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 system Al 2 O 3 -P 2 O 5 -H 2 O contains many phosphate minerals that occur in various geologic environments. The natural occurrence of variscite (AlPO 4 ·2H 2 O, orthorhombic), including its monoclinic polymorph metavariscite, is largely restricted to soils and aluminous rocks like Al-rich igneous rocks and shales, which interacted with P-rich hydrothermal solutions or groundwater. Variscite dehydrates to berlinite (AlPO 4 ) and a hydrous P-Al-rich fluid. This dehydration reaction AlPO 4 ·2H 2 O = AlPO 4  + 2H 2 O is, however, metastable, at low concentrations of P in the fluid, because berlinite breaks down at lower temperature to augelite [Al 4 PO 4 (OH) 3 ] + H 3 PO 4  + H 2 O and trolleite [Al 4 (PO 4 ) 3 (OH) 3 ] + H 3 PO 4  + H 2 O. The variscite/metavariscite = berlinite equilibrium has been investigated by synthesis experiments from mixtures of γ-Al 2 O 3  and excess phosphoric acid at pressures between 1 and 5 kbar and temperatures of 100-200 °C using standard cold-seal vessels. The hydration-dehydration equilibrium is mainly controlled by temperature and only weakly by pressure. At 4 and 5 kbar, variscite/metavariscite were found at temperatures of ~150 °C, at lower pressure at 115-125 °C in accordance with their natural mode of occurrence. In this T range, however, variscite/metavariscite is not the sole phase but is always accompanied by variable but generally minor amounts of wavellite and trolleite Al 4 (PO 4 ) 3 (OH) 3 . Secondary wavellite Al 3 (PO 4 ) 2 (OH) 3 ·5H 2 O, hydrated Al-phosphate AlPO 4 ·xH 2 O (1.1 ≤ x ≤ 1.3) and Al-metaphosphate hexahydrate Al(H 2 PO 4 ) 3  formed during quenching and/or drying of the runs. Berlinite is the reaction product at temperatures 200 °C/4-5 kbar and 150 °C/1-3 kbar and may be associated with augelite and trolleite.

The system Al 2 O 3 -P 2 O 5 -H 2 O at temperatures below 200 °C: Experimental data on the stability of variscite and metavariscite AlPO 4 ·2H 2 O