Production and isolation of pH sensing materials by carbonate melt oxidation of iridium and platinum

O'Malley, Matthew J.; Woodward, Patrick M.; Verweij, H.

doi:10.1039/c2jm16791c

Cited by 19 publications

(25 citation statements)

References 42 publications

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“…Profound crystallographic knowledge of the α-Li 2 IrO 3 -H 3 LiIr 2 O 6 system is essential for understanding and controlling the process presented in (eqn (1)) and in consequence also for the production of stable and reliable pH sensing IrO xbased solid state electrodes.…”

Section: Introductionmentioning

confidence: 99%

“…The compound was recently revealed to be the pH sensing phase in an IrO x -based solid state electrode. 1 The pH electrode is a promising supplement for glass electrodes, as thin glass membranes are incompatible with high pressures and temperatures, as well as with extreme alkaline and hydrofluoric media. [2][3][4] IrO x -based solid state electrodes can be produced by the carbonate melt oxidation process [5][6][7] in which iridium wires are oxidized in an excess of molten lithium carbonate.…”

Section: Introductionmentioning

confidence: 99%

“…The occurrence of stacking faults in α-Li 2 IrO 3 is crucial for the production of H 3 LiIr 2 O 6 , as the degree of cation exchange is the higher, the higher the degree of faulting of the precursor material. 1 by using XRPD data and PDF-analysis. As the XRPD data indicate a strongly stacking faulted crystal lattice, possible structural defects are derived from the crystal structure and investigated by systematic DIFFaX simulations.…”

Section: Introductionmentioning

confidence: 99%

“…This process leads to the formation of α-Li 2 IrO 3 . 1,8 In a subsequent step the excess of lithium carbonate is dissolved by acid treatment and α-Li 2 IrO 3 is transformed into H 3 LiIr 2 O 6 by cation exchange (eqn (1) …”

Section: Introductionmentioning

confidence: 99%

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Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H₃LiIr₂O₆

et al. 2017

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A powder sample of pure H 3 LiIr 2 O 6 was synthesized from α-Li 2 IrO 3 powder by a soft chemical replacement of Li + with H + . The crystal structure of H 3 LiIr 2 O 6 consists of sheets of edge sharing LiO 6 -and IrO 6 -octahedra forming a honeycomb network with layers stacked in a monoclinic distorted HCrO 2 type pattern. Heavy stacking faulting of the sheets is indicated by anisotropic peak broadening in the X-ray powder diffraction (XRPD) pattern. The ideal, faultless crystal structure was obtained by a Rietveld refinement of the laboratory XRPD pattern while using the LiIr 2 O 6 3− -layers of α-Li 2 IrO 3 as a starting model. The low radial distances of the PDF function, derived from synchrotron XRPD data, as constraints to stabilize the structural refinement. DIFFaX-simulations, structural considerations, high radial distances of the PDF function and a Rietveld compatible global optimization of a supercell were employed to derive a suitable faulting model and to refine the microstructure using the experimental data. We assumed that the overall stacking pattern of the layers in the structure of H 3 LiIr 2 O 6 is governed by interlayer O-H⋯O contacts.From the constitution of the layers, different stacking patterns with similar amounts of strong O-H⋯O contacts are considered. Random transitions among these stacking patterns can occur as faults in the crystal structure of H 3 LiIr 2 O 6 , which quantitatively describe the observed XRPD.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H₃LiIr₂O₆

et al. 2017

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“…24) The Li + /Pt ratios in the reports were equal 25)27) or used 5% excess Li 2 CO 3 18),19), 24) to the stoichiometric ratio of Li 2 PtO 3 . Because the melting point of Li 2 CO 3 is 720°C, 28) calcination above 720°C implies that melted Li 2 CO 3 reacts with Pt black.…”

Section: Evaluation Of the Enthalpy Changes In The Formation Of Alkalmentioning

confidence: 99%

Synthesis of alkali metal platinates and their dissolution behavior in hydrochloric acid

Kasuya

Miki

Morikawa

et al. 2013

J. Ceram. Soc. Japan

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To decrease the environmental load due to current Pt dissolution processes that use strong acids in combination with oxidizing agents, the synthesis and dissolution of alkali metal platinates in hydrochloric acid (HCl) were examined. The alkali metal platinates were prepared by calcinating mixtures of Pt black and the alkali metal carbonates (Li, Na, K) at 600800°C in air. Li 2 PtO 3 powder was obtained through the calcination of a Pt black and Li 2 CO 3 mixture at 600°C. The formation of NaPt 3 O 4 and Na 2 PtO 3 was confirmed upon the calcination of Pt black and Na 2 CO 3 at 600800°C; however, unreacted Pt also remained in the calcined samples. The calcination of Pt black and K 2 CO 3 did not yield any Pt-containing oxides, even at 800°C. These results indicated that Li 2 CO 3 was the most active reagent among the examined alkali metal carbonates for the formation of alkali metal platinates. The dissolution of the resulting Li 2 PtO 3 in conc. HCl was monitored by inductively coupled plasmaoptical emission spectrometry. The results showed that Li ions leached into HCl prior to the Pt, and the solubilities of the metals increased with decreasing calcination temperature. The dissolution behavior of Li 2 PtO 3 was discussed based on the crystallite size and anisotropy of the crystal. A Pt dissolution process by way of these platinates is expected to benefit the establishment of recovery processes for PGMs with low environmental loads.

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Monitoring pH in corrosion engineering by means of thermally produced iridium oxide electrodes

Femenias

Angst

Elsener

2017

Materials & Corrosion

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Funding information Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen ForschungA pH sensor to be used in highly alkaline media under continuous long-term immersion conditions is crucial in various engineering applications. This work develops the production protocol and posterior conditioning of thermally oxidized iridium (IrO x ) electrodes to be used as potentiometric pH sensors embedded in highly alkaline environments such as concrete or cathodically protected steel in soil. The main investigated aspects for the desired applications are the potential-pH response, its reproducibility, accuracy, and oxygen dependency. The stability during long-term immersion is also studied in detail. The studied IrO x electrodes responded to pH changes with slopes between −50 and −68 mV/pH unit, even after continuous immersion in alkaline solutions for almost 2 years. Additionally, the electrodes response did not show oxygen dependency. Our results highlight the importance of sufficient conditioning in alkaline media prior to use. When properly produced, conditioned, and pre-calibrated the electrodes reproducibly permit measuring the pH with a maximum error of 0.5 pH units over a range of at least pH 9-13.5. Preliminary results show that the studied electrodes are promising sensors for monitoring pH changes in concrete.

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Production and isolation of pH sensing materials by carbonate melt oxidation of iridium and platinum

Cited by 19 publications

References 42 publications

Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H₃LiIr₂O₆

Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H₃LiIr₂O₆

Synthesis of alkali metal platinates and their dissolution behavior in hydrochloric acid

Monitoring pH in corrosion engineering by means of thermally produced iridium oxide electrodes

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Production and isolation of pH sensing materials by carbonate melt oxidation of iridium and platinum

Cited by 19 publications

References 42 publications

Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H3LiIr2O6

Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H3LiIr2O6

Synthesis of alkali metal platinates and their dissolution behavior in hydrochloric acid

Monitoring pH in corrosion engineering by means of thermally produced iridium oxide electrodes

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Product

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Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H₃LiIr₂O₆

Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H₃LiIr₂O₆