Papers by Keyword: Growth Kinetic

Abstract: A study was conducted to determine the most optimal preservation technique for P. sajor-caju spawns which produce maximum specific growth rate and shortest doubling time by using contois kinetic model. The analyzed experimental data showed that lyophilized P. sajor-caju spawn showed the highest maximum specific growth rate, and shortest doubling time compared to cryopreserved P. sajor-caju spawn and 4oC stored P. spawn. There was no significant difference in aspect of growth rate between the lyophilization and cryopreservation techniques which were; 0.148 (μ_max)/ (g/day) and 0.147(μ_max)/ (g/day) respectively. Based on the result, lyophilization technique was considered as the best preservation technique for preserving P. sajor-caju spawn due to high maximum growth rate which indicates high survival after exposure to preservation treatment.

Abstract: Nanocrystal TiO₂ photocatalystic materials were prepared by melt-phase separation technique, and its preparation principle was discussed in this paper. Anatase nanometer TiO₂ could be obtained by heat-treatment at 550 °C for 10 min, which is well combined with porous glass carrier and the particles size is about 25 nm. The growth kinetics of TiO2 crystalline analysis results showed that the growth activation energy Q1 was about 63.27 KJ/mol (<600 °C), and Q2 was about 22.78 KJ/mol (>600 °C).TiO₂ crystalline growth closely related to glass phase separation. TiO₂ particles grew quickly with the glass phase separation size increase, and then the particles growth rate became slow because of being limited by glass phase separation structure.

Abstract: A study of the coarsening process of the decomposed phases was carried out in the Cu-34wt.%Ni-4wt.%Cr and Cu-45wt.%Ni-10wt.%Cr alloys using transmission electron microscopy. As aging progressed, the morphology of the coherent decomposed Ni-rich phase changed from cuboids to platelets aligned in the <100> Cu-rich matrix directions. Prolonged aging caused the loss of coherency between the decomposed phases and the morphology of the Ni-rich phase changed to ellipsoidal. The variation of mean radius of the coherent decomposed phases with aging time followed the modified LSW theory for thermally activated growth in ternary alloy systems. The coarsening rate was faster in the symmetrical Cu-45wt.%Ni-10wt.%Cr alloy due to its higher volume fraction of precipitates. The activation energy for thermally activated growth was determined to be about 182 and 102 kJ mol-1 in the Cu-34wt.%Ni-4wt.%Cr and Cu-45wt.%Ni-10wt.%Cr alloys, respectively. The size distributions of precipitates in the Cu-Ni-Cr alloys were broader and more symmetric than that predicted by the modified LSW theory for ternary alloys.

Abstract: The present work estimated the growth kinetics of Fe2B layers formed at the surface of AISI 4140 steels. The thermochemical treatment was applied in order to produce the Fe2B phase, considering temperatures of 1123, 1173, 1223 and 1273 K with five exposure times (2, 4, 5, 6, and 8 h), using a 4 mm thick layer of boron carbide paste over the material surface. The growth of boride layers was described by the mass balance equation between phases in thermodynamic equilibrium, assuming that the growth of boride layers obeys the parabolic growth equation and the boron concentration at the interfaces remains constant. Also, the boron diffusion coefficient at the Fe2B ( ) was established as a function of boriding temperature. Likewise, the parabolic growth constant (k), the instantaneous velocity (v) of the Fe2B/substrate interface and the weight-gain of borided steels were established as a function of the parameters and , which are related to the boride incubation time ( ) and boron surface concentration ( ), respectively.

Abstract: A simulation of the growth kinetics of iron boride forming on AISI 1018 carbon steel was done on the basis of a kinetic model. This model including the effect of the incubation time during the formation of iron boride, was applied in order to evaluate the kinetic constant at the ( ) interface, the layer thickness and the mass gain depending on the paste-boriding parameters such as time, temperature and boron potential reflected by the corresponding value of the surface boron content. The simulation results were found to be in a good agreement with the experimental data derived from the literature.

Abstract: This paper presents selected experimental observations of phase constituents, growth kinetics, and microstructural development of aluminide phases that develop in solid-to-solid diffusion couples assembled with U-7wt.%Mo, U-10wt.%Mo and U-12wt.%Mo vs. Al and 6061 alloy after a diffusion anneal at 600°C for 24 hours. Scanning electron microscopy coupled with energy dispersive spectroscopy, electron microprobe analysis, and transmission electron microscopy via focused ion beam in-situ lift-out were employed to characterize the interaction layer that develops by interdiffusion. While concentration profiles exhibited no significant gradients, microstructural analysis revealed the presence of extremely complex and nano-scale phase constituents with presence of orthorhombic--U, cubic-UAl3, orthorhombic-UAl4, hexagonal-U6Mo4Al43 and diamond cubic-UMo2Al20 phases. Presence of multi-phase layers with microstructure, which suggest a significant role of grain boundary diffusion, was observed.

Abstract: The boron diffusion in the Fe2B and FeB borided phases formed at the surface of AISI H13 tool steels during the paste boriding process was estimated. The treatment was carried out at temperatures of 1173, 1223 and 1273 K with 2, 4, 6 and 8 h exposure times for each temperature using a 4 mm layer thickness of boron carbide paste over the material surface. The boride layers were characterized by the GDOES technique to determine in quantitative form the presence of the alloying elements on the borided phases. The boron diffusion coefficients and were determined by the mass balance equation and the boride incubation time assuming that the boride layers obey the parabolic growth law. Also, the mass gain produced by both boride layers at the surface of the tool steels was determined. Finally, the boron diffusion coefficients were interpreted as a function of the treatment temperature, obtaining the activation energy values for the diffusion controlled growth of Fe2B and FeB hard coatings.

Abstract: This work deals with a study of the nitriding potential effect on development of the compound layer during the gas nitriding of Armco Fe samples. The gas nitriding experiments were performed in an atmosphere of partially dissociated gas ammonia (NH3) at 520 °C under a nitriding potential varying from 0.25 to 3.5 atm-0.5 during 2 h. Through this experimental work including XRD analysis, optical and SEM observations of the cross-sections of the treated samples, it is shown that the microstructural nature of the compound layer depends upon the nitriding potential value. By use of the inverse problem based on a diffusion model previously published, it was possible to estimate the diffusion coefficient of N in ' iron nitride as a function of the applied nitriding potential. XRD analysis has shown that the compound layer was composed of iron nitride. A linear semi-logarithmic relationship relating the nitriding potential to the diffusion coefficient of nitrogen in iron nitride was also derived.

Abstract: The reaction behavior and growth kinetic of reaction layer were investigated in the Ni contact to n-type 6H-SiC. Annealing was performed at temperature in the range between 800 and 1000 °C for 1 to 240 minutes in Ar atmosphere. The interface reaction of Ni/SiC starts with Ni diffusion into SiC. Ni3Si is initially precipitated and subsequently forms the continuous layer of d-Ni2Si. Kirkendall voids are formed at the reaction front. Carbon is segregated in the interface layer of nickel silicide. The growth rate of the interface layer follows a parabolic law, meaning that the growth rate is controlled by diffusion. The growth occurs in two steps at all examined temperatures: a fast growth is followed by a slow growth. In addition, in the late stage, the growth rate changes dramatically below and above 850°C. The observed growth kinetic can be explained by the difference of Ni diffusivity and the required concentration change for phase transition depending on the phase composition and structure. The d-Ni2Si is formed in the early stage, while the e-Ni3Si2 and q-Ni2Si are formed in the late stage below and above 850°C, respectively.

Abstract: The growth kinetics of 3C-SiC heteroepitaxial layers on α-SiC substrates by Vapour-Liquid-Solid (VLS) mechanism in Ge-Si melts was investigated. Various parameters were studied such as temperature, melt composition, propane flux and substrate nature (polytype, polarity and misorientation). It was found that the growth rate increases with increasing temperature, propane flux, Si content of the melt and misorientation of the substrate. The calculated activation energy (from 4.7 to 6.6 kcal/mole depending on the substrate type) is very small suggesting that the limiting process is the diffusion of the dissolved carbon inside the melt. The carbon solubility inside the melt mainly affects the carbon dissolution kinetics from the gas phase. The results also suggest that surface effects are important through the layer polarity and crystalline quality.