Showing 13 results for Alumina
Estili M., Paydar M.h., Bahrololoom M.e.,
Volume 2, Issue 3 (9-2005)
Abstract
Dispersion and rheological behaviors of ionically stabilized aqueous alpha alumina suspensions were investigated in various pH values (3, 11) and solid volume fractions (4, 7, 10, 15) Vol% using sedimentation experiment as well as viscosity measurement. Interface separating porous-packed sediment from a relatively clear supernatant at pH 11 was measured over 20 hours with the aim of obtaining linearity range, initial settling velocity, final sediment height and suspension sensitivity factor, whilst it failed to be observed in the case of pH 3 for its turbid supernatant. Thus, the final sediment level instead of interface location was taken into consideration. For all solids loading, final sediment level in the case of pH 3 was smaller than those in pH 11. The interface was observed to be moving downward in a linear fashion, with the steady drive toward an equilibrium state, which was substantiated to be pH and solid loading dependent. As ? increased, linearity time changed in an ascending order. pH 11 suspensions showed good agreement with the well-known Richardson-Zaki equation and displayed dramatic variations in initial settling velocity, whilst it was not the case for pH 3 as understood generally by turbidity observations. In addition, pH and ? appeared to be more effective in giving stability to the suspending systems. On the other hand, rheological behaviors of these suspensions were taken into consideration for better indication of suspension stabilization degree in which suspension yield stress derived using viscosity values was focused. The results showed that ?y at pH 3 is much lower than that of at pH 11. This is a further indication of better dispersion at pH 3. It was also found that for all ? values, pH 3 suspensions were more stable than the flocculated pH 11 ones.
Salahi E., Ebadzadeh T., Moztar Zadeh F., Solati Hashjin M.,
Volume 2, Issue 4 (12-2005)
Abstract
Compositions of Al2O3+Si, SiO2+Al and Al+Si systems were prepared to study the effect of reaction bonding process on the mullite formation. The composition of each system was adopted according to mullite stoichiometery and sintered in 700-1600°C range. Results showed that the formation of reaction bonded mullite starting from Al2O3+Si mixtures, proceeded in two partially overlapping steps, the oxidation of Si to SiO2, and the reaction of SiO2 and Al2O3 to form mullite. In this system, up to 1400°C, conversion of Si to SiO2 was taken place and cristobalite formed, but mullite formation was not observed. Mullite phase started to form at 1450°C. Results indicated that complete reaction was not occurred up to 1600°C and 2 hours soaking time. XRD patterns of samples in Al+ SiO2 system showed that the reaction through sequences: (a) reduction of SiO2 by Al, (b) formation of a- Al2O3 and SiO2-rderived Si oxidation, and (c) mullite formation. X-ray diffraction patterns of heat-treated Al+Si system showed that reaction between Al and oxygen at 900°C was occurred with the reaction product being a- Al2O3 Oxidation of Si and formation of mullite were not detected in this system. SEM micrographs showed that both Al2O3+Si and SiO2+Al systems have similar microstructures, which consisted of a- Al2O3, mullite and free Si. The microstructures of the samples in Al+Si system consisted of a- Al2O3 free Al and Si with intermetallic Al-Si compound.
Moore R.e., Karakus M.,
Volume 2, Issue 4 (12-2005)
Abstract
In situ refractories are defined as brick or unshaped products, which react internally or with furnace atmospheres and/or slag components so as to be enhanced in their performance. Examples of such products are discussed with emphasis on those that are currently employed and are being developed for the melting of iron and steel. Some strategies for the development of future in situ products are outlined.
H. Ghasemi, M. A. Faghihi Sani, Z. Riazi,
Volume 4, Issue 3 (12-2007)
Abstract
Abstract: The effect of phase development on peel strength of alumina-copper metalized joint has
been investigated. The alumina-copper joint was prepared in three stages. The alumina substrate
was, first, metalized at 1500°C in H2-furnace by a new formulation. In the second step, a nickel
layer was electroplated on the metalized layer with approximately 10µm thickness. Finally, copper
strips were bonded to metalized alumina with Ag-Cu (72-28) filler metal. The peel strength of the
joint was 9.5±0.5 Kg/cm which shows approximately 30% increase in comparison to previous
works. By study of fracture surface and crack propagation path, it has been concluded that this
increase is due to the formation of more spinel phase.
M. Pirhadi Tavandashti, M. Zandrahimi, B. Akbari,
Volume 6, Issue 1 (3-2009)
Abstract
Abstract: Nanoparticles exhibit a high reactivity and strong tendency towards agglomeration. In this study, aluminum
oxide (alumina) nanoparticles were characterized by gas adsorption (BET), transmition electron microscopy (TEM)
and photon correlation spectroscopy (PCS) techniques to assess the agglomeration of the particles. There is a good
correlation between the BET and TEM measurements but PCS was larger in the mean and median size and with a
degree of agglomerates being detected. Some agglomeration was evident, but most of the particles existed as discrete
objects as observed in the (HR) TEM images which were in good agreement with the agglomeration factor.
K. Christine Stella, A. Samson Nesaraj,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
as magnetic materials, semiconductors, pigments, catalysts, refractories and electronic ceramics. In this paper, we
reported the preparation of NiAl
The resulting powder was chracterized by XRD, particle size analysis and SEM. The XRD patterns show that the
combustion technique was excellent to prepare single – phased cubic NiAl
found to be around 14 nm. From the particle size analysis, it was found that the 50 % of the particles lie below 30
µm. The micrographs show the formation of fluffy agglomerates composed of fine particles.
Spinels constitute an advanced group of materials with great technologial appeal, being able to be applied2O4 spinels by low temperature combustion technique using glycine and urea as fuels.2O4 particles and the crystallite sizes were
B. Akbari, M. Pirhadi Tavandashti, M. Zandrahimi,
Volume 8, Issue 2 (6-2011)
Abstract
Abstract: Most properties of nanoparticles are size-dependent. In fact, the novel properties of nanoaprticles do not prevail until the size has been reduced to the nanometer scale. The particle size and size distribution of alumina nanoparticle, as a critical properties, have been determined by transmission electron microscopy (TEM), photon correlation spectroscopy (PCS), surface area analysis (BET) and x-ray diffraction peak broadening analysis. The particle size was found to be in the range of 5-95nm. Cumulative percentage frequency plot of the data extracted form TEM images indicates that particle size distribution obeys the log-normal function. The TEM images also reveal that particles are spherical in shape and loosely agglomerated. Comparing of the XRD and TEM results shows that the particles are single-crystal. The HRTEM images also verify that the particles have a single-crystal nature. In comparison, there is a good correlation between the BET, XRD and TEM measurements other than PCS that is sensitive to the presence of the agglomerates.
Sh. Damghanian, H. Omidvar, S. H. Tabaian, A. R. Azadmehr,
Volume 11, Issue 2 (6-2014)
Abstract
The conical nanostructure improves the applications of alumina membranes and provides three dimensional
nanometer scale systems to study the chemical and physical properties. In this study, the nano cone structure is
produced in porous anodic alumina (PAA) by two-step anodizing. This conical nanostructure will improve the
application of PAA membranes. This approach is novel generation of the so-called "gradually decreased voltage"
technique, in which the voltage- time curve is divided into three stages and the effect of each step is investigated for
different electrolytes. The effect of the decreasing voltage is examined in two types of electrolytes oxalic and
phosphoric acid with a constant decrease in voltage rate. The results of SEM, FE-SEM images show the slope of the
inner cone layer in the oxalic acid to be considerably larger compared with phosphoric acid.
Y. Kianinia, A. K. Darban, E. Taheri-Nassaj, B. Rahnama, A. Foroutan,
Volume 12, Issue 1 (3-2015)
Abstract
A method for producing high surface area nano-sized mesoporous alumina from inexpensive Iranian kaolin
as raw material is proposed. In this method, first, kaolin was purified for purifying Kaolin, High Grade Magnetic
Separation and leaching with HCl and chemical bleaching treatment by using sodium dithionite (Na
2
S
2O4
) as reducing
agent in acidic media (H
2SO
4
) were used. Purified kaolin was calcined. After that, Al (hydr) oxide from acid -leachates of calcined kaolin was precipitated with ammonia, in presence of polyethylene glycol. Finally, a white
powder of nano-sized alumina particles was obtained after calcination. BET surface area, X-ray diffraction (XRD),
Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) were used to characterize
the sample. The resulting alumina with relatively high surface area (201.53 m
2
g
-1
) and narrow mean pore diameter
(6.91 nm), consists of a particle size distribution ranging from 22 to 36 nm.
A. R. Amini, A. R. Zakeri, H. Sarpoolaky,
Volume 12, Issue 3 (9-2015)
Abstract
In this paper, the effect of MgO, BaO, Na
2
O and SrO addition to a pre-melted CaO-Al2O3
-Si
2
O synthetic
slag on sulfur removal from plain carbon steel was studied under the same experimental conditions. The slags were
pre-melted at 1400°C in an electric resistant furnace and desulfurization experiments were carried out in a high
frequency induction furnace. The results showed that the optimum reaction time for desulfurization was 15 min. It was
found that while SrO addition to the ternary slag enhances the sulfur removal capability, MgO, Na
2O and BaO
additions reduce desulfurization efficiency of the ternary slag. Moreover, it was observed that restricting access to
oxygen from the atmosphere by using a covered crucible, could increase desulfurization efficiency of the slag by more
than two fold
S. Komeili, M. Takht Ravanchi, A. Taeb,
Volume 14, Issue 1 (3-2017)
Abstract
A series of MAl2O4 (M=Ni, Zn, and Cu) aluminates were prepared by using impregnation method; the metal content of the products was ranged between 5wt% to 25wt%. The samples were characterized by x-ray diffraction (XRD), Brunauer Emmett Teller (BET) surface area, NH3 temperature-programmed desorption (NH3-TPD), and inductively coupled argon plasma (ICP).
The specific surface areas of zinc, nickel and copper aluminates were in the ranges of 47-77m2/g, 63-87m2/g and 1.6-3m2/g, respectively. The surface acidity decreased in the order of CuAl2O4<< NiAl2O4< ZnAl2O4<< Al2O3. By increasing the amount of metals in the samples, the number of acidic sites decreased, but their strength did not significantly change. Ni-aluminates have fewer acidic sites than Zn-aluminates, particularly in strong acid sites
M. Ghamari, M. Ghasemifard,
Volume 17, Issue 2 (6-2020)
Abstract
In this research, the dependence of the optical band gap of nano gamma alumina on the OH/Al ratio and concentration of aluminum sulfate is measured through diffuse reflectance spectroscopy (DRS) in the range of 900-1100nm. The samples were prepared via sol-gel method. The results showed that the band gap is pH and concentration-dependent but in a different way. The direct band gap of alumina was determined to be 3.40, 4.37, 3.90, and 3.65 eV for samples prepared at pH 6, 7, 8, and 9, respectively. A decreasing trend was observed with increasing pH (except for pH6). The lowering of the band gap may be associated with the variations in particles size during synthesis due to the quantum size effect. The values of the band gap increased significantly through increasing concentration from 3.90 to 5.65 eV for 0.1M to 0.3M. The role of concentration in band gap control is remarkably more than pH.
Sara Ahmadi, Reza Momeni,
Volume 20, Issue 4 (12-2023)
Abstract
The polymer modified cementitious tile adhesives are very significant in construction sector. In order to considerably improve the bond qualities of the tile adhesive in polymer modified mortars, the proportions of constituent ingredients should be carefully selected. Consequently, to design high performance tile adhesives, interactions between all the components, such as the adhesion mechanisms between the polymers film and the substrate and the effect of various additives should be recognized. The effect of vinyl acetate ethylene (EVA), high alumina cement (HAC), and additives such as calcium formate and polycarboxylate on the adhesion qualities of ceramic tile adhesive was explored in this study. The findings indicated that these ingredients had an impact on the mortars' adhesive properties, and it is necessary to find their optimal amounts in order to achieve the maximum adherence. The results showed that the tensile strength of mortar was increased with increasing the polymer amounts. A microstructural analysis revealed that the polymer was distributed homogenously throughout the mortar. The optimum amount of the used high alumina cement was determined 3 wt.%. Additionally, increasing the amount of accelerator and super plasticizer increased the tensile strength of ceramic tile adhesive by approximately 20-30%.
