Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

Assessment of reservoir temperatures of thermal springs of the northern areas of Pakistan by chemical and isotope geothermometry

Chemical and isotope geothermometers, i.e. the Na–K, K–Mg, quartz and δ¹⁸O(SO₄–H₂O), have been applied to estimate the reservoir temperature of the thermal springs in the northern areas of Pakistan. The chemical types of the thermal waters and the effects of mixing of shallow cold water with the thermal end-members are discussed. These waters are neutral to slightly alkaline and have low dissolved contents. Sodium is the dominant cation in almost all the cases. In terms of anions, the hot waters of Budelas are of the SO₄ type, those of Tatta Pani are of mixed character (SO₄ and HCO₃), and the waters from the remaining areas show HCO₃ domination. An absence of tritium in Tatta Pani and Tato thermal springs indicates that they do not have any contribution of shallow young water. In the case of the Murtazabad springs, the wide range of tritium concentrations, negative correlations with surface temperature and Cl, and positive correlation between Na and Cl show that the shallow cold groundwater is mixing with thermal water in different proportions. For the mixed water of Murtazabad thermal springs, ‘isochemical modelling’ using the Na–K, K–Mg and quartz geothermometers indicates an equilibrium temperature in the range 185–200 °C. The δ¹⁸O(SO₄–H₂O) geothermometer gives relatively low temperatures for three springs, whereas two samples are close to the 185–200 °C temperature interval. The reservoir temperatures of Tatta Pani springs (100–120 °C), determined by Na–K and quartz geothermometers, are in good agreement. The δ¹⁸O(SO₄–H₂O) geothermometer gives a relatively higher range (140–150 °C) for most of the Tatta Pani springs. For Tato spring, the isotope and chemical geothermometers (except for the K–Mg) agree on an equilibrium temperature of about 170 °C. Reservoir temperatures of the remaining minor fields are not conclusive due to the lack of sufficient data.     

Black cobalt selective coatings by spray pyrolysis for photothermal conversion of solar energy

A low cost technique of spray pyrolysis has been described for the growth of black cobalt selective surfaces on commercially available aluminum and galvanized iron substrates. Parameters of growth have been optimized by a comparative analysis of opto-thermal, structural and optical properties of these films. Optimized films on aluminum were 0.21 μm thick and had α = 0.92 and _100°C = 0.13, Films on galvanized iron substrates gave best results (α=0.91, _100°C=0.12) for film thickness 0.24 μm. Accelerated life test studies indicate that these films have good adhesion to the substrates and are stable up to 220°C.     

Hydrogeological and isotopic survey of geothermal fields in the Buyuk Menderes graben, Turkey

The main high and low enthalpy geothermal fields in the Buyuk Menderes graben (Western Anatolia) and their reservoir temperatures are as follows: Kizildere (242 °C), Germencik (232 °C), Aydin-Ilicabasi (101 °C), Yılmazkoy (142 °C), Salavatli (171 °C), Soke (26 °C), Denizli -Pamukkale (36 °C), Karahayit (59 °C), Golemezli (101 °C) and Yenice (70 °C). The geothermal systems are controlled by active graben faults. The reservoir rocks in the geothermal fields are the limestone and conglomerate units within Neogene sediments and the marble-quartzite units within Paleozoic metamorphic formations. There are clear δ¹⁸O shifts from the Mediterranean Meteoric Water Line (MMWL) in the Kizildere, Germencik and Aydin fields, where a good relation between high temperatures and δ¹⁸O shift has also been observed, indicating deep circulation and water rock interactions. In the Pamukkale, Karahayit, Golemezli and Yenice fields and in Soke region, low temperatures, small isotope shifts, shallow circulations and mixing with shallow cold water have been noted.     

Fabrication and electrochemical performance of thin-film solid oxide fuel cells with large area nanostructured membranes

Thin-film solid oxide fuel cells (SOFCs) with large (5-mm square) membranes and ultra-thin La_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (LSCF) cathodes have been fabricated and their electrochemical performance was measured up to 500 °C. A grid of plated nickel on the cathode with 5–10 μm linewidth and 25–50 μm pitch successfully supported a roughly 200-nm-thick LSCF/yttria-stabilized zirconia/platinum membrane while covering less than 20% of the membrane area. This geometry yielded a maximum performance of 1 mW cm⁻² and 200 mV open-circuit voltage at 500 °C. Another approach toward realizing large area fuel cell junctions consists of depositing the membrane on a smooth substrate, covering it with a high-porosity material formed in situ, then removing the substrate. We have used a composite of silica aerogel and carbon fiber as the support, and show that this material can be created in flow channels etched into the underside of a silicon chip bonded to the top of the SOFC membrane. We anticipate these integrated fuel cell devices and structures to be of relevance to advancing low-temperature SOFCs for portable applications.     

Measurement and interpretation of terrestrial heat flow in Israel

Sixty-eight new determinations of terrestrial heat flow in Israel have a range of 0.17-11.07 μcal/cm²s. The average value of deep conductive heat flow in the undisturbed complex of the Arabo-Nubian Massif is 0·94 μcal/cm²s; it is least affected by circulation of groundwater. This value is only slightly higher than the heat flow of 0·88 μcal/cm²s in the Levantine Basin of the Mediterranean Sea. Several values that exceed 2·0 μcal/cm²s are due either to (probable) deep hydrothermal activity or to small domal structures of the basement.Within the sedimentary sequence which blankets the crystalline massif, terrestrial heat flow is often redistributed by circulating groundwater. Recharge regions, particularly Judean-Samarian Galilee, where cool meteoric waters percolate into the subsurface have anomalously low heat flow, ranging from 0·17 to about 1·0 μcal/cm²s. Part of the original deep thermal flux in those regions is intercepted at moderate depths by the recharge flow, and is carried into deeper aquifers of the Foothills, Coastal Plain, or the Jordan-Dead Sea Rift. Movement of groundwater occurs mainly along faults.Deep faults associated with the Jordan-Dead Sea Rift system act as conduits for hot waters ascending from deep confined aquifers. The most tangible surface expression of the convective hydrothermal system are the numerous warm to hot springs, emerging along the margins of the Rift. However, the waters emerging on the surface as the warm and hot springs are a minor fraction of the convective system. Most of the ascending thermal waters are absorbed by shallow aquifers with lower hydraulic potential. Such regions are characterized by anomalously high heat flow; several values exceed 2 and one value is 11 μcal/cm²s.     

Screen printed conductive CuS-poly(acrylic acid) composite coatings

Copper sulfide (CuS) powder precipitated from two different chemical baths (citrate and triethanolamine baths) was dispersed in a poly(acrylic acid) aqueous solution and the resulting mixtures were screen-printed over glass slides. Compared to the coatings of the same composite materials obtained by casting, the screen-printed coatings show better homogeneity and an improved thermal stability (up to 300°C). Sheet resistances of 50 Ω/□ were typical in 20 μm thick coatings and these values remained stable even after baking in nitrogen or vacuum at 200–300°C. The X-ray diffraction pattern indicates degradation of CuS to Cu_1.8S and Cu_1.96S, particularly in air-baked samples at 250–300°C. The XRD, TGA and R_□ results show CuS(Cit)–PAA samples as superior conductive coatings.     

Crystallographic analysis of high quality poly-Si thin films deposited by atmospheric pressure chemical vapor deposition

Crystallinity of thin film polycrystalline silicon (poly-Si) grown by atmospheric pressure chemical vapor deposition has been investigated by X-ray diffraction measurement and Raman spectroscopy. Poly-Si films deposited at high temperatures of 850–1050°C preferred to 2 2 0 direction. By Raman spectroscopy, the broad peak of around 480–500 cm⁻¹ belonged to microcrystalline Si (μc-Si) phase was observed even for the poly-Si deposited at 950°C. After high-temperature annealing (1050°C) 3 3 1 direction of poly-Si increased. This result indicates that the μc-Si phase at grain boundary became poly-Si phase preferred to 3 3 1 direction by high-temperature annealing. Effective diffusion length of poly-Si films deposited at 1000°C was estimated to be 11.9–13.5 μm and 10.2–12.9 μm before and after annealing, respectively.     

Transition from subcritical to supercritical bifurcation in penetrative convection in a vertical cylinder

The stability of a vertical cylindrical column of water with the horizontal bottom boundary maintained at 0°C and the temperature of the top boundary varying between 4 and 8°C is considered. A weakly non-linear analysis shows that the bifurcation is either supercritical or subcritical depending upon the values of two parameters: the aspect ratio of the cylinder (height/radius) which is varied between 2 and 4, and the penetration parameter μ defined as the ratio of the whole height over the height of the 4°C isotherm. For a given value of the aspect ratio, the bifurcation is supercritical when the whole height is unstable (μ = 1) and becomes subcritical above a particular value of μ when penetration occurs (μ > 1).     

Repeated production of hydrogen by sulfate re-addition in sulfur deprived culture of Chlamydomonas reinhardtii

Biological hydrogen production by the green alga, Chlamydomonas reinhardtii can be induced in conditions of sulfur deprivation. In this study, we investigated the repeated and enhanced hydrogen production afforded by the re-addition of sulfate with monitoring of pH and concentration of chlorophyll and sulfate. Without adjustment of the pH, the optimal concentration of re-added sulfate was 30 μM for the hydrogen production. By the re-addition of 30 μM of sulfate and the adjustment of the pH during 4 cycles of repeated production, we obtained the maximum amount of 789 ml H₂ l⁻¹ culture, which is 3.4 times higher than that of one batch production without adjustment of pH, 236 ml H₂ l⁻¹ culture. This means that the enhancement of the hydrogen production can be achieved by the careful control of the sulfate re-addition and pH adjustment in the sulfur deprived culture.     

Prevention of supercooling and stabilization of inorganic salt hydrates as latent heat storage materials

Various inorganic salt hydrates have been studied as a latent heat storage medium. A super-absorbent polymer (SAP) made from an acrylic acid copolymer is proposed as an effective thickener to prevent undesirable phase separation of the high hydrate inorganic salts (Na₂SO₄· 10H₂O, Na₂HPO₄·12H₂O, Na₂CO₃·10H₂O). Most of these materials can be stabilize by the addition of 3 to 5 wt% SAP as a thickener. For the low hydrate inorganic salts (CH₃COONa· 3H₂O, Na₂S₂O₃·5H₂O), carboxymethyl cellulose (CMC) is found to be an effective thickener. Similarly, the phase separation of the low hydrate salts can be prevented by the addition of 2 to 4 wt% thickener. To overcome the supercooling of the thickened phase change materials, various potential nucleators have been evaluated. For the thickened Glauber's salt, borax reduces supercooling of the salt from 15 to 3–4°C. Three different powders of carbon (1.5–6.7 μm), copper (1.5–2.5 μm) and titanum oxide (2–200 μm) are found to reduce the supercooling of thickened Na₂HPO₄·12H₂O. Also, the supercooling of thickened CH₃COONa·3H₂O is reduced from 20 to 2–3°C by adding 2 wt% potassium sulfate. New compositions for preventing supercooling and phase separation of PCMs are developed in the temperature range 30–60°C: Glauber's salt/SAP/borax (94/3/3 wt%, T_m = 35°C), Na₂CO₃·10H₂/SAP/Sr(OH)₂ (93/3/4 wt%, T_m = 32°C), Na₂HPO₄·12H₂O (92.8/3.5/3.7 wt%, T_m = 35°C), Na₂S₂O₃·5H₂O/CMC/ SrSO₄ (92/3/5 wt%, T_m = 48°C), CH₃COONa·3H₂O/CMC/K₂SO₄ (95/3/2 wt%, T_m = 58°C).     

Photoelectrochemical and physical properties of WO3 films obtained by the polymeric precursor method

Tungsten trioxide (WO₃) films were prepared by a solution-based method using ammonium metatungstate as the precursor and polyethylene glycol as the structure-directing agent. With the measurements of thermogravimetric and differential thermal analysis, X-ray diffraction, scanning electron microscopy, and ultraviolet and visible absorption spectroscopy, the effect of substrates and temperature on the crystal structure and crystalline formation of WO₃ was investigated. The results show that the WO₃ films were crystallized by sintering at over 400 °C, and the films prepared on fluorine–tin oxide glass substrates were distorted cubic in crystalline phase. However, a monoclinic crystal was formed by coating films on graphite and quartz glass substrates. Photoelectrochemical activity was evaluated under visible light irradiation. The WO₃ electrode calcined at 450 °C exhibited a photocurrent density of up to 2.7 mA/cm² at 1.4 V (vs. RHE) under incident 100 mW/cm² 500 W Xe lamp and donor carrier density N_D = 2.44 × 10²² cm⁻³ in 0.5 M H₂SO₄ electrolyte. The photoanode was stable up to 90 min, and the photocurrent decreased 39% with continuous gas evolution.     

Geothermal development in Hungary—country update report 2000–2002

This paper describes the status of geothermal energy utilization—direct use—in Hungary, with emphasis on developments between 2000 and 2002. The level of utilization of geothermal energy in the world increased in this period and geothermal energy was the leading producer, with 70% of the total electricity production, of all the renewable energy sources (wind, solar, geothermal and tidal), followed by wind energy at 28%. The current cost of direct heat use from biomass is 1–5 US¢/kWh, geothermal 0.5–5 US¢/kWh and solar heating 3–20 US¢/kWh. The data relative to direct use in Hungary decreased in this period and the contribution of geothermal energy to the energy balance of Hungary, despite significant proven reserves (with reinjection) of 380 million m³/year, with a heat content of 63.5 PJ/a at ΔT=40 °C, remained very low (0.25%). Despite the fact that geothermal fluids with temperatures at the surface higher than 100 °C are available, no electricity has been generated. As of 31 December 2002, the geothermal capacity utilised in direct applications in Hungary is estimated to be 324.5 MW_t and to produce 2804 TJ/year. Geothermal heat pumps represent about 4.0 MW_t of this installed capacity. The quantity of thermal water produced for direct uses in 2002 was approximately 22 million m³, with an average utilization temperature of 31 °C. The main consumer of geothermal energy is agriculture (68% of the total geothermal heat dedicated to direct uses). The geothermal water is used only in five spas for space heating and sanitary hot water (SHW), although there are 260 spas in the country, and the thermal water produced has an average surface temperature of 68 °C. The total heat capacity installed in the spas is approximately 1250 MW_t; this is not provided by geothermal but could be, i.e., geothermal could provide more than three times the geothermal capacity utilized in direct uses by 31 December 2002 (324.5 MW_t).     

Solar absorber coatings based on CoCuMnOx spinels prepared via the sol–gel process: structural and optical properties

Titanium-doped and undoped CuCoMnO_x spinel films were deposited on Al substrates from sols which were made from the following: Co-acetate, Cu-chloride and Mn-acetate (Ti:CoCuMnO_x-I); and Co-acetate, Cu-nitrate and Mn-acetate (CoCuMnO_x-II). The precursors’ ratio Co:Cu:Mn was equal to 1:3:3. The solar absorptance (α_s) and the thermal emittance (_T) of the films, which were annealed at 450°C for 15 or 30 min, were determined from the corresponding diffuse reflectance spectra in the 0.32–20 μm range. The results show that the CoCuMnO_x-II films with SiO_x protective over-coatings exhibited values of α_s=0.85–0.91 and _T below 0.036 after just a single dipping/annealing cycle.The structure of the films was studied with X-ray diffraction (XRD), infrared (IR) absorbance and near-grazing incidence angle (NGIA) reflection-absorption spectroscopy. Our results suggested that the films have a spinel structure with the composition CoCuMnO_x. The stability of the films was tested by soaking them in boiling water for 2 h. NGIA IR spectra of the treated films confirmed the formation of the hydrated mixed oxide (Mn-, Co-, Cu-) phases. To improve the stability of the films two kinds of protective over-coatings were tested: one over-coating was based on polysiloxane resin and the other on high-density silica (T-resin). Films that were resistant to boiling water were obtained by applying the high-density silica protective over-coating, which was cured at 140°C for 30 min.     

Oxidative photoelectrochemical technology with Ti/TiO2 anodes

Rutile and anatase TiO₂ films have been grown on Ti plates by thermal (500–800°C) and anodic oxidation followed by thermal annealing (400–500°C), respectively. The photoelectrochemical efficiency of these photoanodes, evaluated by current density measurements in the photooxidation of 4-methoxybenzyl alcohol in deaerated CH₃CN, has been determined. The photocurrent efficiency increases with the thickness of the TiO₂ rutile film up to 1 μm (the most efficient thickness). At the wavelengths furnished by the irradiation apparatus similar thicknesses of anatase and rutile films show nearly the same efficiencies. Anodic bias produces similar relative increases of current intensity in both crystalline forms.     

A computational method for determining segmental and overall geothermal gradients and geothermal heat flow values

A new computational method is presented which calculates geothermal heat flow values and geothermal gradients with more precision than permitted by previously published techniques. The data required are: geothermal temperature at a known depth, mean surface temperature, the rock types in the stratigraphic column and the thermal resistivity values for the different types of rocks. This method is valuable in areas that have no measured gradient values. Basic equation used was the Fourier heat transfer equation where is heat flux in μcal/(cm² s), ρ_i is thermal resistivity (°C s cm/μcal) and ∂T/∂x is the x component of the temperature gradient (°C/cm). The thermal resistivity was allowed to vary linearly with temperature ρ_i = ρ_i^o [1 + K_i (T − 30)] where ρ_i is thermal resistivity of the lithographic segment «iå at a temperature T, ρ_i^o is thermal resistivity at 30°C and K_i is the temperature coefficient of thermal resistivity. The procedure consisted of integrating the combined equation for heat flux in terms of temperature dependent resistivity.Two iterative solutions were used to simplify the calculations: exact and approximate. The heat flux for each well was assumed to be 1.0 HFU and segmental temperatures were calculated from the bottom (arbitrarily) up, until a surface temperature was obtained. The calculated surface temperature could then be compared with the mean surface temperature (MST). Correction in the heat flux value was made until the calculated surface temperature and MST agreed. An analysis of three deep Appalachian test wells was made and the results showed the critical importance of lithographic ordering and the temperature dependence of thermal resistivity upon calculated geothermal quantities.     

Selective absorbing surface for evacuated solar collector tubes

The absorptance of AlN-Al(absorbing coating)/Al solar spectrum(0.34 ≈ 2.5 μ m) selective absorbing surface, containing 8-layer AlN-Al composite materials and with distinctive or non-boundaries between the layers, deposited by sputtering technology and heat-treated at 400 °C (60min) is about 0.95 and its thermal emittance is close to 0.07 ≈ 0.08(80 °C). But on the condition that the absorptance is unchanged, the thermal emittance dropped to 0.04 for the AlN-Al coating composed of matel volum fractionic 0.42, 0.25 and 0.00 films.     

Angular distribution of clear sky short wavelength radiance

Over 3000 scans of the clear sky short wavelength (0.3–3.0 μm) radiance were used to produce sky radiance contour maps for solar zenith angles 32° to 80°. The radiance contours are symmetrical about the solar meridian with minimum radiance in the solar meridian at approximately 90° to 110° from the sun. There is no significant change in contour for a change in aerosol optical depth from 0.1 to 0.5. The clear sky radiance is given analytically by N(ψ) = (1.63 + 53.7e−5.49ψ + 2.04 cos² ψ cos θ^*) (1 − e^{−1.90 sec θ}) (1 − e^{−0.53 sec θ}*) where θ^* is the solar zenith angle, θ the zenith angle of the sky radiance direction, and Ψ is the scattering angle between sky and sun directions.     

Polycrystalline silicon solar cells on mullite substrates

Polycrystalline silicon layers have been grown on various alumino-silicate substrates in a rapid thermal chemical vapor deposition (RTCVD) system at high temperatures (>1000°C). Structural analysis shows a columnar growth with grain sizes up to 15 μm and growth rates up to 5 μm/min. Solar cell devices on this fine-grained Si material result in a short-circuit current of about 13 mA/cm² but a poor open-circuit voltage (<0.4 V). Larger grains obtained by the zone melting recrystallization (ZMR) technique boosted the current up to 26.1 mA/cm², thanks to the light-trapping by the mullite substrate. Best efficiency is 8.2% on a 1 cm² cell made on a 20 μm thick poly-Si layer.     

Geochemical approach to the Bou Hadjar hydrothermal system (NE Algeria)

The Bou Hadjar low-temperature hydrothermal system is located in northeast Algeria. The four main thermal springs that are the subject of the study emerge ith temperatures between 32 and 60°C from allochthonous formations. The reservoir temperature has been estimated from chemical compositions by utilizing simultaneously the silica, gas and sulfate-water oxygen isotope geothermometers, fluid-mineral equilibrium calculations, and a mixing model. According to these thermometric methods, the most probable subsurface temperature is in the range 75–106°C. The mixing model suggests a temperature of 125°C for the parent water.