Crystallization,structure and properties of MgO-Al2O3-SiO2 highly crystalline transparent glass-ceramics nucleated by multiple nucleating agents

Generally, highly crystalline transparent glass-ceramics possess excellent physical and chemical properties compared to organic and other inorganic optical materials. We have successfully prepared highly crystalline transparent glass-ceramics in the MgO-Al₂O₃-SiO₂ system by "extreme-time" nucleation & "finite-time" crystallization processes using P₂O₅, ZrO₂ and TiO₂ as multiple nucleating agents. The results revealed that the crystallization of glass is controlled by a three-dimensional interfacial crystal growth process. These glass-ceramics mainly consisted of cordierite crystals with a residual glassy phase, and crystallinity increased with crystallization time, but light transmittance decreased with crystallization time due to enlarged grain sizes. EDS mapping revealed a uniform distribution of elements within the glass-ceramic. In the optimal preparation condition (825?°C/96?h?+?990?°C/3?h), these glass-ceramics exhibited a high crystallinity (87.3?vol. %), high transmittance (78%), and excellent mechanical properties. This work provides a roadmap for preparing highly crystalline transparent glass-ceramics for applications in optical engineering.     

Glass forming,crystallization, and physical properties of MgO-Al2O3-SiO2-B2O3 glass-ceramics modified by ZnO replacing MgO

This study focused on the glass forming, crystallization, and physical properties of ZnO doped MgO-Al₂O₃-SiO₂-B₂O₃ glass-ceramics. The results show that the glass forming ability enhances first with ZnO increasing from 0 to 0.5 mol%, and then weakens with further addition of ZnO which acted as network modifier. No nucleating agent was used and the crystallization of studied glasses is controlled by a surface crystallization mechanism. The predominant phase in glass-ceramics changed from α-cordierite to spinel/gahnite as ZnO gradually replaced MgO. The phase type did not change; however, the crystallinity and grain size in glass-ceramics increased when the glasses were treated from 1030 °C to 1100 °C. The introduction of ZnO can improve the thermal, mechanical, and dielectric properties of the glass-ceramics. The results reveal a rational mechanism of glass formation, crystal precipitation, and evolution between structure and performance in the xZnO-(20-x)MgO-20Al₂O₃-57SiO₂-3B₂O₃ (0 ≤ x ≤ 20 mol%) system.     

Effect of ZnO/K2O ratio on the crystallization sequence and microstructure of lithium disilicate glass-ceramics

The effect of ZnO/K₂O (Z/K) ratio on the crystallization sequence and microstructure of lithium disilicate (Li₂Si₂O₅: LS2) glass-ceramics was carefully investigated for the SiO₂-Li₂O-K₂O-ZnO-P₂O₅ system. The Z/K ratios of precursor glasses were varied from 0 to 3.5 while the nucleating agent of P₂O₅ and glass modifiers of ZnO plus K₂O were fixed to have 1.5 and 4.5 mol% relative to LS2, respectively. For the samples prepared by two-stage heat treatments of 500 °C for 1 h and 800 °C for 2 h in air, the LS2 nucleation rate was increased with increasing the Z/K ratio due to the variation in crystallization sequence from type II (Li₂SiO₃: LS) to type I (LS + LS2) in addition to an amorphous phase separation in base glass. Consequently, with increasing the Z/K ratio, the LS2 crystalline phase within the glass matrix continuously changed from larger acicular ones to smaller equiaxed ones.     

Thermo-magnetic properties of Fe2O3-doped lithium zinc silicate glass-ceramics for magnetic applications

The crystallization behaviour and thermo-magnetic characteristics of glass-ceramic based on the 15Li₂O–20ZnO–10CaO–55SiO₂ system doped with varied Fe₂O₃ additions (0.0125, 0.025, and 0.05 mol) are described in this work. In some cases, Al₂O₃ was also added to the iron-containing sample. Glasses were successfully prepared by melt-quenching technique and converted into glass-ceramics by controlled heat-treatment, using DTA, SEM, XRD, and VSM techniques. The density, thermal expansion coefficients (TCE), and magnetic characteristics of the glass-ceramic were examined. XRD results confirmed characteristic peaks for various phases like quartz, Li₂ZnSiO₄, wollastonite, Li₂Si₂O₅, ZnFe₂O₄, and β-spodumene. By doping Fe₂O₃ and Al₂O₃ with lowering annealing temperature, the particle size was reduce, resulting in glass-ceramics with a more uniform and dense microstructure. The density of glass-ceramics rises from 2.74 g/cm³ to 3.45 g/cm³, whereas the TCE values in average 14–78 × 10⁻⁷/°C with temperature range of 25–500 °C. The doped glass-ceramics have superior magnetic properties with saturation magnetization (0.143–0.548 emu/g), the coercivity force (65.116–86.359 G), and remanence magnetization (0.074–0.436 emu/g). Under an alternating magnetic field, the presence of the Zn-ferrite phase in the glass-ceramics improves their magnetic properties and increases their heat-generating capability. Certain features of the doped glass-ceramics control the extensive variety of possibilities for their usage in various magnetic applications particularly for cancer hyperthermia treatment.     

Combined sodium and fluorine promote diopside continuous growth to achieve one-step crystallization in CaO-Al2O3-SiO2-Fe2O3 glass-ceramics

In CaO-Al₂O₃-SiO₂-Fe₂O₃ (CASF) glass-ceramics, a dense silicon and aluminum tetrahedral network barrier layer is formed around the diopside nucleus, which hinders the continuous growth of the crystal. In this work, the continuous growth of the diopside crystals was achieved by introducing sodium and fluorine. A combination of FTIR, XRD, SEM and EDS were used to analyze the evolution mechanism of the precursor glass network structure and the growth process of the diopside. The modification mechanism of sodium and fluorine action on the glassy structure was revealed by ²⁹Si NMR. The results showed that sodium and fluorine can selectively destroy the [SiO₄]/[AlO₄] network structure. The Ca²⁺ diffusion channels formed around diopside, which facilitated the continuous growth of the crystals. The diopside crystals can grow to an expected size, approximately 1 μm, when the value of NBO/T reaches 1.44.     

Effects of B2O3 substitution for Al2O3 on the crystallization and properties of translucent mica glass-ceramics

The effects of substituting Al₂O₃ with B₂O₃ on the structure, crystallization, mechanical properties, thermal properties and optical properties of translucent mica glass-ceramics were thoroughly investigated. The results demonstrated that the addition of 0.5 wt% B₂O₃ was optimum for glass precipitation, which increases the crystallinity of glass-ceramics and provides good translucency. When the content of B₂O₃ was greater than 0.5 wt%, both crystallinity and translucency decreased noticeably. The replacement of B₂O₃ for Al₂O₃ had no influence on the type of crystal phase and the precipitation of tetrasilicic fluoromica with non-stoichiometric ratio, while it did have an effect on the crystallinity and structure. The crystal sizes of glass-ceramics were in the nanoscale range and the transmittance test results indicated that they exhibit excellent translucency.     

含Bi2O3的MgO-Al2O3-SiO2玻璃核化与晶化动力学研究

使用差热分析(DTA)的方法研究了含Bi2O3的MgO-Al2O3-SiO2玻璃粉末(粒度≤0．054mm)的核化与晶化动力学。由此方法确定了样品最大成核速度温度，同时计算出晶体生长的活化能和动力学参数。结果表明，含Bi2O3玻璃的晶化指数(n)和晶体生长维数(m)都为1．15(约等于1)，这说明该玻璃的晶化机制是表面晶化。由Kissinger和Augis—Bennett方程计算出的活化能较为接近，平均值为401kJ／mol。     

Effects of crystallization temperature on phase evolution and energy storage properties of BaO-Na2O-Nb2O5-SiO2-Al2O3 glass-ceramics

Barium sodium niobate (BNN) glass ceramics were successfully fabricated with controllable crystallization by technology for heating processing and the effects of crystallization temperatures on phase evolution, microstructure, dielectric properties and breakdown strength were investigated systematically. In addition, the empirical power-law dependence of breakdown strength on thickness ($E_b\propto d^{-n}$) was confirmed in BNN glass-ceramic system with an exponent n of 0.21. Based on the results, the BNN glass ceramic crystallized at 800?°C presents a remarkable breakdown strength (BDS) of 2322?kV/cm with the tested thickness of 30?μm, and the highest energy density of 16.6?J/cm³ was achieved.     

Effect of Li2O on the crystallization behavior of CaO-Al2O3-SiO2-Li2O-Ce2O3 mold slags

The effect of Li₂O on the crystallization properties of CaO-Al₂O₃-SiO₂-Li₂O-Ce₂O₃ slags was investigated. With increasing the Li₂O content, LiAlO₂ and CaCeAlO₄ were the main crystalline phases. LiAlO₂ formed for the charge compensating of Li⁺ ions to [AlO₄^5?]-tetrahedrons, and CaCeAlO₄ formed as a result of the charge balance of Ce³⁺ ions, Ca²⁺ ions, and [AlO₆^9?]-octahedrons. Increasing the content of Li₂O to 10%, the crystallization temperature was the highest, and the incubation time was the shortest. The crystallization ability was strong due to the three factors of strengthening the interaction between ions and ion groups, decreasing the polymerization degree, and increasing the melting temperature. Further increasing the content of Li₂O, the crystallization performance was obviously suppressed, because the melting temperature and the force between the cations and the anion groups decreased.     

Effect of TiO2 on the crystallization,thermal expansion and wetting behavior of Nd2O3-Al2O3-SiO2 glass ceramic filler

The crystallization behavior, microstructure, crystalline phases, microhardness, coefficient of thermal expansion (CTE), and wetting behavior of Nd₂O₃-Al₂O₃-SiO₂ (NAS) glass ceramics with different TiO₂ content were investigated. The results show that the content of crystals increases and the size of crystals decreases with the increase of TiO₂ content. Moreover, the formation of Nd₂SiO₅ leads to the increase and the precipitation of Al₆Si₂O₁₃ results in the decrease in the CTE value of NAS glass ceramics. As a result, the CTE of NAS glass ceramics can be controlled in the range of 4.2–9.2 × 10⁻⁶/℃. These values are suitable for matching bonding to most ceramics with different CTE. Indeed, contact angle measurement demonstrates that the NAS glasses with 3 %, 6 % and 9 % TiO₂ possess excellent wettability on the Al₂O₃, ZrO₂ and zirconia toughened alumina (ZTA) ceramic, respectively.     

Effect of crystallization temperature on dielectric and energy-storage properties in SrO-Na2O-Nb2O5-SiO2 glass-ceramics

The SrO-Na₂O-Nb₂O₅-SiO₂ (SNNS) glass-ceramics were prepared through the melt-quenching combined with the controlled crystallization technique. XRD results showed Sr₆Nb₁₀O₃₀, SrNb₂O₆, NaSr₂Nb₅O₁₅ with tungsten bronze structure and NaNbO₃ with the perovskite structure. With the decrease of crystallization temperature, dielectric constant firstly increased and then decreased, while breakdown strength (BDS) was increased. High BDS of the glass-ceramics is attributed to the dense and uniform microstructure at low crystallization temperature. The optimal dielectric constant of 140±7 at 900 °C and BDS of 2182±129 kV/cm at 750 °C were obtained in SNNS glass-ceramics. The theoretical energy-storage density was significantly improved up to the highest value of 15.2±1.0 J/cm³ at 800 °C, which is about 5 times than that at 950 °C. The discharged efficiency increased from 65.8% at 950 °C to 93.6% at 750 °C under the electric field of 500 kV/cm by decreasing crystallization temperature.     

Preparation and luminescence properties of Eu2O3 doped glass-ceramics containing NaY(MoO4)2

Eu₂O₃ doped transparent glass-ceramics containing NaY(MoO₄)₂ crystalline phase were prepared via melting-crystallization. The optimum heat treatment condition (660℃/3h) was determined by DSC, XRD, SEM and transmittance curves. The transmittance of glass-ceramic can reach 80 % in the visible region. The emission spectra of Eu₂O₃ doped glass-ceramics consist of Eu³⁺ ions characteristic emission peaks at 591nm (⁵D₀→⁷F₁) and 614nm (⁵D₀→⁷F₂). The optimal doping concentration of Eu₂O₃ in the glass-ceramics is 0.9 mol%, and fluorescence lifetime is 1.37042ms. The change of the ratio of red emission intensity to orange emission intensity leads to the shift of chromaticity coordinates from orange to red region, and the chromaticity coordinate (0.6337, 0.3635) of 0.9 mol% Eu₂O₃ doped glass-ceramic is closest to the standard red light coordinate. The results show that this kind of glass-ceramic is expected to be good red emission material.     

TiO_2对MgO-Al_2O_3-SiO_2-TiO_2-La_2O_3系微晶玻璃相变和微波介电性能的影响

采用高温熔融法和-步法微晶化热处理制备了MgO-Al_2O_3-SiO_2-TiO_2-La_2O_3(MASTL)微晶玻璃。利用差热分析、X射线衍射、扫描电子显微镜和网络分析仪等手段研究了TiO_2含量对MASTL玻璃析晶相变过程、显微结构和微波介电性能的影响。结果表明,在玻璃热处理过程中先后有硅钛铈矿、金红石(TiO_2)、镁铝钛酸盐、尖晶石(MgAl_2O_4)和堇青石(Mg_2Al_4Si_5O_(18)))5种晶相析出。其中,镁铝钛酸盐含量相对较低,尖晶石是一个亚稳过渡相。随着TiO_2含量的增多,原始玻璃的析晶倾向增大,初晶相硅钛铈矿和主晶相金红石的析晶温度显著降低,而尖晶石的析晶温度升高;材料的介电常数和谐振频率温度系数均显著增大,这主要由样品中具有高介电常数(100.0)和较大正温度系数(400×10~(-6)/℃)的金红石相含量增多引起。同时,由于高品质因数相堇青石(40000GHz)的析出量略有减少,品质因数有所降低。     

MO对B2O3-Al2O3-SiO2系统玻璃析晶性能的影响

研究了添加BaO、CaO、MgO对B2O3-Al2O3-SiO2系统玻璃析晶性能的影响。用DSC测试了玻璃的析晶温度，用XRD分析了玻璃析晶后的晶相组成，用SEM观察了析出晶粒的形貌特征。结果表明：BaO、CaO均可有效促进BAS玻璃的形成，而MgO易导致玻璃分相。MO-BAS玻璃的析晶温度在770～810℃之间。添加BaO时析出的主晶相为硼酸铝（Al18B4O33）和少量勃来石（Al16B6Si2O37），以针柱状晶为主。用CaO替代BaO，析出的主晶相不变，但析晶能力增加，以细小的粒状晶为主。添加MgO时析出的主晶相为偏硼酸铝（Al4B2O9）和勃来石，晶粒较粗大。     

Effect of boron on crystallization,microstructure and dielectric properties of CBS glass-ceramics

Herein, we demonstrate the preparation of CBS glass-ceramics by using chemically pure CaO, SiO₂ and B₂O₃ as raw materials. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrical measurements have been carried out to explore the effect of boron addition on crystallization, microstructure and dielectric properties of CBS glass-ceramics. Furthermore, the influence of sintering temperature and sintering schemes has been systematically investigated. Results show that the increase of boron content reduces crystallization temperature of CBS glass-ceramics. For instance, with the increase of boron oxide from 10.8?wt% to 19.4?wt%, crystallization temperature decreased by 130?°C. However, excessive boron affects the precipitation of wollastonite crystal phase, destroys crystal structure and damages close arrangement of crystal grains. Moreover, higher boron content weakens dielectric properties of CBS glass-ceramics. In this study, the best molar ratio of ingredients, meeting the ideal target material, is n(Ca): n(Si): n(B) =?1:1:0.6. After optimal sintering procedure, dielectric constant of the best sample was 6 (1?MHz), 6 (10?MHz), and dielectric loss was 2.27?×?10^?3 (1?MHz) and 3.37?×?10^?3 (10?MHz). We demonstrate that the optimal boron content and sintering procedure is required to attain desired dielectric properties of CBS glass-ceramics.     

Influence of barium oxide on the crystallization, microstructure and mechanical properties of potassium fluorophlogopite glass-ceramics

The influence of barium oxide, heat treatment time and temperature on the crystallization, microstructure and mechanical behavior of the system Ba_x·K_1−2x·Mg₃·Al·Si₃O₁₀·F₂ (where x = 0.0, 0.3 and 0.5) was investigated in order to develop novel, high strength and machinable glass-ceramics. Three glasses were prepared and characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscope (SEM) techniques and some mechanical testing methods.The crystallization kinetics of glass-ceramics was also studied. Activation energy and Avrami exponent calculated for the crystallization peak temperature (T_p) of three different glass batches. The Vickers hardness decreased slightly on formation of the potassium fluorophlogopite and barium fluorophlogopite phases, but decreased significantly on formation of an interconnected ‘house of cards’ microstructure.     

Influence of Cr2O3, LiF, CaF2 and TiO2 nucleants on the crystallization behavior and microstructure of glass-ceramics based on blast-furnace slag

Glass-ceramics based on blast-furnace slag (56.78 wt%) were prepared by mixing quartz sand, dolomite, limestone, clay as other batch constituents.The nucleating agents Cr₂O_3, LiF, CaF₂ and TiO₂ were added to the batches to study their effects on the crystallization, phase assemblages, and microstructure. Glass-ceramics were obtained by single and double heat-treatment schedules and examined by DTA, XRD and polarizing microscope. The presence of Cr₂O_3, TiO_2, CaF₂ and LiF was found to enhance the crystallizability of the glass. Cr₂O₃ and TiO₂ are much better than LiF and CaF₂ in promoting homogeneous nucleation and the formation of extremely fine-grained microstructure of aluminous pyroxene and magnetite.     

Phase evolution and microwave dielectric properties of MgO-B2O3-SiO2-based glass-ceramics

The densification and crystallization behaviors of MgO-B₂O₃-SiO₂ (MBS) glass with various amounts of TiO₂ additions (0-10 wt.%) were investigated by means of thermal analysis, X-ray powder diffraction and scanning electron microscopy. A microwave dielectric characterization was performed in order to evaluate the suitability of MBS glass-ceramics as a low-permittivity dielectric substrate. The densification of the MBS glass started below 700 °C. The main crystalline phases of Mg₂B₂O₅ and MgSiO₃ appeared at 800 and 950 °C, respectively. The Mg₃TiB₂O₈ and TiB_0.024O₂ phases additionally crystallized in TiO₂-added MBS glass-ceramics at 1000 °C. The permittivity increased from 6.1 in pure MBS glass to 6.9 in MBS glass with 10 wt.% of TiO₂. The addition of TiO₂ enhanced the crystallization and consequently increased the Qxf-values of the MBS glass (11 300 GHz) up to 16 500 GHz. The improvement of the Qxf-values became the most evident at 1050 °C. Dense MBS glass-ceramics sintered at 850 ≤ T ≤ 950 °C exhibited Qxf-values of 5000-8000 GHz (at ∼12 GHz), which are comparable with the values of CaO-B₂O₃-SiO₂-based glass-ceramics.     

Magnetite-based glass-ceramics prepared by controlled crystallization of borosilicate glasses: Effect of nucleating agents on magnetic properties and relaxation

The specific magnetic structure and magnetic relaxation phenomena in magnetite nanoentities grown in a glassy matrix by controlled crystallization of Fe-containing borosilicate and boroaluminosilicate glasses in the presence of two types of nucleating agents, Cr₂O₃ and P₂O₅, were investigated. The structure, morphology and magnetic properties are strongly influenced by the nucleating agents. Cr₂O₃ generates magnetite-based glass ceramics with magnetite configurations showing an upward relaxation of magnetization at low and high temperatures but downward at intermediate temperatures. The magnetite grown with P₂O₅ displays only downward relaxation but with different signs of the temperature derivative of the relaxation rate S in different temperature ranges. The observed effects are discussed with respect to the following factors: i) the existence of a multimodal size distribution of the magnetite (nano)particles as revealed by high resolution electron microscopy; ii) the degree of occupation of different sublattices of the magnetite structure with Fe³⁺ and Fe²⁺ ions; and iii) the interplay between the relaxation mechanisms in different temperature ranges.     

Effect of different nucleating agent ratios on the crystallization and properties of MAS glass ceramics

The effects of different kinds of nucleating agents on crystallization, microstructure and performances of Magnesium Aluminosilicate (MgO-Al₂O₃-SiO₂, MAS) glass-ceramics which were fabricated by melting method in this study. Also, this paper systematically investigated the mechanism of glass stability, crystallization kinetics and element distribution of MAS glass-ceramics. Herein, we used three kinds of nucleating agents, which was TiO₂, ZrO₂ and composite nucleating agent (TiO₂/ZrO₂). The results showed after the doping of nucleating agent, the content of α-cordierite was increased, the stability and crystallization kinetics of glass was changed, the precipitated crystal phase was finer and more compact. Wherein, the sample with composite nucleating agents (TiO₂, ZrO₂) has the best performance due to the highest contents of α - cordierite, uniform distribution of elements without agglomeration in the crystal phase and the most compact structure, whose Vickers hardness and bending strength can reach 9.70 GPa and 312 MPa, respectively.