Dissolution rates, electrochemical and passivation properties of alpha ZrO solid solutions in HF

James, William Joseph; Custead, Wayne G.; Straumanis, M. E.

doi:10.1016/0010-938x(62)90029-x

Cited by 8 publications

(4 citation statements)

References 19 publications

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“…However, oxygen may affect the potential of an anode in two or three ways. Taking, as an example, a metal in which O can be dissolved (formation of a solid solution) the free energy of the metal becomes less negative and its potential more noble (17). The same is also achieved by the development of oxides on the surface, presumably because of a mixed potential (18) formation and/or because of a reduction of the effective surface area.…”

Section: Discussionmentioning

confidence: 99%

Current Density-Anodic Potential Curves of Single Crystal GaAs at Low Currents in KOH

Straumanis

Krumme

James

1968

J. Electrochem. Soc.

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Single p-type, GaAs crystals of high purity, Zn doped, were used to determine whether or not the inverse octahedral {ill} faces show potential differences and various rates of anodic dissolution. The Ga(lll}, As(ill}, (If0}, and (100} faces, were polished, etched, and etch-polished with concentrated H2SO4 ~ H=,O.~, and immersed in IN KOH. The Ga(lll} faces were found to be the most noble with respect to rest and anodic dissolution potentials. The potential difference between the inverse (lll} faces was as large as 0.14v for the rest and 0.123v for the dissolution potentials. The 4 anodic polarization curves gave nearly parallel Tafel lines, with a slope of 66.0 ~-1 mv/log i, up to current densities of 0.5 ma/cm 2. The rate of anodic dissolution of the As{lll} faces was 69 X as high as the inverse Ga(lll}. The activation energies of dissolution of all 4 faces were equal within experimental limits: 16.7 _ 0.7 kcal mole -I. It is concluded that the slow step in the dissolution of GaAs is a one electron discharge with subsequent steps leading to the formation of Ga (OH)3 to provide a protective coating not readily soluble in KOH. From this point of view all observed phenomena can be explained in a qualitative manner.Crystals without a symmetry center are polar; the polarity shows up through differences in chemical and physical behavior of the inverse planes of the respective crystals. The cubic HI-V semiconductor compounds of diamond-type structure belong to this class, of which the best known are GaAs and InSb. Their polarity is displayed by the behavior of the inverse octahedral planes III{lll} and V(lll}, e.g., GaAs by Ga{lll} and As{lll}.Reaction of III-V semiconductors in various media, with or without applied current have been studied by Gatos et aI. (1), Pleskov (2), Gerischer (3, 4), Harvey (5), Brummer (6), Arthur (7), and others (8). They found that the various crystal planes react differently in aqueous media, such that the III(lll} and V{lll} inverse planes can be distinguished by the formation of specific etch patterns (1, 3, 8). The distinction can also be made from etching rates (1) from the inclination of etch tunnels produced by an anodic current on the GaAs octahedral planes (the tunnels run perpendicularly to As{lll} and at an angle of 20 ~ to Ga(lll}) (8), and from LEED patterns (9). Furthermore, the two inverse planes exhibit different activation energies of oxygen desorption (as Ga20): 54• from the Ga(lll} and 42• kcal/mole from the As face. Since there is little transfer of charges over the valence bridges (9, 10-13), the Ga atoms on the III(lll} side retain their 3-valence electrons, while the As atoms on the inverse side retain 5. All this suggests that the two planes should also develop potential differences in electrolytes.However, in this respect there are major disagreements. Gatos et al. reported that group III{lll} planes exhibit more noble electrode potentials than group V(lll} surfaces: for instance InSb inverse octahedral planes show a potential difference of 75 and more mv (1)....

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Section: Discussionmentioning

confidence: 99%

Current Density-Anodic Potential Curves of Single Crystal GaAs at Low Currents in KOH

Straumanis

Krumme

James

1968

J. Electrochem. Soc.

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“…A similar value of 16.7 kcal/mole was also obtained for the anodic dissolution reaction of the compound GaAs in KOH (2). Much lower activation energies were found for metals simply dissolving in acids, e.g., 5.3 • 0.5 kcal for Hf dissolving in 1N HF or in a mixture of HF and HC1 (8) and 3.8 to 4.2 kcal for Zr in 0.2N HF or 0.1N HF ~ 1.0N HCI respectively (9). However, when the oxygen content of Zr was increased up to 7% b.w., the Ea increased to 5.9 kcal.…”

Section: Table I Ea For the Anodic Reactions On Various Planes Af Ins...mentioning

confidence: 93%

Dissolution Potentials and Activation Energies of InSb Single Crystals

Straumanis

1972

J. Electrochem. Soc.

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The rest (or corrosion) and dissolution potentials of normalInSb single crystals in normalHCl were determined. There is no potential difference (within error limits) between the inverse {111} faces in pure normalHCl . A difference of up to 44 mV and more develops as soon as the normalInSb electrode is anodically dissolved.The potential becomes less noble in the sequence In {111}, {100}, {110}, normalSbfalse{true1¯true1¯true1¯false} . The Tafel relationship is observed over three decades of current density. With additions of FeCl3 , FeCl2 , K3normalFefalse(CNfalse) 6 , K4normalFefalse(CNfalse) 6 , H2C4H4O6 to 2N normalHCl , the anodic potentials of both inverse {111} faces are shifted to more active values; the ɛ́Η of In{111} is always nobler than that of normalSbfalse{true1¯true1¯true1¯false} . There are indications that the various potentials observed are a function of current density within the pores of a protective layer, Sb4O5Cl2 . The apparent activation energy, ca. 20 kcal/mole, of the anodic dissolution reaction is nearly the same on all crystallographic planes of normalInSb . The rate of anodic dissolution of normalSbfalse{111false} in pure 2NnormalHCl is 3–7 times larger than that of the inverse face at the same potential.

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“…Chemical etching was attempted to analyze the microstructure of the coating's cross‐section. HF acid was chosen as etchant owing to its moderate capacity to dissolve zirconia, as reported in Lowalekar and Raghavan 16 and James et al 17 . The polished specimens were immersed into HF acid (50 wt%) for 3 min, rinsed in pure water with ultrasonic cleaner, and dried afterwards.…”

Section: Methodsmentioning

confidence: 99%

Twin‐Structured Yttria‐Stabilized t′ Zirconia Coatings Deposited by Plasma Spray Physical Vapor Deposition: Microstructure and Mechanical Properties

Huang

et al. 2007

Journal of the American Ceramic Society

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In this work, we report a twin-structured yttria-stabilized t 0 zirconia (YSZ) coating which was fabricated through an advanced plasma spray physical vapor deposition process with a highpower hybrid plasma spraying system. The as-deposited YSZ structure, entirely different from those deposited by conventional atmospheric plasma spraying and electron beam physical vapor deposition, is characterized by coarse grains of over 5 lm size which compose the entire coating, differently sized t 0 -ZrO 2 twins which fill the coarse grains, and micron-scaled lenticular t 0 colonies in which twins on the submicrometer scale arrange alternatively. The indentation tests show that both the nanohardness and microhardness of the peculiar coating are markedly higher than those of the ordinary YSZ coatings, even comparable with those of the sintered YSZ polycrystal bulks.

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Dissolution rates, electrochemical and passivation properties of alpha ZrO solid solutions in HF

Cited by 8 publications

References 19 publications

Current Density-Anodic Potential Curves of Single Crystal GaAs at Low Currents in KOH

Current Density-Anodic Potential Curves of Single Crystal GaAs at Low Currents in KOH

Dissolution Potentials and Activation Energies of InSb Single Crystals

Twin‐Structured Yttria‐Stabilized t′ Zirconia Coatings Deposited by Plasma Spray Physical Vapor Deposition: Microstructure and Mechanical Properties

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