Turan Gurgenc

Improving fuel efficiency while controlling exhaust emissions is important for the wider use of biodiesel blends. The effects of barium carbonate and barium titanate were compared using a base fuel composed of equal volumes of diesel and biodiesel derived from olive pomace oil. Each additive was evaluated at 25, 50, and 100 ppm, with diesel, untreated BP50, and neat biodiesel serving as reference fuels. Tests used a single-cylinder diesel engine operated at 2000 rpm over a brake power range of 1.0–3.0 kW. Performance, exhaust gas concentrations, smoke opacity, exhaust temperature, and sound pressure level were measured. For neat biodiesel, the largest increases relative to diesel were 24.52% in brake specific fuel consumption and 42.86% in nitrogen oxide concentration. At 2.0 kW, the formulations containing 50 ppm BaCO₃ and BaTiO₃ exhibited brake specific fuel consumption values 3.80% and 3.79% below that of BP50, respectively. Both formulations raised brake thermal efficiency from approximately 22.38% to 23.27%. Relative to BP50, maximum reductions were 44.32% in carbon monoxide concentration with 50 ppm BaTiO₃ at 2.5 kW, 40.00% in hydrocarbon concentration with 100 ppm BaCO₃ at 2.5 kW, and 31.25% in smoke opacity with 50 ppm BaCO₃ at 1.0 kW. However, NO_X concentrations increased by up to 19.87% with 100 ppm BaTiO₃ at 2.0 kW compared with BP50. Under the tested conditions, 50 ppm BaCO₃ provided a favorable balance among fuel consumption, smoke opacity, and sound pressure level, with a smaller NO_X increase than the corresponding BaTiO₃ formulation.

Rare-earth oxide nanoparticles offer a strategy to tune dielectric films via interfacial polarization while maintaining low-loss insulating behavior. Here, polystyrene/samarium oxide (PS/Sm ₂ O ₃ ) nanocomposite films containing 0, 1, 3, 5, and 10 wt.% Sm ₂ O ₃ were fabricated by solvent casting and evaluated as a low-loss dielectric for frequency-sensitive electronic applications. FTIR, XRD, SEM/EDX, and XPS confirmed successful Sm ₂ O ₃ incorporation, preservation of the PS structure, formation of PS/Sm ₂ O ₃ interfacial regions, and Sm ³⁺ /Sm–O species. XRD revealed amorphous PS with increasingly intense crystalline Sm ₂ O ₃ reflections, whereas SEM/EDX showed relatively uniform filler distribution at low and moderate loadings and partial agglomeration at 10 wt.%. Dielectric spectroscopy at room temperature from 1 kHz to 1 MHz showed a frequency-dependent response governed by interfacial polarization and limited charge transport. At 1 kHz, the dielectric constant increased from 8.67241 ± 0.00280 for pure PS to 10.13061 ± 0.00641 for PS-10, while the loss tangent remained low ( ∼ 0.068). The dielectric loss increased moderately from 0.59535 ± 0.00236–0.69194 ± 0.00710, and AC conductivity rose from (3.31202 ± 0.01314) × 10 ⁻¹⁰ to (3.84935 ± 0.03948) × 10 ⁻¹⁰ S cm ⁻¹ . These results indicate interface-controlled dielectric enhancement without conductive percolation, highlighting PS/Sm ₂ O ₃ films for capacitor dielectric layers, insulating films, flexible electronics, and frequency-sensitive dielectric technologies.

Supercapacitor modules are limited not by thermal runaway but by cumulative self-heating, managed at module scale almost exclusively by active air cooling. This work reports passive thermal management of a four-cell series supercapacitor module, 10.8 V and 125 F, using undoped and vanadium nitride doped RT44HC and RT54HC paraffins. A 27-run campaign spanned PCM configuration, current at 15 and 25 A and ambient at 25 and 35 °C, with 25 thermocouples inside a chiller-regulated cabinet. A three-dimensional transient model reproduced all fifteen instrumented cases to a mean heating-phase root mean square error of 0.64 °C. At 25 A the module without PCM was stopped short of the 200-cycle duty at both ambient temperatures, whereas every PCM-filled configuration completed it without parasitic power, suppressing the peak by at least 9.4 to 14.4 °C for RT44HC and 4.5 to 4.9 °C for RT54HC. Even without melting the enclosure still cut the peak by 7.1 °C, through conduction and added mass alone. Vanadium nitride reached 2.9 °C at 2 wt% with melting fully engaged and stayed at or below 0.63 °C elsewhere, against a measured resolvable-difference threshold of 0.5 °C. Latent buffering carried a recovery penalty, extending the half-recovery time from 1671 to 6934 s, which nano-enhancement shortened to 5332 s. The validated model shows that surface sensors underestimate the interior most where cooling works best: the computed core exceeded the surface average by 5.85 °C with PCM against 0.28 °C without, and reached 66.7 to 67.4 °C for RT54HC while the surface read 58.8 to 59.5 °C. Melting-point matching dominated intrinsic property improvement, a 59 % conductivity gain producing no resolvable benefit because the melting window lay above the duty.

Cu‐based sliding‐contact materials require abalance of hardness, wear resistance, corrosion stability, and structural integrity. Pure Cu and Cu–Co, Cu–WC, and Cu–Co–WC composites were fabricated by powder processing followed by pressure‐assisted solid‐state hot pressing at 700 °C under 35 MPa for 60 min in Ar. The hybrid architecture combines WC as a hard load‐bearing constituent with Co‐containing metallic regions that enhance local matrix constraint, contact continuity, and reinforcement retention. Correlated SEM/EDX, XRD, density, hardness, dry‐sliding, and electrochemical analyses were used to establish the corresponding structure–property relationships. All compositions achieved relative densities above 99.5%. Cu remained the dominant crystalline matrix, while WC‐related diffraction features were retained in the WC‐containing compositions. Hardness increased from 57 HV30 for pure Cu to 156 HV30 for Cu–3Co–3WC. The same composition exhibited the lowest specific wear rate, 3.31 × 10 ⁻⁵ mm ³ N ⁻¹ m ⁻¹ , corresponding to a 90.47% reduction relative to pure Cu. Pure Cu exhibited the lowest absolute corrosion rate, whereas Cu–3Co–3WC showed the lowest corrosion rate among the reinforced compositions. Thus, Cu–3Co–3WC provided the most favorable combined mechanical, tribological, and electrochemical response among the reinforced materials investigated.

Paraffin phase change materials (PCMs) are limited by low thermal conductivity, commonly raised with nanofillers that often erode the specific heat. Here, vanadium nitride (VN), a metallic nitride best known as a supercapacitor electrode, was introduced as a conductivity filler and dispersed at 0.5-2.0 wt% in paraffin RT44HC by a surfactant-assisted two-stage melt-dispersion method, and the composites were characterised by XRD, FT-IR, FE-SEM/EDX, DSC, TGA and transient hot-wire thermal-conductivity analysis. DSC phase-change parameters are given as mean ±SD (n=3). The same dose was tested in a second, higher-melting matrix (RT54HC-2VN). XRD and FT-IR confirmed that VN retains its rock-salt structure and is physically dispersed, without new phases or chemical bonds. At 2 wt% VN, solid-phase thermal conductivity increased from 0.207 to 0.295 W/(m·K) (+42.5 %) and liquid-phase from 0.190 to 0.217 W/(m·K) (+14.2 %), while solid specific heat decreased only from 2.02 to 1.95 J/(g·K) (-3.5 %). The melting enthalpy was 246.9 J/g for pure RT44HC and 238.9 J/g at 2 wt% VN, with the melting onset unchanged (38.9 °C). The maximum decomposition temperature rose from 222 to 263 °C, and the melting enthalpy was unchanged after 1000 melt-freeze cycles (239 to 240 J/g). In RT54HC, 2 wt% VN raised solid conductivity by 41.3 % and preserved the specific heat (+2.9 %) where cubic boron nitride had lowered it by 19.4 %. This VN gain came at the cost of a 16 % latent-heat reduction. VN thus enhances paraffin-PCM thermal conductivity with a near-neutral specific heat, a balance well suited to passive thermal management of self-heating devices such as supercapacitors and power electronics.

High-velocity oxy-fuel (HVOF)-sprayed NiCrBSi coatings containing 0, 10, 30, and 50 wt.% WC-Co were evaluated on AZ91D magnesium alloy to determine how the discrete reinforcement level affects surface topography, phase constitution, Vickers microhardness, dry-sliding friction, mass loss, and wear-track microchemistry. As-sprayed surfaces were characterized by three-dimensional profilometry; coating cross-sections and worn surfaces by optical microscopy and SEM/EDS; phase constitution by XRD; and mechanical response by HV_0.1 indentation. Dry-sliding tests were performed at 10, 30, and 50 N over 100–1000 m. Increasing WC-Co content raised Sa from 8.8 ± 0.3 to 13.0 ± 0.5 µm and Vickers microhardness from 776 ± 4 to 959 ± 5 HV_0.1. XRD indicated a γ-Ni-based matrix containing boride/carbide constituents, while WC, W₂C, and Co became increasingly prominent in the reinforced coatings. Boride assignments are based on diffraction evidence, whereas B and C EDS signals were treated semi-quantitatively. The 50 wt.% WC-Co coating exhibited the lowest mass loss and mean coefficient of friction at every load. Its mean friction coefficients were 0.31, 0.35, and 0.41 at 10, 30, and 50 N, corresponding to reductions of 40.1%, 38.9%, and 36.2% relative to AZ91D. At 1000 m, its mass-normalized wear rate indices were 9.0 × 10⁻⁴, 4.0 × 10⁻⁴, and 5.3 × 10⁻⁴ mg N⁻¹ m⁻¹, respectively. Post-wear mapping showed the largest field-scale W-Co-rich fraction in the 50 wt.% coating; however, isolated spectra containing more than 94 wt.% Mg are compatible with local coating penetration/substrate exposure and/or Mg-rich debris. The 50 wt.% composition therefore provided the best combined response among the four tested levels, while intermediate compositions are required to identify a continuous-composition optimum.

This study tailors titanium nitride (TiN)-reinforced RT70 HC nanocomposite phase change materials (PCMs) for medium-temperature thermal energy storage. TiN nanoparticles were incorporated into commercial RT70 HC at 0.1–2.0 wt.% by a two-stage method combining sodium dodecyl sulfate, magnetic stirring, and ultrasonication, and characterized by FT-IR, XRD, SEM-EDX, elemental mapping, DSC, thermal conductivity, Cp, TGA, and 1000-cycle tests. FT-IR and XRD confirmed the physical integration of TiN into RT70 HC without new chemical bonds or secondary phases, and SEM-EDX showed a concentration-dependent dispersion. The phase change temperatures were largely preserved. The latent heat varied non-monotonically with TiN content, increasing at low loadings (0.1–0.5 wt.%) and decreasing at higher loadings. Because each composition was prepared as a single batch and measured on small specimens, the low-loading latent-heat increase (up to about 9%) is indicative rather than statistically proven and may fall within the subsampling variance. The 0.5 wt.% sample reached the highest values of 306/296 J/g in the first cycle and 286/268 J/g after 1000 cycles. The thermal conductivity increased with TiN content, reaching a maximum enhancement of about 24.09% in the liquid phase (0.1785 to 0.2215 W/(m·K) at 80 °C) and 35.7% in the solid phase at 2.0 wt.%, whereas the specific heat capacity was lower at higher loadings, an indicative trade-off given the single-run measurement uncertainty. TGA showed degradation onset temperatures above 240 °C, a wide safety margin relative to the ~72 °C working range. Overall, the 0.1–0.5 wt.% formulations offered the most balanced thermal performance for medium-temperature applications.