Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Keqing Han is active.

Publication


Featured researches published by Keqing Han.


Journal of Macromolecular Science, Part B | 2010

Simultaneously Enhancing Mechanical Properties and Melt Flow Ability of Polyamide 6 by Blending with a Hyperbranched Polymer

Keqing Han; Xiong Zhang; Shan Zhan; Muhuo Yu

A series of polyamide 6/hyperbranched polymers (PA6/HBP) blends with different HBP contents was prepared by melt processing using a twin-screw extruder. The HBP was synthesized on the basis of pentaerythritol and dimethyl terephthalate according to a one-step method. The melt flow behavior, crystallization behavior, morphology, and mechanical properties of the PA6/HBP blends were investigated. The results showed that the melt flow index of the blends was greatly improved by a small amount of HBP. The yield strength, tensile modulus, Izod impact strength, and flexural strength of samples were simultaneously enhanced from 54.6 MPa, 0.5 GPa, 3.8 kJ/m2, 56.9 MPa for pure PA6 to 61.1 MPa, 0.7 GPa, 5.3 kJ/m2, 67.1 MPa for PA6 blends with 2.0 wt% HBP, respectively. The PA6/HBP blends showed the higher content of α-form crystal and a higher degree of crystallinity than those of pure PA6.


Journal of Macromolecular Science, Part B | 2009

Precursor Based on Polyborylborazine for BN Fiber: Preparation and Rheology Properties

Shutong Li; Yimiao Cao; Keqing Han; Xi Zhao; Muhuo Yu

A polyborylborazine precursor for hexagonal boron nitride (h-BN) was obtained by reaction of boron trichloride with methylamine and its structure was characterized by 11BNMR, 13CNMR, 1HNMR, and FTIR. The results show that the molecular precursor consists of borazine rings connected via a cross-linked network. The results of shear rheological tests indicated that the polymer is capable of being melt spun at moderate temperature, which implies that the structure of the molecular chains of the precursor polymer is branched. The precursor polymer was spun into a continuous polymer fiber in the melt state and then subsequently heat-treated under NH3 up to 1000°C for conversion into BN fibers. Its surface morphology was observed by scanning electron microscopy (SEM); the fiber was free of defects and cavities.


Materials | 2018

Debinding and Sintering of an Injection-Moulded Hypereutectic Al–Si Alloy

Jiaqi Ni; Muhuo Yu; Keqing Han

Hypereutectic Al–Si (20 wt.%) alloy parts were fabricated by employing a powder injection moulding (PIM) technique with a developed multi-component binder system composed of high-density polyethylene (35 wt.%), carnauba wax (62 wt.%) and stearic acid (3 wt.%). The feedstocks contained 83 wt.% metal powders. The debinding process was carried out by a combination of solvent extraction and thermal decomposition. The effects of solvent debinding variables such as kind of solvents, debinding temperatures and time, and the bulk surface area to volume ratios on the debinding process were investigated. Thermal debinding and the subsequent sintering process were carried out in a heating sequence under a nitrogen atmosphere. The influences of sintering temperature and sintering time on the mechanical properties and structure were considered. Under the optimal sintering condition, sintering at 550 °C for 3 h, the final sintering parts were free of distortion and exhibited good mechanical properties. Relative sintered density, Brinell hardness, and tensile strength were ~95.5%, 58 HBW and ~154, respectively.


Journal of Wuhan University of Technology-materials Science Edition | 2018

Microstructural and Mechanical Characterization of SiBNC Coated Carbon Fibers Prepared via PIP Method

Yong Liu; Yongjie Cui; Keqing Han; Hui Zhang; Muhuo Yu

The preparation of SiBNC ceramic oxidation-resistant coating on carbon fiber via precursor-solution infiltration and pyrolysis (PIP) method was presented and discussed in detail. Moreover, the microstructures and the components of the coating were characterized. The experiment results showed that the 0.5% polyborosilazane (PBSZ) solution in the coating preparation gave fewer defects, in contrast with the 1% and the 5% PBSZ solutions. The strength of the carbon fiber coated with SiBNC-0.5wt%(3.08GPa) was decreased by 12%. Compared with uncoated carbon fiber, the starting oxidation temperature and the reaction activation energy of the coated carbon fibers (SiBNC-0.5wt%) have increased by about 300 °C and 104%, respectively. The oxidation resistance of the SiBNC coated carbon fiber was improved dramatically.


Fibers and Polymers | 2018

Synthesis and Characterization of a Novel Preceramic Polymer for SiBNC Ceramic Fibers

Chenyu Zhang; Yong Liu; Yongjie Cui; Minqiang Jiang; Keqing Han; Hui Zhang; Muhuo Yu

A new approach for the synthesis of polymer precursor for quaternary SiBNC fibers is presented. The inexpensive, commercially available reactants n-propylamine (C3H7NH2), trichlorosilane (SiHCl3) and boron trichloride (BCl3) were used in a simple one-step reaction. The reaction mainly involved the co-polymerization between Si-Cl, B-Cl and N-CH2CH2CH3 with C3H7NH2 evaporation. Characterization of synthesized polymer was performed by FT-IR and NMR. The polymer has a relatively linear-chain chemical structure, and could be easily converted into flexible green fibers by melt-spun with diameter of 24 μm. After pyrolysis process at 1000 °C under nitrogen atmosphere, SiBNC ceramic fibers were obtained with a diameter of about 19 μm. Those fibers showed average tensile strength of 1.05 GPa and it remained in the amorphous state up to 1600 °C, which made them as the promising candidates for reinforcements in ceramic matrix composites for hightemperature application.


Advances in Materials Science and Engineering | 2018

Development of Hypereutectic AlSi Alloy Powder Injection Molding Feedstocks by Rheological Analysis

Jiaqi Ni; Keqing Han; Muhuo Yu

The comprehensive properties of a feedstock have a critical influence on the powder injection molding process. Proper feedstock with homogeneous structure, favorable flow characteristic, and moldability is the prerequisite for obtaining a final part with excellent comprehensive properties. The objective of the present work was to develop an optimal feedstock for fabrication of hypereutectic AlSi (20 wt.%) alloy parts by the powder injection molding technique. For this purpose, micron-sized hypereutectic AlSi (20 wt.%) alloy powder was mixed with different amounts of a binder which consisted of 35 wt.% high-density polyethylene, 62 wt.% carnauba wax, and 3 wt.% stearic acid. The binder contents of the feedstocks were in the range from 13 wt.% to 21 wt.%. The influences of binder content, shear rate, and temperature on the rheological behaviors of feedstocks have been investigated via a capillary rheometer. The feedstock with 21 wt.% binder exhibited a variable flow behavior and was culled. The rest of the feedstocks showed a pseudoplastic behavior. Comprehensive analysis of rheological parameters such as the flow behavior index, yield stress, flow activation energy, and the general moldability index, the feedstock with 17 wt.% binder exhibited the best rheological performance and favorable moldability. The molded part with 17 wt.% binder had constant density, good shape retention, and stiffness as well as homogeneous distribution of the powder and binder. After solvent debinding, the debound item showed a homogeneous porous structure which is suitable for the subsequent thermal debinding and sintering processes.


Chinese Materials Conference | 2017

Effect of Boron Content on Structure and High Thermal Stability of Polyborosilazane Precursor

Chenyu Zhang; Yong Liu; Keqing Han; Xuefeng Chang; Muhuo Yu

In this paper, a novel polyborosilazane (PBSZ) for preparing SiBNC ceramics was successfully prepared via co-polymerization of propylamine (C3H7NH2), trichlorosilane (HSiCl3) with different amounts of boron trichloride (BCl3). Pyrolysis of these precursors yields amorphous SiBNC ceramics, which with different boron content whereas similar Si/C/N ratio. The FTIR, NMR, EA and TGA were used to analyze the polymerization mechanism, composition, structure and ceramic yield of PBSZ samples with different boron content. The results indicated that these PBSZ contained the major framework of –Si–N–B– and six-membered boron-nitrogen rings. As boron content increased, the residual ceramic weight of PBSZ at 900 °C increased. When the molar ratio of BCl3:HSiCl3 was 1:1, the ceramic yield of PBSZ was 71.6%. However, the ceramic yield decreased when the boron content was further increased.


Ceramics International | 2015

Synthesis and characterization of amorphous SiBNC ceramic fibers

Shiwei Mou; Yong Liu; Keqing Han; Muhuo Yu


Materials Letters | 2011

A novel precursor route for the production of Si―B―N ceramic fibers

Xi Zhao; Keqing Han; Yuqing Peng; Jia Yuan; Shutong Li; Muhuo Yu


Ceramics International | 2017

A novel high yield polyborosilazane precursor for SiBNC ceramic fibers

Chenyu Zhang; Keqing Han; Yong Liu; Shiwei Mou; Xuefeng Chang; Hui Zhang; Jiaqi Ni; Muhuo Yu

Collaboration


Dive into the Keqing Han's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge