G. Paschina

On the structure of methyl alcohol at room temperature

Methyl alcohol has been examined at room temperature by means of x‐ray diffraction technique. The radial distribution curve straightforwardly shows O ⋅⋅⋅ O interactions at about 2.8 A, which indicate that extensive hydrogen bonding is occurring in liquid methanol. The other prominent peaks of the radial curve fulfill the zig–zag chain model found in solid methanol. A direct analysis of the structure function leads to the conclusion that the average number of nearest oxygen neighbors per oxygen atom lies between 1.40 and 1.55. On the contrary, no unique conclusion, as far as the shape of the chain is concerned, can be obtained through the x‐ray scattering data.

Interactions and structure in aqueous NaNO3 solutions

Two concentrated (5 and 7 mol l−1) aqueous solutions of NaNO3 were investigated by x‐ray diffraction. The features of the total radial functions calculated from experimental intensity data show that the positional correlation is not very strong in the systems investigated. However, it is possible to account for experimental data only by using models in which hexahydrated Na+ ions have definite correlations with NO3− ions, even if not through formation of isolated ion pairs. The compatibility of our observations with spectroscopic results is also discussed.

Coordination of Ag+ ions in AgI–Ag2O–B2O3 glasses by x‐ray diffraction

X‐ray diffraction measurements have been performed on glasses of the Ag2O–B2O3 and AgI–Ag2O–B2O3 systems. When silver iodide is present, the radial distribution function is dominated by a large peak at 2.85 A, due to Ag–I interactions, with a shoulder at ∼2.40 A, due to Ag–O pairs. The average number of Ag–I contacts has been calculated through analysis of the high angle structure functions si(s)’s, either by using the total si(s)’s or by using the partial si(s)’s, the latter obtained by subtracting the experimental structure function of the Ag2O–B2O3 glasses from that of the corresponding AgI‐doped glasses. The compatibility of the results obtained with recently proposed models of AgI–Ag2O–B2O3 glasses is examined.

X-ray diffraction study of aqueous SrCl2 solutions

Two aqueous solutions of SrCl2 of concentration 1.53 and 2.00 mol dm−3 have been investigated by X-ray diffraction. A model in which the Sr2+ ion was considered as having eight nearest-neighbour water molecules at a distance of 2.64 A and a second outer shell came out in best agreement with the experimental data. Octahedral water coordination for Cl− ions has been confirmed in agreement with the results obtained by other X-ray studies.

X‐ray diffraction study of Na+ ions coordination in sodium borate glasses

X‐ray diffraction measurements were performed on glasses of the type Na2O–B2O3 and Li2O–B2O3, in which the maximum content of Me2O is 0.3 mol per 1 mol of B2O3. By subtracting the radial distribution functions of the Li2O–B2O3 samples from those of Na2O–B2O3 glasses having the same molar ratios, difference curves were obtained in which peaks coming from the distribution of nearest neighbor atoms around Na+ ions were observed. The quantitative analysis showed that the environment of Na+ ions is not a regular polyhedron. About 5.0–5.5 O atoms surround Na+ ions; on the average 3.4–3.6 O atoms are 2.40–2.44 A distant from Na+ ions while 1.5–2.0 other O atoms are at a distance of 2.75–2.80 A.

4-Methylpentan-2-ol dehydration over zirconia catalysts prepared by sol-gel

Zirconia samples have been prepared from xerogels and aerogels obtained using zirconium n-propoxide as precursor. Structure and texture have been investigated by X-ray diffraction, thermal analysis, transmission electron microscopy, nitrogen adsorption/desorption. Surface acidity and basicity have been assessed by adsorption microcalorimetry, using ammonia and carbon dioxide as probe molecules. 4-Methylpentan-2-ol dehydration has been tested at atmospheric pressure in a fixed-bed flow microreactor. The xerogel gives tetragonal zirconia upon calcination, during which a mesoporous system is formed. The crystal phase depends on the presence of oxygen during the cooling step in the case of the aerogel, whose texture is partially retained upon calcination. Both kinds of catalysts have well-balanced concentrations of acid and base sites, but the acid sites are weaker in comparison with the basic ones. At 603 K the initial conversion of 4-methylpentan-2-ol over the calcined xerogel and aerogel is 45 and 63%, respectively; the selectivity to 4-methylpent-1-ene is 77% for both. The occurrence of an E2-like mechanism with the activated complex having a marked carbanionic character seems probable. The aerogel catalyst is quite stable during operation, whereas changes in activity and selectivity are observed for the xerogel catalyst.

Fe-Co-B amorphous alloy powder by chemical reduction

Fine boride powders, prepared by reactions between sodium or potassium borohydride and aqueous (or alcoholic) solutions of transition metal salts have long been known to be good catalysts for hydrogenation reactions. New interest around them has recently grown, because they were found to exhibit amorphous structure. Classical chemical reactions may thus offer a simple route to prepare amorphous metal powders, paralleling more sophisticated methods so far used to reach the same goal. To explore the potential of these reactions, we considered the system Fe-Co-B with the aim of examining the characteristics of the product obtained in the easiest way and without any particular precautions. The structure of the amorphous alloy appears to be different from that of materials with a similar Me/B ratio prepared via melt spinning.

Iron oxide–silica aerogel and xerogel nanocomposite materials

Abstract The sol–gel method was used to prepare iron oxide–silica nanocomposite materials. Different drying conditions were used in order to obtain aerogel and xerogel materials. The samples were characterized by thermal analysis, X-ray diffraction (XRD), N 2 -physisorption and transmission electron microscopy (TEM) techniques. Aerogel samples have a much higher surface area than the xerogel samples; moreover, different supercritical drying conditions give rise to a different porous structure. The stabilization of the maghemite phase in the xerogel nanocomposites depends on the iron content and it is more difficult in the aerogel samples. The early sol–gel preparation stages also play an important role.

Ni–Cl bonding in concentrated Ni(II) aqueous solutions at high Cl− /Ni2+ ratios. An x‐ray diffraction investigation

Three concentrated Ni(II) solutions at Cl−/Ni2+ ratios of 4 and 5 have been examined by the x‐ray diffraction technique. The Fourier transformed scattering data straightforth indicate inner complex formation between Ni2+ and Cl− ions. Octahedral Ni(H2O)6−nCl2−nn (n = 0, 1, 2) complexes are the species which are consistent with the distribution curves and the structure functions. The average numbers of bonded chloride ions per nickel atom have been determined in each solution and the reliability of the complexation numbers as well as of the structural parameters critically examined. The existence of an intermediate‐range order in NiCl2 solutions is discussed within the frame of the current literature and the present findings.

On the coordination of iron ions in sodium borosilicate glasses. I: A wide angle X-ray diffraction investigation

Abstract Three sodium borosilicate glasses, containing approximately 4%, 8% and 12% by weight of Fe2O3, have been investigated by X-ray diffraction technique in order to determine the structural arrangement of iron ions in these glasses. The radial distribution functions of the iron glasses have been compared to suitable distribution functions obtained from an appropriate iron-free sodium borosilicate matrix. The analysis of the resulting distribution difference curves leads to the unambiguous conclusion that in 4% and 8% glasses iron ions are surrounded by four oxygen atoms at the distance expected for a tetrahedral coordination. The structural arrangement of iron ions in the 12% glass is very likely to be the same, although the analysis of the data is complicated by an initial crystalline phase separation within the amorphous network. In addition to the structural parameters obtained for the first iron shell, a tentative model to explain the second order interactions around iron ions is discussed.