The Phase-Formation Behavior of Composite Ceramic Powders Synthesized by Utilizing Rice Husk Ash from the Biomass Cogeneration Plant

The development and utilization of biomass as a vital source of renewable energy were stimulated in order to reduce the global dependency on fossil fuels. A lot of rice husk ashes (RHA) were generated as the waste after the rice husk as the main fuel was burnt in the biomass cogeneration plant. The phase-formation behavior of composite ceramic powders synthesized by using rice husk ash from the biomass cogeneration plant at the different carbon ratios and temperatures was investigated. The sequence of phase formation with the calcining temperatures ranging from 1773 K to 1853 K was followed by O′-Sialon→SiC + Si3N4→SiC in samples with C/SiO2  =  1 : 1–4 : 1. Ca-α-Sialon formed in samples with C/SiO2  =  5 : 1 and 6 : 1. The results highlighted that series of reactions happening sensitively depended on C/SiO2 and the temperature and demonstrated that the carbothermal nitridation provided an alternative for converting RHA waste into composite ceramic powders

Effects of SnO2 Addition on the Synthesis of Magnesium Aluminate Spinel Microplatelets

In order to prepare platelet-like spinel expected as the reinforcing phase, different amounts (5 – 20 at %) of SnO2 were added into the mixture of magnesia and alumina platelets, and then heated at 1300 – 1600 °C for 5 h. Effects of SnO2 addition on the synthesis of magnesium aluminate spinel microplatelets were investigated. The synthesized spinel was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Spinel platelets like “sesame cookie” formed derived from platelet alumina based on the template process. The highest spinel content in samples with 10 % of SnO2 addition achieved. The amount of Al2O3 and SnO2 in solid solution and degree of orneriness for spinel depended on SnO2 addition.DOI: http://dx.doi.org/10.5755/j01.ms.24.1.17530</p

Altered function in medial prefrontal cortex and nucleus accumbens links to stress-induced behavioral inflexibility

The medial prefrontal cortex (mPFC) and its output area, the nucleus accumbens (NAc), are implicated in mediating attentional set-shifting. Patients with posttraumatic stress disorder (PTSD) exhibit difficulties in the disengagement of attention from traumatic cues, which is associated with impairments in set shifting ability. However, unknown is whether alterations in corticostriatal function underlie deficits in this behavioral flexibility in individuals with PTSD. An animal model of single prolonged stress (SPS) has been partially validated as a model for PTSD, in which SPS rats recapitulate the pathophysiological abnormalities and behavioral characteristics of PTSD. In the present study, we firstly found that exposure to SPS impaired the ability in the shift from visual-cue learning to place response discrimination in rats. Conversely, SPS induced no effect on a place-to-cue set-shifting performance. Based on SPS-impaired set-shifting model, we used Western blot and immunofluorescent approaches to clarify SPS-induced alternations in synaptic plasticity and neuronal activation in the mPFC and NAc. Rats that were subjected to SPS exhibited a large increase in pSer845-G1uA1 and total G1uA1 levels in the mPFC, while no significant change in the NAc. We further found that exposure to SPS significantly decreased c-Fos expression in the NAc core but not the shell after set-shifting behavior. Whereas, enhanced c-Fos expression was observed in prelimbic and infralimbic cortices. Collectively, these findings suggest that abnormal hyperactivity in the mPFC and dysfunction in the NAc core underlie long-term deficits in executive function after traumatic experience, which might play an important role in the development of PTSD symptoms. (C) 2016 Elsevier B.V. All rights reserved.</p

Strengthening mechanism and slag corrosion-resistance of low-carbon Al2O3–C refractories: Role of h-BN

The corrosion resistance of low-carbon Al2O3–C refractories was improved by a novel preparation method to satisfy the requirements of a newly developed smelting process. Improving the corrosion resistance of Al2O3–C refractories is crucial for extending the service life of industrial furnaces and reducing carbon emissions. In this study, the effects of graphite-like h-BN on the microstructure, mechanical properties and corrosion resistance of low-carbon Al2O3–C refractories were investigated. The results shows that the mechanical properties of low-carbon Al2O3–C refractories can be improved by adding h-BN. This was due to the fact that the microstructure of the material was regulated by h-BN to form the Sialon structure of the folded space. Simultaneously, the corrosion resistance of low-carbon Al2O3–C refractories was enhanced by h-BN, resulting in an increase of up to 70.3 %. According to phase change and microstructure analysis, the introduction of h-BN was beneficial to avoid the formation of decarbonized layer and promote the continuous structure precipitation of Al8B2O15, spinel and anorthite. This change promoted the densification of the slag/refractories interface, thereby hindering the corrosion of the slag. Thermodynamic simulations verified that by introducing h-BN, the generation of the high-melting-point material was increased and the absolute content of each phase material was reduced. As a result, the low-carbon Al2O3–C refractories exhibited enhanced corrosion resistance

Performance Investigation of an Exhaust Thermoelectric Generator for Military SUV Application

To analyze the thermoelectric power generation for sports utility vehicle (SUV) application, a novel thermoelectric generator (TEG) based on low-temperature Bi2Te3 thermoelectric modules (TEMs) and a chaos-shaped brass heat exchanger is constructed. The temperature distribution of the TEG is analyzed based on an experimental setup, and the temperature uniformity optimization method is performed by chipping peak off and filling valley is taken to validate the improved output power. An automobile exhaust thermoelectric generator (AETEG) using four TEGs connected thermally in parallel and electrically in series is assembled into a prototype military SUV, its temperature distribution, output voltage, output power, system efficiency, inner resistance, and backpressure is analyzed, and several important influencing factors such as vehicle speed, clamping pressure, engine coolant flow rate, and ambient temperature on its output performance are tested. Experimental results demonstrate that higher vehicle speed, larger clamping pressure, faster engine coolant flow rate and lower ambient temperature can enhance the overall output performance, but the ambient temperature and coolant flow rate are less significant. The maximum output power of AETEG is 646.26 W, the corresponding conversion efficiency is 1.03%, and the increased backpressure changes from 1681 Pa to 1807 Pa when the highest vehicle speed is 125 km/h

A novel method for synthesis of β–Sialon/Ti(C, N) composites using nitridation of Ti3SiC2 powder

In this investigation, we have employed a novel approach to fabricate β–Sialon/Ti(C, N) composites through the nitridation treatment of Ti3SiC2 powder. At temperatures ranging from 1373 to 1773 K, the reaction process was subjected to a comprehensive analysis to explore the transformation of phase and microstructure. The findings unequivocally highlight the influence of α–Al2O3 presence and the high specific surface area of Ti3SiC2 powder, resulting in distinctive phase and structural evolutions post nitridation, distinctly different from those observed in bulk Ti3SiC2. The β–Sialon/Ti(C, N) composites produced via this innovative method exhibit uniform local chemical composition and meticulous regulation of grain morphology. Moreover, the synthesis mechanism of β–Sialon/Ti(C, N) composites under nitrogen ambiance was thoroughly discussed. This straightforward approach has the potential for extensive–scale synthesis of β–Sialon/Ti(C, N) composites, offering promising avenues for their application in developing high–performance refractories or structural ceramics tailored to withstand severe high–temperature environments

Improvement of Mechanical Properties of Composites with Surface Modified B₄C for Precision Machining

In order to solve the problem of difficult sintering and high brittleness of B4C-based ceramics, B4C@ZrB2-TiB2 composite powder was synthesized by molten salt method, and B4C–(Zr, Ti)B2 composite ceramics were successfully prepared by spark plasma sintering. The effects of different raw material ratios on the composition, microstructure, and mechanical properties of the prepared composite ceramics were characterized by XRD, XPS, SEM, and TEM. The results show that ZrB2 and TiB2 were grown on the surface of B4C by template mechanism to form a dense nanocrystalline coating, and the original surface of B4C was exposed gradually with the decrease of the ratio of metal powder. When the composite powders were sintered at 1700 °C, ZrB2 and TiB2 formed a solid solution, which can refine grains and improve strength. When the raw material ratio is n(B4C): n(Zr): n(Ti) = 12:1:1, the composite ceramics have excellent comprehensive properties, the Vickers hardness reaches 41.2 GPa

Oxidation behavior of Al3BC3 powders at 800–1400 °C in ambient air

The non-isothermal and isothermal oxidation behavior of Al3BC3 powders at 800–1400 °C in the air was studied. The results revealed that the oxidation resistance of Al3BC3 powders was better than that of “Al8B4C7” powders. At 800–1100 °C, the sintering accelerated the adhesion between the aluminum borate layer and the Al3BC3 core. No micro-crack was observed on both surface and cross-section, thus effectively blocking the diffusion of oxygen and volatilization of reactant gases. The oxidation behavior changed due to the oxidation products growing into a rod shape higher than 1200 °C. The interlocking structure of Al18B4O33 micro-rods made the surface of oxidized powder porous. Therefore, the oxygen diffused quickly into Al3BC3 through the porous structure on its surface, leading to rapid oxidation. Jander model could deal with oxidation kinetics and be in good agreement with the experimental data. The calculated apparent activation energy of Al3BC3 powder was equal to 212.76 kJ/mol at 800–1100 °C