Subsolidus crystallization behaviour in the system KAlSi3O8–NaAlSi3O8–H2O

1969 ◽  
Vol 37 (286) ◽  
pp. 173-180 ◽  
Author(s):  
Ian Parsons
Keyword(s):  
Water Vapour ◽  
Alkali Feldspar ◽  
Starting Material ◽  
Crystallization Behaviour ◽  
Temperature Range ◽  
Feldspar Composition ◽  
Normal Zoning

SummaryWhen gels and glasses of alkali feldspar composition are crystallized hydrothermally below their solidus the crystals present when crystallization is incomplete do not have the same Na:K ratio as the starting material but bear a relation to the starting material analogous to that between crystals and liquids coexisting at the liquidus. This effect has been investigated in the temperature range 700–850 °C at water-vapour pressures between 5000 lb/in.2 and 30000 lb/in.2 Fractionation and normal zoning of crystals may, in principle, occur within fixed bulk compositions held under isothermal, isobaric conditions.

The alkali-feldspar solvus at 1 kilobar water-vapour pressure

1974 ◽  
Vol 39 (307) ◽  
pp. 747-767 ◽  
Author(s):  
Peter Smith ◽  
Ian Parsons
Keyword(s):  
Critical Point ◽  
Water Vapour ◽  
Vapour Pressure ◽  
Best Approximation ◽  
Stable Equilibrium ◽  
Bulk Composition ◽  
Alkali Feldspar ◽  
Crystallization Behaviour ◽  
Water Vapour Pressure ◽  
The Best Approximation

SummaryThe compositions of feldspar pairs crystallized from stoichiometric alkali feldspar gels with water at PH2O ≈ 1 kbar in runs of up to 3000 hours' duration vary with Na:K in the starting material. This is because, for most bulk compositions, rapid nucleation in the gel leads to growth of one feldspar phase outside the solvus. The composition of this initial feldspar phase can be thought of as reflecting the configuration of the liquidus-solidus curves in the system Ab-Or. In general, the attainment of the stable equilibrium solvus (binodal) requires that one phase approach the binodal from outside; for compositions with < 30 mole % Or this phase becomes more potassic with time, with > 30 mole % Or, more sodic. Homogeneous gels of bulk composition Ab70Or30 initially crystallize feldspar pairs inside the binodal, which rapidly (< 17 hours) unmix to define a solvus-like curve (probably the spinodal, with an apparent critical point at 602 °C and 31 mole % Or) and then unmix slowly, giving a solvus after 3000 hours with a critical point at 657 °C and 36 mole % Or.Because this curve has been approached from two directions it is the best approximation to the binodal (metastable only with respect to Al-Si order) obtained. It is similar to the 2 kbar ‘peralkaline’ solvus of Orville, 1963, provided an adjustment for pressure of 16 °C/kbar is made. Differences between solvi determined by Luth and Tuttle (1966) for ‘non-stoichiometric’ bulk compositions may reflect differences in initial crystallization behaviour, as may the breaks in the solvus limbs suggested by Luth et al. (1974).

The dissolution of beryllia in molten alkali metal hydroxides

1965 ◽  
Vol 18 (11) ◽  
pp. 1719 ◽  
Author(s):  
ME Shying ◽  
RB Temple
Keyword(s):  
Alkali Metal ◽  
Water Vapour ◽  
Beryllium Oxide ◽  
Major Product ◽  
Kcal Mole ◽  
Metal Hydroxides ◽  
Temperature Range ◽  
Alkali Metal Hydroxides ◽  
Reversible Formation

Beryllium oxide shows a limited reversible solubility in molten alkali-metal hydroxides only when dissolved water vapour is present. The reaction taking place has been studied in detail. The results obtained are consistent with the reversible formation of the beryllate ion [Be(OH)4]2- as the major product, according to the overall equation BeO(solid) + H2O(dissolved) + 2OH- ↔ [Be(OH)4]2-(dissolved) The enthalpy of the reaction has been calculated to be 4.8 kcal/mole over the temperature range 240-510�.

Study of the reaction CaSO4.½H2O (β-hemihydrate) = CaSO4 (β-soluble anhydrite)+½H2O in the temperature range 20–100° C

1965 ◽  
Vol 34 (268) ◽  
pp. 327-345 ◽  
Author(s):  
J. D. C. McConnell
Keyword(s):  
Water Vapour ◽  
Vapour Pressure ◽  
Physical Adsorption ◽  
Linear Increase ◽  
Water Vapour Pressure ◽  
Hydration Reaction ◽  
Temperature Range ◽  
Dehydration Reactions ◽  
Adsorption Of Water ◽  
Hydration And Dehydration

SummaryA thermogravimetric vacuum microbalance has been used to study the reaction between β-soluble anhydrite and water vapour in the temperature range 20–100° C. Equilibrium water-vapour pressures for the hydration reaction in this temperature range were determined directly and have been compared with available data obtained by Kelly, Southard, and Anderson (1941) in the temperature range 80–120° C. The kinetics of the hydration and dehydration reactions have also been studied in a series of isothermal experiments with varying water-vapour pressure. These experiments indicate that in a vapour-pressure range close to the equilibrium value very low rates for both hydration and dehydration are observed. Outside this range of vapour pressures both hydration and dehydration rates increase suddenly and show an approximately linear increase with imposed water-vapour pressure.At low temperatures (25° C) the dehydration reaction has an associated activation energy of approximately 10 kcal mole−1. In the same temperature range additional, physical adsorption of water vapour by the specimen was noted.

An experimental study of ordering in sodium-rich alkali feldspars

1968 ◽  
Vol 36 (284) ◽  
pp. 1061-1077 ◽  
Author(s):  
Ian Parsons
Keyword(s):  
Experimental Study ◽  
Water Vapour ◽  
Low Temperatures ◽  
Hydrothermal Crystallization ◽  
Equilibrium Degree ◽  
Temperature Range ◽  
Degree Of Order ◽  
Alkali Feldspars

SummaryVariations in the value of 2θ131 – 2θ13̄1 of two anorthoclase feldspars of compositions Ab95Or5 and Ab90Or10 were investigated by hydrothermal crystallization of gels for long periods in the temperature range 500–950 °C, at water vapour pressures up to 15 000 lb/in.2. The results are compared to those obtained by MacKenzie (1957) for pure albite. It is shown that the variation in 2θ131 – 2θ13̄1 is largely the result of Al-Si order-disorder and that at 700 °C and above the magnitude of the variation in the anorthoclases suggests that the degree of order is like that in albite, but at lower temperatures, particularly below 600 °C, the variation is less, and the anorthoclases are less ordered than albite at the same temperatures. At 600 °C and above the rate of attainment of equilibrium is the same for all three compositions. Below 600 °C Ab95Or5 behaves differently to albite. At low temperatures the equilibrium degree of Al-Si order in mixed Na-K feldspars is a function of composition as well as of temperature of crystallization.

Heating device for high temperature X-ray powder diffraction studies under controlled water vapour pressure (0–1000 mbar) and gas temperature (20–200 °C)

2000 ◽  
Vol 15 (1) ◽  
pp. 30-37 ◽  
Author(s):  
Martin Oetzel ◽  
Franz-Dieter Scherberich ◽  
Gernot Heger
Keyword(s):  
High Temperature ◽  
Water Vapour ◽  
Environmental Conditions ◽  
Vapour Pressure ◽  
Water Vapour Pressure ◽  
Gas Temperature ◽  
X Ray ◽  
Temperature Range ◽  
Heating Device ◽  
Dehydration Reactions

In this paper we present a high temperature heating device, working under defined environmental conditions, for a Siemens D500 Bragg–Brentano powder diffractometer. The powder sample is prepared in a flat mould on a metal block consisting either of copper or of platinum depending on the temperature range selected for investigations. Although the heating cell can be used separately under ambient conditions up to sample temperatures of 1000 °C, it is possible to work under defined environmental conditions in the temperature range between 20 and 200 °C and up to a water vapour pressure of 1000 mbar. For that purpose a special cover for the in situ control of temperature and water vapour pressure has been constructed. It is important to note that the three sample conditions (sample temperature, gas temperature, and gas humidity) can be adjusted separately by the user. Current studies have shown that the described X-ray heating device is a powerful tool to study dehydration reactions in the frame of fundamental research as well as to understand industrially relevant processes concerning dehydration reactions and their mechanisms.

Composition and structural state of coexisting feldspars, Salton Sea geothermal field

1986 ◽  
Vol 50 (355) ◽  
pp. 75-84 ◽  
Author(s):  
S. Douglas McDowell
Keyword(s):  
Excellent Agreement ◽  
Structural State ◽  
Alkali Feldspar ◽  
Geothermal Field ◽  
Salton Sea ◽  
Geothermal System ◽  
Temperature Range ◽  
Fine Grained ◽  
Alkali Feldspars

AbstractActive metamorphism of fine grained sandstone in the c.16000 year old Salton Sea geothermal system has produced a suite of chemically equilibrated coexisting authigenic alkali feldspars and re-equilibrated detrital feldspars in the 250–360°C temperature range. At c.335°C the average compositions, 2 Vs, and (t1o+t1m) and Z ordering parameters of coexisting authigenic feldspars are [Or0.52Ab97.40An2.08, 2Vx = 91.3±4.8, (t1o + t1m) = 0.89±0.05, Z = 0.79±0.09], and [Or94.42 Ab5.10An0.48, 2Vx = 70, (t1o + t1m) = 0.90, Z = 0.81]. At c.360°C authigenic albite becomes more An-rich and less ordered [Or1.21Ab92.83An5.97, 2Vx = 87.5±3.4, (t1o + t1m) = 0.85±0.03, Z = 0.70±0.07] and K-feldspar is no longer stable. Detrital plagioclase (An up to 40%) is preserved metastably to temperatures up to c.190°C in strongly carbonate-cemented sandstone which forms part of a geothermally produced permeability cap. It undergoes rapid alkali exchange at temperatures near 200°C, and by 250°C no plagioclase with An-content over 12% is observed. At > 250°C authigenic and most detrital alkali feldspar compositions are in excellent agreement with the Bachinski and Muller (1971) microcline-low-albite solvus.

Reverse zoning between myrmekite and albite in a quartzofeldspathic gneiss from Broken Hill, New South Wales

1974 ◽  
Vol 39 (306) ◽  
pp. 654-657 ◽  
Author(s):  
Evan R. Phillips ◽  
Ian J. Stone
Keyword(s):  
Grain Boundary ◽  
New South ◽  
Boundary Migration ◽  
Alkali Feldspar ◽  
Igneous Rocks ◽  
Grain Boundary Migration ◽  
Broken Hill ◽  
South Wales ◽  
Normal Zoning ◽  
Reverse Zoning

SummaryGrain boundary migration and the exsolution of albite from alkali feldspar, followed by the precipitation of myrmekite from the same source on to adjacent plagioclase grains, will explain the reversed zoning of these phases in contrast to the normal zoning seen in igneous rocks.

Thermal expansion of some salts of graphite

1964 ◽  
Vol 279 (1378) ◽  
pp. 291-301 ◽  
Keyword(s):  
Thermal Expansion ◽  
Proportional Counter ◽  
Starting Material ◽  
High Angle ◽  
X Ray ◽  
Axis Direction ◽  
Temperature Range ◽  
Diffraction Peaks ◽  
Ray Methods

X-ray methods have been applied to measure c axis thermal expansion of nitrates, perchlorates, and bisulphates of graphite. Three different intercalation sequences were prepared from each of these acids, stress-annealed graphite being used as starting material. Positions of high angle 00 l diffraction peaks were recorded over the temperature range + 25 to — 60 °C, by means of a proportional counter diffractometer. Thermal expansions of all these salts in the c axis direction, are up to three times as large as in the parent graphite. In addition, the three nitrates show a thermal expansion anomaly at about — 20 °C and one of the bisulphates shows a small anomaly at — 3 °C. These may be due to λ -type transformations in these salts.

Alkali-feldspar and Fe-Ti oxide exsolution textures as indicators of the distribution and subsolidus effects of magmatic ‘water’ in the Klokken layered syenite intrusion, South Greenland

1980 ◽  
Vol 71 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Ian Parsons
Keyword(s):  
Gas Phase ◽  
Water Distribution ◽  
Alkali Feldspar ◽  
Sharp Change ◽  
Magmatic Evolution ◽  
Fine Grained ◽  
Rock Types ◽  
Ti Oxides ◽  
Normal Zoning ◽  
Granular Layers

ABSTRACTThe layered syenites in the Klokken intrusion consist of horizons of fine-grained, granular-textured ferroaugite syenite showing inverted cryptic layering, interleaved with coarser, laminated, more fractionated hedenbergite syenite. Distribution of hydrous mafic phases indicates build-up of water in parallel with magmatic evolution, and druses and pegmatitic segregations in the laminated syenites are evidence for late development of a gas phase. Feldspar bulk compositions are close to the minimum on the Ab-Or binary, with An decreasing from An7 to An1 with fractionation, and normal zoning in cryptoperthite crystals. Feldspars in granular syenites are transparent coherent cryptoperthites or braid microperthites; An-content is probably the main control of fine-perthite coarseness. Laminated syenite feldspars are turbid, coarse patch microperthites with rare relics of braid textures. This non-coherent coarsening was caused by interactions between feldspars and water entrapped at magmatic temperatures which was retained within the original lithologies to low subsolidus temperatures. Fe-Ti oxides reflect this water distribution, with regular trellis ilmenite-titanomagnetite intergrowths in less fractionated rocks and ragged granule exsolution in more advanced syenites. The sharp change in exsolution textures at granular-laminated syenite boundaries implies steep water-gradients within these interleaved rock types. Water was unable to penetrate the granular layers and did not circulate freely in the cooling intrusion.

scholarly journals The thermal decomposition of hydrogen peroxide vapour

1946 ◽  
Vol 185 (1001) ◽  
pp. 207-224 ◽  
Keyword(s):  
Hydrogen Peroxide ◽  
Thermal Decomposition ◽  
Water Vapour ◽  
Surface Reaction ◽  
High Pressures ◽  
Reaction Rates ◽  
Bimolecular Reaction ◽  
Temperature Range ◽  
Low Pressures ◽  
Absolute Reaction

The decomposition of hydrogen peroxide vapour at pressures less than 1 mm. in silica vessels has been investigated, mainly at 80° C, but also over the temperature range 15-140° C. Oxygen at low pressures was found to have no appreciable influence on the rate of decomposition; water vapour retarded the rate slightly. The reaction was predominantly a surface one. In one vessel, the decomposition was bimolecular with respect to the peroxide pressure, the rate being given by k [H 2 O 2 ] 2 /(1+ b [H 2 O]) 2 in another, the bimolecular reaction of the final stages at low peroxide pressures was preceded by one of order approximately 0.7 at the high pressures. Higher pressures of oxygen and nitrogen retarded the decomposition appreciably. At higher pressures of water vapour, a pronounced periodicity in rate was evident. The apparent heat of activation over the temperature range investigated was not constant, being calculated as 4200 cal. from rates at 15 and 70° C and 8400 cal. from rates at 80 and 140° C. On the assumption that the lower value more nearly represents the surface reaction, the velocity of decomposition, calculated for 1 mm. pressure of peroxide at 50° C by the theory of absolute reaction rates, was 0.70 x 10 13 mol.cm. -2 sec. -1 , in agreement with the experimental value of 0.76 x 10 13 mol.cm. -2 sec. -1 .

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