Function Of Heat Treatment Temperature Research Articles

Dynamics of defects and surface structure formation in reticulated vitreous carbon

Morphological and microstructure properties of reticulated vitreous carbon (RVC) were analyzed by scanning electron microscopy (SEM), micro-Raman spectroscopy and x-ray diffraction (XRD) techniques as a function of heat treatment temperature (HTT). Samples produced in the HTT range of 1000 to 2400 K have demonstrated a strong dependence of HTT in their structural order mainly attributed to the presence of hydrogen and oxygen (heteroatoms), originated from precursor. In this range, the material is changed from pyropolymer to carbon. The polyfurfuryl alcohol precursor has furanic groups and its cure originates methylenical bonds and sulphur atoms. At HTT higher than 1300 K, these atoms are gradually liberated from the material generating a discrete structure ordering.

The effect of heat treatment temperature on the microstructure and magnetic properties of Ba 2Co 2Fe 12O 22 (Co 2Y) prepared by sol–gel method

Ferroxplana type hexagonal ferrite with composition Ba 2Co 2Fe 12O 22 (Co 2Y) was prepared by polymeric sol–gel method from the aqueous solution of their corresponding metal salts. All the samples were characterized by using X-ray diffraction and scanning electron microscopic technique. The formation and the microstructure of the Ba 2Co 2Fe 12O 22 was studied as a function of heat treatment temperature and it was observed that well defined hexagonal plate-like fine particles with particle sizes between 130 and 400 nm were formed at relatively lower temperature (900 °C) as compared to conventional solid state reaction method (1100 °C). Magnetic properties of the samples were also studied as a function of heat treatment temperature and it showed large saturation magnetization ( M s) ranging from 30.9 to 47.6 emu/g and a wide range of coercivity (130∼1566 Oe) depending on the heat treatment temperature. The very high saturation magnetization at relatively lower temperature (say 800 °C) arises due to the presence of several high magnetic impurities, such as BaFe 12O 19 and CoFe 2O 4. The saturation magnetization increases with increasing heat treatment temperature above 900 °C, while the coercivity showed a reversed order.

Quantification of the cleaning of egg albumin deposits using micromanipulation and direct observation techniques

Cleaning of food fouling deposits in processing equipment is costly and time consuming. Fouling deposits form as a result of adhesion of species to the surface and cohesion between elements of the material. Proteins constitute the major fraction of many food fouling deposits and are notably difficult to remove. Work has been carried to determine the factors controlling removal of egg albumin deposits. A micromanipulation technique was used to measure the adhesive/cohesive strength of egg albumin deposits on a stainless steel surface. The apparent adhesive strength between the fouling deposits and the substrate was measured as the work required to remove the deposits per unit area from the surface. Measured values were between 0 and 4 J/m 2, these were a function of heating temperature and time, albumin concentration, cleaning agent concentration and exposure time. The cohesive strength was greater than adhesive strength at room temperature. Observation of cleaning showed that micromanipulation measurements would be related directly to the effect of concentration on the cleaning time.

Raman scattering study of adsorption/desorption of water from single‐walled carbon nanotubes

AbstractWe utilized Raman spectroscopy to investigate H2O adsorption in and desorption from single‐walled carbon nanotubes (SWCNTs). SWCNT tips were opened by known chemical methods and H2O was inserted into the tubes via capillary action over periods up to 136 h. The wavenumbers in the OH bending region of H2O increase almost exponentially with H2O treatment time. Following H2O adsorption for 136 h, Raman spectra were also measured as a function of heat‐treatment temperature. These data lead to 0.07 eV for the H2O desorption energy from SWCNTs. Copyright © 2005 John Wiley & Sons, Ltd.

Thermoelectric properties of SiC/C composites from wood charcoal by pulse current sintering

SiC/C composites were investigated by sintering a mix of wood charcoal and SiO 2 powder (32–45 μm) at 1400, 1600 and 1800 °C under N 2 atmosphere with a pulse current sintering method. Thermoelectric properties of SiC/C composites were investigated by measuring the Seebeck coefficient and the electrical and thermal conductivities as a function of heat treatment temperature and reaction time. The Seebeck coefficient showed a p-type to n-type transition at a heat treatment temperature around 1600 °C. The electrical conductivity showed a steady increase with temperature for all three heat treatment temperatures. For the thermal conductivity, the samples heated at 1800 °C showed high values at room temperature which strongly decreased with increase in measurement temperature. In total, thermoelectric properties were improved with an increase in measurement temperature. A maximum in the figure of merit of 3.38 × 10 −7 K −1 was reached at 200 °C in the sample heated at 1400 °C for 30 min.

Thermal analysis of vacancy defects in quenched tin bronze-α

Investigations have been carried out on the thermal dilatation (Δ L/ L 0) and lattice parameters (Δ a/ a 0) of the α-solution of industrially smelted tin bronze-type CuSn6P as a function of heating temperature from 20 to 900 °C after quenching within the temperature range 750–910 °C. These investigations have made it possible to determine the concentration of vacancies after solution heat treatment and quench ageing up to 800 °C and to assess preliminarily the formation energy of vacancies ( E V F ≈ 0.5–0.9 eV) depending on the parameters of heat treatment.

Phase formation stages of MgTa 2O 6 and Pb(Mg 1/3Ta 2/3)O 3

Reaction stages during the B-site precursor formation (from MgO and Ta 2O 5) as well as those from PbO and MgTa 2O 6 were examined by X-ray diffraction (XRD), as a function of heat-treatment temperatures. The powders were then analyzed in terms of phase development. The results are compared with other perovskite compositions.

Thermal stability and structural changes of double-walled carbon nanotubes by heat treatment

We describe, for the first time, the sequential structural changes of bundles of double-walled carbon nanotubes (DWNTs) as a function of heat treatment temperature. DWNTs (inner diameters >0.9 nm) are structurally stable up to 2000 °C. Above 2100 °C, the outer walls of adjacent DWNTs start coalescing into large diameter tubes. At temperatures higher than 2100 °C, three different types of structures were observed: (a) large-diameter DWNTs; (b) multi-walled carbon nanotubes (MWNTs), and (c) flaky carbons. The results demonstrate that DWNTs are much more stable than SWNTs, and their stability is comparable to that of MWNTs.

Phase and microstructural development in alumina sol-gel coatings on CoCr alloy.

Phase transformation of gamma-Al(2)O(3) to alpha-Al(2)O(3) in alumina sol gel coatings on biomedical CoCr alloy was studied as function of heat treatment temperature and time. Transformation in unseeded coatings was significant only above approximately 1200 degrees C. Addition of alpha-Al(2)O(3) seed particles having an average size of approximately 40 nm lowered the phase transformation temperature to around 800 degrees C. These particles were considered to act as heterogeneous nucleation sites for epitaxial growth of the alpha-Al(2)O(3) phase. The kinetics and activation energy (420 kJ/mol) for the phase transformation in the seeded coatings were similar to those reported for seeded monolithic alumina gels indicating that the transformation mechanism is the same in the two material configurations. Avrami growth parameters indicated that the mechanism was diffusion controlled and invariant over the temperature range studied but that growth was possibly constrained by the finite size of the seed particles and/or coating thickness. The phase transformation occurred by the growth of alpha-Al(2)O(3) grains at the expense of the precursor fine-grained gamma-Al(2)O(3) matrix and near-complete transformation coincided with physical impingement of the growing grains. The grain size at impingement was approximately 100 nm which agreed well with that predicted from the theoretical linear spacing of seed particles in the initial sol.

Structural changes of injection molded starch during heat treatment in water atmosphere: Simultaneous wide and small‐angle X‐ray scattering study

AbstractNative starches with wide varying amylose content were processed by injection molding. The injection‐molded materials were conditioned in water for 20 days and sealed in glass capillaries. Simultaneous wide‐ and small‐angle X‐ray scattering (WAXS and SAXS, respectively) were recorded during thermal heating using a synchrotron source. Crystallinity, SAXS invariant, Q, and long period, L, were measured as a function of heating temperature. The injection‐molding process provokes a destruction of the crystal forms A (cereal starch) and B (tubercle starch) but favors a development of the crystal form Vh. After wet conditioning, WAXS of the injection‐molded samples shows again the appearance of the crystal forms A or B, and crystallinity reaches values similar or larger than those of native starch. A constant heating rate (5°C/min) was particularly used for a comparison of potato and corn starch with a similar amylose content. While the crystallinity associated to forms A and B slowly decreases below 55°C and then rapidly decreases until its disappearance at 85–90°C, the invariant shows a maximum around 40°C and rapidly decreases thereafter. The total nanostructure disappearance occurs at temperatures about 10°C higher for the case of potato starch. In addition, a recovery of the WAXS and SAXS maxima during the subsequent cooling process before reaching room temperature was observed only for potato starch. Analysis of WAXS and SAXS for the rest of the starch materials reveals clear differences in the structural parameters of the samples that cannot be easily explained solely on the basis of the amylose content. Thus, for Cerestar and Roquette, it is noteworthy that there was a continuous decrease of L until its total disappearance as well as the persistence of crystallinity (form B), presumably stabilized by the presence of the Vh structure (12–15%). Real‐time crystallization experiments on two amorphous injection molded samples, waxy maize (free amylose starch) and potato starch, are also discussed. It is shown that the absence of amylose delays the recrystallization of amylopectine during the experiment. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 301–309, 2004

Oxidation behavior of biomass chars: pectin and Populus deltoides

Biomass chars of pectin and cotton wood ( Populus deltoides) were prepared by using a heating rate of about 1 °C/s, peak pyrolysis temperatures of 400–800 °C, and residence times of 10–60 min at peak temperatures. Char samples were pyrolyzed in a helium atmosphere using a thermogravimetric analyzer (TGA). Oxidation reactivity measurements of the same char samples in the TGA were collected after converting the helium atmosphere to an oxygen containing atmosphere. Reactivities were measured using an isothermal method at various reaction temperatures from 400 to 700 °C and oxygen concentrations of 2–21%. Oxidation kinetic parameters such as apparent reaction order and apparent activation energies were obtained. Scanning electron microscopy (SEM) was employed to study morphological and structural development in the char samples as a function of heat treatment temperature. An interesting morphological development on the surface of the char was observed by SEM, which showed evolution of vesicle formation and whisker growth as heat treatment temperatures increased. Its implication on char reactivity is discussed. Preliminary results showed decreasing reactivity with increasing peak heat treatment temperatures. Char reactivity was affected more by the heat treatment temperature than by the hold times (10–60 min).

Sintering behavior of partially crystallized barium titanate monolithic xerogels with different nano-crystalline structure

The densification behavior of partially crystallized barium titanate (BaTiO3) monolithic xerogels prepared by a high concentration sol-gel method with different degree of hydrolysis was examined as a function of sintering temperature. The structural evolution of the xerogels during thermal treatment has been monitored by nitrogen adsorption/desorption porosimetry, XRD, TG/DTA, TEM, and SEM measurements. Sintering behavior of the xerogels can be significantly influenced by their initial microstructure that was affected by the content of water used for hydrolysis. Density change with sintering temperature was different between xerogels with different degrees of hydrolysis. Hydrolysis water content is H2O/Ba molar ratio, denoted as rw. Xerogels with rw=5.0, having a lower porosity and smaller pore size with less agglomerated particles, were sintered to form ceramics with a relative density of about 97% at a temperature of 1100 °C, whereas this was only 83% for xerogels with rw=5.7 having relatively larger pore volume and pore size. The average pore size of the xerogels increased with increasing sintering temperature up to 700 °C. For temperatures over 700 °C, it continued to increase for xerogels with rw=5.7, but it fell for xerogels with rw=5.0 due to rapid densification. Microstructural changes of the xerogels are discussed as a function of heat treatment temperature.

Correlation between the pore and solvated ion size on capacitance uptake of PVDC-based carbons

A nonaqueous electrolyte solution is employed to form double layers on a poly(vinylidene chloride) (PVDC)-based carbon material, thereby extending the application of PVDC-based carbon to nonaqueous systems. Thermal behavior of the Npv-series, which was obtained by simple heat treatment under an inert atmosphere, and the Apv-series, which is obtained by potassium hydroxide (KOH) addition, is confirmed by thermal gravimetric analysis (TGA). The KOH activation affect on the structure of PVDC-based carbon is shown and demonstrates a high capacitance in nonaqueous electrolyte systems. Variation of the pore size distribution on the double layer capacitance is explained on the basis of computer simulation. Carbons with different porous structures are prepared by KOH impregnation as a function of heat-treatment temperature (HTT). The effects of the porous structure on the electrochemical behavior and the capacitance of the resulting electric double layer capacitors (EDLCs) are investigated.

Physical and optical properties of sol-gel nano-silver doped silica film on glass substrate as a function of heat-treatment temperature

Nano-silver doped silica films were deposited on glass slides using a sol-gel process and heat-treated at different temperatures. The films were characterized by ultraviolet-visible spectroscopy, x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy for their optical, chemical, and structural properties. The absorption peak of silver colloids (wavelength from 400 to 460 nm) was present and a blueshift and intensity reduction of the absorption peak was observed during heat-treatment. Particle size reduction and surface morphology changes in the films were observed by AFM as a function of varying heat treatment temperatures. Silver nanoparticles were formed through spontaneous reduction of silver ions. The oxidation of silver occurs during heat-treatment, causing a reduction of absorption intensity. An interdiffusion between the Ag in the film and Na in the substrate glass was observed by XPS and RBS. Sodium in the coating likely increased the stability of silver oxide at high temperature treated samples.

Gelation of β-lactoglobulin in the presence of propylene glycol alginate: kinetics and gel properties

The role of the non-gelling polysaccharide, propyleneglycol alginate (PGA), on the dynamics of gelation and gel properties of β-lactoglobulin (β-lg) under conditions where the protein alone does not gel (6%) was analyzed. To this end, the kinetics of gelation, aggregation and denaturation of β-lg in the mixed systems (pH 7) were studied at different temperatures (64–88 °C). The presence of PGA increased thermal stability of β-lg. The rate of β-lg denaturation was decreased and the onset and peak denaturation temperatures increased by 2.2–2.4 °C. PGA promoted the formation of larger aggregates that continued to grow in time. An average aggregate diameter of approximately 300 nm is reached at the gel point in the mixed β-lg+PGA systems, irrespective of the heating temperature. Comparing the activation energies for the aggregation (193 kJ/mol), denaturation (422 kJ/mol) and formation of the primary gel structure (1/ t gel) (256 kJ/mol) processes in the mixed protein–polysaccharide system, it can be concluded that the rate determining step in the formation of the primary gel structure would be the aggregation of protein. E a values for the processes after the gel point (solid phase gelation) suggest a diffusion limited process because of the high viscosity of the solid gelling matrix. The characteristics of the mixed β-lg+PGA gels in terms of rheological and textural parameters, water loss and microstructure were studied as a function of heating temperature and time. The extent of aggregation and the type of interactions involved, prior to denaturation seem to be very important in determining the gel structure and its properties.

Optical properties of Coumarin 314 doped sol-gel silica rods

Summary Silica rods containing Coumarin 314 have been fabricated by the sol-gel method and their optical properties have been investigated under a linear Xenon flashlamp excitation. The fluorescence spectra of Coumarin 314 peaked at 508 nm in sol-gel silica while they peaked at 476 nm in ethanol. The fluorescence spectra of Coumarin 314 doped sol-gel silica rods were measured as function of heat treatment temperature. As heat treatment temperature of the rods increases, the fluorescence spectra band becomes somewhat broader. The photodegration of Coumarin 314 doped sol-gel silica rods was also studied under linear Xenon flashlamp excitation. The bulk transmission losses of the rods immersed in water were measured to be 0.51–0.57%/cm.

大変形ガラス状ポリメタクリル酸メチルにおける残留ひずみ回復挙動の時間および温度依存性

Time and temperature dependence of recovery behavior of residual strains in largely compressed glassy poly (methyl methacrylate) (PMMA) has been studied. At several temperatures lower than the glass transition temperature Tg, uniaxially compressed specimens were isothermally kept in the stress-free state for a variation of time tf, and then subjected to thermally stimulated strain recovery measurement. Thermally stimulated recovery of residual strains in specimens right after the compression began at heating temperatures lower than Tg. With increasing time tf, residual strains recoverable at heating temperatures below Tg decreased simply from those recoverable at the lowest heating temperature. The decrease of residual strains recovering at a heating temperature less than Tg was examined as a function of time tf and was found to be expressed by a single exponential retardation function. Thus, the sub-Tg strain recovery was revealed to be a simple viscoelastic process with distribution of retardation times. Temperature dependence of the retardation time allowed us to calculate activation energy of sub-Tg strain recovery as a function of heating temperature. The activation energy of sub-Tg strain recovery was found to be approximately the same function of temperature as that of the linear viscoelastic relaxation of the polymer. This result led us to a conclusion that, as a first approximation, the molecular mechanism governing the sub-Tg recovery of strains given by large deformation is almost the same as that of linear viscoelastic relaxation.

Effects of Postdeposition in situ Heat Treatment on the Properties of Low Dielectric Constant Plasma Polymer Films Deposited Using Decahydronaphthalene and Tetraethyl Orthosilicate as the Precursors

We investigated effects of postdeposition heat treatment (HT) on the properties of plasma polymer films deposited by plasma-enhanced chemical vapor deposition using a mixture of decahydronaphthalene and tetraethyl orthosilicate as the precursors, which were referred to as plasma-polymerized decahydronaphthalene:tetraethyl orthosilicate (PPDHN:TEOS) films. HTs at 350, 450, and 500 °C decreased the relative dielectric constant k of the PPDHN:TEOS films from 3.16, the k value of the as-deposited film, to 2.82, 2.72, and 3.02, respectively. The change of k value as a function of HT temperature was correlated with the change of Fourier transform infrared absorption peaks of O–H, C = O, and Si-related groups. As the HT temperature increased, the thermal stability of the PPDHN:TEOS film increased. PPDHN:TEOS films, as-deposited or heat treated, showed leakage current density in the order of 10−7 A/cm2 at 1 MV/cm.

Fluorescence characterization of LaRC PETI-5, BMI, and LaRC PETI-5/BMI blends

In the present study, the fluorescence behavior of a phenylethynyl-terminated imide (LaRC PETI-5) resin, a bismaleimide (BMI) resin, and various LaRC PETI-5/BMI blends with different blend compositions has been characterized as a function of heat-treatment temperature, using a steady-state fluorescence technique with a front-face illumination method for solid-state films. It is observed that there are distinguishable changes in the spectral shape, size, and position of fluorescence with varying heat-treatment temperature in the pure and blend samples. The result is qualitatively explained in terms of charge transfer complex formation as well as microenvironmental change with local mobility and viscosity occurring in the LaRC PETI-5, BMI, and their blends during the cure process. The result also implies that a steady-state fluorescence technique may be a useful tool to understand the processing conditions of polyimides and their blends in the film form on the basis of their thermo-photophysical responses.

Effect of thermal cycling on R-phase stability in a NiTi shape memory alloy

The stability of R-phase during thermal cycling has been studied for the near equiatomic, 40% cold worked, NiTi wire samples using electrical resistivity measurements. Thermal cycles are given to the specimens heat treated in the temperature region of 340–620 °C. In the samples having only M↔A transformations after heat treatment, successive thermal cycles promote and result in the stabilisation of intermediate R-phase. During the initial thermal cycles, M s is found to decrease facilitating the development of intermediate R-phase as indicated by the emergence of peak in the cooling part of the transformation profile. Once the R-phase is completely developed, the transformation parameters such as R s, R f, M s, M f and peak resistivity of the transformation profile remains unaffected during thermal cycling. There exists a critical number of thermal cycles for the complete development of R-phase and this critical number is a function of heat treatment temperature.