Homogeneous Dissolution Research Articles

From Injectivity to Integrity Studies of CO2Geological Storage

The technical and economical success of a CO<sub>2<sub/> geological storage project requires the preservation of the site injectivity and integrity properties over its lifetime. Unlike conventional hydrocarbon gas injection, CO<sub>2<sub/> injection implies geochemical reactions between the reactive brine and the in situ formations (reservoir and cap rock) leading to modifications of their petrophysical and geomechanical properties. This paper underlines the experimental difficulties raised by the low permeability of samples representative either of the cap rock itself or at least of transition zones between the reservoir and the effective cap rock. Acidification effects induced by CO<sub>2<sub/> injection have been studied using an experimental procedure of chemical alteration, which ensures a homogeneous dissolution pattern throughout the rock sample and especially avoids any wormholing process that would lead to erroneous measurements at the core scale. Porosity, permeability and geomechanical properties of outcrop and field carbonate samples of various permeability levels have been measured under their native state and different levels of alteration. The present work has been conducted within the framework of ANR GeoCarbone-INJECTIVITY and GeoCarbone-INTEGRITY projects. Each experimental step: chemical alteration, petrophysical measurements and geomechanical testing, is considered from the point of view of injectivity and integrity issues. The obtained experimental data show clear trends of chemically induced mechanical weakening.

Characterization of the anodic growth and dissolution of antimony oxide films

The anodic growth, morphology and stability of antimony oxide films grown in buffered phosphate electrolytes has been characterized by electrochemical methods, in situ ellipsometry and atomic force microscopy. The anodic voltammetric behaviour for the growth of antimony oxide films at low potentials can be interpreted as the stepwise electroformation of different antimony species with formation of soluble species up to give Sb 2O 3. This is followed by the anodic film growth at higher potentials through an ionic conduction mechanism caused by a ‘high field’, which drives the ionic migration as in typical “valve” metals. Ellipsometric results indicate that anodic films dissolve in the electrolysis media. Anodic Sb 2O 3 films are anisotropic, with complex refractive indices lower than those of crystalline antimony oxides. This is ascribed to hydration, anions incorporation or lack of crystalline structure in anodic oxides. The electric field strength obtained from the thickness/potential dependence, results 2.25 × 10 6 V cm −1, which also supports that anodic Sb 2O 3 growth takes place by an ionic current driven by a high electric field within the oxide film. Morphology of anodic Sb 2O 3 films obtained by AFM shows that surfaces are smooth and flat and films are pore-free. The grain texture depends on concentration of electrolyte as a consequence of a different chemical dissolution rate. The stability of passive antimony oxide films at open circuit was analyzed by cyclic voltammetry with either constant or increasing anodic switching potentials. The overall growth and dissolution of antimony oxide films is described in terms of the oxide film growth by the high-field migration model coupled with a homogeneous dissolution process. The parameters A and β in the equation i = A exp ( βε) that characterize the dependence between current growth and field strength in the high-field growth as well as dissolution current for different conditions are obtained. Dissolution current dependence with electrolyte properties, indicate that antimony oxide dissolution is promoted by phosphate ions and is almost independent of pH.

Annealing behavior of an ultrafine-grained Fe–Ni–Mn steel during isothermal aging

An ultrafine-grained maraging steel was fabricated by cold rolling and aging of iron–nickel–manganese lath martensite. Transmission electron microscopy was used to study precipitation behavior at grain boundaries during isothermal aging at 753 K. Relatively coarse precipitates were found at triple junctions of grain boundaries after aging for 0.36 ks. During further aging, precipitates coarsen at triple junctions at the expense of fine precipitates embedded at ultrafine grains. Mass-conservative dissolution of matrix precipitates occurs homogeneously as a result of which the precipitate-free zone around coarse particulates is eliminated. The phenomena of exclusive precipitation at grain boundary triple junctions and homogenous dissolution of matrix precipitates are attributed to the reduced length scale in the ultrafine-grained microstructure.

ICP-MS, SKPFM, XPS, and Microcapillary Investigation of the Local Corrosion Mechanisms of WC – Co Hardmetal

hardmetal exhibits high corrosion susceptibility in aqueous solutions, related to complex microscale reaction mechanisms. This paper presents developed methods to characterize the local distribution of surface reactions difficult to assess by conventional electrochemical methods. Laterally resolved electrochemical potential distributions measured using scanning Kelvin probe force microscopy (SKPFM) under controlled humidity identified the more noble nature of and the microscale galvanic coupling with the Co areas acting as anodes. Inductively coupled plasma mass spectrometry (ICP-MS) element analysis, carried out using an online flow cell, provided simultaneous, time-resolved detection and quantitative concentration measurement of the dissolved elements. W ions in solution at the open-circuit potential indicated chemical dissolution due to the pH increase on the cathodes in addition to electrochemical anodic Co dissolution. Various mechanisms attributed to homogeneous dissolution of microscale phases or dissolution transients related to localized corrosion attack are identified. X-ray photoelectron spectroscopy (XPS) revealed a carbon-rich surface layer on the grains supporting a mechanism of selective W dissolution. These different techniques provided information on the microscale reactions on surfaces in aqueous solution and allowed construction of a comprehensive model.

The influence of Ti and Zr on electrochemical properties of aluminum sacrificial anodes

The electrochemical behavior of Al–5% Zn–0.02% In sacrificial anode was studied in 3 wt.% sodium chloride solution. The experiments focused on the influence of Ti and Zr as additional alloying elements on the electrochemical behavior of aluminum sacrificial anodes. For this purpose Ti and Zr were added in different levels from 0.01 to 0.2 wt.%. NACE efficiency and polarization tests were used. It was found that by using 0.03–0.05 wt.% Ti and 0.05 wt.% Zr as the alloying elements; incremental homogeneous dissolution could be achieved resulting in improved electrochemical properties of aluminum sacrificial anodes, such as current capacity and anode efficiency. The results suggest that corrosion behavior seems to be strongly related to the presence of bifilms (doubled-over oxide films) suspended in the liquid alloy. Higher levels of Ti and Zr additions precipitate on the bifilms and cause them to sediment out from the liquid alloy prior to casting, thus depleting the cast alloy of a useful dispersion of corrosion centers, and impairing the uniform distribution of dissolution of the cast alloy.

Influence of Casting Temperature on Electrochemical Behavior of Al-Zn-In Sacrificial Anodes

Aluminum anodes have been widely used in the cathodic protection of marine structures. However there are conditions in which these anodes become passivated or face some localized or unwanted corrosion, which influences their efficiency. Addition of alloying elements such as Zn and In not only have improved the efficiency of the anodes but also the effect of casting parameters such as ultra melt temperature Tm , mold temperature and grain refiners can adversely influence the capacity of aluminum anodes. In this work the effects of ultra melt temperature and mold temperature have been studied on the potential and current capacity of Al-Zn-In anodes. Electrochemical polarization and NACE standard methods were used to evaluate the anodic behavior, potential and current capacity of the anodes. It is shown that metallic molds having higher temperatures could provide better condition for obtaining homogenous structures with minor inclusions. The optimum condition of anode operation may be provided where mold and pouring temperatures equal to 400 oC and 710 oC respectively, in which a fine structure, phase distribution and lack of casting faults are obtained. The microstructures that can provide a homogenous anodic dissolution bring by itself optimum efficiency of the anodes.

Poling and its relaxation studies of polycarbonate and poly(styrene- co-acrylonitrile) doped by a nonlinear optical chromophore

Spin-coated films of poly(bisphenol A carbonate) (PC) and poly(styrene- co-acrylonitrile) (SAN) doped by 4-( N, N-dimethylamino)-4′-nitrostilbene (DANS) were prepared, and their poling and depoling behaviors were investigated mainly by UV–visible absorption spectra and second-harmonic generation (SHG). The absorbance of DANS in the PC and SAN films proportionally increased with increasing its weight concentration up to 5 wt%, indicating homogeneous dissolution of DANS in the host polymers. However, above this concentration, heterogeneous structures due to DANS crystallites could be observed under a polarizing microscope. Poling of the films was performed using a triode corona discharging system. The maximum d coefficients were obtained at slightly lower poling temperature than the glass transition temperature of the corresponding dye-doped polymer. The KWW stretched exponential function could be fitted to the experimental temporal relaxation data of SHG for the SAN system. Relatively high long-term stability was observed for the PC system because of its relatively rigid backbone structure.

An analytical model for the dissolution of different particle size samples of Bioglass ® in TRIS-buffered solution

We analyzed the early stages of reactivity of three different particle size samples of Bioglass ® 45S5 and a bulk sample in TRIS-buffered solution at pH 8. Ion release, measured with ion-coupled plasma emission spectroscopy, and pH variations are reported. It was demonstrated that differences in the initial surface area influence the increase in pH, the rate of elemental release, and the rate of calcium phosphate reprecipitation. In particular, a thicker Ca/P layer was obtained on larger particles. The equilibrium value of Si in solution was independent of sample form and amount of sample dissolved, and was always close to the value observed when bulk silica is dissolved at pH 8. An analytical model is proposed for cation release, based on a two-step mechanism. It was found that the early stage of dissolution was nearly diffusion controlled for larger particles and bulk samples. The second stage was similar to a first-order homogeneous dissolution. The influence of sample surface area/solution volume ratio seemed to be more complex than that proposed in the early works presented in the literature. It is suggested that variation of surface area has a significant impact on the course of the dissolution.

Characterization of Ferrite-Austenite Boundary Region of Duplex Stainless Steels by SAES

Scanning Auger electron spectroscopy (SAES) has been used to investigate the phase boundary region between ferrite and austenite in three duplex stainless steels. Of the elements investigated Cr and Mo are partitioned to the ferrite phase, while Ni and N are partitioned to the austenite phase. The composition gradient across the phase boundary occurs within a few micrometers. The results are in accordance with previous results of the same phase boundary region obtained with complementary techniques. They form evidence of galvanic interaction between the ferrite and austenite phases and suggest this to be the main cause of the higher initial dissolution rate of ferrite adjacent to the austenite phase. The addition of alloying elements improves corrosion resistance of both the ferrite and austenite phases, the weaker sites are comparatively more strengthened. In the highly alloyed duplex stainless steel, the alloying elements are also partitioned, but in such a way that the corrosion resistance of the two phases is very similar, which results in a homogeneous dissolution behavior. © 2004 The Electrochemical Society. All rights reserved.

Corrosion behaviour of Al–Cu–Fe alloys containing a quasicrystalline phase

Corrosion of quasicrystalline and related crystalline phases coexisting in Al–Cu–Fe alloys with the compositions of Al 60Cu 27.5Fe 12.5, Al 62.5Cu 25Fe 12.5, Al 65Cu 20Fe 15 and Al 67.5Cu 20Fe 12.5 was studied in saline, acidic, neutral and basic solutions. The corrosion behaviour of the alloys was explored by potentiodynamic polarisation experiments, while the microstructural studies by X-ray diffraction and scanning electron microscopy yielded information on the phase structure and its changes as a result of the polarisation experiments. The results of the study indicated that the composition and relative amount of phases present in Al–Cu–Fe alloys are the key parameters defining the corrosion behaviour of the alloy. In saline solutions, the corrosion potentials were in the range where a homogeneous dissolution of the alloy, followed by a redeposition of Cu, took place, the corrosion rate being mainly determined by the amount of Cu-rich phases present in the structure. In acidic solutions, the Cu-rich phases remained untouched by corrosion, whereas phases containing less Cu were susceptible to corrosion. In neutral and basic solutions, oxidation was the primary surface reaction. However, Cu was found to introduce pores into the oxide layer and Fe to inhibit the oxidation process. Therefore, in neutral and basic solutions, the quasicrystalline phase, with intermittent Cu and Fe contents with respect to other phases present in the Al–Cu–Fe alloys studied, showed the best corrosion performance.

Preparation and sorption activity of chitosan/cellulose blend beads

Chitosan microspheres prepared by spray-drying process have a spherical geometry and a smooth surface morphology. These microspheres are found to have a particle size below 3 μm and dissolve readily in N-Methylmorpholine- N-oxide (NMMO). A novel natural polymer chitosan/cellulose blend beads were prepared via homogeneous dissolution of chitosan and cellulose in NMMO. The SEM micrographs of chitosan/cellulose blend beads show that a rough and folded surface morphology and an interior pore structure of beads were obtained. Deodorizing properties of these beads against trimethylamine (TMA) was investigated. We also examined the metal ion sorption properties against Cu(II), Fe(III) and Ni(II) ions. From the sorption activity studies of chitosan/cellulose blend beads that show the chitosan/cellulose blend beads have potential applications for odor treatment as well as metal ions adsorption.

Selective porosification of n-InP(100) after focused ion beam implantation of Si

Selective pore formation can be electrochemically initiated on n-type InP(100) on presensitized surfaces. To create this presensitization, defect patterns were written into the surface by focused ion beam (FIB) implantation of Si ++ . These implant sites represent initiation sites for pore growth or for selective material dissolution in the patterns, if anodic polarization is carried out positive to the pore formation potential (PFP) of the defective surface but cathodic to the PFP of the intact surface. A variety of internal and external factors were found to influence the selectivity of the process. Parameters that significantly affect the morphology are polarization voltage, implantation dosage, the time and the anion present in the electrolyte. In the present work it is shown, that pore formation in 1 M HF only occurs for a small potential range and a certain dosage range of the implanted Si ++ ions. At other potentials or dosages, a homogenous dissolution of the implanted patterns takes place. Apart from direct selective porosification of InP surfaces, the process described can be used for a selective surface patterning.

Silicon Anodization in HF Ethanoic Solutions: Competition Between Pore Formation and Homogeneous Dissolution

This work studied the morphology of p-Si anodized in ethanoic HF solutions. Parameters investigated were the anodization duration, the current density, and the HF content of the solutions. Due to the homogeneous dissolution of silicon in low concentrated HF solutions, the “apparent” porosity obtained from mass measurements indicates a drastic change between 22 and 28 wt % HF solutions. Both the homogeneous dissolution and the pore formation are characterized by a valence slightly lower than 2. The chemical dissolution, which can attain 0.25 nm/s, is the reason for deviation from the two-electron electrodissolution. X-ray photoelectron spectroscopy measurements reveal that the anodization conditions, which lead to homogeneous dissolution, increase the O/F ratio at the surface of the sample. These compositional changes and modification of hydrogen termination are responsible for the homogeneous dissolution observed in solutions with low HF content. © 2002 The Electrochemical Society. All rights reserved.

In Situ Local Dissolution of Duplex Stainless Steels in 1 M H 2 SO 4 + 1 M NaCl by Electrochemical Scanning Tunneling Microscopy

Local dissolution behavior of duplex stainless steel UNS S32304, UNS S31803, and UNS S32750 in was studied in situ by electrochemical scanning tunneling microscopy (STM). Submicrometer features could be resolved and events occurring at phase/grain boundary regions could be monitored in the solution. By STM imaging, severe local dissolution was observed on UNS S32304 in the form of both pitting-like dissolution occurring at the active potential region, and selective dissolution of ferrite phase that already started at the corrosion potential. On UNS S31803, no pitting-like corrosion was observed, but a small amount of selective dissolution occurred at anodic potentials in the active region. The phase boundary region seemed to be prone to local dissolution. No noticeable local dissolution was observed on UNS S32750 in this solution in active and passive potential regions. The results show that a sufficient amount of both Mo and N in duplex stainless steel resulted in more homogeneous dissolution of the two phases and strengthened phase boundaries, and thus decreased the risk for local dissolution. © 2002 The Electrochemical Society. All rights reserved.

Hydrodynamic Flows Around Tablets in Different Pharmacopeial Dissolution Tests

ABSTRACTWe investigated the hydrodynamic flows around tablets during several pharmacopeial dissolution tests: the rotating basket (RB), paddle (PD), flow-through cell (FT), and disintegration (DI) tests. The determination of hydrodynamic flow was based on the dissolution rate of United States Pharmacopeial salicylic acid nondisintegrating calibrators, and showed that, compared with the PD and RB methods, the FT method produced a lower hydrodynamic flow value whereas the DI method produced a higher value. The hydrodynamic flows during the PD and RB tests appeared to be similar at the same rotational speed, although the flow patterns around the tablet differed; with the RB method, homogeneous dissolution occurred from all surfaces of the tablet, while with the PD method, dissolution from the lower surface was slower. The use of a sinker seemed to enhance dissolution from the lower surface. Such differences in hydrodynamic flow could explain the apparently different dissolution behaviors of disintegrating prednisone and nondisintegrating acetaminophen tablets when assessed by the PD and RB methods. These differences in hydrodynamic flow between in vitro tests should be considered when choosing dissolution tests for studying in vitro/in vivo relationships and for quality control purposes.

Real time observation of the hydrothermal crystallization of barium titanate using in situ neutron powder diffraction.

The hydrothermal crystallization of barium titanate, BaTiO3, has been studied in situ by time-resolved powder neutron diffraction methods using the recently developed Oxford/ISIS hydrothermal cell. This technique has allowed the formation of the ferroelectric ceramic to be followed in a noninvasive manner in real time and under genuine reaction conditions. In a first set of experiments, Ba(OD)2-8D2O was reacted with two different titanium sources, either crystalline TiO2 (anatase) or amorphous TiO2-H2O in D2O, at 100-140 degrees C and the reaction studied using the POLARIS time-of-flight neutron powder diffractometer, at the ISIS Facility. In a second series of experiments, the reaction between barium chloride and crystalline TiO2 (anatase) in NaOD/D2O was studied at temperatures between 100 and 200 degrees C and at different deuterioxide concentrations using the constant-wavelength D20 neutron powder diffractometer at the Institut Laue Langevin. Quantitative growth and decay curves were determined from analysis of the integrated intensities of Bragg reflections of starting materials and product phases. In both sets of experiments the rapid dissolution of the barium source was observed, followed by dissolution of the titanium source before the onset of crystallization of barium titanate. Using a nucleation-growth model we are able to simulate the growth curve of barium titanate at three temperatures. Our results indicate the predominance of a homogeneous dissolution-precipitation mechanism for the hydrothermal formation of barium titanate, rather than other possible mechanisms that have been discussed in the literature. Analysis of the line widths of the Bragg reflections in the neutron diffraction data indicates that the particle size of the BaTiO3 product phase prepared from the amorphous TiO2-H2O is smaller than that prepared from crystalline TiO2 (anatase).

Potential, Temperature and Doping Dependence for Macropore Formation on n-Si with Backside-Illumination

Applying an anodic bias on a silicon HF contact and illuminating the backside of a n-type silicon wafer allows to create macropores. The formation of “random macropores” is studied in this paper by determination of the influences of the potential, the temperature and the doping level. A statistical approach is used to evaluate the micrographs. The formation of the macroporous layer consists of two phases. Beginning with a plane surface and homogeneous dissolution of silicon, first pores occur after some time. In this nucleation phase the thickness of the homogeneously dissolved Si depends strongly on the doping level and the temperature but only weakly on the applied bias. In a second phase of stable pore growth the density of pores is investigated as a function of temperature and anodic potential. For low doped material we find a strong stabilisation influence of the deep space charge region (SCR) in the nucleation as well as in the stable pore growth phase. Thus an increased anodic bias decreases the density of pores. For highly doped silicon no stabilisation influence of the SCR is found. The pore growth is dominated by the electrochemical dissolution rate, i.e. increasing the potential increases the density of the macropores.

Core Top 14C Ages as a Function of Latitude and Water Depth on the Ontong‐Java Plateau

Radiocarbon measurements on core tops from the Ontong‐Java plateau confirm a previous finding by Berger and Killingley [1982] that at any given water depth, cores taken on the equator have higher accumulation rates and younger core top ages than their off‐equator counterparts. Further, these new results fortify the conclusion by Broecker et al. [1991] that the increase in core top radiocarbon age with water depth rules out homogeneous dissolution within the pore waters as the dominant mechanism. Either most of the dissolution must occur prior to burial or it must occur during the first pass through the respiration‐CO2‐rich upper pore waters after which the calcite grains become armored against further dissolution. A puzzling aspect of this new data set is that despite the sizable difference in accumulation rate, the extent of dissolution as measured by either the CaCO3 content or the ratio of CaCO3 in the &gt;150‐µm size fraction to that in the &lt; 63‐µm fraction is no different off than on the equator. In order to reconcile the results of this study with those obtained by Hales and Emerson [1996] using in situ electrodes, it is necessary to call upon calcite armoring.

Polymer Optimization of Pigmented Photoresists for Color Filter Production

The lithographic performance of pigmented photoresists for color filter production is affected by the structure of the employed polymer. Four polymers with acrylate backbones and pendant reactive acrylate/methacrylate groups were prepared, and the effects of their molecular weights and acid values on the pixel pattern quality, development time, sensitivity and development mode were elucidated. ECHIPTM, a statistical experimental design program was used for optimization studies revealing that the red resist performs best, when polymers with relatively low acid values (<40 mg KOH/g polymer) and high molecular weights >50,000 are used. The green and the blue resists yielded optimal patterns at molecular weights in the range of 20,000–30,000 with acid values of about 50–60 mg KOH/g polymer. The sensitivity of resists containing polymers with pendant acryloyl groups is in general higher than that of the corresponding methacryloyl derivatives. Polymers having butyl acrylate-methacrylic acid backbone units showed the highest sensitivity among the polymers investigated. When developed with an optimized tetramethyl ammonium hydroxide (TMAH) based developer, resists using polymers with methyl methacrylate units showed peeling type development, while butyl acrylate copolymers effected homogeneous dissolution yielding higher resolution.

Long chain branched celluloses by mild trans-glycosidation

Cellulose dissolved in anhydrous dimethylacetamide (DMAc)/LiCl solution and treated with dialkylaminosulfur trifluoride (DAST) became highly branched and actually gained in molecular weight. The branching was thought to arise from the action of HF which is generated from the consumption of DAST. Subsequent experiments involving the direct addition of HF to anhydrous cellulose/DMAc/ LiCl produced highly branched materials with greater polydispersity and greater molecular weight than the starting cellulose. This branching was likely due to the well known reactivity of glycosyl fluoride endgroups. Although the mechanism is not new, the combination of homogeneous cellulose dissolution and low levels of HF under anhydrous conditions represents a novel method for synthesizing a new class of cellulose derivatives. The potential utility of this method for producing branched cellulose derivatives and blocky cellulosic copolymers is discussed.