Transformation of the Fe-mineral associations in coal during gasification

The mineral matter associated with coal undergoes various transformations during the coal gasification process. Optimisation of the gasification process is necessary in the coal to liquids technology. The principle aim of this investigation was to determine the changes that the Fe-containing minerals and mineral associations undergo during gasification of coal. Due to the complexity of the counter-current coal-gas process used, a gasifier dissection was undertaken on one of the Sasol gasifiers. Detailed characterisation profiles of various properties of the coal were undertaken after a commercial-scale gasifier was shutdown for routine maintenance of which the Mössbauer spectroscopy technique will be described here. Representative samples from the gasifier were extracted after sufficient cooling was done to allow the safe turn-out of the gasifier. In the coal samples that entered the gasifier, pyrite was the abundant Fe-containing mineral, whilst the pyrite changed gradually to form, in conjunction with the SiO₂ and Al₂O₃ present in the coal, a Fe-containing glass and hematite at the bottom, or ash grate of the gasifier.     

Chemical stability study of Li2SO4 on the operation condition of a H2/O2 fuel cell

The chemical stability of Li₂SO₄ on the operation condition of a H₂/O₂ fuel cell has been investigated in this work. Thermodynamic calculation indicates Li₂SO₄ can react with H₂ at high temperature. The H₂/O₂ fuel cell using Li₂SO₄–α-Al₂O₃ as electrolyte exhibits good performance, but the stability of performance is not good. XRD analysis indicates that Li₂SO₄ reacts with H₂ at high temperature. Therefore, the Li₂SO₄-based proton conductors are not suitable for electrolytes for H₂/O₂ fuel cells.     

Preparation and characterization of PtRu/C-rare earth using an alcohol-reduction process for ethanol electro-oxidation

PtRu/C (100% C) and PtRu/C-CeO₂, PtRu/C-La₂O₃, PtRu/C-Nd₂O₃, and PtRu/C-Er₂O₃ (85% C and 15% rare earth) electrocatalysts were prepared in a single step by an alcohol-reduction process using H₂PtCl₆ 6H₂O and RuCl₃ xH₂O as metal sources, ethylene glycol as solvent and reducing agent, Vulcan XC72 and rare earth (RE) as support. The electrocatalysts were characterized by energy dispersive X-ray, X-ray diffraction, and transmission electron microscopy. The performance for ethanol oxidation was investigated by cyclic voltammetry and chronoamperommetry at room temperature, and studies on the direct ethanol fuel cell were carried at 100 °C. The Pt:Ru atomic ratios were similar to the nominal used in preparation, and the average particle sizes were in the range of 2.0–3.0 nm. All PtRu/C-RE electrocatalysts showed an increase of performance for ethanol oxidation at room temperature and also on a single direct ethanol fuel cell tests in relation to PtRu/C electrocatalyst at 100 °C.     

氧化还原可逆Nb2TiO7复合阴极电解池高温水蒸气电解研究

系统地研究Nb₂TiO₇与Nb_1.33Ti_0.67O₄材料相互转变的氧化还原循环可逆性能,同时研究Nb2TiO7和Nb_1.33Ti_0.67O₄样品随温度和氧分压变化的电导率,并与复合电极对称电池和电解池的电化学性能相关联. 在830 oC下,对Nb_1.33Ti_0.67O₄复合电极电解池进行水蒸气的电解研究测试. 电流电压曲线和电解池短期性能测试表明在低电压下主要为电极的还原和活化过程;而在高电压下主要为水蒸气的电解. 当3%H₂O/Ar/4%H_{2气体通入阴极时电解池水蒸气电解的法拉第效率为98.9%;而当通入气体转换为3%H2O/Ar时效率为89%.}     

Oxy-combustion of coal in liquid-antimony-anode solid oxide fuel cell system

A novel system based on the indirect oxy-combustion of coal in a liquid Sb anode solid oxide fuel cell (SOFC) has been used to produce electricity for over 48?h. Pulverized anthracite was fed to the liquid-antimony-anode of the fuel cell, and a peak power density of 47?mW cm^?2 was reached at 1023?K and 35?mW cm^?2 at 973?K. The fuel cell was prepared using a porous stainless-steel tube as a support for an LSM cathode, antimony oxide (Sb₂O₃)/yittria stabilized zirconia (YSZ, Y_0.08Z_0.92O_1.96) composite electrolyte (membrane), while liquid antimony acted as the anode. Liquid antimony/antimony oxide served as the intermediate medium for coal oxidation producing mainly carbon dioxide, which evolved as a separate gas stream. The fuel cell will facilitate carbon capture process, and simultaneously convert the chemical energy of coal directly to electricity. The experiment showed that while the fabricated electrolyte was porous, it became dense during the actual operation, preventing nitrogen leakage into the Sb/C side and producing reasonable open circuit voltage. Analysis of the experimental EIS data illustrates that the Ohmic resistance was the primary loss mechanism in the system. It further suggests approaches to improve the design. Continuous operation of this coal fueled oxy-combustion/fuel cell system achieved an overall efficiency of 28.2% despite of its tiny scale. Simple technologies can be employed to scale up this system at relatively low cost of fabrication and materials.     

Submicronic particles synthesis by a supercritical way

Abstract

The chemical transformation of metallic precursors in a supercritical fluid is a new route for obtaining nanometric homogeneous powders. In this paper we present a technique to produce metal, oxide or nitride submicronic particles, with a spherical morphology and mean diameters from a few microns to a few tens of nanometers. Metallic copper, oxides (Cu₂O, Fe₃O₄, Ga₂O₃) and nitrides (Cu₃N, Fe⁴N) have been prepared. This process consists in solubilizatiw and subsequent thermal decomposition of acetylacetonates of metals in a supercritical fluid, either a mixture of CO₂/C₂H₅OH or NH₃.     

In situ observation of water distribution and behaviour in a polymer electrolyte fuel cell by synchrotron X‐ray imaging

In situ visualization of the distribution and behaviour of water in a polymer electrolyte fuel cell during power generation has been demonstrated using a synchrotron X‐ray imaging technique. Images were recorded using a CCD detector combined with a scintillator (Gd₂O₂S:Tb) and relay lens system, which were placed at 2.0 m or 2.5 m from the fuel cell. The images were measured continuously before and during power generation, and data on cell performance was recorded. The change of water distribution during power generation was obtained from X‐ray images normalized with the initial state of the fuel cell. Compared with other techniques for visualizing the water in fuel cells, this technique enables the water distribution and behaviour in the fuel cell to be visualized during power generation with high spatial resolution. In particular, the effects of the specifications of the gas diffusion layer on the cathode side of the fuel cell on the distribution of water were efficiently identified. This is a very powerful technique for investigating the mechanism of water flow within the fuel cell and the relationship between water behaviour and cell performance.     

Effect of alumina additions in YSZ on the microstructure and degradation of the LSM–YSZ interface

The cathode–electrolyte interface in a solid oxide fuel cell is examined to understand why premature delamination is observed in alumina substituted YSZ electrolyte. From XRD, SEM and TEM observations it was concluded that after high temperature sintering a tetragonal (Mn,Al)₃O₄ forms at the interface, which during prolonged fuel cell operation forms a cubic (Mn,Al)₃O₄ phase. This transformation is associated with volume decrease creating voids which ultimately weaken the cathode–electrolyte interface sufficiently for the cathode layer to delaminate off the YSZ–Al₂O₃ electrolyte.     

A one-chamber solid electrolyte fuel cell for chemical cogeneration

A one chamber solid oxide fuel cell (SOFC) which works in a flow of a mixture of CH₄ and air has been studied in the present author's laboratory. This new type cell consists of Pt | Solid Electrolyte | Au, in which both electrodes are exposed to the CH₄₊₂ai r mixture with a CH₄/O₂ ratio of 2 at elevated temperatures, and it generates an electric power producing hydrogen and carbon monoxide (synthetic gas) with a H₂/CO ratio of about 2. A large difference in catalytic activity for the partial oxidation of CH₄ between the Pt and Au electrode materials leads to an oxygen concentration cell which can generate an electric power between them. In this paper the author describes such a one-chamber fuel cell with respect to their structural feature, performance as a fuel cell and their component materials citing the experimental results made by his laboratory's group. Paper presented at the 97th Xiangshan Science Conference on New Solid State Fuel Cells, Xiangshan, Beijing, China, June 14–17, 1998.     

Preparation of PtSnRh/C-Sb2O5·SnO2 electrocatalysts by an alcohol reduction process for direct ethanol fuel cell

PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts with different Pt/Sn/Rh atomic ratios (90:05:05, 70:25:05, and 50:45:05) were prepared by an alcohol reduction process using H₂PtCl₆·6H₂O, SnCl₂·2H₂O, RhCl₃·xH₂O as metal sources, ethylene glycol as solvent and reducing agent, and a physical mixture of Vulcan XC72 (85?wt%) and Sb₂O₅·SnO₂ (15?wt%) as support. The electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. The electro-oxidation of ethanol was studied by cyclic voltammetry and chronoamperometry at 25 and 50?°C and in single direct ethanol fuel cell (DEFC) at 100?°C. The diffractograms of PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts showed the peaks characteristic of Pt face-centered cubic structure and several others peaks associated with ·SnO₂ and Sb₂O₅·SnO₂. Transmission electron micrographs of PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts showed the metal nanoparticles distributed on the supports with particle sizes of about 2?C3?nm. The electrochemical measurements and the experiments in a single DEFC showed that PtSnRh/C-Sb₂O₅·SnO₂ (90:05:05) and PtSnRh/C-Sb₂O₅·SnO₂ (70:25:05) electrocatalysts exhibited higher performance for ethanol oxidation in comparison with PtSnRh/C electrocatalyst.     

Perborate as novel fuel for enhanced performance of membraneless fuel cells

This paper presents the development of membraneless sodium perborate fuel cell using acid/alkaline electrolyte. In the acid/alkaline electrolyte, perborate works both as an oxidant as well as reductant. Sodium perborate affords hydrogen peroxide in aqueous medium. The cell converts the energy released by H₂O₂ decomposition with H⁺ and OH^? ions into electricity and produces water and oxygen. Such a novel design eliminates the need of a membrane, in which acid and alkaline electrolytes contact with each other. At room temperature, the laminar flow-based microfluidic membraneless fuel cell can reach a maximum power density of 34 mW/cm² with the molar ratio of [Perborate]/[NaOH]?=?1 as fuel and [Perborate]/[H₂SO₄]?=?2 as oxidant. The paper reports for the first time the use of sodium perborate as the oxidant and reductant. The developed fuel cell emits no CO₂, features no proton exchange membrane, inexpensive catalysts, and simple planar structure, which enables high design flexibility and easy integration of the microscale fuel cell into actual microfluidic systems and portable power applications.     

H2/Pt/Ce0.9Gd0.1O1.95/Pt/O2 fuel cell operated in the intermediate temperature range 500 – 700°C

Ce_0.9Gd_0.1O_1.95 (GCO), is one of the potential candidate electrolytes for intermediate temperature Solid Oxide Fuel Cells (ITSOFC). GCO has high oxide ion conductivity in the intermediate temperature range (500 – 700 °C) compared to other Ce_1−yGd_yO_2-2/y compositions and the Gd³⁺ ion is the most appropriate dopant material compared to other rare earth materials such as Sm³⁺, Y³⁺, Zr³⁺, etc. Our results show that the fuel cell H₂/Pt/Ce_0.9Gd_0.1O_1.95/Pt/O₂ operated in the temperature range 500 – 700°C gives the maximum power densities 0.0049 W/cm² at 500 °C and 0.0126 W/cm² at 650 °C for cell voltages 0.6275 V and 0.6278 V, respectively, where the electrolyte was kept in 5% H₂ (+ Argon) for 12 hours before use in the fuel cell. Maximum power densities are 0.0038 W/cm² at 500 °C and 0.0270 W/cm² at 650 °C for cell voltages 0.5986 and 0.5913 V, respectively, where the electrolyte was kept in 2 % O₂ (+ Argon) for 12 hours before use in the fuel cell. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

H2S Solid oxide fuel cell based on a modified Barium cerate perovskite proton conductor

Urea combustion method was adopted to prepare precursor powder, MCeO₃ doped with Zr (M is alkaline earth element, such as barium, strontium, and calcium). The precursor powder has typically perovskite structure after being calcined at 873 K. In 773 K∼1,273 K, BaCe_0.425Zr_0.475Y_0.1O₃ has the highest conductivity above 10⁻² S cm⁻¹ and good chemical stability, while the phase transition may exist in H₂S atmosphere for the proton conductors. In the single fuel cell composed of MoS₂-BaCe_0.425Zr_0.475Y_0.1O_3-σ-Ag with BaCe_0.425Zr_0.475Y_0.1O_3-σ as electrolyte, the best performance is obtained. The open circuit voltage of fuel cell is all about 0.72 V, the max power density, 1.55 mW cm⁻². The performance drop is attributed to ohmic loss resulting from the separation of electrolyte and electrode, and improvement is required to bring out new anode materials compatible to the proton conductor, BaCe_0.425Zr_0.475Y_0.1O_3-σ, as electrolyte.     

Ignition and volatile combustion behaviors of a single lignite particle in a fluidized bed under O2/H2O condition

O₂/H₂O combustion, as a new evolution of oxy-fuel combustion, has gradually gained more attention recently for carbon capture in a coal-fired power plant. The physical and chemical properties of steam e.g. reactivity, thermal capacity, diffusivity, can affect the coal combustion process. In this work, the ignition and volatile combustion characteristics of a single lignite particle were first investigated in a fluidized bed combustor under O₂/H₂O atmosphere. The flame and particle temperatures were measured by a calibrated two-color pyrometry and pre-buried thermocouple, respectively. Results indicated that the volatile flame became smaller and brighter as the oxygen concentration increased. The ignition delay time of particle in dense phase was shorter than that in dilute phase due to its higher heat transfer coefficient. Also, the volatile flame was completely separated from particles (defined as off-flame) in dense phase while the flame lay on the particle surface (defined as on-flame) in dilute phase. The self-heating of fuel particles by on-flame in dilute phase was more obvious than that in dense phase, leading to earlier char combustion. At low oxygen concentration, the flame in the H₂O atmosphere was darker than that in the N₂ atmosphere because the heat capacity of H₂O is higher than that of N₂. With the increase of oxygen concentration, the flame temperature in the O₂/H₂O atmosphere was dramatically enhanced rather than that in the O₂/N₂ atmosphere, where the diffusion rate of oxygen in O₂/N₂ atmosphere became the dominant factor.     

Structural characterization study of nickel ferrite particles dispersed in a corrosion product deposit layer

Using X-ray absorption fine structure spectroscopy, both EXAFS and XANES, the cation distributions in NiFe₂O₄ particles dispersed in a corrosion product deposit layer have been studied. The specimen was obtained from a selected fuel rod used in a commercial boiling water reactor plant. EXAFS data allowed the quantitative determination of specific site distributions for all transition metal cations in Ni-ferrite deposits. The results show that the analyzed NiFe₂O₄ particles do not have a totally inverted spinel structure. The relative occupancy of iron and nickel cations in the tetrahedral and octahedral sites of the spinel lattice is determined from the measured data.     

On the observation of a huge lattice contraction and crystal habit modifications in LiMn2O4 prepared by a fuel assisted solution combustion

Two batches of poly-crystalline lithium manganate were prepared by a fuel assisted solution combustion method. LiMn₂O₄(S) was prepared using starch as the fuel and LiMn₂O₄(P) was prepared using poly vinyl alcohol (PVA) as the fuel. XRD studies indicated a significant and consistent shift in the 2θ values of all the hkl peaks to higher values in LiMn₂O₄(P) compared to LiMn₂O₄(S) indicating a lattice contraction in the former. TG/DTA studies indicated a higher formation temperature (∼25 °C higher) for LiMn₂O₄(P). The higher formation temperature most likely promotes the oxidation of some Mn³⁺ to Mn⁴⁺ with a lower ionic radius causing a lattice contraction. This hypothesis is confirmed through XPS studies which indicated the presence of a higher fraction of Mn⁴⁺ in LiMn₂O₄(P) than that present in LiMn₂O₄(S). A crystal shape algorithm was used to generate the crystal habits of lithium manganate from their XRD data leading to an understanding on the exposed hkl planes in these materials. From the atomic arrangement on the exposed hkl planes it is predicted that LiMn₂O₄(P) would be less prone to manganese dissolution and hence would possess a higher cycle life when compared to LiMn₂O₄(S).     

Correlation between Al2O3 particles and interface of Al-Al2O3 coatings by cold spray

Al-Al₂O₃ composite coatings with different Al₂O₃ particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al₂O₃) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al₂O₃ particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al₂O₃ particles. In addition, when the large hard particles of fused Al₂O₃ were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages.     

Spectroscopic and Molecular Modeling Based Approaches to Study on the Binding Behavior of DNA with a Copper (II) Complex

Blocking the division of tumor cells by small-molecules is currently of great interest for the design of new antitumor drugs. The interaction of a new metal complex with DNA was investigated through several techniques. Absorption spectroscopy and gel electrophoresis studies on the interaction of the Cu-complex of (2a-4mpyH)₂ [Cu(pyzdc)₂ (H₂O)₂].6 H₂O with DNA have shown that this complex can bind to CT-DNA with binding constant 3.99?×?10⁵ M^?1. The cyclic voltammetry (CV) responses of the metal complex in the presence of CT-DNA have shown that the metal complex can bind to CT-DNA through partial intercalation mode and this is consistent with molecular docking analysis, quenching process and thermal denaturation experiments. The cytotoxicity of this complex has been evaluated by MTT assay. The results of cell viability assay on DU145 cell line revealed that the metal complex had cytotoxic effects.     

有机金属化学气相沉积法制备的Ni/Al2O3纳米复合材料的氢吸附

研究了通过有机金属化学气相沉积技术及单源分子前躯体方法制备的Ni/Al₂O₃纳米复合材料的氢吸附(存储). 在冷壁的有机金属化学气相沉积反应器中,通过降解Ni(acac)₂粉末基底上的[H₂Al(OtBu)]₂制备的Ni/Al₂O₃纳米复合材料. 通过X射线粉末衍射、扫描电镜、透射电镜以及能量色散型X射线荧光光谱等技术表征该复合材料. 采用自制Sievert's设备研究该复合材料的氢吸附(存储),可以储存约2.9%(重量比)的氢.     

O<Subscript>2</Subscript> photodesorption from a Ag<Subscript>8</Subscript>O<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack> cluster

The decay path of an Ag₈(O₂)^- cluster photoexcited by a 3.1 eV photon is elucidated using time-resolved photoelectron spectroscopy. Photoabsorption results in the formation of an excited state giving rise to a peak in the photoelectron spectra with well-resolved vibrational finestructure. With a lifetime of about 100 fs this bound state decays into an anti-bonding state which dissociates into O₂ and Ag₈^- on a timescale of 10 ps. In the photoelectron spectra, this corresponds to a broad maximum shifting gradually towards higher binding energy while the O₂ and Ag₈^- separate. Finally, the spectrum of bare Ag₈^- appears. This process is unique to small clusters, because on metal surfaces excited state lifetimes are too short to allow for direct dissociation.