Melt Synthesis, Structural, Characterization and Scaling of Swelling 2:1-Layer Silicate Materials
- Melt synthesis, characterization, and refinement of single crystal structures of swelling 2:1-layer silicates were the main fundamental topics of the presented thesis. In particular, large scale syntheses of both lithium and sodium fluorohectorite were successfully achieved. Furthermore, the crystal structure of one-, and two-layer hydrate of sodium fluorohectorite and the one-layer hydrate of sodium brittle mica were thoroughly investigated and characterized in detail.
Swelling sodium fluorohectorite with good crystallinity in an ideal composition of Na0.85[Mg2.15Li0.85]Si4O10F2 was synthesized for investigating the hydrated structure. Melt synthesis was done in closed molybdenum crucibles using pure reagents (glass with composition Na2O-2SiO2, Li2SiO3 MgF2, MgO, SiO2). The crystal structures of one- and two-layer hydrate of sodium fluorohectorite were studied. The one-layer hydrate of sodium fluorohectorite (at relative humidity 45 %) showed two planes of interlayer sodium along . The two-layer hydrate of sodium fluorohectorite showed sodium interlayer cations being located in the middle of the interlayer.
In addition, sodium brittle mica with a target composition Na4[Mg6]Si4Al4O20F4 was successfully synthesized via melt synthesis in a gas tight molybdenum crucible and the refinement of the one-layer hydrate of sodium brittle mica was done. The synthetic sodium brittle mica swells only to the one-layer hydrate and could not be further hydrated to the two-layer hydrate.
Generally, natural swelling layer silicates (smectites) usually contain impurities such as iron oxide (pigmentation material), quartz, and carbonate. However, these impurities hinder the employment of swelling layer silicates in industry for cutting edge and advanced applications. In addition, they suffer from small particle size under 5 µm limiting their aspect ratio. For industrial applications, pure synthetic swelling layer silicates with superior properties are highly desirable.
Therefore, a large scale synthesis of sodium fluorohectorite Na0.6[Mg2.4Li0.6]Si4O10F2 was carried out in three steps. (i) Synthesis of glass, glass was used as precursor and low melting agent, the amorphous glass with composition Na2O-Li2O-6SiO2 was synthesized from sodium carbonate Na2CO3, lithium carbonate Li2CO3, and silicic acid SiO2∙nH2O via melt synthesis in an open glassy carbon crucible at 1075 °C under flowing argon in a high frequency induction furnace, where the temperature was increased with a constant rate of 300°C/hr. (ii) dehydration and decarboxylation of silicic acid SiO2∙nH2O and magnesium basic carbonate MgCO3∙Mg(OH) respectively at 900 °C for one hour in a corundum crucible in a chamber furnace. (iii) Mixing and melting the glass, the material obtained by dehydration and decarboxylation of SiO2∙nH2O and MgCO3∙Mg(OH)2 together with magnesium fluoride to achieve a composition of Na0.6[Mg2.4Li0.6]Si4O10F2. The total mixture was transferred into a glassy carbon crucible and melted at 1265 °C under argon for 15 min. The synthetic sodium fluorohectorite showed uniform and high intracrystalline reactivity, represented a pure phase, which was colorless and of good crystallinity.
High aspect ratio layer silicates would be an optimum functional material for future application in polymer layered silicate nanocomposites. Delamination via osmotic swelling is known in laponite-type clays. High hydration energy of the interlayer cation, such as lithium can force layer silicates to swell infinitely and delaminate. Consequently, the lithium fluorohectorite with variable layer charge was synthesized via melt synthesis in an open glassy carbon crucible in a high frequency induction furnace. The same procedure used for sodium fluorohectorite was applied for lithium fluorohectorite, where the glass with composition Li2O-2SiO2 was prepared via reaction of lithium carbonate with silicic acid at 1200 °C for 1hr. Due to the high fugacity of lithium fluoride, excess of one mole Li and F was added via lithium silicate and magnesium fluoride respectively. The raw material of lithium fluorohectorite was melted at 1350 °C for 10 min.
The synthetic lithium fluorohectorite showed uniform intracrystalline reactivity, came in large well crystalline tactoids and completely delaminated to a single silicate layers in water. The lithium fluorohectorite behavior reveals that these materials have high potential for barrier application and flame retardancy. Furthermore, the lithium fluorohectorite was synthesized in large scale.
Novel Group 4 Metal Amido Complexes - syntheses, reactivity and olefin polymerization catalysis
- A series of amine functionalized electron rich aminopyridinato ligands was synthesized by the methodology developed by Fort and coworkers and subsequent Ulmann thermal amination. In addition to this some tripodal ligands containing nitrogen donor functionalities were also synthesized. The corresponding titanium and hafnium complexes of these ligands were synthesized using the amine / diethyl-ammonium chloride / toluene elimination and salt metathesis routes. These compl-exes were characterized by NMR and elemental analysis. Many of these complexes have been studied on the basis of structure and their catalytic potential was investigated. The overall evaluation of this work tells about the electrophilicity of the metal centre and the steric and electronic effects of the ligand.
Mono Ap di / trichloride complexes of titanium were synthesized by amine / diethyl-ammonium chloride elimination and salt metathesis routes by reacting the corresponding ligand with diethylamido titanium trichloride or titanium tetrachloride respectively. The structural investigation of these complexes gives insight into the more electron donating capability of the aminopyridinato ligands. These complexes were found moderatly active for ethylene and styrene polymerization when activated with d-MAO giving syndiotactic polystyrene of high molecular weight and aluminum terminated polyethylene. The low activity of these complexes was attributed to the ligand transfer to aluminum during catalysis.
Mono Ap trialkyl hafnium complexes were synthesized by reacting the respective aminopyridinato ligand with tetrabenzyl hafnium at room temperature. Some of these complexes were studied by single crystal X- ray analysis. These complexes have shown very low activity towards ethylene polymerization when activated with d-MAO probably due to very fast ligand transfer to aluminum. The low temperature NMR investigations of these complexes indicate the η3-coordination of one benzyl with hafnium metal centre.
To overcome the problem of ligand transfer during catalysis, we synthesized the tri-podal ligands containing nitrogen donors either by Pd2(DBA)3 / DPPP catalysed cross coupling reactions or by Ni(o) / 2, 2 -bipyridine catalyst system followed by thermal amination. The titanium trichloride complexes of these ligands were synthesized by reacting the respective tripodal ligand with [Et2NTiCl3] at room temperature. The titanium complexes containing tripodal ligands were found less active towards ethyl-ene polymerization.