Two-step synthesis of niobium doped Na–Ca–(Mg)–P–Si–O glasses

Abstract

Niobium doped biosolubility glasses in the Na–Ca–(Mg)–P–Si–O system were prepared by using an untypical two-step synthesis route. The parent glass was melted in air atmosphere at 1350 °C followed by re-melting the glass in Nb crucible with the addition of metallic Mg/Ca powder in the nitrogen atmosphere. The second melting step was carried out at 1450–1650 °C, using an induction furnace. The topography and structure of the obtained glasses were characterized by confocal microscopy, X-ray powder diffraction and infrared spectroscopic techniques. The chemical compositions were examined by energy-dispersive X-ray spectroscopy (EDS). The glasses were found to be of grayish color, X-ray amorphous and having network connectivity between ~ 2.5 and 2.7. The network connectivity of re-melted glasses was lower than the one of the parent glass. The glass structure consists of a highly disrupted silicate network of predominantly Q2 groups as well as isolated orthophosphate tetrahedra. The parent glass contains nanocrystallites consisted of apatitic PO43− groups. The re-melted glasses contain non-apatitic or amorphous calcium phosphates. The obtained glass transition temperatures range from 530 to 568 °C and exhibit higher values for glassed doped with Ca metal. These glasses have improved thermal stability as compared to reference bioglasses. The biosolubility test in phosphate buffered saline solution (PBS) confirms that the glasses have biosolubility properties and HAp formation on the surfaces was observed.

DC and AC Conductivity, Biosolubility and Thermal Properties of Mg-Doped Na2O–CaO–P2O5 Glasses

“…To confirm the possible presence of hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ]) layer created during immersion or indicate the higher potential for HAp creation on the sample surface, the Ca/P ratio was studied. For silicate-based glass-ceramics, this value was close to 1.69 (in at %) [48,53], similar to HAp. For all tested glasses, the Ca/P ratio varied between 0.26 and 0.29 and slightly increased after immersion.…”

Niobate in silicate and phosphate glasses: Effect of glass basicity on crucible dissolution

“…This involves mixing oxide precursors, often supported by ball milling, melting of the mixture in an alumina or platinum crucible for certain time and, at the end, fast quenching to room temperature. Methods different than the conventional are also employed for the preparation of glasses including the sol-gel technique [11], melting in a reducing atmosphere [12][13][14][15], and twin roller very fast-cooling [16]. Sometimes, a two-step synthesis route is used as, for example, when incorporating nitrogen into silicate glass networks (e.g.…”

“…Emphasis was placed on glass basicity and its role on niobate dissolution from the crucible, by considering glasses close to metasilicate (~50 mol% SiO 2 ) and pyrophosphate (~30 mol% P 2 O 5 ) compositions as well as glasses with high SiO 2 content (~60 mol% SiO 2 ). The first two series of investigated glassy materials were prepared using a twostep synthesis route, which is only briefly summarized here since it was described elsewhere in more detail [12][13][14]. The last series was directly melted in niobium crucibles.…”

“…Therefore, the real compositions of all glasses were determined with the use of energy dispersive spectroscopy (EDS) technique on the fractured samples. Series I, P-doped meta-silicate [14] and Series II, phosphate rich [12] samples were tested using a high-resolution scanning electron microscope, SEM (LYRA3, TESCAN) equipped with EDS detector (EDAX). Series III, oxynitride silicate glasses [13] were investigated using a SEM (FEI Company Quanta FEG250), with Energy Dispersive X-ray Spectrometer (EDAX GENESIS Apex Apollo X60), as well as using an inductively coupled plasma optical emission spectrometer (ICP-OES, Hitachi High-Technologies Corp., Model SPS3520UV-DD) and a nitrogen and oxygen elemental analyzer (LECO Corp., TC-436AR).…”

“…Three different glass series were synthesized and compared: Series I, phosphate doped-metasilicate glasses Mg/Ca-Na 2 O-CaO-P 2 O 5 -SiO 2 (~50 mol% SiO 2 and up to 5 mol% P 2 O 5 ); Series II, phosphate rich glasses Mg-Na 2 O-CaO-SiO 2 -P 2 O 5 -P 3 N 5 close to the pyrophosphate composition (~30 mol % P 2 O 5 ); and Series III, Na 2 O/Li 2 O-BeO-SiO 2 -Si 3 N 4 glasses with high SiO 2 content (~60 mol% SiO 2 ). Samples of series I and II were prepared using the two step synthesis route and details of the used parameters are listed in Table 1, while the analyzed glass compositions are listed in Table 2 (see previous reports for synthesis details[12][13][14]). In excess to the nominal composition, Al and niobate were found in the as-prepared glasses.…”