共查询到20条相似文献,搜索用时 15 毫秒
1.
O. V. Al’myasheva E. N. Korytkova A. V. Maslov V. V. Gusarov 《Inorganic Materials》2005,41(5):460-467
Thermodynamic analysis of phase equilibria in the Al2O3-H2O system at temperatures from 120 to 380°C and pressures from 1 to 70 MPa is carried out, and the dehydration of aluminum hydroxide under hydrothermal conditions is studied experimentally. The results indicate that -AlOOH (boehmite), which commonly appears in experimental phase diagrams, is a nonequilibrium phase in these temperature and pressure ranges. The dehydration rate and mechanism are shown to strongly depend on the crystallinity of the parent aluminum hydroxide and the pressure in the hydrothermal system.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 540–547.Original Russian Text Copyright © 2005 by Almyasheva, Korytkova, Maslov, Gusarov. 相似文献
2.
Yaxin Sun Longhui Zhu Xiumei Song Dongli Yu Yanguo Liu 《Journal of Superconductivity and Novel Magnetism》2012,25(6):1735-1741
Ultrafine nanostructured MgB2 bulks with an average grain size less than 10 nm have been fabricated by high-energy ball milling and subsequent high pressure sintering. Microstructural evolution in MgB2 subjected to high-energy ball milling has been investigated by means of X-ray diffraction (XRD). The finer grain size of MgB2 powders of about 7 nm has been estimated from Rietveld refinement analysis of XRD data, which is confirmed by a transmission electron microscope (TEM) observation. There is almost no grain growth in the subsequent sintering at low temperature of 600?°C under pressure of 3?C5 GPa for 10?C30 min. The nanocrystalline MgB2 bulks exhibit the lower onset critical transition temperatures (T c onset) of 32?C33?K. The relative wider width of the magnetic hysteresis loops at high external magnetic field and the higher critical current density (J c ) are obtained in nanocrystalline bulks. J c is as high as 105?A/cm2 in 8?T at 10?K and 2.7×103?A/cm2 in 4?T at 20?K. 相似文献
3.
4.
KTa0.6Nb0.4O3粉体溶剂热和水热法合成的对比研究 总被引:1,自引:0,他引:1
以Nb2O5和Ta2O5为前驱反应物,KOH为矿化剂,采用水热法和溶剂热法两种合成工艺制备了KTa1-xNbxO3(KTN)陶瓷粉体.实验结果表明,反应溶剂(水/异丙醇)和矿化剂KOH的摩尔浓度是影响KTN粉体结构和形貌的关键因素.采用水热工艺制备的KTN粉体,当KOH浓度达到3mol/L、反应温度为523K、反应时间8h时,开始出现以焦绿石结构为主的KTN粉体;随着KOH的浓度和反应温度的增加,粉体中的钙钛矿结构成分随之增加,而焦绿石结构则逐渐减少,但始终难以完全消除.采用溶剂热法,在KOH浓度1-2mol/L、反应温度523K、反应时间8h的条件下,合成了立方相钙钛矿结构KTa0.6Nb0.4O3陶瓷粉体,KTN晶粒形状呈规则的立方体,尺寸约为30-50nm;最后对溶剂热法合成纳米粉体的机理进行了分析讨论. 相似文献
5.
6.
以P123为表面活性剂,采用水热法合成CeO2纳米管.研究反应时间、反应温度、表面活性剂浓度对CeO2纳米管形成的影响规律.采用TEM、XRD、N2吸脱附仪对样品的微观结构进行表征.并考察CeO2纳米管对亚甲基蓝溶液的催化性能.结果表明,当反应时间为72 h、反应温度为160℃、n(P123):n(CeCl3.7H2O)=1:5时,可制备出单晶结构的CeO2纳米管.所制备的CeO2纳米管外径为40~60nm,内径为20 nm左右,长度为500~1000nm.CeO2纳米管是由Ce(OH)3晶种的溶解再结晶-异向生长-自我卷曲形成的.相对于CeO2纳米颗粒和CeO2纳米棒,CeO2纳米管对亚甲基蓝染料的脱色率有明显提高.这与CeO2纳米管孔道的吸附作用,暴露的高反应活性面(110)和表面有大量缺陷有关. 相似文献
7.
Yu. V. Kolen'ko A. A. Burukhin B. R. Churagulov N. N. Oleinikov 《Inorganic Materials》2004,40(8):822-828
Data are presented on the phase composition and physicochemical properties of nanocrystalline TiO2 powders prepared via hydrothermal treatment of aqueous titanyl sulfate (TiOSO4), titanyl nitrate (TiO(NO3)2), and aqua complex titanyl oxalate acid (H2TiO(C2O4)2) solutions and amorphous titanyl hydroxide (TiO2 · nH2O) gel (synthesized by precipitating H2TiCl6 with an excess of aqueous ammonia) at 423 and 523 K for 10 min to 6 h at solution concentrations from 0.07 to 0.5 M. The synthesized samples were characterized by x-ray diffraction, thermogravimetry, transmission electron microscopy, and nitrogen BET surface area measurements. It is shown that, independent of the precursor, short-term (10 min) hydrothermal treatment leads to the formation of nanocrystalline anatase (crystallite size d = 10–30 nm), a metastable form of titania. Upon an increase in hydrothermal-treatment time to 6 h, the systems studied exhibit different behaviors. Nanocrystalline anatase may persist (titanyl sulfate solutions and amorphous titanyl hydroxide gel) or transform into rutile (d = 50–100 nm), the thermodynamically stable form of TiO2, through recrystallization processes (titanyl nitrate solutions; 0.07 M H2TiO(C2O4)2 solutions, partial conversion at 423 K and full conversion at 523 K; 0.28 M H2TiO(C2O4)2 solutions, full conversion at 423 K). Also possible is the formation of mesoporous anatase (0.28 M H2TiO(C2O4)2 solution, 523 K, 70- to 90-nm aggregates of crystallites, 10- to 20-nm closed pores containing the solution). A model is proposed according to which the formation of mesoporous oxides is possible at comparable rates of anatase nucleation and growth. 相似文献
8.
9.
10.
11.
《中国粉体技术》2015,(3):16-20
以碳酸铈为铈源,以硅溶胶为硅源,通过喷雾干燥法制备Ce O2-Si O2复合氧化物前驱体,再通过煅烧得到复合抛光粉;利用X射线衍射、扫描电子显微镜、激光粒度仪、zeta电位仪对复合抛光粉的晶体结构、表面形貌、粒径分布、zeta电位进行表征,并进行抛光性能研究。结果表明:当Ce O2与Si O2的质量比大于2∶1时,复合抛光粉中的Si O2能完全掺杂到Ce O2中,并且抛光效果优于Ce O2和Si O2抛光粉的;当Ce O2与Si O2的质量比为4∶1时,复合抛光粉的粒径d50为0.985μm,抛蚀量为0.296 0 g,表面划痕少,抛光效果最好。 相似文献
12.
13.
14.
纳米氧化钛陶瓷的烧结 总被引:3,自引:0,他引:3
将醇盐水解制备的纳米氧化钛粉体(~13nm)在500~800℃下煅烧,用XRD研究氧化钛相变过程中粉体的热稳定性,发现在加入0.4wt%的金红石相作为晶种后;晶粒生长受到较好的控制,同时分别在30、57和200MPa下对纳米氧化钛样品进行热压烧结,用密度仪、压汞仪和SEM对烧结前后的样品进行表征后表明,700℃的热压烧结样品已开始致密化,200MPa、800℃热压烧结样品的相对密度为97.2%,此时3~15nm的小气孔仍难以消除,这些小气孔的存在是纳米氧化钛陶瓷在较高的压力下难以完全致密的主要原因. 相似文献
15.
16.
本文对管道反应制备的纳米微晶ZrO2(Y2O33mol%)粉末的模压数据进行处理.结果表明,该ZrO2粉末压形规律遵循黄培云压形方程.根据黄培云压形方程计算出纳米微晶ZrO2陶瓷粉体的压制模量为11.9~12.7MPa,压制过程的非线性指数为7.15.成形剂量的增加将降低粉末体的压制模量,而其非线性指数却保持不变.结合ZrO2压坯的孔隙、孔径测定,分析得出纳米微晶ZrO2粉末理想的成形压力范围应在40-140MPa;这为纳米微晶ZrO2粉末压形提供了理论基础. 相似文献
17.
CoMnNiO超微细粉体的合成及烧结特性 总被引:1,自引:0,他引:1
以醋酸盐为原料,用喷雾热分解方法(EDS)合成了粒径小于30nm的CoMnNiO纳米粉体。粉体压片后,在600~1000℃温区处理,XRD谱观察了烧结体的不同温度下的晶粒尺寸和相变。烧结体断层的SEM观察表明,纳米粉体的烧结体制不同于常规氧化物粉体,纳米粉体中颗粒的亚结构对烧结过程有显著影响。 相似文献
18.
19.
溶胶-凝胶法制备堇青石粉体的固相反应过程和烧结性的研究 总被引:1,自引:0,他引:1
将TEOS,镁铝硝酸盐以及一定量的尿素溶于乙醇-水溶液。100℃水浴加热形成凝胶。凝胶干燥后,高温煅烧可得到一种镁铝硅复合氧化物粉体。对在不同温度下煅烧的粉体和1350℃烧结的样品进行X射线衍射分析,发现在煅烧过程中,基体形态经历了从无定形态向晶态α-堇青石的转化过程,并伴随有μ-堇青石相,镁铝尖晶石相和β-石英固溶体的出现和消失。1350℃烧结的样品全部为α-堇青石相,烧结致密度最高达99.5%。以扫描电镜观察该样品的表面形貌,可看出其晶粒呈薄片状。并对纯堇青石的致密化烧结过程进行了探讨。 相似文献