Development of a new continuous Si-Ti-C-O fibre using an organometallic polymer precursor

A polytitanocarbosilane, which is useful as the precursor polymer for ceramic fibre, was synthesized using polydimethylsilane, polyborodiphenylsiloxane and titanium tetraisopropoxide. The polytitanocarbosilane was melt-spun and using the continuous heat-treatment process from the polymer fibre to ceramic fibre, flexible Si-Ti-C-O fibre was produced. The density, tensile strength and Young's modulus of this amorphous ceramic fibre were found to be 2.35 g cm^–3, 3.0±0.2 and 220±10 GPa, respectively. The Si-Ti-C-O fibre retained its high tensile strength to higher temperatures (about 1200° C). The specific resistance of this ceramic fibre covered a wide range of 10⁷ to 10^–1cm. This ceramic fibre is considered to be useful as reinforcement fibre for composites.     

Synthesis of SiC fibre with low oxygen content and high tensile strength using a polyblend precursor

SiC fibre with low oxygen content and high tensile strength was first synthesized in our laboratory. The SiC fibre was obtained by using a polyblend of polycarbosilane (PC) and hydroxy-terminated-polybutadiene (HTPB) as a precursor. It was found that PC could react with HTPB to form cross-linked polymers at temperatures around 260 ° C, so the HTPB can be used as a curing agent. Consequently, the need for oxygen to be introduced in the air-curing process is reduced and SiC fibre with low oxygen content and higher tensile strength can be made. The chemical compositions, the oxidation resistance and chemical stability of the SiC fibre were also studied here.     

A model SiC-based fibre with a low oxygen content prepared from a polycarbosilane precursor

A model SiC-fibre has been prepared from a polycarbosilane precursor by means of an irradiation oxygen-free curing process. The chemical composition remains unchanged after heat treatments under an inert atmosphere for pyrolysis temperatures of 1600°C. At this temperature, the fibre consists of SiC nanocrystals (mean size 6–10 nm) and free carbon. However, a slow grain growth takes place as the temperature is increased. The fibre retains a high strength at room and high temperatures up to temperatures of 1600 °C when the pyrolysis has been performed under nitrogen. The electrical conductivity was studied as a function of the pyrolysis temperature Tp: For 1100≤Tp≤1200 °C, the conductivity increases by several orders of magnitude due to the reorganization of the free carbon phase at the SiC grain boundaries. Oxidation kinetics of the filaments remain parabolic from 1000–1400 °C. This revised version was published online in November 2006 with corrections to the Cover Date.     

Thermal behaviour of a polytitanocarbosilane-derived fibre with a low oxygen content: the Tyranno Lox-E fibre

The chemical composition, microstructure and mechanical properties of Tyranno Lox-E fibre were studied in the as-received state and after annealing in inert atmosphere. The fibre consists of SiC nanocrystals of 2–3 nm, free carbon aggregates of 4–5 distorted aromatic layers and 1–3 nm in length and an amorphous silicon (titanium) oxycarbide phase. Except for evolution of residual hydrogen and a slight densification, the fibre is chemically and structurally stable and retains a high strength up to 1300°C. Beyond 1300°C, superficial degradation resulting from decomposition of the oxycarbide into SiO(g) and CO(g) induces a decrease of strength. Compared with bulk polycrystalline SiC, the fibre has a low creep resistance at high temperature, mainly because of the nanometric size of the SiC crystals but also because of the presence at the grain boundary of the oxycarbide phase (viscous and chemically unstable) and of the poorly organized free carbon phase (chemically and structurally unstable). © 1998 Chapman & Hall     

Tensile creep behaviour of a silicon carbide-based fibre with a low oxygen content

The high-temperature mechanical behaviour and microstructural evolution of experimental SiC fibres (Hi-Nicalon) with a low oxygen content (<0.5 wt%) have been examined up to 1600 °C. Comparisons have been made with a commercial Si-C-O fibre (Nicalon Ceramic Grade). Their initial microstructure consists of -SiC crystallites averaging 5–10 nm in diameter, with important amounts of graphitic carbon into wrinkled sheet structures of very small sizes between the SiC grains. The fall in strength above 800 °C in air is related to fibre surface degradation involving free carbon. Crystallization of SiC and carbon further develops in both fibres subject to either creep or heat treatment at 1300 °C and above for long periods. The fibres are characterized by steady state creep and greater creep resistance (one order of magnitude) compared to the commercial Nicalon fibre. The experimental fibre has been found to creep above 1280 °C under low applied stresses (0.15 GPa) in air. Significant deformations (up to 14%) have been observed, both in air and argon above 1400 °C. The stress exponents and the apparent activation energies for creep have been found to fall in the range 2–3, both in air and argon, and in the range 200–300 kJ mol^–1 in argon and 340–420 kJ mol^–1 in air. The dewrinkling of carbon layer packets into a position more nearly aligned with the tensile axis, their sliding, and the collapse of pores have been proposed as the mechanisms which control the fibre creep behaviour.     

Thermal stability of a PCS-derived SiC fibre with a low oxygen content (Hi-Nicalon)

The oxygen free Si–C fibre (Hi-Nicalon) consists of -SiC nanocrystals (5nm) and stacked carbon layers of 2–3nm in extension, in the form of carbon network along the fibre. This microstructure gives rise to a high density, tensile strength, stiffness and electrical conductivity. With respect to a Si–C–O fibre (Nicalon NL202), the Si–C fibres have a much greater thermal stability owing to the absence of the unstable SiOxCy phase. Despite its high chemical stability, it is nevertheless subject to a slight structural evolution at high temperatures of both SiC and free carbon phases, beginning at pyrolysis temperatures in the range 1200–1400°C and improving with increasing pyrolysis temperature and annealing time. A moderate superficial decomposition is also observed beyond 1400°C, in the form of a carbon enriched layer whose thickness increases as the pyrolysis temperature and annealing time are raised. The strength reduction at ambient for pyrolysis temperatures below 1600°C could be caused by SiC coarsening or superficial degradation. Si–C fibres have a good oxidation resistance up to 1400°C, due to the formation of a protective silica layer.     

Extrusion of alumina fibre using sol-gel precursor

Alumina fibres were prepared by extrusion using boehmite sol as binder. The microstructure and mechanical properties of the fibres were studied. The fibres sintered at 1400 oC have relatively dense microstructure and the highest strength.     

Decoration of single-walled carbon nanotubes with Pt nanoparticles from an organometallic precursor

Carbon nanotubes (CNTs) are nanomaterials of high interest due to their unique structural, electrical, and mechanical properties. Carbon materials have been widely employed to support metallic nanoparticles for catalysis and electrochemical applications. In this work, we investigated the synthesis of platinum nanoparticles generated from the complex Pt₂(dba)₃ (tris(dibenzylideneacetone) diplatinum) and stabilized with a long alkyl chain amine, hexadecylamine (HDA) and supported on functionalized single-walled carbon nanotubes (SWCNTs). High resolution transmission electron microscopy (HRTEM) studies revealed isolated Pt nanoparticles (2?C3 nm) on SWCNTs. Powder X-ray diffraction (XRD) was used to assess the structure of Pt nanoparticles dispersed on SWCNTs assigned to Pt face-centered cubic (fcc). Additionally, infrared Fourier transform spectroscopy confirmed the presence of the stabilizer at the surface of the Pt nanoparticles even after the purification step and functional groups at the surface of pre-treated SWCNTs. This synthetic method may be an alternative route to prepare small size Pt nanoparticles supported on functionalized SWCNTs.     

The abrasive wear behaviour of continuous fibre polymer composites

The dry abrasive-dominant wear behaviour of several composite materials consisting of uni-directional continuous fibres and polymer matrices was investigated. Seven materials were examined: neat epoxy (3501-6), carbon fibre epoxy (AS4/3501-6), glass fibre/epoxy (E-glass/ 3501-6), aramid fibre/epoxy (K49/3501-6), neat polyetheretherketone (PEEK), carbon fibre/PEEK (APC2) and aramid fibre/PEEK (K49/PEEK). The wear behaviour of the materials was characterized by experimentally determining the friction coefficients and wear rates with a pin on-flat test apparatus. First, the effects of the operation variables apparent normal pressure, sliding velocity and apparent contact area were observed. The dimensionless wear rate increased linearly as the apparent normal pressure increased and decreased as the apparent contact area increased. Second, through microscopic observations of the worn surfaces and subsurface regions, basic wear mechanisms were identified as a function of fibre orientation. Observations of fibre-abrasive particle interactions allowed for the differentiation of the dominating wear mechanisms. Finally, a network of data was compiled on the wear behaviour in terms of the three material parameters: fibre orientation, fibre material and matrix material. This enabled the systematic selection of an ideal low wear composite material which would consist of a PEEK matrix reinforced with aramid fibres oriented normal to the contacting surface and carbon fibres oriented parallel to the contacting surface.     

Tests of continuous concrete slabs reinforced with carbon fibre reinforced polymer bars

Although several research studies have been conducted on simply supported concrete elements reinforced with fibre reinforced polymer (FRP) bars, there is little reported work on the behaviour of continuous elements. This paper reports the testing of four continuously supported concrete slabs reinforced with carbon fibre reinforced polymer (CFRP) bars. Different arrangements of CFRP reinforcement at mid-span and over the middle support were considered. Two simply supported concrete slabs reinforced with under and over CFRP reinforcement and a continuous concrete slab reinforced with steel bars were also tested for comparison purposes. All continuous CFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. It was also shown that increasing the bottom mid-span CFRP reinforcement of continuous slabs is more effective than the top over middle support CFRP reinforcement in improving the load capacity and reducing mid-span deflections. The ACI 440.1R–06 formulas overestimated the experimental moment at failure but better predicted the load capacity of continuous CFRP reinforced concrete slabs tested. The ACI 440.1R–06, ISIS–M03–07 and CSA S806-06 design code equations reasonably predicted the deflections of the CFRP continuously supported slabs having under reinforcement at the bottom layer but underestimated deflections of continuous slabs with over-reinforcement at the bottom layer.     

Interfacial reactions in aluminum/SiC fibre composite electric power cable using low oxygen SiC fibre reinforcement

We have evaluated the interfacial reactions of SiC fibre reinforced Al electrical power cable using low oxygen SiC fibre (Si : 62.4, C : 37.1, 0 : 0.5 mass%), and determined the relationship between the tensile strength and the amount of reaction products at the interface. The following are occurring at the SiC/Al interface: i) diffusion of Al atoms into the SiC fibre, ii) formation of needle–shape Al₄C₃ compounds, and iii) formation of Al₉Si compounds. Formation of Al₄C₃ and Al₉Si compounds at the interface causes the strength of SiC/Al composite electric power cable to deteriorate.     

Correlation between microstructure and mechanical behaviour at high temperatures of a SiC fibre with a low oxygen content (Hi–Nicalon)

An oxygen free Si–C fibre has been studied in terms of the chemical, structural and mechanical properties produced as a function of annealing treatments. In spite of its high thermal stability with regard to a Si–C–O fibre the Si–C fibre was subject to moderate SiC grain growth, organization of the free carbon phase and densification within the temperature range 1200–1400°C. The strength reduction at ambient for temperatures ≤1600°C could possibly be due to SiC coarsening or superficial degradation. Bend stress relaxation (BSR) and tensile creep tests show that the as-received fibre undergoes a viscous flow from 1000°C. The thermal dependance of the creep strain rate strongly increases at temperatures ≥1300°C. This feature might be partly explained by the structural evolution of the fibre occurring above this temperature. Heat treated fibres (1400–1600°C) exhibit a much better creep strength, probably due to their improved structural organization. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis of polycrystalline alumina-zirconia fibre using chelated aluminium-zirconium precursor

Polycrystalline alumina-zirconia fibres were successfully synthesized by pyrolysis of preceramic fibres formed from mixed aluminium-zirconium chelate compounds. Ethyl 3-oxobutanoatodiisopropoxyaluminium (EOPA) was reacted with zirconium tetrabutoxide (TBZ) in the presence of glacial acetic acid yielding a polymeric product. The infrared absorptions from 500–625 cm^–1 due to Al-O and Zr-O bonds changed from sharp to coalesced bands by treatment with acetic acid. The signal at 40 p.p.m. in the ²⁷Al spectra of EOPA-TBZ increased in intensity on treating with acetic acid. The viscosity of the polymeric product increased as the amount of acetic acid increased. The viscosity of the precursor decreased on increasing the measurement temperature from 60 °C to 75 °C. The precursor polymer pyrolysed at 800 °C in air showed a broad X-ray diffraction of -alumina, and crystallized in a mixture of -alumina and tetragonal zirconia at 1000 °C. The median diameter of tetragonal zirconia in the -alumina matrix was 33 nm, when EOPA-TBZ (Al/Zr=9/1) was heat treated at 1300 °C for 1 h. The precursor fibres were pyrolysed at 1300 °C to yield fine-grained fibres of -alumina including tetragonal zirconia, which was confirmed by Raman microprobe spectroscopy.     

低氧含量液态超支化聚碳硅烷的合成与陶瓷化研究

以甲醇对氯甲基三氯硅烷(Cl3SiCH2Cl)进行烷氧化反应,然后经过格氏偶联反应和还原反应,制备了低氧含量液态超支化聚碳硅烷(HBPCS)。通过凝胶渗透色谱法(GPC)、核磁共振(NMR)以及元素分析对由此制备的HBPCS进行表征。结果表明,提高烷氧化比例,可以有效抑制溶剂四氢呋喃开环的副反应,降低先驱体氧含量。通过热失重分析(TGA)和X射线衍射(XRD)分别对HBPCS的热性能及相应陶瓷在高温下的结晶行为进行研究。     

Rheology of low carbon fibre content reinforced cement mortar

It is recognised that the addition of carbon fibres to a brittle cement matrix results in a less dense composite with enhanced ductility, improved impact resistance and increased toughness. In addition, the reinforcing effect of fibres in the cement often produces superior flexural strength and marked improvements in post-cracking behaviour. Further, carbon fibres influence the electrical properties of the composite which could, potentially, make it a smart material, with a range of applications. Despite attention directed towards the mechanical and electrical properties of carbon fibre reinforced cement (CFRC), there is a dearth of information of the influence of fibre additions on the rheological properties of the resulting composite. To this end, this paper describes an investigation using the Viskomat NT into the influence of carbon fibre additions (fibre length in the range 3–12 mm and volume in the range 0–0.5%) on the rheological properties of CFRC. Within the limitations of the instrument and testing procedure it is shown that CFRC’s conform to the Bingham model: increasing fibre volume and fibre length increase both the yield stress and plastic viscosity.     

Observation of crack growth in PMMA with a low short glass fibre content by optical interferometry

In order to investigate the effect of short glass fibre on crack growth, the crack tip was observed using double-cantilever beam samples machined from injection-moulded PMMA plates with a low short glass fibre content by means of optical interferometry. It was shown that the interference fringes were distorted around the fibre crossing the crack planes over a region two to four times larger than the fibre diameter, and that the fibre depressed the crack opening due to bridging between the crack planes, thus shortening the craze zone length in front of the crack tip and reducing the crack growth rate, leaving the arrest line on the fracture surface. © 1998 Kluwer Academic Publishers