Preferential Precipitation Research Articles

Turning mine-tailing streams into sources of water and mineral salts in a membrane-sustained circular scenario

The discharge of wastewater from the mining industry has a critical ecological impact, potentially endangering both soil and marine ecosystems. Alternatively, recovering pure water and valuable materials from these hypersaline streams through a technologically efficient process, would help reduce the ecological impact of the waste, while providing a viable supply chain for raw materials such as magnesium, potassium and others, considered critical to the economy. In this context, this work aimed to simultaneously recover pure water and mineral salts from mine wastewater by membrane-assisted crystallization (MAC). A prior theoretical study based on thermodynamic parameters attempted to predict salts precipitation at different temperatures. MAC tests were then performed at specific thermal gradients and feed pretreatment conditions, achieving preferential precipitation of solids products of different composition containing large quantities of Ca or Mg/K minerals from the real mine tailing wastewater. The experiments also demonstrated the central impact of heterogeneous nucleation effects.

Study of Intergranular Corrosion Behaviors of Mn-Increased 5083 Al Alloy with Controlled Precipitation States of Al6Mn Formed during Homogenization Annealing

In this study, as a vital part of the production of Mn-increased 5083 Al alloy, i.e., homogenization annealing before hot rolling, the target states of key Al6Mn precipitation, including the dispersed, initial coarsening and intensive coarsening states, were designed, and the corresponding precipitates formed via the control of the temperature and holding time in the annealing process. By means of metallographic corrosion and nitric acid mass loss tests (NAMLT) for assessing the intergranular corrosion (IGC) resistance, temperatures ranging from 175 °C to 225 °C were determined to induce a transition from sensitization to stabilization for this innovative 5083. At a temperature of 175 °C for a duration of up to 24 h (2 h, 4 h, 8 h, 16 h, 24 h), the results show that when the soak time is 24 h, the sample with initially coarsened Al6Mn phases has a lower degree of sensitization (DOS) compared to the samples with Al6Mn phases in both the dispersed and intensive coarsening states, and its NAMLT is reduced by 11% and 15%, respectively. Subsequently, transmission electron microscopy (TEM) analysis has investigated that for the sample with the best IGC resistance, i.e., that with initially coarsened Al6Mn phases, plate-like Al6Mn particles (200~500 nm) can act as heterogenous nucleation sites for β phases, driving their preferential precipitation on Al6Mn particles and resisting their precipitation along grain boundaries, ultimately improving the IGC resistance of 5083 Al alloy after homogenization annealing.

Influence of grain structure and precipitates on fatigue crack propagation behaviors of Al-xCu-1.2Li-X alloys

The fatigue crack propagation (FCP) rates of the Al-xCu-1.2Li-X (x=4.2, 4.5 wt%) alloys with various heat treatment states were systematically investigated and correlated crack growth mechanism was further elucidated. The finer recrystallized grains and more equivalent slip system numbers provided more beneficial conditions for crack deflection and bifurcation, leading to the decreased FCP rate in short-term natural-aged (ST-T4) MC alloy. Moreover, the crack tips hardly activated the slip system within the adjacent grains when their twist angle differences for four slip surfaces were >10°, and the crack tended to propagate along the grain boundaries. With increasing Cu content of T8-aged alloy, the number density and dimension of T1 and θ′ precipitates are simultaneously increased, and the strengthening mechanism of T1 precipitates transformed from shearing to by-passing. Thus, the crack tips required more energy for transgranular propagation, causing the tendency of propagation to the grain boundaries and increased FCP rate in T8-aged HC alloy. However, the high Cu content levels resulted in the preferential precipitation of Guinier-Preston (G.P) zones during T6 aging. The δ′ and θ′ precipitates are increased and the nucleation of by-passed T1 precipitates is suppressed in T6-aged HC alloy, leading to a significantly decreased FCP rate compared to that of MC alloy.

Synergistic coordination-regulated separation of nickel and cobalt from spent Ni(II) and Co(II) bearing choline chloride/ethylene glycol electrolyte: Theoretical and experimental investigations

Developing efficient and environmentally friendly metal recovery technologies from secondary resources is crucial for enhancing resource utilization and promoting environmental sustainability. However, metals with similar physicochemical properties pose significant challenges in the recovery process, particularly for nickel and cobalt. Herein, we present a coordination-regulated approach utilizing water-, temperature-, and pH-codrived to achieve sequential precipitation recovery of nickel and cobalt from waste choline chloride/ethylene glycol (Ethaline) electrolyte containing Ni(II) and Co(II) ions. By carefully adjusting water content, temperature, and pH, we can control the speciation of Ni(II) ([NiCl(H2O)2(EG)2]+) and Co(II) ([CoCl2(H2O)2(EG)2]0) ions in the Ethaline-based electrolyte, thereby facilitating nickel preferential precipitation. Additionally, further introducing water into the Co(II)-rich phase promotes the formation of [CoCl(H2O)3(EG)2]+ complex ions, leading to efficient separation of cobalt. When oxalic acid is used as a precipitant, the recovery efficiencies for nickel and cobalt reach 96.3% and 97.5%, respectively, with purities of 97.8% and 98.5%. Importantly, distilling the water-containing solvent allows for regeneration of Ethaline with a yield rate as high as 97.1%, while maintaining its structural stability. This proposed strategy offers a promising pathway for sustainable metal recovery from spent Ethaline electrolytes containing metal ions while enabling solvent regeneration.

Removal of cadmium and zinc by calcium polysulfide in acidic groundwater: Injection ratio and precipitation mechanism

In this study, we conducted lab-scale experiments to assess the applicability of calcium polysulfide (CPS) for the removal of cadmium (Cd2+) and zinc (Zn2+) from acidic groundwater, with an emphasis on the injection ratio and removal mechanism. For the experiments, CPS was used to treat Cd2⁺ and Zn2⁺ contaminated solution. Solutions were purged with nitrogen gas, and CPS was injected in an anaerobic chamber. After 18 h, solutions were filtered, and heavy metal concentrations were measured using ICP-MS and ICP-OES. Total polysulfide (Sx2⁻) concentration in CPS was determined by converting it to bisulfide (HS⁻) at pH 8.20 and quantifying via UV–Vis spectrophotometry. Precipitates were analyzed using XRD and SEM-EDS after centrifugation. The findings revealed that more than 99.5% of the heavy metals were removed when CPS/Cd2+ (w/w) = 1.45 and CPS/Zn2+ (w/w) = 2.50, determined as the injection ratios for maximum efficiency. These ratios were applicable when Cd2+ and Zn2+ coexisted. From the XRD and SEM-EDS analyses, it was clarified that Cd2+ and Zn2+ precipitated in sulfide forms, consistently showing the preferential precipitation of Cd2+ because of the lower solubility of cadmium sulfide compared to zinc sulfide. In addition, the concentration of Sx2− in the 29% CPS solution was determined to be approximately 2.442 M. Finally, by comparing the injected Sx2− concentration with the concentration of heavy metals removed accordingly, it was concluded that CPS and heavy metals react with a 1:1 M ratio. Based on the above results and precise quantification method, our study suggests that CPS can be effectively utilized to address heavy metal contamination issues and may serve as a valuable tool for the remediation and management of contaminated groundwater globally.

Phase evolution in Ni-based superalloy K439B during thermal process

Based on the difference in element distribution and diffusion in various regions, the phase transformation of the as-cast, heat-treated and long-term aged K439B superalloys was investigated. Ti, Nb, Ta and Al elements segregated to the interdendritic regions, whereas W, Co and Cr elements segregated to the dendrite core regions in the as-cast alloy. During thermal process, the γ/γ' eutectic and the irregular γ' phase formed in the as-cast alloy completely dissolved into γ matrix. Subsequently, the reprecipitated spherical γ' phase gradually grew up and tended to be cubic. γ' phase was surrounded by the dislocations and a few stacking faults, which reduced the elastic strain energy in the long-term aged alloy. In addition, the degeneration of MC carbide was caused by a discrepancy in element diffusion rate and driving force in the interdendritic and grain boundary regions. The degeneration of MC carbide promoted the precipitation of γ' phase, M23C6 carbide and η phase, M23C6 carbide precipitated from γ matrix and γ' phase transformed into η phase. The preferential precipitation of M23C6 carbide was related to the difference in crystal structure, precipitation temperature range and Gibbs free energy.

Microstructure and mechanical properties of TiNbV0.5Ta0.5Crx (x=0, 0.1, 0.2, 0.5) refractory high-entropy alloys

The TiNbV0.5Ta0.5Crx (x = 0, 0.1, 0.2, 0.5) refractory high-entropy alloys (RHEAs) with an excellent combination of ductility and strength were designed and prepared for high-temperature applications. The yield strength, ultimate tensile strength, and elongation of the TiNbV0.5Ta0.5Cr0.1 alloy were 878 MPa, 928 MPa, and 21.6 %, respectively. Important issues of microstructure evolution, precipitation process, and their impact on mechanical properties were concerned. Then, the effect of Cr content on the mechanical properties of TiNbV0.5Ta0.5Crx alloys was evaluated through a quantitative analysis of the strengthening mechanism, which elucidated the trade-off relationship between solid solution strengthening and precipitation strengthening in RHEA. The microstructure evolution of the TiNbV0.5Ta0.5Crx alloys involved the formation and interconversion of titanium allotropes (α-Ti and β-Ti) and the precipitation of the Laves phase. Significant embrittlement was induced by the preferential precipitation of α-Ti on the grain boundary. The TiNbV0.5Ta0.5Crx alloys exhibited an incubation period for Laves phase precipitation, which was related to the Cr content in the alloy. The Laves phase preferentially nucleated next to α-Ti due to the redistribution of elements during the α-Ti precipitation process. The precipitation of the Laves phase played an important role in enhancing the strength of the TiNbV0.5Ta0.5Crx alloys.

Effect of Nucleation Heterogeneity on Mineral Precipitation in Confined Environments

AbstractThe formation of new mineral phases in confined environments, especially in porous media, is crucial for various geological processes like mineralization and diagenesis. The nucleation and precipitation of minerals are initiated at the microscale through fluid‐rock interaction, where dissolution of primary phases leads to supersaturated conditions and nucleation and growth of secondary ones. Previous research has focused primarily on either precipitation or nucleation, without fully exploring their combined impact. Our study introduces a computational framework that integrates classical nucleation theory with the micro‐continuum method. We validated our model by comparing with experiments, and discovered that different surface nucleation rate changes the mode of precipitation from a preferential to uniform precipitate textures. Furthermore, our study uncovered that the conventional deterministic precipitation method tends to underestimate the permeability of the porous matrix. In contrast, the new framework significantly improves model accuracy by incorporating preferential precipitation and heterogeneous nucleation.

Austenite decomposition behavior adjacent to δ-ferrite in a Si-modified Fe-Cr-Ni austenitic stainless steel during thermal aging at 550 °C

The δ-ferrite decomposition has been widely reported in conventional Fe-Cr-Ni austenitic stainless steel during thermal aging. However, a novel phenomenon is found in a Si-modified austenitic stainless steel, that δ-ferrite decomposition is suppressed, replaced by the decomposition of adjacent austenite. Herein, the decomposition behavior of austenite adjacent to δ-ferrite and its effect on impact toughness in a Si-modified austenitic stainless steel during aging at 550 °C up to 3000 h have been investigated. During thermal aging, austenite adjacent to δ-ferrite is decomposed in the following sequence: (1) γ → M23C6 + α transformation takes place. The preferential formation of secondary M23C6 carbides not only rejects Si atoms into the surrounding austenite but also produces a C-depleted zone. The transformation of austenite to ferrite is induced in the Si-riched and C-depleted micro-zone. (2) The growth of secondary M23C6 carbides induces a continuous rejection of Ni and Si atoms into M23C6/γ and M23C6/α interfaces, and the strong attractive interaction between Ni and Si provides the chemical driving force for nucleation of M6C carbides and G-phase. (3) With prolonged aging time, the lower C, high Ni, and high Si concentrations in the frontier of decomposed austenite will promote the preferential precipitation of M6C carbides rather than M23C6 carbides. During impact deformation, microcracks caused by strain incompatibility between secondary M23C6 and α-ferrite, resulting in a slight decrease in impact toughness. As austenite decomposition proceeds, the higher strain incompatibility across M6C/α interfaces leads to brittle cleavage fracture, resulting in a significant decrease in impact toughness.

Research on strength and toughness matching of 1.3GPa ultralow temperature resistant bulb flat steel

In this study, an ultralow temperature resistant bulb flat steel with ultra-high strength and good toughness is prepared to meet the application requirements of hull structural steel for polar ships and large ships. The bulb flat steel with a yield strength of 1292 MPa, elongation of 18.5 % and an impact energy of 53 J at − 196 °C is obtained by quenching and tempering process. In order to reveal the tempering response and strengthening mechanism during the quenching and tempering process of bulb flat steel, multi-scale characterization is carried out to explore the microstructural evolution and nano-precipitation behavior of the ultralow temperature bulb flat steel under different tempering processes. The results indicate that the preferential precipitation of (V, Nb)(C, N) causes dislocation multiplication, and the higher dislocation density in the matrix provides more nucleation sites for M2C. The slower diffusion rate of Mo effectively suppresses the rapid coarsening of M2C, which keep a good coherent relationship between the M2C and the α-Fe matrix. Strain concentration is avoided by synergizing the (V, Nb)(C, N) precipitation and the M2C precipitation of the coherent lattice, thus enabling the ultralow temperature resistant bulb flat steel to maintain ultra-high strength with good plasticity and toughness.

Industrially produced 2.4 GPa ultra-strong steel via nanoscale dual-precipitates co-configuration

An ultra-high strength martensitic steel, strengthened by the dual-precipitation of NiAl and M2C nano-particles, has been successfully developed and produced on an industrial scale. It has achieved a remarkable tensile strength of 2467 MPa and exhibited ductility approaching 10%. The precipitation configurations of NiAl and M2C nano-particles during ageing at 510 °C for durations ranging from 0.5 to 10 h were characterized using atom probe tomography. The results indicate that the preferential precipitation of NiAl, facilitated by minimal lattice misfit and low interfacial energy, promotes the uniform nucleation of M2C particles within the matrix while restricting their growth. As a result, both types of precipitates maintain a high number density. With increasing ageing time, the distribution density of the precipitates decreases, their size increases and the increase in yield strength gradually decreases. Furthermore, the addition of element cobalt effectively reduces the diffusivity of other major alloying elements, synergistically inhibiting the growth of NiAl and M2C particles. The dual precipitates co-configuration provides a substantial hardening effect (1046 MPa at 510 °C for 220 min) compared to the individual hardening effect of M2C observed in AerMet100 steel.

Countercurrent preferential precipitation of acidic variants from monoclonal antibody pools

The process of countercurrent multistage precipitation (CnMP) was developed for reduction of the acidic variant (av) content in monoclonal antibody (mAb) pools. The process was performed in polyethylene glycol (PEG) solutions of low ionic strength, at which av was the most prone to precipitate. To design the process, a mathematical model was formulated, which consisted of steady-state mass balance equations and underlying thermodynamic dependencies. The model was solved for different combinations of the process variables, including the protein concentration in the feed material and the PEG concentration in subsequent precipitation stages. The model solution was projected onto two-dimensional planes, where the performance indicators, such as the separation yield and the av reduction level, were correlated with the process variables. CnMP overperformed crosscurrent multistage precipitation (CsMP) and ion exchange chromatography (IEX) used in previous studies; in the comparison with CsMP, the 3-stage CnMP process allowed up to 28% increase in yield and up to 25% increase in the av reduction level, and in the comparison with IEX, up to 37% increase in yield and up 12.5% increase in the av reduction level. The yield benefit of CnMP depended on the composition of the feed material and the demand for the av reduction. The concept was experimentally verified; the 2- and 3-stage CnMP processes were performed using the input process variables provided by the model solution. The performance indicators calculated by the model and experimentally measured were in a good agreement, which indicated both feasibility and predictability of CnMP.

Numerical analysis of particle radial distribution during spray pyrolysis of dual-solute precursor

This study investigates the droplet-to-particle formation process in spray pyrolysis, focusing on interactions between low-solubility precursor A (KNO3) and high-solubility precursor B (NaNO3). A numerical model simulates evaporation, multi-component transport, and precipitation in droplets, and is validated with experimental data. The numerical results reveal that the preferential precipitation of KNO3 near the surface hinders NaNO3, lowering its surface molar concentration. The radial distribution of NaNO3 varies with parameters, exhibiting monotonic or non-monotonic trends. The presence of a small amount of low-solubility KNO3 decreases NaNO3 near the surface, while a higher KNO3 proportion forms a shell layer, increasing NaNO3 from the center to the surface. The results also show that environmental factors influence particle size and component structure. Adjusting the precipitation rate of KNO3, along with reduced temperature and droplet size, leads to smaller particles, enhancing NaNO3 accumulation inside and decreasing surface concentration. This work deepens understanding of pyrolysis droplet evolution, supporting customizable particle design for improved droplet-based technologies.

Investigation of the acicular aragonite growth behavior in AOD stainless steel slag during slurry-phase carbonation

This study presents a novel method for producing acicular aragonite using argon oxygen decarburization (AOD) slag while controlling the reaction temperature, reaction time, stirring speed, and the magnesium-to‑calcium stoichiometric ratio. This approach provides steel plants with an opportunity to decrease their CO2 emissions and promote efficient resource utilization and CO2 storage through the production of high-quality value-added products. The experimental results showed that reaction temperature was the most significant factor affecting the carbonation efficiency of AOD slag, followed by reaction time, stirring speed, CO2 partial pressure, and the liquid-to-solid ratio (L/S). The study also found that elevated temperature and prolonged reaction duration favored the preferential precipitation of aragonite. Additionally, raising the temperature and the magnesium-to‑calcium stoichiometric ratio was shown to enhance the formation of aragonite, affecting its crystal growth orientation and dimensions. The optimal combination of reaction parameters for the preparation of acicular aragonite was found to be the reaction time of 8 h, the magnesium-to‑calcium stoichiometric ratio of 0.8, the reaction temperature of 120 °C, and the stirring speed of 200 r·min−1. Under these conditions, the resulting acicular aragonite exhibited excellent overall uniformity, a large aspect ratio, and a smooth crystal surface, with a content of 91.49 %, a single crystal length ranging from 9.86 to 32.6 μm, and a diameter ranging from 0.63 to 2.15 μm. This study provides valuable insights into the efficient production of acicular aragonite from steel slag while reducing CO2 emissions and promoting the sustainable use of resources.

Detailed investigation on microstructure and strengthening contribution of Al-xCu-1.3Li-X alloy sheets

The microstructure-mechanical properties connection and strengthening contribution of Al-xCu-1.3Li-X (x = 3.8, 4.2, 4.5 wt%) alloy sheets subjected to various heat treatments were systematically investigated. After solid-solution treatment, the decreased schmid factor value was the main factor for higher strength of Alloy-3 (4.5 wt% Cu). The number density and diameter of T1 precipitates simultaneously increased with rising the Cu content during T8 aging, leading to the highest strength (655.4 MPa) of T8-aged Alloy-3. However, the high Cu content level resulted in the preferential precipitation of Guinier-Preston (G.P) zones during T6 aging at 165 °C. The θ' precipitates were therefore significantly increased and the nucleation of T1 precipitates was suppressed in T6-aged Alloy-3, causing the reduced strength compared to that of T6-aged Alloy-2 (4.2 wt% Cu). Furthermore, the experimental yield strength was successfully predicted by invoking the modified precipitate strengthening model, in which the θ' precipitate-dislocation interaction was by-passing mechanism, whereas the shearable and by-passed T1 precipitates coexisted for all alloys. The strengthening transition from by-passing to shearing occurred in T1 precipitates with a thickness <1.9 nm or diameter <65 nm, and was particularly associated with the decrease in thickness of T1 precipitates.

Effect of in-situ generated Fe3AlC0.5 on the microstructure and mechanical property of twin-wire directed energy deposition-arc fabricated Fe3Al based iron aluminide

Fe3Al-based iron aluminide alloys are known for their satisfactory resistance to corrosion, oxidation, and sulfidation at both ambient and elevated temperatures. However, the brittleness induced by the intermetallic nature of these alloys at room temperature significantly increases the manufacturing costs. To address this issue, a recent innovation called twin-wire directed energy deposition-arc (TW-DED-arc) technique has been developed to fabricate binary Fe3Al alloys with enhanced flexibility and cost-effectiveness. Building upon the feasibility validation of this technique, the present research aims to improve mechanical properties of TW-DED-arc fabricated Fe30Al alloy by in-situ generation of Fe3AlC0.5 precipitates within Fe3Al matrix. The experimental results demonstrate the successful production of the target Fe-30Al-0.3C-1Si-1Mn alloy. The reinforcement Fe3AlC0.5 precipitates exhibit good adherence to Fe3Al matrix, effectively increasing the tensile strength by nearly 15%. During tensile fracture, Fe3AlC0.5 precipitates are observed to obstruct crack propagation. Higher magnification characterization reveals clear dislocation entanglement occurring at Fe3AlC0.5 precipitate, confirming this phenomenon. Furthermore, preferential precipitation of Fe3AlC0.5 at grain boundaries induces clean areas adjacent to the grain boundaries. This has a dual effect: strengthening the grain boundaries and guiding crack propagations.

Microscopic mechanism of mechanical property improvement of the casted Al-7Si-0.4Mg-0.3Y alloy

This paper investigates the effect of different casting conditions on the microstructure of Al-7Si-0.4 Mg alloys with 0.3 wt.% rare earth Y addition and the effect of T6 heat treatment on their mechanical properties. The experimental studies showed that the addition of 0.3 wt.% rare earth Y at 30 min or 1200 k resulted in the optimum microstructure and mechanical properties of the alloys, and the addition of Y led to the formation of Y-containing nanoparticles on eutectic Si, which were re-solidified by T6 heat treatment and precipitated a more stable orthorhombic cubic structure of Al2Si2Y compounds at the grain boundaries. According to the growth kinetic relationship, the addition of Y replaces the nucleation center of the original eutectic Si, and the preferential precipitation of the Y-containing phase destroys the heterogeneous nucleation conditions of the original eutectic Si, which leads to the growth of eutectic Si towards the original growth direction close to 60°, and generates more heterogeneous twins at the interface and gradually builds up, which has an inhibitory effect on the growth of eutectic Si. The fracture morphology and energy spectra show that the precipitated Y-containing coexist in these precipitates will lead to local stress concentration resulting in microcracks and ultimately fracture, which will change the mechanical properties of the alloy significantly.

Microstructural Characterization and Prior Particle Boundary (PPB) of PM Nickel-Based Superalloys by Spark Plasma Sintering (SPS).

This research investigates the microstructure and defects of powder metallurgy (PM) nickel-based superalloys prepared by spark plasma sintering (SPS). The densification, microstructural evolution, and precipitate phase evolution processes of FGH96 superalloy after powder heat treatment (PHT) and sintering via SPS are specifically analyzed. Experimental results demonstrate that SPS technology, when applied to sinter at the sub-solidus temperature of the γ' phase, effectively mitigates the formation of a prior particle boundary (PPB). Based on experimental and computational findings, it has been determined that the presence of elemental segregation and Al2O3 oxides on the surface of pre-alloyed powders leads to the preferential precipitation of MC-type carbides and Al2O3 and ZrO2 oxides in the sintering necks during the hot consolidation process, resulting in the formation of PPB. This study contributes to the understanding of microstructural modifications achieved through SPS technology, providing crucial information for optimizing sintering conditions and reducing the widespread occurrence of PPB, ultimately enhancing the material performance of PM nickel-based superalloys.

Microstructural Evolution and Mechanical Behaviour of Near-Eutectic High Entropy Alloy

In the current work, the thermal stability of the eutectic regions and precipitation and mechanical behaviour of near eutectic high-entropy alloy is studied. The alloy solidified as FCC and underwent sequential ordering to L12 with order–disorder transition temperature between 700°C and 1000°C. Cooling rate, variation in the concentration boundary layer, thermal gradient and interfacial energy were attributed to define the eutectic morphology (L12 and B2). Thermal exposure resulted in homogeneous precipitation of acicular Al-Ni-rich B2 phase within the proeutectic and irregular eutectic regions. The preferential B2 precipitation within the irregular eutectic regions was attributed to the lower stability and higher lattice strain associated with these regions. The FCC: B2 phase fraction after heat treatment was similar to that of the eutectic alloy. Furthermore, lamellar degradation, globularization and Ostwald ripening of the B2 phase were observed after heat treatment. Lamellar degradation occurred via mechanisms like cylinderization, edge spheroidization, termination migration and boundary splitting. The experimental observations on the phase evolution, stability and order–disorder transformation matched well with the CALPHAD predictions except for the σ phase formation. B2 precipitation during heat treatment enhanced the mechanical behaviour of the alloy. However, the work hardening rate was superior for as-cast alloy.

A chance of rain: investigating the effects of stochastic charging on the orbital dynamics and precipitation of nanodust in Saturn’s rings

ABSTRACT The precipitation of dusty material via unstable orbits on to Saturn from the ring plane is a phenomenon known as ring rain. A key open question for Saturn’s rings is whether silicates and organics rain out of the rings on to Saturn faster than water ice. Such preferential precipitation of dusty material would ‘clean’ the rings and make them appear youthful. In this paper, we investigate the stability of orbiting dust that is stochastically charged and may precipitate on to the planet, be ejected from the system, or remain stable over the duration of our numerical integrations. We find no clear relationship between dust particles’ launch locations in the main rings and their final deposition latitudes on the planet because the orbital motion is sensitive to initial conditions and the charging environment, but averaging over distributions of dust particle properties should lead to high-resolution stability maps for dust in the rings and deposition distributions on the planet, and hence predictions for the observable $\rm H_3^+$ emission strength.