High Temperature In Order Research Articles

Polybenzimidazoles for Hydrogen Generation in the Hybrid Sulfur Electrolyzer

The hybrid sulfur thermochemical cycle has seen much attentional recently due to its potential to enable the production of clean hydrogen on a large scale with a higher efficiency than water electrolysis.[1-9] The two step hybrid sulfur (HyS) process involves the high temperature decomposition of sulfuric acid to produce sulfur dioxide, oxygen, and water, as well as a low temperature electrochemical oxidation of sulfur dioxide in the presence of water to produce sulfuric acid and gaseous hydrogen. Due to the internal recycling of sulfur compounds in the HyS process, the overall balance is the decomposition of water to form gaseous hydrogen and oxygen. This process is interesting because the high temperature decomposition step could be coupled to next generation solar power plants or high temperature nuclear reactors in order to produce hydrogen for other applications. Using a proton exchange membrane such as Nafion in the HyS electrolyzer has been thoroughly examined via the prediction of mass transport through the membrane as a function of operating potential and other design variables. However, Nafion presents several drawbacks, including the inability to operate at elevated temperatures and the decreased performance seen when exposed to high acid concentrations.[7, 8] Previously we showed that acid doped polybenzimidazole (PBI) membranes are an alternative to Nafion because they do not rely on water for proton conductivity, and therefore offer the possibility of operating at higher acid concentrations in order to minimize energy requirements necessary for water separation, as well as operation at higher temperatures in order to minimize voltage losses.[8] Previous operation has focused on low temperatures in for comparison to Nafion, however, high temperature operation offers a better utilization of the advantages of PBI. Here, we present the results of high temperature operation of the HyS electrolyzer using sulfonated PBI. The acid concentration and hydrogen production rates are also quantified. Current interrupt was used to determine the membrane resistance under different operating parameters. A discussion of economic operating targets will also be provided. 1. H. R. Colon-Mercado and D. T. Hobbs, Electrochem Commun, 9, 2649 (2007). 2. J. Staser, R. P. Ramasamy, P. Sivasubramanian and J. W. Weidner, Electrochem Solid St, 10, E17 (2007). 3. S. K. Lee, C. H. Kim, W. C. Cho, K. S. Kang, C. S. Park and K. K. Bae, Int J Hydrogen Energ, 34, 4701 (2009). 4. J. A. Staser, K. Norman, C. H. Fujimoto, M. A. Hickner and J. W. Weidner, J Electrochem Soc, 156, B842 (2009). 5. J. A. Staser and J. W. Weidner, J Electrochem Soc, 156, B16 (2009). 6. J. A. Staser and J. W. Weidner, J Electrochem Soc, 156, B836 (2009). 7. J. A. Staser, M. B. Gorensek and J. W. Weidner, J Electrochem Soc, 157, B952 (2010). 8. J. V. Jayakumar, A. Gulledge, J. A. Staser, C. H. Kim, B. C. Benicewicz and J. W. Weidner, Ecs Electrochem Lett, 1, F44 (2012). 9. J. L. Steimke, T. J. Steeper, H. R. Colon-Mercado and M. B. Gorensek, Int J Hydrogen Energ, 40, 13281 (2015).

Multiaxial Viscoplasticity Modelling of Power Plant Steel

The thermo-mechanical fatigue (TMF) of power plant components is caused by the cyclic operation of power plant. A time-dependent plasticity model can be used to simulate the component response under cyclic thermo-mechanical loading. This paper is concerned with the modelling of thermo-mechanical behaviour of power plant steel under various loading conditions. Fully-reversed, strain-controlled tests were conducted on a parent material of P91 steel at high temperatures in order to determine material constants. A unified, Chaboche viscoplasticity model, was used to model the TMF behaviour of the steel. The multiaxial form of the Chaboche constitutive equations have been implemented in the finite element software and validated by comparing to experimental data. Simulation results have been compared with the results of anisothermal cyclic testing in order to validate the performance of the model in cyclic temperature conditions. The model’s performance under multiaxial stress conditions was investigated by testing and simulating the notched bar specimen under load-controlled conditions.

Influence of the curing cycles on the fatigue performance of unidirectional glass fiber reinforced epoxy composites

During the manufacturing process of fiber reinforced polymers the curing reaction of the resin results in shrinkage of the resin and introduces internal stresses in the composites. When curing at higher temperatures in order to shorten up the processing time, higher curing stresses and thermal stresses are built up and frozen, as residual stresses occur. In the present work, a glass fiber reinforced epoxy composite laminate with an unidirectional architecture based on non-crimp fabrics with backing fibers is investigated. Three different curing cycles (time-temperature cycles) are used, leading to different levels of internal stresses. The mechanical properties, static strength and fatigue life time, are measured in three different directions of the material, i.e. the fiber direction, 0°, the 30° off axis direction, and the 90° direction transverse to the fiber direction. It is experimentally demonstrated that the resulting residual stresses barely influences the quasi-static mechanical properties of reinforced glass-fiber composites. It is found that the fatigue performance in the 0° direction is significantly influenced by the internal stresses, whereas the fatigue performance in the off axes directions so is not significantly influenced of these stresses. This is related to the observations that the damage mechanisms in the off axes directions are mainly related to shear failure in the matrix and in the interface between fiber and matrix and different from the damage mechanisms in the fiber direction, where the damage initiates in the transverse backing fibers and is directly related to fiber fractures in the load-carrying axial fiber bundles.

Thickness and temperature depending intermixing of SiOx/SiO2 and SiOxNy/SiO2 superlattices: Experimental observation and thermodynamic modeling

Multilayered SiOx/SiO2 and SiOxNy/SiO2 thin films were fabricated using different techniques and subsequently annealed at high temperatures (≥1100 °C) in order to form Si nanocrystals by means of the well-known superlattice approach. The thickness of the SiOx and SiOxNy layers was varied from 1.5 to 5 nm, while for the SiO2 layers it was fixed at 4 nm. Using transmission electron microscopy, we showed that the multilayered structure generally sustains the high temperature annealing for both types of films. However, for samples with ultrathin SiOx or SiOxNy layers a breakdown of the superlattice structure and a complete intermixing of layers were observed at high temperatures. On the contrary, annealing at lower temperature (900 °C) preserves the multilayered structure even of such samples. Theoretical calculations showed that the intermixing of SiOx/SiO2 and SiOxNy/SiO2 superlattices in the ultrathin layers thickness limit may be explained thermodynamically by the gain in the Gibbs free energy, which depends in turn on the annealing temperature.

Creep compaction behavior of 3D carbon interlock fabrics with lubrication and temperature

This study aims at understanding and improving the compaction of 3D carbon interlock fabrics with water lubrication, high temperature and a combination of them. The creep compaction behavior was characterized in a mechanical testing machine under different lubrication and temperature conditions. Three different interlock fabrics were studied at high temperature in order to assess the influence of the weaving pattern on the creep compaction behavior. Finally, an experimental study was carried out to point the impact of fiber sizing on the creep compaction behavior and its evolution with temperature. The results of this work demonstrate the strong impact of temperature and lubrication on the compaction ability of 3D interlock fabrics and its link to the fiber sizing.

Clay/Polyaniline Hybrid through Diazonium Chemistry: Conductive Nanofiller with Unusual Effects on Interfacial Properties of Epoxy Nanocomposites.

The concept of conductive network structure in thermoset matrix without sacrificing the inherent mechanical properties of thermoset polymer (e.g., epoxy) is investigated here using "hairy" bentonite fillers. The latter were prepared through the in situ polymerization of aniline in the presence of 4-diphenylamine diazonium (DPA)-modified bentonite (B-DPA) resulting in a highly exfoliated bentonite-DPA/polyaniline (B-DPA/PANI). The nanocomposite filler was mixed with diglycidyl ether of bisphenol A (DGEBA), and the curing agent (4,4'-diaminodiphenylsulfone) (DDS) at high temperature in order to obtain nanocomposites through the conventional melt mixing technique. The role of B-DPA in the modification of the interface between epoxy and B-DPA/polyaniline (B-DPA/PANI) is investigated and compared with the filler B/PANI prepared without any diazonium modification of the bentonite. Synergistic improvement in dielectric properties and mechanical properties points to the fact that the DPA aryl groups from the diazonium precursor significantly modify the interface by acting as an efficient stress transfer medium. In DPA-containing nanocomposites, unique fibril formation was observed on the fracture surface. Moreover, dramatic improvement (210-220%) in fracture toughness of epoxy composite was obtained with B-DPA/PANI filler as compared to the weak improvement of 20-30% noted in the case of the B/PANI filler. This work shows that the DPA diazonium salt has an important effect on the improvement of the interfacial properties and adhesion of DGEBA and clay/PANI nanofillers.

Temperature modulates testis steroidogenesis in European eel

This study evaluates the effects of temperature on hCG-induced spermatogenesis in European eel (Anguilla anguilla), subjected to three thermal regimes: T10: 10°C (first 4weeks), 15°C (next 3weeks) and 20°C (last 6weeks); T15: 15°C (first 4weeks) and 20°C (last 9weeks); and T20: constant 20°C for the duration of the experiment. At 10°C, maturation stopped in the A spermatogonial stage (SPG1), and no further maturation was observed until the temperature was ≥15°C. With the aim of explaining these results, the influence of temperature on steroidogenic enzyme gene expression and steroid synthesis was tested. The initial synthesis of androgens (T and 11-KT) increased at SPG1, and was not influenced by temperature. Likewise, the gene expression of the steroidogenic enzymes linked to androgen synthesis (aacyp11a1, aacyp17-I and aa11βHSD) also increased at SPG1. In contrast, no correlation was seen between the increase in E2 and the aacyp19a1 gene expression peak in the testes, with E2 increasing as a consequence of the seawater acclimation carried out before hormonal treatment, and peaking the aacyp19a1 gene expression at B spermatogonial stage (SPG2). Aacyp21 gene expression was also higher at SPG2, and this stage was only reached when the rearing temperature was ≥15°C.In conclusion, androgen synthesis is not dependent on temperature, but further maturation requires higher temperatures in order to induce a change in the steroidogenic pathway towards estrogen and progestin synthesis. This study demonstrates that temperature plays a crucial role in European eel maturation, even perhaps controlling gonad development during the reproductive migration.

Effect of temperature on the release and remobilization of ecotoxic elements in AMD colloidal precipitates: the example of the Libiola copper mine, Liguria, (Italy).

Due to their characteristics, colloidal particles are able to control the dispersion of many organic and inorganic pollutants in soils and streams. Colloidal precipitates generated by acid mine drainage (AMD) process are usually amorphous or nanocrystalline materials, and their stability plays a crucial role in controlling the fate of metals released by sulphide oxydation. This paper describes a study of elements release (Fe, Al, Mn, Cd, Co, Cr, Cu, Ni, S, Zn) due to desorption or destabilization of three different colloidal precipitates, two ochreous and a greenish-blue precipitate, sampled at the Libiola mine site (northwest Italy). The samples were heated at high temperature in order to verify this treatment as inertization process. At room temperature, the most easily extracted element was S (with released percentages from 8.39 to 29.17%), but considerable amounts of Cu, Zn and Mn (up to 16.6, 610.6 and 595.6mg/kg, respectively) were also observed in the leachates for greenish-blue precipitates. The highest release of elements (S > Cu, Zn, Mn, Cd > Co, Ni > Al, Fe, Cr), with minor differences depending on the mineralogical composition of the samples, was observed for heat-treated samples obtained through moderate heating and mainly formed by anhydrous phases. Samples treated at high temperature had the lowest release, with only Cu showing a significant concentration in the leachate of greenish-blue precipitates. The results showed that dissolution/desorption is limited from ochreous natural colloidal precipitates occurring at the Libiola mine site but also that high amounts of some metals can be remobilized from greenish-blue precipitates. The destabilization of all percipitates through dehydratation-dehydroxylation can further remobilize important amounts of ecotoxic elements. Heat treatment at high temperature could be a definitive, although expensive, way to fix heavy metals in the solid fraction, preventing their dispersion in the surrounding environment.

Thermal properties of Ti-doped Cu–Zn soft ferrites used as thermally actuated material for magnetizing superconductors

A great majority of widely used ferrite ceramics exhibit a relatively high temperature of order–disorder phase transition in their magnetic subsystem. For applications related to the magnetization process of superconductors, however, a low value of Tc is required. Here we report and analyze in detail the thermal properties of bulk Ti-doped Cu–Zn ferrite ceramics Cu0.3Zn0.7Ti0.04Fe1.96O4 and Mg0.15Cu0.15Zn0.7Ti0.04Fe1.96O4. They are characterized by a Curie temperature in the range 120–170 K and a maximum DC magnetic susceptibility exceeding 20 for the Cu0.3Zn0.7Ti0.04Fe1.96O4 material. The temperature dependence of both the specific heat Cp and of the thermal conductivity κ, determined between 2 and 300 K, are found not to exhibit any peculiar feature at the magnetic transition temperature. The low-temperature dependence of both κ and the mean free path of phonons suggests a mesoscopic fractal structure of the grains. From the measured data, the characteristics of thermally actuated waves are estimated. The low magnetic phase transition temperature and suitable thermal parameters make the investigated ferrite ceramics applicable as magnetic wave producers in devices designed for magnetization of high-temperature superconductors.

Extending the Truncated Dyson-Schwinger Equation to Finite Temperatures

In view of the properties of mesons in hot strongly interacting matter the properties of the solutions of the truncated Dyson-Schwinger equation for the quark propagator at finite temperatures within the rainbow-ladder approximation are analysed in some detail. In Euclidean space within the Matsubara imaginary time formalism the quark propagator is not longer a O(4) symmetric function and possesses a discrete spectra of the fourth component of the momentum. This makes the treatment of the Dyson-Schwinger and Bethe-Salpeter equations conceptually different from the vacuum and technically much more involved. The question whether the interaction kernel known from vacuum calculations can be applied at finite temperatures remains still open. We find that, at low temperatures, the model interaction with vacuum parameters provides a reasonable description of the quark propagator, while at temperatures higher than a certain critical value $T_c$ the interaction requires stringent modifications. The general properties of the quark propagator at finite temperatures can be inferred from lattice QCD calculations. We argue that, to achieve a reasonable agreement of the model calculations with that from lattice QCD, the kernel is to be modified in such a way as to screen the infra-red part of the interaction at temperatures larger than $T_c$. For this, we analyse the solutions of the truncated Dyson-Schwinger equation with existing interaction kernels in a large temperature range with particular attention on high temperatures in order to find hints to an adequate temperature dependence of the interaction kernel to be further implemented in to the Bethe-Salpeter equation for mesons. This will allow to investigate the possible in medium modifications of the meson properties as well as the conditions of quark deconfinement in hot matter.

連続炭素繊維強化熱可塑性樹脂基複合材料の機械的特性に及ぼす樹脂供給形態の影響

Carbon Fiber Reinforced Thermoplastics (CFRTP) have been attracting attention in various fields due to their excellence in specific strength, specific modulus, productivity and recyclability. A film stacking method is one of the molding methods of CFRTP laminates. In this method, laminated sheets of matrix films and reinforcing fiber sheets are hot pressed. This method needs a long time under high temperature and high pressure in order to obtain good impregnation of the matrix resin into fiber bundles. To improve the productivity of CFRTP, a non-woven stacking method, in which non-woven fabrics and reinforcing fiber sheets are alternately laminated and molded under compressive stress, has been proposed as an alternative means of the film stacking method. Non-woven fabric can be heated faster than the film because of its larger contact area to the heated air. Therefore, productivity is expected to be improved by using non-woven fabric as a matrix of CFRTP. In this study, CFRTP were molded using non-woven fabrics and films for the matrix, and the bending tests of CFRTP were conducted to clarify the effect of resin supply form on mechanical properties of CFRTP. From the observation of melting form, non-woven fabrics melted into individual fibers while films melted into a single mass. For resin supply from, non-woven fabrics showed good impregnation property compared to films. The interlaminar shear strength and the bending strength of CFRTP using non-woven fabrics for the matrix are higher than CFRTP using films with molding time of 240 seconds or less.

An Experimental Investigation into the Impact of Sulfate Ions in Smart Water to Improve Oil Recovery in Carbonate Reservoirs

Carbonate reservoirs are considered to be in the range of mixed to oil wetting state. Their present wetting state seems unfavorable to recover more oil via conventional waterflooding especially as the water cut increases with huge residual oil saturation. In recent years, studies have shown that tuning the injected brine chemistry can help decrease the oil-wetness, resulting in additional oil recovery and reduction in residual oil saturation. Thus, rock wettability is being dictated by the surface chemistry associated with the water-film stability between crude oil and the rock surface. This study presents series of experiments conducted on Middle Eastern carbonate core plugs at high pressure and high temperature in order to determine the impact of sulfate ions in smart brine on oil recovery. Each experiment was initially conducted using the formation brine, and subsequently, various versions of seawater with varying sulfate concentrations were used. Coreflooding experiments showed an additional recovery of about 7–9 % oil originally in core when sulfate concentration was increased while none when decreased. Decrease in rock oil-wetness was observed to be responsible for the improved recovery as demonstrated by the contact angle analysis. Similar trend was observed with the zeta potential analysis which further proved that the magnitude of surface charge alteration contributes immensely to wettability modification toward more water-wetness.

Flow softening of 253 MA austenitic stainless steel during hot compression at higher strain rates

The flow softening of 253 MA austenitic stainless steel was investigated by means of hot compression tests performed over the temperature range of 900–1150°C. Constant true strain rates of 0.01s−1, 0.1s−1, 1s−1, 10s−1 and 20s−1 were used. The effect of deformation temperature and strain rate on the flow softening and the flow softening mechanisms in the high strain-rate regime (1–20s−1) was examined. The flow curves at higher strain rates, i.e. 10s−1 and 20s−1, were characterized by a single peak followed by continuous stress softening at higher strain levels. The degree of flow softening increased with increasing strain rate and increasing temperature. The flow softening was attributed to thermal softening due to deformation heating, microstructural softening by dynamic recrystallization (DRX) and flow instability. Deformation heating produced by plastic work resulted in significant temperature rise in the steel. The thermal softening due to deformation heating was more pronounced at higher strain rates and lower temperatures. DRX was found to take place at higher deformation temperatures and higher strain rates; this was confirmed by the double-differentiation method proposed by Poliak and Jonas. Flow instability in the form of localized deformation bands occurred at the temperatures of 900°C and 950°C. The processing map developed as per Murty–Rao's instability criterion was found to yield an overestimate of the unstable flow region. Based on the flow behavior and microstructure analysis, it is concluded that this steel is suitable to be hot worked at higher strain rates and higher temperatures in order to reduce the flow stress and to refine grain size.

Prediction of Auto-Ignition Temperatures and Delays for Gas Turbine Applications

Gas turbines burn a large variety of gaseous fuels under elevated pressure and temperature conditions. During transient operations, variable gas/air mixtures are involved in the gas piping system. In order to predict the risk of auto-ignition events and ensure a safe operation of gas turbines, it is of the essence to know the lowest temperature at which spontaneous ignition of fuels may happen. Experimental auto-ignition data of hydrocarbon–air mixtures at elevated pressures are scarce and often not applicable in specific industrial conditions. Auto-ignition temperature (AIT) data correspond to temperature ranges in which fuels display an incipient reactivity, with timescales amounting in seconds or even in minutes instead of milliseconds in flames. In these conditions, the critical reactions are most often different from the ones governing the reactivity in a flame or in high temperature ignition. Some of the critical paths for AIT are similar to those encountered in slow oxidation. Therefore, the main available kinetic models that have been developed for fast combustion are unfortunately unable to represent properly these low temperature processes. A numerical approach addressing the influence of process conditions on the minimum AIT of different fuel/air mixtures has been developed. Several chemical models available in the literature have been tested, in order to identify the most robust ones. Based on previous works of our group, a model has been developed, which offers a fair reconciliation between experimental and calculated AIT data through a wide range of fuel compositions. This model has been validated against experimental auto-ignition delay times corresponding to high temperature in order to ensure its relevance not only for AIT aspects but also for the reactivity of gaseous fuels over the wide range of gas turbine operation conditions. In addition, the AITs of methane, of pure light alkanes, and of various blends representative of several natural gas and process-derived fuels were extensively covered. In particular, among alternative gas turbine fuels, hydrogen-rich gases are called to play an increasing part in the future so that their ignition characteristics have been addressed with particular care. Natural gas enriched with hydrogen, and different syngas fuels have been studied. AIT values have been evaluated in function of the equivalence ratio and pressure. All the results obtained have been fitted by means of a practical mathematical expression. The overall study leads to a simple correlation of AIT versus equivalence ratio/pressure.

NMR and Impedance Spectroscopy Studies on Lithium Ion Diffusion in Microcrystallineγ-LiAlO2

AbstractIn this work nuclear magnetic resonance (NMR) and impedance spectroscopy (IS) studies on Li ion dynamics in microcrystallineγ-LiAlO2are presented. The sample was prepared by solid state synthesis between Li2CO3and Al2O3in air, followed by a quenching procedure. The presence of phase-pureγ-LiAlO2was confirmed by X-ray powder diffraction including Rietveld refinement. Further structural characterization was done with6Li,7Li and27Al NMR. Several NMR techniques such as spin-lattice relaxation measurements, motional narrowing experiments, as well as spin-alignment echo were employed for the investigation of Li ion diffusion. The measurements were carried out at high temperatures (up to 970 K) in order to access the regime of Li ion motion being very slow. The dc conductivities measured by IS in the temperature range from 680 K to 870 K were converted to diffusion coefficients being compatible with those obtained by NMR.

Directly patternable high refractive index ferroelectric sol–gel resist

The development of a ferroelectric negative tone sol–gel resist for Ultraviolet (UV) and Electron Beam (EB) lithography is presented. A new system based on Lead Zirconate Titanate (PZT, with formula PbZr0.52Ti0.48O3) was synthesized by sol–gel method. The lithographic performances were investigated and several structures spanning from the micron range down to less than 50 nm have been achieved by UV and EB lithography. The system interaction with UV light and Electron beam was thoroughly characterized by FT-IT spectroscopy. The exposed PZT was annealed at high temperatures in order to study the crystalline phase evolution, the optical constants values and stability of patterned structures. After exposure and annealing, the refractive index of the material can vary from 1.68 up to 2.33 (@400 nm), while the ferroelectric behaviour seems to be maintained after high temperature annealing. These results suggest a possible application of PZT resist not only as ferroelectric but also as nanopatternable high refractive index material. Moreover, direct nanopatterning by means of Focused Ion Beam (FIB) lithography was verified and the potentiality for the preparation of high aspect ratio hollow nanostructures will be presented.

Raman scattering from confined acoustic phonons of silicon nanocrystals in silicon oxide matrix

In this work, silicon-rich silicon oxide films of different stoichiometry were annealed at high temperatures in order to obtain silicon nanocrystals embedded in silica. The low-frequency Raman scattering has been observed and related to acoustic phonons confined in these nanocrystals. It has been found that this scattering consists of two modes: one at a lower frequency and one at a higher frequency. The depolarization ratios for these modes were determined, showing that the lower frequency mode is depolarized and the higher frequency mode is polarized. It has been also found that under specific conditions of film preparation the product of mode frequency and nanocrystal diameter is scale invariant. Finally, it has been shown that the confined acoustic phonon frequencies do not simply depend on the nanocrystal size alone, but also on the Si concentration in the film itself. This effect has been ascribed to the accelerated nucleation and enhanced crystallization occurring in the films deposited with higher Si content.

Electronic structure and the origin of the high ordering temperature inSrRu2O6

SrRu2O6 is a layered honeycomb lattice material with an extraordinarily high magnetic ordering temperature. We investigated this material using density functional calculations. We find that the energy scales for moment formation and ordering are similar and high. Additionally, we find that the magnetic anisotropy is high and favors moments oriented along the $c$-axis. This provides an explanation for the exceptionally high ordering temperature. Finally, the compound is found to be semiconducting at the bare density functional level, even without magnetic order. Experimental consequences of this scenario for the high ordering temperature are discussed.

Fully coupled thermo-mechanical analysis of bi-directional FGM beams using NURBS isogeometric finite element approach

The fully coupled thermo-mechanical behavior of bi-directional functionally graded material (FGM) beam structures is studied using a computationally low cost isogeometric finite element model. In the proposed analysis, the temperature is considered as a primary variable. The kinematical equations of the bi-directional FGM beam are described by a refined high order global–local theory. A combination of polynomial and exponential expressions is used to introduce the in-plane displacement field. This representation of the in-plane displacement field allows avoiding shear correction factors. Concerning the thermal part, a high-order temperature field is considered through the thickness direction of the bi-directional graded beam. The capability of this novel formulation has been assessed through various thermal and thermo-mechanical tests. To this aim, the obtained numerical results from the proposed isogeometric formulation have been compared with thermo-elasticity solutions or other available results in open literature. It is found that the results obtained from the present beam formulation agree quite well with the reference results.

Abrasion resistance of vitreous enamel coatings in function of frit composition and particles presence

Vitreous enamel is an inorganic coating applied on metallic substrates as powder and fired at relatively high temperature in order to cover the surface forming the coating. This kind of layer shows, at the same time, very good functional and aesthetical properties. In several applications, good mechanical resistance together with corrosion protection is required and enamel is a good alternative to other coatings. Enamel presents optimum corrosion protection and high hardness values but the low fracture toughness reduces its resistance to abrasive wear related to brittle fracture. The microstructure of enamel, the chemical composition of the frit, and the deposition parameters are crucial for the final properties. Moreover, it is possible to introduce mill additives in the frit or hard particles inside the layers to improve final resistance. In this paper, abrasion resistance of enamel is tested by Taber Abraser test. Mill additives (spodumene or quartz), hard (WC or SiC) or solid lubricant (graphite) particles have been added to the frit to study their influence on the abrasion resistance. The abrasion resistance of modified enamels was evaluated through mass loss after abrasion and wear track were observed by SEM in order to evaluate the abrasion damage. An improvement of the abrasion resistance was obtained modifying the frit with mill additives. The introduction of SiC and WC particles produced an important modification in wear mechanism of the glassy coating, reducing the crack nucleation due to the low pores quantity and good interface between vitreous matrix and particles. In these cases the wear mechanism is limited to scratches on the surface.