Synthesis of nanocrystalline 8 mol% yttria stabilized zirconia powder from sucrose derived organic precursors

An organic precursor synthesis of 8 mol% yttria stabilized zirconia (YSZ) powder from Zr–Y composite nitrate solution and sucrose has been studied. Oxidation of sucrose in Zr–Y composite nitrate solution containing excess nitric acid in situ generates hydroxy carboxylic acids that forms a white sol which showed peaks at 1640 cm⁻¹ and 1363 cm⁻¹ in IR spectrum corresponding to hydroxy carboxylic acid complexes of Zr and Y. Precursor mass obtained by drying the sol on calcinations at 600 °C produced loosely agglomerated particles of cubic YSZ. Deagglomerated YSZ contain submicron particles with D₅₀ value of 0.5 μm and the particles are aggregates of nanocrystallites of nearly 10 nm size. Compacts prepared by pressing the YSZ powder sintered to 96.7% TD at 1450 °C. The sintered YSZ ceramic showed an average grain size of 2.2 μm.     

Estimation of particle size distribution parameters in animal lungs

A constant of specific solubility of 2·5 × 10⁻⁸ g cm⁻²day⁻¹ was determined for fused aluminosilicate particles, by observing in vivo retention kinetics after intravenous injection into rats. Studies over the past years in this laboratory, in which dogs and rats have inhaled labeled aerosols of these particles, have shown retention half-lives in the lung of 460 and 285 days, respectively. By applying these values for solubility and half-life to Mercer's theory of dissolution from the deep lung, the initial distribution of particles deposited in the pulmonary regions of dogs and rats following inhalation was calculated. From an inhaled aerosol with a mass median diameter, D_m, of 1·0 μm and σ_o = 1·7, a distribution described by D_m = 0·51 μm and σ_o's ranging from 1·16–1·48 was estimated to have been deposited in the Beagle dog lung. and a D_m =< 0·32 μm and σ_o's ranging from 1·18–1·29 was similarly calculated for rats.     

Aerosol measurement by laser doppler spectroscopy—II. Operational limits, effects of polydispersity, and applications

The theoretical basis and the results of a computer simulation are presented which describe the operational limits of size and concentration for aerosol sizing by laser Doppler spectroscopy LDS,. This analysis suggests that a state of the art LDS system has the capability of sizing 0·03 μm diameter particles when the number concentration is 10⁸ cm⁻³ or greater and 0·2 μm diameter for coocentrations as low as 100 particles cm⁻³. An evaluation of the effect on the laser Doppler spectroscopy measurements of a polydisperse aerosol having a log normal size distribution is presented and methods for combining these measurements with other averaged measurements to determine both count median diameter (CMD) and geometric standard deviation (δ_g) are proposed. For aerosols having log normal distributions with 0·3 < CMD < 3 μm and 1·0 < δ_g < 2·0, laser Doppler spectroscopy is able to measure the surface area median diameter within ± 15 per cent, independent of polydispersity. Applications of LDS to aerosol sizing are evaluated and its advantages and disadvantages relative to other sizing methods are discussed.     

Preparation of ultra-active alumina of designed porous structure by successive hydrothermal and thermal treatments of porous anodic Al2O3 films

A porous anodic alumina film was prepared by the anodic oxidation of Al metal sheet in a thermostated and vigorously stirred bath of H₂SO₄ 15% (w/v) at a temperature of 25°C and a current density of 15 mA cm⁻². It had a geometric surface area of 33 cm², a surface density of pores 1.269×10¹¹ cm⁻² and the maximum limiting thickness and porosity achieved at these conditions which are 50.3 μm and 0.42, respectively. This oxide was tried in the catalytic test reaction of the decomposition of HCOOH at temperatures 270–390°C. Then, the oxide was treated hydrothermally in H₂O at 100°C for 5 h and tried in the same test reaction. The procedure of hydrothermal treatment and catalysis experiment was repeated 40 times. In all cases the oxide showed an almost exclusively dehydrative catalytic effect, 98–100%. Both the total activity of the alumina film with the aforementioned constant geometric surface area and its specific activity referred to the unit of oxide mass gave a maximum in the first and a minimum about the fourth hydrothermal treatment; then, they increased strongly with the order of hydrothermal treatment. Despite the decrease of the oxide mass during hydrothermal treatment, the final promotion of the total catalytic activity of oxide was 13.7–10.6 times that of non-treated oxide for temperatures 330–390°C. The corresponding promotion of specific activity was 31.5–24.5 times that of the non-treated oxide. The results of the present study showed that the successive hydrothermal and thermal treatments of porous anodic Al₂O₃ films produce more and more active alumina catalysts. In this way ultra-active alumina catalysts or supports can be prepared.     

Chlorination kinetics of pyrite mineral in two Turkish lignites

The kinetics of the chlorination of pyrite in two Turkish lignites in water and water-carbon tetrachloride media at ambient pressure ( 610 mm Hg) are investigated. The effects of speed of stirring (5–20 s⁻¹), particle size (74–88, 150–180 and 250–425 μm), temperature (13–70°C) and reaction time (0–18 000 s) were studied. The experimental data were analyzed on the basis of the unreacted shrinking core model. The fine pyrite particles are assumed to be embedded inside the coal particles. The rate-controlling step was found to be diffusion of chlorine through the ash (the coal matrix). The activation energies were calculated as 25.1 kJ mol⁻¹ for Dada i coal in water medium and 25.0 kJ mol⁻¹ for Mengen coal in water-carbon tetrachloride medium.     

Hydrothermal synthesis, characterization and structure refinement of chlorate- and perchlorate-sodalite

Chlorate- and perchlorate-sodalites were synthesized hydrothermally in the temperature range of 160°C to 500°C. IR absorption bands indicate the enclathration of NaClO₃ (624 cm⁻¹) and NaClO₄ (624 cm⁻¹ and 2050 cm⁻¹) in the sodalite cages. The thermal decomposition has been characterized by simultaneous thermal analysis (TG, DTG, DTA) and high temperature X-ray powder diffraction. The total collapse of the sodalite framework structure and the formation of nepheline could be observed at 750°C and 1100°C for chlorate-sodalite and perchlorate-sodalite, respectively.

The crystal structure has been determined for NaClO₄-sodalite showing cubic symmetry (a₀=9.071 Å, SG P 3n) and complete ordering of Si and Al in the silicate framework; the Si-O-Al angle is 146.7°. The Cl atoms of the enclathrated perchlorate are located at the central positions of the sodalite cages. For the oxygen atoms of the Cl₄⁻ anions the structure refinement led to orientationally disordered sites having a close resemblance to the well-known O(2) positions of basic sodalite Na₈[AlSiO₄]₆(OH)₂·2 H₂O.     

Novel alumina ‘KK Leaf Structures’ as catalyst supports

A method has been devised in which alumina can be formed into a layer of thin leaf-like structures that have a thickness of 0.2–0.8 μm. This consists of a process in which aluminium iso-propoxide is transformed into a sol–gel and then: frozen (−195 °C), freeze-dried (−60 °C), and finally calcined (450 °C). These special conditions lead to the formation of a structure that is named: ‘KK Leaves’.

After calcining at 450 °C, the leaves have a specific surface area of 282 m²/g, an average pore size of 2.8 nm, and exhibit a curly shape. The structure has the appearance of a loosely packed (but ordered) collection of thin curly leaves with fine ribs resembling leaf veins on trees and plants. They would readily act as a support, e.g., for a catalyst, or adsorbents, or act as a membrane filter.     

Gel Casting of Alumina using Boehmite as a Binder

The process for alumina gel casting was developed using an inorganic binder The monohydroxy aluminium oxide (boehmite, AlOOH) was incorporated with ultrafine alumina of particles (0·5 μm) and the slurry rheology was studied and presented. The effect of boehmite in slurry viscosity was observed with respect to different amounts of boehmite and time. The alumina 54 vol% slurry with 10 wt% boehmite showed the viscosity of 880 mPa s at 93 s⁻¹. An external coagulating agent, HMTA, was incorporated with alumina–boehmite slurry and the effective change in slurry viscosity with respect to concentration and time was studied. The addition of HMTA results in faster gelation and the optimum concentration was determined as 0·21 mol L⁻¹. The alumina gelcast body was dried under humidity conditions at 40°C, RH 70%. The defect free dried green body was obtained and the total linear drying shrinkage was calculated as 3·2% and the green density observed was 59·3% of theoretical value. The sintered density of 98% (TD) was achieved at 1450°C in 2 h. The mechanical hardness of sintered alumina measured as 2286 kg mm⁻². The sintered ceramic showed an extremely fine grained microstructure with an average grain size <2 μm. The boehmite acts as an excellent binder and sintering aid for alumina ceramics.     

Electrochemical reduction of thermally prepared oxides of iron and iron-chromium alloys studied by in situ Raman spectroscopy

Pure Fe and Fe/Cr alloys (3% and 12% Cr) were oxidized at 250–260°C and subsequently electrochemically reduced in borate buffer, pH 8.4. The reduction was followed by in situ Raman spectroscopy as well as chronopotentiometric and chronoamperometric measurements. At several time intervals ex situ Raman control investigations and ESCA analyses were undertaken. Although at −0.7 V vs sce partial reduction of the oxide film was observed, -Fe₂O₃ remained unchanged and reduced at −0.9 V. A mixture of spinel structured oxide, possibly Fe₃O₄, and a ferrous deposit were observed when the oxide film was galvanostatically reduced at 100 μA cm⁻²; after prolonged reduction the bare metal resulted. The thermally created oxide of the Cr alloy possessed an inner Cr rich layer which during the galvanostatic reduction of the oxide film at 50 μA cm⁻² is most likely responsible for an increase in the overpotential of more than 80 mV.     

Two-dimensional near-infrared correlation temperature studies of an amorphous polyamide

Near-infrared spectra of a totally amorphous polyamide measured over the temperature range 25–200°C was analyzed using generalized two-dimensional (2D) correlation spectroscopy. At least, five distinct bands at 5690, 5810, 5900, 5980 and 6010 cm⁻¹ were identified in the region of the CH overtones (5200–6200 cm⁻¹). Among them, two bands at 5810 (aliphatic) and 6010 cm⁻¹ (aromatic) are found to be very sensitive to the temperature-induced structural changes of the polyamide under examination. In the ν(NH) overtone region (6300–6800 cm⁻¹), the asynchronicity of the bands assigned to the vibrations of the free and hydrogen-bonded NH groups indicate a complicated dissociation mechanism and the existence of different hydrogen-bonded species in the investigated totally amorphous polyamide sample. Owing to the spectral resolution enhancement in 2D correlation spectra, a splitting of the first overtone of the free NH stretching vibration into two components at 6780 (totally free) and 6740 cm⁻¹ (free-end) can be observed.     

ß-sialon ceramics with TiN particle inclusions

Fully dense composites of 0–30 wt% discrete TiN particles distributed in a ß-sialon matrix of overall composition Si_5·5Al_0·5O_0·5N_7·5 have been prepared by hot isostatic pressing at 1650 and 1750°C. Pressureless sintering at 1775°C gave materials with an open porosity. Typical sizes of the TiN particles were 1–3 μm, and no intergranular glassy phase was observed in the prepared materials. The grain size of ß-sialon was below 1 μm in the materials HIPed at 1650°C, and 1–2 μm at 1750°C. The Vickers hardness was fairly constant for the TiN-ß-sialon composites with up to 15 wt% TiN added: H_v10 around 17·5 GPa for materials HIPed at 1650° and around 17 GPa at 1750°C, whereas at higher TiN contents the hardness decreased to around 16 GPa. The indentation fracture toughness of the ß-sialon ceramic increased approximatively from 3 to 4 MPam^1/2 at an addition of 15 wt% TiN particulates. The fracture toughness could be further increased to 5 MPam^1/2 by addition of small amounts of Y₂O₃ and A1N to a ß-sialon composite with 30 wt% TiN.     

Synthesis, densification and electrical properties of strontium cerate ceramics

Powders of pure and 5% ytterbium substituted strontium cerate (SrCeO₃/SrCe_0.95Yb_0.05O_3−δ) were prepared by spray pyrolysis of nitrate salt solutions. The powders were single phase after calcination in nitrogen atmosphere at 1100 °C (SrCeO₃) and 1200 °C (SrCe_0.95Yb_0.05O_3−δ). Dense SrCeO₃ and SrCe_0.95Yb_0.05O_3−δ materials were obtained by sintering at 1350–1400 °C in air. Heat treatment at 850 and 1000 °C, respectively, was necessary prior to sintering to obtain high density. The dense materials had homogenous microstructures with grain size in the range 6–10 μm for SrCeO₃ and 1–2 μm for SrCe_0.95Yb_0.05O_3−δ. The electrical conductivity of SrCe_0.95Yb_0.05O_3−δ was in good agreement with reported data, showing mixed ionic–electronic conduction. The ionic contribution was dominated by protons below 1000 °C and the proton conductivity reached a maximum of 0.005 S/cm above 900 °C. In oxidizing atmosphere the p-type electronic conduction was dominating above 700 °C, while the contribution from n-type electronic conduction only was significant above 1000 °C in reducing atmosphere.     

Raman spectroscopic studies on the sulfation of cerium oxide

In the present study, we have examined sulfation of cerium oxide via impregnation of (NH₄)₂SO₄, followed by heating in the temperature range of 220–720°C, using Raman Spectroscopy. Based on the SO and SO stretching frequencies in the range of 900–1400 cm⁻¹, a wide range of surface oxysulfur species and bulk cerium-oxy-sulfur species are identified. At 220°C, a mixture of (NH₄)₂SO₄ crystals, SO²⁻_4(aq) and HSO¹⁻_r(aq) is found to have formed on ceria's surface, whereas complete conversion of (NH₄)₂SO₄ to SO²⁻_4(aq) and HSO¹⁻_4(aq) occurs at 280°C. At 350°C, formation of a mixture of surface pyrosulfate S₂O²⁻_7(surf.0, consisting of two SO oscillators and a bulk type compound identified as Ce(IV)(SO₄)_x(SO₃)_2−x (0 < x < 2) have been observed. Upon introduction of moisture, the former transforms to HSO¹⁻_4(surf.), whereas the latter remains unchanged. At 400°C, only the bulk type compound can be observed. At 450°C, only Ce₂(SO₄)₃ is generated and remains stable until 650°C. Further increase in the temperature to 720°C results in the formation of CeOSO₄. The present study not only provides a more thorough understanding of the sulfation of cerium oxide at a molecular level, but also demonstrates that Raman spectroscopy is a highly effective technique to characterize sulfation of metal oxides.     

Diamond growth by carbon ion implantation of diamond

Medium energy (5–25 keV) ¹³C⁺ ion implantation into diamond (100) to a fluence ranging from 10¹⁶ cm⁻² to 10¹⁸ cm⁻² was performed for the study of diamond growth via the approach of ion beam implantation. The samples were characterized with Rutherford backscattering/channelling spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and Auger electron spectroscopy. Extended defects are formed in the cascade collision volume during bombardment at high temperatures. Carbon incorporation indeed induces a volume growth but the diamond (100) samples receiving a fluence of 4 × 10¹⁷ to 2 × 10¹⁸ at. cm⁻² (with a dose rate of 5 × 10¹⁵ at. cm⁻² s⁻¹ at 5 to 25 keV and 800 °C) showed no He-ion channelling. Common to these samples is that the top surface layer of a few nanometers has a substantial amount of graphite which can be removed by chemical etching. The rest of the grown layer is polycrystalline diamond with a very high density of extended defects.     

Thermoelectric characterization of NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe) polycrystalline materials

Layered -titanate materials, Na_xM_x/2Ti_1−x/2O₂ (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na_0.4Ni_0.2Ti_0.8O₂ were ca. 7×10³ S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm⁻¹ K⁻¹ at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na_0.4Ni_0.2Ti_0.8O₂ and Na_0.4Co_0.2Ti_0.8O₂ was about 1.9×10⁻⁴ and 1.2×10⁻⁴ K⁻¹ around 700 °C, respectively.     

Low temperature synthesis of β-SiC by a metal vapor vacuum arc ion source

β-SiC surface layers were synthesized by implantation of C⁺ into Si substrates at a comparatively low temperature of 400°C with a metal vapour vacuum arc ion source. X-ray diffraction patterns showed that these layers had a strong (111) preferred orientation. The amount of β-SiC formed increased significantly with the rise of the implantation dose, but the crystallinity of the layers formed relied little on the implantation dose. Both the broad X-ray diffraction peaks and the scanning electron microscopy photograph showed that the grain size of the sample with a dose of 7×10¹⁷ cm⁻² is relatively small.     

Droplet evaporation and solute precipitation during spray pyrolysis

The process of spray pyrolysis was investigated theoretically using a model that describes the evolution of the droplet size, solvent vapor concentration in the carrier gas, and both droplet and gas temperatures along the reactor axis. The model also accounts for solute concentration profiles and solute precipitation in the solution droplets. The model was used to describe the evaporation of sodium chloride aqueous solution droplets in diffusion dryers and hot-wall reactors as a function of reactor residence time, droplet size (a few microns), solution molality (up to 2 M), droplet concentration (10⁶–10⁷ cm⁻³), relative humidity of the carrier gas (0–50%) and reactor wall conditions. Decreasing initial droplet size and solution molality accelerated droplet evaporation and resulted in smaller droplets at the onset of solute nucleation. Decreasing droplet concentration and carrier gas inlet relative humidity as well as increasing wall temperature (up to 350°C) or axial wall temperature gradient (up to 100°C cm⁻¹) increased the droplet evaporation rate, but did not change appreciably the droplet size at the point of precipitation for a given droplet size and solute concentration. Thus, control of droplet size at the onset of solute nucleation by varying process parameters other than the solution concentration and initial droplet size is limited.     

Photoelectrochemical treatment of the dye reactive red 198 using DSA electrodes

The study of the oxidation of the dye reactive red 198 on Ti/Ru_0.3Ti_0.7O₂ electrode is presented. Three different techniques were employed: photocatalytic (interaction of UV radiation and electrode surface), electrochemical (application of a constant current) and photoelectrochemical (simultaneous application of a constant current and UV radiation). The effect of temperature (20–45 °C) and current density (5–89 mA cm⁻²) were investigated. No significant temperature effect was observed for the three techniques used. It was observed that at low current densities (5–30 mA cm⁻²) the photoelectrochemical (PhEC) rate of colour and TOC removal is simply the sum of the photocatalytic (PC) and electrochemical (EC) rates. However, as the current density increases, the rate of PhEC removal is much greater. This phenomenon is interpreted as being due to the increased production of O₂, which goes on to interact with the UV radiation and cause the oxidation of the dye.     

Large aerosol particles in a convective storm environment

Concentrations of large (d > 10 μm) inorganic and organic particles varied widely at ground level and at subcloud altitudes. Particle concentration decreased at a slower rate aloft than at ground level; as a result, the relative abundance of large aerosol particles aloft tended to increase with increasing particle size. A substantial fraction of organic particles aloft was found to be responsible for this trend.

Curves of freezing frequency indicate the presence of two distinctive sources of freezing nuclei derived from large aerosol particles active in the − 9 to − 12°C and − 19 to − 22°C temperature ranges.     

Viscoelastic properties of cellulose derivatives: 1. Cellulose acetate

The dynamic mechanical spectrum of cellulose acetate (CA) from −130°C to 240°C has been determined at different frequencies (from 0.1 to 30 Hz). Three relaxations, designated , β and γ in order of decreasing temperature, and one shoulder (β*) above room temperature were found. Comparison with calorimetric and thermogravimetric measurements yields the conclusion that the relaxation (197°C at 3 Hz) is related to the glass-to-rubber transition and the β* shoulder (50°C–100°C) is due to loss of moisture. The β relaxation (−38°C at 3 Hz, ΔH = 100 kJ mol⁻¹) is tentatively assigned to local motions of the main chain (glucopyranose rings). The low-temperature γ relaxation (−88°C at 3 Hz, ΔH = 46 kJ mol⁻¹), is humidity-dependent: its intensity decreases when the samples are dried to moisture contents lower than that obtained by normal room conditioning (about 3%). Higher water contents shift the relaxation to lower temperatures without increasing the intensity of the mechanical loss. It is suggested that water associated with the unesterified methylol groups of cellulose acetate is responsible of the dynamic mechanical γ dispersion.