Zhang, Huixing

Preferred name

Zhang, Huixing

Official Name

Zhang, Huixing

Alternative Name

Zhang, H. X.

ORCID

0000-0003-2715-3261

Gerade angezeigt 1 - 5 von 5

Some of the metrics are blocked by your
consent settings
Water-based freeze casting: Adjusting hydrophobic polymethylsiloxane for obtaining hierarchically ordered porous SiOC
(Wiley, 2017-05-07)
Zhang, Huixing
;
Fidelis, Clara Lana
;
Serva, Ana Luiza Teixeira
;
Wilhelm, Michaela
;
Rezwan, Kurosch
The hydrophobic properties of methyl poly siloxane (MK) were pushed into the“hydrophilic”range by cross-linking it with (3-aminopropyl)triethoxysilane(APTES) and subsequent pyrolysis to enable water-based freeze casting. Fillerproperties are investigated by varying the ratios of MK to APTES (1:1, 1:2, 1:3,1:4, 1:5), and pyrolysis temperatures (400°C, 500°C, 600°C) for the purpose ofdetermining an optimal set of characteristics for freeze casting. Additionally, fillerselection for this purpose is facilitated by analysis of zeta potential values andvapor adsorption. It was found that water-based freeze casting with hybrid fillers,followed by a pyrolysis step (600°C-700°C), leads to a SiOC ceramic monolithwith a lamellar pore morphology and a hierarchically ordered micro/meso/macrop-ore structure. Samples pyrolyzed at 1000°C contain mesopores, having a SSA ashigh as 51.6 m2/g. The hierarchically porous structure is very promising for appli-cations involving gas or liquid transportation.
Wissenschaftlicher Artikel
Band:100
Heft:5
113 191
Some of the metrics are blocked by your
consent settings
Macro/mesoporous SiOC ceramics of anisotropic structure for cryogenic engineering
(Elsevier, 2017-09-01)
Zhang, Huixing
;
Fidelis, Clara Lana
;
Wilhelm, Michaela
;
Xie, Zhipeng
;
Rezwan, Kurosch
Macro/mesopore SiOC ceramic monoliths of anisotropic structure were prepared by freeze casting, using methy phenyl polysiloxane (H44) or methy polysiloxane (MK) and (3-aminopropyl)triethoxysilane (APTES) as precursors. Influence of pyrolysis and testing temperature on compressive strength was investigated. Monoliths pyrolyzed at 700 °C had the highest compressive strength both at 77 K (14.0 ± 4.3 MPa) and 293 K (7.7 ± 1.8 MPa), regardless of precursors. Compressive strength of monolith in parallel direction is around twice as much as perpendicular direction. Compressive strength of both monoliths in liquid nitrogen (77 K) was around twice of that in air (293 K) probably due to low temperature and liquid resistance. Anisotropic expansion was observed, and the shrinkage in parallel direction was almost twice of that in perpendicular direction, which can be verified by the Schapery equation. Monolith made from H44 showed a much higher coefficient of thermal expansion at 77 K than monolith made from MK and APTES, probably due to difference in composition and measurement condition. Thermal conductivities and specific heat capacities displayed an upward trend from low to warmer temperature. The minimum and maximum values for thermal conductivity are 0.2 and 1.2 W m− 1 K− 1. The maximum heat conductivities might be determined mainly by the macroporosity and the thermal conductivity of the hybrid material.
Wissenschaftlicher Artikel
Band:134
97 122
Some of the metrics are blocked by your
consent settings
Hierarchically ordered micro/meso/macroporous polymer-derived ceramic monoliths fabricated by freeze-casting
(Elsevier Science, 2015-10-17)
Zhang, Huixing
;
D’Angelo Nunes, Pedro
;
Wilhelm, Michaela
;
Rezwan, Kurosch
A hierarchically-ordered macro/meso/microporous SiOC monolith was obtained via freeze-casting using commercial polysiloxane as a raw material and silica sol as a binder and template source. The pre-ceramic polymer polysiloxane was pyrolyzed at 600 °C to produce a hydrophilic surface; higher temperatures would fully decompose the organic groups. When silica sol and polysiloxane precursor were combined in freeze-casting method, after pyrolysis a polymer-derived SiOC ceramic monolith with a lamellar pore morphology and a hierarchically-ordered pore structure was obtained. Decomposition of the polysiloxane precursors results in the development of micropores, and particle packing is believed to be responsible for the mesopore formation. Macro/mesoporous hierarchically-ordered ceramics with a specific surface area of 74 m2/g are preserved at pyrolysis temperatures as high as 1000 °C. The influence of H44-derived filler amount (10 wt–40 wt%), freezing temperature (−20 °C, −80 °C, −150 °C), and pyrolysis temperature (600 °C, 700 °C, 1000 °C) on open porosity, pore size distribution, and surface characteristics were investigated.
Wissenschaftlicher Artikel
Band:36
Heft:1
117 102
Some of the metrics are blocked by your
consent settings
Macroporous Polymer-Derived Ceramic Monoliths for Cryogenic Applications Manufactured by Water-Based Freeze Casting
(2018-04-24)
Zhang, Huixing
;
Scheffler, Michael
;
Rezwan, Kurosch
;
Rezwan, Kurosch
Macroporous SiOC ceramics were prepared by a water-based freeze casting process, using polysiloxanes as precursors and silica sol as water phase and binder. The obtained porous monoliths have anisotropic porous structure and thermal and mechanical properties. The macroporous SiOC aimed at cryogenic applications which involve mass transport and thermal transport processes. The first part of the thesis focuses on manufacturing macroporous monoliths, in which process the surface characteristics of preceramic polymers in terms of hydrophobicity/hydrophilicity were modified to be used in the water-based freeze casting process. Two approaches were chosen for the surface modification. The first approach to modify the wettability of the precursor was pyrolysis of hydrophobic methyl phenyl polysiloxanes (H44) in inert gas at low temperature, by which hybrid ceramic materials (H44-derived filler) were generated. Depending on the pyrolysis temperatures, the surface characteristics can be varied from hydrophobic to hydrophilic. H44-derived fillers obtained by pyrolyzing methyl phenyl polysiloxane at 600 degree Celsius were hydrophilic enough to be used as solid phase in water-based process. The influence of solid loading, freeze temperatures and pyrolysis temperatures on porosity and specific surface areas were investigated. The combination of polymer derived filler materials with freezing casting method resulted in the trimodal pore structure (micro/meso/macropore) at pyrolysis temperature of 600 to 700 degree Celsius. Even at pyrolysis temperature of 1000 degree Celsius, the specific surface area was be as high as 74 square meter per gram. The pore shape can be tailored from lamellar to tubular depending on freezing temperatures. The second approach to modify the wettability was to introduce more hydrophilic groups to the hydrophobic methyl polysiloxane (MK) by cross-linking with (3-Aminopropyl)triethoxysilane (APTES). The molar ratios between MK and APTES and pyrolysis temperature led to different amounts of aminopropyl groups in the cross-linked products, which altered the basicity and hydrophilicity. For both approaches, besides the surface characteristics, surface charges also account for stable suspension to prepare final homogenous monoliths. Filler material prepared with MK: APTES molar ratio of 1:1, pyrolyzed at 600 degree Celsius was applicable for freeze casting considering the wettability and suspension stability. The monolith prepared with MK-APTES derived filler had also a hierarchical micro/meso/macroporous structure. The vapor adsorption indicated that the high content of silica sol improved the hydrophilicity greatly, and pyrolysis temperature also influenced the hydrophilicity to a minor degree. Notably, the silica sol is responsible for the formation of mesopores. The second part of the thesis was to investigate the mechanical and thermal properties of the obtained unidirectional porous SiOC ceramics prepared with MK and H44 at cryogenic and room temperatures. The compressive strength of monoliths was investigated both in air (293 Kelvin) and in liquid nitrogen (77 Kelvin). The influence of both liquid and cryogenic temperature on compressive strength was investigated. The compressive strength of monoliths showed not only anisotropy, but also a significant increase in liquid nitrogen. This increase may be due to the liquid nitrogen trapped inside the porous structures and cryogenic temperature. The linear thermal expansion coefficients (CTE), thermal conductivity and specific heat capacity of porous SiOC, were studied from cryogenic to room temperature. Both monoliths show anisotropic linear expansion coefficients, with the parallel direction having almost twice the shrinkage of the perpendicular direction. The monolith prepared with H44 showed thermal shrinkage twice as much as that prepared with MK and APTES, which might be due to the composition differences and measurement condition. The thermal conductivities of both monoliths made from two precursors showed anisotropic features and similar values. The minimum and maximum values for thermal conductivity are 0.2 and 0.9 Watts per meter per Kelvin. Thermal conductivities and specific heat capacities displayed an upward trend from low temperature to room temperature. It was assumed that the maximum heat conductivities of these materials were determined mainly by the macroporosity and the thermal conductivity of the hybrid material.
Dissertation
723 370
Some of the metrics are blocked by your
consent settings
Wicking into porous polymer-derived ceramic monoliths fabricated by freeze-casting
(ECERS, 2017-02-04)
Grebenyuk, Y.
;
Zhang, H. X.
;
Wilhelm, M.
;
Rezwan, K.
;
Dreyer, M. E.
Silicon oxycarbide monoliths of different pore size distribution were fabricated by freeze-casting. The samples revealed a lamellar pore structure with an axial anisotropy. To evaluate the capillary transport abilities we performed wicking experiments. The sample weight measurement method was applied during the imbibition. The samples show deviations in permeability from 10% to 49% at different sample orientations that quantifies the impact of the anisotropy in the axial direction. The deviations were larger for the samples with smaller pore size. For these samples we also observed larger differences in the wicking behaviour. The samples with bigger pore size demonstrated higher permeability and faster wicking. Imbibition results at both sample orientations showed a good agreement with a prediction via the Lucas–Washburn equation with gravity effects. We demonstrate hereby, that our approach of macroscopic modelling predicts wicking behaviour in anisotropic structures reasonably well, providing a simple tool for further porous material investigations.
Wissenschaftlicher Artikel
Band:37
Heft:5
101 87

Zhang, Huixing

Filter

Einstellungen

Sortieren nach

Ergebnisse pro Seite