A kinetic study of the quartz–cristobalite phase transition

Cristobalite is a common silica polymorph in ceramics, as it can crystallize in SiO₂-rich systems during high temperature processes. Its occurrence in final traditional ceramic bodies remarkably affects their thermal expansion, thus playing an important role in the shrinkage upon cooling. The quartz–cristobalite transformation kinetics is investigated by in-situ isothermal X-ray powder diffraction experiments and then correlated to the average particle size (〈d〉) of the starting quartz using a model here developed. An Avrami-like rate equation, i.e. α(t) = 1 ? exp(? k × t)ⁿ, in which the n-term is assumed to account for the dependence on the average particle size, has provided the best fitting of theoretical to experimental data, yielding activation energy values that range from 181 to 234 kJ mol^?1, and exponential n-coefficients from 0.9 to 1.5. Ex-situ observations have demonstrated that the formation of cristobalite from quartz after 50 min, 2, 4 and 6 h at 1200 and 1300 °C, exhibits a remarkable dependence on 〈d〉 of quartz, showing comparable behaviours in the case of 〈d〉 equal to 15.8 and 28.4 μm, but significant differences for 〈d〉 of 4.1 μm. The formation of cristobalite is boosted remarkably at temperature higher than 1200 °C, with an increase by weight even of 500%, with respect to its content at lower temperature. The method of sample preparation (dry powder, wet powder and tablet of compressed dry powder) seems to influence the results only at temperature > 1200 °C and in the case of fine powder.     

Diffuse phase transition and high electric field properties of BaCeyTi1−yO3 relaxor ferroelectric ceramics

Pure perovskite BaCe_yTi_1−yO₃ ceramics with compositions y=0.10, 0.20 and 0.30 have been prepared by solid state reaction. The temperature and frequency dependence of dielectric properties (permittivity, dielectric loss and dielectric modulus) of the ceramics has been investigated. A diffuse phase transition is typical for all the compositions, with a reduction of the Curie temperature with increasing Ce addition. If in the case of the sample with 0.10 Ce content, no frequency shift of the phase transition temperature (T_m) is noticed, a relaxor-like ferroelectric character become predominant for concentrations 0.20 and 0.30. The ceramic with y=0.20 presents higher tunability, a reduced hysteretic behavior and reasonable low dielectric losses at room temperature, which makes this composition a very good candidate for tunable capacitors applications.     

Investigation of morphotropic phase boundaries in PIN–PSN–PT relaxor ferroelectric ternary systems with high Tr-t and Tc phase transition temperatures

New morphotropic phase boundary (MPB) compositions with relatively high T_cs were projected in Pb(In_1/2Nb_1/2)O₃–Pb(Sc_1/2Nb_1/2)O₃–PbTiO₃ (PIN–PSN–PT) solid solution based on the perovskite tolerance factor, and were experimentally confirmed. The phase structure, dielectric, pyroelectric, piezoelectric and ferroelectric properties of PIN–PSN–PT ceramics were investigated. The rhombohedral–tetragonal phase transition temperatures T_r-t on the order of 189–210 °C, Curie temperatures T_c on the order of 274–285 °C and piezoelectric coefficients d₃₃ in the range of 310–360 pC/N, were achieved in xPIN– (1 − x)PSN–0.37PT (x = 0.15–0.23) ceramics, demonstrating a promising relaxor–PbTiO₃ system with high phase transition temperatures. In addition, the maps of T_c, T_r-t, d₃₃ and ε_r with respect to composition were established, based on which, a clear direction for composition screening in future crystal growth of the PIN–PSN–PT system was given.     

Reversible ferroelectric phase transition of 1,4-diazabicyclo [2,2,2]octane N,N′-dioxide di(perchlorate)

1,4-Diazabicyclo [2,2,2]octane N,N′-dioxide di(perchlorate), C₆H₁₄N₂O₂^2 +·2ClO₄⁻, was synthesized and separated as colorless block crystals. Differential scanning calorimetry detected that this compound underwent a reversible phase transition at ca. 216 K with a hysteresis of 5.5 K width, which was also confirmed by dielectric measurements. Single crystal X-ray diffraction data suggested that there was a transition from a room temperature phase with the space group of P2₁/c (a = 6.815(7) Å, b = 12.644(13) Å, c = 8.676(9) Å, β = 101.466(15)°, V = 732.7(13) ų, Z = 4) to a low temperature one with a space group of P2₁ (a = 9.892(8) Å, b = 12.559(10) Å, c = 17.401(13) Å, β = 92.065(8)°, V = 2160(3) ų, Z = 2). Crystallographic analysis showed that it belonged to chiral space group P2₁ with ferroelectric behaviors, and a typical ferroelectric feature of electric hysteresis loop was obtained in the low temperature phase. The disorder-order transformation of H₂-Dabcodo^2 + cation and ClO₄⁻ anion as well as the change of hydrogen bonds may drive the phase transition.     

Effect of brookite phase on the anatase–rutile transition in titania nanoparticles

Nanosized TiO₂ powders were prepared from the precipitation in the TiCl₄ precursor under various pH values. The prepared titania existed in the form of nanocrystalline anatase with some brookite, which was evidenced by X-ray diffraction analysis and Raman spectroscopy. The average crystallite sizes of the TiO₂ particles heat treated at 450 °C for 2 h are in the range of 7–9 nm. The lattice constant c of anatase increased with increasing the synthesized pH value, whereas the volume fraction of the brookite phase increased with decreasing the synthesized pH value. The beginning and ending temperatures for the anatase–rutile transformation were found to decrease with increasing the volume fraction of the brookite phase. The brookite phase in the powder is responsible for enhancing the anatase–rutile transition.     

Structure and phase formation in the Ti–Al–Nb system in the thermal explosion mode

This paper presents the results of the structure and phase formation in the Ti/Nb/2Al, Ti/Nb/2.5Al and Ti/Nb/3Al systems in the thermal explosion mode of self-propagating hightemperature synthesis. The morphology, phase composition, microstructure, and physical properties have been studied. It has been found that compounds with the highest content of aluminum have the most homogeneous composition and the lowest porosity. The main phase of the synthesis product is a phase based a solid solution of Nb in γ-TiAl.     

Are the parameters of the empirical law dependent on the dielectric properties of the ferroelectric relaxors?

The empirical law, ? = ?_m/[1 + (T − T_m)^γ/2σ²] or ? = ?_m/{1+[(T − T_m)/Δ]^ξ}, are usually used to estimate the degree of the diffused phase transition of the ferroelectric relaxors. As the values of γ or σ (ξ or Δ) are larger, the diffused phase transition is more obvious. However, values of T_m and ?_m are different upon different compositions, dopants, synthesized methods, and others. Are the values of γ and σ (ξ and Δ) affected by T_m or ?_m which represents the characteristics of the relaxors? In this paper, we utilize the experimental data of the (1 − x)Pb(Fe_2/3W_1/3)O₃–xPbTiO₃ ceramic system and the mathematical derivation to conclude that the values of γ and σ (ξ and Δ) are not affected by ?_m and T_m. Therefore, they can be used to properly describe and compare the degree of the diffused phase transition between the different samples with different compositions, dopants and synthesized methods since the noises (T_m and ?_m) are filtered in these empirical laws. Furthermore, we can clearly clarify the physical meaning of theses parameters, γ and σ (ξ and Δ), as well as their effect on the composition for the further study.     

Ionic conductivity across the disorder–order phase transition in the SmO1.5–CeO2 system

Samples of Sm_xCe_1 ? xO_2 ? δ (0.05 ≤ x ≤ 0.55) were prepared by solid-state reactions and the disorder–order phase transition and grain ionic conductivity were investigated using XRD and ac impedance spectroscopy technique, respectively. For 0 ≤ x ≤ 0.35 the material has a fluorite structure and gradually stabilizes into a C-type rare-earth structure at 0.40 ≤ x ≤ 0.55 because of oxygen-vacancy ordering. The highest grain ionic conductivity observed is 0.0565(37) S cm^?1 at 700 °C for Sm_0.20Ce_0.80O_2 ? δ with an associated activation energy (E_A) of 0.791(7) eV. The slopes for E_A and pre-exponential factor change during phase transition and the conductivity decreases monotonically. Upon comparison of the E_A between the SmO_1.5–CeO₂ and NdO_1.5–CeO₂ systems, it is seen E_A for the SmO_1.5–CeO₂ system is lower than NdO_1.5–CeO₂ system at compositions with less than 25% trivalent rare earth element while higher E_A is observed for the SmO_1.5–CeO₂ system at Nd/Sm concentrations above 25%.     

Numerical modeling of an electrostatically driven liquid meniscus in the cone–jet mode

A numerical model has been developed for an electrostatically driven liquid meniscus for a dielectric fluid. The model is able to calculate the shape of the liquid cone and the resulting jet, the velocity fields inside the liquid cone–jet, the electric fields in and outside the cone–jet, and the surface charge density at the liquid surface. The mathematical formulas with proper boundary conditions for the relevant physical processes are described in detail. The equations of continuity, momentum and electric potential are solved numerically with an iterative procedure developed for the model. The results of the present model fit well with experimental observations of the cone shape and jet formation.     

Kinetics of the melt – Form II phase transition in isotactic random butene-1/ethylene copolymers

The kinetics of formation of the Form II mesophase from the melt has been investigated as a function of the concentration of ethylene chain defects in isotactic random butene-1/ethylene copolymers, using standard and fast scanning chip calorimetry. Presence of ethylene co-units in the butene-1 chain leads to a distinct reduction of the melt – Form II phase transformation rate which has been quantified by evaluation of the critical cooling rate to suppress ordering, and by isothermal analysis of half-times of Form II mesophase formation. For the first time, the temperature-dependence of the rate of Form II mesophase formation has been evaluated for butene-1/ethylene random copolymers and the butene-1 homopolymer. This study needs to be considered as a complementary addendum to former work about the Form II to Form I polymorphic transformation in isotactic random butene-1/ethylene copolymers.     

Can the COVID-19 Pandemic Disrupt the Current Drug Development Practices?

Therapeutics and vaccines against the COVID-19 pandemic need to be developed rapidly and efficiently, given its severity. To maximize the efficiency and productivity of drug development, the world has adopted disruptive technologies and approaches in various drug development areas. Telehealth, characterized by the heavy use of digital technologies; drug repositioning strategies, aided by computational breakthroughs; and data tracking tool hubs, enabling real-time information sharing, have received much attention. Moreover, drug developers have engaged in open innovation by establishing various types of collaborations, many of which have been carried out across nations and enterprises. Finally, regulatory agencies have attempted to operate on a more flexible review basis than before. Although such disruptive approaches have partly reshaped drug development practices, issues and challenges remain before the completion of this paradigm shift in conventional drug development practices for the post-pandemic era. In this review, we have highlighted the role of a collaborative community of experts in order to figure out how disruptive technologies can be fully integrated into the current drug development practices and improve drug development efficiency for the post-pandemic era.     

Effect of protein fusion on the transition temperature of an environmentally responsive elastin-like polypeptide: a role for surface hydrophobicity?

The limited throughput, scalability and high cost of protein purification by chromatography provide motivation for the development of non-chromatographic protein purification technologies that are cheaper and easier to implement in a high-throughput format for proteomics applications and to scale up for industrial bioprocessing. We have shown that genetic fusion of a recombinant protein to an elastin-like polypeptide (ELP) imparts the environmentally sensitive solubility property of the ELP to the fusion protein, and thereby allows selective separation of the fusion protein from Escherichia coli lysate by aggregation above a critical temperature (T(t)). Further development of ELP fusion proteins as widely applicable purification tools necessitates a quantitative understanding of how fused proteins perturb the ELP T(t) such that purification conditions (T(t)) may be predicted a priori for new recombinant proteins. We report here the effect that fusing six different proteins has on the T(t) of an ELP. A negative correlation between T(t) and the fraction hydrophobic surface area on the fused proteins was observed, which was determined from computer modeling of the available three-dimensional structure. The thermally triggered aggregation behavior of ELP-coated, functionalized gold colloids as well as ligand binding to the tendamistat-ELP fusion protein support the hypothesis that hydrophobic surfaces in molecular proximity to ELPs depress the ELP T(t) by a mechanism analogous to hydrophobic residue substitution in the ELP repeat, Val-Pro-Gly-Xaa-Gly.     

Can the regenerative potential of an alkali-free bioactive glass composition be enhanced when mixed with resorbable β-TCP?

The addition of resorbable β-tricalcium phosphate (β-TCP) to other bone substitute materials such as hydroxyapatite (HA) has been pointed out as a suitable strategy to enhance the regenerative potential of bone grafts made thereof. To check the generalization of this hypothesis, a new synthetic composite bone graft material consisting of a mixture of 30 vol% of pure β-TCP and 70 vol% of FastOs^®BG (an alkali-free bioactive glass - BG) was prepared and tested in vivo. The in vivo performance of the new synthetic bone graft (30β-TCP-70FastOs^®BG) was compared with those of FastOs^®BG alone and of adbone^®BCP, a biphasic calcium phosphate, consisting of 75% of HA and 25% of β-TCP. Two defects with 4 mm diameter were performed in Wistar rats calvaria and filled with the bone graft materials. The animals were sacrificed after 9 weeks of implantation and the calvaria was excised. Empty bone defects were used as negative control. The percentages of new bone formed (von Kossa staining) were always higher in the treated groups (FastOs^®BG, 30β-TCP-70FastOs^®BG and adbone^®BCP) than in empty group. There were differences with statistical significance between empty and FastOs^®BG groups and between empty and adbone^®BCP groups. But the differences observed between empty and 30β-TCP-70FastOs^®BG groups were less remarkable. The results demonstrated the superior bone regeneration ability of FastOs^®BG alone, which was not further enhanced by adding β-TCP in the composition, confirming its already proven regenerative potential.     

Can Drying Be an Alternative Tissue Preservation Method in Cancer Research Biobanking?

The currently available methods for conservation of biobank material are mainly based on formalin fixation or the use of different freezing techniques. For molecular biological analysis, it is common to use quick freezing and low-temperature storage of the tissue materiel. This is a very energy-intensive and expensive method that requires advanced infrastructure, including monitoring and control procedures. The purpose of this work has been to study drying as an alternative process to cryogenic storage of undried biobank material, especially for use in cancer research groups.

Fast freezing has been shown to be suitable to preserve the integrity of RNAs, while traditional formalin fixation preserves proteins and thus morphology in a good way. Various fresh-harvested murine tissues, such as lung, heart, skeletal muscle, liver, and kidney, were quickly frozen in liquid nitrogen and then subsequently dried at +5°C and ?10°C, respectively, in a heat pump dryer. After drying, the RNA integrity was measured. The dried material was then stored for five months at +4°C and ?20°C in commercial refrigerators, with subsequent measurement of RNA integrity. Dried materials were also evaluated with light microscopy and by electron microscopy with respect to tissue and cell structure. The same pattern was found for all five murine tissues. We conclude that drying at temperatures below 0°C is most careful to preserve the RNA integrity, with approximately the same RIN score of dried and non-dried samples for all five tissues. What characterized the general pattern of stored samples is that drying leads to a preservation of RNA integrity. Moreover, architecture in tissue resembled normal sections prepared from fresh tissue. In some places in the rim of the tissue sample, the lung tissue revealed alveolar-like morphology. In the electron microscope, few organelles other than the nuclei could be identified. Drying of biological material is a promising and cost-effective method for biobanks that store tissue, compared to cryogenic storage of undried material. Degradation of RNA, measured by the RIN number, is a critical factor in storing biobank tissue. In low-temperature dried material, the RIN factor is at the same level as storage of undried material at cryogenic temperatures, which is the common way of storing biobank material today. In this study, a heat pump dryer was used successfully to establish drying temperatures below and above the freezing point of the material. Further work has to be done in order to study different drying methods, drying conditions, and drying costs.     

Till which pressures the fluid phase EOS models might stay reliable?

This paper examines the performance of three fluid phase equations of state in predicting the available very high-pressure data of n-pentane, n-hexane, cyclohexane, toluene, dichloromethane, chloroform and methanol. It is assumed that the key for success at such pressures is establishing the appropriate interrelation between the densities of saturated liquids and the imaginary infinity pressure states. The recently proposed EOS that combines SAFT with the cohesive term of cubic EOS (SAFT + Cubic) most likely satisfies this criterion. According to this model, the saturated liquid densities at T_r = 0.4 are approximately 2.1 ± 0.1 times smaller than the densities predicted at the infinity pressure. With this ratio SAFT + Cubic yields reliable density estimations as far as the substances remain liquid (stable or metastable) in all the considered cases. Its pressure limit for accurate predictions of the auxiliary properties such as sound velocities and bulk moduli appear to be lower, typically around 1 GPa.