Different Amounts Of Al2O3 Research Articles

Dielectric Properties of Ultra‐Low Sintering Temperature Al2O3–BBSZ Glass Composite

Ceramic composites of B2O3–Bi2O3–SiO2–ZnO (BBSZ) glass mixed with Al2O3 (10–50 vol%) were sintered at 450°C, and their microstructural and dielectric properties investigated. Dense structures were obtained when the Al2O3 content was lower than 30 vol%. Raman, XRD, and FESEM showed the existence of a secondary phase, Bi24Si2O40, in all samples. The dielectric properties of the composite with 30 vol% addition of Al2O3 showed good dielectric properties with εr of 14.8 and 20.8 and 32.5 at 100 kHz and 100 MHz and 1 GHz, respectively. The tanδ values at the same frequencies were 0.004 and 0.006 and 0.016. The results show that BBSZ glass with different amounts of Al2O3 exhibit widely applicable relative permittivity values and affordable loss and are thus promising candidates for ultra‐low sintering temperature applications.

Conductivity, structure, and thermal properties of chitosan‐based polymer electrolytes with nanofillers

AbstractThis paper focus on the effect of nanosize (<50 nm BET) inorganic alumina (Al2O3) filler on the structural, conductivity, and thermal properties of chitosan‐based polymer electrolytes. Films of chitosan and its complexes were prepared using solution‐casting technique. Different amounts of Al2O3 viz., 3, 4.5, 6, 7.5, 9, 12, and 15 wt% were added to the highest room temperature conducting sample in the chitosan–salt system, i.e. sample containing 60 wt% chitosan–40 wt% NH4SCN. The conductivity value of the sample is 1.29 × 10−4 S cm−1. On addition of 6 wt% Al2O3 filler the ionic conductivity increased to 5.86 × 10−4 S cm−1. The amide and amino peaks in the spectrum of chitosan at 1636 and 1551 cm−1, respectively, shift to lower wavenumbers on addition of salt. The glass transition temperature Tg for the highest conducting composite is 190°C. The increase in Tg with increase in more than 6 wt% filler content is attributed to the increase in degree of crystallinity as proven from X‐ray diffraction studies. Copyright © 2009 John Wiley & Sons, Ltd.

Influence of Si:Al ratio on the microstructural and mechanical properties of a fine-limestone aggregate alkali-activated slag concrete

Three series of fine limestone aggregate, alkali-activated blast furnace slag (AAS) concretes were fabricated and tested; two through activation with waterglass/NaOH solution, of which one included NaCl as a retarding agent, and one activated by Na2CO3. Each of these series was made up of three formulae containing different amounts of Al2O3. The compressive strengths of the series activated by waterglass/NaOH after 28 days were ≈65 ± 5.3 MPa, a 22% increase compared to previously reported formulae containing no additional Al2O3. Increasing the amount of Al2O3 did not further increase strength, however. The Na2CO3-activated formulae had strengths of ≈35 ± 3 MPa after 28 days, representing no increase in strength over formulae not containing Al2O3 previously reported. X-ray diffraction showed the main binding phase to be calcium silicate hydrate (C–S–H) gel, as is commonly found in ordinary Portland cement (OPC). Fourier transform infrared spectroscopy showed little difference from the previously reported results for formulae not containing Al2O3 and strongly resemble the spectra reported elsewhere for C–S–H. Electron microscopy, coupled with energy dispersive spectroscopy, showed the cementing phase to be a single homogenous phase—not a mixed system of geopolymer and C–S–H gel—with a lower volume fraction of unreacted slag than formulae without Al2O3. The reason for the increase in strength of Al2O3-containing formulae is unclear, but is unlikely to be ascribed to the formation of large amounts of ‘geopolymers’ and may be related to a possible increase in reaction temperature of between 2 and 5°C, depending on amount of additive.

Dielectric, thermal and sintering behavior of BaO-B2O3-SiO2 glasses with the addition of Al2O3

In the Pb-free low temperature sinterable glass of the (55)BaO-(35)B2O3-(10)SiO2 system, different amounts of Al2O3 were added and the crystallization behavior, sintering behavior and physical characteristics of the glass were examined. It was found that Al2O3 suppressed crystallization of the glasses because it played the role of a network former. The glass transition temperatures, crystallization temperatures, and optimum sintering temperatures increased as the amount of Al2O3 increased. In the case of a specimen with a large amount of Al2O3, which was not easily crystallized, an over-firing phenomenon was observed when the sintering temperature was higher than the optimum sintering temperature. While the over-firing phenomenon was not observed due to the crystallization in the sample with a little amount of Al2O3. The dielectric constant and thermal expansion coefficient of the glasses were also examined and explained in correlation with the crystallization and densification.

The aluminium effect on gel-derived iron silica glasses

Sol–gel aluminosilicate glasses containing 1 mol% of Fe2O3 and different amounts of Al2O3 (1; 2; 3; 4; 6 and 8 mol%) have been investigated. The ultraviolet–visible–near infrared spectrophotometry (UV–VIS–NIR), electron paramagnetic resonance (EPR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), has been employed to obtain information about the structural evolution of the samples. The concentration of Al2O3, the treatment temperature and the furnace atmosphere play an important role in the structural incorporation of iron. The treatment of the samples, in air and under reducing conditions, results in remarkable changes in the UV–VIS–NIR and EPR spectra. In the samples were detected nanoparticles. The low temperature blocking of the nanoparticles magnetic moments has been clearly evidenced in the EPR derivative spectra at low temperatures.

Creep of particle reinforced aluminium alloy: C.Broeckmann, A.Packeisen. (Ruhr University, Bochum, Germany.) Metall., vol 52, no 12, 1998, 701–711. (In German.)

Samples with various ratios of AlN/Al2O3 were fabricated via vacuum hot-pressing at 1700 °C under an applied pressure of 30 MPa for 90 min using Y2O3 as a sintering aid. The densification process, microstructural development, and formation of AlON phase from Al2O3 and AlN were investigated. Al2O3 additive can improve the physical and mechanical properties, and purification of the grain boundaries. AlON are almost formed completely when the content of Al2O3 is 80 vol%. The effects of composition, microstructure, and exposure time at 1400 °C on the oxidation behavior of AlN samples with different amounts of Al2O3 were investigated. The sample with 80 vol% alumina has the best oxidation resistance.

A ceramic matrix composite obtained by highly exothermic reaction

Ceramic-metal composites have been obtained by the highly exothermic reaction between an intermetallic, Al 2 Zr, and an oxide, Nb 2 O 5 . The reaction has been studied for different conditions of time, temperature and furnace atmosphere. Samples have been prepared with different amounts of Al 2 O 3 , added as a diluent, to control the reaction. The resulting microstructure, characterized by X-ray diffraction, optical microscopy and electron microscopy, always shows a dendritic or globular phase of ZrO 2 , a eutectic region of Al 2 O 3 and ZrO 2 , and large, predominantly metallic, inclusions consisting of niobium with associated niobium oxides. Keramik-Metall-Verbundwerkstoffe wurden durch die äußerst exotherme Reaktion zwischen intermetallischem Al 2 Zr und oxidischem Nb 2 O 5 hergestellt. Die Reaktion wurde bei verschiedenen Zeiten, Temperaturen und Ofenatmosphären untersucht. Die Proben wurden zur Kontrolle der Reaktion mit verschiedenen Mengen an Al 2 O 3 verdünnt. Die sich ergebenden Gefüge wurden mittels Röntgenbeugung, Lichtmikroskopie und Elektronenmikroskopie untersucht. Es zeigte sich in allen Proben eine dendritische oder globulare ZrO 2 -Phase, ein eutektischer Bereich aus Al 2 O 3 und ZrO 2 und große, vorwiegend metallische Einschlüsse aus Niob mit benachbarten Nioboxiden. On a élaboré des composites céramique-métal par mise en oeuvre de la réaction hautement exothermique entre l'intermétallique Al 2 Zr et l'oxyde Nb 2 O 5 . Cette réaction a été étudiée pour différentes conditions de température, de temps et d'atmosphère du four. On a préparé des échantillons présentant différentes teneurs en Al 2 O 3 , ajoutée comme diluant afin de contrôler la réaction. La microstructure finale obtenue, caractérisée par diffraction X et microscopies optique et électronique, présentait toujours une phase ZrO 2 dendritique ou globulaire, un domaine eutectique d'Al 2 O 3 et ZrO 2 et des inclusions de grande taille majoritairement métalliques constituées de niobium, auxquelles étaient associées des oxydes de niobium.

Quartz in Pottery Stones from Various Localities and Its Cristobalitization

Some characteristics of quartz in pottery stones from various localities and its cristobalitization by firing have been examined by various methods. Specimens were prepared from the pottery stones by crushing, classifying to 10-37μm, and purifying by hot phosphoric acid and fluoric acid. Substitution of Al ion in quartz was confirmed from ESR and EPMA analyses. With the increase in the amount of Al2O3 substitution in quartz, following correlations were observed: (1) increase of unit cell volume, (2) increase of lattice strain, (3) lowering of α-β inversion temperature. Some specimens were found to be mixtures of quartz substituting different amounts of Al2O3. Cristobalitization from quartz in the pottery stones by firing was found to be correlated with the amount of Al2O3 substituted in quartz and a temperature at which quartz convert to cristobalite was lowered with the increase in the amount of substituted Al2O3. Larger amount of cristobalite was formed from the pottery stones with increasing the amount of Al2O3 substituted in quartz and with decreasing the amount of flux components in the pottery stones.