title: Modeling and simulation of the dynamic process in high energy ball milling of metal powders

authors: Wang, Wei

abstract: Mechanical alloying/mechanical grounding by using high-energy ball milling has been considered as a promising materials processing technique to synthesize materials. In this study, modeling simulation has been carried out to investigate the impacts, which are basic events in milling, as well as the milling dynamics in order to control and optimize this process. 

A 3-dimensional model has been developed to simulate the head-on impact process between two balls or between a ball and the vial wall with powder in between by considering the elastic deformation of impact objects, and the visco-plastic flow and elastic deformation of the powder compact. The comparison between the experimental results published in literature and the simulation outcome demonstrates that this model is the best to simulate the head-on impact process, which involves powder. Application of the model in high-energy ball milling shows that the ball-ball and ball-wall impacts do have some difference. It was also observed that the ball size, impact velocity and powder thickness all affect the impact pressure, and that the deformation of balls is substantial comparing to the powder thickness involved in an impact. 

3-dimensional models have also been developed to simulate the movement of balls considering the effects of powder, ball spinning and oblique impact of balls. The multi-ball impacts, which have been proved to occupy a substantial fraction among impacts, were also considered. Having realised the importance of knowing the volume of the powder involved in each impact, a model was also developed to estimate this volume. The prediction of the weight of powder involved in each impact made based on this model was in good agreement with the observation reported. 

A 3-dimensional global model has been developed for the SPEX-8000 Mixer/Mill based on the mechanics of the machine. By using this model, the motion of the vial was numerically determined. Then the global model was coupled with the models for the impacts in order to predict the dynamics of milling process. The simulation results revealed that the movement of balls after milling starts can be separated into two stages. The first stage is the unstable stage, which lasts for less than 0.3 second and involves mostly rolling and slipping of balls on the vial wall. The second stage is the stable stage, when the impact frequency, the mean impact velocity and mean spinning velocity of balls do not change significantly over time. Numerical experiments indicate that the frequency of impacts between balls and the vial wall is linearly proportional to the number of balls and the frequency of impacts between balls is nearly proportional to the square of the number of balls and the square of radius of balls. It is also shown that the majority of the impacts occur at low velocities of less than 4 m/s and with impact angles in the range of 15∼75°. The prediction of the impact frequency and impact angle distribution made from the simulation agrees well with the probability analysis. 

An effective model has been developed for the first time to calculate the time needed for mechanical milling based on probability analysis. This model can be used once the effective impact frequency and the fraction of powder effectively mechanically milled powder are known. The latter can be achieved through modeling. The milling efficiency corresponding to various ball numbers and sizes have been evaluated. The results show that there is an optimum number for the best milling efficiency for a given size of balls. 

Global models for the milling process in a planetary mill and an attritor mill have also been developed. Preliminary simulation experiments have been conducted.

text: Modeling and simulation of the dynamic process in high energy ball milling of metal powders Mechanical alloying/mechanical grounding by using high-energy ball milling has been considered as a promising materials processing technique to synthesize materials. In this study, modeling simulation has been carried out to investigate the impacts, which are basic events in milling, as well as the milling dynamics in order to control and optimize this process. 

A 3-dimensional model has been developed to simulate the head-on impact process between two balls or between a ball and the vial wall with powder in between by considering the elastic deformation of impact objects, and the visco-plastic flow and elastic deformation of the powder compact. The comparison between the experimental results published in literature and the simulation outcome demonstrates that this model is the best to simulate the head-on impact process, which involves powder. Application of the model in high-energy ball milling shows that the ball-ball and ball-wall impacts do have some difference. It was also observed that the ball size, impact velocity and powder thickness all affect the impact pressure, and that the deformation of balls is substantial comparing to the powder thickness involved in an impact. 

3-dimensional models have also been developed to simulate the movement of balls considering the effects of powder, ball spinning and oblique impact of balls. The multi-ball impacts, which have been proved to occupy a substantial fraction among impacts, were also considered. Having realised the importance of knowing the volume of the powder involved in each impact, a model was also developed to estimate this volume. The prediction of the weight of powder involved in each impact made based on this model was in good agreement with the observation reported. 

A 3-dimensional global model has been developed for the SPEX-8000 Mixer/Mill based on the mechanics of the machine. By using this model, the motion of the vial was numerically determined. Then the global model was coupled with the models for the impacts in order to predict the dynamics of milling process. The simulation results revealed that the movement of balls after milling starts can be separated into two stages. The first stage is the unstable stage, which lasts for less than 0.3 second and involves mostly rolling and slipping of balls on the vial wall. The second stage is the stable stage, when the impact frequency, the mean impact velocity and mean spinning velocity of balls do not change significantly over time. Numerical experiments indicate that the frequency of impacts between balls and the vial wall is linearly proportional to the number of balls and the frequency of impacts between balls is nearly proportional to the square of the number of balls and the square of radius of balls. It is also shown that the majority of the impacts occur at low velocities of less than 4 m/s and with impact angles in the range of 15∼75°. The prediction of the impact frequency and impact angle distribution made from the simulation agrees well with the probability analysis. 

An effective model has been developed for the first time to calculate the time needed for mechanical milling based on probability analysis. This model can be used once the effective impact frequency and the fraction of powder effectively mechanically milled powder are known. The latter can be achieved through modeling. The milling efficiency corresponding to various ball numbers and sizes have been evaluated. The results show that there is an optimum number for the best milling efficiency for a given size of balls. 

Global models for the milling process in a planetary mill and an attritor mill have also been developed. Preliminary simulation experiments have been conducted.

year: 2000

title: Evaluating the mineral nutrient status of fresh pasture herbage using laser-induced breakdown spectroscopy

authors: Seelye, M.

abstract: Comprehensive determination of the mineral nutrient status of pasture or horticultural crops currently requires leaf or herbage samples to be harvested and taken to a laboratory for analysis, which is both labour-intensive and time-consuming. This study examined the potential of laser-induced breakdown spectroscopy (LIBS) to provide immediate, in-field assessment of the mineral nutrient status of standing plants. Success would offer the prospects of spatially and temporally improved knowledge of plant status and of real-time remediation of nutrient deficiency. The mineral nutrient status of fresh pasture herbage has been evaluated using an Applied Photonics Ltd？ LIBS-6 system, comprising a Qswitched Nd:YAG laser, a SpectroModule-6 spectrometer (covering wavelengths in the range ~185 – 1064 nm) and an ICE 450 water-cooled Laser power supply. LIBS spectra obtained from the fresh pasture samples were collected with the aim of determining the nutrient status of the herbage. An enclosed Modular Sample Chamber housed the Qswitched Nd:YAG laser, generating energy in the near infrared region at λ = 1064nm. The laser power was set to 100mW per pulse. Samples of approximately 50g of fresh ryegrass and ryegrass/clover mixed pasture were loaded into a sample holder which allowed a flat ‗carpet‘ of individual leaves to be presented at a relatively uniform distance from the laser. The optimum vertical distance between sample and laser was determined by maximising spectra amplitudes. Automated control of the translation stage supporting the sample holder was used to ensure each shot of the laser was acquired from a fresh location. Spectrum sets comprising both 100 individual spectra and 100 shot accumulated spectra were obtained from each sample under both air and under the inert gas, argon. Following the spectral analysis of the fresh pasture, each sample was sent to a commercial laboratory for standard nutrient analysis, providing elementary composition on the most common plant elements (N, P, K, S, Ca, Mg, Na, Fe, Mn, Zn, Cu and B). Once standard nutrient analysis was completed a second set of spectra was taken from tablets formed from compressed dried ground powder remaining after laboratory analysis. To date, initial results from simple chemometric analysis have shown limited success in predicting the nutrient content of fresh pasture with slightly improved results in estimating tablet composition. While initial analyses have concentrated on trends and correlations between actual spectra and laboratory analysis, known emission spectra, have for the meantime, been ignored. Further in-depth analysis using more robust chemometric analysis, utilizing known emission spectra and adjusting for variations in plasma intensity are currently underway and are expected to improve the accuracy of composition measurement.

text: Evaluating the mineral nutrient status of fresh pasture herbage using laser-induced breakdown spectroscopy Comprehensive determination of the mineral nutrient status of pasture or horticultural crops currently requires leaf or herbage samples to be harvested and taken to a laboratory for analysis, which is both labour-intensive and time-consuming. This study examined the potential of laser-induced breakdown spectroscopy (LIBS) to provide immediate, in-field assessment of the mineral nutrient status of standing plants. Success would offer the prospects of spatially and temporally improved knowledge of plant status and of real-time remediation of nutrient deficiency. The mineral nutrient status of fresh pasture herbage has been evaluated using an Applied Photonics Ltd？ LIBS-6 system, comprising a Qswitched Nd:YAG laser, a SpectroModule-6 spectrometer (covering wavelengths in the range ~185 – 1064 nm) and an ICE 450 water-cooled Laser power supply. LIBS spectra obtained from the fresh pasture samples were collected with the aim of determining the nutrient status of the herbage. An enclosed Modular Sample Chamber housed the Qswitched Nd:YAG laser, generating energy in the near infrared region at λ = 1064nm. The laser power was set to 100mW per pulse. Samples of approximately 50g of fresh ryegrass and ryegrass/clover mixed pasture were loaded into a sample holder which allowed a flat ‗carpet‘ of individual leaves to be presented at a relatively uniform distance from the laser. The optimum vertical distance between sample and laser was determined by maximising spectra amplitudes. Automated control of the translation stage supporting the sample holder was used to ensure each shot of the laser was acquired from a fresh location. Spectrum sets comprising both 100 individual spectra and 100 shot accumulated spectra were obtained from each sample under both air and under the inert gas, argon. Following the spectral analysis of the fresh pasture, each sample was sent to a commercial laboratory for standard nutrient analysis, providing elementary composition on the most common plant elements (N, P, K, S, Ca, Mg, Na, Fe, Mn, Zn, Cu and B). Once standard nutrient analysis was completed a second set of spectra was taken from tablets formed from compressed dried ground powder remaining after laboratory analysis. To date, initial results from simple chemometric analysis have shown limited success in predicting the nutrient content of fresh pasture with slightly improved results in estimating tablet composition. While initial analyses have concentrated on trends and correlations between actual spectra and laboratory analysis, known emission spectra, have for the meantime, been ignored. Further in-depth analysis using more robust chemometric analysis, utilizing known emission spectra and adjusting for variations in plasma intensity are currently underway and are expected to improve the accuracy of composition measurement.

year: 2014

title: Here to stay: Reshaping the regions through mana Māori

authors: Simmonds, Naomi Beth

abstract: Situated 65 kilometres south-east of Hamilton, Putāruru (population 3747 in the 2013 Census) is typical of the many farming service towns scattered across rural Aotearoa New Zealand. Bakeries, op shops, a sports bar and a farm equipment supplier occupy the main street. Unlike nearby Tirau, which transformed from a one-stop shop into a vibrant boutique village in the late 1990s, Putāruru township remains largely indistinguishable from other rural centres. There are few clues to the substantial farming-based and water-generated wealth that lies beyond the town.

text: Here to stay: Reshaping the regions through mana Māori Situated 65 kilometres south-east of Hamilton, Putāruru (population 3747 in the 2013 Census) is typical of the many farming service towns scattered across rural Aotearoa New Zealand. Bakeries, op shops, a sports bar and a farm equipment supplier occupy the main street. Unlike nearby Tirau, which transformed from a one-stop shop into a vibrant boutique village in the late 1990s, Putāruru township remains largely indistinguishable from other rural centres. There are few clues to the substantial farming-based and water-generated wealth that lies beyond the town.

year: 2016