Jyrki Vuorinen

Thermal analysis of plasma sprayed oxide coatings sealed with aluminium phosphate

Abstract Thermal analysis by thermogravimetry and differential scanning calorimetry was carried out for plasma-sprayed alumina and chromia coatings to study their stability after plasma spraying and for aluminum phosphate sealant to study phosphate reactions during the sealing heat treatment. Thermogravimetric analysis for alumina coating did not show any change in the coating due to the heat treatment, though the phase structure had changed from metastable γ-Al 2 O 3 to stable α-Al 2 O 3 . In the chromia coating thermogravimetric analysis showed 1.7 wt.% weight increase due to the oxidation of the sprayed coating. During plasma-spray process the chromia coating had gained some under-stoichiometry or some of the chromia had decomposed into metallic chromium or other oxides. Thermal analysis for aluminum phosphate sealant showed weight loss of about 27 wt.%. This corresponds well to the formation of metaphosphates via dehydration of aluminum phosphate solution during the sealing heat treatment. Thermal analysis for the mixture of sealant and alumina coating showed slightly different behaviour than plain sealant. The sealant reacted with the alumina coating forming a crystalline phase, berlinite-type orthophosphate AlPO 4 . Thermal analysis for the mixture of sealant and chromia coating showed nearly similar behaviour than plain sealant and no indications of the chemical reactions were detected.

Performance of epoxy filled with nano- and micro-sized Magnesium hydroxide

Magnesium hydroxide (MDH) particles are often used as fillers to improve the flame retardancy of polymers. However, achieving the balance between the enhanced fire resistance and reduced mechanical properties, especially toughness, is still a challenge to the composite community. In this study, the effect of the particle size and silane surface modification of MDH particles on the flame retardant, thermal, and mechanical properties of epoxy was studied. Both nano- and micro-sized MDH particles were modified by a silanization reaction with γ-aminopropyltrietoxysilane in an aqueous solution and filled into epoxy matrix by a high-shear mixer and a three-roll mill. Results show that nano-MDH filled epoxy composites yielded better mechanical properties than their micro-MDH filled counterparts. Furthermore, the adhesion between nano-sized MDH and the matrix was improved by the silane surface modification. When comparing the flame retardant properties, enhancements in heat release rates and total heat released were observed for MDH filled epoxy composites.

Metal–Plastic Adhesion in Injection-Molded Hybrids

Polymer–metal hybrids are replacing steel structures in many applications. Combining metals and plastics is, however, complicated because they have very different physical and chemical characteristics. This study characterizes plastic–metal adhesion in insert-injection-molded hybrids. Diaminofunctional silane was used as a coupling agent between thermoplastic urethane and stainless steel. Before silane treatment, various surface treatments, including electrolytic polishing and different oxidation treatments, were applied to the steel inserts to understand better the bonding between silane and steel. The effects of the surface treatments and silane application on plastic–metal adhesion were studied by means of contact angle measurements, adhesion tests, and microscopic characterizations. Electrolytic polishing and oxidation of the steel inserts significantly improved the silane bonding to the steel insert, and consequently the plastic adhesion to steel.

Heat capacity of hydrogenated diamond-like carbon films

We have used differential scanning calorimetry to measure the heat capacity of diamond-like carbon (DLC) film prepared by a plasma immersion ion processing method. The same calorimeter was used to measure the heat capacity of single crystal natural diamond and of high purity graphite. The amount of atomic hydrogen trapped in the DLC films was determined by elastic-recoil-detection spectrometry. The present data and literature values were used to deduce an expression for the specific heat that factors out the contribution from the sp3/sp2 bonding and from the atomic hydrogen trapped in the carbon. The data shows that the hydrogen contribution to the specific heat of carbon is independent of the sp3/sp2 bonding and amounts to about 0.63kB per hydrogen atom. We propose a simple method to determine the sp3/sp2 bonding ratio in hydrogenated DLC films based on measuring the specific heat and the hydrogen content of the sample.

Elastic constants of an aluminum–alumina unidirectional composite

The five independent second-order elastic constants of a transversely isotropic aluminum/alumina fiber composite have been measured for the first time using a resonant ultrasound spectroscopy technique. These data were used to deduce the elastic constants and engineering moduli for off-axis loading conditions.

Mechanical and tribological property comparison of melt-compounded nanocomposites of atomic-layer-deposition-coated polyamide particles and commercial nanofillers

Mechanical and tribological properties of melt-compounded titanium dioxide nanocomposites of atomic-layer-deposition (ALD)-coated polyamide particles and commercial nanofillers were compared. The nanofiller dispersion in the polyamide matrix was studied using transmission electron microscopy showing very different morphology for the ALD-created and the traditional nanocomposites: former appearing as ribbons in the matrix whereas latter composing from spherical clusters. The effect of such morphology change on the specimen’s mechanical response subjected to tensile and impact loading was investigated. The results demonstrated that ALD-created nanocomposites possess significantly higher Young’s modulus than pure and traditionally filled polyamide matrix. However, transition from ductile to brittle behavior occurs especially for the ALD-created nanocomposites. Notched impact strength experiments supported this, suggesting that the impact strength of ALD-created composites decreased significantly compared to ...

Modification of epoxy resin by silane-coupling agent to improve tensile properties of viscose fabric composites

The modification of epoxy resin by 3-aminopropyltriethoxysilane (APTES) to improve the tensile properties of warp knitted viscose fabric composites is reported in this study. The study evaluates the efficiency of modification methods adopted to modify the epoxy resin and the influence of the resin modification on various properties of the cured castings. The influence of matrix resin modification on the tensile properties of viscose fabric composite is compared to those prepared from chemically modified fibre. The efficiency of the modification was determined through titration method to determine the epoxide content of epoxy resin, viscosity measurement and FTIR. The effect of APTES modification on various properties of cured castings is studied through differential scanning calorimeter, contact angle measurement and tensile testing. The addition of APTES into the epoxy resin decreased the epoxide content in the resin as evident from the titration method. The tensile strength of cured castings decreased after the resin modification. The tensile strength and elongation at break of the viscose fabric composites prepared from modified resin, increased up to 14 and 41%, respectively. The improved adhesion of APTES-modified epoxy resin to the viscose fibre is confirmed from SEM analysis of tensile fracture surface.

Effect of Multiwalled Carbon Nanotubes on the Properties of EPDM/NBR Dissimilar Elastomer Blends

In the presence of multiwalled carbon nanotubes (MWCNT), polar nitrile-butadiene rubber (NBR) and nonpolar ethylene propylene diene rubber (EPDM) blends were prepared following a melt mixing method. For the preparation of MWCNT filled EPDM/NBR blends, two mixing methods were used: direct mixing and the masterbatch dilution method. Various physical, mechanical, and morphological properties are explored to elucidate the dispersion behavior of MWCNTs. It was concluded that the preparation method influences the dispersion of the nanotubes in different rubber phases and the properties of these blends are controlled by the degree of dispersion of the nanotubes in the two phases. GRAPHICAL ABSTRACT

High-Temperature Storage Testing of ACF Attached Sensor Structures

Several electronic applications must withstand elevated temperatures during their lifetime. Materials and packages for use in high temperatures have been designed, but they are often very expensive, have limited compatibility with materials, structures, and processing techniques, and are less readily available than traditional materials. Thus, there is an increasing interest in using low-cost polymer materials in high temperature applications. This paper studies the performance and reliability of sensor structures attached with anisotropically conductive adhesive film (ACF) on two different organic printed circuit board (PCB) materials: FR-4 and Rogers. The test samples were aged at 200 °C and 240 °C and monitored electrically during the test. Material characterization techniques were also used to analyze the behavior of the materials. Rogers PCB was observed to be more stable at high temperatures in spite of degradation observed, especially during the first 120 h of aging. The electrical reliability was very good with Rogers. At 200 °C, the failures occurred after 2000 h of testing, and even at 240 °C the interconnections were functional for 400 h. The study indicates that, even though these ACFs were not designed for use in high temperatures, with stable PCB material they are promising interconnection materials at elevated temperatures, especially at 200 °C. However, the fragility of the structure due to material degradation may cause reliability problems in long-term high temperature exposure.

Characterization of graphene-based inkjet printed samples on flexible substrate for wireless sensing applications

Inkjet printing is one of the emerging methods for fabrication of electronic devices. The important issue in this area is developing nanomaterial-based inks for different applications such as gas sensors for environmental monitoring. In particular, graphene-based materials have recently gained interest due to their extraordinary properties. However, graphene has hydrophobic nature resulting in poor solubility in the most of the solvents. In order to solve this problem, graphene oxide is mostly used instead of graphene. To retrieve the conductivity, the printed samples are reduced to remove the oxygen containing groups. The major contribution of this paper is focused on the production of conductive graphene-based patterns on the flexible kapton substrate utilizing thermal reduction process. Both printed samples and inks were characterized and analyzed to enhance the quality of printing. The effect of different parameters such as surface modification, annealing condition, thermal reduction atmosphere, setting of inkjet printer, and concentration of ink were investigated. The characterization part includes analysis of the morphology, sheet resistance, conductivity, and viscosity of ink. This work is an important step for future research on the development of wireless graphene-based gas sensors.