EFFECT OF CURING TEMPERATURE OF EPOXY RESIN ON THE ELECTRICAL RESPONSE OF CARBON NANOTUBE YARN MONOFILAMENT COMPOSITES

2021 ◽  
Author(s):  
OMAR RODRIGUEZ-UICAB ◽  
JANDRO L. ABOT ◽  
FRANCIS AVILÉS
Keyword(s):  
Carbon Nanotube ◽  
Epoxy Resin ◽  
Electrical Resistance ◽  
Epoxy Resins ◽  
Room Temperature ◽  
Negative Temperature Coefficient ◽  
Electrical Response ◽  
Negative Temperature ◽  
Curing Temperature ◽  
Temperature Coefficient Of Resistance

The cyclic thermoresistive response of individual carbon nanotube yarns (CNTYs) embedded into epoxy resins is investigated. The influence of the temperature at which the epoxy resin cures on the thermoresistive response is investigated by using two epoxy resins, one that cures at room temperature and the other one that cures at 130 °C. Heating-cooling cycles ranging from room temperature (RT, 25 °C) to 80 °C, incremental cycles (RT to 40 °C, RT to 60 °C and RT to 80 °C) and incremental heating-dwell cycles are applied to monofilament composites, while their electrical resistance is simultaneously recorded. The monofilament composites showed a negative temperature coefficient of resistance during the heating-cooling cycles of -7.07x10-4 °C-1 for specimens cured at high temperature, and -5.93x10-4 °C-1 for specimens cured at room temperature. The hysteresis after the different heating-cooling cycles was slightly smaller for specimens cured at 130 °C, in comparison to specimens cured at room temperature. Several factors including the intrinsic thermoresistivity of CNTY, level of infiltration and the effect of curing temperature may explain the thermoresistive sensitivity of the monofilament composites.

CYCLIC THERMORESISTIVITY OF CARBON NANOTUBE YARN/SILICONE RUBBER MATRIX MONOFILAMENT COMPOSITES

2021 ◽  
Author(s):  
TANNAZ TAYYARIAN ◽  
OMAR RODRIGUEZ-UICAB ◽  
TANJEE AFREEN ◽  
JANDRO L. ABOT
Keyword(s):  
Carbon Nanotube ◽  
Electrical Resistance ◽  
Room Temperature ◽  
Electrical Response ◽  
Negative Temperature ◽  
Curing Kinetics ◽  
Rubber Matrix ◽  
Continuous Heating ◽  
Average Value ◽  
Heating And Cooling

Thermoresistive characterization of CNTY monofilament composites was investigated by using the electrical response of a single carbon nanotube yarn (CNTY) embedded in a silicone polymer forming monofilament composites. Two room temperature vulcanizing (RTV) silicone rubbers with different polymerization mechanisms (OOMOO and Ecoflex) were used as the polymeric matrices. Continuous heating-cooling thermal cycling ranging from room temperature (RT~25 °C) to 80 °C was performed in order to determine the thermoresistive sensitivity, hysteresis and residual fractional change in electrical resistance after each cycle. The thermoresistive response was nearly linear, with negative temperature coefficient of resistance at the heating and cooling zones for CNTY/ OOMOO and CNTY/Ecoflex specimens. The average value of this coefficient at the heating and cooling sections was - 6.65×10-4 °C-1 for CNTY/OOMOO and -7.35×10-4 °C-1 for CNTY/Ecoflex. Both monofilament composites showed a negligible negative residual electrical resistance with an average value of ~ -0.08% for CNTY/OOMOO and ~ -0.20% for CNTY/Ecoflex after each cycle. The hysteresis yielded ~19.3% for CNTY/OOMOO and ~29.2% in CNTY/Ecoflex after each cycle. Therefore, the curing kinetics and viscosity play a paramount role in the electrical response of the CNTY immersed into these rubbery matrices.

scholarly journals The electrical resistance of bismuth alloys.

1936 ◽  
Vol 155 (884) ◽  
pp. 111-123 ◽  
Author(s):  
N Thompson ◽  
Arthur Mannering Tyndall
Keyword(s):  
Temperature Coefficient ◽  
Electrical Resistance ◽  
Room Temperature ◽  
Negative Temperature Coefficient ◽  
Principal Axis ◽  
Cleavage Plane ◽  
Negative Temperature ◽  
Hexagonal Symmetry ◽  
Temperature Coefficient Of Resistance ◽  
Long Time

It has been known for a long time that the electrical resistance of bismuth, and more particularly the temperature coefficient of resistance, depends to a great extent on the purity of the sample, but the earlier results are not consistent. In particular it was known that small traces of tin, and possibly also of lead, could make the temperature coefficient at room temperature less than zero, and also that some samples of commercial bismuth showed a negative temperature coefficient at low temperatures. Since a negative temperature coefficient has hitherto been thought to be a distinguishing feature of electronic semiconductors, it seemed desirable that the matter should be investigated in more detail. The results already obtained have shown that the phenomena are much more complex than was at first thought, this complexity being quite adequate to explain the discordant results of the earlier workers. Experimental Preliminary experiments soon showed that very small traces of impurity were sufficient to produce very marked changes in the resistance, and accordingly all the later measurements have been made with Hilger “H. S.” bismuth, with a purity quoted as 99·997% (Lab. Nos. 9506 and 10283). The alloying metals, being present in small percentages, were usually of commercial purity only. It soon became evident that the results depended very much on the crystalline state of the specimen, and that consistent and interpretable results would only be obtained if single crystals were used. A technique for producing these in a suitable shape was therefore developed. The metal was first cast into a rod of about 1 mm square section, and about 3 cm long, using an apparatus essentially similar to that described by Schubnikow. The specimen was next grown into a single crystal by a modification of one of Kapitza's methods whereby the process could be carried out in vacuo to prevent oxidation. Bismuth crystallizes with hexagonal symmetry, and by using a seed, crystals could be grown with any desired orientation. Now the resistance in a direction making an angle α with the principal axis in such a crystal is given by the Voigt-Thomson law ρ α = ρ ‖ cos 2 α + ρ ⊥ sin 2 α, (1) where ρ ‖ and ρ ⊥ are respectively the resistances parallel and perpendicular to the principal axis. Thus d ρ a / d α = sin 2α (ρ ⊥ - ρ ‖ ). If α = 0 or π/2 this vanishes, and thus small errors in the value of α near these limiting positions have little effect on the value of ρ a . For example, for pure bismuth, for which ρ ‖ = 138 × 10 -6 , and ρ ⊥ =109 × 10 -6 ohm-cm at 20° C, an error of as much as 10° in α gives the values (ρ 10 = 109·9) and (ρ 80 = 137·2) which are incorrect by less than 1%. In consequence of this the orientation of the specimen could be determined with sufficient accuracy from the direction of the main cleavage plane, which is perpendicular to the principal axis.

scholarly journals Electrical Resistance Sensing of Epoxy Curing Using an Embedded Carbon Nanotube Yarn

Sensors ◽  
2020 ◽  
Vol 20 (11) ◽  
pp. 3230 ◽  
Author(s):  
Omar Rodríguez-Uicab ◽  
Jandro L. Abot ◽  
Francis Avilés
Keyword(s):  
Carbon Nanotube ◽  
Epoxy Resin ◽  
Electrical Resistance ◽  
Electrical Response ◽  
Curing Kinetics ◽  
Curing Temperature ◽  
Polymerization Process ◽  
Curing Agent ◽  
Resin Curing ◽  
Over Time

Curing effects were investigated by using the electrical response of a single carbon nanotube yarn (CNTY) embedded in an epoxy resin during the polymerization process. Two epoxy resins of different viscosities and curing temperatures were investigated, varying also the concentration of the curing agent. It is shown that the kinetics of resin curing can be followed by using the electrical response of an individual CNTY embedded in the resin. The electrical resistance of an embedded CNTY increased (~9%) after resin curing for an epoxy resin cured at 130 °C with viscosity of ~59 cP at the pouring/curing temperature (“Epon 862”), while it decreased (~ −9%) for a different epoxy cured at 60 °C, whose viscosity is about double at the corresponding curing temperature. Lowering the curing temperature from 60 °C to room temperature caused slower and smoother changes of electrical resistance over time and smaller (positive) residual resistance. Increasing the concentration of the curing agent caused a faster curing kinetics and, consequently, more abrupt changes of electrical resistance over time, with negative residual electrical resistance. Therefore, the resin viscosity and curing kinetics play a paramount role in the CNTY wicking, wetting and resin infiltration processes, which ultimately govern the electrical response of the CNTY immersed into epoxy.

scholarly journals Monitoring of Curing and Cyclic Thermoresistive Response Using Monofilament Carbon Nanotube Yarn Silicone Composites

2021 ◽  
Vol 7 (3) ◽  
pp. 60
Author(s):  
Tannaz Tayyarian ◽  
Omar Rodríguez-Uicab ◽  
Jandro L. Abot
Keyword(s):  
Carbon Nanotube ◽  
Heating Rate ◽  
Electrical Resistance ◽  
Room Temperature ◽  
Electrical Response ◽  
Negative Temperature ◽  
Curing Kinetics ◽  
Curing Process ◽  
Resistance Change ◽  
Electrical Resistance Change

The curing process and thermoresistive response of a single carbon nanotube yarn (CNTY) embedded in a room temperature vulcanizing (RTV) silicone forming a CNTY monofilament composite were investigated toward potential applications in integrated curing monitoring and temperature sensing. Two RTV silicones of different crosslinking mechanisms, SR1 and SR2 (tin- and platinum-cured, respectively), were used to investigate their curing kinetics using the electrical response of the CNTY. It is shown that the relative electrical resistance change of CNTY/SR1 and CNTY/SR2 monofilament composites increased by 3.8% and 3.3%, respectively, after completion of the curing process. The thermoresistive characterization of the CNTY monofilament composites was conducted during heating–cooling ramps ranging from room temperature (RT~25 °C) to 100 °C. The thermoresistive response was nearly linear with a negative temperature coefficient of resistance (TCR) at heating and cooling sections for both CNTY/SR1 and CNTY/SR2 monofilament composites. The average TCR value was −8.36 × 10−4 °C−1 for CNTY/SR1 and −7.26 × 10−4 °C−1 for CNTY/SR2. Both monofilament composites showed a negligible negative residual relative electrical resistance change with average values of ~−0.11% for CNTY/SR1 and ~−0.16% for CNTY/SR2 after each cycle. The hysteresis amounted to ~21.85% in CNTY/SR1 and ~29.80% in CNTY/SR2 after each cycle. In addition, the effect of heating rate on the thermoresistive sensitivity of CNTY monofilament composites was investigated and it was shown that it reduces as the heating rate increases.

scholarly journals Ferrite-based room temperature negative temperature coefficient printed thermistors

2020 ◽  
Vol 56 (24) ◽  
pp. 1322-1324
Author(s):  
J.R. McGhee ◽  
J.S. Sagu ◽  
D.J. Southee ◽  
P.S.A. Evans ◽  
K.G.U. Wijayantha
Keyword(s):  
Temperature Coefficient ◽  
Room Temperature ◽  
Negative Temperature Coefficient ◽  
Negative Temperature

Low temperature dielectric properties and NTCR behavior of the BaFe0.5Nb0.5O3 double perovskite ceramic

2020 ◽  
Vol 22 (5) ◽  
pp. 2986-2998 ◽  
Author(s):  
Vijay Khopkar ◽  
Balaram Sahoo
Keyword(s):  
Dielectric Properties ◽  
Low Temperature ◽  
Temperature Coefficient ◽  
Negative Temperature Coefficient ◽  
Double Perovskite ◽  
Negative Temperature ◽  
Lead Free ◽  
Temperature Coefficient Of Resistance ◽  
Perovskite Ceramic

The microstructure and low-temperature dielectric properties of lead-free BaFe0.5Nb0.5O3 ceramics exhibiting a negative temperature coefficient of resistance behavior.

scholarly journals Anomalous electrical conduction and negative temperature coefficient of resistance in nanostructured gold resistive switching films

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
M. Mirigliano ◽  
S. Radice ◽  
A. Falqui ◽  
A. Casu ◽  
F. Cavaliere ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Temperature Coefficient ◽  
Resistive Switching ◽  
Electrical Conduction ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
High Density ◽  
Gold Films ◽  
Temperature Coefficient Of Resistance ◽  
Nanostructured Gold

AbstractWe report the observation of non-metallic electrical conduction, resistive switching, and a negative temperature coefficient of resistance in nanostructured gold films above the electrical percolation and in strong-coupling regime, from room down to cryogenic temperatures (24 K). Nanostructured continuous gold films are assembled by supersonic cluster beam deposition of Au aggregates formed in the gas phase. The structure of the cluster-assembled films is characterized by an extremely high density of randomly oriented crystalline nanodomains, separated by grain boundaries and with a large number of lattice defects. Our data indicates that space charge limited conduction and Coulomb blockade are at the origin of the anomalous electrical behavior. The high density of extended defects and grain boundaries causes the localization of conduction electrons over the entire investigated temperature range.

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