Impedance Changes and Carbon Stability during the Heat Treatment of Si3N4–Carbon Composites

2009 ◽  
Vol 409 ◽  
pp. 365-368
Author(s):  
Balazs Fényi ◽  
Norbert Hegman ◽  
K. Szemmelveisz ◽  
Csaba Balázsi
Keyword(s):  
Electrical Current ◽  
Carbon Composites ◽  
Electrical Measurements ◽  
Thermo Gravimetric ◽  
Air Atmosphere ◽  
Base Ceramic ◽  
Burn Out ◽  
Nitride Ceramics ◽  
Flow Through ◽  
Carbon Inclusion

Electrical properties of the insulator silicon nitride ceramics may be improved by addition of electrical conductive parts. The conductive carbon parts were mixed with the base ceramic matrix to form a percolation network. Electrical current can flow through the ceramic by using the connected carbon channels. In air atmosphere however, the carbon can oxidize and burn out. Heat treatments were performed to observe the carbon degradation in composites in atmosphere. As resulted, the carbon exhaust started at 400°C from surface and finished above 750°C. Electrical measurements showed the conductor-insulator transformation. Thermo-gravimetric measurements suggested that some carbon inclusion still remained in isolated closed porosities.

Electrical Examination of Silicon Nitride – Carbon Composites

2008 ◽  
Vol 589 ◽  
pp. 203-208 ◽  
Author(s):  
Balazs Fényi ◽  
Péter Arató ◽  
Ferenc Wéber ◽  
Norbert Hegman ◽  
Csaba Balázsi
Keyword(s):  
Impedance Spectroscopy ◽  
Carbon Composites ◽  
Ac Impedance Spectroscopy ◽  
Electrical Measurements ◽  
Resistivity Measurements ◽  
Base Ceramic ◽  
Capacitive Properties ◽  
The Matrix ◽  
Si3n4 Matrix ◽  
Si3n4 Ceramics

The Si3N4 ceramics are usually known as strongly refractory and enduring materials and they have typical insulating material properties on room temperature. If reinforcing phase of the Si3N4 matrix composite is a good electrical conductor, in that case it is worth to investigate the composite in electrical aspect. In our case carbon nanotubes, black-carbon and graphite with good electrical conductivity were mixed in the base ceramic. During our electrical investigations DC resistivity measurements were used to determine the percolation threshold and the conductivity of the composites. In case of high resistance samples AC impedance spectroscopy was applied. As result of the impedance spectroscopy capacitive properties were found. In some cases of conductor samples combined mechanical – electrical measurements were done to study the integrity of the additions in the matrix.

Combustion joining of refractory materials: Carbon–carbon composites

2008 ◽  
Vol 23 (1) ◽  
pp. 160-169 ◽  
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.

scholarly journals Influence of nitrogen and air atmosphere during thermal treatment on micro and nano sized powders and sintered TiO2 specimens

2014 ◽  
Vol 46 (3) ◽  
pp. 365-375
Author(s):  
N. Labus ◽  
S. Mentus ◽  
Z.Z. Djuric ◽  
M.V. Nikolic
Keyword(s):  
Phase Transition ◽  
Particle Size ◽  
Powder Particle ◽  
Rutile Phase ◽  
Nitrogen Atmosphere ◽  
Powder Particle Size ◽  
Nano Tio2 ◽  
Thermo Gravimetric ◽  
Air Atmosphere ◽  
Thermal Techniques

The influence of air and nitrogen atmosphere during heating on TiO2 nano and micro sized powders as well as sintered polycrystalline specimens was analyzed. Sintering of TiO2 nano and micro powders in air atmosphere was monitored in a dilatometer. Non compacted nano and micro powders were analyzed separately in air and nitrogen atmospheres during heating using thermo gravimetric (TG) and differential thermal analysis (DTA). The anatase to rutile phase transition temperature interval is influenced by the powder particle size and atmosphere change. At lower temperatures for nano TiO2 powder a second order phase transition was detected by both thermal techniques. Polycrystalline specimens obtained by sintering from nano powders were reheated in the dilatometer in nitrogen and air atmosphere, and their shrinkage is found to be different. Powder particle size influence, as well as the air and nitrogen atmosphere influence was discussed.

Interaction Between Solid Copper Jets and Powerful Electrical Current Pulses

2010 ◽  
Vol 78 (2) ◽  
Author(s):  
Patrik Appelgren ◽  
Torgny E. Carlsson ◽  
Andreas Helte ◽  
Tomas Hurtig ◽  
Anders Larsson ◽  
...  
Keyword(s):  
Current Pulse ◽  
Current Density ◽  
Energy Deposition ◽  
Current Flow ◽  
Contact Region ◽  
Electrical Energy ◽  
Electrical Current ◽  
Separation Distance ◽  
Flow Through ◽  
Solid Copper

The interaction between a solid copper jet and an electric current pulse is studied. Copper jets that were created by a shaped-charge device were passed through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. The electrodes were connected to a pulsed-power supply delivering a current pulse with amplitudes up to 250 kA. The current and voltages were measured, providing data on energy deposition in the jet and electrode contact region, and flash X-ray diagnostics were used to depict the jet during and after electrification. The shape of, and the velocity distributions along, the jet has been used to estimate the correlation between the jet mass flow through the electrodes and the electrical energy deposition. On average, 2.8 kJ/g was deposited in the jet and electrode region, which is sufficient to bring the jet up to the boiling point. A model based on the assumption of a homogenous current flow through the jet between the electrodes underestimates the energy deposition and the jet resistance by a factor 5 compared with the experiments, indicating a more complex current flow through the jet. The experimental results indicate the following mechanism for the enhancement of jet breakup. When electrified, the natural-formed necks in the jet are subjected to a higher current density compared with other parts of the jet. The higher current density results in a stronger heating and a stronger magnetic pinch force. Eventually, the jet material in the neck is evaporated and explodes electrically, resulting in a radial ejection of vaporized jet material.

scholarly journals Electrical Resistance Tomography for Assessing Water Movement in Cracked Cementitious Mixtures

2018 ◽  
Vol 199 ◽  
pp. 11016
Author(s):  
Keiyu Kawaai ◽  
Isao Ujike
Keyword(s):  
Electrical Resistance ◽  
Water Movement ◽  
Gradual Increase ◽  
Concrete Specimen ◽  
Electrical Measurements ◽  
Electrical Resistance Tomography ◽  
Water Ingress ◽  
Elapsed Time ◽  
Flow Through ◽  
Good Agreement

Electrical resistance tomography (ERT) has been studied for visualizing variations of conductivity in concrete specimens. In recent years, unsaturated water flow through pores formed in concrete has been intensively examined though ERT systems to visualize the permeation front that gradually changes with elapsed time. This study examines water movement through internal cracks which are typically not observed on the surface of mortar or concrete specimens via ERT systems. The results indicate the gradual increase of saturated region owing to the ingress of water through cracked surface up to 120 hours. And, the region with higher conductivity estimated in uncracked parts is evidently in good agreement with higher moisture content measured by moisture meter on the split surface. In addition, the presence of crack in concrete specimen subjected to water ingress is clearly visualized via ERT images owing to rapid water movement in cracked zones. This study has provided the important insight that the ingress and the movement of water through pores and cracks formed in cementitious mixtures could be assessed via electrical measurements.

Solid Solutions Study of BaTiO3 Doped on B Site by Electronic Compensation

2014 ◽  
Vol 976 ◽  
pp. 30-35
Author(s):  
Francisco Raúl Barrientos-Hernández ◽  
Alberto Arenas-Flores ◽  
Iván Alonso Lira Hernández ◽  
Carlos Gómez-Yáñez ◽  
Miguel Pérez Labra
Keyword(s):  
Room Temperature ◽  
Hexagonal Phase ◽  
Ferroelectric Properties ◽  
X Ray Diffraction ◽  
Electrical Measurements ◽  
Solid State Method ◽  
X Ray ◽  
Air Atmosphere ◽  
Conventional Solid State Method ◽  
Electronic Compensation

Several compositions of BaTiO:Nb5+ were made by conventional solid-state method in air atmosphere, according to the general formula BaTi1-xNbxO3; (x= 0.005, 0.04, 0.08, 0.20, and 0.25). The crystal structure, microstructure, dielectric and ferroelectric properties of samples were investigated by XRD, Raman Spectroscopy, Electrical Measurements and SEM. X-ray diffraction results clearly indicated that when x ≥ 0.25 was prepared; the hexagonal phase Ba8Ti3Nb4O24 appeared. Electrical measurements at 1 kHz were carried out and several pellets were made, the relative permittivity was calculated. The dielectric constant of the pristine BaTiO3 is about 7000, and the Curie temperature is ≈120°C at room temperature, decreasing to 90°C with Nb5+ addition (x = 0.005).

scholarly journals The influence of mechanical activation on sintering process of BaCO3-SrCO3-TiO2 system

2012 ◽  
Vol 44 (3) ◽  
pp. 271-280 ◽  
Author(s):  
Darko Kosanovic ◽  
N. Obradovic ◽  
J. Zivojinovic ◽  
A. Maricic ◽  
V.P. Pavlovic ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Mechanical Activation ◽  
Ball Mill ◽  
Sintering Process ◽  
Electrical Measurements ◽  
Air Atmosphere ◽  
Titanate Ceramics ◽  
Scanning Electron

In this article the influence of mechanical activation on sintering process of bariumstrontium-titanate ceramics has been investigated. Both non-activated and mixtures treated in a planetary ball mill for 5, 10, 20, 40, 80 and 120 minutes were sintered at 1100-1400?C for 2 hours in presence of air atmosphere. The influence of mechanical activation on phase composition and crystal structure has been analyzed by XRD, while the effect of activation and sintering process on microstructure was investigated by scanning electron microscopy. It has been established that temperature of 1100?C was too low to induce final sintering stage for this system. Electrical measurements have been conducted for the densest ceramics sintered at 1400?C for 2 hours.

scholarly journals Mathematical Model Predicting the Heat and Power Dissipated in an Electro-Conductive Contact in a Hybrid Woven Fabric

2020 ◽  
Vol 20 (2) ◽  
pp. 133-139
Author(s):  
Carla Hertleer ◽  
Jeroen Meul ◽  
Gilbert De Mey ◽  
Simona Vasile ◽  
Sheilla A. Odhiambo ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Contact Resistance ◽  
Electrical Current ◽  
Woven Fabrics ◽  
Woven Fabric ◽  
Weft Direction ◽  
Flow Through ◽  
Metal Oxide Varistor ◽  
Crossing Point ◽  
Hybrid Fabric

AbstractElectro-conductive (EC) yarns can be woven into a hybrid fabric to enable electrical current to flow through the fabric from one component A to another component B. These hybrid fabrics form the bases of woven e-textiles. However, at the crossing point of an EC yarn in warp and in weft direction, there is a contact resistance and thus generation of heat may occur in this area. Both phenomena are inseparable: if the contact resistance in the EC contact increases, the generated heat will increase as well. Predicting this electrical and thermal behavior of EC contacts in hybrid woven fabrics with stainless steel yarns is possible with a mathematical model based on the behavior of a metal oxide varistor (MOV). This paper will discuss in detail how this can be achieved.

Correlation between morphology and local mechanical and electrical properties of van der Waals heterostructures

2021 ◽  
Author(s):  
Borislav Vasic ◽  
Uros Ralevic ◽  
Sonja Aškrabić ◽  
Davor Čapeta ◽  
Marko Kralj
Keyword(s):  
Charge Transfer ◽  
Close Contact ◽  
Normal Load ◽  
Van Der Waals ◽  
Contact Potential Difference ◽  
Electrical Current ◽  
Potential Difference ◽  
Electrical Measurements ◽  
Contact Potential ◽  
Contact Mode

Abstract Properties of van der Waals (vdW) heterostructures strongly depend on the quality of the interface between two dimensional (2D) layers. Instead of having atomically flat, clean, and chemically inert interfaces without dangling bonds, top-down vdW heterostructures are associated with bubbles and intercalated layers (ILs) which trap contaminations appeared during fabrication process. We investigate their influence on local electrical and mechanical properties of MoS2/WS2 heterostructures using atomic force microscopy (AFM) based methods. It is demonstrated that domains containing bubbles and ILs are locally softer, with increased friction and energy dissipation. Since they prevent sharp interfaces and efficient charge transfer between 2D layers, electrical current and contact potential difference are strongly decreased. In order to reestablish a close contact between MoS2 and WS 2 layers, vdW heterostructures were locally flattened by scanning with AFM tip in contact mode or just locally pressed with an increased normal load. Subsequent electrical measurements reveal that the contact potential difference between two layers strongly increases due to enabled charge transfer, while local I/V curves exhibit increased conductivity without undesired potential barriers.

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