Primary Crystallization Stage Research Articles

Theoretical research on ship desulfurization wastewater freezing desalination system driven by waste heat

This study proposes a novel two-stage freezing and pre-desalination system for desulfurization wastewater driven by the waste heat of marine diesel engine exhaust. Ice crystals and concentrated wastewater are separated and flow to the thermal desulfurization branch and the wet desulfurization branch respectively, so as to realize the preliminary desalination of the desulfurization wastewater, as well as provide the air conditioning and refrigeration which is recovered from the freezing and pre-desalination system. This combined system can effectively reduce the desalination costs on board. In this paper, both the thermodynamic model and economical model for the two-stage freezing pre-desalination subsystem, the absorption refrigeration subsystem and the thermal wet desulfurization branch are established, and the effect of freezing crystallization is experimentally studied. The thermodynamic performance of the proposed system is analyzed under typical onboard working conditions. Besides, the economic performance of this system is compared with traditional desulfurization technology. The results show that the pre-desalination output increases with the increase in temperature, and the salinity of pre-desalinated desulfurization wastewater can be reduced from 11 ppt to 6.8 ppt, the primary crystallization stage reaches stable a desalination rate at 20 %–23 %, and the total desalination rate involving the secondary crystallization stage reaches 30 %–40 %. The distribution rate of cold capacity in the two stage crystallizers exists an optimized value of 0.74. Simultaneously, the pre-desalination system reaches the highest desalination rate at 37.5 % with the ammonia-water concentration at 0.5 and the crystallization temperature in the primary/secondary stage at −15 °C/−9 °C, respectively. The economic performance of the system shows a downward trend as the temperature rises. The increase in initial ammonia-water concentration is benefit for the system economy. The comprehensive cost of the system with refrigeration cycle is greatly reduced by 5 %–30 % compared with that without refrigeration cycle.

Nanocrystallization of amorphous alloy Al87Ni8Dy5 induced by heat treatment

The aim was to investigate the characteristics of the short-range structure and the nanocrystallization kinetics of amorphous alloys in the heat treatment of amorphous alloys. On the basis of X-ray research it is established that at the first stage of primary crystallization (418–465 K) there is a simultaneous nucleation and three-dimensional growth of Al-nanocrystals. Within temperature range 465–580 K the probability that new Al - nuclears are created significantly decreases due to that amorphous phase is enriched with Ni and Dy atoms and the diffusion controlled growth of Al-nanocrystals is the main contribution into kinetics of transformation.

Formation and crystallization behavior of Fe-based amorphous precursors with pre-existing α-Fe nanoparticles—Structure and magnetic properties of high-Cu-content Fe-Si-B-Cu-Nb nanocrystalline alloys

Structure, crystallization behavior, and magnetic properties of as-quenched and annealed Fe81.3Si4B13Cu1.7 (Cu1.7) alloy ribbons and effects of Nb alloying have been studied. Three-dimensional atom probe and transmission electron microscopy analyses reveal that high-number-density Cu-clusters and Pre-existing Nano-sized α-Fe Particles (PN-α-Fe) are coexistence in the melt-spun Cu1.7 amorphous matrix, and the PN-α-Fe form by manners of one-direction adjoining and enveloping the Cu-clusters. Two-step crystallization behavior associated with growth of the PN-α-Fe and subsequent nucleation and growth of newly-formed α-Fe is found in the primary crystallization stage of the Cu1.7 alloy. The number densities of the Cu-clusters and PN-α-Fe in melt-spun Fe81.3−xSi4B13Cu1.7Nbx alloys are gradually reduced with enriching of Nb, and a fully amorphous structure forms at 4 at.% Nb, although smaller Cu-clusters still exist. After annealing, 2 at.% Nb coarsens the average size (Dα-Fe) of the α-Fe grains from 14.0 nm of the Nb-free alloy to 21.6 nm, and 4 at.% Nb refines the Dα-Fe to 8.9 nm. The mechanisms of the α-Fe nucleation and growth during quenching and annealing for the alloys with large quantities of PN-α-Fe as well as after Nb alloying have been discussed, and an annealing-induced α-Fe growth mechanism in term of the barrier co-contributed by competitive growth among the PN-α-Fe and diffusion-suppression effect of Nb atoms has been proposed. A coercivity (Hc) ∝ Dα-Fe3 correlation has been found for the nanocrystalline alloys, and the permeability is inverse with the Hc.

Dynamic changes in the triacylglycerol composition and crystallization behavior of cocoa butter

Dynamic changes in triacylglycerol composition during complete crystallization were investigated by separating crystals from molten cocoa butter (CB) over different lengths of crystallization time. The dynamic crystallization behavior of CB was described by solid fat content (SFC), crystal morphology, and microstructure. The crystallization process was divided into stages, based on the growth mode of crystals: the induction, primary crystallization, and secondary crystallization stages. As crystallization progressed, the relative content of 1,3-dipalmitoyl-2-oleoylglycerol (POP) increased from 12.1% to 29.8%; that of 1,3-distearoyl-2-oleoylglycerol (StOSt) decreased from 37.1% to 20.2%; and that of tristearin (StStSt) decreased from 4.9% to 0.2%. Circular crystals were formed at the induction and primary crystallization stages, and β′-III form and β′-IV form polymorphisms were exhibited. When crystallization entered the secondary crystallization stage, the crystal morphology changed from circular to acicular, and polymorphic transformation from the β′-III form and β′-IV form to the β-form was observed.

Kinetics of non-isothermal crystallization in FeNiPC(Nb) alloys

The effects of minor Nb addition on the crystallization mechanism for a FeNiPC(Nb) amorphous alloy were studied via investigating its non-isothermal crystallization kinetics. With minor Nb addition, the thermal stability of the alloy increases as evidenced by the enlargement of the supercooled liquid region. Meanwhile, the location activation energy of both Nb-added and without Nb-added alloys correlates positively with the crystallized volume fraction during the whole primary crystallization stages, as calculated by the isoconversional methods. However, the kinetics analysis using the modified Johnson-Mehl-Avrami-Kolmogorov equation indicates that the addition of Nb changes the crystallization mode of the alloys, that is, from the growth with a decrease nucleation rate to a constant nucleation rate in a diffusion-controlled manner. This can be further confirmed by the atomic force microscopy showing that Nb would restrain the atomic diffusivity and suppress the crystallization growth rate in this alloy.

Role of P on amorphization, microstructure, thermo-physical and soft magnetic properties of Fe-rich FeB(P)SiNbCu melt-spun alloys

Abstract The influence of P on amorphizing ability, as-quenched microstructure, thermo-physical and soft magnetic properties of Fe–rich (i) Fe81B15-xPxSi2Nb1Cu1 (ii) Fe82B14-xPxSi2Nb1Cu1 and (iii) Fe83B13-xPxSi2Nb1Cu1 (x = 0, 2, 4, 6, 8 at%) melt-spun alloys are investigated. The substitution of P improves amorphization of alloys and restricts the formation of hetero-amorphous microstructure for Fe 83 at% ribbons at around (x = 8). The improvement in short range ordering of P containing clusters with varying Fe content has been discussed within the framework of Cluster-Glue atom model and supported by experimental thermal parameters. The optimal P content in Fe-rich alloys in the range of 4 ≤ x ≤ 6 delivered favourable thermal properties of high primary and secondary crystallization onset temperature viz; Tx1, Tx2 and temperature span ΔT between these onsets. The P substitution drastically restricts the precipitation of secondary crystallites with reduced enthalpy of secondary crystallisation (ΔH2) during annealing and favourably assists in attaining maximum magnetic moment during the primary crystallization stage. Moreover, the P substitution (4–8 at%) effects refinement of α-Fe nanocrystallites and promotes low coercivity (Hc

Tailoring magnetic characteristics of (Fe1−xCox)81Zr9B10 amorphous alloys via engineering crystallization processes

We report on systematic structural and magnetic characteristics’ evolution studies of (Fe1−xCox)81Zr9B10 (x = 0, 1/6, 1/3, 1/2) amorphous alloys prepared by a single roller melt spinning with post-annealing treatments under a vacuum condition. With representative chemical composition, the crystallization processes of the above four typical amorphous alloys are complicated under the dedicated experimental investigations and interpretation. The α-Mn-type phase is detected in Fe81Zr9B10 alloy, while the β-Mn-type phase is observed for high Co concentration alloys. Both α-Mn-type phase and β-Mn-type phase are the transitional metastable phases formed during the dynamic crystallization. Importantly, the precipitations of metastable α-Mn- and β-Mn-type phases boost up corresponding coercivity (Hc). Along with the transformation of metastable phases, Hc decreases considerably. The precipitation of certain of β-Mn-type phase in the primary crystallization stage facilitates gaining low Hc in the second stage of crystallization. Our work paves a new path to tailor the magnetic characteristics in Fe(Co)-based nanocrystalline alloys by engineering the microstructure of metastable phase(s).

Effect of substituting Na2O for SiO2 on the non-isothermal crystallization behavior of CaO-BaO-Al2O3 based mold fluxes for casting high Al steels

The non-isothermal crystallization behaviors of CaO-BaO-Al2O3-based mold fluxes in which SiO2 had been replaced by Na2O were investigated, using an infrared furnace combined with digital microscopy as well as X-ray diffraction. The initial crystallization temperatures, crystalline phases generated at different cooling rates, crystallization rates, Ozawa indices NO (as determined using Mo's equation) and effective crystallization activation energies (as determined using the Friedman equation) were evaluated. The initial crystallization temperature increased along with the Na2O content in the flux. In addition, the precipitation of CaF2 crystals was inhibited while the growth of CaAl2O4 crystals was enhanced at Na2O concentrations over 4 wt%. Increasing the cooling rate inhibited the precipitation of MgAl6O10, and of CaSiO3, MgAl2SiO6 and NaAlSi3O8, respectively, in fluxes containing 0, 4 and 8 wt% Na2O (NS1, NS2 and NS3 samples). The peak instantaneous and average crystallization rates in these specimens were increased as the Na2O level was raised, as a direct result of changes in their NO values. The NS1 flux consistently had the lowest NO value, while the NS2 had the largest value in the primary stage of crystallization but the central value in the secondary stage, and the NO values of the NS3 flux exhibited the opposite trend. The effective crystallization activation energies decreased with increasing Na2O levels, and this was evidently an important factor affecting the initial crystallization temperature.

Effect of heat treatment on phase transformations and magnetization of amorphous Co69Fe4Cr4Si12B11 microwires

The results of qualitative and quantitative changes in phase composition as well as microstructure changes of amorphous Co69Fe4Cr4Si12B11 microwires at three stage crystallization process of are presented. After first and second stages the amount of crystalline Co-phase was 36 wt%. To study magnetization of the alloy during heating, exposure and cooling a unique vibration magnetometer with a chemical microreactor was used. The unique vibration magnetometer was used for low inertia real-time measurements under controlled atmosphere. The Curie temperatures of phases formed in the crystallization process were determined. Based on the analysis of magnetization kinetic curves, nucleation and growth mechanisms were established on the stage of primary crystallization. It was found that a one-dimensional mechanism is responsible for the growth of Co-based crystals and leads to the formation of a specific needle-shaped structure. At the second crystallization stage of a metastable phase with a Co23B6 structure type was formed. The Curie temperature of this phase was 165 °C.

Non-isothermal Crystallization Kinetics of Mold Fluxes for Casting High-Aluminum Steels

This paper investigates the crystallization behavior of CaO-SiO2- and CaO-Al2O3-based mold fluxes for casting high-aluminum steels using single hot thermocouple technology, developed kinetic models, and scanning electron microscope. The results showed that the crystallization ability of the typical CaO-SiO2-based Flux A (CaO/SiO2 0.62, Al2O3 2 mass pct) is weaker than that of CaO-Al2O3-based Flux B (CaO/SiO2 4.11, Al2O3 31.9 mass pct) because of its higher initial crystallization temperature. The crystallization kinetics of Flux A was “surface nucleation and growth, interface reaction control” in the overall non-isothermal crystallization process, whereas that of Flux B was “constant nucleation rate, 1-dimensional growth, diffusion control, in the primary crystallization stage, and then transformed into constant nucleation rate, 3-dimensional growth, interface reaction control in the secondary crystallization stage.” The energy dispersive spectroscopy results for Flux B suggested that the variations in the crystallization kinetics for Flux B are due to different crystals precipitating in the primary (BaCa2Al8O15) and secondary (CaAl2O4) crystallization periods during the non-isothermal crystallization process.

Isothermal crystallization kinetic modeling of poly(etherketoneketone) (PEKK) copolymer

Isothermal melt and cold crystallizations of a poly(etherketoneketone) (PEKK) copolymer prepared from diphenyl ether (DPE), terephthalic acid (T) and isophthalic acid (I) with a T/I ratio of 60/40 have been investigated by differential scanning calorimetry, wide-angle X-ray scattering and polarized optical microscopy. For the first time, the two-stage overall crystallization kinetics of PEKK taking into account effects of nucleation and crystal growth has been identified by using a modified Hillier type model. The primary crystallization stage is found to be an instantaneous two dimensional nucleation growth with an Avrami exponent of 2 whereas the secondary stage is found to be an instantaneous one dimensional nucleation growth with an Avrami exponent of 1. The evolution of the crystallization kinetic constants for two-stage crystallizations has been modeled according to the Hoffman and Lauritzen growth theory. Due to low crystallization kinetics, a crystallization induction time has been added to obtain a good fit with experimental data. Based on this modeling, Time-Temperature-Transformation (TTT) diagrams of the relative volume crystallinity have been established for the overall crystallization mechanism and also for the separated primary and secondary crystallization mechanisms providing an original crystallization mapping of the material.

The isothermal crystallization of poly(ether ether ketone) by two‐dimensional differential scanning calorimetry correlation mapping

ABSTRACTThis article reports the first application of the two‐dimensional differential scanning calorimetry correlation mapping, two‐dimensional‐DSC‐CM to analyze DSC rate–time data of PEEK. This provided evidence that the isothermal crystallization reduced rate–time curves exhibited fractional n values when analyzed by the Avrami equation. These fractional n values, which increased with temperature, were consistent with the presence of two processes, primary and secondary crystallization, with an increasing contribution of the secondary crystallization to the overall crystallinity. In contrast to the known literatures, secondary crystallization was observed to proceed at early stage of primary crystallization. The study of the effect of proton irradiation, up to a dose of 9.9 MGy, showed that the fractional n value was below 3.0, and does not appear to be temperature dependent. DSC analysis of the crystallization kinetics, combined with two‐dimensional correlation mapping proved a powerful tool for investigating irradiation damage of PEEK. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44378.

Synergistic toughening effect of β-nucleating agent and long chain branching on polypropylene random copolymer

β-nucleated long chain branched (LCB) polypropylene random copolymers (PPRs) were prepared via reactive extrusion by introducing β nucleating agent (NA), dicumyl peroxide (DCP) and various contents of 1, 6-Hexanediol diacrylate (HDDA) into PPR. Results of Fourier infrared spectroscopy (FTIR) and the rheological properties demonstrate the existence of LCB polypropylene. Mechanical properties including impact strength, tensile strength and elongation at break were studied. The crystal structure, morphology and crystallization behavior were investigated via wide-angle X-ray diffraction (WAXD), polarized light microscopy (PLM) and differential scanning calorimetry (DSC). Non-isothermal crystallization kinetics using the Jeziorny method was also studied. The results show an increased LCB degree with increasing HDDA amount. For the sample with a moderate LCB level, synergistic toughening effect of NA and LCB is achieved without deterioration of yield strength or elongation at break, partially because of its higher β-phase content and much smaller spherulite size. It exhibits the minimum values of Tc and Zc1, and the maximum values of t1/2 and n1 in the primary stage of crystallization, regardless of the cooling rate, indicating a slower crystallization rate and more complicated nucleation and crystal growth model.

U-Pb geochronology on zircon and columbite-group minerals of the Cap de Creus pegmatites, NE Spain

The Cap de Creus granitic pegmatites in the eastern Catalan Pyrenees were dated using in situ U-Pb geochronology by laser ablation ICP-MS on zircon and columbite-group minerals (CGM), which are present in the different types of pegmatites from type I (K-feldspar pegmatites, least evolved) to type IV (albite pegmatites, most evolved) and therefore allow dating the different pegmatitic pulses. In a type III pegmatite where zircon and CGM are co-genetically associated in the same sample, both minerals were dated using zircon and tantalite reference materials, respectively, to avoid laser-induced matrix-dependent fractionation. In one sample, xenotime genetically associated with zircon was also dated. Two ages were obtained for type I and three ages for type III pegmatites. Three of these 5 ages range from 296.2 ± 2.5 to 301.9 ± 3.8 Ma and are allocated to the primary magmatic stage of crystallization and therefore to the emplacement event. Two younger ages (290.5 ± 2.5 and 292.9 ± 2.9 Ma) obtained on secondary zircon and xenotime, respectively, are interpreted as late post-solidus hydrothermal remobilization. There is no age difference between type I and type III pegmatites. The mean 299 Ma primary magmatic age allows the main late Carboniferous deformation event to be dated and is also synchronous with other peraluminous and calc-alkaline granites in the Pyrenees. However, the youngest ages around 292 Ma imply that tectonics was still active in Early Permian times in the Cap de Creus area.

Molecular mobility and structuring in textured films of the ferroelectric copolymer of vinylidene fluoride with tetrafluoroethylene

The processes of molecular mobility in vinylidene fluoride–tetrafluoroethylene ferroelectric copolymer–based films textured via uniaxial drawing are studied. It is found that the cooperative mobility in the amorphous regions of the copolymer is described by the Vogel–Fulcher equation, whose parameters are sensitive to the drawing conditions. It is shown that a decrease in the drawing temperature causes a reduction in the effective activation energy of the above-mentioned motion. In accordance with the X-ray diffraction data, this circumstance may be explained by an increase in the packing density of chains in interlamellar spaces. This effect is partially provided by deformation-induced processes of formation of small and defective crystals of the paraelectric or antiferroelectric phase in spaces between neighboring lamellar crystals at the primary stage of crystallization. The relationship between the value of the orientational polarization in oriented films and the topology of structure formation in microfibrils is discussed. It is observed that enlargement of the interlamellar space (filled with a liquidlike amorphous phase) between neighboring crystals in microfibrils promotes an increase in the orientational polarization of chains in the amorphous phase.

Effect of Co content on structure and magnetic behaviors of high induction Fe-based amorphous alloys

The replacement of Fe with Co is investigated in the (Fe1−xCox)79Si8.5B8.5Nb3Cu1 (x=0, 0.05, 0.2, 0.35, 0.5) amorphous alloys. The alloys are synthesized in the forms of ribbons by single roller melt spinning technique, and the structural and magnetic properties of annealed ribbons are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM), B–H curve tracer, respectively. All as-cast alloys are structurally amorphous, however, their magnetic properties are varying with Co addition. The Co addition within 5–20at% results in moderate thermal stability, saturation induction, Curie temperature and lowest coercivity, while 35at% Co causes highest saturation induction, coercivity, Curie temperature and lowest thermal stability. On devitrification, the magnetic properties change with the generation of α-FeCo nanocrystallites and (FeCo)23B6, Fe2B phases during primary and secondary crystallization stages, respectively. A small amount Co is advantageous for maintaining finer nanocrystallites in amorphous matrix even after annealing at 600°C, leading to high saturation magnetization (>1.5T) and low coercivity (~35A/m). The improved magnetic properties at elevated temperatures indicate these alloys have a potential for high frequency transformer core applications.

Nonisothermal Crystallization Kinetics of Poly(Vinylidene Fluoride) in a Poly(Vinylidene Fluoride)/Poly(Methyl Methacrylate)/Dipropylene Glycol Dibenzoate System via Thermally Induced Phase Separation

The nonisothermal crystallization kinetics of poly(vinylidene fluoride) (PVDF) in PVDF/polymethyl methacrylate (PMMA)/dipropylene glycol dibenzoate (DPGDB) blends, where DPGDB served as a diluent, via solid–liquid (S-L) phase separation during a thermally induced phase separation process was investigated through differential scanning calorimetry (DSC) measurements. It was found that the Ozawa model could only describe the nonisothermal crystallization behavior of PVDF/PMMA/DPGDB system to some extent. The influence of the cooling rate and PMMA/PVDF weight ratio in the PVDF/PMMA/DPGDB system on the crystallization mechanism was also examined based on the Avrami–Jeziorny method and Mo method. Primary crystallization and secondary crystallization were observed in the Avrami–Jeziorny analysis. The analysis by the Avrami–Jeziorny and Mo models indicated that the increase of PMMA/PVDF weight ratio decreased the crystallization rate during the primary crystallization stage. The results showed that the Mo method could well explain the kinetics of the primary PVDF crystallization. The Avrami–Jeziorny method, however, could not well describe the nonisothermal crystallization process of PVDF in the primary crystallization stage. The activation energy, determined by the Kissinger method, was not suitable to reflect the PVDF crystallization process in the PVDF/PMMA/DPGDB system.

Geochemical features and age of baddeleyite from carbonatites of the Proterozoic Tiksheozero alkaline–ultramafic pluton, North Karelia

On the basis of the local composition, baddeleyite grains that were less altered due to interaction with an alkaline melt and corresponded to the primary stage of crystallization of the intrusion were selected from the carbonatite intrusion of the Proterozoic polyphase Tiksheozero alkaline–ultramafic complex. The single age of carbonatite crystallization characterized of the bulk volume of the intrusion was estimated for the first time on the basis of 40 local U–Th–Pb (SHRIMP II) analyses of these grains. The overall concordant age of baddeleyite is 1994.8 ± 9.4 Ma, and the lower age limit of the polyphase complex formation is less than 1998.4 ± 3.5 Ma.

Niobium and tantalum in minerals: Siderophile, chalcophile or lithophile, and polyvalent

Most geoscientists are convinced that minerals of both niobium and tantalum contain those elements in the 5+ state only. In fact, there are several well-documented minerals containing Nb0, Nb2+, Nb4+ and Nb5+, and tantalum follows a similar pattern. Both elements can exhibit a siderophile, a chalcophile and a lithophile character, as well illustrated empirically, and as documented via XANES and XPS spectra. Of the XPS spectra that we report here on ferroniobium of metallurgical grade, pyrochlore, samarskite, niocalite, synthetic edgarite (FeNb3S6) and NbTe2, only the samarskite and niocalite contain only one valence state of Nb (5+). Vladimir Vernadsky understated the situation when he placed Nb and Ta in the “dispersed” category. Columbite-group minerals are most unusual in exhibiting variable mutual disorder involving (Nb,Ta) and (Fe,Mn). Oddly, samples must be heated to become ordered. We raise the possibility that at the stage of primary crystallization, the relevant magmas contained mixed valences of Nb, Ta, Fe and Mn, which made a disordered distribution along the octahedrally coordinated cations energetically more acceptable. Owing to the relative insolubility of members of this solid-solution series in the ambient aqueous fluid, they have remained metastably frozen in a partly or completely disordered state.

MeV 電子照射による FeSiBPCu 合金のナノ結晶化過程の動的観察

The nanocrystallization of three kinds of nanocrystalline, soft magnetic FeSiBPCu alloys as well as Fe76Si9B10P5 alloy were investigated by using irradiation and ultrahigh voltage electron microscopy. MeV electron irradiation was selected instead of conventional annealing to clarify the early stage of primary crystallization, which is completed during heating in conventional annealing. The dynamic observations of the Fe85Si2B8P4Cu1, Fe85Si2B12Cu1, and Fe86Si2B8P4 as well as Fe76Si9B10P5 amorphous alloys revealed that aFe nanocrystals precipitated at the irradiated region. The amorphous phase could not maintain its original structure; furthermore, aFe nanocrystals precipitated via irradiationinduced crystallization, which resembles thermal crystallization. The dynamic observations of the irradiationinduced nanocrystallization behavior clarified the effect of Cu and P elements on the incubation time and growth behavior of the aFe nanocrystals embedded in the amorphous matrix during nanocrystallization. This is the first detailed evaluation of the early stage in the nanocrystallization of an amorphous phase in NANOMET by in situ TEM observations and the MeV electron irradiation technique. [doi:10.2320/jinstmet.J2014027]