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## Rola monoakryloilopochodnych wybranych oligohydroksyzwiązków w odlewaniu żelowym ceramiki zaawansowanej

### Agnieszka Szudarska

#### Abstract

Dynamic development of the industry and technology gives a lot of high and new demands on all the branches of material engineering. Advanced ceramics finds a lot of new application, what inspires many researches on the technologies of its manufacturing, in particular methods of shaping. One of the newest methods that allows to fabricate ceramic elements of complex shape and high quality at quite low production cost is the gelcasting process. The most essential issue concerning the application of this method is a proper selection of the monomer, which polymerises in situ in the ceramic slurry in a controlled way, transforming the suspension into gel. Commercially available monomers do not meet all the technological expectations. Most commonly used acrylamide is highly toxic, and the low toxic alternative 2-hydroxyethyl acrylate is not efficient enough. That is why the researches on finding new environmentally friendly compounds, that would perform well the role of monomers in gelcasting, are carried out more often. Recently much interest is given to saccharides and their derivatives, as they are renewable, inexpensive and easily available compounds. The literature contains reports on the positive effect of these compounds on the rheological properties of the slurries composed from nanometric alumina. Due to the presence of many hydroxyl groups, they are also able to form hydrogen-bonded crosslinked structures, without the need of a crosslinker, which is a great advantage in the view of the technological process of gelcasting. In this work, the method of selective synthesis of two entirely new monomers from the group of polyhydroxycompounds was elaborated. The synthesised derivatives are: 6-O-acryloyl-D-galactose, as a representative of the group acryloylmonosaccharides, and 1-O-acryloyxylitol – representative of polyols. A number of studies verifying their functionality in gelcasting of ceramics based on alumina has been done, trying to determine their role in this process. As the reference monomer for individual results self-synthesized glycerol monoacrylate was used, whose high efficiency in the gelcasting gel was shown in previous works. The first stage of this research was focused on determining the rheological properties of the ceramic slurries containing alumina with newly synthesized compounds, and selecting the appropriate amount of each component in the suspensions. Alumina powder of average grain size of 0.7 μm (Nabalox) and 0.2 μm (TM-DAR) was used. All prepared slurries are thixotropic fluids, shear thinning, and are characterized by the presence of yield stress. Moreover, dispersing abilities of 6-O-acryloyl-D-galactose was observed and confirmed in the suspensions of alumina with submicron grain size. Then a series of ceramic elements was obtained and thei basic parameters have been measured. The assumption is confirmed, that the hydrogen bonds formed between mers provide a well crosslinked structure of the polymer, without the need of a special crosslinker. The greatest mechanical tensile strength (6.5 MPa) was recorded for the green elements containing small addition of poly(acryloyl-D-galactose) – 3wt% with respect to the amount of aluminum oxide. It makes that monomer outstanding from any other alternative gelling agents described in the literature. The high homogeneity of the microstructure of green products comprising a binder on the basis of all the applied monomers, confirmed by the pore size distribution analysis and SEM micrographs, resulted in their very good performance after sintering at 1600°C - high relative density of 99.3-99.6% and the bending strength 600-760 MPa. The sintering process and removal of the binder was carried out on the basis of a thermal analysis. The experience with gelcasting of alumina with application of 6-O-acryloyl-D-galactose was then used for the studies on the fabrication of textured ceramics by a novel combination of gelcasting in a strong magnetic field (12T). The major factors affecting the efficiency of the method were examined, such as the rheological properties of the slurries solid phase concentration, and particularly the idle time of polymerization and the time of exposure to the magnetic field, on which there is no data in the literature. In a relatively short time the elements were formed, characterized by a very high degree of crystalline orientation – 0.92-0.96, by gelcasting them from suspensions having a high concentration of alumina - 45-50 vol%, which is not possible by the other texturing techniques according to the literature. Thus, the studies have confirmed the mutlifunctionality of acrylol derivatives of selected polyhydroxycompounds, not limiting their role only as monomers providing in situ polymerization during gelcasting a ceramic slurry. As a result, the synthesised compounds can be an interesting alternative for the commercially available monomers and the ceramic industry can be attracted by the perspective of implementing the gelcasting technology.
Record ID
Diploma type
Doctor of Philosophy
Author
Agnieszka Szudarska Agnieszka Szudarska,, Chair of Chemical Technology (FC/CChT)Faculty of Chemistry (FC)
Title in Polish
Rola monoakryloilopochodnych wybranych oligohydroksyzwiązków w odlewaniu żelowym ceramiki zaawansowanej
Language
(pl) Polish
Certifying Unit
Faculty of Chemistry (FC)
Discipline
chemical technology / (technology domain) / (technological sciences)
Status
Finished
Defense Date
16-06-2014
Supervisor
Honored
yes
Pages
187
Keywords in English
alumina, gelcasting, low-toxic monomers
Abstract in English
Dynamic development of the industry and technology gives a lot of high and new demands on all the branches of material engineering. Advanced ceramics finds a lot of new application, what inspires many researches on the technologies of its manufacturing, in particular methods of shaping. One of the newest methods that allows to fabricate ceramic elements of complex shape and high quality at quite low production cost is the gelcasting process. The most essential issue concerning the application of this method is a proper selection of the monomer, which polymerises in situ in the ceramic slurry in a controlled way, transforming the suspension into gel. Commercially available monomers do not meet all the technological expectations. Most commonly used acrylamide is highly toxic, and the low toxic alternative 2-hydroxyethyl acrylate is not efficient enough. That is why the researches on finding new environmentally friendly compounds, that would perform well the role of monomers in gelcasting, are carried out more often. Recently much interest is given to saccharides and their derivatives, as they are renewable, inexpensive and easily available compounds. The literature contains reports on the positive effect of these compounds on the rheological properties of the slurries composed from nanometric alumina. Due to the presence of many hydroxyl groups, they are also able to form hydrogen-bonded crosslinked structures, without the need of a crosslinker, which is a great advantage in the view of the technological process of gelcasting. In this work, the method of selective synthesis of two entirely new monomers from the group of polyhydroxycompounds was elaborated. The synthesised derivatives are: 6-O-acryloyl-D-galactose, as a representative of the group acryloylmonosaccharides, and 1-O-acryloyxylitol – representative of polyols. A number of studies verifying their functionality in gelcasting of ceramics based on alumina has been done, trying to determine their role in this process. As the reference monomer for individual results self-synthesized glycerol monoacrylate was used, whose high efficiency in the gelcasting gel was shown in previous works. The first stage of this research was focused on determining the rheological properties of the ceramic slurries containing alumina with newly synthesized compounds, and selecting the appropriate amount of each component in the suspensions. Alumina powder of average grain size of 0.7 μm (Nabalox) and 0.2 μm (TM-DAR) was used. All prepared slurries are thixotropic fluids, shear thinning, and are characterized by the presence of yield stress. Moreover, dispersing abilities of 6-O-acryloyl-D-galactose was observed and confirmed in the suspensions of alumina with submicron grain size. Then a series of ceramic elements was obtained and thei basic parameters have been measured. The assumption is confirmed, that the hydrogen bonds formed between mers provide a well crosslinked structure of the polymer, without the need of a special crosslinker. The greatest mechanical tensile strength (6.5 MPa) was recorded for the green elements containing small addition of poly(acryloyl-D-galactose) – 3wt% with respect to the amount of aluminum oxide. It makes that monomer outstanding from any other alternative gelling agents described in the literature. The high homogeneity of the microstructure of green products comprising a binder on the basis of all the applied monomers, confirmed by the pore size distribution analysis and SEM micrographs, resulted in their very good performance after sintering at 1600°C - high relative density of 99.3-99.6% and the bending strength 600-760 MPa. The sintering process and removal of the binder was carried out on the basis of a thermal analysis. The experience with gelcasting of alumina with application of 6-O-acryloyl-D-galactose was then used for the studies on the fabrication of textured ceramics by a novel combination of gelcasting in a strong magnetic field (12T). The major factors affecting the efficiency of the method were examined, such as the rheological properties of the slurries solid phase concentration, and particularly the idle time of polymerization and the time of exposure to the magnetic field, on which there is no data in the literature. In a relatively short time the elements were formed, characterized by a very high degree of crystalline orientation – 0.92-0.96, by gelcasting them from suspensions having a high concentration of alumina - 45-50 vol%, which is not possible by the other texturing techniques according to the literature. Thus, the studies have confirmed the mutlifunctionality of acrylol derivatives of selected polyhydroxycompounds, not limiting their role only as monomers providing in situ polymerization during gelcasting a ceramic slurry. As a result, the synthesised compounds can be an interesting alternative for the commercially available monomers and the ceramic industry can be attracted by the perspective of implementing the gelcasting technology.
Thesis file
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urn:pw-repo:WUT652eb6a0a9a94ad7b2788f3443d6cead