فهرست مطالب

Advanced Ceramics Progress - Volume:4 Issue: 3, 2018
  • Volume:4 Issue: 3, 2018
  • تاریخ انتشار: 1397/05/30
  • تعداد عناوین: 6
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  • Mosleh Naderi, Mohammad Farvizi *, Kourosh Shirvani, Mohammad Reza Rahimipour Pages 1-7
    In this study, aluminide coating was employed to enhance the high-temperature cyclic oxidation of Rene-80 superalloy at 950ºC. The microstructural aspects and phase constituents of samples were  investigated with scanning electron microscopy (SEM) and x-ray diffraction (XRD) techniques. The result of oxidation tests showed that the weight gain in the uncoated sample was considerably higher than the aluminide coated sample, which indicates the higher rate of oxide formation on the uncoated surface. With the aid of microstructural and XRD analysis, it was confirmed that with the increment of oxidation cycles, the thickness of aluminide coating reduced and the protective β-NiAl phase was converted to alumina scales. According to the EDS results taken from the top coat, it was found that with the increase of oxidation cycles, the content of aluminium in the top layer was drastically decreased and the weight percentage of oxygen was considerably enhanced. Also, in higher oxidation cycles, other protective elements such as Cr and Ti outwardly diffused from the inter-diffusion zone (IDZ) layer which led to reduction in the content of these elements in inner zones of the aluminide coating.
    Keywords: Rene-80, Aluminide Coating, Cyclic oxidation, microstructural aspects
  • Elaheh Abdollahi, Hamidreza Bakhsheshirad * Pages 8-15

    In this study, mechanical properties and apatite formation ability of synthesized fluorapatite-hardystonite (FA-HT) nanocomposite scaffolds were investigated. Hardystonite (HT; 5 and 10 wt.%) as a reinforcement phase was incorporated into the FA scaffold. FA was mixed with HT for 4 h under argon gas at 220 °C. A space holder method was used for fabricating porous FA-HT scaffolds. Sodium chloride (NaCl) was used as pore-forming agent in this method. Then, the powder was compacted under a pressure of 220 MPa. Finally, the samples were sintered at 1000 ºC for 2 h. The X-ray diffraction (XRD) results of the synthesized scaffolds confirmed the formation of FA and HT powders. Studying the microstructure of the samples showed that synthesized scaffolds had a porous structure with interconnected pores, similar to the porosity degree of natural bones. The results also revealed that the mechanical properties of scaffolds were improved; the compressive strength values of the FA-5HT and FA-HT scaffolds were obtained 1.6 MPa and 2.8 MPa, respectively. The young modulus values for these scaffolds were 5.5 MPa and 12.4 MPa, respectively. Results of bioactivity test showed the ratio of calcium to phosphate (Ca/P) in scaffolds was 1.71±0.3 and 1.60±0.5 for FA-5HT and FA-10HT samples, respectively. Based on the results, FA-HT scaffolds have desirable mechanical properties and suitable level of bioactivity which can be used as new and promising biomaterials in bone tissue engineering and repairing bone defects.

    Keywords: Fluorapatite, Hardystonite, Scaffold, Bone tissue engineering scaffold
  • Ahmad Reza Abbasian *, Najmeh Omidvar Pages 16-22

    In this research, two series of ultra-low cement high alumina refractory castables containing 0 and 0.4 wt.% of nano-titania were prepared using different amounts of polycarbonic acid (DOLAPIX FF 26) as a dispersant. Several characteristics including microstructure, flowability, mechanical strength, bulk density and apparent porosity of the samples were analyzed. The results showed that the optimum amount of the dispersant was 0.13 wt.% and 0.20 wt.% for castable having no nano-titania and the one containing 0.4 wt.% nano-titania, respectively. The strength of castable containing 0.4 wt.% nano-titania dispersed by 0.20 wt.% of DOLAPIX FF 26 was 1.5 times higher than that of castable without nano-titania (dispersed by 0.13 wt.% of DOLAPIX FF 26). This can be explained by the fact that when the optimum amount of dispersant is used, the well-dispersed nano-titania particles act as a catalyst in the cement hydration reactions and will result in higher strength of the refractory castables.

    Keywords: Alumina refractory castable, Ultra-low cement, Dispersant, Nano-TiO2
  • Maryam Shojaie *, Reza Kaveh Pages 23-35

    In the present study, the effect of alumina on the pore structure and hydrothermal stability of nanostructured silica was investigated. SiO2 and SiO2-15wt%Al2O3 membranes were prepared by dip coating on mesoporous γ-Al2O3 coated macroporous α-alumina support. The particle sizes of sol were increased by adding of alumina to silica sol. Through the addition of the alumina up to 15 wt% and heat treatment at 500 °C, the silica structure was remained amorphous and the thickness of the top layer was in the range of 200-500 nm because of an increase in the sol viscosity. FT-IR analysis showed the formation of Si-O-Al bonds after heat treatment in the SiO2-15wt%Al2O3 membrane. After placing the membranes under hydrothermal test, the pore volume and size were slowly decreased by means of alumina addition in that order. Furthermore,  the permeability of gas molecules (H2, He, CO2,…) from the silica membrane was abruptly decreased compared to the SiO2-15wt%Al2O3 membrane. Therefore, the membrane containing the added alumina had a more suitable hydrothermal stability due to the formation of more stable Si-O-Al bonds.

    Keywords: Nanostructure silica, Silica-alumina membrane, Hydrothermal stability, Nanoporous Membrane
  • Alireza Kiani, Pooneh Barfi, Sahar Mollazadeh * Pages 36-42

    In-situ alumina-zirconia composite bodies were fabricated by heat treatment of gibbsite-zircon-kaolinite mixture at 1450℃. The current research investigated crystallization behavior and mechanical properties of the mentioned mixture in the presence of 5 wt.% MgO as an additive. X-ray diffraction (XRD) results showed that alumina, zirconia, and magnesium aluminosilicate were crystallized during the heat treatment at 1250-1550℃. It was expected that mullite and zirconia were crystallized as the final phases; however, the addition of 5 wt.% of MgO changed the behavior of the mentioned mixture during the heat treatment at 1250-1550℃. Energy diffractive X-Ray spectroscopy (EDS) reported that after heat treatment at 1450℃, an Al3+-rich aluminosilicate phase was formed as the matrix of the composite. Crystallization of alumina and zirconia and the existence of the amorphous aluminosilicate phase formed a composite with appropriate hardness and mechanical strength. The diametral tensile strength and Vickers microhardness values of the final composite were 130±7 MPa and 7.49 ± 1.2 GPa, respectively.

    Keywords: Amorphous aluminosilicate phase, Magnesia, Alumina-zirconia composites
  • Marzieh Jalilpour, Mohammad Rezvani *, Khalil Farhadi Pages 43-49
    The sol-gel synthesis method allows greater control over glass morphology at a relatively low processing temperature (200 °C) in comparison with melt-derived glasses. In present study, phosphate-based glasses with the general formula of (P2O5)55-(CaO)25-(Na2O)10-(TiO2)10 was synthesized via a novel and facile sol-gel method for use in biomedical applications. For this purpose, dimethylformamide and acetone were used as the solvent. Glass powders that are obtained from the dried gel was analyzed using several characterization techniques including X-Ray Diffraction, Fourier Transform Infrared Spectroscopy, Simultaneous Thermal Analysis, Brunauer-Emmett-Teller surface area and porosity analyzer and Scanning Electron Microscopy. The X-Ray Diffraction results confirmed the amorphous and glassy nature of prepared samples. The Fourier Transform Infrared spectroscopy results revealed that by adding TiO2, titanium oxide (TiO6) entered into the network which likely acts as an oxide modifier. It was observed that crystallization temperature (Tc) for the sample synthesized by dimethylformamide (DMF) (~646 °C) is more than the one synthesized by acetone (~500 °C). The surface area of the acetone and DMF of synthesized samples is 40 m2/g and 44.5 m2/g, respectively. Furthermore, to examine the bioactive capacity of glasses, the samples were soaked in a simulated body fluid (SBF) for 7 days. The analyses were shown the formation of hydroxyapatite on glass powders after 7 days of immersion in SBF solution. The morphology of hydroxyapatite was spherical and its particle size was ~8 nm.
    Keywords: Phosphate-based glass, Sol-Gel, Acetone, Dimethylformamide, SBF