Spinel refrakterlerde proses parametrelerinin özellikler üzerindeki etkileri

Abstract

Spinel refrakterler cam, çimento ve çelik sanayiin de kullanılmaktadır. Geleneksel refrakterlere( özellikle magnezit-krom) karşı bir alternatif olarak spinel refrakterler geliştirilmiştir. MA-Spinel tuğla üretimi için üç yöntem kullanılmak tadır. a)- Ergitme spinel, b)- Sinter spinel, c)- Pişirme ile spinel oluşumu. Bu çalışmada boksit (Çin kaynaklı) ve sinter magnezya( Kütahya) doğal hammaddeleri kullanılarak magnezya- alumina spinelin (Mg0.Al?0,) pişirme ile oluşturulması yönünde çalışmalar yapılmıştır. Spinel oluşum çalışmalarında iki bileşim kullanılmıştır: D- Periklas - spinel refrakter: %B5 Magnezit - % 15 Boksit. 2)- Mullit - spinel refrakter : %85 Boksit-% 15 Magnezit. Bu amaçla yapılan deneylerde; farklı boyut aralıklarındaki hammaddelerden spinel harmanı hazırlanmıştır. Spinel harmanı hazırlamak için iki tane boyutu fraksiyonu kullanılmıştır. D- %50 ince, %25 orta, %25 iri 2)- %25 ince, %25 orta, % 50 iri Her sıcaklık ve tane boyutunda yapılan pişirmeler den sonra X-ışını analizlerinden tam spinel oluşum sıcak lığı, periklas-spinel bileşimi için 1600 C, mullit, spienel bileşimi için ise 1500DC'nin yeterli olduğu tespit edilmiştir. Yapılan incelemeler, mikroyapı analizi ( T. E. M) X-ışını difraksiyon analizi, hacim ağırlığı ve görünür porozite ölçümleri, soğukta basınç mukavemeti, yük altın da refrakterlik testi ve kalıcı genleşme ölçümleridir. Yapılan incelemeler sonunda, mullit-spinel numunelerin mukavemeti periklas-spinel numunelere göre, ince taneli numunelerin mukavemetinin ise iri taneli numunelere göre daha yüksek olduğu ve sıcaklığın artışı ile mukavemette artış olduğu tespit edilmiştir.

Spinel refractories have been used in glass, cement and steel industries. In magnesia- alumina spinel (MgO. A1?0.,) the ratio Mg0/A12G3 is 26.2 % to 71.8 % by ueight, Taut the ratio varies in the synthetic products. MA-spinel refractory can be made of different start ing materials: Electrically fused spinel; 1GD % fused starting material is taken. * Simultan dead-burned spinel, magnesium carbonate and alumina simultaneously fired to form spinel that is processed into a brick. MgO and A1_0-, processed together into a brick and spinel forms during firing. By using natural rau materials of bauxite (from China) and sintered magnesia (from Kütahya), occurance of magnesia-alumina spinel structure (MgO, A1-0-) with firing has been observed. VI Since the synthetic products have been used in the first two processes, it's expensive to produce MA-spinel because of smelting and shaping processes. Energy consumption is to high in smelting and casting steps of the raw materials used in production of melt spinel. In order to produce sintered spinel the firing is made in two steps and also a high energy consumption is observed. This is one of the reasons increasing the costs. For this reason, the third method (occurance of spinel by firing) has been used in this study. Refrac tories can be produced cheaper than that of the other methods since the raw materials have been used in this method and after the shaping of the mix produced spinel occured in one step by firing. In-situ MgO. (M^O^ spinel formation studies with two compositions: A) Periclase - Spinel Refractory 65% Magnesite - 15 % Bauxite mixture (79.1 % MgO - 12.8 % Al^ - 4.2 % Si02) vii B) Mullite - Spinel Refractory 85 % Bauxite - 15 % Magnesite mixture (U.D % MgO - 72.3 % Al^- 9. D % Si02) Preparation of samples: * Crushing and grinding * Sieving : 3 particle size fractions under industrial conditions D-D. 5 mm (Fine) D.5-1.D mm (Medium) 1.D-2.0 mm (Coarse) Mixing: 2 particle size distributions for each of two compositions. D- 5D % fine 25 % medium 25 % coarse 2)- 25 % fine 25 % medium 5D % coarse - Shaping - Drying - Firing Uniaxial pressing Pressure : 10DD kg/cm2 Samples" : 5D mm diameter 5D mm height a) Temperature ( 12D0-1000DC) b)- Time (3-18 hrs.) Vlll Making Investigations: 1)- X-ray diffraction analysis 2)- Microstructrual analysis (S.E.M.) 3)- Bulk density and apparent porosity measurements k)- Cold crushing strength measurements 5)- Refractoriness under load measurements 6)- Permanent expansion measurements Effect of firing period: - Composition studied : 85% Magnesite + 15 % Bauxite (uith 5G%fine particle size) - Temperature : 15DD C (constant) - Firing periods: 18, 12., 6, 3 hrs. - Spinel formation observed in all samples. - IMo difference observed between inside and outside of samples. - Standard firing time of 3 hrs. for future samples. Effect of firing temperature: - Complete spinel formation observed only above 150D C for both compositions. - Firing temperatures of min 1600 C for periclase spinel, and min. 1500 C for mullite-spinel are apparently required for highest defaity and max. strength development. - Mechanical properties seem to depend on complete spinel formation and development of bonding. - Similar fabrication conditions result in higher strength for mullite-spinel composition than for periclase-spinel one. IX The results obtained after of measuring the cold pressure strengths of spinel refractories can be sum marized as follows: - The higher firing temperatures cause the higher cold pressure strengths. - Fine granular samples have higher cold pressure strengths than that of course granular samples. - Mullite-spinel samples have higher cold pressure strengths than that of periclas-spinel samples. It's been estimated that the spinel refractories might take place with magnesia-chrome refractories in the next future, since the spinel production with firing will be developed and the costs will be reduced to the considerable amounts.