Wee. Stone

PREPARATION AND CHARACTERIZATION OF BIDIMENSIONAL ZEOLITIC STRUCTURES OBTAINED FROM SYNTHETIC BEIDELLITE AND HYDROXY-ALUMINUM SOLUTIONS

Beidellite was synthesized hydrothermally from a noncrystalline gel at 320°C and 130 bar pressure. The beidellitic character of the product was verified by infrared spectroscopy on the NH4+-exchanged form. Intercalation was achieved with hydroxy-aluminum solutions having different OH/Al molar ratios. The solutions were investigated by several methods, including 27Al nuclear magnetic resonance. Essentially, two Al species were detected: monomelic Al and a polymerized form containing Al in four-fold coordination. This latter species was found to be selectively fixed in the interlamellar region, which resulted in a stable spacing of 18 Å at 110°C and 16.2 Å at 700°C. The pillared beidellites had specific surface areas of > 300 m2/g, mainly due to micropores. Both Brönsted and Lewis acid sites were evidenced by infrared spectroscopy using pyridine as a probe molecule.RésuméUne beidellite obtenue par synthèse hydrothermale (320°C, 130 bar) à partir d’un gel précurseur et identifiée comme telle sur base des spectres infrarouges de la forme échangée à l’ammonium, a été pontée par des solutions hydroxy-aluminiques de rapports OH/Al différents. Les solutions de pontage ont été étudiées par différentes méthodes, dont la résonance magnétique nucléaire. Deux espèces d’aluminium, l’une monomérique, l’autre polymérique contenant de l’aluminium en coordination tétraédrique coexistent dans ces solutions. On a observé que l’espèce polymérique s’adsorbe préférentiellement dans l’espace interlamellaire, conférant à l’édifice un espacement de 18 Å à 120°C et de 16,2 Å après calcination à 700°C. La surface spécifique de ces beidellites pontées est de l’ordre de 300 m2/g. La spectrométrie infrarouge de la pyridine adsorbée décèle la présence des acidités Brönsted et Lewis.

The Al pillaring of clays; Part I, Pillaring with dilute and concentrated Al solutions

Saponite, hectorite, and laponite have been pillared with cationic Al clusters, and special attention has been given to the solution chemistry or Al. Pillared saponite is obtained after exchange with refluxed Al solutions; while for hectorite, Al solutions treated with ammonium acetate give a pillared product with 1.8–1.9 nm spacing and thermal stability up to 873 K. In both types of solutions, the Keggin ion Al cluster is a minority species or totally absent. The typical 1.8–1.9 nm spacing is only obtained after washing. The quality of the pillared material can be judged from its thermal stability, its surface area, and the width of the d001 line before and after pillaring. The width should not exceed 0.3 nm before calcination and 0.5 nm after calcination. The latter criterion reflects the importance of the crystallinity of the parent clay for successful pillaring. Pillaring in concentrated conditions occurs by a combination of ion exchange and precipitation of Al and gives materials that exhibit poor thermal stability.

NMR study of micas. I. Distribution of Fe2+ ions on the octahedral sites

Paramagnetic shifted NMR lines have been observed in the H+ spectra of a number of micas (having variable amounts of iron) as a function of frequency and orientation. The position of the shifted lines can be accounted for by a simple point dipolar field interaction. Certain conclusions concerning the occupation by ferrous ions of the two possible octahedral sites within the lattice can be drawn.

Distribution of Ions in the Octahedral Sheet of Micas

In this chapter we will discuss a practical example of the use of NMR in the study of natural samples. It will be shown how NMR can provide information regarding the distribution of Fe2+, F− and OH− ions within the octahedral sheet of micas (7, 9). Various octahedral associations are differentiated by carefully examining the H+ and F− NMR absorption signals as a function of frequency and orientation of the mica crystal in the applied magnetic field. Comparison of this method with x-ray and infrared spectroscopy will also be discussed.

Nmr Applied To Minerals .5. the Localization of Vacancies in the Octahedral Sheet of Aluminous Biotites

The localization of vacancies in the octahedral sheet of aluminous biotites has been investigated by the use of 1H nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The polytype to which the samples belonged was determined by x-ray diffraction methods. The joint use of all three techniques was essential in determining unambiguously the exact position of the vacancies and orientation of the associated O-H and Fe-H vectors. It was found that vacancies are located in the M1 (pseudo-centrosymmetric) sites and that contrary to what is usually assumed the OH dipoles are not, in this case, oriented directly towards the vacancy site.

Interaction of Stable and Metastable Monomeric Iron (III) Species with a Kaolinitic Soil Clay

The polymeric hydrolysis products of Fe(III) solutions recently have received special attention as chemical agents able to promote the flocculation which is necessary for the formation of stable clay microaggregates. (Rengasamy and Oades, 1977a, 1977b; Kavanagh and Quirk, 1978; Oades, 1984). It was shown that polymeric Fe(III) cations of controlled nominal size or molecular weight, when added in appropriate amounts to a clay suspension, were effective for modifying the electrophoretic mobility, and for promoting the coagulation of different types of clay silicates. Other experiments also (Shanmuganathan and Oades, 1982) have revealed the beneficial effects of similar polymers for the promotion of improved structure in clays and soils.

Effect of partially neutralized aluminum solutions on the texture and pore structure of silica

N-2 adsorption measurements at 77 K were performed on two types of silica of different porosities, and on their products obtained by soaking in partially neutralized aluminum solutions of varying R = [OH]/[Al] = 0.5-2.0 (PH 3-4). TG analysis showed that the Al taken by the mesoporous silica was accompanied by its hydroxyls, but with the predominantly microporous silica it was stripped of some of them, where a strong potential field in the narrow pores compensated for any charge differences. IR spectral analysis showed that for microporous silica the peak (due to Si-O stretching of surface OH) is located at 950 cm(-1) instead of approximately 970 cm(-1) in the case of mesoporous silica, which seems to result from the strong perturbation between hydroxyls at close range in the narrow pores. A reduction in this peak lakes place upon Al treatment that increases with R, with the probable formation of a surface complex of the type =Si-O-Al. Uptake of Al ions produced a narrowing of the pores, that increased with the increase in Al content. From pore structure analysis, the micropore fraction could be sorted into ultramicropores (less than or equal to 10 Angstrom) and supermicropores (10-20 Angstrom). The volume of the former is almost unaffected by any change in Al content. The sizes of the supermicropores and mesopores (greater than or equal to 20 Angstrom) are crucial to the Al uptake. Changes in pore sizes at R greater than or equal to 1.0 facilitate the initial attack of the large Al polymeric species.