This paper provides a comprehensive account of the properties, development and extensive utilisation of Tibetan microcrystalline magnesite in industry. Tibetan microcrystalline magnesite has become a significant raw material for refractories, high-temperature insulating materials and magnesium chemical materials due to its high purity, low impurity content (mainly Si and Fe elements) and micrometre-sized crystallisation size (2~4 μm). The article presents a detailed analysis of the microstructure of Tibetan microcrystalline magnesite, its thermal decomposition behaviour and the key technologies employed in preparing high-purity magnesium oxide and sintered magnesia through light burning and electrofusion processes. Furthermore, this paper examines the potential applications of Tibetan microcrystalline magnesite in producing high-performance magnesium materials, including activated magnesium oxide, nano-magnesium oxide, and magnesium hydroxide, which are extensively utilized in environmental protection and high-temperature technology. It is demonstrated that the performance of Tibetan microcrystalline magnesite products can be markedly enhanced by optimising the process parameters and modification techniques, thereby further expanding their application prospects in industrial fields. This review offers a theoretical foundation and technical support for effectively utilising Tibetan microcrystalline magnesite, which possesses significant industrial application value and potential.
Superhard cubic boron nitride (cBN) cutting materials with different contents of cBN were investigated. The compositions of cBN-based materials included ceramic and metallic binders. The sintering of materials was performed by high-temperature hot pressing (HPHT) six-anvil apparatus at pressure 4.5 GPa and temperatures 1400–1450 °C. The process of compaction and processing of superhard cBN materials is followed by numerous chemical reactions. The chemical reactions are very important in compaction and sintering. The volume transformations during chemical reactions affect the shrinkage of the materials and may also impact the residual porosity of the finished products. The adhesion between the grains also depends on these chemical reactions. The research analyzed the volume transformations of various reactions during HPHT sintering of cBN materials, which may play a significant role in forming their structure and properties.
To meet the high-quality requirements for clean steel production and fully exploit the performance advantages of carbon-containing refractories, nanomaterial has been introduced into the matrix to develop advanced carbon-containing refractories. Nanomaterials, as critical additives, play a crucial role in developing novel refractories. The service performances of carbon-containing refractories are affected not only by their physical and chemical properties but also by their microstructure. This review provides a comprehensive overview of the latest research on oxide-carbon composite refractories containing nanomaterials, categorized by their composition: nanocarbons, nano oxides, and nano non-oxides. Incorporating nanomaterials can enhance the service performances of the refractories, optimizing phase composition and microstructure. Furthermore, future research directions in nanomaterial technology for carbon-containing refractories are discussed.
It is very important to clarify the mechanism of high-temperature superconductivity in strongly correlated electron systems. The mechanism of superconductivity in high temperature cuprate superconductors has been studied extensively since their discovery. We investigate the properties of correlated electron systems and mechanism of superconductivity by using the optimization quantum variational Monte Carlo method. The many-body wave function is constructed by multiplying by correlation operators of exponential type. We show that d-wave superconducting phase exists in the strongly correlated region where the on-site repulsive interaction is as large as the bandwidth or more than the bandwidth. The d-wave pairing correlation function is shown as a function of lattice sites, showing that the long-range order indeed exists.
In this paper, (100-m) BaZrO3-mY2O3 (m = 0, 20, 25, 33, 50, 100) crucibles were prepared, respectively. Then, the effect of crucible composition on the interaction between crucibles and highly active titanium alloys (Ti2Ni) was investigated. The degree of the erosion resistance of crucibles was compared before and after melting as well as the contaminated extent of the alloys. The results show that the two-phase crucibles consisting of BaZr1−xYxO3−δ and Y2O3(ZrO2), could be prepared after adding Y2O3 into the BaZrO3 crucible. As the amount of Y2O3 addition in the crucible was increased, the erosion resistance of the crucible to the alloy melt was gradually improved. The two-phase crucible with 50 wt.% Y2O3 addition exhibited the best erosion resistance with a 7 μm thick erosion layer, which was at the same level compared to the pure Y2O3 crucible (6.5 μm). However, the inclusion contaminants caused by this two-phase crucible were smaller than those of the pure Y2O3 crucible. This study provided a theoretical basis for further research on the preparation of highly stable crucibles for melting highly active titanium alloys.
A polycrystalline Cantor alloy, equimolar in Co, Cr, Fe, Mn and Ni, was cast. It was subjected to oxidation in a thermo-balance in a flow of synthetic dry air, at 1000, 1050, 1100 and 1150 °C. The mass gain was globally parabolic but rather irregular. The parabolic constants, ranging from 55 to 700 × 10−12·g2·cm−4·s−1, are much higher than for a chromia-forming alloy. They obey an Arrhenius law with an activation energy equal to 270 kJ/mol. The external oxide scales formed are composed of an outer part made of manganese oxide and an inner part made of (Cr, Mn) oxide containing a thin internal layer of chromia. The Mn and Cr-depleted depths and the Mn and Cr masses lost by the alloy increase with the oxidation temperature. Cr-rich acicular particles precipitated in subsurface at 1100 °C and internal oxidation along the grain boundaries are present in the whole thickness of the sample oxidized at 1150 °C. Oxide spallation occurred during the cooling, at temperatures in the 200–350 °C range, only for the alloys oxidized at 1050 and 1100 °C. Not too thick scale (1000 °C) or deep internal oxidation (1150 °C) may be favorable for scale adherence.
