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Two types of MgO-C refractories with tight particle grading and non-tight particle grading were prepared according to Andreasen's continuous packing theory. Fracture behaviors were investigated using wedge splitting tests combined with digital image correlation method and acoustic emission techniques. The results indicated that MgO-C refractory with non-tight particle grading treated at 1400 ℃ had more in situ phases (e.g., AlN and MgAl2O4) and exhibited less brittleness than specimens with tight particle grading even though they had similar nominal tensile strengths. In contrast, specimens with non-tight particle grading had greater horizontal strain under various loading stages, reflecting their better ability to resist rupture deformation. In addition, more microcracks were initiated earlier in the pre-peak region, and more energy was consumed. The decrease in coarse particles and corresponding increase in fine powder content increased the interface between particles, benefiting for reducing the local stress concentration and improving the thermal shock resistance of refractories.

This study presents novel lightweight periclase-composite (Mg8-xFex + yAl16-yO32) spinel refractories (LPSR) for the high temperature zone of cement rotary kilns. The LPSR was prepared by using microporous magnesia aggregates instead of sintered magnesia aggregates in traditional periclase-composite spinel refractories (TPSR). Hercynite-corundum composite aggregates, as well as microporous magnesia aggregates with a median pore size of 3.50 μm and a 20.1% lower bulk density than those of the sintered magnesia aggregates were used as raw materials. The microstructures, fracture behavior and strength of the LPSR in contrast with those of the TPSR were determined by SEM and three-point bending tests. After substituting the microporous magnesia aggregates for the sintered magnesia aggregates, a rougher surface of the microporous aggregates and wider transition-layer containing a solid solution spinel phase at the microporous magnesia aggregate/composite spinel aggregate interfaces were observed. Thus, a better bonding at the microporous magnesia aggregate/matrix interfaces as well as of the microporous magnesia aggregate/composite spinel aggregate interfaces was achieved. The wider transition-layer and better interfaces impeded crack propagation along the aggregate/matrix interface and increased the percentage of crack propagation within the aggregates. Thus, the mechanical strength of the LPSR was significantly enhanced. Compared with the TPSR, the LPSR had a lower bulk density of 2.56 g/cm3, but also a higher apparent porosity of 27.8% and a higher compressive strength of 46.4 MPa.

h-BN is an ideal substitution candidate for graphite due to its similar crystal structure, better oxidation resistance. In this work, the effect of h-BN on microstructure and comprehensive properties of Al2O3-C refractories are investigated, and the specimen containing 0.5 wt% h-BN (G0.5N0.5) possesses the best comprehensive properties. The addition of h-BN could reduce the diameter of SiC whiskers, which leads to the highest strength of specimen G0.5N0.5 (42.63 ± 3.10 MPa). Moreover, the fracture behavior of the specimens is demonstrated using wedge splitting test. The results show that the specimen G0.5N0.5 possesses the highest crack initiation and propagation resistance, which could be attributed to the collaborative effect of h-BN and SiC whiskers. Noteworthily, the addition h-BN could improve the thermal shock resistance. The specimens containing h-BN possess the higher residual ratio, compared with the specimen containing no h-BN (G1N0), and the specimen G0.5N0.5 shows the highest residual strength (14.12 ± 0.67 MPa). Furthermore, the oxidation resistance could be enhanced with introducing the h-BN.

Mechanical and thermal stresses are one of the main reasons causing the damage of MgO–C refractories in service. An in-depth understanding of the fracture behavior of MgO–C refractories is essential for the further development of high-performance MgO–C refractories. In this paper, effect of graphite content on fracture behavior of MgO–C refractories under wedge splitting test was investigated with the Digital Image Correlation (DIC) and Acoustic Emission (AE) technology. The results showed that the increase of graphite content in MgO–C refractories led to a reduction in brittleness and an improvement of thermal shock resistance. MgO–C refractories with higher graphite content were likely to generate crack at earlier loading stage and to have larger ultimate crack mouth opening displacement. It indicated a lower crack initiation resistance of MgO–C refractories and a better further damage propagation resistance. In addition, the proportion of crack in the MgO grains decreased and the tortuousness of crack path increased with the increasement of graphite content. It promoted the transformation of AE activity and energy dissipation from “burst type” to “slow release type” and the nonlinearity of MgO–C refractories mechanics behavior during failure process.

The present study investigated three lightweight periclase-magnesium aluminate spinel castables containing microporous magnesia aggregates with a varying apparent porosity (12.8%, 30.8% and 39.3%). The effect of the apparent porosity of the aggregates on the phase composition, microstructure, fracture behavior and strength of the lightweight castables was investigated by XRD, SEM and three-point bending tests. Large cracks between the aggregates with an apparent porosity of 12.8% and the matrix reduced the strength of the castable. For the aggregates with an apparent porosity of 30.8%, an excellent interlocking interface with the matrix increased the strength considerably, but also reduced the fracture toughness. At the highest level of the apparent porosity of the aggregates of 39.3%, the formation of a small number of microcracks between the aggregates and matrix reduced the strength, while the fracture toughness was only slightly affected. The lightweight castables with the best combination of properties were achieved at an apparent porosity of the aggregates of 30.8% since they had a low bulk density of 2.63 g/cm3 as well as a high compressive and flexural strength of 70.2 MPa and 20.9 MPa, respectively.

A homemade nanonickel catalyst was made by the ultrasonic liquid-phase reduction method, characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and applied to the isomerization reaction of high linoleic acid sunflower oil. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and particle size analysis showed that the homemade nickel particles were spherical, uniformly dispersed, less agglomerated, 20 to 75 nm in size, and nanoscale nickel powder. Compared with commercially available Raney nickel, the homemade nanonickel powder has a larger specific surface area, smaller pore size and higher catalytic activity. The X-ray diffraction spectrum of the homemade nanonickel powder had distinct diffraction peaks at its characteristic peaks which indicated that the powder was pure nickel. The nanometal nickel particles are fully dispersed in high oleic sunflower oil under the action of ultrasound. The results showed that it could effectively reduce the activation reaction time of nanonickel, and the conversion rate of conjugated linoleic acid could reach 86.24%. The process of activating the catalyst is omitted, the number of times of repeated uses of the nanonickel catalyst is increased, and the environmental pollution of the production is avoided. To obtain sunflower oil rich in CLA, it also provides a new idea for the preparation of conjugated linoleic acid.

Glutaraldehyde is usually used as a cross-linking agent in the immobilization of enzymes, but this will have a negative effect on the enzyme. Dialdehyde starch can effectively replace glutaraldehyde as a cross-linking agent, but the large particle size of dialdehyde starch affects the performance of immobilized enzyme. In this study, dialdehyde starch nanoparticles (DSNP) were combined with modified Fe

As a figure-of-merit, the rising ratio of crack propagation resistance to fracture initiation resistance indicates a reduction of the brittleness and enhances the thermal shock resistance of ordinary refractory ceramics. The significant nonlinear fracture behaviour is related to the development of a fracture process zone (FPZ). The universal dimensionless load–displacement diagram method is applied as a promising graphical method for the determination of R-curves for magnesia refractories showing different brittleness. By applying digital image correlation (DIC) together with the graphical method, the problems arisen with accurate determination of the fracture initiation resistance and the crack length are overcome. Meanwhile, the R-curve is subdivided with respect to the fracture processes, viz the fracture initiation, the development of FPZ and the onset of traction free macro-crack. With the simultaneous crack lengths evaluated from DIC, the contribution of each fracture process to the crack propagation resistance at certain loading stage is quantitatively presented.

A novel modified dog-bone shape direct tensile test is proposed and compared with the wedge splitting test as well as Brazilian test. The acoustic emission and digital image correlation techniques are adopted for monitoring the entire fracture process. The tensile strength determined by Brazilian test and wedge splitting test are higher than that evaluated by the direct tensile test. For direct tensile test, the specimens lost their integrity immediately after reaching the tensile strength and its predominant fracture mode is tensile nature cracking. The wedge splitting test enables the stable crack propagation because of the development of remarkable fracture process zone, which contributes to the presence of intensive shear cracking. The fracture behaviour of Brazilian test has the material brittleness dependence. For brittleness reduced refractories, the quasi-stable failure process is noticed. The deviations of the tensile strength, fracture process and failure mode for the three Mode I tensile tests are attributed to the different mechanical principles, the geometry/size effect and heterogeneity effect.

To investigate the fracture behavior of cement-bonded corundum castables, various cement contents and pre-treating temperatures have been comparatively studied using the wedge splitting method and the digital image correlation technique. The results show that the microstructure enhances the mechanical properties, so the fracture energy and the maximum load as well as the fracture modes are affected correspondingly. The castables demonstrate the highest fracture energy and maximum load at 1600 °C with cement content of 10 wt% due to an appropriate amount of CA6. At the temperatures of 110 and 1100 °C, the crack propagation within the matrix and along the interface are dominated whereas within the aggregates significantly increased at 1600 °C, leading to the brittleness of materials. However, increasing the cement content can reduce their brittleness, caused by the maximum strain in thex-direction, largest length of the main crack, and high ratio of crack propagation in the matrix.

In this study, a new mullite-foamed ceramic, reinforced with in-situ SiC whiskers (MCS) and applied as the insulating lining of thermal equipment used in cement production, was investigated. Compared with a conventional mullite-foamed ceramic (MC), the MCS phase composition, microstructure, compressive strength, thermal conductivity and alkali corrosion resistance were investigated by using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Factsage® software. The results showed that after being fired in granular coke, the SiC whiskers formed into MCS struts and were distributed in the pores between the interconnected needle-like mullite. Although the formation of SiC with higher conduction slightly increased MCS thermal conductivity, it significantly enhanced the compressive strength and alkali corrosion resistance of the foamed ceramic. Compared with the MC, although the MCS had higher bulk density (3.9%), and higher thermal conductivity (9.5% at 800 °C), it was more important that greatly improved compressive strength (by 60%) and better alkali corrosion resistance was achieved.

In this study, the fracture behaviour of magnesia, magnesia chrome and magnesia spinel (MgAl2O4 and FeAl2O4) refractories under wedge splitting test are qualitatively and quantitatively investigated with the acoustic emission (AE) and digital image correlation (DIC). First of all, the concepts of characteristic widths are proposed for estimating the brittleness of refractory materials according to the shape of load-displacement curve and validated by their good correlation with the characteristic length. Besides, the AE data are analyzed with AE parameter-based approaches and offer new insight into the fracture behaviour of refractory materials, including the classification of the cracking events in grains and in matrix, the distinction between the tensile mode and shear mode damage, and the visualization of the fracture process zone development. It confirms that the pre-existing micro-crack networks in refractories are favourable for the brittleness reduction, which enhance their nonlinear fracture behaviour and thermal shock resistance.

Porous MgAl2O4 ceramics were prepared via in-situ decomposition pore-forming (ISDP) technique using Al(OH)3 and magnesite as raw materials. The influence of Al(OH)3 particle size (0-44 μm, 44-88 μm, 88- 100 μm, 100-150 μm) on the microstructures and strengths of porous spinel ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The bimodal distributions were observed among all the pore size distributions of the porous spinel ceramics. The small pores existed inside the particles and the big pores existed between the particles. When the Al(OH)3 particle size decreased from 100-150 μm to 0-44 μm, the peak of large pores shifted towards left while intensity of the peak of small pores decreased. Simultaneously, the neck-bonds formed between particles grew significantly, which resulted in the increase of compressive strength from 1.4 to 10.8MPa. The optimized product is the sample with the Al(OH)3 particle size of 0-44 μm, which has a high apparent porosity (55.2%), a high compressive strength (10.8MPa) and a relatively homogeneous pore size distribution.

Thermal induced cracks and the tensile strength variation of Eibenstock granite subjected to high-speed heating have been studied through lab testing. The Digital Image Correlation (DIC) technique was used for analysing the tensile behaviour of granite at high-speed heating rate and different temperatures. For samples heated to 800 °C with heating rates of 200 °C/min and 300 °C/min, thermal-induced macrocracks become visible to the naked eyes, while no obvious macrocracks are observed on samples heated according to ISO 834 curve. Compared to the influence of temperature, the selected heating rates only have a negligible impact on tensile strength and axial displacement. The DIC analysis shows the crack initiation and progressive crack propagation before the main crack is formed at failure. Compared to the samples heated up to 400 °C, the samples heated up to 800 °C show less brittle fracture behaviour, and the tensile strength is greatly reduced. The final failure patterns prove that different heating scenarios lead to different microcrack structures and consequently influence the failure mode at the macroscopic scale.

In this work, the tensile failure of magnesia, rebound magnesia-chrome and chrome-containing magnesia-spinel refractories under the Brazilian test were investigated. The digital image correlation and acoustic emission were applied simultaneously for ensuring the validity of Brazilian test and studying the fracture process. The brittle refractories fail abruptly while reaching their load peaks because of the unstable crack propagation. However, the chrome-containing magnesia-spinel refractory shows a reduced brittleness due to the pre-existing microcracks, which promotes quasi-stable crack propagation evidenced by the nonlinearity in the pre-peak region and the softening in the post-peak region. Besides, the thickness-to-diameter ratio has a great influence on the fracture behaviour, which also shows brittleness dependence. The fracture behaviour of rebound magnesia-chrome refractory varies from brittle to less brittle while the thickness increasing from 10 mm to 50 mm. The quasi-stable crack propagation favors the central crack initiation and ensures the tensile failure under the Brazilian test.