We have characterized unwashed agglomerate Bayer gibbsite, a major precursor for industrial-grade and specialty aluminas, and the transition aluminas/corundum formed on calcination to follow the migration of sodium with phase evolution. Sodium is found initially to be intercalated, likely in the OH-rich planes in hydroxide precursors, with Na 1s XPS spectra demonstrating much becomes incorporated into the alumina structure with calcination. ²³Na-NanoSIMS, XRF, and XPS measurements reveal sodium then migrates from within the crystallites to accumulate in cracks, interfaces or defects and, eventually, at the grain exterior during calcination without significant losses. Changes in pore structure with acid leaching and subsequent re-calcination suggests sodium occupies surface Al-O-Na environments analogous to surface hydroxide, and that near-surface bulk sites act as a reservoir to repopulate lost surface sodium. These bulk sites are argued to be the alumina cation vacancies, the distribution and occupancy of which is still debated despite implications for bulk and surface chemistry properties, a contention strongly supported by XPS and Na K-edge NEXAFS spectra. This indicates that, while surface segregation is thermodynamically favoured, bulk incorporation of sodium occurs for kinetic reasons. We tentatively suggest that bulk hydrogen may similarly be present in activated transition aluminas due to analogous kinetic considerations.

我们已经表征了未洗涤的附聚物拜耳三水铝石，它是工业级和特种氧化铝的主要前体，并且在煅烧时形成的过渡氧化铝/刚玉会跟随钠的迁移而发生相演化。发现最初会插入钠，很可能是在氢氧化物前体中的富含OH的平面中插入，Na 1 s XPS光谱表明，煅烧将大量钠并入氧化铝结构中。²³Na-NanoSIMS，XRF和XPS测量表明，钠随后从微晶内部迁移，积累在裂纹，界面或缺陷中，并最终在煅烧过程中积累在晶粒外部，而没有明显损失。酸浸出和随后的重新煅烧引起的孔结构变化表明，钠占据了类似于表面氢氧化物的表面Al-O-Na环境，并且近表面的堆积位点起着补充失去的钠表面的作用。这些散装位点被认为是氧化铝阳离子空位，尽管散装和表面化学性质有影响，但其分布和占有率仍在争论中，XPS和Na K-edge NEXAFS光谱强烈支持这一论点。这表明，虽然表面偏析在热力学上是有利的，钠的大量引入是出于动力学原因。我们初步建议，由于类似的动力学考虑，大量的氢可能类似地存在于活化的过渡氧化铝中。