Phase Formation Process Research Articles

Study on the Effect of Condensate-Type and Copolymer-Type Combined Superplasticizers on Hydration of Cement

For the limitation of single-component superplasticizer, condensate-type and copolymer-type combined superplasticizers were prepared. The adsorption of compound superplasticizers on cement paste was tested by Total Organic Carbon (TOC) measurement. Influences of superplasticizers on early hydration process of cement and Organo-mineral phase formation were studied by X-Ray Diffraction Analysis (XRD), Scanning Electron Microscope analysis (SEM) and so on. The results show that owing to the electrostatic repulsion and steric effect cooperative mechanism, condensate-type and copolymer-type combined superplasticizers reduce the superplasticizers adsorption in cement minerals and its hydration products surface, delay the process of hydration of C3A, form Organic-Layered double hydroxides (LDH), increase the early chemical shrinkage and promote the growth of cement early hydration and Ettringite

Phase formation and dielectric properties of lithium fluoride-doped (Na0.5Bi0.5)TiO3–(K0.5Na0.5)NbO3–BiFeO3 ceramics

Single-phase ceramic samples in the morphotropic phase boundary region of the (1–y)[(1–x)(Na0.5Bi0.5)TiO3 ∙ x(K0.5Na0.5)NbO3] ∙ yBiFeO3 system (х = 0.06, 0.08, 0.10; y = 0.025, 0.05, 0.075, 0.10) have been prepared by solid-state reactions, and the effect of LiF as a low-melting-point additive (5 wt %) on the phase formation process and the dielectric properties of the solid solutions has been studied. The addition of LiF has been shown to activate the phase formation process and lower the sintering temperature of ceramic samples. The modification of the ceramics with lithium fluoride slightly increases the unit-cell parameters of the solid solutions. The addition of LiF lowers their Curie temperature.

ZrC formation and the phase relations in the Si–Zr–Mg–O–C system

When MgO+ZrO2 were used as a sintering aid to SiC ceramics, it was found that ZrO2 reacted with SiC and MgO to form ZrC and a magnesium silicate. This reaction may provide a new route to synthesize ZrC or prepare ZrC/SiC composites by reaction sintering using ZrO2, SiC, and MgO as starting materials. In the present work, formation process of the ZrC phase in the SiC–MgO–ZrO2 system was addressed. Subsolidus phase relations at 1550 °C of the SiC–MgO–ZrO2 system and the related SiC–SiO2–ZrC–ZrO2–MgO (Si–Zr–Mg–O–C) system were investigated.

Transcrystallization at the surface of graphene-modified chitosan fibers

Incompatibility between hydrophilic chitosan (CS) fiber and hydrophobic polymer matrices leads to unsatisfactory properties of the composites. The crystallization of polymer on the fiber surface is a promising way to increase interfacial interactions. Here, we coated CS fiber surfaces with graphene oxide via electrostatic self-assembly to improve interfacial interactions between the polymer and the CS fiber. Structures of the CS fiber before and after graphene coating were characterized by various methods. The formation of a polypropylene (PP) transcrystalline (TC) layer on the CS fiber surface was investigated. It is suggested that at low crystallization temperatures the fiber induced TC phase forms faster than at high temperature. There exist α and β crystal of PP in the TC phase formation process as demonstrated by x-ray diffraction. The polarized light optical microscope results demonstrate that graphene coated CS fiber can also enhance the TC phase nucleation ability of poly(l-lactide).

Effect of Copper on the Formation of Ordered L10(FePt) Phase in Nanosized Fe50Pt50/Cu/Fe50Pt50 Films on SiO2/Si (001) Substrates

The effect from thickness of an intermediate copper layer in nanosized Fe50Pt50 (15 nm)/Cu (x)/Fe50Pt50 (15 nm) (x = 7.5, 15, and 30 nm) composite films on SiO2 (100 nm)/Si(001) substrates on the diffusion-controlled phase formation processes—transformation of the disordered magnetically soft A1(FePt) phase into the ordered magnetically hard L10(FePt) phase during annealing in vacuum—is studied by physical materials science methods: X-ray diffraction and measurement of magnetic properties. The A1(FePt) phase forms in all films during deposition. Annealing in vacuum in the temperature range 300–900°C is accompanied by thermally activated diffusion processes between the Cu and FePt layers. When thickness of the intermediate Cu layer increases from 7.5 nm up to 15 nm, the onset temperature of A1(FePt) → L10(FePt) phase transformation raises by 100°C, i.e., to 800°C. Simultaneously, the coercivity in films decreases since Cu dissolves in the FePt lattice.

Evidence of reaction rate influencing cubic and hexagonal phase formation process in CdS nanocrystals

CdS nanocrystals are synthesized by co-precipitation method using 2-mercaptoethanol (ME) as capping agent. Cubic, hexagonal and their mixture are obtained by varying the ME concentration. Lower (higher) ME concentration results in cubic (hexagonal) phase. The crystallite sizes are in the range 3–7nm. Increase in ME concentration lead to lower reaction rate between Cd2+ and S2− of the precursors, and slower reaction rate is found to favor hexagonal phase formation over the cubic one in CdS nanocrystals. Role of reaction rate in the phase formation process provides a way to synthesize CdS nanocrystals in desired crystal phase.

Effects of shear flow on phase nucleation and crystallization.

Classical nucleation theory offers a good framework for understanding the common features of new phase formation processes in metastable homogeneous media at rest. However, nucleation processes in liquids are ubiquitously affected by hydrodynamic flow, and there is no satisfactory understanding of whether shear promotes or slows down the nucleation process. We developed a classical nucleation theory for sheared systems starting from the molecular level of the Becker-Doering master kinetic equation and we analytically derived a closed-form expression for the nucleation rate. The theory accounts for the effect of flow-mediated transport of molecules to the nucleus of the new phase, as well as for the mechanical deformation imparted to the nucleus by the flow field. The competition between flow-induced molecular transport, which accelerates nucleation, and flow-induced nucleus straining, which lowers the nucleation rate by increasing the nucleation energy barrier, gives rise to a marked nonmonotonic dependence of the nucleation rate on the shear rate. The theory predicts an optimal shear rate at which the nucleation rate is one order of magnitude larger than in the absence of flow.

ZrC formation and the phase relations in the SiC–SiO2–ZrC–ZrO2–CaO system

During investigation of the phase relations in the SiC–ZrO2–CaO ternary system, it was revealed that ZrO2 reacted with SiC and CaO to form ZrC and calcium silicate via a series of solid-state reactions. Because these reactions may provide a new route to reaction-sintering of ZrC ceramics, ZrC/SiC and ZrC/salt composites, the formation process of the ZrC phase was analyzed. Subsolidus phase diagram of the related SiC–SiO2–ZrC–ZrO2–CaO (Si–Zr–Ca–O–C) quinary system at 1400°C was presented.

Irreversible phase transition between LiFePO4 and FePO4 during high-rate charge-discharge reaction by operando X-ray diffraction

LiFePO4 is a practically used cathode material for lithium-ion batteries due to a high theoretical capacity, high cycle capability and the high-rate performance. The metastable LixFePO4 (LxFP) phase with an intermediate composition appears in the non-equilibrium state at high-rate condition. However, the formation process of the metastable LxFP phase and its impact to the electrochemical property are still unclear. In order to elucidate these points, we directly observed the phase transition behavior by applying operando XRD during 10C charge-discharge. LxFP phase does not form in charge reaction but preferentially forms in discharge reaction. The phase transition from LxFP to Li-rich phase is less likely to proceed in the end of discharge reaction. The asymmetric phase transition between LiFePO4 and FePO4 results in decreasing the discharge capacity and increasing the irreversible capacity at high-rate conditions.

Effect of NaNO<sub>3</sub> as Enhancer on YBa<sub>2</sub>Cu<sub>4</sub>O<sub>8</sub> Superconductor Phase Formation via Solid State Technique with Heating at Ordinary Oxygen Pressure

YBa2Cu4O8 has emerged as better choice in superconducting application thank to it strong thermal stability. High pressure techniques had been employed for the preparation of YBa2Cu4O8 but it might costly and/or inconvenient. Several research groups had showed that the YBa2Cu4O8 can also be prepared by conventional solid state method with heating at 1 atm oxygen pressure; however the phase formation processes are yet brief and clear. This work infiltrated the phase formation processes in preparing the YBa2Cu4O8 under solid state method with heating at 1 atm oxygen pressure. The effectiveness of the use of sodium nitrate as an enhancer was brought to light by the experiment results. Significant YBa2Cu4O8 phases were successfully synthesized.

Investigation of Influence NH4VO3+HOCH2CH2OH Oxidation of ASD-4 Powder

The thermokinetic data on the process of oxidation, of NH4VO3 + HOCH2CH2OH modified ASD-4 powder have been obtained by the TG and DSC methods during heating in air up to 1473 K at a rate of 10 K / min. The process of phase formation was studied directly during oxidation of the modified ASD-4 powder under similar conditions by the X-ray diffraction method using a synchrotron radiation from the VEPP-3 station of Channel 4 on the basis of equipment available at ISSCM SB RAS. It was found that oxidation of the activated powders is shifted into the low temperature region. Two modifiers: NH4VO3 + HOCH2CH2OH and previously examined V2O5 nH2O were compared.

Вплив інтенсивної пластичної деформації на процеси фазоутворення в аморфних сплавах

Вплив інтенсивної пластичної деформації на процеси фазоутворення в аморфних сплавах

Effect of Pr Additions to Li-doped Bi2212 Bulk Superconductors Sintered at Low Temperature

The physical properties study of the Bi2Sr2CaCu2Oy (Bi2212) ceramics samples sintered at low temperature has been carried out by measurement of electrical resistance and powder X-ray diffraction (XRD). The effects of Pr doping on the formation process of the Bi2212 phase, and its structural and superconducting features were studied. The samples were prepared by a solid-state reaction method from oxides and carbonate powders. The samples with nominal composition Bi2.12Sr1.90Ca1.02Cu1.96Li0.15Cl0.15Oy added with praseodymium oxide (Pr2O3) were sintered in air at 710°C. The Pr2O3 addition ranging between 0.1mass% and 1.2mass% promotes the formation of the Bi2212 phase in low temperature synthesis. The full-width at half maximum (FWHM) value of the (200) and (0010) XRD peaks is slightly decreasing in the samples for low level doping and reaches a minimum around 0.6mass%. The maximum zero resistance temperature (Tc) is observed at 82.5K for the sample with 0.6mass% Pr2O3 addition by sintering even at 710°C, which is about 150°C lower than that of the non-added Bi2212 phase.

Electrochemical phase formation: classical and atomistic theoretical models.

The process of electrochemical phase formation at constant thermodynamic supersaturation is considered in terms of classical and atomistic nucleation theories. General theoretical expressions are derived for important thermodynamic and kinetic quantities commenting also upon the correlation between the existing theoretical models and experimental results. Progressive and instantaneous nucleation and growth of multiple clusters of the new phase are briefly considered, too.

EFFECT OF CARBONITRIDE TiC0,5N0,5 DOPING WITH ZIRCONIUM ON THE MECHANISM OF INTERACTION WITH Ni–Mo MELT

The paper presents a novel study of the effect of titanium carbonitride TiC 0,5 N 0,5 doping with zirconium on the mechanism and kinetic features of contact interaction with the Ni–25%Mo melt ( t = 1450 °C, vacuum 5•10–2 Pa) using the methods of electron microprobe analysis and scanning electron microscopy. It shows the basic effects of a zirconium modifying influence on dissolution, phase and structure formation processes occurring during the interaction between the Ti 1– n ZrnC 0,5 N 0,5 carbonitride ( n = 0,05 and 0,20) and Ni–Mo melt, and analyzes factors contributing to their occurrence. It was found that the chemical role of small zirconium additives is similar to the role of nitrogen in many respects. Experiments confirm the practical absence of zirconium and nitrogen in the K-phase composition. It was shown that the Ti 0,8 0Zr 0,2 0C 0,5 N 0,5 zirconium-rich carbonitride cannot be recommended as a high melting component of a ceramic material (cermet) due to the limitations of a chemical nature.

In Situ Analysis of the Liquid Phase Sintering Process of alpha-SiC Ceramics

The densification process of liquid phase sintered SiC ceramics with Al2O3 and Y2O3 as sintering additives was investigated by in situ measurement apparatus combined with conventional methods. The shrinkage curve, mor- phology of the sample and liquid phase formation process simulation were observed by high temperature in-situ ob- servation furnace. The relative density, flexural strength and microstructure evolution were characterized by analysis of samples sintered at temperatures ranging from 1640℃ to 1920℃ at 40℃ interval. The obvious temperature that liquid phase began to function was confirmed between 1640℃ to 1680℃. The classical liquid phase sintering theory was testified. Highly-densified SiC ceramics were obtained by being sintered at 1880℃, of which the relative density was (99.46 ± 0.37)%, and the flexural strength was (650 ± 26) MPa.

3D Morphology and Formation Process of the Icosahedral Quasicrystalline Phase in Rapidly Solidified Al–Mn Alloy

Three-dimensional morphology and formation process of icosahedral quasicrystal phase have been investigated in a melt-spun Al–18Mn alloy (in wt%). Three distinct layers corresponding to varying temperature gradient have been observed on the cross section of the ribbons. 3D morphologies of cellular and dendritic icosahedral phase have been obtained through electro-etching. A model has been proposed to describe the formation process of the icosahedral phase and α-Al during the rapid solidification. The icosahedral phases are primarily precipitated from the melt into fine cellular and dendritic particles, and subsequently engulfed by the α-Al which propagates in a planar morphology.

Phase Formation of the Yttrium Aluminates in the Y2O3-Al2O3-SiC System

Phase formation sequence of the yttrium aluminates in the Y2O3-Al2O3-SiC ternary system as temperature increases were investigated via x-ray diffraction (XRD). Results showed that YAM (monoclinic), YAP (perovskite) and YAG (garnet) were the yttrium aluminates presented in the solid-state reacted samples at a fixed Al2O3:SiC ratio of 1:1. Formation of the yttrium aluminates depended on the temperature. The YAM, YAP and YAG started to form below 1150 °C, at 1300 °C, and at 1450 °C, respectively. Accordingly, two behavior phase diagrams of the Y2O3-Al2O3-SiC ternary system were recognized, one is in the temperature range of 1150-1300 °C and the other is in 1300-1450 °C, respectively. Thereafter, the phase equilibrium was reached in the temperature range of 1450-1700 °C. Effects of SiC on the phase formation processes in the ternary system were discussed.

Progress on Numerical Reactive Diffusion Modeling of CuInSe2 Phase Formation for Solar Cell Applications

Numerical modeling of chalcopyrite (CuInSe2) absorber layer formation by rapid thermal annealed stacked elemental layers provides a valuable tool to address the microscopic phase formation process, which significantly determines the absorber layer properties in solar cell applications. We present a one dimensional kinetic modeling tool describing the diffusive reaction kinetics for layers of partial miscible systems. The diffusion is described temperature dependent and by calculating the latent heat the results were compared with differential scanning calorimetry measurement curves. Applying the numerical simulation to elemental layers of Cu, In and Se, first binary compounds are observed. With the presented progress in the model the absorber can completely react to CuInSe2, after sufficient intermixing of the elements. The results show a good agreement with experimental data with regard to the temperature range of the reactions taking place.

BaTiO3–CoFe2O4–BaTiO3 trilayer composite thin films prepared by chemical solution deposition

Multiferroic BaTiO3–CoFe2O4–BaTiO3 thin films were synthesized by spin coating of Co(NO3)2–Fe(NO3)3 and Ba(OAc)2–Ti(i-OPr)4 dissolved in a mixture of acetic acid and dimethylformamide. Stepwise thermal treatment at 200, 400 and 800°C led to the desired phases. The phase formation process was monitored by thermoanalytic, XRD, IR and Raman measurements. SEM was used to characterize the structure and thickness of each layer. Two samples with different thicknesses of perovskite and spinel layers are discussed. Sample 1 consists of 120nm CoFe2O4 between two 70nm BaTiO3 layers. For sample 2, the 90nm BaTiO3 top and bottom layers are enclosing 220nm CoFe2O4. The surface qualities were determined by AFM indicating rms roughness values of about 4nm. Magnetic investigations reveal slightly anisotropic behavior. Polarization measurements show hysteresis loops (PS(max)=29μCcm−2; PR(max)=17μCcm−2) with switching peaks at the corresponding coercive fields.