Electrical Properties of CuO Added SrFe<Subscript>11.6</Subscript>Zn<Subscript>0.2</Subscript>Ti<Subscript>0.2</Subscript>O<Subscript>19</Subscript> Ferrite Synthesized by Sol–Gel Combustion Route

Strontium hexagonal ferrite SrFe_11.6Zn_0.2Ti_0.2O₁₉ was prepared by citrate sol gel combustion process. Phase formation behavior and crystal structure analysis were performed using XRD pattern. The sintering behavior of ferrite was investigated with and without the addition of CuO using dilatometry. The on-set temperature of sintering was found to decrease significantly by the addition of CuO. The sintered density of CuO-added ferrite was about 95 % of the theoretical density after sintering at 1000 °C. The effects of CuO addition on microstructural development, permeability and permittivity have been studied using scanning electron microscope and LCR meter respectively. The ferrite with CuO addition showed greater permeability, lower loss and lower permittivity due to higher densification.     

Some crystal-chemical relationships in the activated sintering of highly refractory oxides in the solid phase

Summary On the basis of results of investigations of the activated sintering of highly refractory oxides, some crystalchemical relationships have been found, which determine the influence of the energy of the crystal lattice, coordination number and energy parameters of the cations of the sintered oxide and additions (if the latter are introduced) on the sintering process of highly refractory oxides.The results of the investigations have been applied to the development of certain technological processes in the production of sintered refractories from highly refractory oxides, for example on the basis of alumina with a titanium mineralizer.Paper read at the Seminar on Activated Sintering held on 13–14 November, 1961 by the Theoretical Section of the Powder Metallurgy Coordination Council, Institute of Cermets and Special Alloys, Academy of Sciences, Ukr. SSR and the A. A. Baikov Institute of Metallurgy in Moscow.     

MgO对以细磁铁精矿为主的烧结矿微观结构的影响

研究了MgO对以细磁铁精矿为主的烧结矿显微结构的影响。显微结构分析表明：烧结矿MgO的质量分数从1．4%提高到2．3％时,MgO对烧结矿微观结构具有明显的影响。低MgO时,未氧化的Fe3O4及其部分氧化生成的Fe2O3与铁酸钙粘结相形成了烧结矿良好的显微结构,其烧结矿强度良好。高MgO时,烧结矿生成了大块再结晶磁铁矿,同时生成了铁酸镁和镁铁橄榄石等一系列含镁矿物,MgO稳定了磁铁矿和含镁矿物的晶格,这些矿物与赤铁矿、铁酸钙等共存和互连。但MgO矿化需要较高的烧结温度和较长的高温保持时间,垂直烧结速度和利用系数有明显的降低。     

Phase equilibria and X-ray diffraction investigation of the system Cu−Fe−O

An equilibria investigation for the system Cu?Fe?O determined nine regions of stability which were investigated in the oxygen pressure range of 1×10^?4 to 5×10^?1 atm (P _total=1 atm) and at temperatures of 1173° to 1250°K. Oxygen dissociation pressures were determined for three univariant, four bivariant, and two trivariant equilibria. X-ray examination of selected equilibrated samples established conclusively that 1) cuprous ferrite (delafossite) is a stoichiometric compound, 2) cupric ferrite is a solid solution, and 3) solubility of delafossite in cuprous oxide is negligible. A relationship of lattice parameters with compositional variations was determined for the solid solution. Tetragonal-to-cubic spinel crystal transformation of cupric ferrite solid solution occurs with ac/a ratio at or slightly greater than 1.028. A volume discontinuity accompanies the tetragonal-to-cubic spinel transformation, which is a first-order type of thermodynamic transition.     

A Microscopic study of the transformation of sphalerite particles during the roasting of zinc concentrate

The formation of zinc ferrite (ZnFe₂O₄) during the roasting of iron-bearing zinc concentrates requires substantial additional processing to recover the zinc from this compound by leaching and to eliminate the iron from the leachate. The phase changes that occur in the particles of a typical industrial zinc sulfide concentrate during roasting in a fluidized bed at 1223 K were investigated by the use of light microscopy, electron microprobe analysis, and SEM with EDS. The processes which the iron undergoes during its eventual transformation into ferrite have been clarified by examination of the phases and the morphology of partially roasted marmatitic sphalerite particles (Zn, Fe)S, and by reference to the known phase equilibria involved in the Zn-Fe-S-0 system. The oxidation of ironbearing sphalerite occurs in three stages. The first involves the selective diffusion of most of the iron to the particle surface resulting in the formation of an iron oxide shell enclosing a largely unreacted zinc sulfide kernel. In the second stage, this kernel is oxidized to form a solid solution of zinc oxide and iron oxide. The iron is initially present in the ferrous state but, with the disappearance of the sulfide kernel, is oxidized to ferric iron. In the final stage, this dissolved iron oxide and the iron oxide shell react with the surrounding zinc oxide to form the refractory spinel zinc ferrite.     

Effect of Nickel on Formation Mechanisms of Silico-ferrite of Calcium and Aluminum (SFCA)

Under the pressures of both the decrease of high-grade high-quality iron ore resources and the increase of raw material costs,the iron and steel enterprises in China turn to adopt iron ores which contain special elements such as nickel,manganese,etc.in the sintering blend.Analytical reagents were used for sintering experiments,and the sinters were analyzed with X-ray diffraction,scanning electron microscopy and mineralogical microscopy to study the effect of nickel on the silico-ferrite of calcium and aluminum(SFCA)bonding phase formation during sintering.The results indicated that SFCA was divided into nickel-containing and nickel-free areas due to the presence of nickel.The increasing content of nickel would greatly reduce the content of SFCA and promote the formation of calcium aluminum silicate.A great deal of Fe2O3 participated in the crystal transition to Fe3O4,reducing the amount of Fe2O3 involved in the formation of calcium ferrite.When the blending ratio of NiO,which is used to provide the nickel in the sintering process,is less than 3%,the calcium ferrite is in substantially interleaving corrosion with hematite and magnetite.Both the porosity and silicate glass phase content are low,which contributes to the sintering production.     

Structural transformations taking place in the surface layers of very fine BaFe12O19 powder particles

Conclusions During the comminution of powders of the ferrite BaFe₁₂O₁₉ in an attritor mechanical energy is expended in the disintegration of particles, formation of defects, and plastic deformation of the crystal lattice. The comminution of powders in a vibratory mill is accompanied by the formation of well-developed surface layers on particles, which are characterized by a high degree of defectiveness and crystal lattice disorder. The hypothesis is advanced that during prolonged comminution of powders in a vibratory mill the surface layers of particles can undergo structural transformations, which promote the formation of stable oxygen-containing phases at crystallite boundaries.Translated from Poroshkovaya Metallurgiya, No. 6(258), pp. 50–55, June, 1984.     

碱度对烧结矿液相形成性能和微观结构特性的影响

摘要：采用Factsage 7.1热力学软件模拟计算了碱度对烧结矿液相形成性能和微观结构特性的影响,并开展了不同碱度的烧结杯试验研究。研究表明：随着碱度增加,烧结矿理论液相生成量增加,液相黏度降低,液相中Fe2O3/CaO增加,铁酸钙形成条件改善。当碱度为1.95时,铁酸钙含量最高,CaO与Fe2O3结合形成稳定的铁酸钙粘结相,有利于减少Fe2O3发生还原粉化现象;而继续提高碱度至2.05时,颗粒较粗的褐铁矿和赤铁矿与CaO进一步接触、矿化,使烧结矿赤铁矿含量升高,铁酸钙和磁铁矿含量减少,液相黏度降低,孔隙率增大,烧结矿结构均匀性变差,导致烧结矿基体组织结构抵抗还原过程中产生的晶格畸变能力变差,粉化严重。综合考虑碱度对烧结矿转鼓强度和低温还原粉化性能的影响,在试验所用烧结原料条件下,烧结矿适宜碱度应控制为1.95。     

Redistribution of Carbon Atoms in Differentially Quenched Rail on Prolonged Operation

The change in structure, phase composition, and defect substructure in the head of differentially quenched rail after the passage of gross traffic amounting to 691.8 million t is investigated over the central axis, at different distances from the top surface, by means of transmission electron microscopy. The results confirm that prolonged rail operation is accompanied by two simultaneous processes that modify the structure and phase composition of the plate-pearlite colonies: cutting of the cementite plates; and solution of the cementite plates. The first process involves cutting of the carbide particles and removal of their fragments, accompanied simply by change in their linear dimensions and morphology. The second process involves the extraction of carbon atoms from the crystal lattice of cementite by dislocations. That permits phase transformation of the metal in the rail, which is associated with marked relaxation of the mean binding energy of the carbon atoms at dislocations (0.6 eV) and at iron atoms in the cementite lattice (0.4 eV). The stages in the transformation of the cementite plates are as follows: the plates are wrapped in slipping dislocations, with subsequent splitting into slightly disoriented fragments; the slipping dislocations from the ferrite lattice penetrate into the cementite lattice; and the cementite dissolves with the formation of nanoparticles. The cementite nanoparticles are present in the ferrite matrix as a result of their transfer in the course of dislocational slip. On the basis of equations from materials physics and X-ray structural data, the content of carbon atoms at structural elements of the rail steel is assessed. It is found that prolonged rail operation is accompanied by significant redistribution of the carbon atoms in the surface layer. In the initial state, most of the carbon atoms are concentrated in cementite particles. After prolonged rail operation, the carbon atoms and cementite particles are located at defects in the steel’s crystalline structure (dislocations, grain and subgrain boundaries). In the surface layer of the steel, carbon atoms are also observed in the crystal lattice based on α iron.     

The mechanism of ferrite formation from iron sulfides during zinc roasting

The formation of zinc ferrite (ZnFe₂O₄) during the fluidized-bed roasting of zinc concentrates presents subsequent processing difficulties both for zinc recovery and for iron separation and disposal. A major source of iron in these concentrates is from the iron sulfides — pyrite and pyrrhotite. This study examined the changes undergone by these iron minerals when roasted together with sphalerite at 1223 K in a fluidizing gas mixture of 3 pct oxygen and 97 pct nitrogen. Optical microscopy and electron microprobe analysis were employed to identify the three stages that lead to ferrite formation and to examine the processes that occur within each stage. The first stage is oxidation of the sulfides to highly vesicular, amorphous magnetite particles containing small amounts of zinc. The second stage involves both densification of these particles by sintering and counterdiffusion of iron and zinc cations to form a continuous phase of homogeneous zinc-rich spinel and a precipitate of hematite. In the third stage, continuation of cation diffusion and increasingPo ₂ results in the formation of stoichiometric zinc ferrite. These observations have been interpreted by reference to the established phase relationships that occur in the Zn-Fe-O system, and a detailed, solid state reaction mechanism for the formation of zinc ferrite has been proposed.     

The mechanism of ferrite formation from iron sulfides during zinc roasting

The formation of zinc ferrite (ZnFe₂O₄) during the fluidized-bed roasting of zinc concentrates presents subsequent processing difficulties both for zinc recovery and for iron separation and disposal. A major source of iron in these concentrates is from the iron sulfides — pyrite and pyrrhotite. This study examined the changes undergone by these iron minerals when roasted together with sphalerite at 1223 K in a fluidizing gas mixture of 3 pct oxygen and 97 pct nitrogen. Optical microscopy and electron microprobe analysis were employed to identify the three stages that lead to ferrite formation and to examine the processes that occur within each stage. The first stage is oxidation of the sulfides to highly vesicular, amorphous magnetite particles containing small amounts of zinc. The second stage involves both densification of these particles by sintering and counterdiffusion of iron and zinc cations to form a continuous phase of homogeneous zinc-rich spinel and a precipitate of hematite. In the third stage, continuation of cation diffusion and increasingPo ₂ results in the formation of stoichiometric zinc ferrite. These observations have been interpreted by reference to the established phase relationships that occur in the Zn-Fe-O system, and a detailed, solid state reaction mechanism for the formation of zinc ferrite has been proposed.     

EURO PM2009 in cool Copenhagen

Abstract

The effect of additions of silicon powder on the sintering behaviour and microstructure of compacted 304L stainless powder has been studied. The shrinkage ratio increases substantially with silicon content. Silicon profoundly activates the sintering process through the formation of a eutectic and/or δ ferrite, which is pseudoperitectically formed during sintering. The sintering behaviour is closely related to the microstructures, which depend upon the amount of silicon addition. Ostwald ripening is encountered in the liquid phase sintered specimens (Si≤3 wt-%). The solid phase sintered materials (Si≥ wt-%) containing δ ferrite densify more rapidly than the liquid phase sintered ones. The densification kinetics are governed by the wetting characteristics of the eutectic liquid and the formation of ferrite. As a result of the silicon addition, the austenitic stainless steel powder aggregates are sintered into duplex stainless steels with austenite-ferrite structures. PM/0395     

Physical aspects of the solid-phase reduction of metals

The electric-charge and mass transfer processes in the crystal lattices of oxides are analyzed under conditions of high-temperature reduction of metals. As follows from the ionic character of the bond and defects in real oxide crystals, the electric-charge and mass transfer in them is shown to be caused by ion displacements. During high-temperature reduction, oxides are in a pseudoliquid state, where the cation sublattice is stable and provides the stability of the crystal lattice of an oxide as a whole and the anion sublattice is saturated by vacancies ensuring fast (superionic) oxygen transfer. The removal of oxygen ions from the lattice leads to the localization of “excess” electrons by the cations nearest to a vacancy and the transformation of these cations into metal atoms or cations with a lower charge. As a result, the oxide composition changes gradually from the highest oxide to a metal, and clusters whose structures correspond to all intermediate oxides form in the initial structure.     

Migration and Reaction Mechanism of Barium in BaSO4–CaCO3–Fe2O3 System during Sintering

With the increasingly strict requirements of blast furnaces on the sinter quality, analyzing the phase transition process and reaction mechanism of special elements in the sintering process plays an important role in understanding the sintering process and improving the sinter quality. Herein, the decomposition process of barite during sintering and the influence mechanism on the bonding phase of calcium ferrite are studied by laboratory experiments and thermodynamic calculations. The results show that calcium ferrite and ferric oxide can promote the decomposition of barite and reduce the decomposition temperature in the sintering process. The generated barium enters the calcium ferrite phase and affects the strength and melting point of calcium ferrite. With the increase of barium content, the strength of calcium ferrite sample increases from 1.62 to 2.00 kPa, and the initial melting temperature of calcium ferrite sample stays at 1473 K. However, with the further increase of barium, the sample strength and melting temperature both show a worsening trend. Finally, based on the research results, some suggestions for sintering production are put forward, and the optimal barite content is determined. Results help to better understand the reaction process and action mechanism of barium in the sintering process.     

Formation Characteristics of Calcium Ferrite in Low Silicon Sinter

 Influence of sintering temperature, basicity and MgO content on the formation characteristics of calcium ferrite in low silicon sinter of Baotou Iron and Steel Company was studied by means of mini-sintering test and mineralographic microscope analysis. In addition, the suitable sintering parameters such as temperature and basicity were explored. The results found that optimum temperature for the formation of calcium ferrite is 1280 ℃, the basicity of 25-28 is helpful to the development of acicular or columnar calcium ferrite, and MgO content in the low silicon sintering raw materials should be lower than 28% because MgO can intensively inhibit the formation of calcium ferrite. And calcium ferrite in the sinter belongs to calcium ferrite with low calcium, which is different from that in ordinary sinter at home and abroad. So, it provided theoretical basis for promoting formation of calcium ferrite in low silicon sinter and improving properties of sinter.     

Effects of Si and Al on acicular ferrite formation in C-Mn steel

The influences of Si and Al on the microstructure of Ti-containing C-Mn steels have been studied. Although Si addition up to 1 wt pct did not change the crystal structure of dominant Ti₂O₃ particles dispersed in these steels, the formation of an acicular ferrite microstructure was suppressed at high Si contents. It has been found that the Mn content dissolved in Ti₂O₃ particles decreases with increasing Si content. This seems to weaken the formation of Mn-depleted zones (MDZs) around Ti₂O₃ particles, which act as a dominant driving force for the intragranular nucleation of acicular ferrite. It has also been found that the addition of a small amount of Al greatly reduces the formation of acicular ferrite. This is attributed to the change of dominant oxide particles from Ti₂O₃, which serves as an effective nucleant for acicular ferrite, to inert Al₂O₃. The result of the present study implies that it is advantageous to keep Si and Al contents in Ti-containing steels as low as possible when well-developed microstructures of acicular ferrite are desired.     

新型电弧炉炉底用捣打料技术特性和应用

ＨＹＤＬ－８５炉底用捣打料的主要晶相为方镁石,基质胶结相为低熔点过渡型的Ｃ２Ｆ（４ＡＦ）相。在实际应用中Ｃ２Ｆ具有活化晶格加速烧结的作用,且Ｃ２Ｆ分解成氧化铁及ＣａＯ,分别溶入入镁石形成ＲＯ相及反应生成高熔点Ｃ２Ｓ相,有较强的抗蚀性。     

Martensite lattice changes during tempering

An X-ray diffractometer study of martensite formed in an 18 wt pct nickel, 0.98 wt pct carbon austenite single crystal yields the shapes, positions, and integrated intensities of 200, 020, and 002 peaks. Martensite, which forms below ? 60 °C, was tempered at successively higher temperatures from ?45 to 450 °C. The results show that after subambient aging, during which C atoms in c-oriented octahedral sites have clustered, carbide precipitation starts and small regions (～30Å in the [001]) with negative tetragonality appear. Upon subsequent tempering these are augmented by larger regions which have small positive tetragonality. In this process the “c” lattice parameter changes markedly but the “a” and “b” lattice parameter increase very little. These results indicate the formation of carbon depleted martensite which is coherently strained by the carbide particles. At and just above 100 °C the 200, 020, and 002 peaks all become doublets as the martensite matrix discontinuously breaks free of coherency and becomes highly imperfect ferrite. This change also occurs during the so-called “first stage of tempering.” Further tempering decreases the defect content of this ferrite. The lattice of the martensite is extensively reoriented during tempering just above room temperature. These reorientations probably accommodate the lattice parameter changes described above and may be carried out by movement of twin boundaries.     

Nature of the growth of Al-Cu powder compacts during liquid-phase sintering

Conclusions Arresting the process of liquid-phase sintering of aluminum-copper system powder compacts by rapid cooling does not affect the character of the volume changes experienced by them during subsequent sintering under the same temperature conditions. In the growth stage a decrease in the crystal lattice parameter of aluminum and an appreciable broadening of an x-ray line have been observed, caused by the formation of aluminum base solid solutions. These findings bear out the hypothesis that the growth of aluminum-copper powder compacts above their eutectic melting point is mainly due to diffusion of copper from the liquid phase into aluminum particles.Translated from Poroshkovaya Metallurgiya, No. 5(305), pp. 16–19, May, 1988.