Rise In Heat Treatment Temperature Research Articles

Effects of heat treatments and cross‐linking on the crystal structure and torsional properties of polyester fibers

AbstractArtificial muscles have attracted great attention as actuators and coiled and twisted monofilament actuators are considered the most promising ones. In the present work, the torsional properties of poly(hexamethylene adipamide) (PA66), poly(ethylene terephthalate) (PET), and high‐strength PET (HTPET) monofilaments were investigated. Furthermore, cross‐linked PET (CPET) monofilaments were melt‐spun by adding 1 wt% of 2‐dimethoxy‐2‐phenylacetophenone (ultraviolet (UV) initiator) and triallyl iso‐cyanurate (cross‐linking agent) in PET chips under UV radiation. The HTPET monofilaments had the highest torsional modulus of 1.1 GPa followed by the PET (0.8 GPa) and PA66 (0.6 GPa) monofilaments. Subsequently, the HTPET monofilaments were subjected to heat treatments under tension. When the heat treatment time was 10 min, the mechanical properties of the HTPET monofilaments also tended to first increase and then decrease with the rise of heat treatment temperature. The molecular arrangement and crystal structure of the HTPET monofilaments were gradually improved with the prolongation of tension heat treatment. The tensile strength and initial modulus of the HTPET monofilaments were 871.4 MPa and 15.8 GPa, respectively. The mechanical properties of the CPET monofilaments first increased and then decreased with the increase of the drawing ratio. When the drawing ratio was 10, the CPET monofilament had a tensile strength of 717.2 MPa, an initial modulus of 16.7 GPa, and a maximum torsional modulus of 1.3 GPa. Therefore, both heat treatment and cross‐linking increased the mechanical strength of the PET monofilaments. CPET and HTPET are possible to be used as artificial muscles.

Co-sorption/co-desorption mechanism of the mixed chlorobenzenes by fresh bulk and aged residual biochar

Since little is known about the sorption/desorption behaviors of the mixed chlorobenzenes (CBs) on fresh and aged biochar, this study evaluated the co-sorption/co-desorption mechanism of the mixed monochlorobenzene (MCB), 1,2-dichlorobenzene (1,2-DCB) and 1,2,4-tirchlorobenzene (1,2,4-TCB) on the fresh bulk biochar derived from pinewood sawdust and corn straw under the heat treatment temperature (HTT) of 300 and 500 °C, and elucidated the aging-induced changes in the sorption/desorption of mixed CBs by biochar. The distinct sorption capacities of MCB< 1,2-DCB< 1,2,4-TCB were observed on all the tested biochar with the differences being further enhanced following the rise of HTT, as the main sorption mechanism was converted from phase partitioning to π-π interaction between graphitized biochar moieties and more hydrophobic aromatic chemicals. In comparison to the fresh biochar, the sorption suppression of the mixed CBs on the aged biochar was likely attributable to the reduction in accessibility to the aromatic carbon in biochar by introducing O-containing polar moieties on the biochar surfaces. Intriguingly, the kinetics of desorption was decreased with the aging of biochar may be caused by the increase in surface steric hindrance. These findings can provide new insights on understanding the co-sorption/co-desorption mechanism of the mixed CBs and help assess and manage the application of biochar on the treatment of contaminated soil and groundwater under field conditions.

Influence of heat treatment on microstructure and mechanical properties of Cansas-II SiC/PyC/CVI-SiC mini-composites

The influence of heat treatment at 1300 °C and 1500 °C for 50h on the microstructure and mechanical properties of Cansas-II SiC/PyC/CVI SiC mini-composites was studied in detail. The interfacial shear strength decreases from 98.8 MPa to 13.6 MPa after the heat treatment at 1500 °C for 50h, which was mainly caused by the weak bonding between the SiC matrix and PyC interface due to the decomposition reactions and carbothermic reductions of CVI SiC matrix. The average tensile strength of fibers decreases with the rise of heat treatment temperature, which was primarily attributed to the significant growth of β-SiC grains accompanied by the decomposition of SiC x O y . Due to the protective effect of the PyC interface and CVI SiC matrix on the fibers, the fraction of declined strength of the mini-composites is only 25.8% after the heat treatment at 1500 °C for 50h.

Study on the Effect of High-Temperature Heat Treatment on the Microscopic Pore Structure and Mechanical Properties of Tight Sandstone

The investigation of changes in physical properties, mechanical properties, and microscopic pore structure characteristics of tight sandstone after high-temperature heat treatment provides a theoretical basis for plugging removal and stimulation techniques, such as high energy gas fracturing and explosive fracturing. In this study, core samples, taken from tight sandstone reservoirs of the Yanchang Formation in the Ordos Basin, were first heated to different temperatures (25-800°C) and then cooled separately by two distinct cooling methods—synthetic formation water cooling and natural cooling. The variations of wave velocity, permeability, tensile strength, uniaxial compressive strength, and microscopic pore structure of the core samples were analyzed. Experimental results demonstrate that, with the rise of heat treatment temperature, the wave velocity and tensile strength of tight sandstone decrease nonlinearly, yet its permeability increases nonlinearly. The tight sandstone’s peak strength and elastic modulus exhibit a trend of the first climbing and then declining sharply with increasing temperature. After being treated by heat at different temperatures, the number of small pores varies little, but the number of large pores increases obviously. Compared to natural cooling, the values of physical and mechanical properties of core samples treated by synthetic formation water cooling are apparently smaller, whereas the size and number of pores are greater. It can be explained that water cooling brings about a dramatic reduction of tight sandstone’s surface temperature, generating additional thermal stress and intensifying internal damage to the core. For different cooling methods, the higher the core temperature before cooling, the greater the thermal stress and the degree of damage caused during the cooling process. By taking into consideration of changes in physical properties, mechanical properties, and microscopic pore structure characteristics, the threshold temperature of tight sandstone is estimated in the range of 400-600°C.

Linear and non-linear optical properties of transparent glass-ceramics based on Co2+-doped Zn(Al,Ga)2O4 spinel nanocrystals

Transparent glass-ceramics containing Co2+:Zn(Al,Ga)2O4 spinel nanocrystals with sizes of 6-11 nm were prepared on the basis of the glass of the ZnO-Al2O3-Ga2O3-SiO2 system nucleated by TiO2. The absorption and luminescence properties of these glass-ceramics are defined mainly by tetrahedrally coordinated Co2+ ions located in Zn(Al,Ga)2O4 nanocrystals with spinel structure. Co2+ ions in glass-ceramics exhibit absorption saturation at 1.54 µm (the 4A2(4F)→4T1(4F) transition of Co2+ ions in tetrahedrally coordinated sites). This absorption band is shifted to higher wavelengths by 20 nm as compared with glass-ceramics with no Ga2O3 addition. The concentration of Co2+ ions in Zn(Al,Ga)2O4 nanocrystals changes in a complex way with rise in heat-treatment temperature. Characteristic times of luminescence decay, values of ground-state absorption cross-sections, and absorption saturation recovery time were determined. The developed glass-ceramics are promising as saturable absorbers for 1.6 µm erbium lasers.

Heat treatment effect on the structural, morphological, and optical properties of plasma polymerized furan-2-carbaldehyde thin films

The furan-2-carbaldehyde (PPFCD) amorphous polymer thin films, with several thicknesses, were deposited onto glass substrates using a glow discharge of monomer FCD at ordinary room temperature via plasma polymerization technique. The structural, morphological, and optical characteristics of the as synthesised PPFCD amorphous films were studied as a function of temperature via X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and ultraviolet-visible (UV–Vis) absorption spectroscopy. The amorphous nature of the thin films was ascertained in both as-synthesised and heat treated states using the XRD studies. The SEM micrographs display homogeneous and fracture free surface of PPFCD films and no remarkable variation in the surface morphology of the as synthesised films was detected owing to the heat treatment procedure. However, the EDX, and FTIR analysis represented some structural rearrangement originated from the heat treatment of the PPFCD thin films. The analysis of the UV–Vis absorption spectroscopy revealed that the absorbance of the films depend on the films thickness and the temperature of the heat treatment. The optical band-gaps of PPFCD amorphous films were found to be significantly decreased with the gradual rise in heat treatment temperature.

MnOx/Ti Composite Membrane Anode in the Electrocatalytic Membrane Reactor for Phenolic Wastewater Treatment

MnOx/Ti composite membranes, MnOx coated on the original porous Ti support membrane, were synthesized by sol-gel method. The effect of heat-treatment temperature (220-380°C) on the crystal structure of nano-MnOx was investigated by XRD, FESEM and XPS. The XRD results showed that crystal gain size increased with the rise of heat-treatment temperature, and at the temperature of 220 to 300°C, the crystal structure was mainly Mn3O4, which transformed to Mn3O4 and α-Mn2O3 mixed crystal after 300°C. Electrocatalytic membrane reactor (ECMR) assembled with MnOx/Ti composite membrane as an anode and a stainless steel mesh as a cathode was employed for phenolic wastewater treatment. The phenol, COD and TOC removal rate of ECMR with MnOx/Ti heat-treated at 220°C reached the maximum value of 93.09%, 79.25% and 68.54%, whereas were 54.85%, 40.25% and 35.10% in case of the original Ti membrane as the anode, respectively. The sequence of catalytic activity was as follows: Mn3O4 > Mn2O3, which was also correlated with the grain size of the catalyst. The higher phenol removal obtained were related to the synergistic effect of the electrochemical oxidation and separation in ECMR, whose MnOx as catalysts also played a key role on the electrocatalytic oxidation of the phenolic wastewater.

Simultaneous reconstruction of thermal degradation properties for anisotropic scattering fibrous insulation after high temperature thermal exposures

To probe thermal degradation behavior of fibrous insulation for long-term service, an inverse analysis model was developed to simultaneously reconstruct thermal degradation properties of fibers after thermal exposures from the experimental thermal response data, by using the measured infrared spectral transmittance and X-ray phase analysis data as direct inputs. To take into account the possible influence of fibers degradation after thermal exposure on the conduction heat transfer, we introduced a new parameter in the thermal conductivity model. The effect of microstructures on the thermal degradation parameters was evaluated. It was found that after high temperature thermal exposure the decay rate of the radiation intensity passing through the material was weakened, and the probability of being scattered decreased during the photons traveling in the medium. The fibrous medium scattered more radiation into the forward directions. The shortened heat transfer path due to possible mechanical degradation, along with the enhancement of mean free path of phonon scattering as devitrification after severe heat treatment, made the coupled solid/gas thermal conductivities increase with the rise of heat treatment temperature.

Crystallization characteristics of Ni-W-P composite coatings reinforced by CeO2 and SiO2 nano-particles

Ni-W-P composite coatings reinforced by CeO2 and SiO2 nano-particles on the surface of common carbon steels, were prepared by double pulse electrodeposition. The crystallization course was characterized by phase structures, crystallinity, grain sizes and microstructures. The results indicate that as-deposited composite coating is amorphous. Whereas it turns into the crystalline structure with 98.25% crystallinity, and Ni3P, Ni2P and Ni5P2 alloy phases precipitate from structures at 400 °C. Thereafter, Ni2P and Ni5P2 metastable alloy phases turn into Ni3P stable alloy phase at 500 °C. The crystallization course of the composite coating has finished when being heat-treated at 700 °C. The average sizes of Ni grains increase with the rise of heat treatment temperature from 400 °C to 700 °C. CeO2 and SiO2 nano-particles deposited into Ni-W-P alloys can delay the crystallization course and habit the growth of alloy phases.

SiO2/TiO2 composite aerogels: Preparation via ambient pressure drying and photocatalytic performance

Silica/titania (SiO2/TiO2) (Si/Ti=1:1) composite aerogels have been manufactured via ambient pressure drying using tetraethoxysilane (TEOS) and tetrabutyl titanate (TBT) as precursors. Changes in the structure and the surface properties of the aerogels during the heat treatment were investigated in detail by N2 adsorption–desorption techniques, SEM, TEM, XRD, FTIR, and UV–vis absorption spectra. The results showed that the as obtained aerogel with a porous structure possessed a surface area of 667m2/g, average pore size 3.4nm, and pore volume 0.68cm3/g. After calcination, the surface area decreased while the average pore size and the pore volume increased with the rise of heat treatment temperature. FTIR spectra showed the existence of Si–O–Ti in the aerogels and that after calcination at 800°C, anatase nanoparticle appeared as demonstrated in XRD pattern. The photocatalytic performance was evaluated by degradation of MB and the results demonstrated that the aerogels calcined at 800°C have a better photocatalytic activity than other samples.

Superbasic sodium stannate as catalyst for dehydrogenation, Michael addition and transesterification reactions

It has been shown that sodium stannate with superbasic sites generated on its surface can be obtained through simple thermal treatment of sodium stannate hydrate in pure N 2. In this study, we analyzed the as-prepared materials using powder X-ray diffraction, X-ray photoelectron spectroscopy, and N 2 physisorption methods. The superbasic sites were characterized by techniques of Hammett indicators and temperature-programmed desorption using CO 2 as adsorbate. It was shown that after undergoing calcination at 623 K, there are ample superbasic sites on sodium stannate: up to 0.254 mmol/g. The superbasicity of the materials was further confirmed by employing the 1-hexene as well as cyclohexa-1,4-diene double bond isomerization reactions. The superbasicity is attributed to the higher electron-donating ability of surface O 2−. The sodium stannate samples showed excellent catalytic efficiency towards selected reactions, namely the dehydrogenation of propa-2-nol, Michael addition of electron-deficient olefins, and transesterification of cyclic carbonate with methanol. It was observed that with rise of heat-treatment temperature from 573 to 623 K, both superbasicity and catalytic activity increased, reaching a maximum at 623 K, and then declined. It is deduced that catalytic efficiency is closely related to superbasicity of the sodium stannate catalysts.

NaNbO 3 crystals dispersed in a B 2O 3 glass matrix – Structural characteristics versus electrical and dielectrical properties

Sodium niobate (NaNbO 3) is a crystal with a perovskite structure that exhibits, at room temperature, an antiferroelectric behaviour. It is a very interesting material due to the several phase transitions that it presents as a function of the temperature (ferroelectric–antiferroelectric–paraelectric). Thus, the preparation of glass-ceramics containing NaNbO 3 crystals is scientifically and technologically important. Besides, there is actually few works available about the preparation of NaNbO 3 crystals embedded in a glass matrix. The present work reports the preparation process and the study of glass and glass-ceramics in the B 2O 3–NaNbO 3 system. The glass with the molar composition 60B 2O 3–30Na 2O–10Nb 2O 5 (mol%) was prepared by the melt-quenching method. Sodium niobate (NaNbO 3) crystallites were precipitated through a controlled heat-treatment (HT) process. NaNbO 3 crystallites were detected by X-ray diffraction (XRD) in the samples treated above 500 °C. The treatments above 600 °C favour also the formation of Na 2B 4O 7 and Nb 2O 5 crystalline phases. Scanning electron microscopy (SEM) reveals that the crystallization occurs in volume and that the number of particles increases with the rise in HT temperature. The number of network modifier ions (Na + and Nb 5+) in the glass network is the main factor in the dc and ac conductivity behaviours. The dielectric constant ( ɛ′) value increases with the increase of the volume ratio between the particles and the glass matrix. The sample heat-treated at 550 °C shows two thermally stimulated depolarization current (TSDC) peaks. The high temperature peak can be related to the presence of NaNbO 3 particles.

Studies on the Properties and Structure of Pulse Electrodeposited Ni-W-P Series Multi-Composite Coatings

The hardness, wear rates, phase structure and morphologies of DC(direct current) and PC(pulse current )electrodeposited Ni-W-P-SiC, RE-Ni-W-P-SiC, RE-Ni-W-P-SiC-MoS2 and RENi- W-P-SiC-PTFE composite coatings are studied. The results indicate that the hardness of pulse composite coatings is higher than that of DC composite coatings, but the hardness of RE-Ni-W-PSiC- PTFE composite coating is lower. The hardness of the four kinds of composite coatings increases with the rise of heat treatment temperature and reaches the highest value at 400°C, thereafter, the hardness begins to decrease. The hardness of RE-Ni-W-P-SiC composite coating is the highest when duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz and the hardness of RE-Ni-W-P-SiC composite coatings at 0.8 is higher than that at 0.6; the wear rates of Ni-W-P-SiC, RE-Ni-W-P-SiC, and RE-Ni-W-P-SiC-PTFE pulse composite coatings are lower than that of DC composite coatings and the wear rates of RE-Ni-W-P-SiC-MoS2 and RE-Ni-W-P-SiC-PTFE composite coatings are the lowest. Ni-W-P-SiC and RE-Ni-W-P-SiC pulse composite coatings are amorphous, and RE-Ni-W-P-SiC-MoS2 pulse composite coating is mixture, but the RE-Ni-W-PSiC- PTFE composite coating is crystal as–deposited. The crystalline grain size of PC composite coatings is smaller than that of DC composite coatings, and the addition of rare earth into the coatings can make crystalline grains become fine, all kinds of grains in the coatings distribute equably and there are not cracks on the surface and in the sections.

Microstructure of La-modified Al2O3 support with LaAlO3 nano-particles

Lanthanum modified γ-alumina support that embedded highly dispersed LaAlO3 nano-particles in γ-alumina matrix were prepared by an impregnation process using aqueous lanthanum (III) nitrate. 5 mol% La added alumina was heated in the temperature range of 600-1200°C and characterized by surface area measurement, X-ray powder diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The added lanthanum should react with γ-Al2O3 to form LaAlO3 nano-particles in the secondary particle of alumina. LaAlO3 nano-particles with an average crystallite size of about 11 nm were found after heat treatment at 800°C, and the crystallite size of LaAlO3 nano-particles increased with the rise of heat treatment temperature.

Studies on properties and structure of electrodeposited RE–Ni–W–B–SiC composite coating

A composite coating, containing 1.35wt.%RE, 5.46wt.%W, 3.82wt.%B, 15wt.%SiC and Ni was electrodeposited on the matrix by use of appropriate bath composition and process parameters. The addition of RE(CeO2) enhanced the hardness and wear resistance of the coating remarkably. The hardness and wear resistance of the coating increase with a rise in heat treatment temperature, and the hardness reaches the optimum value at 400°C, while the coating has the best wear resistance at 500°C. The wearing tests show that the wear resistance of the coating is four to five times as high as that of hard chromium, and the corrosion tests indicate that the corrosion resistance of the coating is superior to that of 1Cr18Ni9Ti stainless steel in various corrosive media, except for nitric acid. X-ray diffraction shows that the 1.35wt.%RE–5.46wt.%W–3.82wt.%B–15wt.%SiC–Ni as-deposited composite coating is mainly amorphous, except a few Ni, W, CeO2, B and SiC phases.

Photoelectrochemical Characteristic of Titanium Dioxide Prepared from Heat Treatment of Titanium

The titanium dioxide was prepared from the heat treatment of titanium from room temperature up to different temperatures of 600-900°C in an electric furnace and its photoelectrochemical characteristic was checked by the measurement of photocurrent, carrier density and quantum efficiency based on the photothermal method. The titanium dioxide thus prepared showed a lower carrier density with rise in heat treatment temperature and did not show clear dependence of flatband potential on heat treatment temperature. The heat treatment from room temperature up to ca.800°C provided the titanium dioxide with rutile structure which showed a maximum photocurrent, carrier density of 1-2×1017 cm-3 and quantum efficiency over 50%.

Surface properties of poly(vinyl alcohol) films with a fluoroalkyl group at one end

Surface properties of poly(vinyl alcohol) (PVA) films with a fluoroalkyl group at one end, H(CF 2)− n CH 2O(CH 2)− 3SPVA and F(CF 2)− 7CONHCH 2CH 2SPVA, were studied by contact angle measurements and X.p.s. analysis. H(CF 2)− n CH 2O(CH 2)− 3SPVA and F(CF 2)− 7CONHCH 2CH 2SPVA distributed preferentially on the air-side surface, and the surface showed properties corresponding to the characteristics of the fluoroalkyl end groups. Surface free energy, γ s, was in good agreement with critical surface tension, γ c, for F(CF 2)− 7CONHCH 2CH 2SPVA and n-C 12H 25SPVA, which had no polar component of γ s, and with γ c (max) for a series of H(CF 2)− n CH 2O(CH 2)− 3SPVAs which had a polar component. The γ s of F(CF 2)− 7CONHCH 2CH 2SPVA films altered by heat treatment, gave a minimum value at 80°C and increased with a rise in heat treatment temperature above 120°C, which was thought to be caused by distribution changes of the end groups. γ s was closely related to the distributions of CF 3 and CF 2 groups in the surface layer estimated by X.p.s. analysis.