Coefficient Of Thermal Expansion Values Research Articles

Promoting nanoprecipitates via prefabricated defects to pin dislocations and grain boundaries for trading off high-strength and low-thermal-expansion of invar alloys

Invar alloys that combine high strength with a low coefficient of thermal expansion (CTE) are urgently required for industrial applications. Based on the lower coarsening rate during aging and the CTE values of carbonitrides, a novel strategy is proposed to prepare carbonitrides by reducing carbon and increasing nitrogen to design high-strength and low-thermal-expansion invar alloys. The V(C, N) nanoprecipitate was introduced into the invar alloy, and its effects on the microstructure, thermal expansion behavior, and mechanical properties were investigated. The direct-aged alloy exhibited an enhanced tensile strength of 525 MPa and a ductility of 47.6%. The cold-deformation aging alloy achieved an enhanced tensile strength of 815 MPa while retaining 7.4% ductility and a low CTE value of 1.23×10−6 /°C. The V(C, N) nanoprecipitates effectively immobilized dislocations and grain boundaries, leading to a high dislocation density and small grain size in the alloy. The contributions of each strengthening mechanism were calculated, and the precipitation and dislocation strengthening were found to be the main mechanisms of strength enhancement. These results provide a novel approach for preparing high-strength and low-CTE invar alloys.

A systematic study on linear thermal expansion coefficient of metals based on interferometric measurement with Fresnel bimirror

AbstractLinear thermal expansion coefficient, which is vital for measuring the thermal expansion characteristics of metals, has been attracting considerable attention globally. Herein, a novel design based on Fresnel bimirror has been developed. In this design, when the upper end of the object to be measured comes in contact with a tilted double‐sided mirror, the temperature rises and intersection angle of the Fresnel bimirror decreases. Meanwhile, interference fringe spacing becomes narrower, while the number of fringes increases. An imaging system based on a digital microscope and smartphone is also incorporated in this design, which records the changes in the interference fringes. Then, using a self‐programmed software, the linear thermal expansion coefficients of Cu, Fe, and Al samples are determined at elevated temperatures as 17.85 ± 0.23 × 10−6/°C (), 11.8 ± 0.09 × 10−6/°C (), and 23.34 ±0.16 × 10−6/°C (), respectively, with a relative error of less than 1.6%. A cooling process is also designed, and the average value of the linear thermal expansion coefficient of metal samples during heating and cooling conditions is determined. The measurement results obtained via the finite‐method simulation demonstrate the feasibility and reliability of the system. Overall, this study provides a new idea for measuring the linear thermal expansion coefficient of metals.

Effect of composition on the thermal properties and structure of M-Al-Si-O-N glasses, M = Na, Mg, Ca

The primary objective of this study is to explore the relationship between the composition, structure, and thermal characteristics of M-Al-Si-O-N glasses, with M representing sodium (Na), magnesium (Mg), or calcium (Ca). The glasses were prepared by melting in a quartz crucible at 1650 °C and AlN precursor (powder) was utilized as a nitrogen source. The measured thermal properties studied were glass transition temperature (Tg), crystallization temperature (Tc), glass stability, viscosity, and thermal expansion coefficient (α). The findings indicate that increasing the aluminum content leads to higher glass transition, crystallization temperatures, and viscosities. In contrast, fragility values increase with the Al contents, while modifier elements and silicon content influence thermal expansion coefficient values. FTIR analysis revealed that in all glasses, the dominant IR bands are attributed to the presence of Q2 and Q3 silicate units. The effect of Al is observed as a progressive polymerization of the silicate network resulting from the glass-forming role of Al2O3. In most samples, the Q4 silicate mode was also observed, strongly related to the high Al content. Overall, the study shows that the complexity of composition-property correlations where the structural changes affect the properties of Mg/Ca-based oxynitride glasses has potential implications for their use in various technological fields.

Multi-response optimization of reinforcement parameters of aluminum alloy composites by Taguchi method and grey relational analysis

The present work describes the optimization of reinforcement parameters for hardness, thermal conductivity, and coefficient of thermal expansion while developing LM6 alloy/soda-lime glass particulate composite through Taguchi-based Grey Relational Analysis (GRA). Soda-lime glass particle weight % (1.5, 3.0 and 4.5 %), particle size (100, 150 and 300 μm) and pre-heat temperature (260, 380 and 500oC) are varied accordingly to explore the effect of reinforcement parameters on LM6 alloy/soda-lime glass composite properties. Composites are developed through stir casting based on the L9 Taguchi orthogonal array approach. The properties such as hardness, thermal conductivity and coefficient of thermal expansion of developed composites are assessed. Signal to Noise Ratios (S/N ratios) are calculated and used for the optimization of parameters. GRA is employed for multi-response optimization to find the levels of parameters that affect the desirable properties of the composite. Thus, the reinforcement parameters are optimized for attaining the combined objectives of higher hardness, higher thermal conductivity and lower coefficient of thermal expansion values considered in this investigation. The analysis shows that 4.5 wt %, particle size of 200 μm and pre-heat temperature of 380oC are optimal parameter levels. A confirmation test is carried out with the optimal parameter levels and the GRG value of 0.7778 is obtained. The GRG with the initial parameter settings is 0.4711, and the improvement of GRG is found to be 65.1 %. ANOVA is performed on GRG to find out significant parameters and the contribution of each parameter is identified. The wt.% of soda-lime glass is the most significant parameter and its contribution is 92.6 %.

The Southern Ocean deep mixing band emerges from a competition between winter buoyancy loss and upper stratification strength

Abstract. The Southern Ocean hosts a winter deep mixing band (DMB) near the Antarctic Circumpolar Current's (ACC) northern boundary, playing a pivotal role in Subantarctic Mode Water formation. Here, we investigate what controls the presence and geographical extent of the DMB. Using observational data, we construct seasonal climatologies of surface buoyancy fluxes, Ekman buoyancy transport, and upper stratification. The strength of the upper-ocean stratification is determined using the columnar buoyancy index, defined as the buoyancy input necessary to produce a 250 m deep mixed layer. It is found that the DMB lies precisely where the autumn–winter buoyancy loss exceeds the columnar buoyancy found in late summer. The buoyancy loss decreases towards the south, while in the north the stratification is too strong to produce deep mixed layers. Although this threshold is also crossed in the Agulhas Current and East Australian Current regions, advection of buoyancy is able to stabilise the stratification. The Ekman buoyancy transport has a secondary impact on the DMB extent due to the compensating effects of temperature and salinity transports on buoyancy. Changes in surface temperature drive spatial variations in the thermal expansion coefficient (TEC). These TEC variations are necessary to explain the limited meridional extent of the DMB. We demonstrate this by comparing buoyancy budgets derived using varying TEC values with those derived using a constant TEC value. Reduced TEC in colder waters leads to decreased winter buoyancy loss south of the DMB, yet substantial heat loss persists. Lower TEC values also weaken the effect of temperature stratification, partially compensating for the effect of buoyancy loss damping. TEC modulation impacts both the DMB characteristics and its meridional extent.

Analysis of thermo-mechanical incompatibility of fullerenes with polymer matrices of composites

Unique strength and rigidity properties of carbon nanotubes and fullerenes do them very perspective reinforcing admixtures into composites produced on the basis of polymeric and metallic matrices. It is established that even relatively small their dopes into composites can essentially enlarge physico-mechanical characteristics of polymers. At the same time, comparatively low value of the linear thermal expansion coefficient of carbon nanomolecules results in the possibility of the emergence of the internal mechanism of the additional intrastructural stresses origination in the polymer conditioned due to thermomechanical incompatibility of the composite fractions. To examine this possibility, the theoretical modelling of the thermomechanical deforming of the considered heterogeneous structures under thermal change action was carried out. In doing so, the fullerenes were simulated as a thin elastic shell with adduced (effective) thickness, elasticity modulus, Poissonn’s coefficient and linear thermal expansion coefficient, the polymer matrix was supposed to be a homogeneous elastic medium with the prescribed parameters of thermoelasticity. The system of constitutive ordinary differential equations was deduced, which described the thermoelastic stress-strainedstate of the elastic fragment chosen for consideration. These equations solutions were deduced in the closed form for the case when the system temperature changed in. Fenolformaldegid, epoxy rezin, polycarbonate, polyamide, polystirol, polyester, and polypropylene, possessing increased values of the linear thermal expansion coefficients, were chosen as the matrix materials. With these initial data, the values of the fullerene radial displacements were calculated for two magnitudes of the sphere radius. It is demonstrated that owing to the high value of the fullerene effective elasticity modulus, the thermal deflections of its wall poorly depend on the properties of the encompassing matrix and practically are equal to its free thermal displacements. The thermal stresses of the polymer matrices have the largest values in the zones of the interface surfaces and they decrease proportionally to cube of the radial coordinate, so, the damages provoked by them have localized character.

Density, viscosity, excess properties, and intermolecular interaction of propylene glycol methyl ether + 1,2-propylenediamine binary system

In this work, the systematic measurements of physicochemical properties, viz., density (ρ) and viscosity (η) values of propylene glycol methyl ether (PGME) + 1,2-propylenediamine (1,2-PDA) binary system, including pure substances, over the entire mole fraction range at the temperatures of T/K = (298.15 to 318.15) under atmospheric pressure of P = 100.5 kPa. The fundamental data were used to calculate several excess properties, including excess molar volume (VmE), viscosity deviation (Δη), and excess activation Gibbs free energy (ΔG∗E). Meanwhile, the work further investigated the values of thermal expansion coefficient (αp), partial molar volume (V¯) and apparent molar volume (Vφ), thereby offering a comprehensive understanding on non-ideal behavior of the binary system. Furthermore, the variations in ρ values with various molar ratios and temperatures were evaluated through Jouyban-Acree model and nonlinear least squares method. Simultaneously, Grunberg-Nissan model, Eyring-Margules model, Heric model, and McAllister model, were used to fit the dependence of η values on the molar ratio. Arrhenius equation was employed to fit the temperature dependency of η values. In addition, Redlich-Kister (R-K) equation was utilized to fit the VmE, Δη, and ΔG∗E values of binary system. Based on spectral analyses of Raman, ultra-violet (UV), and 1H Nuclear Magnetic Resonance (NMR) and density functional theory (DFT) calculation, the intermolecular hydrogen bond (IHB) of PGME with 1,2-PDA was discussed in depth.

Fabrication of low thermal expansion Fe–Ni alloys by in-situ alloying using twin-wire arc additive manufacturing

The binary Fe–Ni system offers alloys with notably low linear coefficients of thermal expansion (CTE), contingent upon their Ni content. In this respect twin-wire arc additive manufacturing (T-WAAM) presents the opportunity of in-situ alloying through the simultaneous feeding of two metal wires into a weld pool to obtain desired alloy compositions. This study aims to deposit a graded wall with Ni contents targeted at 42, 46, and 52 wt% in the building direction of the wall, along with a block comprising of 46 wt% Ni, employing the T-WAAM approach. The results show effective incorporation of additional Ni into the weld pool and geometrically stable weld beads in the continuous metal transfer mode during the T-WAAM process. This mode led to the defect-free and chemically stable deposition of the graded wall and the block with average Ni contents of 42.3 ± 1.1, 45.8 ± 1.4, 52.6 ± 0.8 wt%, and 46.4 ± 0.9 wt%, respectively. The measured Curie temperatures of the as-deposited alloys and the mean CTE values of alloy 46 were found to be comparable to the commercial alloys. In summary, this study validates the feasibility of in-situ deposition of low thermal expansion alloy compositions, thereby enabling the possibility of on-demand thermal expansion properties.

Preparing a New Type of Concrete Based on Sulfur-melamine Modifier

في هذا البحث تم تحضير نوع جديد من الخرسانة يعتمد على تحوير الكبريت والميلامين ودراسة خصائصها المختلفة. حضر هذا النوع الجديد من الخرسانة بناءً على تعديل الكبريت والميلامين والمكونات المختلفة. تم اثبات هذه التعديلات من خلال التحليل الطيفي للأشعة تحت الحمراء وتحليل .TG تمت دراسة التشكل السطحي الناتج عن هذا التعديل من خلال تحليل SEM وEDS وتم دراسة نسب المكونات في الخواص الخرسانية والكيميائية والفيزيائية الناتجة عن تعديل الكبريت والميلامين، كما تم دراسة المقاومة الكيميائية والتآكل للخرسانة، وثبات الخرسانة ضد امتصاص الماء، وثبات الخرسانة ضد التجمد، والخصائص الفيزيائية والميكانيكية والمتانة، ومعامل المرونة، والحرارية ومعامل التمدد للخرسانة الكبريتية المدروسة. أكدت نتائج الأشعة تحت الحمراء المجموعات الوظيفية الأمينية (حلقة الميلامين المرفقة) وتشكيل سلاسل متعدد الكبريت. كانت خسارة الكتلة الحرارية لتعديل الكبريت والميلامين خطوة واحدة. كانت عمليات فقد الكتلة للمنتج المعدل عمليات ماصة للحرارة. كشفت نتائج SEM التي تم الحصول عليها أن تعديل الكبريت والميلامين يؤدي إلى بنية مسامية أكثر ، بدون أي أشكال بلورية. أظهر تحليل EDS أن ذرات النيتروجين شكلت 51.33٪ من الكتلة الكلية بينما كان الكربون 30.94٪ من الكتلة الكلية. كان ثبات الخرسانة المعدلة الكبريت والميلامين عاليًا جدًا في المحاليل القوية المختلفة. كان الحجم المنخفض للخرسانة القائمة على الركام أكثر كثافة \، 2417 كجم / م 3. انخفضت كثافة الخرسانة ببطء مع زيادة حجم الركام. كان معدل التشوه للخرسانة المعدلة 0.0030-0.0033 مما يؤكد على ان فعالية الخرسانة المعدلة أفضل من الخرسانة التقليدية. كما أكدت النتائج المتحصل عليها أن قيمة معامل التمدد الحراري للخرسانة المعدلة من الكبريت والميلامين كانت 17.2×10-6\oC درجة مئوية.

Anisotropic thermal expansion and themomechanic properties of α-phase group-VA monolayers

The theoretical investigations of anisotropic thermal expansion are quite few as the huge computational cost. In this work, a scheme of Taylor expansion for phonon free energy is introduced to investigate anisotropic thermal expansion, which can save lots of computational cost. The anisotropic thermal expansion and thermomechanic properties of α-phase group-VA monolayers (α-P, α-As, α-Sb and α-Bi) are investigated systematically by using the first-principles calculations. It is found all the four monolayers show remarkably anisotropic thermal expansion, and very different from each other. In α-As and α-Bi monolayers, remarkable negative thermal expansion appears along armchair direction. From α-P to α-Bi monolayer, the absolute value of linear thermal expansion coefficient becomes larger. In particular the linear thermal expansion coefficient of α-Bi is in terms of order of magnitude close to 10−4 K−1 at 300 K. The macroscopic Grüneisen parameters and elastic constants are also investigated to unveil the underlying physical mechanisms.

Synthesis and properties of modified thermoplastic polyimide films with good dielectric properties at high frequency and enhanced thermal stability via incorporation of rigid ester and biphenyl structural units

AbstractA series of ester‐ and fluoro‐containing thermoplastic polyimide (PI) films, PEsI‐1 ~ PEsI‐4 have been prepared by the two‐step thermal imidization procedure via the soluble poly(amic acid) (PEsAA) precursors from the copolymerization of four monomers, including the dianhydrides of bisphenol A dibenzoate‐3,3′,4,4′‐tetracarboxylic acid dianhydride (TMBPA) and 3,3′, 4,4′‐biphenyl tetracarboxylic acid dianhydride (BPDA) and the diamine monomers of 4‐aminophenyl‐4′‐ aminobenzoate (APAB) and 2,2′‐bis(trifluoromethyl)‐4,4′‐diamino biphenyl (TFMB) in the polar aprotic solvent of N‐methyl‐2‐pyrrolidinone (NMP). The PI films obtained from the high‐temperature dehydration of the PEsAA solutions exhibited the good thermal stabilities with the glass transition temperatures (Tg) over 269°C, the 5% weight loss temperatures (T5%) higher than 480°C, and the linear coefficients of thermal expansion (CTE) values in the range of 17.7 × 10−6/K–33.6 × 10−6/K in the temperature range of 50–250°C. Meanwhile, the PI films showed good thermoplasticity in the dynamic mechanical analysis (DMA) tests, in which the storage modulus of the PI films dropped sharply in the temperature range of glass transition of the polymers. At last, the PI films exhibited the good dielectric properties with the breakdown voltages (Vb) over 5200 V, the dielectric strength (Ds) higher than 210 V/μm, the dielectric constants (Dk) in the range of 3.26 ~ 3.32 at the frequency of 10 GHz, and the dielectric dissipation factors (Df) of 0.0038 ~ 0.0047. Compared with the commonly used PEsI‐ref film for high‐frequency flexible copper clad laminates (FCCL), the currently developed PI films exhibited the obviously increased Tg values, decreased CTE values, and comparable dielectric properties.

Colorless Polyamide–Imide films with tunable coefficient of thermal expansion and their application in flexible display devices

In a previous study, our group reported the fabrication of a series of colorless polyamide–imide (PAI) films (named TFDB-DABPO-TPC-6FDA) with good thermal stability. To further improve their properties, herein, the effect of adding blocks in molecules on the performance of polyimide (PI) films was studied. By changing the order and amount of the four reactants added each time, seven PAIs with different structures and block lengths were obtained. Their glass transition temperatures (Tg) ranged from 359 °C to 368 °C, and their transmittance at 430 nm (T430) was 82.7%–85.1 %. Importantly, the coefficient of thermal expansion (CTE) of these seven PAIs decreased almost linearly from 31.1 to 18.5 ppm/K, making it possible to fabricate PI films with a desired CTE value for specific applications. Furthermore, the PAI-6-T film, which had the longest polyamide block and the best overall performance (Tg = 362 °C, CTE = 18.5 ppm/K, T430 = 83.1 %, tensile strength = 179.4 MPa, dielectric constant (Dk) = 2.53, and dielectric loss (Df) = 0.0088 at 10 GHz) was used as a substrate to fabricate a flexible printed circuit board (FPCB) and an organic light-emitting diode (OLED). Mechanical–electrical test shows that Ag was firmly bonded with the PAI-6-T film, and the resistance of FPCB@PAI-6-T only increased by 14.8 % after 150,000 folding tests. The flexible OLED@PAI-6-T exhibited pure green emission, a turn-on voltage of 3.0 V, a luminance of 1000 cd/m2 at 6 V, a current efficiency of 1.31 cd/A, and an external quantum efficiency of 0.44 %.

Synthesis of colorless transparent poly(amide-imide) with high modulus and low thermal expansion coefficient and its performance study

To meet the needs of high dimensional stability and high transparency of colorless polyimide (CPI) films, a series of poly(amide-imide) (PAI) films were synthesized by copolymerization of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), terephthaloyl chloride (TPC) and 2,2′-bis(trifluoromethyl)benzidine (TFDB). By adjusting the ratio of 6FDA and TPC, the resulting PAI films exhibited high glass transition temperature (Tg) ranging from 347 to 366 °C, low coefficient of thermal expansion (CTE) values of 4–48 ppm/K, excellent optical performance with transmittances at 400 nm (T400) of 79–83 %, and sufficient mechanical performance. The rigid rod-like amide bonds in the molecular chains increased with the introduction of TPC, which increased the hydrogen bonding between the molecular chains, significantly reduced the CTE and improved the tensile strength and modulus. In particular, PAI-7 exhibited excellent comprehensive performance with a high Tg of 366 °C, a relatively low CTE value of 13 ppm/K, excellent transmittance of 81 % at 400 nm and high tensile modulus of 6.5 GPa, which was expected to be used in the field of flexible displays.

Effect of Non-Plastic Raw Materials Particle Size on Technological Properties of the Single-Fired Wall Tile Bodies

This study has investigated the effect of particle size of non-plastic components of quartz and pegmatite on some technological properties of wall tile bodies. For this, quartz-pegmatite mixtures were further milled up to 90 min. before adding into the body composition unlike the standard body composition, where quartz and pegmatite were used as-received. The physical and mechanical properties of the bodies were investigated and compared with the standard values. Thermal expansion coefficient and moisture expansion values were determined by a dilatometer. Phase analyses were carried out by X-ray diffraction and microstructural characteristics were studied using a scanning electron microscope. Changes in various technological properties with reducing particle size of the non-plastic components were reported, particularly the increased green and fired strength. It was discussed that using finer particle size non-plastic raw materials of quartz and pegmatite would enable not only increased industrial productivity but also increased producibility of thinner large format wall tiles.

Search for new apatite-like phases for lead utilization based on crystal structure and thermal expansion

Apatites, being one of the most numerous mineral-like families of compounds, are considered as a matrix for binding lead ions, which is dangerous for the biosphere. The crystal-chemical (composition, structure) and thermophysical aspects (thermal expansion) are considered as the basis for analysing the properties of this kind of material. It is suggested that substances of the composition Pb5(AIVO4)2(BVIO4), Pb5(AIVO4)(CVO4)2 can be a perspective form of lead binding materials based on compounds with the structure of apatite (AIV = Si, Ge; BVI = S, Cr; CV = P). Such compounds, as it was shown by DTA and HTXRD experiments, are distinguished by the absence of polymerphism and the abnormal ordering of structure. Also, they have relatively low values of thermophysical indicators (the rate of change of linear thermal expansion coefficients is 0.02?0.03?106 K-1; values of the volume thermal expansion coefficients are 40?70?106 K-1). Compounds Pb5(SiO4)(PO4)2 (a = 9.78782(16) ?, c = 7.31084(16) ?, V = 606.555(23) ?3, R-bragg = 4.694 %) and Pb5(GeO4)(PO4)2 (a = 9.87697(12) ?, c = 7.33136(11) ?, V = 619.388(17) ?3, R-bragg = 1.730 %) were obtained, identified and crystallographically characterised for the first time.

Enhancing cryogenic thermal conductivity of epoxy composites through the incorporation of boron nitride nanosheets/nanodiamond aerogels prepared by directional‐freezing method

AbstractIn the realm of electronic circuits, materials with high thermal conductivity are sought after as ideal packaging components. It is crucial that such materials not only possess excellent thermal conductivity, but also maintain desirable dielectric properties. To this end, boron nitride nanosheets (BNNS) and BNNS/nanodiamond (ND) aerogels with a three‐dimensional (3D) structure using the ice‐template method were prepared. Subsequently, these aerogels were utilized as a framework to produce 3D‐BNNS/epoxy and 3D‐BNNS/ND/epoxy composites via the vacuum‐assisted impregnation method, which exhibit enhanced anisotropic thermal conductivity. Furthermore, the thermal conductivity exhibited by the 3D‐BNNS/epoxy composites outperforms those containing randomly distributed BNNS. The experiment also reveals sintering the aerogel at elevated temperatures to remove the PVA can significantly improve the thermal conductivity exhibited by the 3D‐BNNS/epoxy and 3D‐BNNS/ND/epoxy composites. Importantly, the 3D‐BNNS/ND/epoxy composites illustrate exceptional thermal conductivity values of 1.326 W/(m·K), indicating a remarkable synergistic effect of BNNS and ND in improving thermal conductivity. It is noteworthy to state that the relative thermal conductivity ratio of the 3D‐BNNS/epoxy and 3D‐BNNS/ND/epoxy composites to pure epoxy resin was markedly higher at lower temperatures than the values measured at room temperature, signifying their superior heat transfer performance at lower temperatures. In addition, the composites depict excellent dielectric properties and lower coefficients of thermal expansion values. Finally, the 3D‐BNNS/ND/epoxy composites also have significantly improved Tg (132.5 and 152.6°C). The high‐performance polymer composites described in this study are envisaged for implementation within the realm of electronic packaging materials.

Microstructural, electrical and thermal characterization of Dy3+, Sm3+, Er3+, Y3+ and Gd3+ multi-doped cerium dioxide as SOFCs solid electrolytes

The production of electrolytes with high ionic conductivity has been a key challenge in the progressive development of solid oxide fuel cells (SOFCs) for practical applications. Conventional approaches use ionic doping to develop electrolyte materials, such as yttria-stabilized zirconia (YSZ), but challenges remain. The doping systems discovered so far can confirm that co-doping/triple doping can introduce more oxygen vacancies to improve the electrical properties of ceria-based electrolytes compared to unitary doping. Therefore, In this work, we select the optimal dopant based on the criterion of optimal doping in cerium dioxide (effective average ionic radius close to 1.093 Å). And propose a novel multi-doped cerium-based Ce1−x(Dy1/5Sm1/5Er1/5Y1/5Gd1/5)xO2-δ (x = 0.10, 0.15, 0.20, 0.25, 0.30, abbreviated as DSEYG1, DSEYG2, DSEYG3, DSEYG4, DSEYG5) electrolytes to study its microstructure, electrical properties and thermal properties. Dy3+, Sm3+, Er3+, Y3+, and Gd3+ multi-doped electrolyte materials. Over 95% of the relative density values were obtained by sintering DSEYG series samples at 1400 °C. The single-phase cubic fluorite structure, high-density surface microstructure, elemental confirmation, and oxygen vacancy concentration were confirmed using X-ray diffraction, scanning electron microscope, energy dispersive spectrum, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electrical analysis by impedance spectroscopy confirmed the highest value of total ionic conductivity (σ800 °C= 4.04 ×10−2 S/cm) and the lowest value of activation energy (Ea= 0.834 eV) for the DSEYG3 composition. Thermal expansion analysis confirmed the moderate thermal expansion coefficient values for all compositions (TEC =11.12 ×10−6 K−1) in the range of RT-800 °C) and was found to be in good agreement with recently developed materials. The enhanced total ionic conductivity and moderate thermal expansion coefficient of DSEYG3 make it a potential electrolyte material for medium-temperature fuel cells.

Preparation and characterization of colorless and transparent semi‐alicyclic fluoro‐containing polyimide nanocomposite films with enhanced high‐temperature dimensional stability via incorporation of colloidal silica nanofillers

AbstractColorless and transparent semi‐alicyclic fluoro‐containing polyimide (PI) nanocomposite films with enhanced high‐temperature dimensional stability and sustained optical transparency were designed and prepared via incorporation of nano‐sized colloidal silica (SiO2) fillers into the PI matrix derived from hydrogenated pyromellitic dianhydride (HPMDA) and 2,2′‐bis[(4‐aminophenoxy)phenyl]hexafluoropropane (BDAF). The derived PI composite films, abbreviated as 6FCPI‐X in which X stands for the weight percent of the SiO2 in the composite films, exhibited superior thermal and comparable optical properties to the pristine 6FCPI‐0 (6FDA‐BDAF) matrix film. For example, as for the thermal properties, 6FCPI‐35 composite film showed a glass transition temperature (Tg) of 279.1°C and a residual weight ratio at 750°C (Rw750) of 66.1%, which were apparently higher than those of 6FCPI‐0 matrix (Tg = 272.2°C; Rw750 = 47.1%). More importantly, the 6FCPI/SiO2 nanocomposite films showed obviously lower linear coefficients of thermal expansion (CTE) values as compared with that of the 6FCPI‐0 matrix. 6FCPI‐35 composite film showed a CTE value of 36.1 × 10−6/K in the temperature range of 50–250°C, which was lower than half of that of the 6FCPI‐0 matrix (CTE = 77.9 × 10−6/K) in the same range of temperature. In addition, incorporation of nano‐sized colloidal SiO2 particles basically maintained the intrinsically good optical properties of the pristine 6FCPI‐0 matrix film. 6FCPI‐35 composite film showed the optical transmittances of 81.7%, 85.3%, and 87.2% at the wavelength of 400 nm (T400), 450 nm (T450), and 500 nm (T500), respectively, which were in the same level with those of the 6FCPI‐0 film (T400 = 84.0%; T450 = 86.3%; T500 = 87.6%). The 6FCPI series of nanocomposite films also exhibited similar CIE Lab color parameters, including the yellow indices (b*) lower than 2.0 and haze values lower than 1.0%.

Application of Sulfur-2,4-dinitrophenylhydrazine as Modifier for Producing an Advantageous Concrete

In this investigative endeavor, a novel concrete variety incorporating sulfur-2,4-dinitrophenylhydrazine modification was developed, and its diverse attributes were explored. This innovative concrete was produced using sulfur-2,4-dinitrophenylhydrazine modification and an array of components. The newly created sulfur-2,4-dinitrophenylhydrazine modifier was synthesized. The surface texture resulting from this modifier was examined using SEM and EDS techniques. The component ratios within concrete, chemical and physical traits derived from the sulfur-2,4-dinitrophenylhydrazine modifier, chemical and corrosion resistance of concrete, concrete stability against water absorption, concrete resilience against freezing, physical and mechanical properties, durability, elastic modulus, and thermal expansion coefficient of the examined sulfur-infused concrete were assessed. The acquired results also substantiated that the thermal expansion coefficient value for sulfur-2,4-dinitrophenylhydrazine modified concrete was 14.8×10-6/0C. The average deformation of the analyzed concrete was 0.0026-0.0051, indicating a superior deformation performance compared to conventional concretes. Concrete with smaller aggregate sizes exhibited greater density, specifically 2283 kg/m3. The concrete density decreased gradually with an increase in aggregate size. The stability of sulfur-2,4-dinitrophenylhydrazine modified concrete was remarkably high in various aggressive environments. EDS analysis revealed that carbon atoms constituted 56.63% of the total mass, while sulfur made up 33.91% of the total mass. The obtained SEM outcomes demonstrated that the sulfur-2,4-dinitrophenylhydrazine modifier exhibited a more porous structure, devoid of crystalline formations. The sulfur-2,4-dinitrophenylhydrazine modification experienced a single-stage thermal mass loss, with the mass loss events being endothermic in nature. The IR findings verified the presence of amino functional groups (connected melamine ring) and the establishment of polymer sulfur chains.

Effects of CaO additive on sintering behaviour and properties of CaO–B2O3–SiO2 glass-ceramics for LTCC applications

The effects of CaO additive on the phase composition, sintering behaviour, microstructure, and properties of CaO–B2O3–SiO2 (CBS) glass-ceramics were investigated. The results revealed that a small amount of added CaO (0.5 wt%, 1 wt%) facilitated the transformation of α-CaSiO3 to β-CaSiO3 and improved the crystallinity. When the amount was greater than 1 wt%, it weakened this transformation and also decreased the crystallinity. The pure CBS sample needed a sintering temperature of 850 °C for maximum densification, whereas the CaO-added samples achieved densification at a sintering temperature of 750–770 °C. The addition of an appropriate amount of CaO significantly enhanced the densification, dielectric properties, and flexural strength of CBS glass-ceramics. However, the addition of CaO had minimal impact on the coefficient of thermal expansion (CTE), which varied from 7.69 to 8.51 ppm/°C. The sample doped with 1 wt% CaO was sintered at 770 °C for 15 min, and it exhibited fairly ideal performance with a bulk density of 2.64 g/cm3, εr of 6.43, tanδ of 0.9 × 10−3 (15 GHz), and a CTE value of 7.69 ppm/°C.