Effect of Bismuth Ferrite Nanometer Filler Element Doping on the Surface Insulation Properties of Epoxy Resin Composites

In the direct current electric field, the surface of epoxy resin (EP) insulating material is prone to charge accumulation, which leads to electric field distortion and damages the overall insulation of the equipment. Nano-doping is an effective method to improve the surface insulation strength and DC flashover voltage of epoxy resin composites. In this study, pure bismuth ferrite nanoparticles (BFO), as well as BFO nanofillers, which were doped by La element, Cr element as well as co-doped by La + Cr element, were prepared by the sol-gel method. Epoxy composites with various filler concentrations were prepared by blending nano-fillers with epoxy resin. The morphology and crystal structure of the filler were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The effects of different filler types and filler mass fraction on the surface flashover voltage, charge dissipation rate, and trap characteristics of epoxy resin composites were studied. The results showed that element doping with bismuth ferrite nanofillers could further increase the flash voltage of the composites. The flashover voltage of La + Cr elements co-doped composites with the filler mass fraction of 4 wt% was 45.2% higher than that of pure epoxy resin. Through data comparison, it is found that the surface charge dissipation rate is not the only determinant of the flashover voltage. Appropriately reducing the surface charge dissipation rate of epoxy resin composites can increase the flashover voltage. Finally, combining with the distribution characteristics of the traps on the surface of the materials to explain the mechanism, it is found that the doping of La element and Cr element can increase the energy level depth and density of the deep traps of the composite materials, which can effectively improve the flashover voltage along the surface of the epoxy resin.

Cement Building Materials with Powdered Optical Discs as a Filler

The object of study is a cement composite material with powdered utilized optical discs. The objective is to establish the dependences of the main strength characteristics – com-pressive strength, bending strength, and density – on the amount of waste added into the mix-ture and the water-cement ratio.The compositions of the mixtures for the production of the cement composite material samples consisted of the following components: cement, sand, powdered waste in the form of utilized optical discs and water.Based on the results of testing the samples, mathematical models have been developed which describe the dependences of the physical and mechanical properties of the cement com-posite material samples on the fraction of waste and water-cement ratio. It was found that with an increase in the amount of powdered waste added into the mixture, it reduces the compressive strength, bending strength, and density of the samples under study, however, the optimization of the water-cement ratio makes it possible to obtain equal strength compositions with a differ-ent fraction of waste.Component compositions of cement composite material mixtures with the addition of powdered utilized optical discs in the amount of 10 to 25 % of the total filler mass, which can provide construction products with a compressive strength class B20, are presented.

Bulk Fill Composites Have Similar Performance to Conventional Dental Composites

The aim of the study was to perform comprehensive characterization of two commonly used bulk fill composite materials (SDR Flow (SDR) and Filtek™ Bulk Fill Flowable Restorative (FBF) and one conventional composite material (Tetric EvoCeram; TEC). Eleven parameters were examined: flexural strength (FS), flexural modulus (FM), degree of conversion, depth of cure, polymerisation shrinkage (PS), filler particle morphology, filler mass fraction, Vickers hardness, surface roughness following simulated toothbrush abrasion, monomer elution, and cytotoxic reaction of human gingival fibroblasts, osteoblasts, and cancer cells. The degree of conversion and depth of cure were the highest for SDR, followed by FBF and TEC, but there was no difference in PS between them. FS was higher for bulk fill materials, while their FM and hardness were lower than those of TEC. Surface roughness decreased in the order TEC→SDR→FBF. Bisphenol A-glycidyl methacrylate (BisGMA) and urethane dimethacrylate were found in TEC and FBF eluates, while SDR released BisGMA and triethylene glycol dimethacrylate. Conditioned media accumulated for 24 h from FBF and TEC were cytotoxic to primary human osteoblasts. Compared to the conventional composite, the tested bulk fill materials performed equally or better in most of the tests, except for their hardness, elastic modulus, and biocompatibility with osteoblasts.

CEMENT BUILDING MATERIALS WITH POWDERED OPTICAL DISCS AS A FILLER

The object of study is a cement composite material with powdered utilized optical discs. The objective is to establish the dependences of the main strength characteristics – compressive strength, bending strength, and density – on the amount of waste added into the mixture and the water-cement ratio. The compositions of the mixtures for the production of the cement composite material samples consisted of the following components: cement, sand, powdered waste in the form of utilized optical discs and water. Based on the results of testing the samples, mathematical models have been developed which describe the dependences of the physical and mechanical properties of the cement composite material samples on the fraction of waste and water-cement ratio. It was found that with an increase in the amount of powdered waste added into the mixture, it reduces the compressive strength, bending strength, and density of the samples under study, however, the optimization of the water-cement ratio makes it possible to obtain equal strength compositions with a different fraction of waste. Component compositions of cement composite material mixtures with the addition of powdered utilized optical discs in the amount of 10 to 25 % of the total filler mass, which can provide construction products with a compressive strength class B20, are presented.

THERMAL CONDUCTIVITY OF COMPOSITE POLYPROPYLENE/CARBON NANOFIBRES

The polymer composite material based on polypropylene (PP) matrix and vapor grown carbon fibers (VGCF) as filler was received by the melt-technology. Dependences of the thermal conductivity on the filler mass fraction and temperature were experimentally obtained. Such dependences have a nearly linear character. It is shown that the material heat-conducting properties don’t depend on the sample geometry. It is found out that in case the concentration of VGCF is more than 5% the material can be used for heat removal in electrical and electronic devices. To describe the heat transfer process a model was built based on the multichannel conduction problem. It allows describing the heat transfer process in composite materials with sharply differing heat-conducting properties of the components taking into account such material characteristics as density, heat capacity, heat conduction, and heat flow velocity.

Rheological properties of the bituminous binder extracted from SMA pavement with hydrated lime

The durability of pavement layers depends on the type of bitumen and changes in its material structure during service life. In 1999, while rebuilding and modernizing road infrastructure in Kielce (Poland), a stone mastic asphalt wearing coarse layer with hydrated lime was placed on one of the town’s main streets. Stone mastic asphalt mixture contained 6.2% of D70 bitumen (currently 50/70) and 4% SBS polymer under the trade name Kraton 1101 CM. The hydrated lime was dosed into the stone mastic asphalt mixture to replace 30% of the filler mass. Pavement surface condition after 12 years of service life was very good. In 2011, bitumen samples were extracted from stone mastic asphalt and tested. The tests were performed on the samples that contained fatty amine and hydrated lime as adhesive agents, obtained from stone mastic asphalt wearing course layer in the rut paths and from between the area limited by rut paths. The hydrated lime additive was found to have a positive effect on rheological properties of the recovered bitumen providing resistance to the water and frost.

Thermal Conductivity of Cage-Like Structures

A two dimensional toy model is developed to study thermal transport in cage like structures such a skutterudites and clathrates. The model consists of host atoms on a rectangular lattice with fillers in the center of each rectangle. The thermal conductivity is calculated by using Green-Kubo equilibrium molecular dynamics simulations. It is generally believed that the smaller and the heavier the filler, the lower is the thermal conductivity. We show that the thermal conductivity decreases with atomic displacement parameter while it has local minima versus filler mass. Our study shows that it is very important to include the correct band dispersion to get the right features of the thermal conductivity. We show that by having a double well potential one can further reduce the thermal conductivity.