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Time-resolved X-ray diffraction measurements were performed in situ on a Pd/C catalyst during two successive thermal treatments from 300 to 873 K. Analysis of the diffraction patterns, as a function of thermal treatment, reveals anomalous features in the evolution of Pd particles. An intermediate Pd1-xCx phase (x ∼ 0.1) is observed and dissolved into pure Pd at ∼700 K. Moreover, the size of metal particles, remaining almost constant (∼10 nm) during the annealing, abruptly increases to 30 nm in close connection with the dissolution of the Pd1-xCx phase. These effects clearly point out an interaction between the metal and the support and suggest that the formation of the Pd1-xCx phase would prevent the metal-particle sintering, thus maintaining the catalyst dispersion at a high level. There is no evidence of the formation of a Pd1-xCx phase during the second temperature treatment since only metallic Pd was detected. As for the growth in particle size, a small increase to 32 nm was observed.

We investigated the nucleation and crystallization behavior of multi-phase glass-ceramic materials (in the Li2O–Al2O3–SiO2 system to which low amounts of oxides such as TiO2, ZrO2, P2O5, BaO, Sb2O3 and ZnO were added), with interest in their transparency properties as glazes for industrial tiles with high scratch resistance. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used. XRD showed that the nucleating oxides produce, during the nucleation stage (at 953 K for 20 h), an orthorhombic ZrTiO4 phase, which maintains a similar crystallite size (about 4 nm) during the subsequent crystallization processes. We succeeded in determining the concentration of nuclei by using XRD data only. This quantity resulted close enough to the corresponding one, determined using the classical TEM method. The formation of each crystalline phase, developed during the crystallization stage, as a function of the thermal treatment, was quantitatively measured using the Rietveld method. In particular, the isothermal transformations at 1003 and 1023 K of the characteristic main phase, i.e., β-eucryptite s.s., which is richer in silica with respect to the relevant stoichiometric phase, into β-spodumene s.s., also richer in silica, were found to be consecutive solid state reactions. Moreover, this preliminary investigation aims at improving knowledge of the mechanisms leading to the development of transparent/opaque materials during the thermal treatment of Li2O–Al2O3–SiO2 glass-ceramics.

The catalytic activity in the isomerization of n-butane of a variety of sulfated zirconia catalysts promoted with different amounts of Al 2 O 3 is reported together with a FTIR analysis of the surface chemical properties.

The application of a modified version of the X-ray Rietveld analysis on Pd-Au/C catalysts, prepared by different methods, is reported. As for monometallic catalysts it is possible to separate in these systems the populations of particles with different size.

In this work we have determined, on a series of 0.5% Pd/C catalysts, the palladium particle sizes by the following physical techniques: (i) X-ray diffraction (XRD) line broadening (LB) method, associated with the Rietveld method, (ii) small-angle X-ray scattering, and (iii) transmission electron microscopy. The catalysts, suitably aged at different temperatures (673, 773, 873, and 973 K), had significantly different metal dispersions. Since the XRD-LB technique is not able to measure directly very small metal particles or clusters (roughly ≤25 A in size), because they give diffuse X-ray scattering spreading out into the background, we have tackled this problem by means of a suitably tailored Rietveld quantitative analysis. This analysis allowed determination of the Pd fraction “visible” in the Voigtian XRD peaks and its average crystallite size using the LB method. As to the nanoparticle size of the undetectable fraction, an average value of 20 A was assumed, corresponding to the size of a cubooctahedral...

Al75Mo25 alloys were synthesized by ball milling of pure elements. The decrease of fcc aluminium peaks from the neutron diffraction patterns as a function of mechanical treatment time suggests the formation of an extended Mo(Al) solid solution, even though no significant change of the bcc lattice parameter is observed. Further evidence of the existence of a metastable phase is supplied a posteriori by in situ annealing of the processed metal powders at temperatures below 750 °C. The main product is the intermetallic Al8Mo3 compound.

Sol–gel preparation of ZrO2–WO3 is reported. The sol–gel technique allows preparation to be simplified and yields a more reliable and reproducible product. Catalysts were characterized by X-ray, BET and were tested in the isomerization of n-butane and 1-butene. Catalysts prove to be active with respect to analogous samples prepared by traditional methods.

A triphasic liquid system fabricated from isooctane, aqueous base, and trioctylmethylammonium chloride/decanol promoted the formation of Pd-nanoparticles in the size range of 2-4 nm which remained immobilised in the onium phase, catalysed organic reactions, and could be recycled.

In this paper, a simple method of obtaining the scale factor that transforms powder intensities from arbitrary units into electron units is proposed. This method, which is suitable for diffraction data collected from polycrystalline single-phase specimens, without fluorescence and preferred-orientation effects, obtains the scale factor analyzing the global scattered intensity in the reciprocal space without the necessity for the peak–background separation. Once the scale factor is found, it is possible to estimate the overall thermal parameter and to trace a physically based background line which is useful in extracting accurate structure factors.

A new procedure to perform quantitative analysis without any internal standard has been developed within Rietveld analysis. This new approach permits solution of the problem due to the presence of an amorphous phase when its chemical composition or the global sample composition is known. The equations developed, based on a study of the global intensities diffracted by each phase in reciprocal space, reduce to the well known formula of Hill & Howard [J. Appl. Cryst. (1987), 20, 467–474] when applied to completely crystalline materials.