Influence of Surface-Modified Conducting Fillers on the Properties of Epoxy Coatings

We have developed a new epoxy composition for antistatic coatings on metallic surfaces, filled with technical carbon and talc, which had been surface-modified by paranitroaniline and phosphoric acid. It has been shown that, with the introduction of modified fillers, the content of gel fraction in an epoxy coating increases by 5–6%, its adhesion becomes 2.5–2.7 times higher, and the amount of organic solvents decreases. We have also established that the electric resistance of the coating is more stable in time as compared with the commercial antistatic ground-coat enamel, and the frequency dependence of the resistance is more clearly pronounced after exposure to a chloride-containing medium, which corroborates the better protective properties of antistatic coatings with modified current conductive fillers. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 4, pp. 53–58, July–August, 2005.     

Influence of the mechanism and parameters of hardening of modified novolac phenol-formaldehyde resins on the physicomechanical properties of the composite

We study the influence of concentrations of the components of reactive compositions and the conditions of production and hardening of phenol-formaldehyde resins with the help of epoxy resins in the presence of polyvinylpyrrolidone on the physicomechanical, thermal, adhesion, insulation, and anticorrosion properties of the composites. The positive effect of modifications with polyvinylpyrrolidone and epoxy resin manifests itself within the following ranges of concentrations: 0.5–1 wt.% of polyvinylpyrrolidone and 25–30 wt.% of ED-20 in the presence of 1 wt.% of N, N-dimethylaniline. Thus, the adhesion strength of a glue based on the developed composition becomes four times higher and constitutes 5–6 MPa; the impact strength, static strength in bending, surface hardness, and the specific bulk electric resistance of the specimens hardened at 150–160°C for 25–30 min become 1.5–2.5 times higher and are equal to 5–6J/m², 15–17 MPa, 350–420 MPa, and (5.5–6.5)⋅10¹⁰ Ω⋅m, respectively. The behavior of these characteristics strongly depends on the conditions of hardening. We optimized the composition of modified phenol-formaldehyde resins, which made it possible to produce materials with predicted properties.     

Carbon black/graphite nanoplatelet/rubbery epoxy hybrid composites for thermal interface applications

Hybrid composites were developed by dispersing carbon black (CB) nanoparticles and graphite nanoplatelets (GNPs) at 4–6 and 12–14 wt%, respectively, into rubbery epoxy resin. SEM analysis showed that CB particles improved the dispersion of GNPs in the hybrid composite. The thermal conductivity of 4 wt% CB/14 wt% GNP-15/rubbery epoxy hybrid composite, 0.81 W/m K, is ca. four times higher than that of rubbery epoxy. When silane-functionalised, the fillers reduced the viscosity of the hybrid dispersion and made the hybrid composite highly electrically insulating. Nevertheless, filler functionalisation decreased the composite’s thermal conductivity by only 16.6%. Compression testing showed that the hybrid fillers increased the compressive modulus and strength of rubbery epoxy by nearly two and three times, respectively. Overall, the hybrid composites with their thermal paste-type morphology, low viscosity, high compliance, improved thermal conductivity and, when fillers are functionalised, low electrical conductivity makes them promising materials as thermal interface adhesives.     

Properties of epoxy-amine coatings modified with petroleum polymeric resins

We study the composition of the gel fraction, water absorption, and impedance characteristics of epoxy coatings modified with petroleum polymeric resin treated with maleic anhydride. It is shown that modified epoxy coatings are characterized by higher water resistance and better protective properties in acid media. We determine the optimal amount of the petroleum polymeric modifier and demonstrate the possibility of improvement of the corrosion resistance of modified epoxy coatings by subsequent thermal treatment. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 4, pp. 81–85, July–August, 1996.     

Influence of the laser-processing parameters on the adhesion strength of adhesive Fe-Cr-B-Si-system coatings

The influence of the laser-processing parameters on the adhesion strength of the Fe-Cr-B-Si-system coating has been investigated. The characteristics of a change in the adhesion strength of coatings, as well as in the amounts of iron borides as functions of the velocity of travel, diameter of a laser beam, and coefficient of overdropping have been studied. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 155–159, November–December, 2006.     

Development of heat-and impact-resistant coatings for main pipelines

We have developed composite layered temperature-resistant silicon-organic sandwich-type coatings with thin polyurethane silicon-organic interlayers. We used the following materials as binding components: KO 921 silicon-organic lacquer with addition of éD-20 epoxy resin for prime coat, the same lacquer with addition of PZ 1040 S polyurethane elastomer for thin soft interlayers, and only KO 921 lacquer for thick hard layers. The mineral filler represented a mixture of coal ash and omiacarb in proportion 70 / 30 mass %. We have manufactured and tested laboratory specimens with two hard layers and two interlayers as well as with three hard layers and two thin interlayers. We have established that the developed composite layered coatings exceed, in their basic characteristics, the requirements of the State Standard Committee of Ukraine and foreign normative documents for the rust protection of steel main pipelines. Our coatings possess high impact strength, heightened elasticity and adhesion strength and, as to their electrical insulating characteristics, exceed these requirements by an order of magnitude. We note the complexity of the technology of applying layered composite coatings and the necessity of its improvement. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 4, pp. 59–65, July–August, 2006.     

Adhesion strength of glass/epoxy composite embedded with heat-treated carbon black on the surface

The surface of a glass/epoxy composite material was embedded with oxidized carbon black by heat treatment to enhance the adhesion strength of the glass/epoxy composite structure. Quantitative chemical bonding analysis with X-ray photoelectron spectroscopy (XPS) was conducted to observe the chemical binding states of the surface of the carbon black particles with heat treatment. The morphological effects of the carbon black on the surface of the composite were observed using SEM and AFM. The surface free energies and lap shear strengths of the glass/epoxy adhesive joints whose adherends were embedded with oxidized carbon black were investigated in terms of the heat-treatment conditions and the amount of embedding. From the experimental results, embedding the heat-treated carbon black particles on the composite surface was found to greatly improve the adhesion strength of the composite due to the increased oxidation radicals on the carbon black surface.     

Dielectric studies of polyvinyl-acetate-based phantom for applications in microwave medical imaging

Phantoms that exhibit complex dielectric properties similar to low water content biological tissues over the electromagnetic spectrum of 2–3 GHz have been synthesized from carbon black powder, graphite powder and polyvinyl-acetate-based adhesive. The materials overcome various problems that are inherent in conventional phantoms such as decomposition and deterioration due to the invasion of bacteria or mold. The absorption coefficients of the materials for various compositions of carbon black and graphite powder are studied. A combination of 50% polyvinyl-acetate-based adhesive, 20% carbon black powder and 30% graphite powder exhibits high absorption coefficient, which suggests another application of the material as good microwave absorber for interior lining of tomographic chamber in microwave imaging. Cavity perturbation technique is adopted to study the dielectric properties of the material.     

炭黑的分散性对抗静电涂层导电性能的影响

通过高速砂磨法制备了以丙烯酸树脂为基底、炭黑为导电填料的导电涂料.分别用X射线衍射和热重分析-差热扫描考察了炭黑/丙烯酸树脂复合涂层的结晶度和热力学性能.重点研究了炭黑添加量、偶联剂、分散程度等因素对涂层导电率的影响.结果表明,炭黑添加量在3％时,以异丙基三(十二烷基苯磺酰基)钛酸酯作为偶联剂,机械研磨时间160min,得到的导电涂层电阻率达到最低值,为533 Ω·cm.     

Cultivation of human fibroblasts and multipotent mesenchymal stromal cells on mesoporous silica and mixed metal oxide films

The application of mesoporous silica and silica–titania-mixed metal oxide films prepared via sol–gel processing as substrates for cell growth was investigated. A deliberate tailoring of the chemical composition of the porous substrates with different Si:Ti ratios was achieved by using a single-source precursor based on a titanium-coordinated alkoxysilane, resulting in mesoporous silica–titania films with hydrophilic surfaces. The different coatings were investigated with respect to their applicability in the cultivation of human cells such as human fibroblasts and multipotent mesenchymal stromal cells. It was found that they promoted cell adhesion and proliferation of human fibroblasts up to a period of 14 days. After 2 weeks only single apoptotic cells could be detected on silica–titania mixed oxide films in contrast to a somewhat higher amount on silica coatings. Furthermore, none of the films inhibited osteogenic differentiation of multipotent mesenchymal stromal cells.     

Influence of an electric field on the hardening process and the properties of an epoxy composite discretely reinforced with phosphocarbon fibers

The influence of an electric field on the hardening process, the structure, and the properties of an epoxy composite in the presence of a phosphorus-containing carbon filler has been investigated. It has been shown that under the action of an electric field the process of formation of a three-dimensional epoxy polymer in the presence in the system of phosphocarbon fibers proceeds more intensively with the formation of a more rigidly bound structure of the polymer as compared to the same composition hardened in the absence of the field. It has been established that the fibrous filler-binder interface has a dominant role in the formation of a spatially cross-linked polymer and in the properties of the product hardened both under the action of the electric field and without it. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 3, pp. 47–54, May–June, 2007.     

Fabrication and characterization of bioactive composite coatings on Mg–Zn–Ca alloy by MAO/sol–gel

High corrosion rate and accumulation of hydrogen gas upon degradation impede magnesium alloys’ clinical application as implants. In this work, micro-arc oxidation (MAO) was used to fabricate a porous coating on magnesium alloys as an intermediate layer to enhance the bonding strength of propolis layer. Then the composite coatings were fabricated using sol–gel method by dipping sample into the solution containing propolis and polylactic acid at 40°C. The corrosion resistance of the samples was determined based on potentiodynamic polarization experiments and immersion tests. Biocompatibility was designed by observing the attachment and growth of wharton’s jelly-derived mesenchymal stem cells (WJCs) on substrates with MAO coating and substrates with composite coatings. The results showed that, compared with that of Mg–Zn–Ca alloy, the corrosion current density of the samples with composite coatings decreased from 5.37 × 10⁻⁵ to 1.10 × 10⁻⁶ A/cm² and the corrosion potential increased by 240 mV. Composite coatings exhibit homogeneous corrosion behavior and can promote WJCs cell adhesion and proliferation. In the meantime, pH value was relatively stable during the immersion tests, which may be significant for cellular survival. In conclusion, our results indicate that composite coatings on Mg–Zn–Ca alloy fabricated by MAO/sol–gel method provide a new type bioactive material.     

Influence of technological factors on the formation of amorphous plasma-sprayed coatings

We investigate the influence of technological factors of the process of pulsed plasma spraying (in particular, of the composition of plasma-forming gases and magnetic fields) on the formation of amorphous coatings. It is experimentally established that the formation of coatings in the presence of a magnetic field applied in the region of spraying favors the formation of amorphous coatings and, thus, increases their adhesion to the base. The application of argon-hydrogen mixtures as plasma-forming gases make it possible to obtain homogeneous coatings with elevated contents of the amorphous component. “L'vivs'ka Politeknika” State University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 77–81. May–June, 1997.     

Effect of acid and TETA modification on mechanical properties of MWCNTs/epoxy composites

Acid treatment and triethylene-tetramine (TETA) modification of multi-walled carbon nanotubes (MWCNTs) purposing to attain better dispersibility and stronger interfacial bonding between MWCNTs and epoxy matrix have been carried out in this paper. The epoxy and MWCNTs/epoxy composites were produced by cast molding method. Stress–strain curves show that TETA-MWCNTs/epoxy hold the greatest toughness of all samples with 0.5 wt.% nanoparticles. The Young’s modulus of TETA-MWCNTs/epoxy has a significant increase about 38% compared to the neat epoxy, while the Young’s modulus of unmodified MWCNTs/epoxy or acid-modified MWCNTs/epoxy has a bit of decrease. Tensile and impact strength tests reflect that TETA-MWCNTs reinforced epoxy composites have an obvious improvement of tensile strength about 30% and an enhancement of impact strength over 34% compared to the pure epoxy composites with only 0.5 wt.% loading of TETA-MWCNTs. Scanning electron microscopy images of fractured surface of MWCNTs/epoxy indicate homogeneous dispersibility of TETA-MWCNTs and strong interfacial adhesion between the TETA-MWCNTs and the epoxy in the MWCNTs/epoxy composite.     

Dielectric properties of carbon black and carbonyl iron filled epoxy–silicone resin coating

The dielectric properties of epoxy–silicone resin coatings containing carbon black (CB) and carbonyl iron (CI) particles as a function of frequency (2–18 GHz) and the CB volume content (0.2–1%) have been investigated. The complex permittivity of the coatings increased with increasing CB content, which mainly attributed to the interfacial polarization at the CB/resin/CI particles interfaces. The complex permittivity also decreased rapidly with increasing frequency in the low frequency range while decreased slowly in the high frequency range. The changes of dielectric properties with frequency and the CB volume content were discussed using the power-law decay and the concept of interfacial polarization.     

Production of conversion oxide-ceramic coatings on zirconium and titanium alloys

We consider the possibilities of surface hardening of zirconium and titanium alloys with conversion oxide-ceramic coatings. These coatings have been produced by the method of plasma-electrolytic treatment in alkaline solutions. We have established that the plasma temperature in discharge spark channels reaches (6–9) · 10³ K. The thickness of the coatings is 100 to 120 and 30 to 40 μm, and their microhardness is ∼ 800 and ∼ 1000 MPa for zirconium and titanium alloys, respectively. The functional properties of the coatings depend on the synthesis conditions, including the electrolyte composition, the cathode and anode current densities, and also the treatment time. We have evaluated the thickness, microhardness, and wear resistance of the coatings under conditions of dry friction and cavitation as well as their fatigue strength and corrosion resistance. We have established that this treatment provides a high wear and corrosion resistance of the alloys under study with insignificant decrease in their fatigue strength. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 2, pp. 117–124, March–April, 2006.     

Evaluation of a.c. conductivity behaviour of graphite filled polysulphide modified epoxy composites

Composites of epoxy resin having different amounts of graphite particles have been prepared by solution casting method. Temperature dependence of dielectric constant, tan δ and a.c. conductivity was measured in the frequency range, 1–20 kHz, temperature range, 40–180°C for 0.99, 1.96 and 2.91 wt% graphite filled and unfilled epoxy composites. It was observed that the dielectric constant, tanδ and a.c. conductivity increase with increasing temperature. Near the transition temperature the materials show anomalous behaviour for the observed properties. Peaks of dielectric constant, tan δ and a.c. conductivity were observed to shift towards lower temperature with increasing frequency. Clear relaxation (tan δ) peaks around 169°C were observed in epoxy resin, which shifted to lower temperature side on increasing the frequency. Addition of 2.91 wt% graphite shifted the tan δ peaks towards higher temperature side by creating hindrances to the rotation of polymer dipoles. Addition of 2–91 wt% graphite leads to an increased relaxation time τ of dipoles in polysulphide epoxy from 1.44 × 10⁻⁵− 3.92 × 10⁻⁵ (s) at 90°C by creating the hindrance to the rotation of dipoles.     

Effect of the nature of fillers and ultraviolet irradiation on the mechanical properties of epoxy composite coatings

The effect of ultraviolet irradiation, the physical nature and percentage of fine-grained fillers on the mechanical properties of composites has been studied. It has been found that the ultraviolet irradiation of epoxy compositions causes a decrease in the adhesive strength and an increase in the cohesive strength of protective coatings. This has been proved to be due to a change in the course of physicochemical processes at the filler/epoxy oligomer interface, owing to which external surface layers, which have a considerable extent and a high degree of cross-linking, are formed around fine particles in the matrix. Translated from Problemy Prochnosti, No. 4, pp. 117–123, July–August, 2009.     

Structure, mechanical properties and corrosion resistance of nanocomposite coatings deposited by PVD technology onto the X6CrNiMoTi17-12-2 and X40CrMoV5-1 steel substrates

This article presents the research results on the structure and mechanical properties of nanocomposite coatings deposited by PVD methods on the X6CrNiMoTi17-12-2 austenitic steel and X40CrMoV5-1 hot work tool steel substrates. The tests were carried out on TiAlSiN, CrAlSiN and AlTiCrN coatings. It was found that the structure of the PVD coatings consisted of fine crystallites, while their average size fitted within the range 11–25 nm, depending on the coating type. The coatings demonstrated columnar structure and dense cross-sectional morphology as well as good adhesion to the substrate, the latter not only being the effect of adhesion but also by the transition zone between the coating and the substrate, developed as a result of diffusion and high-energy ion action that caused mixing of the elements in the interface zone. The critical load L _C2 lies within the range 27–54 N, depending on the coating and substrate type. The coatings demonstrate a high hardness (~40 GPa) and corrosion resistance.     

Preparation of carbon coated ceramic foams by pyrolysis of polyurethane

Electronically conducting carbon coatings over alumina foams were prepared by the foams’ impregnation in a polyurethane solution, followed by pyrolysis of the polymer layer. An optimal coating procedure was developed, using a commercial polyurethane lacquer. Pyrolysis was performed by heating the coated foams to 650–1,200 °C in Argon for 2–8 h. Coating characterization included surface area, phase composition, morphological and electrical conductivity measurements. Auger electron spectroscopy (AES) showed the composition was mostly carbon, with trace levels of oxygen impurities. Thickness, microstructure and interface between the alumina foam surface and the carbon film were analyzed using scanning electron microscopy (SEM and HR-SEM).The carbon film’s specific electrical resistivity was 1–10 (Ω m×10⁻²), depending on the pyrolysis time, temperature and number of coatings. The resistivity was found to decrease by a factor of six when the pyrolysis temperature was increased from 750 to 1,200 °C. A second carbon layer, reduced the resistivity further by about a factor of two. These effects are attributed to densification, improved connectivity between the carbon grains and an overall thickening of the carbon layer. Thermal analysis and Raman measurements on the carbon films point to a grain rearrangement that is consistent with the improved conductivity of the films.