Thermal Stability Temperature Research Articles

Thermal degradation behavior of flame-resistant fabrics exposed to fires: effect of air gap type and thickness

The thermal degradation of flame-resistant fabrics reduces the protective ability of clothing and affects firefighters’ safety. Making clear the influence factors of fabric thermal degradation is important for predicting and prolonging the service life of fire-protection clothing. Experiments were conducted for open and sealed air gaps with different thicknesses under flame exposure. The degradation the of outer shell fabric was evaluated by observing the variation in fabric morphology, mass loss and tensile strength of specimens after heat exposure. The influence mechanism of the type and thickness of the air gap on thermal degradation was analyzed by the surface temperature curve and thermal stability of the fabric, as well as the microstructure of the fiber. The results indicated that the type and thickness of the air gap have a significant effect on thermal degradation, and a more serious negative effect was observed under the condition of an open air gap. After being exposed to heat fluxes of 30 and 50 kW/m2 for 40 s, the mass loss rates were 1.8% and 3.3% higher than those of the sealed air gap, and the tensile strength retention rates were 9.1% and 10.1% lower on average, respectively. Air gap type and thickness affected the heat storage and heat transfer efficiency in the fabric system by changing the heat transfer mode. The decomposition and fracture of the fabric were affected, which made the flame-resistant fabrics show different degrees of thermal degradation.

Accurate Solution and Analysis of the Transient Temperature and Stability of Combustible Micron-Sized Iron Particle in Gaseous Oxidizing Environment

Combustible solid state particles are candidates for alternative fuels with zero carbon emissions. This paper presents the transient and thermal stability analysis of combustible micron-sized iron particle in an oxidizing environment. The governing first-order nonlinear differential equation was solved and analyzed using the continuous piecewise linearization method, which enabled very accurate solutions for the strong nonlinear region of the solution domain i.e. up to the steady-state response. Hence, stability analysis of the heat transfer process was conducted to determine the onset of steady-state response and the temperature attained under the thermally-stable condition. The effect of particle size, surrounding temperature, heat realized, heat radiated, and temperature-dependent density on both the transient temperature profile and thermal stability were investigated and discussed. The theoretical solution for the maximum combustion temperature, which was first derived in this study, showed a good agreement with published experiments. The investigations on the thermal stability revealed interesting new results that provide further insight into the heat transfer dynamics of combustible micro-particles. The study shows that the CPLM algorithm is capable of providing simple, fast converging and very accurate results for the entire solution domain of the transient temperature response, especially in the highly nonlinear asymptotic region.

Controlling the high temperature deformation behavior and thermal stability of ultra-fine-grained W by re alloying

Due to their outstanding properties, ultra-fine-grained tungsten and its alloys are promising candidates to be used in harsh environments, hence it is crucial to understand their high temperature behavior and underlying deformation mechanisms. Therefore, advanced nanoindentation techniques were applied to ultra-fine-grained tungsten–rhenium alloys up to 1073 K. A continuous hardness decrease up to 0.2 T_{text{m}} is rationalized by a still dominating effect of the Peierls stress. However, the absence of well-established effects of Rhenium alloying, resulting in a reduced temperature dependence of strength for coarse-grained microstructures, was interpreted as an indication for a diminishing role of kink-pair formation in ultra-fine-grained metals with sufficiently fine grain size. Despite slight grain growth in W, dislocation–grain boundary interaction was identified as the dominating deformation mechanism above 0.2 T_{text{m}}. Interaction and accommodation of lattice dislocations with grain boundaries was affected by a reduced boundary diffusivity through alloying with Re.Graphic abstract

Synthesis and characterization of novel energetic plasticizers based on poly glycidyl nitrate

ABSTRACT Energetic plasticizers are used in propellants to increase the energy content and improve the glass transition temperature and mechanical properties. The compatibility between polymer and plasticizer is an important criterion for obtaining the best thermomechanical properties. In this research, novel energetic plasticizers were synthesized via end-group modification of poly glycidyl nitrate. Firstly, low molecular weight poly glycidyl nitrate (PGN) (Mn = 523 g.mol−1) and dinitropropyl poly glycidyl nitrate (DNPPGN) (Mn = 1700 g.mol−1) were synthesized by ring-opening polymerization of glycidyl nitrate with 1,4-butanediol and 2,2-dinitro-1,3-propanediol as initiators, respectively, and in the presence of boron trifluoride etherate (BF3.OEt2) as the catalyst. Tetra nitro poly glycidyl nitrate (TNPGN) was synthesized through end-group modification of DNPPGN and also azide-terminated GAP (GAPA) synthesized via modification of PGN as novel energetic plasticizers. The chemical structure of plasticizers was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (NMR). Thermal behaviors were investigated by differential scanning calorimeter (DSC). The thermal analysis of plasticizers indicated Tg of TNPGN is lower than PGN and other synthesized plasticizers. Also, decomposition temperature (thermal stability) of TNPGN (251°C) is higher than PGN (209°C). Therefore, TNPGN has potential as a novel energetic plasticizer for propellant.

Experimental Research on Turning of Superalloy GH4169 under High Pressure Cooling Condition

Superalloy GH4169 possesses excellent high temperature strength, thermal stability, and thermal fatigue, and is widely used in aerospace and other fields. However, it is a typical difficult-to-cut material owing to its poor thermal conductivity, high plastic toughness, severe workpiece hardening, and difficult chip breaking. In this study, high pressure cooling was used for GH4169 cutting test. The effects of high pressure cooling on the cutting force, chip morphology, and tool wear were analyzed, which can provide technical support to achieve high efficiency turning of GH4169.

Study on Preparation of Quartz Ceramics Toughened with Mineralizer

Quartz ceramics have excellent properties such as low thermal conductivity, low expansion coefficient, high temperature resistance and thermal stability, but low toughness. The quenching method of quartz ceramic is as follows: (1) A hard phase is formed in the quartz ceramic. (2) Improve the surface coating. (3) Short fiber reinforcement. (4) The graphite particles are dispersed and quenched. (5) Have silicone resin reinforcer. (6) Improve mineralizers. In order to improve the toughness of quartz ceramics, a hardening mineralizer is selected in this experiment. In this experiment, quartz is used as the main raw material, and a mineralizer is selected as the aluminate, feldspar and Al2O3 powder cement. Quartz ceramics are prepared by molding. Adding 10% Al2O3 powder, adding Al2O3 powder can improve the flexural strength of quartz ceramics, and the flexural strength of quartz ceramics can reach 10 MPa. SEM analysis shows that the addition of Al2O3 can inhibit the grain boundary motion speed better and prevent grain growth, enhancement and enhancement. XRD analysis shows that the addition of aluminate cement, feldspar and calcium oxide may be beneficial to the conversion of quartz to cristobalite and the addition of Al2O3 to the conversion of quartz to phosphorus quartz.

Measurement of Magnetic Field Properties of a 3.0 T/m Air-Core HTS Quadrupole Magnet and Optimal Shape Design to Increase the Critical Current Reduced by the Incident Magnetic Field

Air-core high-temperature superconducting quadrupole magnets (AHQMs) differ from conventional iron-core quadrupole magnets, in that their iron cores are removed, and instead high-temperature superconductors (HTSs) are applied. The high operating temperature and high thermal stability of HTS magnets can improve their thermodynamic cooling efficiency. Thus, HTS magnets are more suitable than low temperature superconducting magnets for withstanding radiation and high heat loads in the hot cells of accelerators. AHQMs are advantageous because they are compact, light, and free from the hysteresis of ferromagnetic materials, due to the removal of the iron-core. To verify the feasibility of the use of AHQMs, we designed and fabricated a 3.0 T/m AHQM. The magnetic field properties of the fabricated AHQM were evaluated. Additionally, the characteristics of the air-core model and iron-core model of 9.0 T/m were compared in the scale for practical operation. In comparison with the iron-core model, AHQM significantly reduces the critical current (IC) due to the strong magnetic field inside the coil. In this study, a method for the accurate calculation of IC is introduced, and the calculated results are compared with measured results. Furthermore, the optimal shape design of the AHQM to increase the critical current is introduced.

Liquid crystalline epoxies bearing biphenyl ether and aromatic ester mesogenic units: Synthesis and thermal properties

Two liquid crystalline epoxies containing biphenyl ether and aromatic ester mesogenic units, oxybis(4,1-phenylene)bis(4-(oxiran-2-ylmethoxy)benzoate)(LCE1) and oxybis(4,1-phenylene) bis(4-(4-(oxiran-2-yl)butoxy)benzoate)(LCE2), were synthesized and characterized. Subsequently, the epoxy monomers were cured with diaminodiphenylsulfone (DDS). From DSC, XRD and POM results, monomers did not show liquid crystalline phase while the cured samples exhibited nematic phase. The cured samples showed good mechanical properties with strength of 99.1MPa and excellent thermal stabilities with high glass transition temperature up to 168.0 °C, 5% weight loss temperature at 343 °C and high char yield of 24.5% at 800 °C. The relationship between thermal conductivity and network structure was discussed in this work. Due to the introduction of mesogenic units into epoxy networks, the cured resins showed high thermal conductivity as high as 0.292 W/(m*K), more than 1.5times higher than conventional epoxy resins. By introducing alumina (Al2O3) into LCE1/DDS cured system, composites of LCE1/DDS/Al2O3 with the highest thermal conductivity of 1.61 W/(m*K) was obtained with the content of 80 wt% while that of diglycidyl ether of bisphenol A (DGEBA, E51) epoxy resin/DDS/Al2O3 was 1.10 W/(m*K). The as-prepared epoxy resins showed high glass transition temperature and excellent thermal stabilities, indicating the potential of application in microelectronics.

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.

Processing, Tensile, and Thermal Studies of Poly(Vinyl Chloride)/Epoxidized Natural Rubber/Kenaf Core Powder Composites with Benzoyl Chloride Treatment

ABSTRACTThe kenaf core powder (KCP) has been treated with benzoyl chloride (BC) in poly(vinyl chloride)(PVC)/epoxidized natural rubber (ENR)/KCP composites. The presence of BC grafted on KCP was evident by infrared analysis. PVC/ENR/KCP samples were prepared using Haake Polydrive with the temperature of 140°C and KCP loading of 5, 10, 15, and 20 phr. The processing, tensile and thermal properties of the composites were investigated. The enhancement of tensile properties showed that the treatment improved the interfacial adhesion between KCP with PVC/ENR matrix. Higher glass transition temperature and higher thermal stability after treatment with BC support the enhancement of the composites’ tensile properties.

Processing, Structure and Properties of Melt Blown Polyetherimide

Polyetherimide (PEI), an engineering plastic with very high glass transition temperature and excellent chemical and thermal stability has been processed into membranes of varying pore size, performance, and surface characteristics. A special grade of the polyetherimide was processed by melt blowing to produce microfiber nonwovens suitable as filter media. The resulting microfiber webs were characterized to evaluate their structure and properties. The fiber webs were further modified by hot pressing, a post processing technique, which reduces the pore size in order to improve the barrier properties of the resulting membranes. This ongoing research has shown that polyetherimide can be a good candidate for filter media requiring high temperature and chemical resistance with good mechanical properties.

Thermal study of the influence of chemical composition on CRT glass crystallization

The influence of alumina oxide on the crystallization of silica–strontium–barium glass from cathode ray tube (CRT) was studied by means of thermal analysis. Thermal characteristics of glasses such as the transition temperature T g, the crystallization temperature T c and thermal stability parameter were determined by DTA/DSC method. The crystallization ability of the obtained glasses was also determined independently by the gradient furnace technique. The crystalline phase was determined by the X-ray diffractometry. The microstructure of the samples was studied by SEM technique. The linear expansion coefficients of glasses as a function of temperature were measured. Analysis of the local atomic interactions in the structure of glasses was used to explain the course of the crystallization. The effect of Al2O3 content on the CRT glass composition was studied by FTIR and solid-state 19F MAS–NMR spectroscopy.

Thermal properties of poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) modified with divinyl benzene and vinyltrimethoxysilane

ABSTRACTThe effect of butyl acrylate (BA), divinyl benzene (DVB) and vinyltrimethoxysilane (TMVS) on the thermal properties of poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) was investigated. Glass transition temperature (Tg), melting temperature (Tm) and specific heat capacity of the copolymers were investigated using Differential Scanning Calorimetry. Thermal stability of the copolymers which is associated with the degradation temperature (Td) was studied by Thermogravimetric Analysis. Polyacrylates with Tg ranges between -19°Cand 19°C were obtained. With the incorporation of >7 wt% of DVB, the Tg of the copolymer increases from about −17°C to −10°C even though they have not undergone UV irradiation. Gel content results prove that crosslinking has occurred in the copolymers. With increasing amount of TMVS from 0 wt% to 7 wt%, the Tm of the copolymers prepared at acidic pH is about 40-60°C higher than that at the alkaline pH. However, the addition of TMVS gives no significant effect to the Tg and Td of the copolymer films. The thermal stability of the copolymer has improved with increasing amount of BA and DVB, with DVB being more effective. The highest Td of 425°C with 8% of DVB has been obtained. Consequently, a polyacrylate copolymer with a Tg of about −13°C, a Tm of 170 °C and a Td of about 424°C has been successfully synthesized. Hence, the soft polyacrylate with its relatively high Tm and Td could serve as a superb material especially to be applied in the areas that require high melting temperature and good thermal stability.

High performance poly(imino imino ether ether ketone ketone) (PIIEEKK) films with intermolecular hydrogen bondings

Poly(imino imino ether ether ketone ketone) (PIIEEKK) was synthesized via palladium-catalyzed C–N cross coupling reaction of 1,4-bis(4-bromobenzoyl) benzene and 1,4-bis(4-amiophenoxy) benzene. In view of its good solubility, PIIEEKK film with high transmittance was prepared via casting method. Fourier Transform Infrared Spectrum of the PIIEEKK film revealed that in the solid state intermolecular hydrogen bonding (N–H···O=C) is present. Differential Scanning Calorimetry and Thermo Gravimetric Analysis showed that PIIEEKK film possessed high glass transition temperature (T g = 172°C) and good thermal stability with high decomposition temperature (T d,5% = 460°C). Due to intermolecular hydrogen bonding between PIIEEKK chains, the PIIEEKK film exhibited higher tensile strength.

Polyacrylamide/metakaolinite nanocomposites by in-situ intercalative polymerization

ABSTRACTA series of polyacrylamide (PAM) organoclay nanocomposites were synthesized by in-situ intercalative polymerization using acrylic amide, sodium hydrogen sulfite, and ammonium peroxydisulfate in the presence of various contents of metakaolinite (MK) modified with potassium acetate (KAc). Both x-ray diffraction data and atomic force microscopy images of PAM/MK nanocomposites indicate that the MK was homogeneously dispersed on the nanoscale into the polymer matrix. Infrared and Raman spectroscopy indicated the formation of hydrogen-bonding interactions between PAM and MK and the distortion of the Si–O tetrahedron and Al–O polyhedron in the polymerization process. In addition, DSC results revealed that when the nanocomposites with MK modified with KAc were less than 10%, they have higher decomposition temperature and better thermal stability in comparison with the pure PAM.

The Experimental Research and Analysis of a HTS SMES Hybrid Magnet

A conduction-cooled HTS hybrid magnet is developed for a 150-kJ/100-kW SMES system used for power conditioning. As a main component of a dynamic operation system, it is necessary to evaluate the current carrying ability, temperature characteristic, and thermal stability of the magnet. In this paper, the magnet structure is introduced. Then, a series of experiments were conducted to investigate the voltage variations of every coil and the magnet when the HTS magnet is fed with different transport current at 77 and 20 K. The temperature variation and thermal stability of the magnet at 20 K are observed. In addition, the current carrying ability of the HTS magnet is presented, and the performance of 1G and 2G HTS coils are discussed.

Multifunctional Nanobiocomposite of Poly[(butylene succinate)-co-adipate] and Clay.

The processing and characterization of multifunctional nanobiocomposite of biodegradable poly[(butylene succinate)-co-adipate] (PBSA) and organically modified synthetic fluorine mica (OSFM) are reported. The nanobiocomposite of PBSA with OSFM was prepared using melt- blending, and the structure and morphology of the nanocomposite were characterized using X-ray diffraction and transmission electron microscopy. The mechanical and material properties measurements showed the concurrent improvement in temperature dependence storage modulus, tensile properties, gas barrier, and thermal stability of neat PBSA after nanocomposite formation. Such improved inherent properties along with the environmentally-friendly feature are expected to widen the use of PBSA for short-term food-packaging applications.

Poly(imino imino ether ether ketone ketone) as novel soluble heat-resistant polymer

In this paper, we introduce a novel high-performance polymer, poly(imino imino ether ether ketone ketone), which has been synthesized by the palladium-catalyzed C-N cross coupling reaction of 1,4-bis-(4-bromobenzoyl) benzene and 1,3-bis-(4-aminophenoxy) benzene. The structure of the polymer is characterized by means of 1H NMR spectroscopy and elemental analysis, and the results show a good agreement with the proposed structure. Compared with traditional poly(ether ether ketone)s, the solubility of the synthesized polymer in common organic solvents was higher; it also exhibited high glass transition temperature (T g = 176°C) and good thermal stability with high decomposition temperature (T 5 = 400°C).

Changes in TCR of amorphous Ni–P resistive films as a function of thermal stabilization parameters

Purpose – This paper aims to select parameters such as temperature thermal stability and temperature coefficient of resistance (TCR) for Ni–P resistive alloys obtained by electroless metallization. Ni–P alloys are used in the manufacture of precision resistors characterized by TCR in the range of ± 10 ppm/K. The correlation of the technological parameters with the electrical properties of resistors enables the accurate prediction of the TCR resistors. Design/methodology/approach – The Ni–P layers were obtained by a continuous process at about 373 K in a solution with the acidity of pH = 2 and then dried for two hours at 393 K. Subsequently, the Ni–P layer was stabilized for two hours in the temperature range of 453-533 K. Resistance was measured with an accuracy of 1 mΩ. TCR was determined with an accuracy of 1 ppm/K in the temperature range 298-398 K. In the next stage of the investigation, the increase in TCR of the Ni–P alloy was correlated with the increase in stabilization temperature. Scanning electron microscope images of the alloy surface were studied to assess grain sizes and to relate the average grain size with TCR values of resistive alloys. The X-ray diffraction analysis was performed to determine the crystallization temperature of Ni–P alloy. Findings – The conducted investigation showed that the TCR increase in alloy is a linear function of stabilization temperature in the temperature range in which transition from amorphous phase to crystalline phases did not occur. TCR increase in Ni–P alloy arises from the increase of average size of grains resulting in decrease of scattering of electrons on grain boundaries. The analysis of alloy composition in chosen fragments of surface shows inhomogeneity growing with decreasing analyzed surface dimensions which proves that, before the stabilization, the structural arrangement of alloy is inconsiderable. Originality/value – The obtained results are the first attempt to relate the morphology of surface with TCR of alloy and demonstration of linear dependence between an increase in TCR of amorphic Ni–P alloy and stabilization temperature of resistive layer. Such correlations are not described in available literature.

Siloxane Core-Modified Organo Soluble Novel Polyimide/Multi-walled Carbon Nanotube Nanocomposites

Siloxane core-modified polyimides (PI)/multi-walled carbon nanotubes (MWCNTs) nanocomposites were designed and developed. The confinement of segmental motion of the PI chain due to high dispersion uniformity of the MWCNTs caused the increment in the glass transition temperature (T g ) and remarkable elevated thermal stability. All the PIs could afford better solubility with high dielectric constants of 3.5–5.9 and low water absorptions of 0.42–0.68%. These PIs emitted a strong blue fluorescent at 380 nm, assigning the structural confirmation of PI matrix. Heterogeneous morphology of MWCNT/PI nanocomposites was evidenced by SEM and TEM images, resulted from the incorporation of MWCNT.