diplomsko delo
Rubina Viriant (Author), Matija Tomšič (Mentor)

Abstract

Razmerje strižne napetosti in strižne hitrosti pri pretoku tekočine imenujemo dinamična viskoznost tekočine. Dinamična viskoznost predstavlja merilo za notranji upor tekočine oziroma odraža odziv tekočine na ireverzibilno spremembo zaradi pretakanja. Dinamična viskoznost newtonskih tekočin je neodvisna od strižne hitrosti. Če v newtonskih tekočinah dispergiramo manjše trdne delce, pa takšne disperzije lahko kažejo lastnosti nenewtonskih tekočin. Viskoznost nenewtonskih tekočin je odvisna od strižne hitrosti pri pretakanju in jo običajno prikazujemo kot funkcijo strižne hitrosti. Večja kot je polidisperznost dispergiranih delcev v tekočini v smislu njihove velikosti, bolj gosto je lahko njihovo pakiranje v tekočini oziroma višja je lahko koncentracija njihove suspenzije. Energijska disipacija se lahko pri pretakanju nenewtonskih tekočin z višanjem strižne hitrosti poveča ali zmanjša. Povečanje energijske disipacije vodi k lastnosti, ki jo imenujemo dilatanca, ki pomeni višanje viskoznosti s povečevanjem strižne hitrosti in je v praksi običajno neželena, njeno zmanjšanje pa k psevdoplastičnosti, ki pomeni manjšanje viskoznosti s povečevanjem strižne hitrosti. Pri nekaterih nenewtonskih tekočinah lahko med pretakanjem in po njem opazimo pojav tiksotropije, ki pomeni časovno odvisno obnašanje s histerezno zanko strižne napetosti v odvisnosti od strižne hitrosti. Nekatere nenewtonske tekočine kažejo tako elastične kot tudi viskozne lastnosti, kar s skupnim izrazom imenujemo visko-elastične lastnosti. Pri našem delu smo obravnavali pet kompleksih nenewtonskih visoko koncentriranih kalcijevo karbonatnih suspenzij, ki se običajno uporabljajo v papirni industriji kot pigmentne suspenzije in se dodajajo v premazne mešanice za tretma površine papirja. Po sestavi so se med seboj razlikovale glede na porazdelitve velikosti kalcijevo karbonatnih delcev. Ovrednotili smo reološke lastnosti teh osnovnih pigmentnih suspenzij in tudi njihovih premaznih mešanic s škrobom in lateksom.

Keywords

disperzni sistemi;nenewtonske tekočine;porazdelitev velikosti delcev;premazne mešanice;reometri;diplomska dela;

Data

Language: Slovenian
Year of publishing:
Typology: 2.11 - Undergraduate Thesis
Organization: UL FKKT - Faculty of Chemistry and Chemical Technology
Publisher: [R. Viriant]
UDC: 544.77.023.522:532.135(043.2)
COBISS: 128994307 Link will open in a new window
Views: 48
Downloads: 6
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Other data

Secondary language: English
Secondary title: The influence of the size distribution of calcium carbonate particles on the rheological properties of their suspensions
Secondary abstract: The ratio between shear stress and shear rate as the fluid flows is called the dynamic viscosity of the fluid. Dynamic viscosity is the measure of the internal resistance of the fluid – it reflects the response of the fluid to the irreversible change due to flow. The dynamic viscosity of the Newtonian fluids is independent of the shear rate. When small solid particles are dispersed in Newtonian fluid, such dispersions can exhibit the properties of non-Newtonian fluids. The viscosity of non-Newtonian fluids depends on the shear rate during flow and is usually expressed as a function of shear rate. The greater the polydispersity of the dispersed particles in the fluid in terms of their size, the denser their packing in the fluid can be or the higher the concentration of their suspension can be. Energy dissipation can increase or decrease with the increase of shear rate when flowing non-Newtonian fluids. The increase in energy dissipation leads to the property of dilatancy, i.e., the increase in viscosity with increasing shear rate, which is usually undesirable in practice; its decrease leads to the pseudoplasticity, i.e., the decrease in viscosity with increasing shear rate. In some non-Newtonian fluids, the occurrence of thixotropy during and after flow can be observed, i.e., time-dependent behaviour with a hysteresis loop of shear stress as a function of shear rate. Some non-Newtonian fluids exhibit both elastic and viscous properties, commonly referred to as visco-elastic properties. In our work, we studied five complex, non-Newtonian, highly concentrated calcium carbonate suspensions commonly used as pigment suspensions in the paper industry and added to coating mixtures for surface treatment of paper. They differed in composition due to the different calcium carbonate particle size distributions. We studied the rheological properties of these basic pigment suspensions and their coating colours with starch and latex.
Secondary keywords: calcium carbonate;rheology;non-Newtonian fluids;coating colours;particle size distribution;Kalcijev karbonat;Reologija;Univerzitetna in visokošolska dela;
Type (COBISS): Bachelor thesis/paper
Study programme: 1000373
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za kemijo in kemijsko tehnologijo, UNI Kemija
Pages: 42 str.
ID: 16411117