Microstructure and Properties of Pressureless-Sintered Zirconium Carbide Ceramics with MoSi2 Addition.

Zirconium carbide (ZrC) ceramics have a high melting point, low neutron absorption cross section, and excellent resistance to the impact of fission products and are considered to be one of the best candidate materials for fourth-generation nuclear energy systems. ZrC ceramics with a high relative density of 99.1% were successfully prepared via pressureless sintering using a small amount of MoSi2 as an additive. The influence of the MoSi2 content on the densification behavior, microstructure, mechanical properties, and thermal properties of ZrC ceramics was systematically investigated. The results show that the densification of ZrC was significantly enhanced by the introduction of MoSi2 due to the formation of a liquid phase during sintering. In addition, the ZrC grains were refined due to the pinning effect of the generated silicon carbide. The flexural strength and Vickers hardness of ZrC ceramics with 2.5 vol% MoSi2 sintered at 1850 °C were 408 ± 12 MPa and 17.1 GPa, respectively, which were approximately 30% and 10% higher compared to the samples without the addition of MoSi2. The improved mechanical properties were mainly attributed to the high relative density (99.1%) and refined microstructure.

Effect of Ti Doping on the Microstructure and Properties of SiCp/Al Composites by Pressureless Infiltration.

The effects of Ti doping on the microstructure and properties of SiCp/Al composites fabricated by pressureless infiltration were comprehensively investigated using first-principles calculations and experimental analyses. First-principles calculations revealed that the interface wetting and bonding strength in an Al/SiC system could be significantly enhanced by Ti doping. Subsequently, the Ti element was incorporated into SiC preforms in the form of TiO2 and TiC to verify the influence of Ti doping on the pressureless infiltration performance of SiCp/Al composites. The experimental results demonstrated that the pressureless infiltration of molten Al into SiC preforms was promoted by adding TiC or TiO2 due to the improved wettability. However, incorporating TiO2 leads to the growth of AlN whiskers under a N2 atmosphere, thereby hindering the complete densification of the composites. On the other hand, TiC doping can improve wettability and interface strength without deleterious reactions. As a consequence, the TiC-doped SiCp/Al composites exhibited excellent properties, including a high relative density of 99.4%, a bending strength of 287 ± 18 MPa, and a thermal conductivity of 142 W·m-1·K-1.

A cyclodextrin-based reagent for cis/trans-geometrical isomers separation by mobility measurements and chemical calculations.

Identification of cis/trans-carbon-carbon double-bond (CC) isomers remain challenging. Herein, a simple and rapid method for the separation and analysis of cis/trans-maleic acid (MA) and aconitic acid (AA) using Trapped Ion Mobility Spectrometry (TIMS) was developed. α-, ß-, γ-cyclodextrin (CD) were served as the separation reagent, slight difference in mobility separation was obtained by [CD-MA/AA-H]-. Specially, with the addition of divalent metal ion (G2+) as coordination metal ion, the separation effect was much increased by [CD-MA/AA + G-H]+, and α-CD has better mobility separation effect than ß-/γ-CD. Moreover, chemical calculations revealed the binary and ternary complexes are in the inclusion forms, and microscopic interactions between cis/trans-MA/AA, CDs, and G2+ are somewhat different that making their mobility separation. Finally, quantifications of cis/trans-isomers were analyzed in food samples, with good linearity (R2 > 0.99) and recoveries obtained from 87.25 % to 100.73 %.

Simultaneous Differentiation of C═C Position Isomerism in Fatty Acids through Ion Mobility and Theoretical Calculations.

Fatty acids play a pivotal role in biological processes and have many isomers, particularly at the C═C position, that influence their biological function. Distinguishing between isomers is crucial to investigating their role in health and disease. However, separating the isomers poses a significant analytical challenge. In this study, we developed a simple and rapid strategy combining ion mobility spectrometry and theoretical chemical calculations to differentiate and quantify the C═C positional isomers in 2-/3-butenoic acid (BA), 2-/3-/4-pentenoic acid (PA), and 2-/3-/5-hexenoic acid (HA). C═C positional isomerism was mobility-differentiated by simple complexation with crown ethers (12C4, 15C5, and 18C6) and divalent metal ions (Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Zn2+, Sr2+, and Ba2+), that is, converting C═C positional isomers with small structural differences into complexes with large structural differences through the interaction with metal ions and crown ethers. Metallized isomers were formed but could not be differentiated due to their complex and overlapping extracted ion mobiliograms (EIMs). Binary crown ether-isomer complexes were not observed, indicating that C═C positional isomers could not be separated by simple mixing with crown ethers. However, significant EIM differences were obtained for the formed ternary complexes, allowing baseline separation for the isomers. Notably, all crown ethers and metal ions have a separation effect with the isomers, with a calculated separation resolution (Rp-p) of 0.07-2.44. Theoretical chemical calculations were performed to provide in-depth structural information for the complexes and explain the separation principle. Theoretical conformational space showed that the divalent metal ions act as a bridge connecting the crown ether and the isomer. Additionally, the ternary complex becomes more compact as the distance between C═C and -COOH increases. Theoretical results can reflect the features of mobility experiments, with relative errors between the experiment collision cross-section (CCS) and theoretical CCS of no more than ±8.06%. This method was also evaluated in terms of quantification, accuracy, and precision repeatability. Overall, this study establishes that the crown ether-metal ion pair can function as a robust unit for differentiating C═C positional isomerism.

Joining of SiC Ceramic by Si-C Reaction Bonding Using Organic Resin as Carbon Precursor.

In this study, the joining of silicon carbide (SiC) ceramics was achieved via a Si-C reaction bonding method using the phenolic resin (PF)-MgCl2 system as the carbon precursor. Specifically, by adding MgCl2 to the phenolic resin mixture, the average pore size of the product of carbonization of the PF resin mixture increased from 14 ± 5 nm to 524 ± 21 nm, which was beneficial for the infiltration of molten silicon at high temperature. The microstructure of the joined specimens and the effect of the inert filler on the joint strength were investigated. It was demonstrated that SiC-SiC joints with strong interfacial bonding and high flexural strength could be obtained by the Si-C reaction bonding method using a phenol formaldehyde resin/alcohol sol-gel system as the carbon precursor. The flexural strength of the joined specimens reached the highest value, i.e., 308 ± 27 MPa when the solid loading of the inert filler was 26%. Overall, stable joining of silicon carbide ceramics was achieved by the proposed method, which has significance for realizing the preparation of complex-shaped or large silicon carbide ceramic parts.

Recognition of Cis-Trans and Chiral Proline and Its Derivatives by Ion Mobility Measurement of Their Complexes with Natamycin and Metal Ion.

Discrimination of isomers is an important and valuable feature in many analytical applications, and the identification of chiral isomers and cis-trans isomers is the current research focus. In this work, a simple method for direct, simultaneous recognition of d-/l-proline (P), d-/l-/cis-/trans-4-hydroxyproline (4-HP), and d-/l-/cis-/trans-N-tert-butoxycarbony (N-Boc-4-HP) was investigated by means of trapped ion mobility spectrometry-mass spectrometry (TIMS-MS). The isomers with cis-/trans-/d-/l-configuration can be directly recognized based on their mobility upon reaction with natamycin (Nat) and metal ions through noncovalent interactions. The results indicate that the recognition of the enantiomers has certain specificity, and the structural difference of the enantiomers was increased in a complex with Nat and metal ions. Herein, d-/l-P can be recognized through the ternary complexes [P + Nat + Mg - H]+, [P + 2Nat + Ca - H]+, [P + 2Nat + Mn - H]+, and [P + Nat + Cu - H]+. Similarly, c-4-HPL, c-4-HPD, t-4-HPL, and t-4-HPD can be recognized by [4-HP + Nat + Ca - H]+, [4-HP + 2Nat + Ca - H]+, and [4-HP + Nat + Cu - H]+, while N-Boc-c-4-HPL, N-Boc-c-4-HPD, N-Boc-t-4-HPL, and N-Boc-t-4-HPD were recognized through the enantiomer complexes [N-Boc-4-HP + Nat + Li]+, [N-Boc-4-HP + Nat + 2Na - H]+, [N-Boc-4-HP + Nat + K]+, [N-Boc-4-HP + Nat + Mn - H]+, and [N-Boc-4-HP + Nat + Ba - H]+. Moreover, tandem mass spectrometry (MS/MS) results indicated that different collision energies were obtained for the same fragment ions, which implied that the enantiomer complexes that contributed to their mobility separation shared identical interaction mode but had different gas-phase rigid geometries. Furthermore, the relative quantification for the enantiomers was performed, and the results were supported by a satisfactory coefficient (R2 > 0.99). The developed method can provide a promising and powerful strategy for the separation of chiral proline and its d-/l-/cis-/trans derivatives, bearing the advantages of higher speed, better accuracy, high selectivity, and no need for chemical derivatization and chromatographic separation.

Pore structure control of porous carbon obtained from phenol formaldehyde resin and ethylene glycol: the effect of H3BO3 on the pore structure.

Boric acid was used as a source of complexing agent to change phase separation kinetics and dynamics of the resin-glycol system to regulate the pore structure of porous carbon. The results show that the addition of H3BO3 in the resin mixtures can change the polymerization dynamics during curing of resin-glycol mixtures. For the complexation of H3BO3 to diols, the size of the ethylene glycol-rich phase produced during the curing of the resin mixture increase with the increase of the content of H3BO3. Similarly, the pore size of porous carbon after pyrolysis increases with the increase of H3BO3 content. The average pore size of resulting porous carbon can be regulated in the range from 15 to 2754 nm. These results reveal that H3BO3 exhibited obvious effects in changing the pore structure of resin-glycol system during pyrolysis.

Peripapillary choroidal thickness in Chinese children using enhanced depth imaging optical coherence tomography.

AIM: To evaluate the peripapillary choroidal thickness (PPCT) in Chinese children, and to analyze the influencing factors. METHODS: PPCT was measured with enhanced depth imaging optical coherence tomography (EDI-OCT) in 70 children (53 myopes and 17 non-myopes) aged 7 to 18y, with spherical equivalent refractive errors between 0.50 and -5.87 diopters (D). Peripapillary choroidal imaging was performed using circular scans of a diameter of 3.4 mm around the optic disc. PPCT was measured by EDI-OCT in six sectors: nasal (N), superonasal (SN), superotemporal (ST), temporal (T), inferotemporal (IT) and inferonasal (IN), as well as global RNFL thickness (G). RESULTS: The mean global PPCT was 165.49±33.76 µm. The temporal, inferonasal, inferotemporal PPCT were significantly thinner than the nasal, superonasal, superotemporal segments PPCT were significantly thinner in the myopic group at temporal, superotemporal and inferotemporal segments. The axial length was significantly associated with the average global (ß=-0.419, P=0.014), superonasal (ß=-2.009, P=0.049) and inferonasal (ß= -2.000, P=0.049) PPCT. The other factors (gender, age, SE) were not significantly associated with PPCT. CONCLUSION: PPCT was thinner in the myopic group at temporal, superotemporal and inferotemporal segments. The axial length was found to be negatively correlated to PPCT. We need more further studies about the relationship between PPCT and myopia.

Agreement between spectral domain optical coherence tomography and retinal nerve fiber layer photography in chinese.

PURPOSE: To compare spectral domain optical coherence tomography (OCT) and fundus photography to identify localized retinal nerve fiber layer defects (RNFLD) in Chinese patients with early-to-medium advanced glaucoma. METHODS: Thirty-nine patients (48 eyes) with localized RNFLDs by fundus photography and 48 age-matched control individuals were included into the study. The individuals underwent spectral domain OCT of the retinal nerve layer. In OCT, a localized RNFLD was defined as a dipping of the retinal nerve fiber layer thickness curve into the red-colored band of the graph, measured at a peripapillary circle with a diameter of 3.46 mm. RESULTS: In the 48 eyes of the study group, 63 localized RNFLDs were seen on the fundus photographs. On the OCTs, 58 of these 63 localized RNFLDs were detected, whereas 5 defects were not detected. Two localized RNFLDs seen on the OCTs were not found on the corresponding fundus photographs. The resulting sensitivity and specificity of OCT for detecting localized RNFLDs were 92% and 96%, respectively. The overall agreement rate between both methods was 94% (90/96), and the κ value was 0.90 (P<0.001). The results of both techniques correlated with each other for the determination of the location (Pearson correlation coefficient (r)=0.99; P<0.001) and the width of the localized RNFLDs (201 ± 123 degrees vs. 207 ± 115 degrees; r=0.93; P<0.001). CONCLUSIONS: Spectral domain OCT as compared with examiner-performed assessment of conventional fundus photographs is capable of detecting and measuring localized retinal nerve fiber layer defects with a relatively high diagnostic precision.

[Is normal-tension glaucoma different from primary open-angle glaucoma].

Based on the clinical consideration, Chinese glaucoma specialist reached a consensus (2008) that normal-tension glaucoma (NTG) is a subtype of primary open-angle glaucoma (POAG), and the dividing line is whether the intraocular pressure (IOP) more than 21 mm Hg or not. But it is still a controversial problem in the world that whether NTG is different from POAG or not. Some studies have confirmed that the pathogenesis of optic neuropathy, clinical features, risk factors for glaucomatous optic neuropathy progression and treatment strategy in NTG are different from those of POAG, indicating that they may be two different disorders.