Characteristics of Multi-Phase Alternating Current Arc for Glass In-Flight Melting

An innovative in-flight melting technology with multi-phase AC arc was developed for glass industry. The enthalpy probe and high speed video camera were used to characterize the temperature, velocity, and discharge behavior of multi-phase AC arc. The effects of input power and sheath gas flow rate on arc and melting behavior were investigated. Results show that the temperature and velocity on arc center are increased with input power or sheath gas flow increase. The fluctuation of luminance area ratio and coefficient of variation reflects the change of arc discharge behavior. High temperature of plasma enhances the melting of granulated raw particles during in-flight heating treatment. The shrinkage of particle and the volatilization degree of Na₂O increase under a larger flow rate of sheath gas. The characterized arc behavior agrees with the melting behavior of glass raw materials, which can provide valuable guidelines for the process control of glass melting.     

Particle Injection in Direct Current Air Plasma Spray: Salient Observations and Optimization Strategies

External injection of high-melting point low thermal conductivity ceramics orthogonal to a typical direct current thermal plasma jet plays a vital role in determining the in-flight state of the particles and the process downstream. The interactions between low density ceramic particles and high temperature plasma jet is quite complex, which influences the spray process and associated deposition. Detailed in-flight particle diagnostics as well as spray stream visualization have significantly enhanced our capability to diagnose and control the process. In this paper we present some salient observations on the role of key variables on particle injection. A number of experiments were conducted using a 7MB torch (Sulzer Metco, Westbury, NY) with both Ar–H₂ and N₂–H₂ plasma gases, where the carrier gas flow to inject Yttria Stabilized Zirconia (YSZ) was varied systematically and the resulting in-flight particle state was captured using an array of particle and spray stream sensors arranged in a 3D set-up. A notable observation is the existence of a “sweet-spot” in the plasma jet where the particle temperatures and velocities achieved a maximum. This sweet-spot can be characterized by the plume position (location of centroid of the spray stream) rather than carrier gas flow rate and is independent of primary gas flows and other process/material conditions. This result suggests a possible approach to optimize particle injection independent of plasma-forming-torch-parameters. Controlling particle injection at this sweet-spot has shown to benefit the overall process efficiency (in terms of melting) and process reliability (both in-flight measurement and coating build-up) with concomitant application benefits.     

Study of Injection Angle and Carrier Gas Flow Rate Effects on Particles In-Flight Characteristics in Plasma Spray Process: Modeling and Experiments

This paper investigates the influence of particle injection angle on particle in-flight behaviors and characteristics at different primary and carrier gas flow rates through an integrated modeling and experimental approach. Particle in-flight status such as temperature, velocity, size and their distribution are analyzed to examine particle’s melting status before impact. Results from the experiments and numerical simulations both show that, when carrier gas flow rate is fixed, a small injection angle favors the particle melting and flattening. This behavior is independent of primary and secondary gas flow rates, spray distance and carrier gas flow rate. When both carrier gas flow and injection angle vary, a high carrier gas flow rate and a small injection angle are recommended for high particle temperature and velocity.     

New In-Situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors in a rf Thermal Plasma Reactor. Part 2: Analysis of CeO<Subscript>2</Subscript> Powders,Fuel Addition,and Image Analysis

A novel reactor design, sampling probe and wet collection system were used to investigate the combined effects of plasma operating parameters and particle collection mechanisms on the synthesis of CeO₂ particles from liquid precursors. The sampling of particles in-flight and the collection of particles at several reactor regions were used to provide experimental evidence of particle size at different reactor locations at various plasma operating conditions, i.e., power and plasma gas flow rates. This information provided a picture of how CeO₂ particles were formed and how these particles were collected in various locations. The effect of adding water-soluble fuels (alanine and glycine) to the original cerium nitrate solutions was also investigated. Fuel addition decreased the temperature of CeO₂ formation by acting as a local heat source as a result of fuel auto-ignition. Photographs of the particles in-flight were taken using a fast speed CCD camera.     

Le cyclone réacteur IV: Mesure de l'efficacité des transferts de chaleur entre les parois et les phases gazeuse et solide

The purpose of the present paper is the experimental study of different mechanisms of heat transfer for both gas and the solid phases inside a cyclone reactor. The measurements are based on the study of the outlet temperature of the gas and of the particles as a function of the inlet Reynolds number (385–11 000), of the wall temperature (630–1150 K), of the nature of the carrier gas (air, argon, CO₂, (helium) and of the particles (sand, bronze), and of the particle size (radius of particles from 0.1 to 0.5 × 10⁻³ m). It is shown that the particles are heated mainly during their contact with the heated wall and that the efficiency of the wall-particle and wall-carrier gas transfers decrease when the solid flow rate increases. Simple scale-up relationships are proposed to represent the extent of these two mechanisms as a function of operating conditions.     

Study of the crystallization and melting region of PET and PEN and their blends by TMDSC

The cold crystallization and melting of poly(ethylene therephthalate) (PET), poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) and their blends were studied using temperature modulated differential scanning calorimetry (TMDSC) at underlying heating rates of between 1 and 3 K min^-1 and periods ranging from 30 to 90 s. The amplitude of modulation was selected in order to give an instantaneous heating rate β≥0. Heat flow is analyzed by the total heat flow signal o, which is equivalent to the conventional DSC signal, and the reversing heat flow o_REV, which only detects the glass transition and the melting processes. The dependence of the melting region in the reversing heat flow on the frequency of modulation is analyzed. The use of the so-called non-reversing heat flow o_NREV (=o-o_REV)) and the effect of frequency and amplitude on the complex heat capacity are also studied. The results show the complexity of these magnitudes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of GC temperature and carrier gas flow rate on on‐line oxygen isotope measurement as studied by on‐column CO injection

Although deemed important to δ¹⁸O measurement by on‐line high‐temperature conversion techniques, how the GC conditions affect δ¹⁸O measurement is rarely examined adequately. We therefore directly injected different volumes of CO or CO–N₂ mix onto the GC column by a six‐port valve and examined the CO yield, CO peak shape, CO–N₂ separation, and δ¹⁸O value under different GC temperatures and carrier gas flow rates. The results show the CO peak area decreases when the carrier gas flow rate increases. The GC temperature has no effect on peak area. The peak width increases with the increase of CO injection volume but decreases with the increase of GC temperature and carrier gas flow rate. The peak intensity increases with the increase of GC temperature and CO injection volume but decreases with the increase of carrier gas flow rate. The peak separation time between N₂ and CO decreases with an increase of GC temperature and carrier gas flow rate. δ¹⁸O value decreases with the increase of CO injection volume (when half m/z 28 intensity is <3 V) and GC temperature but is insensitive to carrier gas flow rate. On average, the δ¹⁸O value of the injected CO is about 1‰ higher than that of identical reference CO. The δ¹⁸O distribution pattern of the injected CO is probably a combined result of ion source nonlinearity and preferential loss of C¹⁶O or oxygen isotopic exchange between zeolite and CO. For practical application, a lower carrier gas flow rate is therefore recommended as it has the combined advantages of higher CO yield, better N₂–CO separation, lower He consumption, and insignificant effect on δ¹⁸O value, while a higher‐than‐60 °C GC temperature and a larger‐than‐100 µl CO volume is also recommended. When no N₂ peak is expected, a higher GC temperature is recommended, and vice versa. Copyright © 2015 John Wiley & Sons, Ltd.     

The Particle In-Flight Characteristics in Plasma Spraying Process Measured by Phase Doppler Anemometry (PDA)

Detailed measurements of particle in-flight characteristics have been carried out using a PDA system for benchmarking as well as to provide further information to aid the development of simulation models. The parameters studied included four conditions of primary gas flow rate and carrier gas flow rate. The particle velocities, diameters, and the corresponding volume flux at different locations were obtained. Due to the one port particle injection arrangement, it was noted that particles in general sprayed with an angle deviated from the nozzle axis Z_n, to the opposite side of the powder feeder port. The particles would also deviate from the spraying cone axis with a divergence angle (). The deviation and divergence angles were examined under different plasma spraying conditions. The measurement data rates at different cross-sectional planes were also obtained so as to compare the results derived from the volume flux measurement and the actual coating on a substrate at the equivalent standoff distance. It was found that the spraying area obtained from the measurement-data-rate increased with downstream distance and a linear relationship between spraying area and distance was also established. Comparing the integrated results, it was noted that the spraying areas derived from the measurement data rate were close to the actual spraying areas obtained from the coordinate measurement machine (CMM) results.     

Thermal properties of vitrified llw hospital waste incineration ash

The low level nuclear waste (LLW) resulting from the use of radioactive isotopes in medicine, industry, laboratories, and other purposes can be immobilized by vitrification, using methods applied in the nuclear power industry. Borosilicate glass is providing the very suitable medium for the majority of the species present in these wastes. Management of LLW waste begins with combustion reducing their amount. The paper presents the results of model studies of vitrification of hospital waste by incorporating it into the composition of boro-aluminosilicate glass, similar to those used in nuclear power industry. The proposed borosilicate waste glass composition was: SiO₂-56.0, B₂O₃-15.0, Na₂O-21.0, and Al₂O₃-8.0 (mass %). The ashes were mixed in different amount with the glass frit and then remelted to obtain homogenous melt which was vitrified. The influence of the main ash components on the thermal properties of the vitrified waste was studied using DSC and heating microscopy methods. The glass transformation, crystallization and melting temperatures, and Hruby glass stability against crystallization parameter were determined. The correlations between ΔC _p , T _g, and K _H were observed and discussed.     

Crystallization of MgFe2O4 from a glass in the system K2O/B2O3/MgO/P2O5/Fe2O3

Spherical magnetic Mg-Fe-O nanoparticles were successfully prepared by the crystallization of glass in the system K₂O/B₂O₃/MgO/P₂O₅/Fe₂O₃. The magnetic glass ceramics were prepared by melting the raw materials using the conventional melt quenching technique followed by a thermal treatment at temperatures in the range 560–700 °C for a time ranging from 2 to 8 h. The studies of the X-ray diffraction, electron microscopy and FTIR spectra confirmed the precipitation of finely dispersed spherical (Mg, Fe) based spinel nanoparticles with a minor quantity of hematite (α-Fe₂O₃) in the glass matrix. The average size of the magnetic nano crystals increases slightly with temperature and time from 9 to 15 nm as determined by the line broadening from the XRD patterns. XRD studies show that annealing the glass samples for long periods of time at temperature ≥604 °C results in an increase of the precipitated hematite concentration, dissolution of the spinel phase and the formation of magnesium di-borate phase (Mg₂B₂O₅). For electron microscopy, the particles were extracted by two methods; (i) replica extraction technique and (ii) dissolution of the glass matrix by diluted acetic acid. An agglomeration of the nano crystals to larger particles (25–35 nm) was observed.     

Study of size-dependent glass transition and Kauzmann temperatures of tin dioxide nanoparticles

The size and shape effects on melting, glass transition, and Kauzmann temperatures of SnO₂ nanoparticles using Lindemann??s criterion have been studied. The melting temperature of SnO₂ nanoparticles decreases as the size of the particle decreases. As the particle size increases, melting temperature increases and approaches to the melting temperature 1,903?K of bulk irrespective of the shape. The glass transition and Kauzmann temperatures are analyzed through the size effect on the melting temperature. The glass transition and Kauzmann temperatures decrease with the decrease in size of SnO₂ nanoparticles.     

Determination of the amount and retention efficiency of aerosols arising during the vitrification of medium-level activity wastes from nuclear power plants

During the vitrification of medium-activity liquid wastes simulating the wastes from nuclear power plant aerosols are formed that enter into the gas pumped off from the vitrification furnace. The dependence of solid-aerosol carryover on the parameters characterizing the glass composition and its eluability were investigated in laboratory scale experiments. The aerosol carryover was determined either gravimetrically or radiometrically using radioactive tracers.¹³⁷Cs with a carrier was added to the wastes and the aerosol carryover was determined by following the¹³⁷Cs activity. In the case of the¹³⁷Cs-labeled aerosol it was observed that a higher alkali content in the melted wastes results in a higher carryover of the¹³⁷Cs-labeled aerosol. Using a multicomponent laboratory gas cleaning system a decontamination factor of 6.7·10⁶ was achieved for the removal of the¹³⁷Cs-labeled aerosol from the gas pumped off from the vitrification furnace.     

The vitrification of alkali borate and alkali silicate melts

Glasses and crystals of compositions corresponding to the congruently melting compounds M₂O·2SiO₂ (M = Na. Rb, and Cs) and M₂O·4SiO₂ (M = K, Rb, and Cs) were studied by differential scanning calorimetry. The structure temperatures (T _f) and excess entropies at T _f of glasses were measured depending on the rate of cooling of the corresponding melts. The activation energies of glass formation (ΔE) and scale of cooperative motion in the transition region (ξ_a) were estimated. The totality of the data obtained were used to compare the thermodynamic (the ratio between the excess (with respect to the corresponding crystals) entropy of glass at T _f and the entropy of crystal melting), kinetic (fragility m = f(ΔE, T _f)), and microscopic (ξ_a) parameters of the vitrification of alkali silicate melts. The behaviors of alkali silicate and alkali borate melts were shown to be similar.     

In situ monitoring of reaction-induced phase separation with modulated temperature DSC

A linearly polymerizing and network forming epoxy-amine system, DGEBA-aniline and DGEBA-MDA, respectively, will be modified with 20 wt% and 50 wt% of a high-T_g thermoplastic poly(ether sulphone) (T_g=223°C), respectively, both showing LCST-type demixing behavior. Reaction-induced phase separation (RIPS) in these modified systems is studied using Modulated Temperature DSC (MTDSC) as an in situ tool. Phase separation in the linear system can be probed by vitrification of the PES-rich phase, occurring at a higher conversion than the actual cloud point from light scattering measurements. The negative slope of the cloud point curve in a temperature-conversion-transformation diagram unambiguously shows the LCST-type demixing behavior of this system, while the relation between the composition/glass transition of the PES-rich phase and the cure temperature is responsible for the positive slope of its vitrification line. Phase separation in the network forming system appears as reactivity increases at the cloud point due to the concentration of reactive groups. Different mixture compositions alter the ratio between the rate of phase separation and the rate of reaction, greatly affecting the morphology. Information about this in situ developed structure can be obtained from the heat capacity evolutions in non-isothermal post-cures.     

Carbon Nanosheets Synthesis in a Gliding Arc Reactor: On the Reaction Routes and Process Parameters

Non-thermal plasma is a promising technology for high purity nanomaterial synthesis in a fast, flexible and controllable process. Gliding arc discharge, as one of the most efficient non-thermal plasmas, has been widely used in gas treatment but rarely studied for the nanomaterial synthesis. In this study, a comparison study for carbon nanosheets synthesis including toluene dissociation and graphite exfoliation was investigated in a 2D gliding arc reactor at atmospheric pressure. The effects of gas flow rate, precursor concentration and power input on the structures of carbon nanosheets produced through the two synthesis routes were explored and compared. Amorphous carbon nanosheets were produced in both approaches with a few crystalline structures formation in the case of toluene dissociation. The thickness of carbon nanosheets synthesized from graphite exfoliation was less than 3 nm, which was thinner and more uniform than that from toluene dissociation. The flow rate of carrier gas has direct influence on the morphology of carbon nanomaterials in the case of toluene dissociation. Carbon spheres were also produced along with nanosheets when the flow rate decreased from 2 to 0.5 L/min. However, in the case of graphite exfoliation, only carbon nanosheets were observed regardless of the change in flow rate of the carrier gas. The generated chemical species and plasma gas temperatures were measured and estimated for the mechanism study, respectively.

     

Application of Pulsed Traveling Hydrogen Arcs for Metal Oxide Reduction

A plasma reactor that has a transient traveling arc has been used to study hydrogen in relation to in-flight reduction of metal oxide particles. Experiments were done to determine the nature of the arc and its interaction with the reactor gas. The lifetime of the excited atomic hydrogen was measured and it was found to be more than 4 ms after the arc had ceased. Powders and tablets of oxides were exposed to the pulsed-arc treated hydrogen and found to react much more rapidly and intensely than when exposed to hot molecular hydrogen. The results suggest that atomic hydrogen will exist throughout the volume of such a reactor for a period that is sufficient to reduce particles of FeO, Cr₂O₃, and TiO₂.     

Vitrification/devitrification phenomena during isothermal and nonisothermal crystallization of poly(aryl–ether–ether–ketone) (PEEK) and PEEK/poly(ether–imide) blends

We have established time–temperature transformation and continuous-heating transformation diagrams for poly(ether–ether–ketone) (PEEK) and PEEK/poly(ether–imide) (PEI) blends, in order to analyze the effects of relaxation control on crystallization. Similar diagrams are widely used in the field of thermosetting resins. Upon crystallization, the glass transition temperature (T_g) of PEEK and PEEK/PEI blends is found to increase significantly. In the case of PEEK, the shift of the α-relaxation is due to the progressive constraining of amorphous regions by nearby crystals. This phenomenon results in the isothermal vitrification of PEEK during its latest crystallization stages for crystallization temperatures near the initial T_g of PEEK. However, vitrification/devitrification effects are found to be of minor importance for anisothermal crystallization, above 0.1°C/min heating rate. In the case of PEEK/PEI blends, amorphous regions are progressively enriched in PEI upon PEEK crystallization. This promotes a shift of the α-relaxation of these regions to higher temperatures, with a consequent vitrification of the material when crystallized below the T_g of PEI. The data obtained for the blends in anisothermal regimes allow one to detect a region in the (temperature/heating rate) plane where crystallization proceeds in the continuously close proximity of the glass transition (dynamic vitrification). These experimental findings are in agreement with simple simulations based on a modified Avrami model coupled with the Fox equation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 919–930, 1998     

Langmuir probe measurements during plasma-activated chemical vapor deposition in the system argon/oxygen/Aluminum isopropoxide

A Langmuir probe investigation of Ar/O₂/Al(OPr¹)₃ plasmas is described. The probe contamination depends on the probe position and the flow of tine carrier gases. Whereus far from the working gas inlet characteristics without any hysteresis were obtained, near to the inlet undisturbed characteristics were recorded only for small gas flows or a low vapor pressure of the precursor. Condensation of the precursor ai the probe surface prior to the plasma excitation was the main source of probe contamination. A decrease ire the plasma potential with respect to the ground observed during experiments was attributed to the formation of a dielectric film on the rf electrode. This resulted in a self-bias responsible for the decrease in plasma potential.     

Reversible and irreversible heat capacity of poly[carbonyl(ethylene‐co‐propylene)] by temperature‐modulated calorimetry

The heat capacity of poly[carbonyl(ethylene‐co‐propylene)] with 95 mol % C₂H₄? CO? (Carilon EP®) was measured with standard differential scanning calorimetry (DSC) and temperature‐modulated DSC (TMDSC). The integral functions of enthalpy, entropy, and free enthalpy were derived. With quasi‐isothermal TMDSC, the apparent reversing heat capacity was determined from 220 to 570 K, including the glass‐ and melting‐transition regions. The vibrational heat capacity of the solid and the heat capacity of the liquid served as baselines for the quantitative analysis. A small amount of apparent reversing latent heat was found in the melting range, just as for other polymers similarly analyzed. With an analysis of the heat‐flow rates in the time domain, information was collected about latent heat contributions due to annealing, melting, and crystallization. The latent heat decreased with time to an even smaller but truly reversible latent heat contribution. The main melting was fully irreversible. All contributions are discussed in the framework of a suggested scheme of six physical contributions to the apparent heat capacity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1565–1577, 2001     

Generation of Water-In-Oil-In-Water (W/O/W) Double Emulsions by Microfluidics

Novel compartment microparticles prepared with double emulsion droplets as templates provide a protected internal space for material encapsulation. The effect of three-phase flow rate on the micro-droplet generation of double emulsion mechanism is available for reference to produce precise size and highly monodisperse particles. The influence of three-phase flow rate on the formation mode and size of the emulsion droplets is investigated by combination of experiment and numerical simulation. The size of compound droplets decreases and frequency increases with the increasing outer fluid flow rate. The monodispersity of the double emulsion reduces due to transition from dripping to narrowing jetting regime. Outer droplet size increases with the increasing flow rate of the middle fluid, whereas inner droplet size is the opposite. The frequency increases and then stabilizes, which leads to a widening regime. When Q₂/Q₁ > 6, the multi-core type double emulsion droplets are produced. Droplet coalescence occurs when surfactants is not involved. As Q₁ increases, there is an increasing tendency for inner drop size. The outer drop size is proportional to the sum of the inner and middle flow rate, and that is irrelevant to Q₁/Q₂. For drop size, the ratio of core-shell and internal structure is precisely controlled by adjusting three-phase flow rate respectively.