A study of a simulated low Earth environment on the degradation of FEP polymer

Spacecraft flying in a low Earth orbit environment require thermal blankets to provide protection from direct solar heat from the sun. Fluorinated ethylene propylene copolymer is one of the major components of these thermal blankets. In this study, the effect of a simulated low Earth orbit environment on FEP was investigated. UV and VUV degradation of fluorinated ethylene propylene (FEP) copolymer was studied using ESR and XPS. The ESR study revealed the formation of a terminal polymer chain radical. The stability of this radical has been investigated under different environments. An XPS study of FEP film exposed to VUV and atomic oxygen showed that oxidation takes place on the polymer surface. The study revealed also that the percentage of CF₂ in the polymer surface decreased with exposure time and the percentage of CF, CF₃ and carbon attached to oxygen increased. SEM micrographs of FEP film exposed to VUV and atomic oxygen produced a rough surface with regular undulations similar to sand dunes. © 1998 John Wiley & Sons, Ltd.     

Design,photochemistry and antibacterial evaluation of novel light-harvesting antenna

Abstract

Novel light-harvesting compound 6, based on 1,8-naphthalimide donors and perylenediimide acceptor were synthesized. The light-harvesting compound 6 showed intensive absorption band in range between 390 and 560?nm, that is 50?nm wider in comparison with the absorption of the model perylene dye. The novel antenna 6 has a higher ability to collect photons from environment in comparison with the single perylene diimide dyes. The chosen fluorophore units are suitable donor–acceptor pair for light-harvesting materials which was in agreement with their good antibacterial activity.     

Double Schiff bases derivatives of chitosan by selective C-6 and C-2 oxidation mediated by 5-fluorosalicylaldehyde aniline by TG-GC-MS and TG-FTIR analysis

Abstract

This enhancement in the activity may be efficient on the basis that ligands mainly possess CH=N bond. The use of a structure-based drug design approach (SBDD) provides a way for investigation as well as to understand the molecular basis of the target protein and ligand molecule interactions at the atomic level. Structure-based drug design is the design and optimization of a chemical structure to identify a compound suitable for clinical testing the drug candidates. Chitosan is a polysaccharide with recognized biological activities for improving the functionality of polysaccharide 5-Fluorosalicylaldehyde aniline system. The used for selectively oxidized chitosan to produce tailored derivatives. C-2-5-Fluorosalicylaldehyde-C-6 aniline double Schiff base derivatives of chitosan were synthesized. The structure and properties of the newly synthesized product were characterized by FT-IR, ¹H-NMR, ¹³C-NMR, GC-Mass spectroscopy, and thermal analysis (DSC/TGA). An exothermic process discusses a DSC and TGA analysis of thermal behavior of this polymer was shown to be a possible thermal polymerization of the double bonds in the polymer chains and thermo-oxidation of the polymer.     

Structure–activity relationship of thermal interaction between arylmalonamide[70]fullerocyclopropane stabilizer and nitrocellulose

The thermal decomposition or even explosion of nitrocellulose during long-term storage is prevented by adding stabilizers to nitrocellulose-based propellants. A series of novel arylmalonamide[70]fullerocyclopropane (3a–c) were synthesized through Bingel reaction. The molecular structures of 3a–c were verified through ¹H NMR, ¹³C NMR, Fourier transform infrared spectroscopy (FT-IR), UV–visible spectroscopy, and mass spectrum. The thermal stability of 3a–c to nitrocellulose was studied by methyl violet paper test and iso-thermogravimetry method, and the results showed that the stability of 3a–c to nitrocellulose was significantly better than that of the [60]fullerene-based stabilizers. The thermal stability of 3a–c to nitrocellulose improved as the increase of the carbon chain length on the p-position of the benzene ring. The effects of 3a–c on the thermal decomposition of nitrocellulose were obtained by differential thermal analysis, and the results showed that the critical temperature of the thermal explosion of nitrocellulose can be increased by 0.1–2.8 °C by 3a–c. The thermal stability of 3a–c to nitrocellulose in adiabatic environment was confirmed by accelerating rate calorimetry. In addition, the stabilization mechanism was studied through ESR and FT-IR, and the results showed that 3a–c can react with nitrogen oxide radicals released by nitrocellulose. These arylmalonamide[70]fullerocyclopropane with excellent thermal stability and strong radical scavenging ability can be used as a promising stabilizer for single and double based propellants.

     

Response to Geoffrey Neuss on how to teach the 4s and 3d orbital conundrum

In the accompanying article in this issue Neuss challenges the explanation that was first suggested by Schwarz for how to teach the relative occupation and ionization of atomic orbitals in the atoms of metals in the first transition series. The present article is a response to Neuss’ critique which includes a detailed examination of his claim that there is no conclusive evidence for the view that the scandium and other first transition metal atoms lose 4s electrons in preference to those located in 3d orbitals.

     

Atomic layer deposition of metal-oxide thin films on cellulose fibers

Abstract

Atomic layer deposition (ALD) is a vapor-phase technique capable of producing inorganic thin films with precise control over the thickness of the film. The ALD method offers high precision in the design of advanced 3D nanostructures. In this article, silica and alumina thin films have been grown over fibers of cellulose by the ALD process. The morphology and the chemical composition of the fabricated thin films are characterized, as well as their thermal durability through elevated temperatures. Moreover, XPS is used to confirm the phases of the alumina nanofilms and to further understand the deposition process on the cellulose microfibers.     

Optimization and sensitivity analysis of magneto-hydrodynamic natural convection nanofluid flow inside a square enclosure using response surface methodology

This article studies buoyancy-driven natural convection of a nanofluid affected by a magnetic field within a square enclosure with an individual conductive pin fin. The effects of electromagnetic forces, thermal conductivity, and inclination angle of pin fin were investigated using non-dimensional parameters. An extensive sensitivity analysis was conducted seeking an optimal heat transfer setting. The novelty of this work lies in including different contributing factors in heat transfer analysis, rigorous analysis of design parameters, and comprehensive mathematical analysis of solution domain for optimization. Results showed that magnetic strength diminished the heat transfer efficacy, while higher relative thermal conductivity of pin fin improved it. Based on the problem settings, we also obtained the relative conductivity value in which the heat transfer is optimal. Higher sensitivity of heat transfer was, though, noticed for both magnetic strength and fin thermal conductivity in comparison to fin inclination angle. Further studies, specifically with realistic geometrical configurations and heat transfer settings, are urged to translate current findings to industrial applications.

     

Ein einfaches Modell zur Beeinflussung der atomaren Spin—Bahn-Kopplung durch einen Ringstrom

A simple model has been made for the interaction of a ring current in excited states with the spin—orbit coupling of a one-electron-atom. It is shown that there exists a condition where the atom cannot be placed in the middle of the ring.

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Mit 2 Abbildungen     

Thermal conductivity of insulations approached from a new aspect

In the literature, several definitions can be found for the thermal conductivity; however, many of them are not clearly explained. The easiest explanation is the following: the property of a material to conduct heat. It is evaluated primarily in terms of Fourier’s Law for heat conduction. Nowadays, the examination of the thermal conductivity of building materials is very important both for the manufacturers and for the consumers. Nonetheless in real, confusing definitions and interpretations can be found regarding the exact meaning of the thermal conductivity of the materials. In physics and in engineering practice, the following appellations are used as heat conductivity, thermal conduction coefficient, design and declared values of the thermal conductivities as well as the effective thermal conductivity. In this article we would give an overview about the correct explanations of the above-mentioned values. At first thermal conductivity measurements of four different types of expanded polystyrene materials (EPS, 80, 100, 150, 200) will be presented by using Holometrix Lambda 2000 type Heat Flow Meter after drying them in a Venticell 111 type laboratory oven to changeless mass.

     

Preparation of novel methyl methacrylate/fluorinated silsesquioxane copolymer film with low surface energy

Random copolymers of methyl methacrylate and fluorinated polyhedral oligomeric silsesquioxane (F-POSS) were synthesized and the corresponding thin films were prepared from solvent casting. Their microstructure was confirmed by ¹H NMR, elemental analysis and GPC. Separation occurs in the bulk of the film during solvent evaporation which can be evidenced by Transmission Electron Microscopy, TEM, with POSS-rich nanophase sizes from 20 to 50 nm. Nanostructuration is attributed to the self-assembly of F-POSS due to the cluster-cluster interactions resulting from the nature of their ligands, i.e., cycloaliphatic ligands and perfluorinated chains. Thermogravimetric analysis was used to investigate the thermal degradation temperature. It was shown that when F-POSS content is higher than 2.8 mol%, the incorporation of F-POSS could improve the thermal stability of PMMA significantly. In addition, it was shown that these fluorinated POSS-based copolymer surfaces could reduce the surface energy and could be used to design water-repellant nanocomposite coatings.

     

Investigation on The Thermal Properties of Fe2O(SO4)2. Part I

The data on the thermal decomposition of FeSO₄?H₂O upon various regimes of heating and gaseous environment prove the formation of intermediate products of the types Fe₂O(SO₄)₂ and FeOHSO₄, their stability and amount being determined mainly by temperature and oxygen-reduction potential.

This communication aims at presenting results on the synthesis and characterization of Fe₂O(SO₄)₂. The synthesis was carried out using a laboratory thermal equipment operating under isothermal conditions in the temperature range 713–813 K in a gaseous environment either poor in oxygen or containing 100% oxygen. The experimental conditions under which Fe₂O(SO₄)₂ is stable are established. The effect of three basic parameters on the synthesis of Fe₂O(SO₄)₂ is clarified: the oxygen partial pressure, the ratio P_H2O/P_O2 and the temperature and the mode of heating. Mössbauer spectroscopy and X-ray diffraction data for Fe₂O(SO₄)₂ are presented.

     

Complete spin-orbit interaction in many-electron atoms

The complete spin-orbit coupling constants have been evaluated, including both the spin-own orbit and the spin-other orbit terms, for all the positive ions, neutral systems, and negative ions from He to Kr, as well as for various isoelectronic series.

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Zusammenfassung Für alle positiven und negativen Ionen und für die neutralen Atome von He bis Kr sowie für verschiedene isoelektronische Serien werden die kompletten Spin-Bahn-Kopplungskonstanten einschließlich der Spin-Bahn-Wechselwirkung verschiedener Elektronen berechnet.

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This work has been supported in part by the National Research Council of Canada.     

Energy Resonance Crossing Controls the Photoluminescence of Europium Antenna Probes

The energy transfer pathways in lanthanide antenna probes cannot be comprehensively rationalized by the currently available models, and their elucidation remains to be a challenging task. On the basis of quantum-chemical ab initio calculations of representative europium antenna complexes, an innovative energy resonance model is proposed, which is controlled by an overall nonet–quintet intersystem crossing on the basis of spin–orbit coupling among the sublevels of the involved states.     

Lightweight lignocellulosic foams for thermal insulation

Foams are mainly composed of dispersed gas trapped in a liquid or solid phase making them lightweight and thermally insulating materials. Additionally, they are applicable for large surfaces, which makes them attractive for thermal insulation. State-of-the-art thermally insulating foams are made of synthetic polymeric materials such as polystyrene. This work focuses on generating foam from surfactants and renewable lignocellulosic materials for thermally insulating stealth material. The effect of two surfactants (sodium dodecyl sulphate (SDS) and polysorbate (T80)), two cellulosic materials (bleached pulp and nanocellulose), and lignin on the foaming and stability of foam was investigated using experimental design and response surface methodology. The volume-optimized foams determined using experimental design were further studied with optical microscopy and infrared imaging. The results of experimental design, bubble structure of foams, and observations of their thermal conductivity showed that bleached pulp foam made using SDS as surfactant produced the highest foam volume, best stability, and good thermal insulation. Lignin did not improve the foaming or thermal insulation properties of the foam, but it was found to improve the structural stability of foam and brought natural brown color to the foam. Both wet and dry lignocellulosic foams provided thermal insulation comparable to dry polystyrene foam.

Graphical abstract

     

Combustion of Waste Waters Containing Organic Alkaline Salts

Abstract

The biological treatment of waste waters from chemical industry containing organic and inorganic salts causes problems because these materials inhibit the metabolic activity of the bacteria. One possible and economically feasible way to convert the organic materials into less toxic forms is a thermal oxidation process, which can take place either in a fluidized bed combustor or in a vertical combustion chamber.

The process is described and parameters of the process are discussed. Results from particle measurements on a vertical combustion chamber for the combustion of various artificial waste waters are presented. The chemical analysis of the particulate matter from different stages of the process allows a detailed characterization of the decomposition of the organic material. Conclusions are drawn both with respect to the process and the environment.     

Thermal performance evaluation of a nanofluid‐based flat‐plate solar collector

The thermal performance of a flat-plate solar collector (FPSC) is investigated experimentally and analytically. The studied nanofluid is SiO₂/deionized water with volumetric concentration up to 0.6% and nanoparticles diameter of 20–30 nm. The tests and also the modeling are performed based on ASHRAE standard and compared with each other to validate the developed model. The dynamic model is based on the energy balance in a control volume. The system of derived equations is solved by employing an implicit finite difference scheme. Moreover, the thermal conductivity and viscosity of SiO₂ nanofluid have been investigated thoroughly. The measurement findings indicate that silica nanoparticles, despite their low thermal conductivity, have a great potential for improving the thermal performance of FPSC. Analyzing the characteristic parameters of solar collector efficiency reveals that the effect of nanoparticles on the performance improvement is more pronounced at higher values of reduced temperature. The thermal efficiency, working fluid outlet temperature and also absorber plate temperature of the modeling have been confirmed with experimental verification. A satisfactory agreement has been achieved between the results. The maximum percentage of deviation for working fluid outlet temperature and collector absorber plate temperature is 0.7% and 3.7%, respectively.

     

Bournonite PbCuSbS3: Stereochemically Active Lone‐Pair Electrons that Induce Low Thermal Conductivity

An understanding of the structural features and bonding of a particular material, and the properties these features impart on its physical characteristics, is essential in the search for new systems that are of technological interest. For several relevant applications, the design or discovery of low thermal conductivity materials is of great importance. We report on the synthesis, crystal structure, thermal conductivity, and electronic‐structure calculations of one such material, PbCuSbS₃. Our analysis is presented in terms of a comparative study with Sb₂S₃, from which PbCuSbS₃ can be derived through cation substitution. The measured low thermal conductivity of PbCuSbS₃ is explained by the distortive environment of the Pb and Sb atoms from the stereochemically active lone‐pair s² electrons and their pronounced repulsive interaction. Our investigation suggests a general approach for the design of materials for phase‐change‐memory, thermal‐barrier, thermal‐rectification and thermoelectric applications, as well as other functions for which low thermal conductivity is purposefully sought.     

Photopolymerisation of composite material in simulated free space environment at low Earth orbital flight

Inflatable Gossamer’s structures which can be deployed in Earth orbit have great prospects in the future. Material for use in inflatable structures must be soft before and during unfolding and harden after unfolding. The best way for solidification of Gossamer’s structures is by chemical polymerisation of a composite material in space environment. The polymerisation processes of liquid polymer matrix in a free space environment are sensitive to microgravitation, temperature variations (−150 to +150 °C), high vacuum (10⁻³ to 10⁻⁷ Pa), atomic oxygen flux (in LEO), UV and VUV irradiations, X-ray and γ-irradiations, high energy electron and ion fluxes. In this paper experiments of the photopolymerisation processes under simulated free space conditions were carried out. The influences of high vacuum, temperature variations, high energy ion beam, radio-frequency and microwave plasma on polymerisation of UV-curing resin were observed. The effects of low molecular components evaporations, acceleration of curing kinetics, additional chemical reactions and mixing processes during polymerisation were observed. The photopolymerisation of inflatable structure was carried out under simulated temperature conditions of space flight in low Earth orbit. The results indicate a technology for large-size inflatable constructions in Earth orbit, in far space and on space bodies as for deployed antennas, solar sail stringers, solar shield stringers, frames for large-size space stations, frames for Moon, Mars, asteroids bases and frames for space plant on Earth orbit and other celestial bodies.     

A unique control strategy to improve the life cycle of the battery and to reduce the thermal runaway for electric vehicle applications

This paper presents a unique thermal control strategy to improve the ageing of the battery and to maintain the internal temperature of the battery within the optimum limit of 20 °C–40 °C for electric vehicle (EV) applications. The hybrid EV system encompasses photovoltaic (PV) module, high power density device supercapacitor (SC) and high energy density Li-ion battery (LIB) as an energy storage element. The vehicle dynamics encounter frequent voltage fluctuations in the direct current (DC) bus, which ultimately reduces the lifecycle of the battery and also the heat is generated inside the battery when it is connected in parallel to the DC bus. The frequent charging/discharging of LIB is controlled by the unique thermal control strategy of the hybrid EV system. The DC bus voltage is controlled by the SC bi-directional converter (BDC) where, the battery BDC delivers the essential constant current from the main source (PV) to the DC bus. This unique thermal control strategy supports the distribution of power from the PV/LIB/SC hybrid source system to the EV and also improves the battery life cycle. Due to constant charging/discharging of battery the thermal runaway (TR) problem such as leak, smoke, gas venting, rapid disassembly, flames etc., can be eliminated. Decoupling of load power and battery power comprises the growth in the battery lifecycle and to maintain the optimum internal temperature of the LIB by conditional flow of current through hybrid thermal management system (HTMS). To certify the thermal control strategy and to estimate the performance of HTMS, a simulation of a hybrid source system with vehicle dynamics is performed in MATLAB/Simulink. Numerical analysis of the LIB during constant charging/discharging is performed using ANSYS fluent software to validate the temperature effect of HTMS.

     

Bark-mimetic layer-by-layer assembled montmorillonite/poly(p-aminostyrene) flexible nanocomposites shielding atomic oxygen erosion

Inspired by the birch bark, which has multilayered structures, we fabricated layer-by-layer (LbL) assembled montmorillonite (MMT) and poly(p-aminostyrene) (PPAS) nanocomposites on cotton fiber curved surfaces to provide protection from atomic oxygen (AO) erosion. The multilayer coated fibers had high flexibility, uniformity, defect free, ease of preparation and low cost. The AO erosion durability has been dramatically enhanced which was evidenced by testing in the ground-based AO effects simulation facility. And the dimension and surface morphologies of the fibers observed by SEM had few changes, indicating excellent AO erosion resistant ability of the coatings. These results provide us a new method to design fibrous materials exposed directly in low earth orbit environment.