Growth Of Precipitates Research Articles

Impact of ionic composition of groundwater on oxidative iron precipitation

Abstract In the Netherlands, approximately 60% of drinking water is obtained from (generally anaerobic) groundwater. This requires aeration followed by rapid sand filtration (RSF) to remove iron, manganese, arsenic and ammonium. The mechanisms responsible for their removal or the clogging of RSFs and breakthrough of colloidal iron or manganese oxides have not been fully elucidated in previous studies. In this work, factors affecting iron precipitation have been studied in aerated, continuously stirred bench scale jar experiments to simulate the supernatant layer of submerged sand filters. Time series data of filtered iron concentration and precipitate size have been collected in experiments with synthetic groundwater with and without P, Si, HCO3 and Ca at neutral pH. We observed that precipitate growth is not influenced by different HCO3 concentrations but is reduced drastically when natural organic matter (NOM) is present in water and, to lesser extent, Si as well. The addition of P appears to hamper precipitate growth to some extent, but requires more research to fully understand the implications. We also observed that addition of Ca improved the growth of Fe precipitates in the presence of Si and especially NOM. These results have great significance for improving Fe removal efficiency of groundwater treatment plants in The Netherlands and abroad.

Effects of Zr on microstructural evolution and mechanical property of Cu-15Ni-8Sn alloy

The Cu-15Ni-8Sn-XZr (wt.%, X=0–0.7) alloys were prepared by vacuum melting, and their microstructural evolutions during the solidification and heat-treatment processes were systematically investigated as well as the corresponding mechanical properties. Zr addition could offer a significant effect on the dendritic morphology by controlling the constitutional supercooling in solidification front, and it also made the γ-phase more likely to form in the needlelike-shape rather than the lamellar-like shape in subsequent cooling process. After solution treatment, the Zr atoms with a low content of 0.1 wt% were completely solidly dissolved in the α-matrix. With its content increasing to 0.3 and 0.5 wt%, the existence form was changed into the nano-scale precipitation phase (Ni5Zr) and then to micron-scale segregation phase (Ni4SnZr). The presence of Zr could significantly extend the aging window of alloy and improve its mechanical properties by inhibiting the nucleation and growth of discontinuous precipitation (DP), and there was few DP even after 16 h aging. The optimal combination of properties was obtained for Cu-15Ni-8Sn-0.5Zr alloy aged at 673 K for 4–16 h, including a hardness of 330HB, ultimate tensile strength (UTS) of 980 MPa and electrical conductivity of 9%IACS.

Insight into the recrystallization behavior and precipitation reaction of in-situ nano TiB2/Al Cu Mg composite during heat treatment

In this study, the quantitative results from both electron backscattered diffraction and transmission electron microscope analyses provided the fundamental insight into the recrystallized behavior and precipitation reaction of the in-situ nano TiB2/AlCuMg composite during heat treatment. The difference of coefficient thermal expansion between TiB2 particles and Al matrix enabled the formation of deformation zone around TiB2 clusters during water quenching which promoted the recrystallized behavior. Besides, the strong pinning effect induced by TiB2 distributed at recrystallized grain boundary was also observed. As a result, the fine recrystallized grains were generally distributed around particle clusters. During artificial aging process, the trace Mg remarkably enhanced the kinetics of precipitation reaction in the composite. The coexistence of θ″ and θ' precipitates confirmed the continuous transformation of θ″ into θ' via the atomic Cu rearrangement. Herein, the θ'/Al interface acted as a heterogeneous nucleation site of the Al3Zr precipitate was able to improve the nucleation and growth rate of the precipitate. Moreover, the misfit dislocations at TiB2/Al interface with larger lattice mismatch were confirmed. The synergistic effect of stress field caused by misfit dislocations and geometrically necessary dislocations facilitated the pipe diffusion was responsible for transporting solute atoms under depleted vacancy and solute atoms around the interface, benefited to the nucleation and growth of precipitates.

Accelerated precipitation of the B2 particles and its effect on Al0.3CoCrFeNi high-entropy alloy by electric current assisted annealing

Precipitation of the B2 particles in Al0.3CoCrFeNi high-entropy alloy requires a considerably long time of the thermal exposure. Electric current has proved its capacity to accelerate atomic diffusion. We carried out electric current assisted annealing and proposed a finite precipitation growth model considering gradually reduced growth rate in this study. The proposed model reveals that current boosts precipitation growth by lowering its diffusion activation energy QD leading to the reduction of the required annealing time into 90 min. Owing to the combined contribution of the precipitation strengthening and twinning, the ultimate tensile strength increases from 781.3 to 870.2 MPa after annealing. The precipitated B2 particles also increase Vickers hardness of the sintered sample from 196.6 ± 4.7 to 227.2 ± 4.9 HV. As a consequence, its wear resistance enhances as the volumetric loss vs decreases from 2.392 × 10−1 to 1.897 × 10−1 mm3.

ПРИМЕНЕНИЕ ЭЛЕКТРОТЕХНОЛОГИЙ ДЛЯ ВОССТАНОВЛЕНИЯ ДЕТАЛЕЙ СЕЛЬСКОХОЗЯЙСТВЕННОЙ ТЕХНИКИ

The technology of non-galvanized ironing of parts in the electrolyte flow with simultaneous hydromechanical activation of the plated surface is proposed, its advantages over the traditional type of coating are shown. The technological process of coating hydraulic control valve spools has been developed. The technological process of restoring spools consists of the following operations: preliminary surface preparation (mechanical treatment), degreasing, washing, anodic treatment, electrodeposition and final mechanical treatment. The designs of the installation and the electrochemical cell for ironing hydraulic control valve spools, providing optimal hydrodynamic conditions when applying coatings on worn surfaces, are proposed. Optimal modes and composition of ironing electrolyte have been defined, providing a high rate of precipitation growth (1.5...3 mm/h), adhesion strength and wear resistance of coatings. Bench and field tests of hydraulic valves with restored spools were performed, which confirmed the results of laboratory studies and the high efficiency of the proposed technology.

Bioavailable Nutrients (N and P) and Precipitation Patterns Drive Cyanobacterial Blooms in Missisquoi Bay, Lake Champlain.

Anthropogenic activities release large amounts of nitrogen (N) and phosphorus (P) nutrients into the environment. Sources of nutrients include surface and sub-surface runoffs from agricultural practices with the application of chemical fertilizers and manure as well as combined sewer overflows (CSOs). Nutrient runoffs contribute to the eutrophication of aquatic ecosystems and enhance the growth of cyanobacteria. Precipitation is an important driving force behind the runoff of nutrients from agricultural fields into surrounding water bodies. To understand the dynamics between nutrient input, precipitation and cyanobacterial growth in Missisquoi Bay, Lake Champlain (Quebec), one location in Pike River (a major tributary into the bay) and four locations in Missisquoi Bay were monitored from April to November in 2017 and 2018. Biweekly water samples were analyzed using chemical methods and high-throughput sequencing of 16S rRNA gene amplicons. High concentrations of N and P were typically measured in April and May. Three major spikes in nutrient concentrations were observed in early and mid-summer as well as early fall, all of which were associated with intense cumulative precipitation events of 40 to 100 mm within 7 days prior to sampling. Despite the high concentrations of nutrients in the spring and early summer, the cyanobacterial blooms appeared in mid to late summer as the water temperature increased. Dolichospermum sp. was the major bloom-forming cyanobacterium during both summers. A second intense bloom event of Microcystis was also observed in the fall (October and November) for both years. Variation in the cyanobacteria population was strongly associated with inorganic and readily available fractions of N and P such as nitrites and nitrates (NOx), ammonia (NH3) and dissolved organic phosphorus (DOP). During blooms, total Kjeldahl nitrogen (TKN) and total particulate phosphorus (TPP) fractions had a substantial influence on total nitrogen (TN) and total phosphorus (TP) concentrations, respectively. The abundance of bacteria involved in the metabolism of nitrogen compared to that of phosphorus revealed the importance of nitrogen on overall microbial dynamics as well as CB formation in the bay. Our findings emphasize the combined influence of precipitation events, temperature and several bioavailable fractions of nitrogen and phosphorus on cyanobacterial bloom episodes.

Understanding of surface segregation of Cu and Zn on nano Si precipitates to the mechanical property improvement of high pressure die casting Al9Si3CuFe alloy

To understand Si precipitation and its influence on mechanical property improvement in high pressure die casting (HPDC) Al9Si3CuFe alloy under direct ageing heat treatment, the precipitates in Al9Si3CuFe alloy containing in-situ MgAl2O4 particles is analyzed via atomic-resolution scanning transmission electron microscopy. It is shown that lath-like Si precipitates form in an average size of 50 nm in length, and a good orientation relationship of {010}<001>Al//{111}<01–1>Si is observed between Si precipitate and matrix. Interestingly, Cu and Zn are observed to segregate onto Si/Al interface, which has a coarsening resisting effect on precipitate growth. The presence of these Si precipitates is the main factor contributing to the further improvement of mechanical properties of Al9Si3CuFe alloy, which results in an increase of 70 MPa in yield strength compared to the alloy without Si precipitates.

Precipitation behaviour in an Al-Zn-Mg-Cu alloy subjected to high strain rate compression tests

A peak aged (T6 heat treatment: 743 K /1.5 h + 393 K/24 h) Al-Zn-Mg-Cu alloy was subjected to compression tests at different strain rates from 1.0 × 10 −3 s −1 to 5.0 × 10 3 s −1 . The yield strength of the Al alloy is increasing with strain rates from 1.0 × 10 −3 s −1 to 4.0 × 10 3 s −1 and is decreasing with increasing strain rate from 4.0 × 10 3 s −1 to 5.0 × 10 3 s −1 showing strain rate sensitivity (SRS). A large number of Al 3 Zr, GP zones, η’, T (Al 2 Mg 3 Zn 3 ) and S (Al 2 CuMg) precipitates are present in the Al alloy after compression at 1.0 × 10 −3 s −1 and Al 3 Zr, η’, η, T and S phases are dominant after high strain rate compression from 3.5 × 10 3 s −1 to 5.0 × 10 3 s −1 . The precipitates average size is increased after compression at 1.0 × 10 −3 s −1 . High strain rate compression leads to the growth of precipitates and overlapping. Coarse precipitates are mainly found along the grain boundaries and dislocations. The increasing SRS with increasing strain rates up to 4.0 × 10 3 s −1 owes to the growth of precipitates which are hindering dislocations motion and generating more dislocations. Increasing strain rates to 5.0 × 10 3 s −1 , the coarse precipitates are no longer effective in pinning dislocations, leading to a decrease in yield strength and a negative SRS value. • The precipitates average size is increased after compression at 1.0×10 -3 s -1 . • The growth of precipitates and overlapping are dominant after high strain rate compression. • Coarse precipitates are formed either in the vicinity of dislocations or across the grain boundaries. • The SRS increases with increasing strain rates from 1×10 -3 s -1 to 4.0×10 3 s -1 and becomes negative after 5.0×10 3 s -1 .

HIGH RESOLUTION TRANSMISSION ELECTRON MICROSCOPY STUDY OF CRYSTALLOGRAPHY AND MORPHOLOGY OF TiC PRECIPITATES IN ARGON IRRADIATED 18Cr10NiTi STEEL

This work encompasses identification of the crystal structure and analysis of the TiC precipitates in 18Cr-10Ni-Ti austenitic stainless steel under Ar-ions irradiation. High resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) are used. Orientation relationship of TiC particles in surrounding matrix are indicated by HRTEM and diffraction patterns. The size of the precipitates is found to be critical: the coherency of TiC is kept at the interfaces when the precipitate is in the stage of nucleation, whereas the growth of precipitate up to 10 nm can lead to the loss of coherency in the austenitic steel. The findings suggest that the incoherent precipitate-matrix interface is an important point defect sink and contributes to inert gas bubble formation at elevated irradiation temperatures.

Effect of addition of Pt, Pd and Ir to β-NiAl-bond coat on oxidation resistance and growth of interdiffusion zone

The addition of Pt to the β-NiAl bond coat enhances the service life of the turbine blade in jet engine application. However, it increases the growth of the unwanted precipitate containing an interdiffusion zone between the bond coat and superalloy. The role of Pd and Ir addition is examined in this study by comparing the growth of the interdiffusion zone without compromising the thermal cycle resistance of the oxide layer. The oxide layers on all the bond coats grow with duplex morphology. Ni and Ir-containing precipitates are found inside α-Al2O3 oxide layer on Ir-containing bond coats. The microstructural evolution of the interdiffusion zone is explained with the help of the diffusion path. The addition of Ir is found to decrease the growth of the interdiffusion zone significantly compared to the Pt containing bond coat without compromising the thermal cycle resistance of the oxide layer, which could be considered as an important addition in next-generation turbine blades.

Morphogenesis of digitate structures in hot spring silica sinters of the El Tatio geothermal field, Chile

In silica‐rich hot spring environments, internally laminated, digitate sinter deposits are often interpreted as bio‐mediated structures. The organic components of microbial communities (cell surfaces, sheaths and extracellular polymeric substances) can act as templates for silica precipitation, therefore influencing digitate sinter morphogenesis. In addition to biologic surface‐templating effects, various microenvironmental factors (hydrodynamics, local pH and fluctuating wind patterns) can also influence silica precipitation, and therefore the morphology of resulting digitate sinters. Digitate sinter morphology thus depends on the dynamic interplay between microenvironmentally driven silica precipitation and microbial growth, but the relative contributions of both factors are a topic of continuing research. Here we present a detailed study of digitate silica sinters in distal, low‐temperature regimes of the El Tatio geothermal field, Chile. This high‐altitude geothermal field is extremely arid and windy, and has one of the highest silica precipitation rates found in the world. We find that digitate silica sinters at El Tatio always accrete into the prevailing eastward wind direction and exhibit laminar growth patterns coinciding with day–night cycles of wind‐ and thermally driven evaporation and rewetting. Subaerial parts of digitate sinters lack preserved organics and sinter textures that would indicate past microbial colonization, while filamentous cyanobacteria with resistant, silicified sheaths only inhabit subaqueous cavities that crosscut the primary laminations. We conclude that, although fragile biofilms of extremophile micro‐organisms may have initially been present and templated silica precipitation at the tips of these digitate sinters, the saltation of sand grains and precipitation of silica by recurrent wind‐ and thermally driven environmental forcing at El Tatio are important, if not dominant factors shaping the morphology of these digitate structures. Our study sheds light on the relative contributions of biogenic and abiogenic factors in sinter formation in geothermal systems, with geobiological implications for the cautious interpretation of stromatolite‐like features in ancient silica deposits on Earth and Mars.

РАСЧЕТНО-ТЕОРЕТИЧЕСКОЕ ИССЛЕДОВАНИЕ МОРФОЛОГИИ ГИДРИДОВ ЦИРКОНИЯ ПРИ СУЩЕСТВЕННО РАЗЛИЧНЫХ СКОРОСТЯХ ОХЛАЖДЕНИЯ

Computation study of the average zirconium hydride length on the cooling rate was performed using the precipitate nucleation and growth model. The cooling rate was varied in the range equal to six orders between typical values for the spent nuclear fuel dry storage conditions to values typical for laboratory tests modeling the dry storage. The calculations showed that as the cooling rate decreases, the hydrides concentration decreases, and their average length increases linearly on a double logarithmic scale. These dependencies have no limit if hydrides were abscended in the sample before the cooling began. If there were hydrides in the sample before the start of cooling, then they will grow and new hydrides will not nucleate in the limit of low cooling rates. For spent nuclear fuel dry storage, these results mean that if hydrides remain in the fuel claddings at the initial storage period, then hydrides morphology and hydrogen embrittlement at the end of the storage period are similar values gained under laboratory conditions with sufficiently slow cooling. If hydrides in fuel claddings are completely dissolved at the beginning of dry storage, then their length will be significantly greater than in laboratory tests at the end of the storage. Therefore, if the threshold values for the circumferential stresses are exceeded in fuel claddings, the hydrogen embrittlement can be expected to be higher than after faster cooling in typical laboratory studies. In this case, the hydrogen embrittlement assessment should be performed in a conservative approach assuming that radial hydrides have an average length equal to the thickness of the fuel cladding.

Synergistic effect of LPSO and eutectic phase on mechanical properties of Mg-Gd-Nd-Zn-Zr alloy during equal channel angular pressing

In this paper, the homogenized Mg-9Gd-2Nd-1.6Zn-1Zr (wt%) alloys were subjected to various equal channel angular pressing (ECAP) passes (1, 2, 4 and 8) with Bc route at 400 °C. Then, the microstructure evolution and strengthening mechanisms of alloys were systematically investigated. The results show that the coarse deformed grains are completely consumed by the dynamic recrystallized (DRX) grains, the number of dynamic precipitates gradually increases, and the intensity of basal texture of the alloy is gradually weakened with increasing ECAP passes. After 8 passes ECAP, the grain size is dramatically refined from 50 μm (homogenized) to 2.1 μm (8p-ECAPed), which is mainly due to the DRX, particle-stimulated nucleation (PSN) induced by broken eutectic phase and hinder grain growth of dynamic precipitates. The excellent comprehensive mechanical properties are achieved by 4 passes, and the corresponding yield strength (YS) and ultimate tensile strength (UTS) as well as elongation (EL) are 321 MPa, 378 MPa and 14.4％, respectively. This can be mainly ascribed to the combined effect of broken eutectic phase, DRX grains, kinked long period-stacking order (LPSO) and dynamic precipitates.

Evolution of strain-induced precipitates in Inconel 617B alloy and their effect on flow behavior

Strain-induced precipitation was systematically investigated in austenitic Inconel 617B superalloy (IN617B) after deformation of 0.2 true strain in its service temperature range (700–850 °C). The precipitation-time-temperature (PTT) curves obtained by stress relaxation experiments showed a classic C-shape with the nose temperature of 800 °C, and a minimum incubation period of 30 s, and the main strain-induced precipitate was M23C6 carbide. After specimens deformed at 800 °C to a strain of 0.2 were held between 10 and 1000 s, they underwent a second-pass strain test, during which the M23C6 precipitates evolved and influenced the flow stress; this behavior was investigated. During the nucleation, growth, and coarsening of the strain-induced precipitates, the morphology of the M23C6 particles gradually changed from spherical to polygonal with increasing size, but the precipitates always maintained their cube-on-cube orientational relationship with the austenitic matrix. During the nucleation stage before 30 s, many pre-precipitation clusters and weak static recovery softening led to low second-deformation flow stress, which persisted at approximately 630 MPa. In the precipitation growth phase before 360 s, recovery softening balanced precipitation hardening. The strain-induced precipitates grew larger, and they were able to pin dislocations. In addition, some complex microstructures resulting from particle collisions were observed. This resulted in the maximum rate of increase of the second deformation flow stress, which quickly reached almost 700 MPa. When the holding time was extended to 1000 s, the recovery softening effect further increased, while the M23C6 particles gradually coarsened; this weakened the increasing trend of the second deformation flow stress, which increased to only 715 MPa at 1000 s

Restoration of sand-stabilizing vegetation reduces deep percolation of precipitation in semi-arid sandy lands, northern China

Changes in precipitation patterns and vegetation variability generally affect deep percolation and increasingly limited groundwater resources in arid and semi-arid regions. However, the dynamics of deep percolation and its response to precipitation patterns after vegetation restoration in semi-arid sandy lands are not well understood. Thus, in this work, four typical geomorphologic landscapes with different vegetation types (M: mobile sandy land without vegetation; SH: semi-mobile sandy land with Caragana microphylla shrub but not herbaceous plants; SH&H: semi-fixed sandy land with C. microphylla shrub and herbaceous plants; H: fixed sandy land with herbaceous plants but not C. microphylla shrub) were simulated by an underground observation chamber to monitor daily variability in deep percolation, and characteristics of precipitation and vegetation growth were recorded during the growing seasons from 2010 to 2018. Our results showed that precipitation amount and duration were the most critical factors affecting deep percolation in M, H, SH and SH&H. The response of deep percolation to precipitation events in M was more sensitive than that in SH, H, and SH&H. The amount of deep percolation in M varied consistently with precipitation, and was significantly higher than that in SH, H and SH&H. Deep percolation had a weak negative correlation with species richness and mean height, and a strong negative correlation with mean plant cover and total aboveground biomass. Restoration of sand-stabilizing vegetation reduced deep percolation, and the reduction was greater in H than in SH. Average annual coefficients of deep percolation were 53.3 %, 9.9 %, 7.3 %, and 4.7 % in M, SH, H, and SH&H, respectively. Our results highlight that restoration of sand-stabilizing vegetation and subsequent increases in plant cover and aboveground biomass significantly reduce deep percolation and even groundwater recharge in semi-arid sandy lands.

Fatigue and dynamic aging behavior of a high strength Al-5024 alloy fabricated by laser powder bed fusion additive manufacturing

A high strength Al-5024 alloy containing Sc and Zr with a bi-modal microstructure consisting of fine equiaxed and coarse columnar grains was successfully fabricated by laser powder bed fusion (LPBF) additive manufacturing. The formation of the bi-modal microstructure was mainly due to both the formation of primary Al3Sc precipitates that act as nucleation sites and the steep temperature gradient during LPBF. By simulating the thermal field of a single melt pool, the formation mechanism of the bi-modal microstructure was explained. It was found by simulation that a solidification interface velocity less than 110 mm/s was beneficial to the nucleation of Al3Sc precipitates and, hence, facilitated the formation of a fine grain microstructure. Applying different heat treatments revealed a trade-off trend between yield strength and ductility as a function of the heat treatment time, and a correlation in fatigue life and yield strength was observed, both of which were closely related to the status of the secondary Al3Sc precipitates. The highest ultimate tensile strength of 450 MPa and corresponding 107 cycle fatigue strength of 105 MPa were achieved after hot isostatic pressing for 4 h at 325 °C with 100 MPa pressure. Dynamic strain aging was found to occur in both as-built and some heat treated samples, which was related to magnesium (Mg) solute atom clustering attributed to: (i) the formation of a diffuse “Mg wall” due to the repetitive melting and rapid cooling in LPBF, and (ii) the growth of intragranular (Al3Sc) and intergranular precipitates (Fe-, Mn-rich) during subsequent heat treatment, thereby leading to an increasing number of misfit dislocations that promote the formation of Mg atom clusters.

Influence of the Evolution of 9CrMoCoB Steel Precipitates on the Microstructure and Mechanical Properties during High-Temperature Aging

In this study, the short-term aging was carried out to reveal the evolution of precipitates and mechanical properties of heat resistant 9CrMoCoB steel during the early creep, replacing the conventional creeping. The tempered martensite lath structure (TMLS) and precipitates were observed in the as-aged 9CrMoCoB steel. TMLS in the matrix underwent a transition to the polygonal ferrite after aging only for 300 h. In comparison, the mean diameter of the precipitates increased from 183 to 267 nm after aging at 650 °C for 300 h. Also, the mean diameter of the precipitates increased from 183 to 302 nm at 700 °C. The room-temperature and high-temperature strength of 9CrMoCoB steel decreased after high-temperature aging, which may be mainly due to precipitates coarsening. Many M23C6 phases precipitate in the prior austenite grain boundary (PAGB) and lath boundary. After aging 100 h, TMLS transformed into polygonal ferrite, and the size of the precipitate at the subgrain boundary was about 100 nm, while after 300 h of high-temperature aging, large precipitates appear (400 nm) in the matrix. After 200 h of high-temperature aging, the obvious growth of precipitates on the PAGB and lath boundary weakens the pinning effect on the PAGB and martensite lath boundary and accelerates the transformation of microstructure and mechanical properties.

Molecular Dynamics Research on the Impact of Vacancies on Cu Precipitation in BCC-Fe.

The molecular dynamics (MD) simulation method was used to explore the impact of vacancy concentration (0 at%, 0.1 at% and 0.2 at%) on the diffusion and precipitation rate of Cu atoms in the Fe-3.5Cu alloy and the growth of Cu precipitation during the aging process of the alloy. The mechanism of the influence of Cu precipitation relative to the tensile properties of Fe-3.5Cu alloy was investigated. The results showed that the presence of vacancies will promote the diffusion and precipitation of Cu atoms in the Fe-3.5Cu alloy, but the diffusion and precipitation rate of Cu atoms does not always increase with the increase in vacancies. In the alloy containing 0.2 at% vacancies, the diffusion and precipitation rate of Cu atoms is lower than that in the alloy containing 0.1 at% vacancies. During the aging process, when the alloy contains no vacancies, no Cu precipitates will be produced. In the alloy containing 0.1 at% vacancies, the size of the Cu precipitates produced is larger than the size of the Cu precipitates produced in the alloy containing 0.2 at% vacancies, but the number of precipitates is less than that in the alloy with 0.2 at% vacancies. During the tensile process, the Cu precipitates will promote early occurrence of phase transition of the internal crystal structure in the Fe-3.5Cu alloy system, and lead to the generation of vacancy defects in the system, thus weakening the yield strength and strain hardening strength of the alloy.

Ni0.67Fe0.33 Hydroxide Incorporated with Oxalate for Highly Efficient Oxygen Evolution Reaction.

As the oxygen evolution reaction (OER) imposes a high energy barrier during electrochemical water splitting, designing highly efficient, stable, and cost-effective electrocatalysts for OERs is an ongoing challenge. In this study, we present a facile approach to prepare villi-shaped Ni-Fe hydroxides incorporated with oxalate derived from Ni-Fe oxalate through the in situ precipitation growth and subsequent immersion in an alkaline solution. The electrode with an optimized Ni-Fe ratio improves the OER kinetics, on which the electronic structure of the active site is adjusted based on a mutual effect between the adjacent nickel and iron atoms. The OER performance was significantly better than that of monometallic Ni(OH)2 and pristine Ni foam, with a low overpotential of 277 mV at 100 mA cm-2 and excellent stability. The enhanced OER performance is ascribed to the advanced intrinsic electrocatalytic activity of the electrode as a result of the synergetic effect of optimized Ni-Fe ratio mixing at the atomic level which leads to an increased surface area, a high number of active sites, and a reduced charge transfer resistivity.

Antecedent Rainfall, Excessive Vegetation Growth and Its Relation to Wildfire Burned Areas in California

AbstractIn recent years, California has experienced wildfire seasons of increasing frequency and magnitude, especially in terms of wildfire burned areas. Here, we investigate the precipitation and vegetation growth preceding each wildfire season for the 2001–2020 period to determine if antecedent rainfall led to enhanced vegetation growth in wildfire burned areas in California. Precipitation data from the Global Precipitation Measurement (GPM) Mission and Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI) data are examined to determine if antecedent rainfall and vegetation were normal, above, or below average, for the peak wet (December–February) and peak growth (March–May) periods preceding each wildfire season, as well as for the two previous wet and growth seasons. Then spatial correlations are done between precipitation and the vegetation indexes to determine the statistical significance of the relationships. Eleven of the 20 wildfire seasons were generally found to be preceded by above average levels of precipitation and vegetation growth. In three of the six seasons with more wildfire activities, linear regression model results show high positive correlations between precipitation and vegetation, suggesting that antecedent rainfall fueled vegetation growth that might have caused a significant impact on wildfire burned areas. Most of the larger wildfires in California, including the largest on record, exhibited positive correlations between antecedent rainfall and vegetation. Our results suggest that antecedent rainfall in California led to enhanced vegetation growth that later fueled more than half of the wildfire seasons analyzed in this study.