Good Thermal Stability In Air Research Articles

Air-Stable and Eco-Friendly Symmetrical Imine with Thiadiazole Moieties in Neutral and Protonated form for Perovskite Photovoltaics.

This paper proposes molecular and supramolecular concepts for potential application in perovskite solar cells. New air-stable symmetrical imine, with thiadiazole moieties PPL2: (5E,6E)-N2,N5-bis(4-(diphenylamino)benzylidene)-1,3,4-thiadiazole-2,5-diamine), as a hole-transporting material was synthesised in a single-step reaction, starting with commercially available and relatively inexpensive reagents, resulting in a reduction in the cost of the final product compared to Spiro-OMeTAD. Moreover, camphorsulfonic acid (CSA) in both enantiomeric forms was used to change the HOMO-LUMO levels and electric properties of the investigated imine-forming complexes. Electric, optical, thermal, and structural studies of the imine and its complexes with CSA were carried out to characterise the new material. Imine and imine/CSA complexes were also characterised in depth by the proton Nuclear Magnetic Resonance 1H NMR method. The position of nitrogen in the thidiazole ring influences the basicity of donor centres, which results in protonation in the imine bond. Simple devices of ITO/imine (with or without CSA(-) or CSA(+))/Ag/ITO architecture were constructed, and a thermographic camera was used to find the defects in the created devices. Electric behaviour was also studied to demonstrate conductivity properties under the forward current. Finally, the electrical properties of imine and its protonated form with CSA were compared with Spiro-OMeTAD. In general, the analysis of thermal images showed a very similar response of the samples to the applied potential in terms of the homogeneity of the formed organic layer. The TGA analysis showed that the investigated imine exhibits good thermal stability in air and argon atmospheres.

Are (Co)Polymers of 1,1,3,3,3-Pentafluoropropene Possible?

The copolymerization and terpolymerization of 1,1,3,3,3-pentafluoropropene (PFP) with various combinations of fluorinated and hydrogenated comonomers were investigated. The chosen fluoromonomers were vinylidene fluoride (VDF), 3,3,3-trifluoropropene (TFP), hexafluoropropene (HFP), perfluoromethylvinyl ether (PMVE), chlorotrifluoroethylene (CTFE) and tert-butyl-2-trifluoromethacrylate (MAF-TBE), while the hydrocarbon comonomers were vinylene carbonate (VCA), ethyl vinyl ether (EVE) and 3-isopropenyl-α,α-dimethylbenzyl isocyanate (m-TMI). Copolymers of PFP with non-homopolymerizable monomers (HFP, PMVE and MAF-TBE) led to quite low yields, while the introduction of VDF enabled the synthesis of poly(PFP-ter-VDF-ter-M3) terpolymers with improved yields. PFP does not homopolymerize and delays the copolymerizations. All polymers were either amorphous fluoroelastomers or fluorothermoplastics with glass transition temperatures ranging from -56 °C to +59 °C, and they exhibited good thermal stability in air.

Deposition and Thermal Stability of DLC/Si-N Composite Films Synthesized Using a Sputtering-PBII Hybrid System

Diamond-like carbon (DLC) is a metastable amorphous material that exhibits unique properties. However, there are many limitations regarding the use of this material due to factors such as its tribological characteristics at high temperature and limited thermal stability. In this study, the thermal stability and tribological properties of DLC/silicon-nitrogen (DLC/Si-N) composite films were investigated and compared to those of pure DLC films. All the films were synthesized using a combination of radio frequency (RF) magnetron sputtering and plasma-based ion implantation (PBII) (a so-called sputtering-PBII hybrid system) which is newly developed by us. A high purity silicon nitride (99.9%) disk was used as the target, applying an RF power in the range of 500 - 700 W and a negative pulsed bias voltage of 5 kV to the substrate. An Ar-CH4 mixture was used as the reactive gas. The CH4 partial pressure was varied between 0 and 0.15 Pa, while the total gas pressure and total gas flow were fixed at 0.30 Pa and 30 sccm, respectively. The structures of the resulting films were characterized using Raman spectroscopy, while the thermal stabilities were assessed using thermogravimetric-differential thermal analysis (TG-DTA) and friction coefficients were obtained via ball-on-disk friction tests. The results indicate that the DLC/Si-N composite films produced in this work exhibit improved thermal stability relative to that of pure DLC owing to the presence of thermally stable atomic-scale Si-N compound in the carbon main flame networks. A DLC/Si-N film containing approximately 11 at.%Si and 18.5 at.%N shows good thermal stability in air over 800°C up to 1100°C, together with excellent tribological performance at 500°C in air. Overall, the data demonstrate that DLC/Si-N composite films offer improved thermal stability and superior tribological performance at high temperatures.

High-temperature air-stable solar selective coating based on MoSi2–Si3N4 composite

The thermal stability in air of solar selective coatings based on the novel MoSi2–Si3N4 hybrid composite has been investigated here for the first time. Although thermal stability of solar absorbers is typically examined under vacuum, high temperature air stability is required for practical applications in concentration solar power (CSP) technologies: solar tower systems receivers operate in air and, on the other hand, air stability is highly preferred in parabolic trough collector systems due to occasionally undesired losses of vacuum conditions. In this work, the effect of different layers combination, prepared by sputtering, on the optical performance after high temperature annealing has been investigated. Two different standard substrates (stainless steel and Inconel) have been explored. It is shown that silver layer, typically used in SSC as IR reflector, strongly affects the stack thermal stability in air, leading to important degradation. For SSC stacks with the Inconel/MoSi2-Si3N4/Si3N4 structure (onto Inconel substrate), a good thermal stability in air is obtained, leading to just a slight variation of the absorptivity after air annealing at 600°C, probably due to partial Si3N4 oxidation. Best optical performance is achieved for the Inconel substrate, using and additional Al2O3 barrier on top, comprising the stack the following structure: Inconel/MoSi2-Si3N4/Si3N4/Al2O3. This combination exhibits very good optical performance, even after annealing at 700°C in air. The Performance Criterion (PC) according to the International Energy Agency, evaluated after successive air annealing cycles of 100h at 600°C, gets 0.02, which is considerably smaller than 0.05, fulfilling this material the PC for practical applications. Our results evidence that the MoSi2–Si3N4 absorber deposited onto Inconel substrate and capped with a Si3N4/Al2O3 layer on top (acting as antireflective and protective barrier) is a very promising selective coating for solar receivers operating in air at temperatures about 600°C.

Enhanced optical properties of TiN-based spectrally selective solar absorbers deposited at a high substrate temperature

In this study, the spectrally selective solar absorber coatings of TiN/Al2O3 are deposited onto stainless steels (SS) at a high substrate temperature of 300°C, which exhibits a high absorptance of 0.92 and a low emittance of 0.11 at 82°C. The structure, optical properties and thermal stability have been characterized by ultra-high resolution scanning electron microscopy, UV–vis–NIR spectrophotometry, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The study's results indicate that the substrate temperature (300°C) has an important effect on the solar absorptance and emittance. The SS/TiN/Al2O3 coating exhibits good thermal stability in a vacuum at 500°C for 5h. The coating also exhibits good thermal stability in air at 200°C for 2h. Raman analysis confirms that the oxidation of the SS/TiN/Al2O3 coating in air causes the composition to approach the stable oxide TiO2.

Versatile Metal Nanowiring Platform for Large-Scale Nano- and Opto-Electronic Devices.

A versatile metal nanowiring platform enables the fabrication of Ag nanowires (AgNW) at a desired position and orientation in an individually controlled manner. A printed, flexible AgNW has a diameter of 695 nm, a resistivity of 5.7 μΩ cm, and good thermal stability in air. Based on an Ag nanowiring platform, an all-NW transistors array, as well as various optoelectronic applications, are successfully demonstrated.

Fabrication and high-temperature tribological properties of self-lubricating NiCr–BaMoO4 composites

In the present work, NiCr–BaMoO4 self-lubricating composites have been fabricated by hot pressing to evaluate their tribological properties at elevated temperatures. Hydrothermal synthesis method has been used to prepare fine BaMoO4 spherical powders with a size of 500nm by adjusting different technological parameters. The synthesized BaMoO4 powders have a good thermal stability in air after calcining up to 1100°C for 5h. The friction and wear properties of NiCr–BaMoO4 composites were investigated by using a ball-on-disk friction and wear tester in sliding against Si3N4 ball up to 600°C. As contrasted with unmodified NiCr alloy, the composites incorporated with 10wt% or 20wt% BaMoO4 exhibit distinct improvements in effectively reducing friction and wear at elevated temperatures. NiCr–BaMoO4 composites have low friction coefficients of 0.26–0.30 and small wear rates in the order of magnitude of 10−5–10−6mm3/Nm at elevated temperatures. A dense oxidized surface layer is formed on the worn surface of NiCr matrix composites incorporated with BaMoO4. Tribo-oxidation reaction during high temperature wear tests is responsible for the formation of dense oxidized surface layer containing BaMoO4, NiCr2O4, NiO and Cr2O3. The coupled Si3N4 ball is covered with a transfer layer containing BaMoO4, which effectively reduces the friction and wear.

Nanocrystals and nanomaterials of isoreticular zeolitic imidazolate frameworks

By expanding the coordination/deprotonation modulator approach in a rational manner using different zinc salts and modulators we have developed facile high-yield room temperature syntheses of nanocrystals and nanomaterials of a microporous RHO-type zeolitic imidazolate framework (ZIF), ZIF-71. It is shown that the coordination or deprotonation modulation function of the modulator depends upon solution composition. Characterization by means of PXRD, SEM/TEM, FT-IR, TG/DTA, VT-PXRD, DLS and argon physisorption measurements revealed that the ZIF-71 nanomaterials exhibit good thermal stability in air and exist as micrometer-sized particles that consist of agglomerated nanocrystals or very small crystalline domains embedded in an amorphous phase and possess different networks of disordered meso- and macropores. The hierarchically porous structures depend upon the synthesis conditions. Further experiments indicated that the synthetic method can be expanded to produce nanomaterials of two other RHO-type ZIFs, ZIF-25 and ZIF-97. In another related ZIF system, nanomaterials synthesis is hampered by competitive formation of RHO-type (ZIF-93) and SOD-type (SIM-1) phases.

Thermal stability and oxidation resistance of polycrystalline Ba8Al16Si30‐based clathrates

Polycrystalline Ba8Al16Si30‐based clathrate samples (nominal composition Ba8Al15Si31) were prepared by combining arc melting and spark plasma sintering methods. Heat treatments were conducted at 873 K for 0–480 h in air to examine the thermal stability and the oxidation resistance, which are of practical importance when the material is used at elevated temperatures. Thermogravimetry (TG) and differential thermal analysis (DTA) in the range 300–1473 K in air indicated that Ba8Al15Si31 bulk form possessed relatively good thermal stability in air below approximately 1073 K. From X‐ray diffraction measurements, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and X‐ray photoelectron spectroscopy, it was inferred that thin oxide (probably barium aluminates) layer with the thickness of approximately 0.6 µm was formed on the surface by the heat treatment. The decrease in the electrical conductivity was found to be relatively low (less than 15%) by the heat treatment for 480 h in air.

Thermoelectric Properties and Thermal Stability of PEDOT:PSS Films on a Polyimide Substrate and Application in Flexible Energy Conversion Devices

In this study, we investigated the flexibility and thermal stability of films consisting of a complex of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) cast onto a polyimide substrate. We also prepared a PEDOT:PSS-based flexible device for thermoelectric energy conversion. The thermal stability of a PEDOT:PSS film was evaluated by measuring the Seebeck coefficient (S) and electrical conductivity (σ) for 30 heating and cooling cycles at 330 K to 380 K. Furthermore, the durability of the PEDOT:PSS film was examined by heating at 353 K in air for 4000 h. The approximate values of S and σ were 14 μV K−1 and 600 S cm−1, respectively. These values were almost the same before and after repeated bending treatments (10,000 times, radius of curvature 10 mm). In addition, the S and σ values for the PEDOT:PSS film were nearly constant during the heating cycle treatments. In the durability test, σ gradually decreased with increasing heating time (7% at 300 h, 17% at 3600 h). Thus, it was found that PEDOT:PSS films have both flexibility and mechanical toughness as well as relatively good thermal stability in air up to 3600 h. The maximum electric power for the PEDOT:PSS-based flexible device was 0.334 μW at ΔT = 100 K. These results for the power-generating properties of the flexible device are consistent with values calculated from the properties of the constituent materials.

Effect of Heat Treatment in Air on the Surface of a Sintered Ba8Al16Si30-Based Clathrate

A polycrystalline silicon-based clathrate of nominal composition Ba8Al15Si31 was prepared by a combination of arc melting and spark plasma sintering. Its thermal stability in air and the effect on the surface of heat treatment in air, which are of practical importance for use of the material at elevated temperatures, were examined for different temperatures (873 K, 973 K, and 1073 K) and heating times (0–480 h). Thermogravimetry and differential thermal analysis in air in the range 300–1523 K indicated that Ba8Al15Si31 in the bulk form had relatively good thermal stability in air at high temperatures. X-ray diffraction measurements, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy revealed that a thin layer of oxide (probably a barium aluminate, BaAl2O4) was formed on the surface by heat treatment in air. The thickness of the oxide layer increased with increasing temperature and heating time. Growth of the oxide layer can be explained well in terms of a diffusion mechanism. The activation energy for oxidation was estimated to be approximately 201 kJ/mol, which is comparable with that for thermal oxidation of silicon. The chemical composition of the interior of the Ba8Al15Si31 was found to be stable to heat treatment in air.

Synthesis, characterization, and optoelectronic properties of heteroleptic iridium complexes containing substituted 1,3,4-oxadiazole and β-diketone as ligands

The new heteroleptic iridium(III) complexes (BuOXD)2Ir(tta) and (BuOXD)2Ir(tmd) [BuOXD = 2-(4-butyloxyphenyl)-5-phenyl[1,3,4]oxadiazolato-N4,C2, tta = 1,1,1-trifluoro-4-thienylbutane-2,4-dionato, tmd = 2,2,6,6-tetramethylheptane-3,5-dionato] have been synthesized and characterized. These complexes have two cyclometalated ligands (C^N) and a bidentate diketone ligand (X) [C^N)2Ir(X)], where X is a β-diketone with trifluoromethyl, theonyl or t-butyl groups. The color tuning with the change in electronegativity of substituents in the β-diketones has been studied. Photoluminescence spectra of the complexes showed peak emissions at 523 and 549 nm, respectively. The electroluminescent properties of these complexes have been studied by fabricating multi layer devices with device structure ITO/α-NPD/8% iridium complex doped CBP/BCP/Alq3/LiF/Al. The electroluminescence spectra also showed peak emissions at 526 and 570 nm for (BuOXD)2Ir(tta) and (BuOXD)2Ir(tmd), respectively. These metal complexes showed good thermal stability in air to 340°C.

Cis–trans isomerization and optical laser writing in new heterocycle based azo-polyurethanes

Three new azo-polyurethanes containing the s-triazolo[3,4-b]thiadiazole heterocycle have been prepared and characterized. The polymers showed glass transition temperatures between 183 °C and 232 °C and a moderate to good thermal stability in air. The thermal cis– trans isomerization around the azo group was analyzed in solution and the kinetic constant of this process was calculated. One of the synthesized polymers was processed in form of thin films (thickness was 1.2 μm) and some experiments of optical laser writing were performed on it: three different surface relief gratings (SRGs) structures were realized at micrometer scale (a square, a concentric square pattern and a grating) indicating this polymer as an interesting candidate for the azo-lithography.

Controlling Zeolitic Imidazolate Framework Nano- and Microcrystal Formation: Insight into Crystal Growth by Time-Resolved In Situ Static Light Scattering

We report on a simple and straightforward method that enables the rapid room-temperature production of nanocrystals (finely tuned in size between ∼10 and 65 nm) and microcrystals (∼1 μm) of the prototypical microporous zeolitic imidazolate framework (ZIF) material ZIF-8. Control of crystal size is achieved in a novel approach by employing an excess of the bridging bidentate ligand and various simple auxiliary monodentate ligands with different chemical functionalities (carboxylate, N-heterocycle, alkylamine). The function of the monodentate ligands can be understood as a modulation of complex formation and deprotonation equilibria during crystal nucleation and growth. Using time-resolved static light scattering, the functioning of modulating ligands is monitored for the first time by in situ experiments, which offered significant insight into the crystal growth processes. Formation of nanocrystals is characterized by continuous, comparatively slow nucleation and fast crystal growth occurring on a time scale of seconds. Although nucleation and growth are not separated from each other, a significant narrowing of the particle size distribution during early stages results in rather monodisperse nanocrystals, before broadening of the particle size distribution occurs, as observed by complementary ex situ electron microscopy studies. Microcrystal growth is dominated by a particle−monomer addition mechanism, but indications for the operation of a coalescence process during early stages of growth have been also obtained. During later stages of microcrystal growth crystals change their shape from cubes to rhombic dodecahedra. The prepared phase-pure ZIF-8 nanoscale materials exhibit good thermal stability in air and large surface areas, which are comparable to those of large macrocrystals. Nanocrystal powders exhibit dual micro- and mesoporosity.

Soluble Polyimides Based on Diaminobenzoic Acid Alkylester

The synthesis and characterization of a novel series of soluble polyimides, that are based on diaminobenzoic acid alkylester (DBAE) having long-chain alkyl groups with 8–14 carbon atoms, are described. Polyimides obtained from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and DBAE-8–14, and copolyimides based on BTDA, DBAE-8–14, and 4,4′-diaminodiphenylether (DDE) were insoluble in polar solvents such as N-methyl-2-pyrrolidone (NMP) and the effect of long-chain linear alkyl groups for the enhancement of solubility was not recognized. However, it was found that two methods improve the solubility. One is the use of branched alkyl groups such as nonan-5-yl and 2,6-dimethylheptane-4-yl, and the other is the use of relatively flexible diamine co-monomer, 4,4′-diaminodiphenylmethane (DDM). These polyimides and copolyimides based on DBAE were soluble in various polar solvents and exhibited good thermal stability in air and under nitrogen. The effect of DBAE for the enhancement of solubility was lower than the effects of alkyloxydiaminobenzene (AODB) and alkyldiaminobenzophenone (ADBP), probably due to the rigid ester linkage group in DBAE.

Synthesis and Characterization of Novel Poly(Arylene Ether)s from 1,3‐bis(4‐Hydroxyphenyl) Benzene

Several poly(aryl ether)s have been prepared by the condensation of 1,3‐bis(4‐hydroxy phenyl) benzene with different trifluoromethyl activated bis‐fluoro compounds. IR, 1H and 13C NMR, and elemental analyses have established the resulting polymer structures. The properties of the polymers have been evaluated by DSC, TGA, dynamic mechanical analysis (DMA) and stress–strain analysis. The polymers 1a and 1c showed semi‐crystalline behavior as evident by sharp crystalline melting peaks at 299°C and 330°C along with glass transitions at 202°C and 216°C, respectively. The polymers showed very good thermal stability in air, high modulus, and high tensile strength with low elongation at break.

Poly(4‐vinylpyridine) as the host ligand of metal‐containing chromophores for second‐order nonlinear optical active materials

AbstractTwo formulas of grafted polymers with metal‐containing chromophores, potentially suitable for second‐order nonlinear optics applications, are described. Two chromophores were obtained from a tridentate ligand coordinated to Cu(II) or Pd(II) ions. The organometallic chromophore fragments were grafted to poly(4‐vinylpyridine) by the pyridinic nitrogen of the host polymer. Some qualities displayed by the new metallated polymers are remarkable: (1) a high value of the first hyperpolarizability coefficient of the chromophores, (2) a high content of the grafted chromophore in the polymers (up to 60 wt %), (3) a considerable increase in the glass‐transition temperatures (up to 240 °C), (4) good thermal stability in air (ca. 280 °C), and (5) good optical transparency of the films. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2987–2993, 2002

La (1− x) Sr xCoO 3 for thin film thermocouple applications

In this study, the LSCO (lanthanum strontium cobalt oxide) family has been investigated for thin film thermocouple applications. Thin films of La (1− x) Sr x CoO 3 ( x=0.3,0.5,0.7) were prepared on sapphire substrates by pulsed laser deposition. The films were annealed at different temperatures in air and characterized for phase, composition and microstructure to determine their thermal stability. From the phase and composition analyses, it is clear that as the Sr content in LSCO increases, the thermal stability decreases. Among the three compositions studied, x=0.3 had the best phase and chemical stability, and microstructural properties. It was observed that La 0.7Sr 0.3CoO 3 possesses excellent phase, composition and microstructural stability up to 1273 K. Above 1273 K, however, LSCO decomposes resulting in the loss of cobalt and formation of individual oxide phases. Electrical resistivity and Seebeck coefficients were measured in situ as a function of temperature in air up to 1023 K. The electrical and Seebeck coefficient properties were found to be stable for all the three compositions up to 1023 K and studies indicated that electrical conduction occurs through a small polaron hopping mechanism. In conclusion, LSCO possessed good thermal stability in air up to 1273 K and exhibits excellent potential in thin film thermocouple applications.

Polymerization and polymer properties of diarylacetylenes

The polymerization of three diarylacetylenes, namely 1-( p-benzylphenyl)-2-phenylacetylene ( p-BzDPA), 1-( p-phenylphenyl)-2-phenylacetylene and 1-(β-naphthyl)-2-phenylacetylene, was examined. These monomers polymerized in good yields with TaCl 5-cocatalyst systems. Poly( p-BzDPA) was soluble in various organic solvents and had high molecular weights of 6 × 10 5−9 × 10 5 according to gel permeation chromatography. In contrast, the other two polymers were insoluble in all solvents. All these polymers had fairly good thermal stability in air (their onset temperatures of weight loss in air were 330–450°C). The oxygen permeability coefficient of poly( p-BzDPA) at 25°C was 18 barrers, which was close to that of natural rubber (23 barrers).

Polymers with indane units by cationic polymerization

In spite of the difunctionality of the monomers, cationic polymerization of 1,3- and 1,4-diisopropenylbenzene does not lead to branched or cross-linked products. Instead, soluble polymers are obtained, containing the 1,1,3-trimethylindane system as repetitive unit along the backbone. These polymers are interesting materials because of their high glass transition temperature (200°C-250°C) and good thermal stability in air (2% weight loss at 450°C). Although the molar mass of the polyindanes seems to be limited due to a side reaction, it is possible to produce telechelic polyindanes. Substitution of an alkyl side chain onto the isopropenyl groups of 1,4-diisopropenylbenzene leads to monomers which yield substituted polyindanes with glass transition temperatures as low as 26°C. Such polymers still exhibit good thermal stability: at 340°C a weight loss of only 2% occurs. 1,4-Diisopropenylbenzene can even be anionically polymerized to linear polymers. In this case, the resulting polymer possesses isopropenyl phenyl side groups, which can be used as initiators for cationic polymerization of isobutene to obtain grafted copolymers.