The Effect of Microwave on the Crystallization Behavior of CMAS System Glass-Ceramics

The current status and future of solid waste recycled building bricks

Solid waste (SW) has become a problem hindering the economic and social development. Achieving the full green cycle from raw material to production of recycled building bricks (RBB) using SW is the focus of future research. In this paper, the research results of RBB manufacturing using SW in recent years are reviewed. According to the consolidation principle of RBB, the effects of different types of SW on the physicochemical properties and microstructure of RBB are summarized based on the recycled unsintered brick (RUSB) and recycled sintered brick (RSB). By comparing and evaluating the two consolidation methods, it is proposed that RSB has good practicality due to its higher SW utilization rate, higher strength, and faster consolidation speed. Furthermore, the difference between MWS and conventional sintering (CS) is analyzed, and the research on the application of MWS in SW-RBB manufacturing in recent years is reviewed in detail. It is pointed out that microwave sintering (MWS) technology can solve many drawbacks in traditional sintering technology and has great prospects in manufacturing SW-RBB due to the low energy consumption, low pollution, and high efficiency. Finally, the shortcomings and possible challenges in the current research on manufacturing SW-RBB using MWS technology are discussed, which provides guidance for the future development of SW-RBB manufacturing.

Study of microwave non-thermal effects on hydrogen bonding in water by Raman spectroscopy

Microwave chemistry plays an important role in organic synthesis. It has been debatable whether or not there are microwave non-thermal effects. Through analyzing the Raman spectra of pure water under two different heating methods (oil bath and microwave), the existence of microwave non-thermal effect is verified in this paper. The findings demonstrate that temperature has a significant impact on the Raman shift of the OH stretching band, which shifts to a high wave number as temperature rises and deforms the hydrogen bond (HB) network structure. Because microwave electric fields selectively heat water molecules (polar molecules) and destroy hydrogen bond structures in water, results in microwave heating more severe destruction of fully hydrogen-bonded structure than oil bath and transforms it more quickly into the partially hydrogen-bonded and free H₂O structure. Under the non-thermal effects of microwaves, hydrogen bonds that initially existed as stable tetrahedral structures are transformed into chain-like structures more rapidly. By comparing the Raman shift, it can be found that the microwave non-thermal effect can affect the hydrogen bonding in water for a long time (>1h). This study provides an experimental basis for enriching the mechanism of microwave non-thermal effects on hydrogen bonding.

A Heterogeneous Bifunctional Carbon Nanocatalyst from Plastic Waste to Efficiently Catalyze Waste Cooking Oil into Biodiesel

In this study, black carbon derived from polyethylene terephthalate (PET) wastes was utilized as the precursor for heterogeneous bifunctional nanocatalyst, which successively catalyzed waste cooking oil into biodiesel. The nano-sized catalysts were prepared by impregnation method with different heat treatment techniques, such as reflux, hydrothermal, and microwave solvothermal, to provide good distribution of K2O and NiO particles on PET activated carbon mesoporous surface. The sample treated with microwave solvothermal technique (MAC-K2O-NiO) exhibited a high surface area of 120 m2/g with good dispersion of nanoparticles, as shown by FESEM image, large crystallite size of 62.2 nm, and consisted of a highest density of basicity (2.58 mmol/g) and acidity (1.79 mmol/g) for improving transesterification to a maximum yield. The catalytic transesterification of MAC-K2O-NiO was optimized with 3 wt.% of catalyst loading, 18: 1 methanol-oil molar ratio, 65 °C for 3 h of reaction, with a maximum yield of 97.2%. The catalyst reusability was performed, and it was found to maintain the catalytic activity up to six reaction cycles, with a yield of 72.9%. The physiochemical quality of the optimized biodiesel was examined in accordance with the American Society for Testing and Materials, ASTM D6751 testing method.

Structure and Crystallization of High-Calcium, CMAS Glass Ceramics Synthesized with a High Content of Slag

In this work, more than 70 wt % of ferromanganese slag (containing 40 wt % CaO) was used to synthesize high-calcium, CaO-MgO-Al₂O₃-SiO₂ (CMAS) glass ceramics. The effect of SiO₂/CaO on the structure, crystallization behavior and microstructure of high-calcium, CMAS, slag glass ceramics was studied by IR, NMR, DSC, XRD and SEM. The results showed that in the high-calcium, CMAS glass ceramics, the main existing forms of silicon-oxygen tetrahedra (Qⁿ) were Q⁰ and Q¹. With the increase in the SiO₂/CaO, Qⁿ changed from Q⁰ and Q¹ (main units) to Q¹ (main units) and Q², and then to Q¹ and Q² (main units). The polymerization degree of Qⁿ changed from low to high, making the glass more stable, which led to the increase in crystallization temperature and the decrease in crystallization kinetic constant (k) and frequency factor (υ). At the same time, the change in the Qⁿ structure resulted in a gradual change to the main crystal, from akermanite to diopside-wollastonite.