Mechanochemical synthesis of Na-β/β″-Al2O3

Na-β/β″-alumina powders were synthesized by a mechanochemical processing. The influences of mechanical activation in the phase composition and microstructure of the final powders were investigated. Fine Na-β/β″-alumina powders were obtained at a lower temperature than that of a conventional solid-state reaction processing. The mechanism of the mechanical activation was studied. It was found that mechanical activation greatly affected the calcining process and phase composition of the precursory powders.     

High resolution adsorption isotherms of N2 and Ar for nonporous silicas and MFI zeolites

The high resolution adsorption isotherms of N₂ (77.4 K) and Ar (87.3 K) have been measured for two nonporous silicas with different silanol contents (3.3 and 0.35 OH/nm²) and for two MFI zeolite with different Al contents (Si/Al=12.5 and 500). Silanol groups and Al sites (acid sites) gives the significant effect on the N₂ isotherms at submonolayer, but the Ar isotherms are independent of silanols and Al sites. The Ar isotherms, therefore, are preferable in calculation of microporosity of zeolites. The N₂ and Ar isotherms for MFI zeolite (Si/Al=500) have been measured at temperatures of 77–94 K, from which the differential adsorption energies of N₂ and Ar are calculated. The interaction of N₂ with channel surface of MFI zeolite is greater than that of Ar in the range of α _s =0.1–0.7. The hystereses are detected for the N₂ isotherm in p/p ^o=0.1–0.3 at 77.4 K and for the Ar isotherm in p/p ^o=3×10⁻⁴–2×10⁻³ at 87.3 K. However, it is difficult to explain the hysteresis phenomenon using differential adsorption energy.     

Thermal Behaviour Studies on Some Heterotrinuclearpolyacids

An improved method for the synthesis of four heterotrinuclearpolyacids of the type: H_x[EM′_yM″_zO₄₀⋅nH₂O (E=P, Si; M′=Mo, W; M″=V, W) was elaborated. The studied compounds were characterized by elemental analysis, IR spectra and thermal behaviour over 20–800°C temperature range. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of phenyl group on the structure and formation of transitional alumina from Al (OPh)<Subscript>3</Subscript>

The structure of freshly prepared Al(OPh)₃, its decomposition product, the hydrolyzed products and their structural evolution were investigated employing ²⁷Al MAS NMR spectroscopy, PXRD, TGA/DTA/DSC/FTIR techniques. In the ²⁷Al MAS NMR spectrum of the aluminium phenoxide, three signals with the chemical shift at 3.78, 21 and 45 ppm were observed. The chemical shift at 3.78 and 45 ppm revealed the presence of four and sixfold coordinated aluminum. The signal at 21 ppm corresponded to fivefold coordinated aluminium. When the aluminium phenoxide was directly decomposed in air at 600 °C, it resulted in amorphous product as evidenced from the PXRD pattern. The observed signals with chemical shifts at 10.1, 42, 73.6 ppm in the ²⁷Al MAS NMR spectrum indicated the presence of 6, 5 and 4 coordination for the aluminium atoms suggesting disordered transitional γ-alumina to be the product. The hydrolysis studies of Al(OPh)₃ with excess of water at 70 °C yielded bohemite (γ-AlOOH). The alumina obtained after dehydration at 600 °C was X-ray amorphous. The dehydrated product at 600 °C showed the presence of four and six coordinated aluminium atoms in the ²⁷Al MAS NMR spectrum confirming it to be ordered γ-Al₂O₃. Crystalline γ-Al₂O₃ was obtained on further heating at 800 °C.     

Analytical Techniques Applied in Optimization of Electrophoretic Deposition of Thin Film YBCO Superconductors

 YBa₂Cu₃O _7−x (x = 0.1–0.2) compounds (YBCO) were produced by the oxalate coprecipitation and the solid state reaction methods. The powders obtained were used for the production of YBCO superconducting coatings on Pt/Si wafers, by the electrophoretic deposition technique. The optimum process conditions for the production of both powders and coatings were found by using a combination of modern analytical techniques. The thermal treatment of the samples was followed by thermogravimetry (TG) and differential scanning calorimetry (DSC). The optimization and characterization of the superconducting properties of the powders and coatings were achieved by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), optical microscopy, magnetic susceptibility and electrical resistivity measurements.     

The effect of iron phosphate,alumina and silica coatings on the morphology of carbonyl iron particles

Carbonyl iron powders were coated with iron phosphate using phosphating method and boehmite (γ‐AlOOH) or silicon hydroxide (Si(OH)₄) nanoparticles derived from the hydrolysis of tri‐sec‐butoxide (Al(OC₄H₉)₃) or tetramethylsilane (Si(OCH₃)₄) using sol–gel method. The coated powders were dried and calcined at 400 °C for 3 h in air. Cross‐section morphology of coated carbonyl iron powders were investigated by scanning electron microscopy energy dispersive X‐ray analysis. Coated Fe micro‐particles were spherical in shape with ‘shell/core’ structures. The shells consisted of an amorphous layer with varying thickness (100–800 nm) and the core represented a carbonyl iron. Gelatinous morphology of dried FePO₄ coating composed from nanoparticles of iron oxyhydroxides and hydrated iron phosphate with a shell thickness of ～100 nm around iron particles was observed. In coatings based on alumina or silica xerogels with a thickness of ～100–150 nm or ～200–500 nm, the coatings were composed of iron oxyhydroxides and γ‐AlOOH or Si(OH)₄. The resulting XRD diffractograms revealed the hematite (α‐Fe₂O₃) and magnetite (Fe₃O₄) that were formed in phosphated and sol–gel coated iron powders. The X‐ray diffraction patterns did not verify the presence of phosphates, alumina or silica and indicate the amorphous or nanocrystalline structure of FePO₄, γ‐Al₂O₃ and SiO₂. Copyright © 2009 John Wiley & Sons, Ltd.     

A novel chromone-substituted trimeric dihydroflavonol from <Emphasis Type="Italic">Anogeissus pendula</Emphasis>

A new chromone-substituted dihydrotriflavonol, (2S,3S)[6-{(3S) 3″,5″-dihydroxy-6″-methoxydihydrochromone}5,3′,4′,5′-tetrahydroxy-7-methoxy-3-O-8-dihydroflavone]₂ 3-O-8[6-{(3S) 3″,5″-dihydroxy-6″methoxydihydrochromone}3,5,3′,4′,5′-pentahydroxy-7-methoxydihydroflavonol] was isolated from the leaves of Anogeissus pendula. The structure was determined by UV, ¹H NMR, ¹³C NMR, HMBC, and CD data.     

Analysis of Precipitation Hardening of 6061/10% SiC Composite by Differential Scanning Calorimetry

The precipitation of a supersaturated 6061 Al alloy reinforced with 10% SiC_pwas monitored by using a DSC technique. DSC thermal curves were used to predict peak-aging temperatures and durations. The activation energies for precipitation of the β″ phase were found to increase with elevation of the solution temperature from 510 to 600°C, and hence the peak-aging temperature and duration also increased. Microstructural examination revealed an increase in grain size when a high solution temperature was applied. To compare predicted peak-aging temperatures and durations, hardness measurements were carried out after artificial aging. The studies revealed that peak-aging hardening was obtained when the aging temperatures and durations corresponded to about 95% to 97% precipitation of β″ phase from conversion plots. This revised version was published online in July 2006 with corrections to the Cover Date.     

Coordination compounds of sodium,potassium, and calcium with benzo-15-crown-5-substituted terpyridines

Sodium and potassium complexes with 4′-(4‴-benzo-15-crown-5)methyloxy-2,2′:6′,2″-terpyridine (L¹) and 4′-(4′-benzo-15-crown-5)oxy-2,2′:6′,2″-terpyridine (L²) and heteronuclear Na, K, Ca, and transition metal complexes with L¹ were synthesized. The structure of the complexes was proposed on the basis of elemental analysis data, IR spectra, and the results of earlier X-ray diffraction studies of L², [NaL¹NCS], and [Na₂{Cu(L¹)₂}(NCS)₃]NCS · CH₃CN.     

Silver containing sol–gel derived silica thin films: effect of aluminum incorporation on optical,microstructural and bactericidal properties

Silver containing silica (Ag–SiO₂) thin films with and without aluminum (Al) were prepared on soda-lime-silica glass by spin coating of aqueous sols. The coating sol was formed through mixing tetraethyl orthosilicate [Si(OC₂H₅)₄]/ethanol solution with aqueous silver nitrate (AgNO₃) and aluminum nitrate nonahydrate [(AlNO₃)₃·9H₂O] solutions. The deposited films were calcined in air at 100, 300 and 500 °C for 2 h and characterized using x-ray diffraction, UV-visible and x-ray photoelectron spectroscopy. The effect of Al incorporation and calcination treatment on microstructure and durability of the films, and chemical/physical state of silver in the silica thin film have been reported. The bactericidal activity of the films was also determined against Staphylococcus aureus via disk diffusion assay studies before and after chemical durability tests. The investigations revealed that the optical, bactericidal properties and chemical durability of Ag–SiO₂ films can be improved by Al addition. The Al-modified Ag–SiO₂ thin films do not exhibit any coloring after calcination in the range of 100–500 °C, illustrating that silver is incorporated within the silica gel network in ionic form (Ag⁺). Al incorporation also improved the overall durability and antibacterial endurance of Ag–SiO₂ thin films.     

Thermal and environmental effects on Oligothiophene low-energy singlet electronic excitations in dilute solution: a theoretical and experimental study

The absorption spectra in dilute dichloromethane solution at 300 K of four Oligotiophenes (OT), namely 2,2′:5′,2″-Terthiophene, 2,2′:5′,2″:5″,2″′-Quaterthiophene, 4,4″′-Didodecyl-2,2′:5′,2″:5″,2″′-quaterthiophene and 5,5′′′′′-Dihexyl-2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′:5′′′′,2′′′′′-sexithiophene, have been studied both experimentally and theoretically by using a combination of molecular dynamics simulations, time-dependent density functional theory (TD-DFT) and perturbed matrix method calculations. A deep analysis of the theoretical results, affected by a systematic although not dramatic underestimation of the absorption maxima due to the well-documented TD-DFT limitations, clearly indicates that both the environmental (solvent) and thermal effects significantly alter the Oligotiophenes photophysical properties mainly because of the wide repertoire of the S₀–S₁ energy gaps and electronic densities experienced in solution by the different conformers actually populated. In particular, all the investigated OT display a very high flexibility resulting in a very high repertoire of sampled conformations. The comparison of the calculated and experimental lineshape of the S₀–S₁ electronic transition has clearly indicated that for a correct modeling of OT spectral features, the lack of an exhaustive sampling of semiclassical configurational space of the overall system, i.e., solute in interaction with the solvent, might result in an incomplete picture even in the presence of well-documented important aspects such as reliable definition of excited electronic states and the inclusion of quantum vibronic effects.     

Dibromo and diiodo derivatives of [4.4]dibenzo-24-crown-8 as novel efficient sorbents of elements from mineral acid solutions

The sorption behavior of novel functionalized endoreceptors, halogen (Br, I) derivatives of [4.4]dibenzo-24-crown-8, with respect to sorption of 34 elements from 1–5 M HNO₃ solurions and 29 elements from 1–5 M HCl solutions were studied. The receptors poorly extract elements from nitric acid solutions but are strong sorbents of some elements from concentrated hydrochloric acid solutions. The highest distribution ratios of elements (D, cm³/g) for sorption from 5 M HCl were observed for 4′,4″,5″[4.4]dibromodibenzo-24-crown-8: Au (D = 880) > Ga (469) > Sb (70) > Fe (55) > Sn (14.3) > Mo (10.3) > Re (2.9) > Cd (1.4) > Ge (0.61) > In (0.33) ≈ Zn (0.32) ≈ Ni (0.31) > Zr (0.29) ≈ Cr (0.28) > Sr, Tl (0.25) > Be (0.24) > Mn (0.22) ≈ La (0.21) ≈ Ba (0.20) > Ca, K, Mg, Si (< 0.1). A new way for increasing the sorption properties of dibenzocrown ethers by introducing bromine substituents into the polyether benzene rings was established. The sorption of elements from concentrated hydrochloric acid solutions follows an anion exchange mechanism by analogy with extraction of these elements.     

Sol–gel synthesis and characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> nanocrystalline powder

Al₂O₃–TiO₂ nanocrystalline powders were synthesized by sol–gel process. Aluminum sec-butoxide and titanium isopropoxide chemicals were used as precursors and ethyl acetoacetate was used as chelating agent. Thermal and crystallization behaviors of the precursor powders were investigated by thermal gravimetric-differential thermal analysis, Fourier-transform infrared spectrum and X-ray diffraction. The average crystalline size of heat treated Al₂O₃–TiO₂ powders at 1,100 °C is ~100 nm.     

Reaction pathway and phase transitions in Al–Ti–Si system during differential thermal analysis

The present paper mainly studied the phase formation and reaction pathway of the Al–Ti–Si system in detail by thermal analysis combined with XRD and SEM observations. The phase formation sequence in Al–Ti–Si system from starting mixtures to final products with increasing temperature can be described as following: Al_(l) + Ti_(s) + Si_(s) → (Al–Si)_(l) + Ti_(s) + Si_(s) → Ti(Al,Si)_3(s) + Si_(s)Ti₅(Si,Al)₃ + Al_(l). More importantly, the solubility of Si in Ti(Al,Si)₃ decreased gradually while that of Al in Ti₅(Si,Al)₃ increased with temperature increasing, suggesting the transportation of Si atoms from intermediate aluminides Ti(Al,Si)₃ to final stable silicides Ti₅(Si,Al)₃ and hence further confirming the formation of Ti₅(Si,Al)₃ at the expense of Ti(Al,Si)₃.     

New molecular compound precursor for aluminum chemical vapor deposition

A new type of precursor for aluminum chemical vapor deposition (Al‐CVD) has been developed by mixing dimethylaluminum hydride (DMAH) and trimethylaluminum (TMA). The new precursor has proven itself to be effective for Al‐CVD, where a good selectivity between the Si and the SiO₂ mask, a 3.0 μΩ cm resistivity and a pure Al film with low C and O contamination levels (under 100 ppm) were achieved. Quadrupole mass and infrared absorption analysis have shown that the precursor contains a new molecular compound, consisting of a DMAH monomer and a TMA monomer. The mixture has lower viscosity than DMAH and can be easily bubbled for a stable precursor vapor supply. Copyright © 2000 John Wiley & Sons, Ltd.     

Polyanilme-montmorilltonite (PANl-MMT) nanocomposites: Mechanochemical synthesis,structure, thermostability and electrical properties

Polyaniline (PANI)-montmorillonite (MMT) nanocomposites were prepared by direct intercalation of aniline molecules into MMT galleries, followed by in situ mechanochemical polymerization under solvent free conditions. X-rays diffraction, Fourier Transform Infra Red analyses and UV-vis spectroscopy confirmed the successful synthesis of polyaniline chains between the MMT nano-interlayers. On increasing the amount of MMT basal spacing decreased gradually, suggesting less intercalation with decreasing amount of aniline. Scanning electron micrographs demonstrated strong differences between the morphologies of PANI-MMT nanocomposites and those of pure MMT and PANI. DC conductivity was measured in the temperature range from 145 K to 303 K using four probe methods. Temperature dependent DC conductivity of PANI and all the PANI-MMT composites followed 3 dimensional variable range hopping (3D VRH) model. Frequency dependent AC conductivity (σ_AC), dielectric constant (ɛ′) and loss factor (ɛ″) have been measured in the frequency range 10²–10⁶. All these measured quantities; σ_AC, ɛ′ and ɛ″ decreased with the increase in MMT content in the composites at all frequencies. The frequency dependence of σ_AC displayed a low frequency region below 10⁴ Hz with almost constant conductivity, while above this frequency a rapid rise in σ_AC was observed with a power law of frequency dependence with an exponent equal to 0.7. Both real and imaginary parts of the permittivity exhibited a low frequency dispersion which has been attributed to hopping of polarons and bipolarons in PANI and its composites. The thermal stability was checked by thermogravimetric analysis (TGA) and was found to be enhanced due to addition of MMT in the PANI.     

Preparation and Studies of ZnO:Al Films and Powders

ZnO:Al (0–10 at% Al) films and powders were produced using acac-modified methoxy-ethoxide precursors, obtained from Zn(C₂H₅)₂ and Al₄(OPr ⁱ )₁₂. The conversion to oxide powders was monitored with TGA and DSC, and the phase development was investigated with XRD, FT-IR spectroscopy, and TEM-EDS. The gels obtained by air-hydrolysis contained ca 0.5 acac/(Zn + Al) and a small amount of water and hydroxyls. All residual groups were removed to yield ZnO:Al by heating to ca 400°C. The powders obtained at 400 and 500°C were elementally homogeneous, and consisted of hex-ZnO:Al as ca 3–5 (10 at% Al) or 20–30 (3 at% Al) nm sized crystalline particles. Spin-coating on quartz, Si/SiO₂, and window glass, followed by heating to 500°C resulted in 150–200 nm thick films of hex-ZnO:Al. 500 nm thick films were obtained by repeating the deposition and heat-treatment twice. The films were visually very clear and the measured transmittance high over the 400–800 nm range (91–93% at 800 nm) for ca 300 nm thick films.     

Si-Containing Amides of Phosphoric Acid

The first representative of the N-silylmethylamides of phosphoric acid O=P[NMe(CH₂SiMe _n (OEt)_3-n ]₃ have been synthesized by interaction of MeNHCH₂SiMe _n (OEt)_3-n (n = 2, 3) with POCl₃. The interaction of the N,N′,N″-trimethyl-N,N′,N″-tris[(ethoxydimethyl- silyl)methyl]triamide phosphoric acid with BF₃·Et₂O or BCl₃ results in the formation of the N,N′,N″-trimethyl-N,N′,N″-tris[(fluorodimethyl-silyl)methyl]triamide phosphoric acid or N,N′,N″-trimethyl-N,N′,N″-tris[(chlorodimethylsilyl)methyl]triamide phosphoric acid. NMR data show on the tetracoordinate state of silicon in these products.     

Deposition and Characterization of Metastable Cu3N Layers for Applications in Optical Data Storage

 Cu₃N films for optical data storage were deposited on Si(100) wafers and 0.6 mm thick polycarbonate DVD base material discs at a temperature of 50 °C by reactive magnetron sputtering. A copper target was sputtered in rf mode in a nitrogen plasma. For basic investigations concerning the composition and structure of Cu₃N, Si wafers were used as substrate material. To study the suitability of Cu₃N as an optical data storage medium under technical conditions, Cu₃N/Al bilayers were deposited on polycarbonate discs. The composition and structure of the films were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The decomposition of Cu₃N into metallic copper and nitrogen was induced and characterized with a dynamic tester consisting of an optical microscope with an integrated high power laser diode. The change in reflectivity induced by the laser pulses was measured by a high sensitivity photo detector. Optimized Cu₃N films could be decomposed into metallic copper at pulse lengths of 200 ns. The reflectivity change from 3.2% to 33.2% for completely transformed areas and to 12% for single bits as well as the maximum write data rate of 3.3 Mbit/s demonstrated the suitability of Cu₃N for write once optical data storage. Especially the carrier to noise ratio of 41 dB shows an increase of a factor of 3 for this novel material as compared to conventional optical data storage media.