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1.
The reactive sintering of zinc ferrite, i.e. firing without previously calcining, has been studied using three types of iron oxide. The conversion into ferrite as well as the simultaneous densification were investigated upon variations in morphology and impurity content. The formation reaction is shown to be accompanied by a strong increase of the median pore size. This phenomenon appears responsible for the generally smaller density of the final material as compared with single-phase sintering. It is shown that reactive sintering is inevitably accompanied by expansion, irrespective of molecular volume variations. A calcining step appears indispensable for the preparation of the highest quality of ferrites. 相似文献
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Xiaojun Guo Hudong Yan Shengguo Zhao Yutian Li Xiaohu Liang 《Advanced Powder Technology》2013,24(6):1034-1038
Using diammonium phosphate, calcium nitrate tetrahydrate and sodium bicarbonate as raw materials, hydroxyapatite (HAP) was facilely synthesized by solid-state reaction at room temperature. The crystallinity, phase, morphology and particle size of the products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry/differential thermal analysis (TG–DTA) and particle size analyzer. The influence of calcining temperature on the crystallinity and composition of HAP phase was also investigated. 相似文献
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纳米氧化锌-煅烧高岭土复合材料的制备 总被引:1,自引:0,他引:1
以煅烧高岭土和纳米氧化锌为主要原料,用水解沉淀法在煅烧高岭土表面包覆纳米氧化锌,制备一种无机复合型抗紫外材料;采用分光光度计分别测定在波长325、350、375、400nm紫外光下复合材料的紫外光吸光度。结果表明:反应温度、氧化锌包覆量、改性时间、改性剂滴加速度、矿浆浓度、煅烧温度等对纳米氧化锌-煅烧高岭土复合粉体材料的紫外光吸收性能有重要影响。在制备条件为:氧化锌包覆量为8%、反应温度为90℃、改性时间为10min、改性剂滴加速度为3mL/min、矿浆中m(水)∶m(煅烧高岭土)=10∶1、煅烧温度为400℃时,所制备的纳米氧化锌-煅烧高岭土复合粉体材料的紫外光吸收性能较好。 相似文献
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晶体生长用TiO2纳米晶的改良工艺研究 总被引:4,自引:0,他引:4
针对晶体生长的具体应用,分别以硫酸氧钛铵(ATS)和改良硫酸氧钛铵(M-ATS)为原料,采用高温焙烧法制备了TiO2纳米晶,用XRD分析了原料和纳米晶的物相,用SEM分析了纳米晶的形貌,结果表明虽然两种原料具有相似的物相结构,但所得纳米晶的性状不同,M-ATS焙烧所得纳米晶分散性更高,均匀性更好,此外,研究了焙烧温度,保温时间,急烧,缓烧等工艺条件对纳米晶形貌,物相的影响,并给出了批量制备TiO2纳米晶粉体的最佳工艺条件。 相似文献
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This paper presents scientific and experimental data for low-firing hydraulic binders: hydraulic lime and Roman cement based on local mineral raw materials. The binders were prepared by firing representative samples of carbonate–clay magnesian raw materials from Tatarstan. Using X-ray diffraction, we identified the firing products, including a hydraulically active phase, and determined the structural characteristics of its minerals. The compositions of the binders were determined as functions of firing conditions. We examined the influence of the firing temperature and duration of magnesian raw materials in the preparation of binders on MgO activity and demonstrated for the first time the possibility of ensuring an active state of the MgO resulting from firing (up to 21%) and suppressing its negative effect on Roman cement and hydraulic lime hardening processes. 相似文献
6.
《Materials Letters》2007,61(8-9):1615-1618
NiO nanoparticles have been successfully prepared by calcining malate gel, using basic nickel carbonate (BNC) and malic acid as the raw materials and H2O as the solvent. The reaction was studied by TG–DTA, XRD and FT-IR. The particle size and morphology of NiO nanoparticles was characterized by TEM. The results show that nickel malate could be formed by the reaction of BNC and malic acid; the gel was composed of nickel malate and residual malic acid; the precursor can translate into NiO nanoparticles completely at 400 °C under the air, and the as-prepared sample has a cubic crystal structure with about 14 nm of average diameter by the Scherrer formula. The NiO calcined at 400 °C for 1 h was of narrow particle size distribution, weak agglomeration and small particle size. The particle size of NiO increased with the increase in temperature. Compared with other methods, the developed method is simple and the raw materials were inexpensive, so that it has the potential for further scale-up application in the industry. Furthermore, the reason for the metallic nickel formation in the course of the preparation was explained. 相似文献
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PbTiO3纳米晶的制备及表征 总被引:2,自引:0,他引:2
以硬脂酸、乙酸铅和钛酸丁酯为原料用硬脂酸凝胶法合成PbTiO3纳米晶原粉,利用改进的烧结设备,同时采用N2气氛下预烧,通过调节N2和O2的流量控制烧结气氛,得到粒径重复性好的PbTiO3纳米晶,用差热分析,热重分析和X-射线衍射对合成过程进行了研究,用透射电镜考查纳米晶的粒度和形貌,用5DX-红外光谱仪对PbTiO3纳米晶的红外透射谱进行了测试分析。 相似文献
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The firing behaviour of two self-vitrifying ceramic materials, coming from a magmatic rock of the aplite type consisting basically of quartz, feldspar and kaolin, both in the raw and purified (iron-free) state, were investigated as a function of the compacting pressure over the range 14 to 280 MN m–2. The materials exhibit a linear relationship of firing shrinkage versus the logarithm of the cold compacting pressures in the temperature range where vitrification processes occur, while the linearity falls down outside this range. The iron oxide content lowers the vitrification temperature as well as the vitrification range. The observed linear relationship is quite similar to that exhibited by other self-vitrifying ceramic materials for wall and floor tiles previously investigated, and it does not seem to depend on the compacting characteristics of the powders. It has therefore to be related to the gradually growing glassy phases which arise during firing at increasing temperatures. This relationship may thus be considered as a general characteristic of the firing behaviour of strongly self-vitrifying ceramic materials when subjected to green density changes. 相似文献
14.
Positive temperature coefficient of resistance ceramics of composition (Ba0.89Ca0.08Pb0.03)TiO3 + Y2O3 + MnO + SiO2 have been produced using barium titanate powder with an average crystallite size of 125 nm prepared by calcining barium titanyl
oxalate at 900°C. The effect of firing temperature on their microstructure and electrical properties has been studied. The
results demonstrate that the ceramics possess semiconducting properties starting at a firing temperature of 1205–1215°C. The
room-temperature resistivity of the ceramics has a minimum at t
firing ≈ 1245–1250°C. The samples sintered at 1250–1260°C have the largest positive temperature coefficient of resistance. The highest
electric strength (360 V/mm at ρ25°C = 290 Ω cm) is offered by the thermistor materials sintered at 1260°C, which is 60–70°C below the firing temperature of analogous
ceramics produced by solid-state reaction. 相似文献
15.
硅藻土微粒负载纳米TiO2的制备 总被引:1,自引:0,他引:1
以硫酸氧钛为原料,硅藻土微粒为载体,尿素为沉淀剂,通过改变硫酸氧钛的浓度、硅藻土与二氧化钛质量比、尿素浓度、pH值、水解温度、反应时间和焙烧温度等工艺条件,采用混合均匀沉淀法制备出了硅藻土基负载型纳米二氧化钛.利用SEM和XRD对样品的结构性能进行测定,得出在最佳制备条件下,二氧化钛在硅藻土表面的最大覆盖率为75%,二氧化钛平均粒径为150nm,并初步探讨了二氧化钛粒子和载体之间的结合机理.该产品对模拟室内甲醛的降解实验表明,在可见光范围内本产品对甲醛的处理效果是明显的。 相似文献
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A process for preparation of PZT by precipitation from butoxide precursors is described. The reactivity of the powders during low temperature firing (calcining) has been determined using weight loss, x-ray diffraction, and DTA-TGA techniques. 相似文献
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Esmeralda Mendoza-Mendoza Karinjilottu P. Padmasree Sagrario M. Montemayor Antonio F. Fuentes 《Journal of Materials Science》2012,47(16):6076-6085
Lanthanum-based LaBO3 oxides adopting the very stable perovskite structure are currently considered attractive materials for a growing number of applications in the field of solid-state ionics. In particular, LaAlO3-based perovskites are promising electrolyte materials for solid oxide fuel cells because they show almost pure oxygen ion conductivity at low oxygen partial pressures and high temperatures as well as excellent thermal and chemical stability under the standard operating conditions. This article describes a low-temperature synthesis of pure and acceptor-doped perovskite-type LaAlO3 nanopowders via a facile and environmental-friendly molten salts method. Using hydrated metal nitrates and sodium hydroxide as raw materials, the proposed methodology consists of two steps: a mechanically induced metathesis reaction and short firing above NaNO3's melting point. The purpose of the first is twofold: i.e., to generate in situ the NaNO3 flux and to obtain a suitable precursor for the synthesis of the target materials in molten nitrates. Accordingly, pure and Mg- and/or Sr-doped LaAlO3 powders were obtained directly without using any purification step at temperatures ≤500 °C. When preparing the Mg-containing samples, NaNO2 was also added to the reaction mixture to increase melt reactivity. The formation of the target series in the molten salt is thought to proceed through a “dissolution–precipitation” mechanism with LaAlO3 particles precipitating during cooling from a solution oversaturated with reactants. Electrical properties of the as-prepared materials were measured as a function of temperature and frequency by means of impedance spectroscopy and found comparable to those shown by similar materials prepared using more complicated routes. 相似文献
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K. Qiu C. X. Wan C. S. Zhao X. Chen C. W. Tang Y. W. Chen 《Journal of Materials Science》2006,41(8):2429-2434
Porous calcium polyphosphate (CPP) scaffolds with different polymerization degree and crystalline phases were prepared, and
then analyzed by scanning electron microscopy (SEM), Thermmogravimetry (TG) and X-ray diffraction (XRD). Number average polymerization
degree was calculated by analyzing the calcining process of raw material Ca(H2PO4)2, as a polycondensation reaction. Amorphous CPP were prepared by the quenching from the melt of Ca(H2PO4)2 after calcining, and CPP with different polymerization degree was prepared by controlling the calcining time. Meanwhile,
CPP with the same polymerization degree was prepared to amorphous or different crystalline phases CPP which was made from
crystallization of amorphous CPP. In vitro degradation studies using 0.1 M of tris-buffered solution were performed to assess the effect of polymerization degree or
crystalline phases on mechanical properties and weight loss of the samples. With the increase of polymerization degree, the
weight loss during the degradation decreased, contrarily the strength of CPP increased. The degradation velocity of amorphous
CPP, α-CPP, β-CPP and γ-CPP with the same polymerization degree decreased in turn at the same period. The full weight loss
period of CPP can be controlled between 17 days and more than 1 year. The results of this study suggest that CPP ceramics
have potential applications for bone tissue engineering. 相似文献
20.
Cubic Al5O6N nanocrystals were successfully synthesized via a novel strategy called shock wave plasma technique, using trinitrotoluene (TNT) and aluminum powder as raw materials and water as protection medium. The precursor including carbon and Al5O6N was engendered firstly during the detonation of compound dynamite, and then the pure Al5O6N nanoparticles were obtained when the carbon was removed through calcining at high temperature. The precursor and the final as-synthesized Al5O6N powder were characterized by X-ray diffraction (XRD), Raman spectrum and high-resolution transmission electron microscope (HRTEM), respectively. The calcining temperature schedule of the precursor was decided through DTA/TG analysis. The results indicate that the precursor consists of 37.7% carbon and 62.3 °C Al5O6N. After calcining at 600 °C for 1 h, the average diameter of the as-synthesized Al5O6N nanocrystal is 30-40 nm and the morphology micrograph takes on uniform spherical shape. The lattice parameters are consistent completely with the standard cubic Al5O6N (JCPDS 48-0686). The well-dispersed Al5O6N nanocrystals synthesized by shock wave plasma technique can be attributed to the covering of carbon and fast cooling of water medium. A possible reaction mechanism was also proposed preliminarily based on the experimental results. 相似文献