Use of Onion-Like Carbon to Reinforce Carbon Composites

Onion-like carbon reinforced carbon-carbon composite was fabricated, and the influence of onion-like carbon (OLC) on the microstructure and mechanical and friction properties was investigated by porosity analysis, scanning electron microscopy, three-point bending test, nanoindentation test and ring-on-ring friction test. The results show that the sample containing OLC has a higher flexural strength (by 7.3%) and compressive strength (by 29.3%), hardness (by 2.1 times) and apparent density (by 1.1%) and smaller open porosity (7.9% vs 9.8%) and mesoporevolume, which is confirmed by porosity analysis and is attributed to improved fiber/matrix interface performance. The presence of OLC results in higher hardness and elastic modulus of carbon matrix under nanoindentation testing, which leads to modification of friction mechanism and a decrease in the wear rate under friction (by 3.3 times). Besides, OLC particles form self-lubricating film and show a graphitic carbon solid lubricant properties

Propargylated Novolac Resins for Solvent-Free Technology for High-Performance Composites

Propargyl substituted novolac phenolic resin diluted with unsaturated bisphenol-A ethers was used for glass fiber solvent-free impregnation for the formation of high-performance composites. The addition of 20% mass of diallyl (DAEBA) or dipropargyl (DPEBA) bisphenol-A to propargyl substituted novolac phenolic resin resulted in viscosity drop from 2000 mPa∙s to 400‒500 mPa∙s at 140 °C. This proved to be enough to achieve complete impregnation of the twisted glass fibers, as illustrated by SEM analysis. This  improvement in impregnation was shown to result in increasing both flexural strength and modulus of the unidirectional glass fiber composite material approximately with a factor of two compared to the composite impregnated with resin without bisphenol-A ethers. DPEBA was shown to be more suitable for high-temperate applications since its addition does not seem to result in a decrease of the heat deflection temperature (HDT)

Second-order nonlinear optical properties induced by thermal poling in photonic oxide glasses and transparent glass-ceramics

In recent years there has been a resurgence of interest in oxide glasses due to advances in lasers for information transport. Oxide glasses combine low cost of fabrication and good compatibility with silica glass fibers, which offer the opportunity for developing structures with nonlinear optical properties in integrated optical devices. The creation of an axial symmetry under thermal poling is currently necessary to induce Second-Order NonLinear (SONL) optical properties in glasses. A description of theoretical models which have been proposed for charge migration during thermal poling is presented. A review of SONL efficiencies which have been obtained for different glass compositions by this method is reported. Correlations between SONL properties and structural modifications under poling are also presented. Finally, we focus on the challenging fabrication of transparent glass-ceramic composites, especially when they are obtained by the precipitation of ferroelectric nanoparticle phases in the glassy matrix which adds the advantageous SONL properties of ferroelectric crystals

Graphite Laminated Materials Strength Properties and Energy Characteristics of Polymer Binders

The approach for graphite laminated materials strength properties prediction using contact angle measurements was proposed. The tensile strength of laminated materials made of graphite foil and stainless steel with acrylic and silicone adhesives was measured. It was shown that tensile strength depends on energy characteristics of polymer binders, which can be determined by simple and express wetting method. It was found that the highest values of tensile strength, strength of adhesion and the work adhesion to graphite and stainless steel were provided by acrylic adhesive MBM-5C. The delamination occurred when graphite and stainless steel sheets were connected with low surface energy silicone resin, y = 23 mJ/m2, what was not able to maintain sufficient adhesion level to the both types of attached surfaces: polar steel and non-polar graphite. It was demonstrated that the calculation of the work of adhesion to polar and non-polar model liquids (water and octane respectively) can be applied to optimize the choice of polymer binder and design of laminated materials. It's quite important that the proposed technique doesn't require to determine free surface energy for each type of sheet material which is especially difficult and complex task if laminate consists of several different layers

Cu-Expanded Graphite Composite Material Preparation and Thermal Properties

A composite material based on expanded graphite (EG) and copper compounds was obtained by natural graphite oxidation with 95% nitric acid, copper (II) nitrate and granular carbamide addition with further rapid heat treatment at three different exfoliation temperatures: 800, 1000 and 1200 °С. It was found that the composition of copper containing graphite material depends on the temperature and the atmosphere of thermal expansion. The formation of copper oxides can be eliminated if rapid heat treatment is conducted in nitrogen at 1200 °С. Thermal conductive properties: thermal diffusivity and specific heat capacity of obtained Cu-expanded graphite samples were measured. It was revealed that the dependence of thermal conductivity (TC) of Cu-graphite material has non-linear character in the studied range of copper content. The incorporation of 3% copper into expanded graphite allows to increase its thermal conductivity by 20% while the further Cu content growth leads to the TC decrease from 6 to 4.5 W/(m∙K). The specific heat capacity is constant at ω(Cu)<3% and reduces in the range (3‒8)% Cu. The advantage of proposed technique of Cu-expanded graphite materials preparation is exclusion graphite intercalation compounds hydrolysis step with further drying because of carbamide addition