scholarly journals Depth-hoar crystal growth in the surface layer under high temperature gradient

1993 ◽  
Vol 18 ◽  
pp. 39-45 ◽  
Author(s):  
Takuya Fukuzawa ◽  
Eizi Akitaya
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
High Temperature ◽  
Temperature Gradient ◽  
Crystal Growth Rate ◽  
Snow Surface ◽  
Night Time ◽  
High Temperature Gradient ◽  
Series Of Experiments ◽  
The Given

The quick growth of depth-hoar crystals was observed at night-time just below the snow surface on a south-facing slope. This growth was due to a high temperature gradient (> 100 K m−1) near the snow surface under clear skies after a thin deposition of new snow on older and denser snow. The temperature gradient was greater when internal melting had taken place during daytime, keeping the sub-surface snow temperature at 0°C even after sunset until all liquid water had frozen. To understand the relationship between the crystal growth rate and the temperature gradient, a series of experiments was carried out in the laboratory. The snow sample was set under a constant temperature gradient between 100 and 300 K m− and sustained for about 50 h. The average crystal size increased linearly with time and the crystal growth rate increased as the given temperature gradient increased. The growth rates were in the order of 10−9 m s−1, which gave a good agreement with the results of the field observation.

scholarly journals Depth-hoar crystal growth in the surface layer under high temperature gradient

1993 ◽  
Vol 18 ◽  
pp. 39-45 ◽  
Author(s):  
Takuya Fukuzawa ◽  
Eizi Akitaya
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
High Temperature ◽  
Temperature Gradient ◽  
Crystal Growth Rate ◽  
Snow Surface ◽  
Night Time ◽  
High Temperature Gradient ◽  
Series Of Experiments ◽  
The Given

The quick growth of depth-hoar crystals was observed at night-time just below the snow surface on a south-facing slope. This growth was due to a high temperature gradient (> 100 K m−1) near the snow surface under clear skies after a thin deposition of new snow on older and denser snow. The temperature gradient was greater when internal melting had taken place during daytime, keeping the sub-surface snow temperature at 0°C even after sunset until all liquid water had frozen. To understand the relationship between the crystal growth rate and the temperature gradient, a series of experiments was carried out in the laboratory. The snow sample was set under a constant temperature gradient between 100 and 300 K m− and sustained for about 50 h. The average crystal size increased linearly with time and the crystal growth rate increased as the given temperature gradient increased. The growth rates were in the order of 10−9 m s−1, which gave a good agreement with the results of the field observation.

scholarly journals Macrodefects in Cubic Silicon Carbide Crystals

2010 ◽  
Vol 645-648 ◽  
pp. 375-378 ◽  
Author(s):  
Valdas Jokubavicius ◽  
Justinas Palisaitis ◽  
Remigijus Vasiliauskas ◽  
Rositza Yakimova ◽  
Mikael Syväjärvi
Keyword(s):  
Growth Rate ◽  
Silicon Carbide ◽  
Crystal Growth ◽  
High Temperature ◽  
Temperature Gradient ◽  
Early Stage ◽  
Growth Conditions ◽  
Temperature Ramp ◽  
Cubic Silicon Carbide ◽  
Sublimation Growth

Different sublimation growth conditions of 3C-SiC approaching a bulk process have been investigated with the focus on appearance of macrodefects. The growth rate of 3C-SiC crystals grown on 6H-SiC varied from 380 to 460 μm/h with the thickness of the crystals from 190 to 230 μm, respectively. The formation of macrodefects with void character was revealed at the early stage of 3C-SiC crystal growth. The highest concentration of macrodefects appears in the vicinity of the domain in samples grown under high temperature gradient and fastest temperature ramp up. The formation of macrodefects was related to carbon deficiency which appear due to high Si/C ratio which is used to enable formation of the 3C-SiC polytype.

Novel Method for High Speed SiC Vapor Growth

2006 ◽  
Vol 911 ◽  
Author(s):  
Xiaolin Wang ◽  
Cai Dang ◽  
Hui Zhang ◽  
Michael Dudley
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
High Temperature ◽  
High Speed ◽  
Growth Process ◽  
Crystal Growth Rate ◽  
Vapor Transport ◽  
New Method ◽  
Sublimation Rate ◽  
Sublimation Growth

AbstractSilicon carbide is a promising semiconductor material for electrical and optoelectronic applications in the area of high power, high temperature, high frequency and intense radiation. Many groups have worked on growing SiC bulk crystals by sublimation from SiC powder source at a temperature above 2000 oC under an argon environment. They have also worked on improving the crystal growth rate. Traditional approach is to increase furnace temperature to enhance the growth rate. However, high cost of inert crucible at high temperature and impurity caused by crucible degradation set limit on the maximum growth rate which can be achieved. Current existing crucible and other components in the furnace are no longer passive at high temperature. Also understanding of vapor transport during powder sublimation and the interplay between vapor transport and powder sublimation is important for the optimization of the sublimation growth process. A comprehensive numerical model combining heat transfer, sublimation, species transport, and powder porosity evolution of SiC sublimation growth process is developed in this paper. The mechanism of vapor transport is described, in which a driving force is introduced to explain vapor transport. A new method to increase crystal growth rate is proposed based on the model. The new method includes changing the initial powder porosity and creating a hole in the packed powder. Simulation results for the case with a central hole and without hole are presented. The results show that the powder sublimation rate increases by creating a hole, and it is also validated by experiments. The results also reveal that the mass of the as-grown crystal increases if the powder sublimation rate increases. Finally, the powder geometry is optimized using numerical simulations.

scholarly journals Microstructural Evolution And Mechanical Properties of FCAW Joints In 9% Ni Steel Prepared With Two Types of Ni-Based Weld Metals

2022 ◽  
Author(s):  
Jiyong Hwang ◽  
Kwangsu Choi ◽  
Sang Min Lee ◽  
Hyo Yun Jung
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Temperature Gradient ◽  
Weld Metal ◽  
Crystal Growth Rate ◽  
Inconel 625 ◽  
Large Temperature ◽  
Joint Interface ◽  
Weld Metals ◽  
Flux Cored Arc Welding

Abstract The microstructural and mechanical evaluation of 9% Ni steel with Flux-Cored Arc Welding was performed with two different Ni-based weld metals: Inconel 625 and Hastelloy 609. Weld metals showed the microstructural change depending on the temperature gradient and crystal growth rate for each region during the cooling after welding. At the bottom of the weld metal, which is rapidly cooled in contact with the cold base metal, a cellular/planar growth was exhibited due to a large temperature gradient and low crystal growth rate. While, columnar dendrites were exhibited in the central region cooled relatively slowly and precipitates were observed in the interdendritic region. In the low-temperature toughness test, the absorbed impact energies were 89 and 55 J for Inconel 625 and Hastelloy 609, respectively. When Inconel 625 is used as the weld metal compared to Hastelloy 609, the high content of the γ stabilizer and martensite start temperature decreasing elements leads to the formation of a thicker γ-phase layer and thinner martensite layer in the transition region. In addition, high content of these elements suppresses the martensite transformation and maintains the stability of the weld joint interface even at low temperatures, resulting in the higher absorbed impact energy.

TEMPERATURE DEPENDENCE OF THE CRYSTAL GROWTH RATE IN POLAR GLACIERS

1987 ◽  
Vol 48 (C1) ◽  
pp. C1-661-C1-662 ◽  
Author(s):  
J. R. PETIT ◽  
P. DUVAL ◽  
C. LORIUS
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Temperature Dependence ◽  
Crystal Growth Rate

Comparison of copper sulphate pentahydrate growth rates determined by different methods

1990 ◽  
Vol 55 (7) ◽  
pp. 1691-1707 ◽  
Author(s):  
Miloslav Karel ◽  
Jiří Hostomský ◽  
Jaroslav Nývlt ◽  
Axel König
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Fluidized Bed ◽  
Growth Rates ◽  
Copper Sulphate ◽  
Crystal Growth Rate ◽  
Effect Of Temperature ◽  
Rotating Disc ◽  
Shape Factors ◽  
Data Treatment

Crystal growth rates of copper sulphate pentahydrate (CuSO4.5 H2O) determined by different authors and methods are compared. The methods included in this comparison are: (i) Measurement on a fixed crystal suspended in a streaming solution, (ii) measurement on a rotating disc, (iii) measurement in a fluidized bed, (iv) measurement in an agitated suspension. The comparison involves critical estimation of the supersaturation used in measurements, of shape factors used for data treatment and a correction for the effect of temperature. Conclusions are drawn for the choice of values to be specified when data of crystal growth rate measurements are published.

Optical resolution of N-formylphenylalanine succeeds by crystal growth rate differences of diastereomeric salts

2007 ◽  
Vol 18 (2) ◽  
pp. 260-264 ◽  
Author(s):  
Laura Bereczki ◽  
Emese Pálovics ◽  
Petra Bombicz ◽  
György Pokol ◽  
Elemér Fogassy ◽  
...  
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Optical Resolution ◽  
Crystal Growth Rate ◽  
Diastereomeric Salts

Crystal-growth kinetics of protein single crystals along capillary tubes in the gel-acupuncture technique

1999 ◽  
Vol 55 (2) ◽  
pp. 577-580 ◽  
Author(s):  
Abel Moreno ◽  
Manuel Soriano-García
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Capillary Tube ◽  
Crystal Growth Rate ◽  
Equilibrium Studies ◽  
Acta Cryst ◽  
Average Growth ◽  
X Ray Crystallography ◽  
Growing Cell ◽  
Kinetics Of

In attempts to obtain protein crystals of a sufficient size for structural studies, lack of knowledge of the physicochemical properties of protein solutions and of their crystal-growth behaviour lead to a bottleneck for drug design as well as for X-ray crystallography. Most formal investigations on crystal-growth phenomena have been focused on equilibrium studies, where the protein is soluble, and on the kinetics of crystal growth, which is related to both nucleation and crystal-growth phenomena. The aim of this work is to measure the crystal-growth rate along a capillary tube used as a growing cell. These experiments were carried out using the gel-acupuncture technique [García-Ruiz et al. (1993). Mater. Res. Bull. 28, 541–546; García-Ruiz & Moreno (1994). Acta Cryst. D50, 484–490; García-Ruiz & Moreno (1997). J. Cryst. Growth, 178, 393–401]. Crystal-growth investigations took place using lysozyme and thaumatin I as standard proteins. The maximum average growth rate obtained in the lower part of the capillary tube was about 35 Å s−1 and the minimum average growing rate in the upper part of the capillary tube was about 8 Å s−1. The crystal-growth rate as a function of the supersaturation was experimentally estimated at a constant height along the capillary tube.

Phase separation in undercooled molten Pd80Si20: Part I

1999 ◽  
Vol 14 (9) ◽  
pp. 3653-3662 ◽  
Author(s):  
K. L. Lee ◽  
H. W. Kui
Keyword(s):  
Growth Rate ◽  
Phase Separation ◽  
Crystal Growth ◽  
Grain Refinement ◽  
Crystallization Temperature ◽  
Sharp Decrease ◽  
Nucleation And Growth ◽  
Crystal Growth Rate ◽  
Large Undercooling ◽  
Kinetic Crystallization

Three different kinds of morphology are found in undercooled Pd80Si20, and they dominate at different undercooling regimens ΔT, defined as ΔT = T1 – Tk, where T1 is the liquidus of Pd80Si20 and Tk is the kinetic crystallization temperature. In the small undercooling regimen, i.e., for ΔT ≤ 190 K, the microstructures are typically dendritic precipitation with a eutecticlike background. In the intermediate undercooling regimen, i.e., for 190 ≤ ΔT ≤ 220 K, spherical morphologies, which arise from nucleation and growth, are identified. In addition, Pd particles are found throughout an entire undercooled specimen. In the large undercooling regimen, i.e., for ΔT ≥ 220 K, a connected structure composed of two subnetworks is found. A sharp decrease in the dimension of the microstructures occurs from the intermediate to the large undercooling regimen. Although the crystalline phases in the intermediate and the large undercooling regimens are the same, the crystal growth rate is too slow to bring about the occurrence of grain refinement. Combining the morphologies observed in the three undercooling regimens and their crystallization behaviors, we conclude that phase separation takes place in undercooled molten Pd80Si20.

Sign in / Sign up

Export Citation Format

Share Document