Powder compaction is a production method commonly used in the manufacturing industry today. In order to minimize costly experiments and to optimize serial production of details several methods to analyze the powder compaction process are developed and used. One method is to use micromechanical analysis where the local description of contact between two individual particles is of great importance. In this dissertation a visco-plastic contact law has been used and further developed in order to understand the powder compaction process at packing, low relative density compaction up to high relative density compaction. In order to relax some assumptions from previous theoretical studies simulation with the discrete element method (DEM) was performed. Up to 10.000 spherical particles were used in packing and early compaction simulation. It was found that rearrangement of particles is one of the major densification mechanisms in the early phases of compaction. At die compaction this effect of rearrangement was shown to be more pronounced than predicted from theoretical analyses. It was also found that the size ratio of particles is of importance when the number fraction of small particles in the compound is high. The finite element method has been used for numerical analyses to investigate the local contact problem between two particles when self-similarity no longer prevail. Based on the numerical results a suggestion for an approximate compliance relation was made. With this approximate formula the local compliance behaviour between two dissimilar particles was analysed. These findings are directly applicable to simulations with the discrete element method. Finally, an investigation using the finite element method to evaluate the range of the accuracy for theoretical and approximate compliance formula has been done with compounds of different regular lattices. It was found that the range of accuracy is much dependent on the number of contacts within the lattices, specially new forming contacts during the compaction. / QC 20101007

As one category of energetic materials, impact-initiated reactive materials are able to release a high amount of stored chemical energy under high strain rate impact loading, and are used extensively in civil and military applications. In general, polymers are introduced as binder materials to trap the reactive metal powders inside, and also act as an oxidizing agent for the metal ingredient. Since critical attention has been paid on the metal / metal reaction, only a few types of polymer / reactive metal interactions have been studied in the literature. With the higher requirement of materials resistant to different thermal and mechanical environments, the understanding and characterization of polymer / reactive metal interactions are in great demand. In this study, PTFE (Polytetrafluoroethylene) 7A / Ti (Titanium) composites were studied under high strain rates by utilizing the Taylor impact and SHPB tests. Taylor impact tests with different impact velocities, sample dimensions and sample configurations were conducted on the composite, equipped with a high-speed camera for tracking transient images during the sudden process. SHPB and Instron tests were carried out to obtain the stress vs. strain curves of the composite under a wide range of strain rates, the result of which were also utilized for fitting the constitutive relations of the composite based on the modified Johnson-Cook strength model. Thermal analyses by DTA tests under different flow rates accompanied with XRD identification were conducted to study the reaction mechanism between PTFE 7A and Ti when only heat was provided. Numerical simulations on Taylor impact tests and microstructural deformations were also performed to validate the constitutive model built for the composite system, and to investigate the possible reaction mechanism between two components. The results obtained from the high strain rate tests, thermal analyses and numerical simulations were combined to provide a systematic study on the reaction mechanism between PTFE and Ti in the composite systems, which will be instructive for future energetic studies on other polymer / reactive metal systems.

This paper aims to create a hard modification layer of WC/Co/Fe on the surface of SKD11 work steel by using a new closed-type method of surface electrical discharge coating with the self-made tool electrode and CNC electrical discharge machine. The tool electrode is the composition of a semi-sintered powder compacted electrode and a cooper rod. The sintered powder compacted electrode making process is first to mix the WC/Co and Fe powders uniformly at 8:1, 4:1, 2:1 and 1:1 in weight ratio. Continually, it will form the cylinder of 8mm in diameter and 18mm in length approximately by compacting in different pressure (50~200 MPa) and sintering temperature (300~900 ¢J). The EDM condition is 1~12A discharge current, 25~500£gs pulse time, and 50% duty factor. The electrical discharge machining is proceeding in kerosene with tool electrode as cathode and workpiece as anode. The result is as following. It can be concluded that the best condition to fabricate the sintered powder compacted electrode is 1:1 in weight ratio between WC/Co and Fe powders; with 200Mpa compacting pressure and sintering temperature at 900¢J, which results in lowest electrical resistivity. Under such condition, the area covered ratio can reach 100% at best EDM condition, which is pulse time £non = 50 £gs, rest time £noff = 50 £gs, 8A in current and 1.5 min in machining time. The surface hardness of workpiece increases with machining time. The surface hardness dramatically increases to Hv1500 as machining time over 1.5 min. The hardness of modification layer equals to the WC/Co particle itself which brings to the best wear ability. Moreover, the hardness of under surface in between 48 £gm is much higher than it of the SKD11 work steel. The hardness in between 30 £gm can reach up to Hv1200 in particular. The hardness of surface modification layer increases linearly with machining time. However, the limit of surface modification layer is about 30 £gm, and the needed time is below 5 min.

<p>Powder compaction is a production method commonly used in the manufacturing industry today. In order to minimize costly experiments and to optimize serial production of details several methods to analyze the powder compaction process are developed and used. One method is to use micromechanical analysis where the local description of contact between two individual particles is of great importance. In this dissertation a visco-plastic contact law has been used and further developed in order to understand the powder compaction process at packing, low relative density compaction up to high relative density compaction.</p><p>In order to relax some assumptions from previous theoretical studies simulation with the discrete element method (DEM) was performed. Up to 10.000 spherical particles were used in packing and early compaction simulation. It was found that rearrangement of particles is one of the major densification mechanisms in the early phases of compaction. At die compaction this effect of rearrangement was shown to be more pronounced than predicted from theoretical analyses. It was also found that the size ratio of particles is of importance when the number fraction of small particles in the compound is high.</p><p>The finite element method has been used for numerical analyses to investigate the local contact problem between two particles when self-similarity no longer prevail. Based on the numerical results a suggestion for an approximate compliance relation was made. With this approximate formula the local compliance behaviour between two dissimilar particles was analysed. These findings are directly applicable to simulations with the discrete element method. Finally, an investigation using the finite element method to evaluate the range of the accuracy for theoretical and approximate compliance formula has been done with compounds of different regular lattices. It was found that the range of accuracy is much dependent on the number of contacts within the lattices, specially new forming contacts during the compaction.</p>

Recently, the portfolio of compounds approved for inhalation therapy has expanded rapidly for lung disease therapies. The rationale for this delivery approach includes a more targeted and localized delivery to the diseased site with reduced systemic exposure, potentially leading to decreased adverse side effects. We have proposed that brittle matrix powders prepared by thin film freezing (TFF) are a suitable platform for pulmonary drug delivery which can achieve high lung concentrations while limit the corresponding systemic levels associated with toxicity, and enhanced physicochemical and aerodynamic properties can be obtained by varying TFF processing parameters. In Chapter 2, the in vitro and in vivo performance of an amorphous formulation prepared by TFF and a crystalline micronized formulation produced by milling was compared for Tacrolimus (TAC). TFF processed matrix powders was capable of achieving deep lung delivery due to its low density, highly porous and brittle characteristics. When emitted from a Miat® monodose inhaler, TFF processed TAC formulations exhibited a fine particle fraction (FPF) of 83.3% and a mass median aerodynamic diameter (MMAD) of 2.26 µm. Single dose 24-h pharmacokinetic studies in rats demonstrated that the TAC formulation prepared by TFF exhibited higher pulmonary bioavailability with a prolonged retention time in the lung, possibly due to decreased clearance (e.g., macrophage phagocytosis), compared to the micronized TAC formulation. Additionally, TFF formulation generated a lower systemic TAC concentration with smaller variability than the micronized formulation following inhalation, potentially leading to reduced side effects related to the drug in systemic circulation. Chapter 3 investigated the impact of processing parameters in the TFF process on the physicochemical and aerodynamic properties of the resulting formulations. All of these enhanced powder properties resulted from higher freezing rate contributed to a better aerodynamic performance of the obtaining formulations. Moreover, a decreasing trend of FPF was observed for these TFF powders when the initial solid concentrations increased. The variation of the freezing rate and initial solid loading in the TFF process enabled the production of formulations with enhanced physicochemical properties and improved aerodynamic performance. / text

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Background The high prevalence of micronutrient deficiencies among South African preschool children reinforces the need for an intensified micronutrient malnutrition control strategy targeting children at home or in school. The use of recently developed micronutrient powders also known as "in-home fortification" or "point-of-use fortification" can be an effective long-term, sustainable approach in improving early childhood nutrition and cognitive developmental potential. However, before embarking on large-scale, long-term, point-of-use fortification trials, it is imperative to conduct external pilot trials in which the feasibility of implementing full-scale studies can be effectively assessed. Objective The objective of this study was to assess the feasibility of implementing a point-of-use micronutrient fortification trial among African preschool children, which would aid in pilot-testing the study design, logistics and implementation process as well as reveal limitations which can be addressed before the implementation of full-scale trials. Methods Preschool children (n = 151), aged 36 -79 months with haemoglobin concentration (Hb)<= 12.5 g/dL, from eight schools in a low socio-economic community were randomly assigned to an intervention (n = 76) and a control (n = 75) groups, both receiving breakfast maize-meal porridge, either with added micronutrient or placebo powder for 52 school days. Several process evaluation indicators (fidelity, dose delivered, dose received, reach, recruitment and context) were used to assess trial feasibility. Selected indicators of early childhood development (Hb concentration, anthropometric indices and cognitive function) were used to evaluate the outcome of the intervention within the context of a pilot study. Results The process evaluation results indicate that the various implementation components were delivered with high fidelity. Capacity development and strengthening of the front-line staff cognitive assessors and study assistants) was executed as planned. The point-of-use fortificant was well accepted among the children and the mean percentage of days the point-of-use fortificant or placebo was consumed (~85%) did not differ between the groups. There were significant increases in Hb concentration (p < 0.05) from baseline to follow-up in both the intervention [mean change: 0.38 g/dL (95% CI: 0.14, 0.61 g/dL)] and control [mean change: 0.57 g/dL (95% CI: 0.35, 0.80 g/dL)] groups, however, mean change did not differ significantly between the groups (p = 0.250). The intervention did not improve any of the anthropometric indices measured in the intervention group compared to control. However, there was a medium likelihood for practical significance for the two global cognitive scores assessed, nonverbal index [intervention effects: 7.20 (95% C!: 2.60,11.81); P = 0.002, effect size: 0.55] and mental processing index [intervention effects: 2.73 (95% CI: 0.25,5.70); P = 0.072, effect size: 0.36] on the Kaufman Assessment Battery for Children, second edition. Conclusion The feasibility of implementing a point-of-use micronutrient fortification trial was demonstrated among African preschool children with potential benefits of improving their cognitive function. The most important lessons learned from this trial that could help improve similar future large-scale trials included the recruitment and training of the most eligible front-line staff as well as identifying that the use of a simple field-friendly finger prick method to measure Hb concentration may not be sufficiently sensitive to show differences in iron status after the intervention. / Thesis (M.Sc. (Nutrition))--North-West University, Potchefstroom Campus, 2010.

Background The high prevalence of micronutrient deficiencies among South African preschool children reinforces the need for an intensified micronutrient malnutrition control strategy targeting children at home or in school. The use of recently developed micronutrient powders also known as "in-home fortification" or "point-of-use fortification" can be an effective long-term, sustainable approach in improving early childhood nutrition and cognitive developmental potential. However, before embarking on large-scale, long-term, point-of-use fortification trials, it is imperative to conduct external pilot trials in which the feasibility of implementing full-scale studies can be effectively assessed. Objective The objective of this study was to assess the feasibility of implementing a point-of-use micronutrient fortification trial among African preschool children, which would aid in pilot-testing the study design, logistics and implementation process as well as reveal limitations which can be addressed before the implementation of full-scale trials. Methods Preschool children (n = 151), aged 36 -79 months with haemoglobin concentration (Hb)<= 12.5 g/dL, from eight schools in a low socio-economic community were randomly assigned to an intervention (n = 76) and a control (n = 75) groups, both receiving breakfast maize-meal porridge, either with added micronutrient or placebo powder for 52 school days. Several process evaluation indicators (fidelity, dose delivered, dose received, reach, recruitment and context) were used to assess trial feasibility. Selected indicators of early childhood development (Hb concentration, anthropometric indices and cognitive function) were used to evaluate the outcome of the intervention within the context of a pilot study. Results The process evaluation results indicate that the various implementation components were delivered with high fidelity. Capacity development and strengthening of the front-line staff cognitive assessors and study assistants) was executed as planned. The point-of-use fortificant was well accepted among the children and the mean percentage of days the point-of-use fortificant or placebo was consumed (~85%) did not differ between the groups. There were significant increases in Hb concentration (p < 0.05) from baseline to follow-up in both the intervention [mean change: 0.38 g/dL (95% CI: 0.14, 0.61 g/dL)] and control [mean change: 0.57 g/dL (95% CI: 0.35, 0.80 g/dL)] groups, however, mean change did not differ significantly between the groups (p = 0.250). The intervention did not improve any of the anthropometric indices measured in the intervention group compared to control. However, there was a medium likelihood for practical significance for the two global cognitive scores assessed, nonverbal index [intervention effects: 7.20 (95% C!: 2.60,11.81); P = 0.002, effect size: 0.55] and mental processing index [intervention effects: 2.73 (95% CI: 0.25,5.70); P = 0.072, effect size: 0.36] on the Kaufman Assessment Battery for Children, second edition. Conclusion The feasibility of implementing a point-of-use micronutrient fortification trial was demonstrated among African preschool children with potential benefits of improving their cognitive function. The most important lessons learned from this trial that could help improve similar future large-scale trials included the recruitment and training of the most eligible front-line staff as well as identifying that the use of a simple field-friendly finger prick method to measure Hb concentration may not be sufficiently sensitive to show differences in iron status after the intervention. / Thesis (M.Sc. (Nutrition))--North-West University, Potchefstroom Campus, 2010.

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