scholarly journals Thermal Variation of Elastic Modulus on Nanocrystalline NiCuZn Ferrites

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
S. R. Murthy
Keyword(s):  
Particle Size ◽  
Internal Friction ◽  
Curie Temperature ◽  
Temperature Variation ◽  
Room Temperature ◽  
Elastic Moduli ◽  
Anisotropy Constant ◽  
Initial Permeability ◽  
Elastic Behaviour ◽  
Thermal Variation

The nanopowders of Ni0.38Cu0.12Zn0.5Fe2O4 with particle size, 20 nm have been synthesised using Microwave-Hydrothermal method and characterized. Then the ferrite samples were microwave sintered at different temperatures in an air atmosphere and characterized. The magnetic properties were measured at room temperature. The dielectric constant (ɛ), initial permeability (μi) and quality factor (Q) has been measured on sintered samples at 1 MHz. Thermal variation of initial permeability has been measured over temperature range of 300 K–600 K. A detailed study of elastic behaviour of NiCuZn ferrites has been under taken using a composite piezoelectric oscillator method over a temperature of 300 K–600 K. The room temperature elastic moduli is found to be slightly sample dependent and decreases with increasing the temperature, except near the Curie temperature, TC, where a small anomaly is observed. The internal friction at room temperature is also found to be more particle size dependent. The temperature variation of internal friction exhibits a broad maximum around 500 K, just below Curie temperature TC 530 K. The above observations were carried on in the demagnetized state; on the application of a 400 mT magnetic field allowed us to reach the saturated state of the sample at any of the measuring temperature. The anomaly observed in the thermal variation of elastic moduli and internal friction is explained with the help of temperature variation of magneto-crystalline anisotropy constant.

Superparamagnetic Nanocrystalline ZnFe2O4 with a Very High Curie Temperature

2008 ◽  
Vol 8 (8) ◽  
pp. 3955-3958 ◽  
Author(s):  
Sasanka Deka ◽  
P. A. Joy
Keyword(s):  
Magnetic Properties ◽  
Curie Temperature ◽  
Temperature Variation ◽  
Nanocrystalline Materials ◽  
Zinc Ferrite ◽  
Room Temperature ◽  
Magnetic Hysteresis ◽  
High Curie Temperature ◽  
Particle Sizes ◽  
Very High

Studies on the magnetic properties of nanocrystalline ZnFe2O4 synthesized by an autocombustion method are reported. Superparamagnetic behavior is observed for the nanocrystalline materials with particle sizes of 8 nm and 17nm, with superparamagnetic blocking temperatures of 65 K and 75 K, respectively. Magnetic hysteresis with very large coercivities of 533 Oe and 325 Oe, respectively, are observed at 12 K. Studies on the temperature variation of the magnetization above room temperature indicate that the Curie temperature is as high as ∼800 K when compared to the paramagnetic nature of bulk zinc ferrite at room temperature.

scholarly journals EPR Spectra of Sintered Cd1−xCrxTe Powdered Crystals with Various Cr Content

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3449
Author(s):  
Ireneusz Stefaniuk ◽  
Werner Obermayr ◽  
Volodymyr D. Popovych ◽  
Bogumił Cieniek ◽  
Iwona Rogalska
Keyword(s):  
Curie Temperature ◽  
Room Temperature ◽  
Integral Intensity ◽  
Resonance Field ◽  
Epr Spectra ◽  
Paramagnetic Resonance ◽  
Simple Method ◽  
Paramagnetic Curie Temperature ◽  
Cr Content ◽  
Electron Paramagnetic

In this paper, we show a simple method of producing ferromagnetic materials with a Curie temperature above room temperature. The electron paramagnetic resonance (EPR) spectra of Cd1−xCrxTe (0.002 < x < 0.08) were measured with a dependence on temperature (82 K < T < 381 K). Obtained EPR lines were fitted to a Lorentz-shaped curve. The temperature dependencies of the parameters of the EPR lines, such as the peak-to-peak linewidth (Hpp), the intensity (A), as well as the resonance field (Hr), were studied. Ferromagnetism was noticed in samples at high temperatures (near room temperature). For a sample with a nominal concentration of chrome of x = 0.05, a very strong intrinsic magnetic field is observed. The value of the effective gyromagnetic factor for this sample is ge = 30 at T = 240 K. An increase of chrome concentration above x = 0.05 reduces the ferromagnetic properties considerably. Analysis of the temperature dependencies of the integral intensity of EPR spectra was carried out using the Curie–Weiss law and the paramagnetic Curie temperature was obtained.

scholarly journals Back protection of canvas paintings

2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Tim Padfield ◽  
Nicolas Padfield ◽  
Daniel Sang-Hoon Lee ◽  
Anne Thøgersen ◽  
Astrid Valbjørn Nielsen ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Relative Humidity ◽  
Temperature Variation ◽  
Room Temperature ◽  
Single Point ◽  
Confined Space ◽  
Constant Wall Temperature ◽  
Back Plate ◽  
Inner Surface

Abstract In this paper different scenarios for back protection of a canvas painting and their effect on the stability of the relative humidity behind the painting are tested. A painting on canvas, stretched on a wooden frame, was fitted with various styles of back protection and then exposed to a cycle of temperature variation at the back, with the front exposed to a constant room temperature. The painting was also exposed to a constant wall temperature and varying room temperature. The space between the canvas and the back board was fitted with temperature and relative humidity (RH) sensors. The sensors were used to provide the essential single-point data of temperature and RH at the given locations. For more comprehensive understanding of the rather confined space, further numerical simulation (computational fluid dynamics) was adopted as part of the investigation. The computational fluid dynamics was used to understand the natural convection within the microclimate through the depictions of temperature distribution, as well as the corresponding airflow. The unprotected painting suffered a large RH variation at its back, because of the varying canvas temperature interacting with the constant room air moisture content. Effective stabilisation of the RH behind the canvas against temperature variation was provided by a shiny aluminium alloy sheet sealed against the frame. The non-absorbent back board experienced a strong variation in RH, because of humidity buffering of the space by the painting canvas at a different temperature. Either a space or insulation between this back plate and the wall reduced the risk of condensation on the inner surface of the back plate. Insulation will however increase the risk of condensation on the wall surface behind the painting. An absorbent back board de-stabilised the RH at the painting canvas surface by providing a competing humidity buffer at a different temperature. To provide protection against moisture exchange with an unsuitable room RH, extra humidity buffer was placed 3 mm behind the painting canvas, kept close to the painting temperature by insulation between this buffer and the back board. This stabilised RH at the canvas surface but increased both the temperature and the RH variation at the back board and thus increased the risk of condensation on the inner surface of the back board. The RH and the temperature in the narrow spaces between the painting canvas and the wooden stretcher frame were always more nearly constant than in the open canvas area, which suggests an explanation for the widely observed better condition of the areas of canvas paintings which lie close over the support structure. Our conclusion is that a non-absorbent, impermeable back plate gives good RH stability against a changing temperature gradient between wall and canvas painting surface.

Ferroelectric Tunability Studies in Doped BaTiO3 and Ba1−xSrxTiO3

2000 ◽  
Vol 658 ◽  
Author(s):  
Dong Li ◽  
M. A. Subramanian
Keyword(s):  
Curie Temperature ◽  
Phase Change ◽  
Tetragonal Phase ◽  
Cryogenic Temperature ◽  
Room Temperature ◽  
Co Doping ◽  
Structure Changes

ABSTRACTAcceptor and Donor codoped BaTiO3 and Ba1−xSrxTiO3 are prepared. For Ba1−xLaxTi1−xFexO3,BaTiO3 remains as tetragonal phase up to about 5mol% LaFeO3. For x ≥0.06, the structure changes to cubic at room temperature. The phase change shifts the Curie temperature to lower value and increases the tunability at room temperature. Doping of other acceptor (Al, Cr) and donor (Sm, Gd, Dy) ions has the same effect although with varying levels of tuning. BaTiO3: 4%LaFeO3 has the highest tunability among the studied systems, which is even higher than Ba0.6Sr0.4TiO3. Co-doping of (La, Fe) and (La, Al) in Ba1−xSrxTiO3 also lowers the Curie temperature and increases the tunability of high Ba content samples at cryogenic temperature.

scholarly journals Influence of Structural Plane Microscopic Parameters on Direct Shear Strength

2018 ◽  
Vol 2018 ◽  
pp. 1-7 ◽  
Author(s):  
Yanhui Cheng ◽  
Weijun Yang ◽  
Dongliang He
Keyword(s):  
Particle Size ◽  
Shear Strength ◽  
Internal Friction ◽  
Direct Shear Test ◽  
Shear Test ◽  
Friction Angle ◽  
Internal Friction Angle ◽  
Direct Shear ◽  
Stiffness Ratio ◽  
Structural Plane

Structural plane is a key factor in controlling the stability of rock mass engineering. To study the influence of structural plane microscopic parameters on direct shear strength, this paper established the direct shear mechanical model of the structural plane by using the discrete element code PFC2D. From the mesoscopic perspective, the research on the direct shear test for structural plane has been conducted. The bonding strength and friction coefficient of the structural plane are investigated, and the effect of mesoscopic parameters on the shear mechanical behavior of the structural plane has been analyzed. The results show that the internal friction angle φ of the structural plane decreases with the increase of particle contact stiffness ratio. However, the change range of cohesion is small. The internal friction angle decreases first and then increases with the increase of parallel bond stiffness ratio. The influence of particle contact modulus EC on cohesion c is relatively small. The internal friction angle obtained by the direct shear test is larger than that obtained by the triaxial compression test. Parallel bond elastic modulus has a stronger impact on friction angle φ than that on cohesion c. Under the same normal stress conditions, the shear strength of the specimens increases with particle size. The shear strength of the specimen gradually decreases with the increase of the particle size ratio.

Analysis of Thermal Variation of Length and Refractive Index of Lead Fluoride to Study its Optical Properties

1989 ◽  
Vol 172 ◽  
Author(s):  
T. S. Aurora ◽  
D. O. Pederson ◽  
S. M. Day
Keyword(s):  
Refractive Index ◽  
Room Temperature ◽  
Linear Thermal Expansion ◽  
Small Variation ◽  
Published Data ◽  
Thermal Variation ◽  
Lead Fluoride ◽  
Superionic Phase Transition ◽  
Lorenz Relation ◽  
Good Agreement

AbstractLinear thermal expansion and refractive index variation have been measured in lead fluoride with a laser interferometer as a function of temperature. Data has been analyzed using the Lorentz-Lorenz relation. Molecular polarizability, band gap, variation of refractive index with density, and strain-polarizability parameter have been studied as a function of temperature. They exhibit a small variation with temperature except near the superionic phase transition where the variation appears to be more pronounced. The results are in good agreement with the published data near room temperature.

Structural and electrical properties of KCa2Nb5O15 ceramics

Open Physics ◽  
2008 ◽  
Vol 6 (2) ◽  
Author(s):  
Banarji Behera ◽  
Pratibindhya Nayak ◽  
Ram Choudhary
Keyword(s):  
Electrical Properties ◽  
Temperature Variation ◽  
Electrical Transport ◽  
Room Temperature ◽  
Complex Impedance ◽  
Tungsten Bronze ◽  
Transport Processes ◽  
Relaxation Processes ◽  
Orthorhombic Crystal Structure ◽  
Grain Distribution

AbstractA polycrystalline sample of KCa2Nb5O15 with tungsten bronze structure was prepared by a mixed oxide method at high temperature. A preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound shows a uniform grain distribution throughout the surface of the sample. Studies of temperature variation on dielectric response at various frequencies show that the compound has a transition temperature well above the room temperature (i.e., 105°C), which was confirmed by the polarization measurement. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (31–500°C) and frequency (102–106 Hz) range that showed only bulk contribution and non-Debye type relaxation processes in the material. The activation energy of the compound (calculated from both the loss and modulus spectrum) is same, and hence the relaxation process may be attributed to the same type of charge carriers. A possible ‘hopping’ mechanism for electrical transport processes in the system is evident from the modulus analysis. A plot of dc conductivity (bulk) with temperature variation demonstrates that the compound exhibits Arrhenius type of electrical conductivity.

Screening and Design of Novel 2D Ferromagnetic Materials with High Curie Temperature above Room Temperature

2018 ◽  
Vol 10 (45) ◽  
pp. 39032-39039 ◽  
Author(s):  
Zhou Jiang ◽  
Peng Wang ◽  
Jianpei Xing ◽  
Xue Jiang ◽  
Jijun Zhao
Keyword(s):  
Curie Temperature ◽  
Room Temperature ◽  
Ferromagnetic Materials ◽  
High Curie Temperature

Martensitic Transformation and Mechanical Properties of Fe-Doped Ni54Mn21Ga25 Alloys

2011 ◽  
Vol 687 ◽  
pp. 500-504
Author(s):  
S. X. Xue ◽  
S.S. Feng ◽  
P. Y. Cai ◽  
Q T Li ◽  
H. B. Wang
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Magnetic Properties ◽  
Martensitic Transformation ◽  
Curie Temperature ◽  
Directional Solidification ◽  
Transformation Temperature ◽  
Room Temperature ◽  
Martensitic Transformation Temperature ◽  
Polycrystalline Alloys

Ni54Mn21-xFexGa25（x=0,1,3,5,7,9）polycrystalline alloys were prepared by the technique of directional solidification and the effect of substituting Fe for Mn on the martensitic transformation and mechanical properties of the alloys was analyzed. It was found that the Curie temperature increased with increasing substitution while the martensitic transformation temperature decreased. The Fe-doped Ni54Mn21Ga25 alloys exhibit excellent magnetic properties at room temperature; the typical Ni54Mn20Fe1Ga25 alloy shows a large magnetic-induced-strain of -1040 ppm at a magnetic field of 4000 Oe.

Sign in / Sign up

Export Citation Format

Share Document