Sharp Exothermic Peak Research Articles

Kinetics of the plastic crystal transition in neopentyl glycol

The thermal hysteresis exhibited in plastic crystal compounds greatly reduces their cyclic efficiency, limiting their potential for replacing current environmentally harmful refrigerants. A mechanistic understanding of the origins of this hysteresis has yet to be established. Here, we systematically investigate the transformation kinetics of the model plastic crystal, neopentyl glycol (NPG), through microscopic and calorimetric techniques. We reveal an asymmetry between the forward (heating) and reverse (cooling) transitions. We also demonstrate that the forward transformation is rate-limited by the rate of growth of rotationally disordered domains. In contrast, the reverse transformation is rate-limited by the nucleation of the ordered crystal domain, demonstrated by the sharp exothermic peaks in calorimetry and rapid self-nucleation phenomena observed optically. This nucleation limitation is largely responsible for the large thermal hysteresis in NPG, which we observe to be as large as 16.7 °C for an approximately 10 mg sample cooled at 0.5 °C min−1. These findings demonstrate the underlying origin of the thermal hysteresis and introduce a direction to mitigate hysteresis in plastic crystal transformations.

PREFORMULATION STUDIES OF NIOSOMAL GEL CONTAINING DIPIVEFRIN HYDROCHLORIDE FOR ANTIGLAUCOMATIC ACTIVITY

Objective: The present study was focused on developing and characterizing niosomal gel formulations for ocular controlled delivery of an adrenergic agonist; dipivefrin HCl. In the present study, the pre-formulation studies are showed towards the development of Novel formulation. Methods: Preformulation studies of drug were carried out for identification (physical appearance, melting point and UV spectrophotometric analysis), solubility profile, lipophilicity (Partition Coefficient), compatibility studies by FTIR and thermal behavior by DSC. Results: The melting point of dipivefrin HCl was found to be 147.6±3 °C. The log P value was found to be 3.14±0.02, from which it can be interpreted that drug is highly lipophilic in nature. The scanned λmax were found to be 254 nm. No significant changes were found when FTIR spectra of the physical mixture compared with FTIR spectra of pure drug and excipients. This indicates absence of any possible interaction between the drug and excipients which confirms the identity and purity of drug. DSC thermogram of pure drug showed a sharp exothermic peak at 131.202 °C (area=1726.267 mJ, delta H=575.422 J/g), indicating the crystal melting point of the drug. Conclusion: These results suggest that the dipivefrin HCl serve as suitable candidate for ocular drug delivery system.

Mechanical Crystallization of Amorphous Ti<sub>50</sub>Al<sub>30</sub>Ni<sub>20</sub> Alloy Prepared by Mechanical Alloying

Laser diffraction, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) were employed to characterize the particle size, morphology and structure of mechanically alloyed Ti50Al30Ni20 alloy. Cyclic amorphous-crystalline-amorphous phase transformations were investigated during mechanical alloying, using high-energy ball milling technique. After 20 h of milling, an amorphous/nanocrystalline phase was obtained. This amorphous/nanocrystalline phase tended to transform into crystalline grains after 50 h of milling. In a cyclic phase transformation, the obtained crystalline phase is transformed into the amorphous phase after 70 h of milling. This amorphous phase crystallized through a single sharp exothermic peak at 590°C. On the basis of our results, the destabilizing effect of the defects created by the milling media (balls), which leads to the cyclic transformations, depends on the input energy and milling time.

Characterization of cisplatin-loaded chitosan nanoparticles and rituximab-linked surfaces as target-specific injectable nano-formulations for combating cancer

The present study was carried out to develop cisplatin-loaded chitosan nanoparticles (CCNP) and cisplatin-loaded chitosan nanoparticle surface linked to rituximab (mAbCCNP) as targeted delivery formulations. The two formulations (CCNP and mAbCCNP) exhibited significant physicochemical properties. The zetapotential (ZP) values of CCNP and mAbCCNP were 30.50 ± 5.64 and 26.90 ± 9.09 mV, respectively; while their particle sizes were 308.10 ± 1.10 and 349.40 ± 3.20 z.d.nm, respectively. The poly dispersity index (PDI) of CCNP was 0.257 ± 0.030 (66.6% PDI), while that of mAbCCNP was 0.444 ± 0.007 (57.60% PDI). Differential scanning calorimetry (DSC) revealed that CCNP had endothermic peaks at temperatures ranging from 135.50 to 157.69 °C. A sharp exothermic peak was observed at 95.79 °C, and an endothermic peak was observed at 166.60 °C. The XRD study on CCNP and mAbCCNP revealed distinct peaks at 2θ. Four peaks at 35.38°, 37.47°, 49.29°, and 59.94° corresponded to CCNP, while three distinct peaks at 36.6°, 49.12°, and 55.08° corresponded to mAbCCNP. The in vitro release of cisplatin from nanoparticles followed zero order kinetics in both CCNP and mAbCCNP. The profile for CCNP showed 43.80% release of cisplatin in 6 h (R2 = 0.9322), indicating linearity of release with minimal deviation. However, the release profile of mAbCCNP showed 22.52% release in 4 h (R2 = 0.9416), indicating linearity with sustained release. In vitro cytotoxicity studies on MCF-7 ATCC human breast cancer cell line showed that CCNP exerted good cytotoxicity, with IC50 of 4.085 ± 0.065 µg/mL. However, mAbCCNP did not elicit any cytotoxic effect. At a dose of 4.00 µg/mL cisplatin induced early apoptosis and late apoptosis, chromatin condensation, while it produced secondary necrosis at a dose of 8.00 µg/mL. Potential delivery system for cisplatin CCNP and mAbCCNP were successfully formulated. The results indicated that CCNP was a more successful formulation than mAbCCNP due to lack of specificity of rituximab against MCF-7 ATCC human breast cancer cells.

Evaluation and Characterization of Tamarind Gum Polysaccharide: The Biopolymer

Polymers from natural sources are widely used as excipients in the formulation of pharmaceutical dosage forms. The objective of this study was to extract and further characterize the tamarind gum polysaccharide (TGP) obtained from Tamarindus indica as an excipient for biomedical applications. Double distilled water was used as a solvent for the extraction of gum while Ethyl alcohol was used as an antisolvent for the precipitation. The results of the Hausner ratio, Carr’s index and angle of repose were found to be 0.94, 6.25, and 0.14, respectively, which revealed that the powder is free-flowing with good flowability. The gum was investigated for purity by carrying out chemical tests for different phytochemical constituents and only carbohydrates were found to be present. The swelling index was found to be 87 ± 1%, which shows that TGP has good water intake capacity. The pH of the 1% gum solution was found to be neutral, approximately 6.70 ± 0.01. The ash values such as total ash, sulphated ash, acid insoluble ash, and water-soluble ash were found to be 14.00 ± 1.00%, 13.00 ± 0.05%, 14.04 ± 0.57% and 7.29 ± 0.06%, respectively. The IR spectra confirmed the presence of alcohol, amines, ketones, anhydrides groups. The contact angle was <90°, indicating favorable wetting and good spreading of liquid over the surface The scanning electron micrograph (SEM) revealed that the particle is spherical in shape and irregular. DSC analysis shows a sharp exothermic peak at 350 °C that shows its crystalline nature. The results of the evaluated properties showed that TGP has acceptable properties and can be used as a excipient to formulate dosage forms for biomedical applications.

Effect of CuO on the thermal kinetics and combustion properties of Al/MoO3 thermite prepared by ball milling

To explore the influence of CuO additive on the thermal kinetics and combustion performance of thermite, Al/MoO3 thermite composites with different mass fractions of CuO were prepared by ball milling. Field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), and differential scanning calorimeter (DSC) were used to test the samples. From the DSC results, Al/MoO3 thermite and Al/CuO thermite released 1066 J/g and 849 J/g heat, respectively. The peak temperature of the exothermic reaction was 560.22 °C and 609.43 °C. Interestingly, the Al/MoO3 thermite with 5% CuO released higher heat, about 1747 J/g. The temperature of the exothermic peak was also greatly advanced to 526 °C. Thermodynamic analysis results showed that the activation energy (Ea) of Al/MoO3/5% CuO thermite was merely 184.75 kJ mol−1, which was a decrease of 18.3% and 20.8% of the Al/MoO3 and Al/CuO thermite. The reaction mechanism function of Al/MoO3 thermite, Al/MoO3/5% CuO and Al/CuO thermite can be set as f(α)=1−α. The fast electric heating wire ignition experiment showed that the flame brightness of the Al/MoO3/5% CuO thermite was the brightest and the burning time was the longest. Surprisingly, when the mass fraction of CuO additives in Al/MoO3 thermite reached 10% and 20%, the thermal kinetics and combustion performance of the thermite were completely changed. There was a violent and sharp exothermic peak accompanied by a large amount of heat release of 2042 J/g and 2252 J/g, respectively. The reaction mechanism of Al/MoO3 thermite with 10% and 20% CuO addition can be set as f(α)=3/2∗(1−α)[−ln(1−α)]1/3. The burning speed became faster and the flame was bright with sparks. This work lays the foundation for the further study of the thermite mechanism.

PREPARATION OF ACYCLOVIR-ISONICOTINAMIDE COCRYSTAL BY SOLVENT EVAPORATION METHOD WITH METHANOL AND ISOPROPANOL

PREPARATION OF ACYCLOVIR-ISONICOTINAMIDE COCRYSTAL BY SOLVENT EVAPORATION METHOD WITH METHANOL AND ISOPROPANOL. Acyclovir is a nucleoside synthetic analog antiviral group used in the treatment of Herpes simplex virus (HSV-1 &amp; HSV-2) and Varicella zoster virus (VZV). Acyclovir has low water solubility, so it needs to be modified in the form of cocrystal with isonicotinamide. This study aims to obtain the physical characteristics produced by acyclovir-isonicotinamide cocrystal (1:1) made through the solvent evaporation method with methanol and isopropanol. The crystalline formed is characterized by DSC, PXRD, FT-IR and SEM. The characterization results showed the presence of new crystals that formed between acyclovir-isonicotinamide in methanol and isopropanol solvents. Thermograms showed sharp exothermic peaks at 183.31°C and 186.24°C. The diffractogram showed a new peak at 2θ = 5.19 and 5.82. The spectrum showed a shift in wavelength in the cocrystal formed. The cocrystal has a different morphology compared with parent drug and coformer on analysis using SEM. This research shows that acyclovir can form cocrystal with isonicotinamide by solvent evaporation method with methanol and isopropanol.

PREFORMULATION STUDIES OF PILOCARPINE HYDROCHLORIDE AS NIOSOMAL GELS FOR OCULAR DRUG DELIVERY

Objective: Pilocarpine hydrochloride is a direct acting cholinergic parasympathomimetic agent which directly stimulates cholinergic receptor (M3). It is a drug used in the treatment of chronic open-angle glaucoma for over 100 years. Designing a new ophthalmic dosage form for pilocarpine hydrochloride compels performing preformulation studies for drug. Therefore, the current aim of the study was to investigate some of the important physicochemical properties of pilocarpine hydrochloride which can help to select subsequent approaches during the development of niosomal gel for ocular use.&#x0D; Methods: Preformulation studies of drug were carried out for identification (physical appearance, melting point, and UV spectrophotometric analysis), solubility profile, lipophilicity (partition coefficient), compatibility studies by Fourier-transform infrared (FTIR) spectroscopy, and thermal behavior by differential scanning calorimetry (DSC).&#x0D; Results: The melting point of pilocarpine hydrochloride was found to be 204 ± 3○C. The log P value was found to be 1.12 ± 0.02, from which it can be interpreted that drug is highly hydrophilic in nature. The scanned λmax was found to be 215 nm. No significant changes were found when FTIR spectra of physical mixture compared with FTIR spectra of pure drug and excipients. This indicates absence of any possible interaction between the drug and excipients which confirms the identity and purity of drug. DSC thermogram of pure drug showed a sharp exothermic peak at 191.923○C (area=68.890 mJ, delta H = 22.963 J/g), indicating the crystal melting point of the drug.&#x0D; Conclusion: These results suggest that the pilocarpine hydrochloride serves as suitable candidate for ocular drug delivery system.

Study on Thermal Decomposition Behavior, Gaseous Products, and Kinetic Analysis of Bis-(Dimethylglyoximato) Nickel(II) Complex Using TG-DSC-FTIR-MS Technique

The fiber-like bis-(dimethylglyoximato) nickel(II) complex, Ni(DMG)2 was successfully synthesized. The obtained samples were characterized by SEM-EDS, FT-IR, XRD, and XPS. The TG-DSC-FTIR-MS coupling technique was used to characterize the thermal decomposition behavior and evolved gas analysis of Ni(DMG)2. The non-isothermal decomposition reaction kinetic parameters were obtained by both combined kinetic analysis and isoconversional Vyazovkin methods. It was found that Ni(DMG)2 begins to decompose at around 280 °C, and a sharp exothermic peak is observed in the DSC curve at about 308.2 °C at a heating rate of 10 °C·min−1. The main gaseous products are H2O, NH3, N2O, CO, and HCN, and the content of H2O is significantly higher than that of the others. The activation energy obtained by the combined kinetic analysis method is 170.61 ± 0.65 kJ·mol−1. The decomposition process can be described by the random nucleation and growth of the nuclei model. However, it was challenging to attempt to evaluate the reaction mechanism precisely by one ideal kinetic model.

Microwave synthesis of nanocrystalline LaCoO3 samples and their catalytic activity towards decomposition of isopropanol

Nanocrystalline LaCoO3 powders were fabricated via the sol–gel microwave-induced combustion approach using metal nitrates as oxidant and citric acid as fuel. Calcination of the precursor was performed in the temperature range 400–800 °C. The precursor of the LaCoO3 powder as well as the calcination products were investigated using thermal analysis (TGA and DTA), FTIR, XRD and N2 adsorption techniques. In a dynamic air atmosphere, calcination was implemented in the temperature range 400–800 °C. XRD patterns show the fabrication of the perovskite rhombohedral phase of LaCoO3. The average nanoparticle size calculated from the XRD patterns was in the range 8–21 nm. Surface area measurements calculated from the N2 adsorption isotherms show low surface area values. The porosity of these materials was identified to be microporous in nature. SEM and TEM tests endorsed the findings. Analysis of TGA and DTA showed a sharp exothermic peak of about 358 °C and a steady weight loss of up to about 600 °C. The vapor-phase dehydration/dehydrogenation of isopropanol, in the temperature range 350–425 °C, was adopted to assess the catalytic performance. The activity of the LaMnO3 catalysts is mainly directed towards the dehydrogenation reaction forming acetone as a main product. The maximum yield was found for the sample calcined at 600 °C. A strong correlation was identified between the selectivity of dehydrogenation and the redox couple species evaluated. A potential reaction mechanism was suggested that would be compatible with the data obtained.

Advanced Li Metal Batteries: Thermal Safety Evaluation, Analysis and Mechanistic Elucidation

High theoretical capacity coupled with low operating potential makes Lithium the most promising choice for next-generation batteries. Replacing graphite by Li metal can enhance the energy density three times as compared to conventional Li-ion battery. Lithium is also an essential part of the next generation high energy batteries such as Lithium-Sulphur and Lithium-air batteries. However, the high reactivity of Li metal with electrolyte leads to dendritic growth, poor cycle life and safety hazards in Li metal batteries. Till date, there has been no study on the thermal characteristics of Li metal batteries. The thermal characteristics of Li metal batteries using advanced multiple-mode calorimetry (MMC) for the coin cell format under fully charged and discharged conditions is studied. In the conventional differential scanning calorimetry (DSC) ex-situ studies of a component or two from the battery, possibly could lead to some artifacts. Therefore, MMC is utilized to directly study the thermal behavior of whole coin cell comprising anode, cathode, electrolyte, and separator with thermally stable leak proof gasket till 300 oC. Thermal runaway of two types of Li metal batteries with different chemistries namely Li-Sulfur and Li-NMC are measured and compared. The MMC of Li-S battery coin cell in fully charged conditions showed a sharp exothermic peak positioned at 180 °C originating from the reaction between the Li metal and sulfur in presence of the electrolyte. Though Li-S batteries are assumed to be safer, an exothermic reaction between Li and S cathode leads to thermal runaway once the Li metal melts. The MMC of Li-NMC cell in the coin cell format also exhibits endothermic and exothermic peaks arising from the melting of Li and reaction of Li with electrolyte/cathode. This exothermic reaction leads to thermal runaway in Li-NMC around 180°C. The detailed endothermic and exothermic heat generation values in J/g, peak temperature, its source based on interfacial reactions and mechanistic elucidation will be discussed.

Electrospun nanofibers of poly (acrylonitrile-co-itaconic acid)/silver and polyacrylonitrile/silver: In situ preparation, characterization, and antimicrobial activity

In this study, it was aimed to prepare silver nanoparticles by reduction of silver salt (AgNO3) in situ by means of only synthesized polyacrylonitrile (PAN) and poly(acrylonitrile-co-itaconic acid) (P(AN-co-IA)) polymers, and N,N dimethylformamide (DMF). Thereafter, PAN/Ag and P(AN-co-IA)/Ag nanofibers were prepared via electrospinning. Spectroscopic and morphologic characterizations, electrical and thermal features, and antimicrobial activities of the prepared nanofibers against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans were carried out in detail. It was observed that P(AN-co-IA) was much more effective than PAN on the reduction of AgNO3 and formation of silver nanoparticles. Silver nanoparticles and also itaconic acid contributed to decrease the cyclization temperature of PAN by generating sharp exothermic peaks. In addition, electrical conductivity of the nanofibers increased dramatically from E−13 to E−4 related to the presence of silver nanoparticles. Furthermore, incorporation of silver nanoparticles to the nanofiber membranes let bactericidal/fungicidal activities, which started at 6–24 h and continued for up to 168 h, against S. aureus, E. coli, P. aeruginosa, and C. albicans. The prepared silver containing nanofibers can be regarded as good candidates for potential use in the biomedical and pharmaceutical applications.

Experimental investigation of nitrogenation process for heavy rare earth nitrides from their hydrides

We experimentally investigated the nitrogenation process of heavy rare earth (Gd, Tb, Dy, Ho and Er) hydrides dynamically by thermal analysis. The onset temperature of nitrogenation and the absolute value of nitrogenation enthalpy increased as the atomic number of the heavy rare earth elements increased and the onset temperature of nitrogenation with a sharp exothermic peak exhibited a large gap between Tb (406 °C) and Dy (806 °C). The reaction route R→RHx→RN has been done at a relatively low temperature and atmospheric pressure, indicating that the diffusion coefficient of nitrogen into the rare earth hydride is much higher than that of nitrogen into the rare earth metal and/or the activation energy of RHx→RN is lower than that of R→RN. For complete nitriding, ErN requires the highest nitrogenation temperature of at most 1000 °C in N2 flow from ErHx. We obtained the magnetic entropy change ΔS of -14 J/kg K (144 kJ/m3 K, calculated by using the theoretical density of 10.3 g/cm3) at ΔH = 2 T for HoN prepared at the nitrogenation temperature of 1000 °C. This value reached the reported value, indicates that this simple synthesis route without any toxic compounds as a precursor and with normal equipment of an atmospheric furnace without high temperature and pressure can adequately exploit the ability of the rare earth nitride as a magnetic refrigerant for magnetic refrigeration.

Thermal Stability of Athermal ω‐Ti(Fe) Produced upon Quenching of β‐Ti(Fe)

This work shows the formation of the athermal ω phase in alloy Ti–4 wt% Fe. The alloy under study, heat treated at 800 °C for 100 h and subsequently water quenched, is investigated using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The thermal stability of ω‐Ti(Fe) is investigated by differential scanning calorimetry (DSC). The DSC measurements show a cascade of several thermic events between 160 and 450 °C, and one strong and sharp exothermic DSC peak at ∼480 °C. The phase transformations and other microstructural changes behind these events are explained by complementary use of XRD, electron backscatter diffraction (EBSD), and TEM analyses that are performed on samples heated stepwise in the DSC apparatus. These experiments indicate that the embryos of athermal ω‐Ti(Fe) grow up to ∼400 °C and start to decompose into an α‐Ti(Fe) + β assemblage already at 450 °C. At ∼480 °C, the decomposition of the athermal ω‐Ti(Fe) phase is practically finished. Thermal stability of athermal ω‐Ti(Fe) is compared with the thermal stability of ω‐Ti(Fe) produced in a high‐pressure torsion (HPT) process, indicating a higher thermal stability of ω‐Ti(Fe) in the non‐deformed alloys.

Ammonium nitrate-MOF-199: A new approach for phase stabilization of ammonium nitrate

In this work we have utilized MOF-199 as a well known copper-based metal-organic framework (MOF), to study the thermal behavior of ammonium nitrate (AN). Our results indicate that MOFs improve thermal behavior of AN through their Lewis/Brønsted acid sites as well as their porous structure. Accordingly, MOF-199 (at least 5% by weight) stabilizes phase transition of AN up to 125 °C while [Cu2(bdc)2(bpy)]n is not a suitable MOF of choice. In addition, DSC studies showed a sharp exothermic peak for AN-MOF-199 composite related to the rapid catalytic combustion of the composite.

Synthesis, Crystal Structure, and Thermal Behavior of a Novel Insensitive Energetic Cocrystal Composed of 3,3′‐Bis(1,2,4‐oxadiazole)‐5,5′‐dione and 4‐Amino‐1,2,4‐triazole

A novel insensitive energetic cocrystal consisting of 3,3′‐bis(1,2,4‐oxadiazole)‐5,5′‐dione and 4‐amino‐1,2,4‐triazole in a 1:2 molar ratio was prepared and characterized. The structure of this cocrystal was characterized by single‐crystal X‐ray diffraction. The crystal structure of the cocrystal is a monoclinic system with P1 space group. Properties of the cocrystal studied included thermal decomposition and detonation performance. This cocrystal has a crystal density of 1.689 g·cm–3 at 173 K and good detonation performance (D = 6940 m·s–1, P = 20.9 GPa). Moreover, measured impact and friction sensitivities (IS &gt; 40 J, FS &gt; 360 N) show that it can be classified as an insensitive energetic material. Its thermodynamic properties indicate that it has moderate thermal stability with a sharp exothermic peak (244 °C, 5 K·min–1) and a high critical temperature of thermal explosion (523 K). In view of the observations above, it may serve as a promising alternative to known explosives such as TNT.

Distinguishing the thermal behavior of Na- and Li-intercalated hard carbons via differential scanning calorimetry

The thermal stabilities of Na- and Li-intercalated hard carbons were examined by differential scanning calorimetry (DSC) to determine whether Na-ion batteries or Li-ion batteries exhibit superior thermal stability. The DSC profiles of both C6Na0.65 and C6Li0.65 displayed sharp exothermic peaks with enthalpy changes of ~1200 J·g−1, which could be attributed to the reaction between C6Na0.65 (or C6Li0.65) and PF5. Hence, the total amounts of heat generated in these Na- and Li-ion batteries were equal, regardless of the intercalants present. However, the temperatures corresponding to the maximum exothermic peaks differed between the two battery systems (i.e., 184 °C for C6Na0.65 and 264 °C for C6Li0.65), indicating that Na-ion batteries are less thermally stable. The DSC profile of C6Li0.25Na0.37 revealed that this difference is due to differences in the solid-electrolyte interphase films between C6Nax and C6Liy.

Dynamics of Polymorphic Transformations in Palm Oil, Palm Stearin and Palm Kernel Oil Characterized by Coupled Powder XRD-DSC.

The in situ polymorphic forms and thermal transitions of refined, bleached and deodorized palm oil (RBDPO), palm stearin (RBDPS) and palm kernel oil (RBDPKO) were investigated using coupled X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Results indicated that the DSC onset crystallisation temperature of RBDPO was at 22.6°C, with a single reflection at 4.2Å started to appear from 23.4 to 17.1°C, and were followed by two prominent exothermic peaks at 20.1°C and 8.5°C respectively. Further cooling to -40°C leads to the further formation of a β'polymorph. Upon heating, a of β'→βtransformation was observed between 32.1 to 40.8°C, before the sample was completely melted at 43.0°C. The crystallization onset temperature of RBDPS was 44.1°C, with the appearance of the α polymorph at the same temperature as the appearance of the first sharp DSC exothermic peak. This quickly changed from α→β´ in the range 25 to 21.7°C, along with the formation of a small β peak at -40°C. Upon heating, a small XRD peak for the β polymorph was observed between 32.2 to 36.0°C, becoming a mixture of (β´+ β) between 44.0 to 52.5°C. Only the β polymorph survived further heating to 59.8°C. For RBDPKO, the crystallization onset temperature was 11.6°C, with the formation of a single sharp exothermic peak at 6.5°C corresponding to the β' polymorphic form until the temperature reached -40°C. No transformation of the polymorphic form was observed during the melting process of RBDPKO, before being completely melted at 33.2°C. This work has demonstrated the detailed dynamics of polymorphic transformations of PKO and PS, two commercially important hardstocks used widely by industry and will contribute to a greater understanding of their crystallization and melting dynamics.

Ferroelectricity of strained SrTiO3 in lithium tetraborate glass-nanocomposite and glass-ceramic

Glass-nanocomposite (GNCs) sample of the composition [90Li2B4O7-10SrTiO3] (mol %) was prepared by conventional melt quenching technique. The glassy phase and the amorphous nature of the GNCs sample were identified by Differential thermal analysis (DTA) and X-ray diffraction (XRD) studies, respectively. DTA of the GNCs exhibits sharp and broad exothermic peaks which represent the crystallization of Li2B4O7 and SrTiO3, respectively. The tetragonal Li2B4O7 and tetragonal SrTiO3 crystalline phases in glass-ceramic (GC) were identified by XRD and scanning electron microscopic (SEM). The strain tetragonal SrTiO3 phase in GNCs and GC has been confirmed by SEM. The values of crystallization activation energies (Ec1 and Ec2) for the first and second exothermic peaks are equal to 174 and 1452 kJ/mol, respectively. The Ti3+ ions in tetragonal distorted octahedral sites in GNCs were identified by optical transmission spectrum. GNCs and GC samples exhibit broad dielectric anomalies at 303 and 319 K because of strained SrTiO3 ferroelectric, respectively.

Thermal behavior of Al/Zr/KClO4 pyrotechnic compositions at high temperature

A pyrotechnic composition of aluminum, zirconium, and potassium perchlorate was prepared to obtain suitable safety and sensitivity. The thermal behavior, microstructure, and composition of the pyrotechnic compositions heated from 300°C to 600°C were investigated using differential scanning calorimetry (DSC), thermogravimetry (TG), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) to evaluate the properties of the pyrotechnics after the high-temperature process, such as the 1A/1W no-fire test. When the heating temperature increased, the sharp exothermic peak near 530°C decreased, corresponding to the reaction of metal powders with potassium perchlorate. Gradual oxidizing reaction between Zr and KClO4 can occur in solid stage when the temperature exceeds 400°C. With the increase of the heating temperature from 400°C to 600°C, the mass losses in TG curves decreased, and melted particles of KClO4 appeared gradually. The Al/Zr/KClO4 pyrotechnic composition was safe in the of 1A/1W no-fire test. Hence, Al/Zr/KClO4 can be used in flash pyrotechnics, fireworks, and fuel-rich propellants.