Authors:
Mozhdeh Jalali | Islamic Azad University | Islamic Republic of Iran
Dr. Najmeh Lotfian | Arvin Dirgodaz Vijeh Sepano company | Islamic Republic of Iran
Mahsa Masoud | Arvin Dirgodaz Vijeh Sepano company | Islamic Republic of Iran
Marzieh Nourbakhsh | Institute Für Ziegelforschung Essen e.V. | Germany
Hossein Rafiei Boroujeni | Mehrgodaz Refractories Company | Islamic Republic of Iran
Amir Hossein Nourbakhsh | Arvin Dirgodaz Vijeh Sepano company | Islamic Republic of Iran
Prof. Amirabbas Nourbakhsh | Arvin Dirgodaz Vijeh Sepano company | Islamic Republic of Iran
Reza Davoudiandehkordi | Arvin Dirgodaz Vijeh Co | Islamic Republic of Iran
In spite of all positive features of magnesia as a refractory material, the hydration of MgO and formation of Brucite are the main obstacles in using magnesia in monolithic refractories. To overcome this problem, the substitution of calcium aluminate cement for hydratable alumina, and nano MgAl2O4 addition on magnesia–spinel castable have been investigated.
The magnesia spinel castable has been prepared with suitable amount and optimized particle size distribution from dead burned magnesia, reactive alumina, binders (calcium aluminate cement and hydratable alumina), and 6% wt water. The hydration resistance of castables investigated in sequential pH at 25 ℃. Then, 0-5 wt % of nano spinel, synthesized by citrate-nitrate route, substituted for part of fine magnesia. The optimized sample were fired between 1250 and 1700 ℃, then characterized by TGA, XRD, SEM. Physical and mechanical properties of optimized sample have been investigated by PLC, AP, CCS, and thermal gravimetric according to ASTM C113 and C20 standards.
The results approved that magnesia hydration could be reduced by replacing CAC with HA as a binder. The optimized amount of hydratable alumina was 5% according to TGA analysis. The reason is that hydratable alumina addition could decrease castable’s pH, and motivate Hydrotalcite phase formation on the surface of MgO that could decrease MgO hydration. Also, results showed that using hydratable alumina cement with 3wt% nano spinel additive not only increased hydration resistance, but also encouraged spinel formation at 1500 ℃ which increased thermal shock resistance and mechanical properties during the application of refractories.