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The influence of niobium on the structure of Nb2O5–ZnO–P2O5 glasses
摘要： Bulk glasses of the compositional series (A) xNb2O5–(50-x)ZnO–50P2O5 and (B) xNb2O5–50ZnO-(50-x)P2O5 were prepared to investigate possible substitution of cation (Zn2+), series A, and anion (PO3?), series B, with niobium and the effect of this substitution on the structure, density, molar volume, glass transition temperature and coefficient of thermal expansion. The structure was studied by Raman and 31P MAS NMR spectroscopies. The chemical model, based on the idea of chemical compounds as components with the lowest Gibbs energy and therefore the most stable, and on the results of 31P MAS NMR spectroscopy, was proposed for series B. It was found that niobium acts in glasses of series B only as a cation NbO3+, unlike the original idea of forming an anion of NbO?, that is, similarly to series A, where it replaces the cation. This leads to a change in the metaphosphate network of series B to the network that is similar to series A glass. The validity of this idea was verified by experimentally obtained compositional dependencies of molar volume, glass transition temperature and thermal expansion coefficient. Changes observed in thermal measurements indicate the evolution of a more rigid structure and more intensive cross-linking of the phosphate chains with increasing content of niobium.
关键词： Phosphate glasses,Chemical model,Structure,Niobium,Thermal properties
更新于2025-09-10 09:29:36
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Effect of TiO2 on highly elastic, stretchable UV protective nanocomposite films formed by using a combination of k-Carrageenan, xanthan gum and gellan gum
摘要： The hydrogel based composite film was prepared from k-carrageenan (k-C), xanthan gum (X) and gellan gum (G) by solvent casting method. The transparent films made from these gellable materials with synergistic hydrogel composition have soft texture, good elasticity and excellent break strength. The k-C/X/G based nanocomposite films prepared from different weight ratio of TiO2 nanoparticles were characterized for new packaging materials. The morphology, structure and microstructure properties of the k-C/X/G and TiO2 nanocomposite films were characterized by FT-IR, XRD and SEM analysis. By the incorporation of TiO2 in the k-C/X/G nanocomposite films, the tensile strength, tensile modulus, Tg and thermal stability of the films were greatly enhanced. Due to the hydrophobic nature of the TiO2 nanoparticles there is an increase in contact angle whereas moisture content of the films decreased. The water vapor permeability (WVP) and ultra violet lights transmittance decrease upon increasing the TiO2 content. The k-C/X/G and TiO2 nanocomposites effectively shield the UV light, exhibited partial microbial activity against Staphylococcus aureus and have a high potential for the application in food and non-food industries as UV shielding packaging materials.
关键词： nanocomposites,titanium dioxide,thermal properties,gellan gum,xanthan gum,water barrier properties,mechanical properties,k-Carrageenan
更新于2025-09-09 09:28:46
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Elastic moduli of TeO2–PbO glass system
摘要： Binary glasses (1 ? x)(TeO2) ? x(PbO) with x = 0, 0.10, 0.15, 0.20, 0.25, 0.30 mol% prepared using the melt quenching have been studied in this work. The amorphous nature of the glasses is confirmed by XRD analyses. Density, ρ and molar volume, Vm were measured for more information on structural changes. The ultrasonic velocities (longitudinal and shear) were obtained using the method of pulse-echo at 5 MHz resonating frequency. The elastic moduli, namely longitudinal (L), shear (G), Young (E) and the bulk (K) moduli were obtained from the density and ultrasonic velocities measurement. The softening temperature (TS), Debye temperature (θD), Poisson’s ratio (σ), fractal bond connectivity (d), microhardness (H) and acoustic impedance (Z) were obtained from the elastic moduli. The transition temperature ( Tg ) and thermal expansion coefficient (αP) were also calculated. The experimental elastic moduli data and the values calculated theoretically from the bond compression, Makishima–Mackenzie, and Rocherulle models were compared in this work.
关键词： Tellurite glasses,Thermal properties,Ultrasonic velocities,Elastic moduli,PbO
更新于2025-09-09 09:28:46
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Solar Energy Absorbing Materials that are Capable of Withstanding Long-Term Exposure at 600 °C: Research Strategy
摘要： Pipes for parabolic-trough solar energy collectors (PTSC) must be able to operate and withstand high temperatures in corrosive environments for a long time without changing its microstructure and losing its original properties. The stages of development of a new material and technology for solar energy collectors that allows the production of a PTSC solar energy-absorbing material that is capable of withstanding temperatures ≥ 600 °C for at least 250 days are described. This material is a glass-crystalline enamel coating that is adhered to tubular stainless steel pipes. Such enamel coatings have high coefficients of thermal expansion (CTE) that are similar to the metal surface. These matching CTEs allow the enamel coatings to resist flaking during the heating at 900 °C. The high-temperature resistance of the developed coating was ensured not only by specific additives added to the frit of the coating but also by an additional nanosized sol-gel coating over the enamelled metal substrate.
关键词： thermal properties,enamel coatings for steel,anti-reflective coatings,sol-gel coatings
更新于2025-09-09 09:28:46
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Effect of Te Proportion on the Properties of Ge25Sb10Se65-Te Chalcogenide Glasses
摘要： The effect of Te proportion on the physical, thermal and optical properties of Ge-Sb-Se glasses was the goal of this study. In this regards, four different glasses of Ge25Sb10Se65-xTex (x=5,10,15,20) were prepared by conventional melt quenching technique in quartz ampoule. The produced samples were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR spectroscopy), Vickers hardness tester, Differential scanning calorimetry (DSC) and Thermal mechanical analysis (TMA). Based on the obtained results, we known that the overall transmittance of the samples is about 55%. For physical properties, as the Te content increases from 5% to 20%, the glass density increases from 4.52 g·cm-3 to 4.78 g·cm-3 and the Vickers hardness value is improved from 172 kg·mm-2 to 198 kg·mm-2. With respect to the thermal properties, the glass transition temperature is 551.45 K-514.56 K and the difference of Tx-Tg is more than 110 K, where Tx is the initial crystallization temperature, and Tg is the glass transition temperature. While the thermal expansion coefficient varies little, from 1.87×10-5 to 1.82×10-5. In addition, the Tg value achieved by DSC is higher than that of TMA, which gives out a reference for the measurement of characteristic temperature.
关键词： thermal properties,transmittance,characteristic temperature,Chalcogenide glasses
更新于2025-09-09 09:28:46
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Heteroleptic complexes of silver(I) featuring 4′-hydroxy- and 4′-(2-furyl)-2, 2′:6′, 2″-terpyridine: an easy route to synthesis silver nanoparticles
摘要： New coordination complexes of silver(I) containing triphenylphosphine and 4′-hydroxy-2,2′:6′,2″-terpyridine (tpyOH) or 4?-(2-furyl)-2,2′:6′,2″-terpyridine (ftpy) have been synthesized to afford the new compounds [Ag(tpyOH)(PPh3)](NO3) (1) and [Ag(ftpy)(PPh3)](NO3) (2). In addition, the reaction of silver(I) nitrate with ftpy in the presence of excess of 4,4′-bipyridine (bpy) and NH4PF6 led to the formation of binuclear complex [Ag2(ftpy)2(μ-bpy)](PF6)2 (3). The products have been characterized by elemental analysis, IR, UV-Vis, NMR (1H, 31P) spectroscopy and single crystal X-ray diffraction in the case of 3. The 31P NMR data reveal that the interaction of PPh3 with silver(I) is maintained in solution in 1-2. The crystal structure of 3 shows that each Ag+ ion is coordinated by three N-atoms of ftpy and a nitrogen from the bridging ligand of bpy in a slightly distorted square planar geometry. There are some strong noncovalent interactions of hydrogen bonding and Ag-η2-furyl in the crystal structure, connecting molecules to form a supramolecular network. The thermal decomposition of 1-3 has also been investigated. The thermal stability of all complexes, as determined by thermogravimetric analysis (TGA), are almost the same and they are thermally stable up to 220 oC. The complex 3 was used for the preparation of Ag nanoparticles by simple calcination method at two different temperatures of 400 and 600 ?C resulting in the formation of silver nanoparticles, crystalline in nature with the size of 66 and 52 nm, respectively, using Scherrer’s equation. The nano-sized silver particles have also been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDX).
关键词： Crystal Structure,Thermal Properties,Nano Particle,Silver,Terpyridine
更新于2025-09-09 09:28:46
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Two-ply anode X-ray tube for computed tomography scanner
摘要： This report presents a method of the formation of tungsten layer on the graphite surface. The described method can be used to create the anode of powerful x-ray tubes for medical purposes, in particular, a computer tomograph (CT). The thermal properties of the graphite base and the deposited tungsten coating, as well as the strength of the resulting coating were studied. Thermal fields in the CT-anode with a power of 100 kW were calculated.
关键词： tungsten layer,thermal properties,tungsten coating,thermal fields,graphite surface,computer tomograph,x-ray tubes
更新于2025-09-04 15:30:14
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Moisture absorption and hydrothermal aging of phenylethynyl-terminated pyromellitic dianhydride-type asymmetric polyimide and composites
摘要： The effects of moisture on a polymerized monomeric reactant (PMR)-type polyimide (TriA X) and associated composites were investigated. Water uptake tests were performed on the polyimide at various temperatures and relative humidity levels to investigate moisture absorption behavior. Two-stage moisture absorption was observed, in which the first stage was diffusion controlled, whereas the second stage was moisture plasticization controlled. As exposure temperature increased, the equilibrium moisture content of the polyimide decreased, indicating an exothermic absorption process. The Arrhenius temperature dependence and moisture saturation as functions of temperature and humidity in the neat polymer were determined using curve fitting based on the published mathematical models. Long-term hydrothermal aging at 95°C was conducted on the neat polyimide and associated carbon fiber composites. Reversible hydrolytic reactions and a trace of irreversible hydrolysis were observed in the long-term exposure. The tensile ductility of the neat polyimide and the short-beam shear strength of the composites decreased with increasing aging time, while the tensile strength and modulus and thermal properties of the polyimide exhibited little change after 2000-h aging, demonstrating hydrothermal stability. The decrease in the ductility of the neat polymer after long-term moisture exposure was attributed to the network structure change, driven by hydrolysis and moisture plasticization.
关键词： β-relaxation,hydrothermal aging,moisture absorption,thermal properties,hydrolysis,Polyimide,composite,mechanical properties,plasticization
更新于2025-09-04 15:30:14
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Synthesis and characterization of thianthrene-containing preimidized soluble polyimide resins and the derived films with high refractive indices and good optical transparency
摘要： A series of organo-soluble polyimide (PI) resins were prepared from a newly designed and synthesized aromatic thianthrene-containing diamine, 2,7-bis(3-aminophenoxy)thianthrene (APOT) and various aromatic dianhydrides via a one-step high temperature polycondensation procedure with N-methyl-2-pyrrolidone (NMP) as the solvent. The derived PI resins were soluble in polar aprotic solvents, including NMP and N,N-dimethylacetamide (DMAc). For comparison, several unsoluble sulfur-containing PIs were prepared from another para-substituted thianthrene-containing diamine, 2,7-bis(4-aminophenylenesulfanyl)thianthrene (APTT) and aromatic dianhydrides by a two-step polycondensation procedure via poly(amic acid) (PAA) precursors at elevated temperatures as high as 300 °C. Flexible and tough PI films with the tensile strength higher than 88 MPa were successfully cast from the APOT-PI resin solution at a relatively low curing temperature of 250 °C. The meta-substituted molecular skeleton in the APOT- PIs endowed the films good optical transparency with the transmittance higher than 83% at a thickness around 10 um, which was apparently higher than those of the para-substituted APTT-PI analogues. The sulfur-rich thianthrene moiety with high molar refraction endowed the APOT-PI films high refractive indices up to 1.7147 at 632.8 nm and low birefringence in the range of 0.0064–0.0133. In addition, the PI films showed good thermal stability with the glass transition temperatures (Tg) higher than 198.3 °C and 5% weight loss temperatures higher than 510 °C in nitrogen.
关键词： Thermal properties,High refractive index,Polyimide,Optical properties,Thianthrene
更新于2025-09-04 15:30:14
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Thermally resistant photocrosslinked damping poly(phenylene oxide)-fluorosilicone rubber films with broad and high effective damping temperatures
摘要： The development of an energy-ef?cient strategy to prepare thermally resistant damping materials with high damping capacities (tan δ values) and broad effective damping temperature ranges (ΔTs) at high temperatures (>150 (cid:1)C) is still an interesting challenge. In this study, a graft copolymer (PSi-g-APPO) was synthesized through the reaction between hydrogen-terminated ?uorosilicone and allyl poly(phenylene oxide) (APPO), and a unique kind of photocrosslinkable ?lm (coded as GFA) consisting of FSR, APPO and PSi-g-APPO was prepared. The resultant GFA has high thermal resistance, wide ΔT, and high tan δ. When the weight ratio of APPO to FSR to PSi-g-APPO was 81:9:10, the obtained ?lm exhibited a broad ΔT of 64 (cid:1)C and a high tan δ (≤1.01) from 157 to 221 (cid:1)C; this was the best comprehensive performance among the GFA systems. The mechanism behind the excellent integrated performance of GFA was studied and was proven to be due to the unique structure of the heterogeneous GFA system.
关键词： thermal properties,crosslinking,structure–property relationships,blends,?lms
更新于2025-09-04 15:30:14