Controlled undercooling of liquid iron in contact with Al2O3 substrates under varying oxygen partial pressures

The objective of this study was to determine the conditions under which alumina can act as a heterogeneous nucleant to initiate the solidification of undercooled liquid iron. The undercooling of a pure iron sessile droplet in contact with Al₂O₃ substrates was measured under controlled oxygen partial pressures by observing droplet recalescence. The experimental results indicated that the undercooling of liquid iron, in contact with an Al₂O₃ substrate, did not have a unique value, varied from 0 °C to 290 °C, and was significantly affected by the oxygen content of the gas phase and the degree of interaction between the oxide and the metal. Deep undercoolings are possible at low oxygen potentials, provided the oxygen potential is such that substantial substrate decomposition does not occur. The measured undercooling was a strong function of gas phase oxygen content and a maximum in undercooling of 290 °C was measured at PO₂=10⁻¹⁹ atm. The variation in undercooling was related to the wetting of the substrate by the liquid metal, where the deepest undercoolings occurred when the highest contact angle between the substrate and the liquid droplet was achieved.     

2种氧分压下铁矿粉烧结高温熔体的流动行为

铁矿粉烧结高温熔体的流动行为,对烧结矿强度的改善有重要影响,而其受到烧结料层内氧分压的深刻影响.以7种铁矿粉为研究对象,在实验测定2种氧分压下高温熔体流动行为的基础上,通过FactSage热力学计算、XRD矿相分析法及矿相数点法探究其影响机制.结果 表明,当高温保持段的氧分压从0.1 kPa升高至21.0 kPa,高温...     

Equilibria in reactions of Co and Co2 with dissolved oxygen and carbon in liquid iron

Carbon and oxygen activities have been established in molten iron using CO-CO₂ mixtures in the temperature range 1550 to 1750°C. Pressures of up to 70 atm were used to establish the required carbon activities up to carbon saturation at 1550°C in gas mixtures with CO₂ contents between 0.76 and 8.21 pct. The lévitation technique was used to avoid any possible contamination and the effect of thermal diffusion in the gas mixture was measured and corrected for. The data obtained on carbon activities fall between those of previous workers at low carbon but measurements have been extended to the much higher carbon concentrations which had not been investigated previously. By using the same CO-CO₂ mixture and varying the total pressure it was possible to measure the effect of carbon on oxygen concentration at fixed oxygen activity and it was found that carbonincreases the activity coefficient of oxygen.     

Equilibria in reactions of CO and CO2 with dissolved oxygen and carbon in liquid iron

Carbon and oxygen activities have been established in molten iron using CO-CO₂ mixtures in the temperature range 1550 to 1750°C. Pressures of up to 70 atm were used to establish the required carbon activities up to carbon saturation at 1550°C in gas mixtures with CO₂ contents between 0.76 and 8.21 pct. The levitation technique was used to avoid any possible contamination and the effect of thermal diffusion in the gas mixture was measured and corrected for. The data obtained on carbon activities fall between those of previous workers at low carbon but measurements have been extended to the much higher carbon concentrations which had not been investigated previously. By using the same CO-CO₂ mixture and varying the total pressure it was possible to measure the effect of carbon on oxygen concentration at fixed oxygen activity and it was found that carbonincreases the activity coefficient of oxygen.     

Y2O3与MgO复合掺杂ZrO2材料的电性能研究

利用交流复阻抗分析技术对Y2O3与 MgO复合掺杂ZrO2材料的电性能进行了研究.发现随着Y2O3掺入量的增加,参与跃迁的氧空位增多,并促进烧结体的密度提高,气孔率降低,使得晶粒边界的电阻减少,导致(ZrO2)1-x-y(YO1.5)x(MgO)y陶瓷电导率增大.烧结温度的提高也是增加 (ZrO2 )1-x-y(YO1.5)x(MgO)y陶瓷电导率的重要因素之一.     

Thermodynamics of oxygen and nitrogen in liquid iron equilibrated with CaO- SiO2-Al2O3 slags

Nitrogen distribution ratios, L_N ( = (mass pct N)/[mass pct N]), between CaO-SiO₂-Al₂O₃ slags and liquid iron were measured at 1823 and 1873 K as a function of Si (or Al) content in metal, using lime and alumina crucibles. Based on these results and the reported values for activities of SiO₂ (or Al₂O₃), nitride capacities, C_(N), defined by (mass pct N) · PO₂/3/4/PN₂/1/2 were evaluated. Activities of SiO₂ (or Al₂O₃) obtained by using the values for L_N and C_(N) obtained in present and previous gas-slag experiments were compared with previous results. FUMIHIKO TAMURA formerly Graduate Student with the Department of Metallurgical Engineering, Tohoku University.     

Equilibrations of copper matte and fayalite slag under controlled partial pressures of SO2

Equilibrium distributions of Cu, S and O between silica saturated fayalite slags and copper mattes (25 to 79 pct Cu) have been examined experimentally under controlled partial pressures of SO₂. The temperature range of the experiments was 1423 to 1573 K and pSO₂ was varied between 0.1 and 1 atm. Concentrations of copper in the experimental slags were found to be low (<1 pct Cu) under these conditions, as long as the grade of the coexistent matte was below 60 pct copper. Copper in slag concentration rose dramatically, however, when matte grade was increased above this level. The work also showed that whereas FeS has a high solubility for oxygen and is itself soluble in slag under oxidizing conditions, Cu₂S and slag are almost completely immiscible. Cu-Fe-S mattes behave in an intermediate manner. Formerly graduate student with the Department of Mining and Metallurgical Engineering, McGill University.     

MgO和Al2O3对铁矿粉烧结液相生成的影响

为阐述烧结过程熔融机制和成矿机制,明确MgO、Al2O3质量分数对烧结液相生成和矿物组成的影响是至关重要的。利用Factsage软件计算Fe2O3 SiO2 CaO Al2O3 MgO体系的液相生成,计算氧分压在500Pa时,不同温度,不同MgO、Al2O3质量分数下体系液相生成和液相区分布的影响。通过烧结试验,分析烧结矿的矿相和矿物成分,结合软件计算得出烧结矿中MgO质量分数为2.0%、Al2O3质量分数为3.0%时其液相量、矿相、矿物成分达到最优适合烧结冶炼的标准。     

Thermodynamics of oxygen,nitrogen and sulfur in liquid iron equilibrated with CaO-TiOx and CaO-Al2O3-TiOx melts

Equilibria between CaO-TiO_x or CaO-Al₂O₃-TiO_x melts and liquid iron with respect to O, N and S were studied at 1873 K as a function of Ti (or Al) content in metal, using a CaO or an Al₂O₃ crucible. The Al-O and Ti-O relations in liquid iron were studied, and nitride and sulfide capacities defined by and , respectively, were obtained from nitrogen and sulfur distribution ratios, coupled with the analyzed oxygen content in liquid iron or the P_O2 determined by Ti/TiO₂ equilibrium. Based on these results, activities of Al₂O₃ and activity coefficients of TiO₂ and TiO_1.5 were evaluated.     

MgO对烧结矿CaO-Fe2O3系初期液相生成的影响

为了研究MgO对烧结过程中CaO Fe2O3系初期液相生成的影响及作用机理,通过DSC研究了不同MgO含量试样在升温过程中液相生成的变化,并通过XRD确定液相生成前MgO对矿物组成的影响。结果表明,试样中MgO含量的增加使得升温过程中初期液相生成量减少,但是初期液相的生成温度没有明显变化。MgO对初期液相的抑制分为两种方式,一种为MgO与Fe2O3反应生成含镁磁铁矿,另一种为MgO添加导致CaFe2O4分解。这两种方式都使CaO含量升高,促进了高熔点矿物Ca2Fe2O5和含镁磁铁矿的生成,导致液相量降低。通过研究MgO对初期液相生成的影响,为烧结矿中合理添加含镁熔剂提供理论基础。     

The chemical diffusivity of oxygen in liquid iron oxide and a calcium ferrite

Measurements have been made of the chemical diffusion coefficient of oxygen in liquid iron oxide at temperatures from 1673 to 1888 K and in a calcium ferrite (Fe/Ca = 2.57) at temperatures from 1573 to 1873 K. A gravimetric method was used to measure the oxygen uptake during the oxidation of the melts by oxygen or CO₂-CO mixtures. The rate was shown to be controlled by mass transfer in the liquid melt. The chemical diffusivity of oxygen in liquid iron oxide at oxygen potential between air and oxygen was found to be 4.2±0.3 × 10⁻³ cm²/s at 1888 K. That in iron oxide at oxidation state close to iron saturation was established to be given by the empirical expression log D=−6220/T + 1.12 for temperatures between 1673 and 1773 K. For the calcium ferrite (Fe/Ca=2.57) at oxygen potential between air and oxygen, the diffusivity of oxygen was found to be given by log D=−1760/T−1.31 for temperatures between 1673 and 1873 K. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

The contact angle between liquid iron and a single crystal,alumina substrate at 1873 K: Effects of oxygen and droplet size

The contact angle for iron on a single-crystal alumina substrate varied from 40 to 120 deg by changing the gas atmosphere and droplet size. At constant droplet size, the contact angle was a strong function of the partial pressure of oxygen and increased as oxygen partial pressure decreased. However, at oxygen partial pressures less than 10⁻¹⁸ atm, the contact angle markedly decreased as a zone of reactive wetting was reached due to interaction between alumina and the droplet. The effect of droplet size on the contact angle between liquid iron and a single-crystal alumina substrate was measured at constant oxygen activity and temperature. In an argon-hydrogen atmosphere where oxygen activity was constant, the contact angle increased with increasing droplet size and varied from 40 to 80 deg as the droplet radius increased from 1.5 to 4 mm. A similar though smaller effect was measured in CO atmospheres that were in equilibrium with carbon. In this case, the contact angle ranged from 105 to 118 deg as droplet size increased. Experiments in CO/CO₂ atmospheres showed little effect of droplet size at oxygen partial pressures less than 5×10⁻¹² atm, but indicated a significant effect at oxygen partial pressures greater than 10⁻¹¹ atm. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

Effects of sample storage time, temperature and syringe type on blood gas tensions in samples with high oxygen partial pressures

BACKGROUND: Although plastic arterial sampling syringes are now commonly used, the effects of sample storage time and temperature on blood gas tensions are poorly described for samples with a high oxygen partial pressure (PaO2) taken with these high density polypropylene syringes. METHODS: Two ml samples of tonometered whole blood (PaO2 86.7 kPa, PaCO2 4.27 kPa) were placed in glass syringes and in three brands of plastic blood gas syringes. The syringes were placed either at room temperature or in iced water and blood gas analysis was performed at baseline and after 5, 10, 20, 40, 60, 90, and 120 minutes. RESULTS: In the first 10 minutes measured PaO2 in plastic syringes at room temperature fell by an average of 1.21 kPa/min; placing the sample on ice reduced the rate of PaO2 decline to 0.19 kPa/min. The rate of fall of PaO2 in glass at room temperature was 0.49 kPa/min. The changes in PaCO2 were less dramatic and at room temperature averaged increases of 0.47 kPa for plastic syringes and 0.71 kPa for glass syringes over the entire two hour period. These changes in gas tension for plastic syringes would lead to an overestimation of pulmonary shunt measured by the 100% oxygen technique of 0.6% for each minute left at room temperature before analysis. CONCLUSIONS: Glass syringes are superior to plastic syringes in preserving samples with a high PaO2, and prompt and adequate cooling of such samples is essential for accurate blood gas analysis.     

吹氧条件下铁液中硅和硼的氧化规律

研究了吹氧条件下Fe-C熔体、Fe-C-Si熔体、Fe-C-B熔体和Fe-C-Si-B熔体中碳、硅、硼的氧化规律,实验在中频感应炉中进行,实验温度为1 450±25 ℃.结果表明:含硼生铁中硅和硼首先氧化,达到一定程度后碳才开始氧化;含硼生铁中硅、硼氧化是同时进行的,相互影响.     

Grain-growth-inhibiting effects of primary inclusion particles of ZrO2 and MgO in Fe-10 mass pct Ni alloy

Grain-growth inhibition in an Fe-10 mass pct Ni alloy, which was continuously cooled from a melt, was studied at 1673 K in the presence of primary deoxidation products of ZrO₂ or MgO particles. The mean grain size and grain-size distribution in a cross section were measured as a function of holding time for up to 240 minutes. The grain growth was strongly inhibited by the inclusion particles and was influenced by the dissolved Zr. In the Zr deoxidation, the number of particles per unit area (N _A) ranged from 80 to 650 mm⁻², the ZrO₂ particle size ( ) varied from 1.1 to 1.6 μm, and the dissolved Zr level was below 1800 mass ppm. In the Mg deoxidation, the particle-number density was 90 to 270 mm⁻², the MgO particle size was 1.1 to 1.7 μm, and the dissolved Mg level was below 20 mass ppm. In a logarithmic plot of the ratio of limiting mean grain diameter ( ) to the mean particle diameter ( ) against the volume fraction of particles (f _V), both the value for a given f _V value, which ranged from 0.014 to 0.074 pct, and the slope were significantly lower than that predicted from the two-dimensional relation =(4/π) · f _V ^/−1 , i.e., Zener’s limit. This discrepancy is discussed in light of the fraction of particles at the grain boundaries measured experimentally. Normal grain growth was confirmed from the grain-size distribution observed as a function of holding time, which was best described by the log-normal distribution.     

The oxygen pressure of dilute FexO‐CaO‐Al2O3 slag in equilibrium with liquid iron

The relationship between slag composition and oxygen partial pressure of dilute Fe_xO‐CaO‐Al₂O₃ slag in equilibrium with iron the activity of which is below 1 was extrapolated to give the oxygen partial pressure of a slag equilibrated with iron of the activity 1. In the process of extrapolation, the oxygen partial pressure and the activity of iron were unified to give a single thermodynamic quantity which is defined as: , where K(x) is the equilibrium constant for the formation reaction of Fe_xO and is considered to be a function of x. The dependence of on the slag composition was obtained experimentally. On the other hand, it was found that the plot of against log a_Fe has the slope ?1 as expected from the theoretical consideration. The relation has been employed to estimate the composition of slag in equilibrium with liquid iron. Thus, the obtained composition is used to calculate the values of and of the slag in equilibrium with liquid iron.     

The rate of absorption of nitrogen into liquid iron containing oxygen and sulfur

The rate of nitrogen absorption into and desorption from liquid iron containing sulfur and/or oxygen was measured by employing a constant-volume technique with a highly sensitive pressure transducer. Critical evaluation of the results demonstrated conclusively that the chemical rate at high oxygen or sulfur contents is second order with respect to nitrogen content in the metal and probably controlled by the dissociation of the nitrogen molecule on the surface. The effect of sulfur on the rate is complex because of the influence of 1) liquid-phase mass transfer at low sulfur contents, 2) the chemical rate on vacant iron sites at intermediate sulfur contents, and 3) the rate on the adsorbed sulfur layer or the limiting rate at high sulfur contents. However, at intermediate concentrations the limiting case for the adsorption isotherm for sulfur is adhered to and the rate is inversely proportional to the sulfur concentration. For Fe-O melts the rate is inversely proportional to the oxygen content except at low oxygen levels where mass transfer affects the rate. The rate for Fe-S-O melts can be calculated reasonably well from the results for the Fe-S and Fe-0 alloys, assuming that oxygen does not effect the adsorption of sulfur andvice versa and that there is nearly complete coverage of the surface with oxygen and sulfur atoms.     

Phase equilibrium and minor-element distribution between Ni3S2-FeS matte and calcium ferrite slag under high partial pressures of SO2

Calcium ferrite slag has been successfully used in the copper smelting process, but no attempt has been made to use it in the nickel smelting process. The phase equilibrium and the distribution of minor elements between the Ni₃S₂-FeS matte and the CaO-FeO_x-based slag (containing about 2 wt pct MgO) in a magnesia crucible were investigated at 1523 K under controlled partial pressures of S₂, O₂, and SO₂ of 10.1, 50.7, and 101.3 kPa, respectively. The results were compared with those for the iron-silicate-based slag, and the following conclusions were obtained: (1) there is no significant difference in the solubility of nickel between both slags in the high-matte-grade range, (2) the dissolution of cobalt in the calcium ferrite slag is clearly smaller than that in the iron silicate slag, (3) detrimental arsenic, antimony, and bismuth are preferentially collected and fixed in the calcium ferrite slag rather than in the iron silicate slag, and (4) it is considered, with regard to technical feasibility, that the use of the calcium ferrite slag in a converting process of the Bessemer matte will have a prominent future for the nickel converting stage.