PREPARATION AND CHARACTERIZATION OF GLASS-CERAMICS COMPOSITE FOR APPLICATION IN LTCC TECHNOLOGY

V delu opisujemo študijo kompozitov steklo-keramika, ki so primerni za pripravo večplastnih struktur na osnovi keramike z nizko temperaturo žganja (Low Temperature Co-fired Ceramics – LTCC). Osredotočili smo se na sintezo nizko taljivega stekla, pogoje drobljenja in mletja stekla, homogenizacijo steklaste faze in delcev korunda in določanje pogojev žganja kompozitov. Nizko taljivo silikatno steklo na osnovi SiO2, PbO, Al2O3, CaO, B2O3, Na2O, K2O, Cr2O3, CoO in MgO smo pripravili iz homogenizirane zmesi reagentov, ki smo jo kalcinirali pri temperaturi kalcinacije, T = 750 °C. Vzorec kalcinirane zmesi smo segrevali v segrevalnem mikroskopu in ugotovili, da se tali nad 1050 °C. Steklo, ki smo ga sintetizirali pri temperaturi, T = 1200 °, je bilo rentgensko amorfno, z enakomerno mikrostrukturo in z nizko temperaturo sintranja: začetek krčenja je bil pri temperaturi, T = 660 °C in končni skrček pri temperaturi, T = 780 °C, zato smo ga uporabili za nadaljnje delo. Za pripravo kompozitov smo morali steklasto fazo zdrobiti in zmleti. Na podlagi meritev velikosti in porazdelitve velikosti delcev stekla smo ugotovili, da je manjše vzorce z maso, m = 4 g primerneje drobiti s stresalnim mlinom, večje z maso m = 30 g pa z vibracijskim mlinom. Steklo smo nadalje mleli v planetarnem mlinu v vodnem mediju. Povprečna velikost delcev po 6 urah mletja je bila 2,10 µm. Korundni prah je bil precej grob, povprečna velikost delcev je bila 3,15 µm, zato smo ga mleli v atritorju. Po 90 minutah mletja se je povprečna velikost delcev zmanjšala na 1,32 µm. Nadalje smo pomleti fazi stekla in korunda v utežnem razmerju 50:50 homogenizirali v planetarnem mlinu v acetonu. Vzorce smo segrevali v komorni peči s hitrostjo, rs = 2 in 5 °C/min in pri časih t = 30, 60 in 120 min pri temperaturi T = 850 °C. Posnetki mikrostruktur sintranih vzorcev kažejo, da sta steklo in korund v kompozitih homogeno porazdeljena. V vseh vzorcih so bile prisotne pore mikronske velikosti. Vzorci, žgani krajši čas (rs = 2 °C/min, t = 30, min in rs = 5 °C/min, t = 30, 60 min), so bili rentgensko amorfni. Pri vzorcih, ki so bili žgani pri daljših časih, smo tako z rentgensko fazno analizo kot z energijsko disperzijsko spektroskopijo rentgenskih žarkov potrdili prisotnost faze anortita (CaAl2Si2O8). Lastnosti vzorcev kompozita steklo-korund smo primerjali s komercialnim vzorcem LTCC, pripravljenim pri enakih pogojih, to je pri temperaturi, T = 850 °C in pri časih t = 30, 60 in 120 min, in ugotovili, da imajo podobno gostoto, fazno sestavo in mikrostrukturo.We describe the study of the glass-ceramic composites, which could be used for processing of multilayer structures in Low Temperature Co-fired Ceramics (LTCC) technology. We focused on the synthesis of the low melting point glass, the conditions of its crushing and milling, homogenization of the glassy phase and corundum particles, and sintering and characterization of the composites. The glass based on SiO2, PbO, Al2O3, CaO, B2O3, Na2O, K2O, Cr2O3, CoO and MgO was prepared by homogenization of the reagents and calcination at the temperature, T = 750 °C. The as-calcined mixture melted at/above T = 1050 °, as determined by the heating stage microscope. The glass, synthesized at the temperature, T = 1200 °, was amorphous, with a uniform microstructure, and it sintered at low temperature: namely, the onset and the end of the shrinkage were at T = 660 °C and T = 780 °C, respectively, therefore it was selected for further work. Small (4 g) and large (30 g) batches of the mm-sized glass fragments were further crushed in a shaker mill and vibration mill, respectively. After milling in a planetary mill the mean particle size of the glass phase was 2,10 µm. The as-received corundum powder had the mean particle size of 3,15 µm, and before further use it was milled in an attrition mill, resulting in particles with the mean size of 1,32 µm. The as-milled glass and ceramic phases in the 50 : 50 weight ratio were homogenized in a planetary mill. The powder compacts were heated with the heating rate, r = 2 and 5 °C/min and times t = 30, 60 and 120 min at the temperature, T = 850 °C. The microstructures of the sintered samples reveal a homogeneous distribution of the two phases. Micron sized spherical pores were observed in all samples. The samples, which were heated for shorted periods (r = 2 °C/min, t = 30, min and r = 5 °C/min, t = 30, 60 min), were amorphous. The samples, heated for longer times, contained also the crystalline anorthite (CaAl2Si2O8) phase, as confirmed by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. We compared the properties of as-sintered glass-ceramic composites with a commercial LTCC material, sintered at the same temperature, T = 850 °C and times, t = 30, 60 and 120 min, and found that they both had quite similar density, phase composition and microstructure