Structural Influence on the Thermal Conversion of Self‐Catalyzed HfB2/ZrB2 Sol–Gel Precursors by Rapid Ultrasonication of Oxychloride Hydrates

Sol–gel precursors to HfB₂ and ZrB₂ are processed by high‐energy ultrasonication of Hf,Zr oxychloride hydrates, triethyl borate, and phenolic resin to form precipitate‐free sols that turn into stable gels with no catalyst addition. Both precursor concentration and structure (a sol or a gel) are found to influence the synthesis of the diboride phase at high temperature. Decreasing sol concentration increases powder surface area from 3.6 to 6.8 m²/g, whereas heat‐treating a gel leads to residual oxides and carbides. Particles are either fine spherical particles, unique elongated rods, and/or platelets, indicating particle growth with directional coarsening. Investigation of the conversion process to ZrB₂ indicates that a multistep reaction is likely taking place with: (1) ZrC formation, (2) ZrC reacts with B₂O₃ or ZrC reacts with B₂O₃ and C to form ZrB₂. At low temperatures, ZrC formation is limiting, while at higher temperatures the reaction of ZrC to ZrB₂ becomes rate limiting. ZrC is found to be a direct reducing agent for B₂O₃ at low temperature (~1200°C) to form ZrB₂ and ZrO₂, whereas at high temperatures (~1500°C) it reacts with B₂O₃ and C to form pure ZrB₂.     

The spectrum study of blood pressure during the disturbance of organic vascular beds

Abstract

Like electrical circuit components, the vascular beds in organs present impedance to waves in systemic circulation. In this study, the authors design an animal experiment to study the effect of the impedance to the pressure waves. We view the systemic circulation as an electrical circuit network, and interpret the vascular beds in organs as lumped components in the electrical circuit. Nature's designing of the systemic circulation minimizes the pressure wave reflection, and maximizes blood distribution. This is very similar to the concept adopted by electrical engineers in designing electrical circuits.     

Hydrogen-induced intergranular failure in nickel revisited

Using a combination of high-resolution scanning and transmission electron microscopy, the basic mechanisms of hydrogen-induced intergranular fracture in nickel have been revisited. Focused-ion beam machining was employed to extract samples from the fracture surface to enable the examination of the microstructure immediately beneath it. Evidence for slip on multiple slip systems was evident on the fracture surface; immediately beneath it, an extensive dislocation substructure exists. These observations raise interesting questions about the role of plasticity in establishing the conditions for hydrogen-induced crack initiation and propagation along a grain boundary. The mechanisms of hydrogen embrittlement are re-examined in light of these new results.     

Some 19th Century Photographers in Syria,Palestine and Egypt

Abstract

By the middle of the 19th century, tourist travel in the Eastern Mediterranean had become quite common. Thus, in April 1835, The Missionary Herald reports: 'The Delaware line-of-battle ship and the schooner Shark, the former being the flag of commodore Patterson, arrived at Beyroot on the 29th of August. The commodore's lady and three daughters were with him. 'The ships had previously anchored at Joppa, while all the officers but one, and the commodore's family, in two successive companies, went up to Jerusalem. A number of the sailors, also, took that opportunity to visit the Holy City, the zeal of some leading them to travel the whole distance on foot. Such a number of Franks had rarely arrived there in company since the time of the crusades. In the commodore's party, seventy-three Americans entered the gates of Jerusalem together’¹. This may well be one of the earliest accounts of a group tour to the Middle East.     

Modelling powder mixing in mass flow discharge: A kinematic approach

The dynamics of a powder flowing in a mass flow regime through a storage bin with a conical hopper, is a well studied problem. However, many challenges remain, including quantification of the mixing that occurs during discharge through the hopper. We have formulated a model based on the conservation of volume of the powder and a semi-empirical expression for velocity profile, (see [1], [2]), and used this to estimate mixing parameters. We have specifically considered the case of an inflow which is disposed in homogeneous horizontal layers as it enters the storage bin. When the powder, in successive layers, enters the hopper, it accelerates and its velocity along the longitudinal axis of the hopper is greater than at the walls. Portions of layers high in the hopper may overtake layers closer to the exit resulting in mixing of the layers. Using this model we are able to quantify the percentage of each layer in a given output volume and present results for typical hopper geometries.     

Cu wire bond parameter optimization on various bond pad metallization and barrier layer material schemes

The use of copper wire for semiconductor package assembly has been gradually gaining acceptance throughout the industry over the last decade. Although copper has several advantages over gold for wire bonding applications, the manufacturing difficulties using copper wire have made high volume, fine pitch copper bonding slow to materialize. In recent years with the spike in gold prices, copper wire has become even more attractive, and this has driven many studies on the topic.Due to the propensity for copper to work harden upon deformation, which occurs during the ball bonding process as the capillary tip smashes the ball into the bond pad, a high amount of stress is transferred into the bond pad structure. This can result in catastrophic defects such as dielectric cracking or pad cratering. The current study aims to quantify the level of underlying bond pad damage with respect to various bond pad metallization and barrier layer schemes. A first bond parameter optimization was completed on each experimental group. The results indicate that barrier layer structure and composition have a significant impact on the presence of pad cratering. The experimental group containing only TiN as the barrier material showed a high occurrence of cratering, while groups with Ti and TiW barrier metals showed no cratering, even if a TiN layer was on top of the Ti. The bond pad metal thickness, on the other hand, does not appear to play a significant role in the prevention of bond pad cratering. Metal thickness values ranging from 0.825 to 2.025 μm were evaluated, and none had bond pad cratering other than the group with TiN as the barrier metal. In addition to the first bond parameter evaluations with various bond pad and barrier metal combinations, the initial free air ball (FAB) optimization is discussed.