English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The local structural environments in a series of natural and synthetic alunite samples [ideally AAl 3 (SO 4 ) 2 (OH) 6 , A = H 3 O + , D 3 O + , Na + , and K + ] have been probed by solid-state  1 H,  2 H,  23 Na,  27 Al, and  39 K NMR spectroscopy. The natural alunite [KAl 3 (SO 4 ) 2 (OH) 6 ] and synthetic hydronium alunite samples contain few structural defects, whereas the synthetic natroalunite and alunite samples have ca. 10% Al vacancies based on  27 Al NMR. A new  27 Al local environment (Al D ) was observed and assigned to Al with one Al vacancy in the first cation sphere. Three different proton environments, Al 2 -OH, Al - OH 2 , and H 3 O +  are detected by  1 H and  2 H MAS NMR. The hydronium ion (H 3 O + ) is only observed in hydronium alunite, and is associated with the stoichiometric regions of the sample. It was not detected in  1 H and  2 H NMR spectra of alunite and natroalunite despite K (Na) occupancies of significantly less than 100%, as determined from elemental analysis. Thus, our NMR results suggest that the common assumption, namely that an A vacancy and an Al 3+  vacancy are compensated by adding an H 3 O + and 3H +  (creating 3 Al-OH 2  groups), respectively, is too simplistic. Instead, a significant fraction of the Al 3+  vacancies are compensated for by 4 H +  ions, resulting in 4 Al-OH 2  groups per vacancy. This substitution is accompanied by the simultaneous deprotonation of a H 3 O +  ion present on the A site. The resultant H 2 O molecule is unnecessary for charge balance, accounting for the A-site deficiency often observed. The presence of Al 3+  and A +  vacancies appears closely correlated based on NMR.

american mineralogist

Characterization of defects and the local structure in natural and synthetic alunite (K, Na, H 3 O)Al 3 (SO 4 ) 2 (OH) 6  by multi-nuclear solid-state NMR spectroscopy