Low Aluminum Content Research Articles

Differential behaviours in two species of Eucalyptus exposed to aluminium

One of the limiting factors in the growth and development of plants is soil acidity due to high aluminium (Al) content. The aim of this research was to determine the micronutrient contents, photosynthetic pigments, gas exchange and morphological parameters, and to explain the possible tolerance mechanisms involved in two species of the genus Eucalyptus that were exposed to low and high aluminium concentrations. The experiment was conducted in a factorial completely randomised design, with two aluminium concentrations, viz., 0.08 (low) and 1.60 (high) mM Al, and two species, i.e., Eucalyptus platyphylla and Eucalyptus grandis. High Al concentration increased the Al contents in E. platyphylla and E. grandis by 104 and 29%, respectively. Significant reductions of Fe, Zn and Mn contents were detected only in E. platyphylla. Reductions on chlorophyll b and total chlorophyll were observed in both the species, which were more intense in the E. platyphylla. Net photosynthetic rate and water use efficiency increased under high Al concentration, whereas stomatal conductance and transpiration rate decreased in E. grandis. Growth characteristics decreased under high Al concentration in E. platyphylla and increased in E. grandis, while opposite response was observed in both species under low Al concentration. Our results described clearly that E. platyphylla is sensitive, while E. grandis is tolerant to Al. The tolerance mechanism of E. grandis can be explained by the maintenance of the iron, zinc and manganese supplies, combined with an increase in the chlorophyll a, net photosynthetic rate and water use efficiency, resulting in the mitigation of the Al effects on growth parameters.

Effect of Slag Composition on the Oxidation Kinetics of Alloying Elements during Electroslag Remelting of Stainless Steel: Part-2 Control of Titanium and Aluminum Content

Kinetics of slag/metal reaction were investigated experimentally using 50 kg electroslag remelting (ESR) furnace in order to clarify the effect of slag containing different CaO and TiO2 content on titanium, aluminum and silicon content during the ESR process with 1Cr21Ni5Ti stainless steel. The results obtained show that the more CaO content in slag is, the more aluminum content in ingots increases. The lg([Al]4/[Ti]3) increases with the increase of slag temperature in the first 13 minutes during the ESR process, and after the slag temperature tends to be stable, the lg([Al]4/[Ti]3) decreases with the increase of TiO2 content in the rest process. The penetration and film theories were employed to analyze the rate determining step of slag/metal reaction, and it was found that the rate determining step of the reaction was the mass transfer of aluminum through the molten steel, silica through the slag and titanium on both of the metal and slag sides. The slag containing low CaO content combined with extra titania constantly added into molten slag in the first temperature-rising period is suitable for electroslag remelting of 1Cr21Ni5Ti stainless steel with high titanium and low aluminum content.

Association between H3K4me3/BDNF and the cognitive function of workers occupationally exposed to aluminum

Objective: To investigate the influence of occupational aluminum exposure on cognitive function and its relationship with tri-methyl histone H3 lysine residues 4 points (H3K4me3) and brain-derived neurotrophic factor (BDNF) levels. Methods: By cluster random sampling method, a total of 235 cases of male workers selected from a Shanxi aluminum factory were recruited in the study in September 2015. Used the occupational epidemiological investigation questionnaire, which included Mini-Mental State Examination (MMSE) , Clock Drawing Test (CDT) , Digit Span Test (DST, including forward test DSFT and backward test DSBT) , Fuild Object Memory Evaluation (FOME) and Verbal Fluency Test (VFT) , to collect workers' basic information and assess their cognitive function score. Detected the concentration of aluminum in plasma by graphite furnace atomic absorption spectrometry. Workers were divided into three groups by the 25 percentile and 75 percentile of the aluminum content, such as low, middle and high aluminum concentration groups. The concentrations of H3K4me3 in lymphocyte and BDNF in plasma were determined by enzyme-linked immunosorbent assay. Results: The levels of aluminum in plasma was 134.36 (100.14, 178.96) μg/L. The scores of MMSE, DSFT, DSBT, DST of high aluminum concentration group were lower than low aluminum group (27.98±1.25 vs 28.83±1.54, 9.19±2.00 vs 10.64±2.87, 6.08±1.63 vs 7.19±3.07, 15.27±3.11 vs 17.81±4.72, all P<0.05) , the scores of CDT, FOME, VFT among three groups had no statistical significance (all P>0.05) . The expression levels of H3K4me3 and BDNF of high aluminum concentration group were lower than the low group [ (18.45±9.81) ng/μg Pro vs (23.76±9.89) ng/μg Pro, (26.07±10.18) ng/ml vs (31.66±9.24) ng/ml, all P<0.05]. Multiple correlation analysis showed that aluminum concentration were negatively correlated toH3K4me3, BDNF, MMSE, DSFT, DST, respectively (r(s)=-0.307、-0.214、-0.252、-0.197, -0.181, all P<0.01) . Conclusion: Exposure to occupational aluminum for a long time may change cognitive function, which go along with the decreasing of H3K4me3 level in lymphocyte and BDNF protein expression in plasma.

Comparison of the sliding wear of a novel Zn alloy with that of two commercial Zn alloys against bearing steel and leaded brass

Zinc alloys are known for their low melting point, high castability, and useful wear resistance in certain applications, and at a relatively low cost. In the recent years, many attempts have been made to substitute more expensive copper alloys for zinc-based materials in wear-critical parts. In this regard, the most investigated zinc alloy is ZA27, but good wear resistance can be also achieved by using an alloy with lower aluminium content, like Zamak2. In this paper, the sliding wear behavior of a novel zinc alloy ZnAl15Cu1 was compared to that of ZA27 and Zamak2 in order to assess its relative suitability for applications where sliding wear resistance is required. Pin-on-disk tests were carried out using both bearing steel and a leaded brass sliding partners under three loads and various sliding distances. Friction coefficient and wear rates were compared. Analyses of the worn surfaces was done to identify the damage mechanisms and to understand the friction coefficient behaviour. The ZnAl15Cu1 alloy exhibited wear resistance that is comparable to or better than that for ZA27 and Zamak2.

Preparation and Test of Conventional Composite Abrasives Using Recycled Alumina Grains

In this work we report the preparation and evaluation of the mechanical characteristics of resin-bond composite abrasives using virgin and recycled alumina grains. The composite abrasives were made with phenolic resin as binder and as-received virgin and recycled alumina grains. Three different recycled alumina grains were studied: i) alumina from wood firing resin-bond abrasive tools; ii) alumina from wood firing vitrified-matrix abrasive tools; and iii) ground alumina from vitrified-matrix abrasive tools. The virgin alumina grains were employed in order to compare the mechanical performance of the prepared composite abrasive. The composition of alumina grains, analyzed by X-ray fluorescence spectroscopy revealed the recycled alumina grains have lower alumina content and higher concentration of silica in vitrified-matrix abrasives samples. The sand blast penetration tests have shown lower penetration depth in the virgin and the ground vitrified-matrix grains composites. The impact strength test results revealed its dependence on the alumina and silica content: samples with higher alumina content present the higher impact resistance whereas samples with higher silica content present lower impact strength.

Genesis, maturity and weathering of some Upper Cretaceous Egyptian glauconites: Mineralogical and geochemical implications

Mineralogical and geochemical studies were carried out on Upper Cretaceous (Cenomanian – Maastrichtian) glauconites from Egypt by means of polarizing microscope, XRD, SEM, microprobe and XRF techniques. Most of the investigated glauconite grains display zoning-like appearance. X-ray diffraction analyses reveal the presence of glauconite, quartz, dolomite, jarosite, goethite and glauconite (illite)-smectite mixed layer minerals. SEM and microprobe investigations revealed that jarosite is present as a weathering product of pyrite especially in Abu Tartur and Wadi Feiran areas. However, goethite was encountered as oxidation product of both pyrite and glauconite. The microprobe analyses of the glauconite grains reflect clearly their low Alumina (<10%) content at the different localities; suggesting therefore their development at depths from 50 m downwards. The Cenomanian glauconites of Wadi Feiran, Saint Paul and Gabal Dist show slight enrichment in K2O content relative to the Campanian – Maastrichtian glauconite of Abu Tartur, indicating more mineralogical maturity.The microprobe analyses also reflect the loss of K and Fe from the glauconite grains. Fe and K can be contributed to aqueous solution media during weathering, leaving aluminous clay minerals in the soil. As result, argillaceous glauconite (illite)-smectite mixed layer, in some cases, is found associating the green pellets of glauconite in many of the investigated samples; most probably produced by weathering of the glauconite grains.Regarding glauconites, Wadi Feiran bulk samples are enriched in TiO2, Al2O3, MgO, Zr, Ce and La, whereas those of Saint Paul exhibit richness in Y and Rb. Gabal Dist samples display appreciable content of Fe2O3(t), K2O, Pb, Zn, Ni, Co, Sc and V whereas the P2O5 and SO3 show their abundance patterns at Abu Tartur locality. These fluctuations could be attributed to their differences in the mineralogical content (pyrite, goethite, and jarosite).The strong correlation between TiO2/Al2O3 and Zr/Al2O3 ratios may reflects mixed origin or reworking of sedimentary rocks from the continental hinterland in all the studied areas.The values of trace elements indices, such as Ni/Co, V/Cr and V/(V + Ni), suggest oxic to suboxic environments. However, some of the chalcophile elements (Pb, Zn, Ni, Co, Cu, Fe and Ga), which are correlated with pyrite and its alteration product (goethite), occur with relatively high concentrations in some studied glauconite beds reflecting reducing and/or suboxic conditions during the precipitation of these beds.

Aluminum Content of Neonatal Parenteral Nutrition Solutions: Options for Reducing Aluminum Exposure.

Calcium chloride (CaCl2 ) has been the only calcium additive available in the United States that has a low aluminum (Al) content. Calcium gluconate in glass vials (CaGluc-Gl) has a high Al content while calcium gluconate in plastic vials (CaGluc-Pl) has a low Al content. The purpose of this study was to measure Al concentrations in neonatal parenteral nutrition (PN) solutions prepared using various calcium additives. Samples of solutions compounded with CaCl2 or CaGluc-Gl and sodium phosphate (NaPhos) as well as CaGluc-Pl and sodium glycerophosphate (NaGP) with and without cysteine were analyzed for Al content. Samples of the cysteine and calcium gluconate additives were also sent for analysis. Solutions containing CaCl2 and CaGlu-Pl had mean Al concentrations of 1.2-2.3 mcg/dL, while those with CaGlu-Gl had mean concentrations of 14.6-15.1 mcg/dL. Solutions made with NaGP were low in Al content. The measured Al content of 2 lots of the cysteine additive were 168 ± 23 mcg/L and 126 ± 5 mcg/L. The Al concentration equalled 2730 ± 20 mcg/L for the CaGlu-Gl additive and 310 ± 80 mcg/L for the CaGlu-Pl additive. The study indicates that solutions containing CaCl2 or CaGluc-Pl and NaPhos or NaGP are low in Al content. Using these options for calcium and phosphate additives can limit aluminum intake from neonatal PN to levels within the Food and Drug Administration guideline of ≤5 mcg/kg/d.

The influence of low aluminum concentrations on the composition and conditions of crystallization of majorite–knorringite garnets: Experiment at 7.0 GPa and 1500–1700°C

Crystallization of garnet in high-chromium restite formed under the conditions of partial melting in the spinel facies and subsequently subducted into the garnet depth facies was studied experimentally in the MgO–Al2O3–Cr2O3–SiO2 system. The crystallization of garnet and the dependence of its composition on the temperature and bulk composition of the system with low Al concentration were studied as well. Experiments in the knorringite–majorite–pyrope system with 5, 10, and 20 mol % Prp were carried out at 7 GPa. The phase associations for the starting composition of pure knorringite Mg3Cr2Si3O12 included chromiumbearing enstatite MgSiO3 (up to 3.2 wt % Cr2O3) and eskolaite Cr2O3. Addition of Al resulted in crystallization of high-chromium majoritic garnet. The portion of garnet in the samples always exceeded the concentration of pyrope in the starting composition owing to the formation of the complex majorite–knorringite–pyrope series of solid solutions. With increasing content of pyrope (from 5 to 20 mol %) and increasing temperature, the modal concentration of garnet increased significantly (from 6–12 to 22–37%). The garnet was characterized by high concentrations of the pyrope (23–80 mol %) and knorringite (22–70 mol %) components. The excess of Si (>3 f.u.) with decreasing Cr concentration provided evidence for the contribution of the majorite–knorringite trend to the variation in garnet composition. On the basis of the natural data, most of the garnets composing xenoliths of ultrabasic rocks in kimberlites and occurring as inclusions in diamonds are low-chromium; i.e., their protolith was not subjected to partial melting, at least in the spinel depth facies.

Dependence of the mechanical characteristics of fast-quenched amorphous Zr–Cu–Al alloys on their composition

The thermal and mechanical characteristics of fast-quenched amorphous Zr–Cu–Al alloys with various concentrations of copper and aluminum are studied. It is shown that the crystallization temperature of glass-like compositions increases when copper is replaced with aluminum in concentrations of up to 10 at %, and that the hardness, Young’s modulus, and fracture stress increase only at low concentrations of aluminum (no more than 6 at %). Upon a further increase in the concentration of the alloying element, fracture stress σf decreases because σf the change in the fracture mechanism, despite high hardness and Young’s modulus.

The origin of terrestrial pisoliths and pisolitic iron ore deposits: Raindrops and sheetwash in a semi-arid environment

Ooliths evidently form by chemical precipitation in limnic, paralic, fluvial and marine environments, pisoliths, however, appear to be restricted to terrestrial environments. Typically composed of iron, aluminium and manganese sesquioxides with minor admixtures of quartz and kaolinite, they are widely distributed in tropical to subtropical regions overlying deeply weathered soil profiles. Although iron-, aluminium- and manganese-rich end members are important sources of these metals, their genesis is still enigmatic; their formation has never been observed or produced experimentally and current models for their origin are little more than guesses.A new model is presented based on a unique personal observation in which pisoliths are formed by the action of charged raindrops during thunderstorms impacting on dry deeply weathered powdery soils. The pisoliths are transported across pediments by sheetwash, accumulating as thick deposits in the valley floors. Pisolites are characteristically unfossiliferous and typically clearly pedogenic. The absence of fine depositional layering, fossil seeds, leaves and pollen in pisolites is explained by bioturbation and the action of soil organisms during extended pedogenesis while the major coarse bedding features derive from erosional and depositional events in the evolution of the pediment.Pisolitic iron ores (aka channel iron deposits, CID) are a special case of transported pisolitic ferricrust that form an important resource of medium grade iron ore (57–60wt% Fe) in the Pilbara Region of Western Australia. Apart from minor deposits in the northern Yilgarn Province of Western Australia, they have not been found elsewhere. They differ from normal transported ferricrust and terrestrial pisolites not only in the exceptionally high iron and low alumina and silica content but also in containing abundant fossilised wood particles.

Temperature-Dependent Operation of GaAs Quantum Nanodisk LEDs with Asymmetric AlGaAs Barriers

Quantum dot photonic devices such as light-emitting diodes (LEDs), laser diodes (LDs), high-speed modulators, and semiconductor optical amplifiers are attractive because of their small threshold voltages, low power consumption, and temperature stability. We have studied and developed a defect-less top–down dry fabrication process for GaAs quantum nanodisk (QND) LEDs with diameters of less than 20 nm and thicknesses of 8 nm by employing a bionanotemplate, neutral beam etching, and asymmetric AlGaAs/GaAs regrowth via metalorganic vapor phase epitaxy. AlxGa1-xAs barriers with high (Al0.3Ga0.7As) and low (Al0.17Ga 0.83As) aluminum contents were used between QNDs in the in-plane and vertical directions, respectively. This permits the control of the deep band energy offset between GaAs QNDs and AlxGa1-xAs barriers, leading to stable room-temperature operation. The temperature dependence of the optical properties of the QND LED was measured by electroluminescence, and we found that the energies and their transient behaviors were strongly affected by the band offset energies between the QNDs and the aluminum-rich barriers. Therefore, we could enhance the optical performances of our symmetric QND LED with low-Al-content barriers by developing asymmetric AlxGa1-x As barriers with low-Al-content vertical barriers and high-Al-content in-plane barriers.

Influence of calcium to silica ratio on aluminium uptake in calcium silicate hydrate

Aluminium uptake in calcium silicate hydrate (C–S–H) was studied at different Ca/Si ratios from 0.6 to 1.6 at 20°C.Aluminium incorporation in C–S–H depends on the total amount of aluminium present in the sample. At low Al/Si ratio (≤0.05), the major part of the aluminium is taken up in C–S–H while at higher Al/Si ratio, the precipitation of stratlingite and/or katoite limits the Al/Si ratio in C–S–H to ≈0.15, regardless of the Ca/Si ratio.A strong correlation between the aqueous aluminium concentration and the aluminium uptake in the solid phase is observed. At high Ca/Si ratios, aluminium in C–S–H is observed mainly as octahedrally coordinated Al(VI) in TAH and the aluminium uptake increases with the aqueous aluminium concentration. At low Ca/Si ratio (≤0.8), aluminium is observed mainly as tetrahedrally coordinated Al(IV) and low aqueous aluminium concentrations (below detection limit) indicate a high affinity of aluminium towards C–S–H.

Field Assisted Sintering of Nanostructured Zirconia-Alumina Ceramics for Demanding Applications

ABSTRACTFlash and field assisted sintering techniques (FAST) have been demonstrated in many singular ceramic systems. However, little has been done to thoroughly investigate this phenomenon in binary systems. Zirconia-alumina composites are of interest because of their widespread use in demanding situations for health care, petrochemical and energy applications. The prospect of minimizing grain growth associated with FAST whilst achieving maximum densification is vital for the above applications to improve performance. Flash sintering behaviour of several zirconia-alumina formulations was investigated under a range of DC electric fields up to 700V.cm–1. At low alumina contents (<10 wt%) the flash behaviour was controlled by the zirconia phase; intermediate compositions (10-70 wt%) show a composite effect; and at high alumina contents (>75 wt%) the effectiveness of field assisted sintering drops off. These pointers allowed to gain further insight into the mechanisms of flash sintering and will help to develop pathways for the adaptation of the technique to process complex ceramic systems.

Thermodynamic design of electroslag remelting slag for high titanium and low aluminium stainless steel based on IMCT

The advantages of the electroslag remelting (ESR) process as to cleanness and homogeneity of the ingot structure are well known. As to homogeneity of composition, the control of titanium in stainless steel with high titanium and low aluminium contents during the ESR process has not been resolved well so far. The current work focuses on designing appropriate slag for controlling titanium content during 1Cr21Ni5Ti remelting based on the interaction of the slag/metal interface. Several kinds of slag containing different CaO contents combined with steel samples of 1Cr21Ni5Ti were employed to investigate the effect of slag on titanium content in an electrical resistance furnace, and metal samples were taken at different times for investigating the change of titanium and aluminium contents in steel. The results show that slag with low CaO content at low temperature has excellent capacity for avoiding loss of titanium content caused by its reaction with the alumina in slag, especially in case of remelting of stainless steel with high titanium and low aluminium contents. The CaO in slag has great effect on the activities of TiO2 and Al2O3, and thermodynamic analysis was applied to investigate the CaO behaviour based on the ion and molecule coexistence theory of slag. The thermodynamic analysis results show that the increases as CaO content in slag decreases, which is better for preventing loss of titanium caused by its reaction with the alumina in the ESR slag. The slag with low CaO content at low temperature is suitable for ESR of 1Cr21Ni5Ti.

Genesis and Classification of Soils Containing Carbonates in a Toposequence of the Bambuí Group

The Bambui Group, formed from siliciclastic sediments deposited on an extensive epicontinental platform at the end of the Neoproterozoic era, is characterized by limestones with fine to very fine texture. Limestone-derived soils in the southeast of Tocantins state, Brazil, are less notorious than similar soils in other regions of Brazil and their characterization could contribute to the Brazilian System for Soil Classification (SiBCS). Given that little is known of these soils, despitetheir agricultural potential, the objective of this study was to characterize their properties and the processes leading to soil of genesis, and also contribute to developing the Brazilian System of Soil Classification (SiBCS). Soils profiles were located on the summit (P1), shoulder (P2), backslope (P3), and footslope (P4) of a toposequence in the municipality of Lavandeira, Tocantins. Morphological, physical, chemical, and mineralogical properties of the profiles were determined. The soils were classified as: P1 - Chernossolo Rendzico Litico tipico (Lithic Haplustolls); P2 - Cambissolo Haplico Ta Eutrofico leptico hipocarbonatico (Lithic Haplustolls); P3 - Cambissolo Haplico Carbonatico leptico (Lithic Haplustepts); and P4 - Luvissolo Haplico Ortico tipico (Typic Rhodustalfs). All the profiles showed high contents of silt, calcium, and magnesium, which resulted in high pH and low exchangeable aluminum content. Base saturation and calcium carbonate equivalent contents were also high, and the horizons showed dark colors due to high organic matter content, which contained humin as the dominant fraction. Mineralogical analysis of the clay fraction indicated predominance of hydroxy-interlayered vermiculite, followed by illite, kaolinite, and quartz, whereas the sand fraction exhibited reflections characteristic of the quartz mineral. Given P4 contents of calcium carbonate equivalent above 50 g kg-1 and the relevance of this feature for agriculture, we propose the inclusion of hypocarbonate as a criterion for classification of Luvissolos Haplicos Orticos at the subgroup level.

Физическая химия и физика металлургических систем

Yttrium belongs to the same group as lanthanum, and its chemical properties are close to those of the latter. Therefore, yttrium is referred to as a rare earth metal. When added to a heavily deoxidized metal, yttrium refines a primary cast grain, reduces the area of treeing, purifies grain boundaries of non-ferrous inter-metallic compounds, reduces the size of non-metallic inclusions, and enhances heat resistance and high temperature strength of special steels. Optimal yttrium additive in the metal does not exceed 0.3 to 0.5 wt. %. Complex interaction of yttrium with oxygen in the presence of residual concentrations of aluminum, calcium and magnesium in the metal was not studied at all. Thermodynamic modelling of steel deoxidation using yttrium in the presence of low concentrations of aluminum, calcium or magnesium is developed. The surfaces of component solubility in liquid steel are created for Fe–Y–Al–O–C, Fe–Y–Ca–O–C, and Fe–Y–Mg–O–C systems. To make calculations related to oxide systems, all possible phase equilibria are established, coordination of equilibrium constants dependency on temperature is carried out, and energy parameters of the subregular ionic solution theory are specified. The surfaces of component solubility show that deoxidation by yttrium is a complex process due to the presence of calcium and aluminum in steel. Deoxidation products will contain complex phase compositions of oxides based on CaO, Al 2 O 3 , and Y 2 O 3 . In case of steel deoxidation by yttrium and magnesium, the process is performed alternately. Either yttrium or magnesium acts as a deoxidizer.

Recovery of Iron Values from Iron Ore Slimes of Donimalai Tailing Dam

During production of calibrated (sized) ore, more than 50 % of the generated fines and rejects (Slimes) cannot be directly utilised in iron making due to its unfavourable granulometry, low iron content, high alumina and silica content. Approximately 10–20 % of the process plant input is discarded as slimes into slime ponds/tailing dams. Tailing dams are now considered as a threat due to hazardous nature and acute shortage of land for storing. More over these slimes also pose threat to the environment. Recovery of iron values from slimes results in economic benefit by utilisation of waste as a resource and minimizes the land requirement, surface degradation, ground water pollution, destruction of forests. These slimes after beneficiation are agglomerated (Pelletisation) and can be used as burden for the blast furnace. This research work presents the route for beneficiation of slimes by removing gangue in the slimes to an acceptable level to produce hot metal through blast furnace route. Research has been carried out effectively and efficiently to utilise the iron ore slimes from the slime ponds of Donimalai iron ore mine. The slime sample from tailing pond of Donimalai iron ore mine was collected and transported to R&D Centre, NMDC Limited, Hyderabad. The ‘as received’ slime sample assayed 49.40 % Fe, 13.51 % SiO2, 8.44 % Al2O3, 5.16 % loss on ignition and all other trace elements were within the critical limits. The ‘as received’ sample contains around 7 % moisture. It has a bulk density of 1.74 t/m3 and specific gravity of 3.7. Screen assay analysis was carried out with the ‘as received’ sample. Optimisation studies were carried out for desliming by using hydro-cyclone. Hydro-cyclone underflow was subjected to magnetic separation. It is possible to produce a concentrate which assayed 65.93 % Fe, 1.45 % SiO2, 1.94 % Al2O3 and 1.56 % loss on ignition with a yield of 45.18 % with a recovery of 60 % iron values.

Mechanistic contribution of the interplay between microstructure and plastic deformation in hot-rolled Fe–11Mn–2/4Al–0.2C steel

We elucidate here the mechanistic contribution of the interplay between microstructural constituents and plastic deformation behavior in hot-rolled Fe–0.2C–11Mn–2Al (2Al steel) and Fe–0.2C–11Mn–4Al (4Al steel) transformation induced plasticity (TRIP) steels. The steel containing lower aluminum content (2wt%) was characterized by excellent combination of tensile elongation (TE) of 31.4%, ultimate tensile strength (UTS) of 1407MPa, and UTS×TE of 44.2GPa%, where the ultrahigh strength is attributed to the cumulative contribution of the newly transformed martensite with high microhardness and Portevin-Le Chatelier (PLC) effect. In contrast, the higher aluminum (4wt%) containing steel indicated lower UTS of <1200MPa, but higher TE of 34–40%, which resulted from the TRIP effect and the cooperative deformation of α-ferrite and δ-ferrite.

Reactive transport modeling of early diagenesis in a reservoir lake affected by acid mine drainage: Trace metals, lake overturn, benthic fluxes and remediation

The Sancho Reservoir in SW Spain has been impacted by acid mine drainage (AMD) since the Tharsis mine stopped activity in 1998. As a result, the reservoir exhibits low pH (~3.5) and high aqueous concentrations of sulfate, aluminum, iron and trace metals. Thus far, removal of contaminants by sediment burial has not been as effective as expected in improving water quality within the reservoir. To inform potential remediation strategies, a 1-D, non-steady-state reactive transport model with a comprehensive set of equilibrium and kinetic biogeochemical reactions is used to simulate the fate of trace metals and acidity in sediments affected by AMD. Two realizations of the model account for the spatial heterogeneity of bottom water oxygenation. A “permanently oxic” model represents shallow sediments above the thermocline, while a “holomictic” model represents the deeper sediments where bottom water oxygen levels oscillate between completely anoxic and oxic as a result of water-column overturn. The model is calibrated against an extensive dataset on the depth distributions of pore water and solid phase species. Model results imply that, under permanently oxic conditions, the sediments act as a sink for acidity (H+) and aqueous Al, Zn, Cu, Co and Ni, but act as a source of aqueous Mn, Fe and As. The latter are released to the overlying water as a result of Mn and Fe (oxy)hydroxide reductive dissolution in the sediments. Below the thermocline, when bottom waters become anoxic, metal sulfides precipitate in the sediment. When the bottom waters subsequently become oxic, the metal sulfides are oxidized along the downward-penetrating oxygen front and the associated metals are released to the overlying water. On the order of 35% of the sediment pools of sulfide-bound Zn, Cu, Co and Ni, and ~25% of FeS are thus reoxidized. However, overall the sediments act as a net sink for the pollutants considered in the model. On an annual basis, about 10% of the total elemental masses of S, Al, Zn and Cu present in the water column of the reservoir are removed by burial in the sediments, but only ~2% for Co and Ni. For Fe, Mn and As, the corresponding values are 80, 70 and 98% respectively. The model predicts that, if AMD input to the reservoir were to completely cease, the sediments would reach a new steady state with negligible release of aqueous contaminants to the overlying water column within a few years.

The influence of aluminum content on the surface morphology of heavily doped (Al)GaN mesastrip structures grown by selective metalorganic vapor phase epitaxy

Heavily Si-doped Al x Ga1–x N mesastrip structures were grown by selective MOVPE technology. Al x Ga1–x N:Si mesastructures with x ~ 0.01–0.07 possess a smoother top and more even side surfaces as compared to those in analogous GaN:Si structures. During the growth of mesastructures with x ~ 0.03–0.07, a thin nanocrystalline AlN deposit appears on the Si3N4 mask. This deposit is not formed during the growth of structures with sufficiently low aluminum content.