High Temperature Shrinkage Research Articles

Nanofiber membrane coated with lithiophilic polydopamine for lithium metal batteries

Along with the cathode, anode, and liquid electrolyte in lithium-based secondary batteries, the separator is a crucial element for guaranteeing battery safety. However, conventional polyolefin separators suffer from inherent drawbacks such as inadequate compatibility with electrolytes and limited thermal stability. These limitations can lead to issues like high-temperature shrinkage, melting, and even combustion. Moreover, the vulnerability of separators toward lithium dendrite penetration exacerbates safety concerns associated with lithium-ion batteries. Hence, the design of high safety separators is currently a focus and challenge. In this study, we develop a multifunctional polymer-coupled nanofiber membrane by an electrospinning method that addresses the above issue as a separator of lithium metal battery. The nanofiber coating contains carbonyl oxygen, pyrrole nitrogen, and cross-linked networks with tertiary amine groups. These components effectively neutralize acidic compounds generated during the liquid electrolyte side reaction. X-ray micro-computed tomography analysis verifies the exceptional structural stability of the new separator, maintaining its 3D skeleton even after 2000 h of cycling. The nanofiber separator in a full Li||NCM811 cell achieves a high specific capacity of 136.6 mA h g−1 at 0.9 A g−1 and displays outstanding long-cycle stability over 500 cycles with a capacity retention of 88.5%.

Fabrication of PVDF/SiO2 Nanofiber Membrane as A Separator of Li-ion Battery by Double Jet Sprayers Electrospinning Method

The temperature of the lithium-ion battery while running the electric vehicle becomes a severe safety issue. One way to keep the battery work at high temperatures is by a modified battery separator. The separator was used as a component to secure the battery by preventing short circuit current between the electrodes of opposite polarity. This current research reported the high-temperature shrinkage and excellent mechanical strength membrane separator based on PVDF/SiO2 nanofiber produced by double jet sprayers electrospinning method on rotating cylinder collectors. The independent variable in this research was the variation of a SiO2 polymer at 0 ppm, 500 ppm, 1000 ppm, and 3000 ppm. The results of PVDF/SiO2 nanofiber formed have beaded fiber structure with the average size of fiber’s diameter of ~192 nm. The highest amount of SiO2 addition (SiO2 3000 ppm) on PVDF nanofiber’s membrane causes an increase of porosity up to 69%. The addition of SiO2 also strengthens its mechanical and thermal shrinkage properties to 150°C. In the testing of the charge-discharge battery using separator PVDF/SiO2 nanofiber, the specific capacity value is 181 mAh/g.

High-temperature shrinkage suppression in refractory ceramic fiber board using novel surface coating agent

Refractory ceramic fiber (RCF) boards are widely used because their insulating properties allow them to reduce energy consumption during high-temperature industrial processes. However, since conventional RCF boards undergo a linear shrinkage of more than 3% above 1300 °C, furnace lining parts, such as the ceiling, wall, and bottom made of RCF board easily become fragile. In order to suppress the shrinkage of the RCF board above 1300 °C, the RCF board surface was coated with a silica sol containing several types of alumina particles. When a RCF board coated with a silica sol slurry containing 50 mass% alumina platelets was heated at 1400 °C for 8 h, the linear shrinkage of the RCF board decreased from 4.3% to 1.5%. This, in turn, improved the heat resistance of the RCF board up to 1400 °C.

Effects of Powder Additives on Thermal Shrinkage of Nanoporous Silica Insulation

In this study, four powder additives were introduced as high-temperature shrinkage inhibitors to make high performance nanoporous silica insulation. The introduction of fumed alumina could greatly improve the thermal stability of the composites at higher temperatures, and the maximum service temperature could be increased to about 1000°C. When 5% fumed alumina was added, the volume shrinkage decreased from 18.49% to 3.47%. Moreover, better results could be achieved with the increase in mass ratio. In addition, fumed titania also improved the thermal stability of the composites to some extent, while boron carbide and boron nitride led to poor performance

Strategies to control the high temperature shrinkage of fly ash based geopolymers

Abstract Strategies to control thermally induced shrinkage in fly ash based geopolymers are investigated. The use of low ( 100 MPa). Wollastonite addition also improved the flexural strength of the samples which was attributed to its acicular shape imparting fibre-like qualities. Microstructural investigations showed that unfired samples predominantly consisted of spherical particles coated with reaction product. Firing to 1000 °C converted the morphology to a more compact phase with increased pore size.

Effect of Al<sub>2</sub>O<sub>3</sub> Powder on Properties of Fumed Silica Thermal Insulating Composites Using Mechanofusion Technique

This study describes the manufacturing process of thermal insulating composites which made from fumed silica powder, reinforcing fibre and other additives using advanced mechanofusion technique. The research focuses on the effect and mechanism of Al2O3powder on thermal insulating composites, which using as high temperature shrinkage inhibitors to restrain sintering in fumed silica compacts at high temperatures. The results show that nanosize Al2O3powder can effectively improve the volume stability of the compacts above 800°C, but which has little influence on thermal conductivity at higher temperatures. The compacts prepared in this study exhibit fracture strength of 0.26 MPa at room temperature, thermal conductivity of 0.0336 W/(m•K) at 1000°C and tiny volume shrinkage about 1.1% at 1000°C for 12h.

Low-temperature sintering method for NiCuZn ferrite and effect of Mn addition on electromagnetic properties

Low temperature sintering NiCuZn ferrite was employed at most cases due to its co-firability with Ag (below 960 °C). The NiCuZn ferrite sintered body with high-strength and high-frequency magnetic properties was fabricated. Firstly, NiCuZn ferrite powder was synthesized under CO 2 atmosphere at 500 °C from the mixed doxalate synthesized by liquid phase precipitation method. Then a small amount of boric acid (H 3BO 3) was added to the powder, and the NiCuZn ferrite powder compact was prepared with Newton press and CIP methods. Finally, NiCuZn ferrite sintered body was fabricated by sintering at 900 °C under CO 2 atmosphere. The minimum sintering temperature (800 °C) was determined by the study of high temperature shrinkage. By this method, NiCuZn ferrite sintered body with 0.5% (mass fraction) boric acid was obtained, which has the bending strength of 340 MPa. The effect of various Mn addition on electromagnetic properties were studied.

ＮｉＣｕＺｎフェライト焼結体の低温作製とその材料特性評価

NiCuZn ferrite has been widely applied to multilayer chip inductors in recent years. While fabricating the multilayer structure of ferrite and metal alternatively, it is requested to simultaneously sinter in low temperature for the internal conductor Ag (Melting point 960°C) and ferrite materials. The purpose of this study is to fabricate the NiCuZn ferrite sintered body with high-strength and high-frequency magnetic property. The procedures are as follows: firstly, the NiCuZn ferrite powder was synthesized under a CO2 atmosphere at 500°C from the mixed doxalate which was synthesized by liquid phase deposition method from mixed metal chloride and ammonium oxalate; subsequently, a small amount of boric acid [H3BO3] was added to the powder, and then the NiCuZn ferrite powder compact was formed with Newton press and CIP methods; finally, the NiCuZn ferrite sintered body was fabricated by sintering at 900°C under a CO2 atmosphere. Through the experiments of high temperature shrinkage, evaluation of mechanical strength and magnetic property, NiCuZn ferrite fabricated by this study can present good characters on high frequency and high mechanical strength when the sintering temperature and boric acid additive are 900°C and 0.5 mass%, respectively.

Les produits minéraux utilisés en protection incendie face aux nouvelles réglementations

ABSTRACT Two fireproofing materials are studied. These materials cannot be used above 1000—1100°C due to their loss of thermal and mechanical properties. Moreover, at such temperatures, their permeability towards hot (and/or) toxic gases increases dramatically. Results of severe thermal solicitations (based on new European standards) are presented herein. They confirm that the melting of at least one of the compounds completely modifies the thermal transfer conditions. Above a critical temperature, the melting front will diffuse through the material and will affect its permeability as well as its mechanical properties and thickness. Thus, development of new fireproofing materials (presenting a real high temperature resistance) imposes to master high temperature shrinkage. An optimized product is presented herein.

Mechanical Characterization and Influence of the High Temperature Shrinkage of β-PVDF Films on its Electromechanical Properties

Tensile dynamic mechanical analysis at 1 Hz was used to characterize the solid rheological properties of β-PVDF films. Both the elastic and loss moduli and the specific damping capacity were monitored against temperature, allowing the study of the effect of anisotropy upon the viscoelastic properties of the films. The temperature range covered the β- and α-relaxations. These results are compared to dielectric relaxation results in order to elucidate the electrical and mechanical contributions to the observed relaxations. Further, an important shrinking effect upon heating above 364 K has been observed, that influences the material properties. This geometrical effect has been monitored by thermal mechanical analysis. The thermal coefficients of linear expansion have been calculated, giving two different regimes for this parameter. The variations at a molecular level have been monitored by FTIR.

Fiber structure and properties of poly(ethylene-2,6-naphthalate) obtained by high-speed melt spinning

High molecular weight poly(ethylene-2,6-naphthalate)(PEN) has been melt spun at various take-up velocities from 0.9 to 10 km/min to prepare fiber samples. The effect of take-up velocity on the structure and properties of as-spun fibers has been characterized through measurements of birefringence, density, wide-angle X-ray diffraction, infrared analysis, DSC melting behavior, tensile properties and high-temperature shrinkage. With increasing take-up speed, a steady trend toward higher as-spun fiber orientation and crystallinity was observed, accompanied by improved physical properties. The WAXD patterns of the as-spun fibers prepared at a velocity range higher than 1.5 km/min indicate that these samples all possess a developed molecular orientation and crystalline structure. At a relatively low take-up velocity that range from 1.5 to 4 km/min, a high level of molecular orientation in both crystalline and amorphous region has been found. This may be attributed to the high spinning stress generated by the high-molecular weight polymer used. In the high take-up speed region of 5–10 km/min, the molecular orientation becomes saturated. The highest tenacity and initial modulus of the as-spun PEN fibers obtained in this region reached ca 8 and 200 g/d, respectively.

High-temperature shrinkage of single-walled carbon nanotube bundles up to 1600 K

An experimental study of x-ray diffraction of single-walled carbon nanotube (SWNT) bundles in the temperature range from 290 to 1600 K is reported. The lattice constant (L0) of a close-packed trigonal arrangement of SWNTs in the bundles shrank over the entire temperature range. The hysteretic temperature dependence of L0 was observed and discussed in terms of desorption of molecules from the bundle surface and of a magnetic phase transition of ferromagnetic metal catalyst particles. The coefficient of volume thermal expansion for the bundles is suggested to be negative over the measured temperature range by assuming that the tube-axis expansion is similar to the in-plane expansion for graphite.

Effect of initial take-up speed on properties and structure of as-spun and drawn/heat-set poly(ethylene terephthalate) filaments

The effect of initial take-up speed on the properties and structure of both as-spun and drawn/heat-set poly(ethylene terephthalate) filaments was characterized through measurements of birefringence, percent crystallinity, tensile properties, high temperature shrinkage, loss tangent temperature dependence, DSC melting behavior, and wide-angle (WAXS) and small-angle X-ray scattering (SAXS). While a steady trend toward improved as-spun filament orientation and tensile properties occurred with increasing initial take-up speed, the reduced drawability of these more structured precursor filaments resulted in corresponding drawn/heat-set filaments that were of relatively lower overall orientation and tensile strength. The observed trends in tenacity, initial modulus, and high temperature shrinkage of the drawn/heat-set filaments appeared to be well correlated with the extent and distribution of amorphous phase rigidity as perceived through inferences made from the loss tangent temperature dependence. The WAXS patterns of the drawn/heat-set samples indicated that these filaments all possess a well-developed and highly oriented crystalline structure. Application of a simple two phase model allowed the determination of an amorphous orientation factor, which for the drawn/heat-set filaments was generally found to decrease as the draw ratio imposed in order to achieve comparable levels of elongation to break decreased. The SAXS patterns of the drawn/heat-set filaments indicated that comparable long period spacings exist in all cases and that a transition from a four-point pattern to a two-point bar-shaped pattern occurred when the precursor filament possessed some significant amount of as-spun crystallinity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2115–2131, 1998

The cold drawing of polyethylene terephthalate

The cold-drawing behaviour of polyethylene terephthalate has been studied over a wide range of test conditions and polymer constitution. In addition to measurements at different temperatures and strain rates, the influence of pre-orientation, crystallinity and chemical cross-linking was investigated. Although crystallinity and cross-linking altered to some extent the details of the drawing process, the overall pattern of behaviour remained substantially unchanged despite rather severe changes in the microstructure of the polymer. Pre-orientation affected the yield stress and produced marked changes in the natural draw ratio. Previous studies by Pinnock and Ward have shown that pre-orientation is introduced during extrusion in a manner similar to stretching a rubber network and that the degree of stretch can be determined by the subsequent high-temperature shrinkage of the pre-oriented fibre. Measurements of the natural draw ratio and shrinkage of a series of pre-oriented fibres, described here, showed that the natural draw ratio may be regarded as equivalent to stretching a network to a limiting total extension. This limiting extension appeared to be a constant independent of the division of extension between the extrusion and drawing processes, and could provide a geometrical explanation for the large influence of pre-orientation on the natural draw ratio. An alternative view is that the degree of strain hardening achieved for a given elongation during the cold-drawing process will be affected by pre-orientation, and that the natural draw ratio could be very sensitive in this respect. Even with this explanation, the change in strain hardening may be associated with the limiting extension of a network. Measurement of the birefringences and moduli of the cold-drawn fibres showed that the development of optical and mechanical anisotropy could be fitted to a good approxi mation by an aggregate theory. This theory assumes that the drawn fibre consists of an aggregate of optically and mechanically anisotropic units which are aligned by the drawing process.