Synthesis and characterization of polyphosphate glasses with addition of strontium and lanthanum

[V. S. Topalović]

122 str.

Tehnološko inženjerstvo - Hemijsko inženjerstvo / Technological engineering - Chemical engineering

Predmet rada ove doktorske disertacije bio je dobijanje i karakterizacija polifosfatnih stakala sa dodatkom stroncijuma i lantana. U ispitivanjima su korišćene metode: atomska apsorpciona spektroskopija (AAS), spektrofotometrija (SF), rendgenska difrakcija (XRD), metoda piknometra (određivanje gustine), infracrvena spektroskopija (FTIR), diferencijalna skenirajuća kalorimetrija (DSC), skenirajuća elektronska mikroskopija (SEM) i termomikroskopija (HSM). Prva faza istraživanja obuhvatala je sintezu i karakterizaciju četiri fosfatna stakla. Dva stakla su dobijena uvođenjem SrO u sistem, a dva uvođenjem La2O3. Karakterizacija stakala obuhvatala je ispitivanje fizičkih i strukturnih karakteristika stakala, kristalizacionih karakteristika i sinterabilnosti. Za određivanje strukturnih karakteristika stakala- korišćena je metoda infracrvene spektroskopske analize. Kristalizacione karakteristike stakala ispitivane su pri izotermskim i neizotermskim uslovima. Vrednosti energija aktivacije kristalizacije, Ea, rastu sa povećanjem količine stroncijuma i lantana u staklima. Ponašanje prahova stakala pri sinterovanju je ispitivano pomoću termomikroskopa. Dodatkom stroncijum- i lantan-oksida povećava se stabilnost stakla, a relativno visoke vrednosti parametara stabilnosti ukazuju na veću otpornost stakla procesu kristalizacije. Vrednosti energija aktivacije viskoznog toka, ΔGη, rastu sa povećanjem količine stroncijuma i lantana u staklima. Druga faza istraživanja obuhvatila je sinterovanje prahova fosfatnih stakala i ispitivanje uticaja temperature sinterovanja na strukturne karakteristike, fazni sastav, poroznost i tvrdoću. Temperature sinterovanja prahova stakala određene su primenom termomikroskopske i DSC analize. Kristalne faze su identifikovane XRD analizom termički obrađenih uzoraka. Utvrđeno je prisustvo bioaktivnih faza β-CaP2O6, α-Ca3(PO4)2 i β-Ca3(PO4)2. Svi uzorci sinterovani na Tp imaju veću poroznost od uzoraka sinterovanih na Tms, što ukazuje da je ova poroznost uslovljena kristalizacijom. Tvrdoća sinterovanih uzoraka određena je metodom po Vikersu i pokazano je da sa porastom poroznosti tvrdoća uzoraka opada. Treća faza istraživanja obuhvatala je analizu hemijske postojanosti uzoraka u rastvoru simulirane telesne tečnosti. Masa uzoraka je merena na analitičkoj vagi pre i posle eksperimenta, pH vrednost rastvora određivana je pH metrom, a koncentracije elemenata u rastvoru određivane su metodama AAS i SF. Sa porastom sadržaja SrO rastvorljivost stakla u SBF-u se povećava, dok se kod stakala sa lantanom rastvorljivost smanjuje sa povećanjem sadržaja La2O3. Uzorci stakala sa stroncijumom sinterovani na Tms i Tp pokazuju slabu rastvorljivost u SBF-u, čak i za najduže eksperimentalno vreme. Najveću rastvorljivost pokazuje uzorak sa nižim sadržajem lantana, sinterovan na Tms. Rezultati ovog istraživanja omogućavaju određivanje uticaja toplotne obrade na mikrostrukturu staklo-keramike dobijene kontrolisanom kristalizacijom fosfatnih stakala i uticaj uslova sinterovanja na mikrostrukturu staklo-keramike dobijene sinter-kristalizacijom. Ključne reči: polifosfatno staklo, stroncijum-oksid, lantan-oksid, karakterizacija stakla, sinter-kristalizacija, staklo-keramika, hemijska postojanost

The subject of this doctoral dissertation was the preparation and characterization of polyphosphate glasses with the addition of strontium and lanthanum. The following methods were used in the tests: atomic absorption spectroscopy (AAS), spectrophotometry (SF), X-ray diffraction (XRD), pycnometer method (density determination), infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and thermomicroscopy (HSM). The first phase of the research included the synthesis and characterization of four phosphate glasses. Two glasses were obtained by introducing SrO into the system, and two by introducing La2O3. The characterization of the glasses included examination of the physical and structural characteristics of the glasses, crystallization characteristics and sinterability. The method of infrared spectroscopic analysis was used to determine the structural characteristics of glasses. The crystallization characteristics of the glasses were examined under isothermal and non-isothermal conditions. The values of crystallization activation energies, Ea, increase with increasing amounts of strontium and lanthanum in the glasses. The behavior of glass powders during sintering was investigated using a thermomicroscope. The addition of strontium and lanthanum oxide increases the stability of the glass, and the relatively high values of the stability parameters indicate a greater resistance of the glass to the crystallization process. The values of the viscous flow activation energies, ΔGη, increase with increasing amounts of strontium and lanthanum in the glasses. The second phase of the research included sintering of phosphate glass powders and examination of the influence of sintering temperature on structural characteristics, phase composition, porosity and hardness. The sintering temperatures of glass powders were determined using thermomicroscopic and DSC analysis. The crystalline phases were identified by XRD analysis of heattreated samples. The presence of bioactive phases β-CaP2O6, α-Ca3(PO4)2 and β- Ca3(PO4)2 was determined. All samples sintered at Tp have higher porosity than samples sintered at Tms, which indicates that this porosity is due to crystallization. The hardness of the sintered samples was determined by the Vickers method and it was shown that the hardness of the samples decreases with the increase in porosity. The third phase of the research included the analysis of the chemical stability of the samples in a simulated body fluid solution. The samples were measured on an analytical balance before and after the experiment, the pH value of the solution was determined with a pH meter, and the concentrations of elements in the solution were determined by the AAS and SF methods. As the SrO content increases, the solubility of the glass in SBF increases, while the solubility of the lanthanum glasses decreases with the increase in the La2O3 content. Samples of strontium glasses sintered at Tms and Tp show poor solubility in SBF, even for the longest experimental time. The highest solubility is shown by the sample with lower lanthanum content, sintered at Tms. The results of this research allow determining the influence of heat treatment on the microstructure of glass-ceramics obtained by controlled crystallization of phosphate glasses and the influence of sintering conditions on the microstructure of glass-ceramics obtained by sinter-crystallization.

54.057:666.122.5(043.3)

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