Changes In Dissolution Rate Research Articles

Nonlinear dissolution reaction of chalcopyrite

The dissolution experiments of chalcopyrite in 2 mol/L NaCl solutions at 70°C show that the dissolution rate of chalcopyrite oscillates non-periodically with reaction time while in acid solutions (pH = 1.45–2.45) and far from Cu saturation concentration, and Cu concentration oscillates chaotically in solution of weak to intermediate acidity (pH = 3.66–7.0). In nonequilibrium and open systems, the nonlinear coupling between the dissolution of chalcopyrite and formation of cuprous chloride complexes and precipitation of hemitite caused by Cl−, H+ and O2 is the internal mechanism of oscillatory changes of dissolution rate, and the nonlinear coupling between the dissolution of chalcopyrite and precipitation of atacamite induced by Cl− and H+ has caused the chaotic oscillation of Cu concentration. There are consistence and difference between reaction rate oscillation and Cu concentration oscillation. However, both of them suggest that the dissolution of chalcopyrite in NaCl solution is a nonlinear reaction process.

Dissolution Characteristics and Surface Morphology of Chemically Amplified Resists in X-Ray Lithography

The surface morphology of chemically amplified resists was evaluated when a half-tone X-ray mask with high transmittance (low-contrast) was used. The morphology of the top surface of chemically amplified resists is strongly related to the differential of the dissolution rate as a function of the exposure dose, but it is not directly affected by the γ value. A smaller change results in a smoother surface for both positive and negative resists. Increasing the concentration of dissolution inhibitors with t-butoxy groups is an effective way of reducing the change in dissolution rate and making the top surface of a positive resist smooth while maintaining the resolution.

In-situ alteration of minerals by acidic ground water resulting from mining activities: preliminary evaluation of method

The chemical composition of the Cu-mining-related acidic ground water (pH ∼ 3.5 to near neutral) in Pinal Creek Basin, Arizona has been monitored since 1980. In-situ experiments are planned using alluvial sediments placed in the ground-water flow path to measure changes in mineral and chemical composition and changes in dissolution rates of subsurface alluvial sediments. The test results should help refine developed models of predicted chemical changes in ground-water composition and models of streamflow. For the preliminary test, sediment from the depth of the well screen of a newly drilled well was installed in three wells, the source well (pH 4.96) and two up-gradient wells (pHs 4.27 and 4.00). The sediment was placed in woven macrofilters, fastened in series to polyvinyl chloride (PVC) pipes, and hung at the screened level of each well. After interacting with the slowly moving ground water for 48 days, the test sediments were removed for analysis. There was no evidence that any of the materials used were biologically or chemically degraded or that the porosity of the filters was diminished by ferric hydroxide precipitation. These materials included 21-μm-pore (21PEMF) and 67-μm-pore polyester and the 174-μm-pore fluorocarbon Spectra/mesh macrofilters containing the in-situ sediment, the polypropylene (PP) macrofilter support structures, and the Nylon (NY) monofilament line used to attach the samples to the PVC pipe. Based on chemical and mineral composition and on particle-size distribution of the sediment before and after ground-water exposure, the 21PEMF macrofilter was chosen as the most suitable macrofilter for the long-term in-situ experiment. Tests also showed that the PP support structures and the NY monofilament line were sufficiently durable for this experiment.

Photostructural transformations induced by IR radiation in AsSeTe glassy films

Chalcogenide glassy films in which the photostructural transformations are excited by ultra-violet and visible radiation are widely studied and applied in photorecording, photolithography and non-conventional optics. In this communication, we report about preparation of AsSeTe chalcogenide glassy films in that reversible photostructural transformations are excited by red and near IR radiation. Kinetics of photodarkening and photorefraction induced by 630–900 nm radiation, thermal bleaching process and photoinduced change of dissolution rate in some solvents are investigated. Developed films are prospective for application in systems, using semiconductor diode lasers.

Correlation of UVIIHS resist chemistry to dissolution rate measurements

This article describes the correlation of UVIIHS resist chemistry to dissolution rate measurements as a function of resist processing conditions. The acid generation efficiency, α, for the UVIIHS photoacid generator is high, 0.027 cm2/mJ. The dissolution rate versus exposure curves show the excellent developer selectivity of UVIIHS, with n values >8 for all processes. The rmax values for this resist are above 20 000 Å/s, which is higher than any positive resist previously reported. The extent conversion for deprotection is directly related to the dissolution rate changes; ∼30% deprotection correlates to the E0 dose for all process conditions evaluated. At 30%–40% acid produced, all of the deprotection chemistry is essentially completed. The chemical contrast, as measured by extent conversion versus exposure dose, is strongly affected by the postexposure bake (PEB) temperature, with 140 °C PEB showing higher chemical and lithographic contrast than the 130 °C PEB. Mack’s dissolution model has been shown to work for these data sets.

Effects of various formulation factors on dissolution stability of aztreonam, hydrochlorothiazide, and sorivudine capsules

A split-split-plot 3 2 × 2 2 factorial design was used to study the effects of capsule filling machine and formulation factors such as lactose type, lubricant concentration, and capsule shell size on the dissolution stability of 50 mg potency hydrochlorothiazide (HCTZ), sorivudine (BV-araU), and aztreonam capsules packaged in HDPE bottles and stored under different conditions. It was observed that neither magnesium stearate concentration nor the type of capsule machine used to fill the capsule shells had any effect on dissolution stability of capsules of all three drugs for up to 6 months of storage at 50°C. For aztreonam, neither capsule shell size nor the type of lactose had any effect on dissolution stability. On the other hand, HCTZ size no. 1 capsules demonstrated better dissolution stability than size no. 2 capsules. Moreover, dissolution stability of capsules of sorivudine and HCTZ on storage at 50°C, 40°C/75% RH, and 40°C was dependent on the type of lactose used. HCTZ capsules containing Fast-Flo ® lactose, hydrous lactose, or anhydrous lactose showed up to 45, 25, and 10% decrease in dissolution, respectively, compared to initial values, at the 20 min dissolution time point after 6 months storage at 50°C. The extent of decrease in the dissolution rate was less under the conditions of storage at 40°C/75% RH and 40°C. Similar effects of decrease in the dissolution rate with the different types of lactose were observed with sorivudine, although to a much lesser degree compared to HCTZ capsules. No decrease in dissolution rate was observed for any drug after 20 months storage at 30°C. It was hypothesized that the slight decrease in dissolution rate of sorivudine capsules was due to significant caking of the capsule contents in the presence of the moisture liberated from the excipients and the capsule shells. For aztreonam capsules, the caking of their contents was without any discernable effect on dissolution because of the high aqueous solubility. In contrast, for HCTZ capsules, changes in dissolution rate were far too pronounced to be attributed to caking only.

Effect of formaldehyde formation on dissolution stability of hydrochlorothiazide bead formulations

An immediate release hydrochlorothiazide (HCTZ) bead formulation (formulation A) containing drug, lactose hydrous, sodium starch glycolate (Primojel®) and microcrystalline cellulose (Avicel® PH 101), and a control formulation (formulation B), without Primojel®, were exposed to 22°C/80% RH, RT/ambient RH, 40°C/75% RH, and 40°C/ambient RH in open petri dishes for 4 weeks. After the exposure, formulation A exhibited a significant decrease in dissolution rate under all conditions except 40°C/ambient RH. In contrast, no change in dissolution rate was observed for formulation B. It is possible that the decrease in dissolution rate of formulation A was due to the formation of a trace amount of formaldehyde due to hydrolysis of HCTZ in the humid environment and its subsequent reaction with Primojel®, which resulted in formation of an insoluble product and a reduction in disintegrating power of the Primojel®. In a simulated storage environment of high humidity in Conway cells and using the diffusion method, significantly less formaldehyde was detected in the formulation A beads compared to the formulation B beads ( P = 0.03). This may indicate that formaldehyde present in the formulation A was partially consumed through a reaction with Primojel®. In both formulations, a significantly greater amount of formaldehyde was detected in beads containing smaller particles of HCTZ ( P = 0.02). The formation of formaldehyde and its reaction with Primojel® seemed to be confined to the exposed surfaces of the beads since compression of the exposed beads into tablets resulted in faster dissolution of HCTZ.

Factors Affecting Drug Bioavailability in Space

Microgravity-induced changes in the bioavailability of drugs may influence the efficacy or toxicity of drugs. The bioavailability of orally administered drugs may be altered by changes in dissolution rate, intestinal microflora, intraluminal enzymes, epithelial enzymes, rate of passage across the gastrointestinal epithelium, gastric emptying rate, intestinal transit time, hepatic first pass metabolism, and gastrointestinal and hepatic blood flow. Limited data from antiorthostatic bed rest and inflight studies provide preliminary evidence that the bioavailability of orally administered drugs in space may be decreased or subject to more interindividual variation than expected from ground-based studies.

Chemical amplification resists for future lithography.

The technologies for future lithography have been proposed, such as i-line phase-shifting lithography, deep-UV lithography and electron beam lithography. We have proposed several types of chemical amplification resist systems for future lithography. These are based on the change in dissolution rate by acid catalyzed reaction for aqueous development: dissolution inhibitor to dissolution promoter for positive resists and the reverse for negative resist. Deprotection reaction of tetrahydropyranyl protected poly(hydroxystyrene) is used for positive resists. Silanol condensation reaction by acid catalyzed reaction was applied to negative resists. Pinacol rearrangement, etherification and intramolecular dehydration of carbinols can also be used for negative resists.

The application of fast potential steps to noble metal electrodes: a correlation of electrodissolution with changes in the surface morphology and composition

We have studied the electrodissolution of Pd, Rh and Pt electrodes, which is accompanied by changes in surface morphology and composition. These processes were initiated by applying potential steps which lead to passivation-repassivation of the electrodes. The dissolution rate changes with frequency, the upper and lower limits of the potential pulses applied, the concentration of active solution species, agitation of the electrolyte and the electrolyte temperature. It was further observed that sulphate ions effectively support these processes. In-situ scanning tunnelling microscopy, scanning electron microscopy and energy-dispersive X-ray analysis were used to analyse surface topography and composition.

Dissolution kinetics of heulandite at pH 2–12 and 25°C

The dissolution rate of heulandite depends strongly on pH. Based on silica release, the logarithm of the steady-state dissolution rate at pH 2 is −13.1 mol cm −2 s −1. The logarithm of the rate decreases to −15.8 mol cm −2 s −1 at pH 7.2 and increases again to − 14.6 mol cm −2s −1 at pH 12.2. At low pH, Al is released preferentially to silica; but at intermediate and high pH, the release of silica appears to be congruent relative to Al. The change in dissolution rate with pH indicates that at low pH, the dissolution mechanism is controlled by the detachment of a positively charged Al species, > A1-OH 2 +. Below pH 5, however, a silica-rich surface layer is formed requiring diffusion through the layer. At intermediate and high pH, it is likely that the dissolution rate is controlled by the detachment of a negatively charged silica species, > Si −O −. The reaction order of the hydrogen ion under low pH conditions is 0.7, and the reaction order of the OH − ion is 0.3 at high pH. The measured dissolution rates indicate that a 1 mm heulandite crystal would dissolve in 300,000 yrs if the solution composition is maintained undersaturated.

特集「無機材料の合成を支える技術とその評価」 マイクロ波プラズマによるガラスのオキシナイトライド化

Oxynitriding of phosphate glass was made by microwave plasma using nitrogen and ammonia gas. Changes of dissolution rate of Na+ ion into water, Tg and electric resistivity showed the same tendency as those appeared in general oxynitriding of the glasses. ESCA results showed that the increase of nitrogen contents on the treated glass surface was higher in the ammonia plasma treatment than in the nitrogen plasma treatment.

Automated Sampling of In Vitro Dissolution Medium: Effect of Sampling Probes on Dissolution Rate of Prednisone Tablets

The effect of sampling probe size and location on the in vitro dissolution rate of prednisone tablets was examined. Using USP XX Apparatus 2 with an automated sampling system, dissolution rates were determined using two types of large filter-tipped probes and a small capillary probe. Each probe was tested at three locations within the kettle. The large probes caused hydrodynamic changes which, when compared with results obtained through manual sampling, resulted in significant changes in dissolution rates at each location. These changes were less evident when the capillary probe was used, with an insignificant difference between results of automated and manual sampling when the capillary probe was placed midway between the paddle shaft and the kettle wall.

Effects of packaging and storage on the dissolution of model prednisone tablets

The effects of packaging and storage in multiple-unit and unit-dose containers on dissolution rate of model prednisone tablets are reported. USP Prednisone Dissolution Calibrator Tablets were packaged in three multiple-unit and five unit-dose containers. Packaged tablets were stored for three to six months under three conditions: 40 degrees C and 85% relative humidity (R.H.), 37 degrees C and 75% R.H., and 22 degrees C and 75% R.H. Dissolution rate was measured at pre-determined intervals during storage. For each condition tested, two separate runs of six tablets each were performed. Tablets in the least moisture-permeable containers were least affected by storage. The conditions of high heat and humidity caused the greatest change in dissolution rate. When stored at 22 degrees C and 75% R.H., little change in dissolution rate occurred in any packaged tablets. It is concluded that packaging and storage conditions affect tablet dissolution characteristics markedly. The practice of labeling repackaged tablets with the expiration date of the original container is shown to be invalid.

RATE OF DISSOLUTION OF N-ALKANES AND WATER IN MTCROF.MULSIONS OF WATER/SODIUM DODECYL SULFATE (1/3)+ l-PENTANOL (2/3) /N-DODECANE IN RAPID MIXING EXPERIMENTS

ABSTRACT The rate of dissolution of water and dodecane in micro-emulsions (or micellar solutions) made of water/SDS + l-pentanol/dodecane has been measured using a fast mixing equipment. The dissolution rates were found to be much larger than the reciprocal of the time required to achieve an intimate mixing between the microemulsion and water (or dodecane) about 5 × 102 s−1 except in the water-rich region of the pseudo-ternary phase diagram where they range from below 0.1s−1 to above 5 × 102 s−1 The inter-facial tension between oil and microemulsion appears to play only a minor role in determining the changes of dissolution rate. The results have been accounted for in terms of a dissolution process based on diffusion-controlled collisions between oil (or water) droplets and microemulsion droplets. The differences between the rates of dissolution in the water-rich region and the oil-rich region are attributed to electrostatic repulsions occurring only in the water-rich region, and which appear to play a pr...

The dissolution of aluminum oxide in cryolite melts

Several modifications of Al2O3 were prepared. Al2O3 samples pressed to tablets were dissolved in cryolite melts at temperatures between 975 and 1090°C. The dissolution rates obtained are consistent with the consecutive occurrence of two rate laws. The dissolution rate changes at an Al2O3 content of 5 to 6 pct in the cryolite melts. The results are discussed with consideration of other experimental and theoretical work. It is concluded that the alteration of the rate law may be explained by structural changes in the melts.