Investigation of the formation of precipitates of copper cations with sulfhydryl collectors

The formation processes of precipitates of copper cations with diethyldithiocarbamate, xanthates (ethyl and buthyl), and isobutyl dithiophosphate are investigated using potentiometric and optical methods. The minimal value of the potential of the copper electrode (E _Cu) with the formation of precipitates agrees well with the solubility product (SP) and forms the following series: copper diethyldithiocarbamate (E _Cu = −335 mV, SP = 2.8 × 10⁻³⁰) > butyl xanthate (E _Cu = −225 mV, SP ≈ 10⁻²⁶) > ethyl xanthate (E _Cu = −163 mV, SP = 4 × 10⁻²⁴) > isobutyl dithiophosphate (E _Cu = −60 mV, SP ≈ 10⁻¹⁸). The visible agglomerates of precipitate particles are observed for all the studied sulfhydryl collectors (xanthates, dithiocarbamates, dithiophosphates) with the ethyl group of hydrocarbon radical. The butyl xanthate and isobutyl dithiophosphate form colloid precipitates with copper cations.     

The oxidation behavior of unactivated and mechanically activated sphalerite

The oxidation behaviors of unactivated and mechanically activated sphalerites were investigated using the thermogravimetry method (TG) in flowing highly pure oxygen at the heating rate of 10 K min⁻¹. It is found that the remaining mass between 400 and 873 K in the TG curves of mechanically activated sphalerites rises with increasing grinding time. The difference in oxidation reactivity of unactivated and mechanically activated sphalerites was also discussed. The specific granulometric surface area (S _G), the structural disorder, and the content of elemental sulfur of unactivated and mechanically activated sphalerites were determined by X-ray diffraction (XRD) laser particle size analysis, X-ray diffraction, and the gravimetric method, respectively. The results show that the specific granulometric surface areas of mechanically activated sphalerites remain almost constant after a certain grinding period. The elemental sulfur contents of unactivated and mechanically activated sphalerites were determined to be 0.5 mg/g, and the lattice distortions (ɛ) increase but the crystallite sizes (D) decrease with increasing grinding time. All the results imply that the mass increase between 400 and 873 K in the TG curves of mechanically activated sphalerites depends mainly on the increase of lattice distortions (ɛ) and the decrease of the crystallite sizes (D) with increasing grinding time. It was concluded that TG is a useful method for characterizing mechanically activated sphalerites.     

A new model for the volume fraction of martensitic transformations

A model using an energy balance is proposed to describe the volume fraction of multiple-interface martensitic transformations. For martensitic transformations without external stresses at quenching temperature T<M _s , the volume fraction of martensite (ξ) is proportional to the undercooling (M _s −T) and inversely proportional to a linear function of the quenching temperature (T); thus, ξ=(M _s −T)/[M _s −βM _f −(1−β)T], where β is a material constant. For stress-induced martensitic transformations under stress σ _ik ^a with temperature T>M _s , the relationship is ξ = ξ₀[1 - λ _ik ^σ (σ _ik ^Ms ]^-1, where ξ ₀ is the initial detectable amount of martensite formed at martensitic starting stress σ _ik ^Ms and λ _ik ^σ is a material constant. It is found that the results obtained from this model are in good agreement with experimental results.     

Modeling the heat flow to an operating sirosmelt lance

A mathematical model of the heat flow to a Sirosmelt lance is presented, which predicts lance wall and air temperatures and the thickness of the slag layer on the lance. By measuring the distribution of wall temperature and slag thickness on an operating Sirosmelt lance, the model was used to determine both the heat-transfer coefficient between the vessel contents and the lance and the thermal conductivity of the slag layer. The slag layer thermal conductivity was found to be within the range of 0.5 to 1.1 W m⁻¹ K⁻¹, while the outside heat-transfer coefficient varied from 80 to 150 W m⁻² K⁻¹, both of which are smaller than quoted in the literature for metal/slag systems. The discrepancy was attributed primarily to the large quantities of combustion gases that envelop the lance and reduce convection and conduction from the melt to the lance. Other factors causing low thermal conductivity and a low heat-transfer coefficient include the thermal resistance at the slag/lance interface and the mushy region on the outside of the slag layer.     

The thermal behavior of mechanically activated galena by thermogravimetry analysis

The thermal decompositions of mechanically activated and nonactivated galenas were studied by thermogravimetry analysis (TGA) at the heating rate of 10 K min⁻¹ in argon. Results indicate that the initial temperature of thermal decomposition (abbreviated as T _di ) in the TGA curves for different galenas decreases gradually with increased grinding time. The specific granulometric surface area (S _G ), the structural disorder, and the content of elemental sulfur of mechanically activated galenas were analyzed by an X-ray diffraction (XRD) laser particle-size analyzer, XRD analysis, and the gravimetric method, respectively, which shows that the specific granulometric surface area of mechanically activated galenas remains almost constant after a certain grinding time, but the lattice distortions (ɛ) rise, the crystallite sizes (D) decrease, and the elemental sulfur contents of mechanically activated galenas increase with increased grinding time. The results imply that the decrease of the initial temperature of thermal decomposition in the TGA curves for mechanically activated galenas is mainly caused by the increase of lattice distortions, and the formation of new dangling bonds resulted from the production of elemental sulfur of mechanically activated galenas with increased grinding time. Finally, the differences in the thermal-decomposition reactivity between nonactivated and mechanically activated galenas were also discussed.     

The thermal behavior of mechanically activated galena by thermogravimetry analysis

The thermal decompositions of mechanically activated and nonactivated galenas were studied by thermogravimetry analysis (TGA) at the heating rate of 10 K min⁻¹ in argon. Results indicate that the initial temperature of thermal decomposition (abbreviated as T _di) in the TGA curves for different galenas decreases gradually with increased grinding time. The specific granulometric surface area (S _G), the structural disorder, and the content of elemental sulfur of mechanically activated galenas were analyzed by an X-ray diffraction (XRD) laser particle-size analyzer, XRD analysis, and the gravimetric method, respectively, which shows that the specific granulometric surface area of mechanically activated galenas remains almost constant after a certain grinding time, but the lattice distortions (ε) rise, the crystallite sizes (D) decrease, and the elemental sulfur contents of mechanically activated galenas increase with increased grinding time. The results imply that the decrease of the initial temperature of thermal decomposition in the TGA curves for mechanically activated galenas is mainly caused by the increase of lattice distortions, and the formation of new dangling bonds resulted from the production of elemental sulfur of mechanically activated galenas with increased grinding time. Finally, the differences in the thermal-decomposition reactivity between nonactivated and mechanically activated galenas were also discussed.     

Nitridation kinetics of niobium in the temperature range of 873 to 1273 K

The kinetics of Nb (Cb) nitridation and ε-NbN growth obey a parabolic relationship and their temperature dependence can be expressed ask _p = 5.19 × 10⁻⁷ exp (−125,500/RT) and (k _{p ξ} = 1.15 × 10⁻⁴ exp (−61,500/RT), respectively, with the activation energies in joules/mole. The nitrogen diffusion coefficient in niobium, obtained from microhardness traverses, is given byD = 1.02 × 10⁻⁵ exp (−77,000/RT). A diffusion model accounting for the partition of nitrogen between ε-NbN and Nb is proposed. The total nitrogen uptake calculated from the model is compared to that obtained experimentally.     

Some observations on the electrical and thermal properties of the slag-skin region in the electroslag remelting process

An unsteady-state method has been used to determine the electrical resistivity and overall heat-transfer coefficient,U, of the interface region, liquid slag/slag-skin/copper wall, in an electroslag furnace. The value ofU is found to have a slight dependence on slag temperature, slag composition, and slag-skin thickness. It is postulated that the major resistance to the transfer of heat across this composite interface lies in the discontinuity between the slag-skin and the mold wall. The numerical value ofU is found to be approximately 10⁻² cal · cm⁻² s⁻¹ °C⁻¹ for the range of conditions. The electrical resistivity of the interface is found to be a sensitive function of mold wall face temperature. The application of these results to a small ESR furnace is discussed.     

Diffusion of managenese and silicon in liquid iron over the whole range of composition

The measurement of the diffusivities of manganese and silicon in molten binary ferroalloys over the whole range of composition was undertaken to clarify existing but conflicting data at lower concentrations, to present new data at higher concentrations and to indirectly confirm the behavior of both systems observed in thermodynamic studies. The experiments were carried out under argon atmosphere in a Tammann furnace. The diffusion couples were held in 5 mm ID alumina tubes (98 pct Al₂O₃). Electron probe microanalysis of the samples led to a diffusion-penetration curve for the system under consideration. Results obtained over the whole range of composition showed a slight negative deviation for the Fe−Mn system and a very large positive deviation for the Fe−Si system. At lower concentrations (0 to 4 pct Mn), the temperature dependence of managanese diffusivity for the Fe−Mn binary alloy in the temperature range 1550° to 1700°C is as follows:D _Fe−Mn=1.8×10⁻³ exp (−13,000/RT) cm²/sec The concentration dependence of manganese diffusivity for the same system at 1600°C may be expressed asD _Fe−Mn={5.48−0.0137 (%Mn)+0.000276 (%Mn)²}×10⁻⁵ cm²/sec The temperature dependence of silicon diffusivity for the Fe−Si binary system in the temperature range 1550° to 1725°C at various concentrations is as follows:D _Fe−Si=2.8×10⁻³ exp (−11,900/RT) cm²/sec at 20 pct SiD _Fe−Si=2.1×10⁻³ exp (−13,200/RT) cm²/sec at 12.5 pct SiD _Fe−Si=5.1×10⁻⁴ exp (−9,150/RT) cm²/sec at 2.2 pct Si FELIPE P. CALDERON, formerly Graduate Student. University of Tokyo, Tokyo, Japan. This paper is based on a portion of a thesis submitted by FELIPE P. CALDERON in partial fulfillment of the requirements for the degree of Doctor of Engineering at University of Tokyo.     

The diffusivity and solubility of oxygen in liquid tin and solid silver and the diffusivity

The diffusivity and solubility of oxygen in liquid tin and solid silver in the temperature range of about 750° to 950°C (1023 to 1223 K) and the diffusivity of oxygen in solid nickel at 1393°C (1666 K) were determined using the electrochemical cell arrangement of cylindrical geometry: Liquid or Solid Metal + O (dissolved) | ZrO₂ + (3 to 4%)CaO | Pt, air The diffusivity and solubility of oxygen in liquid tin are given by:D _O(Sn) = 9.9 × 10⁻⁴ exp(−6300/RT) cm²/s (9.9 × 10⁻⁸ exp − 6300/RT m²/s) andN _O ^S (Sn) = 1.3 × 10⁵ exp(−30,000/RT) at. pct The diffusivity and solubility of oxygen in solid silver follow the relations:D _O(Ag) = 4.9 × 10⁻³ exp (−11,600/RT) cm²/s ( 4.9 × 10⁻⁷ exp − 11,600/RT m²/s) andN _O ^S (Ag) = 7.2 exp (−11,500/RT) at. pct The experimental value for the preexponential in the expression forD _O(Ag) is lower than the value calculated according to Zener’s theory of interstitial diffusion by a factor of 11. The diffusivity of oxygen in solid nickel at 1393°C (1666 K) was found to be 1.3 × 10⁻⁶ cm²/s (1.3 × 10⁻¹⁰ m²/s). Formerly Graduate Student, Department Formerly Graduate Student, Department Formerly Graduate Student, Department This paper is based upon a This paper is based upon a This paper is based upon a This paper is based upon a     

Evaluation of the reduction of iron oxide from liquid slags using a graphite rotating disk

The rotating disk methodology has been used for examination of the reduction of FeO from CaO-FeO-SiO₂ liquid slags (20 and 60 pct FeO) with a CaO/SiO₂ ratio equal to 0.66 and 1.27, in the temperature range 1350 °C to 1420 °C. It has been found that the reduction proceeds under diffusion control. The calculated diffusion coefficients fall in the range 0.76·10⁻⁷ to 1.6·10⁻⁶ cm²/s. Comparison of these values with those given in the literature suggests that the calculated coefficients are related to the diffusion of oxygen ions in the slag. The calculated thickness of the limiting diffusion layer, δ, ranges from 0.65·10⁻³ to 5.25·10⁻³ cm, depending on the reduction conditions. The largest decrease in the limiting diffusion layer thickness takes place at low rotational speeds, i.e., 100 and 400 rev/min. The maximum value of the mass transfer coefficient is 1.71·10⁻³ cm/s for reduction from slag with a CaO/SiO₂ ratio of 1.27, 60 pct FeO, at 1420 °C and 2000 rev/min, and the minimum value is 0.27·10⁻⁴ cm/s for reduction from slag with a CaO/SiO₂ ratio of 0.66, 20 pct FeO, at 1350 °C and 100 rev/min. Good agreement has been found between experimental and calculated reduction rates at low disk rotations (100 and 400 rev/min).     

High-temperature deformation and failure of an orthorhombic titanium aluminide sheet material

The high-temperature deformation and failure behavior of an orthorhombic titanium aluminide sheet alloy (fabricated by diffusion bonding of six thin foils) was established by conducting uniaxial tension and plane-strain compression tests at 980 °C and strain rates between 10⁻⁴ and 10⁻² s⁻¹. The stress-strain response was characterized by a peak stress at low strains followed by moderate flow softening. Values of the strain-rate sensitivity index (m) were between 0.10 and 0.32, and the plastic anisotropy parameter (R) was of the order of 0.6 to 1.0. Cavity nucleation and growth were observed during tensile deformation at strain rates of 10⁻³ s⁻¹ and higher. However, the combined effects of lowm, low cavity growth rateη, and flow softening were deduced to be the source of failure controlled by necking and flow localization rather than cavitation-induced fracture prior to necking.     

Criterion for judging the homogeneous and heterogeneous nucleation

A criterion for judging the nucleation form in highly undercooled liquid has, respectively, been derived from the nucleation and structure of liquid. It is found that the nucleation form of a highly undercooled liquid can be judged by determining the S _v in the liquid (where S _v is the surface area of the supposed catalyst in a unit volume of the liquid). When the determined value of S _v is equal to 10^10±1 m⁻¹, the liquid has nucleated homogeneously; it has nucleated heterogeneously if the determined value of S _v is less than 10^10±1 m⁻¹. By calculating the values of S _v in highly undercooled aluminum, copper, and silver, it is found that only silver melted under a slag has been undercooled to its undercooling of homogeneous nucleation.     

Microstructure and high-temperature tensile deformation of tiai(si) alloys made from elemental powders

Two ternary TiAl-based alloys with chemical compositions of Ti-46.4 at. pct Al-1.4 at. pct Si (Si poor) and Ti-45 at. pct Al-2.7 at. pct Si (Si rich), which were prepared by reaction powder processing, have been investigated. Both alloys consist of the intermetallic compounds y-TiAl, α₂-Ti₃Al, and ξ-Ti₅(Si, Al)₃. The microstructure can be described as a duplex structure(i.e., lamellar γ/α₂ regions distributed in γ matrix) containing ξ precipitates. The higher Si content leads to a larger amount of ξ precipitates and a finer y grain size in the Si-rich alloy. The tensile properties of both alloys depend on test temperature. At room temperature and 700 °C, the tensile properties of the Si-poor alloy are better than those of the Si-rich alloy. At 900 °C, the opposite is true. Examinations of tensile deformed specimens reveal ξ-Ti₅(Si, Al)₃ particle debonding and particle cracking at lower test temperatures. At 900 °C, nucleation of voids and microcracks along lamellar grain boundaries and evidence for recovery and dynamic recrystallization were observed. Due to these processes, the alloys can tolerate ξ-Ti₅(Si, Al)₃ particles at high temperature, where the positive effect of grain refinement on both strength and ductility can be utilized.     

Catalyzed precipitation in Al-Cu-Si

The work reported here concerns the effect of Si on the precipitation of θ′ phase (metastable Al₂Cu) during the isothermal aging of Al-2Cu-1 Si (wt pct). The binary alloys Al-2Cu and Al-1 Si were studied for comparison. Only two precipitate phases were detected: essentially pure Si in Al-1 Si and Al-2Cu-1 Si, and θ′ (metastable Al₂Cu) in Al-2Cu and Al-2Cu-1Si. On aging the ternary alloy at 225 °C, Si precipitates first and catalyzes the θ′ phase. The precipitates in the ternary alloy are smaller, are more densely distributed, have lower aspect ratios, and coarsen more slowly than those in the binary Al-2Cu aged at the same temperature. While the shapes of individual θ′ precipitates in binary Al-2Cu are strongly affected by the kinetic problem of nucleating growth ledges, which produces a significant scatter in the aspect ratio for samples of given thickness, the overall evolution of particle shape with size follows the predictions of the Khachaturyan-Hairapetyan (KH) thermoelastic theory, which reduces to κ=L/d ∞ √L at large sizes. The KH theory provides an estimate for the interfacial tension of the broad Al-θ′ interface of 85 to 96 mJ/m², which is near the values for other low-energy interfaces in Al, such as the twin boundary energy (100 mJ/m²) and the antiphase boundary energy in δ′ Al₃Li (70 mJ/m²). Si and θ′ precipitates in Al-2Cu-1 Si have a strong elastic interaction because of their compensating strain fields. This elastic interaction promotes the nucleation of θ′ precipitates on Si, decreases the expected aspect ratio of θ′, and inhibits coarsening. Finally, Si precipitation in ternary Al-2Cu-1 Si differs from that in binary Al-1 Si in that the Si precipitates are coarser, more equiaxed, and more extensively twinned. These changes appear to be effects of Cu, which increases the solubility of Si in Al and adsorbs on the Si-Al interface, promoting twinning by a “step-poisoning” effect at the interface.     

Coarsening of Al<Subscript>3</Subscript>Sc precipitates in an Al-0.28 wt pct Sc alloy

The Ostwald ripening of Al₃Sc precipitates in an Al-0.28 wt pct Sc alloy during aging at 673, 698, and 723 K has been examined by measuring the average size of precipitates by transmission electron microscopy (TEM) and the reduction in Sc concentration in the Al matrix with aging time, t, by electrical resistivity. The coarsening kinetics of Al₃Sc precipitates obey the t ^1/3 time law, as predicted by the Lifshitz-Slyozov-Wagner (LSW) theory. The kinetics of the reduction of Sc concentration with t are consistent with the predicted t ^−1/3 time law. Application of the LSW theory has enabled independent calculation of the Al/Al₃Sc interface energy, γ, and volume diffusion coefficient, D, of Sc in Al during coarsening of precipitates. The Gibbs-Thompson equation has been used to give a value of γ using coarsening data obtained from TEM and electrical resistivity measurements. The value of γ estimated from the LSW theory is 218 mJ m⁻², which is nearly identical to 230 mJ m⁻² from the Gibbs-Thompson equation. The pre-exponential factor and activation energy for diffusion of Sc in Al are determined to be (7.2±6.0)×10⁻⁴ m² s⁻¹ and 176±9 kJ mol⁻¹, respectively. The values are in agreement with those for diffusion of Sc in Al obtained from tracer diffusion measurements.     

A new method to dynamically measure the surface tension,viscosity, and density of melts

A new formulation has been developed to describe the fluid dynamics of a liquid draining through an orifice under the influence of gravity. The model relates experimental quantities of head and flow rate, with surface tension, viscosity, and density, facilitating the calculation of all three properties. Experiments performed with molten aluminum at temperatures from 937 to 1173 K indicate that surface tension (N/m) and density (kg/m³) are [0.871 − 0.155 × 10⁻³ (T − T _liq)] and [2390 − 0.15 (T − T _liq)], which is within 6.5 and 2.5 pct, respectively, of values reported in the literature. The viscosity has been determined to be 5.2 × 10⁻⁴ Nsm⁻², which is significantly less than data reported from other sources. The method is unique because the measurements are performed under highly dynamic conditions.     

Effects of CaO, Al2O3, and MgO additions on the copper solubility, ferric/ferrous ratio, and minor-element behavior of iron-silicate slags

The effects of CaO, Al₂O₃, and MgO additions, singly or in combination, on the copper solubility, the Fe³⁺/Fe²⁺ ratio in slag, and on the minor-element behavior of silica-saturated iron silicate slags were examined at 1250 °C and a p _O2 of 10⁻¹² to 10⁻⁶ atm. The results indicated that copper solubility in slag was lowered with the addition of CaO, MgO, and Al₂O₃, in decreasing order. The Fe³⁺/Fe²⁺ ratio in the slag decreased with the additions, but this effect was smaller at lower oxygen potentials. The presence of small amounts (about 4 pct) of CaO, Al₂O₃, and MgO in the slag resulted in increased absorption of Bi and Sb into molten copper, but had a smaller effect at large additions (about 8 to 11 pct). The distribution behavior of Pb was a function of oxygen partial pressure, which indicates the oxidic dissolution of Pb in the slag as PbO, while the behavior of Bi, Sb, and As was found to be independent of oxygen potential, supporting the atomic (neutral) dissolution hypothesis of these elements in the slag. The distribution behavior of Pb and As was not significantly affected by the additions. The activity coefficients of Bi and Sb in the slags were determined to be as follows: (1) for no addition, γ _Bi=40 and γ _Sb=0.4; (2) for small additions (about 4.4 pct), γ _Bi=70 to 85 and γ _Sb=0.8; and (3) for large additions (about 8 to 11 pct), γ _Bi=60 to 75 and γ _Sb=0.5 to 0.7.     

Intermetallic phases formed during DC-casting of an Al−0.25 Wt Pct Fe−0.13 Wt Pct Si alloy

The Al−Fe and Al−Fe−Si particles formed during DC-casting of an Al-0.25 wt pct Fe-0.13 wt pct Si alloy have been examined. The particles were analyzed by transmission electron microscopy (TEM) and energy dispersive spectroscopy of X-rays (EDS). Crystal faults were studied by high resolution electron microscopy (HREM). Samples for electron microscopy were taken at various positions in the ingot,i.e., with different local cooling rates during solidification. At a cooling rate of 6 to 8 K/s the dominating phases were bcc α-AlFeSi and bct Al _m Fe. The space group of bcc α-AlFeSi was verified to be Im3. Superstructure reflections from Al _m Fe were caused by faults on {110}-planes. At a cooling rate of 1 K/s the dominating phases were monoclinic Al₃Fe and the incommensurate structure Al _x Fe. In Al₃Fe, stacking faults on {001} were frequently observed. The structure of Al _x Fe is probably related to Al₆Fe. Some amounts of other phases were detected. For EDS-analysis, extracted particles mounted on holey carbon films were examined. Extracted particles were obtained by dissolving aluminum samples in butanol. Accurate compositions of various Al−Fe−Si phases were determined by EDS-analysis of extracted crystals.