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Sol-jel yöntemi ile alümina jel ve toz üretimi

Alumina gel and powder production by sol-gel progressing

  1. Tez No: 39229
  2. Yazar: SİBEL TARAR SEVİNÇTAV
  3. Danışmanlar: Y.DOÇ.DR. VOLKAN GÜRAY
  4. Tez Türü: Yüksek Lisans
  5. Konular: Kimya Mühendisliği, Chemical Engineering
  6. Anahtar Kelimeler: Alümina, Sol-jel yöntemi, Toz, Üretim, Alumina, Sol-gel method, Dust, Production
  7. Yıl: 1993
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: Belirtilmemiş.

Özet

SOL-JEL YÖNTEMİYLE ALÜMİNA JEL VE TOZ ÜRETİMİ ÖZET Alumina ve alumina bazlı seramikler değişik alanlar da en çok kullanılan seramik malzeme grubunu oluşturmakta dırlar. Teknolojinin hızla ilerlemesi sonucu malzemeler den beklenen özellik ve performanslarda da artış olmuştur. Örneğin; klasik Bayer yöntemi ile üretilen alümina tozları, elektronik amaçlı seramik malzeme üretimi için uygun değildir. Bu nedenlerle, son zamanlarda yeni üretim yöntemlerinin geliştirilmesine ihtiyaç duyulmuştur. Bunlardan bazıları CVD (Kimyasal Buhar Çöktürme), Sol-Jel, polimer pirolizi yöntemleridir. Sol-jel yöntemi, jelleşebilen herhangi bir solüsyonun bulunduğu sistem olup, kimyasal bir seramik üretim yöntemidir. Jelleşme dışında belirli parametrelerin kontrolü ile toz çöktürme işlemide yapılabilmektedir. Bu sistemde, genellikle metal-alkoksitler ve değişik metal tuzları önce bir çözücü içinde çözündürülüp daha sonra su ve bir katalizör yardımıyla hidroliz ve polimerizasyon reaksiyonları oluşturulur. Bu reaksiyonların kontrol e- dilmesi ile jel veya toz ürünler elde edilir. Seramik malzemelerin üretiminde kullanılan başlan gıç tozu son ürünü etkilediği için bu tozun şekil, boyut ve safsızlıklar açısından belirli özellikleri içermesi gerekmektedir. Bu çalışmada, sol-jel yöntemi kullanılarak, alümina jel ve alümina toz üretim parametreleri incelenmiştir. Alüminyum alkoksitlerden yola çıkarak üretilen jellerde, farklı kalsinasyon sıcaklıklarında meydana gelen ağırlık kayıpları, yoğunluk ve faz değişimleri, yüzey alan ve gözenek çaplarmdaki değişimler incelenmiştir. Alümina toz elde edebilmek için de alüminyum-izopro- poksit, alüminyum-tri-sek bütoksit, alüminyum-nitrat ve alüminyum-sülfat hammadde olarak kullanılmıştır. Çöktürme parametreleri olarak değişik pH değerleri ve molariteler incelenmiş olup, çöktürülen alüminyum-hidroksitlerin tane boyutları zetametre cihazı ile ölçülmüştür. Daha sonra çöktürülen alüminyum-hidroksit tozları değişik sıcaklıklarda kalsine edilip meydana gelen ürünün ağırlık kayıpları, yoğunluk, faz değişimleri, tane boyutları incelenmiştir TY

Özet (Çeviri)

ALUMINA GEL AND POWDER PRODUCTION BY S0L-61L PROCESSING ABSTRACT Alumina and alumina - based ceramics have a wide range of applications. The properties and performance of ceramics have to be increased with the progress in technology. For example, alumina powders produced by using conventional Bayer process is not suitable for electronic ceramics, because of their impurity levels and particle sizes. For this reason, novel powder preparation techniques are developed. Some of these are ; CVD (Chemical Vapor Deposition), sol-gel, polymer pyrolysis techniques. Sol-gel is a chemical method of ceramic production which has a gelation step of the solution used. By controlling some parameters, powder precipitation can be realized. In this system, metal alkoxides and metal salts are used. They're dissolved in a solvent, hydrolized and polymerized with water and catalyst. By controlling these reactions, gels or powders can be obtained. The initial powders in ceramic production must have some properties because of the properties of the final ceramic materials depend on the size, shape and chemical composition of these powders. In this work, alumina gel and alumina powder production parameters were studied by using sol-gel method. Aluminium alkoxides were used as precursor materials to produce alumina gels which were calcined at various calcination temperatures and the weight losses, densities, phases, surface areas and pore diameters are investigated.The alkoxides used for these experiments are aluminium- isopropoxide and aluminium-tri-sec-butoxide. The alkoxide/water molar ratio and the acid were chosen as 1/100 and HCI. At the beginning, the distilled water was heated up to 80 C, and the alkoxide was fed and stirred approximately for 15 min. After that 0,07 mol HCI was added to this solution at pH = 2,5. The water was vaporized, and the gel was obtained and dried at room temperature 2 days, in the oven against 1 day. The dried gel samples were calcined with 5 C/min. heating rate. The most important problem was the drying step of the gel in this work. Some cracks took form because of the capillary forces. The rapid drying and calcination caused these cracks. Therefore, the slow drying must be done in this work. The drying on mercury has been spoken of in the literature that it has been tested. The other problem of the gel is the porosity. The gel must be porous since it can be obtained with transparent appearance. According to that the diameter of the pores increases, and the pore area decrease as depend on the increasing temperature. DTA-TGA analysis of the gel was made to determine the calcination conditions. Fig.l- DTA-TGA Analysis of Gel Sample. XIThe weight losses are 38 % until 500°C. This result is justified by weight loss diagram of gel sample and TGA results. w/«gM* Z-9S (%) 0.46 0.-1 0.35 0.3 0.26 - 0.3 0.4 1.1 0.6 0.6 0.7 0.0 0.9 1 Te/«*per*fu'-e <fc * *1°3 Fig. 2- The Weight Losses of Gel Sample 1.2 1.3 1.4 According to DTA analysis results, the reaction is endothermic at 430 C and exothermic at 1080 C. When expressed differently, the physical and chemical water and other volatiles were removed until 500 C, and -Al»0o phase was transformed above 1000 C. The results of X-Ray diffraction analysis of dried gel samples explained the boehmite phase, and the - A1203 phase for calcined gels at 500, 800, 1000°C, J - A1“0”phase for calcined gels at 1200 C. and The porosity results are 0,0057 micron for calcined gels at 500°C, 0,0080 micron for calcined gels at 800°C, 0,011 micron for calcined gels at 1000°G, and 0,092 micron for calcined gels at 1200°C. The total pore area is approximately 142 m /a. at 500°C, 139 m /g. at 800°C, 50m /g. at 1000°C, 6 m /g. at 1200 C. The theoratical density percentage is 99,7 for“ calcined gels at 1200 C. (theoratical density = 3,97 gr/cm ) Aluminium - isopropoxide, aluminium -tri - sec - butoxide, aluminium - sulfate, aluminium - nitrate are used as a precursor materials to produce alumina powder. XIIThe precipitation parameters such as pH value and molarity are studied. The pore size distribution of precipitated aluminium hydroxides powders are measured and the weight losses, density and particle size distribution of these precipitates were investigated. Firstly, the powder/water molar ratio 1/100 to obtain optimum pH and molarity val 3,8 cc. NH.OH, the sample was gelled at pH stirring stopped, then secondly the molar r adjusted as 1/50, and it gelled again at pH afterwards some problems took form at stirr the molar ratio was chosen as 0,1 M. To de optimum pH, the solutions were prepared a 8, 10 and poured into test tubes and precip zetasizer was used and the isoelectric poin determined to justify the results of test t According to these results, the optimum pH 10. 0,1 M solutions which prepared at pH = precipitated for 1 day. Theoratically, the of these solutions must be in nanometer sea results were justified by particle size ana using zetameter. For instance, the partici aluminium - nitrate samples is 0,3 micron. is chosen as ues. By adding =» 5 and the atio was = 6 ing. As last termine the t pH = 2, 4, 6, itated. The ts were ubes. was chosen as 10 were particle size le. These lysis with e size of The agglomeration of dried samples was observed by TEM photographs. The phase analysis of dried samples was made by X-Ray diff Tactometer. The bayerite phase was observed for aluminium - nitrate and aluminium - sulfate, and the boehmite phase was observed for aluminium - isopropoxide and aluminium - tri - sec butoxide. (Bayerite = Al”0o 3H20, Boehmite = A1203. H20) The reason of bayerite formation is the preparation of aluminium - nitrate and aluminium - sulfate samples at room temperature instead of 80 C. Boehmite consists 1 mol H“0 although bayerite consists 3 mol H”0. To decrease this molarity, the solution must be heated up to 80 C. After drying the samples, they were calcined to DTA-TGA analysis results. DTA results demonstrated that the reaction is endothermic at 60 G, and exothermic at XIII1170 C which indicates A1_0“ phase transformation. The theoratical density percentage is 99,5 for calcined samples at 1200 C. (theoratical density = 3,97 gr/cm ). In other words, 1200 G is sufficient for - Al”0o transformation. XIV

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