Cryogenic gas loading in a Mao-Bell-type diamond anvil cell for high pressure-high temperature investigations

A simple system for loading argon fluid at cryogenic temperatures in a Mao-Bell-type diamond anvil cell (DAC) has been developed. It is done in a two step process in which the piston-cylinder assembly alone is submerged in the cryogenic chamber for trapping the liquefied inert gas. Liquid nitrogen is used for condensing the argon gas. This system is now being efficiently used for loading liquid argon in the DAC for high pressure-high temperature experiments. The success rate of trapping liquefied argon in the sample chamber is about 75%. The performance of the gas loading system is successfully tested by carrying out direct conversion of pyrolitic graphite to diamond under high pressure-high temperature using laser heated DAC facility.     

Investigation of the mechanical behavior of a flexible solid metal seal for a cryogenic butterfly valve

Seat tightness at the fully shut position should be a consideration in the development of a butterfly valve for use in a liquefied natural gas (LNG) vessel. A flexible solid metal seal offers sufficient tightness of the butterfly valve and meets the specifications for cryogenic temperature. In the present study, characteristics for a cryogenic butterfly valve, such as the flow coefficient and the pressure loss coefficient, were estimated by numerical fluid analysis carried out to simulate 3-D flow and to study performance as it was affected by the opening angles of the valve disc. A design criterion to ensure the seat tightness of the butterfly valve at the fully shut position was proposed, in which the contact pressure between the metal seal and the valve disc would be compared with the fluid pressure. Numerical structural analysis showed that the contact pressure can be calculated by simulation of the frictional contact behavior on the surface of the metal seal and the valve disc. As a result, an adequate flexibility of the metal seal and the valve disc was required in order to accomplish a contact pressure that would be high enough to satisfy the seat tightness requirement. Under cryogenic temperature, thermal shrinkage caused the metal seal to adhere closely to the valve disc periphery at both sides and raised the contact pressure to a relatively high value, though there was no contact across a small area at the center position, which is susceptible to leakage. An additional displacement of the metal seal and the valve disc appeared at an operating fluid pressure of 6.9 bar and produced sufficient contact pressure at the no-contact area. This was verified by experimental leakage tests performed at room and cryogenic temperatures.     

A modular designed ultra-high-vacuum spin-polarized scanning tunneling microscope with controllable magnetic fields for investigating epitaxial thin films

A room-temperature ultra-high-vacuum scanning tunneling microscope for in situ scanning freshly grown epitaxial films has been developed. The core unit of the microscope, which consists of critical components including scanner and approach motors, is modular designed. This enables easy adaptation of the same microscope units to new growth systems with different sample-transfer geometries. Furthermore the core unit is designed to be fully compatible with cryogenic temperatures and high magnetic field operations. A double-stage spring suspension system with eddy current damping has been implemented to achieve ≤5 pm z stability in a noisy environment and in the presence of an interconnected growth chamber. Both tips and samples can be quickly exchanged in situ; also a tunable external magnetic field can be introduced using a transferable permanent magnet shuttle. This allows spin-polarized tunneling with magnetically coated tips. The performance of this microscope is demonstrated by atomic-resolution imaging of surface reconstructions on wide band-gap GaN surfaces and spin-resolved experiments on antiferromagnetic Mn(3)N(2)(010) surfaces.     

A test setup for the bead cryogenic neutron moderator of the IBR-2 reactor

The design and main characteristics of a test setup for studying the serviceability of the bead cryogenic neutron moderator and determining its optimal operating conditions on the fast pulsed IBR-2 reactor are presented. Using the test setup, the possibility has been demonstrated of filling the moderator chamber with the working medium—beads of a mixture of aromatic hydrocarbons, delivered to the chamber by a cold (T < 85 K) helium gas flow over an intricately shaped cryogenic pipeline system.     

An investigation of a cavitating venturi flow control feature in a cryogenic propellant delivery system

This study details the design and performance characterization for a cryogenic cavitating venturi. This flow control system is intended for mass flow regulation of cryogenic propellants, such as liquid oxygen and liquid methane, in reaction control propulsion systems. Through in situ flow tests, the discharge coefficient for the venturi was calculated and utilized to determine the mass flow rate for specified inlet pressures of the propellants. The test results revealed that the cavitating venturi indeed performed as a flow rate control feature in both liquid water and LCH₄ flow under a steady state operating within pressure ratios below 0.69.     

Cryogenic fracture toughness evaluation for austenitic stainless steels by means of unloading compliance method

Most research to date concerning the cryogenic toughness of austenitic stainless steels has concentrated on the base metal and weld metal in weldments. The most severe problem faced on the conventional austenitic stainless steel is the thermal aging degradation such as sensitization and carbide induced embrittlement. In this paper, we investigate the cryogenic toughness degradation which can be occurred for austenitic stainless in welding. The test materials are austenitic stainless JN1, JJ1 and JK2 steels, which are materials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch (SP) test was conducted to detect similar isothermally aging condition with material degradation occurred in service welding. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless steels. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.     

The effect of nanoparticulate loading on the fabrication and characterization of multi-doped Zn-Al2O3-Cr2O3 hybrid coatings on mild steel

In this paper, an improved approach is proposed to determine the optimal profiles of two controllable process parameters (hydraulic pressure and blank holder force), which improve the forming condition and/or make better use of forming limits in hydromechanical deep drawing (HMD) process. A method based on adaptive finite element analysis coupled with fuzzy control algorithm (aFEA-FCA) was developed using LS-DYNA to determine the optimal loading profiles and thus to maximize the limiting drawing ratio (LDR). Maximum thickness reduction, maximum wrinkle height in the flange region of the sheet metal blank, and position of the nodes in the unsupported portion of the sheet metal blank between punch and die were used as criteria in the fuzzy control algorithm. Different rule-based matrices were compared by considering the maximum thinning occurred in the sheet metal blank, and thus, the most accurate matrices were determined for the control algorithm. The optimal loading profiles could be determined in a single FEA, thus reducing the computation time. The proposed approach enables determining the optimal loading profiles and also could be applied to complex parts easily. In addition, effects of initial blank diameter and coefficient of friction between the sheet-blank holder and sheet-die on the optimal loading profiles were investigated. An attainable LDR of 2.75 for AA 5754-O sheet material in hydromechanical deep drawing process was proven experimentally using the optimal loading profiles determined by adaptive FEA.     

EXPERIMENTAL EVALUATION OF FRICTION COEFFICIENT AND LIQUID NITROGEN LUBRICATION EFFECT IN CRYOGENIC MACHINING

Cryogenic machining is considered an environmentally safe alternative to conventional machining where cutting fluid is used. However, the improved machinability in cryogenic machining has been attributed to the cooling effect of liquid nitrogen (LN2) in past research. Our recent studies indicate that LN2 may possess a lubrication effect in machining, as evidenced by a reduction of tool wear, the apparent coefficients of friction calculated by a mathematical model, and the secondary deformation in chip metallurgy. However, there is a need for a direct proof of LN2's lubrication effect before it can be claimed to be a lubricant in cryogenic machining. This paper presents the methodology and data from an experiment that measures the normal force and friction force directly in an altered machining setup. This procedure simulates the pure frictional behavior of the tool-chip interface in cryogenic cutting. The results show that LN2 cooled condition has a significantly lower coefficient of friction than dry conditions in all cases. The data also shows that the friction is lower for Ti-6Al-4V but mixed results obtained for mild steel AISI 1018 when LN2 is applied properly as in the experiment setup as compared to traditional emulsion flooding. Based on the unique pattern of the friction behavior in the sliding tests, possible lubrication mechanisms using liquid nitrogen are proposed.     

阀门低温试验装置的节约型设计

阀门低温试验装置兼有深冷处理和低温试验的双重功能,是低温阀门生产过程中的重要设备,其冷媒和试验介质等消耗巨大且价格昂贵,对低温阀门的整机成本具有重要影响。提出了一种低温阀门试验装置的节约型设计,从组成装置的低温系统、压力试验系统和测控系统等方面着手,寻找减少消耗的途径,并重点讨论了多种高效保温技术,通过液氮喷淋实现自动调温的方式,贵重试验介质回收重复利用技术,数据采集和智能化操作模式等,提出了应从多渠道实现装置的节约型设计。     

The tribological behavior of Ni–Cu–Ag-based PVD coatings for hybrid bearings under different lubrication conditions

In a cryogenic environment, components like bearings with interacting surfaces in relative motion (tribosystems) often generate undesired heat and experience high wear. Because the properties of conventional bearing materials like stainless steel cannot be applied to this temperature range, the PVD coating based on metal–metal pairs with better frictional properties must be employed. To test the suitability of the Ni–Cu–Ag-based PVD coatings of hybrid bearings for liquid rocket engine turbopumps and to obtain reliable coating material data in the extreme environment, the tribological behaviors of coatings under the cryogenic fluid (liquid oxygen and liquid nitrogen) and water lubricated conditions are studied, respectively. In the paper, the specimens are in a vibrocryotribometer with the ball-on-plane contact type, and various running conditions in terms of lubricants, contacting loading, and contacting velocity are examined. The simulated experiment for testing the actual tribological performance of Ni–Cu–Ag-based PVD coatings for hybrid bearings is tested. The results of the tests indicate that the coatings can be suitable for cryogenic tribosystems of turbopumps. In the cryogenic environment, the volume wear rate of coatings increases rapidly with the contacting loading, but 15 min later, the volume wear volume of coatings turns into 2.5–15×10⁻⁴ mm³. Besides, under the liquid oxygen condition in simulating the liquid rocket engine turbopumps environment, the friction coefficients are 0.03–0.1.     

Environmental electron microscopy (ETEM) for catalysts with a closed E-cell with carbon windows

In a standard high-resolution electron microscope (Jeol 3010), an environmental sample holder designed by Jeol, has been used for in situ observations at the atomic scale of catalysts, during a chemical reaction. Experiments have been performed in H(2) and O(2) at a pressure up to 4 mbar at room temperature, and in the case of H(2), at various temperatures until 350 degrees C. For the first time, Au and Pd clusters supported on TiO(2) and amorphous carbon have been observed with a windows-cell environmental electron microscopy (ETEM) system, with the resolution of the (1 1 1) lattice fringes. Au clusters have been cleaned in H(2) and have got the equilibrium shape of the fcc crystals during annealing. The same Au particles can be observed during successive treatments under O(2) and H(2). For Pd clusters in situ exposed to O(2) , the adhesion has decreased.     

高真空多层绝热低温容器完全真空丧失后升压规律的试验研究

高真空多层绝热低温容器是一种危险性很高的压力容器。绝热夹层完全的真空丧失是可能发生在高真空多层绝热低温容器上的、并会对低温容器带来严重的安全隐患。在搭建了高真空多层绝热低温真空丧失试验台的基础上,用试验的方法研究了低温容器的绝热材料层数和初始充满率对其真空丧失后无排放贮存过程中升压的影响。试验结果表明,高真空多层绝热低温容器绝热夹层内的绝热材料层数及其初始充满率都对容器完全真空丧失后的升压过程有着重要影响。     

低温低噪声放大器噪声测试系统

在低噪声放大器噪声线性的基础上，介绍了负载温度可变法，用于测量低温低噪声放大器的噪声。建立一套低温放大器噪声测试系统，并分析了系统的测量误差。利用系统测量了S波段和C波段低温放大器各1个，测试结果与国外同类测试系统的测试结果相符。系统的建立为我国自主研发低温低噪声放大器提供了必要条件。     

液氢温区冷氦增压试验系统的设计

针对液体火箭冷氦增压系统试验研究的不足,设计并建设了液氢温区冷氦增压试验系统,采用深低温制冷机组配合高压低温换热贮罐来实现液氢温区高压冷氦气源;使用管壳式加热器真实模拟箭上换热器的换热性能与流阻;提出以排气方式模拟贮箱推进剂消耗过程中压力的变化情况。该试验系统安全可靠,更加真实地模拟了液体火箭冷氦增压系统的工作过程。     

In Situ TEM Observation of the Behavior of an Individual Fullerene-Like MoS<Subscript>2</Subscript> Nanoparticle in a Dynamic Contact

Inorganic fullerene-(IF)-like nanoparticles made of metal dichalcogenides (IF-MoS₂, IF-WS₂) have been known to be effective as anti-wear and friction modifier additives under boundary lubrication. The lubrication mechanism of these nanoparticles has been widely investigated in the past and even if the exfoliation and third body transfer of molecular sheets onto the asperities constitute the prevalent mechanism for the improved tribological behavior of IF nanoparticles, it has also been suggested that a rolling friction process could also play a role for well crystallized and spherical particles. In this study, in situ Transmission Electron Microscopy (TEM) observations of the behavior of single IF-MoS₂ nanoparticles were conducted using a sample holder that combines TEM and Atomic Force Microscopy (AFM) which simultaneously can apply normal and shear loads. It was shown that depending on the test conditions, either a rolling process or a sliding of the fullerenes could be possible. These in situ TEM observations are the first carried out with IF nanoparticles.     

Cryogenic linear Paul trap for cold highly charged ion experiments

Storage and cooling of highly charged ions require ultra-high vacuum levels obtainable by means of cryogenic methods. We have developed a linear Paul trap operating at 4 K capable of very long ion storage times of about 30 h. A conservative upper bound of the H(2) partial pressure of about 10(-15) mbar (at 4 K) is obtained from this. External ion injection is possible and optimized optical access for lasers is provided, while exposure to black body radiation is minimized. First results of its operation with atomic and molecular ions are presented. An all-solid state laser system at 313 nm has been set up to provide cold Be(+) ions for sympathetic cooling of highly charged ions.     

低温输油臂紧急脱离装置上切断阀的设计应用

介绍了输油臂低温紧急脱离装置的结构、工作原理和性能特点,重点叙述了切断阀阀座密封和切断阀主要参数的选取.     

A high-pressure atomic force microscope for imaging in supercritical carbon dioxide

A high-pressure atomic force microscope (AFM) that enables in situ, atomic scale measurements of topography of solid surfaces in contact with supercritical CO(2) (scCO(2)) fluids has been developed. This apparatus overcomes the pressure limitations of the hydrothermal AFM and is designed to handle pressures up to 100 atm at temperatures up to ～350 K. A standard optically-based cantilever deflection detection system was chosen. When imaging in compressible supercritical fluids such as scCO(2), precise control of pressure and temperature in the fluid cell is the primary technical challenge. Noise levels and imaging resolution depend on minimization of fluid density fluctuations that change the fluid refractive index and hence the laser path. We demonstrate with our apparatus in situ atomic scale imaging of a calcite (CaCO(3)) mineral surface in scCO(2); both single, monatomic steps and dynamic processes occurring on the (1014) surface are presented. This new AFM provides unprecedented in situ access to interfacial phenomena at solid-fluid interfaces under pressure.     

In Situ Attenuated Total Reflection (ATR/FT-IR) Tribometry: A Powerful Tool for Investigating Tribochemistry at the Lubricant–Substrate Interface

To investigate the chemical changes occurring at metal/lubricant interfaces under tribological conditions in the boundary-lubrication regime, an in situ system for conducting quantitative tribological measurements has been constructed by combining an attenuated total reflection Fourier-transform infrared (ATR/FT-IR) spectrometer with a reciprocating tribometer. By periodically acquiring ATR/FT-IR spectra during sliding, spectroscopic changes due to thermal and/or tribochemical reactions occurring at the metal/oil interface can be monitored and correlated with friction measurements. The usefulness of this tribological test system has been demonstrated by performing ATR tribological experiments in the presence of a poly-α-olefin base oil at high temperature (423 K) on iron-coated germanium ATR crystals.     

Lubrication effect of liquid nitrogen in cryogenic machining friction on the tool-chip interface

The liquid nitrogen as an environmentally safe coolant has been widely recognized in cryogenic machining, its function as a lubricant is plausible due to its chemical inertness, physical volatility and low viscosity. Since a reduced friction is a direct witness of the lubrication effect from a tribological viewpoint, this paper presents an evaluation of the apparent friction coefficient on the tool-chip interface in cryogenic cutting operations to prove and characterize the lubricity of LN2 in cryogenic machining. The cryogenic cutting technology used in this study is based on a cooling approach and liquid nitrogen delivery system which are intended to apply liquid nitrogen in well-controlled fine jets to selectively localized cutting zones and to penetrate liquid nitrogen to the tool-chip interface. It has been found that the apparent friction coefficient can be significantly reduced in cryogenic machining, depending on the approach of liquid nitrogen delivery.