Synthesis of Neodymium-Doped Yttrium Aluminum Garnet (Nd∶YAG) Nano-Sized Powders by Low Temperature Combustion

The homogeneously dispersed, less agglomerated (Nd0.01Y0.99)3Al5O12 nano-sized powders were synthesized by the low temperature combustion (LCS), using Nd2O3, Y2O3, Al(NO3)3·9H2O, ammonia water and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and hard agglomerates brought by the chemical precipitation method. The powders were characterized by TG-DTA, XRD, FT-IR, TEM respectively and the photoluminescence (PL) spectra of (Nd0.01Y0.99)3Al5O12 green and sintered ceramic disks were measured. The results show that the forming temperature of YAG crystal phase is 850 ℃ and YAP crystal phase appearing during the calcinations transforms to pure YAG at 1050 ℃. The particle size of the powders synthesized by the LCS is in a range of 20～50 nm depending on the thermal treatment temperatures. The effectively induced cross section (σin) with the value 4.03×10-19 cm2 of (Nd0.01Y0.99)3Al5O12 ceramics is about 44% higher than that of single crystal.

Synthesis and Characterization of Nano-sized Boron Powder Prepared by Plasma Torch

Hydrogen thermal plasma jet was employed to prepare nano-sized boron powder with hydrogen reduction of BCI3. The maximum yield of nano-sized boron powders was about 50% with the operational conditions of H2/BCl3 of 4.5：1, total feed of 4.9 m3/h, and plasma power of 25 kW. The samples were analyzed by X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM）, and inductively coupled plasma - mass spectrometry （ICP-MS）, inductively coupled plasma - atomic emission spectrometry （ICP-AES）, inductive combustion infrared absorption （ICIA） and infrared thermal conductivity of oxygen and nitrogen analyzer （ITCA）. The results show that the boron powders have different crystal structures with higher dispersion and purity. The average diameter is about 50 nm, and the purity is 90.29% or so. This new technology can use simple process to produce high quality boron powders, and is feasible for industrial production.

Corrosion resistance of waterborne epoxy coating pigmented by nano-sized aluminium powder on steel

A novel kind of waterborne epoxy coating pigmented by nano-sized aluminium powders on high strength steel was formulated. Several coatings with different pigment volume content (PVC) were prepared. The coating morphology was observed using scanning electron microscopy (SEM), and the electrochemical properties were investigated by electrochemical impedance spectroscopy (EIS). Immersion test and neutral salt spray test were also conducted to investigate the corrosion resistance of the coating. It is demonstrated that the critical pigment volume content (CPVC) value is between 30% and 40%. The coating with PVC of 30% exhibits good corrosion resistance in 3.5% (mass fraction) NaCl solution.

Preparation and Sinterability of Mn-Zn Ferrite Powders by Sol-Gel Method

Mn-Zn spinel ferrites were synthesized by sol-gel method. Effects of calcined temperature on structure and particle size of MnZnFe2O4 were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns indicate that the ultra fine Mn-Zn ferrite exhibits a spinel crystal structure. SEM images show that the powder fired at 900℃for 2 h has an average diameter of 60 ~ 90 nm. The particle size becomes larger with the increasing of calcined temperature and the distribution of particle becomes even more homogeneous. Sintering behaviors of synthesized ferrite powders depend on the powder characteristics and high temperatures have induced the good crystallization of particles.

A Facile Route for Synthesis of LiFePO_4/C Cathode Material with Nano-sized Primary Particles

A facile and practical route was introduced to prepare LiFePO4/C cathode material with nano-sized primary particles and excellent electrochemical performance. LiH2PO4 was synthesized by using H3PO4 and LiOH as raw materials. Then, as-prepared LiH2PO4, reduced iron powder andα-D-glucose were ball-milled, dried and sin-tered to prepare LiFePO4/C. X-ray diffractometry was used to characterize LiH2PO4, ball-milled product and LiFePO4/C. Differential scanning calorimeter-thermo gravimetric analysis was applied to investigate possible reac-tions in sintering and find suitable temperature for LiFePO4 formation. Scanning electron microscopy was em-ployed for the morphology of LiFePO4/C. As-prepared LiH2PO4 is characterized to be in P21cn（33） space group, which reacts with reduced iron powder to form Li3PO4, Fe3（PO4）2 and H2 in ball-milling and sintering. The appro-priate temperature for LiFePO4/C synthesis is 541.3-976.7 ℃. LiFePO4/C prepared at 700 ℃ presents nano-sized primary particles forming aggregates. Charge-discharge examination indicates that as-prepared LiFePO4/C displays appreciable discharge capacities of 145 and 131 mA·h·g^-1 at 0.1 and 1 C respectively and excellent discharge ca-pacity retention.

DEPENDENCE OF SINTERABILITY ON STATE OF AGGLOMERATION OF ULTRAFINE ZrO_2，（Y_2O_3） POWDERS

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Thermophysical and Mechanical Properties of ZrO_2 (CaO) Powder and Colloidal Zirconia Sol Dip-Coat Layer Used for Titanium Investment Casting

Both green and residual bending strength of the dip-coat layer composed of ZrO2 (CaO) powder and colloi-dal zirconiz sol binder are sutdied and the effects of process factrs on the strength of dip-coat layer are interpreted,using the results of TG-DTA ,TMA and SEM analyses of the fracture morphology of the coating layer and following the strength theory for porous body.

Preparation and characterization of monodisperse zirconia spherical nanometer powder via lamellar liquid crystal template method

Cubic phase spherical zirconia nano-powder was prepared by a direct template route in the lamellar liquid crystal formed by polyoxyethylene tert-octylphenyl ether(Triton X-100)/sodium dodecyl sulfate(SDS)/H_2O.The precursor powder and zirconia powder were characterized by XRD,FT-IR,TG/DSC,TEM,and SEM methods.Results show that the stability of the lamellar liquid crystal is controlled by NH_3·H_2O concentration.The size of nanoparticles is greatly affected by NH_3·H_2O and ZrOCl_2·8H_2O concentrations.The zirconia nanoparticles show narrow particle size distribution of 10-30 nm.

Preparation of zirconia-alumina powder by co-precipitation

A zirconia alumina powder with a near spherical shape and an average size of 0.1～0.2 μm was prepared by co precipitation. XRD analysis shows that α Al 2O 3 phase may be directly transformed from amorphous in calcining the hydroxide composite. The ZrO 2 Al 2O 3 composite ceramics manufactured from this powder has the maximum fracture toughness of 9 MPa·m -1/2 at 15% ZrO 2 and 740 MPa fracture strength at 5% ZrO 2. Zirconia grains about 1 μm in diameter are dispersed uniformly in the alumina ceramic matrix.

Micro-aluminum powder with bi-or tri-component alloy coating as a promising catalyst:Boosting pyrolysis and combustion of ammonium perchlorate

A novel design of micro-aluminum(μAl)powder coated with bi-/tri-component alloy layer,such as:Ni-P and Ni-P-Cu(namely,Al@Ni-P,Al@Ni-P-Cu,respectively),as combustion catalysts,were introduced to release its huge energy inside Al-core and promote rapid pyrolysis of ammonium perchlorate(AP)at a lower temperature in aluminized propellants.The microstructure of Al@Ni-P-Cu demonstrates that a three-layer Ni-P-Cu shell,with the thickness of~100 nm,is uniformly supported byμAl carrier(fuel unit),which has an amorphous surface with a thickness of~2.3 nm(catalytic unit).The peak temperature of AP with the addition of Al@Ni-P-Cu(3.5%)could significantly drop to 316.2℃ at high-temperature thermal decomposition,reduced by 124.3℃,in comparison to that of pure AP with 440.5℃.It illustrated that the introduction of Al@Ni-P-Cu could weaken or even eliminate the obstacle of AP pyrolysis due to its reduction of activation energy with 118.28 kJ/mol.The laser ignition results showed that the ignition delay time of Al@Ni-P-Cu/AP mixture with 78 ms in air is shorter than that of Al@Ni-P/AP(118 ms),decreased by 33.90%.Those astonishing breakthroughs were attributed to the synergistic effects of adequate active sites on amorphous surface and oxidation exothermic reactions(7597.7 J/g)of Al@Ni-P-Cu,resulting in accelerated mass and/or heat transfer rate to catalyze AP pyrolysis and combustion.Moreover,it is believed to provide an alternative Al-based combustion catalyst for propellant designer,to promote the development the propellants toward a higher energy.

Preparation and Characterization on Nano- Sized Barium Titanate Powder Doped with Lanthanum by Sol-Gel Process

The nano-sized BaTiO3:La3+ powders were prepared by sol-gel process using butyl phthalate, barium acetate and lanthanum oxide as raw material, and these samples were tested by means of TG-DTA, XRD and SEM. The results indicate that with the annealing temperature and the doped concentration rising, the powders' particle sizes will increase and decrease respectively. When annealing temperature is 900℃and doped concentration is 7%, the phase is cubic without other phases, and the particle size of power is 43 .34 nm.

Review on Enhancement of Nitridation of Si Powder

This paper reviewed the effect of powder characteristics and additives including metals,rare earth oxides,and ZrO2 on nitridation of Si powder.The decrease of particle size of Si powder increased nitridation.Most of metal additives inhibited nitridation,while some metal additives such as Fe,Cu,Cr,and Ca increased nitrida—tion.Otherwise,the addition of metals might lead to the degradation of physical and mechanical properties of Si3N4.All the rare earth oxides,especially CeO2 and Eu2O3,showed nitridation enhancing effect.In addition,ZrO2 with small particle size showed a stronger enhancing effect.

Effect of ZrO_2-nitrides Composite Powder Addition on Oxidation Resistance of Al_2O_3-C Refractories

Oxidation of carbon is the main problem or Al2O3 - C refractories. ZrO2 - nitrides composite powder was synthesized through carbothermal reduction and nitridation （CRN） of zircon. The effect of ZrO2 - nitrides composite powder addition on oxidation resistance of the Al2O3 - C refractories was investigated by measuring the thickness of oxidation layer. Phase compositions of the Al2O3 - C refractories before and after oxidation were investigated by X-ray diffraction （ XRD ）. Results show that the oxidation resistance of the Al2O3 - C refractories can be obviously improved by adding the synthesized ZrO2 - nitrides composite powder. The formation of mullite and zircon in the oxidation layer results in the densification of oxidation layer, which prevents oxygen diffusion and bnproves the oxidation resistance of the Al2O3 - C refractories.

Influences of ZrO_2-SiC Composite Powder and Commercial SiC on Properties of Al_2O_3-C Refractories

In order to improve oxidation resistance and ther- mal shock resistance of Al2O3-C refractories, two groups of specimens were prepared with phenolic resin as binder, adding 0, 2 wt% , 4 wt% and 6 wt% commercial SiC or ZrO2-SiC composite powder synthesized from zircon respectively to Al2O3- C refractories, pressing at 200 MPa, drying fully at 250℃, and then carbon embedded firing at 1400℃ for 2 h. Oxidation resistance and thermal shock resistance were researched, phase composition was analyzed by XRD. The results showed that the oxidation of SiC in additives could protect carbon in specimens effectively and thus decreased the mass loss ratio and oxidation area, and improved the oxidation resistance of the specimen. Thermal shock resistance was improved owing to the micro crack toughening of ZrO2 and grain toughening of SiC. In this experiment, the specimens with 6 wt% ZrO2 -SiC composite powder or 6 wt% SiC powder had the best oxidation resistance and thermal shock resistance.

Mechanical Properties of a new Dental all-ceramic Material-zirconia Toughened Nanometer-ceramic Composite

目的 :口腔全瓷修复体以其独特优越性受到医患青睐 ,但脆性问题一直限制其应用范围及使用可靠性。本研究旨在研制用于玻璃渗透全瓷修复的纳米氧化锆增韧陶瓷并全面检测评价其力学性能。方法 :采用化学共沉淀与球磨相结合的方法合成纳米氧化锆增韧陶瓷 (α -Al2 O3 /nZrO2 ceramicspowder ,W) ,扫描电镜评价陶瓷材料的粉体形态特征及粒度分布。预制氧化锆含量不同的陶瓷粉体 (5wt% ,10wt% ,15wt%and 2 0wt% ) ,采用粉浆涂塑技术将材料制成标准试件 ,并在不同温度下 (12 0 0～ 16 0 0℃ )烧结成型 ,用三点弯曲法及单边刀口梁法检测材料试件的抗弯强度和断裂韧性。结果 :1)α -Al2 O3 /nZrO2 材料粉体粒度分布范围大致为 0 .0 2～ 3.0 μm ,其中超细粉体 (低于 0 .1μm)占 2 0 % ;2 )不同烧结温度组试件的力学强度有显著差异 (P <0 .0 5 ) ,14 5 0℃和 16 0 0℃组高于12 0 0℃组 ;3)相同烧结温度下不同氧化锆含量组材料强度有显著差异 ,一定范围内氧化锆含量增高有助于材料的增韧增强。结论 :本研究所研制的纳米氧化锆增韧陶瓷材料组分配比及微观特征能增韧增强材料 。

Effect of Al_2O_3-ZrO_2 Composite Powder on Thermal Shock Resistance of ZrO_2 Sizing Nozzles

ZrO2 sizing nozzles with a basic Jormulation were prepared using 45% （by mass, the same hereinafter ） （ Mg, Y） - PSZ aggregate, 55% （ Mg, Y） - PSZ fines and 5% PVA binder. Al2O3 - ZrO2 composite powders （ 3%, 6%, 9% and 12% ） prepared by sol - gel method were added to replace the equal amount of （ Mg, Y） - PSZfines. Effects of Al2O3 - ZrO2 composite powders on physical properties, phase composition and microstructure of the ZrO2 sizing nozzles were studied. The results show that： the performances of the modified sizing nozzles with 3% Al2O3 - ZrO2 composite powder are better than those of the nobles without composite powder used in current production process, and the thermal shock resistance of the ,former nozzles is six times of that of the latter one.

新微乳液体系下超细ZrO_(2)纳米粉体的可控合成及形成机理探究

ZrO_(2)纳米粉体由于其优异的性能被广泛应用于热障涂层、功能陶瓷、燃料电池、催化剂载体等多个领域。本文开发了一种新的微乳液体系(油酸/2-氨基-2-甲基-1-丙醇(AMP)/正辛醇/煤油/水溶液),经过热脱乳处理和煅烧成功制备出了超细ZrO_(2)纳米粉体。XRD、Raman和SAED分析证实,粉体在550~750℃范围内焙烧,物相结构保持为四方相ZrO_(2),说明该超细纳米粉体具有良好的稳定性。HRTEM结果表明,晶面间距为0.291 nm左右,与四方相ZrO_(2)的(101)面相对应。通过控制不同条件,如溶液用量、正辛醇用量、表面活性剂油酸用量,实现了ZrO_(2)纳米粉体尺寸在10~20 nm的区间内可以精确调控,基于微结构的演变并讨论了上述参数对形成机理的影响。

Promotional effect of silica on the combustion of nano-sized aluminum powder in carbon dioxide

This paper presents how the combustion performance of nano-sized aluminum(nAl)powder in carbon dioxide are affected by silica. The ignition and combustion performance of nAl powder with silica addition were studied by a high-temperature tube furnace. An s-type thermocouple and a high-speed motion acquisition instrument were performed to evaluate the ignition temperature, maximum combustion temperature, maximum change of rate of temperature, and combustion propagation speed. The combustion efficiency and combustion products were measured and analyzed by a gas-volumetric method and an X-ray diffraction. The results show that silica added into nAl powder can enhance its maximum combustion temperature and maximum change of rate of temperature, while its ignition temperature increases slightly. The nAl powders with addition of 6.00 wt.% and 12.00 wt.% silica present high combustion propagation speeds, especially for the latter, it has high combustion efficiency. The effect mechanism of silica on the combustion of nAl powder in carbon dioxide was discussed.

Ceramic membrane separation technique for washing nano-sized ceramic powder precursors

Washing using ceramic micro-filtration membranes was studied in the preparation of nano-sized TiO2 and A1203 powder precursors obtained by wet chemical methods. The key parameters for the washing process, such as operation pressure, cross-flow velocity, and slurry concentration, were examined and optimized. The shape and size of particles influenced the structure of the filter cake, leading to different permeation flux for different systems. The results demonstrated that washing using ceramic membranes is superior to the traditional plate-and-frame filtration and could be considered an advanced technique for ultra-fine powder preparation by wet-chemical method.

钇掺杂氧化锆粉体的制备方法及性能分析

通过不同制备技术(固相合成法、共沉淀法、水解法、自蔓延燃烧法)合成了摩尔分数为8%的钇掺杂氧化锆陶瓷粉体(8YSZ)。研究了不同制备技术对粉体粒度、比表面积和相结构的影响。探讨了pH、焙烧温度、研磨方式与研磨时间等条件因素对共沉淀法制备的8YSZ粉体相结构和粒度的影响。同时对其密度、抗弯强度和离子电导率进行了测试表征。结果表明:共沉淀法制备的8YSZ粉体,控制pH=8~10均可以合成出单一相的样品;焙烧温度对8YSZ粉体结晶度有较大影响,1000℃以上焙烧可生成结晶度较好的粉体;球磨和砂磨方式分别能控制粉体粒度在10μm和1μm以下。此外,共沉淀法制备的8YSZ粉体密度和抗弯强度分别达到了5.78 g·cm^(-3)和207.7 MPa,其在500~750℃具有良好的Arrhenius电导线性关系(相关系数为0.9927)和最低的电导活化能(0.70 eV·K^(-1))。