Common brown colour in natural diamond forms by plastic deformation during storage in the subcontinental lithospheric mantle (SCLM). Dislocation movement generates vacancies, which aggregate into clusters of perhaps 30–60 vacancies. Positron annihilation lifetime spectroscopy (PALS) and electron energy loss spectroscopy (EELS) support such vacancy clusters as the cause of brown colour. Brief treatment in a high-pressure–high-temperature (HPHT) vessel at 1800–2700 °C can destroy the brown colour. There has been speculation that similar colour removal should occur continuously at depth in the SCLM. Diamonds are stored at 900–1400 °C in the SCLM, according to inclusion thermometry. The effect of temperature on the time required to destroy brown colour has been calculated from published data. The activation energy for the breakup of vacancy clusters is a critical component. The time required to destroy brown colour in the SCLM is significant at the scale of geological time. Brown diamonds should easily maintain their colour for millions of years during cooler mantle storage at or below about 1000 °C. Warmer temperatures toward the base of the lithosphere may be able to reduce or eliminate brown colour within thousands of years. The survival of brown colour in the lithospheric mantle does not require the colour to be formed late in the storage history nor does it require metastable storage in the graphite stability field. Crystal strain is preserved upon loss of brown colour during HPHT treatment. Inhomogeneous crystal strain was measured in 18 natural diamonds using micro-X-ray diffraction (μXRD) χ-dimension peak widths. There is a correlation between strain and depth of brown colour. None of the colourless diamonds examined have high strain, as should be expected for a diamond that has gained and lost brown colour. This suggests that removal of brown colour is not a common natural occurrence. Infrared spectroscopy was used to determine nitrogen concentration and aggregation state in 60 natural diamonds. A loose association was found between brown colour and lower total nitrogen content. Within single diamonds, regions with less nitrogen tend to exhibit more anomalous birefringence due to strain. Colour zoned diamonds tend to have less nitrogen in the darker brown regions. This supports the hypothesis that diamonds with less nitrogen are more susceptible to plastic deformation and the development of brown colour. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2009-09-17 17:10:11.078

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Orientadores: Sérgio Tonini Button, Alexandra de Oliveira França Hayama / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-17T14:48:45Z (GMT). No. of bitstreams: 1 Giudice_MariaLeticiaCalil_M.pdf: 38633793 bytes, checksum: 30bf8d7106dd74ad1d146acc8fec1028 (MD5) Previous issue date: 2011 / Resumo: Os implantes metálicos são importantes para restaurar estruturas ósseas danificadas. Para produzir tais implantes, diversos tipos de materiais podem ser empregados, sendo o aço inoxidável a primeira liga metálica utilizada, que mais tarde, perdeu espaço para a liga Co-Cr devido a sua resistência à corrosão e propriedades mecânicas. As características das ligas de titânio do tipo ? fazem dessas ligas materiais promissores na confecção de implantes metálicos. Essas ligas são compostas por materiais biocompatíveis, como o nióbio, o tântalo e o zircônio, e apresentam módulo de elasticidade menor quando comparadas às ligas a+b. Neste trabalho foi estudada a liga b Ti-35Nb-7,5Ta (% em peso). Trabalhos prévios mostraram que esta liga apresenta propriedades compatíveis com as ligas desenvolvidas e utilizadas para implantes ortopédicos. Amostras dessa liga foram obtidas a partir de lingotes com 80g e 100g, fundidos em forno de fusão a arco voltaico, homogeneizados a 1000oC durante 8 horas e resfriados rapidamente em água, para obter-se uma microestrutura formada pelas fases b e martensita ortorrômbica (a"). As amostras foram então deformadas por laminação a frio em múltiplos passes até 84% de redução em espessura. Na sequência, as amostras com 84% de deformação foram recozidas em vácuo em diferentes temperaturas e tempos de recozimento. A caracterização microestrutural foi realizada por microscopia óptica, microscopia eletrônica de varredura e difração de raios-X. Também foram feitos ensaios de dureza Vickers, para a obtenção das curvas de encruamento e de amaciamento das amostras recozidas, e ultra-som para medidas do módulo de elasticidade. Os resultados mostram que na amostra solubilizada a microestrutura apresenta as fases a" e b, com grãos grosseiros, da ordem de 3 mm. As amostras com até 84% de deformação também apresentam somente as fases a" e b. Nas amostras com até 52% de redução da espessura foi verificada uma tendência da fase a" em se alinhar com a direção de laminação. A partir de 63% de redução em espessura há maior fragmentação dos grãos e a microestrutura torna-se majoritariamente lamelar. As amostras deformadas até 84% e recozidas a 600°C por 1, 5, 15, 30, 45 e 60 min e a 700°C por 1min encontram-se majoritariamente recuperadas. Já as amostras deformadas até 84% e em seguida recozidas a 700°C por 5, 15, 30, 45 e 60 min e a 800°C por 1, 5, 15, 30 e 45 min encontram-se parcialmente recristalizadas. Nas amostras recozidas a 800°C por 60 min também foi constatada a presença da fase a" no interior dos grãos totalmente recristalizados que apresentaram tamanho médio de 36 µm, com redução significativa se comparado com o do material solubilizado que era de 3mm / Abstract: Metallic implants are important to replace damaged bone structures. To manufacture such implants, many materials have been used, like stainless steels the first alloy ever applied and later substituted by Co-Cr alloys, which present better corrosion resistance and mechanical properties. Some characteristics of ? type titanium alloys make them a promising material in the manufacturing of metallic implants. These alloys present biocompatible elements such as niobium, tantalum and zirconium, and a lower Young's modulus when compared to a+b alloys. In this work it was studied the ? alloy Ti-35Nb-7.5Ta (%-weight). Previous studies have shown that this alloy presents properties which are compatible to other alloys commonly used in orthopedic implants. Samples of this alloy weighting 80 and 100 g were obtained by electric arc melting, heat treated at 1000oC for 8 hours and water quenched, to produce a microstructure with the phases b and orthorhombic martensite (a"). Then these samples were cold rolled in multiple passes up to a thickness reduction of 84%. Finally these samples were heat treated in vacuum at different temperatures and soaking times. Microstructural characterization was carried out by light optical microscopy, scanning electron microscopy and X-ray diffraction. Hardening and softening curves were obtained by Vickers hardness tests, and an ultrasonic method was used to evaluate the Young's modulus. The solubilized sample presents a a" and b microstructure with coarse grains, near to 3 mm. Cold rolled samples with 84% of thickness reduction also presented only the phases a" and b. In samples with up to 52% of the thickness reduction it was observed the tendency of phase a" to align with the rolling direction. Samples deformed above 63% of thickness reduction presented greater fragmentation of the grains and the microstructure became predominantly lamellar. Cold rolled samples with 84% thickness reduction and annealed at 600°C by 1, 5, 15, 30, 45 e 60 min and at 700°C by 1min are predominantly recovered, while samples annealed at 700°C by 5, 15, 30, 45 and 60 min and at 800°C by 1, 5, 15, 30 and 45 min are partially recrystallized. In samples annealed at 800°C by 60 min the a" phase was found inside fully recrystallized grains, which presented an average size of 36 µm, i.e., with a significant reduction if compared to the 3 mm solubilized mean grain size / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16502号 / 工博第3495号 / 新制||工||1529(附属図書館) / 29159 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 白井 泰治, 教授 乾 晴行 / 学位規則第4条第1項該当

Additive manufacturing (AM) is identified as one of the best techniques in manufacturing components addressing most of the current challenges including material scarcity, design complexity, material compatibility, etc. Stainless steel 316L is one of the promising material candidates in AM due to its extraordinary properties that are useful in a wide variety of industries. Tailoring desired properties locally is heavily investigated in metal AM. This project focuses on investigating the plastic behavior of additively manufactured SS 316L parts printed using laser powder bed fusion (LPBF) specifically to have a strong crystal orientation towards the direction of loading. Parts were printed to have (100), (110), and fiber texture perpendicular to the tensile axis by changing the laser scanning direction. In-situ tensile tests were carried out in a Scanning Electron Microscope (SEM) acquiring electron backscatter diffraction (EBSD) data from the specimen at several strain levels. Schmid Factor (SF) maps, Kernel Average Misorientation (KAM) maps, and Grain orientation spread (GOS) maps were generated using EBSD data. Micromechanisms in plastic deformation of these highly textured AM parts were analyzed based on the crystal orientation and the microstructure. When the influence of crystallographic texture on the micromechanisms of plastic deformation was observed, it was confirmed that a significant difference is present in tensile properties directed with the crystal orientation. During plastic deformation, the crystals were heavily rotated to accommodate slip formations. The slips that are generated at the grains with fiber texture are restricted by the grain boundaries and therefore, showed a higher yield strength. The (100) texture was less prone to plastic deformation. The grains with (110) crystal orientation proved a higher ductility with a perfect slip starting at the grains with higher SFs and showed {111} <110> slip systems.

<p> Gaining insight into the pressworking properties of laminated sheet metal is the aim of this work. One of the deformation processes in which the difference in behaviour between single and laminated sheet metal is most distinct and possibly the easiest to analyze is that of pure plastic bending. A bending theory, initially proposed by Crafoord, is further developed to analyze the pure bending of laminated metals. The bending behaviour of single and laminated nonstrain hardening and strain hardening sheets, with and without Bauschinger effect, is treated extensively from a theoretical point of view. </p> <p> Stretch forming, bending and deep drawing tests on laminated sheets are also performed experimentally. It is found that the orientation of the laminated sheet during the deformation process has a significant influence on the bending behaviour and the deep drawability of laminated sheet. The change in deep drawability can be qualitatively predicted from the bending behaviour. </p> / Thesis / Master of Engineering (MEngr)

Metal additive manufacturing stands poised to disrupt multiple industries with high material use efficiency and complex part production capabilities, however many technologies deposit material with sub-optimal properties, limiting their use. This decrease in performance largely stems from porosity laden parts, and asymmetric solidification-based microstructures. Solid-state additive manufacturing techniques bypass these flaws, using deformation and diffusion phenomena to bond material together layer by layer. Among these techniques, Additive Friction Stir Deposition (AFSD), stands out as unique for its freeform nature, and thermomechanical conditions during material processing. Leveraging its solid-state behavior, optimized microstructures produced by AFSD can reach performance levels near, at, or even above traditionally prepared metals. A strong understanding of the material conditions during AFSD and the phenomena responsible for microstructure evolution. Here we discuss two works aimed at improving the state of knowledge surrounding AFSD, promoting future microstructure optimization. First, a parametric study is performed, finding a wide array of producible microstructures across two material systems. In the second work, a stop-action type experiment is employed to observe the dynamic microstructure evolution across the AFSD material flow pathway, finding specific thermomechanical regimes that occur within. Finally, multiple conventional alloy systems are discussed as their microstructure evolution pertains to AFSD, as well as some more unique systems previously limited to small lab scale techniques, but now producible in bulk due to the additive nature of AFSD. / Doctor of Philosophy / The microstructure of a material describes the atomic behavior at multiple length scales. In metals this microstructure generally revolves around the behavior of millions of individual crystals of metal combined to form the bulk material. The state and behavior of these crystals and the atoms that make them up influence the strength and usability of the material and can be observed using various high fidelity characterization techniques. In metal additive manufacturing (i.e. 3D printing) the microstructure experiences rapid and severe changes which can alter the final properties of the material, typical to a detrimental effect. Given the other benefits of additive manufacturing such as reduced costs and complex part creation, there is desire to predict and control the microstructure evolution to maximize the usability of printed material. Here, the microstructure evolution in a solid-state metal additive manufacturing, Additive Friction Stir Deposition (AFSD), is investigated for different metal material systems. The solid-state nature of AFSD means no melting of the metal occurs during processing, with deformation forcing material together layer by layer. The conditions experienced by the material during printing are in a thermomechanical regime, with both heating and deformation applied, akin to common blacksmithing. In this work specific microstructure evolution phenomena are discussed for multiple materials, highlighting how AFSD processing can be adjusted to change the resulting microstructure and properties. Additionally, specific AFSD process interactions are studied and described to provide better insight into cumulative microstructure evolution throughout the process. This work provides the groundwork for investigating microstructure evolution in AFSD, as well as evidence and results for a number of popular metal systems.

Recent studies demonstrate that mechanical deformation of small volume systems can be significantly different from those of the bulk. One such interesting length scale dependent property is the increase in the yield stress with decrease in diameter of micrometer rods, particularly when the diameter is below a micrometer. Intermittent flow may also result when the diameter of the rods is decreased below a certain value. The second such property is the intermittent plastic deformation during nano-indentation experiments. Here again, the instability manifests due to smallness of the sample size, in the form of force fluctuations or displacement bursts. The third such length scale dependent property manifests as ’smaller is stronger’ property in indentation experiments on thin films, commonly called as the indentation size effect (ISE). More specifically, the ISE refers to the increase in the hardness with decreasing indentation depth, particularly below a fraction of a micrometer depth of indentation. The purpose of this thesis is to extend nonlinear dynamical approach to plastic deformation originally introduced by Anantha krishna and coworkers in early 1980’s to nano and micro-indentation process. More specifically, we address three distinct problems : (a) intermittent force/load fluctuations during displacement controlled mode of nano-indentation, (b) displacement bursts during load controlled mode of nano-indentation and (c) devising an alternate framework for the indentation size effect. In this thesis, we demonstrate that our approach predicts not just all the generic features of nano-and micro-indentation and the ISE, the predicted numbers also match with experiments. Nano-indentation experiments are usually carried-out either in a displacement controlled (DC) mode or load controlled (LC) mode. The indenter tip radius typically ranges from few tens of nanometer to few hundreds of nanometers-meters. Therefore, the indented volume is so small that the probability of finding a dislocation is close to zero. This implies that dislocations must be nucleated for further plastic deformation to proceed. This is responsible for triggering intermittent flow as indentation proceeds. While several load drops are seen beyond the elastic limit in the DC controlled experiments, several displacement jumps are seen in the LC experiments. In both cases, the stress corresponding to load maximum on the elastic branch is close to the theoretical yield stress of an ideal crystal, a feature attributed to the absence of dislocations in the indented volume. Hardness is defined as the ratio of the load to the imprint area after unloading and is conventionally measured by unloading the indenter from desired loads to measure the residual plastic imprint area. Then, the hardness so calculated is found to increase with decreasing indentation depth. However, such size dependent effects cannot be explained on the basis of conventional continuum plasticity theories since all mechanical properties are independent of length scales. Early theories suggest that strong strain gradients exist under the indenter that require geometrically necessary dislocations (GNDs) to relax the strain gradients. In an effort to explain the the size effect, these theories introduce a length scale corresponding to the strain gradients. One other feature predicted by subsequent models of the ISE is the linear relation between the square of the hardness and the inverse of the indentation depth. Early investigations on the ISE did recognize that GNDs were required to accommodate strain gradients and that the hardness H is determined by the sum of the statistically stored dislocation (SSD) and GND densities. Following these steps, Nix and Gao derived an expression for the hardness as a function of the indentation depth z. The relevant variables are the SSD and GND densities. An expression for the GND density was obtained by assuming that the GNDs are contained within a hemispherical volume of mean contact radius. The authors derive an expression for the hardness H as a function of indentation depth z given by [ HH 0 ]2 = 1+ zz ∗ . The intercept H0 represents the hardness arising only from SSDs and corresponds to the hardness in the limit of large sample size. The slope z ∗ can be identified as the length scale below which the ISE becomes significant. The authors showed that this linear relation was in excellent agreement with the published results of McElhaney et al for cold rolled polycrystalline copper and single crystals of copper, and single crystals of silver by Ma and Clarke. Subsequent investigations showed that the linear relationship between H2 verses 1/z breaks down at small indentation depths. Much insight into nano-indentation process has come from three distinct types of studies. First, early studies using bubble raft indentation and later studies using colloidal crystals (soft matter equivalent of the crystalline phase) allowed visualization of dislocation nucleation mechanism. Second, more recently, in-situ transmission electron microscope studies of nano-indentation experiments have been useful in understanding the dislocation nucleation mechanism in real materials. Third, considerable theoretical understanding has come largely from various types of simulation studies such as molecular dynamics (MD) simulations, dis¬location dynamics simulations and multiscale modeling simulations (using MD together with dislocation dynamics simulations). A major advantage of simulation methods is their ability to include a range of dislocation mechanisms participating in the evolution of dislocation microstructure starting from the nucleation of a dislocation, its multiplication, formation of locks, junctions etc. However, this advantage is offset by the serious limitations set by short time scales inherent to the above mentioned simulations and the limited size of simulated volumes that can be implemented. Thus, simulation approaches cannot impose experimental parameters such as the indentation rates or radius of the indenter and thickness of the sample, for example in MD simulations. Indeed, the imposed deformation rates are often several orders of magnitude higher than the experimental rates. Consequently, the predicted values of force, indentation depth etc., differ considerably from those reported by experiments. For these reasons, the relevance of these simulations to real materials has been questioned. While several simulations, particularly MD simulation predict several force drops, there are no simulations that predict displacement jumps seen in LC mode experiments. The inability of simulation methods to adopt experimental parameters and the mismatch of the predicted numbers with experiments is main motivation for devising an alternate framework to simulations that can adopt experimental parameters and predict numbers that are comparable to experiments. The basic premise of our approach is that describing time evolution of the relevant variables should be adequate to capture most generic features of nano and micro-indentation phenomenon. In the particular case under study, this point of view is based on the following observation. While one knows that dislocations are the basic defects responsible for plastic deformation occurring inside the sample, the load-indentation depth curve does not include any information about the spatial location of dislocation activity inside the sample. In fact, the measured load and displacement are sample averaged response of the dislocation activity in the sample. This suggests that it should be adequate to use sample averaged dislocation densities to obtain load-indentation depth curve. Keeping this in mind, we devise a method for calculating the contribution from plastic deformation arising from dislocation activity in the entire sample. This is done by setting up rate equations for the relevant sample averaged dislocation densities. The first problem we consider is the force/load fluctuations in displacement controlled nano-indentation. We devise a novel approach that combines the power of nonlinear dynamics with the evolution equations for the mobile and forest dislocation densities. Since the force serrations result from plastic deformation occurring inside the sample, we devise a method for calculating this contribution by setting-up a system of coupled nonlinear time evolution equations for the mobile and forest dislocation densities. The approach follows closely the steps used in the Anantha krishna (AK) model for the Portevin-Le Chatelier (PLC) effect. The model includes nucleation, multiplication and propagation of dislocation loops in the time evolution equation for the mobile dislocation density. We also include other well known dislocation transformation mechanisms to forest dislocation. Several of these dislocation mechanisms are drawn from the AK model for the PLC effect. To illustrate the ability of the model to predict force fluctuations that match experiments, we use the work of Kiely at that employs a spherical indenter. The ability of the approach is illustrated by adopting experimental parameters such as the indentation rate, the radius the indenter etc. The model predicts all the generic features of nano-indentation such as the Hertzian elastic branch followed by several force drops of decreasing magnitudes, and residual plas¬ticity after unloading. The stress corresponding to the elastic force maximum is close to the yield stress of an ideal solid. The predicted values for all the quantities are close to those reported by experiments. Our model allows us to address the indentation-size effect including the ambiguity in defining the hardness in the force drop dominated regime. At large indentation depths where the load drops disappear, the hardness shows decreasing trend, though marginal. The second problem we consider is the load controlled mode of indentation where sev¬eral displacement jumps of decreasing magnitudes are seen. Even though, the LC mode is routinely used in nano-indentation experiments, there are no models or simulations that predict the generic features of force-displacement curves, in particular, the existence of sev¬eral displacement jumps of decreasing magnitudes. The basic reason for this is the inability of these methods to impose constant load rate during displacement jumps. We then show that an extension of the model for the DC mode predicts all the generic features when the model is appropriately coupled to an equation defining the load rate. Following the model for DC mode, we retain the system of coupled nonlinear time evolution equations for mobile and forest dislocation densities that includes nucleation, multiplication, and propagation threshold mechanisms for mobile dislocations, and other dislocation transformation mechanisms. The commonly used Berkovich indenter is considered. The equations are then coupled to the force rate equation. We demonstrate that the model predicts all the generic features of the LC mode nano-indentation such as the existence of an initial elastic branch followed by several displacement jumps of decreasing magnitudes, and residual plasticity after unloading for a range of model parameter values. In this range, the predicted values of the load, displacement jumps etc., are similar to those found in experiments. Further, optimized set of parameter values can be easily determined that provide a good fit to the load-indentation depth curve of Gouldstone et al for single crystals of Aluminum. The stress corresponding to the maximum force on the Berkovich elastic branch is close to the theoretical yield stress. We also elucidate the ambiguity in defining hardness at nanometer scales where the displacement jumps dominate. The approach also provides insights into several open questions. The third problem we consider is the indentation size effect. The conventional definition of hardness is that it is the ratio of the load to the residual imprint area. The latter is determined by the residual plastic indentation depth through area-depth relation. Yet, the residual plastic indentation depth that is a measure of dislocation mobility, never enters into most hardness models. Rather, the conventional hardness models are based on the Taylor relation for the flow stress that characterizes the resistance to dislocation motion. This is a complimentary property to mobility. Our idea is to provide an alternate way of explaining the indentation size effect by devising a framework that directly calculates the residual plastic indentation depth by integrating the Orowan expression for the plastic strain rate. Following our general approach to plasticity problems, we set-up a system of coupled nonlinear time evolution equations for the mobile, forest (or the SSD) and GND densities. The model includes dislocation multiplication and other well known dislocation transformation mechanisms among the three types of dislocations. The main contributing factor for the evolution of the GND density is determined by the mean strain gradient and the number of sites in the contact area that can activate dislocation loops of a certain size. The equations are then coupled to the load rate equation. The ability of the approach is illustrated by adopting experimental parameters such as the indentation rates, the geometrical quantities defining the Berkovich indenter including the nominal tip radius and other parameters. The hardness is obtained by calculating the residual plastic indentation depth after unloading by integrating the Orowan expression for the plastic strain rate. We demonstrate that the model predicts all features of the indentation size effect, namely, the increase in the hardness with decreasing indentation depth and the linear relation between the square of the hardness and inverse of the indentation depth, for all but 200nm, for a range of parameter values. The model also predicts deviation from the linear relation of H2 as a function of 1/z for smaller depths consistent with experiments. We also show that it is straightforward to obtain optimized parameter values that give a good fit to polycrystalline cold-worked copper and single crystals of silver. Our approach provides an alternate way of understanding the hardness and indentation size effect on the basis of the Orowan equation for plastic flow. This approach must be contrasted with most models of hardness that use the SSD and GND densities as parameters. The thesis is organized as follows. The first Chapter is devoted to background material that covers physical aspects of different kinds of plastic deformation relevant for the thesis. These include the conventional yield phenomenon and the intermittent plastic deformation in bulk materials in alloys exhibiting the Portevin-Le Chatelier (PLC) effect. We then provide background material on nano-and micro-indentation, both experimental aspects and the current status of the DC controlled and LC controlled modes of nano-indentation. Results of simulation methods are briefly summarized. The chapter also provides a survey of hardness models and the indentation size effect. A critical survey of experiments on dislocation microsructure that contradict / support certain predictions of the NixGao model. The current status of numerical simulations are also given. The second Chapter is devoted to introducing the basic steps in modeling plastic deformation using nonlinear dynamical approach. In particular, we describe how the time evolution equations are constructed based on known dislocation mechanisms such as nucleation, multiplication formations of junctions etc. We then consider a model for the continuous yield phenomenon that involves only the mobile and forest densities coupled to constant strain rate condition. This problem is considered in some detail to illustrate how the approach can be used for modeling nano-indentation and indentation size effect. The third Chapter deals with a model for displacement controlled nano-indentation. The fourth Chapter is devoted to adopting these equation to the load controlled mode of nano¬indentation. The fifth Chapter is devoted to modeling the indentation size effect based on calculating residual plastic indentation depth after unloading by using the Orowan’s expression for the plastic strain rate. We conclude the thesis with a Summary, Discussion and Conclusions.

Evaluation of the tableting mixtures containing the paracetamolum by the parameters of the equation of compression The diploma thesis deals with effect of paracetamol on the parameters of compression equation. These parameters characterize compression process in the individual phases of compression: precompression phase, phase of elastic deformation and phase of plastic deformation. Paracetamolum was studied in the five mixtures, where it occurred in different ratio with microcrystalline cellulose. Looseness, Carr's index and Hausner ratio were evaluated for each mixture. The sizes of reductions ai, sizes of energies Ei and Ri, "half-pressures" pHi and the velocity constants 1/ti were calculated using three-exponential equation of compression for the individual phases of pressing. The results showed poor flow properties of tableting mixtures and thus its unsuitability for direct compression. The results of the study have revealed that increasing amounts of paracetamolum in the mixture increase reduction of volume a1 and velocity of volume change 1/t1 in dependence on the amount of the extruded air and decrease the required energy due to the smooth surface and less friction during the precompression phase. Reduction of volume a2 decrease with the increase of content of paracetamol due to...

Charles University in Prague, Faculty of Pharmacy in Hradec Králové Department of Pharmaceutical Technology Student: Natália Pribylincová Consultant: Doc. RNDr. Milan Řehula, CSc. Effect of ascorbic acid on the parameters of compression equation Many mathematical models describing the compressing process are widely used in the development of new medicinal products in form of tablets. This process can be evaluated by means of compaction equations or throughout the viscoelastic properties. Compaction equation expresses dependency on height, volume or density of the used material which is being compressed by the applied compacting pressure. Based on the gained parameters, it is possible to describe specifically various stages of the compaction process, to determine characteristic properties of the studied material and accordingly to examine its mechanism. This thesis deals with the impact of the ascorbic acid on the parameters of compaction equation. The paperwork evaluates a mixture consisting of ascorbic acid (AA) and microcrystalline cellulose (MCC) in the ratio of MCC : AA 100:0, 75:25, 50:50, 25:75, 0:100. . The mostly used compression equations are described in the theoretic part. The three - exponential equation by Řehula created at the Department of Pharmaceutical Technology at Charles...