High-temperature oxidation behavior of SiBN fibers in air

SiBN fibers are one of the most admirable microwave-transparent reinforced materials for high Mach number aircrafts. Currently, the detailed high-temperature oxidation behavior of SiBN fibers has not been studied yet. In this work, we studied the high-temperature oxidation behavior of SiBN fibers with different boron contents at the temperature range of 1000–1400 °C in air. SiBN fibers started to be oxidized at 1100 °C, with Si3N4 and BN phase oxidized to SiO2 and B2O3, respectively. Due to the gasification and the escape of molten B2O3 at high temperatures, amorphous SiO2 could be remained at the fiber surface. As the fiber further oxidized, the molten B2O3 at the inside may infiltrate into the fiber interior to react with Si3N4, causing the precipitation of hexagonal boron nitride (h-BN) nanoparticles and the formation of SiO2/BN layer. Finally, complex oxidation layers with two distinct concentric sublayers accompanied with two transition sublayers could be formed after the oxidizing treatment.

The chemistry of Marchand’s test for strychnine identification

The chemistry of a spot test for identification of a substance with biological activity is important. Besides the academic interest of knowing what is going on in the test, the study reveals the chemical deportment of the active compound, and this is related to biochemistry. This result can be used to enhance, or on the contrary, deter the activity of the compound. In this communication we provide the chemistry involved in the spot test for strychnine identification by means of lead dioxide (Marchand’s test). The electron flow, step by step, is given from the alkaloid to the complex oxidation product. Thus, this toxicological assay has been up-dated.

High-temperature oxidation behavior of SiBN fibers in air

SiBN fibers are one of the most admirable microwave-transparent reinforced materials for high Mach number aircrafts. Currently, the detailed high-temperature oxidation behavior of SiBN fibers have not been studied yet. In this work, we researched the high-temperature oxidation behavior of SiBN fibers with different boron contents at the temperature range of 1000 ~ 1400℃ in air. SiBN fibers started to be oxidized at 1100℃, with Si3N4 and BN phase oxidized to SiO2 and B2O3, respectively. Due to the gasification and the escape of molten B2O3 at high temperature, amorphous SiO2 could be remained at the fiber surface. As the fiber further oxidized, the molten B2O3 at the inside may infiltrate into the fiber interior to react with Si3N4, causing the precipitation of h-BN nanoparticles and the formation of SiO2/BN layer. Finally, complex oxidation layers with two distinct concentric sublayers accompanied with two transition sublayers could be formed after the oxidizing treatment.

The Chemistry of Lindo and Fages Colour Tests

Lindo test for strychnine identification is based on the reaction of the alkaloid with potassium chlorate in the presence of sulphuric acid. Fages identified chlorates and bromates using strychnine in nitric acid. In fact, it is the same reaction but with different strong acid, and the product to be identified being interchanged. The reaction series occurring in these tests has not being described. We provide the electron flow from the alkaloid to the complex oxidation product resulting from the powerful oxidation properties of chloric acid.

Bioactive Natural Spirolactone-Type 6,7-seco-ent-Kaurane Diterpenoids and Synthetic Derivatives

Diterpenoids are widely distributed natural products and have caused considerable interest because of their unique skeletons and antibacterial and antitumor activities and so on. In light of recent discoveries, ent-kaurane diterpenoids, which exhibit a wide variety of biological activities, such as anticancer and anti-inflammatory activities, pose enormous potential to serve as a promising candidate for drug development. Among them, spirolactone-type 6,7-seco-ent-kaurane diterpenoids, with interesting molecular skeleton, complex oxidation patterns, and bond formation, exhibit attractive activities. Furthermore, spirolactone-type diterpenoids have many modifiable sites, which allows for linking to various substituents, suitable for further medicinal study. Hence, some structurally modified derivatives with improved cytotoxicity activities are also achieved. In this review, natural bioactive spirolactone-type diterpenoids and their synthetic derivatives were summarized.