B. L. Zhou

Oxidation protection of carbon fibers by coatings

SiC coatings prepared by chemical vapor deposition and from polycarbosilane (PCS) solution; also, SiO2 and Al2O3 coatings by Sol-Gel method were investigated in detail, to improve the oxidation resistance of carbon fibers as important reinforcement in advanced composites. A beta-SiC coating was obtained on carbon fibers by pyrolysis of CH3SiCl3 and H-2 at 1373-1573 K. The coating thickness could be controlled according to the requirements in practice. A uniform and fine SiC coating was also obtained by immersion and pyrolysis of PCS solutions with PCS contents of 5-15 wt%, and was composed of a mixture of SiC, SiO2, and free carbon after pyrolysis in argon. Fine and dense SiO2 and Al2O3 coatings could be obtained from silica and alumina sols, respectively, under exact control of process parameters. All coatings had good effects on the oxidation resistance of carbon fibers in the sequential order of CVD SiC, PCS-SiC, SiO2, and Al2O3. A composite coating of CVD SiC and a mixing coating of SiO2 and Al2O3 was suggested to decrease defects like pores and microcracks in individual coatings to obtain the best oxidation protection for carbon fibers.

Biomimicry of bamboo bast fiber with engineering composite materials

Bamboo, one of the strongest natural structural composite materials, has many distinguishing features. It has been found that its reinforcement unit, hollow, multilayered and spirally-wound bast fiber, plays an extremely important role in its mechanical behavior. In the present work, on the basis of the study on bamboo bast fiber and wood tracheid, a biomimetic model of the reinforcing element, composed of two layers of helically wound fiber, was suggested. To detect the structural characteristics of such a microstructure, four types of macro fiber specimens made of engineering composites were employed: axially aligned solid and hollow cylinders, and single- and double-helical hollow cylinders. These specimens were subjected to several possible loadings, and the experimental results reveal that only the double-helical structural unit possesses the optimum comprehensive mechanical properties. An interlaminar transition zone model imitating bamboo bast fiber was proposed and was verified by engineering composite materials. In our work, the transition zone can increase the interlaminar shear strength of the composite materials by about 15%. These biomimetic structural models can be applied in the design and manufacture of engineering composite materials.

Reformed bamboo and reformed bamboo/aluminium composite

A new technique has been developed which aims at changing the form of bamboo from its natural circular cross-section into a plate for convenient use. The manufacturing technique covers three major processes: softening, compression and fixture. The microstructure of reformed bamboo was studied both qualitatively and quantitatively. The mechanical properties of reformed bamboo were tested and the results show a remarkable increase compared with normal bamboo. Although the reformed bamboo has many advantages, such as higher specific properties, inexpensive cost, etc., the composition of reformed bamboo with aluminium alloy sheets further improves the comprehensive performance.A new technique has been developed which aims at changing the form of bamboo from its natural circular cross-section into a plate for convenient use. The manufacturing technique covers three major processes: softening, compression and fixture. The microstructure of reformed bamboo was studied both qualitatively and quantitatively. The mechanical properties of reformed bamboo were tested and the results show a remarkable increase compared with normal bamboo. Although the reformed bamboo has many advantages, such as higher specific properties, inexpensive cost, etc., the composition of reformed bamboo with aluminium alloy sheets further improves the comprehensive performance.

In-vitro apatite formation on phosphorylated bamboo.

Natural self-reinforced composite, bamboo, was surface modified by phosphorylation with urea–H3PO4 and NaOH–H3PO4 methods; then precalcification was performed by immersing samples in saturated Ca(OH)2 solution. After that, calcium phosphate can be formed on the surface of bamboo samples in calcification media: simulated body fluid (1.5 SBF) and accelerated calcification solution (ACS). Experimental results reveal that pre-calcification is an inevitable step for the formation of calcium phosphate. The calcium phosphate formed in 1.5 SBF was identified by thin-film X-ray diffraction as apatite which was not well crystallized. Compared with the urea–H3PO4 method, the NaOH–H3PO4 method has the advantages of quicker and continuous apatite formation and stronger adhesive between apatite and bamboo.

Fabrication of carbon fibre-reinforced aluminium composites with hybridization of a small amount of particulates or whiskers of silicon carbide by pressure casting

An investigation was carried out on the fabrication of carbon fibre-reinforced aluminium matrix composites with hybridization of particulates or whiskers of silicon carbide by pressure casting. A small amount of particulates or whiskers was uniformly distributed among carbon fibres and the preforms prepared from the treated fibres were directly infiltrated by molten aluminium under applied stress. It was found that the longitudinal tensile strengths of hybrid composites were greatly improved, although their fibre volume fractions were very low compared to those of conventional composites. With this hybridization method, it is also practical to tailor the fibre volume fraction of composites from 60 to 25 vol %, which is not possible in direct infiltration of fibre preforms by pressure casting. The results obtained lead to the conclusion that particulate or whisker additions act not directly as reinforcements but as promoters to improve the infiltration performances of fibre preforms, and consequently to increase the strength-transfer efficiency of carbon fibres. The addition of particulates or whiskers can also improve other properties of the composites, such as hardness and wear resistance.

Characteristics of several carbon fibrereinforced aluminium composites prepared by a hybridization method

The properties and microstructures of several high-strength and high-modulus carbon fibrereinforced aluminium or aluminium alloy matrix composites (abbreviated as HSCF/Al and HMCF/Al, respectively, for the two types of fibre) have been characterized. The composites evaluated were fabricated by pressure casting based on a hybridization method. It was found that the strength degradation of high-modulus carbon fibres after infiltration of aluminium matrices was not marked and depended upon the type of aluminium matrix. However, the strength of high-strength carbon fibres was greatly degraded by aluminium infiltration and the degradation seemed to be independent of the type of aluminium matrix. The longitudinal tensile strength (LTS) of CF/Al composites was very different between HMCF/Al and HSCF/Al composites. The HMCF/Al composites had LTS values above 800 MPa, but the HSCF/Al composites had only about 400 MPa. In contrast, the transverse tensile strength of the HSCF/Al composites, above 60 MPa, was much higher than that of the HMCF/Al composites, about 16 MPa. Chemical reactions were evident to the interface of high-strength carbon fibres and aluminium matrices. There was no evidence of chemical products arising between high-modulus carbon fibres and Al-Si alloy and 6061 alloy matrices. However, it was considered that some interfacial reactions took place in pure aluminium matrix composites. Fracture morphology observation indicated that the good LTS of CF/Al composites corresponded to an intermediate fibre pull-out, whereas a planar fracture pattern related to a very poor LTS and fibre strength transfer. The results obtained suggested that interfacial bonding between carbon fibres and aluminium matrices had an important bearing on the mechanical properties of CF/Al composites. An intermediate interfacial bonding is expected to achieve good longitudinal and transverse tensile strengths of CF/Al composites.

Study on epoxy resin modified with prepolymers containing spiro orthocarbonate

The paper described the modification of epoxy resin using a new prepolymer containing spiro orthocarbonate. It was found that the addition of prepolymer into epoxy resin system enhanced the conversion of epoxy groups and the T-g and thermal stability of the matrix were slightly reduced. The adhesive tensile and shear strength of the modified epoxy resin increased obviousely as the content of the prepolymer increased. The above observed phenomena were discussed, and the relationship between shrinkage and adhesive strength was investigated.

SiC coating on carbon fibres by a solution coating process

One way of overcoming the shortcomings of carbon fibres is to coat them with SiC. In this work, carbon fibres were coated with a polycarbosilane solution and then pyrolysed continuously at high temperature to obtain the SiC coating. Effects of the coating process on the structure of the coating and the properties of the coated fibres were studied in detail. The results show that the solution coating process is a simple and applicable technique. The uniform and continuous coating improved the oxidation resistance and strength of the carbon fibres, as well as their wettability with aluminium. The coating also controlled the harmful reaction at the interface of aluminium matrix composites and improved composite strength.

Hybridization with SiC particulates to control the fibre volume fraction and improve the longitudinal tensile strength of carbon fibre-reinforced aluminium composites

acad sinica,inst met res,shenyang 110015,peoples r china. nagasaki univ,dept mat sci & engn,nagasaki 852,japan.;cheng, hm (reprint author), govt ind res inst,tosu,saga 841,japan

Biomimetic coating of bioactives ceramic on bamboo for biomedical applications

ACAD SINICA,INST MET RES,SHENYANG 110015,PEOPLES R CHINA.;Li, SH (reprint author), LEIDEN UNIV,BIOMAT RES GRP,PROF BRONKHORSTLAAN 10,NL-3723 MB BILTHOVEN,NETHERLANDS