Untitled

Ziemniak, S.E.; Jones, Michael E.; Combs, K. E. S.

doi:10.1023/a:1022688528380

Cited by 67 publications

(12 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…103 In contrast, the reported solubility for Cr 2 O 3 in alkaline media at 200°C is negligible (nanomolar). 104 Thus, in the present study we find that while both Cr(OH) 3 and CrOOH react with Cu 2 O to form phase-pure 3R-CuCrO 2 ( Figure 6) at 210°C at a moderate hydroxide concentration (>1.0 M), Cr 2 O 3 did not react under similar experimental conditions to form CuCrO 2 . Based on these observations, the chromium oxide system is found to behave similarly to the aluminous phase series, demonstrating that although in general the various hydrated metal oxides are amphoteric, a slow transition to the more solublereactant phase limits the formation of the delafossitetype oxide product.…”

Section: Transition Metals Oxidessupporting

confidence: 53%

“…Although to our knowledge the quantitative alkaline, elevated temperature solubility of Cr(OH) 3 is unknown, the predominance region for Cr(OH) 4 - in the elevated temperature Pourbaix diagram for chromium−water increases with temperature, indicating that the concentration increases . In contrast, the reported solubility for Cr 2 O 3 in alkaline media at 200 °C is negligible (nanomolar) . Thus, in the present study we find that while both Cr(OH) 3 and CrOOH react with Cu 2 O to form phase-pure 3R-CuCrO 2 (Figure ) at 210 °C at a moderate hydroxide concentration (>1.0 M), Cr 2 O 3 did not react under similar experimental conditions to form CuCrO 2 .…”

Section: Synthesis Of Delafossite-type Oxidescontrasting

confidence: 46%

See 1 more Smart Citation

Hydrothermal Synthesis of Delafossite-Type Oxides

et al. 2005

View full text Add to dashboard Cite

The syntheses of copper and silver delafossite-type oxides from their constituent binary metal oxides, oxide hydroxides and hydroxides, by low temperature (<210°C) and low pressure (<20 atm) hydrothermal reactions are described. Particular emphasis is placed on how the acid-base character of a constituent oxide determines its solubility and therefore whether a particular delafossite-type oxide can be synthesized, a strategy utilized by geologists and mineralogists to understand the conditions necessary for the synthesis of various minerals. Thus, the geochemical and corrosion science literature are shown to be useful in understanding the reaction conditions required for the syntheses of delafossite-type oxides and the relationship between reactant metal oxide acid-base character, solubility, aqueous speciation, and product formation. Manipulation of the key parameters, temperature, pressure, pH, and reactant solubility, results in broad families of phase-pure delafossite-type oxides in moderate to high yields for copper, CuBO 2 (B

show abstract

Section: Transition Metals Oxidessupporting

confidence: 53%

Section: Synthesis Of Delafossite-type Oxidescontrasting

confidence: 46%

Hydrothermal Synthesis of Delafossite-Type Oxides

et al. 2005

View full text Add to dashboard Cite

show abstract

“…It exhibits broad, diffuse features in X-ray diffraction patterns that are typical of poorly crystalline or amorphous materials. Extensive studies have addressed the hydrolysis, precipitation, and oligomerization of Cr(III) under aqueous conditions, [20][21][22][23][24][25][26] the preparation and thermal evolution of Cr-(oxy)hydroxide, 14,16,27,28 its solubility and oxidation behavior under different conditions, 8,9,[29][30][31] and its structural properties, which vary with experimental conditions. 11,14,16,[31][32][33] A complete series of mixed composition Cr x Fe 1-x -(oxy)hydroxide compounds can be synthesized between the pure Cr and Fe end members, which, together with solubility and FT-IR evidence, suggests that the series may represent a continuous solid solution.…”

Section: Introductionmentioning

confidence: 99%

Structural Properties of the Cr(III)−Fe(III) (Oxy)hydroxide Compositional Series: Insights for a Nanomaterial “Solid Solution”

et al. 2010

View full text Add to dashboard Cite

Chromium(III) (oxy)hydroxide and mixed Cr(III)−Fe(III) (oxy)hydroxides are environmentally important compounds for controlling chromium speciation and bioaccessibility in soils and aquatic systems and are also industrially important as precursors for materials and catalyst synthesis. However, direct characterization of the atomic arrangements of these materials is complicated because of their amorphous X-ray properties. This study involves synthesis of the complete Cr(III)−Fe(III) (oxy)hydroxide compositional series, and the use of complementary thermal, microscopic, spectroscopic, and scattering techniques for the evaluation of their structural properties. Thermal analysis results show that the Cr end member has a higher hydration state than the Fe end member, likely associated with the difference in water exchange rates in the first hydration spheres of Cr(III) and Fe(III). Three stages of weight loss are observed and are likely related to the loss of surface/structural water and hydroxyl groups. As compared to the Cr end member, the intermediate composition sample shows lower dehydration temperatures and a higher exothermic transition temperature. XANES analysis shows Cr(III) and Fe(III) to be the dominant oxidation states. XANES spectra also show progressive changes in the local structure around Cr and Fe atoms over the series. Pair distribution function (PDF) analysis of synchrotron X-ray total scattering data shows that the Fe end member is nanocrystalline ferrihydrite with an intermediate-range order and average coherent domain size of ∼27 Å. The Cr end member, with a coherent domain size of ∼10 Å, has only short-range order. The PDFs show progressive structural changes across the compositional series. High-resolution transmission electron microscopy (HRTEM) results also show the loss of structural order with increasing Cr content. These observations provide strong structural evidence of chemical substitution and progressive structural changes along the compositional series.

show abstract

“…Ziemniak et al suggest that chromium metal in alkaline media changes the passive film from Cr͑OH͒ 3 to CrOOH at 50°C. 38 ͑iii͒ A change in the kinetics of dissolution where a new reaction pathway is kinetically favored. Further investigations are needed to elucidate which of these mechanism͑s͒ is ͑are͒ responsible for the observed temperature-dependent alloy 22 dissolution.…”

Section: Discussionmentioning

confidence: 99%

Influence of Solution pH, Anion Concentration, and Temperature on the Corrosion Properties of Alloy 22

Gray

Hayes

Gdowski

et al. 2006

J. Electrochem. Soc.

View full text Add to dashboard Cite

We introduce an acid addition technique for the rapid assessment of the influence of solution pH, anion ͑such as chloride͒ concentration, and temperature on the dissolution of metals. We demonstrate the technique with the characterization of the dissolution of alloy 22 ͑Ni-22Cr-13Mo-3W-3Fe͒ exposed to chloride-containing hydrochloric, sulfuric, and nitric acid environments as a function of pH ͑from pH 5 to pH −1͒ and temperature ͑25-90°C͒. A combination of electrochemical techniques ͑electrochemical impedance spectroscopy and linear polarization resistance͒ and atomic force microscopy are used to characterize the influence of the various solutions on the dissolution of alloy 22. Below 50°C, corrosion rates are less than 1 m/yr independent of acid type, pH, and temperature. In contrast, between 50°C and the upper explored limit of 90°C, dissolution rates in sulfuric and hydrochloric acid scale approximately linearly with temperature at rates that depend on the solution pH. In nitric acid, corrosion rates are lower at comparable pH values due to the oxidizing effects of nitrates. An increase in the open-circuit potential in conjunction with electrochemical impedance spectroscopy data suggests that nitrates promote a stable passive oxide film that inhibits alloy dissolution in all environments tested.Nickel-based alloys are employed in a wide range of applications where long lifetimes are vital such as in implant materials and nuclear waste storage. The robustness of alloys in these types of environments is due to the formation of a protective "passive" oxide film at the alloy interface. The nature and composition of these oxide films depends on the alloy composition and the pH, temperature, and electrolyte composition of the formation environment. Alloys can be tailored to fit a specific set of environmental conditions by selection of constituent elements that have strengths that compensate in the areas where other elements fail. For example, for Ni-Cr-Mo alloys, it is generally well established that the Mo provides resistance against reducing acidic environments, Cr against oxidizing conditions, Cr and Mo against localized attack, and Ni, Cr, and Mo against stress corrosion cracking due to chloride ions. [1][2][3][4] This combination of corrosion resistance in both reducing and oxidizing environments makes these alloys particularly well suited as long-term storage materials. As a result, the Ni-Cr-Mo alloy, alloy 22 ͑Ni-Cr22-Mo13-W3-Fe3͒, is the candidate material for the outer wall of nuclear waste packages at the proposed Yucca Mountain nuclear waste repository ͑Nevada, USA͒. Over the past decade, a number of studies have been undertaken to characterize its general and localized corrosion properties. 5-8 These studies demonstrate that alloy 22 is exceptionally corrosion resistant in a broad range of concentrated brines including chloride, fluoride, carbonate, sodium, and calcium with pH values ranging from ϳ2.7 to 13 and temperatures from 25 to 120°C. 9 To date, little work has been done to characterize the allo...

show abstract

Untitled

Cited by 67 publications

References 30 publications

Hydrothermal Synthesis of Delafossite-Type Oxides

Hydrothermal Synthesis of Delafossite-Type Oxides

Structural Properties of the Cr(III)−Fe(III) (Oxy)hydroxide Compositional Series: Insights for a Nanomaterial “Solid Solution”

Influence of Solution pH, Anion Concentration, and Temperature on the Corrosion Properties of Alloy 22

Contact Info

Product

Resources

About