Metalürji ve Malzeme Mühendisliği BölümüMetalürji ve Malzeme Mühendisliği Bölümü'ne ait koleksiyonları içerir.http://hdl.handle.net/11772/5752024-03-29T10:57:32Z2024-03-29T10:57:32ZLuminescence properties of ZnB2O4:Pb2+ phosphors: Suppression of concentration quenchingMükremin, YılmazErtuğrul, Erdoğmuşhttp://hdl.handle.net/11772/20212019-11-28T00:00:05Z2019-11-14T00:00:00ZLuminescence properties of ZnB2O4:Pb2+ phosphors: Suppression of concentration quenching
Mükremin, Yılmaz; Ertuğrul, Erdoğmuş
The UV-A emitting ZnB2O4:Pb2+ crystalline powder phosphors were produced using the conventional solid-state reaction synthesis technique at 830 °C for 6 h in air. The morphology and structure of the phosphors were explored by SEM, XRD and FT-IR analyses. The optical properties of the phosphors were examined by UV–vis diffuse reflectance and steady-state photoluminescence (PL) analyses. The excitation and emission bands of Pb2+ doped ZnB2O4 was observed at 304 nm and 388 nm, respectively. The effects of dopant concentration on the PL emission intensities of Zn1–xPbxB2O4 (0 ≤ x ≤ 0.15) phosphors were studied. The well-known concentration quenching phenomenon was not observed in the studied range. To explain the observation of suppressed concentration quenching the energy transfer between radiative and non-radiative centers has been discussed. Based on the absorption, excitation and emission results of the samples, a tentative configurational coordinate-energy diagram was proposed. Obtained results show that the ZnB2O4:Pb2+ phosphor is a good candidate for UV-A applications as a rare-earth free wavelength converter.
2019-11-14T00:00:00ZAlev geciktirici borlu selülozik çadırYaraş, Alihttp://hdl.handle.net/11772/17312019-08-07T00:00:20Z2016-03-25T00:00:00ZAlev geciktirici borlu selülozik çadır
Yaraş, Ali
Bu tez kapsamında selülozik çadır kumaşlarına alev geciktirici özellik kazandırmak amacıyla fiziksel ve kimyasal modifikasyon yöntemleri uygulanmıştır. Fiziksel modifikasyon yöntemiyle, çadır kumaşının nano boyuttaki hegzagonal bor nitrür (h-BN) tabakaları ile kaplanması neticesinde alev geciktirici etki sağlanamamıştır. Bor nitrür tabakaları sayesinde süper hidrofobik selüloz yüzey elde edilmiş ve su temas açısı 120,2o olarak ölçülmüştür. Borik asit ve boraks emdirme yöntemi ile ayrı ayrı ve birlikte selülozik çadır kumaşına uygulandığında, kütlece %5 borik asit ve %5 boraks konsantrasyonunda en yüksek LOI değerine (45,0) ulaşılmış fakat yıkamaya karşı dayanım sağlanamamıştır. Yıkama dayanımını geliştirmek için boya banyosuna farklı konsantrasyonlarda borik asit, boraks ve çinko borat ilave edilmiş, bor bileşiklerinin selüloz ile tepkimeleri başarısız olduğundan alev geciktirme sağlanamamıştır. Selülozik çadır kumaşına yıkamaya dayanıklı ve alev geciktirici özellik kazandırmak amacıyla sodyum silikat ile sırasıyla kütlece %5 borik asit ve %5 çinko borat emdirme yöntemi kullanılarak uygulanmıştır. Yıkama öncesi kumaşların LOI değerleri sırasıyla 34,5 ve 34,3; 5 yıkama sonrasında ise 31,3 ve 31,5 olarak tespit edilmiştir. Karakterizasyon işlemleri termal gravimetrik analiz (TGA), taramalı elektron mikroskobu (SEM) ve fourier dönüşümlü infrared spektroskopisi (FTIR) kullanılarak gerçekleştirilmiştir.
2016-03-25T00:00:00ZInvestigation of hot corrosion behavior of thermal barrier coating (TBC) systems with rare earth contentsÖzgürlük, YasinDöleker, Kadir MertAhlatcı, HayrettinKaraoğlanlı, Abdullah Cahithttp://hdl.handle.net/11772/16492019-07-12T07:57:48Z2018-01-01T00:00:00ZInvestigation of hot corrosion behavior of thermal barrier coating (TBC) systems with rare earth contents
Özgürlük, Yasin; Döleker, Kadir Mert; Ahlatcı, Hayrettin; Karaoğlanlı, Abdullah Cahit
Thermal barrier coatings (TBCs) are extensively used to protect critical components such as aircraft turbines to provide thermal
insulation at elevated temperatures. At high operating temperatures, damage mechanisms such as oxidation and hot corrosion
result in spallation of TBC system. The spallation occurs due to the phase transformation during penetration of hot corrosion salts
to top coat. YSZ is mainly used as top coat material for TBC systems. However, YSZ cannot be used in temperature higher than
1000 °C. More superior efficiency of gas turbine engines will demand a new generation materials for TBC systems. Nowadays,
rare earth zirconates, Gd
2
Zr
2
O
7
,La
2
Zr
2
O
7
, YSZ/Gd
2
Zr
2
O
7
, and YSZ/La
2
Zr
2
O
used as ceramic top coat materials in gas turbine
engine components owing to their superior thermal isolation and hot corrosion resistance properties. In this study, hot corrosion
mechanism, rare earth zirconates, and their properties as well as their hot corrosion behavior in TBCs were investigated based on
literature studies.
2018-01-01T00:00:00ZApplication of multi criteria decision making methods to leaching process of copper from malachite oreKursuncu, BilalYaraş, AliArslanoğlu, Hasanhttp://hdl.handle.net/11772/16022019-07-06T00:00:24Z2018-01-24T00:00:00ZApplication of multi criteria decision making methods to leaching process of copper from malachite ore
Kursuncu, Bilal; Yaraş, Ali; Arslanoğlu, Hasan
This study concerns with optimization of the leaching conditions of copper from malachite ore in the presence ammonium nitrate solution. In order to select the effective parameter from available dissolution process, all experiments were performed using L25 orthogonal experimental design by Taguchi method and the temperature was found as a more effective parameter. Then multi-criteria decision making (MCDM) method was applied to experimental results and it was found that the process is in concordance with MCDM values. Based on the results, the highest copper extraction value (99.4%) was reached under optimum leaching conditions are as follows: time, 60 min; temperature, 75oC; stirring speed, 450 rpm; concentration of leaching reagent, 4 mol/L and solid/liquid ratio, 8 g/mL. In conclusion, Taguchi and MCDM method can be used effectively for optimization of various hydrometallurgical processes.
2018-01-24T00:00:00Z