, selenate, selenite and selenomethionine uptake by plants. It also considers oxidation/reduction, volatilization, and chemical and biological transformations of selenate, selenite, and selenomethionine. Comparison of boron transport model results with observed data is satisfactory. The model employed with Langmuir isotherm was found to give slightly better simulation results when compared with the model employed with Freundlich. The sensitivity analysis results indicate that the irrigation scheduling and the irrigation water quality are very important parameters for boron accumulation in the soil. Also the adsorption isotherm parameters, which reflect us the soil properties, are found to be important for the boron movement in the soil. Comparison of selenium transport model with observed data is not quite satisfactory in accuracy when compared with the model for boron transport. This may be the result of the complexity of the mechanisms affecting the selenium transport in soil. There are too many parameters, and due to the errors depending on the parameters, the total error for the estimation of the total selenium increases.
  • Master Thesis
    Identification of Genes That Play Roles in Boron Metabolism/
    (Izmir Institute of Technology, 2008) Kaya, Alaattin; Koç, Ahmet
    Boron, is an essential microelement that plays a role in plant and animal development. However, an excess amount of boron is toxic for both types of organisms.The yeast Saccharomyces cerevisiae is an ideal model organism for describing the mechanism and regulation of metal ion transport in eukaryotes. We screened a yeast genomic DNA library to find genes that confer boron resistance to wild-type cells.Thirty transformants were isolated that were able to grow in the presence of a toxic amount of boron and all of them contained the multidrug efflux transporter gene ATR1 (YML116w) in the expression cassette. Our subsequent analysis revealed that ATR1 deletion mutants (.atr1) were sensitive to boron treatment and hyper-accumulated boron inside cells, whereas wild-type cells overexpressing the ATR1 gene were resistant to boron and hypoaccumulated boron in cells. We also analysed the global gene expression pattern in response to boron treatment and found that expression of ATR1 is upregulated along with many other transporter and amino acid biosynthesis genes. Our data suggest that the ATR1 gene functions as a boron efflux pump and is reqired for boron tolerance in yeast cells.
  • Master Thesis
    Investigation of the Reaction of Boron Oxide With Aluminium Powder and Method Development for Boron Determination in the Reaction Mixture
    (İzmir Institute of Technolog, 2007) Demirsar, Yelda; Özgen, Tamerkan
    In this study, a cheap method for the synthesis of elemental boron by the reduction of boron oxide with aluminum was investigated. However after various optimization studies, detectable boron amounts could not be found in the reaction mixtures by XRD and SEM-EDX analysis. Meanly aluminum borates were formed as products and these products were leached by 6 M HCl, however removel of borates could not be achieved. We think that the reason of this outcome is that we worked with simple experimental setup, therefore could not achieving the suitable experiment conditions and because of this we failed in the sythesis of boron. In the second part of the study, a new method for the direct determination of boron was investigated. 96 %pure boron and KBr were mixed and analyzed with Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). No distinct differences for boron was observed in the DRIFT spectra. Then, different sample compositions were prepared with different amounts of boron and KBr. These samples were split as validation and calibration sets and their spectra were collected by DRIFTS. All collected spectral data were processed in a different computer where the data proccessing programs were installed. The genetic inverse least square (GILS) method was used inorder to generate calibration model. Results obtained showed that boron amounts could be directly determined with maximum 3-4 % error. Afterwards, same procedure was also tried for boron and boron oxide binary mixtures and boron, boron oxide and aluminum ternary mixtures. In the binary mixture, determination of boron could be successfully achieved, however boron oxide determination could not be achieved as good as boron determination. In the ternary mixture, better results were obtained compared to binary mixture. Finally, the method was tried with the original samples, but not very satisfactory results were obtained. We think this result is due to the malfunction of FTIR instrument and personal error in the preparation of similar samples. More sample preparation and measurement could not be achieved because the FTIR instrument is not functioning at present.
  • Master Thesis
    Proteomic Analysis of Boron Stress Response in Yeast Saccharomyces Cerevisiale
    (Izmir Institute of Technology, 2011) Avşar, Kadir; Koç, Ahmet
    Boron is a versatile element distributed in every part of the environment but most of its deposit reserves are localized in a few countries, Turkey being one of the most prominent. Boron is known to be an essential micronutrient for plants and some animals. Like any other essential element it has toxicity in high concentrations. Herein the mechanism of toxicity and the elements of the boron stress response were investigated in Saccharomyces cerevisiae with a proteomics approach. Boron is believed to have played a role in the evolution of life on earth. It has strongly electrophile organic compounds, the most important physiological form being boric acid. Boric acid has a capacity to bind cis-located hydroxl groups and some amino groups. Some of these groups are located at the active sites of some enzymes and at the carbohydrates with five-membered furanose rings. The riboses of some metabolically important molecules like S-adenosyl methionine, diadenosine phosphate family members and 3'end of RNAs are prone to be affected. The yeast cells subjected to boron in this study expressed higher amounts of carbohydrate metabolic enzymes, proteins involved in protein synthesis, protein folding and catabolism, redox homeostasis and nucleotide synthesis. All of these proteins are common to metal stress responses in yeasts. Some of them involve in other stress responses like peroxide, salt or herbicide stresses showing complex interplay between responses.