Iranian Journal of Materials Science and Engineering

---

Abstract: Dolomite based refractories are widely used in Iranian steelmaking plants. In the present research, wear and corrosion of refractories used in steel-making converter lining in Esfahan Steel Company was studied. Post-mortem analysis of refractories clarified that the wear started with oxidation of carbon followed by chemical corrosion. Iron oxide from slag reacted with calcia, resulting in formation of low melting phase, and subsequent washout process, caused the refractory corrosion onset from the hot face. In addition, the effect of aluminum as an anti-oxidant and graphite on the corrosion resistance of refractory was investigated. Tar-dolomite samples containing different amount of graphite (0, 4, 7, and 10 wt. %) were prepared in order to study their physical properties, before and after coking. SEM micrographs employed to analyze the microstructures to determine the effect of graphite and antioxidant on corrosion behavior of the refractory. Results showed that oxidation process of carbon in the system was hindered and improved corrosion resistance by introducing graphite and antioxidant into the refractory composition.

---

Metakaolinite-based geopolymer has been synthesized at about 25 °C from metakaolin which has been calcined in different temperatures (600-900 °C) and different Na2O/SiO2 ratio activator (0.3-1.1). Compressive strength and microstructure of cement pastes after 7-28 days curing at ambient temperature were measured. Compressive strength tests on the samples showed that the sample made with calcined kaolin at 700 °C and molar ratio of 0.6 has highest average compressive strength of 32 MPa after 28 days of curing. Evaluation of infrared spectroscopy (FTIR) and microstructure showed that geopolymer cement developed and new molecular structure established

---

The synthesis of micro-sized, uniformly distributed Al₂O₃-15Vol% Ni powders were studied through three step co-precipitation of hydroxides mixtures from proper solution, calcination at air atmosphere and final step of calcined powders in a carbon bed. Al and Ni hydroxide and amorphous phase were first obtained from their salt’s solutions through chemical co-precipitation method by adjusting pH. The precipitated powders were then calcined to obtain a mixture of their oxides as NiO and NiAl₂O₄ which were reduced in a carbon bed at various temperatures up to 1300. Proper temperature for calcination in air was determined through TG analysis; 900. SEM observation of powders after reduction, revealed micro-sized Ni particles, along with fin distribution of Ni and Al₂O₃ elements. XRD analysis of the calcined sample showed the presence of NiAl₂O₄ and NiO and the same analysis for the reduced sample confirmed the formation of Al₂O₃ and Ni.    

---

An accurate prediction of reaction kinetics of silicon nitridation is of great importance in designing procedure of material production and controlling of reaction. The main purpose of the present study is to investigate the effect of temperature on the kinetics of reaction bonded silicon nitride (RBSN) formation. To achieve this, nitrogen diffusion in the silicon nitride layer is considered as a reaction controlling factor and sharp interface method based on this theory is used to develop the analytical model. In the developed model, the variations in the size of silicon particles are calculated for the whole reaction. In the experimental phase, the extent of nitridation is measured for different reaction temperatures and 4 different reaction times and then, the occurrence of full nitridation is shown by EDS analysis. Furthermore, an analytical approach was established for describing the kinetics of compound formation and the performance of the developed model is evaluated through statistical analysis. There was good agreement between experimental data and predictions of the developed model which demonstrates the accuracy of considered presumptions and reaction mechanisms. An accurate prediction of reaction kinetics of silicon nitridation is of great importance in designing procedure of material production and controlling of reaction. The main purpose of the present study is to investigate the effect of temperature on the kinetics of reaction bonded silicon nitride (RBSN) formation. To achieve this, nitrogen diffusion in the silicon nitride layer is considered as a reaction controlling factor and sharp interface method based on this theory is used to develop the analytical model. In the developed model, the variations in the size of silicon particles are calculated for the whole reaction. In the experimental phase, the extent of nitridation is measured for different reaction temperatures and 4 different reaction times and then, the occurrence of full nitridation is shown by EDS analysis. Furthermore, an analytical approach was established for describing the kinetics of compound formation and the performance of the developed model is evaluated through statistical analysis. There was good agreement between experimental data and predictions of the developed model which demonstrates the accuracy of considered presumptions and reaction mechanisms.

---

In this paper the chemical interaction between catalyst and support has been studied to understand the observed different growth rate of CNTs in our previous paper. Both pure MgO and Mg(NO₃)₂ . 6H₂O as sources of the MgO catalyst support and Fe₂(SO₄)₃ · xH₂O as the source of the Fe catalyst, were employed. A Fe catalyst supported on MgO has been synthesized using the wet impregnation method followed by calcination. To compare the catalyst grain size and its distribution, the sample were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and BET specific surface area (SSA) measurement and X-ray photoelectron spectroscopy (XPS). XPS technique have utilized complementary to demonstrate the existence of chemical interaction between MgO support and Fe catalyst. Results revealed that the type of precursor used to prepare the support has a significant influence on the morphology of the support and the associated distribution of the Fe catalysts. The highest yield of MgFe₂O₄ phase was obtained using a pure MgO precursor which after calcination results in a homogenous distribution of nano-sized Fe particles over the support surface

---

In the present study, a soft computing method namely the group method of data handling (GMDH) is applied to develop a new and efficient predictive model for prediction of conversion percentage of silicon. A comprehensive database is obtained from experimental studies in literature. Several effective parameters like time, temperature, nitrogen percentage, pellet size and silicon particle size are considered. The performance of the model is evaluated through statistical analysis. Moreover, the silicon nitridation was performed in 1573 k and results were evaluated against model results for validation of the model. Furthermore, the performance and efficiency of the GMDH model is confirmed against the two most common analytical models. The most effective parameters in estimating the conversion percentage are determined through sensitivity analysis based on the Gamma Test. Finally, the robustness of the developed model is verified through parametric analysis.