Conduction and convection heat transfer characteristics of water-based au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures

The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles’ volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid’s (i.e. water) Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it

Yield strength modelling of formed material using evolutionary computational method

In this paper we propose an evolutionary computation approach for the modelling of yield strength in formed material. One of the most general evolutionary computation methods is genetic programming, which was used in our research. Genetic programming is an automated method for creating a working computer program from a problemćs high-level statement. Genetic programming does this by genetically breeding a population of computer programs using the principles of Darwinianćs natural selection and biologically inspired operations. During our research, material was cold formed by drawing using different process parameters and then determining yield strengths (dependent variable) of the specimens. On the basis of a training data set, various different genetic models for yield strength distribution were developed during simulated evolution. The accuracies of the best models were proved by a testing data set and comparing between the genetic and regression models. The research showed that very accurate genetic models can be developed by the proposed approach

A Study of the Possible Use of Materials With Shape Memory Effect in Shipbuilding

The article presents a study of the possible use of materials with Shape Memory Effect (SME) in shipbuilding, which have two special abilities of transformation and changing shape with changing of temperature or deformation. Among the most well-known SME materials, our study focuses on Ni-Ti and Cu- based alloys. An example of the existing fabrication presents casting of Ni-Ti in the form of a disk, and a new approach – continuous casting of Ni-Ti and CuAlNi alloys in the form of rods. In the article some results are shown of characterisation of microstructure and the basic properties. This was done in accordance with the fact that such scientific approach could define the starting point for further identification of the functional characteristics of these alloys by knowing the their chemical content and microstructure. Numerous studies are being carried out today in order to find the optimal functional characteristics of SME alloys. All of this is aimed at optimising the fabrication of these alloys, with the achievement of suitable properties for application in shipbuilding

A Study of the Possible Use of Materials With Shape Memory Effect in Shipbuilding

The article presents a study of the possible use of materials with Shape Memory Effect (SME) in shipbuilding, which have two special abilities of transformation and changing shape with changing of temperature or deformation. Among the most well-known SME materials, our study focuses on Ni-Ti and Cu- based alloys. An example of the existing fabrication presents casting of Ni-Ti in the form of a disk, and a new approach – continuous casting of Ni-Ti and CuAlNi alloys in the form of rods. In the article some results are shown of characterisation of microstructure and the basic properties. This was done in accordance with the fact that such scientific approach could define the starting point for further identification of the functional characteristics of these alloys by knowing the their chemical content and microstructure. Numerous studies are being carried out today in order to find the optimal functional characteristics of SME alloys. All of this is aimed at optimising the fabrication of these alloys, with the achievement of suitable properties for application in shipbuilding

The new approach of the production technique of discontinuous Cu-C composite

The samples of the Cu-C composite were produced by two different techniques (i) the sintering of powders, and (ii) the internal carbonization of rapidly solidified pure copper. The aim of the present research was to produce a discontinuous Cu-C composite with the submicron dispersion of graphite particles. The results of our microstructural investigation show that the use of the mechanical alloying and sintering of consolidated powders is an inappropriate way to achieve a submicron dispersion of the graphite particles. On the other hand, the combination of rapid solidification and internal carbonization was found to be an efficient technique to obtain the requested microstructure

Metallographic sample preparation of orthodontic Ni-Ti wire

Shape memory alloys (SMA) has been at the forefront of research for the last several decades. In this field especially, Nickel-Titanium (Ni-Ti) alloys have been found to be the most useful of all SMA. The most important applications of SMA Ni-Ti alloys are namely in medicine and dentistry, where they are used as orthodontic wires. In this paper we describe the procedure of preparing metallographic samples of typical orthodontic Ni-Ti wires which are nowadays used in dentistry praxis. We prepared the samples for microstructure observation using a light microscope. Special attention is given to the metallographic preparation, which could result in damages and deformations of the sample surfaces if the procedure is incorrect. Finally, we illustrated the typical metallographic recipe for Ni-Ti SMA alloys for optical observation

Multilayered nano-foils for low-temperature metal-ceramic joining

Over almost two decades metal-ceramic fusing has been the essential step in obtaining materials which benefit from both ceramic and metal materials, i.e. where the combined properties of the metal and ceramic layers are desirable. Soldering and active metal brazing are the most effective when considering fusing methods. This paper presents a low-temperature process for soldering and brazing ceramics to metals, which is based on the use of reactive multilayer foils as a local heat source. The reactive foils range in thickness from 40 μm to less than 100 μm and contain many nanoscale layers and/or domains that alternate between materials with high mixing heat.

Gold in the past, today and future

This paper deals with gold, which is described as a chemical element. Special attention is paid to its physical-chemical properties and, furthermore, where or in what form it can be found in nature. We discuss the role it has played through history and we inform how gold has been developed to the level it has reached today's value. Still more, when gold is broken into nanoparticles, this form could be highly useful for a wide range of processes, including general nanotechnology, electronics manufacturing and the synthesizing of different functional materials. It is important that we know that gold is also used in industry in many engineering applications (contacts in micro-electronics) and medicine (dental alloys, implants)

The Analyses of the Rate of Pitting Corrosion of a NiTi Rod in a Natural Marine Environment

The analysis of the behaviour of new materials in the natural environment is important for their application and commercial use. In order to explore the application of Shape Memory Alloys in the Maritime industry, this research focuses on the corrosive behaviour of the NiTi rod that was produced by means of a continuous casting process. The experiment included three samples of NiTi rods that were exposed to the marine environment for 6, 12 and 18 months at a depth of 3 metres below the surface. The morphological and chemical changes were analysed separately during the experiment. Ultrasonic thickness equipment and the Scanning Electron Microscope (SEM) technique were used for the tests that determined the corrosion rates and detected pitting. The changes in the chemical composition of the NiTi rod were investigated by means of an Energy Dispersive X-ray (EDX) analysis, in order to define the pitting behaviour of the rod`s surfaces during its exposure to seawater. The obtained research results prove that the rate of pitting corrosion follows a progressive curve – the minimum value of corrosion rate equalled 0.04 mm/month, while the maximum value was 0.12 mm/month

Investigation of mechanical and biomedical properties of new dental alloy with high content of Au

The basis for developing a new dental alloy with high Au content is appropriate chemical composition and manufacturing technology. The demands which have to be met when developing a new dental alloy are linked with fulfilling the necessary requirements for making the alloy suitable for use in metal-ceramic restorations. Due to the stress generated by masticatory forces, alloys for dental restorations must have corresponding mechanical properties (yield strength, tensile strength, and elongation), hardness, the coefficient of thermal expansion (CTE), and biocompatibility. Namely dental alloy placed in an oral cavity reacts with the environment and deteriorates. New dental alloy with high Au content is based on the ternary system of Au-Pt-Zn with a nominal composition of 86.9Au-9.9Pt-1.5Zn, and about 1,5 wt.% micro-alloying elements (In, Ir, Rh). The dental alloy was melted and cast in a vacuum-induction melting furnace in Zlatarna Celje. The results analyses of different heat-treated states showed that the optimal mechanical properties and hardness of an Au-Pt-Zn alloy can be reached with combinations of heat treatment for 20 minutes at 723 K and then slowly cooling, if the alloy was annealed at 1223 K for 30 minutes and the water quenched. Research results confirmed that the microstructure of the Au-Pt-Zn alloy consists of two phases: a1-phase rich in Au (main phase) and a2-phase rich in Pt (minor phase). During XRD analysis and use of the Rietveld method, it was found that the a1-phase content is about 98,5 wt.% while the content of a2- phase is 1,5 wt.%. STA analyses show that the Au-Pt-Zn alloy has a solids temperature of about 1292 K and a liquids temperature of about 1412 K. The optical properties of Au-dental alloy were investigated by means of spectrophotometric colourimetry. Spectral reflectance data from the mirror-polished flat samples of initial Au dental alloy were collected under the CIE standard illuminant D65. Finally the test of cytotoxicity of new Au based dental alloys using standard in vitro assays for testing the biocompatibility with establishing new, more sensitive, in vitro tests on cell lines was done. According to the results of our research we can conclude that new dental alloy from Zlatarna Celje satisfied all requested standards regarding mechanical properties, hardness and CTE: Rp0.=550 [N/mm2], Rm =610 [N/mm2], A= 9%, 180 HV and CTE (25-600°C) about 14,45×10-6K-1. This new Au dental alloy has a yellow tinge in comparison to conventional Au-Pt-Zn alloys and did not show cytotoxicity when using standard short-term in-vitro assays on an L929 cell.