Dispersity effects on the ice nucleating activity of copper acetyl acetonate

The dispersity dependence of the ice nucleating activity of copper acetyl acetonate aerosols at −5, −10 and −20°C has been studied over a wide range of particle sizes. A strong dependence of the specific “yield” of ice crystals, and the fraction of the particles forming ice crystals, on the aerosol particle size has been found, this dependence being observed for the first time for nonspherical particles. The ice nucleating activity of copper acetyl acetonate proves to exceed that of Agl at − 5°C and to be slightly lower at − 10 and − 20°C.     

Effect of temperature on the structure and density of ammonium chloride particles

The structure and density of individual ammonium chloride particles formed at 0 and −20°C by homogeneous nucleation were studied using electron microscopy and X-ray diffraction. The crystal size apparently increased at the lower temperature and many of the particles formed at −20°C were single crystals or had an oriented polycrystalline structure. These results differ from those reported previously for particles formed at room temperature (23–26°C), which showed an amorphous or randomly-oriented fine crystal structure. Coagulation was more frequently observed as the temperature decreased and the porosity present in the particles appeared to be much finer and more uniform. The density of these particles decreased from about 0.26 g cm⁻³ for particles of size 0.1–0.2 μm to approximately 0.1 g cm⁻³ for particles slightly smaller than 1 μ.     

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.     

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.     

Vapour pressure determinations of phthalic esters by analysis of a static aerosol with the aid of a flame ionization instrument

A new method for the determination of vapour pressures of high boiling substances has been developed. The substances, in this case phthalic esters, are dispersed at room temperature into a rotating chamber. With this method a small volume of the substance is distributed in a large number of aerosol particles with a corresponding large surface, which is vital for a rapid vapour pressure equilibrium. The concentration of the vapour phase is measured by an analyzing instrument with a flame ionization detector of a special design. Vapour pressure determinations are reported down to the region 10⁻⁵–10⁻⁶ mmHg and are carried out from 20°C to 70°C.     

Mikrokalorimetrische studie über die eisbildung in chloridhaltigem zementstein

Differential scanning calorimetry (DSC) of wet porous materials in the temperature range between + 20°C and − 60°C is a sensitive tool to investigate phase transitions and supercooling of pore water. Storage of hydrated cement paste (hcp) in water containing 5 % chloride at an age of 8 months after freeze drying leads to an increase of the enthalpy change between − 10°C and − 25°C (phase transition of free water in capillary pores with r_H > 10 nm) and to a strong reduction of the enthalpy change between − 43°C and − 52°C (3 nm < r_H < 10 nm) in comparison to hcp without addition of chloride.     

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.     

Silver-silver selenocyanate electrode: determination of standard electrode potential, solubility product of AgSeCN and various thermodynamic parameters at 35, 40, 45 and 50°C

Silver-silver selenocyanate electrode has been prepared and the standard electrode potential determined to be −(0·02975 ± 0·0002), −(0·03022 ± 0·0003), −(0·03105 ± 0·0003) and −(0·03151 ± 0·0005) V at 35, 40, 45 and 50°C respectively (IUPAC convention). The thermodynamic quantities: ΔG°, ΔH° and ΔS° of the cell reaction and the solubility product of AgSeCN have also been calculated at the above temperatures.     

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.     

Nitridation of silicon powder studied by XRD, Si MAS NMR and surface analysis techniques

The nitridation of elemental silicon powder at 900–1475 °C was studied by X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), XRD, thermal analysis and ²⁹Si MAS NMR. An initial mass gain of about 12% at 1250–1300 °C corresponds to the formation of a product layer about 0·2 μm thick (assuming spherical particles). XPS and XAES show that in this temperature range, the surface atomic ratio of N/Si increases and the ratio O/Si decreases as the surface layer is converted to Si₂N₂O. XRD shows that above 1300 °C the Si is rapidly converted to a mixture of - and β-Si₃N₄, the latter predominating >1400 °C. In this temperature range there are only slight changes in the composition of the surface material, which at the higher temperatures regains a small amount of an oxidised surface layer. By contrast, in the interval 1400–1475 °C, the ²⁹Si MAS NMR chemical shift of the elemental Si changes progressively from about −80 ppm to −70 ppm, in tandem with the growth of the Si₃N₄ resonance at about −48 ppm. Possible reasons for this previously unreported change in the Si chemical shift are discussed. ©     

Mercury-mercurous propionate electrode: standard potentials at different temperatures and related thermodynamic quantities

The standard molal potentials E°_m of the Hg/Hg₂(OPr)₂, OPr⁻ electrode at 15°, 20°, 25°, 30° and 35° C have been determined. The E°_m values obtained are 0.5114, 0.5072, 0.5031, 0.4988 and 0.4942 V respectively, which can be fitted to the equation Edg_m/V = 0.5031 −8.56 × 10⁻⁴ (itt/°C − 25)−3.0588 × 10⁻⁶ (t/ °C -25)². The changes in standard free energy, entropy and enthalpy for the cell reaction have been calculated.     

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.     

Preparation of supported Pt-M catalysts (M = Mo and W) from anion-exchanged hydrotalcites and their catalytic activity for low temperature NO-H2-O2 reaction

The NO-H₂-O₂ reaction was studied over supported bimetallic catalysts, Pt-Mo and Pt-W, which were prepared by coexchange of hydrotalcite-like Mg-Al double layered hydroxides by Pt(NO₂)₄²⁻, MoO₄²⁻, and/or WO₄²⁻ and subsequent heating at 600 °C in H₂. The Pt–Mo interaction could obviously be seen when the catalyst after reduction treatment was exposed to a mixture of NO and H₂ in the absence of O₂. The Pt-HT catalyst showed the almost complete NO conversion at 70 °C, whereas the Pt-Mo-HT showed a negligible conversion. Upon exposure to O₂, however, Pt-Mo-HT exhibited the NO conversion at the lowest temperature of ≥30 °C, compared to ≥60 °C required for Pt-HT. EXAFS/XANES, XPS and IR results suggested that the role of Mo is very sensitive to the oxidation state, i.e., oxidized Mo species residing in Pt particles are postulated to retard the oxidative adsorption of NO as NO₃ and promote the catalytic conversion of NO to N₂O at low temperatures.     

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.     

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.     

Electrical conductance of KI in anhydrous acetonitrile

The electrical conductivity of KI solutions in anhydrous acetonitrile has been determined at 0, 25 and 35°C in the concentration range 0·9– 600 × 10⁻⁴ mole/l. The values of Λ₀, K and a calculated from the results are, respectively: 145·9 mho/cm, 0·95 × 10 ⁻² and 1·72 Å at 0°C; 186·2 mho/cm, 8·98 × 10⁻² and 4·6 Å at 25°C; and 204·8 mho/cm, 5·17 × 10⁻² and 3·5 Å at 35°C. The phoreograms at all the three temperatures are catabatic at lower concentration, but become anabatic at 0·017, 0·022 and 0·024 respectively, at 0, 25 and 35°C.     

Characterisation of ceria–zirconia solid solutions after hydrothermal ageing

Ce_1−xZr_xO₂ (x=0–0.84) solid solutions prepared by co-precipitation were characterised after calcination at 700 or 900°C, and after hydrothermal ageing at 1000 or 1200°C. The solid solutions were formed at 700°C, and crystallise as cubic or tetragonal phases depending on their compositions. Despite the rather high surface areas obtained after calcination at 700°C, the sintering is important at 900°C, and tremendous after hydrothermal ageing at 1000°C. For all compositions between 16 and 83 mol% ceria, complete de-mixing of the solid solutions into two phases was observed after ageing at 1200°C: one Zr-rich, tetragonal phase, and one Ce-rich, cubic phase. XPS and ISS measurements show that the phase separation takes place with surface enrichment in Zr, the Zr-rich phase being formed at the periphery of the particles, whereas the core is composed of the Ce-rich phase.     

The effect of the contact between platinum and soot particles on the catalytic oxidation of soot deposits on a diesel particle filter

Experiments were performed with two model soot aerosols brought into different forms of contact with Pt aerosol particles, to investigate the effectiveness of this contact in lowering the catalytic soot oxidation temperature. The contact was either generated between individual particles in the aerosol state (Pt-doped soot to simulate a fuel borne catalyst), or by sequential or simultaneous deposition of separately generated soot and Pt aerosols onto a sintered metal filter. (Formation of a soot cake on previously deposited Pt aerosol would simulate a catalyst coated diesel particle filter.) The catalytic activity was determined in all cases from temperature ramped oxidation in air of the filtered particles, and defined as the 50% conversion temperature.

It was found that Pt-doped soot and simultaneously filtered aerosols were both equally effective in reducing the oxidation temperature by up to 140–250 °C for the spark discharge soot (with 3–47 wt% Pt concentration in the soot cake), and by up to 140 °C for the pyrolysis soot (3 wt% Pt). Conversely, the deposition of a thin soot layer of 5–10 μm thickness onto Pt, or vice versa, produced only a slight temperature reduction on the order of about 13–42 °C. These results suggest that the distance between soot and Pt particles plays a key role in promoting an effective oxidation on the filter, which is consistent with the role of Pt particles as local generators of activated oxygen.     

Oil production from algal cells of Dunaliella tertiolecta by direct thermochemical liquefaction

Algal cells of Dunaliella tertiolecta with a moisture content of 78.4 wt% were converted directly into oil by thermochemical liquefaction at around 300°C and 10 MPa. The oil yield was about 37% on an organic basis. The oil obtained at a reaction temperature of 340°C and holding time of 60 min had a viscosity of 150–330 mPas and a calorific value of 36 kJ g⁻¹, comparable to those of fuel oil.     

Transformation of amorphous silica colloids to nanosized MEL zeolite

Si-MEL molecular sieve is prepared from aged colloidal precursor solutions under hydrothermal treatment (HT) at 90 °C. In situ dynamic light scattering (DLS) investigations of the precursor solutions and the crystalline Si-MEL sols are performed with the original concentrations. Sub-colloidal particles with a mean radius of about 1 nm and colloidal aggregates with a radius of 10 nm are detected in the precursor colloidal solutions after 5 h aging at room temperature. Consumption of the sub-colloidal particles with time and an increase of the colloidal fraction of 10 nm particles after 48 h aging is observed. After heating of the aged precursor solution at 90 °C for 30 h, three particle populations of 1, 10, and 100 nm radius are formed. Complete transformation from amorphous to crystalline colloidal particles is observed after 68 h extended HT of the aged precursor solution. The mean hydrodynamic radius of the crystalline Si-MEL particles is about 100 nm based on the DLS measurements. The size of the MEL crystals was also confirmed with SEM. Additional time-dependent ²⁹Si NMR measurements of the aged precursor colloidal solutions prior to further crystal growth show that the amount of Q⁰ species (δ=−71.2) decreases, while signals of high intensity in the range between δ=−88.6 and −98.9 indicating the formation of Q³₆ and Q³₈ silicon species appear. IR data reveal that with aging of the precursor colloidal solutions at room temperature, an increased ordering of the silica species similar to those found in the final MEL product is observed.