Nanocrystalline ceria powders through citrate-nitrate combustion

Nanocrystalline ceria powders have been synthesized by combustion technique using citric acid as a fuel and nitrate as an oxidizer. The auto-ignition of the gels containing cerium nitrate and citric acid resulted in ceria powders. A theory based on adiabatic flame temperature for different citric acid-to-cerium nitrate molar ratios has been proposed to explain the nature of combustion reaction and its correlation with the powder characteristics. Specific surface area and primary particle size of the ceria powder obtained through fuel-deficient precursor was found to be approximately = 127 m2/g and 2.5-10 nm, respectively. The combustion synthesized ceria powder when cold pressed and sintered in air at 1250 degrees C for 1 hour resulted in approximately = 96% of its theoretical density with sub-micron grains.     

Glycine-nitrate combustion synthesis of nonstoichiometric Mg-Fe spinel nanopowders

Nanopowders based on MgFe_{2 + δ}O_{4 + 1.5δ} (δ = 0.1–8.0) Mg-Fe spinels with an average crystallite size from 45 to 60 nm have been prepared by glycine-nitrate combustion synthesis. As a result of the high combustion temperature (near 1330°C), the phase composition of the synthesized powder corresponds to the equilibrium one.     

焙烧温度对醋酸盐体系液相燃烧合成尖晶石型LiMn2O4的影响

以醋酸锂、醋酸锰为原料，尿素为燃料，用液相燃烧合成方法制备尖晶石型LiMn2O4物质，考察了焙烧温度（300-800℃焙烧5h）对产物的组成结构、晶粒大小及电化学性能的影响。实验结果表明，未焙烧产物中主晶相为LiMn2O4及少量Mn2O3，但在300-800℃焙烧5h后都可得到单相的LiMn2O4粉体材料，焙烧温度为900℃时，LiMn2O4部分分解为Mn3O4；产物颗粒随焙烧温度升高而长大，≤600℃时，产物颗粒〈100nm，≥700℃时产物颗粒〉100nm，可观察到LiMn2O4的特征八面体结构；在焙烧温度800℃以下，产物的电化学性能随焙烧温度的升高而增加。当电流密度为C/3时，焙烧温度为800℃的首次放电容量为105mAh／g，但循环性能较差，30次循环后仅剩83％。     

Nanocrystalline spinel ferrites by solid state reaction route

Nanostructured NiFe₂O₄, MnFe₂O₄ and (NiZn)Fe₂O₄ were synthesized by aliovalent ion doping using conventional solid-state reaction route. With the doping of Nb₂O₅, the size of NiFe₂O₄ is reduced down to 33 nm. Similarly, nanostructured manganese ferrites (MnFe₂O₄) with diameters in the range of 45–30 nm were synthesized by Ti⁴⁺ ion doping. Particle diameters in all the specimens are found to decrease with increasing dopant content. The substitution of Nb⁵⁺ or Ti³⁺ ions essentially breaks up the ferrimagnetically active oxygen polyhedra. This created nanoscale regions of ferrites. Saturation magnetization and coercive field show a strong dependence on the size of the ferrite grains. Superparamagnetic behaviour is observed from the Mössbauer spectra of nanostructured NiFe₂O₄, if the particle size is reduced to 30 nm. Zero field cooled and field cooled curves from 30 nm sized MnFe₂O₄ particles showed a peak at T _B (～ 125 K), typical of superparamagnetic blocking temperature. These results are explained in terms of core/shell structure of the materials. The d.c. resistivity of the doped specimens decreases by atleast five orders of magnitude compared to pure sample. This is ascribed to the presence of an interfacial amorphous phase between the sites.     

Glycerol-assisted solution combustion synthesis of improved LiMn2O4

Spinel LiMn₂O₄ has been synthesized by a glycerol-assisted combustion synthesis method. The phase composition and morphologies of the compound were ascertained by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical characterization was performed by using CR2032 coin-type cell. XRD analysis indicates that single phase spinel LiMn₂O₄ with good crystallinity has been obtained as a result of 5 h treatment at 600 °C. SEM investigation indicates that the average particle size of the sample is 200 nm. The initial discharge specific capacity of the LiMn₂O₄ is 123 mAh/g at a current density of 30 mA/g. When the current density increased to 300 mA/g, the LiMn₂O₄ offered a discharge specific capacity of 86 mAh/g. Compared with the LiMn₂O₄ prepared by a conventional solution combustion synthesis method at the same temperature, the prepared LiMn₂O₄ possesses higher purity, better crystallinity and more uniformly dispersed particles. Moreover, the initial discharge specific capacity, rate capability and cycling performance of the prepared LiMn₂O₄ are significantly improved.     

In situ synthesis of titanium diboride composites through volume combustion

Abstract

Hard in situ synthesis of TiB₂–Fe₂B metal matrix composite (MMC) has been synthesised by volume combustion synthesis (VCS) reactions of Fe–FeTi–FeB system. VCS samples were characterised by SEM, EDX, XRD and DTA. Results show that it is possible to synthesise in situ structured MMC samples (with TiB₂ and Fe₂B phases) by VCS. Metallographic investigations show that Fe₂B and TiB₂ are found dispersed throughout the metal matrix, and other borides are present in microlevel patches dispersed in a eutectic matrix. The Fe–TiB₂ composites sintered at temperature of 1200°C consist of three different regions, i.e. α-Fe, TiB₂ and Fe₂B regions. The increase in sintering temperature to 1400°C leads to a hypereutectic microstructure of the Fe–B binary system having TiB₂ grains uniformly distributed throughout the matrix. A semiliquid phase sintering occurred by increasing eutectic phase transformation temperatures to 1400°C, which increased the efficiency of VCS. On the other hand, increasing sintering time from 1 to 3 h decreased the volume fraction of α-Fe and increased the volume fraction TiB₂ phase.     

Influence of fuels and combustion aids on solution combustion synthesis of bi-phasic calcium phosphates (BCP)

The possibility to obtain biphasic HA/TCP composite by solution combustion synthesis method using urea and glycine as fuels was investigated. Calcium nitrate was taken as a source of calcium, and diammonium hydrogen phosphate served as a source of phosphate ions. Nitric acid and nitrate ions were used as oxidizers. The effect of the nature of fuel (urea and glycine) and fuel to oxidizer ratio on the combustion behavior, as well as, chemical composition and morphology of as-formed powders was investigated. It was found that only monoclinic-TCP was formed in the combustion end-product when glycine was used. In contrast to this, the use of certain amount of urea led to the formation of rhombohedral-TCP. A series of combustion reactions were carried out to study the influence of fuel to oxidizer ratio on HA to TCP ratio in synthesized product.     

Visible photocatalytic activity of Ti-doped LaNi03 synthesized by solution combustion synthesis

采用溶液燃烧法制备了一系列不同Ti掺杂量的LaNiO3光催化剂,研究了Ti掺杂量对其相结构、形貌和光催化性能的影响。采用XRD、SEM、EDS及光致发光光谱（PL）等对其进行了表征和分析。结果表明：采用溶液燃烧法可获得单一钙钛矿相的LaNiO3,随着Ti掺杂量的增加,晶面间距逐渐增大;Ti掺杂量对颗粒的形貌大小影响较小,颗粒近似球形,粒径分布均匀,约为80nm。可见光催化实验结果表明,当Ti掺杂量为3．0％（质量分数）时,所得催化剂的催化效果最好,适量的Ti掺杂可显著降低光生载流子的复合几率。     

Pd掺杂纳米ZnO的燃烧法制备及性能研究

以酒石酸为燃料,硝酸锌为氧化剂,采用溶液燃烧法制备了Pd(0~7%(原子分数))掺杂纳米Zn O。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和荧光光谱仪对产物了进行表征,重点讨论了掺杂对Zn O气敏性能的影响。结果表明,在330℃测试条件下,纯Zn O和7%(原子分数)Pd掺杂Zn O气敏元件对体积分数为5.0×10-5的乙醇气体灵敏度分别为21.4和11.2;元件对5.0×10-5丙酮气体的灵敏度分别为2.0和8.8。Pd掺杂显著提高了元件对乙醇和丙酮气体的选择性。     

An investigation of the synthesis of nickel aluminides through gasless combustion

The formation of nickel aluminidms by the thermal explosion mode of gasless combustion synthesis was investigated for Ni-Al powders ranging in composition from 5 to 3O at% Al. Compound formation was found to take place sequentially starting with the most aluminium-rich and ending with AlNi₃ as the predominant compound in the product. Compounds formed through both solid- and liquid-sate reactions, with the relative contribution of each depending on the rate of heating of the powders to the reaction temperature. The effect of the particle size of nickel on these reactions vvasalso investigated for powders with average diameters from 14 to 58m.     

Synthesis of ZnO nanoparticles through the impregnated layer combustion synthesis process

Zinc oxide nanopowders were synthesized by a solution combustion technique named impregnated layer combustion synthesis (ILCS), involving the impregnation of an active layer with the reactant solution and subsequently the combustion of the impregnated system. In this work three different organic fuels and two different ignition modes were tested in order to optimize the final microstructure and specific surface area (SSA) of the ZnO nanopowders. In particular, the ignition mode was found to significantly affect the final products, discriminating between an explosion procedure (flame combustion) and a self-propagating mode (smoldering combustion). The nitrate–glycine mixture and the smoldering combustion way were found to be the most suitable conditions, giving rise to softly agglomerated nanopowders with an average size of 20 nm and a very high SSA, without the need of any further crystallization treatment.     

Mixture of fuels approach for the solution combustion synthesis of LaAlO3 nanopowders

A modified solution combustion approach was used in the preparation of nanosize LaAlO₃ (～23.6 nm) using mixture of citric acid and oxalic acid as fuels with corresponding metal nitrates. The synthesized and calcined powders were characterized by Fourier transform infra red spectrometry (FTIR), Differential thermal analysis-Thermogravimetry analysis (DTA–TGA), X-ray diffractometry (XRD) and Transmission electron microscopy (TEM). The FTIR spectra show the lower frequency bands at 656 and 442 cm^?1corresponds to metal–oxygen bonds (possible La–O and Al–O stretching frequencies) vibrations for the perovskite structure compound. DTA confirms the formation temperature of LaAlO₃ varies between 830–835 °C. XRD results show that mixture of fuels ratio is influential on the crystallite size of the resultant powders. The average particle size of LaAlO₃-1 as determined from TEM was about 41 nm, whereas for LaAlO₃-2 and LaAlO₃-3 samples, particles are seriously aggregated.     

煅烧工艺对溶液燃烧合成超细ZrO2粉末的影响

以硝酸锆-尿素为原料,采用溶液燃烧合成(SCS)法制备了超细ZrO2粉末,着重研究了后续煅烧处理对合成的ZrO2粉末结构、尺寸和团聚程度的影响.结果表明,利用SCS法可以合成超细ZrO2粉末,对之进一步进行煅烧处理,可明显降低合成产物中残留有机物的含量,并改善合成粉末的分散性;在700℃煅烧1.0h的条件下,可以获得分散性好,粒径小(＜200nm)的ZrO2粉末.     

Effect of fuel characteristics on synthesis of calcium hydroxyapatite by solution combustion route

The effect of fuel characteristics on the processing of nano sized calcium hydroxyapatite (HA) fine powders by the solution combustion technique is reported. Urea, glycine and glucose were used as fuels in this study. By using different combinations of urea and glycine fuels and occasional addition of small amounts of highly water-soluble glucose, the flame temperature (T _f) of the process as well as product characteristics could be controlled easily. The powders obtained by this modified solution combustion technique were characterized by XRD, FTIR spectroscopy, SEM, FESEM-EDX, particle size analyser (PSD) and specific surface area (SSA) measurements. The particle size of phase pure HA powder was found to be <20 nm in this investigation. The effects of glucose addition with stoichiometric (μ = 1) and fuel excess (μ > 1) urea and glycine precursor batches were investigated separately.     

Synthesis of nano-sized hydroxyapatite powders through solution combustion route under different reaction conditions

Calcium hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ (HAp) was synthesized by combustion in the aqueous system containing calcium nitrate-diammonium hydrogen orthophosphate with urea and glycine as fuels. These ceramics are important materials for biomedical applications. Thermo-gravimetric and differential thermal analysis were employed to understand the nature of synthesis process during combustion. Effects of different process parameters namely, nature of fuel (urea and glycine), fuel to oxidizer ratio (0.6-4.0) and initial furnace temperature (300-700 °C) on the combustion behavior as well as physical properties of as-formed powders were investigated. A series of combustion reactions were carried out to optimize the reaction parameters for synthesis of nano-sized HAp powders. The combustion temperature (T_f) for the oxidant and fuels were calculated to be 896 °C and 1035 °C for the stoichiometric system of urea and glycine respectively. The stoichiometric glycine-calcium nitrate produced higher flame temperature (both calculated and measured) and powder with lower specific surface area (8.75 m²/g) compared to the stoichiometric urea-calcium nitrate system (10.50 m²/g). Fuel excess combustion in both glycine and urea produced powders with higher surface area. Nanocrystalline HAp powder could be synthesized in situ with a large span of fuel to oxidizer ratio (φ) in case of urea system (0.8 < φ < 4) and (0.6 < φ < 1.5) for the glycine system. Calcium hydroxyapatite particles having diameters ranging between 20 nm and 120 nm could be successfully synthesized through optimized process variable.     

Carbothermal reduction and nitridation synthesis of silicon nitride by using solution combustion synthesized precursors

Carbothermal reduction and nitridation synthesis of Si₃N₄ was investigated by using precursor powders prepared by a solution combustion synthesis method. Glycine or urea (fuel), ammonium nitrate (oxidizer), silicic acid (Si source), and sucrose (major carbon source) were dissolved completely in water. This solution was dried and then heated to undergo the solution combustion synthesis reaction, resulting in a homogeneous mixture of nano-sized carbon and SiO₂ particles, which was used as the precursor powder for the carbothermal reduction and nitridation synthesis of Si₃N₄. When the carbothermal reduction and nitridation reaction was carried out at 1,425–1,450 °C for 4 h, formation of Si₃N₄ can be detected only when the C/SiO₂ weight ratio is greater than ~2.0. The Si₃N₄ yield increases rapidly as the C/SiO₂ weight ratio is increased from ~2.0 to 2.8 and decreases with further increase in the C/SiO₂ ratio. The α-phase content increases with increasing C/SiO₂ weight ratio and decreases with increasing temperature. Depending on the C/SiO₂ ratio, a Si₃N₄ yield of ~80 wt% and an α-phase content of ~90 wt% could be obtained.     

pH值对溶液燃烧法制备纳米LaFeO3的影响

以硝酸镧和硝酸铁为氧化剂,柠檬酸为燃料,采用溶液燃烧法制备了钙钛矿型LaFeO3.通过XRD和SEM研究了分别以氨水和NaOH溶液为pH调节剂,前驱物溶液pH值对制备的纳米LaFe03粉体的晶相组成和微观形貌的影响.结果表明不同的pH调节剂和前驱物溶液pH值对燃烧产物的晶相组成、晶粒大小和微观相貌都有显著的影响.氨水调...     

Stress and phase purity analyses of diamond films deposited through laser-assisted combustion synthesis

Diamond films were deposited on silicon and tungsten carbide substrates in open air through laser-assisted combustion synthesis. Laser-induced resonant excitation of ethylene molecules was achieved in the combustion process to promote diamond growth rate. In addition to microstructure study by scanning electron microscopy, Raman spectroscopy was used to analyze the phase purity and residual stress of the diamond films. High-purity diamond films were obtained through laser-assisted combustion synthesis. The levels of residual stress were in agreement with corresponding thermal expansion coefficients of diamond, silicon, and tungsten carbide. Diamond-film purity increases while residual stress decreases with an increasing film thickness. Diamond films deposited on silicon substrates exhibit higher purity and lower residual stress than those deposited on tungsten carbide substrates.