Anomalous high-temperature oxidation in the zirconium-copper system

The high-temperature oxidation of the Zr-3 mass% Cu alloy and Zr₂Cu in oxygen is characterized by selective oxidation of zirconium while the excess of copper is accumulated at the alloy-oxide interface forming the Zr₈Cu₅ phase. The oxidation of Zr₂Cu at elevated temperatures shows an anomalous decrease of the oxygen consumption rate in the temperature range 890-975 °C. The oxide layer consists of monoclinic ZrO₂ mainly, with preferentially oriented crystallites in depth region at 900 °C and tetragonal ZrO₂ on the surface below 600 °C, and small amounts of CuO and Cu₂O. The reaction kinetics obeys a parabolic rate law. The activation energy of 117.5 and 54.4 kJ/mol has been estimated for the oxidation of the Zr-3 mass% Cu alloy and Zr₂Cu, respectively.     

Oxidation performance of Mo3Si with Al additions

The Mo₃Si alloys with different aluminum contents were fabricated by the arc-melting and drop-casting technique, heat treated and then exposed to air at 700, 800, 900 and 1000 °C in order to assess their oxidation behavior. Line scan studies led to the assumption that the oxide scale thermally grown at 1000 °C was composed of SiO₂ which was located closer to the alloy matrix and Al₂O₃ around the outer surface of the oxidized sample, while the Mo oxide volatilized at this oxidation temperature. The results also showed that the unalloyed sample (Mo₃Si) underwent a pest reaction in a short time of exposure, while the sample with 16 at.% Al exhibited the best oxidation behavior, which could be attributed to the formation of SiO₂ and Al₂O₃ in the oxide scale.     

Effect of lamellar microstructure on oxidation kinetics of Fe3Al sintered by hot isostatic pressing

The present paper focuses on the investigation of the relationship between microstructure of Fe₃Al prepared by hot isostatic pressing (HIP) and kinetics of alumina layer formation during oxidation at 900 °C, 1000 °C and 1100 °C. As prepared HIPed Fe₃Al sample reveals lamellar microstructure with inhomogeneous Al distribution which originates from the preliminary mechanical activation of Fe-Al mixture. At 900 °C, Fe₃Al oxidation is characterized by selective growth of very rough alumina layer containing only transient aluminium oxides. In addition to these transient oxides, α-Al₂O₃ stable phase is formed at 1000 °C. At the highest temperature (1100 °C), continuous and relatively smooth alumina layer mainly contains fine crystallites of α-Al₂O₃. The initial lamellar structure and phase inhomogeneity in as-HIPed Fe₃Al samples are supposed to be the main factors that determine observed peculiarities after Fe₃Al oxidation at 900 °C and 1000 °C.     

Dielectric and microwave properties of ZrO2 doped CaO-SiO2-B2O3 ceramic matrix composites

The behavior of dielectric and microwave properties against sintering temperature has been carried out on CaO-SiO₂-B₂O₃ ceramic matrix composites with ZrO₂ addition. The results indicated that ZrO₂ addition was advantageous to improve the dielectric and microwave properties. X-ray diffraction (XRD) patterns show that the major crystalline β-CaSiO₃ and a little SiO₂ phase existed at the temperature ranging from 950 °C to 1050 °C. At 0.5 wt% ZrO₂, CaO-SiO₂-B₂O₃ ceramic matrix composites sintered at 1000 °C possess good dielectric properties: ?_r = 5.85, tan δ = 1.59 × 10⁻⁴ (1 MHz) and excellent microwave properties: ?_r = 5.52, Q · f = 28,487 GHz (11.11 GHz). The permittivity of Zr-doped CaO-SiO₂-B₂O₃ ceramic matrix composites exhibited very little temperature dependence, which was less than ±2% over the temperature range of −50 to 150 °C. Moreover, the ZrO₂-doped CaO-SiO₂-B₂O₃ ceramic matrix composites have low permittivity below 5.5 over a wide frequency range from 20 Hz to 1 MHz.     

Oxidation behavior of Al4SiC4 ceramic up to 1700 °C

Isothermal oxidation behavior of Al₄SiC₄ ceramics at the temperature range from 1200 °C to 1700 °C in air for 10-20 h was investigated. The results indicated that this material had an excellent oxidation resistance from 1200 °C to 1600 °C, and the kinetics of oxidation obeyed the parabolic law with an activation energy of 220 ± 20 kJ mol⁻¹. The oxide scales consisted of an outer oxide layer with higher density, a middle oxide layer with a few of large size pores and a reaction layer which is near to the matrix with a number of small size pores over the temperature ranges. A number of pores exist in the middle oxide scale. The oxide surface and cross-sectional morphologies were observed by scanning electron microscope (SEM) technique and the formation mechanism of the oxidation layers was also analyzed.     

Hot corrosion behaviour of Yb2Zr2O7 ceramic coated with V2O5 at temperatures of 600-800 °C in air

To better understand the hot corrosion behaviour of Yb₂Zr₂O₇ ceramic in molten V₂O₅, hot corrosion experiments were performed in a temperature range of 600-800 °C in air. Different reaction products of ZrV₂O₇, YbVO₄ and m-ZrO₂ were identified depending upon the hot corrosion conditions, for example, ZrV₂O₇ and YbVO₄ at 600 °C for 2 h and 8 h; ZrV₂O₇, m-ZrO₂ and YbVO₄ at 700 °C for 2 h; m-ZrO₂ and YbVO₄ either at 800 °C for 2 h or at 700-800 °C for 8 h. The hot corrosion reaction mechanisms were further discussed based on the thermal instability of ZrV₂O₇ at elevated temperatures.     

Microstructure, kinetic analysis and hardness of Sn-Ag-Cu-1 wt% nano-ZrO2 composite solder on OSP-Cu pads

Nano-sized, nonreacting, noncoarsening ZrO₂ particle-reinforced Sn-Ag-Cu composite solders were prepared by mechanically dispersing ZrO₂ nano-particles into Sn-Ag-Cu solder and the interfacial morphology between the solder and organic solderability preservative (OSP)-Cu pads were characterized metallographically. At their interfaces, island-shaped Cu₆Sn₅ and Cu₃Sn intermetallic compound (IMC) layers were found in solder joints with and without the ZrO₂ particles and the IMC layer thickness was substantially increased with reaction time and temperature. In the solder ball region, needle-shaped Ag₃Sn and spherically-shaped Cu₆Sn₅ IMC particles were found to be uniformly distributed in the β-Sn matrix. However, after the addition of ZrO₂ nano-particles, Ag₃Sn and Cu₆Sn₅ IMC particles appeared with a fine microstructure and retarded the growth rate of the IMC layers at their interfaces. From a kinetic analysis, the calculated activation energies for the total (Cu₆Sn₅ + Cu₃Sn) IMC layers for Sn-Ag-Cu and Sn-Ag-Cu-1 wt% ZrO₂ composite solder joints on OSP-Cu pads were about 53.2 and 59.5 kJ/mol, respectively. In addition, solder joints containing ZrO₂ nano-particles displayed higher hardness due to the uniform distribution of ZrO₂ nano-particles as well as the refined IMC particles. The hardness values of the plain Sn-Ag-Cu solder joint and solder joints containing 1 wt% of ZrO₂ nano-particles after 5 min reaction at 250 °C were about 15.0 Hv and 17.1 Hv, respectively. On the other hand, their hardness values after 30 min reaction were about 13.7 Hv and 15.5 Hv, respectively.     

High temperature scaling of Ni-xSi-10 at.% Al alloys in 1 atm of pure O2

The oxidation of Ni-xSi-10Al alloys (with x = 0, 2, 4 and 6 at.%), has been studied at 900 and 1000 °C in 1 atm of pure O₂ to examine the effect of different silicon additions on the behavior of ternary Ni-Si-10Al alloys. The kinetic curves of Ni-10Al are approximately parabolic at both 900 and 1000 °C. Conversely, the kinetics of the ternary alloys at both temperatures correspond generally to a rate decrease faster than predicted by the parabolic rate law, except for the oxidation of Ni-6Si-10Al at 1000 °C, which exhibits a single nearly-parabolic stage. Oxidation of the binary alloy formed at both temperatures an internal oxidation zone beneath a layer of NiO. Oxidation of Ni-2Si-10Al at both temperatures and of the other two alloys at 900 °C formed initially a zone of internal oxidation of Al + Si. However, a layer of alumina forming at the front of internal oxidation after some time blocked the internal oxidation and produced a gradual conversion of the metal matrix of this region into NiO, with a simultaneous decrease of the oxidation rate. Conversely, the oxidation of Ni-4Si-10Al and Ni-6Si-10Al at 1000 °C did not produce an internal oxidation, but formed an alumina layer directly on the alloy surface after an initial stage when also Ni was oxidized. Therefore, silicon exerts the third-element effect by reducing the critical Al content needed for the transition from its internal to its external oxidation with respect to the corresponding Ni-Al alloy. This result is interpreted by means of an extension to ternary alloys of Wagner’s criterion for the same transition in binary alloys based on the attainment of a critical volume fraction of internal oxide.     

Surface analyses and biocompatibility study of 500 °C oxidized Ni50Ti50 and Ni40Ti50Cu10 shape memory alloys

Ni₅₀Ti₅₀ and Ni₄₀Ti₅₀Cu₁₀ shape memory alloys (SMAs) are oxidized at 500 °C. Considering the surface roughness, the thicknesses of oxide layer and Ni-free layer, the surface Ni concentration, the proper oxidation times for oxidized specimens are found to be 60 min for Ni₅₀Ti₅₀ and 30 min for Ni₄₀Ti₅₀Cu₁₀. Experimental results reveal that the oxidation is diffusion-controlled with its oxide layer containing titanium oxide and that the surface Ni concentration is much lower than the nominal composition. When Ni₅₀Ti₅₀ and Ni₄₀Ti₅₀Cu₁₀ SMAs are oxidized at these times, the latter has better corrosion resistance than the former in Hanks' solution at 27 °C. However, the results of cytotoxicity and cell proliferation assays indicate that the biocompatibility of unoxidized Ni₄₀Ti₅₀Cu₁₀ is worse than that of unoxidized Ni₅₀Ti₅₀, but that of oxidized Ni₄₀Ti₅₀Cu₁₀ ranks as good as that of oxidized Ni₅₀Ti₅₀.     

Effect of addition of Ba(W0.5Cu0.5)O3 in Pb(Mg1/3Nb2/3)O3-Pb(Zn1/3Nb2/3)O3-Pb(Zr0.52Ti0.48)O3 ceramics on the sintering temperature, electrical properties and phase transition

In this work, we report on the Pb(Mg_1/3Nb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃-Pb(Zr_0.52Ti_0.48)O₃ (PMN-PZN-PZT) ceramics with Ba(W_0.5Cu_0.5)O₃ as the sintering aid that was manufactured in order to develop the low-temperature sintering materials for piezoelectric device applications. The phase transition, microstructure, dielectric, piezoelectric properties, and the temperature stability of the ceramics were investigated. The results showed that the addition of Ba(W_0.5Cu_0.5)O₃ significantly improved the sintering temperature of PMN-PZN-PZT ceramics and could lower the sintering temperature from 1005 to 920 °C. Besides, the obtained Ba(W_0.5Cu_0.5)O₃-doped ceramics sintered at 920 °C have optimized electrical properties, which are listed as follows: (K_p = 0.63, Q_m = 1415 and d₃₃ = 351 pC/N), and high depolarization temperature above 320 °C. These results indicated that this material was a promising candidate for high-power multilayer piezoelectric device applications.     

Structural and magnetic nanoclusters in Cu50Zr50−xGdx (x = 5 at.%) metallic glasses

It is shown that phase-separated metallic glasses on the nanoscale can be prepared by rapid quenching of Cu₅₀Zr_50−xGd_x melts with a low concentration of gadolinium (x = 5 at.%). Gd-enriched clusters of 2 nm size are formed as early stages of decomposition in the deeply undercooled melt. The key physical parameter to obtaining such a nanoclustered microstructure upon quenching is the critical temperature of liquid-liquid phase separation which has to be close to the glass transition temperature. Thus, the thermodynamic properties of the liquid phase even in the metastable deeply undercooled melt essentially determine the structure formation. Analysis of the spatial atomic arrangement by atom probe tomography after annealing in the supercooled liquid state provides direct evidence of the spinodal character of the decomposition by uphill diffusion. The Gd-enriched nanoclusters exhibit ferromagnetic ordering below 50 K and the cluster size regime derived from magnetization measurements is in good agreement with that obtained from atom probe tomography investigations. The first stage of crystallization of Cu₅₀Zr₄₅Gd₅ glass is observed to be Ostwald-type ripening on a nanoscale. The phase-separated glass acts as a precursor for the formation of a metastable nanocrystalline structure.     

The role of microstructure in the high temperature oxidation mechanism of Cr3C2-NiCr composite coatings

Composites of Cr₃C₂-NiCr provide superior oxidation resistance to WC-Co composites, which has seen them applied extensively to components subjected to combined high temperature erosion and oxidation. This work characterises the variation in oxidation mechanism of thermally sprayed Cr₃C₂-NiCr composites at 700 °C and 850 °C as a function of heat treatment. Carbide dissolution during spraying increased the Ni alloy Cr concentration, minimising the formation of Ni oxides during oxidation. Compressive growth stresses resulted in ballooning of the oxide over the carbide grains. Carbide nucleation with heat treatment reduced the Ni alloy Cr concentration. The oxidation mechanism of the composite coating changed from being Cr based to that observed for NiCr alloys.     

He ion irradiation induced nanocrystallization in Cu50Zr45Ti5 glassy alloy

Partial nanocrystallization induced by ion irradiation can be used to improve the surface properties in metallic glasses. We investigated the crystallization behavior and the structure of the formed nanocrystalline phases in a melt-spun Cu₅₀Zr₄₅Ti₅ glassy alloy irradiated with 140 keV He ions to a fluence of 1.7 × 10¹⁷/cm². Crystalline nanoparticles were precipitated by He ion irradiation. The nanocrystalline phases were identified as a mixture of the orthorhombic Cu₁₀Zr₇ phase, tetragonal CuZr₂ phase and monoclinic CuZr phase. Hardness enhancement was observed at a depth close to the projected range of the He ions, which was related to the formation of the crystalline nanoparticles.     

Thermo-electrochemical activation of Cu3Sn negative electrode for lithium-ion batteries

A Cu₃Sn film electrode (thickness = ca. 3 μm) is prepared by DC magnetron sputtering deposition of Sn on Cu substrate and subsequent annealing at 300 °C for 30 h. At 25 °C, this Cu-Sn binary intermetallic compound is inactive for lithiation, but becomes active at elevated temperatures due to facilitation of Cu-Sn bond cleavage for the conversion-type lithiation. The lithiated product at 120 °C is the most Li-rich Li-Sn alloy (Li₁₇Sn₄). Upon de-lithiation, the Cu-Sn intermetallics of different compositions are generated by the reaction between the metallic Sn that is restored from Li₁₇Sn₄ and the idling metallic Cu. The nature of the resulting intermetallics is dependent on the de-lithiation temperature: Cu₁₀Sn₃ at 120 °C and Cu₆Sn₅ at 25 °C. Only the latter is active for lithiation in the subsequent room-temperature cycling. That is, Cu₃Sn is thermo-electrochemically activated to be Cu₆Sn₅ by lithiation at 120 °C and subsequent de-lithiation at 25 °C. The higher lithiation activity observed with the more Sn-rich phase (Cu₆Sn₅) compared to the initial one (Cu₃Sn) has been accounted for by the higher equilibrium lithiation potential (thermodynamic consideration) and smaller number of Cu-Sn bonds to be broken (kinetic consideration).     

Effect of CuO on the sintering temperature and piezoelectric properties of MnO2-doped 0.75Pb(Zr0.47Ti0.53)O3-0.25Pb(Zn1/3Nb2/3)O3 ceramics

The sintering temperature of 0.75Pb(Zr_0.47Ti_0.53)O₃-0.25Pb(Zn_1/3Nb_2/3)O₃ ceramics containing 1.5 mol% MnO₂ was decreased from 930 to 850 °C with the addition of CuO. The CuO reacted with the PbO and formed a liquid phase during the sintering, which assisted the densification of the specimens. Most of the Cu²⁺ ions existed in the CuO second phase, thereby preventing any possible hardening effect from the Cu²⁺ ions. Variations of the k_p, Q_m, ?₃^T/?₀ and d₃₃ values with CuO were similar to that of the relative density. The specimen containing 0.5 mol% CuO sintered at 850 °C showed the good piezoelectric properties of k_p = 0.5, Q_m = 1000, ?₃^T/?₀ = 1750 and d₃₃ = 300 pC/N.     

An in situ neutron diffraction study of the thermal disproportionation of the Zr2FeD5 system

The Zr₂FeD₅ system has been annealed to 680 °C under ultra high vacuum, and studied in situ by neutron diffraction. The system disproportionates through three distinct regions in temperature. Initially, the tetragonal Zr₂FeD₅ (P4/ncc) is retained up to 330 °C, while steadily depleted of D. From 330 °C to 530 °C, a complex multi-phase disproportionation occurs, with the production of cubic ZrD₂, tetragonal ZrD₂, tetragonal Zr₂FeD₅ (I4/mcm), and growth of the intermetallic ZrFe₂. At the beginning of the 330-530 °C period, the total atom count from quantitative phase analysis (QPA) indicates the formation of amorphous (a-) Zr₅₆Fe₄₄. By 530 °C, QPA and peak breadth analysis indicate that ca. 2/3rd of the sample is consumed as very small nanocrystals (<150 Å coherence length) of strained ZrD₂. From 530 °C to 680 °C, the cubic ZrD₂ is almost entirely consumed and depleted of D to form the final mixture of the intermetallic phases Zr₃Fe and ZrFe₂. QPA of the final intermetallic mixture yields a Zr:Fe ratio greater than that observed in either the arc melted alloy or the initial Zr₂FeD₅ deuteride, indicating that a ca. Zr₇₁Fe₂₉ amorphous component was present in the initial arc melted alloy. According to the total atom count by QPA, crystallisation of the Fe richer amorphous Zr₅₆Fe₄₄ phase formed at 330 °C begins at ca. 530 °C, and later by 680 °C, all amorphous phases have completely crystallised to yield a 70.77:26.75:2.47 mol.% mixture of Zr₃Fe:ZrFe₂:ZrD_2−x.     

Effect of heat-treatment on stress relaxation behavior of plasma-sprayed 7 wt.% Y2O3-ZrO2 stand-alone coatings

The present work studied the effect of heat-treatment temperature (1000 °C and 1200 °C) and time (10, 50, and 100 h) on the compressive stress relaxation behavior of plasma-sprayed stand-alone 7 wt.% Y₂O₃-ZrO₂ (YSZ) coatings at test temperatures of 1000 °C, 1100 °C, and 1200 °C, from stresses of 60 and 20 MPa. As-sprayed coatings were also stress relaxed in the baseline condition at room and elevated temperatures. All coatings demonstrated a two-stage relaxation behavior: fast relaxation (stage I) in the first 10 min and much slower relaxation in the final 170 min of the test (stage II). Stage I relaxation, as measured by percentage of the original stress relaxed, accounts for at least 50% of the total stress relaxed despite occurring in only 5-10 min and was attributed to lamella sliding and compaction, and permanent intralamellar crack closure (for tests conducted at higher temperatures). Stage II relaxation behavior is dominated by diffusion creep mechanisms, where prior densification at 1200 °C resulted in reduced relaxation rates compared to coatings heat treated at 1000 °C and in the as-sprayed condition. The 1200 °C test temperature greatly influenced the percentage of relaxation in the coating, more so than the prior coating heat-treatment conditions.     

Corrosion inhibition during synthesis of Cu2O nanoparticles by 1,3-diaminopropylene in solution

Corrosion inhibition for Cu₂O nanoparticles in solution using the regulators of 1,3-dimorpholinpropylene and 1,3-diethylaminopropylene was studied by experimental and theoretical calculation methods. The inhibition mechanism of regulators was related to the arrangement of cetyltrimethylammonium (CTAB) molecules on the surface of Cu₂O nanoparticles. Control of the type and amount of regulators has been demonstrated to produce well-dispersed and active Cu₂O nanoparticles (∼100 nm). The oxidation temperature of Cu₂O nanoparticles decreased from 297.9-404.4 °C (blank) to 232.3-334.3 °C (containing regulator). For 1,3-dimorpholinpropylene, its arc structure and active sites (C_4C_5, N_2 and O_2) facilitate the formation of stable protective film over Cu₂O surface.     

Nanocarbon-dependent synthesis of ZrB2 in a binary ZrO2 and boron system

Thermodynamically, ZrO₂ may react with boron to form B₂O₃/B₂O₂ and ZrB₂ at room temperature. However, this reaction is incomplete at temperatures lower than 1550 °C, even with the use of metastable reactants, i.e., as-synthesized amorphous hydrous nano-ZrO₂ and amorphous boron powders. In this study, a complete disintegration of ZrO₂ was achieved by introducing nanocarbon to the binary system of ZrO₂ and boron at 1550 °C. The metastable reactants affected the temperature required for the solid-state reactions and also strongly affected the kinetics of the transformation. Single crystal and plate-like ZrB₂ particles with a uniform distribution and a size of ca. 1.0 μm in two-dimensions were obtained using 5 wt.% nanocarbon and a B/Zr molar ratio of 4.     

Early high temperature oxidation behaviour of Ti(C,N)-based cermets in air

Isothermal oxidation behaviour of two Ti(C,N)-based cermets (TiC-10TiN-16Mo-6.5WC-0.8C-0.6Cr₃C₂-(32-x)Ni-xCr, x = 0 and 6.4 wt%) was investigated in air at 800-1100 °C up to 2 h. Mass gains exhibited neither linear nor parabolic law during isothermal oxidation. The oxide scales formed at 800-1100 °C were multi-layered, consisting of NiO outerlayer, NiTiO₃ interlayer and TiO₂-based innerlayer. The internal oxidation zones formed at 1000-1100 °C consisted of Ti-based, Ni-based and Mo-based complex oxides. Cermet with 6.4 wt% Cr exhibited superior oxidation resistance, due to the presences of Cr_0.17Mo_0.83O₂ in TiO₂-based innerlayer of the oxide scale and Cr-rich Ti-based complex oxide in the internal oxidation zone.