Al Amount Research Articles

Tailoring the Electrical Properties of HfO2 MOS-Devices by Aluminum Doping.

In this work dielectric and electrical properties of Al-doped HfO2 layers deposited by plasma-enhanced atomic layer deposition in dependence on the thickness and the added Al amount in the films have been investigated. Special attention is dedicated to C-V and I-V hysteresis analysis as a measure for trapping phenomena in the films. A detailed study of conduction mechanisms in dependence on the composition of the layers has also been performed. The densities and spatial and energy positions of traps have been examined. It is found that only a small amount of Al-doping decreases the trapping which is assigned to a reduction of oxygen vacancy-related traps in HfO2. On the contrary, higher amounts of Al introduced in HfO2 films increase the trapping ability of the stacks which is due to the introduction of deeper Al2O3-related traps. The results imply that by adding a proper amount of Al into HfO2 it is possible to tailor dielectric and electrical properties of high-k layers toward meeting the criteria for particular applications.

Orientation Control of Zeolite Films Using in Situ Electrochemical Method in Ionic Liquids

Zeolite films which rely on molecular sieving characteristics have been widely used in membranes and membrane reactors1. Recently, their other remarked properties make their applications extend to functional coatings2, such as corrosion-resistant coatings3 and low dielectric constant insulators4. Almost all the performance is beneficial to a preferred orientation. The orientation is carefully controlled in seeded growth which requires multi- steps, while simple in situ synthesis often leads to a random orientation. So how to simply control the orientation is a great challenge both in academic and industry. To this end, we invented an in situ electrochemical ionothermal method which introduces an electric field to the ionothermal system to control the orientation. The Al working and counter electrodes were both used as substrate and Al source for zeolite films. And a Pt wire acts as the pseudo-reference electrode within the common three-electrode cell. The synthesis solution consisted of only ionic liquid 1-ethyl-3-methylimidazolium bromide ([emim]Br), phosphorus source H3PO4 and mineralizing agent HF. In the ionothermal tests, only a few cauliflower-like aggregates were found after 4 h at 190 °C since the Al source is insufficient. We had expected, zeolite would be deposited on the anode as electro-oxidation can provide the desired Al3+ amount. However, only dense phase AlPO4 was found. Surprisingly, an in-plane orientated flower-like AlPO4-11 film was successfully synthesized on the cathode after 4 h synthesis. These surprising results promote us to ask why an in-plane oriented film was formed on the cathode instead of the anode. The most important distinction between the two electrodes are the occurring electrochemical reactions, and they bring the opposite surface charges, thereby adsorbing or repelling the [emim]+ cations which act as the structure-directing agents (SDA) by means of electrostatics (Figure.1). Under the effect of electrically adsorbed SDA, the cathode reacts with phosphorus acid and converts to AlPO4-11. This conversion takes place at any bare point of Al cathode under electric field, and the cathode surface was completely covered by a defect-free AlPO4-11 film. And its orientation is underlain by the cathode self-provided Al source and the fast crystallization rate at 190 °C. To control over the out-of-plane orientation, a growth centers layer should be firstly formed at lower temperature than 190 °C. However, only a negative current was not successful to obtain that layer even at 160 °C due to the insufficient amount of Al source. Whereas adjusting Al amount by electro-oxidation is a contradiction to film growth which needs adsorbed [emim]+ cations. To solve this problem, current cycles were developed. And each current cycle constituted of a positive current and a following negative current, which were used to provide Al source and adsorb [emim]+ cations, respectively. Then the layer was expanded to out-of-plane oriented film under a negative potential at 170 °C. The orientation is consistent with the XRD result. It should be highlighted that both in-plane and out-of-plane oriented growth at negative potentials can obtain defect-free films. As evidence, DC polarization test were used. DC polarization is a common technique to test the anticorrosion performance of films, the lower the corrosion current density, the better the corrosion resistance, and the fewer defects of films. The in-plane oriented film was better candidate than out-of-plane oriented one since the corrosive medium could not penetrate to Al substrate through its channels. The excellent corrosion-resistant performance of in-plane oriented film shows the electrochemical synthesized films are defect-free. Figure.1 Schematic illustration of in-situ electrochemical synthesis of AlPO4-11 film on Al electrodes 1. a) M. E. Davis, Nature, 2002, 417, 813; b) S. Gu, R. Cai, Y. S. Yan, Chem. Commun., 2011,47, 2856-2858 2. a) C. M. Lew, R. Cai, Y. S. Yan, Acc. Chem. Res., 2010, 43, 210–219; b) R. Cai, Y. Liu, S. Gu, Y. S. Yan, J. Am. Chem. Soc. 2010, 132, 12776–12777 3. a) R. Cai, M. W. Sun, Z. W. Chen, R. Munoz, C. O'Neill, D. E. Beving, Y. S. Yan, Angew. Chem. Int. Ed., 2008, 47, 525 –528; b) R. Cai, Y. S. Yan, Corrosion , 2008, 64, 271-278 4. a) Z. B. Wang, A. P. Mitra, H. T. Wang, L. M. Huang, Y. S. Yan, Adv. Mater. 2001, 13, 1463; b) S. Li, Z. J. Li, Y. S. Yan, Adv. Mater. 2003, 15, 1528 Figure 1

Influence of cooling rate on microstructure formation during rapid solidification of binary TiAl alloys

Titanium aluminides as structural intermetallics are possible candidates for a potential weight reduction and increased performance of high temperature components. A method for the characterization of the microstructure formation in rapidly solidified alloys was developed and applied for binary Ti–(44–48)Al (at.%). The results show a strong dependency of the microstructure on the Al content at cooling rates between 6⋅102 and 1.5⋅104Ks−1. The formation of α→α2 ordering, lamellar α2+γ colonies and interdendritic TiAl γ-phase were observed, depending on the Al amount. Based on thermodynamic calculations the observed microstructure can be explained using the CALPHAD approach taking into account the non-equilibrium conditions. The presented method provides a useful tool for alloy development for processing techniques involving rapid solidification with varying cooling rates.

Wear and machinability properties of AS series magnesium alloys

This study investigates the effect of the amount of Al amount in AS series magnesium alloys on wear resistance and machinability. Changes in mechanical properties, wear resistance, and machinability were studied depending on the Al amount in magnesium alloys containing 1% Si. Therefore, AS series magnesium alloys (AS11, AS21, AS41, AS61, and AS91) (containing Al in various degrees ranging from 1% to 9%) were used in this study. It was observed that the hardness of intermetallic phases in the microstructure of AS series magnesium alloys affected wear resistance and machinability depending on the increase in Al amount. Mg2Si intermetallic phase in the microstructure of AS91 alloy was established to reduce machinability while increasing hardness and wear resistance.

Effect of acidic properties of mesoporous zeolites supporting pt nanoparticles on hydrogenative conversion of methylcyclopentane.

The effect of acidic properties of mesoporous zeolites on the control of product selectivity during the hydrogenative isomerization of methylcyclopentane has been investigated. A series of mesoporous zeolites with controlled acidic properties were prepared by postdealumination process with hydrochloric acid under hydrothermal conditions, and the resultant zeolites used for supporting colloidal Pt nanoparticles (NPs) with a mean size of 2.5 nm (± 0.6 nm). As compared to the pure Pt NPs supported on catalytically inert mesoporous silica (MCF-17) as the reference catalyst that can produce isomers most selectively (∼80%), the Pt NPs supported on mesoporous zeolites produced C6-cyclic hydrocarbons (i.e., cyclohexane and benzene) most dominantly. The type and strength of the Brönsted (B) and Lewis (L) acid sites of those zeolites with a controlled Al amount are analyzed by using FT-IR after the adsorption of pyridine and NH3 temperature-programmed desorption measurements, and they are correlated with the selectivity change between cyclohexane and benzene. From this investigation, we found a linear relationship between the number of Brönsted acid sites and the formation rate for cyclohexane. In addition, we revealed that more Lewis acidic zeolite having relatively smaller B/L ratio is effective for the cyclohexane formation, whereas more Brönsted acidic zeolite having relatively larger B/L ratio is effective for the benzene formation.

Synthesis of Ti3SiC2 Through Pressureless Sintering

Ternary compound Ti3SiC2 was synthesized by pressureless sintering the powder mixture of 3Ti/1.2Si/2C, 3Ti/1.2Si/2C/0.1Sn, and 3Ti/1.2Si/2C/0.1Al with preliminary liquid magnetic stirring. The Ti3SiC2 was synthesized at 1400°C for 30 min. The addition of appropriate Al amount enhanced the synthesis of Ti3SiC2. The mechanism of Ti3SiC2 synthesis from 3Ti/1.2Si/2C/0.1Al was presumed to be the reactions between the intermediate phases of Ti–Al and Ti–Si intermetallics and other reactants in the starting powder. The Ti–Al and Ti–Si liquid interaction occurring at high temperatures was found to assist the synthesis reaction of Ti3SiC2.

AN INFORMATION-THEORETIC IMAGE QUALITY MEASURE: COMPARISON WITH STATISTICAL SIMILARITY

We present an information-theoretic approach for st ructural similarity for assessing gray scale image quality. The structural similarity measure SSIM, pr oposed in 2004, has been successflly used and verfi ed. SSIM is based on statistical similarity between the two images. However, SSIM can produce confusing results in some cases where it may give a non-trivi al amount of similarity for two different images. A lso, SSIM cannot perform well (in detecting similarity o r dissimilarity) at low peak signal to noise ratio (PSNR). In this study, we present a novel image similarity measure, HSSIM, by using information - theoretic technique based on joint histogram. The proposed method has been tested under Gaussian noise. Simulati on results show that the proposed measure HSSIM outperforms statistical similarity SSIM by ability to det ect similarity under very low PSNR. The average differe nce is about 20dB.

As-synthesized TEA-BEA zeolite: Effect of Si/Al ratio on the Knoevenagel condensation

The zeolite with BEA structure has been obtained using different Al amounts in the presence of tetraethylammonium as a structure directing agent. The effect of the Si/Al molar ratio on the crystal size, morphology, yield, chemical composition and catalytic properties was investigated. The materials have been characterized towards zeolitic properties by XRD, SEM, EDS, TGA, 29Si MAS-NMR, XPS and TEM. The chemical composition of the crystals depends on the concentration of the initial reaction mixture and that a decrease in the Al content is associated with an increase in particle size. The characterization by TGA/DTA of as-synthesized zeolites with BEA structure showed that an increase of Si content resulted in the formation of [SiO−][TEA+] species, this was supported by 29Si MAS-NMR. The XPS results also showed that the chemical composition of the surface differed from that of the bulk material, this was supported by TEM/EDS results. The results of catalytic activity tests indicated that a fraction of the [SiO−][TEA+] species was present on the external surfaces of the crystals, although the largest fraction appeared to be in the interior of the particles. As-synthesized BEA zeolite showed good catalytic activity and suggests that this material can be applied in other reactions involving basic sites.

The Analysis of Morphology Characteristics of Iron Plaque on the Roots of <i>Carex cinerascens</i>

The physico-chemical properties of iron plaques formed on the root surfaces ofCmarex cinerascensunder laboratory conditions were determined using Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectrometry (EDS) analysis. Iron plaques were present as an amorphous coating on root surfaces with an uneven distribution. EDS analysis showed that iron plaques were composed of Fe , Si, Al and lesser amounts of Ca in plaqued root surfaces.

Comparison of the machinability and wear properties of magnesium alloys

AZ and AS series magnesium alloys were used in this study and had different contents (i.e., 0 to 9 wt.% Al). The effect of zinc (Zn) and silicon (Si) on wear resistance and machinability was analyzed in AZ and AS series magnesium alloys. Zn amount in AZ series (1 %) and Si amount in AS series (1 %) were kept at a fixed rate. The effect of the changes in Al amount on hardness, wear resistance, and machinability in AZ and AS series magnesium alloys was comparatively analyzed. A higher increase was observed in the wear resistance of alloys in AS series magnesium alloys due to the rise in Al amount compared with AZ series. Intermetallic phases found in the microstructure of alloys (β-Mg17Al12 and Mg2Si) were established to have an impact on the wear resistance and machinability of alloys.

Nature of the active sites in Al-MCM-41 nano-structured catalysts for the selective rearrangement of cyclohexanone oxime toward ɛ-caprolactam

Al-MCM-41 type nano-structured catalysts with different Al contents were prepared by direct hydrothermal synthesis. All the materials were characterized by XRD, N2 adsorption, TEM, SEM, ICP-OES, FT-IR and adsorption of pyridine coupled to FT-IR spectroscopy. The relationship between the Al contents in the synthesis gel and final solid, the degree of Al introduction in tetrahedral coordination into the framework, the formation of nest silanols and the relative density of the acidic hydroxyl sites has been exhaustively analyzed. We could corroborate that hydroxyl groups present in silanol nests are the direct responsible of the weakly acid character of our materials. Moreover, a critical concentration of framework Al seems to be necessary to generate such nests, after which the acid sites density is strongly increased, according the framework Al amount increasing. The enhancement in the density of acidic nest silanols (active sites for the selective rearrangement of cyclohexanone oxime toward ɛ-caprolactam) reached by increasing the Al content, permitted to us achieve a cyclohexanone oxime conversion about 66%. The ɛ-caprolactam selectivity was 100% for all the evaluated catalysts, indicating that the acidic strength was kept sufficiently weak to not catalyze the formation of by-products.

Long-term manure application effects on phosphorus speciation, kinetics and distribution in highly weathered agricultural soils

Phosphorus (P) K-edge XANES and Fe K-edge EXAFS spectroscopies along with sequential P chemical fractionation and desorption kinetics experiments, were employed to provide micro- and macro-scale information on the long-term fate of manure application on the solid-state speciation, kinetics and distribution of P in highly weathered agricultural soils of southern Brazil.Soil test P values ranged from 7.3 up to 16.5 times as much higher than the reference soil. A sharp increase in amorphous Fe and Al amounts were observed as an effect of the consecutive application of manures. Whereas our results showed that the P sorption capacity of some manured soils was not significantly affected, P risk assessment indices indicated that P losses should be expected, likely due to the excessive manure rates applied to the soils. The much higher contents of amorphous Fe and Al (hydr)oxides (55% and 80% increase with respect to the reference soil, respectively) in manured soils seem to have counterbalanced the inhibiting effect of soil organic matter on P sorption by creating additional P sorption sites. Accordingly, the newly created P sorbing surfaces were important to prevent an even larger P loss potential. Phosphorus K-edge XANES lent complimentary hints on the loss of crystallinity and transformation of originally present Fe–P minerals into poorly crystalline ones as an effect of manuring, whereas Fe K-edge EXAFS provided insights into the structural changes underwent in the soils upon manure application and soil management.

Synthesis of mullite–MoSi2 nano-composite through a mechanochemical processing

Nano-composite mullite–MoSi2 with 40wt.% MoSi2 was produced from the raw materials of MoO3, Al and Si by mechanochemical processing. Different Al amounts (stoichiometric amounts of 1, 1.5 and 2mol) and milling times (15, 23, 30, 60, 180, 300min) were applied to obtain this composite. A planetary ball mill with a rotation speed of 250rpm and a ball-to-powder ratio (BPR) of 40:1 was employed. The composite was formed using 1.5mol of Al and occurrence of mechanically induced self-propagating reaction (MSR) in 23–30min. The evolutions of phases and their microstructure were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDX). By means of transmission electron microscopy (TEM) the particle size and morphology of the obtained powders were examined. The mean crystallite size of the composite changed from 60nm in 30min to 20nm in 5h; the average particle size was about 155nm in 5h.

Investigation of the Precipitation Kinetics of a New Al-Mg-Sc-Zr Alloy

This study investigates the precipitation behavior of two similar cast Al-Mg-Sc-Zr alloys with different solidification and cooling rates. Microstructural analyses and hardness testing were performed after casting and ageing. In addition, the precipitation and hardness evolution after rapid quenching using electron beam re-solidification were studied. It was shown that the amount of Al3(Sc,Zr) phases present after casting or re-solidification increases with decreasing solidification and cooling rate. Consequently, the degree of supersaturation in Sc and Zr at room temperature and thus the hardening potential in a subsequent ageing process increases with the solidification and cooling rate. Therefore, the electron beam re-solidified samples revealed the most pronounced hardening.

Effect of curing regime on degree of Al3+ substituting for Si4+ in C-S-H gels of hardened Portland cement pastes

The effect of curing regime on degree of Al3+ substituting for Si4+ (Al/Si ratio) in C-S-H gels of hardened Portland cement pastes was investigated by 29Si magic angel spinning (MAS) nuclear magnetic resonance (NMR) with deconvolution technique. The curing regimes included the constant temperature (20, 40, 60 and 80 °C) and variable temperature (simulated internal temperature of mass concrete with 60 °C peak). The results indicate that constant temperature of 20 °C is beneficial to substitution of Al3+ for Si4+, and Al/Si ratio changes to be steady after 180 d. The increase of Al/Si ratio at 40 °C is less than that at 20 °C for 28 d. The other three regimes of high temperature increase Al/Si ratio only before 3 d, on the contrary to that from 3 to 28 d. However, the 20 °C curing stage from 28 to 180 d at variable temperature regime, is beneficial to the increase of Al/Si ratio which is still lower than that at constant temperature regime of 20 °C for the same age. A nonlinear relation exists between the Al/Si ratio and temperature variation or mean chain length (MCL) of C-S-H gels, furthermore, the amount of Al3+ which can occupy the bridging tetrahedra sites in C-S-H structure is insufficient in hardened Portland cement pastes.

Screening of Ca- and Fe-rich materials for their applicability as phosphate-retaining filters

Ecology of a large number of lakes and estuaries is affected by external phosphorus (P) loading. Many studies have investigated the applicability of different materials as P-filters for treating runoff or wastewaters. We performed flow-through retention tests and water extractions to estimate the P retention and release properties of potential Ca- and Fe-rich filter materials. In addition to the fresh Ca-rich materials, the P retention tests involved their weathered counterparts. During weathering, the materials were immersed into water to leach out soluble species (e.g., Ca2+ and OH−), thus mimicking aged filters. For the most efficient P-retainers (Filtra P®, steel slag, Sachtofer PR® and mine drainage residual), the cumulative P retentions ranged between 12 and 24mg P/g. The weathering reduced the P retentions of Filtra P® and of slag by 70–80%, but did not affect the abilities of other materials to retain P. No clear relationship existed between the P retentions and water-extractable Ca or oxalate-extractable Fe and Al amounts in the materials. During one month of extraction with a large volume of water, the maximum release of P from the P-saturated materials was 35% of the total P. To recognize the P retention mechanism (precipitation of Ca-phosphates or sorption onto metal hydroxides) and thus predict possible P release, we performed equilibration of P-saturated materials in solutions with variable pH. We suggest incorporation of weathering and P release tests in the screening scheme for identifying potential P-retaining filters.

Spectrofluorometric Method for Determination of Al3+ with 3-Hydroxy-2-Naphthalenecarboxylic Acid and its Application to Milk Samples

On the basis of affinity of Al3+ ions toward functional groups of 3-hydroxy-2-naphthalenecarboxylic acid (3H2NA), a high stable complex between Al3+ and 3H2NA in 5 % methanol/water solution was established. The mole ratio method showed that a stable complex by taking part of acetate and 3H2NA with the stoichiometric ratio of 1:1:1 and stability constant of 8.6 × 106 is formed. Under the optimum conditions for the complex formation, a rapid spectrofluorometric determination of trace amounts of Al3+ (λ ex = 366 nm, λ em = 460 nm) was proposed. The optimum conditions involve 3H2NA concentration of 1.0 × 10−5 M, buffering pH of 4.5 (acetic/acetate system), and ionic strength of 0.01 M. The fluorescence intensity exhibited a good linearity against the Al3+ concentration in the range 5.0 × 10−8–5.0 × 10−6 M with the detection limit of 1.3 × 10−8 M. No considerable interference was observed due to the presence of coexisting anions and cations. The method was applied successfully to the determination of trace amounts of Al3+ in milk. Validation of the measurements was confirmed using graphite furnace atomic absorption spectrophotometry.

Spectroscopic, analytical and DFT calculation studies of two novel Al3+ complexes derived from 2,4,6-tri-(2-pyridyl)-1,3,5-triazine (TPTZ)

In this study TPTZ is used exclusively as an analytical reagent for the determination of micro amounts of Al3+ ions with high accuracy and lower detection limit, which reach 2.7ppm. The developed blue color of Al3+-TPTZ complex was used selectivity to determine the concentration and the geometry of the Al3+ complex using continuous variation and molar ratio methods. Also, the novel Al3+ complexes derived from the reaction of TPTZ were synthesized. The solid complexes were characterized by elemental analyses, spectral (IR, UV–vis., 1H NMR, mass) and magnetic measurements. The isolated complexes have the general formulae, [Al(TPTZ)Cl3]·H2O·1½EtOH (1:1; M:L) and [Al2(TPTZ)Cl6(EtOH)2] (2:1; M:L). IR spectra indicate that TPTZ behaves in a bidentate manner in case of 1:1 and 2:1 (M:L). Elemental analyses and mass spectra of the complexes suggest the existence of an octahedral structure around the Al3+ ions. DFT calculations were used to determine the geometry of complexes.

Effect of substitution of Si by Al on microstructure and synthesis behavior of Ti5Si3 based alloys fabricated by mechanically activated self-propagating high-temperature synthesis

The effect of substitution of Si by Al and mechanical activation on microstructure, phase composition, ignition and combustion temperature of Ti5Si3 based alloys and composites that were prepared by mechanically activated self-propagating high-temperature synthesis (MASHS) method was investigated. For this purpose elemental powders of titanium, silicon and aluminum were mixed according to the 5Ti+3(1−X)Si+3XAl formula, where X=0, 0.2, 0.4, 0.6. The samples were characterized by X-ray diffraction (XRD) analytical technique and scanning electron microscope (SEM) equipped with an energy-dispersive spectrum (EDS) analyzer. The results have shown that formation of Ti5Si3 during milling stage is postponed by adding Al into the system. Presence of Al in the Ti–Si system have a significant effect on the phase composition of the final products. Substitutional solid solution of Ti5(Si, Al)3 and Ti5Si3–Ti3Al composite are formed by increasing Al amount in the system. Furthermore combustion temperature and crystallites size of Ti5Si3 is reduced with addition of Al into the Ti–Si system. Moreover, solubility of Al in Ti5Si3 is increased with enhancing the X up to 0.4, after that, the solubility of Al in Ti5Si3 is ceased, due to achieving the solubility limit of Al in the Ti5Si3. The average crystallites size of Ti5Si3 are decreased with increasing milling time prior to the reaction.

AROMATIZATION OF PROPYLENE OVER HZSM-5: A DESIGN OF EXPERIMENTS (DOE) APPROACH

Aromatization of propylene was performed in a continuous reactor over HZSM-5 catalysts. A full-factorial design of experiments (DOE) methodology identified the effects of temperature (400°–500°C), Si:Al ratio (50–80), propylene feed concentration (8.9–12.5 mol.%), and catalyst amount (0.2–1.0 g) on propylene conversion as well as the yields of benzene, toluene, p-xylene, o-xylene (BTX), and total BTX. The Si:Al ratio and amount of the HZSM-5 catalyst influenced all of the responses, while temperature affected all the responses except the yield of p-xylene. An increase in feed concentration significantly increased the yields of benzene, toluene, and total BTX. An interaction between propylene feed concentration and catalyst amount influenced the yields of benzene, toluene, and total BTX. This interaction indicated that a higher feed concentration promotes aromatization at higher catalyst concentrations. By contrast, the interaction of Si:Al ratio with propylene feed concentration was found significant for p-xylene and o-xylene yields, but not for benzene and toluene, suggesting that xylenes are synthesized on different sites than those for benzene and toluene. These interaction effects demonstrate how the use of DOE can uncover significant information generally missed using traditional experimental strategies.