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Preparation of new polymeric boryl-titanium complexes and studies of their thermal conversion to titanium diboride-based ceramics
Abstract
The reduction of 1,2-catecholatochloroboron by lithium in liquid ammonia/dimethoxyethane produces a reactive mixture containing multiple products. Formation of complexes with 12-crown-4 allows the isolation of one of these, (12-C-4)LiB(O$\sb2$C$\sb6$H$\sb4)\sb2.$ This complex was characterized by chemical analyses, multinuclear NMR, and single crystal x-ray diffraction. Chemical and spectroscopic data suggest that the remainder of this mixture contains boron in an asymmetric electronic environment and a low oxidation state. Reaction of this mixture with TiCl$\sb4$ forms an air stable complex with the formula TiB$\sb2{\cdot2}$((12-C-4)$\cdot$Ti(O$\sb2$C$\sb6 $H$\sb4)\sb2$). $\sp{11}$B and $\sp{47,49}$Ti NMR measurements of this complex indicate that boron and titanium inhabit a highly asymmetric electronic environment possibly with a considerable B-Ti interaction. The complex TiB$\sb2{\cdot}$((dme)$\cdot$Ti(SC$\sb2$H$\sb5)\sb2$(NH$\sb2)\sb2\rbrack,$ was prepared in a similar way. Reaction of this complex with bidentate protic species produced a series of polymeric complexes. TGA of theses polymers showed that mass loss was essentially complete by 400-600$\sp\circ$C. Pyrolysis of this series to 1000$\sp\circ$C formed green ceramic products that were characterized by volatiles analysis, chemical analysis, $\sp{11}$B MAS-NMR, XPS and powder diffraction. Annealing the green products at 1650$\sp\circ$C caused a carbothermic reduction that removed oxide impurities and formed crystalline TiB$\sb2$/TiC. However, this reduction only occurred when the green ceramic contained $>$5% amorphous carbon. In all other cases, the annealed ceramics contained TiBO$\sb3$/TiC. Pyrolysis of TiB$\sb2{\cdot}2$((dme)$\cdot$Ti(O$\sb2$C$\sb6$H$\sb4)\sb2\rbrack$ in a fluidized bed reactor produced a green ceramic with a minimum particle size of 100 nm. For this product, formation of TiB$\sb2$/TiC by carbothermic reduction was complete by 800$\sp\circ$C, 450$\sp\circ$C lower that conventional preparations. Reaction of a boryl-titanium complex with solid supports containing surface hydroxide groups led to thin films of titanium boride.
Subject Area
Inorganic chemistry|Materials science|Chemistry
Recommended Citation
Ayers, Michael Raymond, "Preparation of new polymeric boryl-titanium complexes and studies of their thermal conversion to titanium diboride-based ceramics" (1993). Doctoral Dissertations Available from Proquest. AAI9408251.
https://scholarworks.umass.edu/dissertations/AAI9408251