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Three different Si/Yb-silicate environmental barrier coating systems (EBCs) were atmospheric plasma sprayed using various spray currents (275, 325, 375 A) for Yb-silicate deposition. The EBCs were thermally cycled between room temperature and 1300 °C up to 1000 h in air. Additionally, bare Si coatings were tested under isothermal and thermal cycling conditions in the as-sprayed state and after polishing at 1300 °C in air. Parabolic oxidation kinetics were observed and oxidation protection provided by Yb-silicate was found to be influenced by the spray conditions, i.e. only at 325 A, Yb-silicate was effectively protecting the bond coat. The controlling mechanism was attributed to densification in the Yb-silicate layer during thermal cycling, which was quantified via image analysis. The surface finish of the Si coating was also found to be influencing the oxidation rate. The TGO was thinner and less cracked on polished APS Si coating in comparison with the as-sprayed Si coating surface.

Environmental barrier coatings are necessary to protect fibre reinforced ceramics from high recession rates in fast and hot water vapor-containing gases as they typically are found in the hot gas sections of gas turbines. A standard material to protect SiC/SiC composites is atmospherically plasma sprayed (APS) Yb2Si2O7. For this material, it is difficult to obtain at reasonable substrate temperatures both low porosity and high crystallinity levels during APS. In this paper results of coatings prepared by a so-called high velocity APS process and also more conventional processes are presented. All coatings have been prepared by a single layer deposition method which avoids inter passage porosity bands. Furthermore, the samples were heat-treated in air at 1300 °C for 100 h and the influence of the topcoat density on the growth of the silica scale on the used silicon bond coat was studied.

From the literature, it is known that due to their glass formation tendency, it is not possible to deposit fully-crystalline silicate coatings when the conventional atmospheric plasma spraying (APS) process is employed. In APS, rapid quenching of the sprayed material on the substrate facilitates the amorphous deposit formation, which shrinks when exposed to heat and forms pores and/or cracks. This paper explores the feasibility of using a high-velocity oxygen-fuel (HVOF) process for the cost-effective fabrication of dense, stoichiometric, and crystalline Yb2Si2O7 environmental barrier coatings. We report our findings on the HVOF process optimization and its resultant influence on the microstructure development and crystallinity of the Yb2Si2O7 coatings. The results reveal that partially crystalline, dense, and vertical crack-free EBCs can be produced by the HVOF technique. However, the furnace thermal cycling results revealed that the bonding of the Yb2Si2O7 layer to the Silicon bond coat needs to be improved

The ceramic top coat has a major influence on the performance of the thermal barrier coating systems (TBCs). Yttria-partially-stabilized zirconia (YSZ) is the top coat material frequently used, and the major deposition processes of the YSZ top coat are atmospheric plasma spraying and electron beam physical vapor deposition. Recently, also new thermal spray processes such as suspension plasma spraying or plasma spray-physical vapor deposition have been intensively investigated for TBC top coat deposition. These new processes and particularly the different coating microstructures that can be deposited with them will be reviewed in this article. Furthermore, the properties and the intrinsic–extrinsic degradation mechanisms of the YSZ will be discussed. Following the TBC deposition processes and standard YSZ material, alternative ceramic materials such as perovskites and hexaaluminates will be summarized, while properties of pyrochlores with regard to their crystal structure will be discussed more in detail. The merits of the pyrochlores such as good CMAS resistance as well as their weaknesses, e.g., low fracture toughness, processability issues, will be outlined.

Bu çalışmada, ilk olarak 5-amino-4-arilazo-3-metil-1-fenilpirazol türevleri sentezlenmiştir. Elde edilen bu 5-amino-4-arilazo-3-metil-1-fenilpirazol türevleridaha sonra diazolanarak 5-hidroksi-3-metil-1H-pirazol ve 5-hidroksi-3-metil-1-fenilpirazol bileşiklerine kenetlenmiş ve yeni pirazol türevi dispers disazoboyarmaddeleri elde edilmiştir. Sentezlenen bu iki seri boyarmadde element analizi,UV, FT-IR ve 1H-NMR gibi spektral yöntemlerle karakterize edilmiş ve pH, çözücüdeğişimi, elektron alıcı ve elektron verici grupların o-, m- ve p- köşelerinde bağlıolmasının bu bileşiklerin absorpsiyon yeteneklerini nasıl etkilediği incelenmiştir.Sentezlenen bu boyarmaddelerin tekstilde kullanımını değerlendirmek üzerePoliamid 6.6 (P.A. 6.6), Polyester (PES) ve Polilaktikasit (PLA) kumaşlar tüm eldeedilen boyarmaddeler ile boyanmış ve ISO standartlarına göre haslıklarıdeğerlendirilmiştir. In this study, mainly 5-amino-4-arylazo-3-methyl-1-phenylpyrazolederivatives were synthesized. These obtained 5-amino-4-arylazo-3-methyl-1-phenylpyrazole derivatives then diazotized and coupled with 5-hydroxy-3-methyl-1H-pyrazole and 5-hydroxy-3-methyl-1-phenylpyrazole and eventually novelpyrazole derivative disperse disazo dyes were synthesized. These compounds werecharacterized by UV-vis, FT-IR, 1H-NMR spectroscopic techniques and elementalanalysis. The effect of varying pH, and solvent upon the absorption ability ofpyrazole substituted with electron-donating and electron-withdrawing groups at theiro-, m-, p- position was examined.To evaluate the use of these dyes in textile, Polyamide 6.6 (P.A. 6.6),Poliester (PES) and Polylacticacid (PLA) fabrics were dyed with all of thesynthesized dyes. Fastness properties were evaluated according to ISO standards. 253

Thermal barrier coating (TBC) research and development is driven by the desirability of further increasing the maximum inlet temperature in a gas turbine engine. A number of new top coat ceramic materials have been proposed during the last decades due to limited temperature capability (1200 °C) of the state-of-the-art yttria-stabilized zirconia (7 wt. %Y$_{2}$O$_{3}$-ZrO$_{2}$, YSZ) at long term operation. Zirconate pyrochlores of the large lanthanides((Gd $\rightarrow$ La)$_{2}$Zr$_{2}$O$_{7}$) have been particularly attractive due to their higher temperature phase stability than that of the YSZ. Nonetheless, the issues related with the implementation of pyrochlores such as low fracture toughness and formation of deleterious interphases with thermally grown oxide (TGO, Al$_{2}$O$_{3}$) were reported. The implication was the requirement of an interlayer between the pyrochlores and TGO, which introduced double-layer systems to the TBC literature. Furthermore, processability issues of pyrochlores associated with the different evaporation rates of lanthanide oxides and zirconia resulting in unfavorable composition variations in the coatings were addressed indifferent studies. After all, although the material properties are available, there is a paucity of data in the literature concerning the properties of the coatings made of pyrochlores. From the processability point of view the most reported pyrochlore is La$_{2}$Zr$_{2}$O$_{7}$. Hence, the goal of this research was to investigate plasma-sprayed Gd$_{2}$Zr$_{2}$O$_{7}$ (GZO) coatings and YSZ/GZO double-layer TBC systems. Three main topics were examined based on processing, performance and properties: (i) the plasma spray processing of the GZO and its impact on the microstructural and compositional properties of the GZO coatings; (ii) the cycling lifetime of the YSZ/GZO double-layer systems under thermal gradient at a surface temperature of 1400 °C; (iii) the properties of the GZO and YSZ coatings such as thermal conductivity, coefficient of thermal expansion as well as time and temperature-dependent elastic and creep deformations. Thermal cycling results displayed that the double-layer YSZ/GZO TBC concept is able to provide signicant lifetime improvement at 1400 °C surface temperature compared to the standard YSZ. The investigations on the chemical composition of the as-sprayed GZO revealed that no signicant gadolinia evaporation, which would compromise the performance of the coating, takes place in the examined spray current range (300 A-525 A). The detailed examination of microstructural properties of the as-sprayed GZO highlighted the importance of the process parameters for achieving the desired porosity features assisting superior lifetime performances. A signicant insight was gained intothe elastic and creep deformation of the plasma-sprayed YSZ and GZO coatings which play a critical role on the development of advanced TBCs. The overarching conclusion of this work is that the GZO has the potential to increase the temperature capability of gasturbines, if it is applied in double-layer TBC systems and if its microstructure is tailoredby adapted processing.

Submicron sized boric acid particles are used in traditional lubrication oils as they provide a low friction coefficient and they are friendly to the environment. In the present study, size and structure changes in high energy ball wet milled boric acid particles were investigated and characterized by X-ray diffraction (XRD), BET, and thermo-gravimetric/differential thermal analysis (TG-DTA). It was seen that increasing time of milling resulted in smaller particle formation and a larger specific surface area. Moreover, it appeared that thermal decomposition temperatures were not size dependent.

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2011, Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2011, 2015 yılı itibarıyla 14 milyar dolarlık bir küresel pazara sahip olması beklenen elektrolitik kaplama prosesi ülkemiz ekonomisi içinde de önemli bir paya sahiptir. Dekoratif olarak, korozyondan korunma amaçlı, elektriksel uygulamalar ya da mühendislik uygulamaları için kullanılan elektrolitik kaplama; metallerin kullanım ömürlerini arttırmakta ve fiyat/performans açısından da efektif kullanılmalarını sağlamaktadır. Bu nedenle dünya çapında pek çok üniversite ve enstitü bu elektrokimyasal prosesin bilinmeyenlerinin araştırılması ve bilinenlerinin de geliştirilmesi hususunda çalışmaktadır. Bu tez çalışmasında da Türkiye’de üretimi gerçekleştirilemeyen ve halen ithal edilen, kaplama tesislerince kaplama banyolarında “parlatıcılar” olarak kullanılan; organik ya da inorganik katkıları ihtiva eden çözeltilerin kimyasal kompozisyonu belirlenmiştir Kaplama banyolarına çok düşük konsantrasyonlarda ilave edilen söz konusu katkılar, banyonun tüm özelliklerini değiştirmekte olup, kaplama kalitesi için büyük önem arz etmektedir. Bu çalışmayla Türkiye’de; dünyada 1800’lü yılların başlarından itibaren uygulanan ve en çok kullanılan soy metal kaplama proseslerinden biri olan, elektrolitik gümüş kaplama prosesi için kaplama banyoları geliştirilmiştir Bu çalışma; ayna benzeri parlak elektrolitik gümüş kaplama elde edilmesine yönelik olarak; KAg(CN)2, KCN ve KOH içeren yüksek siyanürlü gümüş kaplama banyolarında parlatıcı, düzleyici ve yüzey ıslatıcı olarak kullanılan bazı organik ve inorganik katkı maddelerinin (EDTA, tiyoüre, Se ve Sb bileşikleri gibi), değişik konsantrasyonlarda ve çalışma koşullarında, kaplama özelliklerine etkisinin incelenmesini ve karakterize edilmesini kapsamaktadır. Çalışmanın ilk aşamasında; katkılar (potasyum antimon tartarat, potasyum seleno siyanat, etilen glikol, metan sülfonik asit, 2-mercaptobenzothiazole, EDTA, tiyodiglikol ethoksilat, sukroz, potasyum sitrat, propargil alkol, sodyum alil sülfonat, tiyoüre, jelatin, boncuk tutkalı); öncelikle tek tek literatür ışığında belirlenen birkaç farklı konsantrasyonda Hull Hücresinde denenmiş ve iyi çalışan katkıların optimum konsantrasyonları belirlenmiştir. Sonrasında iyi çalıştığı düşünülen katkılar, belirlenen optimum konsantrasyonlarında çoklu kombinasyonlar halinde denenerek, katkıların kaplama üzerindeki sinerjik etkileri araştırılmıştır. Üçüncü aşamada, optimum katkı konsantrasyonları ve parlak kaplama veren akım yoğunluğu aralıkları belirlenen banyolarla elektrolitik gümüş kaplama yapılmıştır. Çalışmanın son aşaması kaplamaların karakterizasyonu aşamasıdır. Bu süreçte parlak gümüş kaplamaların renkleri spektrofotometre ile, morfoloji ve yapıları FE-SEM ve XRD analizi ile, yüzey pürüzlülükleri optik profilometre ile, reflektansları reflektans spektrofotometresi ile karakterize edilmiştir., Electroplating world market, which is anticipated to will have reached approximately 14 billion $ by the year 2015, is also having an important place in our country’s economy. Electroplating is used as decorative purposes, corrosion protection, engineering applications and electrical applications, and it increases the life of metals and provides their effective use in terms of price/performance. Therefore today, many universities and institutes are investigating the unknowns and trying to develop the knowns of this electrochemical process around the world. Bright electroplating baths contain some organic and inorganic additives known as brighteners and these additives are still being exported from foreign countries in Turkey. In this thesis, these additives and these additive’s optimum compositions were determined. The additives, which completely alter the properties of baths in a good way in terms of quality of the deposits, added to electroplating baths in a very small amount. In this study, the electroplating baths were developed for silver electroplating process that has used all over the world since the early 1800s and one of the most used process of noble metals electroplating process. In this study for obtaining mirror like bright silver plating; the additive effects of some organic and inorganic chemicals, which are used as levelling and brightening agents, in different concentrations have been investigated in high cyanide silver electroplating baths that are consist of KAg(CN)2, KCN and KOH. In the first stage of this study, primarily Hull cell tests carried out by using additives that are potassium antimony tartrate, potassium selenocyanate, ethylene glycol, methane sulphonic acid, 2-mercaptobenzothiazole, EDTA, thiodiglycol ethoxylate, sucrose, potassium citrate, propargyl alcohol, sodium allyl sulphonate, thiourea, gelatin and animal glue, one by one in a few different concentrations. In this way the optimum concentrations of additives that work well are determined. In the second stage, by using these additives in optimum concentrations and in multiple combinations, the synergistic effects on coating quality of this available additives have been investigated. In the third stage, bright silver mirrors are electroplated from the electroplating baths that are consisted additives in optimum concentrations and which are determined their bright silver current density scale. The third stage of the study is characterizing of bright silver electrodeposits. In this process; colors of bright silver electrodeposits were characterized by spectrophotometer, morphological and structural properties of silver electrodeposits were characterized by SEM, XRD analyses. Optical profilometer and reflectance spectrophotometer were used for roughness and reflectance measurements., Yüksek Lisans, M.Sc.

Carotenoids, responsible for the red, orange and yellow color in foods, consist a part of the pigment family that naturally present in vegetables and fruits. Six main carotenoids found in human blood serum and taken with the diet are β- and α-carotenes, lycopene, lutein, zeaxanthin, and β–cryptoxanthin. Many studies suggest that carotenoids have a positive effect on several diseases such as certain type of cancers, cardiovascular and ocular diseases, especially age related macular degeneration and cataract. The antioxidant properties of carotenoids may be responsible for their beneficial influence on human health. Human organisms are unable to synthesize carotenoids, therefore these compounds have to be supplied with the diet. Main carotenoid sources include carrots, green leafy vegetables, tomatoes, sweet potatoes, egg yolk and corn. In this study, carotenoids in foods and their effects on human health are reviewed, Gıdalardaki kırmızı, turuncu ve sarı renklerden sorumlu olan karotenoidler, meyvelerde ve sebzelerde doğal olarak bulunan renk pigment ailesinin bir kısmını oluşturmaktadır. Diyetlerle alınan ve insan kanı serumunda bulunan temel 6 karotenoid şunlardır; β- ve α-karoten, likopen, lutein, zeaksantin ve β-kriptoksantin. Birçok çalışmada karotenoidlerin belirli kanser tipleri, kalp-damar, göz hastalıkları; özellikle de makula dejenerasyonu ve katarakt gibi hastalıklar üzerine olumlu etkilerinin olduğu ileri sürülmektedir. Karotenoidlerin antioksidan özelliklerinin de insan sağlığı üzerine yararlı etki sağladığı düşünülmektedir. İnsan organizması karotenoidleri sentezleyememekte, bu nedenle diyetlerle birlikte alınması gerekmektedir. Ana karotenoid kaynakları havuç, yeşil yapraklı sebzeler, domates, tatlı patates, yumurta ve mısırdır

In this study, 8 novel pyrazole disperse dyes which were synthesized in our previous work [1] were applied to polyethylene terephthalate (PET), poly (lactic acid) (PLA) and polyamide 6.6 (PA 6.6) fiber fabrics and their colorimetric and fastness properties were evaluated. The measured a*, b* and hue angle (ho) values of all dyed fabrics exhibited yellow, orange and red colour shades. Quite high colour strength values (K/S) were measured particularly for dyes containing substitute groups; p-OCH3 and o-OCH3. Shade changes of all fabrics after standard washing and sublimation tests were in the commercially adequate range. All dyed PET, PLA and PA 6.6 fabrics exhibited commercially acceptable fastness staining performances with very good to excellent levels. Synthesized novel disperse dyestuffs led to moderate to high light fastness levels particularly in the case of PLA and PET fabrics.