Heating copper and aluminium nanopowders in mixtures with aluminium and silicon oxides in air

Oxidation of copper and aluminium nanopowders obtained by the method of electric explosion of wire in mixtures with inorganic oxides at heating has been investigated. It is shown that in the presence of Al2O3, SiO2 and MnO2 oxidation stability of nanopowders raised, which was testified by the values of oxidation parameters: temperature of oxidation start, oxidation degree and maximum velosity of metal oxidation. Oxidation processes taking place in nanopowders slowed down with increase of oxidation additive content

Characterization of copper nanopowders after natural aging

Copper nanopowders after storage under natural conditions can oxidize and change their properties. In this work, the phase composition, morphology and thermal properties of copper nanopowders after natural aging of 10 years were studied. The copper nanopowders were produced by the method of electrical explosion of wires in different gaseous ambient: argon and carbon dioxide. The nanopowders were characterized by X-ray diffraction, thermal analysis, scanning electron microscopy, Fourier transform infrared spectroscopy. The content of copper oxides phases was found to be increased in comparison with freshly synthesized powders. This transformation results in the change of the thermal characteristics of the nanopowders. The effect of the synthesis conditions on the composition and thermal characteristics was shown

Thermal properties of epoxy composites filled with boric acid

The thermal properties of epoxy composites filled with boric acid fine powder at different percentage were studied. Epoxy composites were prepared using epoxy resin ED-20, boric acid as flame-retardant filler, hexamethylenediamine as a curing agent. The prepared samples and starting materials were examined using methods of thermal analysis, scanning electron microscopy and infrared spectroscopy. It was found that the incorporation of boric acid fine powder enhances the thermal stability of epoxy composites

Investigation of Igniting Ability of Heterogeneous Systems by Means of Electric Spark

The article presents a physical model for determining the boundary conditions of ignition of a heterogeneous system, taking into account the heating of the liquid phase and its evaporation. The temperature distribution in a heterogeneous system is described by the obtained analytical expression. An algorithm describing the evaporation rate of the liquid phase is also defined. An expression describing the induction period can be used to determine the critical duration of the discharge, the reduction of which will lead to the ignition of the vapor-gas phase

The Dependence between the Ignition Value of Air Suspension and the Size of the Reaction Chamber

The influence of the geometric factor of the reaction chamber on the limit value of the air suspension ignition is studied. It is found that in determining the lower concentration limit of the flame propagation (LCLFP), it is most promising to use an installation with a cylindrical reaction chamber whose height is equal to the diameter. The dependence of the determination of the LCLFP value on the geometric factor of the reaction chamber is proposed, tested on metal powders and organic dust-forming materials. The expression allowing to carry out the comparative analysis of scientific results received on other technical devices with the results received on the installations executed according to the requirements of normative and technical documentation is received that significantly reduces the volume of experimental works

Comparative study of the effect of flame retardants on the ignition temperature of epoxy composites

The disadvantage of polymeric materials, including epoxy resins, is their increased fire hazard. Reducing the flammability of polymeric materials is a serious problem that needs to be addressed. One of the ways to reduce the flammability of polymers is the introduction of special additives into the polymer matrix with flame retarding properties, which leads to a change in the nature of the processes occurring during the combustion of the polymer, or to blocking the combustion process with non-combustible or inhibiting substances. In this work, aluminum trihydroxide, melamine polyphosphate, and melamine poly(magnesium phosphate) were used as flame retardants to enhance the flame-resistant properties of epoxy resin. The filler loading in the epoxy composites was 10 wt. %. The experimental studies have been carried out to determine the ignition temperature of the produced epoxy composites. The data obtained were compared with the ignition temperature of a control sample of epoxy resin without filler. The results indicated that the incorporation of all the flame retardants studied resulted in an increase in the ignition temperature. The ignition temperature of the samples filled with melamine polyphosphate and melamine poly(magnesium phosphate) increased by 28 and 11 °C, respectively. However, the best result was obtained for a sample filled with aluminum trihydroxide: the ignition temperature of this sample was 40 °C higher than that of the unfilled epoxy resin

Thermal Stability and Flammability of Epoxy Composites Filled with Multi-Walled Carbon Nanotubes, Boric Acid, and Sodium Bicarbonate

Epoxy composites filled with 0.5 wt% of multi-walled carbon nanotubes (MWCNTs), 10 and 15 wt% of boric acid and sodium bicarbonate separately, as well as composites filled with a combination of MWCNTs-boric acid and MWCNTs-sodium bicarbonate were prepared. The thermal behavior of the prepared samples was investigated under heating in oxidative environment using thermogravimetric analysis. The hardness was measured using the Shore D hardness test. To evaluate the flammability of the samples, the ignition temperature and time-to-ignition were determined. It was concluded that sodium bicarbonate in the studied concentrations (10 and 15 wt%) is not appropriate for use as a filler capable of improving the thermooxidative stability and reducing the flammability of epoxy polymers. The improvement in the thermal properties can be achieved by using the combination of boric acid and multi-walled carbon nanotubes as fillers. The thermooxidative destruction of the samples filled with boric acid passes more slowly and more evenly via the formation of B2O3 as a result of its decomposition

The dependence between the ignition value of air suspension and the size of the reaction chamber

The influence of the geometric factor of the reaction chamber on the limit value of the air suspension ignition is studied. It is found that in determining the lower concentration limit of the flame propagation (LCLFP), it is most promising to use an installation with a cylindrical reaction chamber whose height is equal to the diameter. The dependence of the determination of the LCLFP value on the geometric factor of the reaction chamber is proposed, tested on metal powders and organic dust-forming materials. The expression allowing to carry out the comparative analysis of scientific results received on other technical devices with the results received on the installations executed according to the requirements of normative and technical documentation is received that significantly reduces the volume of experimental works