Role of Ag microalloying on glass forming ability and crystallization kinetics of ZrCoAgAlNi amorphous alloy

Bulk metallic glasses(BMGs) with new chemical compositions(ZrCoAgAlNi) were fabricated and the effects of Ag minor addition on the glass forming ability(GFA) and crystallization kinetics were studied. The x-ray diffraction(XRD) test was applied to identify the amorphousness of BMGs or possible crystalline phases. Using differential scanning calorimeter(DSC), the thermal stability and crystallization kinetics under a non-isothermal condition at the different heating rates were studied. Considering the heating rate dependency of glass transition and crystallization kinetics, the activation energy was evaluated and measured for the mentioned processes. It was revealed that the rise in Ag content led to the decrease in activation energy for glass transition, while the activation energy for crystallization increased. The thermal stability and GFA were also studied and it was found that the Ag addition strongly affected the inherent features of BMGs. With the increase in Ag content, the atomic mobility and structural rearrangement changed in the material and consequently, the GFA and thermal stability were significantly improved.

CRYSTALLIZATION KINETICS OF SYNDIOTACTIC POLYPROPYLENE STUDIED BY TIME-DEPENDENT LIGHT ATTENUATION

Crystallization kinetics of syndiotactic polypropylene(sPP)was observed by light attenuation measurements. The initial stages of temperature dependent sPP crystallization fall in the range of Rayleigh scattering and Rayleigh-Debye- Gans scattering.Initial time and growth time of crystallization were obtained,and the trend of crystallization temperature dependent linear attenuation coefficient on the radius and the index of the refraction of the spherulite were evaluated.

Non-Isothermal Crystallization Kinetics of a Rapidly Solidified as-Cast TiZrHfNiCu High Entropy Bulk Metallic Glass

This paper aims to investigate the thermal behavior and crystallization kinetics of TiZrHfNiCu high entropy bulk metallic glass (HE-BMG) alloy using the standard procedure of Differential Scanning Calorimetric (DSC) annealing technique. The alloy was produced using an arc melting machine with a critical diameter of 1.5 mm. The crystallization kinetics and phase transformation mechanism of TiZrHfNiCu HE-BMG was investigated under the isochronal condition at a single heating run based on the Johnson-Mehl- Avrami (JMA) theory. In isochronal heating, the apparent activation energy for glass transition and crystallization events was analyzed by Kissinger and Ozawa methods. The average activation energy value for crystallization of TiZrHfNiCu amorphous alloys in isochronal modes was 226.41 kJ/mol for the first crystallization and 297.72 kJ/mol for second crystallization stages. The crystallization mechanism of the first step was dominated by two- and three-dimensional growth with increasing nucleation rate, while the crystallization mechanism in the second stage was dominated by two-dimensional crystallization growth with a constant nucleation rate. The diffusion mechanism result proved the theory of sluggish atomic diffusion of HEA at elevated temperature.

Isothermal and Non-Isothermal Crystallization Kinetics of Conductive Polyvinylidene Fluoride/Poly(Ethylene Terephthalate) Based Composites

This work deals with isothermal and non-isothermal crystallization kinetics of electrically conductive polyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET) based composites. It completes our previous work in which we related the crystallinity of these conductive PVDF/PET based composites to their through-plane resistivity [1]. Isothermal crystallization was described using the logarithmic form of the Avrami equation and it was observed that the crystallization rate of the PVDF phase inside the composite became slower compared to that of neat PVDF. In non-isothermal crystallization, the Avrami exponent of PVDF phase did not show any noticeable variation;however, that of PET phase, which contains the major part of the conductive carbon black (CB) and graphite (GR) additives, showed an evident decrease compared with neat PET. It was also observed that, at the same cooling rate, the crystallization rate of PVDF and PET phases inside the composite was slower than that of neat PVDF and PET.

Influence of Freezing Layer on the Crystallization Kinetics of PCL on Oriented PE Film

The effect of freezing layer on the crystallization kinetics of poly(ε-caprolactone)(PCL)thin and ultrathin films was investigated by monitor the growth process of it on oriented polyethylene(PE)and CaF_(2)with and without freezing layer,respectively.It was found that the PCL films with similar thicknesses crystallize much faster on oriented PE than on CaF_(2)substrate.For example,the crystallization rate constant of a 102 nm thick PCL film decreases tremendously by 3 orders of magnitude from 1.1×10^(-1) on PE substrate at 50℃to 7×10^(-4)on CaF_(2)surface at 40℃.Moreover,the crystallization of PCL accelerates on CaF_(2)surface while slows down at PE surface with increasing film thickness.The ultrathin films of PCL with thickness less than 14 nm exhibits the fastest crystallization rate on oriented PE with a rate constant of about 3.5×10^(-1),which is 3 times higher than that of a ca.50 nm thick film.This illustrates the great influence of freezing layer on the crystallization process of PCL.The freezing layer thickness of PCL on PE is estimated to be in the range of 14-17 nm.Taking the radius of gyration(R_(g)~15.6 nm)of the used PCL material into account,the obtained results may imply the existence of a correlation between the R_(g)of PCL and its freezing layer thickness at PE substrate.

Preparation, Crystallization and Mechanical Properties of Potassium Aluminosilicate Glass-ceramics

In this study,transparent K_(2)O-Al_(2)O_(3)-SiO_(2)(KAS)glass-ceramics with leucite as the main crystalline phase were prepared by melting-quench method and two-step heat treatment.The effects of SiO_(2)/Al_(2)O_(3) ratio and heat treatment on crystallization and mechanical properties were studied.The crystallization kinetics and X-Ray Diffraction(XRD)results showed that SiO_(2)/Al_(2)O_(3) ratio and heat treatment system had a direct impact on the crystallization behavior of potassium aluminosilicate glass-ceramics.When heat-treated at 680℃/2 h and 780℃/1 h,cracks generated on the surface of the sample with the addition of SiO_(2)/Al_(2)O_(3)=4.8(in mol)due to the huge difference in the coefficient of thermal expansion between glass matrix and surface.When the addition of SiO_(2)/Al_(2)O_(3)(in mol)was 4,the sample with leucite as the main crystalline phase showed an excellent fracture toughness(1.46 MPa·m^(0.5))after the heat treatment of 680℃/2 h and 780℃/5 h.And there was a phase transformation from kaliophilite to leucite.The crystalline phases of the sample heat-treated at 680℃/8 h and 780℃/1 h were leucite and kaliophilite,which resulted in the visible light transmittance of 63%and the fracture toughness of 0.91 MPa·m^(0.5).Furthermore,after the heat treatment of 680℃/2 h and 780℃/5 h,the main crystalline phase of the sample with SiO_(2)/Al_(2)O_(3)=3.2(in mol)was still kaliophilite.Because leucite only grows on the surface of the sample and is hard to grow inward,it is hard to achieve the bulk crystallization of leucite in the sample with SiO_(2)/Al_(2)O_(3)=3.2(in mol).

Discontinuous solid solutions of anthracene-phenanthrene:Thermodynamics and crystallization kinetics

We explored such issues as the formation mechanism,structure and propriety of the solid solutions of anthracene(ANT)-phenanthrene(PHE).Solution crystallization and solid-state grinding were employed to prepare solid solutions under different conditions.The thermal behavior and PXRD scanning results revealed the formation of discontinuous solid solutions,whose melting points and crystal lattices varied linearly with mixed ratio.Combing with Materials Studio,the formation possibility of solid solutions were investigated by evaluating the change of the energy.The crystal morphology of the solid solutions have a positive correlation with the change of the major part.Finally,the solution crystallization process of solid solution were studied using the population balance model.

Fractionated Crystallization Kinetics and Polymorphic Homocrystalline Structure of Poly(_(L)-lactic acid)/Poly(_(D)-lactic acid)Blends:Effect of Blend Ratio

Stereocomplex(SC)crystallization has been an effective way to improve the physical performances of stereoregular polymers.However,the competition between homo and SC crystallizations can lead to more complicated crystallization kinetics and polymorphic crystalline structure in stereocomplexable polymers,which influences the physical properties of obtained materials.Herein,we select the medium-molecular-weight(MMW)poly(L-lactic acid)/poly(D-lactic acid)(PLLA/PDLA)asymmetric blends with different PDLA fractions(f_(D)=0.01-0.5)as the model system and investigate the effects of f_(D) and crystallization temperature(T_(c))on the crystallization kinetics and polymorphic crystalline structure.We observe the fractionated(i.e.,multistep)crystallization kinetics and the formation of peculiar β-form homocrystals(HCs)in the asymmetric blends under quiescent conditions,which are strongly influenced by both f_(D) and T_(c).Precisely,crystallization of β-form HCs is favorable in the MMW PLLA/PDLA blends with high f_(D)(≥0.2)at a low T_(c)(80-100℃).It is proposed that the formation of metastable β-form HCs is attributed to the conformational matching between β-form HCs and SCs,and the stronger constrain effects of precedingly-formed SCs in the early stage of crystallization.Such effects can also cause the multistep crystallization kinetics of MMW PLLA/PDLA asymmetric blends in the heating process.

In Situ Scattering Studies of Crystallization Kinetics in a Phase-Separated Zr-Cu-Fe-Al Bulk Metallic Glass

Thermal stability and the crystallization kinetics of a phase-separated Zr-Cu-Fe-Al bulk metallic glass were investigated using in situ high-energy synchrotron X-ray and neutron diffraction,as well as small-angle synchrotron X-ray scattering.It was revealed that this glass with excellent glass-forming ability possesses a two-step crystallization behavior.The crystalline products and their evolution sequence are more complicated than a homogeneous Zr-Cu-Al glass with average glass-forming ability.The experimental results indicate that a finely distributed nanometer-sized cubic Zr_(2)Cu phase forms first and then transforms to a tetragonal Zr_(2)Cu phase,while the matrix transforms to an orthorhombic Zr_(3)Fe phase.The strength of the Zr-Cu-Fe-Al composite containing cubic Zr_(2)Cu phase and glass matrix increases,and the plasticity also improves compared to the as-cast Zr-Cu-Fe-Al bulk metallic glass.Our results suggest that the formation of multiple and complex crystalline products would be the characteristics of the Zr-Cu-Fe-Al glass with better glass-forming ability.Our study may shed light on the synthesis of bulk-sized glass-nanocrystals composites of high strength and good plasticity.

Isothermal Crystallization Behavior of Poly (ethylene terephthalate)/Carbon Black Masterbatch

Poly(ethylene terephthalate) (PET)/carbon black (CB) masterbatch was prepared by melt blending using a separate feeding technique and its homogeneous dispersion morphology was confirmed by transmission electron microscope (TEM). The Avrami and Hoffman-Lauritzen secondary nucleation theories were employed to analyze the effect of high CB content on crystallization kinetics of PET, providing theoretical support for the development of masterbatch with high content of functional components. The Avrami exponents,average values of n,for PET and PET/CB masterbatch are both greater than 3, which indicates three-dimensional growth of crystals. In addition,no significant evidence for regime transition of PET is found applying Hoffman-Lauritzen secondary nucleation theory,though such observations have been reported previously in the literature. Furthermore,appropriate U* value for PET is determined to be 12 800 J/mol. For PET/CB masterbatch,a transition from regime I to regime II around 225℃ is observed with appropriate U* value (12 800 J/mol) . This phenomenon is consistent with a transition point in plot of G versus Tc . The fold surface free energy σe (100. 3 mJ/m 2) of PET is much greater than that of PET/CB masterbatch (48. 3 mJ/m 2) ,which indicates heterogeneous nucleation effect of CB particles.

Study on crystallization behavior of Tibet butter

Tibetan butter(TB),generally called butter,is a solid oil product extracted from yak milk in the QinghaiTibet plateau area.However,due to the limitations of raw material sources and production technology,there is a shortage of TB,so it is important to find substitutes of TB.This paper studied the crystallization behavior of six kinds of commercial TB products in Tibet to provide the theoretical basis for the development of TB substitutes for the production of TB lamps and flowers.This study assessed the crystallization behaviors of the TB samples,including isothermal crystallization process and non-isothermal crystallization process.The microstructure,isothermal crystallization of TB were evaluated by polarized light microscopy and low-pulse NMR spectrometry,respectively.The non-isothermal crystallization process of TB under temperature scanning were investigated using Rheometer,and the crystallization behavior under different cooling rates were determined by diferential scanning calorimetry(DSC)procedures.The results showed that the TB was crystallized at a higher supercooling(-10,0 and 10℃).Dimensional growth is dominant;at 20℃,spiral growth dominates.The TB has complex crystallization nucleation behavior.The crystal types of TB are mainlyβ’-crystal form andβ’-like crystal form.The lower the cooling rate,the shorter the crystallization induction time,and the more the number of crystal nuclei.Therefore,during producing TB substitutes in the factory,the cooling rate can be controlled at10℃/min to reduce energy consumption and production costs.

Preparation and crystallization action of SiO_2 -Al_2O_3 -CaO-ZnO-R_2O porous glass-ceramics

Using powder-sintering method,SiO2-Al2O3-CaO-ZnO-R2O porous glass-ceramics were produced for analysis. Five samples with different SiO2 /CaO ratios were used in the research. The mechanical properties, microstructures and textures of porous glass-ceramics are investigated by using differential thermogravimetric analysis/differential thermal analysis ( TGA/SDTA) ,X-ray diffraction ( XRD) ,and scanning electron microsco- py ( SEM) . The activity energy of crystallization ( E) and crystallization kinetics parameter ( k) were calculated based on the modified JMA equation. The Avrami parameter n was obtained according to Augis-Bennett function. The results show that the k value of No. 1 sample ( SiO2 /CaO = 61∶ 18) is the largest among all samples, which tends to crystallize more easily,and crystallization processes of all samples are observed bulk crystallization. The main crystal phase observed is parawollastonite ( clinorhombic system) with puncheon shape. Poreforming agents decomposed at 100 - 500 ℃ form a large number of closed pores with micron dimension and several semi-open pores distribute uniformly in the glass-ceramics matrix. This work may be expected to be favorable for industrial scale applications of porous glass-ceramics in the field of building thermal insulation.

Kinetics of Spherical Interface in Crystal Growth

The growth kinetics of spherical NiAl and CuZr crystals are studied by using molecular dynamics simulations.The growth rates of crystals are found to increase with the grain radius. The simulations show that the interface thickness and the Jackson α-factor increase as the growth proceeds, indicating that the interface becomes increasingly rough during growth. Due to the increasing interface roughening, the fraction of repeatable growth sites at interface f is proposed to actually increase in growth. An attachment rate, which is defined as the fraction of atoms that join the crystal interface without leaving, is used to approximate f, displaying a linear increase. With this approximation, we predict the growth rates as a function of the crystal radius, and the results qualitatively agree with those from the direct simulations.

Calcium sulfate whisker prepared by flue gas desulfurization gypsum:A physical–chemical coupling production process

In this paper,the solid waste desulfurization gypsum produced by coal-fired power plants was used as a raw material to prepare calcium sulfate whiskers with high application prospects.Calcium sulfate whiskers with uniform morphology and high aspect ratio can be prepared by hydrothermal method in sulfuric acid solution.A new process of desulfurization gypsum activated by high-energy grinding to reduce the reaction temperature and sulfuric acid concentration was developed.Through the comparison of product morphology,the best grinding time was determined to be 3.5 h.The mechanism of desulfurization gypsum through physical–chemical coupling to reduce energy consumption was clarified.The activation of desulfurization gypsum by grinding and the acidic environment provided by the sulfuric acid solution made the calcium sulfate solution reached rapid saturation and accelerated the nucleation rate.By calculating the conversion and crystallization rate of calcium sulfate whiskers,it was found that there were obvious"autocatalytic"kinetic characteristics during the crystallization process.

Theoretical insights into influence of additives on sulfamethoxazole crystal growth kinetics and mechanisms

In this work,the influence of the initial chemical potential gradient,stirring speed,and polymer type on sulfamethoxazole(SMX)crystal growth kinetics was systematically investigated through density functional theory(DFT)calculations,experimental measurements and the two-step chemical potential gradient model.To investigate the influence of different conditions on the thermodynamic driving force of SMX crystal growth,SMX solubilities in different polymer solutions were studied.Four model polymers effectively improved SMX solubility.It was further found that polyvinylpyrrolidone(PVP)and hydroxypropyl methyl cellulose(HPMC)played a crucial role in inhibiting SMX crystal growth.However,polyethylene glycol(PEG)promoted SMX crystal growth.The effect of the polymer on the crystal growth mechanisms of SMX was further analyzed by the two-step chemical potential gradient model.In the system containing PEG 6000,crystal growth is dominated by the surface reaction.However,in the system containing PEG 20000,crystal growth is dominated by both the surface reaction and diffusion.In addition,DFT calculations results showed that HPMC and PVP could form strong and stable binding energies with SMX,indicating that PVP and HPMC had the potential ability to inhibit SMX crystal growth.

One-step Crystallization Kinetic Parameters of the Glass-ceramics Prepared from Stainless Steel Slag and Pickling Sludge

One-step crystallization is one of the most energy conserving methods for glass-ceramics preparation.However,only a few kinetics studies focused on the glass-ceramics prepared by the one-step crystallization.The onestep crystallization kinetic parameters were studied using differential scanning calorimetry.The activation energy(Ea)and the Avrami parameter(n)were calculated as 152.79kJ·mol-1 and 4.39,respectively.These parameters indicate that continuous nucleation and three-dimensional crystal growth are the dominating mechanisms in the one-step crystallization process of the parent glass.The properties of the obtained glass-ceramics can be compared to the glass-ceramics prepared by the two-stage heat treatment and sintering method.This crystallization kinetics research can be used to evaluate the one-step crystallization potential of a parent glass.

Tailoring the Crystallization Behavior and Mechanical Property of Poly(glycolic acid) by Self-nucleation

Biocompostable poly(glycolic acid)(PGA)crystallizes slowly under fast cooling condition,leading to poor mechanical performance of the final products.In this work,a self-nucleation(SN)route was carried out to promote the crystallization of PGA by regulating only the thermal procedure without any extra nucleating agents.When self-nucleation temperature(Ts)decreased from 250℃ to 227℃,the nuclei density was increased,and the non-isothermal crystallization temperature(Tc)of PGA was increased from 156℃ to 197℃ and the half-life time(t0.5)of isothermal crystallization at 207℃ was decreased by 89%.Consequently,the tensile strength and the elongation at break of the PGA were increased by 12%and 189%,respectively.According to the change of Tc as a function of Ts,a three-stage temperature domain map(Domain I,II and III)was protracted and the viscoelastic behavior of the self-nucleation melt and the homogeneous melt was studied.The results indicated that interaction among PGA chains was remained in Domain IIb,which can act as pre-ordered structure to accelerate the overall crystallization rate.This work utilizes a simple and effective SN method to regulate the crystallization behavior and the mechanical properties of PGA,which may broaden the application range of resulting materials.

Enhancing the Crystallization Performance of Poly(L-lactide) by Intramolecular Hybridizing with Tunable Self-assembly-type Oxalamide Segments

In this work, hydroxyl-terminated oxalamide compounds N^(1),N^(2)-bis(2-hydroxyethyl)oxalamide(OXA1) and N^(1),N^(1)′-(ethane-1,2-diyl)bis(N^(2)-(2-hydroxyethyl)oxalamide(OXA2) were synthesized to initiate the ring-opening polymerization of L-lactide for preparation of oxalamide-hybridized poly(L-lactide)(PLA_(OXA)), i.e., PLA_(OXA1) and PLA_(OXA2). The crystallization properties of PLA were improved by the self-assembly of the oxalamide segments in PLA_(OXA) which served as the initial heterogeneous nuclei. The crystal growth kinetics was studied by HoffmanLauritzen theory and it revealed that the nucleation energy barrier of PLA_(OXA1) and PLA_(OXA2) was lower than that of PLA. Consequently, PLA_(OXA) could crystallize much faster than PLA, accompanied with a decrease in spherulite size and half-life crystallization time by 74.8% and 86.5%(T=125 ℃), respectively. In addition, the final crystallinity of PLA_(OXA1) and PLA_(OXA2) was 6 and 8 times higher, respectively, in comparison with that of neat PLA under a controlled cooling rate of 10 ℃/min. The results demonstrate that the hybridization of oxalamide segments in PLA backbone will serve as the self-heteronucleation for promoting the crystallization rate. The higher the content of oxalamide segments(PLA_(OXA2) compared with PLA_(OXA1)) is, the stronger the promotion effect will be. Therefore, this study may provide a universal approach by hybridizing macromolecular structure to facilitate the crystallization of semi-crystalline polymer materials.

Numerical investigation of the influence of kinetics and shape factor on barium sulfate precipitation in a continuous stirred tank

The effect of kinetics and shape factor on barium sulfate precipitation in a continuous stirred tank has been investigated numerically through solving the standard momentum and mass transport equations in combination with the moment equations for crystal population balance.The numerical method was validated with the literature data.The simulated results include the distribution of the local supersaturation ratio in the reactor,the mean crystal size,and the coefficient of variation.The simulation results show that the value of shape factor used in the model affected greatly the mean crystal size and the moments of the crystal size distribution.The influence of the kinetic expressions on the simulation is also analyzed.It is important to investigate the relationship of the shape factor with the precipitator type and other operation conditions to obtain reliable simulation results and suitable kinetic equations of crystal nucleation and growth rates.

Phase Evolution and Glass Formation in an Fe-Based Alloy

The understanding of phase competing is of pretty importance in designing high glass-forming systems. In this work, it has been investigated experimentally and theoretically the phase evolution and glass formation of a wedge-casting Fe-based alloy. The results indicated that the phase formation was sensitive to the wedge position, i.e., there were amorphous phase, Fe_(2)P, {Fe, Ni} and α-Fe precipitates as well as M_(23)B_(6) phase at the distances of 3, 10 and 20 mm away from the wedge-tip, respectively. These were closely connected with the variation of cooling rate, embodied in the heat transfer at the solidification process. Furthermore, we constructed the time–temperature-transformation (TTT) diagrams of the iron-based alloy and these crystal phases through calculating Rc-related functions. Finally, the glass-forming features of the wedge-shaped Fe-based alloy have been elucidated in accordance with a crystallization kinetics analysis of the recorded temperature data and the phase selection competition. This research provides us an insight into in-depth understanding bulk metallic glass from the perspective of kinetics competition of crystallization phases.