Thermal stability of Na2O–FeO–Fe2O3–P2O5 glasses

Abstract

The crystallization tendencies of five series of Na 2 O-FeO-Fe 2 O 3-P 2 O 5 (NFP) glasses with different O/P (3.0-3.5) and Fe/P (0.13-0.67) ratios were studied. Characteristic temperatures, including the glass transition temperature (T g) and crystallization temperature (T x h), were obtained using differential thermal analysis (DTA), and liquidus temperatures (T L) were determined by microscopic evaluation of heat-treated samples. The compositional dependence of glass structure and the characteristic temperatures are discussed. The glass stability (GS) against crystallization is described using parameters based on the characteristic temperatures. For the glass series with O/P ratios near the pyrophosphate composition (O/P ~3.5), the glass stability goes through a minimum value around Fe/P ~ 0.3 to 0.4, which corresponds to the crystalline phase NaFeP 2 O 7 and Na 7 Fe 3 (P 2 O 7) 4 .

Thermal properties of 60P2O5–20Fe2O3–20Al2O3 glass for salt waste immobilization

“…All of the investigated glasses evidenced a quite good thermal stability comparable with conventional silicate glasses for which K H value varied from 0.14 to about 1.3 [16,[27][28][29][30]. The increasing Na 2 SO 4 addition causes decrease in the K H parameter which means lowering the glass stability against crystallization and at the same ability of glass to vitrify on cooling [30].…”

“…[22][23][24][25][26], and a nice comparison between them for iron phosphate glasses is given in [27], and most of those criterions show the similar dependence on glass composition. In case of iron phosphate glasses, one of the most frequently used is Hruby criterion, and therefore, the glass stability of the investigated materials was evaluated using it [16,27]. According to [22], the higher K H value, the greater would be its stability against crystallization.…”

A review of the structures of oxide glasses by Raman spectroscopy

“…The oxide glasses have variety of applications in the daily use articles as well as advanced technological fields like protection of X-ray, fibre, optical instruments or lab glasswares. The thermal stability of Na 2 O-FeO-Fe 2 O 3 -P 2 O 5 was found to be poorer than sodium-free 75 iron phosphate glasses [28]. In present review article, Raman spectroscopic results for structures of borate, silicate, phosphate, borosilicate, borophosphate, aluminosilicate, phosphosilicate, alumino-borosilicate and tellurite glasses are summarized.…”

Iron polyphosphate glasses for waste immobilization

“…For binary Fe‐phosphate glasses with O/P ratios between 3.0 and about 3.6, increasing the O/P ratio decreases T g , a trend consistent with the relative melting points of Fe(PO 3 ) 3 and Fe 4 (P 2 O 7 ) 3 (Figure ). Crystallization tendency was maximized for compositions with O/P ratios around 3.3‐3.4, with the metaphosphate (O/P = 3) and pyrophosphate (O/P = 3.5) compositions less likely to crystallize.…”

“…Increasing the Fe/Na ratio in these pyrophosphate glasses increased the glass transition temperature, T g , and decreased its difference with the crystallization temperature ( T x ‐ T g ). Ma et al found a similar increase in crystallization tendency for pyrophosphate glasses with the replacement of Na 2 O with Fe 2 O 3 (O/P = 3.49) over the same compositional range, although melts with greater iron contents were less prone to crystallization. Adding high field strength oxides like Al 2 O 3 , B 2 O 3 , and SiO 2 increases the stability of iron phosphate melts against crystallization, whereas the additions of lower field strength oxides like the alkali and alkaline earths generally decrease stability against crystallization …”