This contribution explores the interaction of the fibrous silicates, palygorskite, sepiolite and chrysotile with a wide range of organic agents. Infrared spectroscopy (IR) methods are essential for the characterization of solid surfaces and for the investigation of the kind of bonds formed between the surface of these silicates and the organic moieties. Thus, when sepiolite or palygorskite are treated, e.g., with polyurethanes, alcohols, isocyanates, amines or pyridines, specific SiNHC or SiOC bonds are derived from the linkage of the differently located OH groups in these fibrous silicates with the organic moieties. On the other hand, more stable, covalent SiOSiC bondings are formed when the fibrous silicates, especially chrysotile, are reacted with heterofunctional silylating agents like chlorosilanes or ethoxysilanes carrying, alkyl, alkenyl or aryl groups. Such reactions may occur in the presence or absence of HCl. An absorption band at 960 cm(-1)--which we assigned to SiOH groups--is detected only in the presence of HCl. The evolution of this band is related to the degree of grafting of the organic radicals with the silanol groups of the silicates. HCl-generated silanol groups are the main bridges for the coupling of organosilyl groups on chrysotile and other silicates by covalent bonding, leading the way to the preparation of interesting new materials, including fibrous sheet polymers.
Abstract--Infrared absorption spectra show important changes in the positions and form of the absorption bands of a film of attapulgite after it has been pumped out. An attempt to differentiate among some of the multiple frequencies due to OH groups is based on the information obtained from dehydration and deuteration experiments. The 1198 cm -~ shoulder, characteristic of attapulgite, is assigned to a Si-O vibration. When attapulgite is refluxed with 5N HCI for 5 hr the octahedral layer is dissolved. The acid attack causes the disappearance of the Si-O-Si absorption bands from attapulgite giving rise to a characteristic vibration at 1090 cm -~, as well as another absorption at 960 cm -1. The latter indicates the presence of silanol groups. INTRODUCTION THE i.r. spectra of attapulgite have been reported by Gonzalez Garcia et al. (1956) and by Otsuka et al. (1968). Also, infrared studies of heated attapulgite have been published (Ovcharenko, 1966;Hayashi et al., 1969;Taracevich, 1970).The object of this work is to present additional information on the behavior of attapulgite when evacuated. Moreover, some interpretations regarding the frequencies of the OH groups are based on isotopic exchange experiments.Another aspect of this work deals with the modification of attapulgite upon HC1 attack. I.R. spectra of HC1 treated attapulgite have not been previously reported.
Fe substitution for Al in kaolinite (from Venezuelan laterites) is proved by infrared spectroscopy and chemical techniques. The location of Fe in the octahedral sheet is characterized by two absorption bands, at 865–875 and 3607 cm−1, assigned as δ Al-OH-Fe and v OH respectively. The detection of the 865 cm−1 band requires the use of CsCl for the preparation of the disks heated to 270°C so that the clay delaminates as a result of a kaolinite-CsCl-H2O complex formation. The 3607 cm−1 absorption is detected when KI disks are prepared. These two characteristic frequencies persist after either thermal decomposition or selective chemical dissolution of free iron and aluminium hydroxides.Selective chemical dissolutions by consecutive treatments for; (1) the removal of free iron oxides, (2) gibbsite removal and (3) extractions of Fe and Al from kaolinite, give additional evidence about the occurrence of this solid solution.
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