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The magnesium aluminate spinel (MgAl2O4) is obtained at the end of solid-state reaction of MgO and Al2O3 mixture. In this study, magnesite waste and Al2O3 were used as initial materials for spinel synthesis. In this way, the recycling of waste materials disposed from magnesite factory was aimed. In addition, the effect of ZnO added into beginning mixture on densification of magnesium aluminate spinel was investigated. The initial mixture containing magnesite waste, Al2O3 and 1, 2, 3 and 4 wt. % ZnO addition were dry pressed and the specimens were exposed to sintering process at different temperatures (1300-1350-1400-1450 and 1500 degrees C) for 1 hour. The produced specimens were exposed to XRD, SEM-EDS analysis, bulk density, % apparent porosity and micro-hardness measurements were performed. In the light of findings, the optimum conditions for magnesium aluminate spinel production were determined.

In this study, fine grained SiO2 was exposed to CRN, and then Si3N4 ceramic powders were produced. Initially, 5wt% Li2O-5 wt% Y2O3 (based on the final product) and carbon black were added to SiO2, and then powder samples were processed to carbothermal reduction for 3 hours at 1,450 degrees C and 1,475 degrees C under nitrogen gas flow (1 lt/m). In order to burn the access carbon, the powder samples were held at 900 degrees C for 1 hour in furnace atmosphere. Having completed to Li2O and Y2O3 added Si3N4 powders, these were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS) methods. In addition, the values of wt% alpha-Si3N4 were estimated from XRD peak heights. The optimum temperature and holding time were determined for the best Si3N4 transformation process.

The powder mixtures of Talc-Kaolinite-Alumina-Basalt-Quartz were mechanically activated in a planetary ball mill for 1 hour. The structural alterations and thermal behaviour of the powder mixture were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis (TG-DTA). The results showed that the mechanical activation led to amorphisation and decreased the temperature of cordierite formation.

The kinetics of grain growth in 1-4 wt. % TiO2-doped ZnO was studied using the simplified phenomenological grain growth kinetics equation together with examination of microstructure and densification of the sintered samples. The grain growth exponent values n were found to be 3 for I and 2 wt. % TiO2-doped ZnO, 5 for 3 and 4 wt. % TiO2-doped ZnO. The apparent activation energy of 435 kJ/mol was found for I and 2 wt. % of TiO2 in ZnO. It was found to be 608 kJ/mol, and 615 kJ/mol for 3 and 4 wt. % TiO2, respectively. The apparent activation energy increased with TiO2 content due to formation of spinel Zn2TiO4 phase at the grain boundaries which inhibited the grain growth of ZnO. Also densification decreased with increasing TiO2 content.

Bu tezin, veri tabanı üzerinden yayınlanma izni bulunmamaktadır. ÖZET Bu çalışmada, Master Batching yöntemi kullanılarak üretilen ZnO - Bİ2O3 - Sb2Û3 - CoO - Q2O3 - MnO - AI2O3 seramik sisteminin mikroyapısal ve elektriksel özellikleri incelenmiştir. İnceleme için üretilen numunelere farklı sıcaklıklarda ve sürelerde sinterleme işlemi uygulanmıştır. Başlangıç olarak ZnO ve diğer metal oksitlerin tuzlan kullanılarak metal hidroksitlerin çökmesi sağlanmıştır. Bu metal hidroksit karışımı kalsine edildikten sonra preslenerek şekillendirilmiş daha sonra da farklı süre ve sıcaklıklarda sinterlenmiştir. Elde edilen sinterlenmiş numuneler bazı karakterizasyon ve elektriksel ölçüm işlemlerinden geçirilmiştir. Varistörlerin elektriksel özellikleri mikroyapıları, kompozisyonları, ilavelerin dağılımları ve homojenlikleri ile belirlenir. Dolayısıyla iyi bir varistör elde edebilmek için tane büyümesinin kontrol edilmesi gerekir. ZnO tane boyutunu, ZnO toz şekli, katkılar, safsızhklar, sinterleme süresi ve sinterleme sıcaklığı etkiler. Bu amaçla çalışmamızda, numuneler 1-2-3 ve 5 saat süreyle 1175-1270 ve 1370°C sıcaklıklarda sinterlenmiştir. Bu işlemlerden sonra tane büyümesi kinetik üssü 6, aktivasyon enerjisi de 170 kj/mol olarak bulunmuştur. Sonuçta, sinterleme süresi ve sıcaklığı artıkça tane boyutu artmış ve yoğunlukta düşüş meydana gelmiştir. XII THE INVESTIGATION OF MICROSTRUCTURE AND ELECTRICAL PROPERTIES OF ZnO VARISTOR PREPARED WITH COPRECD?ITATION MASTER BATCHING SUMMARY Keywords : ZnO Varistors, Grain Growth Kinetic, Electrical Properties. The most important property of the ZnO varistor is its non-linear current - voltage characteristic. Commercial ZnO based varistors are based and complex multicomponent system, containing additive oxides such as Bİ2O3, Sb203, Cr203, NiO, MnO/Mn02, C0O/C02O3/C03O4, TİO2 and AI2O3. Each additive controls one or several parameters, such as voltage breakdown, non-linear coefficient, surge current withstanding, etc. The four basic compounds formed are ZnO, spinel, phrochlore and bismuth-rich phases. The phrochlore disappears at high temperature forming spinel and Bİ2O3. In this study, both controlled chemical process and conventional ceramic process techniques used ZnO varistor powder are prepared. Table 1. The composition used for precipitation powder varistor The isothermal rate of grain growth can be expressed by the well known kinetic grain growth equation: Gn=K0-t-exP{-Q/R1^ The apparent activation energy Q of a grain growth process can be calculated from the Arrhenius plot of log (G7t) vs 10 7T (K"1). The activation energy is obtained from the slope of the line. In this study, grain growth of composition at temperatures between 1175°C and 1370°C revealed the grain growth exponent and activation energy to be 6 and 170 kJ/mol respectively. XUI

ÖZET Bu çalışmada, Master Batching yöntemi kullanılarak üretilen ZnO - Bİ2O3 - Sb2Û3 - CoO - Q2O3 - MnO - AI2O3 seramik sisteminin mikroyapısal ve elektriksel özellikleri incelenmiştir. İnceleme için üretilen numunelere farklı sıcaklıklarda ve sürelerde sinterleme işlemi uygulanmıştır. Başlangıç olarak ZnO ve diğer metal oksitlerin tuzlan kullanılarak metal hidroksitlerin çökmesi sağlanmıştır. Bu metal hidroksit karışımı kalsine edildikten sonra preslenerek şekillendirilmiş daha sonra da farklı süre ve sıcaklıklarda sinterlenmiştir. Elde edilen sinterlenmiş numuneler bazı karakterizasyon ve elektriksel ölçüm işlemlerinden geçirilmiştir. Varistörlerin elektriksel özellikleri mikroyapıları, kompozisyonları, ilavelerin dağılımları ve homojenlikleri ile belirlenir. Dolayısıyla iyi bir varistör elde edebilmek için tane büyümesinin kontrol edilmesi gerekir. ZnO tane boyutunu, ZnO toz şekli, katkılar, safsızhklar, sinterleme süresi ve sinterleme sıcaklığı etkiler. Bu amaçla çalışmamızda, numuneler 1-2-3 ve 5 saat süreyle 1175-1270 ve 1370°C sıcaklıklarda sinterlenmiştir. Bu işlemlerden sonra tane büyümesi kinetik üssü 6, aktivasyon enerjisi de 170 kj/mol olarak bulunmuştur. Sonuçta, sinterleme süresi ve sıcaklığı artıkça tane boyutu artmış ve yoğunlukta düşüş meydana gelmiştir. XII THE INVESTIGATION OF MICROSTRUCTURE AND ELECTRICAL PROPERTIES OF ZnO VARISTOR PREPARED WITH COPRECD?ITATION MASTER BATCHING SUMMARY Keywords : ZnO Varistors, Grain Growth Kinetic, Electrical Properties. The most important property of the ZnO varistor is its non-linear current - voltage characteristic. Commercial ZnO based varistors are based and complex multicomponent system, containing additive oxides such as Bİ2O3, Sb203, Cr203, NiO, MnO/Mn02, C0O/C02O3/C03O4, TİO2 and AI2O3. Each additive controls one or several parameters, such as voltage breakdown, non-linear coefficient, surge current withstanding, etc. The four basic compounds formed are ZnO, spinel, phrochlore and bismuth-rich phases. The phrochlore disappears at high temperature forming spinel and Bİ2O3. In this study, both controlled chemical process and conventional ceramic process techniques used ZnO varistor powder are prepared. Table 1. The composition used for precipitation powder varistor The isothermal rate of grain growth can be expressed by the well known kinetic grain growth equation: Gn=K0-t-exP{-Q/R1^ The apparent activation energy Q of a grain growth process can be calculated from the Arrhenius plot of log (G7t) vs 10 7T (K`1). The activation energy is obtained from the slope of the line. In this study, grain growth of composition at temperatures between 1175°C and 1370°C revealed the grain growth exponent and activation energy to be 6 and 170 kJ/mol respectively. XUI 103

Hydroxyapatite (HA) is an important material for biomedical implants, because its chemical composition is similar to that of bone tissue. This study focuses on the effect of sintering temperature and the amount of reinforcement phase on the mechanical properties of HA-Ti composites. Firstly, the production of hydroxyapatite powders that are consistent with the natural bone tissue was planned by means of chemical precipitation method. Secondly, the titanium element was added into this hydroxyapatite powder mixture by different amounts to investigate the change of mechanical properties. Titanium isopropoxide, Ti(OCH(CH3)(2))(4), was used as titanium supplier. These were solved and added into calcium solution without phosphate solution addition. In total, 0.5, 1, 2 and 4 mol% Ti were added into pure hydroxyapatite obtained by chemical precipitation method. The powders including different amounts of Ti additions were dried after the precipitation process and exposed to calcination at different temperatures in order to detect the phases obtained during the process. Microstructures have been investigated by SEM and EDS, and the phase analysis has been determined by the X-ray diffraction analysis, FTIR, DTA-TG and Raman spectrometers. The grain size and apparent density were measured. These results showed that titanium could enter into HA.

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır. Karbotermal İndirgeme ve Nitrürleme (KTİN) tekniği nitrür esaslı teknolojik seramiklerin elde edilmesinde tercih edilen etkili bir toz üretim yöntemdir. Yapılan bu tez çalışmasında KTİN işleminin geliştirilmesi ile yeni bir yaklaşım olan dinamik karbotermal indirgeme ve nitrürleme (DKTİN) yöntemi kullanılarak toz üretimi gerçekleştirilmiştir. Bu yöntemde toz karışımı veya granüller hareketli bir sistem içerisinde sürekli olarak hareket etmektedir. Bu üretim prosesi düşük sıcaklık ve sürelerde oldukça iyi morfolojide ürünler elde etmeye imkan vermektedir. Geliştirilen bu yeni yaklaşım ile nitrür esaslı teknolojik seramikler oldukça kaliteli ve ekonomik bir şekilde üretilebilmektedir. Bu çalışmada, dinamik karbotermal indirgeme ve nitrürleme (DKTİN) yöntemi ile TiN ve ZrN seramik tozlarının üretimi incelenmiştir. Hem TiN hem de ZrN toz üretiminde stokiyometrik oranda oksit tozları ve karbon karası karıştırılarak granüle edilmiştir (C/TiO2=2, C/ZrO2=2). Hazırlanan granüllerden N2 gazı atmosferi altında grafit reaktör içerisinde TiN ve ZrN tozları elde edilmiştir. Yenilikçi bir yaklaşım olan DKTİN işlemi ile reaksiyon sıcaklığı (TiN üretimi için 1350 °C ve 1400 oC, ZrN toz üretimi için ise 1400 °C - 1500 °C), reaksiyon süresi (1-3 saat), reaktörün dönme hızı (2-6 dv/dk), gaz akış debisi (60 ve 120 L/sa) gibi çeşitli test parametrelerinin etkileri araştırılmıştır. Ürünlerin fazları ve mikroyapıları XRD ve SEM analizleri ile karakterize edilmiştir. Yapılan analizler sonucunda 1 saat süre ile 4 dv/dk reaktör dönme hızında ve 60L/sa N2 gazı akışı altında homojen bir şekilde TiN tozu 1400 °C'de, ZrN tozu ise 1500 °C'de oldukça küçük boyutlarda üretilebilmiştir. Bu çalışmada literatürde yüksek sıcaklık ve uzun sürelerde KTİN işlemi ile üretilebilen TiN ve ZrN tozlarının DKTİN ile dahga homajen yapıda ve çok daha ince tane boyutlarında, daha kısa sürelerde ve daha düşük sıcaklıklarda üretilebileceği de kanıtlanmıştır. The Carbothermal Reduction and Nitridation (CRN) method is an effective method for obtaining nitride based technological ceramics. This thesis study was carried out by using dynamic carbothermal reduction and nitridation (DCRN) method. In this method, the powder mixture or granules is moved continuously in a dynamic system. This production process allows to obtain very good quality products in low temperature and time economically. In this study, the production of TiN and ZrN ceramic powders were obtained by dynamic carbothermal reduction-nitridation (DCRN) method. In the production of TiN and ZrN powders, granules were prepared with stoichiometry proportions of oxide powders and carbon black (C/TiO2=2, C/ZrO2=2). TiN and ZrN were obtained from the prepared granules in the graphite reactor under N2 gas flow. By DCRN process which is an innovative approach, the effects of various test parameters such as reaction temperature (1350 °C and 1400 °C for TiN production, 1400 °C-1500 °C for ZrN powder production), reaction time (1-3 hours), rotation speed of the reactor (2-6 rpm), gas flow rate (60L/h) was investigated. The phases and microstructures of the samples were characterized by XRD and SEM analyzes. As a result of these analyzes, at a reactor rotation speed of 4 rpm in 1 hour under N2-gas flow rate of 60 L/h, powders of micron in size and homogeneously form were produced at 1400 °C and 1500 °C for TiN and ZrN phase, respectively. In this study, it is proved that TiN and ZrN powders produced by CRN process in high temperature and long time can be produced using DCRN process much less time and lower temperatures with fine size and more in homogeneity form.

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır. Anahtar Kelimeler: Bor Karbür, Bor oksit, Dinamik Karbotermal İndigeme (DKTİ), Toz Üretimi. Karbotermal İndirgeme yöntemi, ileri teknolojik seramik malzemelerin üretim yöntemlerinden biridir. Yapılan bu tez çalışmasında karbotermal indirgeme yönteminin biraz daha geliştirilmesiyle Dinamik Karbotermal İndirgeme yöntemiyle toz üretimi gerçekleştirilmiştir. Bu yöntem ile kullanılan hammaddeler reaksiyon boyunca hareket ettirilmektedir. Bu durum üretilen ileri teknolojik seramiklerin üretim kalitesini arttırmakta, ayrıca üretim sıcaklığını ve süresini de azaltmaktadır. Bu çalışmada, başlangıç hammaddeleri olarak bor oksit (B2O3) ve karbon karası kullanılmaktadır. Uygun stokiometride hammaddelerden karışımlar hazırlanmış ve bor karbüre (B4C) dönüşümleri incelenmiştir. Ayrıca, katkı ilavesi olarak ise yitrium oksit (Y2O3) ve alümina (Al2O3) kullanılarak ürün özelliklerine ve prosese etkileri incelenmiştir. Kullanılacak olan toz karışımları granülatör ile granül haline getirilmiştir. Hazırlanan granüllerden Ar atmosferi altında grafit reaktör içerisinde B4C tozu elde edilmiştir. Bu çalışmada, geliştirilen DKTİ yöntemi ile 4 dv/dk'lık reaktör dönme hızında granül hazırlama aşamasındaki granülatörün hızı (300 dv/dk ve 6000 dv/dk), reaksiyon sıcaklığı (1400 oC, 1450 oC ve 1500 oC), reaksiyon süresi (1 dk, 60 dk ve 120 dk), kullanılan gaz (Ar ve C3H8) ve katkı ilaveleri (Y2O3 ve Al2O3) gibi çeşitli test parametreleri incelenmiştir. Elde edilen ürünler XRD ve SEM analizleri ile karakterize edilerek optimum şartlar belirlenmiştir. Keywods: Boron Carbide, Boron Oxide, Dynamic Carbothermal Reduction, Powder Production The Carbothermal Reduction (CR) is one of the methods used in the synthesis of advanced ceramics. In this thesis, the method of carbothermal reduction has been optimized by realizing the synthesis in a moving system using the novel method of Dynamic Carbothermal Reduction (DCR). In this method, the raw powders are in move throughout the reaction, which consequently increases the quality of the advanced technical ceramic's powders. Furthermore, both the synthesis temperature and duration are decreased. Boron oxide (B2O3) and carbon black were used as starting raw powders in this study. The mixing of raw powders was adapted in the appropriate stochiometric conditions and boron carbide (B4C) synthesis was examined. Moreover, the effects of yttrium oxide (Y2O3) and alumina (Al2O3) additives on the product properties and the process, were investigated. Granules of the powder mixtures were obtained using a granulator, at a speed varying between 300 and 6000 rpm. B4C powders were obtained from the prepared granules in graphite reactor under Ar atmosphere, at a 4 rpm reactor rotation. The reaction temperatures investigated were 1400°C, 1450°C and 1500°C, whereas the reaction times were 1, 60, 120 min. various parameters such as gas mixtures (Ar and C3H8) and additives (Y2O3 and Al2O3) were investigated. The synthesized powders were characterized by XRD and SEM analysis and the optimum conditions were determined.

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır. Bu çalışmada MgO-Al2O3-SiO2 (MAS) cam-seramiğinin ekonomik olarak üretimi için manyezit atığı kullanılmıştır. Isıl işlem sıcaklığının üretilen cam-seramiklerin kristalizasyon davranışına ve oluşan fazlara olan etkisi araştırılmıştır. Camların kristalizasyon davranışı, çekirdeklendirici olarak Li2O ve TiO2 kullanılarak çalışılmıştır. Kordiyerit bileşimi olan 2MgO.2Al2O3.5SiO2 kimyasal kompozisyonuna göre hammadde olarak %20 Kuvars, %35 Manyezit atığı, %25 Kaolinit, %20 Alümina, %2,5, 5, 10 Li2O ve %8 TiO2 kullanılmıştır. Karıştırma işlemi zirkonya bilyeler ile kuru olarak 8 saatte gerekleştirilmiş ve daha sonra hazırlanan karışım etüvde 110 oC'de 24 saatte kurutulmuştur. Toz karışımı alümina potada 1500oC'de 2 saatte ergitilmiştir. Ergiyen cam grafit kalıba dökülmüş ve daha sonra kalıntı termal gerilmeleri gidermek için 600oC'de 1 saat tavlama işlemi yapılmıştır. Kristalizasyon sıcaklığını saptamak için üretilen camlara diferensiyel termal analiz (DTA) ve termogravimetrik analiz (TGA) yapılmıştır. Numuneler cam-seramik dönüşümü için 1000oC, 1050oC, 1100oC, 1150oC and 1200°C'de 1,3,5 ve 10 saat sinterlenmiştir. Üretilen örnekler X ışını difraktometresi (XRD) ve taramalı elektron mikroskobu (SEM-EDS) ile karakterize edilmiştir. Cam tozunun sinterlenmesi viskoz akış ile gerçekleştiğinden, camın viskozitesinin düşürülmesi sinterlenebilme davranışını olumlu etkilemektedir. Yoğun cam seramik üretmek için kritik faktör camın viskozitesini düşürecek uygun cam kompozisyonu ve ergitici seçimidir. Birçok araştırmacı TiO2, NiO, ZrO2, MgF2, CeO2 ve ZnO gibi çekirdekleşticilerin ve ısıl işlemin MgO-Al2O3-SiO2 camının kristalizasyonuna etkilerini çalışmalarında incelemiştir. Buna rağmen Li2O'in kristalizasyon davranışına etkileri ulaşılabilen literatürde henüz detaylıca çalışılmamıştır. Bu çalışmanın temel amacı, daha önce tek başına çekirdeklendirici olarak çalışılmamış olan Li2O'nun MAS sistemine etkilerini incelemek ve çekirdeklendirici olarak TiO2 ilavesi ile beraber çeşitli kompozisyonlar hazırlanarak, endüstriyel bir atık malzemeden ekonomik olarak (düşük sıcaklık, düşük süre ve düşük hammadde maliyeti) MgO-Al2O3-SiO2 cam seramiği üretmektir. Anahtar kelimeler: MAS cam-seramik Manyezit atığı In this study, the magnesite waste is used for MgO-Al2O3-SiO2 (MAS) glass-ceramics production, economically. The effects of heat treatment temperature on crystallization behavior and precipitated phases in the produced glass-ceramics are investigated. Crystallization behavior of glasses in the presence of Li2O as a nucleation agent was studied. As raw materials, 20%wt. quartz, 35% magnezite waste, 25% kaolinite, 20% alumina and excess 2.5% Li2O are mixed according to cordierite chemical formula (2MgO.2Al2O3.5SiO2). Mixing process is carried out for 2 h using zirconia balls in the distilled water media and then prepared mixture is dried at 110°C for 24 h. The powder mixture is melted in an alumina crucible at 1500oC for 2 h. The glasses are casted into a graphite mould, and then an annealing process is carried out at 600oC for 1 h to remove thermal residual stresses. Produced glasses are applied to differential thermal analysis (DTA) and thermo gravimetric analysis (TGA) to detect the crystallization temperatures. The samples are heated for the glass-ceramic transformation at 1000oC, 1050oC, 1100oC, 1150oC and 1200° for 1,3,5 and 10 h. Produced samples are characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM-EDS). Because glass powder sintering proceeds by viscous flow, the decreasing glass viscosity shows good effect on its sinterability. In order to fabricate dense glass-ceramics, it may be a critical factor to select adequate glass composition and flux, which reduces glass viscosity. Many researchers have reported the effects of nucleating agent and heat treatments, such as TiO2, NiO, ZrO2, MgF2, CeO2 and ZnO, on the crystallization of MgO-Al2O3-SiO2 glass. However, the effect of Li2O on crystallization behavior hasn't been researched in detail. The main goal of this study is to analysis the effects of Li2O of the MAS system, which hasn't been studied before, and preparing several compositions using the most efficient nucleating agent TiO2 for produce MgO-Al2O3-SiO2 glass ceramics from the industrial waste economically (low temperature, low time, low raw material cost). Keywords: MAS glass-ceramics Magnesite waste

The aim of this research was to investigate microstructural and mechanical properties of the WC-Co-Cr coatings by high velocity oxygen fuel spraying. Woka 3653 (WC10Co4Cr) powder was used as coating material. This powder is widely used as a tribological coating material providing a combination of high toughness, high hardness, and good strength. The coatings were produced for the different high velocity oxygen fuel spraying parameters. The treated samples were characterized by using scanning electron microscopy/energy dispersive X-ray spectrometry and X-ray diffractometry. Microhardness measurements were executed to evaluate the mechanical properties of the coatings. Also the wear performance of the coatings was investigated. The scanning electron microscopy and energy dispersive X-ray spectrometry analyses were applied to worn surfaces. The results indicated that the coating shows slightly higher microhardness and better abrasive wear resistance than the conventional counterpart.

Fine grain alpha-phase silicon nitride (Si3N4) ceramic powders were produced via carbothermic reduction of colloidal SiO2, which contained pre-mixed additives of sintering aids primarily consisting of oxides such as MgO and Y2O3. The powders that were pre-mixed in the starting reactants were chosen based on the final powder composition and on type and amount of the secondary phases desired for sintering. After synthesizing, powder properties were examined using standard characterization techniques (XRD, SEM, BET, etc). This technique of ceramic synthesis has advantages in providing nitride-based ceramic powders, which contain secondary in situ phases that are distributed as sintering additives. Silicon nitride ceramic powders synthesized using this method might therefore be readily sintered because the homogeneously distributed sintering additives were present in the starting materials. In this work, the processing parameters are described in terms of the synthesis conditions. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All fights reserved.

In this study, the influence of Bi2O3 on the crystallization kinetics of the MgO–Al2O3–SiO2–TiO2 glass ceramics system produced from industrial waste was investigated. The Bi2O3-added MgO–Al2O3–SiO2–TiO2 glass ceramics systems were prepared by melting method. The crystallization behaviour and crystallization kinetics of a sample with glass ceramic composition were examined. DTA and XRD analysis revealed the crystallization of Ca0.965Mg2Al16O27 cordierite (Mg2Al4Si5O18) and Fe2TiO5 phases. The activation energy for the crystallization of cordierite phase has been evaluated, and the crystallization mechanism has been studied by applying DTA measurements taken at various heating rates. The results indicate that the dominant crystallization mechanism for this system is bulk crystallization dominated by three-dimensional growth. At 2.5, 5 and 10% Bi2O3 addition, the crystallization activation energy was calculated to be 336 ± 4, 218 ± 1 and 170 ± 3 kJ mol−1, and the viscous flow activation energy was measured to be 377 ± 2, 403 ± 7 and 407 ± 21 kJ mol−1, respectively.

In this work, the Woka 5810 powders (88% tungsten carbide–12% cobalt) were used to produce coating by high velocity oxy-fuel spraying. WC–Co is widely used as a tribological coating material providing a combination of high toughness, high hardness, and good strength. The treated samples were characterized by using optical micrograph, stereo microscope and scanning electron microscopy, X-ray diffractometry, and microhardness tests. Also the wear performance of the coatings was investigated. The results indicated that the coating shows slight higher microhardness and better abrasive wear resistance than the conventional counterpart. The friction coefficient of coating was low. The scanning electron microscopy and energy dispersive spectroscopy analyses were applied to worn surfaces.

This method can be used for the surface modification treatment of materials producing different surface properties. This paper presents the results obtained from an experimental work investigating the changes in some mechanical and microstructural surface properties of a 1.3343 steel (M2 high speed steel). In this work, a battery capacity of 800 0, and four different sample plasma gun nozzle distances were used. The consumable electrode is tungsten in this work. The samples were subjected to micro-hardness measurements and it was found that the hardness values of modified surfaces are five-seven times higher than that of untreated samples. The modified surface layers were examined using an optical microscope and X-ray analyses were carried out for all samples. It was observed that surface treatment had led to the formation of new phases in surface layers. SEM and EDS analyses were applied to modified surface.