Jin Liang Sun

Preparation and Properties of Epoxy Matrix for Composite Cable Core

According to the requirements of aluminum conductor composite cores, a kind of resin system was developed with TGDDM as main body, and self-made flexible epoxy SUC-1 as auxiliary, plus methyl hexahydrophthalic anhydride as curing agent. The gel rate of the system was high enough to meet the demands of pultrusion technique. The heat deformation temperature of cured sample reached 194°C, and the tensile strength achieved 62.95Mpa. The elongation at break matched that of carbon fibers. The interfacial bonding between the matrix and the fibers, observed by scanning electron microscope, was tight without debonding phenomenon.

Toughness and Thermal Properties of a Dimer Acid Modified Tetrafunctional Epoxy Resin

In order to improve the toughness of the cured aromatic tetrafunctional epoxy resins in the premise of influencing the thermal properties as little as possible, the aromatic tetrafunctional epoxy named N,N,N’,N’-tetraglycidyl-4,4’-diaminodiphenyl ether (TGDDE) was modified by a dimer carboxylic acid (DFA), and then the epoxies were cured with methyl nadic anhydride (MNA). In the present work, the toughness was characterized with the impact resistance tested by pendulum impact testing. Besides, the thermal properties of the cured epoxy resin were investigated with the thermo-gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The impact testing results indicated that the toughness of the cured resins could be improved after the modification and increased with the increasing content of DFA. The thermal analysis showed that the thermal properties of the cured resins were not influenced obviously since the thermal stabilities of the products could be improved and the glass transition temperature of them were not influenced obviously when the tetrafunctional epoxy modified with appropriate content of DFA.

Thermal Shock Resistance of Yb2SiO5/Si and Yb2Si2O7/Si Coatings Deposited on C/SiC Composites

Rare-earth silicates, especially ytterbium silicate (Yb2SiO5 and Yb2Si2O7), have been developed for promising environmental barrier coatings (EBCs) for SiC-matrix composites. In this study, double-layer Yb2SiO5/Si and Yb2Si2O7/Si EBC systems were deposited on C/SiC composites by air plasma spray (APS) technique, respectively. Both systems were subjected to thermal shock tests at 1400 °C. The evolution of phase composition and microstructure of those samples before and after thermal shock test were characterized. Results showed that there were penetrating microcracks in the top Yb2SiO5 layer and horizontal microcracks at the Yb2SiO5-Si interface after thermal shock test. While extremely few microcracks and no horizontal microcracks were presented in the Yb2Si2O7/Si sample. The EDS analysis also showed that the Si bond layer of the Yb2SiO5/Si sample was oxidized more serious than that of the Yb2Si2O7/Si sample. The different thermal shock behaviors of both systems were clarified based on the thermal expansion behavior, phase composition and microstructure analysis.

The Characterization of Fibrous Material in CVI Graphite Cylinder Wall

By isothermal chemical vapor infiltration (ICVI) preparation of carbon/carbon composites, We found fibrous materials with silver metallic luster in CVI furnace graphite cylinder outer wall, fiber diameter is 1 ~ 2 mm, length is 4 ~ 15 mm. The characterization of fibrous material have been systematically studied by scanning electron microscopy (SEM),element analysis, energy dispersive X-rays spectroscopy (EDS).After 2300 degrees heat treatment, the fibrous material were characterized by ultra-violet laser Raman spectroscopy. The SEM examination shows that these fibrous materials have a spherical top, the cross-section reveals a unique structure in which layers like growth rings lie concentrically on top of each other. The EDS analysis show the main element of fibrous material is carbon and a small amount of metallic element. Raman spectra show after 2300°C high temperature treatment ,the carbon fibrous material transformed from layer structure to graphite structure.

Effect of DFA Modification on Thermal Properties of Multifunctional Epoxy/Anhydride Systems

The thermal stabilities of two amine based multifunctional epoxy resins (TGDDE/MNA & TGBAPP/MNA) and two dimer carboxylic acid (DFA) toughened resins (DFA-TGDDE/MNA & DFA-TGBAPP/MNA) were comparatively investigated with the thermo-gravimetric analysis (TG). The TG parameters of the resins indicated that the thermal stability of the resins was increased after the modification. Furthermore, the thermal degradation kinetics was studied with a dynamic method according to Ozawa model, which explained this phenomenon.

Ablation Behavior of Low Pressure Plasma Sprayed TiB2-MoSi2 Composite Coatings

In this work, TiB2-MoSi2 composite coatings with various contents of MoSi2 (20 vol. % and 40 vol. %, respectively) were fabricated on SiC coated C/C substrates by low pressure plasma spray (LPPS) technique. The microstructure and phase composition of the coatings were characterized. The ablation behaviors of the composite coatings were evaluated and compared with the pure TiB2 coating using a plasma flame of about 2200°C. The results showed that MoSi2 was uniformly distributed in the TiB2 matrix. All the coatings kept intact after the ablation for 60s - 180s, indicating their excellent ablation resistance. The addition of MoSi2 had great influence on the ablation behavior of the composite coatings. The TiB2 coating gained mass after the ablation. The mass of the TM20 coating increased firstly (60s and 120s) and then decreased at 180 s. Mass loss was observed for the TM40 coating during the whole procedure of ablation test.

Preparation and Properties of Rectorite/Epoxy Nanocomposites

The Org-rectorite, which was used as a filler in the Rectorite/Epoxy nanocomposites, was prepared by the intercalation and exfoliation of rectorite with dodecyl-bis (2-hydroxyethyl)-methylazanium chloride as the organic cation exchange agent. The two curing agents methyl hexahydrophthalic anhydride (MHHPA) and m-phenylenediamine were employed at working temperature ranging from 70 °C to 190 °C. The samples were characterized by Fourier Transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and differential scanning calorimeter (DSC) analysis. The results show that the d001 (55.9 Å) of Rectorite/Epoxy composites cured with MHHPA at 70 °C was larger than the Org-rectorite (28.7 Å), and the Org-rectorite was exfoliated at 90 °C working temperature. While the d001 of Rectorite/Epoxy composites cured with m-phenylenediamine at 70 °C and 90 °C were 40.9 Å and 42.1 Å , and were exfoliated at 140 °C. The apparent activation energy (Ea) of Rectorite/Epoxy composites cured with MHHPA and m-phenylenediamine were obtained to be 74.85 and 59.15 KJ/mol, respectively. The higher apparent activation energy (Ea) of MHHPA systems may be responsible for the lower exfoliation temperature.

Ablation Properties of C/C-ZrC-SiC Composites

The ablation properties of C/C-ZrC-SiC composites prepared by precursor infiltration and pyrolysis processes were studied by the H2-O2 ablation method. The results indicate that the C/C composite of 1.28 g•cm-3 was densified to C/C-ZrC-SiC composite of 1.42 g•cm-3 after infiltration and pyrolysis once, the density increased 10.94%. The linear ablation rate and mass ablation rate of the C/C-ZrC-SiC composites (ρ=1.42g•cm-3) were 7.22μm•s-1and 3.88mg•s-1, which decreased 79.31% and 65.46% comparing with C/C composite of 1.28 g•cm-3 respectively. The introduction of ZrC-SiC into the matrix greatly enhanced the anti-oxidative and ablation property of the C/C composite. The ablation mechanisms of the C/C-ZrC-SiC composites were supposed to be the synergistic effects of thermo-chemistry ablation (oxidation and sublimation) and mechanical erosion.

Preparation of C/C-SiC Composite with Hydrogen-Containing Polysiloxane as Ceramic Precursor

This study focuses on the conditions of preparation of C/C-SiC composites through polymer infiltration and pyrolysis method using hydrogen-containing polysiloxane as the precursor and divinylbenzene as cross-linking agent. The densities of different C/C composites (ρ=1.02, 1.21, 1.60, 1.78g·cm-3) increased to 1.24, 1.36, 1.69, 1.84g·cm-3 respectively after infiltration and pyrolysis four times. The appropriate ratio of hydrogen-containing polysiloxane and divinylbenzene was 1/0.5. The appropriate cross-linking temperature was 250°C. In pyrolysis process, the appropriate increasing rate of pyrolysis temperature should be 50°C/h in the range of 300-800°C. SiC was formed when pyrolysis temperature reached 1550°C.The linear ablation rate and mass ablation rate of C/C-SiC composites were much lower than those of C/C composites.

Dynamic Mechanical Thermal Analysis of Pultruded Carbon Fiber/Resin Composite Cable Cores

The viscoelastic property of the CTC composite cores was investigated through dynamic mechanical thermal analysis (DMTA) in single cantilever mode. The effect of the frequency on the glass transition temperature (Tg) was studied. The results show that the peaks were shifted to higher temperatures with increasing frequencies. Tgof CTC was approximately 180 °C, much higher than that of a home-made composite core (Composite I). The activation energy ΔH of CTC is also greater than that of Composite I. The CTC sample exhibit better stiffness and toughness.