Effect of MnO to hydrogen dissolution in CaF2–CaO–SiO2 based welding type fluxes

Abstract

The effect of MnO on the hydrogen solubility in the CaF₂–CaO–SiO₂ based welding flux system at 1823 K has been studied. At an acidic slag composition of CaO/SiO₂ molar ratio or basicity of 0·8 and below, MnO addition decreased the hydrogen solubility. At an intermediate slag composition of CaO/SiO₂ molar ratios of 1·1 and 1·3, the hydrogen solubility as a function of MnO additions resulted in a parabolic behaviour showing a minimum and then increasing with higher MnO content. MnO was found to behave as a basic oxide, which decreases the hydrogen solubility when the incorporation hydroxyl mechanism is dominant for an acidic slag and increases the hydrogen solubility when the free hydroxyl mechanism is dominant for a basic slag. This change in the dominant hydrogen dissolution mechanism was also apparent from the hydrogen solubility results at various CaO/SiO₂ molar ratios and fixed MnO contents. A higher hydrogen solubility in the slag is likely to lower the diffusible hydrogen content in the weld metal, and optimum MnO additions were suggested depending upon the basicity of the slag. Fourier transformed infrared analysis of as quenched slags showed that MnO depolymerised the slag network structure and correlated well with the effect on the hydrogen solubility in slags.     

Experimental investigation of phase equilibria and thermodynamic modeling of the CaO–Al2O3–CaS and the CaO–SiO2–CaS oxysulfide systems

Phase equilibria of the CaO–Al₂O₃–CaS and the CaO–SiO₂–CaS systems were experimentally investigated using equilibration and quenching techniques. Equilibrium phases were analyzed by means of electron probe X-ray microanalysis, X-ray diffraction analysis and differential thermal analysis. Solubility limits of all solid phases in these liquid oxysulfide phases were successfully constructed in the temperature range investigated in the present study (1500–1600 °C). In order to supplement understanding the phase equilibria, a thermodynamic modeling of these liquid oxysulfides was conducted by taking into account strong chemical short-range ordering (SRO) in the framework of the modified quasichemical model in the quadruplet approximation. As for the solubility of CaS in the liquid oxysulfides, the solubility increases with increase in CaO in the case of the CaO–Al₂O₃–CaS system, whereas it decreases with increase in CaO in the case of the CaO–SiO₂–CaS system. Such opposite behavior is explained by differences in the effect of the SRO in different liquid phases. It is shown that consideration for the SRO in the thermodynamic modeling is essential in order to properly describe the Gibbs energy of the liquid oxysulfide phase. Using the thermodynamic model and the database developed in the present study, liquidus projections of these oxysulfide systems are proposed for the first time.     

Effects of MgO/Al2O3 ratio on viscous behaviors and structures of MgO–Al2O3–TiO2–CaO–SiO2 slag systems with high TiO2 content and low CaO/SiO2 ratio

The effects of MgO/Al₂O₃ ratio on the viscous behaviors of MgO–Al₂O₃–TiO₂–CaO–SiO₂ systems were investigated by the rotating cylinder method. Raman spectroscopy was used to analyze the structural characteristics of slag and Factsage 7.0 was adopted to demonstrate the liquidus temperature of slag. The results show that the viscosity and activation energy for viscous flow decrease when the MgO/Al₂O₃ ratio increases from 0.82 to 1.36. The break point temperature and liquidus temperature of slag initially decrease and subsequently increase. The complex viscous structures are gradually depolymerized to simple structural units. In conclusion, with the increase of MgO/Al₂O₃ ratio, the degree of polymerization of slag decreases, which improves the fluidity of slag. The variations of liquidus temperature of slag lead to the same changes of break point temperature.     

Effect of Al2O3 content on the synthesized products by the laser ignited self-propagating high-temperature synthesis reaction of Al2O3–Ti–C system

The effect of Al₂O₃ content on ignition temperature and combustion temperature, the phase composition, the density of the products and the grain size of TiC was investigated by self-propagating high-temperature synthesis reaction of Al₂O₃–Ti–C system. The results show ignition temperature increases and combustion temperature decreases with the increasing of Al₂O₃ content; the density of the products varies with Al₂O₃ content, TiC and Al₂O₃ are the two stable phases after SHS, TiC particle size decreases with the increasing of Al₂O₃ content, furthermore, the fracture type of the sintered specimens is a nearly completely intergranular mode.     

Preparation of Al2O3–ZrO2–SiO2 ceramic composites by high-gravity combustion synthesis

By a furnace-free technique of high-gravity combustion synthesis, Al₂O₃–ZrO₂–SiO₂ ceramic composites were prepared via melt solidification instead of conventional powder sintering. The solidification kinetics and microstructure evolution of the ceramic composites in high-gravity combustion synthesis were discussed. The phase assemblage of the ceramic composites depended on the chemical composition, where both (Al₂O₃ + ZrO₂) and (mullite + ZrO₂) composites were obtained. The ceramic composites consisted of ultrafine eutectics and sometimes also large primary crystals. In the (mullite + ZrO₂) composites, two different morphologies and orientations were observed for the primary mullite crystals, and the volume fraction of mullite increased with increasing SiO₂ content. The ceramic composites exhibited a hardness of 11.2–14.8 GPa, depending on the chemical composition and phase assemblage.     

电渣重熔用CaF2＋Al2O3和CaF2＋Al2O3＋CaO系熔渣传氧的研究

利用ＺｒＯ２固体电解质氧浓差电池测定了电渣重溶用ＣａＦ２＋Ａｌ２Ｏ３和ＣａＦ２＋Ａｌ２Ｏ３＋ＣａＯ系熔渣的氧渗透率，考察了熔渣成分及温度对熔渣传氧性能的影响。在１６７３－１８７３Ｋ和０．１ＭＰａ的氧气氛下，测得这两个渣系熔渣的氧渗透率分别为１×１０＾－２０－６×１０＾－１９和１×１０＾－２１－５×１０＾－１８ｍｏｌＯ２．ｃｍ＾－１．ｓ＾－１；随ＭｎＯ２，Ｆｅ２Ｏ３，Ｃｒ２Ｏ３，ＴｉＯ２，ＣａＦ２含     

Phase reaction and sintering behavior of a Al2O3–20wt%AlN–5wt%Y2O3 system

Two major problems exist in the processing of AlN. The first is the difficulty in achieving full densification even at relatively high sintering temperatures. The second is the formation of the spinel phase, AlON. Pure AlN sintered at temperatures up to 2000°C have produced no more than 90–93% densification in the former case, while AlN rich ternary systems (AlN–Al₂O₃-sintering agent) have resulted in the detrimental formation of AlON well before full densification can occur. This paper reports on the phase reaction and sintering behavior of a ternary Al₂O₃–AlN–Y₂O₃ system near the critical temperature range of 1600–1700°C, in a carbo-thermal reduction furnace in a fully nitrogen environment. Full densification (>98%) for AlN without the formation of AlON was achieved by sintering an initial Al₂O₃ rich ternary system (Al₂O₃–20wt%AlN–5wt% Y₂O₃) at a relatively low temperature of 1680°C. Formation of the AlON was delayed until 1700°C, at which a stoichiometric γ-AlON (Al₃O₃N) with spinel type structure was obtained. Thermal conductivity values for a sintered substrate obtained with low oxygen content within the AlN matrix reached 125 W m⁻¹ K⁻¹.     

A Comparative Study of High Temperature Corrosion of Al2O3, SiO2 and Al2O3–SiO2 Forming Alloys in a Na2SO4–NaCl Atmosphere

The present paper is designed to provide a summary of our study on the high temperature corrosion of Al₂O₃, SiO₂ and Al₂O₃–SiO₂ forming alloys in the gas phase and liquid phase of Na₂SO₄–NaCl system by comparing their corrosion resistance at 1000 °C. The obtained results show that the alumina-forming alloy experiences severe internal corrosion in the gas phase compared to in the liquid phase due to oxide cracking. This results in an increase in the inward diffusion and/or penetration of constituents of the salts and oxygen to form internal Al-oxide and Cr-sulfides. In the liquid phase, however, the formation of yttrium sulfide beneath a continuous double oxides layer of Al₅Y₃O₁₂ and Al₂O₃ may be related to the high affinity of yttrium for sulfur. On the other hand, it is apparent from the cross-sectional observations that a SiO₂ and Al₂O₃–SiO₂ forming alloys form a continuous and dense oxides layer, and demonstrate a high resistance against internal oxidation and corrosion in both corrosive environments.     

The influence of BaO additives on the reaction of Al2O3–SiO2 ceramics with molten Al and Al–Si alloys

BaO considerably affects the composition and the microstructure of the reaction zone formed between BaO-doped aluminosilicate ceramics and molten aluminium alloys under vacuum. The reduced Ba and Si form AlBaSi precipitates, found adhered to the interface and dispersed in the metal Al-matrix, whose formation apparently controls the reaction kinetics.     

SiO2—MgO—TiO2—Al2O3—CaO—CaF2焊剂渣系的研究及应用

研制出适合于８００ＭＰａ级低合金高强钢的ＳＧ８焊剂和适用于中厚度低碳钢深坡口多层焊的ＳＧ９焊剂。这些焊剂电弧稳定，焊缝成型美观，不易产生气孔，夹杂，裂纹等缺陷，焊缝力学性能满足要求，尤其在深坡口焊时脱渣性能极佳。其中ＳＧ９焊剂已成功地应用于蒸压釜，汽车部件等结构的焊接。     

Hydrothermal conversion of Ti-containing minerals in system of Na_2O–Al_2O_3–SiO_2–CaO–TiO_2–H_2O

Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution.Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na_2O–Al_2O_3–Si O_2–Ca O–Ti O_2–H_2O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to Al_4Ti_2 SiO_(12) at low temperatures(60–120 °C), which is similar to anatase in crystal structure. As the temperature continues to rise, Al4Ti2 Si O12decomposes gradually and converts to Ca_3 Ti Si_2(Al_2Si_(0.5)Ti_(0.5)O_(14) at 200 °C. When the temperature reaches 260 °C, Ca Ti O_3 forms as the most stable titanate species for its hexagonal closest packing with O_2-and Ca_2?. The findings enhance the understanding of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.     

Recovery of valuable metals from spent lithium ion batteries by smelting reduction process based on FeO–SiO2–Al2O3 slag system

A novel smelting reduction process based on FeO–SiO₂–Al₂O₃ slag system for spent lithium ion batteries with Al cans was developed, while using copper slag as the only slag former. The feasibility of the process and the mechanism of copper loss in slag were investigated. 98.83% Co, 98.39% Ni and 93.57% Cu were recovered under the optimum conditions of slag former/battery mass ratio of 4.0:1, smelting temperature of 1723 K, and smelting mass ratio of time of 30 min. The FeO–SiO₂–Al₂O₃ slag system for the smelting process is appropriate under the conditions of m(FeO):m(SiO₂)=0.58:1–1.03:1, and 17.19%–21.52% Al₂O₃ content. The obtained alloy was mainly composed of Fe–Co–Cu–Ni solid solution including small amounts of matte. The obtained slag mainly consisted of fayalite and hercynite. Meanwhile, the mechanism of copper loss is the mechanical entrainment from strip-like fayalite particles in the main form of copper sulfide and metallic copper.     

Weld shape comparison with iron oxide flux and Ar–O2 shielding gas in gas tungsten arc welding

Abstract

The influence of iron oxide flux and O₂–Ar mixed shielding gas on weld shape and penetration in gas tungsten arc welding is investigated by bead-on-plate welding on SUS 304 stainless with low oxygen and low sulphur contents. The oxygen content in the weld metal is measured using a HORIBA EMGA-520 oxygen/nitrogen analyzer. The results show that both the iron oxide flux and the O₂–Ar mixed shielding gas can significantly modify the weld shape from shallow wide to deep narrow. A large weld depth/width ratio around of 0.5 is obtained when the oxygen content in the shielding gas is in the range of 3000–6000 vol. ppm. Oxygen over a certain critical value, i.e. 70 wt. ppm, in the weld pool alters the temperature coefficient of the surface tension on the pool surface, and hence changes the Marangoni convection. A thick oxide layer on the weld pool surface is generated when the oxygen content in the shielding gas is over 6000 vol. ppm, which becomes a barrier for the oxygen conveyance to the liquid pool and prevents the liquid pool from freely moving, and therefore, decreases the intensity of the Marangoni convection on the pool surface.     

Effect of the aluminum content on the mechanochemical behavior in ternary system Al–B2O3–C

The effect of aluminum content on the mechanochemical behavior of ternary system Al–B₂O₃–C to fabricate Al₂O₃/B₄C composite was investigated. A mixture of boron oxide powders along with different amounts of aluminum and graphite was activated in a ball mill. The value of Al content varied from 2 mol to 7 mol compared to the stoichiometric mole ratios (4 mol). Thermodynamics evaluation indicates that the value of Al content in the mixture plays a key role and overall reaction enthalpy and adiabatic temperature altered by variation of aluminum and carbon content. Experimental findings revealed that at low aluminum content (2 mol Al), aluminothermic reaction proceeded in gradual mode and no carbothermal reduction took place. Increase in Al content up to 3 mol led to a change in the mode of aluminothermic reaction to MSR (mechanically induced self-propagating reaction) and gradual occurrence of carbothermic reaction. By increasing the amount of Al (10/3–4 mol Al), aluminothermic reaction provided sufficient heat for activating endothermic carbothermic reduction; hence, both reducing reactions happened simultaneously. Further increase in Al content (7 mol Al) led to gradual aluminothermic reaction and excess Al acted as inert matrix.     

Mechanical Properties and the Microstructure of Al2O3/Al/Al2O3 Joints with the Surface Modification of Alumina by a Thin Layer of Ti + Nb

Al₂O₃/Al/Al₂O₃ joints were formed by liquid-state bonding of alumina substrates covered with a thin Ti + Nb coating of 900 nm thickness with the use of an Al interlayer of 30 μm at 973 K under a vacuum of 0.2 mPa for 5 min. The bond strength of the joints was examined by a four-point bending test at 295, 373, and 473 K. Optical, scanning, and transmission electron microscopies were applied for detailed characterization of the interface structure and failure characteristics of fractured joint surfaces. The analysis of the results has shown that (i) bonding occurred due to the formation of a reactive interface on the metal side of the joint in the presence of Al₃Nb(Ti) precipitates and (ii) modification of Al₂O₃ by a thin layer of Ti + Nb increases the hardness at the interface and makes it possible to achieve reliable joints working at elevated temperatures.     

Preparation of Al2O3–ZrO2–Y2O3 Composite Coatings by a Modified Sol–Gel Technique for Thermal Barrier Application

Spatial-network Al₂O₃–ZrO₂–Y₂O₃ composite coatings were prepared by a modified sol–gel technique, so-called thermal pressure and filtration of sol–gel paint. The composite coatings were derived from a composite paint of yttria partially stabilized zirconia (YSZ) particles, Al₂O₃ particles and Al₂O₃–Y₂O₃ sol. Their microstructure showed that YSZ particles were covered with spatial-network Al₂O₃–Y₂O₃ blanket. Cyclic oxidation at 1,050 °C in air for 200 h demonstrates that the oxygen diffusion rate in the coatings could be effectively inhibited. Meanwhile, suitable coefficients of thermal expansion (CTE) gave the composite coatings better spallation resistance than that of Al₂O₃–Y₂O₃ or ZrO₂–Y₂O₃ coatings. The positive results of cyclic oxidation indicated that the composite coating can be used as an interlayer between the bond coat and the top ceramic layer in traditional TBCs. Not only the depletion rate of aluminum-rich phase in MCrAlY alloy could be slowed down by spatial-network Al₂O₃–Y₂O₃, but also different thermal expansion between thermally grown oxides layer and top layer could be relieved by suitable CTE. In this paper, the mechanisms of the inhibition of oxygen diffusion and thermal match between ceramic coating and alloy are also discussed.     

CO还原CaO—SiO2—Al2O3—FetO渣系研究

研究了在１７２３Ｋ下ＣＯ还原ＣａＯ－Ａｌ２Ｏ３－ＦｅｔＯ渣系，根据ＣＯ２红外分析仪测定的出口气体中ＣＯ２浓度变化，计算了炉渣的表现还原速度常数Ｋａ和还原速度常数Ｋ结果表明，加入Ａｌ２Ｏ３，提高了ＣａＯ－ＳｉＯ２－ＦｅｔＯ的Ｋａ和Ｋ值，炉渣碱度不变时，随着ＦｅｔＯ含量的增加，Ｋａ呈增加趋势，但Ｋ则呈抛物线趋势变化；当ＦｅＯ的光学碱度∧ＦｅＯ为１．０或０．８７时，Ｋａ随该四元渣系光学碱度的增加而线性增     

Al2O3 coated α-Fe solid solution nanocapsules prepared by arc discharge

Al₂O₃ coated α-Fe solid solution nanocapsules are prepared by arc-discharging a bulk AlNiCo permanent magnet. The size of the nanocapsule is in range of 3–300 nm and the thickness of the shell is 1–6 nm. Al atoms in the AlNiCo magnet form the shell of amorphous Al₂O₃ to prevent the nanocapsules from further oxidation. The magnetic properties of saturation magnetization J_s=85 A m²/kg and coercive force ${}_{\mathrm{j}}\text{H}{}_{\mathrm{<mtext>c</mtext>}}\text{=27.5}$ kA/m are achieved for the nanocapsules.     

Non-equilibrium phase synthesis in Al2O3–Y2O3 by spray pyrolysis of nitrate precursors

The phase evolution in the Al₂O₃–Y₂O₃ system has been studied for 4, 10, 15 and 37.5% Y₂O₃ amorphous powders prepared by spray pyrolysis of nitrate precursor solutions. Two distinct metastable transformation sequences were identified for the amorphous powders upon heat treatment. Crystallisation accompanied by partitioning leads to a mixture of hexagonal YAlO₃ and γ-Al₂O₃ (spinel structure). Partitionless crystallisation, on the other hand, leads directly to a γ-Al₂O₃ solid solution in dilute alloys, and garnet at temperatures as low as 800°C in the stoichiometric composition provided segregation is avoided during decomposition. Further heat treatment of a yttria-supersaturated γ-Al₂O₃ leads to the precipitation of the orthorhombic YAlO₃ that is stable up to temperatures as high as 1600°C, while hexagonal YAlO₃ converts to garnet, Y₃Al₅O₁₂. A rationalisation of the phase evolution sequence has been attempted on the basis of kinetic considerations, cation coordination and semi-quantitative free energy–composition curves for the various competing phases.