The effect of ball milling on the ph of Mg-based metals,oxides and Zn in aqueous media

The pH variation induced electrochemical reactions for Zn, Mg, MgO and the mixture MgMgO (25 wt.% Mg and 75 wt.% MgO) fabricated by high-energy mechanical ball milling in 3.5 wt.% NaCl have been investigated using the potentiodynamic method and electrochemical impedance spectroscopy to control the rate of magnesium dissolution as cathodic protection. It is known that pH variation is a good measurement of dissolution for cathodic protection materials. The pH of Zn was modestly increased because of the formation of ZnO. Mg showed a relatively high pH value when forming as Mg(OH)₂. Highly activated MgMgO showed the highest pH value, located between Mg and MgO, of equilibrium potentials and impedance. This indicates that the electrochemical reaction in 3.5 wt.% NaCl has been changed by mechanical ball milling. This implies that the dissolution rate can be controlled by high-energy mechanical ball milling.     

The analysis of 2′-fucosyllactose concentration in Korean maternal milk using LC–MS/MS

Food Science and Biotechnology - Despite health benefits reported recently, 2′-fucosyllactose (2′-FL) concentration in maternal milk was not conclusively reported because it varies...     

Bioleaching: A microbial process of metal recovery; A review

The present review describes the historical development and mechanisms of bioleaching. Recent development has shown commercial application of the process and, concurrently, details pertaining to the key microorganisms involved in these processes have been described. Bioleaching of metal sulfides is caused by diverse groups of bacteria. The dissolution biochemistry signifies two types of pathways, which are specifically determined by the acid-solubility of the sulfides, the thiosulfate and polysulfate pathways. This sulfide dissolution can be affected by ‘direct’ and ‘indirect’ mechanisms. In the ‘indirect’ mechanism bacteria oxidize only dissolved iron (II) ions to iron (III) ions and the latter can then attack metal sulfides and then be reduced to iron (II) ions. The ‘direct’ mechanism requires the attachment of bacteria to the sulfide surfaces. In the case of thiobacilli, bacteria secrete exopolymer that facilitates attachment of the bacteria to a metal surface, thus enhancing the leaching rate. In terms of eco-friendliness and process economics, within the field of biohydrometallurgy the technology is considered robust.     

Nondestructive Evaluation of Far-Side Corrosion Around a Rivet in a Multilayer Structure

This paper presents a sensor system for inspection of far-side defects around rivets in a multilayer structure. The sensor system includes 64 InSb Hall sensors arrayed in 0.52-mm intervals, over a total length of 33.28 mm. The sensor system was tested on two flat specimens, which have two layers of an aluminum alloy, with and without far-side defects around rivets. The sensor system performance was estimated via both the receiver operating characteristic and the probability of detection (POD) curves. Furthermore, a quantitative evaluation of the surface area, depth, and volume of a defect having a POD greater than 90% was carried out.     

Spin-capable carbon nanotube sheet as a substitute for TCO in transparent electronics and displays

Spin-capable carbon nanotubes (CNTs) are proposed as a promising material for transparent conductive films (TCFs) to replace indium tin oxide (ITO) in optoelectronic and flexible applications. CNT-TCFs were prepared by a dry-spun method, a straightforward transfer process for fabricating CNT-based films. The effects of acid treatment on the electrical and optical properties of CNT-TCF were evaluated. After acid treatment, the CNT-TCF possesses a much higher electrical conductivity and slightly improved transparency compared to films that have not undergone acid treatment. The electrical properties of the CNT films were dramatically affected by the type of acid treatment. The CNT-TCF treated with a fuming acid treatment exhibited better performance than the CNT-TCF treated with immersion acid treatment only, with a low sheet resistance (210 Ω/sq) and high transmittance (90%) comparable to those of ITO films.     

Fabrication of four-point biped robot foot module based on contact-resistance force sensor and its evaluation

This paper presents the design of robot foot module of four-point biped walking robot and its fabrication. The foot module has four sensor units based on contact-resistance force sensor. The thin-film-type force sensor is fabricated by coating resistive ink on thin polyimide film using silk screening technique. The simple structure is devised and fabricated to assemble the thin force sensor rigidly. The unit force sensor module is evaluated by the calibration setup to obtain the characteristics of repeatability and hysteresis. The sensor module presents hysteresis error of about 5% and repeatability error of about 0.37%. The calculated zero moment point (ZMP) of the foot module is also compared with the measured position using static load of 50 N. The maximum location error of ZMP is less than 10%. The robot foot module shows the possibility of applying it to humanoid walking.     

Fabrication of robot head module using contact-resistance force sensor for human-robot interaction and its evaluation

This paper presents a design of a robot head module with touch sensing algorithms that can simultaneously detect contact force and location. The module is constructed with a hemisphere and three sensor-units that are fabricated using contact-resistance force sensors. The surface-part is designed with the hemisphere that measures 300 mm in diameter and 150 mm in height. Placed at the bottom of the robot head module are three sensor-units fabricated using a simple screen printing technique. The contact force and the location of the model are evaluated through the calibration setup. The experiment showed that the calculated contact positions almost coincided with the applied load points as the contact location changed with a location error of about ±8.67 mm. The force responses of the module were evaluated at two points under loading and unloading conditions from 0 N to 5 N. The robot head module showed almost the same force responses at the two points.     

Failure Investigation of Counterweight Separation from Aircraft Propeller

The counterweight of a propeller in a turboprop aircraft was separated during an engine run-up inspection. If this separation occurs in-flight, it may result in an accident involving serious damage or injury. In this investigation, the failed counterweight clamping assembly was studied to determine the root cause of failure. Both experimental and computational investigations were performed to explore and confirm the effects of experimentally observed anomalies on potential clamping assembly failure. Dimensional measurement of the failed clamping thread area by X-ray CT scanning revealed significant deviation from requirements in the major diameter of the thread. Fractographic and microscopic examination along with chemical analysis confirmed that the clamping bolts were pulled out due to overload stripping failure of the internal threads. Detailed computational fracture modeling utilizing the XFEM crack simulation technique provided further insight proving that thread engagement length had a significant effect on the clamping assembly failure. Based on these observations, it was concluded that the main root cause of the stripping failure was the dimensional nonconformance of the internal thread from the requirements in standard 7/16-20UNF-3B that resulted in the loss of thread engagement length.     

Failure analysis of X-Msn oil cooler fan blade on helicopter

An analysis on cracks found on AZ91C-T6 X-MSN oil cooler fan blades of a HH-47 helicopter was performed. Cracks on oil cooler fan blades, which are conditional parts, are variously distributed between 199 and 1023 operating hours. All cracks initiated from the blade root mid span as a form of multi-origin, and then developed by HAF (high amplitude fatigue). Cracks were initiated from gas porosity formed in the casting process, a shrinkage cavity and a pit instigated between base metal and coating layer. The blade with 1238 operating hours had a crack 42 mm out of the total length of 45 mm. This crack began from the convex side and penetrated through the concave side causing blade fracture. Therefore, improvement of blade manufacturing process is required and blades in operation are recommended to be eddying current inspected after paint coating removal every 250 h and to be replaced every 1000 operation hours to prevent fracture.     

Failure of the J79 Engine Compressor Blade Due to Stall

The fractured and damaged compressor rotor blades of a J79 engine have been examined. Optical, stereoscopic, microhardness testing, and SEM examinations were carried out to find out the causes of the fracture. The material of the blades was STS403 and blades were used without coating. From the 15th through the 17th compressor stages the rotor blades, stator vanes, combustion, and turbine sections were damaged. The fractured surface of the 17th blade show multiple origins, secondary cracking in the blade’s convex surface, and extensive propagation before separation and rougher surfaces. The metallographic analysis of the microstructure suggested work hardening. Based on the results, the cause of the fractured blade was high-amplitude fatigue, due to severe stall. After normal engine usage of 5 months, the blade fractured and blade fragments hit the other compressor blades, stators, and casing, and caused damage in both combustion and turbine sections.