X-ray study of thermal transformations in some magnesian chlorite minerals

Ramos

2007

Ceramics International

Mullite was produced from a mixture of raw wastes with high contents of silica and aluminium hydroxides. The first were wastes from slate rocks and had muscovite, chlorite and quartz as their main crystalline phases. The second were aluminium sludges resulting from the physicochemical treatment of the wastewaters generated by aluminium surface treatment industries. As-received raw materials were weighed to produce the 2:1 alumina:silica stoichiometric mixture, corresponding to an excess of alumina relatively to the ideal 3:2 mullite composition. The nonisothermal activation energies for primary (431 kJ/mol) and secondary mullite crystallization (454 kJ/mol) were determined by differential dilatometry. Sintered products were composites of mullite and a-alumina dispersed in a glassy phase and presented flexural strengths higher than 100 MPa after sintering temperatures at 1285 8C. #

Section: Phase Developmentsupporting

confidence: 62%

Mullitization kinetics from silica- and alumina-rich wastes

Ramos

2007

Ceramics International

“…The 14-A phase, which most closely approximates the early concept (Brindley and Ali 1950) of the modified chlorite structure, is relatively well-crystallized and maintains the 2:1 layer of the parent phase. A preliminary report of the structure is presented; a major structural feature is that the interlayer consists of only two planes, each containing both cations and oxygen.…”

Section: Discussionmentioning

confidence: 99%

“…The resulting "modified chlorite structure" (Brindley and Ali 1950) persists for long periods, even for samples immersed in water. The X-ray powder pattern of the modified chlorite structure is characterized by an increased intensity of the (001) peak and a general loss in intensity of higher order (00l) peaks relative to untreated chlorite.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Dehydroxylation of Chlorite and the Formation of Topotactic Product Phases

Zhan

Guggenheim

1995

Clays and clay miner.

Abstract--Single-crystal, X-ray examination of Mg,Fe-rich chlorites that were heated at 650"C for 24 hours in air and have undergone dehydroxylation of the interlayer shows that two product phases result with a topotactic relationship, with the c axis of both phases parallel One phase ("modified chlorite" or "14-A phase") has relatively sharp reflections with a 14-A c-axis repeat, indicating that it is well crystallized and maintains the 2:1 layer from the parent. Cell parameters are a = 5.368(1)A, b = 9.297(2)A, c = 14.215(6)A, a = 89.86(3) ~ 3 = 97.15(3) ~ 3' = 89.98(2)*, and it crystallizes in Ci symmetry. A structure refinement, details of which will be reported later, indicates that the interlayer consists of two planes, each containing (M + O), where M is the interlayer cation species. These planes show about +0.SA positional disorder along the [001] direction. There is no evidence for scattering material at z = 0.5 between the 2:1 layers. The second phase in the topotactic relationship is based on a 27-A unit c axis ("27-A phase"). The diffraction data are limited with about 15 diffuse reflections observed, indicating that it is poorly crystallized. The 27-A spacing suggests that both octahedral sheets in the parent chlorite contribute to the formation of this phase.Heating Mg,Fe-rich chlorite powder in a closed system to 550"C, under either reducing or oxidizing conditions, prevents the formation of the 27-A phase. Because the 27-A phase forms in an open system, we infer that water fugacity is an important factor in its formation. Heating experiments involving samples with different polytypes and octahedral "type" (dioctahedral vs trioctahedral) of the 2:1 layer suggests that these two variables are important. However, the results are equivocal, and an ill-defined B-rich chlorite from Madagascar breaks the observed trends for both variations in stacking sequence and octahedral type. However, B-content may be a factor in the transformation also for those chlorites that contain B.

Clays clay miner. (Natl. Conf. Clays Clay Miner.)

“…At approximately 500 ~ the intensity of the 002 increases and remains nearly constant until about 750 ~ where the intensity falls off rapidly and the spacing shifts to 10.0/~. Total collapse occurs at about 800 ~ The increase in intensity at 500 ~ is characteristic of chlorites (Weiss and Rowland, 1956) and is due to the loss of hydroxyl ions from the interlayer "brucite" (Brindley and Ali, 1950).…”

Section: Regularly Interstratified Chlorite-vermiculitementioning

confidence: 99%

Hydrothermal Regularly Interstratified Chlorite-Vermiculite and Tobermorite in Alteration Zones at Goldfield, Nevada

Harvey

1960

Hydrothermal alteration of andesitic and dacitie rocks in the Goldfield District, Nevada, has produced regularly interstratified chlorite-vermiculite and tobermorite. X-ray di~rac-tion and oscillating-heating data indicate the regular interstratification of the chloritevermiculite. This mineral is found in the zone of least alteration and was formed by the alteration of hornblende phenocrysts. Penninite is an intermediate stage in this reaction. Increased intensity of alteration resulted in the disappearance of chlorite-vermiculite and the development of montmorillonite. Tobermorite, found only in the dacite, is associated with alunite as pseudomorphs after plagioclase phenocrysts in the most intense zone of alteration. The intermediate stage of hydration for tobermorite is indicated by the l 1/~ spacing of the 002 diffraction peak. Oscillating-heating X-ray data at atmospheric pressure show that tobermorite decomposes thermally in two stages. The (001) planes collapse at approximately 520 ~ and crystal planes having an 8/~ periodicity collapse at about 760 ~ WoUastonite develops from tobermorite above 700 ~ under static heating conditions.