Electrical and Mechanical Behavior of Aerosol Jet–Printed Gold on Alumina Substrate for High-Temperature Applications

There is a growing interest in the development of microelectronics that can perform reliably and robustly at temperatures above 300 °C. Such devices require stable thermal properties, low thermal drift, and thermal cycling resistance. Conventional hybrid circuit technology demonstrates high-temperature packages, but the high costs and lead time are significant drawbacks. In contrast, additive manufacturing processes, including aerosol jet printing (AJP), offer cost and time benefits, as well as 3D structures and embedded features. However, the properties and reliability of additive packaging materials at extreme temperatures are not well known. Herein, the reliability at temperatures up to 750 °C in terms of electrical performance and mechanical strength of aerosol jet printed gold thick films onto ceramic substrates are assessed. Thermal coefficient of resistance of printed gold films is measured. The electrical resistance stability and leakage current of printed gold structures are also characterized during over 100 h of aging at temperatures up to 750 °C. Finally, the mechanical adhesion strength of the printed gold films is evaluated after aging for 100 h at temperatures up to 750 °C. The adhesion of the printed gold to the ceramic substrates remains high after aging, very stable resistances and minimal leakage currents have been observed.     

Role of nanoscale Cu/Ta interfaces on the shock compression and spall failure of nanocrystalline Cu/Ta systems at the atomic scales

Molecular dynamics (MD) simulations are used to investigate the role of size and distribution of nanoscale Cu/Ta interfaces on the nucleation and evolution of defects during shock loading and spall failure of nanocrystalline (nc) Cu/Ta alloys. Cu/Ta interfaces are introduced through the embedding of Ta clusters in nc-Cu matrix. The phase stability of the embedded Ta clusters either as FCC or BCC clusters is first investigated and reveals that the FCC Ta clusters have a lower energy for diameters less than 4 nm, whereas the BCC Ta clusters have a lower energy for the larger diameters. The shock simulations are then carried out for Ta clusters with an average diameter of 1 and 3 nm and concentrations of 3.0, 6.3 and 10.0% to investigate the role of size and distribution of Cu/Ta interfaces (due to presence of clusters) on the nucleation and evolution of dislocations as well as the spall strength of the alloy. The MD simulations indicate that the Cu/Ta interfaces reduce the capability of nc-Cu to accommodate plasticity through nucleation of dislocations and create void nucleation sites during spallation. The MD simulations further reveal that the impact strengthening effects due to the presence of nanoscale Cu/Ta interfaces are strongly dependent upon the size and distribution of Ta clusters, as well as the grain size of Cu matrix. Smaller size of interfaces (cluster size), higher concentration of Ta (smaller spacing between interfaces) and larger matrix grain size render higher spall strengths of nc-Cu/Ta microstructures.     

Measuring strain distributions in amorphous materials.

A number of properties of amorphous materials including fatigue, fracture and component performance are governed by the magnitude of strain fields around inhomogeneities such as inclusions, voids and cracks. At present, localized strain information is only available from surface probes such as optical or electron microscopy. This is unfortunate because surface and bulk characteristics in general differ. Hence, to a large extent, the assessment of strain distributions relies on untested models. Here we present a universal diffraction method for characterizing bulk stress and strain fields in amorphous materials and demonstrate its efficacy by work on a material of current interest in materials engineering: a bulk metallic glass. The macroscopic response is shown to be less stiff than the atomic next-neighbour bonds because of structural rearrangements at the scale of 4-10 A. The method is also applicable to composites comprising an amorphous matrix and crystalline inclusions.     

Enrichment of single-walled carbon nanotubes by diameter in density gradients

The bulk enrichment and separation of single-walled carbon nanotubes (SWNTs) by diameter has been achieved through ultracentrifugation of DNA-wrapped SWNTs in aqueous density gradients. The separation is identified by the visual formation of colored bands of SWNTs in the density range of 1.11-1.17 g cm(-3). The optical absorbance spectra of the separated SWNTs indicate that SWNTs of decreasing diameter are increasingly more buoyant. This nondestructive and scalable separation strategy is expected to impact the fields of molecular electronics, optoelectronics, and sensing where SWNTs of a monodisperse band gap are essential.     

Metal dusting (catastrophic carburization) of a waste heat boiler tube

A waste-heat boiler at a chemical plant suffered an unusual tube failure. The boiler is part of the partial oxidation (POx) syngas production for a 2-ethyl hexanol unit. The syngas primarily consists of H₂, CO and CO₂ with trace amounts of CH₄. Steam is also reportedly injected into the process. The syngas enters the boiler at approximately 1800°F (980°C) on the internal side of the tube and is cooled, while generating approximately 640 psi (4.41 MPa) steam at 490°F (255°C) on the outside of the tube. The internal surface of the tube contained a region of metal loss that was approximately 1 inches long by inch wide (44.5 mm by 19 mm). The metal loss was very localized with little evidence of attack elsewhere on the tube's surface. Molten salt attack, sulfidation and metal dusting were considered as possible mechanisms for the metal loss. It was determined that metal dusting, also called catastrophic carburization, was the cause of the metal loss. The cause of the metal dusting was localized overheating of the tube, which developed because of water/steam flow disruption due to contact of the tube baffle with the tube. Approximately one year after this tube failure, the boiler suffered two more tube failures, which were also attributed to metal dusting.     

Galvanomagnetic Phenomena in Layered Organic Conductors

The dependence of the resistance and the Hall field in organic metals with the quasi-two-dimensional electron energy spectrum on the magnetic field strength and orientation is analyzed in the strong field limit. The inter-plane resistance is shown to be strongly dependent on the of magnetic field orientation. When the angle between the field and the highly conducting plane is zero, the resistance increases linearly in a relatively wide field range. The angle dependence of magnetoresistance at small is nonmonotonic: it exhibits a local minimum and then a sharp peak around = 0. The Hall constant in strong magnetic field does not depend on the field orientation.