Thermodynamic Stabilities of Lanthanum Tungstates Using a Calcium Fluoride Solid Electrolyte Galvanic Cell

Abstract

A knowledge of the thermodynamic stabilities of the lanthanum tungstates measured as the Gibbs energies of formation from the free oxides is important as lanthanum is used as a powerful desulphurizing agent and tungsten as a special alloying element in the production of clean steels and special steels. These data will also be useful as the system La₂O₃ WO₃ can be a model since it exhibits many compounds between the end members. Excepting one EMF work, no information is available in the literature on the thermodynamics of this system. This system exhibits the compounds 5 La₂O₃·22 WO₃, La₂ O₃ · 3 WO₃, La₂O · 2 WO₃, 7 La₂O₃ · 8 WO₃,La₂O · WO₃, 3 La₂O₃ · 2 WO₃ and 5 La₂O₃ · 2 WO₃. The compounds were prepared from reagent grade free oxides by solid state sintering at high temperature followed by X-ray diffraction. The standard Gibbs energies of formation of the compounds from the free oxides were determined by operating the following galvanic cells with calcium fluoride as solid electrolyte.

O₂(g), Pt/ La₂O₃ · LaOF// CaF₂/ / 5 La₂O₃ · 22 WO₃, WO₃, LaOF/Pt, O₂(g)

O₂(g), Pt/La₂O₃ · LaOF//CaF₂//5 La₂O₃ · 22 WO₃, La₂O₃ · 3 WO₃, LaOF/Pt, O₂(g)

O₂(g), Pt/La₂O₃ · LaOF//CaF₂// La₂O₃ · 3 WO₃, La₂O₃ · 2 WO₃ LaOF/Pt, O₂(g)

O₂(g), Pt/La₂O₃ · LaOF//CaF₂// La₂O₃ · 2 WO₃, 7 La₂O₃ · 8 WO₃, LaOF/Pt, O₂(g)

O₂(g), Pt/La₂O₃ · LaOF//CaF₂//La₂O₃ · WO₃, 3La₂O₃ · 2 WO₃ LaOF/Pt, O₂(g)

O₂(g), Pt/La₂O₃ · LaOF//CaF₂//3 La₂O₃ · 2 WO₃, 5La₂O₃ · 2 WO₃ LaOF/Pt, O₂(g)

O₂(g), Pt/ La₂O₃ LaOF// CaF₂/ / 3 La₂O₃2 WO₃, La₂O₃, 2 WO₃ LaOF/Pt, O₂(g)

Stable, reproducible EMFs were obtained in the temperature range 1123 to 1273 K. The net cell reactions are respectively as follows:

5 La₂O₃ + 22 WO₃ = 5 La₂O₃ · 22 WO₃

7 La₂O₃ + 3 (5 La₂O₃ · 22 WO₃) = 22 (La₂O₃ · 3 WO₃)

La₂O₃ + 2 (La₂O₃ · 3 WO₃) = 3 (La₂O₃ · 2 WO₃)

3 La₂O₃ + 4 (La₂O₃) = 7 La₂O₃ · 8 WO₃

La₂O₃ + 7 La₂O₃ · 8 WO₃ = 8 (La₂O₃ · WO₃)

La₂O₃ + 2 (La₂O₃ · WO₃) = 3 La₂O₃ · 2 WO₃

2 La₂O₃ + 3 La₂O₃ · 2 WO₃ = 5 La₂O₃ · 2 WO₃

The standard Gibbs energies of formation of the different lanthanum tungstates are then calculated by appropriately combining from the above cell reactions and their Gibbs energy changes obtained from the experimental EMF data. The present data are discussed in the light of EMF data reported in the literature for WO₃-rich compounds in the system.     

Influence of the mechanical activation of REE oxides on the electrical conductivity of borate melts

The influence of the mechanical activation of oxides M₂O₃ (La₂O₃, Ce₂O₃, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Yb₂O₃, and Lu₂O₃) on electrical conductivity (æ) of the B₂O₃-M₂O₃ molten systems is investigated. It is assumed that the majority carriers in these melts can be protons which enter the melts due to the hydration of B₂O₃. The variation in the magnitude of for various M₂O₃ contents is explained by the corresponding variation in the structure of structural units as a result of the dissociation of the boron-oxygen groups, which include the OH groups. The activation energy of electrical conductivity in the B₂O₃-M₂O₃ melts increases due to the decay of superstructural units [B₃O_4.5] and B₃O₃O_3/2OH as the temperature increases. The dependence of is found. In the B₂O₃-La₂O₃ → B₂O₃-Lu₂O₃ melts series, this energy follows the intraseries periodicity, which depends on the stabilization energy of fundamental terms of the ions of rare-earth elements (REE).     

Experimental study of phase equilibria in the PbO-Al2O3-SiO2 system

Equilibrium phase relations in the PbO-Al₂O₃-SiO₂ system have been investigated experimentally by means of high-temperature equilibration, quenching, and electron probe X-ray microanalysis (EPMA). The system has 21 primary phase fields including three monoxides (PbO, Al₂O₃, and SiO₂), seven binary compounds (Al₆Si₂O₁₃, PbAl₂O₄, PbAl₁₂O₁₉, Pb₂Al₂O₅, PbSiO₃, Pb₂SiO₄, and Pb₄SiO₆), and eleven ternary compounds (PbAl₂Si₂O₈, Pb₃Al₁₀SiO₂₀, Pb₄Al₂Si₂O₁₁, Pb₄Al₄SiO₁₂, Pb₄Al₄Si₃O₁₆, Pb₄Al₄Si₅O₂₀, Pb₅Al₂Si₁₀O₂₈, Pb₆Al₂Si₆O₂₁, Pb₈Al₂Si₄O₁₉, Pb₁₂Al₂Si₁₇O₄₉, and Pb₁₂Al₂Si₂₀O₅₅). Three new ternary compounds, Pb₄Al₄SiO₁₂, Pb₄Al₄Si₅O₂₀, and Pb₁₂Al₂Si₁₇O₄₉, were observed and characterized by EPMA. No extensive solid solution in any of the compounds was found in the present study. The liquidus isotherms were experimentally determined in most of the primary phase fields in the temperature range from 923 to 1873 K, and the ternary phase diagram of the PbO-Al₂O₃-SiO₂ system has been constructed.     

Preparation and performance of electrodeposited Ni-TiB2-Sm2O3 composite coatings

Sm₂O₃ and TiB₂ were used as codeposited particles in electrodeposition Ni-TiB₂-Sm₂O₃ composite coatings to improve its performance. Ni-TiB₂-Sm₂O₃ composite coatings were electrodeposited in the nickel sulfate, hexadecylpyridinium bromide and cetyltrimethylammonium bromide solution containing TiB₂ and Sm₂O₃ particles. The content of codeposited Sm₂O₃ in the composite coating was controlled by changing the concentrations of Sm₂O₃ particles in the solution. The composite coatings were characterized with X-ray diffraction (XRD) and inductively coupled plasma-atomic emission spectrometer (ICP-AES). The effects of Sm₂O₃ content on microhardness, wear weight loss and friction coefficient of composite coatings were investigated, respectively. The microhardness of the Ni-TiB₂-Sm₂O₃ composite coatings was 19.35%, 16.58%, 2.03% higher than that of the Ni coating, Ni-Sm₂O₃ and Ni-TiB₂ composite coatings, respectively. The wear weight loss of the Ni-TiB₂-Sm₂O₃ composite coatings was 7, 2.33, 1.22 times lower than that of the Ni coating, Ni-Sm₂O₃ and Ni-TiB₂ composite coatings, respectively. The friction coefficient of the Ni coating, Ni-Sm₂O₃, Ni-TiB₂ and Ni-TiB₂-Sm₂O₃ composite coatings were 0.712, 0.649, 0.850 and 0.788, respectively. The loading-bearing capacity and the wear-reducing effect of the Sm₂O₃ particles were closely related to the content of Sm₂O₃ particles in the composite coatings.     

Superconductivity and magnetism of complex rhodium borides

A number of complex rhodium borides with an LuRu₄B₄-type structure is synthesized; these are DyRh₄B₄ (samples HP) with T _c ≈ 4.5 K, DyRh_3.8Ru_0.2B₄ (samples AM) with T _c ≈ 4.5 K, Dy_0.8Er_0.2Rh_3.8Ru_0.2B₄ (samples AM) with T _c ≈ 6.3 K, and HoRh_3.8Ru_0.2B₄ (samples AM) with T _c ≈ 6.0 K. The temperature dependence of upper critical field B _c2(T) for all the samples under study exhibits an anomalous behavior. In all cases, the curve B _c2(T) demonstrates a point of inflection, after which the curve deviates from the classical parabolic law abruptly upward for DyRh₄B₄ and DyRh_3.8Ru_0.2B₄ (the 1st group of compounds) and downward for the Dy_0.8Er_0.2Rh_3.8Ru_0.2B₄ and HoRh_3.8Ru_0.2B₄ compounds (the 2nd group). These compounds are found to be characterized by of the following phase transitions: paramagnet → ferrimagnet → superconductor (retained ferrimagnetism) → antiferromagnet (retained superconductivity). The latter transition to the antiferromagnetic state occurs only in the compounds of the 1st group. It is found that, for the DyRh_3.8Ru_0.2B₄ compound, no traditional Meissner effect is observed but the so-called Volleben effect (paramagnetic Meissner effect) takes place.     

Directional phase formation on melting via peritectic reaction

Directional melting and solidification of Ba₂YCu₃O₆₊₈ in low oxygen partial pressures were investigated by the laser-heated floating zone (LHFZ) technique. The following reaction was observed on melting at Po₂ > 8 Pa: Ba₂YCu₃O₆₊₈→ BaY₂CuO₅ + L where BaY₂CuO₅ phase comprised equiaxed particles. At < 8 Pa < Po₂ < 10³ Pa, the preceding reaction occurred, and at higher temperatures, the following reaction also occurred to produce a rodlike BaY₂O₄ phase, oriented in the growth direction: BaY₂Cu0₅ ar BaY₂O₄ + L At pressures below about 8 Pa, the low temperature reaction observed was Ba₂YCu₂O₆₊₈ → BaY₂O₄ + L In this case, the oriented BaY₂O₄ phase formed directly from Ba₂YCu₂O₆₊₈ and was platelike in morphology. Directional growth of the BaY₂O₄ phase from BaY₂CuO₅ was modeled in a simple way. The BaY₂Cu0₅ particles ahead of the BaY₂O₄ interface dissolve in the superheated liquid, and solute transport for BaY₂O₂ growth is assumed to be limited by diffusion along the growth direction over distances equal to half the rod or plate spacing. A relation between supereating at the growth interface and growth rate was derived from the present model. Some possibilities for making use of such aligned structures in the growth of the superconducting compound Ba₂YCu₃O₆₊₈ are discussed.     

Crystal structures and textures in the hot-forged Ni-Mn-Ga shape memory alloys

Three ferromagnetic shape-memory alloys with the chemical compositions of Ni₅₃Mn₂₅Ga₂₂, Ni₄₈Mn₃₀Ga₂₂, and Ni₄₈Mn₂₅Ga₂₂Co₅ were prepared by the induction-melting and hot-forging process. The crystal structures were investigated by the neutron powder diffraction technique, showing that Ni₅₃Mn₂₅Ga₂₂ and Ni₄₈Mn₂₅Ga₂₂Co₅ have a tetragonal, 14/mmm martensitic structure at room temperature, while Ni₄₈Mn₃₀Ga₂₂ has a cubic, L2₁ austenitic structure at room temperature. The development of textures in the hot-forged samples shows the in-plane plastic flow anisotropy from the measured pole figures by means of the neutron diffraction technique. Significant texture changes were observed for the Ni₄₈Mn₂₅Ga₂₂Co₅ alloy after room temperature deformation, which is due to the deformation-induced rearrangements of martensitic variants. An excellent shape-memory effect (SME) with a recovery ratio of 74 pct was reported in this Ni₄₈Mn₂₅Ga₂₂Co₅ polycrystalline alloy after annealing above the martensitic transformation temperature, and the “shape-memory” influence also occurs in the distributions of grain orientations.     

Surface tension of pseudo binary and ternary sulphide matte phase systems Ni3S2, Cu2S and FeS by sessile drop technique

Abstract

The surface tensions of pseudo binary systems Ni₃S₂–FeS, Cu₂S–FeS and Cu₂S–Ni₃S₂ and pseudo ternary system FeS–Cu₂S–Ni₃S₂ as a function of composition, at a constant temperature of 1200°C, have been determined. For the Ni₃S₂–FeS and Cu₂S–Ni₃S₂ pseudo binary systems, the surface tensions increased with an increase in Ni₃S₂ content. The amount of Cu₂S has a small effect on the surface tension of the Cu₂S– containing pseudo systems investigated in this study.

On a déterminé la tension superficielle de systèmes pseudo binaires Ni₃S₂–FeS, Cu₂S–FeS, Cu₂S–Ni₃S₂ et du système pseudo ternaire FeS–Cu₂S–Ni₃S₂ en fonction de la composition, à une température constante de 1200°C. Pour les systèmes pseudo binaires Ni₃S₂–FeS et Cu₂S–Ni₃S₂, la tension superficielle augmentait avec une augmentation de la teneur en Ni₃S₂. La quantité de Cu₂S avait un petit effet sur la tension superficielle des pseudos systèmes contenant du Cu₂S, examinés dans cette étude.     

Thermodynamic assessment of CaO‐SiO2‐Al2O3‐MgO‐Cr2O3‐MnO‐FetO slags for refining chromium‐containing steels

The slag system of CaO‐SiO₂‐Al₂O₃‐MgO‐Cr₂O₃‐MnO‐Fe_tO relevant to refining chromium‐containing steels such as bearing steel is thermodynamically assessed at 1873 K. The activity coefficient of Fe_tO shows an initially rapid increment followed by a gradual reduction according to Cr₂O₃ content at a constant basicity, and decreases with increasing slag basicity. γ_MnO is decreased abruptly by increasing Cr₂O₃ content and thereafter, maintains a nearly constant level. From the standpoint of inclusion control, the Cr₂O₃ presence in ladle refining slags is thermodynamically harmful in that it minimizes the inclusion level by inducing the increment of γ_FetO even though Cr₂O₃ exists in extremely small amounts. However, it is beneficial in that it diminishes AI reoxidation by decreasing γ_MnO. The presence of carbon in slag decreases γ_FetO and γ_MnO, which turns out to be favourable for the reduction of Al reoxidation. The thermodynamic equilibria of chromium and manganese are quantified in terms of Fe_tO and Cr₂O₃ content as well as slag basicity by using multiple regression analysis. L_Cr and L_Mn are increased by the presence of Cr₂O₃, indicating a low recovery efficiency of Cr and Mn in the treatment of ferroalloy addition. In determining L_S values, Cr₂O₃ is not so important as the basicity of slags.     

Effects of iron and temperature on solubility of light rare earth sulfates in multicomponent system of Fe2(SO4)3-H3PO4-H2SO4 synthetic solution

Numerous light rare earth elements (LREE) minerals containing Fe and P were processed by sulfuric acid roasting method, and the leaching solution mainly comprises LREE sulfate, Fe₂(SO₄)₃, H₃PO₄, and H₂SO₄, however, the solubility data of LREE sulfates in this system is few. This work studies the solubility of LREE sulfates in independent LREE sulfate system RE₂(SO₄)₃-Fe₂(SO₄)₃-H₃PO₄-H₂SO₄ (RE = La, Ce, Pr or Nd) and mixed LREE sulfates system (La,Ce,Pr,Nd)₂(SO₄)₃-Fe₂(SO₄)₃-H₃PO₄-H₂SO₄ at different temperature (25–65 °C) and concentrations of Fe₂(SO₄)₃ (Fe₂O₃, 0–50.13 g/L), H₂SO₄ (0.5 mol/L), and H₃PO₄ (P₂O₅, 20.34 g/L) based on the industrial operating condition at low liquid and solid ratio 2:1. The solubility of each LREE sulfate in the independent system (La₂O₃, 12.25–20.88 g/L; CeO₂, 41.93–62.35 g/L; Pr₆O₁₁, 37.34–56.69 g/L; Nd₂O₃, 26.60–37.63 g/L) is much higher than that of the mixed system (La₂O₃, 6.95–11.03 g/L; CeO₂, 10.63–21.51 g/L; Pr₆O₁₁, 11.56–20.36 g/L; Nd₂O₃, 12.36–19.79 g/L) under the same other conditions. The results also indicate that, in the two systems, both Fe and the temperature have negative effects on the solubility of LREE sulfates. That may occur due to the complication reactions between the complexes of RESO₄⁺ and Fe(SO₄)₂^–. However, the influence degree of temperature and iron concentration on the LREE sulfates solubility varies in the two systems and among different LREE species. This research is of theoretical significance for optimizing the conditions of the sulfuric acid process for recovering the LREE from the mixed LREE bearing minerals as well as the single LREE containing secondary rare earth scraps.     

The Sulphation of Tricobalt Tetroxide and Nickel Monoxide with Fused Sodium Hydrogen Sulphate

Abstract

The results of differential thermal, X-ray powder diffraction analyses and thermogravimetric analyses have heen used to identify the reactions that occur when NaHSO₄ is heated between 150°C and 400°C with NiO and with Co₃O₄. The initial reactions occur on fusion of NaHSO₄ and produce monohydrated sulphates Ni and Co, Na₂SO₄ and Na₃H(SO₄)₂. The Na₃H(SO₄)₂ decomposes to Na₂SO₄ and Na₂S₂SO₇ at higher temperature NiSO₄·H₂O reacts with Na₂SO₄, forming NiSO₄·Na₂SO₄, H₂O, which subsequently dehydrates; but CoSO₄·H₂O dehydrates before reaction occurs to produce-CoSO₄·Na₂SO₄.     

Decomposition of Y<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> Particles in 8 Pct Cr Oxide-Dispersion-Strengthened Martensitic Steel during Tempering

Chemical composition analysis using inductively coupled plasma spectroscopy and phase identification using X-ray were performed on the extracted residues of 8 pct Cr martensitic steel strengthened by nanoscaled complex oxides, which consist of yttrium, titanium, and oxygen. Some Y₂Ti₂O₇ particles, which were stable during normalizing, decomposed into Y₂O₃ and Ti₂O₃ during tempering. This reaction reversibly occurred between normalizing and tempering. Y₂Ti₂O₇ particles formed in the steel had other constituents in solid solution as compared to the completely stoichiometric Y₂Ti₂O₇ particles synthesized artificially in air. As for the mechanism of the decomposition of Y₂Ti₂O₇ particles in the steel, segregation of oxygen to dislocations induced by normalizing caused the decomposition of Y₂Ti₂O₇ during tempering. In addition to that, the interfacial strain between Y₂O₃ particles or Ti₂O₃ particles within Cr₂₃C₆ carbides, which are formed by tempering, was lower than the strain between Y₂Ti₂O₇, which precipitated in Cr₂₃C₆ carbides or the matrix. This difference in interfacial strain could also promote the decomposition of the Y₂Ti₂O₇ particles in the steel.     

Phase structure and hydrogen storage properties of REMg8.35Ni2.18Al0.21 （RE=La, Ce, Pr, and Nd） hydrogen storage alloys

REMg 8.35Ni2.18Al0.21 (RE=La, Ce, Pr, and Nd) alloys were prepared by induction melting and following annealing. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the alloys were composed of Mg2Ni, (La, Pr, Nd)Mg2Ni, (La, Ce)2Mg17 , (Ce, Pr, Nd)Mg12 and Ce2Ni7 phases. The above phases were disproportioned into Mg2NiH4 , MgH2 and REH x (x=2.51 or 3) phases in hydriding. CeH2.51 phase transformed into CeH2.29 phase in dehydriding, whereas LaH3 , PrH3 and NdH3 phases remained unchanged. The PrMg8.41Ni2.14Al0.20 alloy had the fastest hydriding kinetics and the highest dehydriding plateau pressure while the CeMg8.35Ni2.18Al0.21 alloy presented the best hydriding/dehydriding reversibility. The onset hydrogen desorption temperature of the CeMg8.35Ni2.18Al0.21 hydride decreased remarkably owing to the phase transformation between the CeH2.51 and the CeH2.29 .     

Significantly improved high k dielectric performance: Rare earth oxide as a passivation layer laminated with TiO2 film

In order to achieve a super gate dielectric performance,rare earth oxides featuring for large band gap,good thermodynamic stability and relatively high k value were selected to be laminated with TiO₂ film to prepare bilayer dielectric films.As an example,the microstructure,morphology,band gap structure and electrical performance of TiO₂-Y₂O₃ bilayer films were systematically investigated.Results show that stacking sequence of TiO₂ and Y_...     

Thermal Shock Resistance of Al2 O3/ZrO2 (Y2O3) Composites

ZrO₂ containing 2% (mol fraction) Y₂O₃ and 3% (mol fraction) Y₂O₃ were added into Al₂O₃ matrix, compositing composites with 15% volume fraction of addictives mentioned above. The testing of property and analysis of SEM presented that, after vacuum sintering at 1550 °C, thermal shock resistance of two composites was superior to Al₂O₃ ceramic. The experiment showed that the properties of Al₂O₃ composites was higher than Al₂O₃ ceramic, and Al₂O₃/ZrO₂(3Y) was higher than Al₂O₃/ZrO₂(2Y) in thermal shock resistance. Improvement of thermal shock resistance of composites was attributed to many toughness machanisms of ZrO₂(Y₂O₃). By calculation, the fracture energy of Al₂O₃, Al₂O₃/ZrO₂ (2Y) and Al₂O₃/ZrO₂(3Y) was 38100.8 and 126.2 J·m⁻², respectively. Cracks initiation resistance (R') of Al₂O₃/ZrO₂(3Y) and Al₂O₃/ZrO₂(2Y) was higher than Al₂O₃ ceramic by 1.57 and 1.41 time, respectively, and cracks propagation resistance (R″″) was higher than Al₂O₃ ceramic by 1.46 and 1.38 time, respectively, which was corresponding to the results of residual strength.     

Effect of La2Sn2O7 content on Ag-La2Sn2O7/SnO2 arc erosion behavior and mechanism

La₂ Sn₂ O₇/SnO₂ powder was synthesized by chemical co-precipitation method,and Ag-La₂ Sn₂ O₇/SnO₂ composites were prepared by hot-pressing sintering.The electrical resistivity,density,Brinell hardness and flexural strength of Ag-La₂ Sn₂ O₇/SnO₂ composites were measured.Moreover,the effect of La₂ Sn₂ O₇ content on the arc erosion beha...     

Effects of Phosphorus and Carbon Contents on Amorphous Forming Ability in Fe-based Amorphous Alloys Used for Thermal Spray Coatings

Cost-effective Fe-based amorphous alloys used for thermal spray coatings were developed by varying contents of P and C, and their microstructure, hardness, and corrosion resistance were analyzed. In order to achieve chemical compositions having high amorphous forming ability, thermodynamically calculated phase diagrams of Fe-Al-P-C-B five-component system were used, from which compositions of super-cooled liquid having the lowest driving force of formation of crystalline phases were obtained. The thermodynamic calculation results showed that only phases of Fe₃P and Fe₃C were formed in the Fe₇₈Al₂P_(18.3?x)C _x B_1.7 alloy system. Considering driving force curves of Fe₃P and Fe₃C, the carbon contents were selected to be 6.90 and 7.47 at. pct, when the thermodynamic calculation temperatures were 697 K (414 °C) and 715 K (442 °C), respectively. According to the microstructural analysis of suction-cast alloys, the Fe₇₈Al₂P_10.83C_7.47B_1.7 alloy showed a fully amorphous microstructure, whereas the Fe₇₈Al₂P_11.40C_6.9B_1.7 and Fe₇₈Al₂P_10.3C_8.0B_1.7 alloys contained Fe₃P and Fe₃C phases. This Fe₇₈Al₂P_10.83C_7.47B_1.7 alloy showed the better hardness and corrosion resistance than those of conventional thermal spray coating alloys, and its production cost could be lowered using cheaper alloying elements, thereby leading to the practical application to amorphous thermal spray coatings.     

Formation and Evolution Mechanism of the Inclusions of Al2O3·SiO2·CaO and Al2O3·SiO2·CaO·MgO in Seamless Steel Tube Steel

Herein, the formation and evolution mechanism of inclusions of Al₂O₃·SiO₂·CaO and Al₂O₃·SiO₂·CaO·MgO in seamless steel tube steel are investigated. In the long strip defects on the longitudinal cross section of the steel tube after the rolling bar piercing, the defect is mainly formed by Al₂O₃·SiO₂·CaO·MgO inclusions and Al₂O₃·SiO₂·CaO·inclusions dotted with·CaS inclusions after the rolling. The typical inclusions in the different steelmaking stages are mainly composed of CaS, Al₂O₃·(SiO₂), CaO·(SiO₂), MnS·(TiN), Al₂O₃·SiO₂·CaO·(CaS)·(MnS), Al₂O₃·SiO₂·CaO·MgO·(MnO), Al₂O₃·SiO₂·CaO·MgO·(CaS)·(MnS), etc. In the billet, the average sizes of Al₂O₃·SiO₂·CaO-based and Al₂O₃·SiO₂·CaO·MgO-based inclusions are much larger than those of the other types of inclusions. Part of SiO₂ in the deoxidized products SiO₂ can be reduced by [Al], resulting in the formation of the Al₂O₃·SiO₂ composite inclusions. The SiO₂ in Al₂O₃·SiO₂ inclusions can continuously be reduced by the dissolved [Ca] to form the Al₂O₃·SiO₂·CaO composite inclusions. The SiO₂ in the Al₂O₃·SiO₂·CaO inclusions can be reduced by the dissolved [Mg] to form the Al₂O₃·SiO₂·CaO·MgO composite inclusions. Another formation process of Al₂O₃·SiO₂·CaO·MgO inclusions is the entrapment of ladle slag in the vacuum degassing (VD) stage, due to the strong agitation of the rising Ar bubbles in the vacuum condition of the VD stage.     

Effect of C on Phase Evolution,Microstructure, and Magnetic Properties of Pr2Fe14B-Type Nanocomposites

The phase evolution, microstructure and magnetic properties of melt-spun Pr-rich Pr₁₁Fe_bal.B_8-yC_y (y = 0–8) and Pr-lean Pr₉Fe_bal.Ti_xB_11–yC_y (x = 0, 2.5 and 4; y = 0–11) ribbons have been investigated intensively. A slight substitution of C for B (y=2) was proven to be effective in improving the magnetic properties of Pr-rich Pr₁₁Fe_bal.B_8–yC_y nanocomposites. C atoms prefers to enter 2:14:1 phase in forming Pr₂Fe₁₄(B, C). But the volume fraction of Pr₂Fe₁₇C_z, α-Fe and 1:2 carbide increases, due to the dissociation of 2:14:1 phase and the suppression of Fe₃B phase, with further increase of carbon content. The optimal magnetic properties of B_r = 9.4 kG, _iH_c = 9.3 kOe, and (BH)_max = 17.3 MGOe were obtained for Pr₁₁Fe_bal.B₆C₂. In contrast, the increase of C substitution in Pr₉Fe_bal.Ti_2.5B_11–yC_y (y=0–11) ribbons degrades the B_r, _iH_c, and (BH)_max monotonically, which is arisen from the increase of vol % of Pr₂Fe₁₇C_z and α-Fe phases, and the rapid decrease of 2:14:1 phase. In comparison with those of Pr₉Fe_bal.B_11–yC_y (y=0–5.5) ribbons, improved magnetic properties of (BH)_max=15.3–17.8 MGOe with higher coercivity of _iH_c=9.7–10.8 kOe have been obtained in Ti-containing Pr₉Fe_bal.Ti_2.5B_11–yC_y (y=0–5.5) ribbons. However, in higher Ti concentration Pr₉Fe_bal.Ti₄B_11–yC_y, ribbons, a slight substitution of C for B (y = 0.5–1) is beneficial in improving the coercivity and magnetic energy product, simultaneously. The optimal properties of B_r = 9.4 kG, _iH_c = 11.1 kOe, (BH)_max = 18.0 MGOe and α = −0.146 %/°C, β = −0.576 %/°C were achieved in Pr₉Fe_bal.Ti₄B_10.5C_0.5 nanocomposites.     

Effect of TiO2 on the crystallisation behaviour of CaF2–CaO–Al2O3–MgO slag for electroslag remelting of Ti-containing tool steel

The crystallisation characteristics of CaF₂–CaO–Al₂O₃–MgO slags with various TiO₂ contents from 0 to 9.73 mass% were studied using a single hot thermocouple technique, SEM-EDS and X-ray diffraction. The crystallisation mechanism of TiO₂-bearing slag was identified based on kinetic analysis. It was found that increasing TiO₂ from 0 to 6.43 mass% inhibited the crystallisation ability of electroslag remelting-type CaF₂–CaO–Al₂O₃–MgO slag, whereas further increasing TiO₂ content up to 9.73 mass% enhanced the slag crystallisation signally. When increasing TiO₂ content to 6.43 mass%, the crystalline phase shift from CaO to Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ at high temperatures. At lower temperatures, the crystalline phase change from polygonal Ca₁₂Al₁₄O₃₂F₂ to need-like CaTiO₃. Further increasing TiO₂ content to 9.73 mass%, the crystalline phase are Ca₁₂Al₁₄O₃₂F₂ and CaTiO₃ in the range of 1473–1613?K. The crystallisation of crystalline phase in the isothermal crystallisation is surface nucleation and controlled by interface reaction when TiO₂ content is lower than 6.43 mass% in the slag. It is bulk nucleation and diffusion-controlled one-dimensional growth in slag with 9.73 mass% TiO₂.