Thermal degradation and flammability behavior of fire-retarded wood flour/polypropylene composites

Sun, Lichao,Wu, Qinglin,Xie, Yanjun,Cueto, Rafael,Lee, Sunyoung,Wang, Qingwen Technomic Publising 2016 Journal of Fire Sciences Vol.34 No.3

<P>Magnesium hydroxide, expandable graphite, and ammonium polyphosphate were used to enhance the thermal stability and fire retardant properties on wood flour/polypropylene composites. The thermal decompositions and flammability properties were investigated using modulated thermogravimetric analysis and cone calorimeter, and the activation energy of each decomposition process was also determined by modulated thermogravimetric analysis. The results showed that both expandable graphite and ammonium polyphosphate promoted thermal degradation of wood flour and char formulation, and magnesium hydroxide did not influence on the wood flour decomposition. Unlike in nitrogen atmosphere, magnesium hydroxide and ammonium polyphosphate increased the peak temperature of wood flour thermal degradation and diminished the decomposition peaks of polypropylene in air atmosphere. Cone calorimeter results showed that expandable graphite greatly reduced the heat and smoke release. A general activation energy range of 187-226kJmol(-1) (in nitrogen), 165-206kJmol(-1) (in air) at wood flour degradation stage, 237-262kJmol(-1) (in nitrogen), and 185-269kJmol(-1) (in air) at polypropylene degradation stage were proposed for wood flour/polypropylene composite with and without fire retardants.</P>

On-Line Prediction of Impulse Spark and Arc Discharge Removals of Metal Bond in Dry Electrical Discharge Dressing of Diamond Grinding Wheel

Yanjun Lu,Jiajing Sun,Xiaoyu Wu,Fumin Chen 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.10 No.2

The electrical discharge is able to realize efficient dressing for metal-bonded diamond wheel, but the monitoring and prediction of dressing status have been technical bottleneck in industrialization. Hence, the metal bond removal model of impulse spark and arc discharges is proposed to realize on-line monitoring and prediction for micro grain protrusion on diamond grinding wheel surface. The relationship between microremovals of metal bond and impulse spark and arc discharge parameters was investigated for controllable dressing. First, the static and dynamic impulse discharge experiments were carried out to reveal metal bond removal mechanisms of impulse spark and arc discharges; then the relationship between characterized impulse discharge parameters and removal of metal bond was quantitatively analyzed; finally, the dry electro-contact discharge (ECD) dressed coarse diamond wheels were applied to perform smooth surface and mirror grinding of optical glass and mold steels against mechanical dressed wheels. It is found that the critical transition value of arc discharge to spark discharge under static discharge and dynamic discharge conditions were 0.059 and 0.038, respectively. In comparison with mechanical dressing, the dry ECD can obtain higher grain protrusion height to improve ground surface quality, leading to a microscopic smooth surface of BAK3 optical glass and macroscopic mirror-like surface of model steels. It is confirmed that the established relationship model can be effectively used to on-line predict the removal of metal bond with the average prediction error of 10.1% and microscopic grain protrusion by characterized impulse discharge parameters.

Memristive effect with non-zero-crossing current-voltage hysteresis behavior based on Ag doped Lophatherum gracile Brongn

Yanjun Xu,Lu Tan,Bai Sun,Ming Lei,Yiluo Zhao,Tengteng Li,Liang Zheng,Shouhui Zhu,Yong Zhang,Yong Zhao 한국물리학회 2020 Current Applied Physics Vol.20 No.4

The memristive effect become a bio-electronics research focus with the development of sustainable systems and the application of multifunctional electronic devices. In this paper, the natural Lophatherum gracile Brongn (LGB) was employed as active layer to prepare Ag/LGB/fluorine-doped tin oxide (FTO) bio-memristor. Further, different doping ratios nano silver powders (Ag nanoparticle) were doped into LGB functional layers at 0 wt%, 0.2 wt%, 0.33 wt%, 1.0 wt%, 2.0 wt%, 10.0 wt% and 20.0 wt%. It is found that the capacitive-coupled memristive performance of the Ag/Ag-doped-LGB/FTO devices was markedly changed. Finally, it is confirmed that Ag ions transferring and Ag filament formation under the applied voltage are responsible for capacitive-coupled memristive behavior. This research has revealed the realization of capacitive-coupled memristive effect of biomemristor, which opens a new way to achieve multifunctional performance for electronic device.

Impedance Coordinative Control for Cascaded Converter in Bidirectional Application

Yanjun Tian,Fujin Deng,Zhe Chen,Xiaofeng Sun,Yanting Hu 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

Two stage cascaded converters are widely used in bidirectional applications, but the negative impedance may cause system instability. Actually the impedance interaction is much different between forward power flow and reversed power flow, which will introduce more uncertainty to the system stability. This paper proposes a control method for the constant power controlled converter in cascaded system, and consequently it can change the negative impedance of constant power converter into resistive impedance, which will improve the cascaded system stability, as well as merge the impedance difference between forward and reversed power flow. This paper addresses the analysis with the topology of cascaded dualactive - bridge converter (DAB) with inverter, and the proposed control method can also be implemented in unidirectional applications and other general cascaded converter system. The effectiveness has been validated by both simulation and experimental results.

Impedance Interaction Modeling and Analysis for Bidirectional Cascaded Converters

Yanjun Tian,Fujin Deng,Zhe Chen,Xiaofeng Sun,Yanting Hu 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

For the cascaded converter system, the output impedance of source converter interacts with the input impedance of load converter, and the interaction may cause the system instability. In bidirectional applications, when the power flow is reversed, the impedance interaction also varies, which brings more uncertainty to the system stability. An investigation is performed here for showing that the forward and reverse interactions are prominently different in terms of dynamics and stability even though the cascaded converter control remains unchanged. An important guideline has been drawn for the control of the cascaded converter. That is when voltage mode converter working as the load converter; the constant power mode converter as the source converter, the system is more stable. The concluded findings have been verified by simulation and experimental results.

Some large values of in-situ stress and related engineering geological problems in China

Yanjun Shang,박형동,Yongyue Shi,Guangxiang Yuan,Yuanchun Sun 한국지질과학협의회 2010 Geosciences Journal Vol.14 No.2

In recent years, different methods have been applied to in-situ stress estimation for stability analysis of increasing large-scale tunnels in China. It was found that some extraordinary stress values are mostly associated with, although not a necessity of, engineering geological problems such as collapse, rock burst and squeezing. This paper focuses on finding the relationship among abnormal in-situ stress component values. The exposure in ground surface with unloading and erosion contributes a lot to relatively higher horizontal stress and lateral coefficient values of igneous and metamorphic rocks, while this situation is not the case for sedimentary rocks. Comparing stress data and connecting some abnormal values with typical case examples for better understanding and estimating stress is the main feature of this paper.

From in situ stress and discontinuities to the strength of granites: comparison and case study

Yanjun Shang,박형동,Guangxiang Yuan,Yuanchun Sun,Qian Gao 한국지질과학협의회 2008 Geosciences Journal Vol.12 No.4

The distinctive weathering profile and discontinuity of granites, dipping slightly at shallow depths and steeply in larger depths, are regarded as being due to their physical and geo-mechanical properties. This paper compares vertical stress (Sv) and overlain weight (h) drawn from different kinds of in situ stress measurements, as well as coefficients of lateral stress. Stress trends are connected with discontinuities (joints and dykes), which reveal their relationships in space and dip angles of joints and dykes are compared in space, together with shear plane plunges and the strength of rocks from laboratory tests. As a result, it was found that the relict structural geo-stress contributes to maximum horizontal stress, especially at shallow depths. The most common feature is the high coefficient of lateral stress, which is mostly attributed to unloading in shallow depths and stress concentration at a certain depth after the erosion of overlain beds and the exposure of granites at the ground surface. Therefore, the weathering profiles and weathered capsule of granites could be interpreted from this viewpoint. One of the two main features of this paper is the connection of the extraordinary values of the lateral coefficient of in situ stress with unloading and the typical weathering profile at shallow depths. Another is the comparison of the shear stress and strength from in situ and laboratory tests, with a series of data from the same location and depth. The distinctive weathering profile and discontinuity of granites, dipping slightly at shallow depths and steeply in larger depths, are regarded as being due to their physical and geo-mechanical properties. This paper compares vertical stress (Sv) and overlain weight (h) drawn from different kinds of in situ stress measurements, as well as coefficients of lateral stress. Stress trends are connected with discontinuities (joints and dykes), which reveal their relationships in space and dip angles of joints and dykes are compared in space, together with shear plane plunges and the strength of rocks from laboratory tests. As a result, it was found that the relict structural geo-stress contributes to maximum horizontal stress, especially at shallow depths. The most common feature is the high coefficient of lateral stress, which is mostly attributed to unloading in shallow depths and stress concentration at a certain depth after the erosion of overlain beds and the exposure of granites at the ground surface. Therefore, the weathering profiles and weathered capsule of granites could be interpreted from this viewpoint. One of the two main features of this paper is the connection of the extraordinary values of the lateral coefficient of in situ stress with unloading and the typical weathering profile at shallow depths. Another is the comparison of the shear stress and strength from in situ and laboratory tests, with a series of data from the same location and depth.

Relationship between the degree and spatial pattern of urban shrinkage based on nighttime light data: a case study of the old industrial area in Northeast China

Hongri Sun,Guolei Zhou,Yanjun Liu,Hui Fu 서울시립대학교 도시과학연구원 2024 도시과학국제저널 Vol.28 No.1

Urban shrinkage is a common phenomenon worldwide, but the relationship between the degree and spatial pattern of urban shrinkage is unclear. This paper takes the old northeastern industrial base, a region with a concentration of shrinking cities in China, as the study area. With the help of multi-source remote sensing images, this study first identified the degree and spatial pattern of urban shrinkage, and then investigated their relationship using the chi-square test. A total of 63 physical urban areas were identified as shrinking cities during the period 2013–2018. Among them, the proportion of cities with moderate and severe shrinking was relatively high. The spatial patterns of urban shrinkage are classified as central shrinkage, peripheral shrinkage, perforation shrinkage and global shrinkage. The results of the chi-square test proved that the spatial pattern and degree of urban shrinkage are correlated. Mild shrinkage was usually peripheral shrinkage; moderate shrinkage was usually central and perforation shrinkage; and severe shrinkage was usually global shrinkage. Identifying the degree and spatial pattern of urban shrinkage and investigating their relationship help deepen the understanding of the urban shrinkage phenomenon at a theoretical level and help urban planners and policy makers propose multidimensional strategies to alleviate the development dilemma of shrinking cities on a practical level.

A novel rechargeable hybrid Na-seawater flow battery using bifunctional electrocatalytic carbon sponge as cathode current collector

Zhang, Yanjun,Park, Jeong-Sun,Senthilkumar, Sirugaloor Thangavel,Kim, Youngsik Elsevier 2018 Journal of Power Sources Vol.400 No.-

<P><B>Abstract</B></P> <P>A novel rechargeable hybrid Na-seawater flow battery, using natural seawater as an abundant source of active materials, have been developed recently. In this kind of metal-air battery, electrochemical oxygen evolution and reduction are the two key processes taking place during charging and discharging, respectively. In general, powder form of electrocatalysts are attached to the current collectors by using inactive and insulating polymer binders, which inevitably impede the overall performance, and increase the manufacturing costs of the battery. Therefore, a simple way to construct the 3D current collector combined with efficient electrocatalytic activities remains a big challenge. In this work, a 3D macroporous carbon sponge is prepared by the direct carbonization of commercially available polymer “Magic Eraser”. The obtained carbon sponge has interconnected macroporous open 3D scaffold structure and exhibits good flexibility and tailorability. The 3D macroporous carbon sponge shows good bifunctional electrocatalytic activities toward oxygen evolution and reduction reactions in seawater. The fabricated hybrid Na-seawater flow battery using 3D macroporous carbon sponge as cathode current collector displays small charge-discharge voltage gap with high voltage efficiency, excellent rechargeability, and long-term cycling stability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A carbon sponge is prepared by carbonization of commercially available “Magic Eraser”. </LI> <LI> The carbon sponge shows bifunctional electrocatalytic activities toward OER and ORR. </LI> <LI> The carbon sponge can be used as current collector in hybrid Na-seawater flow battery. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Creep analysis of bamboo high‐density polyethylene composites: Effect of interfacial treatment and fiber loading level

Xu, Yanjun,Lee, Sun‐,Young,Wu, Qinglin Wiley Subscription Services, Inc., A Wiley Company 2011 Polymer composites Vol.32 No.5

<P><B>Abstract</B></P><P>The effect of chemical treatment at fiber–plastic interface and fiber loading level on creep property of bamboo fiber high‐density polyethylene (BF/HDPE) composites was investigated. For single modifier systems, the use of maleic anhydride grafted polyethylene (PE‐<I>g</I>‐MA) as a coupling agent helped reduce the creep and achieved the optimum effect at the 5.7% loading level. The addition of either a semicrystalline or an amorphous MA grafted ethylene propylene rubber (sEPR‐<I>g</I>‐MA or aEPR‐<I>g</I>‐MA) as an impact modifier increased the creep. For the combined modifiers, the use of PE‐<I>g</I>‐MA in EPR‐<I>g</I>‐MA modified composites gradually improved creep performance. Four‐element Burgers model was shown to fit measured creep data well only within the specified test period. However, both partially stretched Burgers (PSB) model and fully stretched Burgers (FSB) model could be applied for characterization and prediction when the stretching exponent was fixed at certain given values. The FSB model offered a better long‐term prediction based on the short‐term creep data. Time‐temperature superposition technique produced smooth master creep curves through horizontal shifts, but it slightly over‐predicted the long‐term creep for most composite systems. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers</P>