Initial Heating Rate Research Articles

Template-based electrophoretic deposition of perovskite PZT nanotubes

Template-based electrophoretic deposition of perovskite lead zirconate titanate (PZT) nanotubes was achieved using anodic alumina (AA) membranes and sols, containing lead, zirconium and titanium precursors. The effect of various anodizing voltages on the size of the channels in the anodic alumina template was investigated. The prepared sol was driven into the channels under the influence of various electric fields and subsequently sintered at about 700 °C. The effects of the initial heating rates and the burn-out temperature on the phase evolution of the samples were studied and a modified firing process was employed. The effects of the electrophoretic voltage and the deposition time on the average wall thickness of the tubes were investigated. Scanning and transmission electron microscopy (SEM and TEM) revealed the efficiency of electrophoresis in the growth of lead zirconate titanate nanotubes in a close-packed array. The X-ray diffraction analyses indicated the presence of perovskite as the principal phase after a modified firing schedule.

MAGNETIC PROPERTIES AND INDUCTION HEATING OF NiZn FERRITE NANOPARTICLES

A series of nanoparticle powders of Ni x Zn 1-x Fe 2 O 4 (x = 0, 0.30, 0.40, 0.50, 0.55, 0.60, 0.70 and 1.0) ferrites was synthesized by the refluxing method at relatively low temperatures. The average size of nanoparticles is about 20 nm. The magnetic properties and induction heating behavior were investigated. On increasing the Ni content, x, from 0 to 0.50, the saturation magnetization and permeability increased, and then decreased with further increasing Ni content with the bulk Ni – Zn ferrite. The maximum value of magnetization was about 50 emu/g near x = 0.50, where the induction heating rate and induction heating final temperature of the ferrite-water suspension also showed maximum values. The specific absorption rate obtained from the initial induction heating rate curve was found to be linearly proportional to the square of the alternating magnetic field, which is roughly consistent with the theoretical power loss of magnetic materials in the alternating field.

Processing of bulk nanostructured ceramics

Conventional ceramic forming routes have been adapted for the processing of ∼16 nm, 3 mol% yttria-stabilised zirconia nanopowders leading to the production of ∼99% dense nanostructured ceramics that display average grain sizes as fine as ∼65 nm. The precursor material is in the form of ∼5 vol.% solids content nanosuspensions produced commercially; these can now be concentrated up to ∼37 vol.% whilst retaining the viscosity at ∼0.05 Pa s. A patent application has been submitted related to the process. The concentrated suspensions have then been used to produce granulated powders suitable for dry forming via spray-freeze drying. Whilst powders have been produced that will yield green bodies with densities of ∼50% of theoretical, currently the powders suffer from either poor flow and low fill densities or granules that are too strong to crush during pressing, even at pressures up to 500 MPa. The same suspensions have also been slip cast into extremely homogeneous green bodies with densities of ∼54% of theoretical after drying using a humidity drier. Higher densities are currently blocked by cracking of the samples during drying and/or burn out of the organics if the solids content of the suspensions exceeds ∼20 vol.%. Radiant and hybrid pressureless sintering experiments have been performed on the dry and wet processed green bodies using both conventional single-step and two-step sintering cycles. Whilst densities >98% of theoretical were achievable by all combinations, a nanostructure could only be retained using the two-stage sintering approach. With hybrid heating the average grain sizes for die pressed samples were in the range 70–80 nm whilst for the more homogeneous slip cast samples a final average grain size of just 64 nm was achieved for a body with a final density of ∼99.5%. It is believed that the primary advantage offered by hybrid heating is the ability to use a much faster initial heating rate, 20 °C min −1 versus just 7 °C min −1, without risking damage to the samples. Whilst detailed characterisation of the properties of these nanostructured ceramics has begun, preliminary results have suggested that the toughness is lower and hardness roughly equivalent to submicron grain-sized 3YSZ, although the resistance to wear and hydrothermal ageing may have been improved. As a result of detailed crystallographic characterisation this is believed to be due to a grain size-dependent shift in the phase boundary composition for nanoYSZ ceramics leading to ‘over stabilisation’ at any given yttria content. Current work is focused on investigating the effect of both yttria content and average grain size on the properties of these new materials.

Effect of the Annealing Conditions on the Microstructure and Mechanical Properties of a 0.04% C Al Killed Steel

The present investigation evaluates the effect of static annealing variables on the grain structure and mechanical properties of a 0.04 %C-Al killed steel. The experimental variables selected were the heating rate and the initial heating temperature. The results showed that an increase in the initial heating temperature and heating rates inferior to 500°C and 100°C/h, respectively, do not have a major influence in the grain structure of the material. These annealing conditions lead to a full "pancake" type of microstructure of the recrystallized ferrite grain, and as consequence, the mechanical properties of the material are in the intervals required for deep drawing applications.

Hydrothermal synthesis of a continuous zeolite Beta layer by optimization of time, temperature and heating rate of the precursor mixture

Abstract Highly crystalline zeolite Beta coatings in a range of Si/Al ratios of 12–23 were synthesized on a surface-modified molybdenum substrate by hydrothermal synthesis. The average thickness of the coatings was ca. 2 μm corresponding to a coverage of 2.5 g m−2. The coatings were obtained from a viscous Na, K, and TEAOH containing aluminosilicate precursor mixture with silica sol as reactive silicon source. A mechanism for the in situ growth of zeolite Beta coatings is proposed. According to this mechanism, the deposition of an amorphous gel layer on the substrate surface in the initial stage of the synthesis is an important step for the crystallization of continuous zeolite Beta coatings. The heating rate of the precursor mixture and the synthesis temperature were optimized to control the level of supersaturation and to stimulate the initial formation of a gel layer. At a Si/Al ratio of 23, fast heating and a temperature of 150 °C are required to obtain high coverage, while at a Si/Al ratio of 15, hydrothermal synthesis has to be performed with a slow initial heating rate at 140 °C.

Conversion of programmed-temperature retention indices from one set of conditions to another

In order to make programmed-temperature retention index (PTRI) data be shared by other chromatographers and laboratories, conversion of PTRI from one set of experimental conditions to another is investigated in detail in this work. It was found that the differences between the PTRIs at different heating rates are structurally dependent, especially the number of ring in molecules. Thus, with the help of molecule constitutional descriptors, equations of PTRI conversion to certain initial temperature, heating rate, and stationary phase were obtained with high correlation coefficients and low standard deviations. Calculation errors of PTRI conversion between different heating rates and between different initial temperatures were from 1.1 to 2.9 retention index units (i.u.), which is in the same order with experiment errors. It is well known that reproducibility of PTRI on a polar column is not as good as that on an apolar column because of the apolarity of the n-alkane homologues. Thus, topological descriptors were used for PTRI conversion between two columns with different polar stationary phases, giving better results than those obtained by constitutional descriptors. This shows that topological descriptors could provide more molecular structural information than constitutional descriptors. However, as constitutional descriptor has the advantages of clear physical meaning and very simple calculation, it is our first selection when the PTRI calculation accuracy is satisfied. The method developed is simple in calculation, easy to be performed with high accuracy.

Citrate-Derived Carbon Nanocoatings for Poorly Conducting Cathode: A Detailed Study Using Substrate Materials

Preparation of conductive coatings is an effective way for improvement of kinetics in Li battery materials. Although carbon-based conductive coatings are most often used, they have been studied less systematically than, for example, phosphides or phosphocarbides. In this study we tried to find the most important correlations between the preparation conditions and the resulting composition, morphology, and electrical properties of selected carbon-coated materials. As a model substrate material we mainly used particles while as a carbon precursor we employed citric acid. For comparison, other substrates and precursors were occasionally used. It is shown that in the typical temperature range between and , the carbon yield varies from 3 to %, depending on the initial heating rate and on the duration of heat-treatment. Correlations between the composition, morphology, and the conductivity of final composites are thoroughly discussed. The steep increase in conductivity beyond the percolation threshold (between of carbon) can be correlated with the occurrence of a uniform, thick carbon film that appears to be continuous on a micrometer scale. Finally, we show that the activation energies for conduction in various carbon-coated samples are strikingly similar to those found previously for phosphide- or phosphocarbide-based coatings and even for doped with supervalent ions.

Study of defect levels in CdTe using thermoelectric effect spectroscopy

We have studied the defect levels in as grown and post growth processed cadmium telluride (CdTe) using thermoelectric effect spectroscopy (TEES) and thermally stimulated current (TSC) techniques. We have extracted the thermal energy (Eth) and trapping cross section (σth) for the defect levels using the initial rise and variable heating rate methods. We have identified 10 different defect levels in the crystals. Thermal ionization energy values obtained experimentally were compared to theoretical values of the transition-energy levels of intrinsic and extrinsic defects and defect complexes in CdTe determined by first-principles band-structure calculations. On the basis of this comparison, we have associated the observed ionization levels with various native defects and impurity complexes.

Flux Pinning in RHQT-Processed<tex>$rm Nb_3rm Al$</tex>After Various Transformation Heat Treatments

Jelly-roll Nb-Al strands were rapidly heated and quenched (RHQ) to bcc phase from temperatures around 1900/spl deg/C. Transformation heat treatments were subsequently applied to convert the as-quenched bcc phase into superconducting A15 phase. These heat treatments consisted of a fast ramp (0.5 to 10 min) to 1000/spl deg/C followed by a long hold (10 h) at 800/spl deg/C. Magnetization measurements performed by vibrating sample magnetometry under fields up to 30 T were used to determine the irreversibility field, the upper critical field and the dependence of the critical current density on the field. These properties were all found to be higher for samples with high initial heating rate in the transformation heat treatment. Some variability of the critical current density was observed for samples prepared under apparently the same conditions. The scaling of the bulk pinning force density over temperatures ranging from 4.2 K to 8 K is analyzed.

Pyrolysis of saccharide tobacco ingredients: a TGA–FTIR investigation

Thirteen saccharide tobacco ingredients have been pyrolysed in a thermogravimetric analyser (TGA) under 10% oxygen in nitrogen. The saccharides comprised seven sugars, three cellulosic materials (a cellulose fibre, hydroxypropyl cellulose and carboxymethyl cellulose), starch and two gums (xanthan and acacia). The objective of the study was to measure the formation rates of low molecular weight products that were not detected in a mass spectrometry based system, in particular the formation rates of formaldehyde. A two-stage ramped temperature programme was used that simulated the burning conditions of a smouldering cigarette: an initial heating rate of 0.5 °C s −1 to 300 °C followed by 2.9 °C s −1 from 300 to 900 °C. This was followed by further holding the temperature at 900 °C for 108 s to allow char combustion to occur. The yields of 10 products, selected for their relevance to cigarette smoke and their suitability to be detected by infrared spectrometry, were measured by a Fourier-transform infrared spectrometer (FTIR). The infrared spectra were deconvoluted off-line using a multivariate (target-factor) analysis, which tested the significance of individual hypothetical compounds in the presence of a host of other unknown analytes. The common degradation products monitored from the 13 saccharides were carbon dioxide, carbon monoxide, water and methane. In addition, acetic acid, formaldehyde, acrolein, acetaldehyde, ethanol and furfural were produced from some saccharides but not all. The formation rate for each compound identified was monitored as a function of temperature. Some products were generated in several distinct temperature regions, indicating that more than one mechanism of pyrolysis was operating in a given saccharide. The work has indicated that formaldehyde is generated from the pyrolysis of most of the saccharides in 10% oxygen in nitrogen.

Austenite formation during intercritical annealing

A systematic experimental study has been conducted on ferrite recrystallization and intercritical austenite formation for two low-carbon steels with chemical compositions typically used for dual-phase and transformation-induced plasticity (TRIP) steels. Different initial heating rates, holding temperatures, and times were applied to the materials to examine the ferrite recrystallization and austenite formation kinetics. An Avrami model was developed to describe the isothermal ferrite recrystallization behavior and was applied successfully to the nonisothermal conditions. It was found that the initial heating rate affects the isothermal austenite formation kinetics for both the hot-rolled and cold-rolled materials albeit the effect is more pronounced for the cold-rolled material. This can be attributed to the interaction between the ferrite recrystallization and austenite formation processes. Furthermore, it was found that the distribution of austenite phase is also affected by the ferrite recrystallization process. When ferrite recrystallization is completed before the austenite formation (i.e., under sufficiently slow heating rate conditions), austenite is to a large extent randomly distributed in the ferrite matrix. On the other hand, incomplete recrystallization of ferrite due to higher heating rates leads to the formation of banded austenite grains. It is proposed that this observation is characteristic of simultaneous recrystallization and austenite formation where moving ferrite grain boundaries do not provide suitable sites for austenite nucleation.

Rapid synthesis of silicalite-1 nanocrystals by conventional heating

The effect of room temperature aging on the crystallization rate and size of MFI-type crystals synthesized under high temperature was investigated. First, synthesis mixtures yielding MFI-type zeolite were aged at room temperature for periods of time between 1 and 60 days. This was followed by a rapid synthesis in a pre-heated at 230 °C conventional oven. The utilization of a pre-aged initial systems and high heating rates allowed very rapid synthesis of zeolite. The effect of aging time, crystallization temperature, duration of synthesis and aluminum content on the crystal size and yield was systematically studied. Zeolite nanoparticles with sizes ranging from 130 to 260 nm and relatively narrow particle size distributions were synthesized employing the pure-silica system. The obtained nanocrystals were characterized by X-ray diffraction, scanning electron microscopy, dynamic light scattering and N 2 adsorption measurements.

Influence of transformation heat treatment on microstructure and defects in RHQT-processed Nb/sub 3/Al

Nb-Al jelly-roll composite wires of stoichiometric composition (25 at% Al) have been processed by Rapid Heating-Quenching (RHQ) to temperatures just above the bcc formation reaction. Transformation heat treatments going to 800/spl deg/C and 1000/spl deg/C with various initial heating ramp-up times (from 30 sec to 30 min) and followed by 800/spl deg/C/10 hrs were applied to samples so obtained. The microstructure and planar defect distribution were investigated by transmission electron microscopy; the concentration of planar defects was found to decrease as the initial heating rate is increased. In situ high temperature X-ray diffraction studies were used to investigate the transformation heat treatment. It is proven that less ordering of the bcc solid solution prior to conversion to A15 occurs at high heating rates.

Mortality of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) at grain temperatures ranging from 50°C to 60°C obtained at different rates of heating in a spouted bed

Heat disinfestation of grain has the potential for high market acceptance. However, the technology would be more affordable if less energy was used during the process. The paper explores two interrelated ways in which this could be achieved. The first is to decrease typical grain treatment temperatures, but hold those temperatures without the addition of subsequent energy for a time sufficient for disinfestation. The second is to increase the rate of heating to induce physiological heat shock and thereby bring about faster insect mortality. Using a spouted bed, rates of mortality of the heat-tolerant species Rhyzopertha dominica were determined over a range of grain temperatures from 50°C to 60°C at 12% m.c. The grain temperatures were gained at four rates of heating obtained by using different air inlet temperatures from 80°C to 200°C. From the data, a probit model was developed to predict LT values for five arbitrary immature development stages. At LT 99.9 and above, immature stage 2 was generally found to be the most heat-tolerant stage, while stage 5 was generally the most susceptible. When the initial rate of heating was increased by increasing air inlet temperature from 80°C to 100°C, the time required for a given level of mortality was significantly decreased. While subsequent rate increases had limited further impact on increasing rates of mortality, there was an increase in the efficiency of heating. Furthermore, decreasing the target grain temperature and increasing the treatment period accounted for additional cost savings. For example, at the most rapid rate of heating, grain that reached 60°C required 0.73 min of heat soak for 99.9% mortality and cost a theoretical $2.72/t, while grain that reached 55°C required 23.62 min for the same level of mortality and cost $1.87/t. By 50°C, some 22 h were required, but the theoretical running cost was reduced to $1.25/t. Thus, within practical boundaries, increasing the air inlet temperature or rate of heating, and decreasing the grain target temperature, increases the efficiency of the system and reduces operation costs. With the system used here, obtaining grain at 50°C using air at 200°C was 75% efficient and 80% cheaper than obtaining grain at 60°C using air at 80°C, which was only 18% efficient. An assessment of possible impact on grain quality due to the various heat treatments was also carried out, both initially and after 6 months storage. Using several criteria of germination measurement as a quality indicator, no adverse effects were observed.

Delayed cooling of the Earth’s mantle due to variable thermal conductivity and the formation of a low conductivity zone

The thermal conductivity of mantle materials decreases with higher temperatures and increases with greater pressure due to phonon mechanism, but increases with temperature for radiative transfer. This trade-off attribute allows for the formation of a low conductivity zone (LCZ) within the top thermal boundary layer in mantle convection. We have studied with a two-dimensional (2-D) cartesian model the potential of this low conductivity zone in retarding secular cooling of the mantle for a longer period of time than models with constant thermal conductivity. Using a recently proposed model for thermal conductivity and an adiabatic boundary condition for the bottom of the mantle, we have carried out a set of numerical experiments within the framework of the extended Boussinesq approximation for constant viscosity, depth-dependent thermal expansivity and variable thermal conductivity with surface Rayleigh numbers between around 106 and around 107. We have employed internal heating between two and four times the chondritic level and half-life time values of 2.5 Ga and 5 Ga. The cooling rate of the mantle can be decreased by the feedback interaction between mantle conductivity and internal heating, which gives rise to slower sinking cold currents. The retardation time increases with the strength of radiogenic heating and can be as long as a couple of billion years for high initial heating rates, four times the chondritic value. However, increasing the radiative contribution of the conductivity speeds up the cooling process. The less the radiative contribution is, the more mantle cooling would be retarded. In the course of adiabatic cooling we find the paradoxical situation in which the effective Rayleigh number of the mantle can actually increase with time. We suggest then that, because of the possibilities for the formation of low conductivity zones adjacent to the thermal boundary layers, which bring forth unexpected consequences, mantle thermal conductivity should be considered as a fundamentally important factor in constraining the thermal evolution of both the core and mantle.

Polar coronal jets

We present ultraviolet spectroscopy of polar coronal jets obtained with the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory. They correlate with the Extreme—Ultraviolet Imaging Telescope Fe XII (195Å) and Large Angle Spectrometric Coronagraph white—light jet events. We found that the jets typically undergo two phases: at the first phase the O VI lines show a brief intensity enhancement and narrowing, while the H I Lyα line is not enhanced, and the second phase, about 25 minutes later, when the H I Lyα line shows maximum intensity enhancement and narrowing, while the O VI line is relatively unchanged. We modeled the observable properties of the jets from 1997 August 5, detected at 1.71 R ⊙. We interpret the first phase as the fast, dense centroid of the jet passing by the slit, and the second phase as a passage of cooler, lower density material following the centroid. Possible scenarios of the electron temperature variations needed to account for observed conditions on 1997 August 5 indicate that some heating is required. We computed models of the temperature and nonequilibrium ionization state of an expanding plasma using various forms for the heating rates. We discuss the model results and estimate the initial electron temperature and heating rate required to reproduce the observed O VI ionization state. We also place some constraints on the origin of the jet material based on the inferred plasma properties.

High-resolution thermogravimetric analysis of poly(trimethylene terephthalate) with different molecular weights

Poly(trimethylene terephthalate) samples with different molecular weights and poly(ethylene terephthalate) were investigated by high-resolution thermogravimetry in nitrogen at an auto-stepwise heating rate. The auto-stepwise heating-rate approach consists of two steps. The sample is heated at an initial rate until a weight change begins, and then is heated further at a step rate until the end of this weight change. The two-step sequence of heating is repeated for each weight change encountered. Both the beginning and the end of the weight change are defined as the step on and the step off criteria, of which the corresponding weight-loss rates are decided by the operator. Experiments were performed from ambient temperature to 600°C at an initial heating rate of 50 K/min and three step-heating rates of 0.5 K/min, 1.0 K/min, and 2.0 K/min. The step on (off) criterion used was 2%/min (1%/min). The thermogravimetry and derivative thermogravimetry curves of poly(trimethylene terephthalate) samples obtained from auto-stepwise heating-rate mode indicated a degradation of multiple weight-loss stages. The first small weight-loss stage (weight loss 2∼4%) was highly sensitive to molecular weight. The temperature at the maximum weight-loss rate of this stage increased significantly with molecular weight. The weight loss during this step decreased steadily with increasing molecular weight, and was in good agreement with the value predicted on the basis of complete volatilization of the 1,3-propanediol unit and carbon dioxide devaluated from chain ends and the residual catalysts. For the poly(trimethylene terephthalate) samples with high molecular weight the first small weight-loss stage diminished. Molecular weight also affected the major decomposition process (weight loss 83∼90%). The temperature at the maximum weight-loss rate of the major stage increased slightly with increasing molecular weight. The influence of step-heating rate on the thermal decomposition characteristics was preliminarily investigated. Additionally, the difference among various themogravimetric analysis algorithms was discussed.

Experimental Investigation of the Transformation and Release to Gas Phase of Potassium and Chlorine during Straw Pyrolysis

When straw undergoes thermal treatment the initial process is a pyrolysis at which some K and Cl can be volatilized, and this may result in problems with deposit formation and corrosion of the reactor containment. A laboratory batch reactor was applied to study the release and transformation of K and Cl as a function of temperature, at an initial heating rate of approximately 50 °C/s. To facilitate the interpretation of the batch reactor experiments thermodynamic equilibrium calculations at reducing condition were conducted, and SEM (scanning electron microscopy) and leaching investigations were carried out on straw and char samples. The experiments showed that chlorine was released in two steps, about 60% was released when the temperature increased from 200 to 400 °C and most of the residual chlorine was released between 700 and 900 °C. Below 700 °C no significant potassium release was observe; above that temperature it increased progressively until about 25% potassium release at 1050 °C. During pyrolysi...

The role of char surface structure development in pulverized fuel combustion

The present work is concerned with the effect of different bituminous coal chars pore surface structure on their combustion behavior. The chars were sampled in a semi-industrial coal jet flame of 2.5 MW thermal input. The solid samples from the jet flame were compared with samples tested in an isothermal plug flow reactor. For surface characterization, N 2-adsorption and scanning electron microscopy were applied. Differences in the BET-surface area up to one order of magnitude were observed for char samples collected in both combustion facilities. It was concluded that the larger surface area of the plug flow reactor char samples was due to a micropore structure, which was developed during devolatilization. The higher the initial particle heating rate was, the larger was the micropore structure and thus larger pore surface area resulted. Thus chars were expected to show different intrinsic reactivities. Nevertheless, since the control of internal structure on char consumption decreases as the temperature grows, an attempt was made to model char burnout in the jet flame making use of the kinetic parameters derived from the plug flow reactor experiments. Theoretical burnout curves fit remarkably well the experimental data, revealing that the porous structure may play a minor role in pulverized fuel combustion processes. Diffusive transport and reaction rates were of the same order of magnitude. Thus bulk diffusion may play a significant role, governing the global rate so that the internal porous structure is not significantly involved in the combustion process.

Maize Starch Biphasic Pasting Curves

The pasting of commercial maize starches was found to be a biphasic phenomenon, exhibiting an expected first viscosity peak as well as an unexpected, relatively large second viscosity peak under specific cooking conditions when using a Rapid Visco Analyser (RVA). The second peak formed at long holding times (between 32 and 45 min), holding temperatures within the range of 82 to 95 °C, starch concentrations from 8 to 13% with a wide range of initial heating rates (0·5–10 °C/min) and shear conditions (150–500 rev/min). The second pasting peak is attributed to the formation of complexes between amylose and low levels of lipid present in maize starch. When lipid was partially removed by extraction with methanol-chloroform (1 : 3 v/v), the second pasting peak disappeared. When, however, the starch sample was treated with solvent and the solvent removed by evaporation, the second peak remained, but formed earlier. Increasing the holding temperature gave a slightly higher first viscosity peak, slightly earlier, and led to a decrease in the area and height of the second viscosity peak. Increasing heating rate also led to an earlier, slightly higher first peak and earlier but lower second viscosity peak. Increasing starch concentration led to an increase in height and area of both the first and second peaks and their later occurrence. Increasing shear led to a decrease in height and area of both the first and second peaks and their later appearance.