Temperature‐dependent mechanical and oxidation behavior of in situ formed ZrN/ZrO₂‐containing Si₃N₄‐based composite

In this work, Si₃N₄ and Zr(NO₃)₄ were used as raw materials to prepare ZrN/ZrO₂‐containing Si₃N₄‐based ceramic composite. The processing, phase composition, and microstructure of the composite were investigated. Hardness and fracture toughness of the ceramics were evaluated via Vickers indentation in Ar at 25°C, 300°C, 600°C, and 900°C. During spark plasma sintering, Zr(NO₃)₄ was transformed into tetragonal ZrO₂, which further reacted with Si₃N₄, resulting in the formation of ZrN. The introduction of ZrN enhanced the high‐temperature mechanical properties of the composite, and its hardness and fracture toughness reached 13.4 GPa and 6.1 MPa·m¹/² at 900°C, respectively. The oxidation experiment was carried out in air at 1000°C, 1300°C, and 1500°C for 5 h. It was shown that high‐temperature oxidation promoted the formation and growth of porous oxide layers. The microstructure and phase composition of the formed oxide layers were investigated in detail. Finally, it was identified that the obtained composite exhibited a higher thermal diffusivity than that of monolithic Si₃N₄ in the temperature range of 100°C–1000°C

Phase composition, microstructure, and mechanical properties of polymer-derived SiOC glass-ceramics reinforced by WC particles

In this work, a tungsten carbide (WC)-containing silicon oxycarbide (SiOC) glass-ceramic was prepared from WCfilled polysiloxane via pyrolysis and subsequent spark plasma sintering (SPS). The sintering behavior of SiOC was investigated by monitoring the densification temperature and shrinkage displacement. The phase composition and microstructure of ceramics were characterized by using FTIR, XRD, SEM, Raman spectrum, and optical microscope. It was shown that upon increasing the sintering temperature from 1400 degrees C to 1600 degrees C, the densification of ceramics was further improved, and the disorder of free carbon in SiOC was linearly decreased with sintering temperature. In addition, it was found that the incorporation of WC particles was effective to reinforce the mechanical properties of ceramics, and relevant strengthening mechanisms were discussed here. Finally, a correlation between phase composition, microstructure, and macroscopic performances of SiOC glass-ceramics was successfully derived

Sn-containing Si3N4-based composites for adaptive excellent friction and wear in a wide temperature range

Ceramic design based on reducing friction and wear-related failures in moving mechanical systems has gained tremendous attention due to increased demands for durability, reliability and energy conservation. However, only few materials can meet these requirements at high temperatures. Here, we designed and prepared a Sn-containing Si3N4-based composite, which displayed excellent tribological properties at high temperatures. The results showed that the friction coefficient and wear rate of the composites were reduced to 0.27 and 4.88 x 10(6) mm(3) N-1 m(-1) in air at 800 degrees C. The wear mechanism of the sliding pairs at different temperatures was revealed via detailed analyses of the worn surfaces. In addition, the tribo-driven graphitization was detected on the wear surfaces and in the wear debris, and the carbon phase was identified by SEM, TEM, and Raman spectrum

Transcriptome analysis of adipose tissues from two fat-tailed sheep breeds reveals key genes involved in fat deposition

Abstract Background The level of fat deposition in carcass is a crucial factor influencing meat quality. Guangling Large-Tailed (GLT) and Small-Tailed Han (STH) sheep are important local Chinese fat-tailed breeds that show distinct patterns of fat depots. To gain a better understanding of fat deposition, transcriptome profiles were determined by RNA-sequencing of perirenal, subcutaneous, and tail fat tissues from both the sheep breeds. The common highly expressed genes (co-genes) in all the six tissues, and the genes that were differentially expressed (DE genes) between these two breeds in the corresponding tissues were analyzed. Results Approximately 47 million clean reads were obtained for each sample, and a total of 17,267 genes were annotated. Of the 47 highly expressed co-genes, FABP4, ADIPOQ, FABP5, and CD36 were the four most highly transcribed genes among all the known genes related to adipose deposition. FHC, FHC-pseudogene, and ZC3H10 were also highly expressed genes and could, thus, have roles in fat deposition. A total of 2091, 4233, and 4131 DE genes were identified in the perirenal, subcutaneous, and tail fat tissues between the GLT and STH breeds, respectively. Gene Ontology (GO) analysis showed that some DE genes were associated with adipose metabolism. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that PPAR signaling pathway and ECM-receptor interaction were specifically enriched. Four genes, namely LOC101102230, PLTP, C1QTNF7, and OLR1 were up-regulated and two genes, SCD and UCP-1, were down-regulated in all the tested tissues of STH. Among the genes involved in ECM–receptor interaction, the genes encoding collagens, laminins, and integrins were quite different depending on the depots or the breeds. In STH, genes such as LAMB3, RELN, TNXB, and ITGA8, were identified to be up regulated and LAMB4 was observed to be down regulated. Conclusions This study unravels the complex transcriptome profiles in sheep fat tissues, highlighting the candidate genes involved in fat deposition. Further studies are needed to investigate the roles of the candidate genes in fat deposition and in determining the meat quality of sheep

Temperature‐dependent mechanical and oxidation behavior of in situ formed ZrN/ZrO2‐containing Si3N4‐based composite

In this work, Si3N4 and Zr(NO3)(4) were used as raw materials to prepare ZrN/ZrO2-containing Si3N4-based ceramic composite. The processing, phase composition, and microstructure of the composite were investigated. Hardness and fracture toughness of the ceramics were evaluated via Vickers indentation in Ar at 25 degrees C, 300 degrees C, 600 degrees C, and 900 degrees C. During spark plasma sintering, Zr(NO3)(4) was transformed into tetragonal ZrO2, which further reacted with Si3N4, resulting in the formation of ZrN. The introduction of ZrN enhanced the high-temperature mechanical properties of the composite, and its hardness and fracture toughness reached 13.4 GPa and 6.1MPa center dot m(1/2) at 900 degrees C, respectively. The oxidation experiment was carried out in air at 1000 degrees C, 1300 degrees C, and 1500 degrees C for 5 h. It was shown that high-temperature oxidation promoted the formation and growth of porous oxide layers. The microstructure and phase composition of the formed oxide layers were investigated in detail. Finally, it was identified that the obtained composite exhibited a higher thermal diffusivity than that ofmonolithic Si3N4 in the temperature range of 100 degrees C-1000 degrees C

Polymer-derived SiOC ceramics: A potential catalyst support controlled by the sintering temperature and carbon content

A series of silicon oxycarbide ceramics with varying carbon content from ca. 10 wt% to ca. 40 wt% were prepared by thermal pyrolysis of four commercially available polysiloxanes and subsequent spark plasma sintering (SPS) at 1200 degrees C, 1400 degrees C, and 1600 degrees C. The results showed that the high carbon content led to a porous microstructure, and for SiOC with ca. 40 wt% carbon content, its porosity and specific surface area at 1600 degrees C reached 34% and 262 m(2)/g, respectively. The electrochemical behavior of materials was evaluated. It was shown that SiOC has a certain degree of electrocatalytic activity, and the sample with 10 wt% carbon content obtained at 1200 degrees C exhibited an overpotential of 450 mV vs. RHE at 10 mA.cm(-2) in acid medium. Finally, it was analyzed that the electrochemical behavior of SiOC is closely related to the phase composition and microstructure of the resulting ceramics

Phase evolution and oxidation resistance of Si₃N₄/HfB₂/HfBxCyN₁₋x₋y ceramic nanocomposites prepared from tailored preceramic polymers

Single-source-precursor derived ceramics exhibit advantages for the preparation of Si-based ceramics with controllable phase composition and adjustable functional/mechanical properties, which has significant potential for (ultra)high temperature ceramic materials. Within the present work, a series of hafnium/boron-containing Si3N4-based ceramics (SiHfBCN) are prepared upon pyrolysis/annealing of the corresponding single-source-precursors in N2 atmosphere at different temperatures ranging from 1000 °C to 1700 °C. The high-temperature (micro)structural evolution with respect to the annealing temperatures and boron concentration was studied using X-ray powder diffraction, Raman spectroscopy, and transmission electron microscopy. The results show that the amorphous SiHfBCN ceramics convert upon crystallization into ceramic nanocomposites consisting of a α-Si3N4 matrix with embedded Si, HfB2, and HfBxCyN1–x–y. The formation and stability of HfBxCyN1–x–y solid solution were discussed in detail. Finally, the oxidation resistance of the obtained α-Si3N4/HfB2/HfBxCyN1–x–y ceramic nanocomposites was investigated by thermal gravimetric analysis in air