Aqueous Ammonium Chloride Research Articles

Phase change materials (PCM) based cold source for selective freezing 3D printing of porous materials

Selective freezing three-dimensional (3D) printing is a promising manufacturing process, which can fabricate multi-scale and multi-functional porous structures with excellent geometrical and functional integrity. In this process, the fabrication temperature affects both the macroscopic and microscopic structures of the resulting part; therefore, the cold substrate plays an important role in controlling the process reliability and part quality. To improve its thermal stability and efficiency both temporally and spatially, we propose a novel cold source design based on phase change materials (PCM). Aqueous sodium chloride and ammonium chloride with different concentrations and volumes are experimentally studied to verify the effectiveness of the PCM serving as the cold source for the printing process. A holistic thermal enhancement strategy is applied to improve the duration and thermal stability. The feasibility and effectiveness is well validated by the hardware-in-loop experimental study. The results demonstrate that the proposed cold source design can lead to more reliable and stable printing process and consequently promote its wider industrial applications in various areas.

Role of Impurity Nanoparticles in Laser-Induced Nucleation of Ammonium Chloride

Results of experiments on laser-induced nucleation (LIN) in supersaturated (120%) aqueous ammonium chloride solutions are presented. Measurement of the particle-size distribution in unfiltered solutions near saturation (95%) indicates a population of nanometer-scale species with a mean hydrodynamic diameter of 750 nm, which is almost entirely removed by single-pass filtration through a poly(ether sulfone) membrane (0.2 μm pores). Analysis of filter residues reveals iron and phosphate as major impurities in the solute. Experiments show that the number of nuclei induced by LIN can be reduced substantially by preprocessing (filtering or long-term exposure to laser pulses) and that this reduction can be reversed by intentional doping with iron-oxide (Fe3O4) nanoparticles. The use of surfactant to assist dispersion of the nanoparticles was found to increase the number of laser-induced nuclei. We discuss the results with reference to mechanisms of non-photochemical laser-induced nucleation.

Modeling transport phenomena of ice slurry in an ice forming unit

In this article, multiphase convective and solidification transport phenomena of ice slurry is investigated by developing a one-domain macroscopic model to simulate its formation in a rectangular ice forming unit. Convection, sedimentation, interfacial drag, permeability, remelting and viscosity variations are incorporated into this model through the appropriate governing multiphase transport equations. Validation studies with literature data are performed to determine the most suitable drag law by comparing the position of the interface between the coherent and non-coherent zones. After establishing modified Stokes' Law as the best-suited drag model, solidification study of an aqueous ammonium chloride solution is performed. The results for the evolution of ice fraction, species distribution, temperature profile and multiphase velocity field are presented. Solid fraction gradient, due to the generation of ice particles, has a major influence on the density gradient leading to a counter-clockwise flow current resulting in the homogenization of temperature and species in the generated ice slurry.

On the mechanism of boiling heat transfer enhancement by surfactant addition

In our previous study, bubble jet and bubble explosion around a heated wire were discovered in aqueous cetyltrimethyl ammonium chloride (CTAC) solutions (Wang et al., 2016), in which the bubble explosion process was explained. The bubble explosion phenomenon was proven to be a failed coalescence of unstable bubbles which caused local disturbance and enhanced boiling heat transfer. In this paper, comparative experiments of boiling around a heated wire for different types of surfactant solutions, ethanol and silicone oil were carried out in order to explore the mechanism of surfactant addition enhancing boiling heat transfer. All these fluids had lower surface tensions than that of water. Cationic surfactant of CTAC, anionic surfactant of sodium dodecylbenzenesulfonate (SDBS) and nonionic surfactant of alkyl polyglycoside (APG) were used. Bubble jet and bubble explosion phenomenon were found in all three kinds of surfactant solutions, exhibiting excellent heat transfer effect. For the pool boiling in ethanol, only bubble jet around the heated wire was found, showing better heat transfer efficiency than water. However, weaker boiling heat transfer occurred in silicone oil without bubble jet and bubble explosion. Due to the heat sensitivity characteristics, APG solution had a lower critical heat flux (CHF) than water, while CTAC and SDBS solution had higher CHF. With all phenomena and heat transfer performances, the mechanism of boiling heat transfer enhancement by surfactant addition was confirmed, i.e., the bubble jet and bubble explosion process enhanced the boiling heat transfer in surfactant solution rather than low surface tension.

Solidification with Buoyancy Induced Convection: Evaluation of Different Mushy Zone Formulations

A comparative assessment is performed between purely porous formulation of the mushy zone controlled by permeability and the hybrid formulations controlled by both permeability and viscosity of the mushy zone during solidification of a binary alloy. The Darcy’s Carman-Kozeny equation is used to model the permeability of the mushy zone in porous formulation for all the models. The first hybrid model employs switching functions to simultaneously control the permeability and viscosity of the mushy zone up to a critical solid fraction and thereafter it switches to a purely permeability controlled porous formulation. The second hybrid model assumes mushy zone to be non-newtonian slurry with the liquid viscosity following a power law up to the critical solid fraction and a permeability controlled porous medium thereafter. A twodimensional computational domain of aqueous ammonium chloride (NH 4 Cl-H 2 O) solution employing continuum mixture approach is considered for the analysis. Model with purely porous mushy zone formulation showed higher solutal gradients in the mushy zone resulting in higher solutal buoyancy driven convection in mushy zone along with higher bulk macrosegregation effects in comparison to the hybrid models. Both the hybrid models showed potential of capturing the settled free floating particles and broken dendrites with the non-newtonian slurry hybrid model showing potential of capturing the liquidus irregularities.

Heatline Visualization During Solidification of a Eutectic Solution in a Rectangular Cavity

The present work is focused on the visualization of heatline during solidification. The investigation considers a rectangular cavity filled with eutectic aqueous ammonium chloride solution. In order to develop Rayleigh-Bennard convection in the cavity, the temperatures of the top and bottom walls are maintained below and above eutectic temperature of the solution, respectively, whereas the vertical walls are assumed to be adiabatic. The solidification process is modelled by a set of mass, momentum and energy conservation equations coupled with boundary conditions. The governing differential equations are solved using semi-implicit finite volume method according to SIMPLER algorithm with the help of line-by-line TDMA solver. The evolution of heatline pattern during solidification is presented. From the evolution of solid–liquid interface, it is found that the solidified layer undergoes remelting at the solid–liquid interface during later stages of solidification as a consequence of thermal superheat. In the present work, the cause of the remelting phenomenon during solidification is investigated in details using energy flux vectors. It is observed that convection loop pattern i.e. energy flow below the remelted interface changes at the time of remelting.

Removal of ammonia nitrogen from leachate of Muribeca municipal solid waste landfill, Pernambuco, Brazil, using natural zeolite as part of a biochemical system

The inadequate disposal of leachate is one of the key factors in the environmental impact of urban solid waste landfills in Brazil. Among the compounds present in the leachates from Brazilian landfills, ammonia nitrogen is notable for its high concentrations. The purpose of this study was to assess the efficiency of a permeable reactive barrier filled with a natural zeolite, which is part of a biochemical system for the tertiary treatment of the leachate from Muribeca Municipal Solid Waste Landfill in Pernambuco, Brazil, to reduce its ammonia nitrogen concentration. This investigation initially consisted of kinetic studies and batch equilibrium tests on the natural zeolite to construct the sorption isotherms, which showed a high sorption capacity, with an average of 12.4 mg NH4+.L−1, a value close to the sorption rates found for the aqueous ammonium chloride solution. A permeable reactive barrier consisting of natural zeolite, as simulated by the column test, was efficient in removing the ammonia nitrogen present in the leachate pretreated with calcium hydroxide. Nevertheless, the regenerated zeolite did not satisfactorily maintain the sorption properties of the natural zeolite, and an analysis of their cation-exchange properties showed a reduced capacity of 54 meq per 100 g for the regenerated zeolite compared to 150 meq per 100 g for the natural zeolite.

Plasma electrolytic modification of the VT1-0 titanium alloy surface

The features of the anodic plasma electrolytic treatment of commercial titanium in an aqueous ammonium chloride solution with ammonia and glycerol additions are investigated. It is revealed that the modified layer comprises an external TiO2 or TiO layer with micropores of up to 100 nm and a diffusion sublayer after nitriding in the solution with the ammonia addition. It is ascertained that the anodic dissolution of the titanium alloy dominates over its oxidation at treatment voltages reaching 210 V and an ammonium chloride concentration of 100 g/L. This effect is accompanied by a decrease in the sample mass. The sample mass grows due to an increase in the oxide layer exceeding the dissolution losses at higher voltages and ammonium chloride concentrations. It is shown that the corrosion current density in Ringer’s solution can be decreased after commercial titanium is treated in the ammonium chloride and glycerol solution.

H2O-NH4Cl system: Thermodynamics and structure of supersaturated (8÷28m) solutions at 298.15 K

Thermodynamic characteristics are determined for supersaturated (8÷28m) aqueous ammonium chloride solutions at 298.15 K: activity as well as partial molar enthalpy, volume, and excess entropy of water, osmotic coefficients, density, and salt hydration numbers. The relative humidity above the solution decreases from 75.6% (8m solution) to 44.7% (28m solution). A directly proportional dependence is found between the enthalpy and entropy characteristics. The negative values of the nonideal portion of the Gibbs energy are due to structural effects (excess entropy). The excess entropy of water has the same value 1.8 J/(mol·K) in supersaturated 12m NaCl and 28m NH4Cl. The ratio 12/28 = 3/7 is also valid for other “isoentropic” molalities of the said salts.

Remelting and interface dynamics during solidification of a eutectic solution in a top-cooled rectangular cavity: A numerical study

The present work is a numerical investigation on the occurrence of remelting phenomenon during solidification of a eutectic aqueous ammonium chloride solution in a top-cooled rectangular cavity. The analysis is performed following a fixed-grid single-domain approach. Accordingly, the solidification process is represented by a set of mass, momentum and energy conservation equations, where the enthalpy update scheme is used to trace the solid–liquid interface during solidification. The set of governing differential equations is solved using semi-implicit finite volume method, based on SIMPLER algorithm, applying line-by-line TDMA solver. The present simulation predicts the distribution of temperature and streamline along with fraction of solid in the computational domain, and evolution of the solidified layer during solidification. The simulation shows remelting of solidified layer at the solid–liquid interface during later stages of solidification due to irregular superheat of the bulk solution convected towards the solid–liquid interface. Hence, the occurrence of the remelting phenomenon during solidification is studied by evaluating the interface growth history as a function of the process parameters, namely, cavity height and thermal gradient imposed across the cavity. It is found that there is a small increase in the solidification growth rate with increase in cavity height, where the possibility of remelting is high. With the increase in imposed thermal gradient, the solidification growth rate increases significantly and the occurrence of remelting disappears.

Reduced Limestone Consumption in Steel Manufacturing Using a Pseudo-catalytic Calcium Lixiviant

A mineral carbonation method for using anthropogenic carbon dioxide emissions is discussed. In this method, steel manufacturing slags are carbonated with gaseous carbon dioxide at atmospheric pressure and temperature using an aqueous ammonium chloride solution. This lixiviant extracts calcium selectively from the slag material, after which the dissolved calcium is precipitated as calcium carbonate. A flue gas stream can be used as a CO2 source without pre-separation. The reactions occur pseudo-catalytically in one vessel, resulting in considerable savings regarding process capital costs and reagent usage compared to a previously developed two-step carbonation method (Slag2PCC). The one-step method uses steel slag more efficiently, potentially reducing the amount of landfilled slag while capturing significantly more carbon dioxide in the same amount of slag. The two-step method produces >95% pure calcium carbonate, which can be used, e.g., in papermaking, while the one-step method is capable of manufacturi...

Filling-box process during solidification of a liquid hypoeutectic binary solution

Solidification of binary solutions often occurs in many industrial applications, including the casting of binary alloys. In this study we consider the effect of a side cooling wall on the development of double-diffusive convection during solidification of a hypoeutectic aqueous ammonium chloride (NH4Cl–H2O) solution. To study flow development during solidification of this solution, we used the shadowgraph technique, particle image velocimetry, and a thermochromic-liquid-crystal slurry. In addition, the transient temperature distribution within the test cell was measured by type-T thermocouples. The results of these experiments revealed that the filling-box process originated from the bottom of the test cell to the top. This process induced several double-diffusive layers and counterclockwise roll cells in the melt, mainly caused by double-diffusive convection. Consequently, the filling-box process may cause serious V-segregates and material defects in solidified ingots.

小型水样氨氮自动光学检测装置

A compact optical sensor for the automatic detection of ammonia nitrogen in water was developed based on a combination of liquid-gas separation and gas-phase reversible colorimetry.The sensor consists of a sample chamber,a test chamber,aprogram-controlled sampling unit and a data-processing circuit module.The sensor performance was investigated by using a series of aqueous ammonium chloride solutions with different concentrations as the ammonia nitrogen samples.The linear relationship between the measured absorbance and the ammonia-nitrogen concentration was obtained and the high reliability of sensor was demonstrated by comparing the measured and given concentrations of standard ammonia nitrogen samples.The experimental results indicate that the sensor works continuously and automatically for a long time at a room temperature and has good repeatability.The detection limit is 0.04mg/L(NH3-N).The sensor is characterized by its smaller volume,light-weight,lower cost and power consumption,high-level automation,and it is suitable for on-site rapid detectionof ammonia nitrogen in a practical water environment.

Experimental Study of Aqueous Ammonium Chloride in Pool Boiling Heat Transfer

Saturated nucleate boiling of aqueous ammonium chloride on a nichrome wire heater has been experimentally investigated. The boiling performance is enhanced by using of ammonium chloride as an additive. The maximum level of enhancement is observed up to 2,600 ppm concentration of additive. For concentrations more than 2600 ppm, significant enhancement is not recorded. Enhancement observed is due to the change in the thermo-physical properties of the aqueous solution. It is observed that as ammonium chloride is added to distilled water, the surface tension of the mixture considerably reduces. The experiment is carried out above critical heat flux to observe the behavior of boiling at higher heat flux.

Study of Freckles Formation During Directional Solidification Under the Influence of Single-Phase and Multiphase Convection

Formation of freckles during directional solidification of hypereutectic aqueous ammonium-chloride in a bottom cooled cavity is studied numerically. The system studied is thermally stable but solutally unstable, which causes plume type convection and formation of channels in the growing solid mush. Solidification of hypereutectic solutions is usually characterized by detached and drifting solid crystals, thus resulting in multiphase convection. The numerical simulation is performed using a fixed grid single domain approach with single-phase and multiphase convection phenomena. For the multiphase convection modeling in the solidifying system under consideration, the mushy region is assumed to consist of an immobile coherent zone containing packed equiaxed crystals and a mobile noncoherent zone where the solid crystals are able to move. The two zones are demarcated by a critical solid fraction criterion, referred to as the coherency point. The overall effects of drifting solid phase on the freckles formation are compared with the results from conventional single-phase convection model.

Aqueous ammonia and ammonium chloride hydrates: Principal infrared spectra

The infrared (IR) spectra of aqueous ammonia (NH3) and aqueous ammonium chloride (NH4Cl) were recorded by attenuated total reflectance to obtain their molecular organizations. Factor analysis (FA) of the spectra revealed two hydrates for each species: (NH3)2⋅H2O and NH3⋅3H2O; NH4+,Cl-2·H2O; and (NH4+,Cl-)·3H2O, respectively. The hydrate spectra and species abundances were obtained as a function of total concentrations. From this the equilibrium equation between the two ammonia hydrates was determined: 2[(NH3)2·H2O]+5(H2O)2⇌4[NH3·3H2O] with its equilibrium constant Kα=(2.3±0.6)×10−5L3mol−3. Similarly, for the two ammonium chloride hydrates the equation is 2[(NH4Cl)2·H2O]+5(H2O)2⇌4[NH4Cl·3H2O] with its equilibrium constant: Kβ=(4±1)×10−7L3mol−3. Band simulations of the hydrate spectra were compared to that of pure liquid water and parent molecules. For aqueous ammonium chloride solutions the water and all ammonium hydrate bands are slightly displaced from that of pure water and pure ammonium chloride, respectively. However, for ammonia hydrates the situation is different: compared to the gas situation the hydrate water bands have similar displacements as that of pure liquid water; the ammonia deformation bands are also little displaced but the stretching bands are strongly red shifted. These shifts, which are even greater than that in pure liquid water, are attributed to strong hydrogen bonding situations: water–H with N–ammonia and ammonia–H with O–water. This explains the high solubility of ammonia in water. The comparison between the spectra of aqueous ammonium chloride and ammonia hydrates indicates that ammonium ion is not present in aqueous ammonia from 11.3M down to at least our detection limit of 3mM NH3.

Critical profiles of chiral diether-mediated asymmetric conjugate aminolithiation of enoate with lithium amide as a key to the total synthesis of (−)-kopsinine

Chiral diether-mediated asymmetric aminolithiation of indolylpropenoate with lithium amide in toluene at −78 °C for 15 min gave, after aqueous ammonium chloride quench, the corresponding conjugate addition product with 97% ee in 89% yield. If hydrogen chloride in methanol was selected as a quencher, however, aminolithiation at −78 °C for 3 h gave the corresponding adduct with 97% ee in 54% yield, along with recovery of the starting enoate in 39% yield. Based on this finding of an incomplete and slow reaction at −78 °C, the aminolithiation conditions were optimized to be at −60 °C for 15 h and subsequent enolate trap with alkyl halide upon an addition of DMPU afforded the desired aminoalkylation product with 98% ee in 89% yield. Further approach toward total synthesis of (−)-kopsinine was carried out by examining asymmetric aminolithiation with N-hydroxyethylamine equivalent, one-pot piperidine formation, and Claisen condensation.

Mushy-layer dynamics in micro and hyper gravity

We describe the results of experiments on mushy layers grown from aqueous ammonium chloride solution in normal, micro, and hyper gravity environments. In the fully developed chimney state, the chimney plume dynamics differ strikingly when conditions change from micro to hyper gravity. In microgravity, we find fully arrested plume motion and suppressed convection. As gravity exceeds Earth conditions, we observe a host of phenomena, ranging from arched plumes that undergo forced Rayleigh-Taylor instabilities to in-phase multiple plume oscillatory behavior. For the same initial solute concentrations and fixed boundary cooling temperatures, we find that, in runs of over two hours, the averaged effects of microgravity and hypergravity result in suppressed growth of the mushy layers, a phenomenon caused by a net enhancement of convective heat and solute transport from the liquid to the mushy layers. These behaviors are placed in the context of the theory of convecting mushy layers as studied under normal laboratory conditions.

Suppressing freckles during solidification due to periodic motion of top liquid layer

In the past, one main area of focus in the solidification of a liquid binary alloy has been the investigation of strategies for the elimination or minimization of the presence of “double-diffusive convection”, the main cause of poor quality alloys. In particular, “freckles” occurring in the solidification process cooled from the bottom can result in severe material defects in the final product. The objective of this study is to investigate the effect of a periodic lid-driven flow on the development of double-diffusive convection during solidification from below to aid in the removal or reduction of the occurrence of this convection that causes the formation of freckles. A hyper-eutectic aqueous ammonium chloride (NH4Cl–H2O) solution was used as the test sample and was contained in an enclosure cooled from the bottom to study flow development and heat and mass transport phenomena during solidification. Flow visualization using the shadowgraph technique and measurements of the temperature distribution, the concentration distribution, and the movement of the liquid–mush interface were conducted during solidification. The experimental results revealed that the imposed periodic lid-driven flow had a positive effect on the process by suppressing the plumes emanating from the channels and reducing the strength of the double-diffusive convection.

Finite-sample-size effects on convection in mushy layers

AbstractWe report theoretical and experimental investigations of the flow instability responsible for mushy-layer convection with chimneys, drainage channels devoid of solid, during steady-state solidification of aqueous ammonium chloride. Under certain growth conditions a state of steady mushy-layer growth with no flow is unstable to the onset of convection, resulting in the formation of chimneys. We present regime diagrams to quantify the state of the flow as a function of the initial liquid concentration, the porous-medium Rayleigh number, and the sample width. For a given liquid concentration, increasing both the porous-medium Rayleigh number and the sample width drove a transition from a weakly convecting chimney free state to a state of mushy-layer convection with fully developed chimneys. Increasing the concentration ratio stabilized the system and suppressed the formation of chimneys. As the initial liquid concentration increased, onset of convection and formation of chimneys occurred at larger values of the porous-medium Rayleigh number, but the critical cell widths for chimney formation are far less sensitive to the liquid concentration. At the highest liquid concentration, the mushy-layer mode of convection did not occur in the experiment. The formation of multiple chimneys and the morphological transitions between these states are discussed. The experimental results are interpreted in terms of a previous theoretical analysis of finite amplitude convection with chimneys, with a single value of the mushy-layer permeability consistent with the liquid concentrations considered in this study.