Heat-treated aluminum–silicon (Al-Si)-based alloys have dominated the cast lightweight alloy industry for several decades. However, in the last decade, Al-Ce-based alloys have shown promise in ...replacing Al-Si alloys as they remove the need for costly heat treatments. As the properties of Al-Ce alloys depend on the as-cast microstructure, it is important to characterize the solidification kinetics of these alloys. Therefore, this study focused on characterizing the solidification of an Al-Ce alloy with additions of Ni and Mn (nominal composition Al-12.37Ce-3.26Ni-0.94Mn-0.12Fe in weight percent). The alloy was cast in a wedge mold configuration, resulting in cooling rates between 0.18 and 14.27 °C/s. Scanning electron microscopy (SEM) coupled with the energy dispersive x-ray spectroscopy (EDS) and differential scanning calorimetry (DSC) techniques characterized the evolution rate of solid phases. The SEM/EDS data revealed that an Al10CeMn2 phase was present at higher cooling rates. At lower cooling rates, near the center of the casting, a primary Al23Ce4Ni6 phase was more present. It was observed that up to 2.6 atomic percent (at.%) of Mn was dissolved in this primary Al23Ce4Ni6 phase, thereby removing a large portion of the available Mn for forming the Al10CeMn2 phase. DSC analysis showed differences in the samples’ liquidus temperatures, which indicated compositional variations. Inductively coupled plasma–atomic emission spectroscopy (ICP-OES) and Scheil solidification simulations correlated the compositional differences with phase formation, which agreed with the SEM and DSC results. This experiment provides insight into novel Al-Ce-Ni-Mn alloys and where their potential lies in industrial applications.
In this work, a new computer-aided cooling curve analysis method (CA-CCA) called metal/mold energy balance method (MEB) is presented. Its originality relies on taking into account the thermal ...history, the mass, and the heat capacity of both the sample and the mold containing it, for the determination of the latent heat of fusion and the evolution of the solid fraction of metallic samples contained into metallic molds without using a baseline curve. The MEB method is based on the numerical processing of the cooling curves of the sample and the mold, which are obtained using two thermocouples, one located at the thermal center of the sample and the other placed into the mold wall. The mold containing the sample is thermally isolated at its top and bottom. The method was applied to explore its capability to determine values of latent heat of fusion and solid fraction evolution when compared to reported values in the literature of five metals of commercial purity (Cd, Zn, Sn, Pb, and Al) and two Al-based alloys (Al–7%Si and Al–14%Cu). The performance of the MEB method was compared with the results obtained by processing the cooling curves of the metal and alloys under study using the Newton baseline method, the dynamic baseline method, and the equation-based Newtonian method. The obtained results suggest that MEB method offers a simple and easy way to obtain accurate experimental values of latent heat of fusion with small errors respect to the reference reported values, while results on solidification paths are similar to those predicted by the other CA-CCA methods.
Rheological characterization and an in-situ temperature measurement were carried out to investigate the solidification behavior and crystallization kinetics of injection-molded (IM) high-density ...polyethylene (HDPE) samples. The temperature profiles obtained via the enthalpy transformation method (ETM) were also used to disclose the effect of cooling rate on the solidification kinetics during the IM process. A four parameter model (FPM) was developed in the present work, based on a three-parameter model (TPM) we proposed previously, with the FPM shown to have an obviously better fitting effect. It was seen that heat transfer at locations χ ≤ 0.5 was primarily dominated by a thermal conduction mechanism, which was unlike the situation when χ > 0.5, with χ being the fractional distance from the mold surface to the center. The results of the present study are suggested to be of significance to further research on the correlation between microstructures and properties of IM products.
The shrinkage porosity of castings made from cast iron with spherical graphite (SGI) depends on a combination of intrinsic (density and volume of phases, solidification kinetics) and extrinsic ...conditions related to casting-mold thermo-mechanical interactions. Precipitation of graphite nodules increases the specific SGI volume, and control of the nucleation rate in solidified castings can be used for improving casting soundness. In this article, the method of structural reconstruction of solidification kinetics was used to link the nucleation rate of graphite nodules to experimentally observed shrinkage porosity in a specially designed test casting. An automated SEM/EDX system was used to determine the “true” two-dimensional graphite nodule distributions in the casting sections. These two-dimensional distributions were converted into the volume particle distribution functions (
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), and the solidification kinetics were reconstructed by applying inverse simulations. The experiments were performed with variations in inoculation and pouring temperature. The shrinkage porosity was compared to the restored sequence of graphite nodule nucleation in the specific casting volumes. It is shown that the second nucleation wave in low-temperature poured and inoculated SGI eliminated interdendritic microporosity. The suggested method could be used in industry to improve the soundness of SGI castings.
The solidification kinetics of polyolefins (PO) under three cooling conditions were investigated using an in situ measurement of the temperature decay within the PO resins. The phase-change ...temperature range of high-density polyethylene (HDPE) was located between 110 and 120°C, and those of low-density polyethylene (LDPE) and polypropylene (PP) were 90-110°C and 100-120°C, respectively. The cooling rate of the liquid-state stage is larger than that of the crystallization stage, primarily owing to the release of the latent heat of crystallization as well as the reduced temperature difference between the sample and cooling medium; they jointly slow down the cooling rate to an extent. The time with respect to phase transformation and its lasting period have close relations to the materials' molecular characteristics (e.g., Mw, MWD, LCB, etc.). Three empirical equations were proposed, and found to be applicable for the cooling analysis of the PO molten materials at relatively low cooling rates prior to crystallization.
The largest part of an injection molding cycle is occupied by melt cooling, which significantly influences the properties of the final parts, especially for crystalline polymers which undergo both ...solidification and crystallization processes simultaneously. Based on non-isothermal crystallization characterization, solidification kinetics of high density polyethylene was investigated via an in-situ measurement of in-cavity temperature profiles throughout the injection molding process. Existence of the turning point in the cooling curve of ln θ vs. ln t, which can be employed for estimation of the minimum cooling time, was for the first time validated experimentally. Good agreement was achieved through the comparison between experimental observations and theoretical predictions using the enthalpy transformation method (ETM). The present study will be instructive for the optimization of processing variables, and gives insight into the formation of various crystalline structures in injection molded articles, as well as forecast of cooling time of injection moldings of crystalline polymers.
A blue calcium phosphate cement with optimal self-hardening properties was synthesized by doping whitlockite (β-TCP) with copper ions. The mechanism and the kinetics of the cement solidification ...process were studied using energy dispersive X-ray diffraction and it was found out that hardening was accompanied by the phase transition from TCP to brushite. Reduced lattice parameters in all crystallographic directions resulting from the rather low (1:180) substitution rate of copper for calcium was consistent with the higher ionic radius of the latter. The lower cationic hydration resulting from the partial Ca→Cu substitution facilitated the release of constitutive hydroxyls and lowered the energy of formation of TCP from the apatite precursor at elevated temperatures. Addition of copper thus effectively inhibited the formation of apatite as the secondary phase. The copper-doped cement exhibited an antibacterial effect, though exclusively against Gram-negative bacteria, including E. coli, P. aeruginosa and S. enteritidis. This antibacterial effect was due to copper ions, as demonstrated by an almost negligible antibacterial effect of the pure, copper-free cement. Also, the antibacterial activity of the copper-containing cement was significantly higher than that of its precursor powder. Since there was no significant difference between the kinetics of the release of copper from the precursor TCP powder and from the final, brushite phase of the hardened cement, this has suggested that the antibacterial effect was not solely due to copper ions, but due to the synergy between cationic copper and a particular phase and aggregation state of calcium phosphate. Though inhibitory to bacteria, the copper-doped cement increased the viability of human glial E297 cells, murine osteoblastic K7M2 cells and especially human primary lung fibroblasts. That this effect was also due to copper ions was evidenced by the null effect on viability increase exhibited by the copper-free cements. The difference in the mechanism of protection of dehydratases in prokaryotes and eukaryotes was used as a rationale for explaining the hereby evidenced selectivity in biological response. It presents the basis for the consideration of copper as a dually effective ion when synergized with calcium phosphates: toxic for bacteria and beneficial for the healthy cells.
•A blue, copper-doped CaP cement with clinically optimal TCP→DCPA setting kinetics•Ca→Cu substitution reduces lattice parameters in all crystallographic directions.•The cement is antibacterial, though exclusively against Gram-negative bacteria.•Simultaneously, the cement increases the viability of a range of human cell lines.•More proliferative for primary than cancer cells, suggesting anti-tumorigenicity
The nucleation behavior of primary aluminium phase in a hypoeutectic Al–Si foundry alloy is studied using the 3DXRD microscope during the liquid–solid phase transformation for continuous cooling. ...Grain nucleation and grain growth for few different casting conditions of a commercial aluminium alloy (A356: Al-7Si-0.4
Mg-0.1Fe-0.1Ti
wt.%) were investigated using three dimensional X-ray diffraction microscope (3DXRD) located at ID11 at European Synchrotron Radiation Facility (
www.ESRF.eu). To conduct the study a monochromatic hard X-ray beam (energy of 70
keV) with a beam size of 200×200
µm
2 was used and using a special furnace the microstructure evolution during solidification of a commercial Al–Si foundry alloy (A356) was monitored in-situ. Results gathered from solid fraction information showed adding 0.1
wt.% Ti (as Al-3Ti-B) changes the primary aluminium nucleation temperature and aluminium grain size. Furthermore, it showed that at slower cooling rate (0.04–0.1
K/s) grain refiner can alter the primary aluminium nucleation temperature by 20
°C, whereas at higher rates (2
K/s) this figure was reduced down to 5
°C.
Experimental Study of Geopolymer Solidification Kinetics Siyal, Ahmer Ali; Pauzi, Ahmad Hafizi; Azizli, Khairun Azizi ...
Applied Mechanics and Materials,
09/2014, Letnik:
625, Številka:
Process and Advanced Materials Engineering
Journal Article
Recenzirano
Geopolymers are formed from silica and alumina oxides mixed with alkali hydroxide or alkali silicate. This paper presents the findings on the study of the solidification of fly ash geopolymer through ...setting time by varying alkaline activators, their concentrations and geopolymer curing temperature. This work focuses on the transformation of geopolymer from liquid paste to solid through Avrami’s Kinetic Theory. From the experimental results, alkaline activation with sodium silicate produced shortest time for geopolymer solidification as compared to KOH and NaOH. The increase in concentrations of alkaline solution and curing temperatures were found to reduce setting time for geopolymer’s solidification. From Avrami theory perspective, the growth forms of geopolymer in the geopolymerization process exhibit two and three dimensional structure with the presence of secondary nucleation.
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