Thermal Stability Behavior Research Articles

Effects of Y and Ho doping on microstructure evolution during oxidation of extraordinary stable Hf-B-Si-Y/Ho-C-N films up to 1500 °C

Hard, and optically transparent amorphous Hf6B12Si29Y2C2N45 and Hf5B13Si25Ho3C2N48 films were prepared by reactive pulsed dc magnetron co-sputtering and annealed up to 1500 °C in air. The evolved microstructures were studied by X-ray diffraction and transmission electron microscopy to understand the Y- and Ho– doping effects on thermal stability and oxidation behavior. A three-layered microstructure developed in both annealed films. A fully oxidized layer formed at the top surface consisting of cubic fluorite Hf(Y/Ho)O2 nanoparticles embedded in an amorphous SiOx-based matrix. The oxide layer is about 36 % thinner compared to undoped films with similar composition [1]. A recrystallized structure formed at the bottom of both films composed mainly of Hf(Y/Ho)N and α-/β-Si3N4. All Hf(Y/Ho)N in the middle layer was oxidized producing vertically oriented Hf(Y/Ho)O2 nanocolumns surrounded by Si3N4 nanocrystalline. The Y- and Ho– doping found to stabilize the cubic fluoride oxide structure and promoted its (1 1 1) columnar texture. The oxidation mechanism of Si3N4 nanodomains occurs via formation of β-SiO2 first followed by its transformation to amorphous SiOx. It is suggested that substitution of Hf4+ with Y3+ and Ho3+ ions within the Hf(Y/Ho)O2 formed an anion vacancy defect structure to preserve charge neutrality affecting the oxidation mechanism in the doped films.

Studies on the thermal stability and exothermic behaviour of imidazolium-based ionic liquid binary mixture

Studies on the thermal stability and exothermic behaviour of imidazolium-based ionic liquid binary mixture

Study of Immersion Behavior and Thermal Stability of Green Composite PLA/Bamboo

One way to address environmental problems caused by the use of synthetic materials is by exploring the potential of new materials that are more environmentally friendly. This research aims to develop PLA/bamboo green composites by investigating the effects of fiber composition and alkali treatment on the thermal stability and immersion behavior of the composites. PLA/bamboo composites were produced using the hot press method with bamboo fibers at 10, 20, and 30 wt.% concentrations. Alkaline treatment was conducted using a 5% NaOH concentration for 24 hours. The PLA/bamboo composite exhibited weight gain due to water absorption during the soaking process. The inclusion of bamboo composition increases the water absorption of the composite, whereas alkali treatment decreases the water absorption of the composite. Furthermore, the introduction of fibers also reduces the degradation temperature of the composite. This research is expected to provide valuable insights for the broader utilization of green composite materials.

‘Spider-like’ POSS in NIPU webs: enhanced thermal stability and unique swelling behavior

PEO-based non-isocyanate polyhydroxyurethane (NIPU, PHU) networks physically modified with octa(3-hydroxy-3-methylbutyldimethylsiloxy)POSS (8OHPOSS) were synthesized via one-pot one-step approach. POSS was introduced into the polymer matrix in the amount of 1–10 wt%. Polar hydroxyls on the vertex groups of POSS allowed for uniform dispersion even up to high loadings (10 wt%). Composites exhibit enhanced thermal stability in comparison to the pristine matrix. FTIR analysis confirmed that POSS strengthens the hydrogen bonding in the material. Upon POSS introduction, plasticization was observed with a peculiar trend change at POSS loadings over 5 wt%. Glass transition temperature of highly crystalline 8OHPOSS was measured and reported to be at around 3 °C. NIPUs at hand exhibit high water absorption (around 200 wt%) typical for hydrogels. Swelling studies show that 8OHPOSS enhances PHUs hydrogels absorption capacity in phosphate-buffered saline (PBS). Higher absorption capacity in PBS solution in comparison to distilled water is an uncommon phenomenon in hydrogels.

Enhanced piezoelectric properties and thermal stability of LiNbO3-modified PNN–PZT ceramics

Piezoelectric PZT ceramics with high piezoelectric properties and good thermal stability are urgently desired concerning the practical application. New compositions of LiNbO3 modified Pb(Ni1/3Nb2/3)O3PbZrO3PbTiO3 ceramics have been prepared in this study. The effects of the introduction of the LiNbO3 on the system were comprehensively investigated in terms of the phase structure, microstructure, electric properties, and thermal stability behavior of the ceramics. All compositions are located in the morphotropic phase boundary (MPB) region, and the ratio of the rhombohedral (R) phase increases obviously with the increase of LiNbO3 concentration. With increasing the LiNbO3 content, the piezoelectric properties were significantly enhanced. The sample added with 2% (in mole) LiNbO3 shows excellent electric properties, including Tm = 185 °C, εr = 5,643, kp = 0.626, Qm = 51, d33 = 902 pC/N. More importantly, no thermal depolarization behavior was observed in the temperature range of 25–100 °C. For PNN-PZT-x%LN ceramics, which is mainly attributed to the pinning effect resulted by the LiPb'−NbZr/Ti∙ defect dipoles.

Preparation and tribological properties of different kinds of metal foam-polytetrafluoroethylene co-continuous phase composites

Co-continuous phase composites of polytetrafluoroethylene (PTFE) interpenetrated with five kinds of open-cell metal foams, Cu, Ni, Fe, CuNi and FeNi, were prepared via emulsion impregnation, vacuum impregnation and free sintering. The microstructure, mechanical performance, thermal stability and tribological behavior characteristics of these materials were investigated. The results showed that the filling efficiency of PTFE was between 76.1% and 98.7%. The developed composites generally exhibited enhanced strength and thermal stability. In particular, their wear rate under dry friction conditions was reduced by 63–95% compared with pure PTFE resin, which was ascribed to the effective transfer of friction heat and the enhanced load bearing capacity. However, their tribological performance weakened in a simulated seawater environment because of the diffusion of seawater in the materials and corrosion of the metal skeletons.

Modifications of Phase Morphology, Physical Properties, and Burning Anti-Dripping Performance of Compatibilized Poly(butylene succinate)/High-Density Polyethylene Blend by Adding Nanofillers.

A twin-screw extruder was used to fabricate poly(butylene succinate) (PBS)/high-density polyethylene (HDPE) blends (7:3 weight ratio) and blend-based nanocomposites. Carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), and organoclays (15A and 30B) served as the nanofiller, while maleated HDPE (PEgMA) acted as an efficient compatibilizer for the blend. In the composites, individual nanofillers were mostly localized in HDPE domains, but some fillers were also observed at PBS-HDPE interfaces. The sea-island morphology of the compatibilized blend evolved into a pseudo-co-continuous morphology in the composites. Differential scanning calorimetry results confirmed that PEgMA with HDPE evidently accelerated the crystallization of PBS in the blend. The possible nucleation effect of added fillers on PBS crystallization was obscured by the formation of quasi-connected HDPE domains, causing fewer PBS nucleation sites. The presence of nanofillers improved the thermal stability and burning anti-dripping behavior of the parent blend. The anti-dripping efficiency of added fillers followed the sequence CNT > 15A > 30B > GNP. The rigidity of the blend was increased after the formation of nanocomposites. In particular, adding GNP resulted in 19% and 31% increases in the Young's modulus and flexural modulus, respectively. The development of a pseudo-network structure in the composites was confirmed by measurement of rheological properties. The electrical resistivity of the blend was reduced by more than six orders of magnitude at 3 phr CNT loading, demonstrating the achievement of double percolation morphology.

Development of New Dermato-Cosmetic Therapeutic Formulas with Extracts of Vinca minor L. Plants from the Dobrogea Region.

A new trend in the use of indole alkaloids from natural products is the preparation of topical pharmaceutical formulations with applications in the field of regenerative medicine. These formulations can be characterized through the ease of administration, the proven healing action of indole alkaloids, the protection of skin lesions, and the assurance of oxygen permeability. Based on the numerous benefits that indole compounds extracted from the Vinca minor plant show externally, the purpose of this study was to develop new semi-solid biocomposites for topical application obtained from hydroalcoholic macerates of 40%, 70%, and 96% concentrations from the stems and leaves of the Vinca minor L. plant from the Dobrogea area. A total of 12 pharmaceutical formulations (named P1-P12) were prepared for which the physicochemical properties, pH, thermal stability, spreading capacity, and rheological behavior were determined. The optimal formulas with antioxidant and antimicrobial capacity were evaluated and determined (P3, P4, P9, and P10). Antioxidant activity was elicited using the photochemiluminescence method. The microorganisms used for the evaluation of antimicrobial activity were Gram-positive Staphylococcus aureus (ATCC 25923), Gram-negative Escherichia coli (ATCC 25922), and a fungal species, Candida albicans (ATCC 900288). The study of the rheological profile for the obtained composites revealed Newtonian, pseudoplastic, and thixotropic fluid behaviors. Following determinations using the photochemiluminescence method, the best antioxidant activity was obtained in the P3 and P9 preparations. The results of the antimicrobial analysis confirmed that both the leaves and the stems of the Vinca minor plant represent a valuable source of antibacterial substances, and the biocomposites analyzed may represent an alternative in the realization of new pharmaceutical preparations with topical applications based on hydroalcoholic macerates obtained from the Vinca minor plant.

Synthesis and DFT calculations of metal(II) oxime complexes bearing cysteine as coligand and investigation of their biological evolutions in vitro and in silico

New complexes with the formula of [ML(Cys)(H2O)2] were obtained as a result of the reaction between the oxime ligand [HL: 4-(4-bromophenylaminoisonitrosoacetyl)biphenyl], cysteine (Cys), and the metal(II) salts (Mn, Ni, Co, Zn, Cu). The newly synthesized compounds were characterized using conventional techniques such as molar conductance, magnetic measurements, elemental analysis, infrared spectroscopy, and thermal analysis (TGA/DTA). Based on the conductivity measurements in DMF, it was determined that the complexes were non-electrolytes. The TGA/DTA analysis was performed to examine the thermal stability and degradation behavior of all samples, and results demonstrated that metal oxides or sulfides formed as a result of the decompositions. In conjunction with other data obtained, the elemental analysis confirmed the octahedral coordination of the complexes with deprotonated oxime (O, O-donor) and amino acid (N, S-donor) ligands and two coordinated waters. The compounds’ optimized geometries, molecular electrostatic potential diagrams, and frontier molecular orbitals were computed at the DFT/B3LYP level using the 6-311 G(d,p) and LANL2DZ basis sets. The antibacterial and DNA cleavage activities of all synthesized compounds were also screened, and molecular docking simulations were performed. According to the results of molecular docking studies conducted with three different proteins, the best interaction was found to be between HL-1HNJ with a binding energy of −9.5 kcal/mol. The stability of the HL-1HNJ complex was also verified by a molecular dynamics simulation performed for 50 ns. Communicated by Ramaswamy H. Sarma

A thermally stable lithium yttrium phosphate phosphor for solid-state lighting

In this work, trivalent dysprosium was incorporated with lithium yttrium phosphate LiY5P2O13 (LYP), obtaining a yellow-emitting material. The crystallographic sites of introduced Dy3+ activators are determined through the comprehensive analysis of the XRD investigation, DFT computation, and experimental luminescence spectra. Under 353 nm excitation, the LYP:Dy3+ phosphor shows bright yellow emission owing to dominant 4F9/2 → 6H13/2 transition (577 nm) of Dy3+. The luminescence quenching occurs when the Dy3+ content exceeds 0.07 mol, originating from the dipole–dipole interaction. Furthermore, the excellent thermal stability behavior (84 % at 423 K) and good resistance to color shifting (0.00634 at 473 K) for title phosphor are manifested by temperature-dependent investigation. Eventually, the w-LED fabricated with LYP:0.07Dy3+ and commercial materials exhibits stable white-emitting output (0.3595, 0.3179) with high Ra (85) and low CCT (4203 K). All the study demonstrates that the LYP:Dy3+ material is a perspective candidate in solid-state illustration field.

Enhanced dielectric and hydrophobic behaviour of aurin based polybenzoxazine dye composites

Herein, three novel bi-functional benzoxazines were synthesized using aurin as the precursor phenol with three different aromatic amines (i.e.) aniline, fluoroaniline, and trifluoromethylaniline with paraformaldehyde through Mannich condensation. The structural confirmation was done using FTIR and proton NMR. The effects of substituents present in the amines on the curing behaviour and thermal stability were studied using DSC and TGA. The aurin based trifluoromethyl substituted benzoxazine shows better thermal stability than that of the other two benzoxazines and it was selected for the preparation of composites with varying weight percentages of graphitic carbon nitride derived from dicyandiamide (Dicy-GCN) to utilize them for high k applications. The dielectric behaviour and thermal properties of both neat polymer matrix and composites were studied and compared. The 15 wt% Dicy-GCN reinforced composite shows the highest dielectric constant value of 10.25, with a low dielectric loss value of 0.046 at 1 MHz frequency. The polybenzoxazine composites developed show better thermal stability and superhydrophobic behaviour than those of neat polybenzoxazine matrix. These properties ascertain that the aurin based bifunctional polybenzoxazines and its composites can be considered for high-performance high k applications.

Exploring the Relationship between the Structural Characteristics and Mechanical Behavior of Multicomponent Fe-Containing Phases: Experimental Studies and First-Principles Calculations.

A comprehensive understanding of the structural characteristics and mechanical behavior of Fe-containing phases is important for high-Fe-level Al-Si alloys. In this paper, the crystal characteristics, thermal stability, thermophysical properties and mechanical behavior of multicomponent α-AlFeMnSi and α-AlFeMnCrSi phases are investigated by experimental studies and first-principles calculations. The results indicate that it is easier for Fe and Cr to substitute the Mn-12j site in α-AlMnSi in thermodynamics; Cr is preferred to Fe for substituting Mn-12j/k sites due to its lower formation enthalpy after single substitutions at Mn atom sites. The α-AlFeMnCrSi phase shows higher thermal stability, modulus and intrinsic hardness and a lower volumetric thermal expansion coefficient at different temperatures due to the strong chemical bonding of Si-Fe and Si-Cr. Moreover, the α-AlFeMnCrSi phase has a higher ideal strength (10.65 GPa) and lower stacking fault energy (1.10 × 103 mJ/m2). The stacking fault energy evolution of the different Fe-containing phases is mainly attributed to the differential charge-density redistribution. The strong chemical bonds of Si-Fe, Si-Mn and Si-Cr are important factors affecting the thermophysical and mechanical behaviors of the α-AlFeMnCrSi phase.

Rheological and Electrochemical Properties of Biodegradable Chia Mucilage Gel Electrolyte Applied to Supercapacitor

The flexible energy storage device of high demand in wearable and portable electronics. Flexible supercapacitors have benefits over flexible batteries, and their development relies on the use of flexible components. Gel polymer electrolytes have the merits of liquid and solid electrolytes and are used in flexible devices. In this study, a gel derived from chia seed was used as a flexible electrolyte material, and its rheological, thermal, and electrochemical properties were investigated. High thermal stability and shear thinning behavior were observed via the electrolyte state of the chia mucilage gel. Compared to the conventional salt electrolyte, the chia mucilage gel electrolyte-based supercapacitor exhibited a more rectangular cyclic voltammetry (CV) curve, longer discharging time in galvanostatic charge–discharge (GCD) analysis, and low charge transfer resistance in electrochemical impedance spectroscopy (EIS). The maximum specific capacitance of 7.77 F g−1 and power density of 287.7 W kg−1 were measured, and stable capacitance retention of 94% was achieved after 10,000 cycles of charge/discharge with harsh input conditions. The biodegradability was also confirmed by the degraded mucilage film in soil after 30 days. The plant-driven chia mucilage gel electrolyte can facilitate the realization of flexible supercapacitors for the energy storage devices of the future.

Study of the complex of properties of carbon-filled polyphenylene sulfides

The thermal and technological characteristics of carbon-filled compositions based on polyphenylene sulfide are investigated. It has been found that the identified low-molecular impurities are of raw material origin and do not significantly affect the thermal stability and rheological behavior of the studied carbon-filled compositions during processing by extrusion and injection molding. The thermal characteristics of carbon-filled compositions are significantly influenced by the chemical nature of the introduced technological and modifying additives.

Mg-Doped PLA Composite as a Potential Material for Tissue Engineering-Synthesis, Characterization, and Additive Manufacturing.

Magnesium (Mg)/Polylactic acid (PLA) composites are promising materials for bone regeneration and tissue engineering applications. PLA is a biodegradable and biocompatible polymer that can be easily processed into various shapes and structures, such as scaffolds, films, and fibers, but has low biodegradability. Mg is a biocompatible metal that has been proven to have good biodegradability and osteoconductivity, which makes it suitable for bone tissue engineering. In this study, we prepared and characterized a Mg/PLA composite as a potential material for direct ink writing (DIW) in 3D printing. The results showed that the addition of Mg has a significant impact on PLA's thermal and structural properties and has also significantly increased the degradation of PLA. XRD was used to determine the degree of crystallinity in the PLA/Mg composite, which provides insight into its thermal stability and degradation behavior. The crystallization temperature of PLA increased from 168 to 172 °C for a 15 wt% Mg incorporation, and the melting temperature reduced from 333 °C to 285 °C. The surface morphology and composition of these films were analyzed with SEM. The films with 5 wt% of Mg particles displayed the best-ordered honeycomb structure in their film form. Such structures are considered to affect the mechanical, biological and heat/mass transfer properties of the Mg/PLA composites and products. Finally, the composite ink was used as a feed for direct ink writing in 3D printing, and the preliminary 3D printing experiments were successful in resulting in dimensionally and structurally integral scaffold samples. The shape fidelity was not very good, and some research is needed to improve the rheological properties of the ink for DIW 3D printing.

Synthesis and Characterization of Molybdenum- and Sulfur-Doped FeSe.

During the past decade, two-dimensional (2D) layered materials opened novel opportunities for the exploration of exciting new physics and devices owing to their physical and electronic properties. Among 2D materials, iron selenide has attracted much attention from several physicists as they provide a fruitful stage for developing new superconductors. Chemical doping offers a powerful approach to manipulate and optimize the electronic structure and physical properties of materials. Here, to reveal how doping affects the physical properties in FeSe, we report on complementary measurements of molybdenum- and sulfur-doped FeSe with theoretical calculations. Mo0.1Fe0.9Se0.9S0.1 was synthesized by a one-step solid-state reaction method. Crystal structure and morphology were studied using powder X-ray diffraction and scanning electron microscopy. Thermal stability and decomposition behavior in doped samples were studied by thermogravimetric analysis, and to understand the microscopic influence of doping, we performed Raman spectroscopy. First-principles calculations of the electronic structure illustrate distinct changes of electronic structures of the substituted FeSe systems, which can be responsible for their superconducting properties.

Role of Transition Metals in Metal-Organic Frameworks as Nanoporous Ion Emitters for Thermal Ionization Mass Spectrometry.

Thermal ionization mass spectrometry is a powerful analytical technique that allows for precise determination of isotopic ratios. Analysis of low abundance samples, however, can be limited by the ionization efficiency. Following an investigation into a new type of metal-organic hybrid material, nanoporous ion emitters (nano-PIEs), devised to promote the emission of analyte ions and reduce traditional sample loading challenges, this work evaluates the impact that changing the metal in the material has on the ionization of uranium (U). Being derived from metal-organic frameworks (MOFs), nano-PIEs inherit the tunability of their parent MOFs. The MOF-74 series has been well studied for probing the impact various framework metals (i.e., Mg, Mn, Co, Ni, Cu, Zn, and Cd) have on material properties, and thus, a series of nano-PIEs with different metals were derived from this isoreticular MOF series. Trends in ionization efficiency were studied as a function of ionization potential, volatility, and work function of the framework metals to gain a better understanding of the mechanism of analyte ionization. This study finds a correlation between the analyte ionization efficiency and nano-PIE framework metal volatility that is attributed to its tunable thermal stability and degradation behavior.

Synthesis of novel nitrogen‐phosphorus flame retardants and their flameproof to flammable polymers

AbstractTo prepare the efficiently flame retardants (FR) for the highly flammable polymers, the novel nitrogen‐phosphorus based FRs (P‐N FR) (PN‐3, PN‐4, PN‐5, and PN‐6) were prepared via phosphorus halides and amine derivatives with 40‐90 % in yields. The appearances of P‐N FRs are lightly white solid. All P‐N FRs are water‐insoluble and show a melting point above 40 oC. The success of the synthesis was confirmed by NMR analysis. Both 1H and 31P NMR data show clearly the same as the predicted chemical shift signals. The thermal stability behavior of these FRs was studied via TGA analysis. Thermal decomposition occurs in the range of 220‐260oC under N2 gas. The 80% of a mass loss with one step decomposition and 5‐20% of the char residues at 700oC were obtained. The UL‐94 test with self‐extinguishing behavior on ABS and EVA was realized at 20‐25wt% loadings of P‐N FRs. It was observed that the addition of 18‐20 wt% of PN‐5 acquires UL‐94 V‐0 rating for the highly flammable resins (ABS and EVA) whereas to achieve the UL‐94 V‐0 rating, 20‐30 wt% of loadings of PN‐4 and PN‐6 are needed. It was concluded that the structure moieties of P‐N FR affect its FR behaviors.

Large-area deposition of protective (Ti,Al)N coatings onto polycarbonate

Polycarbonate (PC) and protective (Ti,Al)N coatings exhibit extremely different material properties, specifically crystal structure, thermal stability, and elastic and plastic behavior, as well as thermal expansion coefficients. These differences present formidable challenges for the deposition process development as low-temperature synthesis routes have to be explored to avoid a thermal overload of the polymer substrate. Here, a large-area sputtering process is developed to address the challenges by systematically adjusting target peak power density and duty cycle. Adhering (Ti,Al)N coatings with a critical residual tensile stress of 2.2 ± 0.2 GPa are obtained in the pulsed direct current magnetron sputtering range, whereas depositions at higher target peak power densities, realized by high power pulsed magnetron sputtering, lead to stress-induced adhesive and/or cohesive failure. The stress-optimized (Ti,Al)N coatings deposited onto PC with a target peak power density of 0.036 kW cm−2 and a duty cycle of 5.3% were investigated by the cross-cut test, confirming adhesion. By investigating the bond formation at the PC|(Ti,Al)N interface, mostly interfacial CNx bonds and a small fraction of (C−O)−(Ti,Al) bonds are identified by x-ray photoelectron spectroscopy, indicating reactions at the hydrocarbon and the carbonate groups during deposition. Nanoindentation reveals an elastic modulus of 296 ± 18 GPa for the (Ti,Al)N coating, while a Ti–Al–O layer is formed during electrochemical impedance spectroscopy in a borate buffer solution, indicating protective passivation. This work demonstrates that the challenge posed by the extremely different material properties at the interface of soft polymer substrates and hard coatings can be addressed by the systematical variation in the pulsing parameters to reduce the residual film stress.

A versatile, highly effective intumescent flame-retardant synergist for polypropylene and polyamide 6 composites

A novel phosphorus-based macromolecular flame-retardant synergist named DPS was designed and synthesized via three steps from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), dihydroxybenzophenone (DHBP) and pentaerythritol (PER). The prepared synergist was used in combination with a base flame-retardant (melamine-coated ammonium polyphosphate (APP-M), or aluminum diethylphosphinate (ADP)) to create novel binary intumescent flame retardant (IFR) systems for polypropylene (PP) and polyamide 6 (PA6) matrices. The structure of DPS was characterized by fourier transform infrared (FTIR), phosphorus nuclear magnetic resonance spectroscopy (31P NMR) and gel permeation chromatography (GPC) analysis. The thermal stability and combustion behaviors of the flame-retardant polymer composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 vertical burning tests. It was found that with a low fraction of DPS (20–25 wt%), the developed binary IFR systems significantly enhanced the flame-retardant performance of both PP and PA6. The results indicate that owing to the rich phosphorus content and abundant aromatic structures, DPS has synergistic actions with the base flame retardants to scavenge free radicals and promote char formation in the gaseous and condensed phases, respectively. Additionally, the mechanical properties of the PP composites were also evaluated, revealing the mechanical reinforcement effect of the binary IFR, i.e., simultaneous improvement of tensile modulus, ultimate tensile strength and impact toughness. This further demonstrates the effectiveness of the developed IFR formulations in terms of well-balanced flame-retardant performance and mechanical properties.