Magnetic properties and magnetic structure of the Mn5Si3-type Tb5Si3 compound

Neutron diffraction and magnetization measurements have been performed on the Tb₅Si₃ compound (hexagonal Mn₅Si₃-type, hP16, P6₃/mcm) to understand its magnetic structure and magnetic properties. The temperature-dependent neutron diffraction results prove that this intermetallic phase shows a complex flat spiral magnetic ordering, presenting three subsequent changes in magnetization at on cooling. However, the magnetization data depict two transitions at 72 K (T_N1) and 55 K (T_N2). The extended temperature range between and over which the neutron diffraction patterns slowly evolve might correspond to the high-temperature antiferromagnetic transition at T_N1 and low-temperature antiferromagnetic transition at T_N2 of the magnetic data. Between Tb₅Si₃ shows a flat spiral antiferromagnetic ordering with a propagation vector K₁ = [0,0, ±1/4]; then, between the flat spiral type ordering is conserved, but by two coexisting propagation vectors K₁ = [0,0, ±1/4] and K₂ = [0,0, ±0.4644(3)]. The terbium magnetic moments arrange in the XY(ab) plane of the unit cell. Below the magnetic component with K₁ = [0,0, ±1/4] vanishes and magnetic structure of Tb₅Si₃ is a flat spiral with K₂ = [0,0, ±0.4644(3)], only. Low field magnetization measurements confirm the occurrence of complex, multiple magnetic transitions. The field dependence of the magnetization indicates a metamagnetic transition at a critical field of 3 T.     

Synthesis and crystal structure of a new calcium borate, CaB6O10

A new calcium borate, CaB₆O₁₀, has been prepared by solid-state reactions at temperature below 750 °C. The single-crystal X-ray structural analysis showed that CaB₆O₁₀ crystallizes in the monoclinic space group P2₁/c with a = 9.799(1) Å, b = 8.705(1) Å, c = 9.067(1) Å, β = 116.65(1)°, Z = 4. It represents a new structure type in which two [B₃O₇]⁵⁻ triborate groups are bridged by one oxygen atom to form a [B₆O₁₃]⁸⁻ group that is further condensed into a 3D network, with the shorthand notation 6: ∞³[2 × (3:2Δ + T)]. The 3D network affords intersecting open channels running parallel to three crystallographically axis directions, where Ca²⁺ cations reside. The IR spectrum further confirms the presence of both BO₃ and BO₄ groups.     

Magnetic ordering and magnetic properties of ErAuxNi1−xIn (0 ≤ x ≤ 1) solid solution

The ErAu_xNi_1−xIn (0 ≤ x ≤ 1) quasiternary compounds crystallize in the hexagonal layered crystal structure of ZrNiAl-type. ErAuIn was reported to be an antiferromagnet with T_N = 3 K and magnetic moments having triangular arrangement within the basal plane (the magnetic order is described by the propagation vector ). On the contrary ErNiIn is a ferromagnet with T_C = 9 K and magnetic moments pointing along the c-axis. The magnetic ordering in ErAu_xNi_1−xIn (0 < x < 1) solid solution, has been investigated by neutron diffractometry in the temperature range between 1.5 and 15 K. Moreover, bulk magnetic measurements have been carried out in the range 1.72–400 K. All alloys of intermediate composition were found to be antiferromagnets with T_N between 4.6 and 7 K. Below 2 K their magnetic order is described by the propagation vector and magnetic moments are aligned along the c-axis. However, for alloys with 0.2 ≤ x ≤ 0.7 the propagation vector was found to turn into with increasing temperature.     

Corrosion behaviour of vacuum induction-melted Ni-based alloy in sulphuric acid

A vacuum induction-melted (VIM) Ni-based alloy was immersed in 60% H₂SO₄ solution to investigate its corrosion behaviour and resistance. The results indicate that the microstructure contains a γ-Ni solid solution + Ni₃Si particles, dendrite Ni₃Si, Ni₃B, Cr₇C₃, and CrB. The corrosion started at the zones of the γ-Ni solid solution + Ni₃Si particles and dendrite Ni₃Si. These zones transformed to oxide films and protected the alloy from significant attack. However, the pitting corrosion created paths for acid solution and/or to further attack. Therefore, the corrosion rate decreased and then stabilised at a high value as the immersion time increased.     

Al-rich region of Al–Pd–Ru at 1000 to 1100 °C

Partial isothermal sections of the Al–Pd–Ru phase diagram at 1000, 1050 and 1100 °C are presented here. The Al–Pd orthorhombic -phases dissolve up to 15.5 at.% Ru, Al₁₃Ru₄ <2.5 at.% Pd and Al₂Ru up to 1 at.% Pd. Between 66 and 75 at.% Al, ternary quasiperiodic icosahedral phase and three cubic phases: C (, a = 0.7757 nm), C₁ (, a = 1.5532 nm) and C₂ (, a = 1.5566 nm) were revealed. An additional complex cubic structure with a ≈ 3.96 nm was found to be formed at compositions close to those of the icosahedral phase.     

An investigation of thermal aging effects on the mechanical properties of a Ni3Al-based alloy by nanoindentation

Ni₃Al-based intermetallic alloys are composed of a γ network and γ′ domains. In general, through precipitation, the γ′ phase is used as a hardening source for this alloy. This study examined how γ′ acts as a hardening material in a cast Ni₃Al-based intermetallic alloy. Specimens cut from a centrifugally cast tube were aged in Ar at elevated temperatures for up to 1600 h. Hardness tests were then performed in air at room temperature. Vickers microhardness and nanoindentation tests were carried out on specimens aged at 900 °C and 1100 °C. The microstructures were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microhardness of bulk Ni₃Al decreased dramatically with increasing thermal aging time at 900 °C, but the nanohardness measured by the nanoindenter did not significantly decrease. The nanohardness data suggested that the hardening effects were caused by the precipitation of the γ′ phase on the γ and γ′ cells.     

Corrosion rate of iron and iron–chromium alloys in CO2 medium

In the present paper corrosion of iron (99.95%) and iron–chromium alloys (1–5% Cr) were investigated by mass loss and ac impedance. These low-chromium content alloys have been proposed as an intermediate corrosion-performance material between C-steel and stainless steels to be used in oil plants. It was observed that small contents of chromium in the alloy decrease the corrosion attack only in very specific pH range 4 < pH < 5.In CO₂ medium, mass loss showed a linear behaviour with respect to time whereas in the presence of acetate the results were not monotonic. By ac impedance, it was found that and vary proportionally with respect to mass loss. A discussion concerning the online monitoring of the corrosion rate is presented.     

Formation of Fe(III)-containing mackinawite from hydroxysulphate green rust by sulphate reducing bacteria

The interactions between Fe(II–III) hydroxysulphate GR() and sulphate reducing bacteria (SRB) were studied. The considered SRB, Desulfovibrio desulfuricans subsp. aestuarii ATCC 29578, were added with GR() to culture media. Different conditions were envisioned, corresponding to various concentrations of bacteria, various sources of sulphate (dissolved  + GR() or GR() alone) and various atmospheres (N₂:H₂ or N₂:CO₂:H₂). In the first part of the study, CO₂ was deliberately omitted so as to avoid the formation of carbonated compounds, and GR() was the only source of sulphate. Cell concentration increases from 4 × 10⁷ to 7 × 10⁸ cells/mL in 2 weeks. The evolution with time of the iron compounds, monitored by Raman spectroscopy and X-ray diffraction, showed the progressive formation of a FeS compound, the Fe(III)-containing mackinawite. This result is consistent with the association GR()/SRB/FeS observed in rust layers formed on steel in seawater. In the presence of CO₂ and additional dissolved sulphate species, a rapid growth of the bacteria could be observed, leading to the total transformation of GR() into mackinawite, found in three physico-chemical states (nanocrystalline, crystalline stoichiometric FeS and Fe(III)-containing), and siderite FeCO₃.     

Determination of the crystal structure of the phase in the Fe–Al system by high-temperature neutron diffraction

The crystal structure of the high-temperature phase of the Fe–Al system has been determined by in-situ high-temperature neutron diffraction for the first time and the crystallographic parameters have been established by Rietveld refinement of the data. The phase was found to have a body-centered cubic structure of the Hume-Rothery Cu₅Zn₈-type (space group I3m (No. 217), Z = 4, Pearson symbol cI52, Strukturbericht designation D8₂). Accordingly, the ε phase has the formula Fe₅Al₈. Its lattice parameter is a = 8.9757(2) Å at 1120 °C, which is 3.02 times that of cubic FeAl (B2) at the same temperature. All fractional atomic coordinates, site occupation factors and interatomic distances were determined and it was examined how this phase can meet the rules for Hume-Rothery-type phases.     

The strain rate and prestrain dependences of the flow stress of Ni3Ga single crystals

Two Ni₃Ga single crystals were tested in compression by introducing upward strain rate jumps over the stress strain curve at temperatures ranging from 290 to 840 K. A Cottrell-Stokes-type law is observed below the yield stress peak temperature when the strain rate sensitivity parameter, is plotted against the workhardening increment τ_h. With increasing temperature, the slopes decrease indicating an increase in the activation volume at a given τ_h. The microstructure sensitivity of this ordered L1₂ alloy is demonstrated by two prestrain experiments. First, a high temperature prestrain reduces the initial values of β, on subsequent deformation at room temperature, compared to that of a virgin specimen at room temperature. Second, a room temperature prestrain weakens the anomaly of the yield stress. The results of the present study are shown to be in broad agreement with earlier results on Ni₃(Al,Hf)B single crystals.     

Subsolidus phase relationships in the system ZnO–Li2O–WO3

The subsolidus phase relationships of the system ZnO–Li₂O–WO₃ have been investigated by X-ray diffraction (XRD) analyses. There are one ternary compound, five binary compounds and eight 3-phase regions in this system. The new ternary compound Li₂Zn₂W₂O₉ was found by the powder diffraction pattern. The corresponding crystal structure of this compound was refined by Rietveld profile fitting method. It belongs to a trigonal system with space group and lattice constants are a = 5.1438(2) Å, c = 14.1052(3) Å, and its thermal property was studied.     

High-temperature oxidation behavior of pure Ni3Al

The high-temperature oxidation behaviour of pure Ni₃Al alloys in air was studied above 1000°C. In isothermal oxidation tests between 1000 and 1200°C, Ni₃Al showed parabolic oxidation behavior and displayed excellent oxidation resistance. In cyclic oxidation tests between 1000 and 1300°C, Ni₃Al exhibited excellent oxidation resistance between 1000 and 1200°C, but drastic spalling of oxide scales was observed at 1300°C. When Ni₃Al was oxidized at 1000°C, Al₂O₃ was present as -Al₂O₃ in a whisker form. But, at 1100°C the gradual transformation of initially formed metastable -Al₂O₃ to stable -Al₂O₃ was observed after oxidation for about 20 hr. After oxidation at 1200°C for long times, the formation of a thick columnar-grain layer of -Al₂O₃ was observed beneath a thin and fine-grain outer layer of -Al₃O₃. The oxidation mechanism of pure Ni₃Al is described.     

The isostructural phase transition and frustrated magnetic ordering in TbPd0.9Ni0.1Al studied by neutron diffraction

By using powder neutron diffraction we provide a detailed structural and magnetic investigation of the pseudo-ternary compound TbPd_0.9Ni_0.1Al with hexagonal ZrNiAl-type crystal structure and disorder of palladium and nickel atoms on two crystallographic sites. We provide experimental evidence for the occurrence of an isostructural phase transition in TbPd_0.9Ni_0.1Al at 157 K, which is affected by structural disorder compared to that observed in TbPdAl. In TbPd_0.9Ni_0.1Al the step of the c/a ratio at the first-order phase transition appears about four times smaller than in TbPdAl. TbPd_0.9Ni_0.1Al undergoes two successive magnetic phase transitions at T_N1=41 K and T_N2≈21.5 K. Two third of non-frustrated ordered Tb moments form commensurate antiferromagnetic chains () and coexist with one third of frustrated ordered Tb moments, which change from a commensurate structure () between T_N2 and T_N1 to an incommensurate structure () below T_N2. Due to the strong magneto-crystalline anisotropy all ordered Tb moments stay perpendicular to the ab-plane and reach at 1.5 K saturation values of 8.6 (2) μ_B (non-frustrated) and 7.2 (2) μ_B (frustrated). The symmetry of the magnetic structure of TbPd_0.9Ni_0.1Al is lower than that of TbNiAl.