Thermal stability and fire behavior of aluminum diethylphosphinate-epoxy resin nanocomposites

The flame retardancy of 2, 2-bis(4-glycidyloxyphenyl)propane (DGEBA)-aluminum diethylphosphinate (AlPi) nanocomposites (EP-AlPi/(P ? x), x = 1, 2, 3 %) was greatly enhanced by ultrasonic dispersion of nano-sized AlPi into epoxy resin. The UL 94 V-0 rating can be reached for EP-AlPi nanocomposites with a relatively low addition amount of AlPi (on the account of 8.4 wt% or phosphorus content of 2 wt%) as well as the LOI value over 37.2. The glass transition temperature (T _g) enhanced properties were investigated by DTA, which showed that: T _gs were about 5 °C higher than that of neat epoxy resin; T _g increased along with content increasing of AlPi. Based on TGA results under a non-isothermal condition, the thermal degradation kinetics of EP-AlPi/(P ? x) composites were studied by Kissinger’s, Ozawa’s, Flynn–Wall–Ozawa’s and Coast-Redfern’s methods, which suggested the conversion function f (α) = 1/2α ^?1 or f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 1 %); f (α) = [?ln(1 ? α)]^?1 for EP-AlPi/(P ? 2 %) and EP-AlPi/(P ? 3 %) during the investigated process. The epoxy resin nanocomposites obtained in this study are green functional polymers and will become flame retardant potential candidates in electronic fields such as printed wiring boards with high performance.     

Comparative analysis of the factors associated with citation and media coverage of clinical research

Our objective was to study the relationship between the design and content of randomized clinical trials (RCTs) and the subsequent number of citations in the medical literature and attention in online news and social media. We studied RCTs published during 2014 in five highly cited medical journals. This was a retrospective review focusing on characteristics of the individual trials and measures of citation and lay media attention. Primary outcome measures included citation count and Altmetric^® scores (a composite score measuring attention in news, blogs, Twitter^®, and Facebook^®). Two hundred and forty two RCTs were included in the final analysis. Trial characteristics that were positive predictors of citation count included investigation of Hepatitis C treatment (r = 0.35, p < 0.001), private funding (r = 0.24, p < 0.001), mortality-related endpoint (r = 0.22, p < 0.001), and research setting within the United States (r = 0.13, p < 0.001). The trial characteristic that positively predicted Altmetric score was the population size potentially affected (r = 0.39, p < 0.001). The only negative predictor of citation count was the size of the population potentially affected (r = ?0.21, p < 0.001). Negative predictors of the Altmetric score included investigation of Hepatitis C treatment (r = ?0.21, p < 0.001) and private funding (r = ?0.13, p < 0.001). While correlation magnitudes were weak, the predictors of biomedical literature citation and non-academic media coverage were different. These predictors may affect editorial decisions and, given the rising influence of health journalism, further study is warranted.     

Doping mechanisms and electrical properties of bismuth tantalate fluorites

Phase-pure bismuth tantalate fluorites were successfully prepared via conventional solid-state method at 900 °C in 24–48 h. The subsolidus solution was proposed with the general formula of Bi_3+x Ta_1?x O_7?x (0 ≤ x ≤ 0.184), wherein the formation mechanism involved a one-to-one replacement of Ta⁵⁺ cation by Bi³⁺ cation within ~4.6 mol% difference. These samples crystallised in a cubic symmetry, space group Fm-3 m with lattice constants, a = b = c in the range 5.4477(± 0.0037)–5.4580(± 0.0039) Å. A slight increment in the unit cell was discernible with increasing Bi₂O₃ content, and this may attribute to the incorporation of relatively larger Bi³⁺ cation in the host structure. The linear correlation between lattice parameter and composition variable showed that the Vegard’s law was obeyed. Both TGA and DTA analyses showed Bi_3+x Ta_1?x O_7?x samples to be thermally stable as neither phase transition nor weight loss was observed within ~28–1000 °C. The AC impedance study of Bi₃TaO₇ samples was performed over the frequency range 5–13 MHz. At intermediate temperatures, ~350–850 °C, Bi_3+x Ta_1?x O_7?x solid solution was a modest oxide ion conductor with conductivity, ~10^?6–10^?3 S cm^?1; the activation energy was in the range 0.98–1.08 eV.     

Oscillating cylinder in viscous fluid: calculation of flow patterns and forces

Laminar and large-eddy-simulation (LES) calculations with the dynamic Smagorinsky model evaluate the flow and force on an oscillating cylinder of diameter D = 2R in otherwise calm fluid, for β = D ²/νT in the range 197–61400 and Keulegan–Carpenter number K = U _m T/D in the range 0.5–8 (ν kinematic viscosity, T oscillation period, U _m maximal velocity). Calculations resolving the streakline patterns of the Honji instability exemplify the local flow structures in the cylinder boundary layer (β ~ 197–300, K ~ 2) but show that the drag and inertia force are not affected by the instability. The present force calculations conform with the classical Stokes–Wang solution for all cases below flow separation corresponding to K < 2 (with β < 61400). The LES calculations of flow separation and vortical flow resolve the flow physics containing a large range of motion scales; it is shown that the energy in the temporal turbulent fluctuations (in fixed points) are resolved. Accurate calculation of the flow separation occurring for K > 2 has strong implication for the force on the cylinder. Present calculations of the force coefficients for K up to 4 and β = 11240 are in agreement with experiments by Otter (Appl Ocean Res 12:153–155, 1990). Drag coeffients when flow separation occurs are smaller than found in U-tube experiments. Inertia coefficients show strong decline for large K (up to 8) and moderate β = 1035 but is close to unity for K = 4 and β = 11240. The finest grid has 2.2 × 10⁶ cells, finest radial Δr/R = 0.0002, number of points along the cylinder circumference of 180, Δz/R = 0.044 and a time step of 0.0005T.     

Influence of different sulfur sources on the phase formation of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> (CZTS) nanoparticles (NPs)

Wurtzite (Wz) and kesterite (Ks) phases of Cu₂ZnSnS₄ (CZTS) nanoparticles (NPs) have been selectively synthesized via hot injection method using 1-octadecene (1-ODE) as solvent. The solvents, 1-dodecanethiol (1-DDT) and tert-dodecanethiol (t-DDT) were utilized to control the reactivity of metal precursors and to tune the desirable crystallographic phases. The phase purity of the as synthesized CZTS NPs was confirmed using X-ray diffraction results. TEM images indicate that the developed nanoparticles consist of a mixture of triangular shaped (height 20?±?3 nm, width 17?±?2 nm) and sphere shaped NPs (13.4?±?0.4 nm). These nanoparticles were formed due to the influence of thiols without any additional capping ligands. The band gap of as-synthesized CZTS NPs were calculated as 1.41 eV for wurtzite phase (Wz—1-DDT) and 1.47 eV for kesterite phase (Ks—t-DDT) from UV–Visible absorption results. CZTS thin films were prepared via spin coating and the electrical properties were analysed using Hall Effect measurements. Both the phases of CZTS films exhibit p-type conductivity. Wurtzite phase of CZTS has higher mobility (23.6 cm^?3) and carrier concentration (2.64?×?10¹⁷) compared to kesterite phase of CZTS films.     

Structural relaxation and electrical conductivity of molybdovanadate glass

⁵⁷Fe Mössbauer spectrum of conductive barium iron vanadate glass with a composition of 20BaO·10Fe₂O₃·70V₂O₅ (in mol%) showed paramagnetic doublet peak due to distorted Fe^IIIO₄ tetrahedra with isomer shift (δ) value of 0.37 (±?0.01) mm s^?1. Mössbauer spectra of 20BaO·10Fe₂O₃·xMoO₃·(70???x)V₂O₅ glasses (x?=?20–50) showed paramagnetic doublet peaks due to distorted Fe^IIIO₆ octahedra with δ’s of 0.40–0.41 (±?0.01) mm s^?1. These results evidently show a composition-dependent change of the 3D-skeleton structure from “vanadate glass” phase, composed of distorted VO₄ tetrahedra and VO₅ pyramids, to “molybdate glass” composed of distorted MoO₆ octahedra. After isothermal annealing at 500 °C for 60 min, Mössbauer spectra also showed a marked decrease in the quadrupole splitting (Δ) of Fe^III from 0.70 to 0.77 to 0.58–0.62 (±?0.02) mm s^?1, which proved “structural relaxation” of distorted VO₄ tetrahedra which were randomly connected to FeO₄, VO₅, MoO₆, FeO₆ and MoO₄ units by sharing corner oxygen atoms or edges. DC-conductivity (σ) of barium iron vanadate glass (x?=?0) measured at room temperature was 3.2?×?10^?6 S cm^?1, which increased to 3.4?×?10^?1 S cm^?1 after the annealing at 500 °C for 60 min. The σ’s of as-cast molybdovanadate glasses with x’s of 20–50 were ca. 1.1?×?10^?7 or 1.2?×?10^?7S cm^?1, which increased to 2.1?×?10^?2 (x?=?20), 6.7?×?10^?3 (x?=?35) and 1.9?×?10^?4 S cm^?1 (x?=?50) after the annealing at 500 °C for 60 min. It was concluded that the structural relaxation of distorted VO₄ tetrahedra was directly related to the marked increase in the σ, as generally observed in several vanadate glasses.     

Investigation of earth-alkaline (EA = Mg,Ca, Sr) containing methylammonium tin iodide perovskite systems

Methylammonium tin iodide systems containing earth-alkaline ions (CH₃NH₃Sn_1?x (EA) _x I₃, EA = Ca²⁺, Sr²⁺, Mg²⁺, 0 ≤ x ≤ 0.30) were investigated. The X-ray diffraction patterns detected the formation of tetragonal nearly cubic CH₃NH₃SnI₃ (space group P4mm), SnI₂, and not identified phases. The morphological analysis confirmed the presence of secondary phases with formation of irregularly shaped crystallites. The Sn3d and I3d photoemission spectra revealed the typical position and separation of spin–orbit components for Sn²⁺ in halides. Static thermogravimetric measurements (T = 85 °C) showed a barely measurable weight loss for EA = Mg, a dramatic decrease of the weight loss rate for EA = Ca, and recorded weight losses till t ≈ 1.5 h only for EA = Sr, respectively. The optical spectra displayed absorption edges which increased at increasing the (EA)-content with maximum values for x = 0.050 (λ _on-set = 1754 nm, EA = Mg; λ _on-set = 1692 nm, EA = Ca; and λ _on-set = 1338 nm, EA = Sr, respectively). The Tauc plots revealed a direct semiconducting behavior with band energy gaps depending on the nature and amount of the (EA)-ions. The photoluminescence (PL) spectra showed, for EA = Mg, an increase of the PL-band intensity at increasing the Mg content with a maximum at x = 1.0 and, for EA = Ca, an increase of band intensity at increasing the Ca-content and for EA = Sr, a band intensity maximum at x = 0.025. This was explained by the similar ionic radius between Sn²⁺ and Sr²⁺ ions which can be easily exchanged in the SnI₆ ^2? octahedra.     

Vacancies in as-grown CZ silicon crystals observed by low-temperature ultrasonic measurements

By means of the low-temperature ultrasonic measurement, we try to observe the elastic softening due to the vacancies in as-grown silicon crystals grown by the Czochralski (CZ) method. We prepared a high-resistivity CZ silicon crystal ingot comprising the following defect-regions: the void region, the region of ring-like oxidation stacking fault, the Pv-region, the Pi-region, and the region of the dislocation clusters. Both of the elastic constants C ₄₄(T) and [C ₁₁(T) ? C ₁₂(T)]/2 measured for the samples taken from the Pv-region exhibit the softening of the type C _Γ(T) = C _Γ ⁽⁰⁾ [1 ? Δ_JT/(T ? Θ)] which was also found in our previous study for the non-doped FZ silicon and attributed to the neutral vacancy. No response of the softening to the applied magnetic field is found, as in our previous case of the non-doped FZ silicon. The observed softenings are attributed to the triply degenerate T ₂ states of the vacancy accommodating two electrons with anti parallel spins. The samples in the Pi-region exhibit no such softening, confirming that the origin of the softening is the vacancies. A qualitative explanation is given to the measured distribution of the vacancy concentration.     

Effect of inter-electrode spacing on structural and electrical properties of RF sputtered AlN films

An attempt has been made to correlate the morphological and electrical properties of RF sputtered aluminum nitride (AlN), with target to substrate distance (D _ts) in sputter chamber. AlN films, having thickness around 3,000 Å, were deposited on silicon substrates with different D _ts values varying from 5 to 8 cm. XRD results indicated that the crystallinity of c-axis oriented films increase significantly with decrease in D _ts and the FTIR absorption band of the films became prominent at shorter D _ts. The surface roughness increased from 1.85 to 2.45 nm with that in D _ts. A smooth surface with smaller grains was found at shorter D _ts. The capacitance–voltage (C–V) measurements revealed that the insulator charge density (Q _in) increased from 3.3 × 10¹¹  to 7.3 × 10¹¹ cm^?2 and the interface state density (D _it) from 1.5 × 10¹¹  to 7.3 × 10¹¹ eV^?1cm^?2 with the increase in D _ts.     

Synthesis and characterization of nanocrystalline TiO<Subscript>2</Subscript> thin films

Nanocrystalline thin films of TiO₂ have been synthesized by sol gel spin coating technique Thin films of TiO₂ annealed at 700 °C were characterized by X-ray diffraction(XRD), Atomic Force Microscopy, High resolution TEM and Scanning Electron Microscopy (SEM), The XRD shows formation of tetragonal anatase and rutile phases with lattice parameters a = 3.7837 Å and c = 9.5087 Å. The surface morphology of the TiO₂ films showed that the nanoparticles are fine with an average grain size of about 60 nm. Optical studies revealed a high absorption coefficient (10⁴ cm^?1) with a direct band gap of 3.24 eV. The films are of the n type conduction with room temperature electrical conductivity of 10^?6 (Ω cm)^?1.     

Microwave dielectric properties of Sr<Subscript>0.7</Subscript>Ce<Subscript>0.2</Subscript>TiO<Subscript>3</Subscript>–Sr(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> ceramics

xSr_0.7Ce_0.2TiO₃–(1???x)Sr(Mg_1/3Nb_2/3)O₃ ceramics, referred to xSCT–(1???x)SMN, were successfully produced by conventional solid-state sintered technology. The compounds, belonging to perovskites with a secondary phase of CeO₂, can be detected even with x down to 0.1 of SCT composition. The overall trend for grain growth illustrates the increase with increasing SCT doping level. The Raman peak at 825 cm^?1 splits into two peaks and causes red shift phenomenon. XPS spectra indicate that Ti and Nb ions exist respectively in tetravalence and pentavalence, and Ce ions exist in trivalence and tetravalence. Dielectrics constant (ε _r ) of SCT–SMN ceramics gradually increases with increasing theoretical dielectric polarizabilities. A wider width of the 825 cm^?1 for FWHM of A_1g mode Raman peaks suggests to a lower Q?×?f value. The increasing tolerance factor in agreement with temperature coefficient of resonant frequency (τ _f ), denotes that the rise of perovskite symmetry. The 0.1SCT–0.9SMN ceramic sintered at 1450?°C for 4 h illustrates excellent microwave dielectric properties with ε _r ?~?35.4, Q?×?f?~?11282 GHz and τ _f ?~?1.7 ppm/°C. Activation energies of 0.1SCT–0.9SMN ceramic at 100, 300 and 500 V, are ~0.436, 0.427 and 0.331 eV, respectively, indicative of a decreased trend with external electric field.     

Crystal structure,microstructure and microwave dielectric properties of novel MgAl<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript> ceramic

In the present work, a novel MgAl₂Ti₃O₁₀ ceramic was obtained using a traditional solid-state reaction method. X-ray diffraction and energy dispersive spectrometer showed that the main MgAl₂Ti₃O₁₀ phase was formed after sintered at 1300–1450 °C. With rising the sintering temperature from 1300 to 1450 °C, the bulk density (ρ), relative permittivity (ε _r ) and Q?×?f value firstly increased, reached the maximum values (3.61 g/cm³, 14.9, and 26,450 GHz) and then decreased. The temperature coefficient of resonator frequency (τ _f ) showed a slight change at a negative range of ??94.6 to ??83.7 ppm/°C. When the sintering temperature was 1400 °C, MgAl₂Ti₃O₁₀ ceramics exhibited the best microwave dielectric properties with Q?×?f?=?26,450 GHz, ε _r ?=?14.9 and τ _f ?=???83.7 ppm/°C.     

Very high thermal stability with excellent dielectric,and non-ohmics properties of Mg-doped CaCu<Subscript>3</Subscript>Ti<Subscript>4.2</Subscript>O<Subscript>12</Subscript> ceramics

In this work, the nominal CaCu_3?xMg_xTi_4.2O₁₂ (0.00, 0.05 and 0.10) ceramics were prepared by sintering pellets of their precursor powders obtained by a polymer pyrolysis solution method at 1100 °C for different sintering time of 8 and 12 h. Very low loss tangent (tanδ)?<?0.009–0.014 and giant dielectric constant (ε′) ～?1.1?×?10⁴–1.8?×?10⁴ with excellent temperature coefficient (Δε′) less than ±?15% in a temperature range of ??60 to 210 °C were achieved. These excellent performances suggested a potent application of the ceramics for high temperature X8R and X9R capacitors. It was found that tanδ values decreased with increasing Mg²⁺ dopants due to the increase of grain boundary resistance (R_gb) caused by the very high density of grain, resulting from the substitution of small ionic radius Mg²⁺ dopants in the structure. In addition, CaCu_3?xMg_xTi_4.2O₁₂ ceramics displayed non-linear characteristics with the significant enhancements of a non-linear coefficient (α) and a breakdown field (E_b) due to Mg²⁺doping. The high values of ε′ (14012), α (13.64) and E_b (5977.02 V/cm) with very low tanδ value (0.009) were obtained in a CaCu_2.90Mg_0.10Ti_4.2O₁₂ ceramic sintered at 1100 °C for 8 h.     

Surface morphology and thermal figure of merit of a new compound thin film

The third nonlinear optical properties of a new compound 4,4′-bis(3-methoxy benzylidene amino) biphenyl doped poly-methyl methacrylate (PMMA) have been studied using Z-scan technique. Experiments are performed using a continuous waveguide (cw) diode laser at 532 nm wavelength and 0.68 kW/cm² laser intensity. The optical power limiting behavior of sample doped PMMA was also investigated. It also shows a very good optical limiting behavior with a limiting threshold of 4.7 mW. We attribute the nonlinear absorption and optical limiting property of the sample film to two photon absorption effect at 532 nm. The experimental evidences of observing diffraction pattern in compound 4,4′-bis(3-methoxybenzylideneamino) biphenyl doped PMMA has been present. The refractive index change, Δn, and nonlinear refractive index, n ₂ determined from the number of observed ring. We obtained good values of Δn = 105.154 × 10^?4and n ₂ = 154.154 × 10^?7 cm²/W. Variation of refractive index with temperature, dn/dT, and figure of merit, H, are found to be 8.858 × 10^?6 1/°C and 5.316 × 10^?6, respectively. This large nonlinearity is attributed to a thermal effect resulting from linear absorption. Theoretical diffraction pattern that agree well with experimental one are generated using a wave theory.     

Effect of sintering temperature on microstructures and microwave dielectric properties of Ba<Subscript>2</Subscript>MgWO<Subscript>6</Subscript> ceramics

The microwave dielectric properties of Ba₂MgWO₆ ceramics were investigated with a view to the use of such ceramics in mobile communication. Ba₂MgWO₆ ceramics were prepared using the conventional solid-state method with various sintering temperatures. Dielectric constants (? _r ) of 16.8–18.2 and unloaded quality factor (Q _u  × f) of 7000–118,200 GHz were obtained at sintering temperatures in the range 1450–1650 °C for 2 h. A maximum apparent density of 6.76 g/cm³ was obtained for Ba₂MgWO₆ ceramic, sintered at 1650 °C for 2 h. A dielectric constant (? _r ) of 18.4, an unloaded quality factor (Q _u  × f) of 118,200 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?34 ppm/°C were obtained when Ba₂MgWO₆ ceramics were sintered at 1650 °C for 2 h.     

Density,Surface Tension,and Viscosity of CMSX-4<Superscript>®</Superscript> Superalloy

The surface tension, density, and viscosity of the Ni-based superalloy CMSX-4^® have been determined in the temperature ranges of 1,650–1,850 K, 1,650–1,950 K, and 1,623–1,800 K, respectively. Each property has been measured in parallel by different techniques at different participating laboratories, and the results are compared with the aim to improve the reliability of data and to identify recommended values. The following relationships have been proposed: density-ρ (T) [kg· m^?3] = 7,876 ? 1.23(T ? 1,654 K); surface tension-γ (T) [mN·m^?1] = 1,773 ? 0.56 (T ? 1, 654 K); viscosity-η (T) [mPa·s] = 8.36 ? 1.82 × 10^?2(T ? 1,654 K). For a comparison, surface-tension measurements on the Al-88.6 at% Ni liquid alloy with the same Al-content as the CMSX-4^® alloy were also performed. In addition, the surface tension and density have been theoretically evaluated by different models, and subsequently compared with new experimental data as well as with those reported in the literature. The surface-tension experimental data for the liquid CMSX-4^® alloy were found to be close to that of the Al-88.6 at% Ni alloy which is consistent with results from the compound formation model (CFM).     

Synthesis and thermoelectric characterization of bulk-type tellurium nanowire/polymer nanocomposites

A simple method to fabricate three-dimensionally (3-D) aligned thermoelectric nanowires attached polymer particle was demonstrated by combination of solution casting of thermoelectric nanostructures (e.g., tellurium nanowires (Te NWs)) on the surface of thermoplastic polymer (e.g., poly(methyl methacrylate (PMMA)) microbeads followed by hot compaction of thermoplastic matrix. The percolation threshold of composite with 3-D assembled Te NWs (i.e., 3.45 vol%) significantly was lower than that of a randomly dispersed Te NWs (i.e., 5.26 vol%), which resulted in an order of magnitude greater thermoelectric figure of merit (ZT of 2.8 × 10^?3) compared to randomly dispersed Te NWs in PMMA matrix (ZT of 6.4 × 10^?4) at room temperature by enhancing the electrical conductivity without increasing thermal conductivity.     

Structural and electrical properties of Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–Sr<Subscript>3</Subscript>CuNb<Subscript>2</Subscript>O<Subscript>9</Subscript> lead-free piezoelectric ceramics

The structure, microstructure, field-induced strain, ferroelectric, piezoelectric and dielectric properties of (1 ? x) (Bi_0.5Na_0.5)_0.935Ba_0.065TiO₃–xSr₃CuNb₂O₉ (BNT-BT6.5–xSCN, with x = 0, 0.003, 0.006, 0.009) ceramics were investigated. X-ray diffraction patterns show that all samples are pure perovskite structure and Sr₃CuNb₂O₉ (SCN) effectively diffused into the 0.935Bi_0.5Na_0.5TiO₃–0.065BaTiO₃ (BNT–BT6.5) solid solution which also reflected in the Raman spectra and the energy disperse spectroscopy (EDS) analysis. With the increases of SCN content, the coercive field (E _c  = 18.41 kV/cm) decreases greatly, whereas the remnant polarization (P _r  = 29.11 μC/cm²) increases a little at x = 0.003 which is showed in the polarization hysteresis (P–E) loops, the result indicate that the ferroelectric order would be disrupted. Around critical composition (x = 0.003) at a driving field of 60 kV/cm, a large unipolar strain of 0.29 % with a normalized strain (d ₃₃ ^*  = 483 pm/V) is obtained at room temperature. The results indicate that BNT-BT6.5-xSCN ceramics with excellent properties are promising to replace lead-based piezoelectric ceramics and can be used in practical applications.     

A new niobate-based CaO–2CuO–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> microwave dielectric ceramic composite for LTCC applications

A novel CaO–2CuO–Nb₂O₅ (CCN) ceramic composite was prepared by the solid-state reaction method in the temperature range of 810–890 °C. Typically, the CCN sintered at 870 °C exhibited the excellent microwave properties of ε _r ?=?15.7, Q?×?f?=?28,700 GHz, τ _f = ? 38.4 ppm/°C. The τ _f of CCN was turned to be near zero by adding TiO₂, while the ε _r increased slightly and the Q?×?f decreased. The 0.91CCN–0.09TiO₂ ceramic sintered at 920 °C showed modified properties of ε _r ?=?16.9, Q?×?f?=?21,500 GHz, τ _f = ? 1.6 ppm/°C, which shows potential in LTCC applications.     

Temperature-Dependent Thermal Conductivity of High Strength Lightweight Raw Perlite Aggregate Concrete

Twenty-four types of high strength lightweight concrete have been designed with raw perlite aggregate (PA) from the Erzincan Mollaköy region as new low-temperature insulation material. The effects of the water/cement ratio, the amount of raw PA, and the temperature on high strength lightweight raw perlite aggregate concrete (HSLWPAC) have been investigated. Three empirical equations were derived to correlate the thermal conductivity of HSLWPAC as a function of PA percentage and temperature depending on the water/cement ratio. Experimentally observed thermal conductivities of concrete samples were predicted 92 % of the time for each set of concrete matrices within 97 % accuracy and over the range from 1.457 W · m^?1 · K^?1 to 1.777 W · m^?1 · K^?1. The experimental investigation revealed that the usage of raw PA from the Erzincan Mollaköy region in concrete production reduces the concrete unit mass, increases the concrete strength, and furthermore, the thermal conductivity of the concrete has been improved. The proposed empirical correlations of thermal conductivity were considered to be applicable within the range of temperatures 203.15 K ≤ T ≤ 303.15 K in the form of λ = a(PAP ^b ) + c(T ^d ).