The Reversible Dehydroxylization of Clay Minerals
01 Feb 1954-Clays and Clay Minerals (Springer Science and Business Media LLC)-Vol. 3, Iss: 1, pp 66-72
TL;DR: In this paper, the structural character of the rehydrate prepared in this way is determined from X-ray and DTA data, and the mechanism of the reactions by which rehydrates can be formed is also considered.
Abstract: Rehydroxylization of the anhydrous modification of dioctahedral montmorillonites can be carried out under DTA conditions with controlled atmosphere techniques. The structural character of the rehydrate prepared in this way is determined from X-ray and DTA data. The mechanism of the reactions by which the rehydrate can be formed is also considered. Thermal analysis curves of the rehydrate form of several pure mont-morillonite samples failed to show any large variation such as is shown by the curves of the original clays themselves. The possibility is considered that such large variations in the dehydroxylization curves of montmorillonites are related to structural instead of compositional variations within the sample. It is suggested that montmorillonites showing two reactions attributable to dehydroxylization may be mixtures of the rehydrate form and montmorillonite.
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TL;DR: In this article, half of each heated sample was subsequently autoclaved under steam at 200 degrees C (approximately 1.5 MPa) to promote rehydroxylation.
Abstract: Li (super +) , Na (super +) , Ca (super 2+) , Sr (super 2+) , Cu (super 2+) , or Zn (super 2+) -saturated samples of a cis-vacant montmorillonite from Linden, Bavaria, were heated to temperatures between 200-700 degrees C. Half of each heated sample was subsequently autoclaved under steam at 200 degrees C ( approximately 1.5 MPa) to promote rehydroxylation. The smectites were characterized by cation-exchange capacity (CEC), determination of exchangeable cations, infrared (IR) spectroscopy, and thermoanalytical investigations of evolved water in a thermobalance linked with a mass spectrometer. Changes in the montmorillonite structure and dehydroxylation behavior are related to three respective mechanisms: type of the interlayer cation, interlayer cation radius, and the movement of the interlayer cation. The migration of the smaller Li (super +) , Cu (super 2+) , and Zn (super 2+) ions after heating produces a strong reduction of CEC due to the Hofmann-Klemen effect before the initiation of dehydroxylation. Thereafter, the CEC of these smectites remains constant over a large temperature interval during dehydroxylation. After rehydroxylation, Cu (super 2+) and Zn (super 2+) -rich samples release 16-23 meq/100 g of Mg (super 2+) from the structure. No Mg (super 2+) release is observed for the Li (super +) -rich montmorillonite. Also the dehydroxylation behavior after rehydroxylation differs between the Cu (super 2+) , Zn (super 2+) , and Li (super +) -rich samples. The mass curves of the evolved water during thermoanalysis of the rehydroxylated Cu (super 2+) and Zn (super 2+) -rich smectites show a peak doublet between 480-700 degrees C. For the Li (super +) , Na (super +) , Ca (super 2+) , and Sr (super 2+) -rich montmorillonites, the second peak disappeared and a third peak at approximately 760 degrees C developed after rehydroxylation. The resulting structure after rehydroxylation of all samples is celadonite-like.
106 citations
TL;DR: In this article, the presence of two O-D stretching bands, one between 2702-2728 cm and another near 2680 cm -~, was revealed for six partially-deuterated montmorillonites.
Abstract: FTIR studies of six partially-deuterated montmorillonites (MS) reveal the presence of two O- D stretching bands, one between 2702-2728 cm ~ and another near 2680 cm -~ . For homoionic (Li, Na, Mg, Ca, or La) Wyoming-type MS, the position of the higher frequency band, designated as (O--O)h , is between 2714-2728 cm -t, whereas for homoionic Cheto-type MS it is between 2702-2706 cm -l. The lower frequency band, designated as (O-D)~, is in the narrow range of 2674-2684 cm ~. Resolution of two corresponding O-H bands, appearing near 3670 and 3635 cm -~, was observed only after partial dehydroxylation of the smectites. The changes in the relative intensities of the two O-D stretching bands as a function of the smectite type and of the Lewis acidity (charge density) of the exchangeable ion were determined. For Wyoming-type MS, the intensity of the (O-D)h band is much lower than that of the (O- D)t band, whereas for Cheto-type MS, the intensity of the (O-D)h band is about equal or slightly higher than that of the (O-D)z band. The observed resolution can be ascribed tentatively to the presence of (at least) two types of octahedral OH groups in the smectites, the (O-D)h band being assigned to A1MgOH and the (O-D)~ band to A1A1OH groups. Pillaring of Cheto-type MS with hydroxy-Al~3 oligocations resulted in products showing much higher thermal stability between 400-600~ compared to that of identically pillared Wyoming-type MS. Compositional and other factors, e.g., CEC values and mode of pillaring, may cause this difference in stability.
88 citations
Cites background from "The Reversible Dehydroxylization of..."
...There were re la t ive ly few references (McConnell, 1950; Jonas, 1955) in the older literature indicating any level of corroboration for the EdelrnanFavejee structure, although some recent work on clay pillaring has tended to provide some reference to it (Plee et aL, 1985; Pinnavaia et al....
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TL;DR: In this paper, Drits et al. investigated the structure of dehydroxylated montmorillonite and found that a completely dehydroxymated state of the dioctahedral 2:1 layer silicates can be achieved by a slow heating rate and duration of heating.
Abstract: In general, montmorillonite and other dioctahedral 2:1 layer silicates are characterized by dehydroxylation temperatures between 500–700°C ( e.g., Mackenzie, 1957; Grim and Kulbicki, 1961; Schultz, 1969; Guggenheim, 1990). Differences in dehydroxylation temperature are primarily related to the kind of octahedrally coordinated cations present and their distribution and movement in dioctahedral 2:1 layer silicates (Drits et al., 1995), although the interlayer cation may have an effect also ( e.g., Guggenheim and Koster van Groos, 1992).
Trans -vacant (tv) smectites and micas are characterized by dehydroxylation temperatures which are 150–200°C lower than those for the same minerals consisting of cis -vacant (cv) 2:1 layers. Most montmorillonites consist of a mixture of cv and tv 2:1 layers and lose their hydroxyls in two steps near ~550 and ~700°C (Drits et al., 1995). Hence, the investigation of the structure of dehydroxylated montmorillonite is of great interest to understand the dehydroxylation process ( e.g., Jonas, 1954; Heller et al., 1962; Drits et al., 1995).
Dioctahedral 2:1 layer silicates are expected to produce well defined dehydroxylates after heating for a short time at temperatures between 500–700°C and cooling under laboratory atmosphere ( e.g., Grim and Bradley, 1948; Heller-Kallai and Rozenson, 1980; Drits et al., 1995). However, the heating rate (Hamilton, 1971) and duration of heating (Horvath, 1985) are important in determining if an anhydrous state is achieved. A slow heating rate lowers the apparent dehydroxylation temperature, which is a well known but often neglected phenomenon.
Emmerich et al. (1999) found that a completely dehydroxylated state of montmorillonites that …
35 citations
Cites background from "The Reversible Dehydroxylization of..."
...Hence, the investigation of the structure of dehydroxylated montmorillonite is of great interest to understand the dehydroxylation process (e.g., Jonas, 1954; Heller et al., 1962; Drits et al., 1995)....
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TL;DR: In this paper, CEC measurements, determination of exchangeable cations and X-ray diffraction were supplemented by thermoanalytical investigations of the evolved water in a thermobalance linked to a mass spectrometer, infrared (IR) and electron spin resonance (ESR) spectroscopy were employed to obtain information about the state of expandability and structural changes of swellable montmorillonite and the sites of interlayer and octahedral cations after heating and rehydroxylation.
27 citations
TL;DR: In this article, the rehydration and rehydroxylation properties of homoionic rectorites (saturated with Ca 2+, Mg 2 § Na § or K +) were further investigated.
Abstract: The rehydration and rehydroxylation properties of homoionic rectorites (saturated with Ca 2+, Mg 2§ Na § or K +) were further investigated. The rehydration properties of the rectorite were characterized as follows: (l) basal spacings of rehydrated materials after heating above 500~ changed to 22.5 A for H20-complexes, 26.85 A for ethylene glycol-complexes, and 27.65 A for giycerol-complexes; (2) rehy- drated Ca- and Mg-materials exhibited single layer hydrates at <50% RH, and rehydrated K-material showed double layer hydrates at 80% RH; (3) IR absorption spectra due to rehydrated H20 and OH exhibited the same or very close absorption intensities and frequencies to each other; (4) DTA-TGA curves of rehydrated materials indicated that the amount of rehydrated H20 approached about 4.2 wt. %, and about one-half of OH was rehydroxylated after heating at 800"C; and (5) interlayer cations of expandable layer components became non-exchangeable after heating above 500"C. These results suggest the following rehydration mechanism of rectorite: the interlayer cations migrate into the hexagonal holes of the SiO4 network by thermal dehydration. The cations migrated below 400~ easily return to the interlayer space and their original hydrated configurations have been recovered completely on rehydration. However, those migrated above 500"C are fixed to the hexagonal holes but water molecules are regained in the interlayer space. Consequently, electrostatic effects of interlayer cations on formation of water molecule layers are considerably reduced.
4 citations
Cites background from "The Reversible Dehydroxylization of..."
...Larger amounts of OH can be regained in the dehydroxylated structure under a high temperature water vapor condition (Jonas, 1955; Heller et al., 1962; Vedder and Wilkins, 1969)....
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References
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92 citations
TL;DR: In this paper, an Inconel sample holder and its attendant parts were mounted on a movable vertical shaft so that the assembly could be lowered into or raised out of the furnace and the gas was carried to the powders under very slight pressure through 1 2-in-diameter porcelain tubes, called the injector, which fit snugly into the sample holder cavities.
Abstract: An apparatus was designed so that an atmosphere (a continuously flowing atmosphere) containing any partial pressure of the active vapor such as H2O, CO2, or SO3, could be maintained around the particles of a mineral powder while the differential thermal analysis was being run. The sample holder and its attendant parts were mounted on a movable vertical shaft so that the assembly could be lowered into or raised out of the furnace. The gas was carried to the powders under very slight pressure through 1/2-in.-diameter porcelain tubes, called the injector, which fit snugly into the sample holder cavities. The bottoms of the cavities were the ends of two 4-hole porcelain tubes which carry the thermocouples and also support the sample holder. Two types of sample holders were used, (1) Inconel tubes, 1/2 in. in outside diameter and 3/4 in. long with a wall thickness of 0.008 in., and (2) a solid Inconel block 3/4 in. in diameter and 3/4 in. long with two symmetrically placed holes 0.234 in. in diameter drilled parallel to the length. These sample holders accommodate about 0.15 gm. of clay or 0.20 gm. of alumina as the reference material. There were four 28-gauge thermocouple wires in each cavity. In the sample cell, two wires were one leg of the differential couple and the other two wires were dummies to balance the cell. In the reference cavity were the other leg of the differential couple and the measuring couple. All four wires in each cell were fused into a single bead and the wires were spread as far apart as possible, forming a sturdy unit. The furnace was 41/2 in. square and 5 in. long with an Alundum tube core, 11/16 in. in outside diameter, on which 45 ohms of 28-gauge Nichrome V wire was noninductively wound. A motor-driven Powerstat was used to control the temperature rate at 16°C. per minute.
19 citations
"The Reversible Dehydroxylization of..." refers methods in this paper
...The apparatus which provided these experimental conditions was similar to the one described by Stone (1952) in his thermal analysis of kaolinites,...
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