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ABSTRACT Mortars with high aggregate:binder ratios of 10:1 and 8:1 were investigated with binders of blast furnace slag activated with 2.5%, 3.4%, 4.5%, and 6.5% [Na.sub.2]O relative to the mass [...]

We investigate the effect of cation size in the dc activation energy needed for oxygen ion conductivity, Edc, in highly disordered pyrochlore-type ionic conductors A2B2O7. Twenty compositions of general formula Ln2Zr2-yTiyO7 (Ln = Y, Dy and Gd) and Gd2-yLayZr2O7, were prepared by mechanical milling and their electrical properties measured by using impedance spectroscopy at different temperatures. We also evaluate, by using Ngai’s Coupling Model, the effect of cation radii RA and RB, on the microscopic potential-energy barrier, Ea, that oxygen ions encounter when jumping into neighboring vacant sites. We find that for a fixed B-site cation radius RB, both activation energies decrease with increasing A-site cation size, RA, as a consequence of the increment in the unit cell volume. In contrast, and for a given RA size, the dc activation energy Edc of the Ln2Zr2-yTiyO7 series increases when the average RB size increases. The latter behavior is explained in terms of the enhanced interactions among mobile oxygen ions as the structural disorder increases when RB approaches RA.

A new ceramic pigment with the cordierite high temperature structure was synthesised by sol–gel processing. A small region of a solid solution phase was detected containing <5 wt-%V2O5. The crystallisation behaviour and thermal stability of the pigment was studied. Unit cell parameters, crystallite size, and the phase constitution of calcined powders were determined by X-ray diffraction. The xerogel powders were studied by thermal analysis and infrared spectroscopy. The compositions of fired samples were obtained by inductively coupled plasma analysis and the L *a*b*colour parameters were measured.

A first survey of elemental contents in airborne particulate matter from Monterrey, Nuevo León, Mexico, was performed using PIXE. This second largest industrial city is located 715 km north of Mexico City, and counts with a population of nearly three million inhabitants in its conurbation. Air pollution in the place comes from a great variety of industries ranging from iron smelters to furniture manufacturing, as well as from fuel combustion in vehicles and industries. This study presents results of elemental contents in airborne particulate matter in two particle size fractions: PM2.5and PM15. The samples were collected during five weeks on working days, Monday–Friday, from 9 December 1996 to 14 January 1997. Two samples a day were collected, 12 h each, night-time and day-time. These first results show local pollution as typical from a large urban area in conjunction with an active industry. Thirteen elements were consistently detected in most of the samples and some episodes due to both industrial and human activities were identified. A general discussion about the results obtained is presented.

AbstractAn FTIR method is described and evaluated for the low concentration analysis of volatile anaesthetics (halothane, isoflurane) and nitrous oxide. It has been found that no serious problem occurs in the trace determination of volatile anaesthetics but nitrous oxide introduces lack of sensitivity (<10 ppm) and non linearity problems at lower concentrations (<40 ppm) in the described analysis method.