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Lubrication of Electrical Components
Published in Bella H. Chudnovsky, Lubrication of Electrical and Mechanical Components in Electric Power Equipment, 2019
Contact Design. Lubricant function depends on application. In separable connectors, it reduces friction during installation, minimizes mechanical wear during connector service, and slows down the destructive effect of fretting corrosion. In most applications, lubrication is advantageous to electrical contacts because it provides lower insertion forces and less wear. Solid and liquid lubricants are often used to enhance the performance of electronic and electrical connectors. In the connector industry, one of the solid lubricants often used in power contacts is lamellar graphite, particularly with electrical brushes in machinery and electric trains, to take advantage of the unique lubrication and electrical conductivity properties of that material. Liquid lubricants reduce friction and minimize mechanical wear; they also must mitigate fretting corrosion and protect against atmospheric corrosion in contact areas of connectors [5]. The results of series of cycling tests showed that all lubricants had a beneficial effect on the performance of bolted joints as manifested by stable operation [6]. In contactor applications, the insertion and withdrawal force can be reduced to as low as 20% of the non-lubricated surface [7].
Quantum Mechanics of Graphene
Published in Andre U. Sokolnikov, Graphene for Defense and Security, 2017
Synthetically, graphite has been produced from carbonaceous materials at high temperatures and pressure. The process is called HOPG (Highly Oriented Pyrolytic Graphite) which means that pyrolytic graphite is received by thermal decomposition of hydrocarbon gas on a heated substrate. Pressure is also applied in order to improve the quality. The subsequent annealing under compression gives HOPG. The typical temperatures range from 2800°C to 3500°C and pressures are in the range of 4000 to 5000 psi. Pyrolytic graphite (carbon) is a material which is close to graphite that has covalent bonding between the layers as a result of defects in its production. The typical production process includes heating of hydrocarbon almost to its temperature of decomposition and then permitting the graphite to crystallize. The angular misalignment of the crystal is improved by annealing of the graphite at temperature of 3300°C. As a result, we have a specimen about 1 mm long (0.1 μm in c-direction). Graphite in general has a lamellar structure, i.e. a microstructure that is composed of thin, alternating layers of various materials which exist in the form of lamellae. Similar to other layered materials, it consists of stacked planes. The forces within the lateral planes are much stronger than between the planes. Because of this, HOPG cleaves like mica. In an atomic resolution scanning tunneling microscopy there are several typical images: one is a close-packed array where each atom is surrounded by six nearest neighbors. The distance between them is 0.246 nm. The hexagonal rings have the center to center distance of 0.1415 nm (see Fig. 4.6).
Electrical Contacts
Published in Bella H. Chudnovsky, Transmission, Distribution, and Renewable Energy Generation Power Equipment, 2017
Lubrication as a technique to provide better performance and protection of electrical contacts is a very complex subject [19–26]. Solid and liquid lubricants are often used to enhance the performance of electronic and electrical connectors. In connector industry, one of the solid lubricants often used in power contacts is lamellar graphite, particularly with electrical brushes in machinery and electric trains, to take advantage of the unique lubrication and electrical conductivity properties of that material. Liquid lubricants reduce friction and minimize mechanical wear, they also must mitigate fretting corrosion and protect against atmospheric corrosion in contact areas of connectors [26].
Synthesis and properties of supramolecular gels based on tetrathiafulvalene and cyanobiphenyl units
Published in Soft Materials, 2021
Lina Ma, Li Wang, Yongqi Bai, Yan Xia, Dongfeng Li, Bingzhu Yin, Ruibin Hou
To understand the molecular packing pattern of D-σ-A molecules in the gel phase, X-ray diffraction patterns of the xerogels of gelator 1a obtained from CCl4 and ethanol were analyzed. In both cases, the diffraction patterns were characterized by three reflection peaks in the small-angle region. For the xerogel obtained from CCl4, three broad Bragg reflections appeared, indicating low crystallinity in the dried gel (Fig. 10a). The corresponding d-spacings of these peaks were 2.51, 1.25, and 0.84 nm, with an approximate ratio of 1:0.50:0.33, which were indexed to (100), (200), and (300) planes, suggesting lamellar packing of the gelators. However, the XRD pattern showed a layered lamella thickness of ~2.5 nm, which was much smaller than the estimated molecular length of 1a (~3.0 nm, see supporting information Figure S27). This showed that the alkyl chains of one molecule presumably wrapped around the adjacent molecule of 1a. Therefore, each repeating layer consisted of a monomolecular arrangement forming a 2D lamellar structure. In contrast, for the xerogel obtained from ethanol, the scattering pattern of the xerogel was characterized by reflection peaks in the low-angle region with a scattering vector ratio of 1:√2:3, corresponding to a 2D rectangular columnar structure with a = 4.32 nm and b = 3.91 nm, as shown in Figure S27b. The proposed packing modes of the gelators in the original and CT complex gels are shown in Figure 11.
Crystal structure evolution in mehcanical alloying and spark plasma sintering of AlxCoCrCuFeNi HEAs
Published in Powder Metallurgy, 2021
Hosein Ziaei, Niloofar Ebrahimzadeh, Zeinab Marfavi, Behzad Sadeghi, Pasquale Cavaliere
It seems that the morphology of powder particles is a lamellar structure with thickness of less than 30 and 15 µm for x = 0.5 and 4 moles HEA alloy, respectively. It seems that mechanical alloying process leads to facilitating the diffusion and alloying among different metallic elements and subsequently gradual refinement. After 20 h milling, the particle size less than 30 and 15 µm are obtained for x = 0.5 and 4 moles HEA alloy, respectively. The crystallite size obtained by XRD results, reveals that these hard agglomerated particles containing of nanoscaled crystallines in scale less than 100 nm. The trend of the formation of these lamellar structures could be explained through the formation of thin sheets containing nanoscaled crystals. Figure 4 depicts the backscattering electron SEM of SPSed Al0.5CoCrCuFeNi HEA alloy. The micrograph consists of two phase contrast in BSE image which are attributed to BCC and FCC phases.
Revealing the apparent and local mechanical properties of heterogeneous lattice: a multi-scale study of functionally graded scaffold
Published in Virtual and Physical Prototyping, 2023
Xiangyu Zhang, Lan Jiang, Xingchen Yan, Zhipeng Wang, Xiaowei Li, Gang Fang
The acicular martensite α′ of as-built (AS) TPMS samples gradually transfer to lamellar α+β after sub-transus heat treatment (Zhang et al. 2018). The decomposition of supersaturation solid solution causes grain coarsening and element segregation, further affects the overall mechanical performance of heat treatment (HT) samples. As shown in Figure 8(a), HT samples generally possess lower and and gentler stress plateau stage. HT samples show superior plasticity and load-bearing capacity, the unloading process is greatly suppressed and the stress–strain curves slowly rise up and exhibit a more significant densifying effect. The plateau strength of G-FGS-HT and I-FGS-HT samples is higher than that of as-built materials. Moreover, the stable stress–strain responding behaviour slightly contributes to the energy absorption efficiency of FGSs, as can be confirmed by Figure 8(a) that increases by 3.8–12.6%. The fracture morphology has also been characterised to illustrate the effect of heat treatment on the failure mechanism (Figure 8(b)). Different from the river-like brittle fracture surface of as-built materials, α+β lamellar structure was observed after sub-transus heat treatment. Vanadium, which is the stabilising elements of β phase, diffused and concentrated at the boundary of α lamellae (Figure 8(b)). The lamellar microstructure was considered to possess superior plasticity and ductility but lower strength that as-built materials (Lütjering 1998; Yan et al. 2018).