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

Author(s):  
Juan Manuel Montes Martos ◽  
Francisco Gómez Cuevas ◽  
Fátima Ternero Fernández ◽  
Raquel Astacio López ◽  
Eduardo Sánchez Caballero ◽  
...  

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.

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2131
Author(s):  
Fátima Ternero ◽  
Eduardo S. Caballero ◽  
Raquel Astacio ◽  
Jesús Cintas ◽  
Juan M. Montes

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.


2021 ◽  
Vol 876 ◽  
pp. 1-6
Author(s):  
Fátima Ternero Fernández ◽  
Petr Urban ◽  
Raquel Astacio Lopez ◽  
Rosa M. Aranda Louvier ◽  
Francisco G. Cuevas

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.


Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 994
Author(s):  
Raquel Astacio ◽  
Fátima Ternero ◽  
Jesús Cintas ◽  
Francisco G. Cuevas ◽  
Juan Manuel Montes

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.


Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1140 ◽  
Author(s):  
Petr Urban ◽  
Fátima Ternero ◽  
Eduardo S. Caballero ◽  
Sooraj Nandyala ◽  
Juan Manuel Montes ◽  
...  

A novel processing method for amorphous Al50Ti50 alloy, obtained by mechanical alloying and subsequently consolidated by electrical resistance sintering, has been investigated. The characterisation of the powders and the confirmation of the presence of amorphous phase have been carried out by laser diffraction, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The amorphous Al50Ti50 powders, milled for 75 h, have a high hardness and small plastic deformation capacity, not being possible to achieve green compacts for conventional sintering. Moreover, conventional sintering takes a long time, being not possible to avoid crystallisation. Amorphous powders have been consolidated by electrical resistance sintering. Electrically sintered compacts with different current intensities (7–8 kA) and processing times (0.8–1.6 s) show a porosity between 16.5 and 20%. The highest Vickers hardness of 662 HV is reached in the centre of an electrically sintered compact with 8 kA and 1.2 s from amorphous Al50Ti50 powder. The hardness results are compared with the values found in the literature.


Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2106
Author(s):  
Chris J. Barnett ◽  
James D. McGettrick ◽  
Varun Shenoy Gangoli ◽  
Ewa Kazimierska ◽  
Alvin Orbaek White ◽  
...  

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.


1972 ◽  
Vol 18 (10) ◽  
pp. 1543-1550 ◽  
Author(s):  
Robert G. Brown

A strain of Penicillium lilacinum, isolated from soil, produced pustulanase, β-(1 → 3)-glucanase, (EC. 3.2.1.6) and cellulase (EC.3.2.1.4) when cultivated on a medium containing pustulan as the sole source of carbon. If pustulan was replaced by ketopustulan, the production of pustulanase was stimulated about 10-fold although the amount of stimulation was dependent on the degree of oxidation of pustulan. β-(1 → 3)-Glucanase production was stimulated slightly by ketopustulan; however, the degree of oxidation did not affect significantly the yield of this enzyme. Cellulase production was either unaffected by the oxidized polymer, or at higher degrees of oxidation, decreased. Tween 80 stimulated the production of the three enzymes in media containing ketopustulan with a low degree of oxidation but was inhibitory to pustulanase and cellulase production in media containing ketopustulan with a high degree of oxidation. A combination of gel filtration and isoelectric focusing revealed that each enzyme activity was attributable to at least two proteins.


2004 ◽  
Vol 04 (02) ◽  
pp. L345-L354 ◽  
Author(s):  
Y. HADDAB ◽  
V. MOSSER ◽  
M. LYSOWEC ◽  
J. SUSKI ◽  
L. DEMEUS ◽  
...  

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.


2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Liudmyla Trykoz ◽  
Svetlana Kamchatnaya ◽  
Dmytro Borodin ◽  
Armen Atynian ◽  
Roman Tkachenko

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.


2020 ◽  
Vol 161 (47) ◽  
pp. 1979-1988
Author(s):  
Dávid Pilecky ◽  
Enikő Kovács ◽  
Endre Zima

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.


2014 ◽  
Vol 881-883 ◽  
pp. 1083-1088 ◽  
Author(s):  
Li Lai Liu ◽  
Mao Zhong An ◽  
Shan Chao Xing ◽  
Xiao Jun Shen ◽  
Chen Yang ◽  
...  

Graphene oxide with high degree of oxidation and peelable has been prepared by two-step oxidation method used large flake graphite. The expanded graphite was prepared firstly and then prepared graphene oxide via further oxidation. The influence of oxidation time, oxidant dosage and high temperature reaction on the structure and degree of oxidation were studied. The morphology and structure of graphene oxide were characterized by X-ray diffraction, fourier transform infrared spectra, scanning electron microscope and transmission electron microscope. It was found that high degree of oxidation and large specific surface area graphene oxide was prepared at the ratio of sulfuric acid and expanded graphite was 75 mL : 1 g, the ratio of potassium permanganate and expanded graphite was 4 g : 1 g and the oxidation time at 35 °C was 24 h. This technology is simple without high-temperature reaction process, and solved the problem of low oxidation efficiency when used the large flake graphite as raw materials.


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