Lucien Van Poucke

Sulphur group analysis in solid matrices by atmospheric pressure-temperature programmed reduction

The atmospheric pressure-temperature programmed reduction (AP-TPR) has become an established and reliable method amongst the different sulphur characterisation techniques for solid materials, like coal and coal derived products, rubber and clay. The analytical method is based upon the fact that specific sulphur functional groups are hydrogenated at specific temperatures. During the last few years, several adjustments have been made to the hard- and software as well as to the experimental parameters. The changes and the reliability of the method are extensively discussed in this paper.

Phase formation of ferroelectric perovskite0.75 Pb(Zn1/3,Nb2/3)O3–0.25BaTiO3 prepared by aqueous solution–gel chemistry

Here we report on the synthesis and phase formation of perovskite n0.75 Pb(Zn1/3,Nb2/3)O3–0.25 nBaTiO3 n(PZN–BT) by means of a new aqueous solution–gel nmethod. The gelation process was optimized for an ammonium PZN acetate citrate nprecursor. The chemical homogeneity of this precursor was investigated by nmeans of TEM–EDX analysis (Transmission Electron Microscopy–Energy nDispersive X-ray analysis). All metal ions were found to be homogeneously ndispersed in the precursor gel at least down to 10xa0nm. An aqueous BaTiO3 nprecursor was synthesized and its oxide formation was investigated by means nof HT-XRD (High Temperature X-ray Diffraction) and TGA–MS (Thermogravimetric nAnalysis on-line coupled to Mass Spectrometry). The gel-to-oxide transition nof the PZN–BT precursor was studied using HT-XRD and TGA–MS. It nwas concluded that 96+ weight% perovskite PZN–BT could be nformed out of the gel precursor if proper thermal treatment is applied (14 nminutes sintering at 800u2006°C after fast firing at 50u2006°Cxa0min−1). nFinally a phase formation mechanism for perovskite PZN–BT is proposed: nperovskite 0.75 Pb(Zn1/3,Nb2/3)O3–0.25 nBaTiO3 is formed out of a cubic pyrochlore PZN. At 850u2006°C nthe perovskite decomposes irreversibly into that same pyrochlore together nwith volatile PbO and ZnO. The evolution of PbO was proved with TGA.

Interaction of the organic matrix with pyrite during pyrolysis of a high-sulfur bituminous coal

Abstract High-sulfur bituminous coal containing 4.17 wt% of pyritic sulfur and the pyrite concentrate separated from this coal were used to examine the interaction between pyritic sulfur and the organic part of coal during pyrolysis. At 330–500°C, as a result of the reaction of sulfur derived from pyrite decomposition with the coal organic matrix, a significant increase in the organic sulfur in the char is observed, from 1.47 to 3.17 wt%. The enrichment in sulfur is most pronounced between 400 and 450°C, corresponding to the most intensive thermal degradation of this coal. At these temperatures, some of the pyrite is converted to pyrrhotite. The organic sulfur content is a maximum at ∼ 500°C, when all the pyrite is reduced to pyrrhotite. The pyrite in the coal undergoes conversion to troilite via pyrrhotite at lower temperatures than does pure pyrite. Compared with the thermal decomposition of pure pyrite, the pyrite present in coal starts to decompose at a lower temperature (330 vs. 400°C). The conversion to troilite also proceeds to completion at a much lower temperature. This demonstrates that the decomposition of pyrite is markedly affected by the presence of the organic coal substance.

Rank dependence of organic sulfur functionalities in coal

Organic sulfur functionalities were characterized and quantified by atmospheric-pressure temperature-programmed reduction (AP-TPR). Nine coals were chosen to cover the entire rank range from subbituminous coal to anthracite. To be able to study the organic sulfur groups, the vitrinite concentrates were separated from each coal sample. The results confirm the larger amount of sulfide in low-rank coals. The amount of thiophenes generally increases with rank. Nevertheless, sulfur functionality distribution can vary from coal to coal even at the same rank.

Effect of calcium and calcium minerals in coal on its thermal analysis

Abstract The effect of the presence of limestone and dolomite in coal, and calcium in lignite, on atmospheric-pressure temperature-programmed reduction (AP-TPR) analysis was studied. AP-TPR experiments were carried out on a bituminous coal with added limestone and dolomite and on a demineralized lignite. The results showed that both calcium minerals captured the gaseous H 2 S formed under AP-TPR conditions and produced CaS. Consequently the sulfur recovery monitored was too low and the AP-TPR kinetograms were deformed. The study also showed that the influence of dolomite is greater than of limestone. AP-TPR analysis of lignite demineralized and then loaded with calcium ions again showed a clear lowering of sulfur comparable with that of dolomite, but starting at a higher temperature.

Sulfur functionalities and physical characteristics of the Maritza Iztok Basin lignite

Abstract The use of selective functional group modification procedures has been investigated for the determination sulfur forms in low-rank coals. A Bulgarian lignite from the Maritza Iztok Basin was submitted to a variety of chemical treatments. The fresh lignite and residues were studied by atmospheric pressure temperature-programmed reduction (AP-TPR) and sulfur K-edge X-ray absorption near-edge structure (XANES) analysis to investigate the distribution of sulfur forms. The impact on the physical characteristics of the lignite following each treatment was studied by thermal analysis (d.t.a.) and scanning electron microscopy (SEM-EDX). The results have demonstrated the ability of selective procedures to simplify sulfur functionality determination by AP-TPR and have provided a clear insight into the impact of treatments on the thermal characteristics of the lignite.

Absorption-Reflection Infrared Spectroscopy Studies of Sol-Gel Prepared Ferroelectric Pb(Zr,Ti)O3 Thin Films on Pt Electrodes

Although the sol-gel method is ideally suited for the preparation of ferroelectric PZT thin films, poor reproducibility and the need to lower crystallization temperatures remain an issue. To address these problems, we have studied the mechanism of thin film formation using absorption-reflection infrared spectroscopy for a novel and less harmful precursor solution system based on butoxyethanol. By recording in situ infrared spectra we were able to monitor hydrolysis, condensation, decomposition and crystallization phenomena versus temperature. We speculate that the lower reactivity of butoxyethanol is responsible for the higher quality of Ti rich PZT based ferroelectric capacitors prepared by a butoxyethanol precursor solution compared with the more widely used methoxyethanol one. Finally, we observed that films decomposition kinetics is faster as compared to bulk samples and depends on film thickness and electrode layer.

Automated iodimetric determination of Cu+, Cu2+ and Cu3+ in the superconductor YBCO using a modified Gran plot technique

Abstract An automated potentiometric determination of the oxygen content of the superconductor YBCO is described. The end- point of the titration is found using a linear Gran plot technique. Suitable equations are derived by which the number of titration points can be considerably reduced and the titration can be stopped even before the equivalence point is reached. Automation of the iodimetric titration can be performed in an easy manner. During the titration a good estimate of the equivalence volume can be calculated using only two titration points.

Influence of Heat Treatment on Sr0.9Bi2.2Ta2O9 Thin Films Prepared by Aqueous CSD

Sr0.9Bi2.2Ta2O9 thin films were prepared on a Pt-substrate by aqueous chemical solution deposition. The applied heat treatment seems to have a significant influence on the ferroelectric response, crystallinity and surface morphology. For two-layer thin films annealed at 700°C in oxygen, the Pr-value increased from 3.6 until 5.5 μ C/cm2, c-axis preferred orientation was considerably lowered and rod-like instead of spherical grains were grown when the second pyrolysis step at 520°C was omitted.