Al Solubility Research Articles

Recrystallization and texture evolution of Mg–3%Al–1%Zn–(0.4–0.8)%Sr alloys during extrusion

Microstructure and texture evolution during the extrusion of AZ31 magnesium alloy containing 0.4 and 0.8wt%Sr has been investigated. Following extrusion at 250°C, the microstructure consists of fine recrystallized and large elongated grains along with Al4Sr stringer precipitates. Extrusion at 350°C results in larger and more uniform grain size. Grain refinement and nucleation of new grains were associated with sub-grain formation in the elongated grains, grain boundary bulging, and nucleation at the particle interfaces. Texture measurements in the extrusion deformation zone show an increase in the basal ring fiber-texture from the undeformed zone toward the die opening. Compared to AZ31 without Sr, the texture intensity increases with increasing Sr at 250°C, whereas the strength of extrusion fiber texture decreases at 350°C. The Al solubility in the α-Mg matrix decreases with increasing the Sr and the Al solute atmosphere around the dislocations weakens. Due to the reduction of the solute drag effect, dislocation movement is facilitated and dynamic recrystallization becomes more intensive resulting in strengthening the texture during extrusion at 250°C. The decrease in texture intensity at 350°C extrusion is attributed to the activation of particle-stimulated nucleation (PSN) that leads to the nucleation of new grains with high orientation mismatch to the parent grains.

Magnetic Properties of Al–SiC Co-Sputtered Films Grown by Radio Frequency Sputtering

Room-temperature ferromagnetism was observed in the Al-SiC co-sputtered films fabricated by radio frequency (RF) sputtering. When the annealing temperature (Ta) was increased from 800 to 1100 degrees C, the ferromagnetic ordering was present with the formation of Al-C bonds. Both annealing and Al-doped the films can improve the crystallization of SiC and induce long-range magnetic order in the Al-SiC co-sputtered films. Experiments show that the Al solubility was less than 0.8 at% in SiC matrix. As a possible explanation for the existence of local magnetic moment in Al-doped SiC, unpaired spins arise in a conversion from sp3 to the sp3/sp2 hybridization. The partial Si-C bonds in SiC were converted to Al-C bonds when the trivalent aluminum entered into Si sites. Al atoms introduce some net spins in Al doped film with the calculated integrated spin density 0.467 microB. The structural defects produced by Al-doping have provided an exciting possibility of nonmagnetic atoms-doped to control the spin moments and induce ferromagnetism in wide-gap semiconductor.

Phosphorus in Soils of Temperate Forests: Linkages to Acidity and Aluminum

We used P fractionation techniques to study the accumulation, mobilization, and availability of soil P in six watersheds of the eastern United States and Europe, two of which included paired long‐term acidification experiments. Although total soil P concentrations varied widely among these watersheds, the proportions of P fractions were relatively uniform. The mean for the P fraction operationally defined as being associated with Al in the reference watersheds was 71% of total extractable P (SE ≤ 1%). Experimental whole‐watershed acidification resulted in significant depletion of Al‐P concentrations from the upper mineral soil in treated watersheds due to the dissolution of Al hydroxide by acidic solutions traveling along shallow flow paths. Acidic soil solutions mobilize both Al and P, leading to P depletion from the Al‐P fraction in the mineral soils. Across this suite of watersheds, lower pH appears to decrease Al/P ratios in the Al‐P fraction of these mineral soils through changes in Al solubility. Biocycling in these forests can play a critical role in linking subsurface mineral soil P to surface O horizon available P. In this study, sites with the lowest mineral subsoil Al/P ratios generally had the lowest mineral soil pH values and the highest O horizon available P concentrations. The net effect was to leave subsoil P more bioavailable at the lower pH values because of a lower Al/P ratio in the mineral subsoil at the pH range of 3.1 to 4.6 found in this study. These results suggest that changes in soil acidity due to management, air pollutants, or pedogenesis could shift P availability by altering acidity and the Al/P balance.

Effect of cyclodextrins on lonidamine release and in-vitro cytotoxicity

The objective of this work was to study the effect of natural, hydroxypropyl and partially methylated cyclodextrins on the solubility of lonidamine and the cytotoxicity of the inclusion complex. The solubility study was conducted according to Higuchi et al. where HP-α-CD, HP-β-CD and HP-γ-CD showed type AL solubility curves indicating the formation of inclusion complexes with molar ratio of 1:1 with lonidamine. However, AP and AN type phase solubility behaviors were observed with PM-CD and α-CD, β-CD and γ-CD, respectively. Solubility enhancement factors and stability constants (K1:1 and K1:2) were calculated from the phase diagrams as appropriate. The characterization of the above inclusion complexes was evaluated using differential scanning calorimetry, Fourier transform infrared, and dissolution. Lonidamine solubility was improved with all tested cyclodextrins and specifically with PM-β-CD (1148 mg/L) where the solubility increased by 380-fold compare to its solubility in water (3 mg/L) leading to a fast dissolution rate of the latter in less than 3 min. In addition, the in-vitro cytotoxicity studies showed a modest increase in the cytotoxicity of lonidamine complex with CD against the human glioblastoma cell line SNB-19. Cyclodextrins could be useful to improve the solubility of lonidamine and hence its bioavailability, which is a drug of interest in the cancer treatment.

Aluminum polymers formed following alum treatment of lake water

Alum (aluminum sulfate) is increasingly being used in lake management to control internal recycling of phosphorus from bottom sediments. Alum added to water undergoes rapid hydrolysis reactions, forming an amorphous Al(OH) 3 floc with a high capacity for sorption of phosphorus. While it is known that the Al(OH) 3 floc transforms over time to more ordered microcrystalline and crystalline gibbsite phases, there remains an incomplete understanding of the forms of Al present immediately following alum addition to lake water. A laboratory study was thus undertaken to evaluate the forms of Al present following alum addition using ferron (8-hydroxy-7-iodo-5-quinolinesulfonic acid) timed-colorimetric and 27Al-NMR measurements. A polymeric Al species with moderate reactivity with ferron (Al b2) was initially formed, although it rapidly transformed to a less ferron-reactive colloidal form (Al c) and also decomposed at low alum doses to monomeric Al (Al a) in response to pH increases associated with outgassing of CO 2. The Al a fraction in these solutions could be adequately estimated based upon measured pH assuming Al solubility was controlled by an amorphous Al(OH) 3 phase. Al 13 was inferred from ferron measurements to be present, but only at quite low concentrations in the alum-treated waters.

Relationship between Aluminum and Lithium and Annealing for Reducing Lithium Contamination in Aluminum-Implanted Zinc Oxide

The relationship between Al and Li during diffusion was studied using Al-implanted ZnO. The Al donor in ZnO acts to increase the concentration of Li contamination from the atmosphere during the annealing. It is difficult to decompose the relationship formed by diffusion between Al and Li during high-temperature annealing. The most effective method to decompose the relationship is to anneal the as-implanted ZnO at a pressure of 5×10-3 torr. This annealing increases the Al solubility limit because the ZnO surface evaporates.

Friction stir processing of thixoformed AZ91D magnesium alloy and fabrication of Al-rich surface

The microstructural evolution characteristics of thermo-mechanically affected zone were investigated during friction stir processing (FSP) of the thixoformed AZ91D alloy. Simultaneously, an Al-rich surface layer was prepared by combination of Al powder using FSP method. The results indicate that the dynamic recrystallization and mechanical separation (including splitting and fracture of the primary grains) are the main mechanisms of grain refinement. For the thixoformed alloy, the operation efficiency of these mechanisms is less than that of the permanent mould casting AZ91D alloy, thus its microstructural evolution is relatively slow and the resulting grain size is relatively large. These are attributed to the differences in their original microstructures. The Al-rich surface layer can obviously improve the corrosion resistance in NaCl aqueous solution. A proper solution heat treatment (at 415 °C for 1 h) can further increase the corrosion resistance. In order to improve corrosion resistance, increasing the amount and improving the distribution uniformity of the Al-rich phase are more effective than increasing the Al solubility in the matrix.

Study of the role of Al, Cr and Ti additions in the microstructure of Nb–18Si–5Hf base alloys

The effects of Cr, Al and Ti on the microstructure and hardness of as cast and heat treated Nb–18Si–5Hf–5Cr (YG1), Nb–18Si–5Hf–5Al (YG2) and Nb–18Si–5Hf–24Ti (YG3) alloys were studied. The phases present in the as cast alloys were the Nb ss, Nb 3Si, Nb 5Si 3 and HfO 2 in YG1-AC, the Nb ss, Nb 5Si 3 and HfO 2 in YG2-AC and the Nb ss, Nb 3Si and Nb 5Si 3 in YG3-AC. In the YG1 the formation of Nb 3Si was sensitive to cooling rate, in the YG3 the volume fraction of Nb 5Si 3 was low and in the YG3 and YG1 Ti and Hf rich areas were formed respectively in the Nb ss and Nb 5Si 3. The phases present in the heat treated alloys were the Nb ss, Nb 5Si 3 and HfO 2 in YG1-HT and YG2-HT and the Nb ss, Nb 5Si 3 (including the hexagonal γNb 5Si 3), Nb 3Si and HfO 2 in YG3-HT. Nb 2N and TiN formed near the surfaces of YG1-HT and YG3-HT. Compared to YG1, in the microstructure of YG2 (i) there was a significantly higher volume fraction of a thermally stable lamellar Nb ss and Nb 5Si 3 microstructure and (ii) a lower volume fraction of Nb ss. In YG1 the eutectoid transformation of Nb 3Si was enhanced and the solubility of Si in Nb ss was reduced significantly. In the Nb ss a reduction in the Hf solubility led respectively to increase and decrease in the Cr and Al solubility in YG1 and YG2. In YG3 the synergy of Hf and Ti stabilised the 5–3 silicide and the transformation Nb 3Si → Nb ss + αNb 5Si 3 (tI32) was replaced by an alternate eutectoid transformation in which the 5–3 silicide had the hexagonal (hP16) structure. In YG3-HT the consumption of Ti to ≤12 at% to form TiN near the surface led to the formation of a heavily contaminated fine lamellar structure via the eutectoid decomposition (Nb,Ti) 3Si → (Nb,Ti) ss + (Nb,Ti) 5Si 3. The hardness of Nb 5Si 3 was reduced as the solubilities of Hf and Al in the silicide increased.

Microstructure and electrical properties of aluminium-substituted La(Sr)Ga(Mg)O3–δ-based solid electrolytes

A study of the influence of the substitution of Al for Ga in the ceramic processing and electrical properties of La0.95Sr0.05Ga0.90–x Al x Mg0.10O3–δ (0 ≤ x ≤ 0.3) solid electrolytes is presented. The materials retained orthorhombic symmetry over the entire substitution range, whereas a deviation from Vegard’s law for x > 0.20 suggested a maximum Al solubility of x = 0.20. Scanning electron microscopy analysis of ceramic samples revealed that grain growth was inhibited for x ≥ 0.2. This microstructural change was related to an apparent deterioration of mechanical properties, as suggested by room-temperature Vickers hardness measurements. Impedance spectroscopy revealed a significant degradation of the grain-boundary electrical properties for x ≥ 0.20, whereas the bulk conductivity was enhanced for 0.10 ≤ x ≤ 0.15. Oxygen-permeability measurements confirmed that the studied materials remain essentially pure ionic conductors. An ionic conductivity maximum of 0.047 S/cm at 700 °C was obtained for x = 0.10. The effect of aluminium in the grain-bulk ionic conductivity is discussed in terms of defect cluster models and assuming fast oxygen diffusion along domain walls.

Al-doped ZnO powdered materials: Al solubility limit and IR absorption properties

Al-doped ZnO powder was synthesized via the Pechini route with a doping rate varying from 1 to 4 mol.%. A solubility limit has been estimated under 0.3 mol.% of Al using X-ray diffraction refinements. The incorporation of aluminium into the ZnO lattice was investigated by 27Al NMR, which suggests an extremely low amount of Al in a distribution of sites in ZnO. In order to assess the impact of such a low dopant amount, diffuse reflection experiments were performed for a wavelength range from 200 to 2500 nm. If the effect of doping was negligible for samples prepared at 850 °C, annealing at 1200 °C clearly reveals enhanced IR absorption properties for the doped samples, which are similar whatever be the nominal Al content.

Organic acid exudation by mycorrhizal Andropogon virginicus L. (broomsedge) roots in response to aluminum

Elevated aluminum (Al) availability limits plant growth on acidic soils. Although this element is found naturally in soils, acidic conditions create an environment where Al solubility increases and toxic forms of Al impact plant function. Plant resistance to Al is often attributed to organic acid exudation from plant roots and the chelation of cationic Al in the rhizosphere. The association of arbuscular mycorrhizal (AM) fungi with the roots of plants may alleviate Al toxicity by altering soil Al availability or plant exposure through the binding of Al to fungal structures or through the influence of fungi on exudation from roots. Diverse communities of AM fungi are found in soil ecosystems and research suggests that AM fungi exhibit functional diversity that may influence plant performance under varying edaphic environments. In the present study, we evaluated acidic isolates of six AM species in their responses to Al. Andropogon virginicus (broomsedge), a warm-season grass that commonly grows in a range of stressful environments including acidic soils, was used as a plant host for Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, and Scutellospora heterogama. Fungal spores were germinated and exposed to 0 or 100 μM Al on filter paper in sand culture or were grown and exposed to Al in sand culture in association with A. virginicus. Short- and long-term responses to Al were evaluated using direct measurements of fungal spore germination, hyphal elongation, and measurements of A. virginicus colonization and plant growth as a phytometer of AM function in symbio. Spore germination and hyphal elongation varied among AM species in response to Al, but patterns were not consistent with the influences of these AM species on A. virginicus under Al exposure. Exposure to Al did not influence colonization of roots, although large differences existed in colonization among fungal species. Plants colonized by G. clarum and S. heterogama exhibited the least reduction in growth when exposed to Al, produced the highest concentrations of Al-chelating organic acids, and had the lowest concentrations of free Al in their root zones. This pattern provides evidence that variation among AM fungi in Al resistance conferred to their plant hosts is associated with the exudation of Al-binding organic acids from roots and highlights the role that AM fungal diversity may play in plant performance in acidic soil environments.

The effect of β-cyclodextrin on the solubility and dissolution rate of meloxicam and investigation of the driving force for complexation using molecular modeling

The aim of this study was to investigate the effect of β-cyclodextrin (β-CD) on the solubility and dissolution rate of meloxicam. The methods that were employed to prepare meloxicam–β-cyclodextrin complexes were physical mixture, kneaded dispersion, and spray drying. Spray drying method was found to be the best to form a true inclusion complex. Complexes were characterized by thermal analysis, X-ray diffractometry (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The apparent stability constant of the complex, Kc, calculated from the slope and intercept of the AL solubility diagram was found to be 429.73, 259.96, 183.31, and 36.50 L mol−1 at pH 2, 3, 6.5, and 10.3, respectively. The dissolution rate of meloxicam from the complexes was higher than from meloxicam alone. Molecular modeling was also used to investigate the interaction between meloxicam and β-CD. The dominant driving force for the complexation was evidently Van der Waals force with very little electrostatic contribution.

Surface chemistry and reactivity of plant phytoliths in aqueous solutions

In order to better understand the reactivity of plant phytoliths in soil solutions, we determined the solubility, surface properties (electrophoretic mobilities and surface charge) and dissolution kinetics of phytoliths extracted from fresh biomass of representative plant species (larch tree and elm, horsetail, fern, and four grasses) containing significant amount of biogenic silica. The solubility product of larch, horsetail, elm and fern phytoliths is close to that of amorphous silica and soil bamboo phytoliths. Electrophoretic measurements yield isoelectric point pH IEP = 0.9, 1.1, 2.0 and 2.2 for four grasses, elm, larch and horsetail phytoliths respectively, which is very close to that of quartz or amorphous silica. Surface acid–base titrations allowed generation of a 2-pK surface complexation model (SCM) for larch, elm and horsetail phytoliths. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 1 ≤ pH ≤ 8, were found to be very similar among the species, and close to those of soil bamboo phytoliths. Mechanistic treatment of all plant phytoliths dissolution rates provided three-parameters equation sufficient to describe phytoliths reactivity in aqueous solutions: R ( mol / cm 2 / s ) = 6 ⋅ 10 − 16 ⋅ a H+ + 5.0 ⋅ 10 − 18 + 3.5 ⋅ 10 − 13 ⋅ a OH − 0.33 Alternatively, the dissolution rate dependence on pH can be modeled within the concept of surface coordination theory assuming the rate proportional to concentration of > SiOH 2 +, > SiOH 0 and > SiO − species. In the range of Al concentration from 20 to 5000 ppm in the phytoliths, we have not observed any correlation between their Al content and solubility, surface acid–base properties and dissolution kinetics. It follows from the results of this study that phytoliths dissolution rates exhibit a minimum at pH ∼ 3. Mass-normalized dissolution rates are similar among all four types of plant species studied and these rates are an order of magnitude higher than those of typical soil clay minerals. The minimal half life time of larch and horsetail phytoliths in the interstitial soil solution ranges from 10–12 years at pH = 2–3 to < 1 year at pH above 6, comparable with mean residence time of phytoliths in soil from natural observations.

The solubility and deposition of aerosol Fe and other trace elements in the North Atlantic Ocean: Observations from the A16N CLIVAR/CO 2 repeat hydrography section

Aerosol and precipitation sampling as part of the 2003 Climate Variability and Predictability (CLIVAR)-CO 2 Repeat Hydrography trace element sampling program has produced an aerosol chemistry dataset for a region of the central Atlantic Ocean between 65°N and 5°S. This dataset includes analyses of aerosol particle chemistry as well as Fe and Al solubility (measured using a rapid, flow-through leaching technique). Several factors thought to influence aerosol Fe solubility including chemical weathering and aerosol source are evaluated as well. Air mass back-trajectories were used to characterize the atmospheric regime of each aerosol sample. Aerosol concentrations varied greatly with the highest concentrations observed between 23°N and 8.7°N. Aerosol Fe solubility was 9% ± 5% in seawater and 15% ± 8% in ultrapure deionized water. The concentration of soluble aerosol Fe in seawater was estimated with reasonable accuracy from the concentration of soluble aerosol Fe in deionized water by the relationship logFe SW = (0.85 ± 0.039) logFe DI + log (1 ± 1.2), ( r 2 = 0.93).

Relationship between Aluminum in Soils and Soil Water in Mineral Horizons of a Range of Acid Forest Soils

Previous studies suggest that the solubility of Al in acid forest soils may be expressed as the log Al3+ activity = −n pH + log KH‐Al + log Alp/Cp concentration ratio, with Alp and Cp representing pyrophosphate‐extractable Al and C, respectively, and KH‐Al is the binding constant of Al to protonated complexation sites on soil organic matter (SOM). We show that a slightly modified model, in which Alp is replaced by Alorg (= Alp − KCl‐extractable Al), successfully describes the concentration of Al in A and B horizons of a wide range of acid forest soils (Typic Dystochrepts) developed in different parent materials from a large number of spruce [Picea abies (L.) Karst.] and mixed forest stands in southern Poland. Analysis of the data suggests a reaction stoichiometry of n = 1.27 and log KH‐Al = 1.98 with R2 = 0.76. Furthermore, statistical analysis of a large set of published data, in addition to our own data from the Polish soils, indicates that log[Alorg/Cp] is significantly correlated with soil pH measured in 1 mol L−1 KCl (pHKCl), suggesting that the Al binding to SOM is less at small pHKCl due to increased competition with H+: log[Alorg/Cp] = 0.82 pHKCl − 4.16 (R2 = 0.77, n = 276). Combining the two equations gives a simple Al solubility model for mineral horizons in acid forest soils: log Al = −1.27pH + 0.82pHKCl − 2.18 (R2 = 0.82, n = 127). In this equation, pHKCl relates to chemical soil properties, whereas the pH of soil water also depends on solution characteristics like ionic strength. The equation may be applied to acid forest soils having a soil solution pH in the range of 3.0 to 4.2. Such conditions are rather common in surface horizons (A, E, and upper B) of acid forest soils of the temperate and boreal zones.

The zinc-rich corner of the 450 °C isothermal section of the Zn–Al–Fe–Si quaternary system

The 450 °C isothermal section of the Zn–Al–Fe–Si quaternary system with Zn being fixed at 93 at.% has been studied experimentally by means of optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. Three Al–Fe–Si ternary phases, τ 1 , τ 23 and τ, have been found in this section and the Zn solubility in those three phases are 6.9, 8.3 and 5.9 at.%, respectively. FeSi was found to be in equilibrium with FeSi 2 , Si, η-Zn, τ 1 , ζ and τ. The Al solubility in the FeSi phase is 11.2 at.%, and that in the FeSi 2 phase is rather limited. The Zn–Al–Fe ternary phase T(Fe 8 Al 6 Zn 86 ) was found to be in equilibrium with η-Zn, Fe 2 Al 5 and τ 1 phase. Experimental findings indicated the possibility of three-phase equilibrium between FeSi, FeSi 2 and Si. The obtained isothermal section of Zn–Fe–Al–Si quaternary is compatible with the Zn–Al–Fe, Zn-Al-Si and Zn–Fe–Si ternary systems. Because of the lack of the precise Al–Fe–Si system phase relations at 450 °C, the checking of the consistency with this system needs more works.

Constraining oceanic dust deposition using surface ocean dissolved Al

We use measurements of ocean surface dissolved Al, a global Biogeochemical Elemental Cycling (BEC) ocean model, and the global Dust Entrainment and Deposition (DEAD) model to constrain dust deposition to the oceans. Our Al database contains all available measurements with best coverage in the Atlantic. Vertical profiles and seasonal data exist in limited regions. Observations show that surface dissolved Al is distributed similarly to the dust deposition predicted by DEAD and other models. There is an equatorial Atlantic Al maximum that decreases toward higher latitudes. There are high Al concentrations in the Mediterranean Sea and the Arabian Sea and low concentrations in the Pacific and the Southern Ocean. The ocean basins maintain more distinct Al profiles than Fe profiles in the upper ocean, consistent with a weaker biological influence on Al than Fe. The BEC‐predicted surface dissolved Al compares relatively well with observations. The Al distribution reflects the combined effects of Al input from dust and Al removal by particle scavenging and biological uptake by diatoms. Model‐observed biases suggest a southward shift of maximum dust deposition compared to current dust model predictions. DEAD appears to overestimate deposition north of 30°N in the Pacific and to underestimate deposition south of 30°N. Observed Al concentrations and the ocean model–predicted surface Al lifetime provide a semi‐independent method to estimate oceanic dust deposition. This technique indicates that DEAD may overestimate dust deposition to the north equatorial Atlantic but underestimate in other Atlantic regions, the Southern Ocean, and the Arabian Sea. However, spatial variations in aerosol Al solubility may also contribute to the model‐observation mismatch. Our results have implications for all dust‐borne ocean nutrients including Fe and demonstrate the potential of marine geochemical data to constrain atmospheric aerosol deposition fields.

PACl: A simulation of the change in Al concentration and Al solubility in RO

Polyaluminium chloride (coagulant) is a very complex compound. The change in the ratio HCO3/CO2 during coagulation cause a change in pH in the subsequent RO unit (because CO2 is not rejected by the RO membrane), and it was found that this change is constant for any given recovery, e.g. at 75% recovery, the pH change between the RO feed water and concentrate water is 0.6. The simulation of aluminium solubility and concentration along RO systems were performed assuming the presence of three aluminium species, Al137+, Al(OH)4−, Al(OH)2+. The simulation of aluminium solubility was performed at two temperatures, 20°C to represent the summer period and 5°C to represent the winter period. Results showed that for winter (5°C) an RO feed water pH of at least 7.2 and for warm weather (20°C), a feed water pH of at least 6.7 are required respectively, to avoid scaling of aluminium on the RO membranes.In conclusion, theoretical simulation of aluminium solubility and results of deposition factor showed that aluminium more than likely plays a role in fouling of the RO membranes and could be a reason for the frequent cleaning.

Trace elements in hydrothermal quartz: Relationships to cathodoluminescent textures and insights into vein formation

High-resolution electron microprobe maps show the distribution of Ti, Al, Ca, K, and Fe among quartz growth zones revealed by scanning electron microscope-cathodoluminescence (SEM-CL) from 12 hydrothermal ore deposits formed between ~100 and ~750 °C. The maps clearly show the relationships between trace elements and CL intensity in quartz. Among all samples, no single trace element consistently correlates with variations in CL intensity. However in vein quartz from five porphyry-Cu (Mo-Au) deposits, CL intensity always correlates positively with Ti concentrations, suggesting that Ti is a CL activator in quartz formed at >400 °C. Ti concentrations in most rutile-bearing vein quartz from porphyry copper deposits indicate reasonable formation temperatures of <750 °C using the TitaniQ geothermometer. Titanium concentrations of <10 ppm in all veins that formed at temperatures <350 °C suggest a broad correlation between Ti concentrations and temperature of quartz precipitation. In quartz from most deposits formed at 2000 ppm, but in high-temperature quartz, Al concentrations are consistently in the range of several hundred ppm. Aluminum concentrations in quartz reflect the Al solubility in hydrothermal fluids, which is strongly dependent on pH. Aluminum concentrations in quartz therefore reflect fluctuations in pH that may drive metal-sulfide precipitation in hydrothermal systems.

Factors controlling soil water and stream water aluminum concentrations after a clearcut in a forested watershed with calcium-poor soils

The 24 ha Dry Creek watershed in the Catskill Mountains of southeastern New York State USA was clearcut during the winter of 1996–1997. The interactions among acidity, nitrate (NO 3 − ), aluminum (Al), and calcium (Ca2+) in streamwater, soil water, and groundwater were evaluated to determine how they affected the speciation, solubility, and concentrations of Al after the harvest. Watershed soils were characterized by low base saturation, high exchangeable Al concentrations, and low exchangeable base cation concentrations prior to the harvest. Mean streamwater NO 3 − concentration was about 20 μmol l−1 for the 3 years before the harvest, increased sharply after the harvest, and peaked at 1,309 μmol l−1 about 5 months after the harvest. Nitrate and inorganic monomeric aluminum (Alim) export increased by 4−fold during the first year after the harvest. Alim mobilization is of concern because it is toxic to some fish species and can inhibit the uptake of Ca2+ by tree roots. Organic complexation appeared to control Al solubility in the O horizon while ion exchange and possibly equilibrium with imogolite appeared to control Al solubility in the B horizon. Alim and NO 3 − concentrations were strongly correlated in B-horizon soil water after the clearcut (r 2 = 0.96), especially at NO 3 − concentrations greater than 100 μmol l−1. Groundwater entering the stream from perennial springs contained high concentrations of base cations and low concentrations of NO 3 − which mixed with acidic, high Alim soil water and decreased the concentration of Alim in streamwater after the harvest. Five years after the harvest soil water NO 3 − concentrations had dropped below preharvest levels as the demand for nitrogen by regenerating vegetation increased, but groundwater NO 3 − concentrations remained elevated because groundwater has a longer residence time. As a result streamwater NO 3 − concentrations had not fallen below preharvest levels, even during the growing season, 5 years after the harvest because of the contribution of groundwater to the stream. Streamwater NO 3 − and Alim concentrations increased more than reported in previous forest harvesting studies and the recovery was slower likely because the watershed has experienced several decades of acid deposition that has depleted initially base-poor soils of exchangeable base cations and caused long-term acidification of the soil.