Primary Solidification Phase Research Articles

Effect of C Addition on as-Cast Microstructures of High Nb Containing TiAl Alloys

Two high Nb-containing TiAl alloys, Ti46.6Al7.5Nb0.5Si0.2B (Alloy A) and Ti46.1Al7.4Nb5C0.5Si0.2B (Alloy B), were prepared by graphite mold casting. As-cast microstructures of the two alloys were characterized to clarify the effect of carbon addition. The results show that 5 at.% carbon addition can change the primary solidification phase from β phase to α phase. The as-cast microstructure of Alloy A consists of a fully α2 + γ lamellar structure and interdendritic eutectic silicide with a volume fraction of 2.3%. However, in Alloy B, the lamellar structure only forms in the dendritic stem and the massive γ is observed in the interdendritic regions. Two types of carbides, Ti2AlC and TiC, are produced in Alloy B. A large number of randomly distributed primary Ti2AlC particles with volume fraction of 14.9% are observed in both the dendritic and interdendritic regions. Irregularly shaped TiC remains inside of the large Ti2AlC particle, suggesting TiC carbides transformed to Ti2AlC during cooling. The addition of carbon also changes the morphology of the silicides from a eutectic structure to a blocky structure in the massive γ matrix or at the interface of the Ti2AlC and the γ matrix. High level of niobium greatly increases the solid solution limit of carbon, since C content in the matrix is much higher than the solid solubility of that in the TiAl binary system. The hardness of the matrix increases from 325 HV to 917 HV caused by the addition of carbon.

Microstructural evolution and magnetic property of a rapidly solidified ternary Fe37.5Cu37.5Sn25 peritectic-type alloy

The liquid Fe37.5Cu37.5Sn25 peritectic-type alloy was rapidly solidified by glass fluxing, drop tube, and melt spinning techniques. The solidification structures consisted of three phases, including the αFe solid solution and the Cu3Sn and Cu6Sn5 intermetallic compounds under different conditions. In this work, the bulk undercoding ΔT equals the liquidus temperature TL minus the nucleation temperature TN of the primary solid phase. During the bulk undercooling process, a maximum liquid undercooling of 272 K (0.18TL) was achieved. Metastable liquid phase separation was induced if the undercooling exceeded 177 K. Within a moderate undercooling range from 8 to 177 K, the solidified structures showed coarse dendrites, and the dendritic growth velocity increased to 41.5 mm/s following a power relation. As the drop tube technique provided a containerless state, a maximum surface cooling rate of 3.5 × 104 K/s was achieved. The alloy droplets displayed metastable liquid phase separation even at the largest droplet diameter of 944 μm. The cooling rate and thermal Marangoni migration were found to greatly influence the phase-separated patterns of the alloy droplets. Under the melt spinning condition, the microstructures of the Fe37.5Cu37.5Sn25 alloy ribbons were significantly refined and displayed soft magnetic characteristics. Furthermore, the experimental results demonstrated that the grain size of the αFe phase affected the coercivity of the alloy ribbons.

Room temperature plastic deformability in V-rich V–Si–B alloys

In the present study compressive strength data and room temperature (RT) deformability of three V-rich V–Si–B alloys are reported. All alloys were taken from the VSS (V solid solution)-V3Si-V5SiB2 three-phase region of the respective phase diagram and differ in their primary solidification phase of either VSS, V3Si or V5SiB2. The RT yield stresses were determined by the 0.2% offset method and the plastic strain was obtained by subtracting the combined compliance of the testing machine and the specimen from the individually measured load-displacement curves. The microstructures in the as-cast and deformed state were analyzed using SEM, EBSD and TEM. Dislocation activity was only observed in the VSS phase while the intermetallic phases were dislocation-free. Thus, the RT plasticity in V-rich V–Si–B alloys is mainly governed by the volume fraction of the VSS phase. Hence, the alloy containing primary VSS dendrites has the highest plastic strain compared to the V5SiB2 and V3Si primary crystallizing alloys. Investigations of the VSS phase on binary V–Si alloys reveal that silicon acts as solid solution strengthener, but ductility of the VSS phase is retained throughout the solubility range.The present results are quite astonishing since Mo–Si–B alloys containing similar amounts of Si and B are known to be fairly brittle at RT.

Co-In-Sb Ternary System (II): Isoplethal Section and Thermodynamic Modeling

Thermoelectric devices have attracted worldwide attention, primarily due to their ability to convert heat directly into electricity. The ternary Co-In-Sb system with a CoSb3 skutterudite phase is one of the most promising thermoelectric materials. In this paper, vertical section CoSb3-InSb was experimentally determined with the aid of the X-ray diffraction method and electron probe microanalysis of samples equilibrated at 450 °C, 650 °C, 700 °C, 750 °C, 800 °C, 825 °C, and 850 °C. Based on information in the literature and data obtained in the current study, the thermodynamic model of the ternary Co-In-Sb system was developed. The proposed thermodynamic description agrees well with most available experimental data, except for some points from the primary solidification-phase experiment. The thermodynamic model can be applied in future studies on ternary thermoelectric materials or studies on higher-order systems where the Co-In-Sb system is involved.

The System K2CO3–CaCO3–MgCO3 at 3 GPa: Implications for Carbonatite Melt Compositions in the Shallow Continental Lithosphere

Potassic dolomitic melts are believed to be responsible for the metasomatic alteration of the shallow continental lithosphere. However, the temperature stability and range of compositions of these melts are poorly understood. In this regard, we performed experiments on phase relationships in the system K2CO3–CaCO3–MgCO3 at 3 GPa and at 750–1100 °C. At 750 and 800 °C, the system has five intermediate compounds: Dolomite, Ca0.8Mg0.2CO3 Ca-dolomite, K2(Ca≥0.84Mg≤0.16)2(CO3)3, K2(Ca≥0.70Mg≤0.30)(CO3)2 bütschliite, and K2(Mg≥0.78Ca≤0.22)(CO3)2. At 850 °C, an additional intermediate compound, K2(Ca≥0.96Mg≤0.04)3CO3)4, appears. The K2Mg(CO3)2 compound disappears near 900 °C via incongruent melting, to produce magnesite and a liquid. K2Ca(CO3)2 bütschliite melts incongruently at 1000 °C to produce K2Ca2(CO3)3 and a liquid. K2Ca2(CO3)3 and K2Ca3(CO3)4 remain stable in the whole studied temperature range. The liquidus projection of the studied ternary system is divided into nine regions representing equilibrium between the liquid and one of the primary solid phases, including magnesite, dolomite, Ca-dolomite, calcite-dolomite solid solutions, K2Ca3(CO3)4, K2Ca2(CO3)3, K2Ca(CO3)2 bütschliite, K2Mg(CO3)2, and K2CO3 solid solutions containing up to 24 mol % CaCO3 and less than 2 mol % MgCO3. The system has six ternary peritectic reaction points and one minimum on the liquidus at 825 ± 25 °C and 53K2CO3∙47Ca0.4Mg0.6CO3. The minimum point resembles a eutectic controlled by a four-phase reaction, by which, on cooling, the liquid transforms into three solid phases: K2(Mg0.78Ca0.22)(CO3)2, K2(Ca0.70Mg0.30)(CO3)2 bütschliite, and a K1.70Ca0.23Mg0.07CO3 solid solution. Since, at 3 GPa, the system has a single eutectic, there is no thermal barrier for liquid fractionation from alkali-poor toward K-rich dolomitic compositions, more alkaline than bütschliite. Based on the present results we suggest that the K–Ca–Mg carbonate melt containing ~45 mol % K2CO3 with a ratio Ca/(Ca + Mg) = 0.3–0.4 is thermodynamically stable at thermal conditions of the continental lithosphere (~850 °C), and at a depth of 100 km.

Al8Mn5 Particle Settling and Interactions with Oxide Films in Liquid AZ91 Magnesium Alloys

Al8Mn5 particles form as primary solidification phases in Mg-Al-based alloys and are important for ensuring adequate corrosion resistance. However, excessive Al8Mn5 formation above the α-Mg liquidus temperature can lead to sludge formation, and the clustering of Al8Mn5 particles on oxide films can generate deleterious casting defects. Here, we use analytical SEM and real-time synchrotron x-ray radiography to study Al8Mn5 particle settling, the formation of a sludge layer, and the mechanism of Al8Mn5 clustering on oxides in AZ91 containing two Fe levels. It is shown that settling Al8Mn5 can become trapped in entrained oxide and that new Al8Mn5 particles also seem to nucleate on oxide films. On cooling, these Al8Mn5 particles continue to grow, creating large Al8Mn5 clusters.

New data on the system Na2CO3–CaCO3–MgCO3 at 6 GPa with implications to the composition and stability of carbonatite melts at the base of continental lithosphere

Subsolidus and melting phase relationships in the system Na2CO3–CaCO3–MgCO3 have been studied at 6 GPa and 900–1250 °C using a Kawai-type multianvil press. At 900 and 1000 °C, the system has four intermediate compounds: Na2Ca4(CO3)5 burbankite, Na2Ca3(CO3)4, Na4Ca(CO3)3, and Na2Mg(CO3)2 eitelite. The Na-Ca compounds dissolve noticeable amounts of Mg component, whereas eitelite dissolves a few percents of Ca component: Na2(Ca≥0.91Mg≤0.09)4(CO3)5, Na2(Ca≥0.94Mg≤0.06)3(CO3)4, Na4(Ca≥0.67Mg≤0.33)(CO3)3, and Na2(Mg≥.93Ca≤0.07)(CO3)2. At 1050 °C, the system is complicated by an appearance of dolomite. Na-Ca burbankite decomposes at 1075 ± 25 °C to aragonite plus Na2Ca3(CO3)4. Na4Ca(CO3)3 and eitelite disappear via congruent melting between 1200 and 1250 °C. Na2Ca3(CO3)4 remains stable through the whole studied temperature range. The liquidus projection of the studied ternary system has eight primary solidification phase regions for magnesite, dolomite, calcite-dolomite solid solutions, aragonite, Na2Ca3(CO3)4, Na4Ca(CO3)3, and Na2CO3 solid solutions. The system has five ternary peritectic reaction points and one minimum on the liquidus at 1050 °C and 48Na2CO3·52(Ca0.75Mg0.25)CO3. The minimum point resembles a eutectic controlled by a four-phase reaction, by which a liquid transforms into three solid phases upon cooling: Na2(Ca0.94Mg0.06)3(CO3)4, Na4(Ca0.67Mg0.33)(CO3)3, and Na2(Mg0.93Ca0.07)(CO3)2 eitelite. Since at 6 GPa, the system has a single eutectic, there is no thermal barrier preventing continuous liquid fractionation from alkali-poor toward Na-rich dolomitic compositions. Cooling of the Na-Ca-Mg carbonatite melt from 1400 to 1100 °C within the lherzolite substrate will be accompanied by magnesite crystallization and wehrlitization keeping calcium number of the melt at 40 and shifting the Na2CO3 content to ≥40 mol%. In the case of the eclogitic wall rock, the cooling will be accompanied by dolomite crystallization keeping calcium number of the melt at 60–65 and shifting the Na2CO3 content to ≥30 mol%.

Phase relations in the system Na2CO3–CaCO3–MgCO3 at 3 GPa with implications for carbonatite genesis and evolution

The phase relations in the system Na2CO3−CaCO3−MgCO3 have been studied at 3 GPa and 700–1285 °C using a Kawai-type multianvil press. At 700 °C, the system has five intermediate compounds: dolomite, Mg-bearing Na2Ca4(CO3)5 burbankite, Na2Ca3(CO3)4, Na4Ca(CO3)3, and eitelite. As temperature increases to 800 °C, the system is complicated by an appearance of Ca-dolomite and Mg-bearing shortite, while Na2Ca4(CO3)5 disappears. At 850 °C, Na4Ca(CO3)3 decomposes to produce Na carbonate and nyerereite. The latter melts incongruently at 875 ± 25 °C to form Na2Ca3(CO3)4. Incongruent melting of eitelite to magnesite and liquid, occurs at 925 ± 25 °C. Mg-bearing shortite melts incongruently at 950 ± 50 °C, producing Na2Ca3(CO3)4 and liquid. Na2Ca3(CO3)4 disappears at 1000 °C via incongruent melting to calcite and liquid. The liquidus projection of the studied ternary system has seven primary solidification phase regions for magnesite, dolomite-calcite solid solutions, Na2Ca3(CO3)4, Mg-bearing shortite, nyerereite, eitelite, and Na carbonate. The primary solidification regions are separated by five peritectic and three cotectic monovariant lines. The system has six ternary peritectic points and one minimum on the liquidus at 850 °C and 52Na2CO3∙48(Ca0.62Mg0.38)CO3. The minimum point resembles a eutectic controlled by a four-phase reaction, by which, on cooling, a liquid transforms into three solid phases: shortite, Na carbonate, and eitelite. Since the system has a single eutectic at 3 GPa, there is no thermal barrier preventing continuous liquid fractionation from Na-poor toward Na-rich dolomitic compositions more alkaline than eitelite and nyerereite. Considering the present results and previous data, a range of Na-Ca-Mg double carbonates changes in the following sequence upon pressure and temperature increase: Na2Ca2(CO3)3 (Amm2) shortite, Na2Ca(CO3)2 (P21ca) nyerereite, Na2Mg(CO3)2 (R3¯) eitelite (0.1 GPa) → Na2(Ca0.97–0.98Mg0.02–0.03)4(CO3)5 (P63mc), Na2(Ca≥0.91Mg≤0.09)3(CO3)4 (P1n1), Na2(Ca ≥ 0.81 Mg0≤0.19)(CO3)2 (R3¯) nyerereite, Na2(Ca0.77–0.93Mg0.07–0.23)2(CO3)3 (Amm2) shortite, Na4(Ca0.90–0.98Mg0.02–0.10)(CO3)3 (Ia3d), Na2(Mg≥0.9Ca0≤0.1)(CO3)2 (P21ca) eitelite (3 GPa) → Na2(Ca≥0.87Mg0≤0.13)4(CO3)5 (P63mc), Na2(Ca≥0.89Mg≤0.11)3(CO3)4 (P1n1), Na4(Ca ≥ 0.7 Mg0≤0.3)(CO3)3 (Ia3d), Na2(Mg≥0.92Ca0≤0.08)(CO3)2 (P21ca) eitelite (6 GPa). Using the present results at 3 GPa and previous data at 6 GPa in the Na2CO3−CaCO3−MgCO3 system, we constrained isopleths of the Na2CO3 content in melt coexisting with Ca-Mg carbonates. We found that the cratonic geotherms cross the isopleths so that the carbonatite melt percolating upward via the continental mantle lithosphere should become progressively enriched in Na, evolving from alkali-poor dolomitic composition at depths exceeding 200 km toward sodic dolomitic with the ~52 mol% Na2CO3 at 80–120 km depths.

Microstructural characterisation of Tristelle 5183 (Fe-21%Cr-10%Ni-7.5%Nb-5%Si-2%C in wt%) alloy powder produced by gas atomisation

Nitrogen gas atomised powders of the hardfacing alloy Tristelle 5183 (Fe-21%Cr-10%Ni-7%Nb-5%Si-2%C in wt%) were sieved into different particle size ranges and their microstructures have been investigated. Powder particles larger than approximately 53 μm are composed of dendritic fcc γ-Fe as the principal phase with smaller quantities of: α-Fe, an interdendritic silicide phase isostructural to Fe5Ni3Si2, and Nb(C,N). Particles <53 μm have increasing quantities of either dendritic α-Fe or cellular silicide phase with decreasing amounts of γ-Fe as the particle size decreases, along with ~5% Nb(C,N). Coarse (> 10 μm) sized Nb(C,N) particles, that are seen in all powder size fractions, pre-existed in the melt prior to atomisation, whereas micron-sized Nb(C,N) particles that are found within α-Fe, γ-Fe or silicide are the primary solidification phase. Nanoscale Nb(C,N) also formed interdendritically in the last stages of solidification. Compared with a mould cast sample, a significant difference is the suppression of M7C3 formation in all powder size ranges. The increasing quantities of α-Fe and silicide in smaller sized powder particles is consistent with increased undercooling prior to nucleation permitting metastable phase formation.

Experimental investigation and thermodynamic calculation of the B-Fe-W ternary system

The ternary B-Fe-W system is of interest for the wear resistant applications. Its liquidus projection in the Fe-rich region was experimentally determined and thermodynamic modeling was performed in this work. The microstructures of the solidified samples were observed by scanning electron microscopy, the compositions of the primary crystallization phases were obtained by electron probe microanalysis, and the reaction temperatures were determined by differential scanning calorimetry. The observed primary solidification phases are BCC (Fe), FCC, WFeB, Fe2B, μ, and BCC (W), respectively. A thermodynamic model of the B-Fe-W system based on thermodynamic models of the three constituent binary systems and the experimental results for the ternary system was developed using the CALPHAD approach. A set of self-consistent thermodynamic parameters for the B-Fe-W system was obtained and reasonable agreement between the experimental and calculated isothermal sections and liquidus projection was obtained.

Epitaxial growth and oxidation behavior of an overlay coating on a Ni-base single-crystal superalloy by laser cladding

An overlay coating material was deposited on a single crystal superalloy SRR99 by laser cladding. The microstructure and oxidation behavior of this coating was investigated through scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that although the composition of the coating was chosen based on the γ' composition in René N5 superalloy, the primary solidification phase of this coating during laser cladding was γ-Ni. Furthermore, under the laser cladding condition, fine parallel dendrites grew epitaxially in the coating from the substrate, indicating the single crystal structure of the substrate was reproduced. When the single crystal MCrAlY coating was oxidized at 1000℃, both θ-Al2O3 and α-Al2O3 formed during initial oxidation process. As the oxidation time proceeded, the presence of θ-Al2O3 facilitated the formation of NiAl2O4 spinel oxide. Once the spinel was observed, it flourished and induced some porosity in the scale. When the scale thickness increased to 6–7 μm, large area spallation of the scale began.

Liquidus projection and isothermal section of Sb-Se-Te ternary system

Sb-Se-Te alloys have great application potential for infrared, phase memory change, thermoelectric and solar cell devices. The liquidus projection and 400 °C isothermal section of Sb-Se-Te ternary system are experimentally determined. No ternary compound is found. There is a miscibility gap along the Sb-Se side, and there are six primary solidification phase regions, (Sb), δ-(Sb2Te), γ-(SbTe), Sb2Te3, (Se,Te) and Sb2Se3. There are four invariant reactions involving the liquid phase. The reactions with the lowest and highest reaction temperatures are L + Sb2Te3↔Sb2Se3+(Se,Te) at 415±1 °C and L+(Sb)↔δ-(Sb2Te)+Sb2Se3 at 515°±1C, respectively. In the 400 °C Sb-Se-Te isothermal section, there are five tie-triangles, which are Sb2Se3+δ-(Sb2Te)+(Sb), Sb2Se3+δ-(Sb2Te)+γ-(SbTe), Sb2Se3+γ-(SbTe)+Sb2Te3, Sb2Se3+Sb2Te3+(Se,Te), and Sb2Se3+Liquid+(Se,Te).

Liquidus Projection and Thermodynamic Modeling of a Sn-Ag-Zn System

Sn-Ag-Zn alloys are promising Pb-free solders. In this study, the Sn-Ag-Zn liquidus projection was determined, and the Sn-Ag-Zn thermodynamic modeling was developed. Various Sn-Ag-Zn alloys were prepared. Their as-cast microstructures and primary solidification phases were examined. The invariant reaction temperatures of the ternary Sn-Ag-Zn system were determined. The liquidus projection of the Sn-Ag-Zn ternary system was constructed. It was found that the Sn-Ag-Zn ternary system has eight primary solidification phases: e2-AgZn3, γ-Ag5Zn8, β-AgZn, ζ-Ag4Sn, (Ag), e1-Ag3Sn, β-(Sn) and (Zn) phases. There are eight ternary invariant reactions, and the liquid + (Ag) = β-AgZn + ζ-Ag4Sn reaction is of the highest temperature at 935.5 K. Thermodynamic modeling of the ternary Sn-Ag-Zn system was also carried out in this study based on the thermodynamic models of the three constituent binary systems and the experimentally determined liquidus projection. The liquidus projection and the isothermal sections are calculated. The calculated and experimentally determined liquidus projections are in good agreement.

Liquidus Projection and Isothermal Section of the Sb-Se-Sn System

Sb-Se-Sn ternary alloys are promising chalcogenide materials. The liquidus projection and 673.2 K (400 °C) isothermal section of the Sb-Se-Sn ternary system are determined. Numerous Sb-Se-Sn alloys are prepared, and their primary solidification phases are examined. In addition to the three terminal phases, (Sb), (Se) and (Sn), there are Sb2Sn3, SbSn, SnSe, SnSe2, Sb2Se3, Sn2Sb9Se9, and SnSb2Se4 phases. In addition, there are two miscibility gaps along the Sb-Se and Se-Sn and sides. There are ten invariant reactions in the Sb-Se-Sn ternary system, and seven of them are experimentally determined in this study. The lowest reaction temperature of determined invariant reaction is L + SbSn = (Sn) + SnSe at 515.4 K ± 5 K (242.2 °C ± 5 °C). There are nine tie-triangles, which are Liquid + SbSn + SnSe, SbSn + SnSe + (Sb), SnSe + (Sb) + Sn2Sb9Se9, (Sb) + Sb2Se3 + Sn2Sb9Se9, SnSe + Sn2Sb9Se9 + SnSb2Se4, Sb2Se3 + Sn2Sb9Se9 + SnSb2Se4, SnSe + SnSe2 + SnSb2Se4, SnSe2 + SnSb2Se4 + Sb2Se3, and SnSe2 + Sb2Se3 + Liquid in the 673.2 K (400 °C) isothermal section of the Sb-Se-Sn ternary system.

Bi-In-Te phase diagram

The Bi-In-Te ternary system is an important thermoelectric material system, but phase diagram encompassing the entire compositional range of this system is missing. To provide fundamental information for thermoelectric and related studies, this study experimentally determines the Bi-In-Te phase diagram, including the 250 °C isothermal section and liquidus projection. At 250 °C, there are ten equilibrium phases, which are Bi, (Bi2)m(Bi2Te3)n, Bi2Te3, Te, In2Te5, In2Te3, InTe, In4Te3, Liquid, and BiIn2Te4. The last of which, BiIn2Te4, is a new ternary compound. (Bi2)m(Bi2Te3)n represents a group of compounds between the Bi and Bi2Te3 phases. In the liquidus projection, in addition to the terminal solid solution phases, there are (Bi2)m(Bi2Te3)n, Bi2Te3, In2Te5, In2Te3, InTe, In4Te3, ε In2Bi, In3Bi5, and InBi primary solidification phase regimes can be found. The BiIn2Te4 phase is formed via solid-state transformation involving no liquid phase.

The effect of heating rate on the microstructural breakdown required for thixoformability

AbstractThixoforming processes depend upon three basic features of the semisolid slurry: the thermodynamics of the liquid-to-solid transition; the morphology of the microstructure; and the slurry's rheological properties. By studying the thermodynamics of the solid-to-liquid transition of a specific alloy, one can determine whether the entire thixoforming process can be controlled when the alloy is used as the raw material. The rheology of the semisolid material is determined not only by the morphology of the microstructure of the primary solid phase immersed in the liquid, but also by the relative amounts of liquid and solid. In thixoforming operations the raw material is heated up to the semisolid state and injected into the die. Hence, the heating procedure has a significant impact on the morphology of the remaining solid and, consequently, its viscous behaviour, as shown in this paper. A heating rate close to 50 K min−1 was found to produce the most suitable morphology for semisolid processing as the mechanisms involved (Ostwald ripening and coalescence) were present to an equal extent.

Novel design of ferronickel smelting slag by utilizing red mud as a fluxing agent: Thermochemical computations and experimental confirmation

The effect of red mud on the melting behavior of ferronickel slag was investigated in a laboratory-scale horizontal tube furnace. Melting and softening of slag samples fluxed with different amounts of red mud were examined by an in-situ visualization technique in the temperature ranges from 1673K to 1823K. FactSage™ 7.0 was used to perform thermodynamic calculations of the multi-component system of ferronickel slag and red mud. The liquid phase area was extended to lower temperatures by adding red mud, and this implied that red mud was an excellent flux. The primary solid phase field was confirmed to be dependent on the red mud content from X-ray diffraction measurements. Microscopic observations using a scanning electron microscope (SEM-EDX) confirmed that the primary solid phase changed from olivine to spinel with the addition of red mud.

Experimental Analysis of the Reaction Rate of Hydrated Class G Cement Powder at 11 bar PCO2 and Ambient Temperature

The aim of this work is to study the alteration of class G Cement at ambient temperature under a relatively high CO2 partial pressure through suitably designed laboratory experiments, in which cement hydration and carbonation are taken into account separately. First, the hydration process was carried out for 28 days to identify and quantify the hydrated solid phases formed. After the completion of hydration, accompanied by partial carbonation under atmospheric conditions, the carbonation process was investigated using a stirred micro-reactor by reacting cement powder with pure CO2(g) (PCO2 = 11 bar) and MilliQ water for different reaction times. The reaction time was varied to constrain the reaction kinetics of the carbonation process and to investigate the evolution of primary and secondary solid phases. Mineralogical analyses (X-ray Powder Diffraction and Scanning Electron Microscope) were carried out to this purpose. Water analyses were also performed by ion chromatography at the end of each experimental run to investigate the chemical effects of cement carbonation on the aqueous solution. The carbonation degree was calculated from the results of Thermo-Gravimetric analysis (TGA). The main results of these experiments is the quick conversion of portlandite and Ca1.60SiO3.6·2.58H2O (C-S-H) to calcite. In fact, the carbonation degree attains 80% after 6 hours of reaction time. Experimental outcomes will be simulated by means of the PHREEQC software package to obtain further indications on cement carbonation

粒子法を用いた遠心鋳造時の遠心分離挙動解析

Centrifugal force is applied to a molten metal during a centrifugal casting process. Therefore, grains of primary solidified phase, inclusions or other additional agents are separated if centrifugal force is strong. The centrifugally separated structure is strongly influenced by a relationship between solidification rate of castings and centrifugal separation speed. However, it is difficult to observe or measure what happens in the process because the process is carried out under high temperatures and the material is usually opaque. Therefore, we tried to observe the centrifugal separation behavior during the centrifugal casting process by using 2-phase flow simulation based on MPS (Moving Particle Semi-implicit) method which is one of particle methods. We simulated centrifugal separation behaviors in the process and investigated an influence of density difference between the phases, particle size, viscosity and rotation speed. As a result, the centrifugal separation behavior was well simulated by the particle method, and also well evaluated by Stokes’s law by considering an influence of an apparent viscosity increase caused by an error included in the MPS method.

Influence of basicity and MgO/Al2O3ratio on the viscosity of blast furnace slags containing chloride

The viscosities of CaO–SiO2 –Al2 O3 –MgO–CaCl2 slags under conditions of CaCl2 = 0–10%, C/S = 0.90–1.30 and MgO/Al2 O3 = 0.40–0.67 have been experimentally measured to elucidate the effect of chlorine, basicity and MgO/Al2 O3 ratio on the viscous behavior of the blast furnace slag. Slag viscosity gradually increases with decreasing temperature, then sharply increases at the critical temperature, and it decreases with increasing chlorine content at temperatures over 1673 K. The critical temperature decreases from 1660 K to 1590 K with increasing chlorine content from 0% to 10% CaCl2 ; this may be attributed to the variation of chemical potential of primary solid phase caused by adding chloride. Slag viscosity diminishes with increase in basicity, while MgO/Al2 O3 ratio does not significantly affect the viscosity at temperatures higher than 1645 K. The tendency of the effect of basicity on the slag viscosity corresponds closely with that of corresponding CaO–SiO2 –Al2 O3 –MgO slags obtained from literature, while the trend of MgO/Al2 O3 ratio influence is distinct from that. The activation energy of chlorine-containing slags under the range of 182.8 kJ/mol to 213.8 kJ/mol generally decreases with increasing chlorine content, basicity and MgO/Al2 O3 ratio in slags. Due to the dual effect of the variation of polymerization and the primary phase by adding chloride, the MgO/Al2 O3 ratio almost has no influence on the viscosity of the chlorine-containing slags at higher temperatures.