An aqueous-solution based low-temperature pathway to synthesize giant dielectric CaCu3Ti4O12-Highly porous ceramic matrix and submicron sized powder

A simple, cost-effective and environment-friendly pathway for preparing highly porous matrix of giant dielectric material CaCu3Ti4O12 (CCTO) through combustion of a completely aqueous precursor solution is presented. The pathway yields phase-pure and impurity-less CCTO ceramic at an ultra-low temperature (700 degrees C) and is better than traditional solid-state reaction schemes which fail to produce pure phase at as high temperature as 1000 degrees C (Li, Schwartz, Phys. Rev. B 75, 012104). The porous ceramic matrix on grinding produced CCTO powder having particle size in submicron order with an average size 300 nm. On sintering at 1050 degrees C for 5 h the powder shows high dielectric constants (>10(4) at all frequencies from 100 Hz to 100 kHz) and low loss (with 0.05 as the lowest value) which is suitable for device applications. The reaction pathway is expected to be extended to prepare other multifunctional complex perovskite materials. (C) 2010 Elsevier B.V. All rights reserved.

Wet chemical syntheses of ultrafine multicomponent ceramic powders through gel to crystallite conversion

Coarse (BOn/2)-O-n+/xH(2)O (10ceramics in terms of operational cost and procedural simplicity.

Investigations of the reduction behavior of Iron-impregnated alumina gels (Fe/AlOOH) and the formation of Fe0-Al2O3 metal-ceramic composites

Fe/AlOOH gels calcined and reduced at different temperatures have been investigated by a combined use of Mossbauer spectroscopy, x-ray diffraction, and electron microscopy in order to obtain information on the nature of the iron species formed as well as the various reduction processes. Calcination at or below 1070 K mainly gives reducible Fe3+ while calcination at higher temperatures gives substitutional Fe3+ in the form of Al2-xFexO3. The Fe3+ species in the calcined samples are, by and large, present in the form of small superparamagnetic particles. Crystallization of Al2O3 from the gels is catalyzed by Fe2O3 as well as FeAl2O4. Fe (20 wt. %)/AlOOH gels calcined at or below 870 K give FeAl2O4 when reduced in hydrogen at 1070 K or lower and a ferromagnetic Fe0-Al2O3 composite (with the metallic Fe particles >100 angstrom) when reduced at 1270 K. Samples calcined at 1220 K or higher give the Fe0-Al2O3 composite when reduced in the 870-12,70 K range, but a substantial proportion of Fe3+ remains unreduced in the form of Al2-xFexO3, showing thereby the extraordinary stability of substitutional Fe3+ to reduction even at high temperatures. Besides the ferromagnetic Fe0-Al2O3 composite, high-temperature reduction of Al2-xFexO3 yields a small proportion of superparamagnetic Fe0-Al2O3 wherein small metallic particles (<100 angstrom) are embedded in the ceramic matrix. In order to preferentially obtain the Fe0-Al2O3 composite on reduction, Fe/AlOOH gels should be calcined at low temperatures (less-than-or-equal-to 1100 K); high-temperature calcination results in Al2-xFexO3. Several modes of formation of FeAl2O4 are found possible during reduction of the gels, but a novel one is that involving the reaction, 2Fe3+ + Fe0 --> 3Fe2+.

Insertion of nickel nanoparticles in the interlayers of alpha-zirconium phosphate by the decomposition of the intercalated nickel acetate

By employing EXAFS and magnetic measurements, it is shown that nanoparticles of nickel along with those of NiO are incorporated between the layers of a-zirconium phosphate (ZrP) by the thermal decomposition of nickel acetate intercalated in ZrP. The nickel nanoparticles are superparamagnetic. Hydrogen reduction produces small ferromagnetic nickel particles, most of which appear to be outside the interlayer space of ZrP.

Interaction of sheep liver apo-serine hydroxymethyltransferase with pyridoxal-5'-phosphate: A physicochemical, kinetic, and thermodynamic study

Sheep liver serine hydroxymethyltransferase (EC 2.1.2.1) is a homotetramer of M(r) 213,000 requiring pyridoxal-5'-phosphate (PLP) as cofactor, Removal of PLP from the holoenzyme converted the enzyme to the apo form which, in addition to being inactive, was devoid of the characteristic absorption spectrum. Upon the addition of PLP to the apoenzyme, complete activity was restored and the visible absorption spectrum with a maximum at 425 nm was regained. The interaction of PLP with the apoenzyme revealed two phases of reaction with pseudo-first-order rate constants of 20 +/- 5 s(-1) and 12.2 +/- 2.0 x 10(-3) s(-1), respectively. However, addition of PLP to the apoenzyme did not cause gross conformational changes as evidenced by circular dichroic and fluorescence spectroscopy. Although conformationally apoenzyme and holoenzyme were indistinguishable, they had distinct apparent melting temperatures of 51 +/- 2 and 58 +/- 2 degrees C, respectively, and the reconstituted holoenzyme was thermally as stable as the native holoenzyme. These results suggested that there was no apparent difference in the secondary structure of holoenzyme, apoenzyme, and reconstituted holoenzyme, However, sedimentation analysis of the apoenzyme revealed the presence of two peaks of S-20,S-w values of 8.7 +/- 0.5 and 5.7 +/- 0.3 S, respectively. A similar pattern was observed when the apoenzyme was chromatographed on a calibrated Sephadex G-150 column. The first peak corresponded to the tetrameric form (M(r) 200,000 +/- 15,000) while the second peak had a M(r) of 130,000 +/- 10,000. Reconstitution experiments revealed that only the tetrameric form of the apoenzyme could be converted into an active holoenzyme while the dimeric form could not be reconstituted into an active enzyme. These results demonstrate that PLP plays an important role in maintaining the structural integrity of the enzyme by preventing the dissociation of the enzyme into subunits, in addition to its function in catalysis. (C) 1996 Academic Press, Inc.

Pyroelectric and Electrostrictive Properties of (1 –x–y) PZN ·xBT ·yPT Ceramic Solid Solutions

The pyroelectric and electrostrictive properties of lead zinc niobate-lead titanate-barium titanate (PZN-BT-PT) ceramic solid solution were investigated. These properties of the (1 - x)PZN.xBT series were qualitatively explained with a composition fluctuation model. The pyroelectric depolarization temperatures of (1 - x - y)PZN.xBT.yPT ceramics were utilized to select compositions for room-temperature electrostrictive applications. Among them, 0.85PZN.0.10BT.0.05PT ceramic with Q11 = 0.018 m4/C2, Q12 = -0.0085 m4/C2, S2 at 25 kV/cm = -6.1 x 10(-4), T(max) = 75-degrees-C at 1 kHz, and T(t) = 27-degrees-C shows optimum properties for micropositioner applications.

Phosphate derivatives of 123 cuprates of the formula LnSr(2)Cu(3)O(7) (Ln=Gd, Dy, Ho)

Partial substitution of Cu in the chain by the phosphate ion stabilizes LnSr(2)Cu(3)O(7) (Ln = Gd, Dy or Ho) in the 123 structure. The LnSr(2)Cu(2.8)(PO4)(0.2)O-y derivatives exhibit incommensurately modulated structures. The holmium oxy-phosphate derivative has been rendered superconducting by the partial substitution of Ho by Ca.

Synthesis, structure and IR absorption studies of LnBaCuCoO(5) (Ln equal earth) oxides

A series of oxides LnBaCuCoO(5) (Ln = Pr, Nd, Sm, Dy, Gd, Ho and Er) have been synthesized by ceramic method. The oxides crystallize in a tetragonal structure, isostructural to YBaCuCoO5. All the oxides in the series are semiconducting. IR spectra of these oxides show distinct absorption bands at 630 cm(-1), 550 cm(-1) and 330 cm(-1) which are assigned to E, A(2) and A(1) modes respectively. Doping of holes in these oxides, by calcium substitution in Er1-xCaxBaCuCoO5-x (up to x similar or equal to 0.3) was done but, these oxides did not show metallic behaviour.

Sliding wear of YTZP ceramic against steel: observations on ceramic transfer and wear transition

Sliding tests were conducted, in air, of YTZP ceramic pins against steel discs at an applied pressure of 15.5 MPa over a speed range of 0.3 to 4.0 ms(-1). Pin wear was not detectable until 2.0 m s(-1), after which a finite but small wear rate was observed at 3.0 m s(-1), accompanied by a red glow at the contacting surface. A transition in wear behaviour and friction (mu) occurred at 4.0 ms(-1), increasing the former by over two orders of magnitude. Both mu and wear behaviour changed with time at 4.0 m s(-1). During initial periods mu was high and wear rate increased steadily with time accompanied by ceramic transfer onto the disc, which increased with time. When disc coverage exceeds a certain threshold value, mu decreased rapidly and the wear rate stabilized at a very high value. Metal transfer was not observed at any speed. High surface temperatures brought about significant adhesion between TZP and steel and this together with enhanced plastic deformation brought about a transition in wear behaviour.

Spatial gradients of calcium in the slug of Dictyostelium discoideum

Starved amoebae of D. discoideum aggregate and give rise to a long and thin multicellular structure called the slug. The cells within the slug eventually differentiate according to a simple anterior/posterior dichotomy. This motivates a search for gradients of putative morphogens along its axis. Calcium may be one such morphogen. On the basis of observations made by using the calcium-sensitive fluorescent dyes fura-2 and chlortetracyline, we report that there are spatial gradients in cytoplasmic and sequestered calcium in the slug. Anteriorly located and genetically defined prestalk cells (ecmA/pstA, ecmB/pstAB) contain significantly higher levels of calcium than the prespore cells in the posterior. However, the proportion of 'calcium-rich' cells in the slug is greater than that of the subset of prestalk cells defined by the expression of the ecmA or ecmB genes.

Investigations on sodium tin phosphate and tin pyrophosphate glasses

Glasses of the alkali tin phosphate system have been investigated. The infrared absorption and fluorescence spectra of the glasses have been examined. It is found that tin is present in both + 2 and + 4 oxidation states. Also tin ions occupy four- or six-coordinated sites in the glass.

New open-framework phosphate and phosphite compounds of gallium

Five new open-framework compounds of gallium have been synthesized by hydrothermal methods and their structures determined by single crystal X-ray diffraction studies. The compounds, C8N4H26]Ga6F4(PO4)(6)], I, C5N3H11]Ga3F2(PO4)(3)]center dot H2O, II, C6N3H19]Ga-4(C2O4)(PO4)(4)(H2PO4)]center dot 2H(2)O, III, Ga2F3(HPO4)(PO4)]center dot 2H(3)O, IV, and C3N2H5](2)Ga-4(H2O)(3)(HPO3)(7)], V, possess three-dimensional structures. All the compounds are formed by the connectivity between the Ga polyhedra and phosphite/phosphate units. The observation of SBU-6 (I and II) and spiro-5 (IV) secondary building units (SBUs) are noteworthy. The flexibility of the formation of gallium phosphate frameworks has been established by the isolation of two related structures (I and II) from the same SBU units but different organic amines. Some of the present structures have close resemblance to the gallium phosphate phases known earlier. The compounds have been characterized by CHN analysis, powder XRD, IR, and TGA. (C) 2011 Elsevier B. V. All rights reserved.

Laboratory studies on the volume change characteristics of kaolinite contaminated with sodium phosphate/sulfate

Reported distress to an industrial structure from phosphate/sulfate contamination of kaolinitic foundation soil at an industrial location in Southern India prompted this laboratory study. The study examines the short-term effect of sodium sulfate/phosphate contamination on the swell/compression characteristics of a commercial kaolinite. Experimental results showed that the unsaturated contaminated kaolinite specimens exhibited slightly higher swell potentials and lower compressions than the unsaturated uncontaminated kaolinite specimens. It is suggested that the larger double layer promoted by the increased exchangeable sodium ion concentration is responsible for the slightly higher swell potentials and lower compressions of the unsaturated contaminated kaolinite specimens.