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1.
Dilute copper-aluminium alloys were oxidized in air from 700 to 1000 °C. Two distinctive behaviours were observed: alloys with at least 3 wt% aluminium showed excellent oxidation resistance in the whole temperature range. Alloys with 2 wt% or less aluminium exhibited good oxidation resistance up to 800 °C; but as the temperature was further increased, the oxidation rate of these alloys increased and became comparable to that of pure copper. A kinetic model was developed to explain the oxidation behaviour and indirectly determine the amount of dissolved oxygen in the alloys tested. It was found that the oxygen dissolved in alloys with up to 2 wt% Al exceeded its solubility limit in copper, whereas the dissolved oxygen in alloys with higher aluminium contents was below the solubility limit. This difference may account for the significantly different oxidation resistance. 相似文献
2.
Industrial Tokyo and Sinter 75 nickel oxides were reduced with 35 and 80% volume hydrogen-argon mixtures between 350 and 1000 °C in a TGA apparatus. Several abnormalities were observed. At low temperature and in 35% H2, an incubation period was observed. As the temperature was increased the rate of reduction increased up to some temperature, following which a decrease in the reaction rate was observed, which again was followed by an increase in the rates as the temperature exceeded 900 °C. It was found that reduction kinetics of these oxides strongly depend on the morphological features of the oxides. It became clear that the shrinking core model was not applicable and instead the kinetic parameters were assessed by the grain model. 相似文献
3.
Thermal gravimetric analysis was used to investigate the weight change of Ni/Cu/Co calcines upon heating in an inert as well
as hydrogen atmosphere. The two calcines investigated contained approximately 50 wt pct combined of hematite and magnetite
in addition to sulfides of Ni, Cu, Co, and Fe. Mass spectrometry was used to analyze the gas species evolved during heating
and reduction.
The calcine samples are 100 pct less than 100 μm with hematite/magnetite rims around a central sulfide core. When heating
the calcines at 10 °C/min in hydrogen, reduction starts at around 400 °C and is nearly complete at about 700 °C with all the
reducible oxygen removed. Isothermal reduction tests show that at temperatures from 650 °C to 800 °C, half the oxygen is removed
in less than 4 min. The TGA results combined with microscopic analysis show that the reduction followed a uniform internal
reduction model. The reduced calcines will quickly get re-oxidized if they are allowed to contact air while they remain hot. 相似文献
4.
T. Utigard 《Metallurgical and Materials Transactions B》1994,25(4):491-496
The density of FeO-MgO-SiO2 and FeO-Fe2O3-SiO2 based slags has been analyzed in terms of smelting of lateritic ores for the production of ferronickel. The density of these
slags decreases with increasing MgO, SiO2, and Fe2O3 contents as well as with increasing temperature. During the electric furnace smelting of calcined and prereduced garnieritic
ores, the slag temperature decreases from the upper layer down toward the slag/metal interface. Together with precipitation
of either olivine or silica, this leads to the formation of a dense and stagnant slag layer at the slag/metal interface. For
limonitic ores, the use of deep electrode immersion and high currents leads to slag reduction and increased slag temperatures
toward the bottom part of the slag layer. The reduction of Fe2O3 to FeO increases the slag density. In this manner, it may be possible to maintain a hot slag layer in the region of the slag/metal
interface, without buoyancy-induced flow. 相似文献
5.
The oxidation of three nickel concentrates from two Canadian smelters was studied by thermogravimetric analysis. Concentrate
samples were heated to 1223 K (950 °C) in inert or oxidizing atmospheres to determine the reaction behavior. By recording
the mass change as well as the SO2 content in the outlet gas, the oxidation behaviors were quantified. Isothermal roasting tests were carried out on the concentrates
over the temperature range of 673 K (400 °C) to 1123 K (850 °C). When heated in air, the samples gain mass as a result of
sulfate formation at temperatures up to approximately 873 K (600 °C) to 973 K (700 °C), whereas at higher temperatures, the
samples exhibit a large mass loss attributed to sulfate decomposition as well as direct SO2 formation by oxidation. In a 4 pct O2 gas atmosphere, significantly less sulfates were formed. Mixed reactions take place, in which some lead to mass loss and
SO2 generation, and others lead to mass gain and SO2 consumption. The relative importance of the various reactions depends on the experimental conditions. 相似文献
6.
Mark Li Torstein Utigard Mansoor Barati 《Metallurgical and Materials Transactions B》2014,45(1):221-228
A combination of solvent refining and flux treatment was employed to remove boron and phosphorus from crude silicon to acceptable levels for solar applications. Metallurgical grade silicon (MG-Si) was alloyed with pure copper, and the alloy was subjected to refining by liquid CaO-SiO2-Na2O-Al2O3 slags at 1773 K (1500 °C). The distribution of B and P between the slags and the alloy was examined under a range of slag compositions, varying in CaO:SiO2 and SiO2:Al2O3 ratios and the amount of Na2O. The results showed that both basicity and oxygen potential have a strong influence on the distributions of B and P. With silica affecting both parameters in these slags, a critical $ P_{{{\text{O}}_{2} }} $ could be identified that yields the highest impurity pick-up. The addition of Na2O to the slag system was found to increase the distributions of boron and phosphorus. A thermodynamic evaluation of the system showed that alloying copper with MG-Si leads to substantial increase of boron distribution coefficient. The highest boron and phosphorus distribution coefficients are 47 and 1.1, respectively. Using these optimum slags to reduce boron and phosphorus in MG-Si to solar grade level, a slag mass about 0.3 times and 17 times mass of alloy would be required, respectively. 相似文献
7.
T. Marin T. Utigard T. Marin 《JOM Journal of the Minerals, Metals and Materials Society》2005,57(7):58-62
The rate of liquid copper oxidation plays an important role in the separation of impurities from copper during fire refining.
However, the importance of factors affecting the rate of oxygen uptake by liquid copper is not clear. Top blowing oxidation
of molten copper shows that the rate of oxidation is almost independent of the average oxygen concentration of the copper
and proportional to the oxygen flow rate of the gas mixtures used. A pressure monitoring technique was used to determine the
effect of a carrier gas such as N2, helium, and CO2, and the effect of the lance distance from the liquid surface on the partial pressure of oxygen in the gas phase. A numerical
model was developed to help understand the mechanism of oxygen mass transfer into the molten copper.
For more information, contact T. Marin, University of Toronto, Department of Materials Science and Engineering, 184 College
St., Toronto, Canada M5S 3E4; e-mail tanai.marin@utoronto.ca. 相似文献
8.
Aleksandar M. Mitrašinovi? Ryan D'SouzaTorstein A. Utigard 《Journal of Materials Processing Technology》2012,212(1):78-82
The research presented analyzes the effect of low pressure on the amount and reduction of impurity elements in upgraded metallurgical grade silicon. The achieved pressure was 5 kPa in the commercial electro-resistance furnace in the magnesia and mullite refractory material. The chemical composition was determined by ICP-MS method. Elements such as Al, Fe, Mn, Cu or Zn had the highest evaporation rates where higher evaporation was achieved at higher melt temperatures. The overall rate constant was deduced for four melt temperatures indicating high values even for low melt temperatures. The interfacial boundary between Si and mullite refractory showed no dissolution of Al into the liquid Si. 相似文献
9.
Gabriel Plascencia Torstein Utigard Tanai Marín 《JOM Journal of the Minerals, Metals and Materials Society》2005,57(1):80-84
In this study, the high-temperature oxidation resistance of copper and copper-aluminum alloys in air was investigated using
thermo-gravimetric analysis. Upon heating in air, copper starts to noticeably oxidize at temperatures above 400°C. It was
found that as the temperature increased, more aluminum was required in order to protect the copper. Alloying with 4 wt.% aluminum
leads to a remarkable improvement in oxidation resistance. The atmosphere used to heat the samples to the required test temperatures
had a noticeable impact on the subsequent oxidation rates. When heated in argon before being oxidized, copper alloys with
3 wt.% and 4 wt.% aluminum showed excellent oxidation resistance with rates 1,000 times less than that of pure copper at 1,000°C.
However, when these alloys were heated in air, they were much less effective at providing oxidation resistance.
For more information, contact Gabriel Plascencia, University of Toronto, Materials Science & Engineering Department, 184 College
St., Toronto, ON, Canada, M5S 3E4; (416) 978-0912; fax (416) 978-4155; e-mail g.plascencia@utoronto.ca. 相似文献
10.
Disposal of arsenic in copper discharge slags 总被引:3,自引:0,他引:3
Arsenic, which is a toxic pollutant, is present in copper minerals in concentrations to around 1 wt.%. During processing of such copper feed materials, the arsenic has to be transformed into an environmentally acceptable form. Laboratory experiments have been carried out to determine the feasibility of incorporating the arsenic in discharge slags for long-term disposal.Iron arsenate (FeAsO(4)) samples were prepared and tested under various conditions. Upon heating to about 900 degrees C, basically no arsenic was lost. However, at and above 1000 degrees C, iron arsenate decomposes rapidly and arsenic volatilizes. The incorporation of iron arsenate in liquid slags at around 1250 degrees C was difficult due to rapid arsenate decomposition and dust losses during the injection process. Although the leaching tests showed that the slags could meet environmental regulations, the fraction of arsenic leached was no less for the slag samples than for the initial iron arsenate itself. 相似文献