Inorganic Matrix Composites Research Articles

Mechanical characterization of textile reinforced inorganic-matrix composites

This paper presents the results of the mechanical characterization of composite materials comprising high strength textiles embedded in inorganic matrices. These materials are commonly termed Textile Reinforced Mortars (TRM) or, when comprising cementitious matrices, Fabric-Reinforced Cementitious Matrix (FRCM – despite the fact that this term is often extended to composites with cement-free matrices). Different types of fibers were employed, namely carbon, glass, and basalt, as well as steel cords, which were embedded in lime- or cement-based matrices. Results of tensile tests on single fiber yarns and composite prismatic specimens with a rectangular cross-section are shown and discussed. The effect of fiber coating and stitch-bonded joints between warp and weft yarns on the tensile behavior observed is studied. The results obtained help to shed light on the different parameters that affect tensile testing of inorganic-matrix composites contributing to the appropriate mechanical characterization of these materials.

Cure cycle optimization of an inorganic polymer matrix material for high temperature fiber reinforced composites

We investigated the potential effects of inorganic polymer processing conditions on the residual stress generation of fiber reinforced inorganic polymer matrix composites. By optimizing various stages of processing it was found that process-induced shrinkage can be reduced by as much as 20%, while simultaneously, the compression strength can be improved by over 30% compared to baseline processing parameters. Further with the optimization of the process parameters, the pore diameter reduced by over 65%, while the relative density increased by a little over 5%. These results suggest high temperature dimensional stability and reduced pore content. Also SEM images indicate a continuous thermodynamic transformation in the bonding strength between the precipitated particles. Thus, it is demonstrated that, through the process modification, a path exists to reduced cure shrinkage, high mechanical strength and thermodynamic stability that results in a potential reduction in residual stresses in continuous fiber reinforced, inorganic matrix composites.

Research of Behaviour of Inorganic Matrix Composites Exposed to Extreme Temperatures

The article is focused on complex analysis of the principles of degradation of composites based on alkali-activated materials exposed to extreme temperatures (max. temperature 1200 degree of Celsius). Thanks to specific properties these materials show a remarkable potential for the special application, for example for construction with high risk of fire etc. The effect of high temperatures shall be tested not only at such extreme levels but also at gradually increasing temperatures. The temperature effects shall be evaluated not only in of changes physic-mechanical parameters but also the physic-chemical determinations.

Sol–gel route to carbon nanotube borosilicate glass composites

Dense borosilicate glass matrix composites containing up to 3 wt% of multiwalled carbon nanotubes were produced by a sol–gel process. The three different silicate precursors employed (tetramethylsilane (TMOS), methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS)) yielded transparent xerogels which were subsequently crushed and densified by hot pressing at 800 °C. The dispersion of the carbon nanotubes was aided by using an organic–inorganic binder (3-aminopropyl triethoxysilane) which limited flocculation of the CNTs in the silica sol. After densification, the borosilicate glass composites containing up to 2 wt% CNTs showed significant improvements in hardness and compression strength, as well as thermal conductivity, whilst percolation effects lead to a dramatic increase in electrical conductivity above 1 wt%. This simple approach to disperse CNTs into a technical silicate glass matrix via the sol–gel process focusses specifically on the borosilicate system, but the procedure can be applied to produce other inorganic matrix composites containing CNTs.

Ceramic matrix composites containing carbon nanotubes

Due to the remarkable physical and mechanical properties of individual, perfect carbon nanotubes (CNTs), they are considered to be one of the most promising new reinforcements for structural composites. Their impressive electrical and thermal properties also suggest opportunities for multifunctional applications. In the context of inorganic matrix composites, researchers have particularly focussed on CNTs as toughening elements to overcome the intrinsic brittleness of the ceramic or glass material. Although there are now a number of studies published in the literature, these inorganic systems have received much less attention than CNT/polymer matrix composites. This paper reviews the current status of the research and development of CNT-loaded ceramic matrix composite (CMC) materials. It includes a summary of the key issues related to the optimisation of CNT-based composites, with particular reference to brittle matrices and provides an overview of the processing techniques developed to optimise dispersion quality, interfaces, and density. The properties of the various composite systems are discussed, with an emphasis on toughness; a comprehensive comparative summary is provided, together with a discussion of the possible toughening mechanism that may operate. Last, a range of potential applications are discussed, concluding with a discussion of the scope for future developments in the field.

Carbon nanotube–SiO2 composites by colloidal processing

The surfactants assisted colloidal processing of 1˙0 wt-% carbon nanotube (CNT)–SiO2 composites using acid treated CNTs and colloidal silica has been investigated. By using different combinations of anionic and cationic surfactants five systems were developed with the aim of coating the CNTs with silica particles and creating a homogenously dispersed composite. Sintering of CNT–SiO2 composites was performed for 3 h at 1300°C in argon atmosphere. Pressureless sintering yielded composites with a density >95% of the theoretical. X-ray diffraction analysis showed the presence of cristobalite, but no other crystalline phases were detected in the sintered composites. Microstructural observation revealed isolated CNTs in the SiO2 matrix both in the as dried powder and in the sintered samples. It is concluded that the simple colloidal process developed here can be a convenient alternative to the sol–gel based methods used for fabrication of inorganic matrix composites containing CNTs.

X-ray microtomography of materials

X-ray microtomography allows imaging of the interior microstructure of materials non- destructively and with spatial resolution which can approach that of optical microscopy (typically, no better than 1 μm in samples whose cross-sectional diameter is on the order of 1 mm, and 10 &µm for 10 mm specimens). First, X-ray microtomography's origin in medical imaging and the physics behind computed tomography are reviewed. Summaries of apparatus, radiation sources, data collection schemes, and of materials applications follow. To date, most materials applications fall into one of four areas: inorganic matrix composites, transport in porous media, calcified tissue, and fatigue crack closure. Details of studies in each area highlight the advantages X-ray microtomography brings, and the final section focuses on future directions suggested by recent work using imaging modalities other than X-ray attenuation.

Designing Interfaces in Inorganic Matrix Composites

The key to controlling and predicting the properties of metal matrix composites lies in understanding and controlling the interface. When properly designed, the interface between reinforcing fibers and the matrix or protective coating can act as a mechanical fuse through a controlled delamination mechanism.Controlled delamination, in effect, results in the decoupling of fibers from early damage due to stress concentrations in the vicinity. The delamination event must precede the crack bridging and frictional pull-out mechanisms that have been so effectively demonstrated in ceramic matrix composites. The delamination event, therefore, is the necessary precondition, and so analysis of composite toughening must start with a definition of the conditions for interface debonding.This decoupling can be expressed in terms of cohesive strength of the interface, shear strength of the interface, and fiber fracture stress. In a related but alternative manner, debonding can be expressed in terms of the intrinsic work of fracture of the interface as compared to the transverse work of fracture of the fiber.

Reactive Chemical Vapor Deposition (R.C.V.D.) as a Method for Coating Carbon Fibre with Carbides

AbstractCarbon fibre is an ideal material for reinforcing inorganic matrix composites, especially for high temperatures. Its main drawback is its susceptibility to oxidation and to reaction with metals.Our challenge was to perfect a method of producing a carbon fibre in which each elementary filament is covered and protected by a very thin and adherent layer of a refractory carbide such as SiC, B4C, etc…For this purpose, we use reactive chemical vapor deposition (R.C.V.D.) in which only the M element of the M C carbide is carried by the gas phase, carbon being supplied by the fibre itself. The growth rate is self regulated by the solid state diffusion.This method has been developed in a continuous reactor with ex-PAN (6K) or ex-PITCH (2K) fibres.The mechanical behaviour of the coated fibres is very near that of the initial ones, but their oxidation rate at 600°C is 100 times lower.

Thermal expansion of organic and inorganic matrix composites: A Review of theoretical and experimental studies

AbstractThis paper reviews theoretical and experimental studies conducted in organic, ceramic, and metal matrix composites containing cylindrical, lamellar, and spheroidal inclusions as reinforcements. Mathematical formulations proposed to predict thermal expansion coefficients of fiber, disc, and sphere reinforced organic and inorganic matrix composites have been reviewed. Experimental studies undertaken to confirm theoretical predictions of thermal expansion coefficients of a variety of reinforcement geometry composites have also been discussed.