Incipient Precipitation Research Articles

Quench sensitivity of a heat treatable aluminum alloy

A series of aging treatments were made on samples cut from bars of a 6063 heat treatable aluminum alloy that were solubilized for 4h at 520°C, and were cooled down to room temperature by placing one of their ends into a shallow tank of water to produce a continuous thermal gradient along their length. Heating and cooling cycles were recorded by inserting thermocouples in different positions along the length of the bars, the output of these devices was fed into a data logging system. Aging was carried out at three different temperatures (130, 180 and 230°C) for periods of time ranging from 0.5 to 64h on samples cut from positions close to those at which the thermocouples were located in the bars. A continuous cooling precipitation (CCP) diagram was constructed from the cooling curves and, from it, the time available for precipitation during cooling was computed. It was found that the maximum value of hardness after aging depended on the cooling rate, when this was conducted at rates lower than 10°C/s. It can be concluded that quench sensitivity is caused by incipient precipitation taking place during cooling, and that the maximum value in hardness that can be achieved by aging the material depends on the length of time available for precipitation while cooling.

The Effects of Inorganic Solid Particles on Water and Crude Oil Emulsion Stability

Small inorganic particles strongly enhance water−crude oil emulsion stability when interactions with asphaltenes promote particle adsorption at the oil−water interface. A variety of particle types have been studied to investigate the controlling factors for particle-stabilization effectiveness. Emulsion stabilities were determined by the extent of water resolved after centrifugation and the electric field required for emulsion breakdown. All particles used were hydrophilic and stabilized oil-in-water emulsions if small enough to be interfacially active. When dried and exposed to asphaltene-containing oil phases, the particles stabilized water-in-oil emulsions. Decreased extents of preadsorbed water, decreased particle sizes, and increased particle concentrations enhanced water-in-oil emulsion stability. Investigations with model emulsions showed that an intermediate state of asphaltene aggregation, near the point of incipient precipitation, is required for particle modification and emulsion stabilization. Increased asphaltene−particle interactions increased emulsion stabilization effectiveness.

Effect of oxidised starch on calcium pectinate gels

Small-deformation oscillatory measurements have been used to study the effect of low-viscosity oxidised starch on the rheology of calcium pectinate gels formed by controlled cooling from the sol state at high temperature. Large reductions in modulus (G′; 0.5% strain; 10°C) were observed at starch concentrations below the minimum critical concentration for gelation of oxidised starch alone under the same conditions (∼32wt%). This behaviour is tentatively ascribed to thermodynamic incompatibility between the two polymers causing incipient precipitation of calcium pectinate within the gel network.

Ca 2+-induced gelation of low methoxy pectin in the presence of oxidised starch. Part 1. Collapse of network structure

The effect of oxidised starch on the networks formed by low-methoxy pectin (2.0 wt%), on cooling (from 90 to 5°C) in the presence of Ca 2+ (10–100% stoichiometric) has been explored by rheological measurements under low-amplitude oscillatory shear, and by light microscopy. At low concentrations of Ca 2+, incorporation of increasing concentrations of starch (across the range 0–30 wt%) causes a progressive increase in modulus ( G′ at 5°C), attributed to segregative interactions between the two polymers promoting conversion of pectin from the expanded coil conformation to a more compact associated form. Incorporation of starch at higher Ca 2+ concentrations, however, causes large reductions in gel strength, which arise from sharp drops in G′ during cooling. The Ca 2+ concentration at the transition from enhancement to depletion of network strength is independent of starch concentration, and increases with increasing degree of esterification of the pectin component (across the DE range 31.1–55.8%). Reduction in gel strength is attributed to incipient precipitation of pectin into large aggregates within a supporting calcium pectinate network. This interpretation is supported by microscopy, which shows conversion from a homogeneous distribution of the two polymers to a grossly heterogeneous structure (length-scale ∼10–50 μm) with increasing concentration of Ca 2+, and by quantitative analysis of gel moduli reported in the following paper.

Probing the Kinetics of β-Amyloid Self-Association

Spontaneous conversion of β-amyloid peptide (Aβ) from soluble monomer to insoluble fibrillar precipitate may underlie the neurodegeneration associated with Alzheimer's disease. A complete description of Aβ self-association kinetics requires identification of the oligomeric species present and the pathway of association, as well as quantitation of rate constants and reaction order. Previously published work delineating progress in developing quantitative kinetic models is reviewed briefly. The use of light scattering to probe Aβ fibril size and shape as a function of time and concentration is described. Data describing Aβ self-association at physiological pH starting from the urea-denatured state are presented. High-molecular-weight species formed rapidly, within minutes of dilution. At 70 μM, the size of the major fibrillar species was virtually constant with time, whereas at 280 μM two populations were detected, each of which increased in size with time. Incipient precipitation, prior to the appearance of a visible solid phase, was detected reliably by dynamic light scattering. Surprisingly, precipitates appeared earliest at the lowest concentration, and the physical state of the precipitate changed markedly with concentration. A gel diffusion assay showed that monomer Aβ dissociates from preformed fibrils, indicating that reversible heterogeneous association must be incorporated into any realistic model of Aβ association.

Hydrochemistry of spring water associated with travertines. Example of the Sierra de la Alfaguara (Granada, southern Spain)

In some springs draining the carbonate aquifer of the Sierra de la Alfaguara an incipient precipitation of calcium carbonate occurs due to common-ion effect. This process together with the CO 2 outgassing of the water have originated travertines during the Quaternary. The travertines were deposited coinciding with warm and wet climatic periods and are currently at altitudes higher than the springs as a result of the base level deepening through the tectonic uplift of the aquifer.

Effects of Asphaltene Aggregation in Model Heptane–Toluene Mixtures on Stability of Water-in-Oil Emulsions

As part of an ongoing investigation into the stability of water-in-crude oil emulsions, model oils have been utilized to further probe the effects of crude solvency as well as specific resin–asphaltene interactions on emulsion stability. These model oils were constructed by dissolving varying amounts of resins and/or asphaltenes in a mixture of heptane and toluene. The resins and asphaltenes used in this study were isolated from four different crude types—Arab Berri (AB), Arab Heavy (AH), Alaska North Slope (ANS), and San Joaquin Valley (SJV)—and characterized in a previous study using heptane precipitation of the asphaltenes followed by an extrographic separation of the resins from silica gel. Asphaltenes dissolved in heptol at concentrations of just 0.5% were shown to generate emulsions which were even more stable than those generated from their respective whole crude oils. Some types of resins (e.g., from AH and SJV) also demonstrated an ability to stabilize emulsions although these resin-stabilized emulsions were considerably less stable than those prepared with asphaltenes. The primary factors governing the stability of these model emulsions were the aromaticity of the crude medium (as controlled by the heptane:toluene ratio), the concentration of asphaltenes, and the availability of solvating resins in the oil (i.e., the resin/asphaltene or R/A ratio). The model emulsions were the most stable when the crude medium was 30–40% toluene and in many cases at small R/A ratios (i.e., R/A ≤1). This strongly supports the theory that asphaltenes are the most effective in stabilizing emulsions when they are near the point of incipient precipitation. The types of resins and asphaltenes used to construct these model oils also played a role in determining the resultant emulsion stability which indicates the importance of specific resin-asphaltene interactions. The interfacially active components that stabilized these model systems were the most polar and/or condensed portions of the resin and asphaltene fractions as determined by elemental and neutron activation analyses. All of these results point to the significance of the solubility state of the asphaltenes in determining the emulsifying potential of these crude oils.

Research is Good, But Does It Help?

Introduction The continuous search for energy routinely forces us in North America to analyse reservoirs classified as more challenging than those in other parts of the world. The problems associated with these reservoirs can sometimes lead to a fairly complex optimization problem. This is the point at which the approach taken by various engineers and companies may deviate. The best engineers are those who can guess the approach to be taken and, due to their intuition, have great success. There is no substitute for prophecy. Unfortunately, the majority of us are faced with the necessity of trying to describe the optimal exploitation strategy by comparison to experimental and/or theoretical devices which tend to identify key parameters and improve our forecasting capability. With this in mind, it is obvious that much of scientific and engineering research has been applied to improve our ability to resolve the challenges of deeper, hotter, solids-containing and tighter reservoirs, but how much has this science really helped us? I would like to take three separate areas of petroleum engineering and address improvements which have occurred in the last few years and the impact that these technologies have had on the costeffective production of hydrocarbons from difficult reservoirs. Organic Solids Precipitation Much research and development has been perfomed in this area, particularly over the last 10 years. Many experimental techniques and theoretical models have been developed for assessing such things as incipient precipitation conditions, solid phase envelope determination, influence of chemical additives and techniques for remediating solids precipitation problems in the wellbore, such as coated tubing. The work conducted by many authors(1–8) notwithstanding, questions still abound as to what is the best way to minimize the expense associated with solids precipitation. For paraffinic systems, a test commonly performed is cloud point determination. For the type of system analysed in Figure I, where a cloud point for a specific fluid is observed, this is important information to have. Nevertheless, giving this to an operating engineer may be of little use. This information, however, can be used in conjunction with available wellbore models to produce the type of scenario shown in Figure 2, where one can identify the depth at which solid precipitation is going to occur. This technology has been applied within the last 18 months and new wells which have been drilled in this formation are being completed with a down to the depth indicated by a combination of the experimental results and the theoretical models. In this case, the benefit of being able to identify the pressurized cloud points and where the cloud point constraint was going to be violated was essential information to have when designing the wellbore. For asphaltene-dominated precipitation aromatic solvents (xylene toluene) have been routinely used to solubilize the solids once precipitated. There have been improvements in chemical technology whereby the use of high molecular weight additives appears to stabilize solids in the oil, thus changing the mechanism by which solids precipitation occurs.

The role of surfactants in a cold sealing solution for anodic films on aluminium

SUMMARYAlthough the key in present cold seating solution formulation practice is the presence of nickel fluoride, its performance can be optimized through the use of other parameters. In particular the effect of surfactants has been studied as a means of providing better penetration into the pores of the nickel salts before incipient precipitation occurs. Non-ionic and anionic surfactants appear to be best, but the effect depends upon the type and concentration of surfactant used.

Flux creep in cation deficient Bi/sub 2/(Sr,Ca)/sub 3/Cu/sub 2/O/sub 8+d/

Flux pinning in Bi/sub 2/(Sr,Ca)/sub 3-x/Cu/sub 2/O/sub 8+d/ was investigated as a function of cation deficiency and thermal history. A comparison of polycrystalline samples of cation stoichiometric and highly alkaline earth deficient composition (x=0.3) shows a marked difference in the magnetization hysteresis ( Delta M) and time-dependent decay of magnetization at temperatures below 40 K. The pinning energy (95-140 meV at 10-20 K) derived from flux creep data for an x=0.3 cation-deficient composition is 4-7 times greater than that for a stoichiometric composition. The difference in Delta M between stoichiometric and nonstoichiometric compositions increases with increasing field out to 5.5 T and is greatest at 20 K, but still significant at 40 K. The intragranular J/sub c/ of an x=0.3 composition exceeds that of the stoichiometric by >10/sup 2/ at a field of 1 T. The dependence of pinning characteristics in cation-deficient samples on thermal history suggests that defect clustering or incipient precipitation plays an important role in improving pinning.

Increased flux pinning in cation-deficient Bi2(Sr,Ca)3−xCu2O8+δ

We show that flux pinning in Bi2(Sr,Ca)3−xCu2O8+δ is increased by intentional deviations in cation nonstoichiometry. Polycrystalline samples of alkaline earth-deficient composition (x=0.24–0.32) show a larger irreversibility in magnetization (ΔM), and a slower decay of ΔM with both increasing field and time than stoichiometric compositions. The difference between compositions grows with increasing field out to 5 T, and is greatest at T≤20 K but still significant at 40 K. The critical state model yields a difference in intragranular current density (Jcm) at 20 K and 2 T of ≳102 between stoichiometric and x=0.3 compositions. Flux pinning energies determined from relaxation of magnetization are several times greater for cation-deficient than for stoichiometric compositions. These improvements are only achieved upon slow cooling or low-temperature annealing, indicating that defect clustering or incipient precipitation is necessary to form more effective pinning defects.

The hydrolysis of the neodymium(III) ion, nd 3+, in3 m (Li) clo 4 medium at 60°c

The hydrolysis equilibria of the neodymium(III) ion have been studied in 3 m (Li)ClO 4 ionic medium at 60°C by electrometric measurements with a glass electrode. The neodymium(III) concentration ranged from 0.03 to 1 m, whereas the acidity was decreased, with coulometrically generated OH − ions, down to the incipient precipitation of neodymium(III) hydroxide. This occurred when less than 2% of the metal ion was transformed into reaction products. The species Nd(OH) 2+, Nd 2(OH) 2 4+ and Nd 6(OH) 12 6+ were assumed in dilute solutions, ⩽ 0.3 m Nd III. At higher concentrations the data were best explained by replacing Nd 6(OH) 12 6+ with Nd 6(OH) 8 10+. Formation constants in the inert 3 m LiClO 4 medium are reported.

Precipitation of calcium oxalate hydrate by titration of acidified calcium nitrate solutions with potassium oxalate

The precipitation of calcium oxalate during the titration of acidified solutions of calcium nitrate with potassium oxalate was studied in the temperature range 13–69°C by monitoring changes in pH with time. A critical supersaturation ratio of 30 for incipient precipitation of the solid phase at 25°C was measured that proved to be independent of the titration speed or initial calcium concentration. With increasing temperature this critical supersaturation is observed to decrease. An analysis of the observed change in supersaturation with titration time at relatively high supersaturation, but under conditions where three-dimensional nucleation is not possible, indicates that the rate of growth of the precipitated phase, calcium oxalate monohydrate, varies with the relative supersaturation raised to the power 3.4. This empirical result is different from the observed parabolic rate law in seeded growth experiments and can be explained by a layer-by-layer growth mechanism based on a polynuclear, surface nucleation model.

Decomposition kinetics of supersaturated solid solutions in ion implanted silicon

Supersaturated solid solutions have been prepared by low temperature (550°C) furnace annealing of ion implanted silicon. The stability of such alloys has been investigated as a function of the annealing temperature. Sb and Ga have been implanted in a wide fluences range in Si(100) substrates and annealed in the (550–1050)°C temperature range. Channeling effect technique has been adopted to determine the concentration of substitutional dopants. Electrical measurements and layer removal techniques have been used to determine the concentration profile of electrically active centers. The temperature at which the substitutional concentration decreases depends upon supersaturation ratio. As a general trend the larger is the concentration the lower is the temperature at which incipient precipitation is detected. The kinetics of decomposition is analysed in terms of the dopant diffusivity in the Si solid phase.

Supersaturated solid solutions after solid phase epitaxial growth in Bi-implanted silicon

The lattice location of Bi-implanted (100) Si after thermal treatment at 550 °C has been studed by a channeling effect technique. Supersaturated substitutional solid solutions are formed with a Bi concentration in excess of 500 times the maximum solid solubility. After growth good crystallinity is observed in the single-crystal Si host. Post-treatments at higher temperature up to 925 °C produce incipient precipitation of the Bi atoms. Both formation and stability of these solid solutions are accounted for by diffusion process. The proposed model has been tested using a high-diffusivity impurity Cu-implanted Si, which inhibits the regrowth of the Si hosts.

Mechanism of gel formation by low methoxyl pectins

SummaryFor stable gel formation, low methoxyl pectin (LMP) should contain at least 50% of the galacturonic acid (GA) in the free carboxylic form. This is achieved by precipitating acid and sodium hydroxide deesterified LMP at pH 0.5, 1.5 or 3.0, and ammonia deesterified LMP at pH 0.5 or 1.5, but not at pH 4.5. With such LMP, depending on the concentration of calcium added and methoxyl content, the sol becomes gel. The changes are classified into five regions: (i) sol, (ii) soft gel, (iii) good gel, (iv) brittle gel and (v) coagulated gel.The mechanism of gel formation by LMP involves the reaction of 40–50% of the GA present in the free carboxylic form with calcium which causes the precipitation of 75–90% of the total LMP including the entire galacturonic acid units present in the esterified form. The LMP so precipitated, holds 50–60 g of water per gram and forms a stable gel. Higher concentrations of calcium than the optimum increases the reactivity to 80–90% which results in strong cross linkages, incipient precipitation of LMP and loss of gel state.

A light scattering study of the hydrolytic polymerization of aluminum

Rayleigh turbidity measurements at 24, 35, 50, and 75°C were made on hydrolyzed aluminum solutions containing 1.0, 2.0, 2.25, 2.35, and 2.40 bound hydroxide ions per aluminum ion. The results indicate that the size of the polynuclear hydroxocomplexes formed reaches a minimum of eight or nine aluminum atoms per isopolycation before incipient precipitation. It is unlikely that any solutions save those with OH Al = 1.0 represent equilibrium conditions. The study was over a tenfold aluminum concentration range, 0.02–0.30 M aluminum, in a constant ionic medium of 1 M sodium perchlorate.

Polymer solutions IX. Molecular weights of polystyrenes from viscosity measurements

AbstractA new method of molecular weight determination of polymers from solution viscosities involving one empirical parameter was suggested earlier. The various assumptions of the method have been examined in detail in the case of polystyrene. A linear plot of k″ [η]2 vs. [η] obtained for one sample of the polymer in a number of solvents and solvent mixtures shows that the corresponding ln ηr/C vs. C plots (when extrapolated) meet at a point. The intercept [η]R obtained is identical with the limiting viscosity number at the point of incipient precipitation as well as the limiting viscosity number at the point of incipient precipitation as well as the limiting viscosity number in cyclohexane at 35°C. It has been further shown that except for high molecular weight samples, the In ηr/C vs. C plot in cyclohexane at 34°C. has a zero slope and values of [η]R agree very well with the values of the limiting viscosity number at the Θ temperature. The double logarithmic plot of [η]R and number average molecular weight is very much scattered but when viscosity average molecular weights are used, the requirement of 0.5 value of slope is satisfied showing the departure is mainly due to heterogeneous distribution of molecular weights.

5-amino-2-benzimidazolethiol as an analytical reagent—I: Spectrophotometric determination of palladium

The orange coloured complex formed by palladium II with 5-amino-2-benzimidazolethiol in the pH range 2–4 forms the basis of a very sensitive colorimetric method for the determination of trace amounts of the metal. The complex shows maximum absorption at 390 m sm , where the reagent has negligible absorption, and it obeys Beer's law from 1 to 8 ppm of palladium II, the optimum range being 2–7 ppm where the percentage relative error per 1% absolute photometric error is 2.95. The sensitivity of the reaction is 0.008 μg cm 2 . Most of the common cations and anions are without effect on the complex. The interferences of some of the platinum metals are avoided by developing the complex in the cold and using EDTA (disodium salt) as a masking agent. A composition study by the molar ratio method shows that at pH 3.42 the solution contains both 1:1 and 1:2 complexes, the dissociation constant of the latter being 1.32 × 10 −11. However, above pH 5.5 incipient precipitation of the orange-red palladium complex occurs, and the precipitation is quantitative above pH 10. The analysis of this precipitate shows a ratio of 1:2 between the metal and the reagent.

EFFECTS OF ELECTRIC FIELDS ON WATER-DROPLET COALESCENCE

Abstract Growth of incipient precipitation particles by collision and coalescence with cloud droplets is one of the primary mechanisms of natural rain. Comparison of previous research shows wide divergence between various theoretical and laboratory values of collision efficiency and coalescence efficiency. In an effort to obtain additional laboratory measurements of droplet coalescence, high-speed photographs were taken of colliding droplets at the breakup point in a Rayleigh jet. With 700-micron diam droplets, less than 30 per cent of the collisions result in coalescence under no field condition. At fields of about 40 v per cm, the coalescence was about 100 per cent under all conditions of field.