scholarly journals The low-frequency conductivity of snow near the melting temperature

2001 ◽  
Vol 32 ◽  
pp. 14-18 ◽  
Author(s):  
Iwao Takei ◽  
Norikazu Maeno
Keyword(s):  
Activation Energy ◽  
Particle Size ◽  
Melting Temperature ◽  
Low Frequency ◽  
Dielectric Dispersion ◽  
Average Particle ◽  
Temperature Range ◽  
Ice Surfaces ◽  
Increasing Temperature ◽  
Snow Samples

AbstractDielectric measurements of snow were carried out in the temperature range –15° to 0°C and in the frequency range 50 Hz to 5 MHz. The snow samples (about 400 kg m–3 density) used were stored snow (average particle size: 2 mm) and hoar-frost (particle size: <1 to 5 mm). The frequency characteristics of dielectric parameters showed a dielectric dispersion (Davidson-Cole type) around 30 kHz and a low-frequency dielectric dispersion (Cole-Cole circular law type). The a.c. conductivity showed a dielectric dispersion around 30 kHz and two characteristic constant values in the frequency ranges above 1 MHz and below 100 Hz (the high-frequency conductivity σ∞ and the low-frequency conductivity σLOW). The low-frequency conductivity σLOW showed a peak at about –2°C. This behavior has never been noted by previous researchers. The σLOW showed an activation energy of about 1 eV below –5°C. This means that the σLOW is mainly caused by a surface conduction. The activation energy increased with increasing temperature above –5°C. This means that the σLOW in this temperature range is affected by the quasi-liquid layer on ice surfaces. The σLOW above –2°C decreased with increasing temperature. The apparently curious behavior near the melting temperature is attributed to the numerous free ice surfaces within the porous snow. This conclusion was reached because our measurements without the free ice surfaces showed no such conductivity peaks for solid polycrystalline ice samples and for snow samples soaked with kerosene in the cooling process.

Dielectric and mechanical alterations of snow properties near the melting temperature

2003 ◽  
Vol 81 (1-2) ◽  
pp. 233-239 ◽  
Author(s):  
I Takei ◽  
N Maeno
Keyword(s):  
Melting Temperature ◽  
Propagation Velocity ◽  
Low Frequency ◽  
Dielectric Measurements ◽  
Frequency Range ◽  
Temperature Range ◽  
Snow Properties ◽  
Response Method ◽  
Dielectric And Mechanical Properties ◽  
Snow Samples

The dielectric and mechanical properties of snow were investigated in the temperature range –15 to 0°C. Dielectric measurements were carried out in the frequency range 50 Hz – 5 MHz; the low-frequency conductivity (at 100 Hz) of snow samples shows a peak in the temperature range –3 to –0.3°C and the dielectric dispersion-strength also shows a minimum in this same range. The propagation velocity of an elastic wave through snow samples was measured with a vibration response method in the frequency range 10 Hz – 1 MHz; the propagation velocity shows an increase with the bond growth as a result of progressive sintering, and a significant decrease above –0.6°C. The temperature dependence of the low-frequency conductivity and the propagation velocity for snow samples show a hysteresis near the melting temperature. A boundary between ice particles in snow samples is discussed as a means for understanding these phenomena. PACS Nos.: 61.43Gt, 77.22Gm, 46.40-f, 73.25+i

Nitrocellulose Catalyzed With Manganese Oxide Nanoparticles: Advanced Energetic Nanocomposite With Superior Decomposition Kinetics

2021 ◽  
Author(s):  
Sherif Elbasuney ◽  
M. Yehia ◽  
Shukri Ismael ◽  
Yasser El-Shaer ◽  
Ahmed Saleh
Keyword(s):  
Activation Energy ◽  
Particle Size ◽  
Manganese Oxide ◽  
Energetic Materials ◽  
Average Particle Size ◽  
Active Surface ◽  
Propagation Rate ◽  
Hydroxyl Groups ◽  
Average Particle ◽  
Decomposition Enthalpy

Abstract Nanostructured energetic materials can fit with advanced energetic first-fire, and electric bridges (microchips). Manganese oxide, with active surface sites (negatively charged surface oxygen, and hydroxyl groups) can experience superior catalytic activity. Manganese oxide could boost decomposition enthalpy, ignitability, and propagation rate. Furthermore manganese oxide could induce vigorous thermite reaction with aluminium particles. Hot solid or liquid particles are desirable for first-fire compositions. This study reports on the facile fabrication of MnO2 nanoparticles of 10 nm average particle size; aluminium nanoplates of 100 nm average particle size were employed. Nitrocellulose (NC) was adopted as energetic polymeric binder. MnO2/Al particles were integrated into NC matrix via co-precipitation technique. Nanothermite particles offered an increase in NC decomposition enthalpy by 150 % using DSC; ignition temperature was decreased by 8 0C. Nanothemrite particles offered enhanced propagation index by 261 %. Kinetic study demonstrated that nanothermite particles experienced drastic decrease in NC activation energy by - 42, and - 40 KJ mol-1 using Kissinger and KAS models respectively. This study shaded the light on novel nanostructured energetic composition, with superior combustion enthalpy, propagation rate, and activation energy.

scholarly journals Synthesis and Optical Performances of a Waterborne Polyurethane-Based Polymeric Dye

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Xianhai Hu ◽  
Xingyuan Zhang ◽  
Jin Liu
Keyword(s):  
Molecular Weight ◽  
Particle Size ◽  
Waterborne Polyurethane ◽  
Average Particle ◽  
Particle Sizes ◽  
Hypsochromic Shift ◽  
Absorption Bands ◽  
Polymeric Dye ◽  
Emulsion Particle ◽  
Increasing Temperature

A waterborne polyurethane-based polymeric dye (WPU-CFBB) was synthesized by anchoring 1, 4-bis(methylamino)anthraquinone (CFBB) to waterborne polyurethane chains. The number molecular weight, glass transition temperature, and average emulsion particle size for the polymeric dye were determined, respectively. This polymeric dye exhibited intriguing optical behaviors. The polymeric dye engendered two new absorption bands centered at about 520 nm and 760 nm if compared with CFBB in UV-vis spectra. The 760 nm peak showed hypsochromic shift with the decrease of average particle sizes. The polymeric dye dramatically demonstrated both hypsochromic and bathochromic effects with increasing temperature. The fluorescence intensity of the polymeric dye was much higher than that of CFBB. It was found that the fluorescence intensities would be enhanced from 20°C to 40°C and then decline from 40°C to 90°C. The fluorescence of the polymeric dye emulsion was very stable and was not sensitive to quenchers.

Melting Behavior in Granular Metal Thin Films

1990 ◽  
Vol 195 ◽  
Author(s):  
Karl M. Unruh ◽  
B.M. Patterson ◽  
S.I. Shah
Keyword(s):  
Particle Size ◽  
Melting Temperature ◽  
Average Particle Size ◽  
Melting Behavior ◽  
Multilayer Films ◽  
Relative Reduction ◽  
Average Particle ◽  
Scanning Calorimetry ◽  
Metal Thin Films ◽  
Solid Liquid

ABSTRACTGranular metal films consisting of small Sn, Bi, and Pb particles, typically from less than 100 Å to several 1000 Å in size and embedded in a SiO2 matrix, have been fabricated over a range of metal compositions by RF sputter deposition. Two different film geometries have been prepared, homogeneous films and multilayer films consisting of alternating layers of granular metal and SiO2. These films have been characterized by x-ray diffraction and transmission electron microscopy and their melting behavior studied by differential scanning calorimetry. As the concentration of the metal component is decreased, the average particle size decreases and the particle size distribution becomes more narrow. When the solid-liquid transition is studied, the melting temperature has been found to be increasingly depressed as the particle size is reduced. In the smallest particles the relative reduction in the melting temperature is greater than 10 percent. No strong evidence for melting point enhancements, due to pressureeffects arising from the different thermal expansions of the metal particles and the SiO2 matrix, has been observed in either the homogeneous or multilayer films.

Hydration of Partially Sulfated Lime Particles From Fluidized Bed Combustors

2000 ◽  
Vol 123 (2) ◽  
pp. 173-178 ◽  
Author(s):  
M. F. Couturier ◽  
Y. Volmerange ◽  
F. Steward
Keyword(s):  
Activation Energy ◽  
Particle Size ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Hydration Reaction ◽  
Order Kinetic ◽  
First Order ◽  
Thermogravimetric Analyzer ◽  
Order Kinetic Model ◽  
Increasing Temperature

The reaction between water and partially sulfated lime particles was studied under isothermal conditions using a microcalorimeter. Experiments were performed with spent sorbent particles from two industrial circulating fluidized bed combustors and with lime particles sulfated in the laboratory using a thermogravimetric analyzer. The rate of hydration of the partially sulfated lime particles was found to be independent of particle size, to increase with increasing temperature, and to decrease with increasing level of sulfation of the particles. A first-order kinetic model is shown to correlate well the effect of time and temperature on the extent of hydration of spent sorbent particles from fluidized bed combustors. The apparent activation energy of the hydration reaction is 45 kJ/mol.

On the Sintering Activation Energy of α-Al2O3

2008 ◽  
Vol 368-372 ◽  
pp. 686-687 ◽  
Author(s):  
Wei Quan Shao ◽  
Shaou Chen ◽  
Da Li ◽  
Ping Qi ◽  
Yong Wan ◽  
...  
Keyword(s):  
Activation Energy ◽  
Particle Size ◽  
Temperature Interval ◽  
High Purity ◽  
Powder Compact ◽  
Isothermal Condition ◽  
Particle Sizes ◽  
Higher Temperature ◽  
Lower Temperature ◽  
Increasing Temperature

The sintering activation energy of high-purity alumina powders with different particle sizes was evaluated under non-isothermal condition. It was found that, during sintering, the activation energy for the lower temperature stage is higher than that for higher temperature stage. The value of the activation energies for the powder compact with larger particle size was higher than that for the powder compact with smaller particle size. If the selected temperature interval for calculation was narrow enough, the evaluated activation energy values varied with the increasing temperature continuously.

Molten Salt Synthesis of Anisotropy BaBi4Ti4O15 Powders in K2SO4-Na2SO4 Flux

2011 ◽  
Vol 687 ◽  
pp. 333-338 ◽  
Author(s):  
Yong Jun Gu ◽  
Jin Liang Huang ◽  
Li Hua Li ◽  
Ke Zhang ◽  
Xiao Wang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Particle Size ◽  
Molten Salt ◽  
Process Parameters ◽  
Average Particle Size ◽  
Particle Growth ◽  
Molten Salt Synthesis ◽  
Average Particle ◽  
Synthesis Conditions ◽  
Arrhenius Dependence

Anisotropic BaBi4Ti4O15 powder was synthesized by a molten salt synthesis (MSS) method in K2SO4-Na2SO4flux and the effects of different process parameters such as calcining temperature, and ratio of salt to reactant (R) on the phase formation and morphology of anisotropic BaBi4Ti4O15particles were also investigated. The as-synthesized powder calcined at 850-950°C exhibits a single tetragonal BaBi4Ti4O15phase. The morphology of BaBi4Ti4O15powder could be adjusted by changing the synthesis conditions. The average particle size (APS) of BaBi4Ti4O15powder increased with R changing from 0.8 to 1.0, while it decreased with further increasing of R to 1.2. In addition, the APS increased with increasing calcining temperature and it showed an Arrhenius dependence on the temperature. The corresponding apparent activation energy for particle growth is 31.9kJ/mol for calcining temperature of 850-1000°C.

Development of the Process of Pseudo-Ligatures Manufacturing from Aluminum and Nickel Powders for the Modification of Alloys

2014 ◽  
Vol 698 ◽  
pp. 452-456 ◽  
Author(s):  
Ekaterina A. Nosova ◽  
Antonina A. Kuzina ◽  
Anna V. Kuts
Keyword(s):  
Particle Size ◽  
Specific Surface ◽  
Surface Area ◽  
Melting Temperature ◽  
Specific Surface Area ◽  
Aluminum Powder ◽  
Nickel Powder ◽  
Average Particle Size ◽  
Average Particle ◽  
Powder Sintering

Compacting after pressing and sintering of briquettes made from an aluminum powder with an average particle size from 50 to 150 microns, the specific surface area Ssp=0.26 m2/g and a nickel powder with an average particle size from 25 to 100 microns, the specific surface area Ssp= 0.03 m2/g has been investigated. Pressing load varied from 15 to 25 MPa for the aluminum powder and from 20 to 45 MPa for the nickel powder. Sintering of aluminum powder briquettes was carried out at temperatures (0.5-0.83) of melting temperature, (0.3-0.46) of melting temperature from the nickel powder. It is shown that the application of high pressure, low temperatures and short time makes it possible to receive pseudo-ligatures from an aluminum powder with porosity about 32% and a nickel powder with porosity about 30%.

Dielectric Properties of Polyester Reinforced with Carbon Black Particles

2011 ◽  
Vol 110-116 ◽  
pp. 170-176
Author(s):  
Omed Ghareb Abdullah ◽  
Dana Abdull Tahir ◽  
Gelas Mukaram Jamal ◽  
Salah Raza Saeed
Keyword(s):  
Activation Energy ◽  
Dielectric Constant ◽  
Carbon Black ◽  
Low Temperatures ◽  
Ac Conductivity ◽  
Low Frequency ◽  
Frequency Range ◽  
Exponential Factor ◽  
Increasing Temperature ◽  
Dielectric Permittivity And Loss

Dielectric constant and ac conductivity of Polyester doped with carbon black are investigated in the frequency range (0.5-103) KHz and within the temperature range (26-80) oC. Dielectric permittivity and loss tangent reduced with increasing frequency and increase with increasing temperature. The ac conductivity σac for all samples were found to be weak frequency dependent at low frequency, however vary with frequency as a power law ωs at higher frequency range. The variation of frequency exponential factor s between 0.63 and 0.77, indicates a dominant hopping process at low temperatures. From the temperature dependence of dc conductivity, the increase of activation energy was observed with carbon black concentrations.

scholarly journals SYNTHESIS AND ELECTRICAL CONDUCTIVITY OF SOLID SOLUTIONS OF THE SYSTEM PbF2–NdF3–SnF2

2020 ◽  
Vol 86 (5) ◽  
pp. 24-37
Author(s):  
Pohorenko Yuliia ◽  
Omel’chuk Anatoliy ◽  
Nagornyi Anton
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Solid Solutions ◽  
Basic Structure ◽  
Elementary Cell ◽  
Initial Structure ◽  
Temperature Range ◽  
The Individual ◽  
Increasing Temperature ◽  
Transfer Numbers

In the system PbF2–NdF3–SnF2 are formed solid solutions of the heterovalent substitution Pb0,86-хNdхSn1,14F4+х (0 < x ≤ 0,17) with structure of β–PbSnF4. At x > 0,17 on the X-ray diffractograms, in addition to the basic structure, additional peaks are recorded to the reflexes of the individual NdF3. For single-phase solid solutions, the calculated parameters of the crystal lattice are satisfactorily described by the Vegard rule. The introduction of ions of Nd3+ into the initial structure leads to an increase in the parameter с of the elementary cell from 51.267 Å for x = 0,03 to 51.577 Å for x = 0.17. The replacement of a part of leads ions to neodymium ions an increase in electrical conductivity compared with Pb0.86Sn1.14F4. The slight replacement (3.0 mol. %) of Pb2+ ions by Nd3+ in the structure of Pb0.86Sn1.14F4 causes an increase in the electrical conductivity at T> 530 K (6.88·10-2 S/cm compared to 2.41·10-2 S/cm for the initial sample compound Pb0.86Sn1.14F4). In the region of lower temperatures, the electrical conductivity of the samples of this composition decreases, and below that temperature, on the contrary, slightly reduces the electrical conductivity, approaching the values characteristic of β-PbSnF4. The activation energy of the conductivity thus increases over the entire temperature range. A further increase in the concentration of Nd3+ ions in the synthesized samples causes an increase in their fluoride-ion conductivity throughout the temperature range. It should be noted that samples with a content of 10-15 mol% NdF3 at T>500 K have comparable conductivity values. At lower temperatures, the higher the conductivity, the higher the concentration of the substituent. The highest conductivity and the lowest activation energy have the sample Pb0.69Nd0.17Sn1.14F4.17 (σ373=3.68·10-2 S/сm, Ea=0,1 eV). The fluorine anions in synthesized phases are in three structurally-equivalent positions. The charge transfer is provided by the highly mobile interstitial fluorine anions, whose concentration increases with increasing temperature and concentration of NdF3. The transfer numbers for fluorine anions are not less than 0.99, practically independent of the concentration of neodymium trifluoride.

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