Thermodynamic Properties of Si–Ge and Si–Sn Melts

The mixing enthalpies of Si–Ge and Si–Sn liquid alloys were measured in an isoperibolic calorimeter. The results demonstrate that the formation of Si–Ge melts is accompanied by a small heat release, while the formation of Si–Sn melts is an endothermic process. Calculations of the Si activity in Si–Sn melts by Schroeder's equation indicate large positive deviations from Raoult's law.     

New phase Ti3Co2Si in the Ti-Co-Si ternary system at 1100℃

1. IntroductionIt is reported that there are seven ternary compounds in the Ti--Co-St systems which are CoTiSi(E), Co4Ti4Si7(V), Co3TiSiZ(G"), Co3TiZSi(G'),ColoTi6Siv(G) and Co,TiSill]. In constitution of theCo--Ti-St 1100'C isothermal section, a new phase withthe composition of Ti3CoZSi was found. In the beginning, this phase was found in several alloys to have acomposition that is differeds from known binary andternary phases from the WDX composition microanalysis. Latter it …     

Oxidation of NiAl-Ag Alloys at 1000℃ in 0.1 MPa O2

Small amounts of silver have been added to the intermetallic compound NiAl with the purpose of improving its mechanical properties. Four ternary NiAl-Ag alloys containing 0.5, 1, 5 and 10 at. pct Ag, denoted as NiAl-0.5Ag, NiAl-1Ag, NiAl-5Ag and NiAl-10Ag, and the Ag-free NiAl have been oxidized at 1000℃ for 24 h in 0.1 MPa O2 to study the effect of the presence of silver on the oxidation behavior of NiAl. All the NiAl-Ag alloys are composed of a matrix of β-NiAl containing a dispersion of isolated particles of a second silver-rich phase. A continuous external layer of Al2O3 formed on all the alloys. In addition, the scales formed on NiAl-5Ag contained a thin and discontinuous layer of pure silver located at the alloy/Al2O3 interface, while those formed on NiAl-10Ag contained isolated particles as well as discontinuous layers of silver at various locations in the scale extending up to the gas/scale interface. The kinetic curves of all the alloys were generally composed of two main parabolic stages with smaller parabolic rate constants for the final stage. The addition of silver does not significantly affect the oxidation behavior of the NiAl intermetallic compound in all cases, as expected because silver is essentially present only as a second phase due to its very small solubility in β-NiAl.     

Oxidation of NiAl-Ag Alloys at 1000℃ in 0.1 MPa O_2

Small amounts of silver have been added to the intermetallic compound NiAl with the purpose of improving its mechanical properties. Four ternary NiAI-Ag alloys containing 0.5, 1, 5 and 10 at. pct Ag, denoted as NiAI-0.5Ag, NiAI-1Ag, NiAI-5Ag and NiAI-10Ag, and the Ag-free NiAl have been oxidized at 1000℃for 24 h in 0.1 MPa O2 to study the effect of the presence of silver on the oxidation behavior of NiAl. All the NiAI-Ag alloys are composed of a matrix of β-NiAI containing a dispersion of isolated particles of a second silver-rich phase. A continuous external layer of AI2O3 formed on all the alloys. In addition, the scales formed on NiAI-5Ag contained a thin and discontinuous layer of pure silver located at the alloy/AI2O3 interface, while those formed on NiAI-10Ag contained isolated particles as well as discontinuous layers of silver at various locations in the scale extending up to the gas/scale interface. The kinetic curves of all the alloys were generally composed of two main parabolic stages with smaller parabolic rate constants for the final stage. The addition of silver does not significantly affect the oxidation behavior of the NiAl intermetallic compound in all cases, as expected because silver is essentially present only as a second phase due to its very small solubility in β-NiAI.     

Phase Equilibria in Zn-Al-Cu-Si System at 285℃

As a part of the systematic investigationon phase relationships of Zn-Al based alloyscontaining Cu and/or Si, the equilibrium phasetransformations of the quaternary Zn-Al-Cu-Sisystem at 285℃ were investigated by using X-raydiffracti on, scanning electron microscopy andelectron probe microanalysis techniques. A five-phase of (α+β+εT'+σ) and a four-phase of (β+ε+η+σ) were detected separatelycoexisting in the Zn-Al-Cu-Si system at 285℃.Then the 285℃ isothermal section of Zn-Al-Cu-Sisystem (with 0.1% -Si content) was established,and an equilibrium reaction was determined at286℃ as the following pattern, β+T'=α+ε     

Corrosion of Iron and Four Commercial Steels in a Cl-Containing Oxidizing Atmosphere at 500℃～600℃

The corrosion behaviors of Fe and four commercial steels with different Cr contents were investigated in an oxidizing atmosphere containing HCl at 500~600℃, which simulated the environment to which materials are usually exposed in waste incineration. All the test materials underwent an accelerated corrosion in this atmosphere and small amounts of chlorine could be detected a t the metal/scale interface. The corrosion mechanism is discussed on the basis of thermodynamic considerations for the reactions between metals and mixed O-Cl gases.     

The Mechanism of kIH in Delayed Hydride Cracking of Zr-2.5wt% Nb at 150 ℃

This work studies the KIH mechanism of delayed hydride cracking (DHC) in Zr-2.5wt% Nb alloys. A modified experimental method was developed, in which specimens are fatigued between consecutive experiments, and a constant load instead of a decreasing load is used in each experiment. The hydride clusters formed and fractured at the crack tip during different experiments are thus separated and studied individually. A new R-curve phenomenon that characterizes the resistance to DHC was observed. KIH is thus more rigorously defined. Based on the measurement of the critical hydride cluster length at different K1, the threshold phenomenon of KIH is explained.     

Interaction of Iodine with 2-Hydroxypropyl-α-cyclodextrin and Its Bactericidal Activity

ABSTRACT

To obtain an effective iodine solution, the use of 2-hydroxypropyl-α-cyclodextrin (2-HP-α-CD) as solubilizer was examined in comparison with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), potassium iodide (KI), and polyvinylpyrrolidone (PVP). The stability constants for inclusion of iodine with cyclodextrin and KI were ascertained by the solubility method. The apparent stability constants increased in the following order: KI<β-CD<α-CD<2-HP-α-CD. This order was nearly in accordance with that of the stabilization ability. The largest volatile depression effect was exhibited by 2HP-α-CD. The measurement of the minimum inhibitory concentration (MC) using Escherichia coli NIH-J-2 and Staphylococcus aureus FDA209P suggested that the bactericidal activity of the iodine/2-HP-α-CD system was the same as that of the iodine/α-CD, iodine/β-CD, and iodine/PVP systems. The present results suggest that the combination of 2-HP-α-CD and iodine is useful for a stable and effective iodine solution.     

Activity of MnO in Blast Furnace-type Slags

The activity of MnO in blast furnace-typeslags CaO-SiO_2,CaO-SiO_2-Al_2O_3 andCaO-SiO_2-Al_2O_3-MgO at 1500℃ has been measuredin a graphite crucible with Ag and Sn as solventmetals.The agreement between the values ofγMnO obtained from the experimental resultsusing Ag and Sn separately as the solvent metalis excellent.The major errors in the previousstudies have proved to be the failure to takeinto account the exchange reactions involvingSi and Mn and insufficient time for theestablishment of equilibrium between slag andsolvent metal.A new method is suggested for determiningthe activities of elements in metallic solutions.The method involves the separate equilibrationof two metallic alloys,one of which containsthe component of interest at a known activity,with a single slag.     

Activity of NaOH in Sodium Aluminate Solutions

1.IntroductionSodium aluminate solution is one of themost important intermediate products in al-uminium metallurgy.The structure of so-dium aluminate solutions is rather compli-cated.Various anionic species,includingAl(OH)_4~-,Al(OH)_6~(-3) and[(OH)_3-Al-O-Al(OH)_3]~(2-) are co-existent in sodiumaluminate solutions.Using Raman and     

Oxidation Behaviors of C-ZrB_2-SiC Composite at 2100℃ in Air and O_2

The oxidation behaviors of graphite and ZrB2-SiC modified graphite composite were investigated at 2100℃ in1X105 Pa air and 0.2X105 Pa O2. The oxidation tests were conducted in an induction heating furnace. The oxidation of these two materials followed the linear rate law. The determined radius loss rates of graphite and C-ZrB2-Si C at 2100℃ were 2.18X10-2and 1.05X10-2%/s in 1X105 Pa air, and 3.23X10 2 and 2.21X10 2%/s in 0.2X105 Pa O2, respectively. The incorporation of ZrB2 and SiC decreased remarkably the oxidation rate of graphite because the oxide scale formed on the sample surface during oxidation helps in reducing the exposed surface area of the underneath substrate. In two different atmospheres with the same oxygen partial pressure, both graphite and ZrB2-SiC experienced more severe oxidation at 2100℃ in0.2X105 Pa O2than in 1X105 Pa air. The oxidation rate-controlling step for graphite and ZrB2-SiC was proposed to be the inward diffusion of oxygen through the boundary layer and through the pores in the oxide scale, respectively. A model based on diffusion theory was established to discuss the effect of the total gas pressure on their oxidation behaviors.     

Temperature-Induced Reversible Change of Electrical Resistivity in Sn–Bi Melts

Using a dc four-probe method, the temperature dependence of the electrical resistivity of liquid Sn–Bi alloys has been investigated. The results show that there are clear turning points both on heating and cooling for several experimental cycles. Since the electrical resistivity is one of the physical properties sensitive to structure, the unusual change of the resistivity indicates that liquid–liquid transitions (LLT) probably take place in Sn–Bi melts. Moreover, the transitions are reversible. Compared with the experimental results for pure Sn and Bi, it is assumed that Sn plays an important role in the reversible liquid–liquid transitions.     

Fatigue Crack Growth of Al-Li Alloy 2091 in 3.5% NaCl Solution and at 130℃

A study has been made of the fatigue crackgrowth in an Al-Li alloy 2091 in 3.5%NaCl solu-tion and at an elevated temperature of 130℃.Theaging and environmental effects on the crackgrowth behaviour were examined.It is shown thatthe fatigue crack growth resistance decreases withaging.The specimen with underaged structuresshows the highest resistance to fatigue crack growthdue to more deflected crack paths and the resultinghigh crack closure levels.As compared to laborato-ry air,both 3.5% NaCl solution and elevated tem-perature of 130℃ cause an increase of near-thresh-old crack growth rates and a decrease of thresholdlevels.The elevated temperature is more effective.The effect of elevated temperature is mainly due tothe precipitate coarsening which results in anenhancement of slip irreversibility.Hydrogenembritttlement is supposed to be responsible for thedegradation of fatigue crack growth resistance in3.5%NaCl solution     

Nucleation and Formation of Stable and Metastable Phases in Undercooled AI-Li Melts

A modified nucleation and competitive growth kinetic theory considering unsteady nucleation andeffect of composition in dilute binary alloys was suggested,based on which the selections of δ.δ'and α phases in undercooled Al-Li melts were summarized by both isothermal and continuous cool-ing treatment methods.     

Sulphidation of Fe-Nb,Co-Nb and Ni-Nb Alloys in H_2-H_2S at 700℃

The corrosion of alloys based on Fe,Co and Ni containing 15 and 30 wt-% Nb was studied at 700℃in H_2-H_2S mixtures providing 10~(-8) atm S_2.The Fe and Co-based alloys formed duplex scales withan outer layer of pure base-metal sulphide and an inner layer containing both metals.The Nb addi-tions were not able to produce exclusive Nb sulphidation but yielded a significant decrease of thecorrosion rates for both types of alloys with respect to the pure metals even though they were stillmuch higher than that of pure Nb.The Ni-base alloys corroded rapidly forming a single complexscale layer,mainly due to the appearance of a liquid Ni-S solution.     

Thermodynamic Properties of Melts and Phase Equilibria in the Copper–Zirconium System

The vapor composition over and thermodynamic properties of Cu–Zr melts (5.1–85.0 at. % Zr) are studied by Knudsen cell mass spectrometry between 1191 and 1823 K. The data set obtained comprises more than 1100 activity values for various compositions and temperatures. The thermodynamic behavior of Cu–Zr melts is described in terms of the associated-solution approach with an accuracy no worse than the experimental accuracy. The melts are shown to contain two molecular species: CuZr and Cu₂Zr. The contributions of different types of chemical bonding to the Gibbs energy and enthalpy of formation of Cu–Zr melts are asymmetrical and shifted from the equiatomic composition in opposite directions: the extremum of covalent bonding is shifted to the Cu-rich side, while metallic bonding is more significant in Zr-rich alloys. The rapid temperature variation of covalent bonding leads to a large excess heat capacity C _p ^E of the melts and a negative excess entropy _f S ^E, which rapidly drops with decreasing temperature. It is shown that not only C _p ^E and _f S ^E but also their temperature variations are governed by the parameters of association reactions and depend more strongly on the entropy than on the enthalpy of complex formation. This indicates that, in the general case, the glass-forming capabilities of melts are independent of the interparticle interaction and accounts for the pronounced tendency of Cu–Zr melts toward amorphization.     

Corrosion of Iron and Four Commercial Steels in a Cl-Containing Oxidizing Atmosphere at 500-600℃

The corrosion behaviors of Fe and four commercial steels with different Cr contents were investigated in an oxidizing atmosphere containing HCI at 500~600℃, which simulated the environment to which materials are usually exposed in waste incineration. All the test materials underwent an accelerated corrosion in this atmosphere and small amounts of chlorine could be detected at the metal/scale interface. The corrosion mechanism is discussed on the basis of thermodynamic considerations for the reactions between metals and mixed O-CI gases.     

Corrosion of Iron and Four Commercial Steels in a Cl-Containing Oxidizing Atmosphere at 500～600℃

The corrosion behaviors of Fe and four commercial steels with different Cr contents were investigated in an oxidizing atmosphere containing HCI at 500～600℃, which simulated the environment to which materials are usually exposed in waste incineration. All the test materials underwent an accelerated corrosion in this atmosphere and small amounts of chlorine could be detected at the metal/scale interface. The corrosion mechanism is discussed on the basis of thermodynamic considerations for the reactions between metals and mixed O-CI gases.     

Oxidation of Ion Plated Ni—Cr Alloy Film at 300℃

Investigation by using LAS 3000 surfaceanalysis system showed that the oxide of Fe,Cr,Al formed during oxidation were Cr_2O_3,Fe_2O_3and Al_2O_3,but only small amount of nickel oxidewas found.The composition of oxide layers for differentoxidation durations varied in a similar way.In all cases,there exists an oxygen concentrationpeak in the composition profile of oxide layer.There is a transitional zone between oxide layerand alloy film.The thickness of oxide layerincreases logarithmically with the time of oxida-tion.The ion plated Ni-Cr alloy film has verydense oxide layer and good oxidation resistance.     

Enamel coating for protection of the 316 stainless steel against tribo-corrosion in molten zinc alloy at 460℃

Hot-dip galvanizing provides excellent corrosion and wear resistance for steels.However,the equipment itself,such as the steel roller,immerged in corrosive molten zinc suffers serious material loss during steel's production.Its protection has become the main technique problem in modern galvanizing line.In this study,an enamel coating was designed and prepared.Its tribo-corrosion in molten zinc alloy(Zn-0.2 wt%Al)at 460℃was investigated in comparison with the traditional WC-12 Co composite coating and the 316 stainless steel.Results indicate that the steel suffers serious material damage.Various corrosion products of Fe₂ Al₅ Znx form at the worn surface and the wear scar has reached 200μm deep after merely 5 h tribo-corrosion.Though the two coatings provide an improved tribo-corrosion resistance,for the WC-12 Co coating,its chemical reaction with the molten zinc increases brittleness and promotes cracking.The synergistic wear and corrosion cause its degradation.The enamel coating performs better during tribo-corrosion.It is chemically stable in molten zinc thus able to provide high corrosion resistance.In addition,the amorphous[Si04]network and the self-lubricating CaF₂ crystallite help it to build up an intact amorphous glaze layer readily at surface on sliding,leading to a reduced wear loss.During the whole tribo-corrosion process,the enamel coating is completely free of cracking,and the Zn penetration is inhibited.