doktorska disertacija
Tadej Lešer (Avtor), Andreja Goršek (Mentor), Ivan Anžel (Komentor)

Povzetek

Frite so steklaste snovi in so glavna surovina za nastanek emajlov in keramičnih prevlek. Nastanejo s taljenjem v talilnih pečeh, čemur sledi hitra ohladitev taline in tvorba grobega granulata. Za nanos na ustrezno površino se venomer meljejo, večinoma v velikih bobnastih mlinih, kar je časovno dolgotrajno in energetsko neugodno. Na drugi strani tehnologija vodne atomizacije, ki se v svetu večinoma uporablja za proizvodnjo kovinskih prahov, omogoča torbo prahov direktno ob ohlajanju taline. Enostavnost procesa in njegova velika prilagodljivost sta nas privedli, da smo se odločili raziskati možnost uporabe te tehnologije za tvorbo prašnatih frit. Študija je temeljila na raziskavi dveh kompozicijsko različnih frit, frite A in B, ki smo ju primerjali s fritami enakih vhodnih sestav, proizvedenih po klasičnem postopku izdelave. Primerjali smo kemijske in fizikalne lastnosti atomiziranih in ne-atomiziranih (klasično taljenih) prahov frit, kakor tudi emajlov, nastalih iz njih. Prahove smo s pomočjo modernih preiskovalnih metod, kot so: rentgenska fluorescenčna spektrometrija, rastrska elektronska mikroskopija, diferencialna dinamična kalorimetrija s termogravimetrično analizo, dilatometrija itd., podrobno okarakterizirali in ovrednotili. Emajlom smo ocenili njihovo površino, veznost, barvno usklajenost in kislinsko odpornost. Rezultati študije so pokazali, da obstaja velika možnost za uporabo te tehnologije za tvorbo prašnatih frit. Velikost in morfologija prahov sta bili odvisni predvsem od kemijske sestave frit in atomizacijskih parametrov. Atomizirani prahovi so v primerjavi z ne-atomiziranimi izkazovali popolnoma drugačno morfologijo, pri čemer je bolj viskozna frita (frita A) tvorila bolj nepravilne delce, manj viskozna (frita B) pa sferične. Klasično taljeni friti sta obe izkazovali morfologijo tipično za nastanek prahov s procesom mletja, vidni so bili značilno odrezani robovi in ploskve. Z razvitjem enačbe za izračun časa strjevanja (tstr) in z upoštevanjem izračuna časa sferoidizacije (tsfr) smo pridobili model, ki opisuje obliko delcev posameznih velikosti, ob spremembi procesnih parametrov ter lastnosti frit. Izračunana časovna razmerja (R(tstr/tsfr)) so uspešno potrdila nastalo morfologijo atomiziranih frit. Opazili smo tudi izredno močno interakcijo med delci ter med delci in razprševalnim sredstvom (vodo), ki je imela velik vpliv na končno morfologijo. Delci so se pri interakciji poškodovali, deformirali in preoblikovali, kar je pri fritah v primerjavi s kovinskimi sistemi zaradi njihove krhkosti še bolj zaznano. Velikostna porazdelitev delcev je bila odvisna od viskoznosti frit oziroma od stopnje pregretja taline, pri čemer smo za frite dognali, da potrebujejo za uspešno atomizacijo, zaradi svoje velike viskoznosti, višjo temperaturo pregretja (okoli 300%400 °C), kakor kovine in zlitine. Bolj fine porazdelitve so se med drugim tvorile ob višjem tlaku razprševalnega sredstva ter manjši izlivni odprtini vmesne posode (tundisha). Tako atomizirani, kot ne-atomizirani prahovi so imeli podobne lastnosti, pri čemer so atomizirane frite, zaradi višje hitrosti ohlajanja dosežene pri atomizaciji, imele višjo temperaturo steklastega prehoda (Tg) kakor tudi ostale transformacijske temperature (temperatura sintranja, zmehčanja itd.). Emajli atomiziranih frit so imeli podobne kemijske, mehanske in optične lastnosti, kar potrjuje ustreznost uporabljene tehnologije atomizacije. Izračun ekonomske upravičenosti procesa je pokazal, da bi se nam ob predvidenih stroških in prihodkih, ki se vsekakor lahko spremenijo (nižja nakupna cena naprave, boljša optimizacija porabljene energije itd.) in znatno zmanjšajo čas vračanja naložbe, investicija v vodno atomizacijo za proizvodnjo prahov frit povrnila v okoli 35,5 letih.

Ključne besede

frite;emajli;vodna atomizacija;mikrostrukture;mletje;

Podatki

Jezik: Slovenski jezik
Leto izida:
Tipologija: 2.08 - Doktorska disertacija
Organizacija: UM FKKT - Fakulteta za kemijo in kemijsko tehnologijo
Založnik: [T. Lešer]
UDK: 544.431.142:57.012.3(043.3)
COBISS: 18404886 Povezava se bo odprla v novem oknu
Št. ogledov: 1568
Št. prenosov: 167
Ocena: 0 (0 glasov)
Metapodatki: JSON JSON-RDF JSON-LD TURTLE N-TRIPLES XML RDFA MICRODATA DC-XML DC-RDF RDF

Ostali podatki

Sekundarni jezik: Angleški jezik
Sekundarni naslov: Atomization of frits
Sekundarni povzetek: Frits are vitreous materials and the main raw material for the formation of enamel and ceramic coatings. They are produced with melting in melting furnaces, which is followed by rapid cooling of the melt and the formation of coarse granules. For the application to the appropriate surface frits are always milled, mostly in the large ball mills, which is time and energy consuming. On the contrary, water atomization technology, which in the world is being mostly used for the production of powders of metals and alloys, enables the powder to be directly formed upon the cooling of the melt. Ease of the process and its high flexibility lead us to explore the possibility of using this technology for the production of powdered frits. The study was based on the research of two compositionally different frits, frits A and B, which were compared with frits of same input configurations produced by the conventional manufacturing process. We then compared the chemical and physical properties of the atomized and non-atomized (conventional) powder frits, as well as the formed enamels from them. The powders were investigated using modern analytical techniques, such as X-ray fluorescence spectrometry, scanning electron microscopy, differential scanning calorimetry with thermogravimetric analysis, dilatometry, etc. Next the surface of the formed enamels was evaluated for their adherence, color consistency and acid resistance. Results of the study showed that there is a great possibility for using this technology for the formation of powdered frits. The size and morphology of the powders were depended mainly on the chemical composition of the frits and the atomization parameters. The atomized powders in comparison to the non%atomized ones showed a completely different morphology, wherein the more viscous frit (frit A) formed more irregular particles and less viscous (frit B) more spherical. The morphology of both conventional frits showed a typical formation of particles known of the grinding powders, with cut edges and surfaces. By developing the equation for calculation of solidification time (tstr) and by using the expression for spheroidization time (tsfr), we obtained a model that describes the morphology of particles with different sizes with the change of process parameters and properties of frits. The time ratios (R(tstr/tsfr)) have successfully confirmed the resulting morphology of the atomized frits. Additionally, we also observed a strong interaction between the particles, as well as between the particles and the dispersing media (water), which has had a major impact on the final morphology. The particles were due to large interaction damaged, deformed and transformed, which is for frits because of their brittleness in comparison to metal systems a more decisive factor that influences the end morphology. The distribution of the particles was dependent upon the viscosity of the frits and the degree of melt superheating. For frits we have established, that in order to successfully atomize them, because of their high viscosities, a higher temperature of overheating is needed (around 300-400 °C), as for metals and alloys. Finer distributions were formed at higher water pressures and lower orifice openings of the tundish. The atomized and the non-atomized powders had similar characteristics; however, atomized frits, due to the higher cooling rates achieved in atomization, demonstrated higher glass transition temperatures (Tg) as well as all the other temperatures of transformation (sintering temperature, softening temperature, etc.). Enamels formed from the atomized frits had similar chemical, mechanical and optical properties, which verify the appropriateness of the new technology. The calculation of the economic eligibility of the process has shown that at expected costs and revenues, which certainly can change (e.g. lower purchase price of the atomization device, better optimization of used energy, etc.) and significantly reduce the return on investment, the investment in water atomization to produce frit powders would be recovered in about 35.5 years.
Sekundarne ključne besede: frits;enamels;water atomization;microstructure;miling;
URN: URN:SI:UM:
Vrsta dela (COBISS): Doktorska disertacija
Komentar na gradivo: Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Strani: XVIII, 128 str.
ID: 8702622