Effects of cubic BN addition and phase transformation on hardness of Al2O3-cubic BN composites

The Vickers hardness of dense Al₂O₃-cubic BN (cBN) composites prepared by spark plasma sintering under a moderate pressure of 100 MPa at 1200-1600 °C was investigated at indentation loads of 0.098-19.6 N. The BN grains in the Al₂O₃-BN composite prepared at 1300 °C showed no transformation from the cBN to hBN phase, and the hardness was 59 GPa at 0.098 N. The hardness of the Al₂O₃ matrix in the Al₂O₃-BN composites containing 10-30 vol% cBN prepared at 1300-1400 °C was around 25 GPa at 0.098 N, which was higher than monolithic Al₂O₃ bodies prepared at the same temperatures. The hardness of the Al₂O₃ matrix in the Al₂O₃-BN composites decreased with increasing sintering temperature. The increase in the hardness of the Al₂O₃ matrix may be due to the decrease in the size of Al₂O₃ grains in the Al₂O₃-BN composites owing to the addition of cBN particles and the decrease in sintering temperature. The Meyer exponents of the monolithic Al₂O₃ bodies and Al₂O₃-BN composites were 1.90-1.94 independent of cBN content.     

NAD+‐Dependent Dehydrogenase PctP and Pyridoxal 5′‐Phosphate Dependent Aminotransferase PctC Catalyze the First Postglycosylation Modification of the Sugar Intermediate in Pactamycin Biosynthesis

The unique five‐membered aminocyclitol core of the antitumor antibiotic pactamycin originates from d ‐glucose, so unprecedented enzymatic modifications of the sugar intermediate are involved in the biosynthesis. However, the order of the modification reactions remains elusive. Herein, we examined the timing of introduction of an amino group into certain sugar‐derived intermediates by using recombinant enzymes that were encoded in the pactamycin biosynthesis gene cluster. We found that the NAD⁺‐dependent alcohol dehydrogenase PctP and pyridoxal 5′‐phosphate dependent aminotransferase PctC converted N‐acetyl‐d ‐glucosaminyl‐3‐aminoacetophonone into 3′‐amino‐3′‐deoxy‐N‐acetyl‐d ‐glucosaminyl‐3‐aminoacetophenone. Further, N‐acetyl‐d ‐glucosaminyl‐3‐aminophenyl‐β‐oxopropanoic acid ethyl ester was converted into the corresponding 3′‐amino derivative. However, PctP did not oxidize most of the tested d ‐glucose derivatives, including UDP‐GlcNAc. Thus, modification of the GlcNAc moiety in pactamycin biosynthesis appears to occur after the glycosylation of aniline derivatives.     

Corrosion of MgO—MgAl2O4 Spinel Refractory Bricks by Calcium Aluminosilicate Slag

Microstructural analysis of MgO—MgAl₂O₄ refractory bricks corroded at 1400–1450°C by calcium aluminosilicate slag reveals secondary spinel, monticellite, merwinite, and MgO as microscopic corrosion products, generally forming in this sequence as the brick is penetrated. The secondary spinel forms an incomplete layer close to (but not at) the MgO grain. Thermodynamic calculations are used to support a detailed model of the corrosion mechanism.     

Preparation of (0 2 0)-oriented BaTi2O5 thick films and their dielectric responses

Barium dititanate (BaTi₂O₅) thick films were prepared on a Pt-coated Si substrate by laser chemical vapor deposition, and ac electric responses of (0 2 0)-oriented BaTi₂O₅ films were investigated using several equivalent electric circuit models. BaTi₂O₅ films in a single phase were obtained at a Ti/Ba molar ratio (m_Ti/Ba) of 1.72–1.74 and deposition temperature (T_dep) of 908–1065 K as well as m_Ti/Ba = 1.95 and T_dep = 914–953 K. (0 2 0)-oriented BaTi₂O₅ films were obtained at m_Ti/Ba = 1.72–1.74 and T_dep = 989–1051 K. BaTi₂O₅ films had columnar grains, and the deposition rate reached 93 μm h^?1. The maximum relative permittivity of the (0 2 0)-oriented BaTi₂O₅ film prepared at T_dep = 989 K was 653 at 759 K. The model of an equivalent circuit involving a parallel combination of a resistor, a capacitor, and a constant phase element well fitted the frequency dependence of the interrelated ac electrical responses of the impedance, electric modulus, and admittance of (0 2 0)-oriented BaTi₂O₅ films.     

Effect of sintering temperature on the transparency and mechanical properties of lutetium aluminum garnet fabricated by spark plasma sintering

Transparent lutetium aluminum garnet (Lu₃Al₅O₁₂, LuAG) was fabricated by reactive spark plasma sintering. The effect of sintering temperature on the crystal phase, microstructure, transparency and mechanical properties of LuAG bodies was investigated. Fully dense and single-phase LuAG bodies were obtained at sintering temperatures 1573–1923 K. The average grain size increased from 0.18 to 0.52 μm with increasing sintering temperature from 1573 to 1773 K, and grain growth became significant at 1823 K. Transmittance showed a maximum value of 77.8% at 2000 nm at a sintering temperature of 1773 K after annealing at 1423 K in air for 43.2 ks. The Vickers hardness increased from 14.2 to 17.2 GPa with decreasing grain size from 7.45 to 0.23 μm.     

Non-catalytic vanadium removal from vanadyl etioporphyrin (VO-EP) using a mixed solvent of supercritical water and toluene: A kinetic study

Reaction kinetics and mechanisms of the decomposition of vanadyl etioporphyrin (VO-EP), the most common metal compounds present in heavy crude, were studied in a mixed solvent of supercritical water (SCW) and toluene without the addition of any catalyst, H₂ or H₂S to remove vanadium. The aim of this study was to remove vanadium an environmentally benign way from VO-EP at a high extent and in a short reaction time. The experiments were conducted in an 8.8 mL batch reactor fabricated from Hastelloy C-276. The capability of SCW to remove vanadium from VO-EP was discovered at temperatures of 410–490 °C and a water partial pressure (WPP) of 25 MPa. Experimental results revealed that the overall VO-EP conversion was 90.51% at a temperature of 490 °C, WPP of 25 MPa and reaction time of 180 min. Under the same reaction conditions, approximately 80.26% vanadium was removed by reaction with SCW. The global reaction followed first order kinetics, with Arrhenius parameters of activation energy 8.93 kcal/mol and a pre-exponential factor 5.66 s^?1. A kinetic model of demetallation that well-fit the experimental results, was proposed. The reaction kinetics may be critically explained in terms of free radical mechanism. The obtained results suggest that SCW is capable of removing vanadium from VO-EP.     

Chemical‐Free Approach for Z‐Isomerization of Lycopene in Tomato Powder: Hot Air and Superheated Steam Heating above the Melting Point of Lycopene

Z‐isomers of lycopene exhibit higher bioavailability and antioxidant capacity than those of the all‐E‐isomer. Therefore, it is important to develop an efficient and environmentally friendly procedure for Z‐isomerization. The current methods for Z‐isomerization of (all‐E)‐lycopene use toxic chemicals such as organic solvents and catalysts. This study is aimed to develop a chemical‐free method for Z‐isomerization of (all‐E)‐lycopene in tomato powder by hot air and superheated steam heating. The Z‐isomerization reaction is promoted by heating above the melting point of lycopene. When heated with superheated steam, the thermal decomposition of lycopene is suppressed compared to that when heated with hot air. When tomato powder is heated at 240 °C for 5 min by superheated steam, the total Z‐isomer content and remaining lycopene are 69.0% and 90.7%, respectively, while with hot air heating, the total Z‐isomer content and remaining lycopene are 69.9% and 68.0%, respectively. These results indicate that the thermal Z‐isomerization of lycopene occurs in the molten state and heating in a low oxygen atmosphere suppresses the thermal decomposition of lycopene. Practical Applications: Tomato powder rich in lycopene Z‐isomers is an important ingredient for the food and animal feed industries. Since Z‐isomers of lycopene are more soluble in solvents including ethanol which is a low‐toxicity and environmentally friendly solvent, the efficiency of lycopene extraction with ethanol can be improved by using the Z‐isomer‐rich tomato powder as a raw material. The obtained Z‐isomer‐rich extract has a high added value because the Z‐isomers have higher bioavailability and antioxidant capacity than those of the all‐E‐isomer. In addition, since lycopene Z‐isomers exhibit higher accumulation efficiency and better color improvement in hen egg yolks than those of the all‐E‐isomer, Z‐isomer‐rich tomato powder is an effective animal feed.     

High-resolution multi-isotope imaging mass spectrometry enables visualisation of stem cell division and metabolism

MIMS visualises metabolism: A recent publication by Steinhauser and co-workers presents a novel application of multi-isotope mass spectrometry (MIMS) to visualise physiological metabolism in live mammalian organisms, and validate the "immortal strand hypothesis" of asymmetric chromosomal division of stem cells in the small intestine.