Microscopic Growth Rate Research Articles

Investigating calcite growth rates using a quartz crystal microbalance with dissipation (QCM-D)

Calcite precipitation plays a significant role in processes such as geological carbon sequestration and toxic metal sequestration and, yet, the rates and mechanisms of calcite growth under close to equilibrium conditions are far from well understood. In this study, a quartz crystal microbalance with dissipation (QCM-D) was used for the first time to measure macroscopic calcite growth rates. Calcite seed crystals were first nucleated and grown on sensors, then growth rates of calcite seed crystals were measured in real-time under close to equilibrium conditions (saturation index, SI = log ({Ca2+}/{CO32−}/Ksp) = 0.01–0.7, where {i} represent ion activities and Ksp = 10−8.48 is the calcite thermodynamic solubility constant). At the end of the experiments, total masses of calcite crystals on sensors measured by QCM-D and inductively coupled plasma mass spectrometry (ICP-MS) were consistent, validating the QCM-D measurements. Calcite growth rates measured by QCM-D were compared with reported macroscopic growth rates measured with auto-titration, ICP-MS, and microbalance. Calcite growth rates measured by QCM-D were also compared with microscopic growth rates measured by atomic force microscopy (AFM) and with rates predicted by two process-based crystal growth models. The discrepancies in growth rates among AFM measurements and model predictions appear to mainly arise from differences in step densities, and the step velocities were consistent among the AFM measurements as well as with both model predictions. Using the predicted steady-state step velocity and the measured step densities, both models predict well the growth rates measured using QCM-D and AFM. This study provides valuable insights into the effects of reactive site densities on calcite growth rate, which may help design future growth models to predict transient-state step densities.

Fractograpic Observations and Effect of Stress Ratio on Fatigue Striations Spacing in Aluminium Alloy 2024 T351

In this paper, effect of stress ratio was investigated on macro and micro of fatigue crack growth rates (FCGRs) of Al-alloy 2024 T351. Microscopic fatigue crack growth rate present a change of slope with respect to the macroscopic fatigue crack growth rate. In addition, an increasing in stress ratio increases the fatigue life. Fractographic examination showed the presence of striations in Paris domain and secondary cracks at grain boundaries.

Crystal growth from mechanically induced defects

For the first time, infrared microscopy was used to directly confirm the presence of crystallites originating from mechanically induced defects. Differential scanning calorimetry and infrared microscopy were used to study crystallization behavior of the GeTe4 glass. Both non-isothermal and isothermal DSC crystallization data were deconvoluted by state-of-the-art methods, and the identified sub-processes were described in terms of appropriate kinetic models. While the bulk samples showed zero-order (F0) crystallization kinetics, the GeTe4 powders exhibited complex kinetic behavior describable by competing Johnson–Mehl–Avrami and autocatalytic crystallization mechanisms. The concept of crystallization from mechanically induced defects was used to explain the difference in the kinetic behavior of bulk and powdered materials. Microscopic observation of two types of crystallites being present in a partially crystallized powder grain corresponds well to the occurrence of two crystallization mechanisms identified for the DSC data. The zero-order crystallization kinetics found for the DSC data of bulk samples was verified by microscopic crystal growth rate measurements.

Geometric analysis and estimation of the growth rate gradient on gastropod shells

The morphology of gastropod shells provides a record of the growth rate at the aperture of the shell, and molecular biological studies have shown that the growth rate gradient along the aperture of a gastropod shell can be closely related to gene expression at the aperture. Here, we develop a novel method for deriving microscopic growth rates from the macroscopic shapes of gastropod shells. The growth vector map of a shell provides information on the growth rate gradient as a vector field along the aperture, over the growth history. However, it is difficult to estimate the growth vector map directly from the macroscopic shape of a specimen, because the degree of freedom of the growth vector map is very high. In order to overcome this difficulty, we develop a method of estimating the growth vector map based on a growing tube model, where the latter includes fewer parameters to be estimated. In addition, we calculate an aperture map specifying the magnitude of the growth vector at each location, which can be compared with the expression levels of several genes or proteins that are important in morphogenesis. Finally, we show a concrete example of how macroscopic shell shapes evolve in a morphospace when microscopic growth rate gradient changes.

Kolmogorov–Johnson–Mehl–Avrami kinetics for non-isothermal phase transformations ruled by diffusional growth

We report on the functional form of the rate of the transformed volume fraction in non-isothermal phase transitions occurring by nucleation and diffusional growth. The microscopic growth rate is computed by solving the diffusion problem for time-dependent diffusion coefficient. The growth law is further employed in the Kolmogorov–Johnson–Mehl–Avrami (KJMA) theory for describing the time dependence of the transformed volume at constant heating rate. It is demonstrated that the transformation rate separates in the product of volume fraction and actual temperature functions. In the framework of the KJMA approach this factorization is exact. It is also shown that for real systems (due to the high values of the reduced activation energies for nucleation and growth), the kinetics is in excellent agreement with the stretched exponential function appropriate for isothermal transformations.

Modeling of {311} facets using a lattice kinetic Monte Carlo three-dimensional model for selective epitaxial growth of silicon

Using lattice kinetic Monte Carlo, we provide a quantitative physically based atomistic model for the selective grown of Si-based materials, and explain {311} facet formation while remaining computationally efficient. Descriptions of the local atomistic configurations critical for the developing of {100}, {110}, {111}, and {311} facets are given. The model also introduces (a) three different microscopic growth rates for local {100} planes, needed to properly simulate the formation of perfect {100} terraces in miscut substrates and (b) a break-up energy to account for bonding during {311} facet formation. The model has been verified against experimental results.

Strontium as a marker for estimation of microscopic growth rates in a bivalve

Microscopic growth increaments in bivalve shells were measured by marking the shells of the short-necked clam Ruditapes philippinarum with the strontium chloride (strontium marking method, SMM). The results were com- pared with those achieved by the fluorescent marking method (FMM) using calcein. Because strontium has a higher atomic mass than calcium, strontium-enriched areas in the shells are visible as a bright band in the back-scattered electron image under the scanning electron microscope (SEM). R. philippi- narum were immersed in strontium chloride solutions of vary- ing concentrations, and the effects of immersion time (17 or 24 h) and concentration (0.72, 1.44 or 2.88 g l -1 ) were investi- gated. These shells exhibited clearly visible marks 19 or 20 d post-immersion. Using the SMM, a microscopic (single-digit µm) increment in shell growth could be detected under SEM with a magnification of at least 1200 × . Using the FMM, growth increaments of only tens of micrometers were de- tectable under fluorescence optical microscopy up to a mag- nification of 600 × . The SMM is thus superior to previous methods for detecting microscopic increases in shell growth. Marking methods should ideally be based on long-lasting markers that are easily detected and involve simple method- ologies. The SMM meets these requirements. It can be used to estimate growth in small bivalve specimens and growth rates in slow-growing species such as deep-sea and polar

Corrosion fatigue crack propagation of a duplex stainless steel X6 Cr Ni Mo Cu 25-6 in air and in artificial sea water

Fatigue crack growth behavior of a duplex stainless steel has been investigated at a stress ratio of 0.1, in air environment at room temperature and in artificial sea water heated to 70 °C. Growth rates generated under constant load amplitude at a frequency of 0.1 Hz under corrosion fatigue were found to be about 1.7 orders of magnitude higher than those generated in air environment. The study of the crack propagation under both conditions has revealed a significant change in fracture mechanisms between both environments. In air environment, microscopic growth rates in austenite measured by striation spacing in SEM were found to be very close to the macroscopic growth rates whereas in sea water, cyclic cleavage of the ferrite controls the macroscopic growth rates for ΔK between 20 and 60 MPa√m. The cyclic cleavage is induced by hydrogen embrittlement of the ferrite which is produced by an electrochemical reaction between the material and sea water.

Measurement of microscopic growth rates in float zone silicon crystals

The microsegregation of doped silicon crystals grown by the float zone technique was investigated by using a heat pulse technique. The heat pulses (3–10 Hz) generated finely spaced periodic time markers which overlay the dopant inhomogeneities caused by convective instabilities in the melt. The microscopic growth rate was determined by measuring the distance of the markers. For a flow regime governed by time-dependent thermocapillary convection, the average growth rate of 2 mm/min fluctuated from 1.27 to 2.63 mm/min with fluctuation frequencies between 0.01 and 0.15 Hz. The microscopic growth rate becomes constant when applying a static axial magnetic field of 500 mT. The impact of concentration fluctuations within the solute boundary layer ahead of the crystal-melt interface was observed qualitatively by comparing the interface profile given by the pulse markings with the contours of the convectively induced striations.

Microscopic and macroscopic growth rates of fatigue cracks in steels and alloys under the influence of crack closure

On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates.

Temperature and growth rate fluctuations in silicon floating zones

Several earlier μg experiments have shown that time-dependent thermocapillary (Marangoni) convection is the major cause for the formation of dopant striations in floating-zone grown semiconductor crystals, at least in small-scale systems not employing RF heating. To quantify this correlation, a silicon floating-zone experiment was performed on the TEXUS36 flight (February 7, 1998) in a monoellipsoid mirror furnace to measure temperature fluctuations in the melt zone and the microscopic growth rate simultaneously. Fluctuations of 0.5K – 0.7K with main frequencies between 0.1Hz and 0.3Hz were detectable. The microscopic growth rate fluctuated considerably around the average growth rate of 1mm/min: rates from 4mm/min to negative values (backmelting) were observed. Dopant striations are clearly visible in the Sb-doped crystal. The frequencies associated with the dopant inhomogeneities correspond quite well with those of the temperature fluctuations and microscopic growth rates. 3D numerical simulations were performed to predict the optimum position of the temperature sensor, to evaluate characteristic temperature amplitudes and frequencies, and to give insight into the instability mechanisms of Marangoni convection in this configuration. The simulations were in good agreement with the experimental values, showing temperature fluctuations with frequencies f ≤ 0.25Hz and amplitudes up to 1.8K at a position equivalent to that of the sensor tip in the experiment. Future microgravity S-FZ experiments, currently scheduled for a MAXUS flight in 2001, will try to influence the formation of dopant striations by rotating magnetic fields or by vibrational convection.

Measurement of temperature fluctuations and microscopic growth rates in a silicon floating zone under microgravity

A silicon crystal growth experiment has been accomplished using the floating-zone technique under microgravity on a sounding rocket (TEXUS 36). Measurements of temperature fluctuations in the silicon melt zone due to time-dependent thermocapillary convection (Marangoni convection) and an observation of the microscopic growth rate were simultaneously performed during the experiment. Temperature fluctuations of about 0.5–0.7°C with a frequency range <0.5 Hz were detectable. The microscopic growth rate fluctuates considerably around the average growth rate of 1 mm/min: Growth rates up to 3–4 mm/min, close to zero mm/min, as well as negative values (backmelting) were observed. Dopant striations are clearly visible in the Sb-doped crystal. They were characterized by spreading resistance measurements and differential interference contrast microscopy. The frequencies of temperature fluctuations, microscopic growth rates, and the dopant inhomogeneities correspond quite well, with main frequencies between 0.1 and 0.3 Hz. 3D numerical simulations were performed to predict the optimum position of the temperature sensor, and the characteristic temperature amplitudes and frequencies. At a position 3.4 mm above the interface and 1.4 mm inside the melt, equivalent to the sensor tip position in the experiment, temperature fluctuations up to 1.8°C and frequencies ⩽0.25 Hz were found in the simulations.

Bridgman growth of strontium barium niobate single crystals

Vertical Bridgman growth of single crystals of Sr 1− x Ba x Nb 2O 6 is reported for the first time. Large 25 mm diameter crystals of the congruent composition Sr 0.61Ba 0.39Nb 2O 6 have been grown in the 〈0 0 1〉 direction at growth rates of approximately 1 mm/h. Stable growth has been achieved at rates up to about 12 mm/h. Striations and diameter control problems have been virtually eliminated by using this growth method. By modulating the furnace setpoint to intentionally produce striations, the relationship between the induced temperature fluctuations and refractive index striations as well as the interface shape and microscopic growth rate were determined. Surface and core defects were also investigated. The results presented here demonstrate the feasibility of large-scale growth of high optical homogeneity crystals of strontium barium niobate.

Fatigue crack growth with fiber failure in metal-matrix composites : Begley, M.R. and McMeeking, R.M. Compos. Sci. Technol. (1995) 53 (4), 365–382

Fatigue crack propagation is examined using single overload in cyclic condensation environment. Using this environment the growing crack is exposed cyclically to environments with high and low humidity. These environmental changes cause the formation of a periodic pattern on the fracture surface called beach marks when the crack growth is low. A single overload can also cause the formation of beach marks in the overload affected zone when cyclic condensation environment is used. The markings are being formed due to the retardation of the crack growth subsequent to the overload. The markings are also formed close to the stretch zone and the spacing increases with increasing distance from the overload zone; subsequently they stop forming. The microscopic crack growth rate after the overload obtained from measurement of beach mark spacing is compared with the macroscopic one calculated from crack length measurement. The mechanism of beach mark formation after the overload is the same as in the initiation zone of short cracks and near-threshold propagation of the long one.The materials used are centre-cracked-tension (CCT) specimens of 7075-T6, 2024-T3 and 7075 aluminium glass fibre epoxy laminate (GLARE I).

Influence of melt-temperature fluctuations on striation formation in large-scale Czochralski Si growth systems

The effects of melt-temperature fluctuations on growth striations in crystals grown in a commercial-scale growth system were studied by an analysis of the fast-Fourier-transform (FFT) method applied to the melt-temperature fluctuations and to the growth striations as evaluated by X-ray topography and spreading-resistance (SR) methods. The period of the growth striations observed in crystals corresponded exactly to that of temperature fluctuations in the melt; however, the amplitude of these growth striations decreased when temperature fluctuations with a constant amplitude occurred rapidly. This phenomenon results from a delay in the response of the microscopic growth rate to rapid temperature fluctuations. The amplitude of melt-temperature fluctuations and the peak height of the FFT power spectra were observed to decrease in the radial direction toward the crystal center, and this trend was also observed for growth striations. It was concluded that temporal thermal fluctuations caused by melt convection are preserved in growth striations for crystals grown in large growth systems.

Fatigue crack growth studies under combination of single overload and cyclic condensation environment

Fatigue crack propagation is examined using single overload in cyclic condensation environment. Using this environment the growing crack is exposed cyclically to environments with high and low humidity. These environmental changes cause the formation of a periodic pattern on the fracture surface called beach marks when the crack growth is low. A single overload can also cause the formation of beach marks in the overload affected zone when cyclic condensation environment is used. The markings are being formed due to the retardation of the crack growth subsequent to the overload. The markings are also formed close to the stretch zone and the spacing increases with increasing distance from the overload zone; subsequently they stop forming. The microscopic crack growth rate after the overload obtained from measurement of beach mark spacing is compared with the macroscopic one calculated from crack length measurement. The mechanism of beach mark formation after the overload is the same as in the initiation zone of short cracks and near-threshold propagation of the long one. The materials used are centre-cracked-tension (CCT) specimens of 7075-T6, 2024-T3 and 7075 aluminium glass fibre epoxy laminate (GLARE I).

The averaged face growth rates of lysozyme crystals: the effect of temperature

Measurements of the averaged or macroscopic face growth rates of lysozyme crystals are reported here for the (110) face of tetragonal lysozyme, at three sets of pH and salt concentrations, with temperatures over a 4–22°C range for several protein concentrations. The growth rate trends with supersaturation were similar to previous microscopic growth rate measurements. However, it was found that at high supersaturations the growth rates attain a maximum and then start decreasing. No “dead zone” was observed but the growth rates were found to approach zero asymptotically at very low supersaturations. The growth rate data also displayed a dependence on pH and salt concentration which could not be characterized solely by the supersaturation. A complete mechanism for lysozyme crystal growth, involving the formation of an aggregate growth unit, mass transport of the growth unit to the crystal interface and faceted crystal growth by growth unit addition, is suggested. Such a mechanism may provide a more consistent explanation for the observed growth rate trends than those suggested by other investigators. The nutrient solution interactions leading to the formation of the aggregate growth unit may, thus, be as important as those occurring at the crystal interface and may account for the differences between small molecule and protein crystal growth.

Bridgman and Czochralski growth of GeSi alloy crystals

AbstractGe1–xSix crystals were grown with the Bridgman and the Czochralski method over a wide concentration range. With the Bridgman process single crystals up to 40 at.% Si were possible. The reasons for polycrystalline growth were the permanent contact of the interface with the crucible wall in combination with curvature towards the crystal and inclusions of high Si concentration. Analysis of striations in Czochralski grown material showed that in this process the crystal does not continuously grow in one direction but consists of piece‐wise grown crystals in which the composition permanently changes. According to that fact the main reason for polycrystalline growth in the Czochralski process is common due to lattice mismatch between the seed and equilibrium concentration transients in the crystal corresponding to the microscopic growth rates.

Continuous cultivation and drug susceptibility testing of Plasmodium falciparum in a malaria endemic area.

Isolates (UCH-23 and OM) and cloned strains of Plasmodium falciparum (Clones W-2 and D-6) were maintained in continuous culture for 28 to 150 days using culture media supplemented with 10% (v/v) heat inactivated semi-immune human plasma. Microscopic appearance and growth rates (R) of the parasites in media supplemented with semi-immune human plasma [R = 1.13 (W-2), 0.92 (D-6), 0.75 (OM) and 0.84 (UCH-23)] were comparable to those of parallel cultures maintained in media supplemented with 10% (v/v) heat inactivated non-immune human plasma [R = 1.42 (W-2), 0.83 (D-6), 0.66 (OM) and 0.89 (UCH-23)]. In addition, IC50 for chloroquine and mefloquine against the two cloned strains of P. falciparum maintained in culture media supplemented with either non-immune human plasma or semi-immune human plasma were identical. Although growth rates of new isolates (UCH-23 and OM) fluctuated over time, they stabilized between the 12th and 19th day of adaptation to culture. This fluctuation in growth rates of the new isolates underscores the influence of population dynamics during adaptation of P. falciparum to continuous culture. Sixty-eight percent of the primary isolates (170 of 250) obtained from patients in Ibadan were successfully adapted and maintained in continuous culture using semi-immune human plasma. The results of these studies indicate that semi-immune human plasma is a suitable supplement for continuous cultivation and drug susceptibility testing of P. falciparum.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth of AlxGa1− xSb bulk material from metallic solution

Single crystals of Al x Ga 1− x Sb with a diameter of 15 mm, a length of more than 10 mm and an Al solid composition ranging from 0.06 to 0.1 have been successfully grown with the travelling heater method (THM). Crystals were grown in quartz ampoules in the monoellipsoidal mirror furnace (AMF) with a ring focus. By using the lamp pulsing technique (LPT), microscopic growth rates as a function of grown length could be measured. The growth of ternary compounds has been analysed theoretically. Combined with growth results, we estimated the material transport coefficients of Al and Sb in the Ga solution.