Kinetic and thermodynamic description of intermediary phases formation in Ti-Al system during reactive sintering

Reactive sintering is currently considered as a promising production route for titanium aluminides in many research works. However, the published descriptions of the reaction mechanism are contradictory or lacking, especially at the temperatures below the melting point of aluminium. This work aims to fill this gap, providing the description of the reactive sintering process at the temperatures between 400 and 900 degrees C. The phases' formation sequence and reaction kinetics were studied and explained using experimental model (Ti/Al diffusion couple) and real reactively sintered samples of equiatomic Ti-Al compressed powder blend. Moreover, phase formation was thermodynamically assessed. It was revealed that Ti2Al5 phase formed preferentially. This phase has not been reported previously as a starting phase in reactive sintering. According to results obtained by experimental model, its formation is controlled by diffusion at 700 degrees C. This phase reacted with aluminium forming pure TiAl3 phase or with titanium, resulting in TiAl phase. Subsequently, TiAl phase reacted with titanium, leading to the Ti3Al phase, or with already present Ti2Al5 phase yielding TiAl2 intermetallic compound. Titanium-rich Ti3Al phase could form only at the temperature of 600 degrees C or above

How to Supply Assembly Liines

Great efforts are currently dedicated to cost engineering in industry. The lean production approach is a good way to lower production costs. Material flows and treatment should be planned and controlled neither too early nor too late, because early production leads to an increase of stocks of materials and late production to a backlog of orders. This task is especially important in serial production, e.g. in the automotive industry. A buffer stock could be connected with assembly lines in many ways, such as handcarts, fork lift trucks or special cableways. A modern method of material supply in an assembly workshop is the usage of tow trains consisting of a tow truck and several carts. The number of carts in a train can change but it cannot be high because of turnings and crossings. The task is to find and optimize transport routes. This task is considered to be NP-hard. The paper describes several approaches to solving the task

Navigation and Information System for Visually Impaired People

. Orientation is one of the most important problems of visually impaired people. The aim of this paper is to suggest a contribution to the solution of this problem using computer technology. The basic idea is the detection of motion and orientation using sensors and consequent position identification. The detected trajectory is compared with a map and is corrected by means of the algorithm described in the paper. Some problems concerning sensor detection of human motion are also discussed. Based on the determined position other relevant information is provided to the user of system (information describing the neighbourhood of the actual position, optimal way to the chosen destination, possible warnings). 1 Introduction Contemporary information technology o#ers various possibilities for solving many problems of handicapped people. Serious impairment of sight is a considerable limitation for such people. The main problem is a substantial information deficit and its feedback --- communic..

Using Two Stackers on One Rail in a Production System

This paper deals with the possibilities for using two stackers for interoperation transport in a workshop with a technological layout of workplaces. Basic layouts of stacker production systems are discussed. Several strategies for selecting and ordering transport demands in systems with two stackers on one rail have been simulated and evaluated. FIFO strategies are the worst in various layouts of workplaces. On the other hand, the strategy of the choice of the proximate transport demand is simple and very successful. Good technological layout can enhance transport performance

Nanocrystalline Boron-Doped Diamond as a Corrosion-Resistant Anode for Water Oxidation via Si Photoelectrodes

Due to its high sensitivity to corrosion, the use of Si in direct photoelectrochemical (PEC) water-splitting systems that convert solar energy into chemical fuels has been greatly limited. Therefore, the development of low-cost materials resistant to corrosion under oxidizing conditions is an important goal toward a suitable protection of otherwise unstable semiconductors used in PEC cells. Here, we report on the development of a protective coating based on thin and electrically conductive nanocrystalline boron-doped diamond (BDD) layers. We found that BDD layers protect the underlying Si photoelectrodes over a wide pH range (1-14) in aqueous electrolyte solutions. A BDD layer maintains an efficient charge carrier transfer from the underlying silicon to the electrolyte solution. SiIBDD photo electrodes show no sign of performance degradation after a continuous PEC treatment in neutral, acidic, and basic electrolytes. The deposition of a cobalt phosphate (CoPi) oxygen evolution catalyst onto the BDD layer significantly reduces the overpotential for water oxidation, demonstrating the ability of BDD layers to substitute the transparent conductive oxide coatings, such as indium tin oxide (ITO) and fluorine-doped tin oxide (FTO), frequently used as protective layers in Si photoelectrodes