Design and Evaluation of Carbon Nanotube Based Nanofluids for Heat Transfer Applications

2013 ◽  
Vol 1543 ◽  
pp. 143-148
Author(s):  
Sathya P. Singh ◽  
Nader Nikkam ◽  
Morteza Ghanbarpour ◽  
Muhammet S. Toprak ◽  
M. Muhammed ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Rheological Properties ◽  
Gum Arabic ◽  
Step Method ◽  
Potential Measurement ◽  
Heat Treated ◽  
Electron Microscopy Analysis ◽  
Predicted Values ◽  
The Stability ◽  
Ph Range

ABSTRACTThe present work investigates the fabrication, thermal conductivity (TC) and rheological properties of water based carbon nanotubes (CNTs) nanofluids (NFs) prepared using a two-step method. As-received (AR) CNTs heated and the effect of heat treatment was studied using X-ray diffraction and thermogravimetric analysis. The AR-CNTs and heat-treated CNTs (HT-CNTs) were dispersed with varying concentration of surface modifiers Gum Arabic (GA) and TritonX-100 (TX) respectively. It was found that heat treatment of CNTs effectively improved the TC and influenced rheological properties of NFs. Scanning electron microscopy analysis revealed TX modified NFs showed better dispersion ability compared to GA. Surface modification of the CNTs was confirmed by Fourier Transformation Infrared (FTIR) analysis. Zeta potential measurement showed the stability region for GA modified NFs in the pH range of 5-11, whereas pH was between 9.5-10 for TX NFs. The concentration of surface modifier plays an extensive role on both TC and rheological behavior of NFs. A maximum TC enhancement of 10% with increases in viscosity around 2% for TX based HT-CNTs NFs was measured. Finally comparison of experimental TC results with the predicted values obtained from a model demonstrated inadequacy of the predictive model for CNT NFs system.

The Stability of γ ’-Co3(Al,W) Phase in Co-Al-W Ternary System

2010 ◽  
Vol 654-656 ◽  
pp. 448-451 ◽  
Author(s):  
Yuki Tsukamoto ◽  
Satoru Kobayashi ◽  
Takayuki Takasugi
Keyword(s):  
Heat Treatment ◽  
Ternary System ◽  
Microstructural Evolution ◽  
Treatment Time ◽  
Bulk Alloy ◽  
Epma Analysis ◽  
Heat Treated ◽  
Cold Rolled ◽  
The Stability ◽  
Couple Method

The thermodynamic stability ’- Co3(Al,W) phase (L12) in the Co-Al-W ternary system at 900 °C was investigated through microstructure and EPMA analysis on a heat-treated bulk alloy. To promote microstructural evolution, the bulk alloy was cold rolled before heat treatment. By heating at 900 °C, the ’ phase was formed discontinuously in contact with the -Co (A1) phase. With increasing heat treatment time, however, the fraction of ’ phase decreased while that of , CoAl (B2) and Co3W (D019) phases increased. These results are consistent with our previous work with a diffusion-couple method, indicating that the ’ phase is metastable, and the three phases of, CoAl and Co3W are thermodynamically stable at 900 °C.

Preparation of YBa2Cu3O7−y films on SrTiO3 and MgO by the dipping-pyrolysis process under low-p(O2) heat treatment

1992 ◽  
Vol 7 (9) ◽  
pp. 2337-2342 ◽  
Author(s):  
T. Manabe ◽  
K. Arai ◽  
W. Kondo ◽  
S. Mizuta ◽  
T. Kumagai
Keyword(s):  
Heat Treatment ◽  
Stability Region ◽  
Pyrolysis Process ◽  
Axis Orientation ◽  
Ag Addition ◽  
Upper Limit ◽  
Treatment Conditions ◽  
Heat Treated ◽  
The Stability ◽  
Annealing Method

Superconducting YBa2Cu3O7−y (YBCO) films having a thickness of 1 μm were prepared on SrTiO3(100) and MgO(100) by the dipping-pyrolysis process using a low-p(O2) annealing method. Heat-treatment conditions were varied along the upper limit of the stability region of the YBCO phase. Films on SrTiO3(100) exhibited strong c-axis orientation with sharp rocking curves (FWHM = 0.8°). The highest Tc,zero of 87 K was obtained for the film heat-treated at 750 °C. On the other hand, films on MgO(100) showed broader rocking curves and their Tc's remained lower. Moreover, Ag addition was found to enhance the Tc values (Tc,zero = 91 K) of films on SrTiO3 heat-treated at 750 °C.

Nanotubes Obtained from Mono and Bimetallic Carbides Produced by Mechanical Alloying

2007 ◽  
Vol 539-543 ◽  
pp. 2731-2736
Author(s):  
Lucia Díaz-Barriga Arceo ◽  
L. Rendón-Vázquez ◽  
Eligio Orozco ◽  
V. Garibay-Febles ◽  
E. Palacios Gonzalez ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Mechanical Alloying ◽  
High Energy ◽  
Step Method ◽  
Heat Treated ◽  
Microstructural Characterisation

The main purpose of this work was to produce nanotubes using a two step method: mechanical alloying and heat treatment. Mechanical Alloying (MA) was used to prepare the monometallic Co3C carnide and the bimetallic C-25%at Ni-25%at Mo carbide with Ti impuririties by milling of pure elemental powders of cobalt, molibdenum, titanium and carbon, in a high-energy rotatory mill under an Ar atmosphere. The nanocrystalline carbides were used to produce metal filled nanotubes and nanoparticles, by means of precipitation after heating for 15 minutes at 800°C. Microstructural characterisation of the as-milled and heat-treated powders was performed using Transmisssion Electron Microscopy (TEM) techniques. It was possible to obtain filled nanotubes, carbide nanorods, and observe a nucleation phenomena inside carbon cavities.

Study of the effect of Al, Cr and Sn additions on the microstructure and properties of Nb silicide based alloys

2011 ◽  
Vol 1295 ◽  
Author(s):  
P Tsakiropoulos ◽  
K Zelenitsas ◽  
N Vellios
Keyword(s):  
Heat Treatment ◽  
Phase Stability ◽  
Alloying Additions ◽  
Microstructure And Properties ◽  
Heat Treated ◽  
Cast Alloys ◽  
The Stability ◽  
Cast Microstructure

ABSTRACTThe effects of Al, Cr and Sn on segregation, microstructure, phase stability and hardness of Nb-24Ti-18Si-5X (X = Al, Cr, Sn, at%) alloys were studied. The microstructure of the as cast alloys with Cr, Al and Sn respectively contained (Nb,Ti)ss, Nb3Si, αNb5Si3 and C14-NbCr2 Laves, (Nb,Ti)ss and βNb5Si3 and (Nb,Ti)ss, Nb3Sn and Nb5Si3. The microstructures of the heat treated alloys with Al and Cr (1500 oC/100 h) contained (Nb,Ti)ss and αNb5Si3 and the alloy with Sn (1200 oC/100 h) contained (Nb,Ti)ss, Nb3Sn and αNb5Si3. Compared with Al and Cr, alloying with Sn enhanced the stability of the as cast microstructure, caused strong macrosegregation of Si and Ti, suppressed the segregation of Ti in the (Nb,Ti)ss that was promoted by Al and Cr, had the strongest effect on the macrohardness of the cast and heat treated alloys and on the vol% of the Nbss. All three alloying additions promoted the transformation of βNb5Si3 to αNb5Si3 during heat treatment and decreased the hardness of Nb5Si3 in the as cast alloys with Sn having the strongest effect and Al the weakest. After the heat treatment the hardness of Nb5Si3 increased in the alloys containing Cr and Sn and decreased in the Al containing alloy with Cr having the strongest effect.

Formation of High-Resistivity Silver-Silicon Dioxide Composite Thin Films Using Sputter Deposition.

2004 ◽  
Vol 843 ◽  
Author(s):  
Ann Marie Shover ◽  
James M.E. Harper ◽  
Nicholas S. Dellas ◽  
Warren J. MoberlyChan
Keyword(s):  
Thin Films ◽  
Composition Range ◽  
High Mobility ◽  
Sputter Deposition ◽  
High Resistivity ◽  
Electron Microscopy Analysis ◽  
Tunneling Conductivity ◽  
Microscopy Analysis ◽  
Predicted Values ◽  
The Stability

ABSTRACTComposite Ag-SiO2 thin films were deposited to examine the stability of materials with high resistivity above 5000 μΩ-cm. We found that the resistivity increases exponentially with SiO2 volume fractions larger than 0.50 which is consistent with a tunneling conductivity mechanism. In order to obtain a broad composition range, these films were deposited on a stationary substrate placed above Ag and SiO2 sputtering sources. This configuration allowed compositions ranging from 0.8 to 56.3% SiO2 to be deposited on the same sample. Resistance measurements were made using a four-point probe and a profilometer was used to measure thickness. Predicted values of thickness and composition were obtained by calibrating deposition rates from the separate sources, and were verified using Rutherford Backscattering Spectroscopy. Electron microscopy analysis revealed Ag agglomerating on the surface of the film. Because of the high mobility of Ag, the films should be capped to prevent Ag agglomeration. The results of this research demonstrate that high-resistivity thin films can be grown using Ag-SiO2 composites.

scholarly journals A Study of the Effect of 2 at.% Sn on the Microstructure and Isothermal Oxidation at 800 and 1200 °C of Nb-24Ti-18Si-Based Alloys with Al and/or Cr Additions

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1826 ◽  
Author(s):  
Zhen Xu ◽  
Claire Utton ◽  
Panos Tsakiropoulos
Keyword(s):  
Heat Treatment ◽  
Cooling Rate ◽  
Rate Constant ◽  
Isothermal Oxidation ◽  
Primary Phase ◽  
Parabolic Oxidation ◽  
Heat Treated ◽  
Cast Alloys ◽  
The Stability ◽  
Oxidation In Air

Alloying with Al, Cr, Sn, and Ti significantly improves the oxidation of Nb silicide-based alloys at intermediate and high temperatures. There is no agreement about what the concentration of Sn in the alloys should be. It has been suggested that with Sn ≤ 3 at.% the oxidation is improved and formation of the brittle A15-Nb3Sn compound is suppressed. Definite improvements in oxidation behaviour have been observed with 5 at.% Sn or even higher concentrations, up to 8 at.% Sn. The research reported in this paper is about three model alloys with low Sn concentration and nominal compositions Nb-24Ti-18Si-5Cr-2Sn (ZX3), Nb-24Ti-18Si-5Al-2Sn (ZX5), and Nb-24Ti-18Si-5Al-5Cr-2Sn (ZX7) that were studied to understand the effect of the 2 at.% Sn addition on as-cast and heat-treated microstructures and isothermal oxidation in air at 800 and 1200 °C for 100 h. There was macrosegregation of Si and Ti in the alloys ZX3 and ZX5 and only of Si in the alloy ZX7. The Nbss was stable in all alloys. Tin and Ti exhibited opposite partitioning behaviour in the Nbss. The βNb5Si3 was the primary phase in all three cast alloys and had partially transformed to αNb5Si3 in the alloy ZX3. Aluminium in synergy with Sn increased the sluggishness of the βNb5Si3 to αNb5Si3 transformation during solidification. After the heat treatment the transformation of βNb5Si3 to αNb5Si3 had been completed in all three alloys. Fine precipitates were observed inside some αNb5Si3 grains in the alloys ZX5 and ZX7. In the latter alloys the A15-Nb3X (X = Al, Si, and Sn) formed after the heat treatment, i.e., the synergy of Al and Sn promoted the stability of A15-Nb3X intermetallic in these Nb-silicide-based alloys even at this low Sn concentration. A Nbss + Nb5Si3 eutectic formed in all three alloys and there was evidence of anomalous eutectic in the parts of the alloys ZX3 and ZX7 that had solidified under high cooling rate and/or high melt undercooling. A very fine ternary Nbss + Nb5Si3 + NbCr2 eutectic was also observed in parts of the alloy ZX3 that had solidified under high cooling rate. At 800 °C none of the alloys suffered from catastrophic pest oxidation; ZX7 had a smaller oxidation rate constant. A thin Sn-rich layer formed continuously between the scale and Nbss in the alloys ZX3 and ZX5. At 1200 °C the scales formed on all three alloys spalled off, the alloys exhibited parabolic oxidation in the early stages followed by linear oxidation; the alloy ZX5 gave the smallest rate constant values. A thicker continuous Sn-rich zone formed between the scale and substrate in all three alloys. This Sn-rich zone was noticeably thicker near the corners of the specimen of the alloy ZX7 and continuous around the whole specimen. The Nb3Sn, Nb5Sn2Si, and NbSn2 compounds were observed in the Sn-rich zone. At both temperatures the scales formed on all three alloys consisted of Nb-rich and Nb and Si-rich oxides, and Ti-rich oxide also was formed in the scales of the alloys ZX3 and ZX7 at 1200 °C. The formation of a Sn-rich layer/zone did not prevent the contamination of the bulk of the specimens by oxygen, as both Nbss and Nb5Si3 were contaminated by oxygen, the former more severely than the latter.

Effect of a Complex Heat Treatment on the Structure of 300M Steel

1981 ◽  
Vol 39 ◽  
pp. 312-313
Author(s):  
R. Padmanabhan ◽  
W. E. Wood
Keyword(s):  
Heat Treatment ◽  
Metal Carbides ◽  
Austenite Grain Size ◽  
300M Steel ◽  
Heat Treated ◽  
Strain Fracture ◽  
Prior Austenite Grain Size ◽  
Short Time ◽  
Final Tempering ◽  
Similar Yield

Intermediate high temperature tempering prior to subsequent reaustenitization has been shown to double the plane strain fracture toughness as compared to conventionally heat treated UHSLA steels, at similar yield strength levels. The precipitation (during tempering) of metal carbides and their subsequent partial redissolution and refinement (during reaustenitization), in addition to the reduction in the prior austenite grain size during the cycling operation have all been suggested to contribute to the observed improvement in the mechanical properties. In this investigation, 300M steel was initially austenitized at 1143°K and then subjected to intermediate tempering at 923°K for 1 hr. before reaustenitizing at 1123°K for a short time and final tempering at 583°K. The changes in the microstructure responsible for the improvement in the properties have been studied and compared with conventionally heat treated steel. Fig. 1 shows interlath films of retained austenite produced during conventionally heat treatment.

Influence of ion-milling on the T2 phase in Al-2.5%Li-2.5%Cu alloy

1989 ◽  
Vol 47 ◽  
pp. 288-289
Author(s):  
J. R. Reed ◽  
D. J. Michel ◽  
P. R. Howell
Keyword(s):  
Thin Foil ◽  
Icosahedral Symmetry ◽  
Ion Milling ◽  
Cu Alloy ◽  
Thin Foils ◽  
Heat Treated ◽  
Aluminum Solid Solution ◽  
In Situ Heating ◽  
The Stability

The Al6Li3Cu (T2) phase, which exhibits five-fold or icosahedral symmetry, forms through solid state precipitation in dilute Al-Li-Cu alloys. Recent studies have reported that the T2 phase transforms either during TEM examination of thin foils or following ion-milling of thin foil specimens. Related studies have shown that T2 phase transforms to a microcrystalline array of the TB phase and a dilute aluminum solid solution during in-situ heating in the TEM. The purpose of this paper is to report results from an investigation of the influence of ion-milling on the stability of the T2 phase in dilute Al-Li-Cu alloy.The 3-mm diameter TEM disc specimens were prepared from a specially melted Al-2.5%Li-2.5%Cu alloy produced by conventional procedures. The TEM specimens were solution heat treated 1 h at 550°C and aged 1000 h at 190°C in air to develop the microstructure. The disc specimens were electropolished to achieve electron transparency using a 20:80 (vol. percent) nitric acid: methanol solution at -60°C.

“In vitro” and in Animal Model Studies on a Double Virus- Inactivated Factor VIII Concentrate

1995 ◽  
Vol 74 (03) ◽  
pp. 868-873 ◽  
Author(s):  
Silvana Arrighi ◽  
Roberta Rossi ◽  
Maria Giuseppina Borri ◽  
Vladimir Lesnikov ◽  
Marina Lesnikov ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Animal Model ◽  
Factor Viii ◽  
Hepatitis A ◽  
Hepatitis A Virus ◽  
Virus Inactivation ◽  
Enveloped Viruses ◽  
Model Studies ◽  
Heat Treated

SummaryTo improve the safety of plasma derived factor VIII (FVIII) concentrate, we introduced a final super heat treatment (100° C for 30 min) as additional virus inactivation step applied to a lyophilized, highly purified FVIII concentrate (100 IU/mg of proteins) already virus inactivated using the solvent/detergent (SID) method during the manufacturing process.The efficiency of the super heat treatment was demonstrated in inactivating two non-lipid enveloped viruses (Hepatitis A virus and Poliovirus 1). The loss of FVIII procoagulant activity during the super heat treatment was of about 15%, estimated both by clotting and chromogenic assays. No substantial changes were observed in physical, biochemical and immunological characteristics of the heat treated FVIII concentrate in comparison with those of the FVIII before heat treatment.

Vanadium Additions to a High-Cr White Iron and its Effects on the Abrasive Wear Behavior.

MRS Advances ◽  
2020 ◽  
Vol 5 (59-60) ◽  
pp. 3077-3089
Author(s):  
Alexeis Sánchez ◽  
Arnoldo Bedolla-Jacuinde ◽  
Francisco V. Guerra ◽  
I. Mejía
Keyword(s):  
Heat Treatment ◽  
Abrasive Wear ◽  
Volume Fraction ◽  
Wear Behavior ◽  
Wear Behaviour ◽  
White Iron ◽  
Heat Treated ◽  
Bulk Hardness ◽  
Abrasive Wear Behavior ◽  
Vanadium Carbides

AbstractFrom the present study, vanadium additions up to 6.4% were added to a 14%Cr-3%C white iron, and the effect on the microstructure, hardness and abrasive wear were analysed. The experimental irons were melted in an open induction furnace and cast into sand moulds to obtain bars of 18, 25, and 37 mm thickness. The alloys were characterized by optical and electronic microscopy, and X-ray diffraction. Bulk hardness was measured in the as-cast conditions and after a destabilization heat treatment at 900°C for 45 min. Abrasive wear resistance tests were undertaken for the different irons according to the ASTM G65 standard in both as-cast and heat-treated conditions under a load of 60 N for 1500 m. The results show that, vanadium additions caused a decrease in the carbon content in the alloy and that some carbon is also consumed by forming primary vanadium carbides; thus, decreasing the eutectic M7C3 carbide volume fraction (CVF) from 30% for the base iron to 20% for the iron with 6.4%V;but overall CVF content (M7C3 + VC) is constant at 30%. Wear behaviour was better for the heat-treated alloys and mainly for the 6.4%V iron. Such a behaviour is discussed in terms of the CVF, the amount of vanadium carbides, the amount of martensite/austenite in matrix and the amount of secondary carbides precipitated during the destabilization heat treatment.

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