Precipitation Phase Boundary Research Articles

Effect of recrystallization annealing on microstructure and tensile properties of Inconel 617B alloy cold rolled pipes

The effects of recrystallization annealing on the microstructure evolution of Inconel 617B alloy pipes and its tensile behavior at 750 °C were investigated. As the annealing temperature increases, the grain size and grain growth rate increase dramatically due to the dissolution of the precipitated particles and the enhanced diffusion of solute atoms. Oil-quenched (OQ) samples generated evenly dispersed Cr-rich carbides with stacking faults (SFs) and Lomer-Cottrell (L-C) locks near the carbides, whereas water-quenched (WQ) samples had comparatively clean grain boundaries and matrix. The interaction of Cr-rich phases and dislocations in the oil-quenched sample resulted in the strengthening of the alloy. Besides, because the precipitation of the Cr-rich phase led to the reduction of localized stacking fault energy (SFE), the alloy could coordinate the deformation by forming nano-deformation twins, which significantly improved the tensile ductility and allowed the alloy to have a larger work hardening index (n). At 1180 °C, holding 4 min, then oil quenched annealing conditions, the sample achieved the excellent strength-elongation combination, i.e., the ultimate tensile strength (UTS) of 445 MPa and the elongation (EI) of 47.8% under tensile loading at 750 °C, since the appropriate grain size cooperated with the precipitated phase. The stress concentration caused by the Cr-rich phase in the grain leads to cavitation nucleation. However, the cavitation nucleation at the triple junction of grain boundaries caused by the precipitation phase and grain boundary slips in the samples with other annealing conditions was still the foremost responsible for the fracture.

Dislocations of Ti-600 Alloy Crept at 600°C with Two Stresses

Microstructure and dislocations were observed for Ti-600 alloy crept at the temperature of 600°C with the stress of 200MPa and 300 MPa. The results indicate that more precipitation phases could be found both in β phases and at phase boundaries for the alloy after creep tests, and the width of the phase boundary become broader obviously. Also more dislocations could be seen at or around the precipitation phases for the alloy crept at 600°Cwith the stress of 200MPa. Dislocation density is rather big in some regions, dislocations aggregate in precipitation phases, phase boundaries and sub-grain boundaries. Some tangled dislocations or regular arranged dislocations could also be found around precipitation phases. Condensed three-dimensional dislocation meshes could be found in the alloy crept for the alloy crept at 600°Cwith two stresses. For the alloy crept at 600°Cwith the stress of 200MPa, faults originated from boundaries of α lamellar could be found in α lamellar. Some of these faults extend to boundaries of α lamellar, and some stop or end off in α lamellar. While for the alloy crept at 600°Cwith the stress of 300MPa, dislocation tend to arrange in dislocation walls, form bamboo-like structure along the direction of α lamellar, which would expand and penetrate the whole grain of elongated dislocation walls, and at last stop at grain boundaries.

Synergisms in Binary Mixtures of Anionic and pH‐Insensitive Zwitterionic Surfactants and Their Precipitation Behavior with Calcium Ions

AbstractThis work aims to investigate synergy in anionic and zwitterionic surfactant mixtures, as they result in better interfacial properties and micellization behavior. Various mixtures of the pH‐insensitive zwitterionic surfactant 3‐(decyldimethylammonio) propanesulfonate (Zwittergent 3–10) and sodium dodecylsulfate (SDS) were prepared in aqueous solution at a range of pH values between 2 and 13. The thermodynamic parameters during mixed surfactant adsorption at the air/water interface are obtained and the results show the mixed surfactant systems having superior properties to the constituent surfactants. Experimentally, the mixed surfactant solutions clearly improve the surface activities by lowering the critical micelle concentration (CMC) and lowering the surface tension at the air/water interface. The synergisms are investigated through the interaction parameters estimated from regular solution theory that is used to quantitatively describe the nonideality of surfactant mixtures. High negative interaction parameters are obtained from these surfactant mixtures. Experimental precipitation phase boundaries of SDS in the presence of CaCl2 were also investigated in mixtures containing pH‐insensitive zwitterionic surfactant at different pH levels from 2 to 13 and SDS mole fractions of 0.25, 0.50, 0.75, and 1.00. Changes in the precipitation phase boundaries are due to the changes in the speciation or activities of the major components both below and above the CMC. As a result, the precipitation phase boundaries are pH dependent. In addition, mixed micellization and counterion binding to the micelle also change the precipitation phase boundary above the CMC. The activity‐based solubility product of calcium dodecylsulfate is also determined from the precipitation phase boundaries below the CMC. X‐ray diffraction patterns and SEM images confirm that only calcium dodecylsulfate precipitates in the soap scum for all pH and surfactant compositions studied.

Modeling of Precipitation Phase Boundaries in Mixed Surfactant Systems Using an Improved Counterion Binding Model

AbstractAnionic surfactants, commonly used in household products and the detergency industry, tend to precipitate with divalent counterions in hard water. The unsightly soap scum thus formed also removes the surfactant from the cleaning action. The current research has improved prediction of the precipitation phase boundary for mixtures of surfactants in hard water in two ways: firstly, an accurate value of the solubility product (KSP) has been determined for the calcium salt of 4‐octylbenzene sulfonate, and accurate temperature dependent KSP values have been determined for the calcium salts of dodecyl sulfate and decyl sulfate; secondly, improvements in prediction of the precipitation phase boundary have been achieved using an improved model. The KSP values of the decyl sulfate and dodecyl sulfate salts strongly increase with increasing temperature, with the shorter chain surfactant having significantly higher KSP than its longer chain analogue. At 30 °C the KSP of the 4‐octylbenzenesulfonate salt is similar to that of the dodecyl sulfate salt, perhaps due to the similarity in the length of their hydrocarbon tails. A recent counterion binding model proposed by our research group and micellization models have been used to model the precipitation phase boundaries for both single anionic surfactant and binary mixed anionic surfactant systems, improving thermodynamic modeling of the precipitation phase boundary of single and binary mixed anionic surfactant systems. In particular, the improved model of counterion binding has allowed the model to predict the phase boundary accurately over a range of temperatures.

Precipitation and Micellar Properties of Novel Mixed Anionic Extended Surfactants and a Cationic Surfactant

AbstractSurfactant‐modified mineral surfaces can provide both a hydrophobic coating for adsorbing organic contaminants and, in the case of ionic surfactants, a charged exterior for adsorbing oppositely charged species. This research evaluates the precipitation phase boundaries and synergistic behavior of the mixtures of carboxylate‐based anionic extended surfactants with a pyridinium‐based cationic surfactant. One cationic surfactant (cetylpyridinium chloride) and four anionic extended surfactants were studied. The anionic surfactants studied were ethoxy carboxylate extended surfactants with average carbon chain lengths of either 16 and 17 or 16 and 18 with 4 mol of a propylene oxide group and a different number of moles of an ethylene oxide group (2 and 5 mol). Precipitation phase boundaries of mixed anionic extended surfactants and cationic surfactant were evaluated to ensure that the surface tension studies are in regions without precipitate. Surface tension measurements were conducted to evaluate the critical micelle concentration of individual and mixed surfactant systems. Precipitation phase boundaries of these novel mixed surfactant systems showed greatly reduced precipitation areas as compared to a conventional mixed surfactant system which is attributed to the presence of the ethylene oxide and propylene oxide groups and resulting steric hindrances to precipitation. Moreover, it was demonstrated that the CMC of mixed surfactant systems were much lower than that of individual surfactant systems. Synergism was evaluated in the four systems studied by the β parameter which found that all systems studied exhibited synergism. From these results, these novel mixed surfactant systems can greatly increase formulation space (reduce the precipitation region) while maintaining synergism, although slightly reduced from conventional anionic‐cationic mixtures reported previously.

Explanation for the Increased Induction Times in Binary Mixed Anionic Surfactant Mixtures

The induction time for precipitation of pure sodium dodecylsulfate (NaDS) solutions by CaCl2 both below and above the cmc at a specific temperature depends only on the supersaturation ratio of the precipitating species in the bulk solution, rather than the means of achieving the supersaturation (changes in calcium ion concentration or in surfactant concentration). For mixed NaDS/sodium decylsulfate (NaDeS) systems precipitated by CaCl2, the induction time is only a function of the supersaturation ratio calculated based on Ca(DS)2, which is formed from these solutions, since its solubility product is orders of magnitude less than that of Ca(DeS)2. The increase in induction time in mixtures of these surfactants, compared to pure systems of the same total surfactant content, is only due to the change in the concentration of the precipitating species (DS) because of changes in the molar ratio of the surfactants present and thermodynamic changes due to mixed micellization. For mixed NaDS/sodium octylbenzenesulfonate (NaOBS) systems precipitated by CaCl2, the precipitation of calcium surfactant salts can result in either Ca(DS)2 or Ca(OBS)2, depending on the conditions, due to the similar KSP values of these two salts. Precipitation of Ca(OBS)2 occurs in systems of approximately 0−50 mol % NaDS, and inhibition of precipitation is not found in mixed NaDS/NaOBS systems for this range of surfactant compositions. For precipitation of Ca(DS)2 in systems between 50 and 100 mol % NaDS, the value of the induction time as a function of supersaturation ratio calculated based on Ca(DS)2 is slightly larger than that found in the pure NaDS systems. Inhibition in these mixtures is mainly due to the change in concentration of the precipitating species (monomer DS) because of changes in surfactant composition in the solution phase and changes in the precipitation phase boundary because of the thermodynamic changes resulting from mixed micellization; however, there is also a small amount of kinetic inhibition.

Interaction Between an Anionic and an Amphoteric Surfactant. Part II: Precipitation

AbstractUse of amphoteric and anionic surfactants is very common in practical formulations such as shampoos and hand dishwashing products. Precipitation of mixtures of dimethyldodecylamine oxide (DDAO) as an amphoteric surfactant and sodium dodecyl sulfate (SDS) as an anionic surfactant were studied at different pH levels. The DDAO is a pH‐sensitive surfactant and its protonation can be expressed in terms of a pKa similar to an acid dissociation constant. The protonated form of DDAO carries a positive charge and precipitates with the oppositely charged SDS. Therefore, precipitation phase boundaries are pH dependent due to the varying degree of DDAO protonation. By combining the use of regular solution theory and the pseudophase separation model to describe micellar mixing nonidealities with the precipitate solubility product constant and the protonation dissociation constant, a model to predict the precipitation phase boundary is presented here. The model agrees well with experimental phase boundaries at different pH levels.

Physical Behavior of Asphaltenes

Asphaltenes are molecules which can undergo a thermodynamic liquid−liquid phase separation from sufficiently paraffinic solutions. The asphaltene-rich phase thus formed often has a high glass-transition temperature, and thus a fractal morphology results. Here, we report temperature and time-dependent neutron scattering studies which elucidate the solution behavior of asphaltenes. The temperature−composition dependence of the asphaltene precipitation phase boundary is shown to be consistent with that expected due to solution theory. We report temperature- and concentration-dependent viscosity data which demonstrate that the high viscosity of asphaltene-containing systems is due to their proximity to the glass transition and the reduction of viscosity with dilution is no more than a plasticization effect, or a reduction of the glass transition with dilution.

Polyelectrolyte chain dimensions and concentration fluctuations near phase boundaries

We have measured the temperature (T) dependence of the correlation length (ξ) for concentration fluctuations in aqueous solutions of sodium–poly(styrene sulfonate) with a fixed level of added barium chloride salt. Apparent critical behavior is observed upon lowering the temperature to precipitation phase boundaries that complements our earlier work on salt-dependent behavior. We interpret experimental deviations from ξ−2 versus T−1 as crossover from the mean field to the Ising universality class. We also measured the radius of gyration (Rg) of labeled chains and ξ for semidilute polyelectrolyte solutions at low ionic strengths. We recovered the familiar result of ξ scaling with polymer concentration (Cp) and degree of polymerization (N), such that ξ=(73±9) N0Cp−0.48±0.03 [Å], and using SANS high concentration labeling Rg=(400±28)Cp−0.24±0.01 [Å] (for N=577) and Rg=(2.8±2.1)N0.6±0.1 [Å] (for Cp=206 gL−1), respectively. The indices recovered are in agreement with theoretical predictions for low ionic strength semidilute solutions. Such experiments offer insight into relatively unexplored phase behavior in charged macromolecular solutions.

Multicarboxylic Biosurfactants as a Model for Designing Hard Water and High Salt Tolerance

It was shown that the salt and hard water tolerance, and precipitation phase boundary behavior of spiculisporic acid salts were different from monobasic fatty acid soaps. It was demonstrated that spiculisporic acid salts showed considerable surface activities even in the presence of sodium and Ca2+ in spite of anionic surfactants. These characteristics and the significant difference of precipitation phase boundary may be attributed to the difference of the hydrophilicity caused by carboxylic, carboxylate, and lactone moieties due to the extent of neutralization or saponification degrees of spiculisporic acid to mono-, di-, to tri-sodium salt.

Precipitation of Tricarboxylic Acid Biosurfactant Derived from Spiculisporic Acid with Metal Ions in Aqueous Solution

The precipitation phase boundary of trisodium salt of 2-(2-carboxyethyl)-3-decyl maleic anhydride (DCMA-3Na) was determined with various metal ions, such as Ca +2, Mg +2, Zn +2, Cu +2, and Al +3. The tricarboxylic-acid-type biosurfactant DCMA-3Na was synthesized from spiculisporic acid. Solid precipitates were analyzed by FT-IR and an optical microscope. The precipitation boundary diagrams were prepared through both the measurement of the supernatant solution concentration and the visual inspection of precipitate formation. The multivalent ion concentration necessary to cause the precipitation of the surfactant (i.e., tolerance) decreased as the DCMA-3Na concentration increased, up to a certain critical concentration in the same way as with chemically synthesized commercial surfactants such as SDS. However, unlike the commercial surfactants, the tolerance of DCMA-3Na toward hardness ions did not increase when the concentration of surfactant increased further above the critical point. This interesting phenomenon is due to the fact that excess amounts of sodium ions dissociated from the three carboxylate groups in the head group of DCMA-3Na compete with the multivalent ions over binding onto the micelle surface.

Colloidal properties of ?-sulfonated fatty acid methyl esters and their applicability in hard water

The calcium salts of α-sulfonated fatty acid methyl esters were prepared, and the physico-chemical properties such as solubility, critical micelle concentration, aggregation number, and precipitation phase boundary were studied to clarify the reasons for the good hardness tolerance manifested by α-sulfonated fatty acid methyl esters.

Precipitation of mixtures of anionic and cationic surfactants: II. Effect of surfactant structure, temperature, and pH

Precipitation phase boundaries for sodium alkyl sulfate/dodecylpyridium chloride were measured over a wide range of surfactant concentrations as a function of pH, temperature, and anionic surfactant alkyl chain length. Increasing temperature and decreasing surfactant alkyl chain length generally tend to decrease the tendency to precipitate. A previously developed model for predicting anionic/cationic surfactant precipitation phase boundaries described the experimental results very well except in some high surfactant concentration regions where coacervate and gels formed. This model uses a simple solubility product relationship, with regular solution theory, to describe mixed micelle formation. The environment of the alkyl chains is more favorable in the precipitate than in the micelles, from measured thermodynamic properties.

Precipitation phenomena in mixtures of anionic and cationic surfactants in aqueous solutions

The precipitation phase boundary for mixtures of sodium dodecyl sulfate (NaDS) and dodecylpyridinium chloride (DPCl) is determined over a wide range of concentrations. The phase boundary is composed of a monomer—precipitate equilibrium curve, where no micelles exist in solution, and two branches (one NaDS-rich and one DPCl-rich) where monomer, micelles, and precipitate exist in equilibrium. A model is developed to predict the precipitation boundary by combining regular solution theory, to calculate monomer—micelle equilibrium, with a solubility product relationship between surfactant monomer concentrations, to calculate monomer—precipitate equilibrium. Results from the model are shown to work well, except in regions where coacervate formation occurs. An empirical modification to the model is used to account for coacervate formation so that all experimental phase boundaries can be described quite well. The model can also predict the amount of precipitate that will form in any NaDS—DPCl mixture and the results are shown to agree well with experimental measurements.

Surfactant precipitation in aqueous solutions containing mixtures of anionic and nonionic surfactants

AbstractThe salinity tolerance (precipitation phase boundary) is measured for a mixed anionic/nonionic surfactant system above the CMC. For any total surfactant concentration, the salinity tolerance is shown to increase as the percentage of nonionic surfactant in the system is increased. A model is developed which can predict the phase boundaries for the mixed surfactant system from the pure anionic surfactant phase boundary and information about mixed micelle formation. In the model, precipitation is viewed as a solubility product relationship between the anionic surfactant monomer and the total unassociated counterion. The reason that salinity tolerance (or counterion concentration necessary to cause precipitation) increases with addition of nonionic surfactant is that mixed micelle formation reduces the anionic surfactant monomer concentration. For the experimental studies, sodium dodecyl sulfate is the anionic surfactant, a polyethoxylated nonylphenol is the nonionic surfactant, and sodium chloride is the added salt.