Electrodeposition of zinc–nickel alloys from ammonia-containing baths

This paper describes the use of ammonia-containing baths for Zn–Ni alloy electrodeposition. Buffering properties of the ammonia/ammonium couple limit the local change in pH in the vicinity of the electrode surface caused by simultaneous hydrogen evolution. In addition, it is shown that the divalent zinc and nickel species exist in the form of Zn(NH₃) ₄ ²⁺ and Ni(NH₃) ₆ ²⁺ complexes over a large pH range. The electrochemistry of the deposition at pH 10 was investigated by galvanostatic experiments and cyclic voltammetry, and compared with deposition from ammonium chloride baths at pH 5. The Ni content in the alloys were found to be 40–60% higher from the ammonia-containing bath than from the acidic baths. Reduction of divalent ions and hydrogen evolution were shown to occur at potentials 250mV more cathodic than with baths at pH 5; the deposition mechanism may be affected by complexation of the metal cations by ammonia.     

Pyrolysis synthesis of Si–B–C–N ceramics and their thermal stability

Si–B–C–N ceramics were synthesized by co-pyrolyzing hybrid polymeric precursors of polycarbosilane (PCS) and polyborazine (PBN). The pyrolysis behavior and structural evolution of the hybrid precursor, the microstructure and composition of the prepared Si–B–C–N ceramics were fully investigated. It was found that the copyrolysis of hybrid polymeric precursors in Ar led to the release of CH₄, CH₃NH₂ and CH₃CN gases at temperatures ranging from 200 to 1100 °C, and finally resulted in the formation of amorphous Si–B–C–N ceramics. In particular, the Si–B–C–N ceramics formed from the hybrid precursor with PBN/PCS mass ratio of 1 could keep amorphous state up to the annealing temperature of 1800 °C with weight change of only 2.08%. But this amorphous ceramics would decompose to form crystalline SiC, BN and Si₃N₄ at 2000 °C. Additionally, compared with PCS-derived SiC ceramics, the Si–B–C–N ceramics showed improved anti-oxidation performance up to 1300 °C due to the formation of borosilicate layers covering the ceramics.     

Water resistance and thermal stability of hybrid lignocellulosic filler–PVC composites

In this study, composites based on polyvinyl chloride (PVC), pulp fiber (PF), and wood flour (WF) were made by injection molding. The effects of two variable factors, namely the filler form and filler loading level, on the composite physical properties were examined. The result clearly showed that the major part of water absorption was due to water absorption of PF. It was found that the water absorption in the lignocellulosic material base composites is significantly higher than the neat PVC. Besides, the water absorption increased sharply with increasing cellulosic filler loadings in the composites. In case of hybrid composites, the rate of water uptake correlated with percentage weight of WF, lower WF (higher PF) loadings in composites exhibit higher rate of absorption. The higher onset of degradation temperature indicates the improved thermal stability of the samples. In other words, the result clearly illustrates that the thermal property of the composites increases after using PF and further increases after addition of WF.     

Structure, thermal stability and electrical conductivity of CaMoO4+δ

Single-phase tetragonal scheelite CaMoO₄ (space group, Pmmm) was prepared via the conventional solid state reaction method. The oxidation state of the transition metal species for the as-sintered CaMoO₄ was analyzed by X-ray photoelectron spectroscopy (XPS). The average thermal expansion coefficient was measured as about 11 × 10⁻⁶ K⁻¹ over the temperature range of 303-1373 K. From the thermodynamic point of view, the phase diagram for CaMoO₄ was constructed by computing the equilibrium phase boundaries. Finally, the electrical conductivity of CaMoO₄ was also investigated by an AC impedance analyzer. The activation energy of bulk conductivity for CaMoO₄ was 2.1 eV.     

Transformation and thermal stability of Li-α-sialon ceramics

Two phase α/β and single phase α lithium sialons with different m and n values were produced by hot pressing at 1730–1750°C at 30 MPa for 30–40 min in a graphite resistance furnace. When the two-phase samples were heat-treated at lower (1200–1450°C) temperatures in different packing powders, an increase in the amount of α was observed, due to β-sialon in the as-sintered material reacting with grain boundary liquid to form more α. β→α transformation at low temperatures has not been reported previously in any sialon system and in the present case is believed to occur because the α-sialon phase field in the lithium sialon system shifts slightly towards the β-sialon line at lower temperatures. The thermal stability of lithium α-sialon is good in the centre of the single-phase α region when surrounded by a Li-containing powder bed. However, towards the edges of the single-phase region, compositional changes occur on heat-treatment. Thus, samples with high m, n values decompose into β-sialon plus other Li-containing phases. During heat-treatment of other compositions when surrounded by a BN powder bed, the composition of the α-sialon phase continually readjusts towards the α/β sialon phase region as a function of time and this is followed by decomposition of the α phase. Evaporation of the Li⁺ stabilising cation is believed to be the main reason for this behaviour. The effects of m and n value, heat treatment parameters and packing powder on the thermal stability of Li α-sialons are discussed.     

Synthesis,mechanical property,and thermal stability of reduced graphene oxide–zinc oxide/cyanate ester/bismaleimide resin composites

Reduced graphene oxide–zinc oxide/cyanate ester/bismaleimide resin (RGO–ZnO/CE/BMI) composites were synthesized via a blending method. The RGO–ZnO composite was incorporated into the CE/BMI copolymer to improve the properties of RGO–ZnO/CE/BMI composites. The structure, elements, and morphology of the RGO–ZnO composite were studied with XPS, FTIR, XRD, and SEM analyses. It indicated that the ZnO micro-sphere was attached to RGO by electrostatic attraction and the RGO–ZnO composite was prepared successfully. The mechanical properties and thermal stability of RGO–ZnO/CE/BMI composites were investigated. When RGO–ZnO composite was 1 wt.%, the flexural and impact strengths of RGO–ZnO/CE/BMI composites were 1.07 and 1.35 times of the CE/BMI copolymer, respectively. However, the RGO–ZnO composite tended to aggregate in the CE/BMI matrix with high loading. According to the SEM analysis, appropriate RGO–ZnO composite was evenly dispersed in the CE/BMI copolymer. Compared to the CE/BMI copolymer, the thermal stability of the RGO–ZnO/CE/BMI composites was good. Thus, the RGO–ZnO composite was successfully filled in the CE/BMI matrix; the mechanical properties and thermal stability of the RGO–ZnO/CE/BMI composites were enhanced.     

Effect of Mn/Co substitutions on the resistivity and dielectric properties of nickel–zinc ferrites

Nickel-zinc ferrite nanoparticles with suitable chemical modifications by Mn or Co substitutions for Zn as two systems (namely, Ni–Zn–Mn and Ni–Zn–Co) were synthesized by sol-gel autocombustion method. X-ray diffraction measurements on the synthesized nanoparticles confirm that the samples attain single phase cubic spinel structures only. The powders were then used to obtain pellets in desired dimensions by employing usual ceramic procedure for carrying out measurements of resistivity and dielectric properties. The variations of dc resistivity as a function of composition and temperature, and the corresponding variation of activation energies for both the systems are presented and discussed. Also, the results of dielectric constant as a function of substituent concentration, dielectric dispersion and dielectric loss tangent are discussed. Effect of Mn/Co substitutions in Ni–Zn ferrites and possible mechanisms responsible for variations in resistivity and dielectric properties of both the ferrite systems have been evolved independently. Also, comparison of the trends between the dielectric constant and the resistivity with substituents’ concentration and their inter-relation with conduction mechanisms has been thoroughly analyzed for both the ferrite systems.     

Characterization of zinc–nickel alloys obtained from an industrial chloride bath

Zinc–nickel electrocoatings obtained from an industrial bath containing two additives were characterized by analysing their morphology, structure, microhardness, residual stress and corrosion resistance. Changes in deposit characteristics following the addition of saccharin were also studied. All coating, with or without saccharin, presented a good appearance, good mechanical properties and a high corrosion resistance. Moreover, by varying certain plating conditions it was observed that the deposits maintained their properties over a wide interval of experimental conditions, which suggests their suitability for use in batch bath.     

Preparation and thermal stability investigation of Al2O3–mullite–ZrO2–SiC composite ceramics for solar thermal transmission pipelines

To obtain composite ceramics with excellent thermal shock resistance and satisfactory high?temperature service performance for solar thermal transmission pipelines, SiC additive was incorporated into Al₂O₃?mullite?ZrO₂ composite ceramics through a pressureless sintering process. The effect of the SiC additive on thermal shock resistance was studied. Also, the variations in the microstructure and physical properties during thermal cycles at 1300 °C were discussed. The results showed that both thermal shock resistance and thermal cycling performance could be improved by adding 20 wt% SiC. In particular, the sample with 50 wt% Al₂O₃, 35 wt% Coal Series Kaolin (CSK), 15 wt% partially yttria?stabilized zirconia (PSZ), and 20 wt% SiC additional (denoted as sample A2) exhibited the best overall performance after firing at 1600 °C. Furthermore, the bending strength of sample A2 increased to 124.58 MPa, with an increasing rate of 13.63% after 30 thermal shock cycles. The increase in thermal conductivity and the formation of mullite were the factors behind the enhancement of thermal shock resistance. During the thermal cycles, the oxidation of SiC particles was favorable as it increased the microstructure densification and also facilitated the generation of mullite, which endowed the composite ceramics with a self?reinforcing performance.     

The effect of addition of acrylic acid and thioglycolic acid on the nanostructure and thermal stability of PMMA–montmorillonite nanocomposites

Poly(methyl methacrylate) (PMMA)/organophilic montmorillonite (OMMT) nanocomposites were synthesized by the in situ free radical bulk polymerization of methyl methacrylate. The effect of small amount of acrylic acid as the co-monomer and thioglycolic acid as the chain transfer agent on the nanostructure of these nanocomposites was investigated by X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS) analyses. No reflection was discernible in the XRD patterns of all samples. In SAXS experiments, a great amount of small clay montmorillonite aggregates (less than 40 Å) were observed. The acrylic acid used as the co-monomer increased the affinity between the montmorillonite and the polymer, resulting in better dispersion of the montmorillonite particles. The glass transition temperature of the nanocomposites was evaluated by differential scanning calorimetry (DSC) and the thermal stability was investigated by thermogravimetric studies (TGA). As expected, the presence of the montmorillonite increased the glass transition temperature. The thermal stability of nanocomposites was distinctly higher than of pure PMMA and was increased by the presence of small amounts of acrylic acid as the co-monomer.     

Structure and thermal properties of heat treated plasma sprayed ceria–yttria co-stabilized zirconia coatings

Thick plasma sprayed thermal barrier coatings are suitable for thermal and hot corrosion protection of metal components in land-based turbine and diesel engines. In this work, ceria–yttria co-stabilized zirconia coatings were deposited by atmospheric plasma spraying in a mixture of non-transformable tetragonal t′ and cubic c zirconia phases. Free-standing coatings were isothermally annealed at 1315 °C for different times and their crystal structure was studied by XRD. No phase decomposition occurred. Columnar grains grew in the molten splats with increasing annealing time according to a preferential direction and, after 50 h of heat treatment, they were partially replaced by equiaxed grains. Both in-plane and out-of-plane thermal expansion coefficients (CTEs) were measured from coating expansion during heating. The CTE was slightly sensitive to thermal exposure in out-of-plane direction, whereas it kept almost constant in plane direction. The specific heat capacity Cp of annealed coatings, measured by differential scanning calorimetry (DSC), decreased in comparison with as-sprayed coating, due to high-temperature sintering.     

Improved thermal shock stability and oxidation resistance of low-carbon MgO–C refractories with introduction of SiC whiskers

This research focuses on the utilization of SiC whiskers synthesized from rice husk powders in low-carbon magnesia–carbon (MgO–C) refractories, and attempts to reduce the flake graphite content in refractories by adding synthesized SiC whiskers. The effect of the addition amount of SiC whiskers on the microstructure, mechanical properties, thermal shock stability and oxidation resistance of MgO–C refractories with different graphite content was studied. The results indicated that the introduction of SiC whiskers facilitated the generation and growth of ceramic phases in MgO–C refractories. By adding 1 wt% SiC whiskers, the graphite content could be reasonably reduced (from 5 wt% to 4 wt%), and the strength, thermal shock stability and oxidation resistance of refractories were enhanced by the synergistic effect of the introduced SiC whiskers and the generated ceramic phases, the CMOR, CCS, residual CCS, and oxidation resistance were increased by 44, 6, 12 and 27% respectively.     

Modulation of magnetoelectric coupling through systematically engineered spin canting in nickel–zinc ferrite

A nickel–zinc ferrite system, which is one of the well-known versatile soft-ferromagnetic oxides, was investigated in terms of magnetoelectric (ME) coupling at room temperature. Herein, we demonstrated that spin canting is manipulated through a composition-induced structural transition from an inverse to a normal spinel structure, leading to modulation in the ME coupling. The ME coefficient was maximized at 60 at.% Zn substitution with a value of 0.1 mV/(Oe·cm), denoting ∼70% enhancement compared to that of the pure nickel ferrite. It was revealed that the interspin angle is enhanced along the octahedral site at up to ∼60 at.% Zn substitution, consistent with the composition level at the culmination of the ME coupling, evidenced by X-ray diffraction profiles and magnetic hysteresis loops combined with density functional theory calculations. Given that this approach is based on a tractable fabrication method, this study is expected to be widely used in modulation of the ME coupling in spinel-structured oxides.     

Preparation and characterization of nanocrystalline Fe–Ni–Cr alloy electrodeposits on Fe substrate

Fe–Ni–Cr alloy layers were prepared by electrodeposition from trivalent chromium plating bath in chloride-sulfate based solution. The influences of bath composition and plating parameters on the alloy electrodeposition process and the properties of deposited alloy were studied. The effects of plating parameters and bath composition such as current density, bath pH, bath temperature, the concentrations of FeSO₄ · 7H₂O and CrCl₃ · 6H₂O on the contents of Fe and Cr in Fe–Ni–Cr alloy layer were investigated. Electrodeposited Fe–Ni–Cr alloy layers on Fe substrate were characterized by X-ray diffraction (XRD), Electronic Differential System (EDS) and a CHI600B electrochemistry workstation. The composition of the Fe–Ni–Cr coatings depends on bath composition and plating conditions including pH, current density, and temperature. The internal structure of the alloy is nanocrystalline, the average grain size is 87 nm, and the corrosion resistance of the alloy layers is better than that of pure nickel layers.     

Novel nonlinearity–transparency–thermal stability trade-off of thiazolylazopyrimidine chromophores for nonlinear optical application

Novel, nonlinear optical thiazolylazopyrimidine chromophores were synthesized and characterized by UV–vis spectroscopy, hyper-Rayleigh light scattering and thermogravimetric analysis. The thiazolylazopyrimidine chromophores exhibited large molecular hyperpolarizabilities which were larger than that of a chromophore derived from 4-nitroaniline, owing to the presence of the electron-deficient thiazole ring at the acceptor end of the molecule. Moreover, in comparison with an analogous aniline based chromophore, the thiazolylazopyrimidine chromophores displayed a large blue shift due to the presence of the electron-poor pyrimidine ring at the donor end molecule, resulting in an improvement in optical transparency. The thiazolylazopyrimidine chromophores displayed high thermal stability owing to the presence of the thiazole and pyrimidine rings. Such novel, nonlinear optical thiazolylazopyrimidine chromophores are distinguished by good nonlinearity–transparency–thermal stability trade-off for nonlinear optical application.     

High energy storage efficiency and thermal stability of A-site-deficient and 110-textured BaTiO3–BiScO3 thin films

The development of thin film dielectrics having both high energy density and energy conversion efficiency, as well as good thermal stability, is necessary for practical application in high-temperature power electronics. In addition, there is a demand for the development of new Pb-free high-energy density dielectric materials due to environmental concerns. In this regard, thin films of weakly coupled relaxors based on solid solutions of BaTiO₃–BiMeO₃ have shown good promise, because they exhibit a remarkably large polarization over a wide temperature range. Nevertheless, the performance of Pb-free thin films has lagged behind that of their Pb-based counterparts in terms of thermal stability and energy conversion efficiency. Toward this end, most recent studies on BaTiO₃–BiMeO₃ systems have focused on the optimization of material composition, while relatively less attention has been paid to other aspects such as defect chemistry and crystallographic texture. In this study, we examine the effects of A-site vacancy and crystallographic texture on the energy storage performance of BaTiO₃–BiScO₃ thin films synthesized using pulsed laser deposition (PLD). It is shown that a high energy storage density (W_r) of ~28.8 J/cm³ and a high efficiency of η >90% are achieved through a combination of moderate A-site vacancy concentration and (110) crystallographic texture. Furthermore, W_r remains nearly temperature independent while a high efficiency of η >80% is maintained for temperatures up to 200°C, which constitutes one of the best performances for Pb-free ferroelectric films for high-temperature capacitor applications.     

Enhancing the electrical and thermal stability of metallic fiber-filled polymer composites by adding tin–lead alloy

This article presents a novel way of greatly enhancing the electrical and thermal stability of copper fiber (CuF)-filled acrylonitrile–butadiene–styrene (ABS) composites via the incorporation of small amount of tin–lead (Sn–Pb) alloy. It was observed that many fibers are soldered together by Sn–Pb, and a continuous CuF/Sn–Pb network is formed throughout the ABS matrix. As a result, the percolation concentration of ABS/CuF composite containing 1 vol% Sn–Pb is lower than for ABS/CuF composite, and the addition of Sn–Pb to the ABS composites containing 5 vol% CuF leads to a further decrease of electrical resistivity compared to ABS/CuF composites with corresponding filler contents. Furthermore, the electrical resistivity of ABS/CuF/Sn–Pb composite shows no temperature dependence, and remains constant during the thermal post-treatment.     

Mechanical properties and thermal stability of ambient-cured thick polysiloxane coatings prepared by a sol–gel process of organoalkoxysilanes

Ambient-curable polysiloxane coatings were prepared by pre-hydrolysis/condensation of phenyltrimethoxysilane (PTMS) and dimethyldimethoxysilane (DMDMS) in the presence of ammonia solution and subsequently mixing with aminopropyltriethoxysilane (APS). The mechanical properties of coatings were thoroughly examined at both macro- and micro-level and the thermal stability of coatings was characterized by thermogravimetic analysis, both of which were correlated with coating composition and the hydrolysis/condensation degree of polysiloxane oligomer. It was found that pro-hydrolysis step is essential for fabrication of thick crack-free coatings (18–35 μm). Higher DMDMS molar ratio, more APS dosage and lower hydrolysis/condensation degree of polysiloxane oligomer favor enhancing the hardness. Excellent impact resistance (50 cm kg) of coatings was obtained at 5% and 10% APS dosage, despite of the type and structure of polysiloxane oligomer. Whatever, the best scratch resistance of coatings was attained using the polysiloxane oligomer, prepared at PTMS-to-DMDMS molar ratio of 2:8 and water-to-precursor molar ratio of 1:1, and 5% APS dosage. The polysiloxane coatings exhibit high thermal stability, however, which strongly depends on the coating composition.