RESUMEN
Materials combining the hardness and strength of diamond with the higher thermal stability of cubic boron nitride (cBN) have broad potential value in science and engineering. Reacting nanodiamond with cBN at moderate pressures and high temperatures provides a pathway to such materials. Here we report the fabrication of Cx-BN nanocomposites, measuring up to 10 mm in longest dimension, by reacting nanodiamond with pre-synthesized cBN in a large-volume press. The nanocomposites consist of randomly-oriented diamond and cBN domains stitched together by sp(3)-hybridized C-B and C-N bonds, leading to p-type semiconductivity. Dislocations near the sutures accommodate lattice mismatch between diamond and cBN. Nanotwinning within both diamond and cBN domains further contributes to a bulk hardness ~50% higher than sintered cBN. The nanocomposite of C2-BN exhibits p-type semiconductivity with low activation energy and high thermal stability, making it a functional, ultrahard substance.
RESUMEN
The use of detailed chemical reaction mechanisms of kerosene is still very limited in analyzing the combustion process in the combustion chamber of the aircraft engine. In this work, a new reduced chemical kinetic mechanism for fuel n-decane, which selected as a surrogate fuel for kerosene, containing 210 elemental reactions (including 92 reversible reactions and 26 irreversible reactions) and 50 species was developed, and the ignition and combustion characteristics of this fuel in both shock tube and flat-flame burner were kinetic simulated using this reduced reaction mechanism. Moreover, the computed results were validated by experimental data. The calculated values of ignition delay times at pressures of 12, 50 bar and equivalence ratio is 1.0, 2.0, respectively, and the main reactants and main products mole fractions using this reduced reaction mechanism agree well with experimental data. The combustion processes in the individual flame tube of a heavy duty gas turbine combustor were simulated by coupling this reduced reaction mechanism of surrogate fuel n-decane and one step reaction mechanism of surrogate fuel C12H23 into the computational fluid dynamics software. It was found that this reduced reaction mechanism is shown clear advantages in simulating the ignition and combustion processes in the individual flame tube over the one step reaction mechanism.
RESUMEN
This article theoretically investigates the lateral support on cubic high-pressure anvil using finite element analysis. The results show that to gain the same chamber pressure, the value of system oil pressure can be decreased by reducing the lateral support area and the anvils' lifetime is extended when the lateral support area grows. The optimal lateral support area to maximize anvils' lifetime is 27.96 cm(2). Furthermore, the chamber pressure will increase by about 6.99% when the value of lateral support area reduces from 33.16 to 27.96 cm(2) under same hydraulic rams. Our simulation results have been verified by many high-pressure synthesis experiments and illustrated by breakage of anvils.
RESUMEN
A hybrid-anvil used in cubic high pressure apparatus is presented, which makes it possible to pressurize samples of 36 mm(3) volume up to 5.5 GPa and to heat simultaneously up to 1350-1400 degrees C for routine operation. The hybrid-anvil has been designed based on the theory of multilayered pressure vessels and massive support, which can save weight about 60.00% compared to the traditional anvil. We note from 10 000 times of experiments that the rate of failure crack decreases about 16.67% and the cost of anvil saves about 66.40% after the modification of the anvil. This represents a relatively simple and inexpensive anvil for material synthesis and research.