Microstructure,Properties,and Grain Growth Kinetics of Mo-5Ta Refractory Sputtering Targets Prepared by SPS

Mo-5Ta targets were prepared by the spark plasma sintering(SPS)technology under the sintering temperatures of 1400-1600℃,the holding times of 0-20 min,and the axial pressure of 30 MPa.The microstructure,performance,and grain growth kinetics of Mo-5Ta sputtering targets were studied.With the increase of sintering temperatures and times,Ta can more dissolve in Mo and form a Mo(Ta)solid solution.The grain sizes of Mo-5Ta targets remain unchanged at low temperatures(1400-1500℃)while increasing significantly at high temperature(1600℃)with the extension of the holding time.In addition,the densities and Vickers hardness(HV_(0.5))first ascend and then decrease with sintering proceeding.The thermal conductivity is positively correlated with the grain size and density,as a result of their joint action.Based on the comprehensive analysis,the grain growth is dominated by the combination of boundary diffusion and volume diffusion.When n=2,the activation energies of grain growth under holding times of 5,10,20 min are calculated as 762.70,617.86,and 616.52 kJ/mol,respectively.

Isothermal Growth Kinetics of Ultra-fine Austenite Grains in a Nb-V-Ti Microalloyed Steel

Ultra-fine austenite grains with size of i-3 μm were prepared in a Nb-V-Ti steel through repetitive treatment of rapid heating and quenching. A model for the growth kinetics of these ultra-fine austenite grains was successfully created through successive 2 processes, and the activation energy Q for growth was estimated to be about 693.2 kJ/mol, which directly shows the inhibition effect of microalloy elements on the growth of ultra-fine austenite grains.

Growth kinetics and mechanism of microarc oxidation coating on Ti-6Al-4V alloy in phosphate/silicate electrolyte

Microarc oxidation(MAO)is an effective surface treatment method for Ti alloys to allow their application in extreme environments.Here,binary electrolytes consisting of different amounts of sodium phosphate and sodium silicate were designed for MAO.The surface morphology,composition,and properties of MAO coatings on Ti-6Al-4V alloy treated in 0.10 mol/L electrolyte were investigated to reveal the effect of PO_(4)^(3-)and SiO_(3)^(2-)ray diffraction,and potentiodynamic polarization.The results showed that PO_(4)^(3-)is beneficial for generating microarcs and forming pores within the coating,resulting in a thick but porous coating.SiO_(3)^(2-)eration of microarcs,resulting in a thin dense coating.The thickness,density,phases content,and polarization resistance of the MAO coatings are primarily affected by the intensity of microarcs for low SiO_(3)^(2-)ciently high.The thickness of MAO coatings obtained in P/Si electrolytes shows a piecewise linear increase with increasing process time during the three stages of microarc discharge.SiO_(3)^(2-)discharge,but slows down the growth of the coating formed in the next stage.

Growth Kinetics of Nanocrystals and Nanorods by Employing Small-angle X-ray Scattering (SAXS) and Other Techniques

In this article, we report the results of our detailed investigations of the growth kinetics of zero-dimensional nanocrystals as well as one-dimensional nanorods by the combined use of small angel X-ray scattering （SAXS）, transmission electron microscopy （TEM） along with other physical techniques. The study includes growth kinetics of gold nanocrystals formed by the reduction of HAuCl4 by tetrakis（hydroxymethyl） phosphonium chloride in aqueous solution, of CdSe nanocrystals formed by the reaction of cadmium stearate and selenium under solvothermal conditions, and of ZnO nanorods formed by the reaction of zinc acetate with sodium hydroxide under solvothermal conditions in the absence and presence of capping agents. The growth of gold nanocrystals does not follow the diffusion-limited Ostwald ripening, and instead follows a Sigmoidal rate curve. The heat change associated with the growth determined by isothermal titration calorimetry is about 10 kcal·mol^-1 per I nm increase in the diameter of the nanocrystals. In the case of CdSe nanocrystals also, the growth mechanism deviates from diffusion-limited growth and follows a combined model containing both diffusion and surface reaction terms. Our study of the growth kinetics of uncapped and poly（vinyl pyrollidone） （PVP）-capped ZnO nanorods has yielded interesting insights. We observe small nanocrystals next to the ZnO nanorods after a lapse of time in addition to periodic focusing and defocusing of the width of the length distribution. These observations lend support to the diffusion-limited growth model for the growth of uncapped ZnO nanorods. Accordingly, the time dependence on the length of uncapped nanorods follows the L3 law as required for diffusion-limited Ostwald ripening. The PVP-capped nanorods, however, show a time dependence, which is best described by a combination of diffusion （L^3） and surface reaction （L^2） terms.

Liquid State Undercoolability and Crystal Growth Kinetics of Ternary Ni-Cu-Sn Alloys

The liquid state undercoolability and crystal growth kinetics of ternary Ni-5%Cu-5%Sn and Ni-10%Cu-10%Sn alloys are investigated by the glass fluxing method. In these two alloys, experimental maximum undercoolings of 304 K （0.18TL ） and 286K （0.17TL ） are achieved and the dendritic growth velocities attain 39.8 and 25.1 m/s, respectively. The transition of morphology from coarse dendrite into equiaxed structure occurs and the grain size of the a （Ni） phase decreases remarkably when the undercooling increases. Both the lattice constant and microhardness increase obviously with the enhancement of undercooling. The enrichment of Cu and Sn solute contents reduces the dendritic growth velocity, while enhances the lattice constant and microhardness of a （Ni） phase.

Formation and Growth Kinetics of Intermediate Phases in Ni-Al Diffusion Couples

Formation and growth of the intermediate phases in the Ni-Al diffusion couples prepared by pouring technique were investigated. Electron probe microanalysis, scanning electron microscopy and X-ray diffraction were used to characterize the product phases in the joints. The results show that two intermediate phases form in the sequence of NiAl3 and Ni2Al3 during solidification. After annealed, Ni2Al3 and NiAl3 still exist in the joints of the couples. The reasons for the formation of Ni2Al3 and NiAl3, as well as the absence of NiAl, Ni5Al3 and Ni3Al were discussed, respectively. The growth kinetics of both product phase layers indicates that their growth obeys the parabolic rate law. The activation energies and frequency factors for NiAl3 and Ni2Al3 phases were also calculated according to the Arrhenius equation.

A Study of Grain Growth Kinetics in Sintered NdFeB Magnets

The Nd2Fe14 B grain growth kinetics in sintered NdFeB magnets with nominal compositions of Nd30+xDy1.5Fe67.08-xAl0.4B1.02 (%, x = 0, 3) was studied. The grain size parameters were determined by means of the linear intercept method on SEM secondary electron images. It is observed that the grain growth process is more sensitive to sintering temperature than to sintering time although the grain size rises with both sintering temperature and time. It is also found that magnets prepared from the pre-alloy powder with a higher oxygen content exhibit a lower grain growth rate and magnets made from the pre-alloy powder with a broader particle size distribution demonstrate a higher grain growth rate. It is believed that the presence of appropriate amounts of Nd oxides effectively impedes the grain growth process and a larger difference in sizes between pre-alloy powder particles significantly accelerates the grain growth process. On the basis of experimental results, the grain growth exponent and the corresponding activation energy were obtained. A possible grain growth mechanism in NdFeB magnets during sintering was briefly discussed.

A growth kinetics model of rate decomposition for Si_(1-x)Ge_x alloy based on dimer theory

According to the dimer theory on semiconductor surface and chemical vapor deposition（CVD） growth characteristics of Sil_xGex, two mechanisms of rate decomposition and discrete flow density are proposed. Based on these two mech- anisms, the Grove theory and Fick＇s first law, a CVD growth kinetics model of Sil-xGex alloy is established. In order to make the model more accurate, two growth control mechanisms of vapor transport and surface reaction are taken into account. The paper also considers the influence of the dimer structure on the growth rate. The results show that the model calcuated valne is consistent with the experimental vahles at different ternnerntllres.

HIGH-TEMPERATURE TEM IN SITU STUDY OF GROWTH KINETICS OF BAINITE IN β BRASS

In situ observation of the growth process of bainitic plate in βbrass by means of high-temper- ature TEM is conducted.The lengthening and thickening kinetics of bainitic plate is analysed with Trivedi's model and Zener-Hillert's model,respectively.It is found that the stacking fault substructure exists just in the growth tip of fresh bainitie plate and so does the shear stress in the matrix around the tip.The measured lengthening rate of bainitic plate is not con- sistent with Trivedi's model.The thiekening process is only macroscopieally controlled by vol- ume diffusion but its nature is a shear process.

Grain Growth Kinetics of SnO_2 Nanocrystals Synthesized by Precipitation Method

Monodispersed spheroidal SnO2 nanocrystals with the grain size of 8-30 nm were synthesized by the precipitation method using SnCl4·5H2O （stannic chloride hydrate） as raw materials.Differential scanning calorimetry/thermogravimetry （DSC/TG）,X-ray diffraction （XRD） and transmission electron microscope （TEM） were used to characterize the structure of SnO2 nanocrystals.The influences of the calcination temperature and time on the lattice constant,the lattice distortion and the grain size of SnO2 nanocrystals were discussed based on the XRD results.The grain growth kinetics of SnO2 nanocrystals during calcination process was simulated with a conventional grain growth model which only took into account of diffusion and with a new isothermal model proposed by our group,which took into account of both diffusion and surface reactions.Using conventional model,the grain growth rate constant of SnO2 crystals is 1.55×104nm5/min with a pre-exponential factor of 5 and an activation energy of 108.62 kJ/mol.Compared with the convention model,the new isothermal model is more realistic in reflecting the grain growth behavior of SnO2 nanocrystals during the calcination process.This indicates that the grain growth of SnO2 nanocrystals is controlled by both diffusion and reaction factors,and the effect of surface reactivity on the grain growth of SnO2 nanocrystals could not be ignored.A combined activation energy estimated with the new isothermal model is 53.46 kJ/mol.

Growth Kinetics of γ′ Particles in Incoloy 907

The kinetics of growth of the γ' precipitate in an lncoloy 907 alloy have been studied. The kinetics of particle growth obeyed the tirne law predicted by the Lifshitz-Wagner theory. The distribution of γ'particle sizes was found to be significantly broader than the theoretical distribution of LifshitZ-Wagner theory. It is suggested that this is due to the relatively large lattice parameter mismatch between γ' and the Fe-Ni-Co matrix

Modeling of Growth Kinetics of Conifer Trees

The kinetics of growth of conifers is modeled by the dependence of the area of tree rings on time. The data on the growth of 46 coniferous trees varying in age from 35 to 242 years, found in the literature are analysed. To identify the common patterns in the growth kinetics, we investigate the series of standard increments of tree rings for pine, spruce, and larch. The curves obtained reflect adequately the ontogeny of trees. These allow the analysis of the environmental effects’ on the physiology of trees. In such a way the accelerated growth of trees in the Tunguska meteorite explosion zone is established. The proposed method of dendrochronology based on the area of tree rings is more adequate and informative than the method based on tree-rings’ widths.

Growth Kinetics of Vegetative and Reproductive Organs of Guava(Psidium guajava L.)in Iguala Guerrero,Mexico

In the Mexican tropics the guava trees can grow and produce in any season, so they can be har-vested out of the period of high competition marketing (Summer). It?studied the growth kinetics of leaves and fruits of guava trees at the dry tropical conditions of the State of Guerrero, in guava trees of four years old and was evaluated a non-destructive method for measuring leaf area from November to May. 100 sheets of 10 randomly selected trees were cut. It was found that leaf length X the width X 0.72581647 (conversion factor) gave an estimated leaf area which?was significantly correlated with that obtained by the integrator of leaf area. Both in length and width the leaf growth kinetics were sigmoid with three growth stages: In Stage I (15 days) leaves grew 21.2% and 21.5%;in Stage II (26 days) grew 73.6% and 68%;and in Stage III (30 days). They Increased 5.2% and 10.5% in the primary and secondary sprouts. The fruit growth in its equatorial and polar diameters corresponded to a double sigmoid kinetics. In Stage I (61 days) it reached 1.9 and 2.3 cm;in Stage II (62 - 102 days) it reached 3.09 and 3.62 cm;and in Stage III (103 to 126 days) it reached 4.63 and 5.13 cm, as well the physiological maturity of fruit.

Theoretical insights into influence of additives on sulfamethoxazole crystal growth kinetics and mechanisms

In this work,the influence of the initial chemical potential gradient,stirring speed,and polymer type on sulfamethoxazole(SMX)crystal growth kinetics was systematically investigated through density functional theory(DFT)calculations,experimental measurements and the two-step chemical potential gradient model.To investigate the influence of different conditions on the thermodynamic driving force of SMX crystal growth,SMX solubilities in different polymer solutions were studied.Four model polymers effectively improved SMX solubility.It was further found that polyvinylpyrrolidone(PVP)and hydroxypropyl methyl cellulose(HPMC)played a crucial role in inhibiting SMX crystal growth.However,polyethylene glycol(PEG)promoted SMX crystal growth.The effect of the polymer on the crystal growth mechanisms of SMX was further analyzed by the two-step chemical potential gradient model.In the system containing PEG 6000,crystal growth is dominated by the surface reaction.However,in the system containing PEG 20000,crystal growth is dominated by both the surface reaction and diffusion.In addition,DFT calculations results showed that HPMC and PVP could form strong and stable binding energies with SMX,indicating that PVP and HPMC had the potential ability to inhibit SMX crystal growth.

A comprehensive study on the processing of Co:ZnO nanostructured ceramics:Defect chemistry engineering and grain growth kinetics

In this report,we present a systematic study on the preparation of Co:ZnO ceramics via a standard solid-state route from different Co precursors(Co_(3)O_(4),CoO,and metallic Co)and atmospheres(O_(2)and Ar).Particular emphasis is given to defect chemistry engineering and the sintering growth kinetics.First-principles calculations based on density functional theory are employed to determine the formation en-ergy of the main point defects in ZnO and Co:ZnO systems.Based on the theoretical results,a set of chemical reactions is proposed.Detailed microstructural characterization is also performed to determine the degree of Co incorporation into the ZnO lattice.The samples prepared in Ar atmosphere and metal-lic Co present the highest Co solubility limit(lower apparent Co incorporation activation energy)due to the incongruent ZnO decomposition.Determination of the parameters of the sintering growth kinetics reveals that Co_(3)O_(4)is the best sintering additive to achieve larger grain sizes,and possible higher densi-ties,in both sintering atmospheres,while metallic Co is the best to achieve the smallest grain size with higher Co concentration and homogeneous spatial distribution for a subsequent reduction of dimension-ality.The results show that the sintering in O_(2)effectively promotes zinc vacancies in the ZnO structure,while the sintering in Ar promotes zinc interstitial defects.Our findings contribute to understanding the preparation of Co-doped ZnO ceramics and the sintering growth kinetics,which may improve the state of the art in processing the material at both bulk and nanometric scales.

Post Cryopreservation Growth Kinetic and Photosynthetic Assessment of an Acid Tolerant Strain of Stichococcus bacillaris

Preserving microbial diversity has become a strategic undertaking. Thus, ex situ microalgal culture conservation results in strategic and functional resource in both biodiversity protection and application domains. Cryopreservation of microalgae has been practiced since the 1960s and is now considered the optimal preservation strategy. Furthermore, the overall monitoring during growth of cultures after freezing/thawing protocols was hardly investigated and there is poor evaluation related to preserve especially the photosystem apparatus. The present study focuses on Stichococcus bacillaris as case study for short-term cryopreservation at −80 °C storage. Various freezing pretreatments using cryoprotective agents, and two thawing methods were compared introducing a novel variable to evaluate viability recovery and assessing growth kinetics of cultures immediately after thawing and after a series batch cultivation. Photosynthetic rate and pigments assessment were proposed to evaluate hidden metabolic cell damage. Results underline cryoprotective agents can increase the kinetic recovery of preserved cells in terms of reduction of lag phase during batch cultivation tests: the use of dimethyl sulfoxide and glycerol granted a growth comparable to unpreserved cells when sudden thawing occurs after 24 hours of storage, but recovery after preservation is less sensitive to cryoprotective agents when gradual thawing and 1 month of storage is considered. However, cells are always able to restore their physiological pathways even without agents, so their kinetic effect has been proved and quantified. Interestingly, both the photosynthetic efficiency and the ratio between total chlorophyll and carotenoids are comparable (0.75 Fv/Fm, 2.2 ± 0.25 g/g) to unpreserved cells and they are unsensitive to chosen agents, but the ratio between chlorophyll a and chlorophyll b was clearly altered (up to 10 times), suggesting that photoactive pigments relative proportions can result in similar growth kinetic performances. Long-term studies will be carried out to assess whether the differences found could cause chronic damage to photosystem efficiency of S. bacillaris cultures.

Growth kinetics of MgH2 nanocrystallites prepared by ball milling

MgH2 is one of promising hydrogen storage materials due to its high hydrogen capacity of 7.6 wt%.However,MgH2 nanocrystallites easilygrow up during hydrogen absorption-desorption cycling,leading to deterioration of hydrogen storage properties.To clarify the growth kinetics of MgH2 crystallites,the growth characteristics of MgH2 nanocrystallites are investigated in this work.The growth exponents of MgH2 nanocrystallites in pure MgH2 and MgH2-10 wt% Pr3 Al11 samples are evaluated to be n=5 and n=6,respectively.Meanwhile,their activation energies for crystallite growth are also determined to be109.2 and 144.2 kJ/mol,respectively.The increase of growth exponent and rise of activation energy for crystallite growth in MgH2-10 wt% Pr3 Al11 composite are ascribed to the presence of nano-sized Pr3 Al11phase.

Growth Characteristics and Kinetics of Niobium Carbide Coating Obtained on AISI 52100 by Thermal-reactive Diffusion Technique

Niobium carbide coating was produced by thermal-reactive diffusion technique on AISI 52100 steel in salt bath at 1 123 K, 1 173 K, and 1 223 K for 1, 2, 4, and 6 hours. The salt consisted of borax, sodium fl uoride, boron carbide, and niobium pentoxide. The presence of NbC phase on the steel surface was confi rmed by X-ray diffraction analysis. Microscopic observation showed that niobium carbide coating formed on the substrate was smooth and compact. There was a distinct and fl at interface between the coating and substrate. The micro-hardness of niobium carbide coating was 2892±145HV. The thickness of coating ranged from 1.6 μm to 14μm. The forming kinetics of niobium carbide coating was revealed. Moreover, a contour diagram derived from experimental data was graphed for correct selection of process parameters. Some mathematical equations were built for predicting the coating thickness with predetermined processing temperature and time. The results showed that these mathematical equations are very practical as well as the kinetics equation.

Grain growth kinetics and densification mechanism of(TiZrHfVNbTa)C high-entropy ceramic under pressureless sintering

The grain growth kinetics and densification mechanism of(TiZrHfVNbTa)C high-entropy carbide ceramic are investigated in this work.A single phase carbide with a rock-salt structure is formed until 2300°C,below which an apparent aggregation of V,Zr and Hf exists.It is associated with the slow diffusion rate of V element as well as the relatively poor solubility of VC in HfC(as well as ZrC).The grain growth mechanism gradually changes from surface diffusion to volume diffusion and then grain boundary diffusion with increasing sintering temperature.This is attributed to the variation of activation energy of grain growth.The densification mechanism is principally dominated by the mass transport through lattice diffusion with the activation energy of 839±53 k J/mol.Through the design of two-step sintering,it is verified that the solid solution formation can effectively promote the densification process.

Drag Effects of Solute and Second Phase Distributions on the Grain Growth Kinetics of Pre-Extruded Mg-6Zn Alloy

In order to control the grain size during hot forming,grain growth behavior of a pre-extruded Mg-6Zn magnesium alloy and its correlation with solute and second phase distribution were investigated.Isothermal annealing was conducted on a Gleeble-1500 thermo-mechanical simulator.The mean grain size Dg of each annealed specimen was measured by the quantitative metallography technique.The grain growth kinetics of the Mg-6Zn alloy annealed at 473-623 K was obtained as Dg^4- Dg0^4=2.25 ×10^11 exp（-95450）by the least square linear regression method.The deviation of grain growth exponent n = 4 from the theoretical value of 2 may be attributed to the presence of solute zinc and second phases which will retard the boundary migration.Microscopic observations show that the non-uniform distribution of grain size for samples pre-extruded or annealed at low temperatures is closely related to the non-uniform distribution of fine and dispersed second phases but not to the non-uniform distribution of solute zinc.This indicates that second phase pinning effect plays an important role in microstructure refinement.