High-temperature Volatilization Research Articles

Triple Templates Directed Synthesis of Nitrogen-Doped Hierarchically Porous Carbons from Pyridine Rich Monomer as Efficient and Reversible SO2 Adsorbents.

Herein, a variety of 2,6-diaminopyridine (DAP) derived nitrogen-doped hierarchically porous carbon (DAP-NHPC-T) prepared from carbonization-induced structure transformation of DAP-Zn-SiO2-P123 nanocomposites are reported, which are facilely prepared from solvent-free co-assembly of block copolymer templates P123 with pyridine-rich monomer of DAP, Zn(NO3)2 and tetramethoxysilane. In the pyrolysis process, P123 and SiO2 templates promote the formation of mesoporous and supermicroporous structures in the DAP-NHPC-T, while high-temperature volatilization of Zn contributed to generation of micropores. The DAP-NHPC-T possess large BET surface areas (≈956-1126 m2g-1), hierarchical porosity with micro-supermicro-mesoporous feature and high nitrogen contents (≈10.44-5.99 at%) with tunable density of pyridine-based nitrogen sites (≈5.99-3.32 at%), exhibiting good accessibility and reinforced interaction with SO2. Consequently, the DAP-NHPC-T show high SO2 capacity (14.7mmolg-1, 25°C and 1.0bar) and SO2/CO2/N2 IAST selectivities, extraordinary dynamic breakthrough separation efficiency and cycling stability, far beyond any other reported nitrogen-doped metal-free carbon. As verified by in situ spectroscopy and theoretical calculations, the pyridine-based nitrogen sites of the DAP-NHPC-T boost SO2 adsorption via the unique charge transfer, the adsorption mechanism and reaction model have been finally clarified.

Effect of Ca2+/Cr3+doping ratio on the infrared radiation performance and Cr6+ formation in LaAlO3 ceramics

Ca2+/Cr3+ co-doped LaAlO3 has been considered as important ceramic to achieve energy-savings in thermal equipment due to excellent infrared radiation (IR) performance. However, following problems restricted its industrial applications: one is the correlation between emissivity and the valence state of Cr which is not clear, then there is no quantitative evaluation of Cr6+ content in ceramics. In this work, Ca2+/Cr3+ co-doping LaAlO3 ceramics have been fabricated. By adjusting Ca2+/Cr3+ doped ratio (0 ≤ n(Ca2+)/n(Cr3+) ≤ 0.75), the “Cr3+→(Cr4+/Cr6+)” transformation ratio has been controlled. The results show that a higher concentration of Cr4+ in the material can significantly enhance the emissivity, while Cr6+ has no such effect. In addition, the Cr6+ content was measured by leaching method and high-temperature volatilization methods, respectively. This work can be used to guide the fabrication of environment-friendly Ca2+/Cr3+ co-doped LaAlO3-based ceramics with high emissivity in the field of energy-saving for thermal equipment.

Effect of Sewage Sludge Addition on Microstructure and Mechanical Properties of Kaolin-Sewage Sludge Ceramic Bricks

The dramatic increase in sewage sludge production requires researchers to develop and explore more commercially viable ways for alleviating current environmental and socioeconomic challenges connected with its routine management. It has been established that sewage sludge can be processed to fabricate various valuable products or as fuels for electricity generation. In this research, kaolin (calcined from coal gangue) and sewage sludge were successfully used to prepare porous ceramic bricks without any additives. The effect of sewage sludge on the microstructure, phase composition, and mechanical properties of kaolin-sewage sludge ceramic bricks was investigated. The results show that the kaolin-sewage sludge ceramic bricks are mainly composed of mullite (3Al2O3·2SiO2), sillimanite (Al2SiO5), aluminum phosphate (AlPO4), hematite (Fe2O3) as well as a small amount of quartz (SiO2). The ceramic bricks present a typical porous structure, and the number and size of micropores increases noticeably with the increase of sewage sludge content. The sintering shrinkage rate and porosity of ceramic bricks increased significantly with the increase of sewage sludge content, which is mainly attributed to the increase of liquid phase proportion and high temperature volatilization. Sewage sludge can significantly improve the mechanical properties of kaolin-sewage sludge ceramic bricks. When the sewage sludge content is 30 wt.%, the ceramic bricks present the maximum compressive strength and flexural strength and high porosity (32.74%). The maximum sintering shrinkage rate and porosity are 12.17% and 40.51%, respectively.

Preparation of an MHC Alloy by Direct Doping of HfC and Its High Temperature Oxidation and Volatilization Behavior.

An HfC-doped molybdenum (Mo-Hf-C; MHC) alloy was prepared via a powder metallurgy process, including dry direct doping followed by ball-milling, cold-isotactic-pressing, and vacuum sintering. An oxidation comparison experiment was conducted, and the oxidation and volatilization behaviors were analyzed using the mass change, volatile generation rate, and morphology transformation. The results show that relatively uniform powder morphology can be obtained by the direct doping of carbide and high-energy ball milling. The oxidation of the MHC alloy at a lower temperature was characterized by the oxygen-absorption and a slight weight gain, while at a higher temperature and longer holding time, it was characterized by the mass volatile weight loss. A significant weight change appeared at 800 °C for 30 min with a weight loss rate of 4.8%. Surface oxidation products developed horizontally from ridged oxides at lower temperature stages to a flaky oxide layer at higher temperatures. The peeling of the oxide layer was the result of interfacial pore development, which led to exposure of the alloy matrix and further oxidation. Based on the oxidation and volatilization characteristics of HfC-doped MHC alloys, we conclude that the oxidation and volatilization of the MHC alloy conformed to the general law; however, the significant weight loss temperature, weight loss rate, volatilization temperature, and volatilization rate were improved compared with pure molybdenum and traditional molybdenum alloys, thus, indicating that the precipitation of the second phase HfC particles at the grain boundaries and within the grains can inhibit the oxidation and volatilization of matrix elements to a certain extent.

Sintering of Metakaolin-based Na-Pollucite ceramics and their immobilization of Cs

Metakaolin-based Na-Pollucite ceramics (high-temperature sintered Na-pollucite ceramics: HTNP), with a target composition close to Pollucite (CsAlSi2O6), were fabricated at sintering temperatures above 1000 °C to immobilize Cs as waste form material. The sintering behaviors of Metakaolin-based Na-Pollucite ceramics were investigated, in particular with respect to sintering temperature, grain size, and microstructure. The results indicate that major phases of the pollucite ceramics consist of pollucite phase and a small fraction of other mineral phases like Albite, SiO2, and Al2O3, and the microstructures greatly depends on the molar Cs/Na ratio. Furthermore, with increasing Cs content in the pollucite ceramics, the sintering temperature increases gradually, and the pollucite grain size decreases accordingly. On the other hand, to avoid the high-temperature volatilization of Cs-ions during sintering, low-temperature sintered Na-pollucite (LTNP) ceramics were prepared below 950 °C by introducing H3BO3 into the metakaolin-based Na-Pollucite ceramics. After the LTNP ceramics were sintered using a low-temperature liquid-phase process, even when the sintering temperature was decreased to 650 °C, they remained structurally as pollucite phase. In addition, the sintering-temperature and grain-size dependency on the molar Cs/Na ratio in LTNP ceramics is consistent with that in HTNP ceramics. Leaching in the PCT (Product Consistency Test) indicates that the leaching concentrations of HTNP ceramics are, in total, lower than in LTNP ceramics. However, the LTNP and HTNP ceramics samples, with the molar Cs/Na ratios 1:1.5, 1:0.67, and 1:0.25 show better immobilization abilities for the Cs ion. This indicates that, besides the pollucite phase formation, the immobilization of the Cs ion correlates also with dense microstructures, grain size, and good crystallization. More importantly, low sintering temperatures and the fabrication of Cs crystalline ceramics are the important factors to improve the Cs ion immobilization.

Volatilization characteristics of high-lead slag and its influence on measurement of physicochemical properties at high temperature

Volatilization causes measurement deviations of physicochemical properties for volatiles-containing slag at high temperature. Hence, investigating the degree of volatilization and identifying the volatilization mechanism and deviation rules are crucial to improve the accuracy of the measured properties. Here, PbO-FeOx-CaO-SiO2-ZnO slag system was selected as a research subject. The volatile characteristics and non-isothermal intrinsic kinetic models of high-temperature volatilization for lead slag were established by thermogravimetric analysis (TGA), and the volatilization mechanism and deviation in the measured properties were determined by analyzing the phase and chemical composition of the residues. In addition, experimental measurements of the melting temperature/ viscosity were compared with theoretically calculated results. The volatilization of PbO decreased the lead-containing phase, but increased the amount of precipitated spinel phase, which led to the deviation in the measured physicochemical properties of the studied slags. The volatilization kinetics for PbO in the slags followed three-dimensional diffusion. The diffusion of PbO gas from PbO-FeOx-CaO-SiO2-ZnO slag was the restrictive step of volatile reaction, and mechanism function was g(?)=1-(1-?)1?3. Moreover, during the slag properties measurement at high temperatures, a high heating rate and protective gas can be used to reduce volatilization of lead slag and avoid consequent properties deviation.

The high-temperature volatilization of sylvite and solid reaction process between sylvite and minerals

The effects of volatilization of sylvite were investigated when the mineral was added in it and the reaction mechanism of solid phase between potassium and minerals such as CaCO3, SiO2, Al2O3, Fe2O3 were conducted at the same time by means of high temperature calcination, thermal analysis and XRD analysis. Results show that four kinds of mineral components can restrain the volatilization of potassium in different extents, KCl and K2SO4 are relatively stable at high temperatures, which can only react with Al2O3 to produce KAl5O8; K2CO3 is the most active, and it can not only react with CaCO3 to produce K2Ca(CO3)2 in low temperature but also decompose to K2O that co-melt with SiO2, which can also react with Al2O3 or Fe2O3 to form stable and high melting point KAlO2 and KFeO2 respectively.

Effect of Iridium and Rhodium on High-Temperature Volatilization Behavior of Platinum Alloys

Effect of Iridium and Rhodium on High-Temperature Volatilization Behavior of Platinum Alloys

Influence of High-Temperature Volatilization on Performance of Bituminous Binder

Two bituminous binders were used in this research to investigate the influence of high-temperature volatilization on the binder performance. The results indicated that at higher temperature, the weight of bituminous binder reduced and the reducing rate was decreasing with heating time. After certain volatilization period, the softening points of bituminous binder increased while the penetration reduced significantly. The volatilization condition of oxygen and vacuum did not have significant differences on the asphaltene and colloid. The bitumen binder modified with 3% of Layered double hydroxides (LDHs) would reduce the amount of VOC fumes.

Enhanced sinterability of mechanical alloyed La9.33Si2Ge4O26 oxyapatite powders for IT-SOFC electrolytes

Dense oxyapatite-based La9.33Si2Ge4O26 electrolytes have been successfully prepared by electrical sintering at 1400°C in static air for 1h from dry milling La2O3, SiO2 and GeO2 powders, in adequate atomic proportions, at 350rpm for 15h, under controlled environmental conditions, in a planetary ball mill. The densification behaviour of apatite-type phase La9.33Si2Ge4O26 powders synthesized by mechanical alloying was investigated through microstructural evolution with sintering temperature by means of XRD and SEM/EDS analyses. The content of germanium in the sintered samples remained almost constant, suggesting that its incorporation in the apatite phase hinders the high temperature (>1250°C) volatilization process.

Curium vaporization from (Cm,Pu) 2O 3 and from irradiated oxide fuel: Mass spectrometric measurement

The equilibrium vapour pressure over a mixed curium oxide of type ( 244Cm 0.76, 240Pu 1.24)O 3 was measured by Knudsen-effusion experiments. Plutonium was formed in the samples during 25 years decay of curium in an initial Cm 2O 3 sintered pellet. The same measurements were repeated on seven reactor-irradiated UO 2 and MOX samples to obtain the vaporization enthalpy of curium present in typical spent nuclear fuel. The samples were annealed in a tungsten Knudsen cell up to 2800 K and the effusion rates of the different vapour components were analyzed on line by a quadrupole mass spectrometer. The vapour pressures of the curium-bearing species were accurately measured and the results compared with published data obtained under different conditions. The obtained results show that CmO(g) is the only effective vapour species and the measured equilibrium pressure confirms the trend observed in the actinide oxides that the high temperature volatility is more pronounced in compounds where the cation can easily attain a higher oxidation state than that of the condensed phase.

Structural defects of Pb(Mg 1/3Nb 2/3)O 3–PbTiO 3 single crystals grown by a Bridgman method

The types, formation mechanism and suppressing approaches of structural defects in PMNT crystals grown by a Bridgman method were investigated in this paper. The structural defects include composition non-uniformity, scattering particles, pores, negative crystal structures, cellular structures, fissure structures and point defects. They are formed due to one or several of the following: composition deviation, incomplete melting and diffusion, high-temperature volatilization, temperature fluctuation and instability of the position and shape of growth interfaces. On understanding the formation mechanism of structural defects, one can restrain them by means of adjusting stoichiometry of starting materials, using PMNT crystal bulks, suppressing composition volatilization and modifying growth parameters.

Time dependence of environmental pollution in Vienna measured by RNAA of samples taken from dated repairs on St. Stephen's cathedral

Trace element concentrations in weathering crusts are determined by neutron activation analysis. A high temperature volatilization technique was applied to determine mercury. Comparing the concentrations in samples of different ages, the variations of the air pollutants are shown.

Purification of activated charcoal for use as sorbent in NAA of trace elements in volcanic exhalations

Activated charcoals were analyzed by neutron activation analysis to test their applicability as sorbents for some volatile trace elements in volcanic exhalations. A high temperature volatilization process was applied, which reduces the concentrations of some trace elements, in particular Br, Hg, Sb and Zn.

A high temperature volatility technique for determination of atmospheric aerosol composition

Size segregated atmospheric aerosol composition, over the radius range 0.05 μ m ≤ r ≤ 1.5μm, is inferred using an optical particle counter equipped with a high temperature heater tube cycling through temperatures from 20°C to 870°C. The volatility system infers the presence of common atmospheric constituents such as H 2 SO 4 , (NH 4 ) 2 SO 4 , NaCl, and soot carbon. This system has been successfully used to determine the physico-chemical characteristics of accumulation mode aerosol associated with air masses of different origin. Results from ship-borne and ground based measurements are presented. For continental and modified maritime air, (NH 4 ) 2 SO 4 was observed to be the dominant species, whilst H 2 SO 4 was more abundant in Arctic aerosol. Sea-salt aerosol accounts for ≈75% of accumulation mode particle concentration for maritime aerosol in periods of high wind speeds. We also show that soot carbon can be identified in polluted air using this technique.

Determination of mercury in mineral samples by employing a high temperature volatilization technique and activation analysis

A high temperature volatilization technique was applied to lower the detection limit for the determination of mercury in mineral samples by neutron activation analysis to the 10–15 pg range. Activated charcoal was used to trap evaporated mercury. Geologic standard samples and weathering crusts from limestone buildings were analyzed. The data obtained indicate how the concentration of air pollutants varies.

Intrinsic fugacity measurements of some Allende Type B inclusions

Intrinsic oxygen fugacity (IOF) measurements ( T = 800–1150° C) for whole rock samples of two Type B Ca-, Al-rich inclusions (CAI) from the Allende meteorite show them to be 6–8 orders of magnitude ( H 2 H 2O = 1–10 ) more oxidized than the canonical solar nebular gas ( H 2 H 2O = 100–2000 ). Melilite separates from the two CAI give IOF measurements 8–9 orders of magnitude more oxidized than the solar nebular gas. Melilite crystallized in a reducing solar gas and later underwent a solid-state oxidation. Vacancies due to crystallization in a reducing solar gas and an open crystal structure were filled, probably through an O diffusion mechanism, during equilibration at temperatures higher than 700°C with an oxidized gas. O-rich vapors released from an unaltered Vigarano inclusion during high-temperature volatilization may have caused oxidation of fassaite ( DAvis and Macpherson, 1988) and possibly melilite in the inclusion and this may be a mechanism for oxidation in Allende inclusions. IOF measurements of fine-grained alteration/rim minerals in one Type B inclusion yield an oxidation state more oxidized than the whole rock CAI but more reduced than melilite from the same inclusion. Disequilibrium between melilite and alteration minerals with respect to ƒO 2 may seem unlikely in light of their similar O isotope compositions ( clayton et al., 1977) but recent O isotope measurements of an unaltered Vigarano CAI ( clayton et al., 1987) indicate that melilite exchanged O with the nebula without being altered. Allende melilite's isotope exchange may involve CO but its oxidation requires a source of O which might also supply the Na, Fe, Cl, etc. of the alteration minerals. Whether the oxidation of melilite actually occurred with its alteration is unknown.

Coal burnout in the IFRF No. 1 furnace

A coal combustion model is used to match burnout measurements for four coals of different rank in a one-dimensional furnace and is then combined with a flow and heat transfer model to predict burnout in the IFRF No. 1 furnace. The coals show a continuous decrease in high temperature volatility and char reactivity with rank. Predicted and measured flame temperatures are shown to depend on the high temperature volatility and the char reactivity, varying by 300°C for the coals. For the residence time available in the flame, a proportion of fine coal is burned; the low reactivity of the high rank coals is partially compensated by a grinding characteristic giving more fine coals. Final burnout levels are shown to depend principally on the char reactivity as well as the furnace cooling, as this determines furnace temperatures. The sensitivity to volatility, grind, the flow model, and uncertainties in the combustion model are quantified. It is shown that the furnace cooling must be reduced to obtain acceptable levels of burnout for the two coals of lowest volatility.

The application of atomic absorption spectrometry in the analysis of metallic sodium: Part 1. Volatilization Characteristics of Sodium Salts During Electrothermal Atomization

The volatilization characteristics of six common sodium salts from the graphite rod of an electrothermal atomizer are described. Most of the salts have a relatively simple volatilization behaviour and can be completely removed from the graphite rod during a 20 s heating stage at temperatures 200–300°C above their melting points. This predictable and controllable vaporization behaviour shows the potentiality of the graphite rod atomizer for selectively volatilizing a sodium salt matrix and leaving behind less volatile trace metals for subsequent high temperature volatilization and measurement by atomic absorption spectrometry.

Trace elements in fly ash. Dependence of concentration on particle size

Concentrations of 25 elements in fly ash emitted from a coal-fired power plant were measured as a function of particle size using spark source mass spectroscopy, optical emission spectrography, atomic absorption spectroscopy, and x-ray fluorescence spectroscopy. Of these elements, the concentrations of Pb, Tl, Sb, Cd, Se, As, Zn, Ni, Cr, and S increased markedly with decreasing particle size. To account for the trace element concentration dependence on particle size, a mechanism is proposed involving high-temperature volatilization of a species containing the trace element followed by preferential condensation or adsorption onto the smallest particles. Environmental significance of the measurements is discussed.