Diopside-Based Glass-Ceramics Research Articles

Synthesis of schorl doped iron ore tailings glass-ceramics with superior performance

The diopside-based glass-ceramics were prepared by using iron ore tailings as main raw materials and schorl as additive. The addition of schorl was found to effectively reduce the crystallization activation energy and to promote the crystallization of diopside. The diopside and schorl were evenly distributed and sufficiently interlocked together, which improved the flexural strength and bulk density of glass-ceramics. The far-infrared emissivity of glass-ceramics increased with the addition of schorl due to intrinsic far-infrared characteristics of schorl, while the replacement of Mg and Si ions in diopside by Fe ions also contributed to the enhancing far-infrared emissivity due to lattice distortion and symmetry reduction of diopside crystal. At 10 wt.% schorl addition, the glass-ceramics was at its best, with flexural strength of 107.03 MPa, bulk density of 2.66 g/cm3, and far-infrared emissivity of 0.928. This work lays foundation to manufacture of high value glass-ceramics with superior properties utilizing waste iron ore tailings and schorl.

Diopside glass-ceramics were fabricated by sintering the powder mixtures of waste glass and kaolin

Glass-ceramics with diopside (CaMgSi2O6) as the main crystalline phase were prepared via low-temperature powder sintering method using waste glass and kaolin as starting materials. The effects of kaolin content and sintering temperature on phase composition, micro-structure and properties of as-prepared glass-ceramics were investigated by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. Research results showed that the addition of kaolin could promote the devitrification of waste glass during sintering. The formation of diopside crystalline phase mainly originated from the decrease of sodium ion contents in glass phase, which was caused by the crystallization of sodium aluminum silicate. Diopside-based glass-ceramics could be achieved under proper combination ratio of waste glass and kaolin, and raising sintering temperature was beneficial to formation of diopside. Glass-ceramics prepared by adding 25 wt% kaolin and sintered at 825 °C for 2 h showed a maximum bending strength of 114.9 MPa and a bulk density of 2.484 g/cm3.

Preparation and characterization of glass-ceramics with granite tailings and titanium-bearing blast furnace slags

The resource utilization of granite tailings and titanium-bearing blast furnace slags is an emphasis of current research and is widely considered. In this work, by adopting these two slags as raw materials, diopside-based glass-ceramics were synthesized by melting-cooling-monolithic crystallization. The influence of the content of granite tailings, namely, the ratio of (SiO2+Al2O3/CaO+TiO2) on the structure and properties of glass-ceramics was characterized with differential scanning calorimetry, X-ray diffraction, scanning electron microscope, volume density and microhardness. The results suggest that the introduction of granite tailings makes the melting quality of glass deteriorate and the crystallization tendency decrease, the number of microcrystalline in glass-ceramics decreases and the glass phase increases. Moreover, the increase of Si/O ratio is advantageous to the precipitation of wollastonite but not diopside, and the volume density and microhardness of glass-ceramics decrease with the increase of granite tailings. When the content of granite tailings is 40 wt%, the crystal structure of glass-ceramics is moderate, the volume density and microhardness are 3.0207 g/cm3 and 8.6 GPa, respectively, which are excellent for architectural decoration.

Recycling of Blast Furnace Slag and Fluorite Tailings into Diopside-Based Glass-Ceramics with Various Nucleating Agents’ Addition

Diopside-based glass-ceramics are successfully produced by recycling blast furnace slag and fluorite tailing with the addition of supplementary elements such as TiO2, Fe2O3 and Cr2O3 as nucleation agents, using a conventional melting method. The effects of various nucleating agents on the phase components and structure of the prepared glass-ceramics were evaluated by a differential scanning calorimeter, X-ray diffraction and scanning electron microscope–energy disperse spectrometer methods to determine the optimal dosage of nucleating agents. The results show that, in the preparation of diopside-based glass-ceramics, the suitable percentages of blast furnace and fluorite tailing are 55% and 45%, and the recommended composite nucleating agents consist of 1.5% Cr2O3, 2% TiO2 and 3% Fe2O3. Heat treatment was conducted at a nucleation temperature of 720 °C and a crystallization temperature of 920 °C, and the nucleation and crystallization durations were 1.0 h and 1.5 h, respectively. Under the abovementioned parameters, the obtained diopside-based glass-ceramics displayed a Vickers hardness of 7.12 GPa, density of 2.95 g·cm−3, water absorption of 0.02%, acid resistance of 0.23% and alkali resistance of 0.02%.

Crystal Growth Behavior, Nanometer Microstructure, and Mechanical Properties of Diopside-Based Glass-Ceramics.

In this study, to increase the light transmittance of diopside type crystallized glass, crystals with size of less than 100 nm, which is smaller than the visible light wavelength, were generated in the specimen. For this purpose, the so-called two-step process encompassing heat treatment at the nucleation temperature followed by heating the crystal at the crystal growth temperature was employed. The crystallization behavior of the prepared specimen was studied and the optical and mechanical properties were investigated according to the heat treatment conditions. The glass used in the experiment was CaO-MgO-2SiO₂, which is a stoichiometric composition of diopside crystals. Heat-treating temperatures for nucleation and crystal growth were determined by a nonisothermal thermal analysis using Differential Thermal Analysis (DTA). The most suitable heattreating conditions were nucleation at 761 °C/6 h and crystal growth at 880 °C/1 h. The generated diopside crystal size was below 100 nm on average and the light transmittance was as high as ~75% for most of the specimens and the parent glass specimen showed higher light transmittance than that of conventional commercialized semitransparent crystallized glass products. The bending strength of diopside-based glass-ceramics was 30 MPa and the fracture energy was 1.56 N/mm. The Avrami constant calculated from the Kissinger equation and the Augis-Bennett equation was 1.38 and the activation energy was 355.63 kJ/mol, and these value indicate surface crystallization behavior.

Comparison between incorporation and conventional fabrication techniques of diopside-based glass-ceramics

Crystallization kinetics was widely used for studying nucleation and crystallization mechanism in the materials. In this study, the crystallization kinetics via non-isothermal method of diopside glass-ceramics prepared by incorporation and conventional techniques, have been investigated. The difference between incorporation and conventional method is the use of a simple mixed-oxide technique for producing diopside powder and the powder is then mixed with a glass batch while that of conventional one uses only simple oxides as starting precursors. Therefore, in this work, the diopside powder was calcined at 1200 °C for 4 h and subsequently mixed with SiO2, Al2O3 and ZnO in the 30CaMgSi2O6:40SiO2 + 20Al2O3 + 10ZnO (mol%). For, the conventional method, the simple oxide powders of CaMgSi2O6 (stoichiometric composition) were used instead of the calcined CaMgSi2O6 powders, in similar glass formula. From the heating rate dependence on crystallization temperature, the activation energy (Ea) of crystallization and Avrami parameter (n) were calculated by Kissinger and Ozawa equation, respectively. It was found that these two methods show similar crystallization mechanism but the incorporation method tends to crystallize easier than that of conventional one.

Effect of CuO Addition on Thermal Properties of Diopside-Based Glass-Ceramics for LED Packaging

Effect of CuO Addition on Thermal Properties of Diopside-Based Glass-Ceramics for LED Packaging

Dependence of Eu3+ photoluminescence properties on structural transformations in diopside-based glass-ceramics

Herein, diopside based glass-ceramics (GCs) were produced by sintering of glass powder compacts at 850 °C for 300 h. A special attention was paid on understanding the influence of structural transformations upon substituting strontium for calcium on the Eu3+ emission behavior. X-ray diffraction and Raman spectra showed the formation of diopside (CaMgSi2O6) in Sr-free glasses. Introduction of Sr led to the appearance of Sr-akermanite (Sr2MgSi2O7), whose formation increased continuously with increasing Sr/Ca ratio. The photoluminescence spectra exhibited intense 5D0 →7Fj transitions of Eu3+ ions. The intensity parameters (Ω2 and Ω4) and the Eu–O ligand behavior were determined using the Judd-Ofelt (JO) theory from the emission spectra as a function of various Sr concentrations. The as obtained JO intensity parameters Ω2 (5.31–5.21 pm2) and Ω4 (4.89–5.84 pm2) indicated the ligand behavior of the Eu–O bonds and a high asymmetrical and covalent environment around Eu3+ ions in the present host matrix. In comparison with other Eu3+-doped GCs, diopside based GCs containing high fraction of SrO exhibited adequate photoluminescence for optical lighting and display devices.

Effect of a ZnO addition on the thermal properties of diopside-based glass ceramics for LED packages

Effect of a ZnO addition on the thermal properties of diopside-based glass ceramics for LED packages

Fabrication and Characterization of Diopside-based Glass-Ceramics from Granite Wastes

Diopside-based glass-ceramics were obtained by mixing 58.2∼61.5 wt% granite wastes with other components. Based on the CaO-MgO-Al2O3-SiO2 (CMAS) system, the effects of CaO/MgO ratio and heat treatment on crystallization, microstructure and properties of the glass-ceramics were investigated. Results showed that the crystallization peak temperature decreased with the replacement of CaO by MgO. Bulk crystallization of CMAS glass-ceramics by one stage heat treatment was achieved by optimizing the CaO/MgO ratio. The most suitable mass ratio of CaO to MgO in this work was 1.25, because of higher crystallinity of diopside and its desirable fine grained microstructure. The mechanical properties of glass-ceramics obtained by one stage heat treatment were a little worse than that of two stage heat treatment. Considering the simpler manufacturing process and lower energy consumption, one stage heat treatment was a more promising and economical method for rolling process.

Influence of Strontium Oxide on Structural Transformations in Diopside-Based Glass-Ceramics Assessed by Diverse Structural Tools

A full understanding of the structural glass variations and of the nucleation and growth of crystalline phases in glass-ceramics (GCs) induced by compositional changes is highly relevant for applications such as sealants for solid oxide fuel cells, bio- and dental materials, and photonics. Systematic substitution of Ca with Sr in diopside (Di-CaMgSi2O6) has a significant impact on the crystalline-phase assemblage after heat treating at 850 °C for 500 h. A high percentage of Di crystallized from Sr-free glass; however, with increasing Sr content the tendency toward crystallization decreased, and Sr-akermanite (Sr-Ak) was preferentially crystallized. In this study, the structural transformations in the Di-based-GC system upon the substitution of calcium with strontium have been examined by X-ray powder diffraction (XRD), 29Si and 27Al magic angle spinning (MAS)-nuclear magnetic resonance (NMR), and Raman spectroscopies. XRD Rietveld refinement results indicate that up to a maximum of ∼25 at. % of Sr occupie...

Effect of Sintering Temperature on the Thermal Properties of Diopside-Based Glass-Ceramics of Varying CaO/MgO Ratio

The thermal properties of diopside (CaMgSi2O6)-based glass-ceramics of varying CaO/MgO ratio were investigated as a function of sintering temperature. The crystallization behavior of the glass was studied by a non-isothermal method using a differential thermal analysis (DTA) with various heating rates. Diopside, as a main crystalline phase, and cordierite, as a minor phase, were formed in the glass-ceramics with an - 0.67-2.23 CaO/MgO ratio. The X-ray diffraction peak for diopside in the glass-ceramic becomes higher with an increase of the CaO/MgO ratio. The crystallization volume fraction with sintering temperature was calculated showing that both the initiation temperature for crystallization and a temperature range of crystallization increased with an increased heating rate. The microstructure of all glass-ceramics had a lump area composed of several tens-of-nanometer particles and a matrix composed of rows of particles, and the matrix area decreased with a decreasing CaO/MgO ratio. The thermal conductivity of glass-ceramics of CaO/MgO = 2.23 was 44% higher than that of CaO/MgO = 0.67 owing to the higher crystallinity and less voids in a microstructure. All glass-ceramics fabricated in this study were sintered at below 955 degrees C, which makes them applicable to the LTCC process for light-emitting diode packaging.

Diopside-Based Glass-Ceramics from Chrysotile Asbestos Tailing

By utilizing chrysotile asbestos tailing from Shannan ore in Sichuan as the main raw material, diopside-based glass-ceramics were successfully synthesized in the laboratory by adding some limestone, quartz sand, Al2O3, H3BO3, Na2CO3 and CaF2. The optimum procedure for glass-ceramics was as follows: melting at 1400 for 60 min, sintering at 1100 for 120 min. Through the tests of physical and mechanical properties, the glass-ceramics materials with more crystalline phase had high density, fine performance of resisting compression (366MPa) and negligible water absorption. Through chemical resistance tests, the glass-ceramics samples showed strong corrosion resistance. Overall result indicated that it was a feasible attempt to produce glass-ceramics materials for building and decorative materials from chrysotile asbestos tailing.

Effects of Al 2O 3 addition on physical properties of diopside based glass–ceramics for LED packages

One of the main problems of currently used Al 2O 3/glass composites for LED (light emitting diode) packaging materials is deterioration of the heat emission property due to the lower thermal conductivity of glass. In the present study, glass frit of a CaO–MgO–SiO 2 system of stoichiometric diopside composition with the addition of various amounts of Al 2O 3 was milled, pressed into pellets isostatically, and heat-treated to fabricate diopside-based glass–ceramics. Effects of microstructure and crystallinity of the diopside phase produced in the glass–ceramics on the thermal conductivity, thermal diffusivity, density, and specific heat capacity were analyzed as a function of Al 2O 3 addition to investigate the feasibility of utilizing diopside-based glass–ceramics in LED packaging applications.

Diopside-based glass-ceramics from MSW fly ash and bottom ash

By utilising MSW fly ash from the Shanghai Yuqiao municipal solid waste (MSW) incineration plant as the main raw material, diopside-based glass-ceramics were successfully synthesized in the laboratory by combining SiO 2, MgO and Al 2O 3 or bottom ash as conditioner of the chemical compositions and TiO 2 as the nucleation agent. The optimum procedure for the glass-ceramics is as follows: melting at 1500 °C for 30 min, nucleating at 730 °C for 90 min, and crystallization at 880 °C for 10 h. It has been shown that the diopside-based glass-ceramics made from MSW fly ash have a strong fixing capacity for heavy metals such as lead (Pb), chromium (Cr), cadmium (Cd) etc.

Chemical Resistance of Silicate Glass-Ceramics

ABSTRACT This work is concerned about the chemical characterization of monolithic diopside-based glass ceramics (GCs). Variations from this composition were carried out through the addition of P2O5 to increase crystal density and Al2O3 to optimize the chemical properties of the GCs. The addition of MgO was sufficient for the crystallization of diopside, but additions of P2O5 made the formation of this crystalline phase difficult. The highest volume of diopside crystals was about 76% for the formulation with 5% weight of alumina. As expected, chemical resistance is directly influenced by the composition of the glass ceramic, but not so much by the fraction of crystals volume.