Temperature Change Of Crystal Research Articles

Investigation the optical and structural properties of Mn-doped Sb2S3 nanocrystals embedded in host glass

The search for earth-abundant and non-toxic elements is essential for the manufacture of sustainable optical devices. In this context, dilute magnetic semiconductor (DMS) xMn-doped Sb2S3 nanocrystals (NCs) embedded in host glass were synthesized by the fusion method. Differential Thermal Analysis shows evidence of Sb2S3 phase crystallization peak and changes in glass transition and crystallization temperatures of the host glass with the presence of xMn-doped Sb2S3 NCs. Transmission electron microscopy images show the formation of xMn-doped Sb2S3 NCs with increasing size (2.1–3.8 nm) as a function of concentration (x = 0.00 to 0.40), respectively. X-ray diffraction measurements reinforced the evidence for the orthorhombic structure of xMn-doped Sb2S3 NCs embedded in glass. Energy dispersive X-ray spectroscopy analyses confirm the S, Sb and Mn precursor elements of DMS NCs. Atomic and magnetic force microscopy measurements show the magnetic contrast patterns resulting from the incorporation of Mn atoms into the Sb2S3 structure. The electronic paramagnetic resonance spectrum confirms the presence of Mn2+ ions (3d5) located in the crystal field of the Sb2S3 semiconductor due to six hyperfine transitions. The redshift of the Raman vibrational mode (1Ag) with increasing xMn concentration gives strong evidence for the presence of Mn2+ ions in sulfur vacancies (VS) in the Sb2S3 unit cell. Optical absorption and photoluminescence (PL) spectroscopy measurements for xMn-doped Sb2S3 NCs show the subtle tunable redshift of the band gap and excitonic recombination in the green-red region, with increasing x concentration. PL confirms that dopant Mn2+ ions fill VS2 that are dominant in Sb2S3. Therefore, the position of the energy states after the increasing concentration of Mn2+ dopant ions gives rise to insight into luminescence for future research scenarios and applications involving sustainable DMS NCs.

Development of Pickering water-in-oil emulsions using a dual stabilization of candelilla wax and acylated EGCG derivatives to enhance the survival of probiotics (Lactobacillus plantarum) powder.

Probiotics have considerable interest due to their inseparable link to human health. However, probiotic products are seriously challenged during processing, preservation, and intake. Food-grade probiotic delivery systems need to be further explored as an effective way to enhance cell viability. In this study, water-in-oil (W/O) Pickering emulsions were fabricated by adding candelilla wax (CLW) as a network stabilizer based on acylated EGCG derivatives in the crystalline form as a Pickering stabilizer. The effects of acylated EGCG derivatives' concentration, CLW concentration, and oil phase volume fraction on the droplet size distribution, microstructure, and physical stability of Pickering emulsions were explored. The presence of CLW reduced the particle size and improved the physical stability of acylated EGCG-based emulsions, and the effect was more positive with increasing concentration. The protective effect of emulsions with different oil phase volume fractions on Lactobacillus plantarum during freeze-thaw cycles, storage, and gastrointestinal digestion was evaluated. The outer-phase physical barrier of W/O emulsions co-stabilized with acylated EGCG derivatives and CLW facilitated the sensitivity of probiotics to ice crystal growth, temperature changes, acidic environments, and digestive enzymes. The emulsions formulated with 40% oil phase volume fractions allowed Lactobacillus plantarum to survive up to 7.75 log CFU g-1 in the harsh gastrointestinal environment. The results offer promising strategies for applying W/O emulsion probiotic delivery systems in food processing, storage, and oral administration.

Dynamic evolution investigation on crystal size and morphology of sodium sulfate based on a combination of ultrasonic and image on-line testing

Crystallization is widely used in the fine chemical processes of purification and separation, where the crystal size variation, together with the crystallization temperature, plays a crucial role. An online measurement system for the simultaneous characterization of crystal size and other morphological parameters was studied, in which an ultrasonic spectrometer and image analysis was effectively combined for the monitoring and understanding of key parameters during the entire crystallization of sodium sulfate solution. The change in crystallization temperature, crystal size, and morphology at different cooling rates and stirring rates were analyzed, which shows that the cooling rate plays a dominant role in the variation of the critical time of crystal precipitation and average crystal size. In the middle stage of the crystallization, the median diameter change obtained by the ultrasonic and image analysis is close together, with a relative deviation of less than 10%. While the aspect ratio is mainly distributed in the range of 1–1.6, the crystal size has a relatively stable growth rate. An ultrasonic spectrometer can be used to measure particle size distribution of higher concentrations compared with image analysis. The combination actually provides an effective complement to implementing straightforward testing during the relatively complete crystallization process.

Effect of gamma irradiation on shape memory, thermal and mechanical properties of polycaprolactone

In the present study, the effect of gamma irradiation on the shape memory, thermal and mechanical properties of polycaprolactone (PCL) was investigated. Triallylisocyanurate (TAIC) was used as crosslinker. It was found that gamma irradiation influence the shape memory and mechanical properties of PCL by introducing crosslinking in its network. The degree of crosslinking was analysed by gel content. Gel content up to 50% was obtained with 50 kGy irradiation dose. With the incorporation of crosslinking via irradiation, shape memory property was generated in PCL. Shape recovery up to 95% was observed with 25 kGy radiation dose. Thermal analysis by DSC showed no significant change in melting and crystallization temperature after irradiation. XRD analysis revealed that the crystallized domains of PCL remain intact after irradiation. Mechanical properties viz. tensile strength and Young's modulus increases with irradiation, meanwhile a decrease in elongation was observed. The findings revealed that crosslinking introduced through gamma irradiation along with TAIC is effective in tailoring the shape memory, thermal and mechanical properties of polycaprolactone for different applications.

Investigation of polyamide 12 isothermal crystallization through the application of the phase‐field model

AbstractCrystallization of polyamide 12 (PA12) is an essential process requiring thorough investigation for evaluating the mechanical properties after the polymer parts are manufactured. The change in crystallization temperature results in different crystallization behaviors for PA12. Hence, the crystal morphology of PA12 achieved provides important information about crystallization behavior, especially for those produced through additive manufacturing due to its heterogenous cooling rate in a single print bed. Considering the need of investigating PA12 crystallization using phase‐field modeling, this paper aims to simulate the spherulite morphology of PA12 undergoing isothermal crystallization. This model is compared with the spherulite morphologies obtained from the optical microscopy test. The model shows that PA12 spherulites have thicker dendrites when the isothermal temperature is higher. The present phase‐field model can determine the spherulite morphologies of bulk printed PA12 based on the crystallization condition and be used to evaluate the properties of the printed part.

Tuning isothermal crystallization kinetics by minor similar solute element substitution in novel La‐(AlGa)‐C metallic glasses

AbstractIn the present text, the effects of minor similar solute element Ga substitution for Al on the isothermal crystallization kinetics of novel light RE‐based La‐(AlGa)‐C metallic glasses (MGs) were systematically investigated between La60Al26Ga4C10 MG and the precursor La60Al30C10 MG by using phase analysis, Johnson–Mehl–Avrami and Arrhenius using x‐ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The incubation period, the accomplishment time of the whole process, and the diversity of both the precipitated phases and the varying trend of the local Avrami exponent are elevated by minor similar solute element Ga substitution for Al, respectively. Additionally, the Avrami exponent of different isothermal crystallization temperature changes from g n > 2.5 to a combination of values 1.5 < n < 2.5 and a value n > 2.5 given by minor similar solute element Ga substitution for Al, corresponding to the crystallization characteristics changing from crystallization with promoting nucleation rate to a combination of crystallization with a reducing nucleation rate and crystallization with promoting nucleation rate. Moreover, the isothermal crystallization process becomes more difficult after minor similar solute element Ga substitution for Al, due to the reduced Avrami exponent and the intensified local activation energy.

Pyroelectric-controlled bending of a self-trapped optical beam in a photorefractive iron doped lithium niobate crystal

We present the experimental demonstration of a self-trapped optical beam bending in a photorefractive Fe-doped lithium niobate (LN:Fe) crystal controlled by the pyroelectric effect. Formation of self-trapped beams with typical [Formula: see text]50[Formula: see text][Formula: see text]m diameter and large bending of [Formula: see text]140[Formula: see text][Formula: see text]m are depicted in a 1[Formula: see text]cm length LN:Fe crystal for a laser beam at 632.8[Formula: see text]nm wavelength and 0.5[Formula: see text]mW power with a 30∘C crystal temperature change. The self-trapped beam bending is opposite to the crystal [Formula: see text]-axis. The underlying physics is elaborated and numerical simulations are performed. The long-living waveguiding channels with controlled curvilinear trajectories are promising for optical information routing.

Polypropylene/talc foams with high weight-reduction and improved surface quality fabricated by mold-opening microcellular injection molding

Microcellular injection-molded part can save materials usage and reduce energy consumption. However, the part molded by conventional microcellular injection molding often encounters problems of a limited weight-reduction and poor surface quality. Focusing on these problems, this paper adopted mold-opening microcellular injection molding and talc as nucleating agent to prepare foamed polypropylene (PP) part. Different PP/talc composites were obtained by twin-screw extruder compounding, and their crystallization and rheological behaviors were investigated. The results show that talc can significantly promote PP crystallization, and the crystallization temperature changes slightly with talc content. However, the viscoelasticity of PP melt cannot be enhanced by the added talc. Then, the effects of packing time, mold-opening distance and talc content on the foaming behavior of PP were studied. It is found that a high packing pressure for long time can effectively eliminate the cells generated in melt filling process, thus a transparent part is obtained. With increasing packing time, the unfoamed skin layer of the part increases and cell size decreases. With increasing mold-opening distance, cell density increases. At a same mold-opening distance, cell density remarkably increases because of the heterogeneous nucleation of talc, thus cell size decreases. When talc content is 10 wt.% and weight-reduction of the part is 62.1%, the average cell size is 56.5 μm and the cell density reaches 1.54 × 107 cells/cm3. Because the high packing pressure is employed in the mold-opening microcellular injection molding, the surface quality of the part is improved.

Enhanced ferroelectric properties of P(VDF-TrFE) thin film on single-layer graphene simply adjusted by crystallization condition

Ferroelectric polymer/graphene hybrid systems have received considerable attention due to their promising utilization in flexible electronics. The crystallization of ferroelectric polymers such as poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) can obviously affect the electronic properties of the hybrid systems. Here, the effects of thermal treatment temperature and crystallization temperature on the structure, morphology, and piezoelectric/ferroelectric properties of P(VDF-TrFE) on graphene substrate are reported. Moreover, the dependence of coercive voltage and piezoelectric coefficient (d33) on thermal treatment temperature or crystallization temperature is explored. It is identified that coercive voltage is only relying on the crystallization temperature other than thermal treatment temperature. Once crystallization temperature changes, both coercive voltage and d33 alter significantly and an optimum crystallization temperature exists at which the sample shows the best properties. The relationship between structure and piezoelectric/ferroelectric properties is built. These findings provide useful guidance for fabricating piezoelectric/ferroelectric P(VDF-TrFE)/graphene devices with high performance.

Mechanism of Nano-Structuring Manipulation of the Crystallization Temperature of Superlattice-like [Ge8Sb92/Ge]3 Phase-Change Films.

Superlattice-like (SLL) phase-change film is considered to be a promising phase-change material because it provides more controllabilities for the optimization of multiple performances of phase-change films. However, the mechanism by which SLL structure affects the properties of phase-change films is not well-understood. Here, four SLL phase-change films [Ge8Sb92(15 nm)/Ge (x nm)]3 with different x are fabricated. Their behaviors of crystallization are investigated by measuring sheet resistance and coherent phonon spectroscopy, which show that the crystallization temperature (TC) of these films increases anomalously with x, rather than decreases as the interfacial effects model predicted. A new stress effect is proposed to explain the anomalous increase in TC with x. Raman spectroscopy reveals that Raman shifts of all phonon modes in SLL films deviate from their respective standard Raman shifts in stress-free crystalline films, confirming the presence of stress in SLL films. It is also shown that tensile and compressive stresses exist in Ge and Ge8Sb92 layers, respectively, which agrees with the lattice mismatch between the Ge and Ge8Sb92 constituent layers. It is also found that the stress reduces with increasing x. Such a thickness dependence of stress can be used to explain the increase in crystallization temperature of four SLL films with x according to stress-enhanced crystallization. Our results reveal a new mechanism to affect the crystallization behaviors of SLL phase-change films besides interfacial effect. Stress and interfacial effects actually coexist and compete in SLL films, which can be used to explain the reported anomalous change in crystallization temperature with the film thickness and cycle number of periods in SLL phase-change films.

A Method to Increase the Frequency Stability of a TCXO by Compensating Thermal Hysteresis.

Due to the rapid growth of electronic information technology, the need for the higher stability of crystal oscillators has increased. The temperature-compensated X’tal (crystal) oscillator (TCXO), a type of crystal oscillator with high frequency stability, has been widely used in communications, sensor networks, automotive electronics, industrial control, measuring devices, and other equipment. The traditional TCXO only performs frequency compensation based on the current temperature, without considering the error caused by thermal hysteresis. As the frequency stability of the TCXO improves, the thermal hysteresis of the crystal oscillator has a negligible influence on the frequency stability of the crystal oscillator. This study measured different compensation tables for hysteresis curves at different temperatures and used a microprocessor to store the historical information of crystal temperature changes. Furthermore, corresponding algorithms were designed to select the correct values, according to the temperature change history, to compensate for the thermal hysteresis of the crystal oscillator error. Experiments show that this method can reduce the hysteresis error of the crystal oscillator from 700 to 150 ppb (−40 to 80 °C).

Selective laser sintering of polyamide 12/flame retardant compositions

In this work, various flame retardants (FR) and clays were added to polyamide 12 (PA12). The processability by Selective Laser Sintering (SLS), thermal behaviour and flame retardancy of these compounds were evaluated. The observations show an important impact on powder flowability of some formulations containing melamine cyanurate and melamine polyphosphate leading to difficulties during SLS process. The incorporation of FRs also leads to changes in melting and crystallization temperatures of polyamide as a function of the FR type. Furthermore, in order to evaluate the influence of the process on thermal properties of samples, a comparison between thermocompression (TC) and SLS techniques was performed for the formulations containing the flame retardants alone. The addition of flame retardants impacts the porosity of the SLS samples as a function of the FR type. For the additives which are able to melt during SLS process, a lower porosity was observed. Samples made by TC containing 30 wt% of ammonium polyphosphate, zinc diethylphosphinate and a pentaerythritol ester of methane phosphonic acid showed a better thermal stability and flame retardancy compared to the ones made by SLS, probably due to the porosity of the SLS samples and some degradation of the flame retardant by the laser beam. For the formulation containing only zinc borate, no difference was observed between TC and SLS. In order to evaluate possibly synergistic effects between flame retardants, binary and ternary formulations were prepared by SLS. On the whole, these formulations led to an improvement of flame retardancy compared to neat PA12. Moreover, XRD results showed the formation of borophosphates for binary and ternary formulations, indicating interactions between flame retardants. EDX results showed that at least 95% of the phosphorus remained in the residue for the formulations containing zinc borate, thus corroborating the results obtained by XRD. The partial substitution of zinc borate by kaolinite led to a further improvement of flame retardancy at the expense of a porosity increase in the samples.

Effects of oxidation on pyroxene visible-near infrared and mid-infrared spectra

Pyroxene spectral features in the visible near-infrared (VNIR) and mid-infrared (MIR) wavelengths are affected by oxidation resulting from traditional metamorphic processes as well as impact metamorphism. The observed effects are due to modifications in the crystal arising from changes in crystallization temperature or pressure or from substituting Fe3+ for Fe2+. Highly oxidized pyroxenes from terrestrial mantle xenoliths and shock experiments indicate that the spectral effects of oxidation are greater in clinopyroxene than orthopyroxene because clinopyroxene can accommodate more Fe3+ structurally. Changes in clinopyroxene VNIR related to increasing oxidation include a shift in the 0.8 μm absorption band to shorter wavelengths and a strengthening of the Fe2+↔Fe3+ intervalence charge transfer (IVCT) band, which reduces the band depth of the 1.0 μm feature by ~20%. Although shocked clinopyroxenes are oxidized to similar levels to that seen in the mantle xenoliths, the effects of shock overprint those of oxidation in the VNIR. These include a decrease of ~76% intensity of the 2.35 μm feature and a decrease of ~70% intensity of the 1.0 μm feature. In the MIR, the effects of oxidation and shock are minimal, resulting in a 5% overall decrease in band depth. These shifts and changes can be interpreted as a result of changes in the polyhedra surrounding the Fe cations which reduce crystal field splitting and the order of the crystal structure. Determination of planetary surface composition through VNIR remote sensing methods requires careful consideration of potential changes induced via shock and/or oxidation processes.

The effect of cooling on crystallization and physico-chemical properties of puff pastry shortening made of palm oil and anhydrous milk fat blends

Commercial shortenings and margarines are mainly produced via rapid cooling with scraped surface heat exchangers (SSHE) and therefore, controlling fat crystallization in the cooling process of these systems plays an important role. In this study, four batches of puff pastry shortening were produced from palm oil blends containing 25% and 50% anhydrous milk fat (AMF) using a bench-top SSHE. The outlet temperature of SSHE was investigated at 20 °C and 12 °C relating to the difference of crystallization temperature between palm oil and milk fat. Physico-chemical properties, crystal morphology and fat stability of these shortenings during storage at 5 °C were determined by various classical technologies including differential scanning calorimetry (DSC), polarized light microscopy (PLM), rheological and texture analyzer. Our results showed that fat blends crystallized at 12 °C had a stronger crystal network after production but the discrepancy of hardness diminished after the first storage week at 5 °C. Besides, the change of crystallization temperature did not affect significantly melting behavior as well as fat polymorphism of products. Upon storage, some big aggregates were detected in shortenings as a combined result of the recrystallization of palm fat crystals and the post-crystallization of milk fat triacylglycerols (TAGs). • Fat blends crystallized at 12 °C had a stronger crystal network than at 20 °C. • The discrepancy of hardness between fat blends diminished in storage at 5 °C. • Crystallization temperature (12 °C–20 °C) did not affect polymorphism of products. • Post-crystallization of AMF promoted the formation of big aggregates in products.

Effect of multiple recycling on properties of poplar fiber reinforced high density polyethylene wood-plastic composites

Wood-plastic composites have developed rapidly in recent years and are used in various fields, so their recycling is crucial. This research aims to understand the recyclability of poplar fiber (PF) reinforced high density polyethylene (HDPE) wood-plastic composites. The PF/HDPE composites were prepared by melt blending and injection molding process, and were recycled six times. The composites were subjected to mechanical tests, thermogravimetric analysis, differential scanning calorimetry and water absorption tests. The surface and tensile fracture surface of the composites were also observed by scanning electron microscope. The results showed that after recycling, the mechanical properties of PF/HDPE composites decreased and the flexural modulus decreased the most. The thermal stability of the composite gradually increased with the increase of recycling times. Recycling also improved crystallinity and crystallization and melting rates, but there is no significant change in crystallization and melting temperature. The water absorption of the recycled composites was reduced, and the waterproof performance is improved. Scanning electron microscopy revealed that the surface and interface defects of the composites were reduced by recycling, and PF was better combined with HDPE. Experimental results show that the performance change of the recycled composites is within an acceptable range and have application value in some fields.

Kinetic and Thermodynamic Studies for Zeolites Synthesis

Zeolites are compounds which have many applications in chemistry and industry; therefore, studies of synthesis of zeolites are of great importance. In this work, kinetic and thermodynamic study of hydrothermal crystallization for zeolite synthesis process performed at different time intervals (17, 20, 23 and 26 h) and various temperatures (70, 90, 110 and 125 0C). By time intervals we got out the rate of the zeolite synthesis reaction in this research was first order. The synthesized zeolites were similar in their crystallinity according to the Zeolites synthesis at different of the time intervals. The thermodynamic parameters indicated that the change in Gibbs free energy was negative value. The degrees of crystallinity of the synthesized zeolites decreased with increasing the hydrothermal crystallization temperature. Moreover, the change of hydrothermal crystallization time and temperature caused synthesis of different types of zeolites. The synthesized zeolite samples characterized by Infra-Red (IR), X-ray diffraction (XRD), X-ray Fluorescence (XRF) and scanning electron microscopy (SEM). The variation of chemical compositions led to differences in morphologies and crystallinity of the synthesized zeolites.

Temperature dependence of the C13 hyperfine structure of the negatively charged nitrogen-vacancy center in diamond

The nitrogen-vacancy (NV) center is a well utilized system for quantum technology, in particular quantum sensing and microscopy. Fully employing the NV center's capabilities for metrology requires a strong understanding of the behavior of the NV center with respect to changing temperature. Here, we probe the NV electronic spin density as the surrounding crystal temperature changes from 10 K to 700 K by examining its $^{13}$C hyperfine interactions. These results are corroborated with \textit{ab initio} calculations and demonstrate that the change in hyperfine interaction is small and dominated by a change in the hybridization of the orbitals constituting the spin density. Thus indicating that the defect and local crystal geometry is returning towards an undistorted structure at higher temperature.

PHBV-graft-GMA via reactive extrusion and its use in PHBV/nanocellulose crystal composites

Reactive extrusion was used for dicumyl peroxide (DCP)-initiated grafting of glycidyl methacrylate (GMA) to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The effects of GMA and DCP content and their weight ratio on the GMA grafting percentage (GP%), the polymer melt viscosity, and the PHBV molecular weight were investigated. FTIR spectroscopy determined that the DCP did indeed initiate GMA grafting. However, the changes in both the zero-shear viscosity (η0) and the molecular weight suggested the existence of crosslinking products in the extruded polymers. A negative correlation between the degree of crystallinity (χc) of the PHBV-g-GMA and the GP% suggested the influence of chain branching on crystallinity. In addition, the GMA content was found as a key factor determining the GP%. The PHBV-g-GMA was used as a matrix polymer in cellulose nanocomposites to evaluate its effects on CNC dispersion and CNC-matrix adhesion relative to the unmodified PHBV matrix. The SEM images and the change in crystallization temperature suggested enhanced dispersion of CNC in a PHBV-g-GMA matrix. However, little increase in strength properties were found with CNC addition suggesting inadequate stress transfer between the matrix and CNCs.

Catalytic behavior of magnetic Ni–Zn alloy

Ni–Zn alloy with various compositions of zinc was synthesised using a sodium borohydride-assisted chemical reduction method. The as-synthesised Ni–Zn alloy samples were annealed at 673 K for 2 h in nitrogen atmosphere. The atomic absorption spectroscopy measurement reveals the zinc-rich composition in all alloy samples. Field emission scanning electron microscopy shows that the surface morphology of Ni–Zn alloys has a flake-like nature. The X-ray diffraction pattern of as-synthesised samples shows the presence of nickel hydroxide while the annealed samples show formation of Ni2Zn11 phase. The phase transition temperature of as-synthesised Ni–Zn alloy was observed using differential scanning calorimetry and crystallization temperature changes with zinc composition was also examined. The room temperature magnetic behaviour of both as-synthesised and annealed samples was studied using vibrating sample magnetometer. This shows that as-synthesised samples have a weak ferromagnetic nature and annealed samples have a soft ferromagnetic nature. The decreasing magnetization value and Curie temperature with zinc composition was observed. The catalytic activity of Ni–Zn alloy was studied for the reduction of 4-nitrophenol. The rate constant value changes with zinc composition in the alloy.

Preparation and characterization of poly(2‐methyl‐1,5‐pentamethylene oxamide) (PM52) polymer

Poly(2‐methyl‐1,5‐pentaneoxamide) (PM52) with relative viscosity up to 3.3 were synthesized using 2‐methyl‐1,5‐pentanediamine (M52) and dibutyl oxalate via spray/melt polycondensation. The obtained polyoxamide was characterized by FTIR, 1H‐NMR, WAXD, DSC, and TGA. The Tm of PM52 was 200°C with a heat of fusion (ΔHf) of 59.7 J·g−1, crystallization temperature of 125°C, and a crystallization enthalpy (ΔHc) of 42.6 J·g−1. Isothermal crystallization studies revealed a 2‐dimensional crystallization phenomenon which didn't vary with change in crystallization temperature. TGA analysis revealed that the thermal stability of PM52 compared well with commercial PA6, and XRD studies revealed an α form of crystal structure and that the polymers possessed good crystallinity. Saturated water absorption of 4.6 wt% was recorded for the new polyoxamide synthesized as compared with 10.6 wt% for commercial PA6; such properties are good for applications in the food industry, plastics, and electronics industry where dimensional stability is a key requirement.