Microstructural Engineering of Hydroxyapatite Membranes to Enhance Proton Conductivity

Abstract

A new approach to enhancing proton conductivity of ceramics is demonstrated by aligning proton conductive pathways and eliminating resistive grain boundaries. Hydroxyapatite (HAP) membranes are synthesized by multistage crystallization onto palladium. The synthesis involves three steps: electrochemical deposition of HAP seeds, secondary hydrothermal crystallization onto the seed layer to promote c‐axis growth normal to the substrate, and tertiary hydrothermal crystallization to promote a‐axis growth to fill the gaps between the aligned crystals. The c‐axis alignment with crystal domains spanning the membrane thickness significantly enhances proton conduction since protons are primarily transported along the c‐axes of HAP crystals. The novel HAP membranes display proton conductivity almost four orders of magnitude higher than traditional sintered HAP ceramics. The HAP membranes on palladium hydrogen membrane substrates hold promise for use in intermediate‐temperature fuel cells, chemical sensors, and other devices. The synthesis approach presented may also be applied to other ion‐conducting membrane materials to enhance transport properties.

Electrochemical growth of composite hydroxyapatite coatings for controlled release

“…The morphology of the coating is similar to other reports of electrochemical growth of HA under slightly longer reaction times [21,33]. The HA nanocrystals appear rod-shaped with the long axis associated with the crystallographic c-axis [20]. In the second stage, a 5 minute reaction was carried out with 1 mM Rhodamine 6G added to the electrolyte solution.…”

“…Many approaches, including plasma spraying, sputter coating, electrophoretic deposition, electrochemical, hydrothermal, sol-gel and biomimetic synthesis methods have been developed to fabricate HA coatings on different substrates [17][18][19][20][21][22][23]. Electrochemical synthesis of HA is a wet chemical method that enables well crystallized coatings to be synthesized on metallic substrates under mild conditions [24][25][26][27].…”

Calcium orthophosphate deposits: Preparation, properties and biomedical applications

“…ACCEPTED MANUSCRIPT 39 Hydrothermal process was used to deposit CaPO 4 on both metallic [408,409,[487][488][489][490][491][492][493][494][495][496][497][498] and polymeric [499,500] substrates. Ones this technique was called as "a chemical bath method" [501].…”

“…Besides, ECD might be combined with other deposition techniques. Namely, ECD was used to deposit CaPO 4 seeds, followed by the secondary growth of CaPO 4 crystals under hydrothermal conditions[408,409]. Further details on the ECD are available in literature[301].To conclude, electrochemically deposited CaPO 4 coatings on implants are commercially available, for example, BONIT ® (DOT GmbH, Rostock, Germany) and BoneMaster ® (BIOMET Corp., Warsaw, IN, USA).…”

Enhanced high-temperature electrical response of hydroxyapatite upon grain size refinement

“…[3,4] Different strategies like microstructural engineering [5] and single valence ion doping [6] were applied to enhance conductivity of hydroxyapatite.…”