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Showing 7 results for Subject: Ceramics and refractory materials
Effect of Ion Concentration on Viscosity of Doped Alumina Suspensions for Electrophoretic Deposition
En M. Milani, Dr S. M. Zahraee, Dr S. M. Mirkazemi,
Volume 36, Issue 2 (9-2017)
Abstract

Electrophoretic Deposition (EPD) weight is highly affected by electrophoretic mobility of powders in suspension. In theoretical aspect, electrophoretic mobility is influenced by suspension viscosity in opposite direction, and increasing in viscosity can decrease electrophoretic mobility and consequently can decrease EPD weight. In non-aqueous suspension, viscosity is determined by ion strengths of suspension. In this study, viscosity, electrical conductivity and deposit weight were determined for electrophoretic deposition (EPD) of alumina suspended in ethanolic solvent of Y-, Mg-, Ce- and La- salts, prepared in dispersant level between 350 to 1350 ppm. The concentration of XCly, (X: Mg, Y, Ce and La), is also found to be a critical factor to control  the viscosity. It is shown that the deposit weight is influenced by precursor concentration, and on the other hand, electrical conductivity, viscosity or the pH of the suspension cannot change the yield. All concentrations interactions, except Mg × Ce concentration are significant in ANOVA model. The viscosity of suspension reached 2.5 mPa.s with Mg-, Y-, La- and Ce- decreased to 100, 100, 100 and 0 ppm in low iodine concentration (400 ppm). The reason is that heavier cations can be adsorbed to alumina surface with iodine adsorption, but lighter Mg- cations can be adsorbed under the influence of OH groups excited on alumina surface.
 


Optimization of Slip Casting Parameters of Alumina Yttria Nanocomposite Powder for Obtaining Transparent Yttrium Aluminum Garnet Ceramics
G. Kafili, B. Movahedi, M. Milani,
Volume 36, Issue 3 (11-2017)
Abstract

In this study, Spark Plasma Sintering (SPS)  of both slip casted and powder specimens of alumina/ yttria core-shell nanocomposite were utilized for fabricating transparent Yttrium Aluminum Garnet (YAG) ceramics. Phase evolution, optical transmittance and the microstructure of sintered samples were compared. In slip casting process, Dolapix CE64 was used as a dispersant for preparing the stable aqueous slurry of this nanocomposite powder. The effect of Dolapix concentration and pH value on the stability of the suspension was described, and the viscosity diagrams were investigated at different pH value and different weight percents of Dolapix. The rheological behavior of the nanocomposite powder slipped at 60-70 wt% solid loading was studied by measuring their viscosity and shear stress as a function of shear rate of the slurry. The results showed that, the suspension has a minimum viscosity at pH of 10 by addition of 2.5 wt% Dolapix. Also, the slurry with solid loading of 60 wt% showed the Newtonian behavior and this rheological behavior was preserved even above this solid loading values. Slip casting technique caused the uniform size and pores distribution as well as eliminating large pores in the green body. Consequently, transparent YAG ceramic with 60% optical transmittance was achieved after SPS process of slip casted green body which was much higher than that of nanocomposite powder, i.e. about 30% at the same sintering conditions.
 


The Effect of Rheological Parameters on the Behavior of Silicon Nitride-Starch Slurry Used in Gelcasting Porous Silicon Nitride
M. Haghshenas Gorgani, M. Mirkazemi, F. Golestanifard,
Volume 37, Issue 4 (3-2019)
Abstract
In this research, the rheological behavior and stability of suspensions containing Si3N4, Al2O3, Y2O3 and starch were investigated in order to use them in the starch consolidation casting of porous silicon nitride. Dolapix CE64 was used as the dispersant. Then, the effect of some parameters such as Si3N4 surface oxidation, dispersant content, solid loading and starch content on the viscosity and rheological behavior of Si3N4-starch slurry was determined. Surface oxidation of Si3N4 powder at 800°C for 2 hours reduced the viscosity of the slurry, effectively. The best dispersant content was 0.4 wt. %, relative to ceramic powders. Slurries containing 30 to 40 vol. % and 7.5 to 25 vol. % starch, relative to total solid loading, had the suitable viscosity and the sufficient stability for casting by the starch consolidation method.

Synthesis & Characterization of CaB4O7 Powder by Solid-State Reaction
S. Solgi, M. Jafar Tafreshi, M. Sasani Qhamsari,
Volume 38, Issue 1 (6-2019)
Abstract
The synthesis of calcium tetraborate was investigated in a temperature ranging from 800℃ to 900℃ using the solid-state reaction method. The synthesis was done using ammonium tetraborate tetrahydrate as the source of boron. At temperatures of 800 ℃ and 880 ℃, the mixed phases from different compounds were formed. At the optimum temperature of 840℃, the mixed phase was only composed of meta and tetraborate phases. A 2wt% excess of ammonium tetraborate tetrahydrate led to the calcium tetraborate phase formation. X-ray diffraction analysis (XRD) confirmed the monoclinic structure at the optimum temperature of 840℃ and by 2wt% excess of ammonium tetraborate tetrahydrate. Formation of BO3 and BO4 units  composition and morphology of the prepared sample were studied by Field emission scanning electron microscopy (FE-SEM). The stoichiometry of the prepared powders was almost the same as the theoretical amounts, and powder particles exhibited some monoclinic characteristics.

Investigation of Glass- Steel Slag Foam Composite Sintering in Presence of SiC
A. Faeghinia, H. Mardi,
Volume 38, Issue 4 (1-2020)
Abstract
Amorphous steel slag was blended with different concentrations of waste glass (20, 40, 50, 60, 70 wt.%) and SiC to obtain a composite. According to Hot Stage Microscopy images, slag-glass composite contractions started at 1050 ºC. scanning electron microscope micrographs of slag-SiC (foaming agent) composite revealed tunnel-like porosities of 500 to 1000 microns. Gaseous products of carbide decomposition led to the formation of these tunnel-like porosities. By adding up to 50 wt. % of waste glass to this composite and sintering at 1200 ° C, the size of cavities decreased by 10 times and achieved 50 microns to form spherical cavities. By increasing glass content, the total porosity of slag-glass-SiC increased to 80 wt.% followed by a decrease in the strength to 3.2 MPa. Having an overall density of 0.8 g/cm3, the slag-glass composite could be classified as a porous foam material. Pseudo Waltonite phase was also detected in this composite after sintering.

Pressureless Sintering & Mechanical & Thermal Properties of ZrB2-ZrC-SiC Nanocomposite
I. Forooghi , M. Mashhadi,
Volume 39, Issue 4 (2-2021)
Abstract
Due to their unique features, Ultra-High Temperature Ceramics (UHTCs) have potential applications in aerospace, military and industry. ZrB2-SiC composite as one of these ceramics has been at the center of researches due to its attractive mechanical, thermal and oxidation resistance. In this study, the effect of ZrC addition on pressureless sintering behavior, mechanical, microstructural and thermal properties of ZrB2-SiC nanocomposite were investigated. For this purpose, micron-sized ZrB2 and ZrC powders and nano-sized SiC powder were used. ZrB2-20vol% SiC nanocomposites with addition of (3, 6, 9, 12, 15) vol% ZrC were sintered by pressureless sintering method at 2100 ºC. The results showed that the addition of ZrC improved relative density, hardness and fracture toughness of ZrB2-20vol% SiC nanocomposite. Optimum properties were obtained in a sample containing 12 vol% ZrC and the relative density, hardness and fracture toughness of this sample were reported to be 99.01%, 16.95 Gpa and 5.43 Mpa.m0.5, respectively. Thermal analysis of the samples showed that by adding ZrC, thermal diffusivity of this nanocomposite reduced. The highest thermal diffusivity at room temperature equaled 35.3 mm2 /s and was obtained for ZS composite.

INVESTIGATION OF SUPERCONDUCTIVITY AND MAGNETIC PROPERTIES OF BI2SR2CA2CU3O10+Θ CERAMIC SUPERCONDUCTOR WITH ADDITION OF SILICON CARBIDE NANOPARTICLES
H. Fallah-Arani, N. Riahi-Noori, S. Baghshahi, A. Sedghi, F. Shahbaz Tehrani,
Volume 40, Issue 4 (3-2022)
Abstract
In this research, the effect of addition of silicon carbide (SiC) nanoparticles on the improvement of the structural, superconductivity, magnetic, and flux pinning properties of high-temperature superconductor Bi1.6Pb0.4Sr2Ca2Cu3O10+θ (Bi-2223) was investigated. The Bi-2223 ceramic superconductor was prepared using the sol-gel method, and silicon carbide nanoparticles were modified by Azobisisobutyronitrile (AIBN). The X-ray diffractometry, feild emission scanning electron microscopy, magnetic susceptibility, and hystersis loop measurements were performed to characterize the synthesized compounds. Based on the magnetic measurements, the superconductivity transition temperature dropped with an increase in the content of nanoparticles. Also, the maximum magnetization, hysteresis loop width, critical current density, and magnetic flux pinning force belonged to the sample with 0.4 wt.% SiC nanoparticles.

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