Anomalous Low Thermal Conductivity of Atomically Thin InSe Probed by Scanning Thermal Microscopy

The ability of a material to conduct heat influences many physical phenomena, ranging from thermal management in nanoscale devices to thermoelectrics. Van der Waals 2D materials offer a versatile platform to tailor heat transfer due to their high surface-to-volume ratio and mechanical flexibility. Here, the nanoscale thermal properties of 2D indium selenide (InSe) are studied by scanning thermal microscopy. The high electrical conductivity, broad-band optical absorption, and mechanical flexibility of 2D InSe are accompanied by an anomalous low thermal conductivity (κ). This can be smaller than that of low-κ dielectrics, such as silicon oxide, and it decreases with reducing the lateral size and/or thickness of InSe. The thermal response is probed in free-standing InSe layers as well as layers supported by a substrate, revealing the role of interfacial thermal resistance, phonon scattering, and strain. These thermal properties are critical for future emerging technologies, such as field-effect transistors that require efficient heat dissipation or thermoelectric energy conversion with low-κ, high electron mobility 2D materials, such as InSe.     

Inertia effects in a conical porous bearing with a viscoelastic lubricant

The effects of the inertia and porosity of the bearing material were investigated for conical and squeeze film bearings with a viscoelastic lubricant by the method of averaged inertia. The inertia forces reduce the loadbearing capacity. The porosity of the material decreases the pressure and the load capacity. The effect of the elasticity of the lubricant is to increase the pressure and the load-bearing capacity at any point. The effects of the characteristics of the bearing on the pressure and the load-bearing capacity are presented graphically.     

Polymer-assisted co-precipitation route for the synthesis of Al$$_{}$$O$$_{3}$$3–13% TiO$$_{}$$ nanocomposite

The present investigation reveals the effect of processing parameters on the properties of alumina–titania (Al\(_{2}\)O\(_{3}\)–TiO\(_{2}\)) nanocomposites. A polymer-assisted (Pluronic P123 triblock co-polymer) co-precipitation route has been employed to synthesize \(\hbox {Al}_{2}\hbox {O}_{3}\)–\(\hbox {TiO}_{2}\) nanoparticles. As a surfactant, pluronic P123 polymer exhibits hydrophobic as well as the hydrophilic nature simultaneously which detains the agglomeration and hence the nano size particle have been obtained. Effect of surfactant concentration on morphology and particle size of product has also been investigated. Thermal behaviour of the prepared powder samples have been studied using differential scanning calorimeter/thermal gravimetric analysis and dilatometer. Formation of aluminium-titanate \((\hbox {Al}_{2}\) \(\hbox {TiO}_{5})\) phase has been confirmed using X-ray diffraction analysis. It has been observed by field emission scanning electron microscopy analysis that the particle size reduced effectively (below 100 nm) when polymer-assisted co-precipitation route is used instead of the simple co-precipitation technique. A highly dense microstructure of sintered samples has been obtained, driven by reduced particle size.     

Anisotropic thermal diffusivity characterization of aligned carbon nanotube-polymer composites

The anisotropic thermal diffusivity of aligned carbon nanotube-polymer composites was determined using a photothermoelectric technique. The composites were obtained by infiltrating poly-dimethyl siloxane (PDMS) in aligned multiwall CNT arrays grown by chemical vapor deposition on silicon substrates. The thermal diffusivities are insensitive to temperature in the range of 180 K-300 K. The thermal diffusivity values across the alignment direction are approximately 2-4 times smaller than along the alignment direction and larger than effective media theory predictions using reported values for the thermal diffusivity of millimeter thick aligned multiwall carbon nanotube arrays. The effective room temperature thermal conductivity of the composite along the carbon nanotube alignment direction is at least 6X larger than the thermal conductivity of the polymer matrix and is in good agreement with the effective media predictions. This work indicates that infiltration of long and aligned carbon nanotube arrays is currently the most efficient method to obtain high thermal conductivity polymer composites.     

Microstructural evolution and mechanical, and corrosion property evaluation of Cu-30Ni alloy formed by Direct Metal Deposition process

In the current investigation Cu-30Ni alloy was successfully laser deposited on a rolled C71500 plate substrate by Direct Metal Deposition technology. The microstructural investigation of the clad was performed using optical and scanning electron microscopy. The phase and crystal structure analysis was performed using X-ray diffraction technique and transmission electron microscopy. The microstructure consisted of columnar and equiaxed dendrites with face centered cubic crystal structure. The dendrites grew epitaxially from the substrate and layer and bead boundaries. Dendrites’ growth direction 〈0 0 1〉 and growth angle 60° was maintained in each layer. The average primary dendritic arm spacing at the bottom part of the layers was about 7.5 μm and average secondary dendritic arm spacing in the upper part of the layer varied between 2 μm and 4.5 μm. The lattice parameter of the identified phase was found to be longer than that reported in literature. The reported lattice parameters in literature are however from samples processed under equilibrium conditions. The microhardness of the clad was found to be less than the substrate but very consistent along the clad. Cu-30Ni clad specimen showed higher ultimate tensile strength but lower yield strength and percentage elongation as compared to the C71500 substrate. DMD Cu-30Ni clad/C71500 substrate specimen showed the worst mechanical properties. The corrosion resistance of the specimens was found to decrease in the order DMD Cu-30Ni clad, half-and-half DMD Cu-30Ni clad-C71500 substrate, and C71500 substrate.     

The direct metal deposition of H13 tool steel for 3-D components

The rapid prototyping process has reached the stage of rapid manufacturing via the direct metal deposition (DMD) technique. The DMD process is capable of producing three-dimensional components from many of the commercial alloys of choice. H13 tool steel is a difficult alloy for deposition due to residual stress accumulation from martensitic transformation; however, it is the material of choice for the die and tool industry. This article reviews the state of the art of DMD and describes the microstructure and mechanical properties of H13 alloy deposited by DMD. J. Mazumder earned his Ph.D. at Imperial College, London University. He is a professor at the University of Michigan. J. Choi earned his Ph.D. in mechanical engineering at the University of Illinois at Urbana-Champaign in 1994. He is currently a research fellow at the University of Michigan. K. Nagarathnam earned his Ph.D. in mechanical engineering at the University of Illinois at Urbana-Champaign in 1994. He is currently a research fellow at the University of Michigan. Dr. Nagarathnam is a member of TMS. Justin Koch earned his M.S. in mechanical engineering at the University of Illinois at Urbana-Champaign in 1985. He is currently a project engineer for Caterpillar. Daniel Hetzner earned his Ph.D. in metallurgical engineering at the University of Tennessee in 1980. He is currently a research specialist.     

Mechanism of pre-annealing effect on electromigration immunity of Al–Cu line

In this work, we have investigated effects of pre-annealing, which means annealing performed prior to electromigration (EM) test, on EM lifetime of Al–Cu lines. We also investigated the relationships between void formation and size of Cu precipitated area in the line under various pre-annealing conditions. It is found that EM lifetime decreases while the size of the Cu precipitated area increases with lengthening of the pre-annealing period. However, no void is observed after this pre-annealing treatment. The results indicate that the tiny voids generated by formation of Cu precipitation do not move during the pre-annealing period. In the case of EM testing, Cu precipitation occurs followed by void formation at the cathode area, probably due to diffusion of vacancies which are generated by Cu atom movement by electron wind. As a result, resistance of the line increases and eventually it fails completely.It is demonstrated that pre-annealing helps Cu atoms to accumulate at the grain boundary forming the Cu precipitates. However, in samples with no pre-annealing treatment, the accumulation of Cu atoms at the grain boundaries begins just after the start of the EM testing and then the Cu precipitates diffuse toward the anode. Since EM test conditions are the same for samples with and without pre-annealing treatment, the only variation is the incubation time to accumulate Cu atoms at the grain boundaries. This is the reason why EM lifetime of pre-annealed samples is shorter than that of samples with no pre-annealing treatment.     

Gloss and Texture Control of Powder Coated Films

The desired appearance of powder coated film depends upon the specific industrial application. While a glossy, mirror-like finish with a high distinctiveness of image (DOI) is required for automotive clear coat applications, much outdoor equipment and many household appliances require smoothly textured finishes that hide surface irregularities, fingerprints, and surface markings. This textured finish of powder coated film, often termed orange peel appearance, can be controlled by adjusting the chemical formulation and the physical properties of the powder and by optimizing the electrostatic application process. These adjustments allow a wide-ranging control of gloss and orange peel texture. The chemical formulation of the powder is often determined by the functional needs of the coatings: providing protection against corrosion, heat, UV radiation, and physical impact. In many cases where the formulation cannot be changed, the electrostatic spraying process for the powder can be adjusted to achieve the desired gloss and texture.

In electrostatic powder coating, back corona on the deposited powder layer often causes defects in the film. However, if the electrical field intensity inside the powder layer is below the breakdown level, the adverse effect of back corona can be avoided, thus improving the uniformity of the deposited powder layer. In the absence of back corona, increasing the high voltage applied to the corona gun improves both the smoothness and the glossiness of cured films. Back corona can be reduced by increasing the surface conductivity of the powder. Increasing the relative humidity during spraying also decreases the roughness, since the augmented surface conductivity allows the powder layer charge to decay faster. The optimal relative humidity value for applying powder for uniform film thickness was found to be 60%; increasing humidity beyond that point led to surface degradation, possibly due to excess moisture trapped in the powder layer. While the surface smoothness increased, the glossiness did not vary significantly with the change in relative humidity. Another factor for film surface properties is the "hiding power" of the unevenness of the substrate surface. A rough substrate can be responsible for a rough film surface when film thickness is less than 25 µm. It was found that films 40 to 50 µm thick can successfully cover scratches of about 20 µm depth on the substrate. Typical values of film waviness varied from 1.5 to 3 µm, and film roughness varied from 0.2 to 0.4 µm for epoxy film with 60 to 65 µm thickness.     

Al319激光表面合金化

用激光表面合金化的方法加入Ni、Cr等成分在铝合金基体材料表面形成具有良好耐磨性能的合金化层。实验首先将合金粉末调和后涂于试样表面,用CO_2激光以不同功率、不同的光斑移动速度对徐层进行激光合金化处理。分析结果表明,工艺参数极大地影响合金化效果;可得到显微硬度达1400HV的高度硬化层;选用合适的功率、光斑运动速度及预涂层厚度可得到单道轨迹、多道搭接及整个试样表面的无气孔、裂纹缺陷的组织细密的合金化层;层内主要强化相为AlNi和多种Al/Ni金属间化合物。最终得到的全试样表面合金化层的硬度比基体高60—100HV,耐磨性比基材提高3—5倍。     

Li4Ti5O12: A Visible‐to‐Infrared Broadband Electrochromic Material for Optical and Thermal Management

Broadband electrochromism from visible to infrared wavelengths is attractive for applications like smart windows, thermal camouflage, and temperature control. In this work, the broadband electrochromic properties of Li₄Ti₅O₁₂ (LTO) and its suitability for infrared camouflage and thermoregulation are investigated. Upon Li⁺ intercalation, LTO changes from a wide bandgap semiconductor to a metal, causing LTO nanoparticles on metal to transition from a super‐broadband optical reflector to a solar absorber and thermal emitter. Large tunabilities of 0.74, 0.68, and 0.30 are observed for the solar reflectance, mid‐wave infrared (MWIR) emittance, and long‐wave infrared (LWIR) emittance, respectively, with a tunability of 0.43 observed for a wavelength of 10 µm. The values exceed, or are comparable to notable performances in the literature. A promising cycling stability is also observed. MWIR and LWIR thermography reveal that the emittance of LTO‐based electrodes can be electrochemically tuned to conceal them amidst their environment. Moreover, under different sky conditions, LTO shows promising solar heating and subambient radiative cooling capabilities depending on the degree of lithiation and device design. The demonstrated capabilities of LTO make electrochromic devices based on LTO highly promising for infrared‐camouflage applications in the defense sector, and for thermoregulation in space and terrestrial environments.