Enhancement on the hydrothermal stability of ZSM-5 zeolites by the cooperation effect of exchanged lanthanum and phosphoric species

It was explored by density functional calculations that exchanged La or P species exert great influence on the local Al sites as well as on the adjacent exchanged species. In partially exchanged La- or P/H-ZSM-5 zeolite, some of the Al sites will fall off from the zeolite framework even more easily than in H-form ZSM-5, consistent with our XRF experiments. However, when exchanged by both La and P species, Al at either of the two exchanged sites shows better stability compared to H-from. zeolite. La and P species will interact strongly with each other, as evidenced by the charge donation process and the shortening of P-O-1 bond length. It was just the cooperation of La and P species that enabled RSCC catalysts worked normally under severe conditions. (C) 2004 Elsevier B.V. All rights reserved.

Structure of an unexpected trimer from the reaction of ageratochromene II with aluminum chloride

A new trimer from the reaction of ageratochromene [1] (6,7-dimethoxy-2,2-dimethyl-1-benzopyran) with anhydrous aluminum chloride was shown to be 3,4-dihydro-6,7-dimethoxy-2,2-dimethyl-3-(6',7'-dimethoxy-2',2'-di-methyl-2H-1-benzopyran-4'-yl)-4-(3" 4"-dihydro-6", 7"-dimethoxy-2",2"-dimethyl-2H-1-benzopyran-3"-yl)-2H-1-benzopyran. Its structure was confirmed by NMR (H-1, C-13, DEPT-135. COSY, HMBC, HSQC, TOCSY and NOESY), IR, mass spectra and elemental analysis. Copyright (C) 2002 John Wiley Sons, Ltd.

Determination of lead using a poly(vinyl chloride)-based crown ether membrane

A poly(vinyl chloride)(PVC)-based membrane of 15-crown-5 exhibits a good response for lead(II) ions over a wide concentration range. The response time of the sensor is 30 s and the membrane can be used for more than four months without observing any divergence. The selectivity of the sensor is comparable with those reported for other such electrodes. It was possible to determine lead in polluted waters using this electrode assembly.

Calibration of a solid-state copper ion-selective electrode in cupric ion buffers containing chloride

It is shown that near-Nernstian calibration slopes can be obtained with a Cu1.8Se electrode in a range of cupric ion buffers in spite of a high chloride content. Best results are obtained with the ligands ethylenediamine, glycine and histidine. The onset of cupric ion toxicity towards marine organisms falls within the pCu calibration range obtained with glycine, and the Cu1.8Se electrode could, therefore, be useful for monitoring cupric ion activity in bioassays in sea-water media.

Polyamide thin film composite membranes prepared from isomeric biphenyl tetraacyl chloride and m-phenylenediamine

Three novel of isomeric tetra-functional biphenyl acid chloride: 3,3',5,5'-biphenyl tetraacyl chloride (mm-BTEC), 2,2',4,4'-biphenyl tetraacyl chloride (om-BTEC), and 2,2',5,5'-biphenyl tetraacyl chloride (op-BTEC) were synthesized, and used as new monomers for the preparation of the thin film composite (TFC) reverse osmosis (RO) membranes through interfacial polymerization with m-phenylenediamine (MPDA). The results of membrane performance test showed that membranes prepared from om-BTEC and op-BTEC had higher flux at the expanse of rejection compared with membranes prepared from mm-BTEC.

Failure of the plasma-sprayed coating of lanthanum hexaluminate

Lanthanum magnesium hexaluminate (LaMgAl11O19, LMA) is an attractive material for thermal barrier coatings (TBCs), and the failure of its coating was studied in this work by thermal cycling, X-ray diffraction, dilatometric measurement and thermal gravimetric-differential thermal analysis. The dilatometric measurement indicates that even though the bulk material of LMA has a higher sintering-resistance than the typical TBC material, i.e. yttria-stabilized zirconia (YSZ), the plasma sprayed coating of LMA has two serious contractions due to the re-crystallization of LMA and phase transitions of alumina.

Lanthanum zirconate ceramic toughened by BaTiO3 secondary phase

La2Zr2O7 (LZ) is a promising thermal barrier coating material for the high-temperature applications, which could be significantly toughened by the BaTiO3 piezoelectric phase incorporated into the matrix. The composites of xBaTiO(3)/(l-x)LZ (x=5, 10, 15, 20 vol%, LZ-x-BaTiO3) were densified by means of high-pressure sintering (HPS) under a pressure of 4.5 GPa at 1450 degrees C for 10 min, by which a high relative density above 93% could be obtained.

Effects of deposition conditions on composition and thermal cycling life of lanthanum zirconate coatings

Lanthanum, zirconate (La2Zr2O7, LZ) coatings were prepared under four different deposition conditions by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, surface and cross-sectional morphology, cyclic oxidation behavior of these coatings were studied. Elemental analysis indicates that the coating composition has partially deviated from the stoichiometry of pyrochlore, and the existence of excess La2O3 is also observed. The deviation could be reduced by properly controlling the electron beam current or by changing the ingot composition.

Synthesis and high-pressure sintering of lanthanum magnesium hexaaluminate

Lanthanum magnesium hexaaluminate is a very important ceramic material for high temperature applications. In this paper lanthanum magnesium hexaaluminate has been synthesized directly by solid-state reaction. The forming mechanism was investigated by XRD. The SEM photographs show that the prepared powders are made of hexagonal plates. These powders can be well sintered at the high temperature (1600 degrees C) under the high pressure (4.5 GPa), and the relative density reaches 94.8%.

Laser glazing of lanthanum magnesium hexaaluminate

Lanthanum magnesium hexaalumminate (LMA) is an important candidate for thermal barrier coatings due to its thermal stability and low thermal conductivity. On the other hand, laser glazing method can potentially make thermal barrier coatings impermeable, resistant to corrosion on the surface and porous at bulk. LMA powder was synthesized at 1600 degrees C by solid-state reaction, pressed into tablet and laser glazed with a 5-kW continuous wave CO2 laser.