Pigmentary titanium dioxide (TiO2) is the most important white pigment used in several industries, including those that manufacture plastic, coatings and paper. To achieve maximum efficiency in light scattering and to deliver the required opacity to the medium in which the TiO2 is present, the TiO2 particles must be fully dispersed throughout this medium. The particle dispersion in a cured, dry, or solid medium depends on the dispersion efficiency in the wet state, which depends on the effectiveness of the deagglomeration process. Based on the existing technical knowledge, the objective of this study is to investigate fundamental aspects in the dispersion process and to understand the effect of these processes on the required energy to deagglomerate pigmentary TiO2 particles in water. The fundamental aspects of particle wetting, dispersion and stability are reviewed as well as the theories of the tensile strength of agglomerates, particle roughness and liquid surface tension and viscosity. Although liquid surface tension and viscosity are the main factors that influence deagglomeration, some particle-related properties (particle radius, particle shape factor, agglomerate pore volume and specific surface area) play an important role in wetting behavior. The maximum mass of water adsorbed by the agglomerates is proportional to the liquid surface tension. The liquid adsorption rate is a function of the ratio between the liquid and solid surface tensions as well as the shape factor. In the present study, for any shape factor value, the lower the liquid surface energy is in relation to the solid surface tension, the larger the water adsorption rate. After characterizing the particles, the agglomerates and the liquid medium, and obtaining correlations between all properties and the energy to achieve maximum dispersion, a predictive model is proposed to describe the influence of liquid surface tension and the particle roughness on the energy required to produce liquid dispersions with minimum particle size. This model applies to different particles with similar surfaces and to particles with different surfaces but similar sizes. / Dióxido de titânio é o pigmento branco mais importante de diversas indústrias incluindo as de tintas, plásticos e papel. Para atingir sua máxima eficiência no espalhamento de luz, prover a opacidade requerida ao meio em que se encontra presente, as partículas devem estar completamente dispersas neste meio. A dispersão no meio sólido, seco ou curado dependerá da eficiência de dispersão no estado úmido, a eficiência da dispersão no estado úmido dependerá de quão efetivo foi o processo de desaglomeração. O objetivo deste trabalho é compreender como as propriedades do líquido e do sólido impactam a energia requerida para desaglomerar às partículas de dióxido de titânio pigmentário em um meio líquido. As teorias de umectação de partículas, dispersão e estabilidade foram revisadas assim como as teorias de tensão de coesão de aglomerados, rugosidade da partícula e viscosidade e tensão superficial de líquidos. O objetivo destas revisões foi determinar os fatores que influenciam o processo de desaglomeração e a energia requerida para que isso ocorra. Apesar das propriedades do líquido serem os principais fatores que influenciam o processo de desaglomeração (viscosidade e tensão superficial do líquido), as propriedades da partícula, ainda que sempre associadas a propriedades do líquido, desempenham um papel importante no comportamento de umectação (raio da partícula, rugosidade, volume dos poros do aglomerado e área superficial específica). Após a caracterização das propriedades das partículas, dos aglomerados e do meio, e analisar as correlações entre as propriedades e a energia necessária para atingir o máximo da dispersão um modelo preditivo foi desenvolvido para descrever a influencia da tensão superficial e da rugosidade na energia necessária para atingir o tamanho de partícula mínimo. Este modelo se aplica a diferentes partículas com superfícies similares e partículas com superfícies diferentes com tamanhos similares.

Pigmentary titanium dioxide (TiO2) is the most important white pigment used in several industries, including those that manufacture plastic, coatings and paper. To achieve maximum efficiency in light scattering and to deliver the required opacity to the medium in which the TiO2 is present, the TiO2 particles must be fully dispersed throughout this medium. The particle dispersion in a cured, dry, or solid medium depends on the dispersion efficiency in the wet state, which depends on the effectiveness of the deagglomeration process. Based on the existing technical knowledge, the objective of this study is to investigate fundamental aspects in the dispersion process and to understand the effect of these processes on the required energy to deagglomerate pigmentary TiO2 particles in water. The fundamental aspects of particle wetting, dispersion and stability are reviewed as well as the theories of the tensile strength of agglomerates, particle roughness and liquid surface tension and viscosity. Although liquid surface tension and viscosity are the main factors that influence deagglomeration, some particle-related properties (particle radius, particle shape factor, agglomerate pore volume and specific surface area) play an important role in wetting behavior. The maximum mass of water adsorbed by the agglomerates is proportional to the liquid surface tension. The liquid adsorption rate is a function of the ratio between the liquid and solid surface tensions as well as the shape factor. In the present study, for any shape factor value, the lower the liquid surface energy is in relation to the solid surface tension, the larger the water adsorption rate. After characterizing the particles, the agglomerates and the liquid medium, and obtaining correlations between all properties and the energy to achieve maximum dispersion, a predictive model is proposed to describe the influence of liquid surface tension and the particle roughness on the energy required to produce liquid dispersions with minimum particle size. This model applies to different particles with similar surfaces and to particles with different surfaces but similar sizes. / Dióxido de titânio é o pigmento branco mais importante de diversas indústrias incluindo as de tintas, plásticos e papel. Para atingir sua máxima eficiência no espalhamento de luz, prover a opacidade requerida ao meio em que se encontra presente, as partículas devem estar completamente dispersas neste meio. A dispersão no meio sólido, seco ou curado dependerá da eficiência de dispersão no estado úmido, a eficiência da dispersão no estado úmido dependerá de quão efetivo foi o processo de desaglomeração. O objetivo deste trabalho é compreender como as propriedades do líquido e do sólido impactam a energia requerida para desaglomerar às partículas de dióxido de titânio pigmentário em um meio líquido. As teorias de umectação de partículas, dispersão e estabilidade foram revisadas assim como as teorias de tensão de coesão de aglomerados, rugosidade da partícula e viscosidade e tensão superficial de líquidos. O objetivo destas revisões foi determinar os fatores que influenciam o processo de desaglomeração e a energia requerida para que isso ocorra. Apesar das propriedades do líquido serem os principais fatores que influenciam o processo de desaglomeração (viscosidade e tensão superficial do líquido), as propriedades da partícula, ainda que sempre associadas a propriedades do líquido, desempenham um papel importante no comportamento de umectação (raio da partícula, rugosidade, volume dos poros do aglomerado e área superficial específica). Após a caracterização das propriedades das partículas, dos aglomerados e do meio, e analisar as correlações entre as propriedades e a energia necessária para atingir o máximo da dispersão um modelo preditivo foi desenvolvido para descrever a influencia da tensão superficial e da rugosidade na energia necessária para atingir o tamanho de partícula mínimo. Este modelo se aplica a diferentes partículas com superfícies similares e partículas com superfícies diferentes com tamanhos similares.

The distribution of massive ground ice in the ground in Taylor Valley of the McMurdo Dry Valleys, Antarctica, is quite unknown, and could provide answers to questions such as where the ice comes from, if it has been affected and removed by proglacial lakes and how landscapes underlain by massive ground ice responds to climate change. It could also be a source for atmospheric information in the past and hence a key in climate research. The main goal with this project was therefore to map the distribution of massive ground ice mainly in Taylor Valley, but also in the adjacent Salmon Valley and Wright Valley, using ground penetrating radar to see how the distribution varied and if there was any spatial patterns. The technical computing programme MATLAB was used for editing of the raw radar data, merging of GPR profiles and digitalization of reflectors for possible massive ground ice and several compilations of different files. The data obtained from MATLAB was imported and interpreted using the geographic information system ArcGIS. A series of histograms showing the distribution of massive ground ice depending on the parameters elevation, slope and aspect were made by using the spreadsheet application Microsoft Excel. The results showed that the distribution of massive ground ice was more common at elevations up to 200 m, at the mouth of the valleys and also more frequent in Taylor Valley than in Wright Valley. There was a slightly higher amount of massive ground ice at northeast-east aspects, probably due to different incoming solar radiation. The lack of, or not that prominent, differences for slope and aspect can be due to lack of data, a not enough detailed digital elevation model or that it have existed for a too short period of time to display big differences caused by effects from these parameters. The higher frequency of massive ground ice in Taylor Valley can be due to a thicker sediment cover when compared with the situation in Wright Valley. The distribution of massive ground ice at different slopes seems to follow the distribution of radar measurements, whereas the origin of the massive ground ice and sediment cover can be responsible for the distribution across different elevations. The reason why massive ground ice still occurs despite the existence of Glacial Lake Washburn that previously occupied Taylor Valley could be that the glacial lake did not remain for a sufficiently long time to melt all the massive ice. Massive ground ice is very common in a zone that is believed to be very susceptible for future warming, which means that changes that already have been observed in areas rich in massive ground ice can continue to happen and changes in other areas with massive ice can be enabled. The ice can thus play a major role in the development of the landscape in the McMurdo Dry Valleys depending on the amount of warming. / Markis kan hittas i mark som har temperaturer under 0°C under åtminstone 2 år i följd och därav klassas som permafrost, skillnaden mellan markis och permafrost är däremot att permafrost inte behöver vara just is utan kan enbart vara kall mark. För att markis ska klassas som massiv is så ska andelen is i marken vara minst 250 % jämfört med vikten på torr jord. Utbredningen av sådan massiv is i Taylor Valley i McMurdos torrdalar på Antarktis är inte helt känd, och kunskapen om att veta vart den finns (om den finns) skulle kunna ge svar på frågor som vart den kommer ifrån, om den har påverkats och smält bort av isuppdämda sjöar och hur landskap som är grundade av massiv markis påverkas av klimatförändringar. Isen skulle även kunna vara en informationskälla för tidigare atmosfäriska förhållanden. Huvudsyftet med detta arbete var därför att kartlägga utbredningen av massiv is främst i Taylor Valley, men även i de närliggande dalarna Salmon Valley och Wright Valley, och undersöka hur utbredningen varierar beroende på olika landskapsegenskaper som påverkar dess förekomst. Datorprogrammet och programspråket MATLAB användes för att editera rådatat från radar-mätningarna i området, samt för att sammanföra och digitalisera horisonter för möjlig massiv markis i radarfigurerna och för ett antal sammanställningar av olika filer. Data erhållet från MATLAB importerades till det geografiska informationssystemet ArcGIS där det kunde visualiseras i kartor och tolkas. Ett antal histogram skapades i kalkylprogrammet Microsoft Excel för att visa frekvensen av massiv markis vid olika höjder, sluttningsvinklar och olika väderstrecksriktningar. Resultaten visade att det var mer vanligt med massiv is höjder upp till 200 m, vid mynningarna av dalarna samt i Taylor Valley jämfört med Wright Valley. Det var en aning mer vanligt med massiv markis vid nordöst-östliga sluttningsriktningar, vilket antagligen beror på olika mängder inkommande solstrålning till de olika riktningarna. Avsaknaden av, eller inte så märkbara, skillnader för olika sluttningsvinklar och riktningar kan bero på att mängden data var för liten, att höjdkartan inte var tillräckligt detaljerad eller att isen inte har funnits tillräckligt länge för att bli påverkad av dessa parametrar. Anledningen till att det finns mer massiv markis i Taylor Valley än i Wright Valley kan vara att det skyddande sedimenttäcket är tunnare i Wright Valley än i Taylor Valley. Frekvensen av massiv markis vid olika sluttningsvinklar verkar bero på det totala antalet mätningar gjorda, fler mätningar leder till en högre frekvens av markis, medan dess ursprung samt det antagna tunnare sedimenttäcket på högre höjder kan vara anledningen till de olika frekvenserna av massiv markis vid olika höjder. Anledningen till varför det fortfarande finns massiv markis trots existensen av den isuppdämda sjön Washburn som tidigare fanns i Taylor Valley, och att isen således inte helt har smält bort på grund av sjön, kan vara att den fanns under en för kort tid så att de långsamma termodynamiska processerna som skulle orsaka smältningen inte hann agera tillräckligt länge för att smälta all is. Den massiva markisen är vanlig i en zon som tros vara väldigt mottaglig för framtida uppvärmning, vilket betyder att landskapsförändringar som redan har observerats i områden med mycket massiv markis kan fortsätta att ske samtidigt som andra områden med massiv markis kan börja förändras. Isen kan därför spela en stor roll i landskapsutvecklingen i McMurdos torrdalar beroende på hur mycket varmare det blir i området.

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