Thermal expansion behavior of boron-doped cordierite glass-ceramics

The linear thermal expansion coefficients of cordierite glass-ceramics that have been doped with a fixed amount of P2O5 and 1, 2, and 3 wt % of B2O3 show negative expansion in the temperature range of 100 degrees-300 degrees C. The expansion of the undoped cordierite sample is positive. A relative decrease in the degree of negative expansion is observed as the B2O3 concentration increases. These negative expansion coefficients are similar to those of cordierite glass-ceramics that have been doped,vith the potassium cation

Virtual melting and the generation of new glass compositions

To find a glass composition whose properties will match a set of pre-assigned specific properties is a modern problem especially wizen the requirements are unusual. A methodology as well as rite prediction of compositions for six specific cases is described. The examples involve matching optical proper ties including refractive index and mean dispersion with a pre-assigned optical specification. The term virtual melting process (VMP) is used to describe how the solutions are predicted

Synthesis, structure determination and reactivity of a highly stable vanadium(III) complex

The synthesis, characterization, structure determination and reactivity study of a highly stable vanadium(III) complex of picolinic acid (picH)-a monoacid bidentate chelating donor-is reported. It can be kept in open air for days and can be heated up to 180 degrees C without oxidation. The complex [V(pic)(3)]. H2O crystallizes in the monoclinic system with space group C2/c. The V-III acceptor centre is in a highly distorted octahedral donor environment. The reason for this exceptional stability of the complex towards oxidation is evident from the analysis of the structural and electrochemical data. (C) 1997 Elsevier Science Ltd

X-ray crystal structure of [VO(DPA)(H2O)(2)]center dot 2H(2)O (DPA = dipicolinate dianion)

The X-ray crystal structure of the trans-diaqua complex [VO(DPA)(H2O2)]. 2H(2)O (I) (DPA = dipicolinate dianion) has been determined. Comparison with the known structure of [VO(DPA)(o-phen)]. 3H(2)O (2), obtained from (1) by displacement of the two coordinated aqua molecules, shows that the coordination sphere around vanadium is reorganised during this reaction

Complexes of hexadentate NSO donor ligands - III. Nickel(II) complexes of 1,3-di(o-salicylaldiminophenylthio)propane and 1,2-di(o-salicylaldiminophenylthio)xylene

Nickel(II) complexes of the hexadentate N2S2O2 donor ligands, 1,3-di(o-salicylaldiminophenylthio)propane (H(2)DSALPTP) and 1,2-di(o-salicylaldiminophenylthio)xylene (H(2)DSALPTX) have been synthesised and characterised. H(2)DSALPTP reacted with NiCl2.6H(2)O or Ni(ClO4)(2).6H(2)O in presence of ammonia to give the complex [Ni(DSALPTP)] (1). H(2)DSALPTX reacted smoothly with N(ClO4)(2) to yield the corresponding complex [Ni(DSALPTX)] (2). The ligand did not react with NiCl2 in the absence of ammonia but in its presence produced the complex (2). The molecular and crystal structure;of [Ni(DSAL PTX)] exhibits a very unusual deployment of the six donor sites of the ligand. It crystallises in the orthorhombic system with space group P2(1)2(1)2(1). In dichloromethane solution both the complexes are found to exhibit Ni(II)/Ni(III) redox couples in their cyclic voltammograms at room temperature with E-1/2 values 0.87 and 0.78 V (vs. Ag/AgCl). (C) 1998 Elsevier Science Ltd. All rights reserved