Rapid Nucleation Research Articles

Electrochemical Generation of a Hydrogen Bubble at a Recessed Platinum Nanopore Electrode.

We report the electrochemical generation of a single hydrogen bubble within the cavity of a recessed Pt nanopore electrode. The recessed Pt electrode is a conical pore in glass that contains a micrometer-scale Pt disk (1-10 μm radius) at the nanopore base and a nanometer-scale orifice (10-100 nm radius) that restricts diffusion of electroactive molecules and dissolved gas between the nanopore cavity and bulk solution. The formation of a H2 bubble at the Pt disk electrode in voltammetric experiments results from the reduction of H(+) in a 0.25 M H2SO4 solution; the liquid-to-gas phase transformation is indicated in the voltammetric response by a precipitous decrease in the cathodic current due to rapid bubble nucleation and growth within the nanopore cavity. Finite element simulations of the concentration distribution of dissolved H2 within the nanopore cavity, as a function of the H(+) reduction current, indicate that H2 bubble nucleation at the recessed Pt electrode surface occurs at a critical supersaturation concentration of ∼0.22 M, in agreement with the value previously obtained at (nonrecessed) Pt disk electrodes (∼0.25 M). Because the nanopore orifice limits the diffusion of H2 out of the nanopore cavity, an anodic peak corresponding to the oxidation of gaseous and dissolved H2 trapped in the recessed cavity is readily observed on the reverse voltammetric scan. Integration of the charge associated with the H2 oxidation peak is found to approach that of the H(+) reduction peak at high scan rates, confirming the assignment of the anodic peak to H2 oxidation. Preliminary results for the electrochemical generation of O2 bubbles from water oxidation at a recessed nanopore electrode are consistent with the electrogeneration of H2 bubbles.

Morphology-Controlled CaCO3 Nanostructures by Modified Co-Precipitation in Pulsed Mode

Calcium carbonate nanoparticles and nanorods were synthesized by precipitation from saturated sodium carbonate and calcium nitrate aqueous solutions through co precipitation method. A new rout of synthesis was done by both using pulsed mixing method and controlling the addition of calcium nitrate. The effect of the agitation speed, and the temperature on particle size and morphology were investigated. Particles were characterized using X-ray Microanalysis, X-ray analysis (XRD) and scanning electron microscopy (SEM). The results indicated that increasing the mixer rotation speed from 3425 to 15900 (rpm) decreases the average particle size to 64±7 nm. A rapid nucleation then aggregation induced by excessive shear force phenomena could explain this observation. Moreover, by increasing the reaction temperature, the products were converted from nanoparticle to nanorods. The maximum attainable aspect ratio was 6.23 at temperature of 75°C and rotation speed of 3425. Generally, temperature raise promoted a significant homoepitaxial growth in one direction toward the formation of calcite nanorods. Overall, this study can open new avenues to control the morphology of the calcium carbonate nanostructures.

Influence of the operating conditions on the morphology of CaCO3 nanoparticles prepared by modified co-precipitation with pulse mode feeding

Calcium carbonate nanoparticles and nanorods were synthesized by precipitation from saturated sodium carbonate and calcium nitrate aqueous solutions through co precipitation method. A new route of synthesis was done by using pulse mode feeding of calcium nitrate. The effect of the agitation speed, and the temperature on particle size and morphology were investigated. The formed particles were characterized using X-ray microanalysis, X-ray analysis (XRD) and scanning electron microscopy (SEM). The results indicated that increasing the mixer rotation speed from 3425 to 15,900rpm facilitates decreasing the average particle size to 64±7nm. A rapid nucleation followed by aggregation induced by excessive shear forces phenomena could explain this observation. Moreover, by increasing the reaction temperature, the products were converted from nanoparticles to nanorods. The maximum attainable aspect ratio was 6.23 at temperature of 75°C and rotation speed of 3425. Generally, temperature raise promoted a significant homoepitaxial growth in one direction toward the formation of calcite nanorods. Overall, this study opens a new avenue to control the morphology of the calcium carbonate nanostructures.

A novel high-energetic and good-sensitive cocrystal composed of CL-20 and TATB by a rapid solvent/non-solvent method

In this work, through a rapid nucleation solvent/non-solvent process, a novel CL-20/TATB cocrystal explosive has been successfully prepared with a detonation performance superior to HMX and an impact sensitivity almost the same as HMX.

Microstructures of chromia scales grown in CO2

Scales grown on chromia forming alloys in CO2 are less protective than those developed during exposure to oxygen or air. Reaction with CO2 leads to faster chromia scale growth, the more rapid onset of breakaway and internal carburisation of the alloy. Conventional and laser Raman microscopy studies of Fe–Cr alloys show that local fluctuations in scale thickness are associated with varying degrees of chromium depletion. Local conversion of Cr2O3 to spinel leads to rapid outward iron diffusion and nucleation of Fe-rich oxide nodules. A TEM investigation reveals that reaction in CO2 produces finer grained Cr2O3, inward scale growth and more rapid scaling, as well as internal carburisation. Appropriate silicon additions to the alloys lead to the formation of a thin, glassy silica layer beneath the chromia, greatly slowed chromia thickening rates and the prevention of carburisation. Atom probe tomography is used to locate carbon within the chromia.

Synthesis of zinc molybdate and zinc phosphomolybdate nanopigments by an ultrasound assisted route: Advantage over conventional method

In the present study, zinc molybdate (ZM) and zinc phosphomolybdate (ZMP) nanoparticles of white color were synthesized using conventional and innovative sonochemical co-precipitation method without any emulsifier. This new class of pigment is environmental friendly which can be used as an alternative to lead, cadmium and chromium pigment which contain carcinogenic species. Zinc chloride and sodium molybdate precursors were used during synthesis of ZM, and ZMP nanoparticles synthesis was accomplished using sodium molybdate, zinc sulfate and potassium dihydrogen phosphate. The synthesized materials were characterized by XRD, FTIR and TEM to determine the structure, the general type of atom bound in the compound and the morphology of the formed compounds respectively. The rapid saturation of the Zn2+ ions takes place during the synthesis of ZM and ZMP nanoparticles due to ultrasonic irradiation, leading to a faster nucleation of ZM and ZMP nanoparticles with improved solute transfer rate. The average particle size is found to be significantly lower in case of ultrasound assisted synthesis compared to conventional precipitation method. The possible reasons are, improved solute transfer rate and rapid nucleation in the presence of cavitations generated by ultrasonic irradiations.

Study on the supercooling degree and nucleation behavior of water-based graphene oxide nanofluids PCM

This article aimed to study the supercooling degree and nucleation behavior of nanofluids phase change material. The nanofluids were prepared by adding small fraction of graphene oxide nanosheets in deionized water without any dispersants. The supercooling degree of nanofluids with different concentrations was tested experimentally. The results show that the supercooling degree can be reduced by 69.1%, and the nucleation was started in advance, shorting the time by 90.7%. Theoretical analysis based on the heterogeneous nucleation theory indicates that ice crystal nucleus cannot grow on the thickness surface of the graphene oxide nanosheet, while it can grow on the top or bottom surface of the nanosheet only when the supercooling degree ΔT and the nanosheets size D meet the formulaD⋅ΔT≥4.2×10−8. Our study implies that graphene oxide nanofluids have the potential to be used as PCMs in cold storage applications because of their low supercooling degree and rapid nucleation behavior.

Investigation of corrosion inhibition performance of ultrasonically prepared sodium zinc molybdate nanopigment in two-pack epoxy-polyamide coating

In the present work, an innovative approach has been used to synthesize sodium zinc molybdate nanopigment using ultrasound-assisted co-precipitation of sodium molybdate and zinc oxide. X-ray diffraction, Fourier transform infrared and elemental analysis of sodium zinc molybdate nanopigment have been performed which confirmed the formation of sodium zinc molybdate particles. Ultrasound-assisted synthesis gave lower particle size of sodium zinc molybdate nanoparticles (467 nm) which can be explained on the basis of improved solute transfer rate, rapid nucleation, and formation of a large number of nuclei in the presence of ultrasound. The corrosion inhibition effect of sodium zinc molybdate nanopigment in 2K (two-pack) epoxy-polyamide clear coat on low carbon steel has also been studied. The results of the corrosion rate analysis, Tafel plots, and electrochemical impedance spectroscopy of the prepared coatings show better corrosion inhibition performance when sodium zinc molybdate particles were incorporated in the 2K epoxy-polyamide clear coat.

Characterizing reactive oxygen generation and bacterial inactivation by a zerovalent iron-fullerene nano-composite device at neutral pH under UV-A illumination

A nano-composite device composed of nano-scale zerovalent iron (ZVI) and C60 fullerene aggregates (ZVI/nC60) was produced via a rapid nucleation method. The device was conceived to deliver reactive oxygen species (ROS) generated by photosensitization and/or electron transfer to targeted contaminants, including waterborne pathogens under neutral pH conditions. Certain variations of the nano-composite were fabricated differing in the amounts of (1) ZVI (0.1mM and 2mM) but not nC60 (2.5mg-C/L), and (2) nC60 (0–25mg-C/L) but not ZVI (0.1mM). The generation of ROS by the ZVI/nC60 nano-composites and ZVI nanoparticles was quantified using organic probe compounds. 0.1mM ZVI/2.5mg-C/L C60 generated 3.74-fold higher O2− concentration and also resulted in an additional 2-log inactivation of Pseudomonas aeruginosa when compared to 0.1mM ZVI (3-log inactivation). 2mM ZVI/2.5mg-C/L nC60 showed negligible improvement over 2mM ZVI in terms of O2− generation or inactivation. Further, incremental amounts of nC60 in the range of 0–25mg-C/L in 0.1mM ZVI/nC60 led to increased O2− concentration, independent of UV-A. This study demonstrates that ZVI/nC60 device delivers (1) enhanced O2− with nC60 as a mediator for electron transfer, and (2) 1O2 (only under UV-A illumination) at neutral pH conditions.

Deposition of WO3 on Al2O3 via a microwave hydrothermal method to prepare highly dispersed W/Al2O3 hydrodesulfurization catalyst

A microwave hydrothermal method was developed to deposit WO3 on Al2O3 for rapidly preparing W/Al2O3 hydrodesulfurization (HDS) catalysts with both high tungsten dispersion and weak tungsten–alumina interaction. The catalysts were characterized by XRD, XPS, N2 adsorption, H2-TPR, NH3-TPD and HRTEM; their activity was tested by HDS of dibenzothiophene. Compared to the previous hydrothermal deposition method, the microwave hydrothermal method can further increase the dispersion of tungsten and attain the similar weak tungsten–alumina interaction, leading to the shorter and similar stacked WS2 and hence higher HDS activity, whereas the hydrothermal period is dramatically reduced from 12h to 15min. Moreover, this method can highly disperse more tungsten on alumina than the hydrothermal deposition and impregnation methods. It is attributed to the rapid nucleation and inhibited growth of WO3, and the enhanced mobility induced by microwave hydrothermal conditions. The significance of this method lies in its simplicity and efficiency for preparing tungsten-based catalysts with superior HDS activity.

ChemInform Abstract: Applying Quantitative Microstructure Control in Advanced Functional Composites

AbstractReview: 118 refs.

Morphology-controlled fabrication and magnetic properties of nickel assemblies

In this study, nickel assemblies with various morphologies, including nanospheres, pinecone structures, microspheres, and necklace chains, were synthesized in ethylene glycol solution by adjusting the experimental conditions. We propose a possible growth mechanism for the formation of different structures, which involves the rapid nucleation of primary particles followed by slow aggregation and Ostwald ripening crystallization of the primary particles. The saturation magnetization (Ms) of the nickel assemblies decreased as the particle size declined. We found that the coercivity (Hc) of the necklace chains appeared to be higher than that of other structures due to their shape anisotropy. The results of our study indicated that the magnetic properties of the nickel assemblies were morphology-dependent. The coercivities of the nickel samples with different structures prepared in this study were two orders of magnitude higher than that of bulk nickel (0.7 Oe).

Phase-coexistence and thermal hysteresis in samples comprising adventitiously doped MnAs nanocrystals: programming of aggregate properties in magnetostructural nanomaterials.

Small changes in the synthesis of MnAs nanoparticles lead to materials with distinct behavior. Samples prepared by slow heating to 523 K (type-A) exhibit the characteristic magnetostructural transition from the ferromagnetic hexagonal (α) to the paramagnetic orthorhombic (β) phase of bulk MnAs at Tp = 312 K, whereas those prepared by rapid nucleation at 603 K (type-B) adopt the β structure at room temperature and exhibit anomalous magnetic properties. The behavior of type-B nanoparticles is due to P-incorporation (up to 3%), attributed to reaction of the solvent (trioctylphosphine oxide). P-incorporation results in a decrease in the unit cell volume (∼1%) and shifts Tp below room temperature. Temperature-dependent X-ray diffraction reveals a large region of phase-coexistence, up to 90 K, which may reflect small differences in Tp from particle-to-particle within the nearly monodisperse sample. The large coexistence range coupled to the thermal hysteresis results in process-dependent phase mixtures. As-prepared type-B samples exhibiting the β structure at room temperature convert to a mixture of α and β after the sample has been cooled to 77 K and rewarmed to room temperature. This change is reflected in the magnetic response, which shows an increased moment and a shift in the temperature hysteresis loop after cooling. The proportion of α present at room temperature can also be augmented by application of an external magnetic field. Both doped (type-B) and undoped (type-A) MnAs nanoparticles show significant thermal hysteresis narrowing relative to their bulk phases, suggesting that formation of nanoparticles may be an effective method to reduce thermal losses in magnetic refrigeration applications.

The Effect of Alkali Concentration on the Structural and Magnetic Properties of Mn-Ferrite Nanoparticles Prepared via the Coprecipitation Method

MnFe2O4 nanoparticles were synthesized using the coprecipitation method under two different NaOH concentration settings as reaction agents at 355 K (82 °C). Structural and morphological properties of the nanoparticles were examined using X-ray diffraction and a scanning electron microscope. The decrease of NaOH concentration led to the increase of particle size. This result contradicts two recently published reports. Also, the decrease of NaOH concentration led to more crystallinity and a narrower particle size distribution. The results were evaluated from a chemical point of view and were based on the supersaturation level, which was influenced by alkali concentration. It was concluded that the higher NaOH concentration led to a more rapid nucleation and more random cation distribution. The magnetic properties of the nanoparticles examined by permeameter and faraday-balance equipment were consistent with the structural and morphological properties of the particles.

Co-precipitation of Radium with Barium and Strontium Sulfate and Its Impact on the Fate of Radium during Treatment of Produced Water from Unconventional Gas Extraction

Radium occurs in flowback and produced waters from hydraulic fracturing for unconventional gas extraction along with high concentrations of barium and strontium and elevated salinity. Radium is often removed from this wastewater by co-precipitation with barium or other alkaline earth metals. The distribution equation for Ra in the precipitate is derived from the equilibrium of the lattice replacement reaction (inclusion) between the Ra(2+) ion and the carrier ions (e.g., Ba(2+) and Sr(2+)) in aqueous and solid phases and is often applied to describe the fate of radium in these systems. Although the theoretical distribution coefficient for Ra-SrSO4 (Kd = 237) is much larger than that for Ra-BaSO4 (Kd = 1.54), previous studies have focused on Ra-BaSO4 equilibrium. This study evaluates the equilibria and kinetics of co-precipitation reactions in Ra-Ba-SO4 and Ra-Sr-SO4 binary systems and the Ra-Ba-Sr-SO4 ternary system under varying ionic strength (IS) conditions that are representative of brines generated during unconventional gas extraction. Results show that radium removal generally follows the theoretical distribution law in binary systems and is enhanced in the Ra-Ba-SO4 system and restrained in the Ra-Sr-SO4 system by high IS. However, the experimental distribution coefficient (Kd') varies widely and cannot be accurately described by the distribution equation, which depends on IS, kinetics of carrier precipitation and does not account for radium removal by adsorption. Radium removal in the ternary system is controlled by the co-precipitation of Ra-Ba-SO4, which is attributed to the rapid BaSO4 nucleation rate and closer ionic radii of Ra(2+) with Ba(2+) than with Sr(2+). Carrier (i.e., barite) recycling during water treatment was shown to be effective in enhancing radium removal even after co-precipitation was completed. Calculations based on experimental results show that Ra levels in the precipitate generated in centralized waste treatment facilities far exceed regulatory limits for disposal in municipal sanitary landfills and require careful monitoring of allowed source term loading (ASTL) for technically enhanced naturally occurring materials (TENORM) in these landfills. Several alternatives for sustainable management of TENORM are discussed.

Chemical controls on incipient Mg-silicate crystallization at 25°C: Implications for early and late diagenesis

AbstractMg-silicate minerals (e.g., stevensite, kerolite, talc, sepiolite) play an important role in the construction of facies models in lacustrine and peri-marine environments because they are sensitive to changes in solution chemistry. However, the response of Mg-silicate mineralogy to changing aqueous chemistry is only broadly understood because the mechanisms underpinning the coprecipitation of Mg2+and SiO2(aq) from surface water, and subsequent Mg-silicate crystallization, are unclear. Here we describe the results of experiments designed to systematically examine the effects of pH, Mg/Si and salinity of the parent solution on the nature of initially precipitated products. Structural interrogation of the products with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and thermal analysis (TGA/DTA) allow comparison of synthetic products with naturally occurring crystalline counterparts. In general, Mg2+and SiO2(aq) co-precipitation and nucleation of Mg-silicate layer structures first involves the rapid formation of 2:1 layers with trioctahedral occupancy and a mean coherent X-ray scattering domain between 1–2 unit cells with respect to thecaxis. Well defined but diffusehkreflections indicate two-dimensional growth, turbostratic stacking and highly variable interlayer hydration. Diffuse reflectance FTIR shows numerous structural similarities with stevensite, kerolite and sepiolite. However, TGA/DTA analysis indicates the presence of variable kerolite/stevensite interstratification not readily detectable through XRD analyses, as well as a significant degree of surface and interlayer hydration (e.g. 15–20 wt.%).We observe a number of clear trends in the products with respect to solution chemistry. For example, at low salinity, kerolite-like products dominate at high Mg/Si and high pH, whereas sepiolite-like products are formed at lower pH and lower Mg/Si. At high salinity and high Mg/Si, stevensite-like products are favoured at high pH and kerolite-like products dominate at lower pH, whereas a decrease in Mg/Si of the solution leads to sepiolite-like products at low pH and only stevensite-like products at high pH. Higher pH leads to an increase in octahedral vacancies which favour stevensite-like products; this may result from a higher rate of two-dimensional tetrahedral sheet expansion relative to the octahedral sheet, as inferred from studies of silica oligomerization and brucite growth kinetics.Together, our results indicate that the neoformation of Mg-rich silicates from solution may often begin with the rapid nucleation of hydrated 2:1 layers. Subsequent dehydration leads to progressive layer stacking order and could occur in response to wetting/drying cycles, prolonged exposure to high salinity solutions, or burial and heating. The surface and interlayer water associated with these products is undoubtedly an important source of diagenetic water in Mg-silicate-bearing successions, and the chemistry of this water upon later diagenesis should be a focus of future investigation.

Dependence of crystal nucleation on prior liquid overheating by differential fast scanning calorimeter

The degree of overheating of a melt often plays an important role in the response of the melt to subsequent undercooling, it determines the nucleation and growth behavior and the properties of the final crystalline products. However, the dependence of accessible undercooling of different bulk melt samples on prior liquid overheating has been reported to exhibit a variety of specific features which could not be given a satisfactory explanation so far. In order to determine uniquely the dependence of accessible undercooling on prior overheating and the possible factors affecting it, the solidification of a pure Sn single micro-sized droplet was studied by differential fast scanning calorimeter with cooling rates in the range from 500 to 10,000 K/s. It is observed experimentally that (i) the degree of undercooling increases first gradually with increase of prior overheating; (ii) if the degree of prior superheating exceeds a certain limiting value, then the accessible undercooling increases always with increasing cooling rate; in the alternative case of moderate initial overheating, the degree of undercooling reaches an undercooling plateau; and (iii) in latter case, the accessible undercooling increases initially with increasing cooling rate. However, at a certain limiting value of the cooling rate this kind of response is qualitatively changed and the accessible undercooling decreases strongly with a further increase of cooling rate. The observed rate dependent behavior is consistent with a kinetic model involving cavity induced heterogeneous nucleation and cavity size dependent growth. This mechanism is believed to be relevant also for other similar rapid solidification nucleation processes.

Sonocrystallization and sonofragmentation

The application of ultrasound to crystallization (i.e., sonocrystallization) can dramatically affect the properties of the crystalline products. Sonocrystallization induces rapid nucleation that generally yields smaller crystals of a more narrow size distribution compared to quiescent crystallizations. The mechanism by which ultrasound induces nucleation remains unclear although reports show the potential contributions of shockwaves and increases in heterogeneous nucleation. In addition, the fragmentation of molecular crystals during ultrasonic irradiation is an emerging aspect of sonocrystallization and nucleation. Decoupling experiments were performed to confirm that interactions between shockwaves and crystals are the main contributors to crystal breakage. In this review, we build upon previous studies and emphasize the effects of ultrasound on the crystallization of organic molecules. Recent work on the applications of sonocrystallized materials in pharmaceutics and materials science are also discussed.

Nucleation of a new phase on a surface that is changing irreversibly with time.

Nucleation of a new phase almost always starts at a surface. This surface is almost always assumed not to change with time. However, surfaces can roughen, partially dissolve, and change chemically with time. Each of these irreversible changes will change the nucleation rate at the surface, resulting in a time-dependent nucleation rate. Here we use a simple model to show that partial surface dissolution can qualitatively change the nucleation process in a way that is testable in experiment. The changing surface means that the nucleation rate is increasing with time. There is an initial period during which no nucleation occurs, followed by relatively rapid nucleation.

The relationship between dolomite textures and their formation temperature: a case study from the Permian-Triassic of the Sichuan Basin and the Lower Paleozoic of the Tarim Basin

Study of dolomite texture can contribute to understanding the process of dolomitization. This research reports textures and homogenization temperatures of dolomites from the Permian-Triassic strata in the Sichuan Basin and the Lower Paleozoic strata in the Tarim Basin, which provided insights into relationships between dolomite textures and their formation temperatures. Our results are summarized as follows: 1) dolomites with well-preserved texture indicate low dolomitization temperature. However, in certain diagenetic environments, the hydrothermal dolomitization may completely or partially preserve the original texture of dolomites. 2) The formation temperatures of non-planar dolomites are always higher than those of planar dolomites. 3) The formation temperatures of dolomite cements are generally higher than those of replacive dolomites. 4) Although the formation temperatures of saddle dolomite cements have a wide range, they show higher values than those of the planar subhedral to euhedral dolomite cements. Thus, saddle dolomites could generally be an indicator of high precipitation temperature. 5) The fluid Mg/Ca ratio is another element controlling dolomite morphology. Micritic dolomites, which precipitate from hypersaline fluids with a high Mg/Ca ratio in a subaerial environment could also have features of non-planar anhedral crystal shape because of rapid nucleation and crystallization during dolomitization.