Nickel Porous Compacts Obtained by Medium-Frequency Electrical Resistance Sintering

A commercially pure (c.p.) nickel powder was consolidated by Medium-Frequency Electrical Resistance Sintering (MF-ERS). In this consolidation technique, a pressure and the heat released by a high-intensity and low-voltage electrical current are concurrently applied to a metal powder mass. A nickel powder with a high tap porosity (86%) and a low applied pressure (only 100 MPa) is chosen in order to be able to obtain compacts with different levels of porosity, to facilitate the study of the porosity influence on the compact properties. The influence of current intensity and heating time on the global porosity values, the porosity and microhardness distribution, and the electrical conductivity of the sintered compacts is studied. The properties of the compacts consolidated by MF-ERS are compared with the results obtained by the conventional powder metallurgy route, consisting of cold pressing and furnace sintering. A universal equation to describe the porosity influence on all the analyzed properties of powder aggregates and sintered compacts is proposed and validated.

Download Full-text

Influence of Processing Parameters on the Conduct of Electrical Resistance Sintering of Iron Powders

Metals ◽

10.3390/met10040540 ◽

2020 ◽

Vol 10 (4) ◽

pp. 540

Author(s):

Fátima Ternero ◽

Raquel Astacio ◽

Eduardo S. Caballero ◽

Francisco G. Cuevas ◽

Juan M. Montes

Keyword(s):

Electrical Resistance ◽

Low Voltage ◽

Applied Pressure ◽

Processing Parameters ◽

Heating Time ◽

Simultaneous Action ◽

Joule Effect ◽

Furnace Sintering ◽

Short Time ◽

Heat Released

The influence of the applied pressure and electrical parameters on the macrostructure of specimens consolidated by the medium-frequency electrical resistance sintering technique (MF-ERS) is analysed in this work. This technique is based on the application of pressure to a mass of conductive powder that, simultaneously, is being crossed by a high intensity and low voltage electric current. The simultaneous action of the pressure and the heat released by the Joule effect causes the densification and consolidation of the powder mass in a very short time. The effect of the current intensity and heating time on the global porosity, the porosity distribution, and the microhardness of sintered compacts is studied for two applied pressures (100 and 150 MPa). For the different experiments of electrical consolidation, a commercially available pure iron powder was chosen. For comparison purposes, the properties of the compacts consolidated by MF-ERS are compared with the results obtained by the conventional powder metallurgy route (cold pressing and furnace sintering). Results show that, as expected, higher current intensities and dwelling times, as well as higher pressures and the consolidation of compacts with lower aspects ratios, produce denser materials.

Download Full-text

Consolidation of Titanium Powder by Electrical Resistance Sintering: Practice and Simulation

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.876.1 ◽

2021 ◽

Vol 876 ◽

pp. 1-6

Author(s):

Fátima Ternero Fernández ◽

Petr Urban ◽

Raquel Astacio Lopez ◽

Rosa M. Aranda Louvier ◽

Francisco G. Cuevas

Keyword(s):

Electrical Resistance ◽

Titanium Powder ◽

Low Voltage ◽

Pure Titanium ◽

Commercially Pure Titanium ◽

Consolidation Process ◽

Simultaneous Application ◽

Microhardness Distribution ◽

Powder Mass ◽

Furnace Sintering

In this work, a commercially pure titanium powder has been consolidated using the Electrical Resistance Sintering (ERS) process. This technique consists in the consolidation of a powder mass by the simultaneous application of pressure (80 MPa, in this work) and heating caused by the passage of a high intensity (3.5-6.0 kA, in this case) and low voltage current (lower than 10 V), during short dwelling times (0.8-1.6 s, in this work). The resulting compacts have been mechanically characterised by measuring their microhardness distribution. The results obtained are compared with the corresponding values of compacts prepared with the same powders following the conventional P/M route of cold pressing and furnace sintering. The results of some simulations are provided to give information about the temperatures reached inside the compacts during the electrical consolidation process.

Download Full-text

Medium-frequency Electrical Resistance Sintering of Oxidized c.p. Iron Powder

10.20944/preprints201805.0168.v1 ◽

2018 ◽

Author(s):

Juan Manuel Montes Martos ◽

Francisco Gómez Cuevas ◽

Fátima Ternero Fernández ◽

Raquel Astacio López ◽

Eduardo Sánchez Caballero ◽

...

Keyword(s):

Electrical Resistance ◽

Low Voltage ◽

Electrical Current ◽

Medium Frequency ◽

Sintered Compact ◽

Resistance Evolution ◽

Degree Of Oxidation ◽

Powder Mass ◽

Conventional Sintering ◽

High Degree

Commercially pure (c.p.) iron powders with a deliberate high degree of oxidation were consolidated by medium-frequency electrical resistance sintering (MF-ERS). This is a consolidation technique where pressure, and heat coming from a low-voltage and high-intensity electrical current, are simultaneously applied to a powder mass. In this work, the achieved densification rate is interpreted according to a qualitative microscopic model, based on the compacts global porosity and electrical resistance evolution. The effect of current intensity and sintering time on compacts was studied on the basis of micrographs revealing the porosity distribution inside the sintered compact. The microstructural characteristics of compacts consolidated by the traditional cold-press and furnace-sinter powder metallurgy route are compared with results of MF-ERS consolidation. The goodness of MF-ERS versus the problems of conventional sintering when working with oxidized powders is analyzed. The electrical consolidation allows to obtain higher densifications than the traditional route under non-reducing atmospheres.

Download Full-text

Medium-Frequency Electrical Resistance Sintering of Soft Magnetic Powder Metallurgy Iron Parts

Metals ◽

10.3390/met11060994 ◽

2021 ◽

Vol 11 (6) ◽

pp. 994

Author(s):

Raquel Astacio ◽

Fátima Ternero ◽

Jesús Cintas ◽

Francisco G. Cuevas ◽

Juan Manuel Montes

Keyword(s):

Powder Metallurgy ◽

Electrical Resistance ◽

Low Voltage ◽

Vacuum Furnace ◽

Soft Magnetic ◽

Medium Frequency ◽

Joule Effect ◽

Simultaneous Application ◽

Cold Pressing ◽

Furnace Sintering

The fabrication of soft magnetic Fe parts by the medium-frequency electrical resistance sintering (MF-ERS) technique is studied in this paper. This consolidation technique involves the simultaneous application to metallic powders of pressure and heat, the latter coming from the Joule effect of a low-voltage and high-intensity electric current. Commercially pure iron powder was used in the consolidation experiences. The porosity distribution, microhardness, electrical resistivity and hysteresis curves of the final compacts were determined and analysed. The results obtained were compared both with those of compacts consolidated by the conventional powder metallurgy (PM) route of cold pressing and vacuum furnace sintering, and with fully dense compacts obtained by double cycle of cold pressing and furnace sintering in hydrogen atmosphere.

Download Full-text

Effect of Applied Pressure on the Electrical Resistance of Carbon Nanotube Fibers

Materials ◽

10.3390/ma14092106 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2106

Author(s):

Chris J. Barnett ◽

James D. McGettrick ◽

Varun Shenoy Gangoli ◽

Ewa Kazimierska ◽

Alvin Orbaek White ◽

...

Keyword(s):

Photoelectron Spectroscopy ◽

Electrical Resistance ◽

Copper Wire ◽

Applied Pressure ◽

Radial Strain ◽

Electrical Current ◽

Electrical Contacts ◽

Electrical Performance ◽

Macro Scale ◽

Carbon Nanotube Fibers

Carbon nanotubes (CNTs) can be spun into fibers as potential lightweight replacements for copper in electrical current transmission since lightweight CNT fibers weigh <1/6th that of an equivalently dimensioned copper wire. Experimentally, it has been shown that the electrical resistance of CNT fibers increases with longitudinal strain; however, although fibers may be under radial strain when they are compressed during crimping at contacts for use in electrical current transport, there has been no study of this relationship. Herein, we apply radial stress at the contact to a CNT fiber on both the nano- and macro-scale and measure the changes in fiber and contact resistance. We observed an increase in resistance with increasing pressure on the nanoscale as well as initially on the macro scale, which we attribute to the decreasing of axial CNT…CNT contacts. On the macro scale, the resistance then decreases with increased pressure, which we attribute to improved radial contact due to the closing of voids within the fiber bundle. X-ray photoelectron spectroscopy (XPS) and UV photoelectron spectroscopy (UPS) show that applied pressure on the fiber can damage the π–π bonding, which could also contribute to the increased resistance. As such, care must be taken when applying radial strain on CNT fibers in applications, including crimping for electrical contacts, lest they operate in an unfavorable regime with worse electrical performance.

Download Full-text

Medium-Frequency Electrical Resistance Sintering of Highly Oxidized Iron Powder

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.772.113 ◽

2018 ◽

Vol 772 ◽

pp. 113-117

Author(s):

Raquel Astacio ◽

Fatima Ternero ◽

Eduardo Sanchez Caballero ◽

Juan Manuel Montes ◽

Francisco Gomez Cuevas

Keyword(s):

Electrical Resistance ◽

Processing Parameters ◽

High Energy ◽

Heating Time ◽

Current Intensity ◽

Medium Frequency ◽

Consolidation Process ◽

Oxidized Iron ◽

Hardness Change ◽

Compression Resistance

Highly oxidized iron powders were consolidated by means of the medium-frequency electrical resistance sintering technique (MF-ERS). In order to activate the powders and to disperse the oxides coating the particles, prior to the consolidation process, powders were milled in a high-energy mill for 7 minutes. Structural and mechanical characterisations of electrically consolidated compacts were carried out in order to study the effect of two main processing parameters (current intensity and heating time). The compact properties resulted to be very sensitive to these parameters, especially to the current intensity. A change from 5 kA to 10 kA in the current intensity makes the porosity to fall from 30% to 8%. Moreover, using a higher current intensity (10 kA) increases the mechanical properties of the final compacts: micro-hardness change in almost 50 HV, up to 104 HV 1, and compression resistance by around 500 MPa, up to 569 MPa.

Download Full-text

LOW-NOISE SILICON-ON-INSULATOR HALL DEVICES

Fluctuation and Noise Letters ◽

10.1142/s021947750400194x ◽

2004 ◽

Vol 04 (02) ◽

pp. L345-L354 ◽

Cited By ~ 3

Author(s):

Y. HADDAB ◽

V. MOSSER ◽

M. LYSOWEC ◽

J. SUSKI ◽

L. DEMEUS ◽

...

Keyword(s):

Noise Level ◽

Low Voltage ◽

Silicon Layer ◽

Electrical Current ◽

Low Noise ◽

Silicon On Insulator ◽

Technological Parameters ◽

Wide Range ◽

Hall Sensors ◽

Soi Technology

Hall sensors are used in a very wide range of applications. A very demanding one is electrical current measurement for metering purposes. In addition to high precision and stability, a sufficiently low noise level is required. Cost reduction through sensor integration with low-voltage/low-power electronics is also desirable. The purpose of this work is to investigate the possible use of SOI (Silicon On Insulator) technology for this integration. We have fabricated SOI Hall devices exploring the useful range of silicon layer thickness and doping level. We show that noise is influenced by the presence of LOCOS and p-n depletion zones near the edges of the active zones of the devices. A proper choice of SOI technological parameters and process flow leads to up to 18 dB reduction in Hall sensor noise level. This result can be extended to many categories of devices fabricated using SOI technology.

Download Full-text

Protection of railway infrastructure objects against electrical corrosion

Anti-Corrosion Methods and Materials ◽

10.1108/acmm-05-2021-2483 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Liudmyla Trykoz ◽

Svetlana Kamchatnaya ◽

Dmytro Borodin ◽

Armen Atynian ◽

Roman Tkachenko

Keyword(s):

Leakage Current ◽

Electrical Resistance ◽

Electrical Current ◽

Leakage Currents ◽

Destructive Effect ◽

Accelerated Corrosion ◽

Content Type ◽

Pedestrian Bridges ◽

Railway Infrastructure ◽

Bridge Structures

Purpose The purpose of this paper is to develop a technological method of protection against electrical corrosion. One more way to protect the objects is to prevent the electrical current from getting to them. For example, railway objects are surrounded with a material with raised electrical resistance. Design/methodology/approach The railway infrastructure objects (foundations, contact-line supports, reinforced concrete sub-bases, bridge structures, pipelines of engineering networks, supports of passenger platforms and pedestrian bridges, concrete plinth walls of station buildings) are subjected to destruction due to the action of electrical current. One of destruction factors is a corrosion of the concrete constructions which is caused by the leakage current action. Findings Leakage currents and stray currents bypass the structure of supports of high passenger platforms or pipes of engineering networks. These currents spread by the line with the least resistance outside of the structures. Research limitations/implications Electrical leakage current from the rails gets into such structures through sleepers, ballast and soil and leads to accelerated corrosion leaching of concrete. Practical implications The constructions are protected against the destructive effect of electrical corrosion on the metal or concrete of the structure. This scheme is suitable for the construction and reconstruction of railway structures which operate on electrified sections of railways. Originality/value Schemes of technological solution are proposed for protection of foundations, supports of high passenger platforms, pipelines of engineering networks, etc. For this, the arrangement of soil-contained screens with big electrical resistance is suggested.

Download Full-text

Combustion joining of refractory materials: Carbon–carbon composites

Journal of Materials Research ◽

10.1557/jmr.2008.0008 ◽

2008 ◽

Vol 23 (1) ◽

pp. 160-169 ◽

Cited By ~ 29

Author(s):

Jeremiah D.E. White ◽

Allen H. Simpson ◽

Alexander S. Shteinberg ◽

Alexander S. Mukasyan

Keyword(s):

Applied Pressure ◽

Electrical Current ◽

Carbon Composite ◽

Carbon Composites ◽

Refractory Materials ◽

Temperature Combustion ◽

Reaction Media ◽

High Temperature Combustion ◽

Media Layer ◽

Reactive Media

Refractory materials such as carbon possess properties that make joining them difficult. In this work, bonding of a carbon–carbon composite is achieved by employing self-sustained, oxygen-free, high-temperature combustion reactions. The effects of several parameters, such as the composition of the reaction media, and the values of the applied current and pressure, on the mechanical strength of the joint were investigated. It was found that the C–C composite possesses a high activity with the reactive media layer, the level of electrical current used to initiate the reaction and the applied pressure do not need to be excessive to obtain a strong joint. Some aspects of the joining mechanism are discussed in detail.

Download Full-text

Arrhythmiarizikó és cardialis szövődmények áramütéses balesetet követően

Orvosi Hetilap ◽

10.1556/650.2020.31897 ◽

2020 ◽

Vol 161 (47) ◽

pp. 1979-1988

Author(s):

Dávid Pilecky ◽

Enikő Kovács ◽

Endre Zima

Keyword(s):

Emergency Department ◽

Low Voltage ◽

Electrical Current ◽

Developed Countries ◽

The Body ◽

Cardiac Complications ◽

Special Focus ◽

Severe Injuries ◽

Multiple Organs ◽

Severe Burns

Összefoglaló. Az áramütés súlyos esetben hirtelen halállal vagy több szervrendszer kiterjedt károsodásával járhat. A magasfeszültségű áramütés (>1000 V) általában súlyosabb égési sérülésekkel és magasabb kórházi mortalitással jár, mint az alacsonyfeszültségű, de a sérülések súlyosságát a feszültségen kívül a test ellenállása, az áramexpozíció ideje, az áram fajtája, erőssége és útja is befolyásolja. A kritikus állapotú vagy súlyos égési sérüléseket szenvedett betegek sürgősségi ellátása komplex és multidiszciplináris szemléletet igényel. A súlyos szövődményekkel járó áramütéses balesetek ugyanakkor a fejlett országokban ritkák: az áramütés következtében sürgősségi osztályon jelentkező betegek döntő többsége panaszmentesen vagy minor panaszokkal kerül felvételre. A ritmuszavarok az áramütéses balesetek messze leggyakoribb cardialis szövődményei, és rendszerint közvetlenül az áramütés után jelentkeznek. Az elektromos áram kamrafibrillációt vagy asystoliát is kiválthat, mely a baleset helyszínén ellátás nélkül halálhoz vezethet. Bár sok helyen elterjedt gyakorlat az áramütést szenvedett betegek rutinszerű monitorozása, a klinikailag releváns arrhythmiák összességében ritkák, és a felvételi EKG alapján diagnosztizálhatók, ezért EKG-monitorozás csak meghatározott rizikófaktorok esetén szükséges. Jelen munkánk célja összefoglalni az áramütést szenvedett betegek optimális sürgősségi ellátásával kapcsolatos legfontosabb szempontokat, különös tekintettel az áramütéses balesetet követően fellépő cardialis szövődményekre és arrhythmiákra, valamint az EKG-monitorozás indikációira. Orv Hetil. 2020; 161(47): 1979–1988. Summary. Electrical accidents (EA) may cause sudden death or severe injuries of multiple organs. High voltage injuries (>1000 V) are associated with more severe burn injuries and higher in-hospital mortality than low voltage injuries, however, the severity of complications depends on several other factors like resistance of the body, duration of current exposition, intensity, type and pathway of current. Critically ill patients with severe burns and/or other injuries require a multidisciplinary intensive treatment. However, such complications are rare in the developed countries: most patients present in the emergency department with no or minor symptoms and do not require hospital admission. Arrhythmias are the most frequent cardiac complications after EA. Electrical current may cause ventricular fibrillation or asystolia which can lead to death on the scene. In patients presenting in the emergency department, clinically relevant arrhythmias are rare and can be diagnosed by a 12-lead ECG, therefore a systematic monitoring may not be indicated. Aim of our work is to review the most frequent complications after an electrical accident with special focus on cardiac complications and arrhythmias. The other aim of the manuscript is to summarize the most important aspects of emergency treatment and indication for ECG monitoring after electrical accident. Orv Hetil. 2020; 161(47): 1979–1988.

Download Full-text