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By Gerhard Bayer

X-ray and thermoanalytical studies were carried out on the formation and stability of Ca-, Mg-and Mn-tungstate, and of the corresponding minerals scheelite and wolframite. The tungstates were synthesized by different methods: precipitation from solution, solid state reactions, displacement reactions with solutions and in the solid state. The reactivity of natural scheelite and wolframite with different salt solutions and in mixtures with other minerals was investigated.

Jan 1, 1989

By Hye-Sung Kim, Dong-Wha Kum, Gyeungho Kim

"Mechanical alloying is an effective way to finely distribute inert dispersoids in AI-TM (TM is a transition metal element) systems. It is considered that high melting point aluminides are formed by precipitation from the supersaturated aluminum matrix. The analysis is based on the fact that much higher content of TM than the solubility limit can be dissolved in alpha aluminum during the high energy ball milling. Nonetheless, the role of undissolved TM particles affecting the formation of aluminides is not suitably considered. In this paper, authors present experimental observation on the formation of Ab3Ti particles from mechanically alloyed AI-Ti alloys in the hyper-peritectic region. This study showed that, in the mechanically alloyed AI-20wt%Ti specimen, intermediate phase of cubic Ab3Ti and tetragonal AIz4Tis formed at 300 - 400°C and 400 - 500°C, respectively, before the MA-state reaches to the global equilibrium at higher temperatures. The formation behavior of Lh- Ab3Ti is interpreted by interdiffusion of Al and Ti in solid state based on the fact that large amount of nano-sized Ti particles exist in the milled powder. Present analysis indicated undissolved Ti particles of nanosize should have played an important role initiating the formation of Ab3Ti phase during annealing.IntroductionInterest in the hyper-peritectic AI-Ti alloys is based on industrial demand for high-modulus and high-temperature aluminum alloys. Earlier works on hyper-peritectic AI-Ti alloys with 4 to 12wt%Ti show that these alloys are strong at ambient temperature and maintain high strength above 300°C when titanium-trialuminide (e.g., Ab3Ti) is finely distributed in the aluminum matrix [1,2]. High melting point and high stiffness with low density of AbTi make the AI-Ti alloys strong with greater thermal stability while keeping weight savings as much as possible. Titanium in aluminum shares other merits of transition metal additions because Ti solubility in Al is low (i.e., 1.l5wt%Ti at 665°C and virtually zero below 400°C), and fine dispersion of Ab3Ti particles is readily accomplished and resists grain coarsening effectively."

Jan 1, 1996

By Seong-Jong Kim

The formation behavior and corrosion characteristics of anodic oxide films on pure Mg and Mg-AI alloys were investigated focusing on the effects of anodizing potential, Al content, temperature and NaOH concentration. Pure Mg and Mg-AI alloys were anodized for 10 min at 3, 10, 40, and 80 V in NaOH solutions. Mg(OH)2 was generated by an active dissolution reaction at the surface of the specimen and the product was affected by temperature while MgO generation increased with NaOH concentration. Moreover, the current density after anodizing for 10 min at a constant potential decreased with increasing AI content in Mg-AI alloys,

Jan 1, 2003

By Bin Zhu, Mingmei Zhu, Hong Zhou, Xiaofei Dou, Bin Xie, Yu Wang, Tiancheng Lin

In this study, the formation of 2CaO·SiO2 and 3CaO·P2O5 solid solution (nC2S-C3P) in hot metal dephosphorization process is discussed. The variations of CaO and SiO2 mass, both in nC2S-C3P solid solution phase and liquid slag phase with increasing P2O5 mass in CaO-SiO2-FetO-P2O5 slags were calculated using Factsage software. CaO-SiO2-FeOt-P2O5 slag containing up to 18 % P2O5 was melted at 1823 K then cooled to 1673 K. The contents of CaO and SiO2 both in the solid solution phase and liquid slag phase of quenched samples were observed and analyzed by SEM/EDS. Both the calculated and experimental results show that the contents of CaO and SiO2 in the solid solution phase decreased, just opposite in the liquid slag phase, with increasing P2O5 content in the slags. Formation mechanism of nC2S-C3P solid solution in the slags was derived based on the ionic structure theory of molten slag. The SiO4 4- in the nC2S-C3P solid solution can be replaced by PO4 3- in the liquid phase resulting in the increasing of free Ca2+ and SiO4 4- in liquid phase.

Jan 1, 2015

By Feng Liu

A thermal upgrading process by which nickel value can be concentrated in a ferronickel alloy is a possible alternative to treat Sudbury pyrrhotite (Po) tailings with nickel content of 0.5–1.5 wt%. The basis of this process is precipitation of Ni from Po at high temperature once Fe/S ratio in the iron-deficient Po is shifted towards stoichiometric or near stoichiometric FeS (troilite) either by the addition of iron and/or the removal of sulfur. For the iron addition route, the reaction between elemental iron and nickeliferous pyrrhotite to produce ferronickel alloy and Ni-depleted iron sulfide phase plays a critical rule. In this paper, the formation mechanism of ferronickel alloy was investigated using the diffusion couple technique to better understand the nickel diffusion behavior in the iron and sulfide phases.

By Zenjiro Asaki, Teruo Tanabe

"To clarify the formation of light rare earth (R =Ce, Pr, Nd or Sm) -Fe compounds in the reduction-diffusion (RD) process, two kinds of experiments were carried out: (a) RD experiment in which briquettes composed of R oxide powder, Fe (particles or wire) and CaH2 were reacted, and (b) immersion experiment, where an Fe plate was immersed into R-Fe melt having the composition of Fe-side liquidus line in Fe crucible. The compound formation was examined by using XRD, SEM and EPMA. The formation rates of RzFe17 measured by the RD experiment were compared with those obtained by the immersion experiment. The growth rates of compounds obtained in the RD experiment for Pr-Fe and Nd-Fe systems were much lower than those obtained in the immersion experiment. This result was explained by the difference of the reduction rates of R oxides by Ca. The parabolic rate constants for the formation of RzFe17 were separated in two groups of (a) Pr-Fe and Nd-Fe systems and (b) Ce-Fe and Sm-Fe systems. This was discussed in connection with the difference of their crystal structures and the driving force of diffusion. The parabolic rate constants for the formation of compounds in Ce-Fe and Sm-Fe systems decreased in the order of RFez, RFe3 and RzFe17.IntroductionTo understand reaction behaviors in the production of rare earth (R) -iron intermetallic compounds, which have excellent magnetic properties, is very important from engineering point of view. And the reduction-diffusion (RD) process<O has recently attracted attention as one of the promising processes to economically produce R-related materials. A few fundamental studies on the compounds formation in the RD process have previously been reported. Qi, Hino and Yazawa(2) observed the formation of R(Nd, Sm)-Fe and R-Co compounds in the process from various view points. Song and Ogawa(3) measured the growth rates of Nd-Fe and Sm-Fe compounds by using Nd or Sm vapor supplied from Nd-Ca or Sm-Ca melts. The authors have also carried out fundamental studies (4)-(8) to clarify the rate and mechanism in the production of R-Fe intermetallic compounds."

Jan 1, 1998

By Zan Yao, Sha Lv, Geoff Wang, Baojun Zhao, Zongze Huang, Jin Zou, Xiaodong Ma, Zhouhua Jiang

55SiCr steel is one of the important spring steels widely used in automobile manufacturing. The presence of micro inclusions in the steel can significantly influence a number of spring properties such as fatigue strength. It is important to understand the mechanism of the inclusion formation so that size and proportion of the inclusions can be controlled. Inclusions in Si-killed 55SiCr spring steel have been analysed by scanning electronic microscopy and electron probe X-ray microanalysis. The chemistry of the inclusions observed in 55SiCr steels can be represented by the SiO2–Al2O3–CaO–MgO system. It was found that the compositions of the inclusions cover a wide composition range, which indicates that these inclusions were formed from different reactions. The possible mechanisms of the inclusion formation are discussed. It would be possible to characterize and manage the inclusions in the spring steels deoxidized by Si.

Mar 1, 2017

By Y. Ide, K. Kishitake

It is expected that an Al-Cr-N composite nitride film may have a higher resistance to oxidation at elevated temperatures than the well-known Ti-Al-N films. The formation conditions of Al-Cr-N films by a de reactive sputtering method and their properties were studied in this study. The films characterized with respect to their high temperature properties such as chemical composition, crystal structure, microhardness, wear and· friction. The crystal structure of the Al-Cr-N films changed from hexagonal phase to cubic phase with an increase in Cr content in the films. The resistivity to thermal oxidation of the Al-Cr-N films is superior to that of usual TI-Al-N films. A half of the friction coefficient in the Al-Cr-N film was obtained comparing with that in the ordinary TI-Al-N film at room temperature and the wear rate of Al-Cr-N film was 2 order smaller than that of TI-Al-N film. The Al-Cr-N films show a small friction coefficient at 500°C and then they are recognized to have good tribological characteristics.

Jan 1, 2000

By M. L. Mahlatji

Mechanical alloying of an equiatomic mixture of crystalline Ti and Pt elemental powders in a high-energy ball mill formed an amorphous alloy by solid-state reactions. Mechanical alloying was carried out in an argon atmosphere at a rotation speed of 1200 r/min and a 20:1 ball-to-powder weight ratio, for time intervals of 4 to 40 hours. At an intermediate stage of mechanical alloying, scanning electron microscopy showed the formation of characteristic layered structures of inhomogeneous composition within the powder particles. X-ray diffraction analysis showed the gradual disappearance of crystalline Bragg peaks and the emergence of broad amorphous maxima as milling progressed. The amorphization process was completed after 8?12 hours. The amorphous state of the product indicated that temperatures during processing did not exceed the crystallization temperature of the alloy.

Jan 1, 2014

By Masayuki Kudoh, Tohru Maruyama, Yohichi. Ito

When hypo-peritectic carbon steel is quenched during unidirectional solidification, the region of fine columnar grain is observed. It is classified into two coexisting phases. One is coexisting phases of liquid, delta and gamma in the upper part of the region, and the other is coexisting phases of delta and gamma in the lower part of the region. To form the coexisting part of the three phases means that solidification in this experiment proceeds in non-equilibrium state. The size of the narrow side of one fine columnar grain coincides with the arm spacing of a primary dendrite and this result is the same as the hyper-peritectic carbon steel. However, the boundary of the fine grain in the hypo-peritectic carbon steel is formed in different location from that of the hyper-peritectic carbon steel. The former is formed in the skeleton of the dendrite, while the latter is formed in the interspacing of the dendrite. The region of the fine grain changes suddenly to that of the coarse grain when the delta phase in the coexisting part of two phases disappears completely. Therefore, the delta phase in the hypo-peritectic carbon steel might prevent the growth of gamma grain. In order to recognize it, ferrite formers such as Mo, V and Ni are added in the sample. Then, the longitudinal length of the fine columnar grain extends in the sequence of the no addition, Mo, V and Nb.

Jan 1, 2000

By S Kodate, Ö Aydan, Y Suda, J Tomiyama

Fracture zones are commonly found in the Earth’s crust. These zones may cause very severe engineering problems. Therefore, the formation and the assessment of the mechanical characteristics of these zones is of great concern for rock engineers. A new double shearing jig was used to study the formation of shear zones in rock under static and impact loading conditions using the device developed by the authors. A series of experiments were undertaken to investigate formation on the formation and characteristics of fracture zones in laboratory. Although actual fracture zones are more complicated, various tests give some insight view of the formation of fracture zones as well as some information on their mechanical behaviour under both dynamic conditions and static conditions. The authors report the outcomes of these experiments and discuss their implications in practice.

Nov 29, 2022

By K. Hanumantha Rao, A. Javadi

Our recent studies revealed that the sulfide minerals in contact with water during grinding produced hydrogen peroxide (H2O2) where the amount of H2O2 production by the minerals found to be in the order of pyrite > chalcopyrite > sphalerite > galena. The H2O2 effect on the oxidation of pulp components and its influence on the concentrate grade and recovery in flotation have been studied and the results have been presented and discussed in this paper. Studies have also been carried out to build correlation between percentage of pyrite in the concentrate, grinding conditions and concentration of OH•/H2O2 in the pulp and as well of controlling the formation of these species through known chemical means for depressing the generation of the oxidant. Flotation tests using a complex sulfide ore with the same reagent scheme that is being used at Boliden concentrator in Sweden but with the addition of i) collector and depressant, ii) Na2S reductant and iii) inorganic (EDTA) and organic (TETA) surface modifiers, during grinding stage have been performed to judge the beneficial or detrimental role of H2O2 on the selective flotation of sulfides. The results demonstrate that the selectivity of metal sulfides against pyrite increases with increasing generation of H2O2 in the pulp liquid. H2O2 is also found to be a better oxidant in chalcopyrite-galena flotation separation than the commonly used K2Cr2O7.

Jan 1, 2016

By M. Okido, H. Yamamoto, T. Sakamoto, R. Ichino, K. Kuroda

"Hydrogen absorption alloy films have been produced by molten salt electrolysis. Lanthanum-Nickel alloy film can be formed on a nickel substrate in KCl-NaCl-LaCb molten salts by electrolysis diffusion process. LaNi5 alloy was formed by mutual diffusion between La ·and Ni after La deposition on Ni substrate. Though several kinds of La-Ni compound existed in deposits, the alloy compounds on Ni substrate changed by electrolysis condition. According to the open-circuit potential measurement in molten salts after La electrodeposition, the formed compounds had a relation to the potential. In the case of the substrate electroplated a cobalt thin film on nickel, LaNi4_5Co0.5 was formed by the electrolysis in the molten salts with lanthanum ions. This ternary alloy film showed better hydrogen absorption behavior in cyclic charge/discharge test in alkaline solution.IntroductionHydrogen storage alloys have attracted attention as the active materials for batteries with the charge/discharge property at ambient temperature. The alloy of nickel and misch metal, mainly consisting of La and Ce, has been commercially 'used as a metal hydride with rechargeable property. In recent years, researches have been developed many kind of new alloys with better hydrogen absorption properties. The hydrogen absorbing alloy ingots are commonly produced by melting method of both metals in furnace, otherwise, prepared by mechanical grinding and metallurgical sintering technique with metal powders. The film is also made by vapor-phase techniques such as sputtering method, ion plating method, etc. ·We have proposed a new method to produce hydrogen absorbing alloy films by molten salts electrolysis technique [1-3]. The hydrogen absorbing film, LaNi5, Mg2Ni and CaNi5, were obtained in this process through controlling the electrolytic condition. The active metals, La, Mg and Ca, are electrodeposited on Ni substrate, diffuse into the substrate and form various kinds of intermetallic compounds. This technique provides a direct process using metal chlorides as resources to produce functional films without using active metals such as La, Ca and Mg."

Jan 1, 2000

By K. Hanumantha Rao, A. Javadi Nooshabadi

"Formation of hydrogen peroxide (H2O2), an oxidizing agent stronger than oxygen, by chalcopyrite (CuFeS2), which is a copper iron sulfide mineral, during grinding, was investigated. It was observed that chalcopyrite generated H2O2 in pulp liquid during wet grinding and also in the solids when placed in water immediately after dry grinding. The generation of H2O2 during either wet or dry grinding was thought to be due to a reaction between chalcopyrite and water where the mineral surface is catalytically active in producing •OH free radicals by breaking down the water molecule. The effect of pH in the grinding medium or in the water in which solids are added immediately after dry grinding showed that the lower the pH value, the higher the H2O2 generation. When chalcopyrite and pyrite are mixed in different proportions, the formation of H2O2 was seen to increase with increasing pyrite fraction in the mixed composition. The results of H2O2 formation in pulp liquid of chalcopyrite and together with pyrite at different experimental conditions have been explained by Eh-pH diagrams of these minerals. This study highlights the necessity of revisiting the electrochemical and/or galvanic interaction mechanisms between the chalcopyrite and pyrite in terms of their flotation behavior.IntroductionHydrogen peroxide causes nonselective oxidation of sulfide minerals if present in pulp liquid. Oxidation of sulfide minerals takes place when they are exposed to atmosphere and during the grinding process when the particle size is reduced for flotation. The oxidation of chalcopyrite leads to iron dissolution from the particle surface and from a metal-deficient, sulfur-rich surface (Fairthorne et al., 1997). Other studies report the formation of iron hydroxide on the surface with the metal ion dislodged on the surface (Buckley and Woods, 1984; Chander, 1991). The chemical reactions for the oxidation of chalcopyrite in alkaline and in acidic solutions with the addition of oxidants, such as oxygen or hydrogen peroxide, are shown in Eqs. (1) and (2), respectively (Shi and Fornasiero, 2010)."

Jan 1, 2015

By H. R. Hanley

IT is a well-known fact that the solubility of zinc compounds decreases when these compounds are roasted in contact with iron compounds, but descriptions of tests to quantitatively express the fact have not appeared in the literature. Possibly such an expression cannot be uniformly and exactly duplicated by different operators because of the variation in the personal equation. In a general way, however, the reactions between zinc compounds and iron compounds under roasting conditions will show a certain trend with changing conditions and the approximate quantitative expression of this trend appears reasonably well established by experimental work conducted for this purpose.

Jan 1, 1929

By Chunyang Guan, Jilai Xue, Zengjie Wang, Qiaochu Liu

Molten salts electrolysis method to prepare Al-RE alloys has attracted increasing attention recently. CaCl2 and Na3AlF6 were the most often used melts for this purpose. In this work, Al-Sc alloys prepared by electrolytic deposition process in both CaCl2 and Na3AlF6 melts were investigated, respectively. It was found that Sc distributes almost uniformly and Sc contents increase with increasing current intensity in both melts. Current efficiency was measured for comparison among various current densities applied. The alloy products were analyzed using XRD and SEM, where the formation behaviors of Al-Sc intermetallics were investigated in details. The experimental and theoretical results demonstrate that Al3Sc and Al0.968Sc0.032 are the major precipitates in the Al-Sc alloys prepared by molten electrolysis. The results are useful for selection and optimization of the molten salts compositions and the parameters of electrolysis operation.

Jan 1, 2015

By Ruddle R. W.

Magnetite occurs in the reverberatory furnaces, blast furnace and converter (a) as the result of its presence in the materials charged, and (b) as the result of oxidation of the FeS in the charge in the absence of sufficient SiO2 to slag the FeO as it is produced and thus prevent its subsequent further oxidation. Magnetite is reduced by FeS according to FeS+3Fe3O4=10FeO+SO2 and similar reactions. This reaction is markedly affected by temperature and does not proceed to any important extent below about 1200°C. To ensure comparative freedom from magnetite it is therefore necessary to raise the temperature of the furnace to the highest practicable figure and to use plenty of siliceous flux. Since the maximum operating temperature is likely to be limited by the resistance of the refractories to attack by the slag, investigation of the factors affecting this attack should be helpful. It is reasonable to suppose that the formation of magnetite might be minimized by ensuring intimate admixture of matte and slag during conversion so that silica is readily available for combination with ferrous oxide as the latter is formed. The literature gives no clue to the importance of this factor and some experimental work on this aspect might be fruitful

Jan 1, 1953

By Muhammad Tawalbeh

The calculated temperature history of a single particle of MgCl2 hydrates when it came in contact with fused salt electrolyte at 650 °C was determined using the measured heat transfer coefficient for the molten salt bath at 650 °C. The calculations revealed that the entire interior of the particle reached the temperature required for the formation of MgOHCI from hydrated MgCl2 in less than 2 seconds. This was much less than the time required for dissolution of the prills as observed in experiments. It is very likely that the formation of MgOHCI during prill dehydration and dissolution is a result of hydrolysis in the interior of the prills.

Jan 1, 2004

By N. Hiroyoshi, R. D. Corpuz, M. Ito, Hokkaido University, C. B. Tabelin, S. Veerawattananun

"Acid mine drainage (AMD), the very acidic and heavy metal-contaminated leachate generated when pyrite-bearing rocks are exposed to surface oxidizing conditions, is a serious environmental problem encountered after the closure of mines and mineral processing operations. In this study, we investigated the effects of soluble phases and metallic oxides, which are commonly found in strongly weathered pyritic wastes, on pyrite oxidation. Strongly weathered pyrite containing melanterite (FeSO4·7H2O) as the main soluble phase was obtained from Furikusa mine, Japan. The sample was washed using two methods to vary the relative amounts of melanterite in the sample. The effect of metallic oxides on pyrite oxidation was evaluated using ultrapure hematite suspensions. Our results showed that under acidic conditions, the effect of soluble salts on the oxidation of pyrite was stronger than hematite. More thorough washing of the sample resulted in the formation of an arsenic-bearing iron-oxyhydroxysulfate coating that minimized pyrite dissolution. This oxidized layer became relatively thicker and mechanically stronger when hematite was introduced after the more thorough removal of soluble salts. Characterization of this “coating” coupled with geochemical modeling suggest that it is most probably composed of two materials: schwertmannite and scorodite. Based on these results, a new approach to suppress pyrite oxidation by directly using iron-oxyhydroxysulfate as coating material is introduced.INTRODUCTION Acid mine drainage (AMD), the very acidic and heavy metals-contaminated leachate produced in closed/abandoned mine sites (Evangelou, 1995), mineral processing and coal cleaning tailings (Evangelou, 1995), and tunnel construction waste rocks (Tabelin and Igarashi, 2009, Tabelin et al., 2012), is one of the oldest and probably the most serious environmental problem of anthropogenic origin. When released to the environment, it rapidly pollutes river, soil and groundwater systems leading to the destruction of affected ecosystems. AMD is produced when pyrite (FeS2), one of the primary gangue minerals in sulfide ores and coals, is exposed to oxidizing conditions as illustrated by the following reactions:"

Jan 1, 2016

By Qingyu Deng, Shiwei Ma, Wang Hua, Guibao Qiu

"The flow properties of the blast furnace slag bearing high TiO2 at high temperature like the viscocity may change a lot due to the formation of the carbonitride inside, causing serious problems on the separation between the metal and the slag. Therefore, the critical condition of the formation of Ti(C,N) in blast furnace is vital importance for the ironmaking process with iron ore bearing titania. In this study, the formation of Ti(C,N) in blast furnace and the influences of various factors on the Ti(C,N) formation are investigated by FactSage. It is found that the mass of Ti(C,N) would reach the maximum at 1480 oC, and the product is mainly TiN below 1620 oC, while it is mainly TiC above 1620oC. The order of the factors by the importance from strong to weak was: temperature, the content of TiO2 in slag, basicity of slag, the content of MgO and Al2O3.IntroductionThe titanium dioxide (TiO2) in iron ore bearing titania will be partly reduced by carbon to titanium carbonitride (Ti(C,N)) in blast furnace, causing serious problems on the separation between the metal and the slag because of the change of flow property. Therefore, the critical condition of the formation of Ti(C,N) in blast furnace is vital importance for the ironmaking process, especially for the smelting of iron ore bearing titania. Extensive experimental data in regard to the formation of Ti(C,N) has been reported in numerous papers[1-6]. However, only some discrete data can be obtained by experiment, and it is difficult to detect the mass of Ti(C,N) in slag. In addition, the experiment is difficult to be proceeded when the temperature is above 1600oC. Therefore, it is very difficult to make clear the critical condition of the formation of Ti(C,N) by experiment."

Jan 1, 2012