Molten Phase Research Articles

Kinetics of thermal dehydration and decomposition of Fe(III) chloride hydrate (FeCl3·xH 2O)

Fe(III) chloride hydrate (FeCl3·xH2O) undergoes simultaneous dehydration and dehydrochlorination from its molten phase in the temperature range 100–200‡C. The kinetics of these two parallel thermal processes has been studied by both isothermal and non-isothermal methods. Whereas for the dehydration reaction at temperature below 125‡C a second order rate model (F2) fits well, a three-dimensional diffusion (D3) model is found to fit better at temperature above 135‡C. For the dehydrochlorination reaction an interface growth controlled model of 1/3 order (F 1/3) appears to be the most suitable over a wide range of reaction. Dynamic thermogravimetry reveals two major steps in the temperature range 50–250‡C. The first step which corresponds to the loss of about 4 mols of H2O, invariably follows second order kinetics (F2). The second step which is predominantly a process of dehydrochlorination, generally fits mixed diffusion controlled models due to the overlapping with the dehydration process. There is an excellent agreement in results among the isothermal and non-isothermal methods of determining kinetic parameters.

Role of molten phase content of deposits for high-temperature corrosion in waste incineration environment

The effect of the physical properties of boiler tube deposits on high-temperature corrosion of heat-resistant alloys was quantitatively examined to clarify the corrosion mechanism and to establish the most appropriate laboratory test method for the waste incineration environment. Laboratory corrosion tests were conducted in a simulated incinerator gas on four alloys. A crucible method was compared with a coating method at 550°C using synthetic deposits composed of NaCl/KCl/Na2SO4 = 1/1/1 mole containing various amounts of alumina, that was intended to control molten phase content in the deposits (MPC). The tests were conducted with deposits from two working plants. These deposits were found to be low in MPC. In the crucible method, a bell-shaped change of corrosion mass loss was observed for all the alloys. The change is thought to be due to a competitive effect of increase in MPC. The increase in MPC accelerates and depresses the corrosion because the molten phase is aggressive but hinders gas-permeation. In the coating method, a bell-shaped change was observed only in limited cases, probably because the deposit layer is so thin that it does not hinder gas permeation at any MPC. The crucible method is thought to be more appropriate for a low MPC environment as seen in the waste incinerator, because it is more aggressive and less disturbed by changes in the condition of deposit during tests.

Effect of Alkali Metal Oxide Addition on Crystallization and Phase Transformation of Sintered Spherical Silica

A compact of spherical silica with alkali metal oxide addition was fired within a temperature range from 600 to 1200°C for 6h in air. The crystallization and phase transformation behavior of sintered spherical silica were examined by XRD, IR, DTA, density and shrinkage measurements and SEM. The following results were obtained. (1) The silica phases formed in the sintered compacts depended on the kind and amount of added alkali metal oxide and on the firing temperature. (2) The phase transformation behavior of sintered spherical silica proceeded as follows: amorphous silica→keatite→quartz→cristobalite→tridymite. (3) Through SEM observation, it was found that molten phase formed in the sintered compacts with alkali metal oxide. The molten phase is hypothesized to be a factor determining the crystallization and phase transformation of sintered spherical silica.

A Mathematical Model for the Reduction Kinetics of Iron Oxide in Electric Furnace Slags by Graphite Injection.

A three-phase, solid-gas-liquid, reactive jet is mathematically modeled in time domain for the injecting operation of graphite particles in complex electric furnace steelmaking slags to reduce the iron oxide contents. The model takes into account the jet penetration in the liquid, the physical changes that the slag suffers due to chemical composition variations, the surface active effects of silica in molten slags and the coupling-uncoupling flow characteristics between the carrier gas and the solid particles in the molten phase. The mathematical simulations indicate that at small particle sizes (100-150 μm) the reaction kinetics is controlled by the gas-melt interface, under this regime acid slags show higher reduction rates than basic ones. At larger sizes this reaction is controlled by the mass transfer of iron oxide from the bulk phase to the gas-melt interface and basic slags show higher reduction rates than acid ones. To obtain a given reduction rate of iron oxide there is an optimum particle size at which the consumption rate of the reducing agent is minimum. Below this size the particle is consumed by the reaction without reaching high efficiencies. Above this minimum the particle size is so large that it exits the molten bath only partially reached decreasing also the efficiency of the reaction. Just at this minimum the particle is totally consumed by the reaction with a minimum consumption rate of the reducing agent.

Does the Latent Track Occurrence in Amorphous Materials Result from a Transient Thermal Process?

ABSTRACTHeavy ion irradiations in the electronic stopping power (Se.) regime have been performed in amorphous materials. Latent tracks have been observed in amorphous semiconductors (a-Ge, a-Si) and their radii have been deduced from a phenomenological analysis in an amorphous metallic alloy, in vitreous silica and “polymer” like amorphous carbon. A transient thermal model is developed describing the energy diffusion by the electron gas, by the atomic lattice and the energy exchange between the two subsystems. According to Fick's law, the classical equations of heat flow in the two subsystems (electrons and atoms) are numerically solved in a cylindrical geometry taking into account the temperature dependence of all the parameters. A simulation of annealing of nuclear collisions induced defects in crystalline iron allows to determine a local temperature. Electronic defect creation occurs when Se. increases and becomes larger than a threshold which is correlated with the appearance of a molten phase. Using such a criterion, the radii of latent tracks are reproduced in both a - Ge and a - Si with the same value of the electron-phonon coupling despite large differences in their lattice thermodynamic parameters. Such a model is applied to amorphous metallic alloy Fe85B15, vitreous silica and amorphous carbon.

Modification of poly(vinyl alcohol) with aliphatic and aromatic epoxides in the molten phase

A new method for improving the processability and thermal stability of commercially available poly(vinyl alcohol) is presented involving the reaction of the hydroxyl group on the polymer backbone with long-chain aliphatic, cycloaliphatic, and aromatic epoxides. The reaction was performed in the molten phase using a laboratory-scale thermostated reactor. As expected, the extent of the reaction varied with the chemical structure of the epoxide, the properties of polymers obtained being dependent on the amount of the incorporated side group. Specifically, the reactivity of long aliphatic chain epoxides was low and the polymers obtained exhibited a small decrease in the melting points, being directly proportional to the length of the aliphatic chain. They displayed, however, improvement in thermal stability compared to the parent polymer. Cyclohexene oxide was appreciably more reactive and it exhibited a larger melting point reduction and satisfactory thermal stability. Polymers functionalized with aromatic rings and prepared under the same conditions were mostly amorphous, not showing melting point transition or improvement in their thermal stability. Finally, the reactions with aliphatic epoxides were catalyzed with phosphoric acid and the modified polymer exhibited a large decrease in the melting point but not a concomitant improvement in thermal stability.

Modification of poly(vinyl alcohol) with aliphatic and aromatic epoxides in the molten phase

Modification of poly(vinyl alcohol) with aliphatic and aromatic epoxides in the molten phase

Role of environment deposits and operating surface temperature in spallation of air plasma sprayed thermal barrier coatings

Spallation of air plasma sprayed (APS) thermal barrier coatings (TBCs) was investigated on power generation combustors, military turboshaft engines, and commercial turboprop engines. In each case, irrespective of operating conditions or geographic location, spallation was linked to the presence and infiltration of high temperature molten phases of similar composition. Electron microprobe analysis found that, from all the possible oxides available in the external environment, only CaO, MgO, Al 2O 3 and SiO 2 (CMAS) are incorporated in the molten phase that infiltrates the TBC microstructure. Fe and Ni oxides from metallic components and zirconia and yttria from the TBC were also found in varying amounts in the molten phase. The melting and recrystallization behavior of CMAS deposits was carefully defined by differential thermal analysis.

Theoretical and Experimental Investigations of the Melting of Pellets in Co-Rotating Twin-Screw Extruders

Abstract Knowledge of the plasticizing behavior in tightly intermeshing, co-rotating twin-screw extruders is of crucial importance for assessing the compounding process. Experiments were conducted on a laboratory extruder in order to establish the parameters that influence the melting process. Solidified samples of material were taken from the screw and microtome cuts produced from the plasticizing section. These were then assessed on the basis of image analysis. This visualization of the solid and molten phases which are present simultaneously together with the distribution of the two phases made it possible to quantify the reduction that occurs in the amount of solid material over the length of the screw configuration employed. A model is additionally presented for the calculation of the melting lengths and the melting profiles. This works on the basis of individual particles which are uniformly dispersed in the polymer melt. Allowance is made for the temperature increase in the solid material conveying section. A comparison of calculated and experimentally determined melting lengths revealed a satisfactory level of agreement.

Atomic and cluster ion bombardment in the electronic stopping power regime: A thermal spike description

A brief review of experimental results of defect creation in metallic materials supports the assumption that the electron-phonon coupling is the main physical parameter which determines their sensitivity against the irradiation in the electronic stopping power ( dE dx ) regime. Following this idea the thermal spike model is developed using a numerical solution of two coupled equations describing the energy diffusion on the electrons and on the lattice atoms respectively and their coupling. Assuming that the experimental observations may be interpreted by a rapid quench of the induced molten phase, radii of latent tracks in Ti and Zr irradiated by atomic and cluster ions will be calculated and compared to experimental results with quite a good agreement.

Low-fluence excimer laser irradiation-induced defect formation in indium-tin oxide films

DC sputtered indium-tin oxide (ITO) films of 500 nm thickness are irradiated with single pulses of fluences between 190 and 510 mJ/cm2 from a KrF excimer laser. The irradiation induced changes in optical spectra are consistently described through the behaviour of four (Gaussian-like) absorption bands at 0.7, 1.0, 1.6 and 2.6 eV. Being absent in the original films and emerging at fluences exceeding 300 mJ/cm2, the 2.6 eV contribution is most characteristic to excimer laser processing. X-ray photoelectron spectroscopic analysis suggests that the irradiation-induced changes should be associated with oxygen displacement within the atomic network rather than surface reduction via oxygen removal. Thermal model calculations reveal that the principal effect of single pulse processing in this fluence domain is deep melting of the films. Defects created during molten phase resolidification are assumed to be responsible for the irradiation-induced changes in the short range chemical structure of the films.

Production control of metal alloys by laser spectroscopy of the molten metals. Part I. Preliminary investigations

After a short up-to-date survey of the method elaborated for chemical analysis of molten metals, the reason for the choice of time resolved laser induced spectroscopy (TRELIBS) is given. By means of a Nd:YAG laser and a double monochromator, the time resolved spectrum of the solid and molten aluminium alloys is detected using a photodiode array. According to the data obtained for the analytical performance, analysis in the molten phase can be done with sufficient accuracy and precision compared to the solid phase, without time loss for sample taking and preparation. Within the framework of the preliminary investigations, the fundamental analytical characteristics of the laser induced plasma are investigated (dependence of background (BG) and line/BG ratio on the atmosphere, state of the material, delay and gate time, the occurrence of self absorption and wavelength shift). The use of an argon atmosphere, relative line intensities (if possible, spectral lines of equal ionization state and excitation potentials should be near to each other) and an individual delay/gate time optimum can be recommended.

Crystal Structure and Hydrogen-Bonding Characteristics of N,N-Bis(3,5-dimethyl-2-hydroxybenzyl)methylamine, A Benzoxazine Dimer

The X-ray crystal structure of N,N-bis(3,5-dimethyl-2-hydroxybenzyl)methylamine as a model dimer for benzoxazine-based phenolic resins is presented, and a hydrogen-bonding scheme involving both inter- and intramolecular hydrogen bonding is proposed. Hydrogen bonding of this model dimer is further studied with Fourier transform infrared (FT-IR) spectroscopy in crystalline, quenched, and molten phases as well as in solution. Additional hydrogen-bonding schemes are proposed. These results are compared to results obtained from molecular modeling using a model dimer with a tert-butyl functionality. The preferred conformations of methyl functional trimers are modeled based on preferred dimer conformations.

Alternating current conductivity of solid and liquid phases in the tin diiodide-silver diiodide system

Electrical conductivity was measured in the solid and molten Snl2-Agl system between 70 and 85 mol% Agl. High conductivity and a broad region of solid solubility, placed between 80 mol%, 75 mol% and about 40 mol% Agl and 635.8, 380 and 559.8 K, respectively, was confirmed. The addition of the Snl2 to the molten Agl is accompanied by a decrease in the electrical conductivity and an increase in the activation energy. Temperature dependences of the specific conductivity indicate a similarity between molten mixtures and solid superionic phases.

Auto-processing of very fine-scale composite materials by chaotic mixing of melts

A processing technique is presented in which very fine fibres or lamellae emerge from single or multiple, molten, discrete phase precursors contained within a continuous molten phase as a result of three-dimensional chaotic mixing. Conditions for chaotic mixing in a previously uninvestigated cylindrical cavity were established experimentally and numerically with glycerin as a surrogate fluid. Chaotic mixing was then induced within a similar cavity to produce polymeric composites. Optical micrographs of the solidified emergent structures are provided and the association between the fine-scale microstructures and the chaotic mixing process is presented. The results suggest opportunities to produce a variety of very fine-scale composite structures by alternative means.

An Overview on Manganese Alloy Production and Related Fundamental Research in South Africa

South Africa is a major player in the world of manganese. It has about 82% of the worlds manganese ore reserves. It also produces about 19% of manganese ore and about 10% of ferromanganese and ferrosilicomanganese alloys of the total world production. On the other hand, South Africa produces about 51% of the world's electrolytic manganese metal. Ferromanganese and ferrosilicomanganese are produced in submerged and electric furnaces using carbon as the reductant, yielding more or less a carbon saturated alloy. In certain cases the ore is sintered prior to smelting. The Pyrometallurgy Research Group at the University of the Witwatersrand has concentrated its research efforts on problems associated with ferroalloy production. The research on manganese can be summarized in three groups. The first group involves studies on solid-state carbothermic prereduction of manganese ores. The second group involves molten phases where the equilibrium between various metal and slag phases are being studied in conjunction ...

Laser-Raman spectroscopic study of the vapour phase equilibria above molten SnCl 2

Raman spectra of the gaseous phase of SnCl 2 are reported over the temperature range 666 K to 1047 K. The development of a furnace designed for optical studies at temperatures up to 1100 K is described. Agreement with previous Raman studies is excellent and in addition new features are observed which are attributed to the dimeric species Sn 2Cl 4. Extensive force constant calculations have been carried out to establish the structure of this molecule. The results show that the dimer molecule has C s -symmetry with one bridging chlorine atom. The enthalpy of formation of Sn 2Cl 4 has been calculated using second-law methods, and is in agreement with a previous result from mass spectrometry. Predicted vibrational band wavenumbers from force constant calculations are used to calculate values of the heat capacity C p ⦵, the enthalpy H T ⦵ - H 298 ⦵, and the entropy S T ⦵ - S 0 ⦵ of Sn 2Cl 4 from 0 K to 6000 K. The molten phase of SnCl 2 has also been examined.

Synthesis of molybdenum nitride γ-Mo 2N by multipulse laser irradiation of molybdenum in nitrogen

The γ-Mo 2N phase has been synthesized by multipulse laser irradiation of molybdenum foils in pure nitrogen atmosphere. The optical plume emissions produced on the laser irradiation were identified with various atomic, ionic and molecular species present. The obtained molybdenum nitrides were analyzed and characterized by scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. The formation of the molybdenum nitrides results from a nitridation reaction through a molten phase, and it seems that nitrogen activation and Mo surface heating and melting by the laser irradiation are responsible for the efficient incorporation of nitrogen in the Mo lattice and the creation of MoN bonds. It is also found that laser heating and melting and laser-induced shock waves give rise to a densification of the nitride layer microstructure.

Na2SO4‐lnduced Corrosion of Si3N4 Coated with Chemically Vapor Deposited Ta2O5

Hot isostatically pressed Si3N4 was coated with chemically vapor‐deposited Ta2O5, and subjected to oxidative and corrosive environments to determine the feasibility of using a Ta2O5 coating for protecting Si3N4 from hot corrosion. The coated structure was relatively stable at 1000deg;C in pure O2. However, the Ta2O5‐Si3N4 system became unstable in an environment containing Na2SO4 and O2 at 1000deg;C because (1) Ta2O5 and Na2SO4 reacted rapidly to form NaTaO3 and (2) subsequently NaTaO3 interacted destructively with the underlying Si3N4 substrate to form a molten phase.

Processing characteristics and structure development in solid‐state extrusion of a new semicrystalline polyimide (BTDA–DMDA)

AbstractIn this article, we present detailed processing characteristics and structure development in a thermoplastic polyimide BTDA–DMDA in the solid‐state extrusion process. This fully imidized polyimide polymer is known to crosslink at fast rates when it is brought to a molten phase even for short periods of time. This characteristic makes it difficult to process it in the molten phase and attempts at melt processing result in melt fracture and highly distorted extrudates. However, this polymer can be shaped into high‐quality extrudates when it is processed below its melting temperature directly from its postpolymerization powdered state. The solid‐state extrusion of precompacted BTDA–DMDA powder was studied in the temperature range from 250 to 320°C. At the temperatures from 290 to 320°C, high‐quality extrudates were obtained. Below 290°C, solid‐state extrusion was not possible due to the limitation of the load cell capacity of the capillary rheometer used in this research. Above 320°C, the extrudates were found to be of poor quality as a result of degradation and crosslinking in the molten phase. Structural characteristics of the samples produced by solid‐state extrusion was investigated by the microbeam X‐ray diffraction technique. The thermal behavior of the extrudates was also characterized by differential scanning calorimetry (DSC). The DSC results show that at low extrusion temperatures the samples exhibit dual endothermic peaks and are highly crystalline in an extruded state. The higher melting peak located at about 350°C is due to the melting of the new crystalline phase that has developed partially during the solid‐state extrusion process and partially during the recrystallization process that takes place at temperatures at and slightly above the primary melting process during the DSC heating scan. This has been confirmed by DSC, depolarized light hot‐stage video microscopy, and wide‐angle X‐ray diffraction studies. The long spacing of the higher melting crystals was found to be much larger than that of the lower melting crystals, as evidenced by the small angle X‐ray scattering studies. © 1995 John Wiley & Sons, Inc.