Effects of nucleating agents on crystallization and microstructure of fluorophlogopite mica-containing glass–ceramics

Effects of M2+ (M = Ca, Sr, and Ba) Addition on Crystallization and Microstructure of SiO2-MgO-Al2O3-B2O3-K2O-F Glass

“…Potassium (K + ), being the network modifier ion, binds together with silicate anions (SiO 4 4− ) by electrostatic force of attraction and hence effectively acts as ionic bridges between two kinds of nonbridging oxygen (NBO). The addition of CaO, SrO, and BaO replacing K 2 O results in reducing the electrostatic forces between the kinds of nonbridging oxygen (NBO) considerably and hence decreases the value of glasses [12]. Likewise , density of M-2 (CaO content) and M-3 (SrO content) glass is reduced and evaluated as 2.61 and 2.55 g⋅cm −3 , respectively.…”

“…In addition, three low intense crystalline planes (200), (005), and (331) are developed due to phase reflections at 2 = 34.14, 45.50, and 60.34 ∘ . All these crystalline planes appeared due to the formation of crystalline phase fluorophlogopite mica, KMg 3 AlSi 3 O 10 F 2 (monoclinic end centered system, JCPDS file number 10-0494, molecular weight = 421.24, lattice parameter a = 5.299, b = 9.188, and c = 10.13), where the tightly bonded aluminosilicate sheets [Mg 3 (AlSi 3 O 10 )F 2 ] − are weakly bonded together by large 12coordinated K + ions [12]. In presence of CaO, SrO, and BaO, crystalline peak intensity is increased (as seen from Figure 3 Mg-rich phase MgF 2 on heating above annealing temperature (620 ∘ C).…”

“…Ca 2+ , Sr 2+ , and Ba 2+ having larger cationic field strength can form "cluster" to initiate heterogeneous phase separation. During the primary stage of crystallization event, very fine grained crystals of norbergite (Mg 2 SiO 4 ⋅MgF 2 ), MgF 2 , and mullite (3Al 2 O 3 ⋅2SiO 2 ) are developed [1,2,12,13]. Further heating results in increasing the crystallization of mullite phase.…”

“…And then a typical solid phase reaction of norbergite and mullite crystals with K 2 O-SiO 2 glass takes place which finally results in producing two-dimensional fluorophlogopite mica crystalline phase. Increase in the quantity of mica crystals occurs on further heating and, at 1050 ∘ C, the randomly distributed mica crystal predominates in the ceramic matrix [12].…”

“…The mica crystals possess excellent cleavage planes because of the weak attraction of alkali layers. Since the progression of crystallization in silicate based glass (predominated by Si-O-Si network) considerably depends upon the nature and composition of precursor material as well as thermal treatment, the addition of different alkaline earth metal ions can affect the crystallization characteristics and microstructural properties [4][5][6][7][8][9][10][11][12]. In addition, the alkaline earth ion plays significant role in controlling the glass transition temperature, softening point, thermal expansion, and density of aluminosilicate glass.…”