Conventional Stability Tests Research Articles

Beyond RDE characterisation – Unveiling IrRu/ATO OER catalyst stability with a GDE setup

In this study, we have investigated the stability of antimony-doped tin oxide (ATO) supported IrRu nanoparticles, as catalyst for the oxygen evolution reaction (OER). Conventional stability tests using a rotating disc electrode (RDE) are demonstrated to lead to distorted results, a fact typically addressed to the massive formation of O2 gas bubbles which block the catalytic active sites. In agreement with previous results, our investigations suggest that the observed decay in current density is not to be confused with catalyst degradation. To mitigate the limitations of the RDE approach, a gas diffusion electrode (GDE) setup was used instead for the stability measurements. Using a carbon gas diffusion layer (GDL) as substrate for the catalyst film, similar beginning-of-life (BoL) and end-of-life (EoL) activities were observed in the low current density region; however, large disparities were found at larger current densities. For meaningful degradation studies, the carbon GDL had to be replaced by a titanium-based substrate. This way a more accurate assessment of the catalyst stability is demonstrated. Although at steady-state conditions the tested IrRu/ATO catalyst exhibited a slight decrease in current densities with time, the BoL and EoL activities are nearly identical.

Effect of Kraft lignins on the stability and thermal decomposition kinetics of nitrocellulose

In this work, the stabilizing effect of softwood and hardwood Kraft lignins on nitrocellulose (NC) was assessed. Four samples containing 3% of stabilizer were prepared. DSC and FTIR analyses have been used to check the compatibility of the different systems. The effect of these organic compounds on the stability of NC has been investigated using the conventional stability tests (Vacuum Stability Test (VST) and Bergmann-Jung (BJ)) and the kinetic modeling. The obtained results via VST and BJ suggested that the prepared mixtures are stable. Furthermore, Kinetic modeling, performed by isoconversional methods based on DSC data, revealed that the new stabilizers displayed excellent thermal stability. The reactivity between different Kraft lignins and NOx has been well highlighted by means of FTIR and TGA techniques as well, confirming the potential of these environmentally friendly substances as promising stabilizers for NC-based propellants.

Organosolv lignins as new stabilizers for cellulose nitrate: Thermal behavior and stability assessment

Cellulose nitrate, commonly known as nitrocellulose (NC), and its corresponding propellants naturally decompose at normal conditions. To avoid early degradation, unexpected explosion, energy loss, and ensure a safe storage, stabilizing agents are often introduced within its compositions. Conventional stabilizers, such as aromatic amines like diphenylamine (DPA) and urea, can produce carcinogenic/toxic substances during propellants shelf life. Thus, a need for alternative stabilizing agents, which offer similar/better effectiveness and display a non/low toxicity, remains a challenge. This paper investigates the stabilizing effect of two organosolv lignins (OL), obtained from Aleppo pine (AP) and Eucalyptus globulus (EG), on NC. For this purpose, conventional stability tests and kinetic modeling are applied for different samples (S1-S4) using 3% of stabilizer, which are S1, pure NC; S2, NC + DPA; S3, NC + OL(AP); and S4, NC + OL(EG). Beforehand, FTIR spectroscopy and DSC analysis have been used to check the compatibility of these potential stabilizers and NC. The obtained results via Bergmann-Jung and vacuum stability tests suggested that the prepared mixtures are stable. The kinetic study based on DSC data using isoconversional methods shows that both stabilizers display a good stabilizing effect. The reactivity between the different organosolv lignins and NOx released during the degradation of NC has been well highlighted using FTIR and TGA analyses. Hence, these efficient, environmentally friendly and readily available substances can be effectively used as stabilizers for NC-based formulations.

Novel isothermal calorimetry approach to monitor micronutrients stability in powder forms

Oxidative stability is critical in guaranteeing the declared shelf life of new formulations and contributes significantly to time-to-market efficiencies. In this study an innovative method based on isothermal calorimetry is proposed for monitoring the stability of vitamin A acetate formulations with one or more antioxidants, such as butylated hydroxytoluene, ethoxyquin, tocopherol and rosemary extract. The results were correlated with conventional stability tests utilizing liquid chromatography (LC). The efficiency of three drying technologies (spray drying, spray granulation, and beadlet) were compared. The initial heat flow values obtained from isothermal calorimetry experiments were used to identify the most efficient drying technology, antioxidant system, that is beadlet. The resulting rate constants of vitamin degradation calculated from the LC data were positively correlated with the initial heat flow values. This study demonstrated that the performance of isothermal calorimetry was far superior when compared with traditional methods. In addition, this methodology allowed the detection of micronutrient stability in complex powder mixtures in only a few hours without the need for sample preparation. This approach could therefore potentially be applied to industry and academic environments for the prediction of micronutrients stability.

Effect of organic eutectic on nitrocellulose stability during artificial aging

ABSTRACTRecently, the eutectic composition of organic binary mixtures MENA+DPA has been found to be an efficient stabilizer of nitrocellulose. However, the behavior of such new stabilizer must be further investigated, especially after a long period of storage of the energetic composition. In this study, the stabilizing effect of the eutectic MENA+DPA on NC stability during artificial aging (at 338.65 K for 120 days), compared to its pure components, has been investigated by conventional stability tests and kinetic modeling. According to Bergmann & Junk (T = 405.15 K) results and over the entire period of aging, the eutectic MENA+DPA exhibits the best stabilizing effect on NC. The vacuum stability test (T = 353.15, 363.15, 373.15, and 383.15 K) results revealed that the amount of the evolved gas of NC containing this eutectic composition is very close to that of DPA, known as the conventional stabilizer. Furthermore, the kinetic modeling on VST data, obtained at four isothermal temperatures, was performed by two different methodologies, viz, fitting and free models to determine the kinetic triplets, which have been subsequently used to predict the storage lifetime for the studied systems. It was found that the NC stabilized by the eutectic MENA+DPA presents the highest value of the activation energy and has the longest storage lifetime during the entire heating period corroborating the stability tests results and affirming the excellent stabilizing effect of this mixture with respect to its pure component even if a long storage period is expected.

Benchmarking Chemical Stability of Arbitrarily Mixed 3D Hybrid Halide Perovskites for Solar Cell Applications

AbstractAccurate and fast assessment of the intrinsic instability of mixed composition hybrid halide perovskite material is of vital importance for the development of perovskite solar cells. A longer lifetime close to current silicon‐based technology is a mandatory property for perovskite solar cells to reach commercial applications. The conventional method to evaluate the operational stability performance of perovskite solar cells relies on tracking maximum power efficiency on devices. However, this operational stability testing procedure requires a long measurement time, which is an inefficient procedure to screen the huge compositional space of mixed perovskites. Here, a thermal degradation protocol is shown for fast preliminary screening evaluation of the stability of any mixed 3D hybrid perovskite material. This stability assessment determines two independent parameters for stability quantification; 1) degradation temperature and 2) heat absorbed during degradation. Experimental entropic‐like parameter can be derived addressing the relative stability for each mixed hybrid perovskite composition. In addition, a first‐principle theoretical approach is described for the in silico search of optimal mixed composition perovskites. This experimental stability benchmarking protocol is able to signify several general rules of thumb to find enhanced stability trends in mixed composition perovskites prior to device assembly and conventional stability tests.

Volume-based phase stability testing at pressure and temperature specifications

Conventional phase equilibrium calculations at temperature and pressure specifications require the resolution of the equation of state (EoS). In volume-based calculations, the EoS must not be solved for volume, which is a primary variable. The tangent plane distance (TPD) function can be expressed in terms of mole numbers and volume or of component molar densities. The stationary points of the TPD function, as well as the location of the stability test limit locus (STLL) are different for the two formulations. A modified TPD function in terms of mole numbers and volume is proposed here. Using the block structure of the Hessian matrix, it is shown that Newton iterations in volume-based stability are inherently slower than those in the conventional PT stability, since the Hessian matrix is evaluated at a lower implicitness level. The minimization of several TPD functions (in volume-based and conventional stability testing) is analyzed using various sets of independent variables and scaling procedures. A modified Cholesky factorization and a two-stage line search procedure ensure a sequence of decreasing TPD functions in all cases. The proposed methods are tested for several mixtures, with emphasis on the vicinities of singularities (STLL and spinodal). With proper scaling, the modified Newton iterations are robust and converge very fast for most conditions and reasonably fast for very difficult conditions. The proposed algorithm is not model-dependent; any pressure explicit EoS can be used, provided the required partial derivatives are available.

Utilization of New Non‐toxic Substances as Stabilizers for Nitrocellulose‐Based Propellants

AbstractPropellants consisting of nitrocellulose (NC) and/or other nitrate esters are inherently chemically unstable and undergo decomposition even under standard storage conditions. Decomposition of such compounds can be inhibited or nearly stopped when stabilizers are used. However, conventional stabilizers form nitrosamines that have toxic and carcinogenic effects. As a result, these conventional stabilizers should be replaced as soon as possible.A series of NC‐based propellants doped with different novel manufactured stabilizers were investigated using microcalorimetry, conventional stability tests, and sensitivity tests. The results were compared with propellants containing the conventional stabilizer Akardite II. The chemical structure of these new stabilizers and their decomposition products do not enable the formation of toxic N‐nitrosamines.

The Long-term Stability of Sodium Percarbonate in Presence of Zeolite as Measured by Heat Flow Calorimetry

Abstract Heat flow calorimetry has been evaluated as an alternative technique to conventional stability testing of sodium percarbonate [15630-89-4] (SPC) based on analysis of the hydrogen peroxide content. Stability tests were performed with different SPC samples as well as under various experimental conditions. In general, stable samples exhibiting high concentration of hydrogen peroxide were accompanied by low heat flow values. It was found that the results obtained by heat flow calorimetry and conventional stability testing were in agreement. It was also demonstrated that the long-term stability could be predicted from heat flow data obtained during the initial stage of decomposition. Furthermore, different manufacturing and experimental conditions were manifested as a change of the heat flow curve. The results indicate that the rate of heat production is closely associated with the stability of sodium percarbonate, i. e. the rate of decomposition of sodium percarbonate. In presence of zeolite the stability of sodium percarbonate was reduced, particularly under humid conditions.

Evaluation of the physical stability of two oleogels

Oleogels are semisolid systems obtained with an organogelator and a hydrophobic liquid that have been investigated over the past few years and that could play an important role as dermatological bases. Recently, we have developed an oleogel of sorbitan monostearate (19 wt.%) and sweet almond oil (SM–SAO) and another one of cholesterol (3.5 wt.%) and liquid paraffin (Ch–LP). The aim of this work is to access their physical stability using three different methodologies. The gels were stored at different temperatures (20 and 40 °C) over a 3-month period. Appearance and textural properties were assessed on each month. An accelerated test was also performed where the temperature changed between 4 and 40 °C every 24 h, during 7 days. Rheological tests were also carried out as they could provide useful elements to predict stability. The gels were quite stable at 20 °C, being the SM–SAO gel the most stable. The textural properties of both gels were influenced by temperature. The decrease of the textural parameters, observed after storage at 40 °C and in the cycling test, was more significant for the SM–SAO gel. A good correlation was found between rheological analysis and conventional stability tests. The heating/cooling cycle test provided useful information in a short period of time.

Do broad money, output, and prices stand for a stable relationship in India?

This study investigates the stability of the relationship among M3 money, output, and prices. The empirical results derived from conventional stability tests, cointegration and error correction models and a test for structural break in a cointegrating vector provide evidence for the existence of a fairly stable relationship among these variables during 1951–1952 to 2000–2001. The evidence suggests that the growth of M3 money can be used as one of the potential indicators of future movement in prices within the multiple indicators framework of the Reserve Bank of India (RBI). However, evidence regarding the short run dynamic adjustment among these variables indicates that active monetary policy to stabilize short run fluctuation in prices must be handled with caution, as it would amplify rather than moderate price fluctuations in the long run.

Use of microcalorimetry in monitoring stability studies. Example: vitamin A esters.

Vitamin A is very sensitive to chemical degradation caused by oxygen, light, heat, and other stress factors. If light and oxygen are excluded, the dominant degradation reaction for vitamin A derivatives is heat-induced formation of kitols, that is, dimers or higher oligomers. In this study vitamin A esters were used as model systems to evaluate microcalorimetry as a tool for monitoring the stability of heat sensitive substances. To obtain more knowledge about the model reaction, analytical investigations (supercritical fluid chromatography) were also performed. Because analytical and microcalorimetry data were consistent, a quantitative description of the kinetics and thermodynamics of the kitol formation reaction could be obtained. Aside from the academic motivation, this is important for practical purposes such as shelf life stability of vitamin A in feed, food, and pharmaceutical products. The vitamin A stability of a given sample can easily be predicted from the initial heat flow in a simple microcalorimetry experiment. Compared to conventional stability tests, this offers savings of money and time.

Shelf life prediction software finds application with ethical drugs

Applications for approval of new ethical drugs require that stability studies be completed prior to submission to the FDA. If the company chooses packaging which is found (by conventional storage testing) to provide insufficient barrier protection, new packaging must be identified and storage tests re-run. This iterative process must be repeated until packages are found which provide adequate protection. If the chosen package is over-protective, stability studies show adequacy, but do not identify over-protection. A third option is to employ a myriad of test packs which impacts negatively on facilities and personnel, and is expensive and time-consuming. Package optimization requires additional testing and re-submission of the New Drug Application (NDA). A combination of analysis and computer shelf life predictions can be utilized to develop optimal packaging without such repetitive testing. A study was initiated with Searle to apply analytical evaluations and shelf life simulations to identify appropriate packaging for new drugs prior to the initiation of conventional stability testing. The procedure used analytical evaluations of two ethical drugs (without package protection) to identify the susceptibilities of the product to storage-induced changes. The analytical results were then plugged into a computer shelf life modelling program which identified barrier requirements which would provide the protection found to be required for the drug product. This then defined the packaging needs. The efficacy of this modelling approach was confirmed for one product by conducting conventional stability studies with packaging materials which satisfied the barrier requirements which had been specified by the computer simulations. Storage studies for the second product are in process, and performance to date supports the predicted values. Copyright © 1999 John Wiley & Sons, Ltd.

Aging of magnetic coatings

Polyurethanes are often used as binders in high quality flexible magnetic media. This type of binder is sensitive to hydrolytic degradation, which is a function of relative humidity and temperature. Such a degradation can affect the long-term usability and durability of the magnetic media. Knowledge of the degradation mechanism and of the factors that influence it is needed for a reliable prediction of the lifetime of magnetic media. Conventional stability tests on the components may take weeks and the determination of the ultimate performance of the finished product may take years. Therefore the practical value of projection of durability from accelerated test data is obvious. In this paper a fast test for the hydrolytic stability of polyester-urethanes is introduced. The results of the tests can be correlated with conventional aging experiments on complete coatings. Although the basic stability of the coating is governed by the binder system, the other components show small effects of those materials on the long-term stability of the coatings. The decrease in magnetic moment, the increase in gel fraction of the binder system (the non-extractable part), and the changes in Young's modulus give reliable and rapid information about the stability of the system. All these aspects must be taken into account to predict the long-term usability of a magnetic coating layer.