Al2O3–Ag nanopowders: new method of synthesis,characterisation and biocidal activity

Abstract

Abstract

The present paper describes an innovative method of producing silver nanoparticles incorporated into an aluminium nano‐oxide substrate. The method utilises thermal decomposition and reduction, which yields an Al₂O₃–Ag nanopowder with the average size of particles ranging from 43 to 60?nm and the average size of agglomerates between 330 and 870?nm. The average size of the silver nanoparticles incorporated in the aluminium nano‐oxide carrier ranges from 22 to 60?nm. The Al₂O₃–Ag nanopowders thus produced have a largely developed surface area (above 200?m²?g^?1) with a great number of open pores (above 5×10^?4?m³?g^?1), which gives evidence that their tendency to agglomeration is only slight and that the possible agglomerates have a loose structure. Moreover, the nanopowders show good bactericidal and fungicidal properties. The results obtained in the present experiments show that the Al₂O₃–Ag nanopowders produced by the proposed method can be used successfully as the raw material in the production of biocidal biomaterials.     

Low–thermal–conductivity and high–toughness CeO2–Gd2O3 co–stabilized zirconia ceramic for potential thermal barrier coating applications

Yttria partially stabilized zirconia (～4.0?mol% Y₂O₃–ZrO₂, 4YSZ) has been widely employed as thermal barrier coatings (TBCs) to protect the high–temperature components of gas–turbine engines. The phase stability problem existing in the conventional 4YSZ has limited it to application below 1200?°C. Here we report an excellent zirconia system co–doped with 16?mol% CeO₂ and 4?mol% Gd₂O₃ (16Ce–4Gd) presenting nontransformable feature up to 1500?°C, in which no detrimental monoclinic (m) ZrO₂ phase formed on partitioning. It also exhibits a high fracture toughness of ～46?J m^?2 and shows high sintering resistance. Besides, the thermal conductivity and thermal expansion coefficient of 16Ce–4Gd are more competent for TBCs applications as compared to the 4YSZ. The combination of properties suggests that the 16Ce–4Gd system could be of potential use as a thermal barrier coating at 1500?°C.     

Influence of alumina content and thermal treatment on the thermal conductivity of UPE/Al2O3 composite

Ultra high molecular weight polyethylene/alumina (UPE/Al₂O₃) microcomposites with high loading micro alumina (Al₂O₃, 20 to 100 phr) were prepared by casting method. The composites were thermal treated (cooled slowly) and then the thermal properties were studied at temperatures from 25 to 125°C. Thermogravimetric analysis (TGA) and scanning electron microscopic (SEM) proves the homodispersion of Al₂O₃ microparticles in UPE. TGA indicates that the temperature of 5% weight loss of UPE/Al₂O₃ (100 phr) composite is 467.0°C, 10.5°C higher than that of pure UPE. Differential scanning calorimetry (DSC) shows that the melting point and the real degree of crystal (X_rc) of treated UPE/Al₂O₃ composite (100 phr) are 141.4°C and 65.7%, respectively, all higher than that of untreated composite, which can be described by crystal bridge mechanism. The density of the composite is also be enhanced because of crystal volume shrinkage induced by thermal treatment. The thermal conductivity of the treated UPE/Al₂O₃ composite (100 phr) is 1.920 W (m K)^?1 at 25°C, 23.6% higher than that of the untreated composite. Crystal bridge thermal conduction mechanism is proposed. The thermal conductivity of UPE/Al₂O₃ composite has some dependency on the increasing Al₂O₃ content and also thermal treatment. These results can give some advice to design formulations for practical applications in pipe area and other wear area. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40528.     

Non-isothermal crystallisation behaviour of fluorophlogopite/nepheline glass ceramics

Abstract

Fluorophlogopite/nepheline glass ceramics were formed from the system of SiO₂–Al₂O₃–MgO–K₂O–Na₂O–F, and the thermodynamic, crystallisation behaviour and microstructure were investigated using differential thermal analysis, X-ray diffraction, and scanning electron microscopy. It was found that fluorophlogopite crystals and nepheline crystals crystallised simultaneously, and bulk nucleation was the main crystallisation mechanism. Crystal growth was prone to follow the two-dimensional direction and controlled by diffusion. Activation energy for glass transition was 797·43 kJ mol^?1, and crystallisation activation energy was 433·16 kJ mol^?1.     

Phase stability,thermo-physical properties and thermal cycling behavior of plasma-sprayed CTZ,CTZ/YSZ thermal barrier coatings

ZrO₂ co-stabilized by CeO₂ and TiO₂ with stable, nontransformable tetragonal phase has attracted much attention as a potential material for thermal barrier coatings (TBCs) applied at temperatures >?1200?°C. In this study, ZrO₂ co-stabilized by 15?mol% CeO₂ and 5?mol% TiO₂ (CTZ) and CTZ/YSZ (zirconia stabilized by 7.4?wt% Y₂O₃) double-ceramic-layer TBCs were respectively deposited by atmospheric plasma spraying. The microstructures, phase stability and thermo-physical properties of the CTZ coating were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric-differential scanning calorimeter (TG-DSC), laser pulses and dilatometry. Results showed that the CTZ coating with single tetragonal phase was more stable than the YSZ coating during isothermal heat-treatment at 1300?°C. The CTZ coating had a lower thermal conductivity than that of YSZ coating, decreasing from 0.89?W?m^?1 K^?1 to 0.76?W?m^?1 K^?1 with increasing temperature from room temperature to 1000?°C. The thermal expansion coefficients were in the range of 8.98?×?10^?6 K^?1 – 9.88 ×10^?6 K^?1. Samples were also thermally cycled at 1000?°C and 1100?°C. Failure of the TBCs was mainly a result of the thermal expansion mismatch between CTZ coating and superallloy substrate, the severe coating sintering and the reduction-oxidation of cerium oxide. The thermal durability of the TBCs at 1000?°C can be effectively enhanced by using a YSZ buffer layer, while the thermal cycling life of CTZ/YSZ double-ceramic-layer TBCs at 1100?°C was still unsatisfying. The thermal shock resistance of the CTZ coating should be improved; otherwise the promising properties of CTZ could not be transferred to a well-functioning coating.     

Syntheses and characterization of highly transparent ZnAl2O4 ceramic films using poly(acrylamide-co-acrylic acid) assisted microwave approach

Zinc aluminate nanopowders were synthesized via poly(acrylamide-co-acrylic acid) assisted microwave approach. The as-synthesized ZnAl₂O₄ nanopowders were characterized using X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM) and selected area of electron diffraction (SAED). The prepared ZnAl₂O₄ nanopowders exhibited a spinel cubic polycrystalline structure. The increase of poly(acrylamide-co-acrylic acid) amounts decreased the particle size of the ZnAl₂O₄ nanopowders. The poly(acrylamide-co-acrylic acid) enhanced the densification rate of ZnAl₂O₄. The increasing of poly(acrylamide-co-acrylic acid) amount decreased the sintering temperature from 1300 °C to 950 °C. The hot-compressed ZnAl₂O₄ nanopowders in the existence of 2 wt% of poly(acrylamide-co-acrylic acid) exhibited full density at 950?C in just 20 min. The ZnAl₂O₄ ceramic films revealed a high transparency of 83 ± 1% at a wavelength range from 450?1200 nm.     

Preparation and evaluation of nanocomposites of polyfuran with Al2O3 and montmorillonite clay

High yield oxidative polymerization of furan was accomplished in CHCl₃ solvent at 0 °C. A nanocomposite of polyfuran (PF)–Al₂O₃ was prepared through polymerization of furan in a suspension of nanodimensional Al₂O₃ in CHCl₃ at 0 °C. High yield polymerization of furan was also achieved in montmorillonite clay (MMT) without any extraneous oxidant. The formation of PF was confirmed by FTIR and elemental analysis. Thermogravimetric analyses revealed the following trends in thermal stability: PF < PF–Al₂O₃ < Al₂O₃ and PF < PF–MMT < MMT. Scanning electron microscopy showed the average particles sizes to be ca 51 nm and ca 40 nm for PF–Al₂O₃ and PF–MMT composites, respectively. The occurrence of a peak at 19.84 Å in the X‐ray diffraction pattern of the PF–MMT composite was indicative of the intercalation of PF in MMT lamellae. Transmission electron microscopic analyses for the PF–MMT composite also showed incorporation of PF moieties in‐between the MMT layers. The dc conductivity values (S cm^?1) of PF–FeCl₃, PF–Al₂O₃–FeCl₃, PF–MMT and PF–MMT–FeCl₃ systems were in the order of 10^?6, 10^?7, 10^?8 and 10^?7, respectively, and the values were significantly enhanced compared to the dc conductivity value of PF homopolymers (10^?11). Copyright © 2004 Society of Chemical Industry     

Ultrasonic-assisted preparation of AlON from alumina/carbon core-shell nanoparticle

An aluminium oxynitride (AlON) powder was synthesized by carbothermal reduction nitridation (CRN) method. For this purpose, first Al₂O₃/C core-shell nanoparticles were prepared by the pyrolysis of Al₂O₃/polyacrylonitrile (PAN) nanocomposite precursor at 800?°C for 2?h in an argon atmosphere. Alumina/PAN precursor was prepared by ultrasonic method at room temperature. Then, by two-step thermal treatment of Al₂O₃/C core-shell nanoparticles at 1500–1600?°C for 2?h, followed by subsequent heating at 1750?°C for 1?h in N₂ flow, AlON powder was synthesized. The sample was investigated via Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and CHNS elemental analysis.     

Synthesis and thermophysics properties of ferroelastic SmNb1-XTaXO4 ceramics

Monoclinic phase SmNb_1-XTa_XO₄ ceramics are synthesized via solid-state reaction. X-ray diffraction and Raman spectra are applied to characterize the crystal structure. The ferroelasticity of SmNb_1-XTa_XO₄ ceramics is confirmed by the domain structure observed via scanning electron microscopy. The band gap of SmNb_1-XTa_XO₄ ceramics ranges from 4.3 to 5.0?eV and they exhibit excellent absorption for UV light. Thermophysics properties including specific heat, thermal diffusivity, thermal conductivity and thermal expansion coefficients of SmNb_1-XTa_XO₄ ceramics are investigated systematically. The result shows that the thermal conductivity of SmNb_1-XTa_XO₄ ceramics is as low as 1.33?W?m^?1 K^?1 (900?°C) and the thermal expansion coefficients are as high as 11.7?×?10^?6 K^?1 (1200?°C). The unique ferroelasticity and outstanding thermophysics properties indicate that SmNb_1-XTa_XO₄ ceramics are promising thermal barrier coating materials.     

Microstructural evolution in bone china

Abstract

Phase and microstructural evolution in model bone china bodies was determined by XRD and electron microscopy of quenched samples fired for 3 h at 600–1500°C. Unfired but shaped bone china comprised bone ash and clay agglomerates (≤70 μm) in a matrix of smaller (from submicron to 10 μm) mixed clay, feldspar, and bone ash particles. The unfired microstructure and subsequent phase evolution is believed to be strongly dependent on the extent of prior mixing. On firing, the clay component dehydroxylated to metakaolin at ～550°C. Metastable sanidine formed from decomposition of the feldspar component above 600°C and dissolved at 1100°C. The bone ash com ponent decomposed into β-TCP and lime (and/or Ca²⁺ and O^2- ions) beginning at ～800°C. CaO from the bone ash reacts with the clay decomposition products forming liquid and anorthite at ～900°C. Liquid formation is due to reaction of CaO with feldspar and clay relict grains and is discussed in terms of the CaO–P₂O₅–Al₂O₃ ternary phase diagram. Above 1200°C pure bone ash relicts contained small (5–10 μm) β-TCP crystals, CaO penetrated clay relicts contained anorthite, and mixed clay–bone–feldspar regions contained both anorthite and larger (>50 μm) β-TCP crystals in calcium aluminosilicate glass. The major phase in the clay relicts was anorthite although a few elongated (～100 nm) needles resembling mullite in composition and morphology also crystallised in samples fired to 1100°C and grew to ～30 μm in length at 1300°C.     

Preparation of in situ grown silicon carbide whiskers onto graphite for application in Al2O3-C refractories

C-SiC composite powders were prepared by salt-assisted synthesis from Si powders, graphite, and a molten salt medium (NaCl and NaF) with the molar ratio of Si/C =?1/2 at 1300?°C for 3?h. After the C-SiC composite powders part and complete replacement of the graphite, the mechanical properties, oxidation resistance and slag-corrosion resistance of the Al₂O₃-C materials were studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), as well as with dedicated equipment. The results indicated that SiC whiskers, with lengths of 10–50?nm, formed on the surface of the flake graphite, and the activation energy of oxidation of the C-SiC composite powder increased by 45.72?kJ?mol^?1 as compared to that of flake graphite. Furthermore, the decarburization area and slag erosion area of the Al₂O₃-C material decreased after 3?wt% of C-SiC composite powder was substituted for the flake graphite. Meanwhile, the cold modulus of rupture was maintained when 3?wt% of C-SiC composite powder was added. This improved both the oxidation and slag resistance of the Al₂O₃-C materials.     

In situ synthesis of ZrB2–ZrC–SiC ultra-high-temperature nanocomposites by a sol–gel process

ABSTRACT

ZrB₂–ZrC–SiC is one of the ultra-high-temperature ceramic composites with excellent properties. In this research, high-purity ZrB₂–ZrC–SiC nanopowders were synthesised using a carbothermal reduction reaction at a relatively low temperature (1370°C) from cost-effective zirconium(IV) chloride by a sol–gel method. The effect of heat treatment temperature on the synthesis of ZrB₂–ZrC–SiC composite powder was studied. X-ray diffractometry results showed that the phases ZrB₂, β-SiC and ZrC were synthesised at 1370°C. The mean crystallite sizes for each of the phases were calculated using the Scherrer method. The specific surface area for the sample calcined at 1370°C was 81.479?m²?g^?1. SEM observation revealed that the particles had a size lower than 250?nm. Backscattered electron image and map analysis with scanning electron microscopy showed that a suitable phase homogeneity was achieved, as confirmed by energy-dispersive X-ray spectroscopy.     

Synthesis of Nanofiber‐like Mesoporous γ‐Al2O3 toward Its Adsorption Efficiency for Congo Red

Nanofiber‐like mesoporous γ‐Al₂O₃ was synthesized using freshly prepared boehmite sol in the presence of triblock copolymer, P123 following evaporation‐induced self‐assembly (EISA) process followed by calcinations at 400°C–1000°C. The samples were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X‐ray diffraction (XRD), N₂ adsorption–desorption, and transmission electron microscopy (TEM). The adsorption efficiency of the samples with Congo red (CR) was studied by UV – vis spectroscopy. XRD results showed boehmite phase in the as‐prepared sample while γ‐Al₂O₃ phase obtained at 400°C was stable up to 900°C, a little transformation of θ‐Al₂O₃ resulted at 1000°C. The Brunauer‐Emmett‐Teller surface area of the 400°C‐treated sample was found to be 175.5 m²g ^{? 1}. The TEM micrograph showed nanofiber‐like morphology of γ‐Al₂O_3. The 400°C‐treated sample showed about 100% CR adsorption within 60 min.     

Effect of Al3+ doping on mechanical and thermal properties of DyTaO4 as promising thermal barrier coating application

The ceramics of dysprosium tantalate (DyTaO₄) doping with Al³⁺ (the doping content are 0, 2, 4, and 6 mol%, respectively) are successfully synthesized in this work. The results of transmission electron microscopy (TEM) reveal that the DyTaO₄ has the domains within ferroelasticity. The thermal properties indicate that the (Al_xDy_1?x)TaO₄ ceramics have much lower thermal conductivity and better high‐temperature phase stability than that of 8YSZ (yttria‐stabilized zirconia). The elastic properties imply that the (Al_xDy_1?x)TaO₄ have lower elastic properties than that of DyTaO₄. The values of Young's modulus of (Al_xDy_1?x)TaO₄ range from 82 to 135 GPa, and the thermal expansion coefficients (TEC) of (Al_xDy_1?x)TaO₄ vary in the range of (6‐10) × 10^?6 K^?1 when the temperature is below 1200°C.     

Synthesis and properties of hybrid materials obtained by in situ copolymerization of ethylene and propylene in the presence of Al2O3 nanofibers (NafenTM) on catalytic system rac‐Et(2‐MeInd)2ZrMe2/isobutylalumoxane

Nanofibers of Al₂O₃ (commercial product Nafen^TM) with characteristic length of ～100 nm and diameter of ～10 nm were used to create new hybrid materials based on copolymer of ethylene and propylene. Nanocomposites were obtained by in situ catalytic copolymerization on the system rac‐Et(2‐MeInd)₂ZrMe₂/isobutylalumoxane. Formation of the nanocomposites with uniform distribution of Nafen nanoparticles in polymer matrix was confirmed by scanning and transmission electron microscopy. According to dynamic mechanical analysis data, introduction of the nanofiller in an amount of up to 3 wt % leads to an increase in glass transition temperature by 10 °C (E″) and by 21 °C (tan δ). The nanocomposites exhibit improved physico‐mechanical properties (tensile strength and elongation at break). It is shown that the nanofiller significantly improves resistance of the nanocomposite to the thermo‐oxidative and thermal degradation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44678.     

Effect of sintering temperature on the thermal expansion behavior of ZrMgMo3O12p/2024Al composite

A 2024Al metal matrix composite with 10?vol% negative expansion ceramic ZrMgMo₃O₁₂ was fabricated by vacuum hot pressing, and the influence of sintering temperature on the microstructure and thermal expansion coefficient (CTE) of alloys was investigated. Experimental results showed that all ZrMgMo₃O_12p/2024Al composites sintered at 500–530?°C had a similar reticular structure and exhibited different linear expansion coefficients at 40–150?°C and 150–300?°C. The addition of 10?vol% ZrMgMo₃O₁₂ decreased the CTEs of 2024Al by ~ 16% at 40–150?°C and by ~ 7% at 150–300?°C. This addition also increased the hardness of 2024Al by ~ 23%. The density of the composites and the content of Al₂Cu in ZrMgMo₃O_12p/2024Al increased as the sintering temperature increased. The CTEs of the composites decreased, whereas hardness increased. Thermal cycling from 40?°C to 300?°C caused the CTEs of the composites to decrease gradually and reach a stable value after seven cycles. The lowest CTEs of 15.4?×?10^?6 °C^?1 at 40–150?°C and 20.1?×?10^?6 °C^?1 at 150–300?°C were obtained after 10 thermal cycles and were reduced by ~ 32% and ~ 17%, respectively, compared with the CTE of the 2024Al. Among the current reinforcements, ZrMgMo₃O₁₂ negative expansion ceramics showed the highest efficiency to decrease the CTE of Al matrix composites.     

A study of phase evolution and crystal growth for nano-sized monoclinic Y4Al2O9 as a novel thermal barrier coatings

Nano-sized monoclinic Y₄Al₂O₉ was produced by sol-gel process as a novel potential candidate material for thermal barrier coatings. The thermal behavior, structural evolution of the products and the morphological characteristics of the compacted bodies were investigated by Thermogravimetric analysis and differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Field emission scanning electron microscopy (FESEM). Qualitative analyses indicate that monoclinic Y₄Al₂O₉ was formed at about 1000 °C, and exhibited good phase stability throughout the annealing temperature ranging from 1000 °C to 1400 °C. The thermophysical properties of Y₄Al₂O₉ ceramics were also evaluated compared with 8YSZ and La₂Zr₂O₇. The determined activation energy of crystal growth is about 72.71 ± 0.31 kJ mol⁻¹. Meanwhile, Y₄Al₂O₉ represents low thermal conductivity (1.71 W m⁻¹ K⁻¹), moderate thermal expansion coefficient (8.73 × 10⁻⁶ K⁻¹), and high sintering-resistance ability. Such results reveal that nano-sized Y₄Al₂O₉ is favorable for the application of TBCs.     

Improved properties of scandia and yttria co-doped zirconia as a potential thermal barrier material for high temperature applications

Due to the limited temperature capability of current YSZ thermal barrier coating (TBC) material, considerable effort has been expended world-wide to research new candidates for TBC applications above 1200?°C. Our study suggested that Sc₂O₃ and Y₂O₃ co-doped ZrO₂ (ScYSZ) had excellent t’ phase stability even after annealed at 1500?°C for 336?h. The thermal expansion coefficient of ScYSZ was comparable to the value of YSZ. The thermal conductivity of fully dense ScYSZ was in the range of 2.13–1.91?W?m^?1?K^?1 (25–1300?°C), approximately 25% lower than that of YSZ. Although the fracture toughness of dense ScYSZ was slightly lower than YSZ, an evident decline in elastic modulus was found. Additionally, thermal cycling lifetime of plasma sprayed ScYSZ coating (914 cycles) at 1300?°C was about 2.6 times longer than its YSZ counterpart. The superior comprehensive properties confirm that ScYSZ is a prospective candidate material for high-temperature TBC application.     

Interface design in 3D-SiC/Al-Si-Mg interpenetrating composite fabricated by pressureless infiltration

3D-SiC/Al-Si-Mg interpenetrating composites (IPCs) were fabricated by pressureless infiltration method. Interfaces in the 3D-SiC/Al-Si-Mg IPCs were modificated by using two different kinds of aluminum alloy Al-15Si-10Mg and Al-9Si-6Mg to infiltrate into 3D-SiC performs and different treated 3D-SiC preforms unoxidized or preoxidized in air at 1000?°C, 1100?°C and 1200?°C for 2?h respectively. Results showed that desired interfaces can be achieved in both IPCs made with those two aluminum alloys, as demonstrated by their excellent comprehensive properties. When the Al-15Si-10Mg alloy with excessive Si content is used for infiltration, interfaces in 3D-SiC/Al-Si-Mg IPC fabricated with the unoxidized 3D-SiC preform are directly bonded through atomic matching without any interfacial reaction and the composite has the properties of a thermal conductivity (TC) of 224.5?W/(m?°C), a thermal expansion coefficient (CTE) (RT ~ 300?°C) of 7.04?×?10^?6/°C and a bending strength (BS) of 277?MPa. When the Al-9Si-6Mg alloy with a lower Si content is used for infiltration, interface zone with a thickness around 200?nm forms in the 3D-SiC/Al-Si-Mg IPC fabricated with the 3D-SiC preform preoxidized at 1000?°C. The reaction-bonded interface is composed of AlN and MgAl₂O₄ which have better interface affinity with SiC and can isolate SiC effectively from liquid Al against the formation of detrimental Al₄C₃ phase. The composite has the properties of a TC of 219.5?W/(m °C), a CTE (RT ~ 300?°C) of 7.66?×?10^?6/°C and a BS of 318?MPa.     

Ablation behavior and mechanism of bulk MoAlB ceramic at ∼1670–2550 °C in air plasma flame

In this work, MoAlB samples for plasma exposure test were condensed by spark plasma sintering at 1200 °C for 10 min. Ablation resistance of MoAlB ceramic was investigated in a plasma torch facility for about 30 s at high temperature range of ～1670?2550 °C, which provided a quasi-real hypersonic service environment. The results showed that the linear ablation rate was increased from 0 μm/s at ～1670 °C to 86.4 μm/s at ～2550 °C. At ～1670 °C, the ablated surface of MoAlB ceramic was covered by Al₂O₃ layer, presenting excellent ablation resistance. At ～2220 °C, the macroscopic cracks were induced by thermal stress, which opened up channels for the inward diffusion of oxygen and deteriorated the ablation resistance of the substrate. Above ～2400 °C, the volatile MoO₃ and B₂O₃ and the erosion of viscous oxides by the high shearing force of plasma stream were the main ablation mechanisms.