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Hydrogen in aluminum causes the formation of detrimental hydrogen porosity in castings. In order to reduce the formation of hydrogen pores, an approach was targeted using lithium as target for hydrogen. This approach utilizes the affinity of lithium for hydrogen, whereby spodumene (a lithium aluminum silicate) and lithium aluminate were used as lithium providers. Within the scope of this study, the preparation of ceramic foam filters with a coating of lithium-containing raw materials (spodumene) was investigated. Those investigations revealed that the spodumene coating has a detrimental influence on the bending strength of the foams when a certain level of spodumene is exceeded. This observation might be explainable by the intrusion of the spodumene into the alumina matrix of the skeleton foam. Two wetting tests at different temperatures were conducted, verifying the significant influence of the temperature on the reaction between the spodumene and AlSi7Mg. Furthermore, test filters coated with raw materials exhibiting different amounts of lithium were conducted. The hydrogen pores were evaluated by light microscopy and computed tomography. The analyzed pore size distribution in the aluminum did not elucidate the proximate influence of the lithium-coating on the ceramic foam filter on the hydrogen porosity in the aluminum.

The triple oxygen isotope composition of phytoliths (17O-excessphyto) can provide key information on past atmospheric relative humidity (RH) over land. Here, we examined how leaf-to-air temperature gradients and changes in the silica polymerization rate in response to stomatal conductance influence the interpretation of 17O-excessphyto in terms of RH. Further, we assessed the reliability of a theoretical isotope model of leaf water evaporation to predict the triple oxygen isotope composition of leaf water on diurnal and seasonal scale. For this purpose, we monitored a grass plot within a natural Mediterranean woodland for one year. We measured in particular the isotope composition of atmospheric water vapor and plot-scale grass leaf temperatures – two variables that are often only estimated. Grass leaf blades were collected in different seasons and over a 24-hour period for leaf water and phytolith isotope analysis. We found that the steady state model reliably predicts the triple oxygen isotope composition of leaf water during daytime but remains sensitive to uncertainties on the leaf-to-air temperature difference. Deviations from isotope steady state at night are well represented by the non-steady state model. In our study, the 17O-excessphyto best reflects average daytime RH over the growth period, rather than daily RH. Average daytime leaf-to-air temperature gradients of less than 2 °C introduce an insignificant bias to the RH estimate. The results also confirm the established triple oxygen isotope fractionation factors between phytoliths and leaf water. The findings of this study help to better understand how to interpret 17O-excessphyto of fossil phytolith assemblages in terms of past RH.

Calcium sulfates are the dominating salts but the respective sulfate sources are debated. In order to quantify the relative contribution and spatial distribution of sulfate sources and to identify biological sulfate recycling processes, we analyzed δ18OSO4, Δ17OSO4, 87Sr/86Sr, and δ34SSO4 of sulfate from Atacama Desert soils (Chile). Surface samples were taken along four W-E transects from the Pacific coast to the Pre-Andean Cordillera between 19.5°S and 25°S. Additionally, lacustrine gypsum and sulfate extracted from groundwater feeding the Salar de Llamará and sodium sulfates from the Salar del Huasco were analyzed.Sulfur from the ocean comprise high δ34SSO4 values compared with low δ34SSO4 volcanic sulfate allowing to estimate the marine sulfur contribution to the total sulfate sample. δ34SSO4 decreases with distance from the coast principally confirming previously published results [1]. Because Sr substitutes for Ca in Ca-Sulfates, 87Sr/86Sr follows similar systematics, at least for samples taken within the coastal fog zone (34SSO4 and 87Sr/86Sr of samples taken above 1200 m are decoupled indicating sulfate dissolution and re-precipitation or deposition of supra-regional Ca-rich aerosols with high 87Sr/86Sr values.Positive ∆17OSO4 values observed in all analyzed samples (0.1‰ to 1.1‰) suggest a significant contribution from secondary atmospheric sulfate (SAS) to Atacama Desert soils. Distinct mass-independent 17O anomalies of SAS originate from atmospheric oxidation of reduced sulfur species from volcanic or anthropogenic emissions, or biogenic sulfur gases such as dimethyl sulfide (DMS) by O3 or H2O2. Within our dataset we can distinguish between a SAS(DMS) endmember, comprising high ∆17OSO4 and δ34SSO4 and a SASAtacama endmember comprising moderate Δ17OSO4 and low δ34SSO4. Highest Δ17OSO4 values, interpreted to represent a pure SASAtacama endmember, are observed in samples from the Coastal Cordillera of the southernmost transect which is generally higher than the present maximum level of fog advection (1200 m). Lowering of Δ17OSO4 values results from 1) dilution of the positive Δ17OSO4 fromSAS by marine and/or terrestrial sulfate with Δ17OSO4 ≈ 0‰, and 2) resetting of Δ17OSO4 due to biological sulfate reduction and reoxidation. Lowest Δ17OSO4 values are observed in sulfates from salars and soils from alluvial fans.In general, Δ17OSO4 andδ18OSO4 of our data show an inverse relationship reflecting not only the source contributions but also biological sulfate cycling. Thus, large Δ17OSO4 anomalies (≈1‰) that suggest a dominant contribution from SASAtacama, also indicate the relative absence of biologically processed sulfate and thus, low water availability.[1] Rech et al. (2003), Geochim. Cosmochim. Acta 67, 575-586

In industrial applications, filter materials are often chosen according to cost as well as their processing and thermomechanical properties, but rarely in terms of their behavior during filtration, which is largely due to there being insufficient information available on the influence of filter materials and surface quality on filtration behavior. In this study, the manufacture of functionalized Al2O3 nanofilters was investigated, along with their filtration performance in short- and long-term filtration trials. In addition, sessile drop tests were performed to measure the contact angle of the nanofunctionalized materials, and yielded an approximately 10 deg (11 pct) higher contact angle for nanocoated materials sintered at 800 °C and 1250 °C than for those sintered at 1600 °C and an approximately 23 deg (23 pct) higher contact angle compared to surfaces without a nanocoating. The filtration mechanism was assessed by means of Porous Disk Filtration Analysis (PoDFA) and Liquid Metal Cleanliness Analyzer (LiMCA) monitoring systems, as well as by analysis of the used and infiltrated filters using Scanning Electron Microscopy and Energy Dispersive X-ray analysis (SEM/EDX) technology. Both short-term and long-term filtration trials showed that the filtration behaviors of the reference and nanocoated filters were comparable. It was therefore determined that nanocoating of such filters with Al2O3 does not provide any improvement with regard to filtration performance.

RATIONALE Producing robust high frequency time series of raw atmospheric water vapor isotope data by laser spectrometry requires accurate calibration. Especially, the chemical composition of the analyzed sample gas can cause isotope bias. This study assesses the matrix effect on calibrated δ17 O, δ18 O, δ2 H, 17 O-excess, and d-excess values of atmospheric water vapor. METHODS A Picarro L2140-i cavity ring-down spectrometer combined with an autosampler and a vaporizer is used to analyze δ17 O, δ18 O, δ2 H, 17 O-excess and d-excess of two water standards. Isotope data obtained using synthetic air and dry ambient air as carrier gas at water mixing ratios ranging from 2000 to 30000 ppmv are compared. Based on the results, atmospheric water vapor measurements are calibrated. The expected precision is estimated by Monte Carlo simulation. RESULTS The dry air source strongly impacts raw isotope values of the two water standards, but has no effect on the mixing ratio dependency functions. When using synthetic air, δ17 O, δ18 O and 17 O-excess of calibrated atmospheric water vapor are overestimated by 0.6 ‰, 0.7 ‰, and 217 per meg, respectively, while δ2 H and d-excess are underestimated by 1.5 ‰ and 7.3 ‰. Optimum precisions for the calibrated δ17 O, δ18 O, δ2 H, 17 O-excess and d-excess values and 12-min integration time are 0.02 ‰, 0.03 ‰, 0.4 ‰, 14 per meg and 0.4 ‰, respectively. CONCLUSIONS In light of the obtained results, recommendations for the calibration of atmospheric water vapor isotope measurements are presented. The necessity to use dry ambient air as dry air source when running the standards for calibration is pointed out as a pre-requisite for accurate atmospheric water vapor 17 O-excess and d-excess measurements.

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Carbon-bonded foam-filters, such as alumina-carbon foams, are widely used for the filtration of metal melts. The aim of the experimental investigations reported in this paper was to examine the possibility of producing alumina coatings with a porous structure on such alumina-carbon foams by an electrophoretic deposition method. This method utilizes the simultaneous gas evolution by electrolysis to generate channel-like pores during the formation of ceramic layers by the electrophoretic deposition from aqueous suspensions. The foam samples to be coated were found to possess a sufficiently high electrical conductivity to function as deposition electrode. Using an aqueous suspension of a submicron alumina powder with an anionic polyelectrolyte as dispersant, coatings containing the desired pore channels were successfully produced on these foam samples. Voltages of 10 or 15 V proved suitable for the pore formation, as illustrated by tomographic 2D slices of the coated foams and by images that were taken by means of a digital microscope. First tests showed that the sintered coatings were able to resist the thermal shock to which they were exposed by immersing them into an aluminium melt.

Within this study the influence of the sample shape, the cell size and the measurement method on the Young's modulus E of open cell foam alumina was investigated. The measurement methods used for the determination of E were the impulse excitation technique, the longitudinal ultrasonic measurement, the quasi-longitudinal ultrasonic measurement and the three point bending technique (3PB). The samples comprising the smallest height, yielded the highest E values for all measurement methods due to its processing, causing higher densities and homogeneity and hence leading to increased E values. Furthermore, its smaller area moment of inertia results in a higher beam deflection for a fixed force applied in 3PB. Thus, in the case of this shape, the forces involved during the 3PB tests were much lower and a smoother test could be performed and resulted in higher E values. Problems were found for the determination of E by the impulse excitation technique at large cell sizes (10 and 20 ppi). This was attributed to a reduction of the vibrating surface beneath the microphone capturing the audio signal. Ultrasonic methods performed robustly, however have to be conducted with care (e.g. Poisson's ratio assumption).

This study addresses the question of whether mercury intrusion porosimetry is an appropriate measurement devise for the porosity characterization of reticulated ceramic foams which features three kinds of pores: functional pores, material pores and strut cavities remaining after decomposition of the polymeric foam. Reticulated ceramic foam samples made of Al2O3 and Al2O3-C and with functional pore sizes between 10 and 60 ppi (pores per inch) were investigated. The results show that it is feasible to measure the strut cavities and the entryways of the material pores with the help of the mercury intrusion porosimeter. The results for the strut cavity diameter depends strongly on the ppi number of the polyurethane foam used for the preparation of the ceramic foam. For the reticulated Al2O3-C foam samples no extrusion of the mercury is observed. Reasons for the missing extrusion of mercury are discussed. Furthermore, atomic force microscopy (AFM) measurements on Al2O3 and Al2O3-C samples are carried out using a recent AFM method to examine interactions between a mercury droplet and rough surfaces. Factors like approach/retrace speed, reproducibility and applied force are investigated. It is seen that for Al2O3 larger attractive forces are measured than for Al2O3-C.

The filtration of molten metal using ceramic foam filters (CFF) is a purification method often used by the aluminum industry to meet the increasing demands the melt quality. CFFs are in most cases produced by the replica method using polyurethane foam templates, which are coated with a ceramic slurry of targeted composition before being sintered into its final structure. Despite the key role of CFFs in view of metal cleanliness, there are only a few quality parameters for their evaluation. In the present study, an overview of the different material properties essential for CFFs, suitable measurement methods, and their limitations are presented. The focuses of this work are the different densities of ceramic foams and the thermal expansion coefficient measured by dilatometry, as well as the filter porosities and microstructure measured through mercury intrusion porosimetry and computer tomography, respectively. Moreover, elastic (Young’s Modulus) and mechanical properties (compressive strength) are discussed.

Production of high-quality aluminum products requires an extensive melt treatment process, even more so with the increasing focus on recycling and sustainability. Filtration is a commonly used process segment for removal of non-metallic inclusions in aluminum, and ceramic foam filters (CFFs) are often used as the filtration media. In the present study, the chemical stability of phosphate-bonded Al2O3-based CFFs has been investigated. Three filters with different chemical compositions have been submerged into pure aluminum (with traces of Mg) and in an aluminum-magnesium melt (~ 2 wt pct Mg) at 730 °C. In addition to filter characterization before and after exposure to molten metal, using various imaging and X-ray techniques, the melt itself was analyzed by spark optical emission spectroscopy. The generation of phosphine gas was also measured by the use of Dräger tubes, and thermodynamic calculations performed using FactSage™. The phosphate-bonded filters were observed to react with the magnesium present in the molten aluminum even at very low magnesium concentrations (0.00035 wt pct), and as the magnesium concentration increased the severity of the degradation became more and more evident. The exposure time proved to have detrimental effect on the filter structure, with pieces of the filter struts broken off causing melt contamination. Severe filter degradation also resulted in color changes with accompanying diffusion of magnesium and phosphorus to and from the filter, respectively. Moreover, phosphine gas was released in amounts exceeding recommended exposure limits when the filter came in contact with the humidity in the air after testing. Good agreement was established to exist between the results from the thermodynamic calculations performed and the experimental results.

The wetting behavior was measured for Al2O3-C in contact with AlSi7Mg with a conventional sessile drop test (vacuum, 950 &deg, C and 180 min) and a sessile drop test with a capillary purification unit (vacuum, 730 &deg, C and 30 min). The conventional test yielded contact angles of around 92&deg, whereas the sessile drop measurement with capillary purification showed a strongly non-wetting behavior with a determined apparent contact angle of the rolling drop of 157&deg, Filtration tests, which were repeated twice, showed that the Al2O3-C filter possessed a better filtration behavior than the Al2O3 reference filter. For both filtration trials, the PoDFA (porous disc filtration analysis) index of the Al2O3-C filter sample was equal to half of the PoDFA index of the Al2O3 reference filter sample, indicating a significantly improved filtration performance when using Al2O3-C filter. Notable is the observation of a newly formed layer between the aluminum and the Al2O3-C coating. The layer possessed a thickness between 10 &micro, m up to 50 &micro, m and consisted of Al, C, and O, however, with different ratios than the original Al2O3-C coating. Thermodynamic calculations based on parameters of the wetting and filtration trials underline the possible formation of an Al4O4C-layer.

Gypsum crystals capture the isotopic composition (δ2H, δ17O, and δ18O) of ambient water in their structurally bonded water and may serve as a useful tool to reconstruct paleoclimate. Relative humidity, water temperature, wind speed, along with the isotopic composition of atmospheric vapor and inflowing water control, to a variable degree, the relative proportion of equilibrium and kinetic isotope fractionation during evaporation, and, thus, ultimately determine the d-excess and 17O-excess of gypsum-bonded water. Here, we demonstrate that the respective best fit of these variables through measured gypsum-bonded water isotope data using the classic Craig-Gordon evaporation model provides apparent absolute values for the fundamental climate mean state variables humidity and temperature and an empirical wind speed parameter of the geologic past.In this proof-of-concept study, we sampled gypsum crystals within individual stratigraphic units of Pliocene lacustrine deposits from the Atacama Desert, extracted their structurally bonded water, and analyzed the hydrogen and triple oxygen isotope composition. The spread of measured isotope data within each sampled stratigraphic unit suggests variable degrees of evaporation between individual gypsum samples along a common evaporation trajectory. We used the Craig-Gordon evaporation model together with a Monte Carlo simulation to determine the limits of climate mean state variables that fit the measured isotopic data.Our results demonstrate that primary isotope signatures of marine and continental source waters are preserved in structurally bonded gypsum waters. The data coherently suggest a slightly warmer (18-35°C), less windy and much more humid (50-75%) climate for the Pliocene Atacama, which is consistent with marine records and global circulation climate models that agree on “permanent El Niño” conditions for the Pliocene in the equatorial East Pacific.Under the assumption that mixing of different brines or multiple sources is insignificant - as would be evident from scattering of isotopic data below the evaporation trajectory in 17O-excess over δ18O – the combined hydrogen and triple oxygen isotope analyses of gypsum-bonded water provides a powerful tool to quantify past mean states of humidity and temperature, and to estimate paleo-wind conditions.

We systematically investigated the spatial distribution of sulfates, chlorides, and nitrates in Atacama Desert soils in order to identify their relationship to long-term aridity gradients and to secondary redistribution and phase transformation. Thin surface crusts, powdery surface material and subsurface concretions from up to 40 cm depth were sampled along several latitudinal transects between 19.5–25°S and 68.5–70.5°W. The samples were characterized by total soil chemical analysis (ICP-OES and spectrophotometric analysis) complemented by XRD and thermogravimetric analysis to determine contents of chloride, nitrate, and major elements along with gypsum and anhydrite abundance in Atacama Desert soils. Our results demonstrate that the spatial distribution of gypsum, anhydrite, halite, and nitrates in Atacama Desert soils is indeed linked to aridity gradients, but also sources, and secondary dissolution processes. Nitrates and chlorides are best preserved between 19 and 22°S, which thus may constitute the long-term hyperarid core of the Atacama Desert. Remobilization within the soil is ubiquitous south of 22°S, but generally also occurs on the debris fans prograding from the Precordillera into the Central Depression. A near-constant concentration ratio of Na/Cl = 0.83 – very similar to the sea water ratio – throughout the desert and concentration maxima within the reaches of coastal fog penetration below the altitude of 1200 m reveals that sea spray is the primary source of halite in Atacama Desert soils. Calcium sulfates dominate Atacama Desert soils. Deposition is primarily as gypsum, but anhydrite is abundant in the northern Central Depression between 19 and 22°S. The apparent association of anhydrite with high concentrations of nitrate and chloride may point to a formation by dissolution and secondary reprecipitation from salt-concentrated fluids. The predominance of anhydrite in the Central Depression suggest geomorphology and water availability as additional factors remaining to be determined.

Despite the application of aluminum melt filtration with ceramic foam filters since the 1960s the process is not fully understood. Outstanding issues are for example the influence of the wetting behavior and filter chemistry on the filtration efficiencies.Contact angle measurements by the sessile drop method coupled with non-contact heating and capillary purification technique were conducted at 730 °C with AlSi7Mg alloy on the substrates of four different oxides (Al2O3, MgAl2O4, 3Al2O3·2SiO2 and TiO2). The highest contact angle was measured on 3Al2O3·2SiO2, followed by MgAl2O4, Al2O3 and TiO2.Experimental values of contact angles were correlated with the evaluated filtration efficiencies of filtration trials performed at Constellium. They show a good correlation for inclusions smaller than 110 μm - the larger the contact angle the higher is the filtration efficiency.The adhesion forces of alumina inclusions on the four filter materials were experimentally estimated with an AFM in water based model system. The highest adhesion forces were measured on the Al2O3 substrate, followed by the 3Al2O3·2SiO2, the MgAl2O4 and the TiO2 substrate. For inclusions >70 μm, both the measured filtration efficiencies for >70 μm and the adhesion forces increase by the following order of coatings: TiO2, 3Al2O3·2SiO2, MgAl2O4, Al2O3. Keywords: Aluminum, Ceramic, Contact angle, Adhesion force, Filtration

Corrosion of alumina-based metal melt filters functionalized by 3Al2O3·2SiO2 or fused SiO2 was investigated using local chemical and microstructure analyses and thermodynamic calculations. Molten aluminium alloy AlSi7Mg0.6 was employed as corrosion medium. The aluminium alloy was melted in a Spark Plasma Sintering apparatus in order to avoid the melt flow. During the reaction with the AlSi7Mg0.6 melt, 3Al2O3·2SiO2 partly decomposed, and Al2O3 reacted with magnesium from the melt and with oxygen from SiO2 to MgAl2O4. Silicon precipitated in the aluminium alloy. For corundum functionalized by fused SiO2, metastable γ-Al2O3 was detected additionally to the above phases for short reaction times.

The influence of filter surface chemistry on the filtration efficiency of cast aluminum alloys was evaluated for four different filter coating compositions (Al2O3—alumina, MgAl2O4—spinel, 3Al2O3·2SiO2—mullite, and TiO2—rutile). The tests were conducted on a laboratory scale with a filtration pilot plant, which facilitates long-term filtration tests (40 to 76 minutes). This test set-up allows the simultaneous use of two LiMCAs (before and after the filter) for the determination of the efficiency of inclusion removal. The four tested filter surface chemistries exhibited good thermal stability and mechanical robustness after 750 kg of molten aluminum had been cast. All four filter types exhibited a mean filtration efficiency of at least 80 pct. However, differences were also observed. The highest filtration efficiencies were obtained with alumina- and spinel-coated filter surfaces (>90 pct), and the complete removal of the largest inclusions (>90 µm) was observed. The efficiency was slightly lower with mullite- and rutile-coated filter surfaces, in particular for large inclusions. These observations are discussed in relation to the properties of the filters, in particular in terms of, for example, the surface roughness.

Although it is undisputed that the filtration of aluminum melt inside ceramic foam filters is influenced by the wetting behavior between the liquid melt and the material of the filter coating, experimental proof is still pending. For the present study, the contact angle of an AlSi7Mg alloy on substrates made of Al2O3, MgAl2O4, 3Al2O3·2SiO2 and TiO2 was measured by the sessile drop method at 730 °C using non-contact heating and capillary purification technique. The contact angles were compared with filtration efficiencies of filters with identical coating composition measured during filtration trials performed at a pilot casting line. For inclusions smaller than 110 µm, a correlation between contact angle and filtration efficiency was observed. Furthermore, adhesion forces of alumina inclusions on the four coating materials were experimentally determined using atomic force microscopy in a water-based model system. For inclusions larger than 70 µm, the filtration efficiency correlates with the measured adhesion force.

Melt cleanliness is essential for high quality aluminum production. The main cleanliness criteria are the content of dissolved hydrogen as well as the content of non-metallic inclusions. The latter may impair the castability of the aluminum melt as well as the mechanical properties and the machinability of the aluminum castings. A simple and efficient way to remove non-metallic inclusions is the application of filters during the casting process. The influence of the filter roughness on the filtration is undisputed but experimental proof is still pending. Filters with three different levels of roughness were subjected in filtration trials in a filtration pilot setup at Hydro (Bonn, Germany) allowing determination of the inclusion removal efficiency by the application of two LiMCA devices. In addition to the LiMCA measurements, PoDFA, Alscan measurements and investigations of the casted aluminum were done.

Pores exert a dominating influence on the mechanical and thermomechanical properties of refractory material such as strength and thermal shock behavior. Thus, it is essential to characterize and quantify their number, size and size distribution. Mercury intrusion porosimetry (MIP) is an analytical technique used to characterize the material's porous nature relating to the pore diameter distribution, total pore volume, bulk and apparent density. The technique involves the intrusion of non-wetting mercury into the sample as a function of pressure whereby the measurement can be extended by an extrusion process or even a cycling of intrusion and extrusion. Quite a lot of publications using the mercury intrusion/extrusion porosimetry have in common that specifics of the measuring parameter are not provided. This complicates the replication of studies for interested scientists. Measuring parameters can affect mercury intrusion/extrusion porosity results. They are even more relevant when performing combined intrusion/extrusion studies due to a large impact of the measuring parameters on the extrusion step. Therefore, this study attempts to provide an overview of the influence of the measuring parameters on the mercury intrusion/extrusion porosimetry results. The specific parameters are the stem and bulb volume of the penetrometer, equilibrium time, data analysis options, sample/particle size and sample amount.

This study demonstrates the potential of triple O-isotopes to quantify evaporation with recharge on a salt lake from the Atacama Desert, Chile. An evaporative gradient was found in shallow ponds along a subsurface flow-path from a groundwater source. Total dissolved solids (TDS) increased by 177 g/l along with an increase in δ18O by 16.2‰ and in δD by 65‰. 17O-excess decreased by 79 per meg, d-excess by 55‰. Relative humidity (h), evaporation over inflow (E/I), the isotopic composition of vapor (*RV) and of inflowing water (*RWI) determine the isotope distribution in 17O-excess over δ18O along a well-defined evaporation curve as the classic Craig-Gordon model predicts. A complementary on-site simple (pan) evaporation experiment over a change in TDS, δ18O, and 17O-excess by 392 g/l, 25.0‰, and −130 per meg, respectively, was used to determine the effects of sluggish brine evaporation and of wind turbulence. These effects translate to uncertainty in E/I rather than h. The local composition of *RV relative to *RWI pre-determines the general ability to resolve changes in h. The triple O-isotope system is useful for quantitative hydrological balancing of lakes and for paleo-humidity reconstruction, particularly if complemented by D/H analysis.