Phase and microstructural evolution in lithium silicate glass‐ceramics with externally added nucleating agent

Abstract

Development of lithium disilicate‐based glass‐ceramics critically depends on use of nucleating agent in the glass matrix. The present study reports the effect of externally added nucleating agent Li3PO4 in Li2O–K2O–MgO–ZnO–ZrO2–Al2O3–SiO2 system which is compared with a reference composition (GC1) (SiO2:Li2O = 2.16:1) prepared with in situ formed Li3PO4. For externally added Li3PO4, two compositions were studied. In one case (GC2) before addition of Li3PO4, SiO2:Li2O ratio in glass was maintained as 2.87:1 and in another case (GC3) SiO2:Li2O ratio in glass was maintained same as reference GC1 that is, 2.16:1. The glasses were characterized by using MAS‐NMR spectroscopy. Sintering and crystallization behavior of the glass‐ceramics was characterized by using XRD, SEM, DTA. Due to in situ formation of Li3PO4, GC1 resulted in a dense sample with finer crystals of lithium disilicate. In GC2 and GC3, externally added lithium phosphate, which was in the form of ultrafine aggregated particles, formed flower‐like colonies of radially outward crystals. Higher SiO2:Li2O ratio in GC2 resulted in lithium disilicate crystals and high viscous glass causing large air entrapment and so less densification. GC3 with higher lithia in glass showed higher densification than GC2 but only lithium metasilicate crystals were formed.

Influence of heat treatment temperature on the properties of the lithium disilicate‐fluorcanasite glass‐ceramics

“…87–1149) as the minor phases. According to the XRD patterns that correspond to the previous studies, 16,36 it can be illustrated that the LM phase was first precipitated at T C1 . As confirmed by the DTA result, the LM phase reacts with the silica and transforms to the LD phase when the heat treatment temperature increases.…”

“…The results indicate that the samples have well-defined diffraction patterns with sharp and robust diffraction peaks when the heat treatment temperature increases, indicating the increase in the crystallinity of these glass-ceramics. The case of the LF1 and LF2 demonstrates the presence of only one primary crystalline phase of LM (Li 2 SiO 3 ; JCPDS No.70-0330), while the LF3 reveals the LM as the primary phase and two crystalline phases of LD (Li 2 Si 2 O 5 ; JCPDS No.17 correspond to the previous studies, 16,36 it can be illustrated that the LM phase was first precipitated at T C1 . As confirmed by the DTA result, the LM phase reacts with the silica and transforms to the LD phase when the heat treatment temperature increases.…”

A modified random network model for P2O5–Na2O–Al2O3–SiO2 glass studied by molecular dynamics simulations

“…10,18 The lowest priority of Si-O-P might cause immiscibility and phase separation, that is, P could serve as nucleating agent in silicate glasses. 49 Although the percentage of Si-O-Si connection decreases with increased P content, DPC SiSi has an increasing trend, indicating that P obviously improves the priority of Si-O-Si linkage, especially for LAP compositions, suggesting the formation of separated silicon-oxygen rich regions, which could induce the emerging of cristobalite (SiO 2 ) crystals aer heat treating. 50 Such complex bonding geometries might arise from the different value of ionic eld strength, P 5+ > Si 4+ > Al 3+ , leading to different NBO preference causing that [PO 4 ] units are mainly incorporated as ortho-and pyrophosphate units (Q 0 P and Q P 1 ) and show broad Q P n distribution with more NBO while [SiO 4 ] units mainly exist as Q Si 3 and Q Si 4 with less NBO, and [AlO 4 ] units mainly exist as Q Al 4 and are not sensitive with composition, suggesting that Si-NBO is strongly preferred than Al-NBO, which has been veried by 17 O MAS NMR experiments.…”

Crystallization behavior, chemical microstructure and surface morphology of a little HCl assisted lithium disilicate powders prepared by sol–gel method

“…+ ions reacted with Si-OH, and more Q 2 units appeared, as confirmed by the gradual loss of molecular water and Si-OH. In addition, because the crystallization activation energy of the LD phase is higher than that of the LM phase, 51) the LD phase begins to crystallize at higher temperatures, transforming from either Q 3 units or an intermediate LM phase. 50),52) Therefore, LD phase was detected after heat treatment at 600 °C, irrespective of the introduction of the HCl additive.…”