Isothermal Gradient Research Articles

Carbothermic Reduction of Ilmenite Concentrate with Sodium Carbonate Additive to Produce Iron Granules and High Titania Containing Slag

The influences of heating pattern and sodium carbonate addition on the carbothermic reduction of ilmenite concentrate have been experimentally studied. The experiments were carried out using isothermal–gradient temperature technique between 1000 °C and 1500 °C with different temperature profiles for a total reduction time between 110 and 160 min. The sodium carbonate was varied between 0 to 60 wt%. It was found that the temperature profile and sodium carbonate addition play an important role on the separation between metallic iron granule and titania rich slag. The optimum condition was achieved at initial and final reduction temperatures of 1300 °C and 1500 °C, respectively, with sodium carbonate addition of 30 wt%. At the optimum condition, the iron recovery was 97.1% and the solidified slag contained titanium pentoxide (Ti3O5), anatase (TiO2), and sodium titanium dioxide.

Iron nugget formation from iron sand/coal composite pellets under isothermal-temperature gradient profiles

ABSTRACT An iron sand concentrate was mixed with coal as the reductant and binder to produce a composite pellet by a mini rotating disc. The pellet was inserted into an alumina crucible and coal was added to maintain the reducing environment by covering the whole surface of the pellet. The reduction was carried out under the isothermal and temperature gradient profile in a muffle furnace where the starting temperature was isothermal at 1000°C, increased with a heating rate of 6.33°C min−1 to a final temperature of 1380°C. The results show that the total iron content increased from 46.9% in the initial pellet to 72.5% in the reduced pellet. The iron nugget formed on the surface of the reduced pellet at 1380°C. The nugget primarily consisted of iron, and the slag mostly consisted of anatase or brookite. The titanium content increased from 4.8% in the initial pellet to 24.4% in the slag.

Particle-water interactions of bismuth under simulated estuarine conditions

Although the production and usage of bismuth (Bi) have been increasing, very little is known about the environmental behaviour of this heavy metal. In the present study, the particle-water interactions of Bi are examined under controlled conditions in which the metal is added as a tracer to estuarine sediment suspended in different, environmentally-relevant aqueous solutions. Adsorption isotherms were always linear over the Bi concentration range employed (up to 2000 μg L−1) and sediment-water distribution coefficients derived from isotherm gradients, KD (L kg−1), displayed an inverse dependence on pH in river water (and ranging from KD = 106,000 L kg−1 at pH 5.0 to KD = 17,700 L kg−1 at pH 9.0) that were consistent with the adsorption of hydroxo-complexes to the sediment surface. Higher adsorption in ultra-pure water of the same pH as river water and an order of magnitude increase in adsorption in seawater at pH 8.0 (KD = 1,530,000 L kg−1) and 0.7 M NaNO3 at pH 6.5 (KD = 4,290,000 L kg−1), however, required the presence of additional species or processes that are likely related to organic complexation of the metal. Thus, experiments conducted in mixtures of river water and seawater in the absence of sediment suggested that Bi may also be bound to colloidal organic molecules that undergo flocculation and salting out on estuarine mixing. Compared with other metals studied under similar conditions, Bi displays a high reactivity towards sediment particles and is, therefore, predicted to be retained in estuaries to a significant extent from catchment sources.

Change of microstructure and properties of dual titanium alloy join interface in hot working history

In order to get workpiece with high tensile stresses in bore region and high temperature duration, creep strength in outskirts, the dual alloy samples made of high temperature titanium alloy Ti60 and high strength titanium alloy Ti6246 had been joined by inertia friction welding(IFW). Then these samples were isothermal forged at 9400c and 9750c, and different heat treatment followed. Changes of microstructure and properties of dual titanium alloy join interface in hot working history were examined at this article. The results show equiaxed α structure varied into basketweave structureat at as-welded join interface, especially a character of widmannstaten structure emerged from Ti6246 alloy side heat effect region, after gradient heat treatment. Immersed ultrasonic testing prove deformation can availably eliminate weld defect through metal on two side of weld line deeper embedding each other. The results of properties test also show the join strength of dual titanium alloy through isothermal deformation and gradient heat treatment are better than that of as-welded samples. Tensile strength, yield strength, elongating rate, reduction in area of sample at 5500c also increase 51 to145 MPa, 37 to 101 MPa, 1.6% to 5.3%, 15.3% to 3.3% than that of as-welded samples respectively. The rupture life of Ti60/Ti6246 dual titanium samples with join interface can sustain to go beyond 100 hours at 5500c and 320 PMa stress.

FEM thermal analysis of high power GaN-on-diamond HEMTs * * Project supported by the National Natural Science Foundation of China (Nos. 60876042, 61176018, 61627812).

A three-dimensional thermal analysis of GaN HEMTs on diamond substrate is investigated using the finite element method. The diamond substrate thickness, area and shape, transition layer thickness and thermal conductivity of the transition layer are considered and treated appropriately in the numerical simulation. The temperature distribution and heat spreading paths are investigated under different conditions and the results indicate that the existence of the transition layer causes an increase in the channel temperature and the thickness, area and shape of the diamond substrate have certain impacts on the channel temperature too. Channel temperature reduces with increasing diamond substrate thickness and area but with a decreasing trend, which can be explained by the saturation effects of the diamond substrate. The shape of diamond substrate also affects the temperature performance of GaN HEMTs, therefore, to achieve a favorable heat dissipation effect with the settled diamond substrate area, the shape should contain as many isothermal curves as possible when the isothermal gradient is constant. The study of the thermal properties of GaN on diamond substrate is useful for the prediction of heating of high power GaN HEMTs devices and optimal designs of an efficient heat spreader for GaN HEMTs.

Simulation of Polymer Crystallization under Isothermal and Temperature Gradient Conditions Using Particle Level Set Method

Morphological models for polymer crystallization under isothermal and temperature gradient conditions with a particle level set method are proposed. In these models, the particle level set method is used to improve the accuracy in studying crystal interaction. The predicted development of crystallinity during crystallization under quiescent isothermal condition by our model is reanalyzed with the Avrami model, and good agreement between the predicted and theoretical values is observed. In the temperature gradient, the computer simulation results with our model are consistent with the experiment results in the literature.

Small Creep Crack Growth Interacting with Microstructural and Mechanical Factors in a Polycrystalline Ni-Based Superalloy

Behavior of small crack propagation during creep was studied, in comparison with that of physically long crack propagation behavior, based on non-linear fracture mechanics approach. Through the work special attention is paid to understand: (1) microstructural aspect on small creep crack propagation interacting with grain boundaries and dendrite boundaries, (2) difference between small and macroscopic long creep cracks, (3) role(s) of stress concentration and relaxation with creep time in the crack propagation behavior emanating from a notch introduced as a simulation of cooling holes in blades and vane applications. From the experimental results, a specific crack growth behavior was found at the beginning of early crack growth stage (small crack), where the crack growth rate decreased with increasing Jc,st under both the isothermal creep (ITC) and thermal gradient creep (TGC). Also, crack under the TGC showed different crack growth rate than that under the ITC condition, where the higher and lower rates were achieved at lower and higher temperature side, respectively, under a given value of Jc,st.

32. Assessing the performance of a novel cryosurgical platform

The cryogens employed in current cryosurgical devices are almost exclusively a gas, typically argon, undergoing Joule–Thomson (JT) cooling. These devices utilize small diameter probes with near instantaneous ice generation. The effective cryoablation zone, however, is small thus requiring multiple probes and/or multiple freeze and extended freeze application intervals to provide a given size cryolesion. In contrast, liquid nitrogen systems provide high levels of heat extraction with low nadir temperatures, but given its boiling point (−197 °C) and ratio of thermal expansion, probe sizes are often larger and procedure durations longer. Recently, we have developed a novel cryosurgical platform utilizing nitrogen in the super critical state (SCN). In this study, we conducted a quantitative comparison of the performance of the SCN system to that of a JT device. Evaluation of the isothermal gradient generated during the freeze procedure was assessed with thermocouple arrays in various tissue approximations such as water, ultrasound gel, and porcine muscle sections. Additionally, a series of feasibility in vivo studies were conducted to assess the performance of the SCN system for endocardial and epicardial ablation applications in a canine model. The data revealed that the SCN system created significantly colder nadir temperatures (−170 °C as compared to −140 °C) and broader spread of critical isotherms compared to that of the JT system. Further, it was found that the SCN generated this larger and colder iceball in approximately half the time. In a comparison of surface freezing in an ex vivo porcine tissue model (5–10 mm thick muscle) under thermal load to model epicardial cardiac ablation, it was found that the SCN platform created transmural lesions that were colder and narrower than that created by JT devices. In vivo endocardial cardiac ablation canine studies revealed that the SCN system was capable of generating transmural lesions with complete electrical block in fully beating heart in ⩽60 s. The results of these studies demonstrated the SCN system provides for rapid, effective, controllable freezing of targeted tissue. The use of the SCN system allowed for the miniaturization and speed of JT devices, yet maintains the ultra cold nadir temperatures and cooling potential of a liquid nitrogen system. The power, speed and freeze characteristics of the SCN system offers the potential of a reduction in procedural time compared to current cryo devices. Further, these technological developments may open new avenues for the application of cryo to treat other cardiac arrhythmogenic disorders.

Effect of temperature gradient and sulfur dioxide addition on erosion – corrosion of iron- and nickelbased alloys

In this study, high temperature erosion – corrosion with trace amounts of added SO2 and the role of isothermal or thermal gradient conditions are studied. The studies are focused on 304L as the model material, but results for other alloys (Alloy 625 and 9Cr1Mo – steel) are also included to support the results and trends observed. The experiments include 550°C exposures in the erosion – corrosion rig under isothermal and thermal gradient conditions. The internal cooling used to create the thermal gradient meant that the 550°C material temperature could be maintained, despite of the higher bed temperature of 750°C. Laboratory oxidation experiments in a similar environment are also included as reference tests. The evaluation of material degradation was done by using a combination of different techniques such as scanning electron microscopy (SEM) including X-ray microanalyses, Auger and X-ray electron spectroscopy. The results demonstrate three important aspects related to erosion – corrosion attack in fluidized bed combustion. First, provided oxide growth is rapid enough leading to thickness in the micrometer range, low material wastage is obtained as demonstrated for the 9Cr1Mo– steel and also for the 304L and Alloy 625 materials when exposed to air plus 50 ppm added SO2 in isothermal conditions. Because of the large catalytic surface in the test rig for the thermodynamically favored oxidation of SO2 in air, significant presence of SO3 is expected. The material wastage is then also associated with a shift in erosion pattern with maximum material wastage at the impact of erodent (called type B). Detailed microstructure investigation of oxide in question on the 304L showed that the inner part of the oxide then is dense and possibly isolated from the environment and also Cr-rich. Adding a temperature gradient then returns the wastage pattern to type A for both 304L and Alloy 625 and leads to increased wastage for the former material. The resulting oxide thickness is also smaller and always less than 0.2 µm. The laboratory reference tests showed a similar range of average oxide thickness for air and air plus SO2. However, in air plus 50 ppm SO2 the tendency for break away corrosion on 304L was less than for air exposed samples.

Binary chromatographic retention times from perturbations in flowrate and composition

This work is a theoretical and experimental investigation of the binary retention time (t step) when the disturbance is made to a chromatographic system by adding a small flow of one of the pure components. The established theory is for addition of a pulse: in this case, the retention time (t pulse) depends on the two binary isotherm gradients, and should be independent of the choice of pulse gas. From the column material balance, the value of t step also depends on the column pressure drop and perturbation gas—the value of t step should always be greater for the more-adsorbed component. The theory has been validated from results on the nitrogen–argon–5A zeolite system at 25, 54 and 81 °C. For a 50% mixture at 25 °C with a column pressure drop of 0.1 bar, the values of t step are 257 and 254 seconds for the nitrogen and argon perturbations. The values of t step are different because addition of the perturbation flow causes a very small increase in average column pressure (about 0.5 mbar), which causes the binary isotherm gradients to be measured in (slightly) different directions along the isotherm surface. The intention is to determine the value of t step for the case of a zero change in the average column pressure: experimentally, this would require a column with a zero pressure drop. The material balance shows that t step for a column with a zero pressure drop is obtained from a simple weighted function of the values of t step for the two pure-component perturbations. Accurate determination is essential because the “zero pressure drop” values are used to determine binary adsorption isotherms which are, of course, at a fixed pressure.

Chromatographic Detectors in Systems of Three Components

The chromatographic theory for the adsorption in binary systems has been well-established over the years. A binary mixture of known composition flows through a column packed with adsorbent. The system is then disturbed by adding a pulse of one of the pure components, and this causes a composition front to travel through the column. The retention time of this composition front is measured with a detector. This retention time can be related to the isotherm gradients of the two components. The situation is more complicated for a system of three components. In this case there are two composition fronts, and it is not easy to relate the retention times to the three isotherm gradients. In this preliminary investigation, we present a new theory to show how by using another composition detector, it is possible to evaluate the composition retention time for each component. We present some data for the ethane-ethylene-helium-13X zeolite system, and show that a simple detector based on the measurement of viscosity might be suitable.

Compositional Grading—Theory and Practice

Summary This paper quantifies the potential variation in composition and pressure/volume/temperature (PVT) properties with depth owing to gravity, chemical, and thermal forces. A wide range of reservoir fluid systems has been studied using all of the known published models for thermal diffusion in the nonisothermal mass-transport problem. Previous studies dealing with the combined effects of gravity and vertical thermal gradients on compositional grading have been either (1) of a theoretical nature, without examples from reservoir fluid systems, or (2) proposing one particular thermal-diffusion model, usually for a specific reservoir, without comparing the results with other thermal-diffusion models. We give a short review of gravity/nonisothermal models published to date. In particular, we show quantitative differences in the various models for a wide range of reservoir fluid systems. Solution algorithms and numerical stability problems are discussed for the nonisothermal models that require numerical discretization, unlike the exact analytical solution of the isothermal gradient problem. We discuss the problems related to fluid initialization in reservoir models of complex fluid systems. This involves the synthesis of measured sample data and theoretical models. Specific recommendations are given for interpolation and extrapolation of vertical compositional gradients. The importance of dewpoint on the estimation of a gas/oil contact (GOC) is emphasized, particularly for newly discovered reservoirs in which only gas samples are available and the reservoirs are near-saturated. Finally, we present two field case histories—one in which the isothermal gravity/chemical equilibrium model describes measured compositional gradients in a reservoir grading continuously from a rich gas condensate to a volatile oil, and another example in which the isothermal model is grossly inconsistent with measured data and convection or thermal diffusion has apparently resulted in a more-or-less constant composition over a vertical column of some 5,000 ft.

Molecular Orientation in Langmuir Monolayers Containing the [M(dmit)2]n-Anion Determined from Surface Pressure and Surface Potential Isotherms

The behavior of three dmit containing semiamphiphilic salts ([Ni(dmit)2][DDI]2, [Ni(dmit)2][DDI], [Pd(dmit)2][DDI]2) has been investigated in detail at the air−water interface. An osmotic equation of state was fitted to the liquid expanded regions of the π−A isotherms, while the surface potential isotherms were analyzed using the Helmholtz equation (HE). A molecular orientation was proposed for each material based on the cross-sectional areas calculated from the equation of state, and these were consistent with the apparent dipole moments calculated from the HE. The behavior of the palladium salt was found to differ from that of the two nickel salts, with plots of isotherm gradient against water content being coincident for the nickel salts but not so for the palladium containing material. This was explained as being due to the almost identical lipid−lipid Lucassen−Reynders (LR) interaction coefficients calculated for the two nickel salts, which differed significantly from the coefficient calculated for t...

Investigation of Thermal Degradation of Solids in an Isothermal, Gradient Free Reactor

In the past, dynamic methods, e.g., thermogravimetry, have been developed for investigating thermal degradation reactions of solids and for determining parameters of overall rate expressions. In thermogravimetry, temperature gradients occur in the decomposing sample due to the nonstationary heat transfer to the sample. The temperature profile within the sample is dependent on the thermal properties of the sample, the sample size, as well as the heating rate. The nonhomogeneous temperature within the sample causes nonhomogeneous reaction rates, viz., faster reactions in regions of higher temperatures. Therefore, thermogravimetric analysis of thermal decomposition reactions refers more or less to sample-averaged reaction rates. Homogeneous temperatures within the decomposing sample are achieved only under isothermal conditions. In thermogravimetry these can be approximated, applying very low heating rates. This general draw back of thermogravimetry necessitates the validation of kinetic parameters for thermal decomposition of solids obtained from thermogravimetry by comparison with results from isothermal measurements. To measure thermal degradation of solids or liquids under isothermal conditions, an isothermal gradient free reactor (closed loop type reactor) with evolved gas analysis by means of on-line mass spectrometry has been developed in this work. With proper design of the reactor, the heating time of the sample and the free reactor volume are minimized. With the help of the mass spectrometric data, the degree of conversion is determined which enables the calculation of the formal kinetic parameters of the degradation reaction under investigation. Validation of the method is performed by investigating the decarboxylation of malonic acid. Finally, the formal kinetic data of polyamide 6 degradation from thermogravimetry are compared with the date from the isothermal method.

PHASES MODEL FOR BINARY-CONSTITUENT SOLID-LIQUID PHASE TRANSITION, PART 1: NUMERICAL METHOD

Abstract A PHASES (PHysicat Algorithm for Species-Energy Simulation) model was developed for applications to binary-constituent solid-liquid phase-transition problems. A control-volume-based finite-element formulation of the mixture continuum equations was employed in the solid, melt, and liquid regions. An implicit enthalpy-based procedure solved the species and energy conservation equations in conjunction with a phase iteration procedure and the binary phase diagram. The coupled multiphase mass-momentum equation set was solved with a simultaneous colocated variable technique. In this approach, the multiphase pressure-velocity coupling was completed by an implicit closure of the conservation and integration point mass-momentum transport equations instead of a segregated approach. In addition, a diffusion-based nonequilibrium model and an isotherm gradient (IG) procedure were developed for the simulation of nonequilibrium and interdendritic anisotropic conditions during phase transition.

A Model for Chemical Vapor Infiltration of Fibrous Substrates

AbstractA model is presented for CVI of a fibrous preform under isothermal and thermal gradient conditions. Transport and geometric properties during densification are calculated from a novel structural model, allowing prediction of deposition profiles and experimentally observed trends without the use of empiricism.

Surface area estimation from the adsorption isotherm gradient at the linear portion by n-butylbenzene vapour

Using n-butylbenzene vapour having a comparatively low saturation pressure (0.160 Torr at 0°C), small solid surface areas could be measured from the gradient of the linear portion of the Type II adsorption isotherms which were found for most solid adsorbents. In this “gradient method”, surface areas were obtained from the monolayer volumes equated directly to the gradient values [d v/d( P/ P s); where v is the amount adsorbed, and P/ P s is the relative pressure] and the molecular cross section (0.443 nm 2) of the adsorbate calculated from the liquid density. The surface areas thus obtained agreed with the standard BET-N 2 surface areas, with a difference of about ±20% for over 20 solid powder samples. The gradient method for the plate-like solid samples of glass plates and aluminium foil resulted in a slight overestimation of +3% and +12% compared with the geometrical areas; this was reasonable, considering the remaining surface porosity of the sample. The gradient method using n-butylbenzene vapour as well as toluene and ethylbenzene vapours, which have been reported previously, was ascertained to be useful for surface area estimation, especially for very small surface areas, because of the extremely low adsorbate pressure at room temperature.

Sorption and desorption of cobalt by soils and soil components

SUMMARYThe sorption of Co by individual soil components was studied at solution Co concentrations that were within the range found in natural soil solutions. Soil‐derived oxide materials sorbed by far the greatest amounts of Co although substantial amounts were also sorbed by organic materials (humic and fulvic acids). Clay minerals and non‐pedogenic iron and manganese oxides sorbed relatively little Co. It is considered that clay minerals are unlikely to have a significant influence on the sorption of Co by whole soils.Cobalt sorbed by soil oxide material was not readily desorbed back into solution and, in addition, rapidly became non‐isotopically exchangeable with solution Co. In contrast, Co was relatively easily desorbed from humic acid and a large proportion of the Co sorbed by humic acid remained isotopically exchangeable. Cobalt sorbed by montmorillonite was more easily desorbed than that sorbed by soil oxide but less easily than that sorbed by humic acid.Cobalt sorption isotherms for whole soils at low site coverage were essentially linear and the gradients of isotherms increased with pH. A comparison of isotherm gradients for whole soils and individual soil components supported the suggestion that Co sorption in whole soils is largely controlled by soil oxide materials.

Adsorption of toluene vapor on glass plates and surface area estimation from the adsorption isotherm gradient at the linear portion

In order to evaluate a novel method for estimating solid surface areaas from the adsorption isotherm gradient at the linear portion of type II isotherms, the adsorption of toluene on glass plates having a geometrical surface area of 1152 cm 2 at 0° and 10°C was studied. The almost constant isotherm gradient value ( dv d ( P P s ), v : amount adsorbed) in a relative pressure ( P P s ) region from 0.15 to 0.45, as well as in the cases of aluminum foil and mica plates, showed a good fit with the monolayer capacity calculated using the average, proper molecular cross section of toluene. For various materials whose geometrical surface area were not known, the standard BET areas were compared with the areas estimated from the isotherm gradient of toluene adsorption and their reasonable agreement suggested the usefulness of the gradient method for the surface area estimation. Based on these results a theoretical basis and conditions for the use of the method were discussed by considering an alternative two-dimensional gas model on the low-energy adsorption surface. In addition, a small type B hysteresis found in the region of low relative pressure and at submonolayer adsorption on the glass plate sample pile was reported.

Liquid Diffusion in Fibrous Insulation

Vapor condensation in insulated structures degrades their physical properties as well as thermal performance. Motion of the condensate within the insulation is a crucial factor in analyzing annual moisture retention in building shells. The diffusion of liquid can be caused by several driving potentials. A model for isothermal liquid transport in fibrous insulation is presented. The model relates liquid diffusion to the characteristics of the insulation. These are identified as void-fraction and its spatial distribution, mean fiber radius, directionally index, and tortuousity factor. Due to the anisotropic layered structure of the fiberglass insulation, liquid diffusion along the three principal directions are studied. The diffusion of liquid from one layer to the next is controlled by liquid diffusion along the layers and the tortuosity factor. Diffusion along the layers is caused by the suction potential and retarded by the viscous forces. By balancing the suction and the viscous forces, a model for transient diffusion in terms of the five medium properties is obtained. An electrical resistance probe for in-situ measurement of liquid content in insulation samples of high voidage has been developed. Data on liquid diffusion under isothermal concentration gradients for commercial fiberglass insulations have been acquired. The experimental data show consistent agreement with the model predictions.