Effects of Different Boron Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al Alloy

Interfacial reactions between Al alloy and andalusite low-cement castables (LCCs) containing 5 wt pct B₂O₃, B₄C, and BN were analyzed at 1123 K and 1433 K (850 °C and 1160 °C) using the Alcoa cup test. The results showed that the addition of boron-containing materials led to the formation of aluminoborate (9Al₂O₃.2B₂O₃) and glassy phase containing boron in the prefiring temperature (1373 K [1100 °C]), which consequently improved the corrosion resistance of the refractories. The high heat of formation of the aluminoborate phase (which increased its stability to reactions with molten Al alloy) and the low solubility of boron in molten Al were the major factors that contributed to the improvement in the corrosion resistance of B-doped samples.     

Thermodynamic Simulation of the Influence of the Temperature and the Basicity of a Boron-Containing Slag on Steel Desulfurization

The results of thermodynamic simulation of the desulfurization of a medium-carbon steel by slags of the CaO–SiO₂–MgO–Al₂O₃–B₂O₃ system are presented. The HSC Chemistry 6.12 software package is used for the simulation. The thermodynamic simulation is performed for 20 various chemical compositions of slags with various B₂O₃ contents (1–4%)¹ and basicities ((CaO)/(SiO₂) = 2–5). The computations are performed using the Equilibrium Compositions module in the temperature range from 1500 to 1700°C with an increment of 50°C at a gas phase pressure of 0.1 MPa. The main results of the calculations are presented as the dependences of the change in the sulfur content in steel [S] on the temperature, the content of B₂O₃, and the slag basicity. An increase in the temperature of metal desulfurization from 1500 to 1700°C exerts a favorable effect on the sulfur content for the studied range of slag basicities. In particular, the sulfur content in steel decreases from 0.012 to 0.009% when steel is processed with the slag having 3% B₂O₃ and a basicity (CaO)/(SiO₂) = 2. A positive effect of an increase in the slag basicity from 2 to 5 on metal desulfurization is observed: the degree of desulfurization increases from 61.1 to 97.2% at 1600°C and 3% B₂O₃ content in the slag. As the B₂O₃ content in a slag increases from 1 to 4%, its refining properties decrease significantly in the range of basicity not higher than 2. In the range of high slag basicities (3–4), the negative effect of acidic oxide B₂O₃ on the refining properties of the slag decreases, providing low sulfur contents (which do not exceed [S] = 0.003–0.004% at 4% B₂O₃). At a slag basicity of 5, the sulfur content in steel decreases to 0.001%, all other things being equal. The simulation results can be used for the calculation of steel desulfurization processed by slags containing B₂O₃.     

Thermodynamic Modeling of Metal Desulfurization with Boron-Containing Slags of the CaO–SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> System

In thermodynamic modeling of the desulfurization of steel by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag on the basis of HSC 6.12 Chemistry software (Outokumpu), the influence of the temperature (1500–1700°C), the slag basicity (2–5), and the B₂O₃ content (1–4%)1 on the desulfurization is analyzed. It is found that the sulfur content is reduced with increase in the temperature from 1500 to 1700°C, within the given range of slag basicity. At 1600°C, the sulfur content in the metal is 0.0052% for slag of basicity 2; at 1650°C, by contrast, its content is 0.0048%. Increase in slag basicity from 2 to 5 improves the desulfurization, which increases from 80.7 to 98.7% at 1600°C. If the B₂O₃ content in the slag rises, desulfurization is impaired. At 1600°C, the sulfur content in the metal may be reduced to 0.0052 and 0.0098% when using slag of basicity 2 with 1 and 4% B₂O₃, respectively; in the same conditions but with slag of basicity 5, the corresponding values are 0.00036 and 0.00088%, respectively. Note that desulfurization is better for slag without B₂O₃. According to thermodynamic modeling, metal with 0.0039 and 0.00019% S is obtained at 1600°C when using slag of basicity 2 and 5, respectively, that contains no B₂O₃. The results obtained by thermodynamic modeling for the desulfurization of metal by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag of basicity 2–5 in the range 1500–1700°C are consistent with experimental data and may be used in improving the desulfurization of steel by slag that contains boron.     

Response to Thermal Exposure of Ball-Milled Cu-Mg/B2O3 Powder Blends

The response to thermal exposure of ball-milled Cu-Mg/B₂O₃ powder blends was investigated in the current study to explore the potential of powder metallurgy route to produce Cu-B alloys. Cu-20Mg alloy powder was mixed with B₂O₃ and subsequently ball milled for 1 hour. Ball milling alone failed to establish a reaction between Cu-Mg compounds and B₂O₃. When the ball-milled powder blend was heated, however, B₂O₃ was reduced by CuMg₂ <773 K (500 °C). The Cu₂Mg intermetallic phase, which has survived until 773 K (500 °C), was involved in the reduction of the remaining B₂O₃ at still higher temperatures, while excess Mg reacted with B to produce MgB₂ and MgB₆ compounds. Cu-Mg alloy with predominantly the CuMg₂ phase must be utilized to take advantage of the capacity of the CuMg₂ (Cu-43 wt pct Mg) compound to reduce B₂O₃ at temperatures as low as 773 K (500 °C). Once the Cu-43Mg alloy powder is mixed with B₂O₃ and the powder blend thus obtained is ball milled and subsequently heated at 500 °C, B₂O₃ is readily reduced by CuMg₂ to yield Cu, B, and MgO. The latter can be easily removed from the powder blend by acid leaching.     

Silico-ferrite of Calcium and Aluminum (SFCA) Iron Ore Sinter Bonding Phases: New Insights into Their Formation During Heating and Cooling

The formation of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter phases during heating and cooling of synthetic iron ore sinter mixtures in the range 298?K to 1623?K (25?°C to 1350?°C) and at oxygen partial pressure of 5?×?10^?3 atm has been characterized using in situ synchrotron X-ray diffraction. SFCA and SFCA-I are the key bonding phases in iron ore sinter, and an improved understanding of their formation mechanisms may lead to improved efficiency of industrial sintering processes.?During heating, SFCA-I formation at 1327?K to 1392?K (1054?°C to 1119?°C) (depending on composition) was associated with the reaction of Fe₂O₃, 2CaO·Fe₂O₃, and SiO₂. SFCA formation (1380?K to 1437?K [1107?°C to 1164?°C]) was associated with?the reaction of CaO·Fe₂O₃, SiO₂, and a phase with average composition 49.60, 9.09, 0.14, 7.93, and 32.15?wt pct Fe, Ca, Si, Al, and O, respectively. Increasing Al₂O₃ concentration in the starting sinter mixture increased the temperature range over which SFCA-I was stable before the formation of SFCA, and it stabilized SFCA to a higher temperature before it melted to form a Fe₃O₄?+?melt phase assemblage (1486?K to 1581?K [1213?°C to 1308?°C]). During cooling, the first phase to crystallize from the melt (1452?K to 1561?K [1179?°C to 1288?°C]) was an Fe-rich phase, similar in composition to SFCA-I, and it had an average composition 58.88, 6.89, 0.82, 3.00, and 31.68?wt pct Fe, Ca, Si, Al, and O, respectively. At lower temperatures (1418?K to 1543?K [1145?°C to 1270?°C]), this phase reacted with melt to form SFCA. Increasing Al₂O₃ increased the temperature at which crystallization of the Fe-rich phase occurred, increased the temperature at which crystallization of SFCA occurred, and suppressed the formation of Fe₂O₃ (1358?K to 1418?K [1085?°C to 1145?°C]) to lower temperatures.     

Physical Properties and Regulating Mechanism of Fluoride-Free and Harmless B2O3 -Containing Mould Flux

There were certain amounts of CaF2, NaF orNa2Oin traditional mould fluxes ai ming to modifythe melting property of mould fluxes[1 -5], whichwould do great harmto the service performance ofmould fluxes . Meanwhile the environment was pol-luted seriously and health of operators was i mpairedheavily .Calciumfluorideledtothe separating out ofhigh melting point substance as spars , which de-stroyed the glass properties of mould fluxes .If flu-oride-containing mould fluxes entered the coolingwater…     

Low-Temperature Densification Sintering and Properties of Monoclinic-SrAl2Si2O8 Ceramics

The dense monoclinic-SrAl₂Si₂O₈ ceramics have been prepared by a two-step sintering process at a sintering temperature of 1173 K (900 °C). Firstly, the pre-sintered monoclinic-SrAl₂Si₂O₈ powders containing small SiO₂·Al₂O₃ crystal phases were obtained by continuously sintering a powder mixture of SrCO₃ and kaolin at 1223 K (950 °C) for 6 hours and 1673 K (1400 °C) for 4 hours, respectively. Subsequently, by the combination of the pre-sintered ceramic powders with the composite flux agents, which are composed of a SrO·3B₂O₃ flux agent and α-Al₂O₃, the low-temperature densification sintering of the monoclinic-SrAl₂Si₂O₈ ceramics was accomplished at 1173 K (900 °C). The low-temperature sintering behavior and microstructure evolvement of the monoclinic-SrAl₂Si₂O₈ ceramics have been investigated in terms of Al₂O₃ in addition to the composite flux agents. It shows that due to the low-meting characteristics, the SrO·3B₂O₃ flux agent can urge the dense microstructure formation of the monoclinic-SrAl₂Si₂O₈ ceramics and the re-crystallization of the grains via a liquid-phase sintering. The introduction of α-Al₂O₃ to the SrO·3B₂O₃ flux agent can apparently lead to more dense microstructures for the monoclinic-SrAl₂Si₂O₈ ceramics but also cause the re-precipitation of SiO₂·Al₂O₃ compounds because of an excessive Al₂O₃ content in the SrO·3B₂O₃ flux agent.     

High Temperature Oxidation Behavior of Conventional and Nb-Modified MAR-M246 Ni-Based Superalloy

The present investigations focused on the thermal oxidation of two variants of MAR-M246 alloy having the same contents of Ta and Nb in at. pct, considering the effects of total replacement of Ta by Nb. The alloys were produced by investment casting using high purity elements in induction furnace under vacuum atmosphere. The alloys were oxidized pseudo-isothermally at 800 °C, 900 °C and 1000 °C up to 1000 hours under lab air. Protective oxidation products growing on the surface of the oxidized samples were mainly Al₂O₃, Cr₂O₃. Other less protective oxide such as spinels (NiCr₂O₄ and CoCr₂O₄) and TiO₂ were also detected as oxidation products. The conventional alloy exhibited slight internal oxidation at 800 °C and an enhanced resistance at 900 °C and 1000 °C. The Nb-modified alloy presented an exacerbated internal oxidation and nitridation at 900 °C and 1000 °C and an enhanced resistance at 800 °C. At 1000 °C, Nb-modified alloy was particularly affected by excessive spalling as the main damage mechanisms. From a kinetic point of view, both alloys exhibit the same behavior at 800 °C and 900 °C, with k_p values typical of alumina forming alloys (2 × 10⁻¹⁴ to 3.6 × 10⁻¹³ g² cm⁻⁴ s⁻¹). However, Ta modified alloys exhibited superior oxidation resistance at 1000 °C when compared to the Nb modified alloy due to better adherence of the protective oxide scale.

     

Study of the oxidation protection of MgO-C refractories by means of boron carbide

Boron carbide is used as a highly effective antioxidant in carbon-containing refractories. The oxidation-inhibiting action of this additive has not been clearly defined. The work first deals in theory with the stability of boron carbide at high temperatures. The practical section presents the reaction sequence as determined by means of thermogravimetric analysis and X-ray diffraction analysis. The tests showed that B₄C oxidizes during firing at below 1000°C, to give magnesium borate (3 MgO · B₂O₃), which is stable at high temperatures.     

Reaction processes in the interior of an MgO-carbon brick with boron carbide additive

This paper deals with oxidation protection afforded to carbon-containing refractory materials by boron carbide. Following the previous tests on the stability of B₄C at high temperatures and on the microstructural characteristics of a fired MgO-C brick, now the reactions, which are to be expected in the interior of the brick, in a neutral atmosphere are discussed. The results of the theoretical consideration and the experiments carried out provide evidence that MgO is unstable in the presence of boron carbide as from approx. 1300°C. Similar instability is shown by magnesium borate, which is reduced by carbon as from about 1300°C. In both reactions, reactive gases occur (Mg vapour and B₂O₂), which prevent its ingress and hence oxidation of the carbon by binding the oxygen. As well as the dense layer of borate melt on the brick surface, this phenomenon is obviously responsible for the high efficiency of the boron carbide as an antioxidant for MgO-C materials.     

An unusual phenomenon in the formation of Li5B4 compound-alloy

In the course of scientific development, occasionally a phenomenon is encountered which challenges our understanding and defies a complete explanation. Such a phenomenon occurs in the formation of Li₅B₄ compound-alloy which is formed by heating (not cooling). The liquid metallic solution of Li and B which exists at low temperature (300 to 450°C) transforms to a metallic solid at high temperature (500 to 550°C). Following the transformation to solid, Li₅B₄ compound-alloy formation takes place at 550 ± 2°C, accompanied by a heat release of about 2.2 ± 0.3 kcal per gram of B. The compound-alloy thus formed is a totally metallic solid existing from room temperature to 1000°C. Above 1000°C, the compound-alloy sublimes (with Li vaporizing) leaving behind a blackish substance. While these observations are unusual in terms of the wide composition and temperature ranges in which they occur, they are by no means ‘strange’. They are not inconsistent with the thermodynamic principles of phase diagrams and can be interpreted once the whole process is fully characterized.     

Equilibrium boron distribution between Fe–C–Si–Al melt and boron-bearing slag

HSC 6.1 Chemistry software (Outokumpu) and a simplex–lattice experiment design are employed in thermodynamic modeling of the equilibrium boron distribution between steel containing 0.2% C, 0.35% Si, and 0.028% Al (wt % are used throughout) and CaO–SiO₂–Al₂)₃–8% MgO–4% B₂O₃ slag over a broad range of chemical composition at 1550 and 1600°C. For each temperature, mathematical models (in the form of a reduced third-order polynomial) are obtained for the equilibrium boron distribution between the slag and the molten metal as a function of the slag composition. The results of simulation are presented as graphs of the composition and equilibrium distribution of boron. The slag basicity has considerable influence on the distribution coefficient of boron. For example, increase in slag basicity from 5 to 8 at 1550°C decreases the boron distribution coefficient from 160 to 120 and hence increases the boron content in the metal from 0.021% when L _B = 159 to 0.026% when L _B = 121. In other words, increase in slag basicity favorably affects the reduction of boron. Within the given range of chemical composition, the positive influence of the slag basicity on the reduction of boron may be explained in terms of the phase composition of the slag and the thermodynamics of boron reduction. Increase in metal temperature impairs the reduction of boron. With increase in temperature to 1600°C, the equilibrium distribution coefficient of boron increases by 10, on average. On the diagrams, we see regions of slag composition with 53–58% CaO, 8.5–10.5% SiO₂, and 20–27% Al₂O₃ corresponding to boron distribution coefficients of 140–170 at 1550 and 1600°C. Within those regions, when the initial slag contains 4% B₂O₃, we may expect boron concentrations in the metal of 0.020% when L _B = 168 and 0.023% when L _B = 139.     

Synthesis of TiC–TiB–TiB2 composite powders by solid reaction of powders

In the present work, TiC–TiB–TiB₂ diffusion-layer-coated B₄C composite powders were synthesised via a powder immersion method using Ti and B₄C powders as reactants. The phase compositions and microstructure of the treated powders were characterised by employing X-ray diffraction and scanning electron microscopy. No significant reaction between B₄C and Ti could be detected at 800°C. After treatment at 900°C, the products generated were composed of TiC and TiB. After treatment at 1000°C, the products generated were primarily composed of TiC and TiB, with a small amount of TiB₂. The composition and proportions of the produced phases varied with process temperatures and the composition of the initial powders used. Powder mixtures with a Ti/B₄C molar ratio of 3.5:1 and treated at 1000°C for 14?h were more suitable for synthesis of TiC–TiB–TiB₂-coated B₄C composite powders.     

Optimization of Mold Flux for the Continuous Casting of Cr-Contained Steels

To compensate the negative effect caused by the absorption of chromium oxide inclusions during the casting process of Cr-contained steels, a new mold flux system has been designed and investigated. The melting temperature range of the newly designed mold flux system is from [1124 K to 1395 K (851 °C to 1122 °C)]. The viscosity at 1573 K (1300 °C) and the break temperature increase with the addition of MnO and Cr₂O₃ but decrease with the addition of B₂O₃. The crystalline fraction of mold flux decreases from 81 to 42.1 pct with the addition of MnO and Cr₂O₃, and then further decreases to 25.3 pct with the addition of B₂O₃; however, it improves from 54.4 to 81.5 pct when the basicity increases. Besides, the heat-transfer ability of mold flux is inverse to the crystallization ratio of the slag. The comprehensive study of the properties for the four designed mold fluxes suggests that the mold flux with 1.15 basicity-3.01 pct B₂O₃-1.10 pct MnO-2.10 pct Cr₂O₃ shows the best properties for the continuous casting of Cr-contained steels.     

Structural characterization of Nd-doped in silica host matrix prepared by wet chemical process

Silica host matrix containing neodymium which is potentially important for the formation of nanocrystalline metal oxides was prepared by solgel method, using tetra-ethoxysilane and Nd(NO₃)₃ as precursor materials. The prepared samples were changed from amorphous to nanocrystallites phase at sintered temperature 550 °C (4 h), 750 °C (8 h) and 950 °C (12 h). The thermally treated sample microstructures were investigated using X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). While a further increase of the temperature at 750 °C and annealing time (8 h) resulted in the formation of cubic and hexagonal Nd₂O₃ nanocrystallites. At constant sintering temperature 950 °C for 12 h, the samples showed sharper and intense peaks. The sizes of Nd₂O₃ nanocrystallites were characterized by XRD with average size ～46 nm.     

Kinetics of chlorination and oxychlorination of chromium (III) oxide

Thermogravimetric analysis (TGA) is used to study the kinetics of chlorination of Cr₂O₃ with Cl₂+N₂ and Cl₂+O₂ gas mixtures in the temperature range of 550 °C to 1000 °C. The reactivity of Cr₂O₃ toward the chlorine-oxygen gas mixture is higher than that toward the chlorine-nitrogen one. Chlorination of Cr₂O₃ proceeds with an apparent activation energy of about 86 kJ/mol between 550 °C and 1000 °C. The apparent reaction order with respect to chlorine is about 1.23 at 800 °C. At temperatures lower than 650 °C, the shrinking sphere model is the most appropriate for describing the reaction kinetics. Oxychlorination of Cr₂O₃ is characterized by an apparent activation energy of about 87 and 46 kJ/mol for temperatures lower than 650 °C and higher than 700 °C, respectively. At 800 °C and using a Cl₂+O₂ gas mixture, the maximum reaction rate is obtained when the Cl₂/O₂ molar ratio is equal to 4, confirming the formation of chromium oxychloride. At this temperature, the reaction orders with respect to chlorine, oxygen, and Cl₂+O₂ are about 1.08, 0.23, and 1.29, respectively. Mathematical fitting of the experimental data is discussed.     

Viscosity of CaO-SiO2-Al2O3-MgO-B2O3 slags

The viscosity of CaO-SiO₂-Al₂O₃ slags with 8% MgO and 4% B₂O₃ is investigated over a broad range of composition, by means of a simplex-lattice experiment design. For slag of basicity 6–8 in the upper left region of the local simplex, with 15–25% Al₂O₃, 8% MgO, and 4% B₂O₃, the viscosity is high: 9.4–26.4 P over the range 1500–1530°C. Displacement of the slags of basicity 5–8 to the lower region of the local simplex ensures high fluidity in the given range of Al₂O₃ concentration: the viscosity is 1.5–6.1 P over the range 1500–1530°C.     

Equilibrium phase relations and thermodynamics of the Cr-0 system in the temperature range of 1500 °C to 1825 °C

Phase relations and thermodynamic properties of the Cr-O system were studied at temperatures from 1500 °C to 1825 °C. In addition to Cr and Cr₂O₂, a third crystalline phase was found to be stable in the temperature range from 1650 °C to 1705 °C. The atomic ratio of oxygen to chromium of this phase, which decomposes upon cooling to form Cr and Cr₂O₃, was determined as 1.33 + 0.02, in good agreement with the formula Cr₃O₄. Temperatures and phase assem blages for invariant equilibria of the Cr-O system were determined as follows: Cr₂O₃ + Cr + Cr₃O₄, 1650 °C ± 2 °C; Cr₃O₄ + Cr + liquid oxide, 1665 °C ± 2 °C; and Cr₃O₄ + Cr₂O₃ + liquid oxide, 1705 °C ± 3 °C. The composition of the liquid oxide phase at the eutectic temperature of 1665 °C was found to be close to CrO. Relations between oxygen pressure and temperature for the univariant equilibria of the Cr-O system were established by equilibrating Cr and/or Cr₂O₃ starting materials in H₂-CO₂ mixtures of known oxygen potentials at temper atures from 1500 ΔC to 1825 °C. From this information, the standard free-energy changes (ΔGΔ) for various reactions were calculated as follows: 2Cr (s) + 3/2O₂ = Cr₂O₃ (s): ΔG ° = -1,092,442 + 237.94T Joules, 1773 to 1923 K; 3Cr (s) + 2O₂ = Cr₂O₄ (s): ΔG ° =-1,355,198 + 264.64T Joules, 1923 to 1938 K; and Cr (s) + l/2O₂ = CrO (1): ΔG ° =-334,218 + 63.81T Joules, 1938 to 2023 K. Formerly Graduate Research Assistant, The Pennsylvania State University Formerly Professor     

Boron fade

At high temperatures of 900°C or more boron contained in steel escapes readily into an inert atmosphere as many scientists have already observed. The authors have investigated by theoretical analysis of the possible reasons for boron losses of unalloyed and low alloyed steels in an CH₄/H₂-atmosphere at 1000°C and 1 bar, i.e. boron volatilizes in elemental form, in form of boron oxide (B₂O₃) or as diborane (B₂H₆). It was proved that boron escapes from steel primarily as boron oxide, even if the atmosphere does not contain oxygen. Traces of oxygen in an annealing atmosphere seem to be sufficient to combine with the total boron content of the steel when being in the order of up to 100 ppm. A boron containing source such as boron oxide in sufficient amount in the annealing atmosphere can compensate boron losses of steels.     

Reaction sequences in the formation of silico-ferrites of calcium and aluminum in iron ore sinter

Complex silico-ferrites of calcium and aluminium (low-Fe form, denoted as SFCA; and high-Fe, low-Si form, denoted as SFCA-I) constitute up to 50 vol pct of the mineral composition of fluxed iron ore sinter. The reaction sequences involved in the formation of these two phases have been determined using an in-situ X-ray diffraction (XRD) technique. Experiments were carried out under partial vacuum over the temperature range of T=22 °C to 1215 °C (alumina-free compositions) and T=22 °C to 1260 °C (compositions containing 1 and 5 wt pct Al₂O₃) using synthetic mixtures of hematite (Fe₂O₃), calcite (CaCO₃), quartz (SiO₂), and gibbsite (Al(OH)₃). The formation of SFCA and SFCA-I is dominated by solid-state reactions, mainly in the system CaO-Fe₂O₃. Initially, hematite reacts with lime (CaO) at low temperatures (T ∼ 750 °C to 780 °C) to form the calcium ferrite phase 2CaO·Fe₂O₃ (C₂F). The C₂F phase then reacts with hematite to produce CaO·Fe₂O₃ (CF). The breakdown temperature of C₂F to produce the higher-Fe₂O₃ CF ferrite increases proportionately with the amount of alumina in the bulk sample. Quartz does not react with CaO and hematite, remaining essentially inert until SFCA and SFCA-I began to form at around T=1050 °C. In contrast to previous studies of SFCA formation, the current results show that both SFCA types form initially via a low-temperature solid-state reaction mechanism. The presence of alumina increases the stability range of both SFCA phase types, lowering the temperature at which they begin to form. Crystallization proceeds more rapidly after the calcium ferrites have melted at temperatures close to T=1200 °C and is also faster in the higher-alumina-containing systems.