Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Investigation of Sol-Gel Derived Spinel Added Alumina Low Cement Castable Refractories

Magnesia-Alumina (M-A) Spinel refractories have been used succesfully in steel, glass and cement industries. The main reason of the use preference of magnesia-alumina spinel refractories in the world, is the legal strictions emposed on the use of magnesia-chrome refractory bricks whose wastes create enviromental pollution. Hence, the use of magnesia-alumina spinel refractories are continuously increasing compared to the magnesia-chrome refractories.

The most important material characteristics of magnesia-alumina spinel refractories are low thermal expansion, high thermal shock resistance, chemical stability and high resistance against basic slags.

Nowadays, the application of alumina rich spinel refractories in the steel ladle, gives succesfull results and they are preferred because of their excellent properties mentioned above and their low cost.

In the first stage of this study, the production of Magnesia-Alumina (M-A) spinel [MgO-Al2O3] was performed using via sol-gel method. To produce M-A spinel via sol-gel method, aluminum isopropoxide (AIP) was hydrolyzed with water at 90 oC in a reactor and the solution was peptized by HCI by adjusting its pH to 2.3. Solution was stirred for 2 hours after MgO (<63 µm) addition. The mixture was held at 120 oC for 8 hours and gelled. Later, the gel was heated up to 550 oC at speed of 2 oC/min and was holded for 3 hours. Obtained material was heated to 800, 1200 and 1600 oC degrees and magnesia-alumina spinel (MgAl2O4) formations were obtained.

In the second stage of this study, pure (A1), %5 MgO added (M5) and %10 MgO added (M10) samples were produced by standard castable refractory production method. These samples were mixed in the boehmitic sol produced by sol-gel method instead of water. In addition, boehmitic sol+MgO mixer was used as another mixing media at the M+A sample. M5 and M10 samples respectively include %5 and %10 free MgO of the total mixture. M+A sample only included free MgO coming with mixing media.

Refractory matrix was strengthened by magnesia-alumina spinel which was obtained by the result of in-situ reaction of magnesia and alumina which in the refractory concretes fired at 1600 oC.

Physical and mechanical tests such as open porosity, water absorption, bulk density and compression strength were determined and slag-refractory corrosion tests were carried out using crucible method.

The first experiments in trying to obtain M-A spinel by sol-gel method weren’t successful. The experiments resulted the formation of Meixnerite phase instead of M-A spinel. Meixnerite is a magnesium-aluminum hydroxide compound and it is a hydrotalcite group mineral that has layered double structure. Meixnerite is used as an absorbent material in decreasing the emission of sera gases. Lately, a great deal of studies are been carried due to this important property.

It was concluded that A1 sample exhibited the lowest porosity, the highest mechanical strength and the best corrosion resistance under the experimental conditions compared to M5, M+A.

The sample containing %10 MgO (coaded M10), had more porosity than A1 sample, it showed similar corrosion resistance to A1 due to its high contend of M-A spinel phase.

HAPÇI Gökçe

Danışman : Doç. Dr. Gökhan ORHAN

Anabilim Dalı : Metalurji ve Malzeme Mühendisliği

Mezuniyet Yılı : 2009

Tez Savunma Jürisi : Doç. Dr. Gökhan ORHAN

Prof. Dr. İbrahim YUSUFOĞLU

Prof. Dr. Enver OKTAY

Prof. Dr. T. Osman ÖZKAN

Prof. Dr. İ. Servet TİMUR