Properties of materials under hydrothermal conditions. I. Permeation of hydrogen through gold membrane

Permeation rate of hydrogen through a gold cell made as a reaction vessel for a Dickson-type hydrothermal apparatus was measured at 50°intervals from 300°to 450℃ under a hydrothermal condition. The gold cell chosen for the measurement had a shape and size illustrated in Fig. 1 when it was fully expanded, and was a typical one in the meaning that it had been used several times for hydrothermal experiments (its total history may be equivalent to one month at 490℃) and that it had a body enlarged by about 8% in diameter from the original size as a result of pinhole check made by applying a gas pressure to the inside. The cell was filled with an appropriate amount of pure water, placed in a pressure vessel made of Ni-base alloy, pressurized by injecting water to the outside of the cell and kept under predetermined temperatures and pressure (=1 kbar). Meanwhile, small fractions of the waters inside and outside the cell were sampled at times and analyzed for H(2) gas-chromatographically as described in ref. (5). H(2) concentrations in the samples (CH(2)) were converted to H(2) fugacity values by using the conversion factors (Y) given in ref. (6). At each temperature, the permeation rate (k) of H(2) through the cell is evaluated by correlating the measured fH(2) values with time (t) according to eq. (2), where fo is the fH(2) in the outer water and is a constant, and fi and m are the fH(2) in and the mass of the inner water, respectively. The relevant data and results are shown in Table 1. The present data for the permeation rate φ, expressed in c㎥ H(2) at STP per 1c㎡ surface area, 1 mm wall thickness, 1 (bar)(1/2) of (fH(2))(1/2) difference and 1 hour, are plotted in Fig. 2 in relation to 1/T (K) and compared with one available data, which is a combination of reported solubility and diffusion coefficient data for hydrogen into gold at higher temperatures. The present data can be fitted into eq. (3). The present result may be of importance for hydrothermal experimental studies of geochemical redox reactions and of hydrogen isotope exchange reactions, and the technique used may also be important as a new, simple method of measuring hydrogen permeability through noble metals

Properties of materials under hydrothermal conditions: II. Permeability to aqueous NaCl and decomposition of poly(tetrafluoroethylene) (teflon)

A piece of poly(tetrafluoroethylene) (PTFE) enclosing NaCI powder and having the dimensions shown in the inset in Fig. 1 was placed along with water in a deformable gold cell in a Dickson-type hydrothermal apparatus, and heated stepwise up to 410℃ under a constant pressure of 1 kbar. During the heating, small fractions of the solution in the cell were sampled and analyzed gas chromatographically for H(2), O(2), CH(4) and CO(4), and ion chromatographically for F(-) and Cl(-). No evolution of gases (H(2), CH(4), CO(2)) due to decomposition of PTFE, other than that due to decomposition of organic impurities, was observed over the temperature range of the experiment. The ion chromatographic analysis showed (Fig. 1) that : (1) Cl(-)leaching from the PTFE test piece continued even at 340℃ ; (2) F(-) leaching was small in amount and completed within the first step at 200℃ and 12 hours ; (3) F(-) formation due to partial decomposition of PTFE became measurable from 340℃, was linear with time, and was remarkably accelerated at temperatures above 400℃ ; (4) migration of the enclosed NaCl (partly hydrolyzed during the course of the experiment) did not occur even at 410℃ ; but (5) osmosis of water caused a puncture of the test piece within 2 hours after the temperature reached 410℃. The test piece recovered after the run was found to be retaining the original luster and hardness

Oxygen Isotopic Composition of Water in the Living Things : Preliminary Analyses and Discussions

Oxygen isotope analysis was carried out, by use of a new method (oxalate equilibration method) of preparing CO(2) for mass spectrometry, on water samples extracted from a number of biological samples collected in Misasa Town and Hashizu Coast, Tottori Prefecture. The δ values (the per mil enrichment of (18)O in sample waters relative to the Standard Mean Ocean Water) were suggested to be distributed in the living things as follows. The water absorbed by plant roots was supposed to have the same δ value with the water outside it (δs. about -8‰), and in a rapidly transpiring plant, this water reached the leaves, partly infiltrating into the phloem. When transpiration was slow, on the other hand, the isotopic composition of ascending xylem sap was modified by the exchange of water with phloem. where leaf water with a higher δ value was migrating. As Gonfiantini et aI. (1965) and Dongmann et al. (1972) have odserved, leaf waters were enriched markedly in (18)O in the daytime. A criterion of the δ of leaf water may be the sum of δs and △δ that corresponds to the (18)O fractionation factor in the H(2)O(I)-H(2)O(v) system. The sum comes to about 0‰ at ordinary leaf temperatures. and really δ values near 0‰ were observed in leaves of some herbaceous plants, in exudate from a tip of vine of Kudzu, in body fluid of herbivorous insects, etc., but higher δs (up to +19‰) were also observed in some other leaves such as pine needles, Especially leaves showed an increase in δ by about 10 ‰ toward the pnd of November when the average temperature fell below 10℃, probably because of accumulation of the daily enrichment as a resul t of slow water absorption and circulation. A few plant species grown on a dune were analyzed and it seemed that, among them, herbaceous plants were dependent on spraied sea water and pine trees on ground water. δ's of petal water were dispersed (-9～-3‰), probably according to the volume-to-transpirational flux ratio of water in the petals. Succurent fruits in enlarging stage seemed to have lower δ's near δs, but in maturing stagp δ's increaspd to about -4‰, i.e., to the avpraged δ of Ieaf water in the day and night. Herbivorous insects (imagines and la rvae) in general had distinctly higher δ values than carnivorous insects, the border being at -1‰. However, lower δ's at about -5‰ were obserbed on aphides which might have been sucking somewhat dilutpd leaf water from seave tube cells. Sometimes the δ of a herbivorous insect was a few per mil higher than that of the leaf it was nibbling, probably as a result of evaporation of water from the insect and of respiration. The level at about -3‰ common for carnivorous insects could not be explained, although tipula and chironomus making a swarm also showed a δ value on the level. Blood of a heron did not show such a low δ as supposed from its food habit. As compared with the drinking water of -8‰, blood and urine were found to have an identical δ in the range of -4 to -5‰ in either mouse or man, The δ value of the oxidation water produced in man's body was estimated to be about -6‰ from an approximate water balance

Experimental study of sulfur isotope exchange between S0(4)(2-) and H(2)S (aqueous) at 400℃ and 1000 bars water pressure

Experimental procedures used in this study are the same as those developed by Sakai and Dickson (1978). 0.005 M Na(2)S(2)O(3) solutions were heated to 400℃ under 1000 bar water pressure in a gold bag of Dickson gold-bag equipment (Fig. 1). At an elevated temperature Na(2)S(2)O(3) quickly and completely decomposed into 1:1 mixture of SO(4)(2-) and H(2)S (eq. (1)) and subsequent isotope exchange (eq. (2)) was monitored by consecutively withdrawing aliquots of solution for chemical and isotopic analyses at desired time intervals. For the preparation of SO(2) for isotope analyses, 2 to 5 mg BaSO(4) was thoroughly mixed with silica glass powder of 10 times the BaSO(4) in weight and heated to 1400℃ or so in sealed, evacuated silica glass tubings (see Fig. 2 and equation (4)). The technique is a modification of Holt and Engelkemeir (1971). The (18)O/(16)O ratios of SO(2) thus formed stayed constant by exchange with silica glass powder (Fig. 3). Numerical data of the three runs performed in this study are summarized in Tables 1 to 3. In runs 2 and 3, a small aliquot of (34)S- enriched H(2)SO(4) was added into the starting solution and thus equilibrium was approached from above the quilibrium value (see Fig. 4). When isotope exchange occurs between two molecules, X and Y, the reaction rate, r, is related to the extent of exchange, F, at given time, t, by equation (17), where X and Y indicate concentrations of given species, α(e), α(o) and α denote the　fractionation factor at equilibrium, at time　t=0 and at an arbitrary time t, and F = (α - α(o))/(α(e) - α(0)) or the extent of isotope exchange. Assuming the exchange rate is of the first order with respect to both X and Y and to the β'th power of hydrogen ion activity, a(H)(+), eq. (17) reduces to eq. (19), where k(1) denotes the rate constant. If X, Y and pH of solution stayed constant during the run, the half-time, t(1/2), of the exchange reaction can be obtained graphically as shown in Fig. 5. The t(1/2) for runs 1, 2, and 3 are determined to be 5.8, 5.5 and 6.1 hrs, respectively. Introducing F=0.5 and t=t(1/2) into eq. (19), we obtain eq. (20) which is graphically shown in Fig. 6 using the data by the present work and those by Sakai and Dickson(1978). The numerical values of log k(1) + 0.16 may be obtained by extrapolating the lines to pH=0 and, from these values, the rate constant, k(1) , may be calculated for temperatures of 300° and 400℃. From these two values of k(1) and from the Arrhenius plot, the activation energy of the exchange reaction was calculated to be 22 kcal/mole, a much smaller value than 55 kcal/mole obtained by Igumnov (1977). The value of β is found to be 0.29 at 300℃ and 0.075 at 400℃, although the physico-chemical nature of β is not clear to the present authors. Using these values, eq. (24), where C is a constant, is derived which would enable us to calculate the t(1/2) of any system of known ΣS and pH. However, as we do not know yet how β varies with different systems, eq. (24) is applicable only to limited systems in which temperature, total sulfur contents and pH are similar to those of the present study. Fig. 7 illustrates how t(1/2) varies with pH and total sulfur content at 300° and 400℃ and predicts t(1/2) for some solutions obtainable by hydrothermal reactions of seawater with various igneous rocks. The average equilibrium fractionation factor at 400℃ obtained by this study is 1.0153, in good accord with 1.0151 given by Igumnov et al. (1977). Theoretical fractionation factors between SO(4)(2-) and H(2)S have been calculated by Sakai (1968) , who gives too high values compared to the experimental data obtained by this and other researchers (Fig. 9). In the present study, the reduced partition function ratio (R.P.F.R.) of SO(4)(2-) was recalculated using two sets of the vibrational frequencies of SO(4)(2-) (shown in Table 5) and the valence force fields of Heath and Linnett (1947), which reproduces the observed frequencies of SO(4)(2-) better than Urey-Bradley force field used by Sakai (1968). The results of new calculation are shown in Table 6. This table also includes the R.P.F.R. of H(2)S which was calculated by Thode et al. (1971). Using these new R.P.F.R. of SO(4)(2-) and H(2)S, the fractionation factors between SO(4)(2-) and H(2)S were calculated and are listed in the last column of Table 6 and plotted in Fig. 9. Fig. 9 indicates that the new calculation gives values more shifted from the experimental values than before. The major sulfate ions in our solution at 300° and 400℃ exist as NaSO(4)(-) (Sakai and Dickson, 1978; see also Table 4 of this paper) and, therefore, the measured fractionation factors are those between NaSO(4)(-) and H(2)S. The discrepancy between the theory and experiments may, at least, be partially explained by this fact, although other more important reasons, which are not known to us at the moment, may also exist