Fine Thermal Stability Research Articles

Fabrication and swelling properties of a novel superabsorbent composite derived from waste coal gangue

In this work, novel superabsorbent composites made of starch-grafted-polyacrylic acid/coal gangue were prepared via aqueous solution polymerization. The starch-g-polyacrylic acid/coal gangue (St-g-PAA/CG) composite with 10 wt.% CG showed the maximum water absorbency in distilled water (560 g·g−1) and a 0.9 wt.% NaCl solution (102 g·g−1). Moreover, this superabsorbent composite exhibited fine thermal stability and its swelling behavior was dependent on pH. In general, the swelling kinetics of the superabsorbent composites fitted with the Scott’s kinetic model. These composites not only showed excellent water absorption reversibility after five absorption/drying cycles, but also exhibited considerable environmental responsiveness after the swelling medium was changed from distilled water to the 0.9 wt.% NaCl solution. Based on these results, the prepared superabsorbent composites can be applied in several fields such as horticulture, agriculture, health care, and controlled drug delivery, while ensuring comprehensive utilization of solid wastes.

A novel form stable phase change material with comb-like cross-linked polyurethane as supporting skeleton

To improve the homogeneity of phase-change materials (PCMs) composites for thermal energy storage, the poly(ethylene glycol monomethyl ether)-based trimethylolpropane (Ymer-N120) with long side ethyoxyl chains is employed to form comb-like polyurethane which functioned as supporting materials for PCMs. And the results of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, differential scanning calorimetry, accelerated thermal cycling testing, thermogravimetric analysis and field emission scanning electron microscopy (FESEM) suggested a crosslinked polyurethane embedded with micron grade myristic acid (MA) crystals was prepared during the thermal curing process. The obtained comb-like polyurethane (YP) can provide 3D structure supporting materials for melting MA. And the long side ethyoxyl chain of Ymer-N120 promote the melting MA form micron-sized crystals. The results of thermal reliability testing confirmed the advantages of same methylene groups in side chains and suggested the maximal hold capability of YP crosslinks is about 50 wt% of composites. With the 50 wt% addition of MA, YPM50 can supply high latent heat (over 90 J/g of YPM50) with fine thermal stability (due to its initial decomposing temperature reaches 190 °C) without leakage (after 500 times of accelerated thermal cycling testing). All results indicated this structure supplies an effective solution for the leakage of PCMs, which show a promising application in TES.

Optoelectronic properties improvement of double perovskites Cs2Sn(Pb)I6 by the hydrothermal method

AbstractHerein, we report on the synthesis of perovskite Cs2Sn(Pb)I6 powder via a modified hydrothermal method, in which Pb2+ ions are introduced to Cs2SnI6 to optimize the semiconductor properties of double perovskite. Results indicate that the introduction of 2 at% Pb2+ into the Cs2SnI6 not only facilitates fine thermal stability, smoother surface with small grain size, expanding the scope of absorption. Thence the photovoltaic properties of Cs2SnI6 are improved where obtained a higher photocurrent density (∼ 70 µA cm−2). Combined with changes in photoelectric properties, perhaps a small amount of Pb doping plays a role in reducing the formation energy and surface energy of the compounds. On the contrary, excessive Pb doping destroys the synthesis of Cs2SnI6 and reduces the purity of the compound; thus, affecting its application. This study provides useful insights into the development of double perovskites with high stability and efficiency.

Structural, Optical, and Thermal Properties of Cs2SnI6–xBrx Mixed Perovskite Solid Solutions

Cs2SnI6‐xBrx (x = 0–6) solid solutions have been synthesized by chemical solid solution reaction in conjunction with sintering under vacuum. The Rietveld refinements of powder X‐ray diffraction (XRD) patterns indicate that all the samples are cubic, with a symmetry of Fm3m. The lattice parameter a decreases linearly as a function of the Br content in Cs2SnI6‐xBrx. Raman spectra suggest that the new Raman peaks might derive from the short‐range ordering of I/Br anions. The UV/Vis reflection spectra reveal a nonlinear trend of energy band gap (Eg) from 1.25 eV to 3.01 eV with increasing Br content. Hence the wide range of Eg of Cs2SnI6‐xBrx solid solutions are capable to overlay almost the entire visual spectrum. Thermogravimetric analysis (TGA) results suggest that the thermal stability of Cs2SnI6‐xBrx increases gradually with increasing Br content. Cs2SnI6‐xBrx with the fine thermal stability and tunable Eg indicate high potential in the applications of solar cell devices.

Azido‐terminated Hyperbranched Multi‐arm Copolymer as Energetic Macromolecular Plasticizer

AbstractAzido‐terminated hyperbranched multi‐arm copolymer (POGA) with hyperbranched polyether core (PEHO‐c) and linear azido‐terminated glycidyl azide polymer arms (GAPA‐a) has been prepared. The structures of the polymers were characterized by FT‐IR, NMR, GPC and elemental analysis. The molecular weight of POGA was up to ca 17000 g mol−1, far higher than that of common plasticizers (200∼1000 g mol−1). The enthalpy of formation and high nitrogen content of POGA demonstrated its remarkable energy level, and low impact and friction sensitivities indicated its good safety performance in mechanical stimuli. The results of the kinetic and thermodynamic parameters, calculated from non‐isothermal DSC, denoted a fine thermal stability of POGA. Furthermore, the plasticizing effect of POGA, evaluated by plasticizer efficiency and viscosity, was superior to A3 but inferior to Bu‐NENA, however, its exudation was much slower than that of small molecular plasticizers, especially Bu‐NENA. Moreover, the plasticizing mechanism of POGA as energetic macromolecular plasticizer was established by analyzing its structure and performance characteristics.

Polyethylene glycol: An effective agent for isocyanate-based polyimide foams with enhanced foaming behavior and flexibility

A series of polyimide foam materials were prepared via one-step process, and the effect of polyethylene glycol on the morphology and properties of the foams was investigated. The results showed that the mean cellular diameter increased from 0.49 to 0.57 mm with the increase of polyethylene glycol content. Meanwhile, with the addition of polyethylene glycol, the tensile strength of polyimide foams increased from 18 to 23 kPa. It was proved that the foaming behavior and flexibility of polyimide foams were greatly improved due to the introduction of polyethylene glycol. As a kind of chain extender, polyethylene glycol reacted with isocyanate to form the flexible urethane segment, which improved the flexibility of polyimide molecular chain and promoted foaming behavior. In addition, all the foams exhibited fine thermal stability with temperature at 5% weight loss of about 350°C. The limiting oxygen index values of the prepared polyimide foams decreased with the increase of polyethylene glycol content, while the heat release rate increased, indicating certain decrease of the flame retardant properties. However, the fine cell structure can still be observed under the residual carbon structure after the burning, indicating fine flame retardancy.

Unexpected magnetization enhancement in hydrogen plasma treated ferromagnetic (Zn,Cu)O film

The effects of H+ incorporation on oxygen vacancies (HO+) on the giant ferromagnetic behavior (moment up to 3.26 μB/Cu) in ZnO:Cu polycrystalline films have been closely examined using different microstructural and magnetic characterization tools. Fine thermal stability (up to 450 °C) and low resistivity demonstrate a significant correlation between Cu 3d-states and HO+ donor defects in H plasma treated ZnO:Cu films, analogous to dual-donor (VO and Zni) defects mediated case. These HO+ donors can delocalize their electrons to the orbits of Cu atoms and contribute to a stronger spin-orbit coupling interaction. Suitable HO+ defect concentration and matched proportion between Cu2+ and Cu+ species ensure that orbital momentum shall not be quenched. Hence, unexpected moment enhancement, less than spin-orbit coupling upper limit (3.55 μB/Cu), can be also expected in this scenario. The manipulation from spin-only to spin-orbit coupling mode, using a facile thermally-mediated H plasma exposure way, will allow achieving spin transport based diluted magnetic semiconductor device.

SiO2–Al2O3–Y2O3–ZnO glass sealants for intermediate temperature solid oxide fuel cell applications

In this study, eleven alkaline earth metal and B2O3-free SiO2–Al2O3–Y2O3–ZnO glass sealants were prepared. The thermal stability, adhesion, and sealing properties of the glass systems with respect to SUS430 stainless steel (SUS430) were assessed for use in intermediate temperature solid oxide fuel cells (ITSOFCs). The glass transition points fell in the range of 694 °C and 833 °C, while the glass softening points, varying from 725 °C to 885 °C, decreased linearly with the ZnO/SiO2 ratio. Among the glasses evaluated, the YAS1-50, YAS4-50, YAS5-50, and YAS5-90 glasses coupled with SUS430 showed fine adhesion and no detectable inter-diffusion across the interface. The coefficient of thermal expansion (CTE) of the YAS5-50 glass escalated from 7.01 to 9.30 × 10−6/K with 50 wt% Bi1.5Y0.5O3 (BYO) fillers. The leak rates of the composite seals comprising the YAS5-50 glass and 50 wt% BYO fillers were measured at 700 °C after joining at 850 °C. The measurement used helium with a pressure at 1 psi across the glass seals and a slight load of 1.0 psi to minimize compressive seal effect on the glass. It appeared that a low leak rate of 0.052 sccm/cm was obtained and stayed unchanged as the system was soaked at 700 °C for 500 h, indicating a fine thermal stability against the extended duration benefited from the limited crystallization of the YAS5-50 glass. This promising long-term stability qualified the glass for use as SOFC seal.

Studies on Diamond Brazing Process

Through scientific experiments, we studied the binder, diamond, solder, uniform distribution and heating curves in brazing. We selected DH temporary binder, compared two kinds of diamond, selected the diamond with fine thermal stability. The experiments adopted diamond with uniform templates, experimenting 13 kinds of solder of which 9 were mixed with diamond for comparison of brazing effects and thermal damage. We optimized solder and brazing process and comprehensive analyzed experimental results. The analysis showed a small amount of DH temporary binder residue in brazing, fine effect in case of low alloy solder brazing temperature, better adhesion of solder and diamond achieved by elements formed by Cr and other strong carbides, sufficient volatilization of temporary binder and other impurities achieved by insulation before 500°C, heating rate of 1°C/min when the temperature it is higher than 20°C-50°C, the solder melting point, and that cooling should be carried out under high vacuum, brazing diamond should have fine thermal stability.

Studies on Diamond Brazing Process (Part one)

Through scientific experiments, we studied the binder, diamond, solder, uniform distribution and heating curves in brazing. We selected DH temporary binder, compared two kinds of diamond, selected the diamond with fine thermal stability. The experiments adopted diamond with uniform templates, experimenting 13 kinds of solder of which 9 were mixed with diamond for comparison of brazing effects and thermal damage. We optimized solder and brazing process and comprehensive analyzed experimental results. The analysis showed a small amount of DH temporary binder residue in brazing, fine effect in case of low alloy solder brazing temperature, better adhesion of solder and diamond achieved by elements formed by Cr and other strong carbides, sufficient volatilization of temporary binder and other impurities achieved by insulation before 500°C, heating rate of 1°C/min when the temperature it is higher than 20°C-50°C, the solder melting point, and that cooling should be carried out under high vacuum, brazing diamond should have fine thermal stability.

Synthesis and Mesomorphism of Rigid Bridge Triphenylene Discotic Liquid Crystal Dimers

Pd-Cu catalyzed homocoupling reaction has been used for the synthesis of symmetrical triphenylene discotic liquid crystal dimers, [C18H6(OCnH2n+1)5(O2CC6H4C≡C-)]2 (n = 4, 5, 6, 7, 8, 9), which connected two triphenylene discogens via a long rigid spacer. The purity and structure of monomers and dimers have been characterized with 1H NMR, IR and high resolution Mass. Their fine thermal stability has been confirmed by the results of thermogravimetry analysis (TGA). Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) results have shown that the monomers and dimers exhibit columnar mesophases (Col). The dimers display wide mesophase ranges and are room temperature liquid crystals, and their clearing points increased with the lengthening of peripheral alkyl chain.

Morphology and thermal stability of Ti-doped copper nitride films

A weakly Ti-doped copper nitride (Cu3N) film was prepared by cylindrical magnetron sputtering. The XPS results indicate that Ti atoms do not substitute for the Cu atoms but probably locate at the grain boundaries. The columnar grains size is about half of that of the undoped Cu3N film and the surface is smoother. For weakly Ti-doped Cu3N films, a dense layer appears on top of the columnar crystals. The RMS of the Cu film formed by annealing of the weakly Ti-doped Cu3N film is more than twice larger than that of the film before annealing. Compared with the undoped Cu3N film, it possesses fine thermal stability both in vacuum and in atmosphere.

Fabrication of the nanometer Al 2O 3/Cu composite by internal oxidation

The fabrication of the copper matrix composites strengthened with dispersal nanometer Al 2O 3 is investigated. The investigation result shows that aluminum in Cu–Al alloy powder can be oxidated by the action of oxidizer Cu 2O to form nanometer Al 2O 3 in nitrogen atmosphere. the more appropriate temperature of internal oxidation is at 950 °C and the more appropriate time is for 0.5 h. Sintering is at 950 °C for an hour. The results show that the crystal structure of Al 2O 3 is α-Al 2O 3, β-Al 2O 3 and γ-Al 2O 3. The main forming phase is nanometer γ-Al 2O 3 which size is about less than 12 nm. The nanometer γ-Al 2O 3 grains about 35% are not only in crystalline grains of copper but also in crystal boundary of copper. α-Al 2O 3 and θ-Al 2O 3 are all in crystal boundary of copper. As compared with the composite by a previous sintering, the tensile strength and yield strength of Al 2O 3/Cu composite increase respectively from 394 and 150 to 615 and 420 MPa after plastic deformation. And Al 2O 3/Cu composite is provided with fine thermal stability. It shows that the Al 2O 3/Cu composite can be used as the heat-resistant, wear-resistant and electric parts, such as the electrodes resistance welding, the electricity brushes of motors and so on.

Transition metal coordination polymers with polycarboxylic acid as bridging ligands: Synthesis and structure characterization of [Fe(m4-bta)0.5(phen)(OH)

A new 2D (two-dimensional) coordination polymer, [Fe(μ4-bta)o.5(phen)(OH)]n (1), has been hydrothermally synthesized with FeCl3 6H2, Na4bta (h4bta = 1,2,4,5-benzentetracarboxylic acid), 1,10-phen (1,10-phenanthroline) and H2O as raw materials. The crystals of the compound belong to monoclinic P21/n space group, a = 1.0129(2) nm, b = 0.9265(2) nm, c = 1.5696(3) nm, β=91.37(3)°V=1.4721(5) nm3,Z=3, final R1=0.0292, wR 2=0.0798 for 2572 [/>2σ(/)] observed reflections. The result of structure determination shows that in the compound each bta ligand is connected with four Fe3, forming a new μ4-coordination mode. Four deprotonated carboxylic groups of bta link to Fe3 ions alternatively through monodentate and bidentate coordination fashion, constructing 2D layer network. The measurement of variable temperature magnetic susceptibility indicates that there exist antiferromagnetic interactions between Fe3 ions in the compound. The TGA spectrum displays relatively fine thermal stability of the compound. In addition, IR and UV-Vis spectra of compound 1 have also been measured.