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Objective Cerebral infarction has a poor prognosis and causes a serious burden on families and society. Recombinant tissue plasminogen activator (rt-PA) and urokinase (UK) are commonly used thrombolytic agents in the clinic. However, direct and powerful clinical trial evidence to determine the therapeutic effect of rt-PA and UK on intravenous thrombolysis is lacking. Methods In this study, 180 patients with acute cerebral infarction were treated with rt-PA or UK. The National Institutes of Health Stroke Scale (NIHSS) scores, Barthel index, bleeding complications, and biomarkers were evaluated. Results No significant differences in NIHSS or Barthel scores were found between the groups. However, UK increased the risk of intracranial haemorrhage compared with rt-PA. rt-PA had increased activity in reducing serum levels of MMP-9 than UK. Conclusion Intravenous thrombolysis with rt-PA and UK in the time window of acute cerebral infarction can achieve similar therapeutic effects, but rt-PA can further reduce the risk of cerebral haemorrhage and is relatively safer than UK.

A two dimensional silicon carbide fiber reinforced SiC matrix (2D SiC/SiC) composite fabricated by precursor infiltration pyrolysis (PIP) process used a liquid SiC ceramic precursor was obtained. Two key properties including matrix cracking stress and thermal residual stress were investigated for this PIP 2D SiC/SiC composites. Three methods were applied to determine the matrix cracking stress in order to obtained a trusted value, and the value of matrix cracking stress for SiC/SiC composite was 75±4 MPa. The thermal residual stress of the composites was calculated by linear regression line according to the loading-unloading-reloading stress-strain curve of the 2D SiC/SiC composite, and the result showed that the value of thermal residual stress of SiC matrix in composite was 20MPa, which means the PIP SiC matrix in the 2D SiC/SiC composite was under the compressive stress when the composite cooling down from the fabrication temperature to the room temperature.

In the sintering of ceramics, cracks are inevitably encountered after sintering. But very few studies have been presented in the literature for qualifying and quantifying effects of inhomogeneity on sintering kinetics. Therefore, a series of detailed sintering variables such as grain size, surface tension and diffusivity are chosen to study the effects of their inhomogeneity on sintering kinetics through a computational model calculated by computer.Furthermore, there are two main achievements in this computational model that first one is providing a numerical solution for the curvature at triple junction (pore tip) of microscopic particles, and second one is considering the effect of surface diffusion on first-stage sintering where diffusion mechanism is coupled by grain-boundary and surface diffusion.

A ZrB2-SiC multiphase ceramic was fabricated with a precursor pyrolysis method by using zirconium boride organic precursor and polycarbosilane. In order to study the pyrolysis process of complex phase ceramics, the pyrolysis process of the two precursors was studied respectively at the beginning. The precursor and the mixture with different weight ratios both pyrolyzed at 800°C. ~1500°C. under argon atmosphere. The specimens were characterized by thermo-gravimetric analysis, infra-red, X-ray diffraction. It was found that the pyrolysis products of PCS remained amorphous below 1000°C. and converted into crystallization with temperature increasing. ZrO2as the intermediate pyrolysis product of ZrB2precursor initiate convert to t-ZrO2from m-ZrO2at 1200°C.. Finally, all kinds of ZrB2-SiC multiphase ceramic are successful obtained via pyrolysis of precursor after 1500°C. And the 40wt%ZrB2precursor initial carbothermal reduction temperature below the ZrB2precursor reactive temperature and the crystal degree of SiC is higher than pyrolysis product of PCS.

In order to obtain the near net shaped SiC/SiC composite pins without the processing cost, four kinds of SiC fiber pin preforms including the knitting yarn and core yarn with two dimension braided structure were designed. The SiC/SiC composite pins were fabricated by precursor infiltration pyrolysis (PIP) process used a liquid SiC ceramic precursor. The results showed that, the near net shaped SiC/SiC composite pins could be obtained by using the designed SiC fiber preform and the graphite mould with curved groove. The macrostructure and microstructure of the SiC/SiC composite pins were observed by scanning electron microscope. Both the single shear stress-displacement curves and the double shear stress-displacement curves of the different kinds of SiC/SiC composite pins showed the saddle-shaped, which indicated the fracture model of the SiC/SiC composites pins was non-catastrophic, and the SiC/SiC composite pins in this paper possessed the secondary bearing capacity. This paper may provide some new ideas for fiber reinforced SiC ceramic matrix composites components designers.

：SiC/Si-B-C-N and SiC/SiC ceramic matrix composites were prepared through a combination of chemical vapor infiltration (CVI) and polymer impregnation pyrolysis process(PIP). The microscopic morphology and solid phase structure of the SiC/Si-B-C-N and SiC/SiC composites were investigated by SEM and XRD respectively. Moreover,the flexural strength and fracture toughness were measured using three point bending and single-edge notched beam test. Results showed that the formation of crystalline phases transformation was restrained by introduce BN into matrix phase, which might improve the stability of ceramic matrix composites. Furthermore, the flexural strength and fracture toughness of ceramic matrix composites increased to a maximum of 367 MPa and 26.81 MPa·m1/2 with the 30% PBN weight ratios which might be mainly caused by crack arresting, crack deflecting, micro cracks and fiber pullout.

Oxidation thermodynamics of silicon carbide (SiC)ceramic was studied by means of HSC Chemistry code, and the weight change, morphology and phase of oxidation products were analyzed by thermogravimetric analysis(TG), scanning electron microscopy(SEM ) and X-ray diffraction (XRD). The results showed that SiC ceramic could be oxidized to silicon dioxide(SiO2) with release of small molecular gases under oxidizing atmosphere at 800°C, and the formed SiO2 film with appropriate fluidity and low oxygen diffusion coefficient could prevent the spread of oxygen with the oxidation temperature increasing up to 1200°C, which favored the anti-oxidation of SiC ceramic matrix composite.

Equilibrium compositions of chemical vapor deposition progress for silicon carbide (CVD-SiC) coatings with MTS/H2 mixture system were calculated by means of HSC Chemistry5.0 code, and influences of the reaction temperature (T), the system pressure (P) and the composition of raw materials (molar ratio of H2 to SiCH3Cl3, β) were investigated. Thermodynamic analysis showed that the value of nC /nSiC in reaction product decreased to a minimum and then increased with the increase of the reaction temperature between 700-1600°C, which meant an optimal reaction temperature existed theoretically for CVD-SiC coatings with highest purity. Furthermore, CVD-SiC coatings with high purity were obtained by experiments under the reaction pressure of 10kPa, H2/SiCH3Cl3 value of 10 and reacton temperature of 1100°C, which was in accordance with the theoretical prediction.

SiC continuous fiber reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) and SiC fiber reinforced SiC micro ceramic matrix composites (SiCf/SiC micro-CMCs) were prepared through polymer impregnation pyrolysis (PIP) progress, then the structures, mechanical properties and forming mechanisms of SiCf/SiC CMCs were investigated. Results showed that volume shrinkage of SiC matrix occurred, and pyrolysates with bamboo-like layered structure were attached to the surface of SiC multifilament gradually. Furthermore, the mechanical properties of SiCf/SiC micro-CMCs were consistent with SiCf/SiC CMCs, so the PIP process parameters for the preparation of SiCf/SiC CMC might be optimized primarily through SiCf/SiC micro-CMCs, which could enhance the design and preparation efficiency of SiCf/SiC CMCs obviously.Key word: polymer impregnation pyrolysis progress, micro ceramic matrix composites, forming mechanism

The pyrolysis kinetic behaviors and reaction mechanism of polycarbosilane (PCS) were characterized by means of XRD, SEM and on-line TG-DSC-FTIR-MS coupling technique, which showed that the pyrolysis process accorded with the F2 integral model (300-600°C), and the values of apparent activation energy (Ea) and pre-exponential factor (A) were 56.10KJ/mol and 10.84, respectively. During the pyrolysis process, PCS was converted into amorphous inorganic solid from organic polymer with breakage and rearrangement of chemical bonds, then to well-defined crystal structure of good thermal stability. Furthermore, the weight loss occurred mainly among 300°C and 800°C with CH4, (CH3)4Si,(CH3)3SiH,(CH3)2SiH2and other silane gases releasing from pyrolysis product leading to the conversion from organic polymers to inorganic ceramic. The pyrolysis product was converted into β-SiC crystal completely at 1400°C, and the crystallization of α-SiC phase occurred after 1550°C which might influence the stability of SiC matrix. Key words:polycarbosilane, organic precursor, pyrolysis kinetic behavior

In order to investigate the influence of Tension-tension fatigue behavior of fiber reinforced ceramic-matrix composites, SiC/SiC composites with 2.5D fiber architecture were prepared via Precursor Infiltration and Pyrolysis (PIP) method. Tension-tension fatigue behavior of SiC/SiC composites was investigated in 1000°C and 1200°C, under fatigue stresses ranging from 70 to 120MPa at a frequency of 1.0 Hz, under oxidizing atmosphere. Fatigue life of SiC/SiC composites achieved 305, 984 cycles at 1200°C/70MPa, and 252, 988 cycles at 1200°C/108MPa, which were longer than test in 1000°C. Composite microstructure, as well as failure mechanism was investigated. The main reason that cause tension-tension fatigue failure of SiC/SiC composites are oxidation damage and stress damage. The microstructure of SiC/SiC composites demonstrated that the oxidation of interfaces and SiC fibers caused the failure of the composites. Under the load of alternating stress, the original voids and cracks in the material preparation process will be widened, and new cracks will be generated, for cracked SiC/SiC composites, oxygen in is especially serious at intermediate temperatures(∼800°C) where it can reach the SiC fiber before being sealed off by slow-glowing silica on the matrix crack surface, therefore, tension-tension fatigue life of SiC/SiC composites at 1000°C is lower than 1200°C.

The ZrC/SiC multi-components modified C/C composites were prepared by using a hybrid precursor containning polycarbosilane and organic zirconium-contained polymeric precursor as impregnant and C/C composites of low density as preform. The porosity, microstructure and mechanical properties of samples were characterized with mercury injection apparatus, scanning electron microscopy and universal electron testing machine respectively. The results show that the porosity and average pore diameter decrease firstly and increase subsequently with the increase of organic zirconium content of the precursor. When the content of organic zirconium is 50%, the porosity and average pore diameter reach minimum which were7.27% and 0.0795um respectively. The most probabilistic pore diameter shifted from 10-100um to 1-10um at the same time; Meanwhile, the flexural properties also increases and drops immediately as the content of organic zirconium in the precursor adds. When the content of organic zirconium is 25%, the flexural strength reaches maximum of 245.20MPa.The improved flexural properties is attributed to the proper bonding of fiber-matrix interface and the low porosity of samples.

The pyrolysis dynamic process of ZrB2 organic precursor,soluble in benzene homologues with polycarbosilane, was characterized by means of on-line TG-DSC-FTIR-MS coupling technique. The conversion mechanism of ZrB2 ceramic was investigated based on EDS, SEM and XRD. The results show that methylamine, methane, acetone and propene were given off before heat treatment at 1000°C, and the pyrolysis product of ZrB2 precursor existed in the form of ZrO2, B2O3 and amorphous carbon. ZrB2 crystals are obtained completely by the carbothermal reduction process with the release of carbon dioxide at 1500°C. Key words:ZrB2 organic precursor, pyrolysis kinetic behavior, carbothermal reduction process.

The pyrolysis ceramic dynamic process of ZrC ceramic precursor was characterized by means of on-line TG-DSC-FTIR-MS coupling technique, and the conversion mechanism of ZrC ceramic was investigated based on XRD, SEM, TEM and XRF. ZrC ceramic could be obtained at 1400°C lower than theoretic temperature when Zirconium element is reduced by carbon from ZrO2. The results showed that ZrC ceramic precursor presented storage stability and excellent solubility in toluene. Ethanol, carbon dioxide, acetone and tetrahydrofuran (THF) were given off before heat treatment at 1100°C, and the pyrolysis product held in the form of ZrO2 and amorphous carbon. ZrC crystals were gradually formed when heated up to 1200°C and obtained completely at 1400°C. This ZrC ceramic precursor provides promising candidate for oxidation resistance and ablation resistance ZrC-SiC ceramic matrix composites.

SiC fiber reinforced SiC matrix (SiCf-SiC) composites with and without pyrolytic carbon interphase were prepared by polymer impregnation pyrolysis (PIP) progress. The effect of pyrolytic carbon interphase on the fracture behavior and mechanical properties of SiCf/SiC composites was studied. The results show that pyrolytic carbon interphase weakened the bonding between the matrix and the fibers. The mechanical properties of SiCf-SiC composites with carbon coating were improved effectively via fiber debonding and pulling-out from matrix under external loads. The flexural strength and fracture toughness of the above composites reached up to 498.52MPa and 24.09MPa•m1/2, respectively.

This paper investigated the Cf/SiC ceramic matrix composites. By utilizing different interfacial treatment processes to prepare carbon-fiber preform, the preform was then densified by infiltration and pyrolysis(PIP) with polycarbosilan/xylene solution as precursor, and the Cf/SiC ceramic matrix composite specimens were fabricated. Mechanical tests such as bending test and fracture toughness were performed for Cf/SiC samples. The results show that the interfacial bonding strength in the sample with high-temperature treatment process was improved due to removing surface sizing. The samples which were treated up to 1400°C exhibited the highest three-point flexural strength, up to 595MPa; The samples which were treated up to 1400°C and deposited by pyrolytic carbon(PyC) coating shows the highest fracture toughness value which was 20.70MPa•m1/2.

Polycarbosilane (PCS) is one of precursor systems applied in industry for the Polymer Infiltration Pyrolysis (PIP) processing of C or SiC fiber reinforced SiC matrix composites (Cf/SiC or SiCf/SiC CMC) materials. In this work, a series of PCS-derived SiC specimens treated at 300, 550, 800, and 1100 °C was studied by XRF, IR, XRD and XPS methods. The results show that a slight amount of PCS molecules with low softening point evaporates below 300 °C; the cross-link between PCS chains takes place to form a 3D -Si-C-Si- network via the reaction between -Si-CH3, -Si-CH2-Si- and -Si-H groups in the temperature range of 300-550 °C; an amorphous phase of SiC was observed when PCS was heated up to 800 °C, which indicates the completion of transformation from organic to inorganic; above 800 °C, β-SiC domain grows. Furthermore, a surface structure evolution of PCS-derived SiC specimens with temperature is proposed after the analyzing the XPS spectra.

A titanium-boron-carbon coating was fabricated on a graphite substrate by heating TiB2 powder on a graphite surface above the eutectic temperature. The coating consisted of a pure graphite layer on the outer surface and a TiB2-C alloy layer inside. The graphite layer had many wrinkles due to the difference in the thermal expansion coefficients of TiB2 and graphite. The TiB2-C alloy layer had a continuous three-dimensional interpenetrating network microstructure. The d002 value of the graphite in the alloy layer was 0.335 6 nm, which was quite close to that of single crystal graphite (0.335 4 nm). Raman and X-ray photoelectron spectroscopy indicated that the graphite in both layers was doped substitutionally with boron atoms. A water quench thermal shock test verified a high adhesion strength between the coating and the substrate. This method is promising for the fabrication of thermal barrier coatings on carbon materials.