Microstructural, electrical and mechanical properties of MgB2/Mg metal matrix composites

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2004Includes bibliographical references (leaves: 75)Text in English; Abstract: Turkish and Englishx, 81 leavesThe recent discovery of superconducting MgB2 (2001) has risen a great interest because of its relatively high Tc (39 K). Furthermore, simple crystal structure, large coherence lengths, high critical current densities (Jc) and critical fields (Bc2), promise that MgB2 will be a good material for large-scale applications based on production of superconducting wires. However, MgB2 is not a stand-alone material to produce wires because of its brittle nature. The potential of MgB2/Mg composites for producing superconducting wires, is investigated. MgB2/Mg composites were prepared using metal matrix composite fabrication technique, which is an alternative to conventional wire fabrication methods such as powder in tube. MgB2 and Mg powders were mixed at different weight fractions and uniaxially pressed in a cylindrical dye under the pressure of 0.5 GPa and 1GPa for two hours at different temperatures in the air. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Electron Dispersive X-Ray Spectroscopy (EDX) techniques were used for phase identification and microstructural studies. D.C resistivity measurements were carried on the pellet segments of the MgB2/Mg composites in the temperature range 20-300 K. Magnetization measurements were done on the composites using a vibrating sample magnetometer to characterize the magnetic properties of the samples. The effects of pressing temperature on the mechanical properties of MgB2/Mg composites were also investigated. For this purpose, compressive mechanical testing were performed to measure elastic modulus and strength at failure values of the composites. It was found that the relative weight fractions of Mg and the pressing temperature have some considerable effect on the electrical, magnetic, microstructural and the mechanical properties of the composites

Microstructural and electrical characterization of Ti and Mg doped Cu-clad MgB2 superconducting wires

The recent studies on Ti doping effect on the critical current density (Jc) of MgB2 composite superconductors prepared under ambient pressure has shown an important enhancement at 20 K. In the present work, we have fabricated Ti and Mg doped superconducting MgB2 wires by packing reacted MgB2 and Ti or Mg powders together inside Cu tubes with a diameter of 6 mm. The tubes were then cold worked by rolling or drawing to smaller diameters. The prepared Cu-clad Ti and Mg added MgB 2 superconducting wires were annealed at various temperatures to enhance the grain connectivity of the MgB2 bulk materials. The effect of the sintering time has been investigated for high performance characteristics of superconducting Cu-clad Ti and Mg added MgB2 wires. The microstructural evaluation of the superconducting wires has been carried out using XRD and SEM equipped with EDX analysis system. The interfacial properties between Cu sheath and superconducting core was characterized using SEM-EDX. Furthermore, the influence of the presence of Ti and Mg on Tc has been investigated to understand the structural and electronic properties of superconducting Ti and Mg doped MgB2 wires

Diagnostic Value of the Video Head Impulse Test in Patients with Vertigo: Can It Be Used as a Screening Tool?

Background and Aim: Several laboratory tools are used to evaluate balance disorders but, there is still no screening test to determine the site and the severity of the lesion. The aim was to investigate whether video Head Impulse Test (vHIT) can be used as a screening test in patients with chronic or recurrent vertigo and dizziness. Methods: The files of 965 patients who were followed up in our vertigo outpatient clinic were reviewed retrospectively. Vestibulo-Ocular Reflex (VOR) gains and saccadic movements of the right and left lateral canals in the vHIT test, and Canal Paresis (CP) in the Caloric Testing (CT) were noted. Results: A total of 325 patients were included in our study. In CT results, the group that CP was most frequently detected was Menière’s Disease (MD) group (71 patients (74.7%). While vHIT results were found to be pathological in the vast majority of patients in the Vestibular Neuritis (VN) group (72.7%), the results were found to be normal at the highest rate in the vestibular migraine group (77.9%). Correlation analysis showed a significant but weak correlation between the degree of CP in the CT and the VOR gains of the lateral canals in vHIT in all groups. Conclusion: Although it has high sensitivity in cases with VN and vestibulopathy, we think that vHIT cannot be used as a screening tool in patients with vertigo, especially for chronic cases, since its sensitivity rate differs in the long term according to the cause of the disease

The Short-Term Effect of Eugenol on the Prevention of Experimentally Induced Myringosclerosis in a Rat Model

Objective:The aim of our study was to assess the possible short-term effects of topical and oral eugenol on the suppression of experimentally developed myringosclerosis (MS).Methods:Four groups of seven male Wistar albino rats were used in the study. The tympanic membranes (TMs) of all subjects were myringotomized, and group 1 was given no treatment (as control group), group 2 received saline, group 3 had received topical eugenol and group 4 received oral eugenol.Results:In macroscopic evaluation the control and saline groups showed much more MS compared to the topical and oral eugenol groups which had statistically significantly less changes (p<0.05). Fibrosis and inflammation regarding the lamina propria (LP) of the eardrums of the topical and oral eugenol groups were significantly less than those of the control and saline groups (p<0.001). In microscopic evaluation, TMs were found to be thicker in the control and saline groups (p<0.001).Conclusion:Our study showed that the application of topical and oral forms of eugenol reduced fibrosis and prevented the advancement of MS in the LP of the TMs in the short-term. More studies with different extracts are needed to investigate the efficacy of phytotherapeutic agents for preventing MS development following myringotomy

Microstructural, electrical and mechanical properties of MgB2/Mg metal matrix composites

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2004Includes bibliographical references (leaves: 75)Text in English; Abstract: Turkish and Englishx, 81 leavesThe recent discovery of superconducting MgB2 (2001) has risen a great interest because of its relatively high Tc (39 K). Furthermore, simple crystal structure, large coherence lengths, high critical current densities (Jc) and critical fields (Bc2), promise that MgB2 will be a good material for large-scale applications based on production of superconducting wires. However, MgB2 is not a stand-alone material to produce wires because of its brittle nature. The potential of MgB2/Mg composites for producing superconducting wires, is investigated. MgB2/Mg composites were prepared using metal matrix composite fabrication technique, which is an alternative to conventional wire fabrication methods such as powder in tube. MgB2 and Mg powders were mixed at different weight fractions and uniaxially pressed in a cylindrical dye under the pressure of 0.5 GPa and 1GPa for two hours at different temperatures in the air. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Electron Dispersive X-Ray Spectroscopy (EDX) techniques were used for phase identification and microstructural studies. D.C resistivity measurements were carried on the pellet segments of the MgB2/Mg composites in the temperature range 20-300 K. Magnetization measurements were done on the composites using a vibrating sample magnetometer to characterize the magnetic properties of the samples. The effects of pressing temperature on the mechanical properties of MgB2/Mg composites were also investigated. For this purpose, compressive mechanical testing were performed to measure elastic modulus and strength at failure values of the composites. It was found that the relative weight fractions of Mg and the pressing temperature have some considerable effect on the electrical, magnetic, microstructural and the mechanical properties of the composites

Metal stent ve kateterlerin enfeksiyon yönünden karşılaştırılması

TEZ3317Tez (Uzmanlık) -- Çukurova Üniversitesi, Adana, 1999.Kaynakça (s. 39-42) var.vi, 42 s. ; res. ; 30 cm.

AHP TABANLI VIKOR YÖNTEMİYLE OPTİMUM STADYUM KURULUŞ YERİNİN BELİRLENMESİ: BOLU İLİ ÖRNEĞİ

Optimal yer seçimi, tüm işletmelerin en önemli ve uzun vadeli kararlardanbiridir. Şehir stadyumu gibi büyük ve maliyetli yapılar genelde devlet desteklikurulan yapılardır. Bu yapıların yer seçiminde sosyal, ekonomik, kültürel vepolitik birçok etken vardır. Bu çalışmada Bolu’da yapılması planlanan futbolstadyumu için belirlenen kriterler çerçevesinde dört yer alternatif arasından enoptimal yer seçimi çok kriterli karar verme yöntemleriyle belirlenmeyeçalışılmıştır. 3 alan, 3 ulaşım ve ağırlama, 3 şehre katkı ve 4 teknik ve yasalkriter olmak üzere toplam 13 kriterin kullanıldığı çalışmada, kriterlerin önemdereceleri Analitik Hiyerarşi Süreci yöntemiyle elde edilmiştir. Optimal yerinseçiminde alternatifler VİKOR yöntemiyle değerlendirilmiş ve sıralanmıştır.Elde edilen sonuçlara göre en optimal yerin Karaçayır Yerleşkesi olduğu ve bunusırasıyla Gölköy Yerleşkesi, Geçitveren Yerleşkesi ve Mevcut yerin takip ettiğigörülmektedir.Optimal site selection is one of the most important and long-term decisions of all businesses. Large and costly structures, such as the city stadium, are generally state-funded. There are many social, cultural and political factors in the selection of these structures. In this study, it is tried to determine the most optimal location in Bolu by using multi criteria decision making methods among the 4 alternative places within the criteria determined for the football stadium planned to be built. In the study, total of 13 criteria were used, 3 of which were area, 3 of which were transportation and hospitality, 3 of which were contribution to the city and 4 of which were technical and legal criteria.The importance of the criteria was obtained through the Analytical Hierarchy Process and the alternatives in choosing the optimal location are evaluated and sorted by the VIKOR method. According to the results, the most optimal location is Karaçayır campus, followed by Gölköy campus, Geçitveren campus and the current place respectivel

Microstructural and electrical characterization of Ti and Mg doped Cu-clad MgB2 superconducting wires

The recent studies on Ti doping effect on the critical current density (Jc) of MgB2 composite superconductors prepared under ambient pressure has shown an important enhancement at 20 K. In the present work, we have fabricated Ti and Mg doped superconducting MgB2 wires by packing reacted MgB2 and Ti or Mg powders together inside Cu tubes with a diameter of 6 mm. The tubes were then cold worked by rolling or drawing to smaller diameters. The prepared Cu-clad Ti and Mg added MgB 2 superconducting wires were annealed at various temperatures to enhance the grain connectivity of the MgB2 bulk materials. The effect of the sintering time has been investigated for high performance characteristics of superconducting Cu-clad Ti and Mg added MgB2 wires. The microstructural evaluation of the superconducting wires has been carried out using XRD and SEM equipped with EDX analysis system. The interfacial properties between Cu sheath and superconducting core was characterized using SEM-EDX. Furthermore, the influence of the presence of Ti and Mg on Tc has been investigated to understand the structural and electronic properties of superconducting Ti and Mg doped MgB2 wires

Electrical and microstructural properties of superconducting MgB 2/Mg composites

MgB2/Mg composites were prepared to improve mechanical properties of brittle superconducting MgB2. MgB2 and Mg powders were mixed at different weight ratios and uniaxially pressed in a cylindrical dye at 0.5 GPa and at various temperatures for two hours to prepare MgB2/Mg composites. X-ray diffraction, SEM and EDX were used for phase identification and microstructural characterization. In addition to the main MgB2 and Mg phases, the microstructural studies have indicated the presence of a minor amounts of second phases, namely MgO and B-rich compounds. The surface morphology, grain size and porosity ratio of the samples prepared under various temperatures were also investigated. The resistivity measurements were performed in the range of room temperature to 15 K. The effect of excess Mg and secondary phases on critical temperature of MgB2/Mg composites were studied.TÜBİTAK project number TBAG-203

Fabrication of superconducting MgB2 from boron oxide (B 2O3), and its microstructural and electrical characterization

The discovery of superconducting MgB2 (39 K) draws attention to it as a new material for applications based on superconductivity. Many researchers successfully synthesized MgB2 using commercial boron and magnesium. In this study, elementary boron was obtained via an acid leaching process, after reacting B2O3, and Mg in an argon atmosphere at 800°C. Energy Dispersive X-ray Spectroscopy (EDX) results revealed that the powder obtained from the reaction was boron in 92% purity with magnesium as the major impurity. Superconducting MgB2 was produced from this boron and magnesium, in an argon atmosphere at 900°C, by a conventional solid-state reaction. Superconducting MgB2 powders were compressed in a dye to pellets by a hot pressing technique at 500°C and 1 GPa. The microstructural properties of the MgB2 were determined by X-ray Diffraction Spectroscopy, EDX, and Scanning Electron Microscopy techniques. The electrical properties of the fabricated MgB 2 were examined by resistivity measurements in a closed-cycle cryopump system, between 20 and 300 K. The critical temperature (Tc) of the MgB2 pellets was around 32 K