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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Effet de la température et de l'agitation sur les propriétés rhéologiques des bétons fluides à rhéologie adaptée

Pan, Jing January 2015 (has links)
Résumé : Le climat local, le transport avec l’agitation entre l’endroit de bétonnage et le site de fabrication du béton influencent fortement les propriétés du béton frais et durci. Selon les particularités du béton autoplaçant (BAP), le maintien de l’homogénéité et l’ouvrabilité du BAP avant la mise en place est très important. Les propriétés des BAP sont généralement plus sensibles à la température et au transport par rapport à celles des bétons conventionnels. Une meilleure compréhension de l’effet de la température et de l’agitation sur la performance des BAP est nécessaire pour prévoir les conséquences du changement du climat (température) et de l’effet du transport (temps et vitesse d’agitation), puis pour donner des précautions à suivre afin de répondre à la demande des BAP pour un bon rapport performance-coût. De manière pragmatique, il s’avère nécessaire d’utiliser la méthode du mortier de béton équivalent (MBE) afin d’analyser rapidement les influences de la température et de l’agitation sur les propriétés rhéologiques, calorimétriques et mécaniques des BAP. Cinq températures (8, 15, 22, 29 et 36°C) et deux vitesses d’agitation (6 et 18 tr/min) ont été étudiées sur les MBE. Ensuite, quelques compositions spécifiques (type d’adjuvant et ajout cimentaire) ont choisies afin de vérifier avec des températures compasse entre 8 à 36°C et les agitations différentes (2 et 6 tr/min) sur les BAP destinés aux travaux de bâtiment (BAP-B) sans agent entraîneur d’air et sur des bétons semi-autoplaçant destinés aux travaux d’infrastructures (BSAP-I) avec agent entraîneur d’air. La fluidité initiale des MBE et BAP a été fixée en faisant varier la demande en SP, la température et l’agitation. Les résultats montrent qu’il y a un effet important de la température et de l’agitation sur l’efficacité des adjuvants, la fluidité, la teneur en air, les propriétés rhéologiques, calorimétriques et mécaniques des MBE et des BAP. Pour prévoir la performance de MBE à différentes températures, une équation mathématique est proposée pour déduire la demande en SP, la demande en AEA, le flux maximal et la résistance en compression à 1 jour en fonction des mêmes propriétés sur MBE à 22°C et de la température. Enfin, une corrélation linéaire a été trouvée entre les MBE et les BAP sur ces mêmes propriétés. / Abstract : The local climate, the transport of agitated concrete after manufacturing but before being cast strongly influence the properties of the fresh and hard concrete. It’s important to keep the stability and workability of the self-consolidating concrete (SCC) because of its special characteristics. Compare to the normal concrete, the properties of SCC are generally more sensitive to the temperature and the transport. Therefore it’s necessary to understand the effects of the temperature and the agitation on the performance of the SCC in order to predict the consequences of climate change (temperature) and transport (time and speed of agitation), and then to give the better precautions with a good performance-cost report. In this study, the concrete mortar equivalent (CEM) method is used to quickly analyze the influences of the temperature and the agitation on the rheological, calorimetric and mechanical properties of the SCCs. Five temperatures (8, 15, 22, 29 and 36°C) and two agitation speed (6 and 18 tr/min) are varied in CEMs. And then, some compositions (type of adjuvant and supplementary cementing material) are chosen to be valued with the temperature (8-36°C) and the agitation (2 and 6 tr/min) in SCCs for the building without air-entraining admixture (AEA) and semi-flowable SCC for infrastructure with AEA. The initial slump flow of CEM and SCC is fixed, but the demand superplasticizer, the temperature and the agitation were varied. The results show that there are the effects of temperature and agitation on the effectiveness of admixture, the slump flow, the air content, the rheological, calorimetric and mechanical properties of CEM and SCC. A mathematical equation is proposed to predict the performance of SCC at different temperatures for the SP and AEA requirement, the maximum of heat flow and the compressive strength at one day by these same properties of SCC at 22°C and by the temperature. Finally, a good linear correlation is found between CEM and SCC for these properties.
2

Preservation of plywood against biological attack with low environmental impact using tannin-boron preservative / Protection à faible impact environnemental des contreplaqués avec des associations tannins-bore

Efhamisisi, Davood 21 September 2015 (has links)
Une étude expérimentale a été menée afin de protéger des attaques biologiques des contreplaqués faits d'essences non durables (hêtre et peuplier), et ce, avec un faible impact environnemental. Des produits de protection à base de tannins et de bore, nouvellement développés afin de réduire le lessivage du bore, ont été sélectionnés pour ce but. Ce système a été utilisé pour protéger les contreplaqués selon deux approches : (1) au niveau de la colle pour remplacer les adhésives à base de formaldéhyde et coller les plis, (2) en traitement des plis avec des formulations plus diluées, les plis étant collés avec des adhésifs mélamine-urée-formaldéhyde. Les données expérimentales de cette thèse peuvent être classées en trois grands groupes : essais chimiques et thermomécaniques des colles tannin-bore, mesure des propriétés physiques et mécaniques, de la résistance biologique avant et après vieillissement des différents panneaux. Les essais chimiques sur les colles tannin/hexamine ont montré que l'addition de bore sous forme d'acide borique peut contribuer à plus de liaisons inter-flavonoids et à ouvrir les cycles pyranes ce qui accélère les réactions de polymérisation. Des analyses thermomécaniques sur les colles contenant des tannins de mimosa et de quebracho ont confirmé que l'addition d'acide borique (1) abaissait le temps et la température de prise, et (2) augmentait les valeurs du module d'élasticité de la colle. L'addition d'une quantité optimale d'acide borique dans la colle à base de tannin augmente les propriétés physiques et la résistance au cisaillement. Une charge excessive d'acide borique (10%) dans la colle est la cause de pertes de propriétés mécaniques et physiques. Bien qu'en faible quantité, l'introduction de l'acide borique dans la colle de tannin amène une protection efficace contre l'attaque fongique, même après un lessivage selon l'EN 1250-2. Les résultats des essais termites montrent que l'acide borique contenu dans la colle cause le plus faible taux de survie des insectes et de perte de masse, mais présentent un fort degré d'attaque selon une cotation visuelle. Aucune amélioration n'a été obtenue lors d'un essai de choix après lessivage. Les contreplaqués faits de plis traités par des solutions tannin-bore ont montré des résistances au cisaillement plus faibles, mais toujours dans les gammes requises pour des applications en atmosphère humide. Des résultats satisfaisants ont été obtenus par les réseaux polymères de tannins, même après une lessivage sévère, vis-à-vis de l'attaque fongique. Les contreplaqués faits de plis traités à l'acide borique seul ont présenté une sensibilité importante à l'attaque biologique après un lessivage. Les résultats des essais termites ont montré un faible taux de survie des insectes et de perte de masse, même après un lessivage sévère, pour les contreplaqués avec des plis traités par des systèmes tannin-bore. Les résultats d'un essai de choix a montré que les termites préféraient se nourrir des témoins quand l'alternative proposée était des échantillons traités avec des systèmes tannin-bore. / An experimental investigation was conducted to protect plywood panels made of perishable wood species (beech and poplar) against biological attacks with low environmental impact. The newly developed tannin-boron preservative which was proposed to reduce the leaching of borates was selected for this purpose. This system was used to protect plywood with two approaches: (1) in the glue line to replace formaldehyde based adhesives and gluing wood veneers, (2) pretreatment of wood veneers with the diluted formulations and bonded with melamine-urea-formaldehyde resin The research data in this thesis were obtained from three main groups of experiments: chemicals and thermomechanical testing on the tannin-boron resin, measuring physical and mechanical properties, and different biological tests before and after leaching processes. The chemicals testing on the tannin/hexamine adhesive showed that the addition ofboron, in the form of boric acid, can contribute more inter-flavonoid linkages and the opening of pyran rings which leads to the acceleration of polymerization reactions. Thermomechanical analysis on the adhesives of mimosa and quebracheo tannins confirmed that the addition of boric acid (1) lowered time and temperature of hardening, (2) and increased modulus of elasticity values of the adhesive. The addition of optimal boric acid into the tannin adhesive upgraded physical properties and tensile shear strength. An excess loading of boric acid (10%) in the glue line caused imperfect physical and mechanical features. Despite the low uptake of boric acid but its addition into the tannin glue provided effective resistance against fungal attack even after mild leaching test according to the EN 1250-2. The results of termites test showed that increase in the boric acid content of the adhesive caused the lower survival rate and the weight loss but samples underwent the high level of attack. No improvement against termite attack was obtained after leaching by a choice feeding test. The plywoods made of pretreated veneers by tannin-boron solutions showed partially lower tensile shear strength but still in the range of standards requirements for the humid applications. The satisfactory results were obtained even after severe leaching test against fungal attack with a strong polymeric network of tannin. The control plywoods made of pretreated veneers with boric acid alone solutions presented significant sensitivity against biological attack after leaching test. The results of termite tests showed the lower survival rate and the weight loss even after severe leaching test for the plywoods made of pretreated veneers with tannin-boron systems. The results of choice feeding test showed that termites preferred feeding from the controls when alternative samples were treated with the tannin-boron system. In general the evidence from this study suggests that tannin-boron system can significantly slow down the leaching of boron and it rendered high potential to preserve plywood.
3

Spherical Crystallization of Benzoic Acid

Thati, Jyothi January 2007 (has links)
<p>Spherical agglomerates of benzoic acid crystals have been successfully prepared by drowning-out crystallization in three solvent partial miscible mixtures. Benzoic acid is dissolved in ethanol, bridging liquid is added and this mixture is fed to the agitated crystallizer containing water. Fine crystals are produced by crystallization of the substance, and the crystals are agglomerated by introduction of an immiscible liquid called the bridging liquid. The concentration of solute, agitation rate, feeding rate, amount of bridging liquid and temperature are found to have a significant influence on the physico-mechanical properties of the product. The product particle characterization includes the particle size distribution, morphology and mechanical strength.</p><p>Many of the solvents such as chloroform, toluene, pentane, heptane, cyclo hexane, diethyl ether and ethyl acetate were used as bridging liquids. Among the selected solvents ethyl acetate and di ethyl ether could not form the spherical agglomerates. Characteristics of the particles are changing with the bridging liquid used. Range of the operation for spherical agglomeration is very narrow and was shown that only at certain conditions the spherical agglomerates are produced. Increased amount of bridging liquid, decrease in feeding rate and temperature causes the particle size to increase. Particle morphology depends on the bridging liquid used, amount of bridging liquid and the temperature. Particles look completely spherical from the experiments where toluene is used as bridging liquid. </p><p>The mechanical strength of single agglomerates has been determined by compression in a materials testing machine, using a 10N load cell. For single particle compression an approximate estimation of the true stress is presented. Compression characteristics for single agglomerates are compared with data on particle bed compression. Low elastic recovery and high compressibility of the single particles and of bed of particles reveals that the spherical agglomerates prepared in this work have a plastic behavior which is expected to be favorable for direct tabletting. Some of the stress–strain curves are J-shaped with no clear fracturing of the particles, and are well correlated by an exponential–polynomial equation. </p>
4

Spherical Crystallization of Benzoic Acid

Thati, Jyothi January 2007 (has links)
Spherical agglomerates of benzoic acid crystals have been successfully prepared by drowning-out crystallization in three solvent partial miscible mixtures. Benzoic acid is dissolved in ethanol, bridging liquid is added and this mixture is fed to the agitated crystallizer containing water. Fine crystals are produced by crystallization of the substance, and the crystals are agglomerated by introduction of an immiscible liquid called the bridging liquid. The concentration of solute, agitation rate, feeding rate, amount of bridging liquid and temperature are found to have a significant influence on the physico-mechanical properties of the product. The product particle characterization includes the particle size distribution, morphology and mechanical strength. Many of the solvents such as chloroform, toluene, pentane, heptane, cyclo hexane, diethyl ether and ethyl acetate were used as bridging liquids. Among the selected solvents ethyl acetate and di ethyl ether could not form the spherical agglomerates. Characteristics of the particles are changing with the bridging liquid used. Range of the operation for spherical agglomeration is very narrow and was shown that only at certain conditions the spherical agglomerates are produced. Increased amount of bridging liquid, decrease in feeding rate and temperature causes the particle size to increase. Particle morphology depends on the bridging liquid used, amount of bridging liquid and the temperature. Particles look completely spherical from the experiments where toluene is used as bridging liquid. The mechanical strength of single agglomerates has been determined by compression in a materials testing machine, using a 10N load cell. For single particle compression an approximate estimation of the true stress is presented. Compression characteristics for single agglomerates are compared with data on particle bed compression. Low elastic recovery and high compressibility of the single particles and of bed of particles reveals that the spherical agglomerates prepared in this work have a plastic behavior which is expected to be favorable for direct tabletting. Some of the stress–strain curves are J-shaped with no clear fracturing of the particles, and are well correlated by an exponential–polynomial equation. / QC 20101119
5

Impact of different soil tillage technologies on the enviroment / Skirtingų žemės dirbimo technologijų poveikis aplinkai

Buragienė, Sidona 23 January 2014 (has links)
Soil tillage is one of the most important agrotechnological processes having huge influence on the sowing, germination, growing, yield and quality of cultivated plants. At the same time soil tillage is one of the most expensive and energy consuming agrotechnological processes of plant cultivation. The conventional tillage technologies using mouldboard and intensive cultivation machinery have both a positive impact on the preparation of the seedbed for plants and a negative impact as they are rather detrimental to the environment, soil, its properties, biodiversity, pollution of water bodies, etc. During the conventional soil tillage the crop residues of the last yield are incorporated into the deeper layers of the soil and the soil surface is not covered. Such soils are much susceptible to the environmental forces and are easier disturbed by wind and water erosion. Every year around 6 mio ha of fertile soil areas are lost due to inappropriate agricultural activities and changing environmental conditions. Another very important factor is that deep ploughing is an unproductive soil tillage method pertaining to huge time and energy consumption. At the same time multiplex driving of heavy weight agricultural machinery over the soil results in negative influence on its peoperties as well as consuming of huge amounts of diesel fuel results in high pollution of the environment with the greenhouse gas. Therefore, in order to reduce the negative influence of agricultural activities... [to full text] / Žemės dirbimas yra vienas svarbiausių agrotechnologinių procesų, turinčių labai didelę įtaką kultūrinių augalų sėjai, sudygimui, augimui, derliui ir jo kokybei. Tuo pačiu žemės dirbimas yra ir vienas iš brangiausių ir energijai imliausių kultūrinių augalų auginimo agrotechnologinių procesų. Įprastinio žemės dirbimo technologijos, kuriose naudojamos verstuvinės ir intensyviai dirvą purenantys žemės dirbimo agregatai, greta teigiamo poveikio augalų sėklų guoliavietės paruošimui, yra pakankamai žalingos aplinkai, dirvai, jos savybėms, biologinei įvairovei, vandens telkinių taršai ir t.t. Įprastinio žemės dirbimo metu augalinės praėjusio derliaus liekanos yra įterpiamos į gilesnius dirvos sluoksnius ir dirvos paviršius lieka neuždengtas. Tokios dirvos yra žymiai jautresnės aplinkos veiksniams ir lengviau pažeidžiamos vėjo ir vandens erozijos. Kiekvienais metais, pasaulyje, dėl netinkamos žemės ūkio veiklos ir kintančių aplinkos sąlygų prarandama apie 6 mln. ha derlingų dirvos plotų. Kitas labai svarbus aspektas yra tas, kad žemės dirbimas gilaus arimo plūgais yra mažai našus, daug darbo laiko ir energijos sąnaudų reikalaujantis žemės dirbimas. Tuo pačiu daugkartinis didelės masės žemės ūkio agregatų važinėjimas po dirvą ne tik daro neigiamą įtaką jos savybėms, bet ir, sudeginant didelius kiekius dyzelinių degalų, stipriai teršia aplinką šiltnamio efektą sukeliančiomis dujomis. Todėl pastaruoju metu, siekiant mažinti žemės ūkio veiklos daroma neigiamą įtaką dirvos degradacijai... [toliau žr. visą tekstą]
6

Élaboration et caractérisation d’un écociment à base de poudre de mâchefer de charbon / Elaboration and characterization of coal bottom ash powder eco-cement

Savadogo, Nafissatou 15 July 2017 (has links)
Ce travail de recherche s'inscrit dans une dynamique de valorisation des sous-produits industriels locaux dans l'industrie cimentière. Il porte essentiellement sur la possibilité d'utiliser la poudre de mâchefer de charbon produit par la SONICHAR au Niger pour élaborer des ciments composés. Après une caractérisation physico-chimique et environnementale de la poudre de mâchefer, nous avons déterminé sa réactivité pouzzolanique et son indice d'activité mécanique. Les résultats montrent que la poudre de mâchefer présente une pouzzolanicité dont la cinétique relativement lente ne démarre pas avant 14 jours. D'autre part, ce mâchefer peut être considéré comme une addition minérale du type Il selon la norme EN 206-1 avec un indice d'activité de 0,76. C'est pourquoi nous l'avons utilisé pour élaborer trois ciments composés de type CEM 11/A avec une classe de résistance de 42,5 lorsque le taux de substitution est de 10% et une classe de résistance de 32,5 lorsque Je taux de substitution est de 15% et 20%. Des mortiers normaux ont été élaborés à partir de ces ciments et caractérisés sur les plans physiques et mécaniques. La durabilité des mortiers a également été étudiée notamment du point de vue de la cinétique de carbonatation et de lixiviation en présence de nitrate d'ammonium. Il ressort en définitive que la poudre de mâchefer peut bien être incorporée comme addition dans l’élaboration de ciments composés. Les caractéristiques mécaniques à long terme (90 jours) et la durabilité des mortiers confectionnés à partir de ces ciments sont conservées lorsque le taux de substitution n'excède pas 10%. / This research is part of a process of valorization of local industrial by-products in the cement industry. lt focuses on the possibility f using coal bottom ash powder produced by SONICHAR in Niger as cement partial addition. After a physicochemical and environmental characterization of the coal bottom ash powder, we determined its pozzolanic reactivity and it mechanical activity index. The results show that the coal bottom ash powder presents a pozzolanicity whose relatively slow kinetics do ne start before 14 days. On the other hand, this coal bottom ash can be considered as a mineral addition of type 11 according to the standard EN 206-1 with an activity index of 0.76. This is why we used it to develop three CEM 11/A composite cements with a strength class of 42.5 when the substitution rate is 10% and a strength class of 32.5 when the rate of substitution is 15% and 20%. Normal mortars have been formulated with these cements and are characterized physically and mechanically. The durability of the mortars has also been studied, in particular from the point of view of the kinetics of carbonation and leaching in the presence of ammonium nitrate. Finally, it appears that the coal bottom ash powder may indeed be incorporated as an addition in the preparation of composite cements. The long-term mechanical characteristics (90 days) and the durability of the mortars made from these cements are preserved when the substitution rate does not exceed 10%.
7

Effet de la température et de l'agitation sur les propriétés rhéologiques des bétons fluides à rhéologie adaptée / Effect of the temperature and the agitation on the rheological properties of the flowable concrete with a suitable rheology

Pan, Jing 30 June 2015 (has links)
Le climat local, le transport avec l’agitation entre l’endroit de bétonnage et le site de fabrication du béton influencent fortement les propriétés du béton frais et durci. Selon les particularités du béton autoplaçant (BAP), le maintien de l’homogénéité et l’ouvrabilité du BAP avant la mise en place est très important. Les propriétés des BAP sont généralement plus sensibles à la température et au transport par rapport à celles des bétons conventionnels. Une meilleure compréhension de l’effet de la température et de l’agitation sur la performance des BAP est nécessaire pour prévoir les conséquences du changement du climat (température) et de l’effet du transport (temps et vitesse d’agitation), puis pour donner des précautions à suivre afin de répondre à la demande des BAP pour un bon rapport performance-coût.De manière pragmatique, il s’avère nécessaire d’utiliser la méthode du mortier de béton équivalent (MBE) afin d’analyser rapidement les influences de la température et de l’agitation sur les propriétés rhéologiques, calorimétriques et mécaniques des BAP. Cinq températures (8, 15, 22, 29 et 36°C) et deux vitesses d’agitation (6 et 18 tr/min) ont été étudiées sur les MBE. Ensuite, quelques compositions spécifiques (type d’adjuvant et ajout cimentaire) ont choisies afin de vérifier avec des températures compasse entre 8 à 36°C et les agitations différentes (2 et 6 tr/min) sur les BAP destinés aux travaux de bâtiment (BAP-B) sans agent entraîneur d’air et sur des bétons semi-autoplaçant destinés aux travaux d’infrastructures (BSAP-I) avec agent entraîneur d’air. La fluidité initiale des MBE et BAP a été fixée en faisant varier la demande en SP, la température et l’agitation.Les résultats montrent qu’il y a un effet important de la température et de l’agitation sur l’efficacité des adjuvants, la fluidité, la teneur en air, les propriétés rhéologiques, calorimétriques et mécaniques des MBE et des BAP. Pour prévoir la performance de MBE à différentes températures, une équation mathématique est proposée pour déduire la demande en SP, la demande en AEA, le flux maximal et la résistance en compression à 1 jour en fonction des mêmes propriétés sur MBE à 22°C et de la température. Enfin, une corrélation linéaire a été trouvée entre les MBE et les BAP sur ces mêmes propriétés. / The local climate, the transport of agitated concrete after manufacturing but before being cast strongly influence the properties of the fresh and hard concrete. It’s important to keep the stability and workability of the self-consolidating concrete (SCC) because of its special characteristics. Compare to the normal concrete, the properties of SCC are generally more sensitive to the temperature and the transport. Therefore it’s necessary to understand the effects of the temperature and the agitation on the performance of the SCC in order to predict the consequences of climate change (temperature) and transport (time and speed of agitation), and then to give the better precautions with a good performance-cost report. In this study, the concrete mortar equivalent (CEM) method is used to quickly analyze the influences of the temperature and the agitation on the rheological, calorimetric and mechanical properties of the SCCs. Five temperatures (8, 15, 22, 29 and 36 °C) and two agitation speed (6 and 18 tr/min) are varied in CEMs. And then, some compositions (type of adjuvant and supplementary cementing material) are chosen to be valued with the temperature (8-36 °C) and the agitation (2 and 6 tr/min) in SCCs for the building without air-entraining admixture (AEA) and semi-flowable SCC for infrastructure with AEA. The initial slump flow of CEM and SCC is fixed, but the demand superplasticizer, the temperature and the agitation were varied. The results show that there are the effects of temperature and agitation on the effectiveness of admixture, the slump flow, the air content, the rheological, calorimetric and mechanical properties of CEM and SCC. A mathematical equation is proposed to predict the performance of SCC at different temperatures for the SP and AEA requirement, the maximum of heat flow and the compressive strength at one day by these same properties of SCC at 22 °C and by the temperature. Finally, a good linear correlation is found between CEM and SCC for these properties.
8

Particle Engineering by Spherical Crystallization:Mechanisms and Influence of Process Conditions

Thati, Jyothi January 2011 (has links)
Spherical agglomerates of benzoic acid crystals have been successfully prepared by drowning-out crystallization in three solvent partial miscible mixtures. Benzoic acid is dissolved in ethanol, bridging liquid is added and this mixture is fed to the agitated crystallizer containing water as the anti-solvent. Small crystals are produced by crystallization of the substance, and the crystals are agglomerated through the action of the bridging liquid. Different solvents: chloroform, toluene, heptane, pentane, cyclohexane, ethyl acetate and diethyl ether are chosen as bridging liquids, all being low soluble in water and showing good wettability for benzoic acid crystals. The influence of process conditions such as concentration of solute, agitation rate, feeding rate, amount of bridging liquid and temperature on the properties of benzoic acid spherical agglomerates, are investigated. Different sets of experiments were accomplished to track how the properties of the particles gradually change during the normal spherical crystallization experiment. Other sets of experiments were performed to examine the influence of agitation and process time for agglomeration. The product properties such as particle size distribution, morphology and mechanical strength have been evaluated. The mechanical strength of single agglomerates has been determined by compression in a materials testing machine, using a 10 N load cell. Compression characteristics for single agglomerates are compared with the data on bed compression. The present study shows that the bridging liquid has significant influence on the product properties, using diethyl ether and ethyl acetate no agglomerates are formed. Using any of the other five solvents (chloroform, toluene, heptane, pentane, and cyclohexane) spherical agglomerates are formed, as long as a sufficient amount of the bridging liquid is used. Using cyclohexane as bridging liquid at 5°C and toluene at 20°C the particles are larger compared to particles formed at other conditions. The highest particle fracture stress is obtained by using toluene as the bridging liquid at 5 and 20°C. Particle morphology depends on the bridging liquid used and the particles are completely spherical when toluene and pentane are used as bridging liquids. Different process parameters are found to have a significant influence on the physico-mechanical properties of the product. The range of operation for spherical agglomeration is relatively narrow and only at certain conditions spherical agglomerates are produced. With increasing amount of bridging liquid the particle size and strength increase and the morphology improves. Particle size decreases and the fracture force increases with increasing feeding rate, but the morphology remains unchanged. For all the solvents, the particle size and the fracture stress increase with decreasing temperature. For four of the solvents the morphology improves with decreasing temperature. For cyclohexane the result is the opposite, in that the particles are spherical at 20°C and irregular at 5°C. Spherical agglomerates of benzoic acid, both as single particles as well as in the form of a bed, have a high compressibility and low elastic recovery, properties that are favorable for direct tabletting. As the feed solution is supplied to the crystallizer the amount of benzoic acid that can crystallize actually does crystallize fairly rapidly. Hydrodynamics are responsible for bringing particles together for the agglomeration. Experiments reveal that during the gradual addition of the feed to the agitated aqueous solution, both particle size and particle number increases. It is clear from the experiments that not only further addition of feed solution leads to larger product particles but also continued agitation. Along the course of the process the properties of the particles change gradually but substantially. By continued agitation, the particle porosity decreases, density, strength gradually increases and also the spherical shape develops gradually. / QC 20110419
9

Avaliação das propriedades mecânicas e reológicas de composições de borracha nitrílica vulcanizadas com resina fenólica / Avaliação das propriedades mecânicas e reológicas de composições de borracha nitrílica vulcanizadas com resina fenólica / Evaluatin of mechanical and rheological properties of vulcanized nitrile rubber compositions with phenolic resin / Evaluatin of mechanical and rheological properties of vulcanized nitrile rubber compositions with phenolic resin

José Luiz Leite Sanchez 26 June 2008 (has links)
Neste trabalho de Dissertação de Tese, composições do copolímero de butadieno-acrilonitrila (NBR) foram vulcanizadas utilizando como agentes de vulcanização, a resina fenólica e o enxofre, com diferentes proporções de resina fenólica e uma única proporção de enxofre. O sistema ativador foi composto por policloropreno e óxido de zinco para as composições com resina fenólica, enquanto que por ácido esteárico e óxido de zinco para a composição com enxofre. Os materiais foram vulcanizados em uma temperatura de 190C. Foi avaliada a influência da variação dos componentes das composições sobre as propriedades reométricas, físico-mecânicas e reológicas dos materiais. Para auxiliar na interpretação dos resultados obtidos para as propriedades reométricas e físico-mecânicas, foi utilizado um planejamento estatístico de análise de variância para verificar a possibilidade da influência das variáveis e suas possíveis combinações nas propriedades avaliadas. Para as composições vulcanizadas com resina fenólica, os resultados mostraram que a composição de borracha nitrílica se tornou mais rígida com a presença da resina. Também foi observada a ocorrência de pós-cura nas composições vulcanizadas com resina fenólica. Os ensaios reológicos revelaram uma homogeneidade nas amostras submetidas aos testes de varredura de deformação, com desvio de linearidade a partir de 10% de deformação. / In this Thesis Dissertation, acrylonitrile-butadiene rubber (NBR) compositions were vulcanized using phenolic resin and sulfur as vulcanization agents with different proportions of phenolic resin and only one proportion of sulfur. The activator system was composed of polycloroprene and zinc oxide to phenolic resin compositions, while stearic acid and zinc oxide to sulfur composition. The materials were vulcanized in a temperature of 190C. The influence of the components content on rheometric, physico-mechanical and rheological properties of the materials was evaluated. In order to assist in the interpretation of the to physico-mechanical and rheometric properties results, a statistical planning of variant analysis was used to observe a possible influence of the variables and also their possible associations into the evaluated properties. The results showed that the nitrile rubber become more stiffness with the presence of phenolic resin. It was also observed the occurrence of post-vulcanization on the compositions vulcanized with phenolic resin. The rheological results showed homogeneity of the samples submitted to a strain sweep test, with a linear plateau until 10% of strain.
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Avaliação das propriedades mecânicas e reológicas de composições de borracha nitrílica vulcanizadas com resina fenólica / Avaliação das propriedades mecânicas e reológicas de composições de borracha nitrílica vulcanizadas com resina fenólica / Evaluatin of mechanical and rheological properties of vulcanized nitrile rubber compositions with phenolic resin / Evaluatin of mechanical and rheological properties of vulcanized nitrile rubber compositions with phenolic resin

José Luiz Leite Sanchez 26 June 2008 (has links)
Neste trabalho de Dissertação de Tese, composições do copolímero de butadieno-acrilonitrila (NBR) foram vulcanizadas utilizando como agentes de vulcanização, a resina fenólica e o enxofre, com diferentes proporções de resina fenólica e uma única proporção de enxofre. O sistema ativador foi composto por policloropreno e óxido de zinco para as composições com resina fenólica, enquanto que por ácido esteárico e óxido de zinco para a composição com enxofre. Os materiais foram vulcanizados em uma temperatura de 190C. Foi avaliada a influência da variação dos componentes das composições sobre as propriedades reométricas, físico-mecânicas e reológicas dos materiais. Para auxiliar na interpretação dos resultados obtidos para as propriedades reométricas e físico-mecânicas, foi utilizado um planejamento estatístico de análise de variância para verificar a possibilidade da influência das variáveis e suas possíveis combinações nas propriedades avaliadas. Para as composições vulcanizadas com resina fenólica, os resultados mostraram que a composição de borracha nitrílica se tornou mais rígida com a presença da resina. Também foi observada a ocorrência de pós-cura nas composições vulcanizadas com resina fenólica. Os ensaios reológicos revelaram uma homogeneidade nas amostras submetidas aos testes de varredura de deformação, com desvio de linearidade a partir de 10% de deformação. / In this Thesis Dissertation, acrylonitrile-butadiene rubber (NBR) compositions were vulcanized using phenolic resin and sulfur as vulcanization agents with different proportions of phenolic resin and only one proportion of sulfur. The activator system was composed of polycloroprene and zinc oxide to phenolic resin compositions, while stearic acid and zinc oxide to sulfur composition. The materials were vulcanized in a temperature of 190C. The influence of the components content on rheometric, physico-mechanical and rheological properties of the materials was evaluated. In order to assist in the interpretation of the to physico-mechanical and rheometric properties results, a statistical planning of variant analysis was used to observe a possible influence of the variables and also their possible associations into the evaluated properties. The results showed that the nitrile rubber become more stiffness with the presence of phenolic resin. It was also observed the occurrence of post-vulcanization on the compositions vulcanized with phenolic resin. The rheological results showed homogeneity of the samples submitted to a strain sweep test, with a linear plateau until 10% of strain.

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