Conventional Combustion Method Research Articles

Green Aluminate Phosphors Used for Information Display

Well known long-persistent phosphorous strontium aluminates were synthesized by conventional combustion method in a furnace at about 600oC. By incorporating the obtained phosphorous strontium aluminates into organic host polystyrene, we prepared the organic-inorganic composite material (i.e., phosphor-polystyrene) which could be cast into flexible and green-light- emitting films. The morphology of the obtained phosphorous strontium aluminates and the phosphorescence of the organic-inorganic composite films were characterized with the scanning electron microscopy and the fluorescence spectroscopy, respectively. Our results show that the organic-inorganic composite films can be used as green-light- emitting roll-able screens in the industry of information displays.

Luminescence studies on the blue–green emitting Sr 4Al 14O 25:Ce 3+ phosphor synthesized through solution combustion route

New blue–green emitting Sr 4Al 14O 25:Ce 3+ phosphor is reported in this paper. The polycrystalline samples of phosphor were prepared by the conventional solution combustion method and checked for crystallization and phase by X-ray diffraction. Photoluminescence studies reveal the emission at 472 and 511 nm that correspond to the transition between lowest T 2g level of the 5d state to the 2F 5/2 and 2F 7/2 ground state levels of the Ce 3+. The excitation at 275 nm corresponds to O 2−→Ce 4+ charge transfer processes to lowest 5d state of Ce ion (T 2g). Phosphorescence decay procedures reveal the existence of slow, medium, and fast component involved in the process. Varying the γ-dose (1–6 Gy), thermoluminescence (TL) measurements were made and glow curve maximum is obtained at 383 K. The phosphor seems to follow a first-order kinetics due to non-shifting T m property. The T m– T stop method followed by the repeated initial rise method is applied to determine the distribution of activation energies and corresponding maximum positions. Chi-square minimization procedures provide the appropriate peak positions and other trapping parameters. From deconvolution results, the activation energies are found to be 0.84 and 1.06 eV, while the frequency factor is of the order of 10 10 and 10 11 s −1, respectively.

Novel Method for Synthesis of Nano‐Materials: Combustion of Active Impregnated Layers

Solution Combustion of Active Impregnated Layer is a novel method for synthesis of nano-materials. It combines features of impregnation and combustion approaches and allows production of nano-powders using low exothermic reaction systems, which cannot be accomplished by conventional solution combustion method.

In-Situ Preparation of Highly Crystallized ZnO Nanopowders by Ultrasonic Spraying Combustion Method

To obtain a mass production of nanocrystalline ZnO powders, equipment that combines the conventional self-sustaining combustion process (SCP) with the ultrasonic spraying combustion method (USCM) were applied. The droplet was sprayed into the reaction zone of the furnace to carry out USCM that produces softly agglomerated crystalline ZnO particle with spherical shape. It was confirmed that the ZnO powder was prepared from ultrasonic spraying combustion method having smaller primary particle size, spherical shape with weak agglomeration and larger specific surface area than from conventional self-sustaining combustion method. Synthesized nanocrystalline ZnO powders have primary particle size in a range of 20∼30 nm, and specific surface area of about 20 m2/g under the optimum ultrasonic spray conditions.

A novel preparation method of active materials for the lithium secondary battery

LiNi 0.8Co 0.2O 2 is a promising candidate to replace LiCoO 2. The present paper describes the preparation of LiNi 0.8Co 0.2O 2 compounds from nitrate sources and sucrose (or sugar) by the sucrose combustion process (SCP), which involves application of a conventional combustion method. In the proposed approach, sucrose serves as a fuel, a dispersing agent, and a precipitation suppressant. Precursors were made via a combustion reaction, and LiNi 0.8Co 0.2O 2 was subsequently synthesized by heat treatment at 800 °C for 16 h in oxygen atmosphere. The initial discharge capacity was 175 mA h/g when a cell was operated at 2.7–4.3 V at 0.5 C-rate. Furthermore, it shows good cycling stability. When increased amount of sucrose were added as a start material, the final calcined powder displayed smaller particle size and better discharge capacity. It is expected that optimization of the heat treatment conditions would yield LiNi 0.8Co 0.2O 2 with excellent properties. Furthermore, SCP is expected to be applicable to the production of various materials.

Preparation of Eu-doped alkaline-earth silicate phosphor particles by using liquid-phase synthesis method

The liquid-phase synthesis method for preparing Eu-doped alkaline-earth silicate phosphor particles, which is expected to be applied for lighting apparatuses, such as mercury-free fluorescent lamps and flat-plane displays, such as PDP, was investigated. The sols, as the phosphor particle precursors, were synthesized by sol–gel processes under various conditions in the liquid-phase. The particle sizes of the sols were almost uniform, and they were under 200 nm. The metal elements ratio of the sol-particles could be controlled by the initial concentration of the synthesis solutions. The sol-particles were converted from an amorphous composition into an Eu-doped alkaline-earth silicate phosphor by heat-treatment at a lower temperature compared to the conventional premixed combustion method. The crystallinity of the phosphor particles was increased with a heat-treating temperature up to 1300 °C, but an undesirable aggregation was enhanced at a higher temperature closer to its melting point (1391 °C). Therefore, these properties of reactivity and crystallinity at a lower temperature, as the precursors indicated, are very important characteristics for dispersibility because phosphor particles must be well dispersed in order to apply them to the lamp and display applications. The phosphor particles showed spectra with an emission peak of Eu 2+ at a 446 nm wavelength and the emission intensity was sensitive to the composition.

Microwave activated combustion synthesis of titanium aluminides

TiAl and Ti 3Al titanium aluminide intermetallic compounds were synthesized using a microwave activated combustion synthesis (MACS) method and compared to thermal activation (TACS) and conventional combustion (CS) methods. MACS represents an example of our “synergistic processing” philosophy, wherein the useful attributes of microwave processing and combustion synthesis are used synergistically. Thermodynamic calculations indicated activation was required for combustion synthesis to be successful in the Ti–Al system. MACS and TACS yielded Ti–Al products, while no reaction occurred with CS. Peak temperatures for TiAl during combustion were measured at 1500 °C for TiAl and 1450 °C for Ti 3Al in MACS, compared to 1400 °C for TiAl and <1000 °C for Ti 3Al in TACS. The change in peak temperature between the activation routes most likely corresponds to absorption of microwave energy at the reaction front. In MACS, product Ti 3Al was produced in single-phase using an off-stoichiometric reacted mixture of 86:14 Ti:Al (w/w), while TiAl with a minimized Ti 3Al secondary phase was obtained using a reactant mixture of 60:40 Ti:Al (w/w). The level of Ti 3Al present in TiAl was minimized in MACS and could be controlled by changing the reactant mixture. Ti 3Al content in TiAl was higher and consistent for different reactant mixtures in TACS samples. The present results obtained using the simple MACS process are comparable to those obtained using the TACS (at high heating rates) and the field activated combustion synthesis (FACS). An increase in volume and porosity was noted in all samples by all processing routes and was attributed to the intrinsic volume change associated with the reaction and the vaporization of persistent volatile impurities.

Mechanism of NO decomposi-tion on perovskite (-like) catalysts

NOx emitting from industrial and mobile exhaust are serious pollutant in air atmosphere, and the removal of them is an urgent task of today in environment-protection field. Although the present three-way-catalyst (TWC) can remove NOx from the mobile exhaust effectively, it will be out of work as lean-burn strategies are used to increase energy efficiency (for example, the diesel engine operated in the lean-burn condition), hence, the technology that can remove NOx in the presence of excess oxygen is desired. In addition, because the capability of noblemetal catalyst for NOx removal is weak at high temperatures (>873 K), it is thus necessary to comprehend the process of NOx decomposition, which would help to solve the problem of NOx removal. For NO decomposition reaction (2NO = N2 + O2), it is generally accepted that N2 was formed through the decomposition of N2O species, i.e. 2NO N2O + Oads and N2Oads N2 + Oads . While the way of oxygen formation is still unclear at present. According to the literatures, there are two proposed ways for oxygen desorption, that is, i) the direct desorption of two vicinal oxygen, Oads + Oads O2; and ii) the indirect desorption with NO as an intermediate, NOads + Oads NO2, NO2 + Oads NO3 ads, NO3 ads NO + O2. Accordingly, there are two ways for NO2 formation, that is, iii) reaction of gaseous NO and O2 occurring in the downstream, O2 + 2NO 2NO2; and iv) reaction of adsorbed O atom and NO occurring on the catalyst surface, Oads + NOads NO2. Recently, Iglesia et al. suggested that the O2 formation over Cu-ZSM-5 mainly occurred through the decomposition of NO3(a) species, but there is still no literature discussing the way of O2 and NO2 formation over perovskite (-like) oxides. In this work, by discussing the possible reaction steps occurring in the process of NO decomposition, we proposed that the way of NO decomposition over perovskite (-like) mixed oxides occurred with NO2 as an intermediate, and NO2 was mainly formed on the catalyst surface in the way of Oads + NOads NO2, while O2 was formed through the dissociation of NO2 species in the way of 2NO2(g) = 2NO(g) + O2(g). The samples, LaSrNiO4 and La0.4Sr0.6Mn0.8Ni0.2O3, were prepared by the conventional citric combustion method. O2-TPD experiment was carried out on a homemade apparatus equipped with a thermal conductivity detector (TCD). The samples (0.2 g) were first treated in O2 at 1073 K for 1 h and cooled to room temperature in the same atmosphere, then swept with pure He (or 0.5% O2/He) at a rate of 11.8 mL/min until the base line on the recorder remained unchanged. Finally, the sample was heated at a rate of 20 K/min in He (or 0.5% O2/He) to record the TPD profile. Steady-state activities of catalysts were evaluated using a single-pass flow micro-reactor made of quartz, with an internal diameter of 6 mm. The reactant gas (1% NO/He + 0% 10% O2/He) was passed through 0.5 g (in the absence of oxygen) or 1.0 g (in the presence of oxygen) catalysts at a rate of 25 or 40 mL/min (in all, to keep W/F = 1.2 g·s·cm ). The gas composition was analyzed before and after the reaction by an on-line gas chromatography, using molecular sieve 5A column for separating NO, N2 and O2. N2O was not analyzed here because it was difficult to form between 773 and 1123 K as reported in ref. [9]. Before the data were obtained, reactions were maintained for a period of ~2 h at each temperature to ensure the steady-state conditions. According to the literatures reported previously, the possible reaction steps occurring in the process of NO decomposition are summarized in Table 1.

Occurrence and destruction of PAHs, PCBs, CIPhs, CIBzs, and PCDD/Fs in ash from gasification of straw.

Two experiments were performed with an atmospheric circulating fluidized bed gasifier (ACFBG), the first with pelletized straw and the second with loose straw, to investigate the occurrence of polycyclic aromatic hydrocarbons (PAHs), chlorophenols (CIPhs), polychlorinated biphenyls (PCBs), polychlorinated benzenes (ClBzs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) in the bottom ash and fly ash formed during gasification. Only PAHs were present in large amounts, and only in the fly ash, ranging from 300 to 555 mg/kg ash in the tests with pelletized straw and from 73 to 118 mg/kg ash in those with loose straw. These amounts are so high that environmentally safe disposal or reuse of the ash would be difficult, so the development of a technique to handle the problem was included in the project. The method investigated was to burn the fly ash in a circulating fluidized bed (CFB) boiler in order to destroy the PAHs. This worked surprisingly well, eliminating 99% of the PAHs, without any further formation of the other harmful organic compounds analyzed. Thus, this method could actually be useful in practice. Especially the fact that the formation of PCDD/Fs was minimal during gasification and further treatment of the ash in the CFB boiler makes the gasification technique highly competitive relative to conventional combustion methods.

Production of Carbon Clusters by Means of Arc Discharge and Their Application. 4. Revival of Carbon Nano-Onions. Towards Alternatives of the Arc Discharge Method for the Production of Fullerenes.

The advantages and disadvantages of the arc discharge method for preparing fullerenes are briefly discussed in comparison with conventional combustion method. Ways are being sought to overcome inherent disadvantages of the combustion methods by learning from nature. The search, for natural fullerenes led us to discovery of a novel coal which not only contains abnormally large amounts of C60, but also shows unique TEM images which closely resemble those of soot. A series of examinations led us to conclude that carbon blacks are the ideal raw material for the production of C60 and also probably carbon nano-onions as well,

Enhancement of the low‐voltage efficiency in zinc‐gallate phosphors by oxygen vacancy

Abstract— ZnGa2O4:Mn powder phosphors were synthesized by a conventional combustion method. Synthesis conditions such as heat‐treatment temperature, heat‐treatment time, reduction conditions, and activator concentrations were optimized to obtain the maximum intensity of photoluminescence (PL). Then, ZnGa2O4 Mn powder phosphors were mixed with metal oxides WO3 or V2O5, which may modify the surface properties of the phosphors. It was observed that the cathodoluminescence of the phosphor screen was increased up to 20% compared to untreated phosphors. Possible mechanisms are discussed based on the electron‐transport phenomena in the phosphor. Also, a method to enhance the low‐voltage efficiency of ZnGa2O4:Mn phosphors will be proposed based on the aforementioned mechanism.

Determination of carbon in uranium carbide using catalytic oxidation by manganese dioxide

The oxidation of uranium carbide in oxygen is initiated at 548 K, but the reaction is only 80–85% complete even at 673 K in oxygen after 30 min. In this work, the oxidation of uranium carbide with manganese dioxide and potassium nitrate in oxygen and argon atmospheres was studied. With manganese dioxide at 653 K, the oxidation reaction in an oxygen atmosphere was quantitative. This reaction was therefore used for the determination of carbon in uranium carbide. The carbon content of samples determined by the present method agreed well with that obtained using a conventional combustion method. The recovery of carbon from a mixture of U3O8 and graphite was negligible. However, when an intimate mixture of graphite and uranium carbide was analysed, the contribution of the graphite (free carbon) to the calculated carbon content was significant. Hence free carbon was found to interfere seriously. Similar experiments carried out with potassium nitrate gave very low recoveries of carbon at 623 K, and at higher temperatures the recoveries were inconsistent.

The Chemical Characterization of Uranium Nitrides

Chemical analysis techniques were demonstrated for three uranium nitride specimens. Sintered uranium mononitride (UN), unsintered UN powder, and UN1.572 powder were analyzed for the major constituents, and a mass balance of 100.00 ± 0.03% was realized in every case. The gravimetric determination of uranium in these materials by an oxidation-reduction-oxidation method gave good precision and accuracy. Results from the direct oxidation method were strongly dependent on the oxygen content of the gas used to oxidize the sample. The controlled-potential coulometric method was used to confirm the gravimetric uranium results. The Dumas method for nitrogen determinations was shown to be superior to the Kjeldahl for both UN and UN1.572. Inert gas fusion is suitable for the determination of oxygen and a conventional combustion method is suitable for carbon determinations. Sintered UN provided a mass balance of 99.989% with a mole ratio N+O + C/U = 0.997 and a crystal lattice parameter a = 4.8896 ± 0.0001 Å. The microstructure of this sample consisted of single phase mononitride.

Analysis of the Chemical Structure of Coal by Means of Investigation on the High Pressure Hydrogenolysis Reaction Mechanism

High resolution NMR spectroscopy and other physical methods have been used for the study of the chemical structure of coal with the aid of chemical ultimate analysis by the conventional combustion method (JIS) and pyrolysis. However, a more precise ultimate analysis with special reference to oxygen is necessary in order to obtain a truly accurate determination of the chemical structure of coal. In the present report, a discussion was made on the precision of the fast neutron activation analysis for the determination of oxygen content of high pressure coal hydrogenolysis products. The following conclusionswere obtained.(1) A relative error of 2% was achieved by the present neutron activation analysis using gold as the internal standard and solid paraffine and graphite as diluents. It was demonstrated that the method is applicable in the determination of more than 0.2mg of oxygen in a sample of 200mg.(2) The relative error of the pyrolysis method was found to be 1-9% depending on the level of oxygen content in the samples. This method is applicable to samples containing more than 1.0% of oxygen.(3) Oxygen content determined indirectly by the combustion method results in a generally overestimation because of incomplete combustion of the samples used in our present work.

Additive reagents in organic elemental combustions

The role of a wide range of sample-additive reagents has been discussed with reference to both conventional elemental combustion methods and those based on inert carrier-gas systems. The metal oxides of cobalt, copper, and manganese are especially recommended as oxygen donors. For certain refractory hetero-organic or organometallic samples, tungstic oxide, silver tungstate and permanganate are very effective absorptive and oxidative aids.

The absorption of nitrogen oxides in the micro determination of carbon and hydrogen

The examination of a number of reagents in an attempt to Und a. more convenient absorbent for nitrogen oxides, has revealed that manganese dioxide is very active. Granules of the reagent at room temperatures have been used successfully as an external absorbent for nitrogen oxides in the micro determination of carbon and hydrogen, using both the rapid and conventional combustion methods. A modified combustion tube packing has been developed in order to avoid retention of nitrogen dioxide in the water absorption tube when the conventional slow combustion method is used. In the rapid combustion method no special precautions were found to be necessary.