Microwave‐assisted Hydrothermal Synthesis of Single‐crystal Nanorods of Rhabdophane‐type Sr‐doped LaPO4·nH2O

A novel, simple, soft, and fast microwave‐assisted hydrothermal method was used for the preparation of single‐crystal nanorods of hexagonal rhabdophane‐type La_1?xSr_xPO_4?x/2·nH₂O (x = 0 or 0.02) from commercially available La(NO₃)₃·6H₂O, Sr(NO₃)₂, and H₃PO₄. The synthesis was conducted at 130°C for 20 min in a sealed‐vessel microwave reactor specifically designed for synthetic applications, and the resulting products were characterized using a wide battery of analytical techniques. Highly uniform, well‐shaped nanorods of LaPO₄·nH₂O and La_0.98Sr_0.02PO_3.99·nH₂O were readily obtained, with average length of 213 ± 41 nm and 102 ± 25 nm, average aspect ratio (ratio between length and diameter) of 21 ± 9 and 12 ± 5, and specific surface area of 45 ± 2 and 51 ± 1 m²/g, respectively. In both cases, the single‐crystal nanorods grew anisotropically along their c crystallographic‐axis direction. At 700°C, the hexagonal rhabdophane‐type phase has already transformed into the monoclinic monazite‐type structure, although the undoped and Sr‐doped nanorods retain their morphological features and specific surface area during calcination.     

Preparation,mechanical, and leaching properties of CaZrO3 ceramic cores

The CaZrO₃ ceramic core materials with excellent mechanical and chemical properties were successfully prepared using single-phase CaZrO₃ powders. Effects of particle size ratio and sintering temperature on the mechanical and chemical properties of CaZrO₃ ceramic core materials were researched. The chemical property was analyzed by leaching research of core materials in 10 wt% and 20 wt% HNO₃ solution at the boiling point. Results showed that the suitable particle size ratio was important for the preparation of CaZrO₃ ceramic core materials with excellent comprehensive properties. The addition of fine particles in ceramic core materials promoted the densification process owing to the framework formed by coarser particles and sintering neck formed by fine particles between coarse particles, which was beneficial for further improving their bending strength. When the content of particles with 200 mesh size was 80wt%, the highest bending strength was obtained, 54.38 ± 5.28 MPa. The porosity was 17.45% and the volume density was 3.86 g/cm³. The increasing sintering temperature increased the densification of CaZrO₃ ceramic core materials by offering the sintering driving force, further leading to the improvement of bending strength. When the temperature was 1650℃, at the 20% content of particles with 200 mesh size, the highest bending strength of CaZrO₃ cores reached 51.01 ± 5.18 MPa. Meanwhile, the porosity was 18.65% and the volume density was 3.83 g/cm³. Additionally, the CaZrO₃ samples could be effectively leached in 10 wt% HNO₃ solution. Therefore, CaZrO₃ materials with good mechanical and leaching properties were believed to be a suitable candidate for ceramic core materials in the investment casting of alloys with high melting point.     

Sinterability,microstructures and electrical properties of Ni/Sm-doped ceria cermet processed with nanometer-sized particles

Ni/Sm-doped ceria (SDC) cermet was prepared from two types of NiO/SDC mixed powders: Type A—Mechanical mixing of NiO and SDC powders of micrometer-sized porous secondary particles containing loosely packed nanometer-sized primary particles. The starting powders were synthesized by calcining the oxalate precursor formed by adding the mixed nitrate solution of Ce and Sm or Ni nitrate solution into oxalic acid solution. Type B—Infiltration of Ni(NO₃)₂ solution into the SDC porous secondary particles subsequently freeze-dried. Type B powder gave denser NiO/SDC secondary particles with higher specific surface area than Type A powder. The above two types powders were sintered in air at 1100–1300 °C and annealed in the H₂/Ar or H₂/H₂O atmosphere at 400–700 °C. Increased NiO content reduced the sinterability of Type A powder but the bulk density of Type B powder compact showed a maximum at 34 vol.% NiO (25 vol.% Ni). Type B cermet was superior to Type A cermet in achieving fine-grained microstructure and a homogeneous distribution of Ni and SDC grains. The electrical resistance of the produced cermet decreased drastically at 15 vol.% Ni for Type B and at 20 vol.% Ni for Type A.     

Preparation of Plate‐Like Sodium Niobate Particles by Hydrothermal Method

Sodium niobate NaNbO₃ hydrate (NN‐hydrate) particles with a plate‐like morphology were prepared at 140°C for 2 h in 12 mol/L of NaOH by the hydrothermal method. Bar‐like Na₈Nb₆O₁₉·13H₂O particles were synthesized at as low as 100°C for 2 h. This work demonstrates that by carefully optimizing the reaction condition, we can selectively fabricate niobate structures, including the bar‐like, plate‐like, fibers and cube particles through a direct reaction between NaOH solution and Nb₂O₅. It was found that Nb₆O₁₉^8? formed was an important premise for formation of the NN‐hydrate, and lower [OH^–] was not favorable in preparing the NN‐hydrate as there was an optimum [OH^?]. Through researching effects of the reaction temperature, time, concentration of NaOH, and content of Nb₂O₅ on the NN‐hydrate structure and evolution, the formation mechanism from solid reactants to the intermediate were investigated. After calcining at 800°C, the synthesized NN‐hydrate particles made a phase almost transform to the perovskite NaNbO₃, and the morphology of these calcined particles was still plate‐like.     

Significance of sensitization process in electroless deposition of Ni on nanosized Al2O3 powders

The electroless deposition of Ni on nanosized α-Al₂O₃ powders of about 150 nm diameter has been studied by employing SnCl₂ sensitization and PdCl₂ activation approach. The bath for electroless deposition was prepared by using NiCl₂·6H₂O, C₆H₅NaO₇·H₂O, NH₄Cl and NaH₂PO₂·H₂O, and the deposition was carried out at a bath temperature of 70 °C with a pH value of 8.5. The morphology, microstructure and phase structure of Ni-coated α-Al₂O₃ nanopowders were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD), respectively. It is found that, the sensitization process followed by repetitive resining greatly affects the morphology of Ni deposited in the form of nanoparticles onto the ultrafine alumina particles, different from the conventional continuous electroless film/coating deposited on coarser particles. The resining of the SnCl₂ sensitized ultrafine α-Al₂O₃ particles prior to PdCl₂ activation process leads to varied amount of deposited Ni particles with diameters of 50–80 nm on the Al₂O₃. It is revealed that, subsequent reduction process (activation) from Pd²⁺ to Pd is linked to the original sites of Sn²⁺ by simultaneous oxidation process from Sn²⁺ to Sn⁴⁺ on the previously sensitized α-Al₂O₃ nanopowders. Consequently, the form of deposited Ni correlated closely to the surface distribution of reduced Pd which may be continuous or discrete determined predominantly by the density of adsorbed Sn²⁺ on the powders during sensitization process. It demonstrates a possibility of depositing different distribution structures of metals on nanosized α-Al₂O₃ powders through controlling SnCl₂ sensitization process.     

Preparation of Nano-ZrO2 powder via a microwave-assisted hydrothermal method

ZrO₂ nanocrystals were synthesised by a microwave-assisted hydrothermal method using zirconium oxychloride (ZrOCl₂·8H₂O), yttrium chloride (YCl₃·6H₂O), and liquor ammonia (NH₃·H₂O) as raw materials, triethanolamine (TEOA) as mineraliser, and polyethylene glycol (PEG) as dispersant. The obtained products were characterised with thermogravimetry-differential scanning calorimetry (TG-DSC), Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the concentration of ZrOCl₂·8H₂O had little effect on the material properties, whereas the PEG molecular weight, microwave hydrothermal time and temperature, and the concentration of TEOA greatly influenced the dispersibility of the nano-sized zirconia powders. XRD and FT-IR analyses indicated that the ZrO₂ nanocrystals synthesised by the microwave hydrothermal method had a tetragonal phase without any trace of monoclinic or cubic phases. The optimal parameters for preparing nano-zirconia powders with appreciable crystallinity and crystal forms included the use of PEG1000/PEG2000/PEG4000 dispersants, a microwave hydrothermal time of 30–50 min and a temperature of 200–240 °C, and a TEOA concentration of 0.3–0.5 M. Nano-ZrO₂ powder prepared via our optimised microwave hydrothermal method contained mostly tetrahedral, spherically shaped, highly homogeneous, and well-dispersed 20–30 nm particles.     

Understanding the Role of Triblock Copolymers for the Synthesis of Mesoporous Alumina,and Its Adsorption Efficiency for Congo Red

Mesoporous alumina (MA)was synthesized by sol–gel based evaporation‐induced self‐assembly process using aluminum isopropoxide as alumina source in the presence of three different types of triblock copolymers (TBCs), F68, F127, and L64. The role of different TBCs as surfactants on thermal, crystallization, textural, and microstructural properties of the alumina powders was studied. To understand the effects of different copolymers, the adsorption efficiency of the samples for Congo red (CR) was studied. For all the surfactants, the XRD results showed the stability of γ‐Al₂O₃ phase up to 1000°C for 1 h dwell time. A maximum value (431.8 m²/g) of Brunauer–Emmet–Teller surface area was obtained for the 400°C‐treated powder prepared from F68 surfactant. The transmission electron microscopy micrograph exhibited worm‐like mesoporous structures of the 400°C‐treated powders prepared from F68 and F127 surfactants_. The adsorption performance for CR of the 400°C‐treated powders for different surfactants was in the order of F68 > F127 > L64. A tentative mechanism was illustrated to understand the roles of different block copolymers on the properties of the prepared MA.     

Effects of H2O in EtOH–H2O disperse medium on the electrophoretic deposition of CaSiO3 fine powder

The effects of H₂O in the EtOH–H₂O disperse medium on the electrophoretic deposition (EPD) of CaSiO₃ fine powder were investigated. Fine CaSiO₃ powder with average diameter of 1·7 μm was prepared by the coprecipitation method. It was deposited on a stainless steel substrate by EPD in the disperse media with various H₂O concentrations (0–20·2 mass%) under a DC field of 50 V. The amount of the CaSiO₃ deposition increased with increasing H₂O up to 11·2 mass% but decreased rapidly beyond this concentration. The surface potential of the powder showed a similar trend as the amount of deposition against H₂O concentration. The effect of H₂O was summarized as follows: (1) the addition of positive charge on the surface of CaSiO₃ particles (2) the neutralization of the surface charge by OH⁻ caused by the dissolution of CaSiO₃ in the H₂O.     

Preparation of WC/Co composite powders by electroless plating

Ultra-fine WC/Co composite powders were prepared by electroless plating in this study. The Co layers with an average thickness of 50–100 nm were uniformly and completely covered on raw WC particles with a diameter of 0.3–0.5 µm. The influences of electroless plating conditions on the composites were investigated. The Co layer covering on WC particles was controlled by the content of CoSO₄·7H₂O, pH value and bath temperature. With increasing the content of CoSO₄·7H₂O up to 25 g/L, both the weight gain and the plating rate markedly increased. However, when the content of CoSO₄·7H₂O further increased to 30 g/L, while the weight gain displayed a slight decrease, the plating rate continued to increase moderately. Moreover, with the increase of pH value from 9.5 to 11, both the weight gain and the reaction time decreased. Furthermore, the plating rate exhibited an exponential relationship with the bath temperature. When the pH value, bath temperature and the concentration of CoSO₄·7H₂O are 10, 80 °C and 25 g/L respectively, the weight gain of Co-coated WC composite powders is 185.1 mg/g.     

Effects of various factors on capacitive properties of VO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O powders in aqueous electrolyte

In this work, effects of drying temperature, pH of aqueous electrolyte and current density on capacitive performance of VO _x ·nH₂O material were firstly investigated. VO _x ·nH₂O powders were prepared by a melt quenching method. The samples were characterized by X-ray diffraction analysis (XRD) and Fourier transform infrared (FTIR). The capacitive properties of VO _x ·nH₂O samples were examined by cyclic voltammetry and galvanostatic charge/discharge test. VO _x ·nH₂O sample which was obtained at the drying temperature of 80 °C, delivers a maximum specific capacitance of 227.3 F g⁻¹ and exhibits excellent capacity retention in the potential range of −0.3 to 0.7 V at a current density of 200 mA g⁻¹ in NaNO₃ solution with pH 2.     

Synthesis and surface modification of submicron BaTiO3 powders via a facile surfactant-assisted method

Due to their unique properties, well-dispersed barium titanate (BaTiO₃) ultrafine powders can be used in wide-ranging fields. In the present work, by using barium hydroxide octahydrate (Ba(OH)₂·8H₂O) and α titanic acid (H₄TiO₄) as raw materials, uniform submicron BaTiO₃ powders with tetragonal structure and high degree of crystallinity were prepared via a solid-state reaction method at relatively low temperatures. Moreover, by simply using the stearic acid (St) as the modifier to modify the surface of the aggregated BaTiO₃ powders, well-dispersed BaTiO₃ particles could be obtained, which were then examined by complementary characterizations such as XRD, TEM, HRTEM, SEM, Raman, FT-IR, XPS and EDS. The results indicated that the tetragonal BaTiO₃ particles with submicron-size, good uniformity, and high crystallinity could be prepared at 800 °C for 1 h. Moreover, the addition of St for surface modification proved to be an effective way to avoid the agglomeration of the BaTiO₃ particles to get well-dispersed products, where 1 wt % of St was found to be the optimum concentration. The demonstrated surfactant-assisted surface modification method is expected to be applicable for other ultrafine powders to get well-dispersed particles.     

Visible Light Transparency for Polycrystalline Ceramics of MgO·2Al2O3 and MgO·2.5Al2O3 Spinel Solid Solutions

Magnesium aluminate spinel solid solutions with the alumina‐rich compositions MgO·2Al₂O₃ and MgO·2.5Al₂O₃ have been prepared as polycrystalline ceramics with average in‐line transmissions at 550 nm of 85.5 ± 0.3% and 80.9 ± 0.4%, respectively. Starting powders are prepared from combinations of high purity Mg(OH)₂ and γ‐Al₂O₃ thoroughly mixed in an aqueous slurry, and the solids are collected, dried, calcined, mixed with LiF sintering aid, and sieved. The optimum amount of LiF added varies with the alumina composition of the spinel solid solution. The powders are sintered into dense ceramics by hot pressing at 1600°C under vacuum and 20 MPa uniaxial load followed by hot isostatic pressing at 1850°C under 200 MPa in Ar. Both compositions exhibit exaggerated grain growth with average sizes well over 500 μm. Knoop hardness measurements are 11.2 ± 0.3 GPa for MgO·2Al₂O₃ and 11.0 ± 0.4 GPa for MgO·2.5Al₂O₃.     

Combustion synthesis of C/MgAl2O4 composite powders using magnesium oxalate as carbon source

In order to solve the bottleneck problems including uniform distribution, and oxidation resistance of nano carbons in oxide ceramics, C/MgAl₂O₄ composite powders were prepared with MgC₂O₄·2H₂O, MgO₂, Al₂O₃, and Al as raw materials via combustion method under argon atmosphere. The maximum adding amount of MgC₂O₄·2H₂O is 34.34 wt%. The phase compositions and microstructures of combustion products were characterized through X-ray diffraction (XRD), scanning electron microscope (SEM)/EDX, and Raman spectroscopy. The results showed that the phases of products are mainly composed of MgAl₂O₄ and carbon. The prepared MgAl₂O₄ has granular and rod-like morphologies, and the free carbon (1.172 wt%) exists between particles of MgAl₂O₄. Moreover, the addition of FeC₂O₄ as catalyst in raw materials ratio would be beneficial for improving crystallization of in situ carbon generated in the products. The oxidation activation energy of the prepared C/MgAl₂O₄ composite powders was calculated as 143.01 kJ/mol which was 22.17% higher than that of carbon black/MgAl₂O₄ powders (117.06 kJ/mol), suggesting that the C/MgAl₂O₄ composite powders prepared by combustion synthesis have excellent oxidation resistance.     

Fabrication and properties of pressure-sintered reaction-bonded Si3N4 ceramics with addition of Eu2O3–MgO–Y2O3

Dense pressure-sintered reaction-bonded Si₃N₄ (PSRBSN) ceramics were obtained by a hot-press sintering method. Precursor Si powders were prepared with Eu₂O₃–MgO–Y₂O₃ sintering additive. The addition of Eu₂O₃–MgO–Y₂O₃ was shown to promote full nitridation of the Si powder. The nitrided Si₃N₄ particles had an equiaxial morphology, without whisker formation, after the Si powders doped with Eu₂O₃–MgO–Y₂O₃ were nitrided at 1400 °C for 2 h. After hot pressing, the relative density, Vickers hardness, flexural strength, and fracture toughness of the PSRBSN ceramics, with 5 wt% Eu₂O₃ doping, were 98.3 ± 0.2%, 17.8 ± 0.8 GPa, 697.0 ± 67.0 MPa, and 7.3 ± 0.3 MPa m^1/2, respectively. The thermal conductivity was 73.6 ± 0.2 W m^?1 K^?1, significantly higher than the counterpart without Eu₂O₃ doping, or with ZrO₂ doping by conventional methods.     

Highly Transparent Mg0.27Al2.58O3.73N0.27 Ceramic Prepared by Pressureless Sintering

A novel aluminum magnesium oxynitride transparent ceramic with the chemical formula Mg_0.27Al_2.58O_3.73N_0.27 was firstly prepared by pressureless sintering of fine single‐phase powders at 1875°C for 24 h in nitrogen atmosphere. The ceramic was fully dense with the average grain size of 57.5 μm. The sample showed excellent in‐line transmission from the visible to middle‐infrared wavelengths with the maximum transmittance of 84%, which could be attributed to rare pores in the sintering body. The material also exhibited good mechanical properties of Vickers hardness (13.39 ± 0.18 GPa), fracture toughness (2.46 ± 0.3 MPa/m^1/2), and flexural strength (274 ± 6 MPa).     

Preparation of NaA Zeolite Membranes Using Poly(Ethyleneimine) as Buffer Layer,and Study of Their Permeation Behavior

Zeolite NaA membranes were prepared hydrothermally by secondary crystallization process at different temperatures (55°C–75°C) on porous α‐alumina‐based support tubes (inner side) precoated with poly(ethyleneimine) (PEI) buffer layer and NaA seed particles. The NaA seed crystals synthesized at 65°C/2 h in the size range 100–200 nm having BET surface area of 71.57 m²g^?1 were used for secondary crystallization of the membranes. The secondary crystallization at 65°C for (4 + 4) h (double‐stage) showed highly dense NaA grains in the microstructure of the membrane with a thickness of 5 μm. It rendered the permeance values of 50.6 × 10^?8, 2.47 × 10^?8, and 0.55 × 10^?8 molm^?2s^?1Pa^?1 for H₂, N₂, and CO₂, respectively, with their permselectivity of 20.48 (H₂/N₂), 92 (H₂/CO₂), and 4.49 (N₂/CO₂). A tentative mechanism was illustrated for the interaction of PEI with the support substrate and NaA seed crystals.     

Processing and properties of polycrystalline cubic boron nitride reinforced by SiC whiskers

Dense polycrystalline cBN (PcBN)–SiCw composites were fabricated by a two-step method: First, SiO₂ was coated on the surface of cubic boron nitride (cBN) particles by the sol-gel method. Then, silicon carbide whisker (SiC_w)- coated cBN powder was prepared by carbon thermal reaction between SiO₂ and carbon powders at 1500°C for 2 hour. Then, cBN–SiC_w complex powders were sintered by high-pressure and high-temperature sintering technology using Al, B, and C as sintering additives. The phase compositions and microstructures of cBN–SiC_w composites were investigated by X-ray diffraction and scanning electron microscopy, respectively. It was found that the SiC_w and Al₃BC₃ had been fabricated by in situ reaction, which cannot only promote densification but also improve mechanical properties. The relative density of PcBN composites increased from 96.3% to 99.4% with increasing SiC_w contents from 5 to 20 wt%. Meanwhile, the Vickers hardness, fracture toughness and flexural strength of as-obtained composites exhibited a similar trend as that of relative density. The composite contained 20 wt% of SiC_w exhibited the highest Vickers hardness and fracture toughness of 42.7 ± 1.9 GPa and 6.52 ± 0.21 MPa•m^1/2, respectively. At the same time, the flexural strength reached 406 ± 21 MPa.     

Chemical Synthesis,Sintering and Piezoelectric Properties of Ba0.85Ca0.15 Zr0.1Ti0.9O3 Lead‐Free Ceramics

The preparation of Ba_0.85Ca_0.15 Zr_0.1Ti_0.9O₃ (BCZT) powders by wet chemical methods has been investigated, and the powders used to explore relationships between the microstructure and piezoelectric properties (d₃₃ coefficient) of sintered BCZT ceramics. Sol–gel synthesis has been shown to be a successful method for the preparation of BCZT nanopowders with a pure tetragonal perovskite phase structure, specific surface area up to 21.8 m²/g and a mean particle size of 48 nm. These powders were suitable for the fabrication of dense BCZT ceramics with fine‐grain microstructures. The ceramics with the highest density of 95% theoretical density (TD) and grain size of 1.3 μm were prepared by uniaxial pressing followed by a two‐step sintering approach which contributed to the refinement of the BCTZ microstructure. A decrease in the grain size to 0.8–0.9 μm was achieved when samples were prepared using cold isostatic pressing. Using various sintering schedules, BCZT ceramics with broad range of grain sizes (0.8–60.5 μm) were prepared. The highest d₃₃ = 410.8 ± 13.2 pC/N was exhibited by ceramics prepared from sol–gel powder sintered at 1425°C, with the relative density of 89.6%TD and grain size of 36 μm.     

Fabrication and microstructure of 3D Cf /ZrC-SiC composites: through RMI method with ZrO2 powders as pore-making agent

3D C_f/ZrC–SiC composites were prepared by a combination process of slurry infiltration and reactive melt infiltration. ZrO₂ powders and ZrSi₂ alloy, both of which reacted with amorphous carbon, were used as pore-making agent and infiltrator, respectively. After carbothermal reduction at 1650 °C, X-ray diffraction analysis revealed that ZrO₂ powders were completely converted into ZrC by reacting with amorphous carbon, and an in-situ formed submicron porous configuration was observed at the areas containing ZrO₂. Results showed that the matrix in composites mainly consisted of SiC, ZrC and a small quantity of residual metal. SEM and TEM images revealed the formation of ZrC or SiC intergranular particles in the matrix and the characteristic around the residual resin carbon. The composites had a bending strength of 94.89±16.7 MPa, fracture toughness of 11.0±0.98 MPa m^1/2, bulk density of 3.36±0.01 g/cm³, and open porosity of 4.64±0.40%. The formation mechanisms of ZrC–SiC dual matrix and intrabundles׳ structure were discussed in the article.     

Selective Catalytic Reduction of NO by Ammonia over Raney‐Ni Supported Cu‐ZSM–5 I. Catalyst Activity and Stability

Composite materials containing Raney Ni and Cu‐ZSM‐5 are highly active catalysts for the selective catalytic reduction (SCR) of NO by NH₃. Their catalytic properties were studied with particular attention to the influence of moisture and SO₂ in the feed, and to effects of catalyst shaping operations. Composite materials (16–20 wt‐% zeolite) were prepared by mixing the components, with different degree of segregation in the resulting pressed particles, or by growing ZSM‐5 crystallites on the surface of leached Raney Ni, which were then exchanged with Cu ions. Catalytic tests were performed with 1000 ppm NO, 1000 ppm NH₃, 2 % O₂ in He, at 3–6.5 · 10⁵ h^–1 (related to zeolite component). With physical mixtures, the catalytic behaviour strongly depended on the mixing strategy, particles containing both Ni and zeolite being inferior to mixed Ni‐only and zeolite‐only particles. The SCR activity was promoted by 2 % H₂O in the feed, SO₂ (200 ppm) was a moderate poison at low temperatures, but indifferent or slightly promoting at high temperatures. A catalyst prepared from ZSM‐5 grown on Raney Ni, which was ranked intermediate in dry feed, was promoted to excellent performance in H₂O and SO₂ containing feed at T > 700 K and was stable for 38 h at 845 K. The results suggest that SCR catalysts containing highly active zeolites should be produced avoiding shaping operations e.g. by use of zeolite crystallites grown on wire packings.