We report the simultaneous enlarged growth of seven single crystal diamond(SCD) plates free from polycrystalline diamond(PCD) rim by using a microwave plasma chemical vapor deposition(MPCVD) system. Optical microscope...We report the simultaneous enlarged growth of seven single crystal diamond(SCD) plates free from polycrystalline diamond(PCD) rim by using a microwave plasma chemical vapor deposition(MPCVD) system. Optical microscope and atomic force microscope(AFM) show the typical step-bunching SCD morphology at the center, edge, and corner of the samples. The most aggressively expanding sample shows a top surface area three times of that of the substrate. The effective surface expanding is attributed to the utilization of the diamond substrates with(001) side surfaces, the spacial isolation of them to allow the sample surface expanding, and the adoption of the reported pocket holder. Nearly constant temperature of the diamond surfaces is maintained during growth by only decreasing the sample height, and thus all the other growth parameters can be kept unchanged to achieve high quality SCDs. The SCDs have little stress as shown by the Raman spectra. The full width at half maximum(FWHM) data of both the Raman characteristic peak and(004) x-ray rocking curve of the samples are at the same level as those of the standard CVD SCD from Element Six Ltd. The nonuniformity of the sample thickness or growth rate is observed, and photoluminescence spectra show that the nitrogen impurity increases with increasing growth rate. It is found that the reduction of the methane ratio in the sources gas flow from 5% to 3% leads to decrease of the vertical growth rate and increase of the lateral growth rate. This is beneficial to expand the top surface and improve the thickness uniformity of the samples. At last, the convenience of the growth method transferring to massive production has also been demonstrated by the successful simultaneous enlarged growth of 14 SCD samples.展开更多
Gel propulsion systems have many advantages with respect to high performance, the energy management of liquid propulsion systems, storability, high density impulse, and low leakage of liquid propellants. The atomizati...Gel propulsion systems have many advantages with respect to high performance, the energy management of liquid propulsion systems, storability, high density impulse, and low leakage of liquid propellants. The atomization process provides sufficient contact surface area between the gelled fuel and oxidizer jets. It is important to study how injection characteristics of gelled propellants are related with break-up and spray distribution. The break-up and mixing processes are very important in achieving maximum efficiency and necessitate the careful study of combustion instability. Gelled propellants are non-Newtonian fluids in which the viscosity is a function of the shear rate, and they have a high dynamic shear viscosity which depends on the amount of gelling agent contents. The present study has focused on the break-up process, wave development of ligament and liquid sheets formed by impinging jets with various gelling agent contents. Especially, the break-up processes of the impinging jets at the initial conditions are studied. The break-up process of like-on-like doublet impinging jets are experimentally characterized using non-Newtonian liquids which are mixed by ionized water 98.5 wt%, Carbopol 941 0.5wt% or 1.0wt%, and NaOH(concentration 10%) 1.0wt%. For the like-on-like doublet injector, the generation of a liquid sheet at the impinging point of two jets was observed. The spray shape with elliptical pattern is distributed in a perpendicular direction to the momentum vectors of the jets. Gelled propellant simulants with high viscosity jets are more stable and produce less pronounced surface waves than low viscosity jets. Generally, the break-up length decreased due to the increasing Reynolds number. However, surface waves and atomized droplets increased. Gelled propellant simulants from like-on-like doublet impinging jets have the spray shape of closed rim patterns at low pressure. Also, the rim patterns of spray have no disturbances on the spray sheet. As the injection pressure increased, rimless patterns which were composed of ligament sheets and small droplets emerged due to the effect of the aerodynamic action. Periodic wave-like structures observed from the near impingement point and atomized droplets were observed at a location further downstream.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2018YFB0406504 and 2016YFB0400105)the National Postdoctoral Program for Innovative Talents,China(Grant No.BX20190263)
文摘We report the simultaneous enlarged growth of seven single crystal diamond(SCD) plates free from polycrystalline diamond(PCD) rim by using a microwave plasma chemical vapor deposition(MPCVD) system. Optical microscope and atomic force microscope(AFM) show the typical step-bunching SCD morphology at the center, edge, and corner of the samples. The most aggressively expanding sample shows a top surface area three times of that of the substrate. The effective surface expanding is attributed to the utilization of the diamond substrates with(001) side surfaces, the spacial isolation of them to allow the sample surface expanding, and the adoption of the reported pocket holder. Nearly constant temperature of the diamond surfaces is maintained during growth by only decreasing the sample height, and thus all the other growth parameters can be kept unchanged to achieve high quality SCDs. The SCDs have little stress as shown by the Raman spectra. The full width at half maximum(FWHM) data of both the Raman characteristic peak and(004) x-ray rocking curve of the samples are at the same level as those of the standard CVD SCD from Element Six Ltd. The nonuniformity of the sample thickness or growth rate is observed, and photoluminescence spectra show that the nitrogen impurity increases with increasing growth rate. It is found that the reduction of the methane ratio in the sources gas flow from 5% to 3% leads to decrease of the vertical growth rate and increase of the lateral growth rate. This is beneficial to expand the top surface and improve the thickness uniformity of the samples. At last, the convenience of the growth method transferring to massive production has also been demonstrated by the successful simultaneous enlarged growth of 14 SCD samples.
基金(Grants No. 00040486) was supported by Business for Cooperative R&D between Industry, AcademyResearch Institute funded Korea Small and Medium Business Administration in 2010
文摘Gel propulsion systems have many advantages with respect to high performance, the energy management of liquid propulsion systems, storability, high density impulse, and low leakage of liquid propellants. The atomization process provides sufficient contact surface area between the gelled fuel and oxidizer jets. It is important to study how injection characteristics of gelled propellants are related with break-up and spray distribution. The break-up and mixing processes are very important in achieving maximum efficiency and necessitate the careful study of combustion instability. Gelled propellants are non-Newtonian fluids in which the viscosity is a function of the shear rate, and they have a high dynamic shear viscosity which depends on the amount of gelling agent contents. The present study has focused on the break-up process, wave development of ligament and liquid sheets formed by impinging jets with various gelling agent contents. Especially, the break-up processes of the impinging jets at the initial conditions are studied. The break-up process of like-on-like doublet impinging jets are experimentally characterized using non-Newtonian liquids which are mixed by ionized water 98.5 wt%, Carbopol 941 0.5wt% or 1.0wt%, and NaOH(concentration 10%) 1.0wt%. For the like-on-like doublet injector, the generation of a liquid sheet at the impinging point of two jets was observed. The spray shape with elliptical pattern is distributed in a perpendicular direction to the momentum vectors of the jets. Gelled propellant simulants with high viscosity jets are more stable and produce less pronounced surface waves than low viscosity jets. Generally, the break-up length decreased due to the increasing Reynolds number. However, surface waves and atomized droplets increased. Gelled propellant simulants from like-on-like doublet impinging jets have the spray shape of closed rim patterns at low pressure. Also, the rim patterns of spray have no disturbances on the spray sheet. As the injection pressure increased, rimless patterns which were composed of ligament sheets and small droplets emerged due to the effect of the aerodynamic action. Periodic wave-like structures observed from the near impingement point and atomized droplets were observed at a location further downstream.
