Catalytic effect of in-situ formed La2O3 nanoparticles (NPs) on the nitridation of Si powders was studied by X-ray diffraction, field emission-scanning electron microscopy and transmission electron microscope. Thermodynamic analysis and the effects of various processing parameters such as addition of catalyst and firing temperature on the nitridation of Si powders were respectively investigated. The results showed that: 1) The La2O3 NPs significantly promoted the nitridation rate of Si powders, and complete nitridation was achieved at 1623 K by using 1 wt % La2O3 NPs as catalyst; 2) Numerous Si3N4 whiskers of 20-300 nm in diameter and tens of microns in length were fabricated in the final product. The Si3N4 whiskers which was believed to be governed by vapor-vapor-solid mechanism were verified to have single-crystal nature, growing along [101] direction. (C) 2018 The Ceramic Society of Japan. All rights reserved.

以SiC粉和硅粉为原料,原位合成的Cr 2 O 3 为催化剂,采用催化氮化法制备了Si 3 N 4 /SiC耐火材料,研究了催化剂用量及氮化温度对耐火材料物相组成、微观形貌、物理性能和力学性能的影响。结果表明:当氮化温度为1 673K,Cr 2 O 3 含量（与硅粉质量之比,下同）为3%时,硅粉完全氮化,耐火材料主要由颗粒状SiC和晶须状α-Si 3 N 4 、β-Si 3 N 4 等组成;随着Cr 2 O 3 含量的增加,Si 3 N 4 晶须的数量增多,长度增大,耐火材料变得致密;随氮化温度的升高,耐火材料的抗折强度和耐压强度均增大,当氮化温度为1 673K、Cr 2 O 3 含量为3%时,抗折强度和耐压强度均最大,分别为34MPa和132MPa。

Si3N4/SiC composites were prepared by a catalytic nitridation method usingin situ formed NiO nanoparticles (NPs) as a catalyst. The room-temperature and high-temperature mechanical properties of the as-prepared composites were investigated. The results show that the as-prepared Si3N4/SiC composite has the maximum cold compression strength (σCCS) of 131.0MPa and modulus of rupture (σMOR) of 24.6MPa with NiO NPs as a catalyst. The high-temperature MOR (σHMOR) of the as-prepared composite firstly increases and then decreases with the increase of the temperature. The maximumσHMOR is obtained at 1573 K. TheσHMOR of the as-prepared composite even at 1673 K is still greater than that of the composite at room temperature. The residual strength holding ratio of the as-prepared composites is approximately 50％ at 1573K, indicating that the prepared Si3N4/SiC composite has the superior thermal shock resistance. The initial oxidation temperature of the prepared composite is 1173 K, and the oxidation resistance of Si3N4/SiC composite prepared with NiO nanoparticle catalyst is greater than that of the sample without catalyst. The prepared composite has a well resistance to cryolite corrosion. The formation of Si3N4 whiskers with NiO nanoparticles catalyst is promoted, and the Si3N4 whiskers is distributed in aggregates to form a network-like structure, so that the performance of composite material is improved.

以SiC粉和硅粉为原料,原位合成的Cr2O3为催化剂,采用催化氮化法制备了Si3N4/SiC耐火材料,研究了催化剂用量及氮化温度对耐火材料物相组成、微观形貌、物理性能和力学性能的影响.结果表明:当氮化温度为1673 K,Cr2O3含量(与硅粉质量之比,下同)为3％时,硅粉完全氮化,耐火材料主要由颗粒状SiC和晶须状α-Si3N4、β-Si3N4等组成;随着Cr2O3含量的增加,Si3N4晶须的数量增多,长度增大,耐火材料变得致密;随氮化温度的升高,耐火材料的抗折强度和耐压强度均增大,当氮化温度为1673 K、Cr2O3含量为3％时,抗折强度和耐压强度均最大,分别为34 MPa和132 MPa.

以聚乙二醇为表面活性剂,以氨水为沉淀剂,先采用沉淀法将氧化钇（Y 2 O 3 ）纳米颗粒催化剂原位沉积于Si粉表面,再通过催化Si粉氮化工艺制备Si 3 N 4 粉体。研究了催化剂Y 2 O 3 的用量及氮化温度等对Si 3 N 4 粉体合成的影响。采用X射线衍射、扫描电子显微镜及能谱仪对产物的物相组成及显微结构进行了表征。结果表明:当Y 2 O 3 纳米颗粒的加入量为1%（质量分数,下同）时,试样于1350℃/2 h催化氮化后产物中残余单质Si含量最小,低于1%;氮化后产物中存在着长度约为几个微米,直径在20~200 nm的晶须状Si 3 N 4 ,其生长机理主要为气相-气相-固相（VVS）机理。

Effects of Cr2O3 nanoparticles (NPs) on the catalytic nitridation of Si powders were investigated, and the results showed that the Cr2O3 NP catalysts enhanced the nitridation of Si powders and promoted the formation of Si3N4 whiskers. The complete conversion of Si was achieved at [1473 K (1200 °C)] for 3 hours with the addition of 3 wt pct Cr2O3 NPs. First-principle calculations suggested that the electron transfer from Cr2O3 to N2 molecules facilitates the Si nitridation. Moreover, Si3N4-bonded SiC refractories were also prepared using in-situ formed Cr2O3 NPs as catalysts, and the hot modulus of rupture at [1673 K (1400 °C)] of as-prepared refractories was about three times higher than that of samples without catalysts; the corrosion resistance against molten cryolite of the former was remarkably lower than that of the latter. The improvement was attributed to the catalytic effects of Cr2O3 NPs for in-situ formation of a fund of Si3N4 whiskers, which formed a network structure in the samples.

Using PEG as surfactant and NH3 center dot H2O as precipitant, Y2O3 nanoparticle (NP) catalysts were homogeneously deposited on the surface of Si powders by an in-situ precipitation method and Si3N4 was then prepared by nitridation of Si powders. The effects of various processing parameters including the amount of catalyst and nitridation temperature on the synthesis of Si3N4 powders were investigated. Phase composition and microstructure of the Si3N4 were characterized by X-ray diffraction and field emission-scanning electron microscopy equipped with EDS, respectively. The results show that when the sample is nitrided at 1350 degrees C/2 h with 1 wt% of Y2O3 NPs as catalysts, the residual Si content in the final sample is less than 1wt%. Many of Si3N4 whiskers with 20 similar to 200 nm in diameter and several microns in length form in the final products. Vapor-vapor-solid (VVS) growth mechanism is responsible for the growth of Si3N4 whiskers.

A series of Rh/Co bimetallic nanoparticles (BNPs) were synthesized by co-reduction method using ISOBAM-104 as protective reagent.UV-Vis,TEM and HRTEM were used for characterization of the structure and composition of the prepared nanoparticles.The results showed that Rh/Co BNPs are alloy structure,and the particle size of as-prepared BNPs is less than 6.0 nm.The catalytic activities of the prepared Rh/Co BNPs are higher than that of Rh or Co monometallic nanoparticles,and Rh20Co80 BNPs possesses the highest TOF of 12880 mol-H2· h-1 ·mol-Rh-1.

Cr2O3 nanoparticles (NPs) were successfully prepared by a facile surfactant-modified precipitation method, and their phase composition and microstructure were characterized by X-ray diffraction, field emission-scanning electron microscopy and transmission electron microscopy. The effects of various processing parameters including surfactants type and amount, pH value and firing temperature on the synthesis of Cr2O3 NPs were investigated. Highly dispersed Cr2O3 NPs with an average crystalline size of 17nm were obtained under the following optimal conditions: [Cr(NO3)(3)center dot 9H(2)O] = 0.0316 mol/L, PEG/Cr2O3 = 5wt%, pH = 5.2, calcination temperature = 500 degrees C and holding time = 2h. Cr2O3 NPs showed a significant accelerating effect on the nitridation of Si powder, the conversion rate of Si to Si3N4 after 2 h at 1300 degrees C reached 100 wt% upon using 3wt% Cr2O3 NPs as catalysts, but only 40 wt% in the case without using any catalysts. (C) 2017 The Ceramic Society of Japan. All rights reserved.

SiAlON ceramic which possesses excellent mechanical properties at both room temperature and high temperature and good chemical stability is regarded as a kind of important high-temperature structural materials.One-dimensional SiAlON mate-rials (including nanowire,nanorod,nanobelt,etc.) with special monocrystalline structure have potential applications in high-tempe-rature ceramics,optics,electronics and other fields owing to their excellent mechanical properties,unique optical and electrical pro-perties.This paper reviews recent research progress of one-dimensional SiAlON.Meanwhile,the synthesis methods and growth mechanisms of one-dimensional SiAlON are also summarized.Moreover,the future application prospects and developmental direction of one-dimensional SiAlON are proposed.

The monolithic refractories have acquired wide application for its convenient installation,good monolithic structure and firing-free character.Thermal shock resistance and slag resistance of refractories can be significantly improved by the incorporation of flake graphite.However,the poor aqueous wettability and dispersibility of flake graphite make it hard to be directly applied to carbon-containing castables.Surface modification of graphite is generally regarded as one of crucial ways to solve these problems.The advances in surface modification of flake graphite are reviewed in this paper,including the formation of binary oxide coatings (e.g.Al2O3,SiO2,TiO2 and ZrO2) or ternary oxide coatings (e.g.MgAl2O4,mullite and calcium aluminate) by sol-gel method,formation of carbide coatings (e.g.SiC and TiC) at high temperature by in-situ reaction method,and improving aqueous wettahility of the graphite by using appropriate surfactants.The effect of modified graphite on the properties of carbon containing castables and the effect of surface modification methods and preparation processing factors on the coating as well as coating formation mechanism are summarized.Moreover,potential research directions of carbon containing castables are also prospected from the perspectives of improving the bonding between coating and graphite,and developing advanced heating technology and efficient surfactants for preparing of surface-modified graphite etc.

Porous mullite ceramics were prepared at 1300-1600 degrees C for 2h via a foam-gelcasting route using industrial-grade mullite powders as the main raw material, Isobam 104 as the dispersing and gelling agent, triethanolamine lauryl sulphate as the foaming agent and sodium carboxymethyl cellulose as the foam stabilising agent. The effects of firing temperature on the sintering behaviour of green samples as well as microstructures and properties of final porous mullite products were investigated. With increasing the temperature from 1300 to 1600 degrees C, linear shrinkage and bulk density values of fired samples increased, whereas their porosity decreased. Mechanical strength and thermal conductivity values of fired samples decreased with increasing their porosities. Even at a porosity level as high as 79.4%, compressive and flexural strengths of fired samples (with average pore size of 314m) remained as high as 9.0 and 3.7MPa, respectively, and their thermal conductivity (at 200 degrees C) remained as low as 0.21W(m(-1)K(-1)).

To prepared well dispersed ultra-fine nano-Cr2 O3 powders,Cr(NO3 )3 ·9H2 O was used as the main starting material and PVP was used as the dispersant by a two-step precipitation method.Fixing the Cr(NO3 )3 content at 0.031 6 mol·L -1 ,the effects of different kinds of precipitator (NH3 ·H2 O,K2 CO3 , N2 H4 ·H2 O),pH values (4.8,5.2,6.5,7 and 7.9)and calcination temperatures (300,400,450,and 500℃)on the crystalline size of nano-Cr2 O3 were investigated.The prepared Cr2 O3 nanopowders were char-acterized by TG-DSC,FE-SEM and XRD.The results show that crystalline size of nano-Cr2 O3 first decrea-ses and then increases with the elevating calcination temperature and pH value.The well dispersed nano-Cr2 O3 powders with crystalline size of about 20 nm are obtained under the conditions of [Cr(NO3 )3 · 9H2 O]=0.031 6 mol·L -1 ,NH3 ·H2 O as the precipitator,pH value of 7,calcination temperature of 450 ℃and holding time of 2 h.

以Al2O3和SiO2为原料、AlF3·3H2O为添加剂,采用原位反应法经1 373～1 873 K反应5h后制备莫来石晶须.研究了添加剂含量及反应温度等对莫来石晶须合成的影响,探讨了莫来石晶须的生长机理.结果表明:AlF3·3H2O的最佳添加量为4％(质量分数)时,莫来石晶须的长度和长径比均随合成温度的升高(1 373～1 873 K)先增大后减小,当合成温度为1 673K时,样品中莫来石晶须的长径比最大(约为54).莫来石晶须的生长是由气-固反应机理控制.

氮化硅陶瓷由于具有优良的机械性能、化学性能和物理性能而被广泛应用于化工、冶金及航天等领域.催化氮化法制备氮化硅可以有效避免“硅芯”及“流硅”等不完全氮化形为的发生;并促进氮化硅晶须的原位反应合成,改善氮化硅基材料界面的显微结构,提高最终制品的力学性能.本文综述了金属及金属氧化物催化剂催化氮化反应生成氮化硅的最新进展及一维氮化硅的原位生成机理,并在此基础上展望了催化氮化制备氮化硅工艺今后的发展方向.

This paper reported a facile route for synthesizing PVP stabilized Pd/Ni bimetallic nanosol by a chemical co-reduction process. The morphology, size, structure and composition of the resultant Pd/Ni bimetallic nanosol were characterized by transmission electron microscopy (TEM). The effects of PVP amount, reducing agent amount and metal composition on the hydrolysis of NaBH4 were studied. The results indicate that the catalytic activities of the prepared Pd/Ni bimetallic nano catalysts with an average size of 2 nm are superior to those of monometallic Pd nanocatalyst with the same size. The Pd10Ni90 bimetallic nanosol shows the highest catalytic activity with hydrogen generation rates of 8250 mol(H2).mol(Pd)(-1).h(-1) at 303 K, and the activation energy, enthalpy and entropy of Pd20Ni80 bimetallic nanoparticles are 35.7 kJ/mol, 33.3 kJ/mol and -150 J/mol, respectively. In addition, the prepared Pd/Ni bimetallic nanosol has a good catalytic activity even after the fourth cycle. The high catalytic activity of the Pd/Ni BNPs can be ascribed to electronic charge transfer effects. And DFT calculations reveal that Pd atoms are indeed negatively charged with the positively charged Ni atoms. The positively charged Ni atoms and negatively charged Pd atoms act as catalytic active sites for the hydrolysis of the alkaline NaBH4 solution.

Porous ceramics have been extensively studied during the last two decades because of their potential application in the fields of thermal insulators, gas filters, catalytic supports, separation membranes, kiln furniture, and biomedical substitutes for bone and teeth. The properties of porous ceramics are highly dependent on their method of preparation. This mini-review summarizes recent developments in innovative fabrication of porous ceramics such as three-dimensional printing, molten salt synthesis, and the sacrificial template and replica methods. Finally, we conclude with our personal perspectives and recommendations for future research in porous ceramics.