共查询到20条相似文献,搜索用时 218 毫秒
1.
以金属硝酸盐为原料,通过乙二胺四乙酸(EDTA)络合法制备了尖晶石型Ni1-xZnxFe2O4(x=0.0-0.7)晶体。通过TG-DTA考察了制备过程,采用XRD、FT-IR、SEM和VSM等对产物进行了表征,研究了热处理温度和Zn取代量对晶型结构和磁学性质的影响。同传统的固相法相比(1300℃/20h),制备单相Ni-Zn铁氧体所需的焙烧温度降至700℃,焙烧时间缩短至2h。随着Zn取代量的增加,晶胞参数递增,而矫顽力(Hc)和居里温度(Tc)逐渐下降。饱和磁化强度(Ms)随Zn取代量呈先递增至x=0.4后再逐渐下降。在1.5MHz的交变磁场中,所制粒子的感应温度接近设计的居里温度,能够适于感应加热的应用。 相似文献
2.
3.
4.
5.
以β-环糊精和氯乙酸为原料,通过亲核取代反应制备了混凝土减水剂羧甲基-β-环糊精(CM-β-CD),讨论了反应物物质的量比、反应温度和反应时间对CM-β-CD的取代度及应用性能的影响。结果表明,当氯乙酸与β-环糊精物质的量比为6∶1、反应温度为60℃、反应时间为5h时,所得CM-β-CD的取代度最大为0.68。水泥净浆实验表明净浆流动度随着取代度的增加而增加,减水剂的最佳掺量为0.8%,减水率为23.5%。红外光谱(FTIR)和核磁共振光谱(NMR)检测结果表明β-环糊精和氯乙酸发生了反应。 相似文献
6.
7.
8.
9.
利用热重法(TG)和差示扫描量热法(DSC)研究了不同取代度的纤维素油酸酯(CO)在氩气中的热降解及热降解动力学。为确定CO的热降解动力学参数,首先采用Kissinger法计算反应级数n,再利用Coats-Redfern法计算活化能Ea和频率因子A,计算结果适用于起始降解温度(Td)到最大降解速率温度(Tp)附近的温度范围。计算结果表明,CO热降解反应级数n随取代度的增加由2.9(S1)下降为1.4(S3);CO的Td和Tp均随取代度的增加而降低,说明CO的热稳定性随取代度的增加而降低;活化能Ea和频率因子A同样随取代度的增加而降低。 相似文献
10.
采用干法制备马来酸酐酯化淀粉,研究了反应温度和时间对酯化淀粉性能的影响。采用红外光谱(FT-IR)证明了马来酸酐成功酯化到淀粉上。利用化学滴定法、X射线衍射(XRD)、差示扫描量热法(DSC)和热重分析(TGA)对酯化淀粉的取代度、结晶结构、糊化温度和热稳定性进行了分析。结果表明,随着反应温度升高和时间延长,取代度逐渐增大。酯化反应一定程度上破坏了淀粉的结晶结构,随反应温度升高和反应时间延长,结晶度逐渐降低。糊化温度和热稳定性跟酯化淀粉的结晶度密切相关,结晶度降低,糊化温度和热稳定性都逐渐降低。 相似文献
11.
研究了烧结温度及升温速率对氧化硼(B2O3)掺杂钛酸锶钡梯度陶瓷(Ba1-xSrxTiO3,x=0-0.4,步长0.02)的致密化、晶粒尺寸及介电性能的影响.结果表明,随着烧结温度的升高,在氧化硼挥发的同时致密化程度提高,从而居里峰提高且变得尖锐;随着氧化硼含量的增加,晶粒尺寸均匀长大、介电常数和介电损耗都增加;升温速率适中时,掺杂物的挥发、致密化进程及晶粒长大同步完成,梯度陶瓷介电性能才有效提高.此外,钛酸锶钡梯度陶瓷掺杂适量氧化硼明显降低烧结温度,比未掺杂相同成分的陶瓷烧结温度至少降低150℃,且介电损耗明显减小;梯度陶瓷的居里峰温度区间显著展宽,大大降低了该温区的介温系数,可望提高该系列陶瓷元器件精度及稳定性. 相似文献
12.
Gitanjali Dhir Poonam Uniyal N. K. Verma 《Journal of Superconductivity and Novel Magnetism》2014,27(6):1569-1577
In the present report, influence of Dy-substitution and size on the structural, magnetic and dielectric properties of BiFeO3 nanoparticles has been investigated. The synthesis of pure and Dy-doped BiFeO3 nanoparticles has been done successfully using sol–gel method. Size of Dy-doped BiFeO3 nanoparticles was tailored by varying the calcination temperature. Structural analysis reveal that substitution of Dy3+ leads to a change in structure from rhombohedral (x=0) to orthorhombic (x=0.15). The average crystallite size varies from 6 to 15 nm. Magnetic study reveals the enhancement in magnetization with the doping of Dy3+. Further, this value decreases as the particle size increases. Dielectric property improves with the Dy3+ substitution. All the nanoparticles display Debye-type relaxation. The low dielectric loss values observed are attributed to the nanosized grains. Remarkably, enhanced saturation magnetization value (13.8 emu/g) and dielectric constant value (95.8) were observed for Dy-doped BiFeO3 nanoparticles having the smallest particle size. Thereby, the study indicates strong correlation between size and multiferroism. 相似文献
13.
为了研究掺杂BarSr1-xTiO3介电薄膜材料的性能,采用阻抗分析仅等测试方法研究了微量元素钇对Sr0.5Ba0.5-yYyTiO3薄膜介电性能的影响。当Y元素的掺量为0-0.030mol时,相对介电常数εr和tanδ分别为74.2和0.067;最大介电常数温度点Tm(居里温度点)逐渐移向低温;在所测试频率范围内,Y元素的掺量为0.010、0.0150mol(Y2、Y3)时,εr、tanδ均能表现出较好的频散特性。采用XRD、TEM等测试方法分析了薄膜的结构特征。薄膜的矿物组成为四方钙钛矿结构,但Y的溶入改变了晶胞参数的c/a比,减小了薄膜的颗粒尺寸,提高了薄膜的致密度;晶粒的生长为取向一致和无取向生长两种方式。 相似文献
14.
The effects of La3+ partial substitution for Ba2+ on crystal structure and dielectric properties were investigated for modification of Ba5LaTi3Ta7O30 ceramics. When the substitution x > 0.6, the sintering temperature obviously decreased. Superstructure peaks were observed for more La3+ substitution (x ≥ 2.4). The stability of the tetragonal tungsten bronze phase was discussed with electronegativity difference and tolerance factor. Lattice parameters decreased at first, and then slightly increased; while axial ratio decreased with increasing La content. Dielectric constant slightly increased when x < 1.2, then gradually declined with the increase of La substitutions for Ba. Dielectric loss was very low except x = 2.4. Temperature coefficient of dielectric constant (at 1 MHz) was remarkably improved. The variation of dielectric properties was discussed from the change of crystal structure as well as the effects of vacancies at A-sites and superstructure. 相似文献
15.
本文研究了TiCl4对Urea-ZnCl2离子液体体系电化学行为的影响。结果表明:TiCl4的加入能够提高Urea-ZnCl2离子液体的电导率,促进钛以Zn-Ti合金的形式沉积。在铜基体上进行恒电位沉积,可获得均匀致密的Zn-Ti合金层,且晶粒尺寸随沉积温度的升高而增大。 相似文献
16.
Ying Yuan Enzhu Li Bin Tang Li Bo Xiaohua Zhou 《Journal of Materials Science: Materials in Electronics》2012,23(1):309-314
The effects of ZnO and CeO2 on the microstructure and dielectric temperature characteristics of the Mn-modified (Bi0.5Na0.5)0.88Ca0.12TiO3 ceramics were investigated to develop temperature-stable dielectric ceramics. By adding 1–2 wt% ZnO, the overall dielectric
constant increased. With further increasing the amount of ZnO, the dielectric constant at temperatures lower than 25 °C decreased,
whereas the dielectric constant at temperatures higher than 75 °C increased. The temperature characteristic of capacitance
became flatter when more than 4 wt% ZnO was doped. By adding CeO2, the dielectric constant decreased and a flat temperature characteristic of permittivity was obtained. X-ray diffraction
analysis revealed that the perovskite BNT phase formed for all the compositions and the secondary phases Zn2TiO4 and Bi2Ti2O7 occurred, respectively when ZnO and CeO2 was added. Scanning electron microscope indicated that an inhomogeneous microstructure comprising fine and rectangle grains
was observed in the ZnO-free sample. ZnO less than 2 wt% could inhibit the grain growth and decrease long grains. However,
the grain growth was promoted as more than 8 wt% ZnO was added. The dielectric loss with different contents of ZnO and CeO2 were characterized as the function of temperatures for potential use at high temperature. The dielectric loss at 25 °C was
independent of the amounts of ZnO and CeO2. However, the dielectric loss at 250 °C decreased by adding 1 wt% ZnO and then increased with increasing ZnO. This system
is considered to be a potential material for high-temperature capacitors. 相似文献
17.
Dielectric Properties of Porous Reaction-boned Si3N4 Ceramics with Controlled Porosity and Pore Size
This paper presents the microwave dielectric properties of reaction bonded porous silicon nitride ceramics with variant porosity and pore size, which were prepared by adding pore-forming agent grains into the silicon powders. The experimental results show that the dielectric constant and the dielectric loss of the samples reduce evidently with increasing porosity in the sample. When the porosity is constant, the dielectric constant and the dielectric loss of the ceramics decrease visibly as the pore size increases. Among all the obtained samples, the minimum dielectric constant is about 2.4. 相似文献
18.
采用固相反应法合成具有焦绿石立方结构的Bi1.5ZnNb1.5O7(BZN)陶瓷靶材,采用脉冲激光沉积法在Pt/SiO2/Si(100)基片制备立方BZN薄膜。研究了随衬底温度的变化,薄膜的结晶性能,微观形貌以及介电性能的差异。结果表明当衬底温度在550~650℃时,薄膜具有纯的立方BZN结构,并且在600℃时薄膜的晶粒发育比较完整,此时薄膜具有较高的介电常数和较低的损耗。 相似文献
19.
Mongi Amami Shara. A. Dulmani Lamia Ben Farhat 《Journal of Superconductivity and Novel Magnetism》2018,31(11):3525-3533
Multidoped (Zn,Ti) gallium orthoferrite [GaFeO3 and Ga0.98Zn0.02Fe0.98Ti0.02O3] ceramic was synthesized through a solid-state reaction. X-ray analysis of the prepared material provides its basic crystal data of a single-phase orthorhombic system. The scattered crystallite size and lattice strain of the material were estimated. Analysis of the micrograph of field emission scanning electron microscope shows uniform grain distribution in the sample, suggesting the formation of good quality of sample. Founded on the magnetic measurements, it is concluded that (Zn,Ti)-modified gallium ferrite has provided a reduction in the Curie temperature (TC); however, no significant changes in the magnetization values with Zn and Ti integration in GaFeO3 lattice. A noteworthy effect of substitution of multiple elements at the Ga and Fe sites on dielectric constant and tangent loss of GaFeO3 has been observed. Complete studies of temperature (180–400 K) and frequency (10–107 Hz) dependence of dielectric constant and impedance have provided the effect of grains and grain boundaries on the conduction mechanism and dielectric relaxation of the material. 相似文献
20.
Yadav KL 《Journal of nanoscience and nanotechnology》2011,11(3):2682-2686
Multiferroic compounds with general formula BiFe(1-x)Ti(x)O3 (x = 0.1, 0.2, 0.3 and 0.35) have been synthesized by conventional solid state reaction method. The effect of Ti substitution on ferroelectric and magnetic properties is studied. From X-ray diffraction (XRD) analysis, a rhombohedral to orthorhombic phase transition for x > 0.3 was observed. From SQUID measurements, a magnetic field induced phase transition has been observed in the BiFe(1-x)T(x)O3 system for x = 0.3. An anomaly in dielectric constant and dielectric loss in the vicinity of antiferromagnetic Néel temperature (T(N)) and a small enhancement in magnetization have been observed. Magnetization measurements above room temperature showed no systematic variation in antiferromagnetic Néel temperatures on Ti substitution. Further it is seen that this system shows the coupling between electric and magnetic dipoles exhibiting magnetoelectric (ME) effect at room temperature and possess high dielectric constant. 相似文献