In the preparation process of magnesium-cobalt nano-ferrite powder (Mg
0.1
Co
0.9
Fe
2
O
4
) by sol–gel self-propagation method, the effect of complexing agent on the nanostructure and magnetic ...properties of ferrite is studied by changing the type of complexing agent (the complexing agent includes citric acid, oxalic acid, tartaric acid, glucose, and egg white). The XRD pattern of each sample has eight distinct characteristic peaks, and the number of the strongest peak in each map is one i.e., (311) peak. All these evidences can preliminarily indicate that the sample has a spinel structure. In addition, in the FTIR of the sample, it can be seen that there are several distinct characteristic peaks at 580 cm
−1
(i.e., Fe–O peak, etc.) which can also prove the structural characteristics of the sample. In the SEM map, the sample can be seen to have an elliptical shape with a crystalline grain size between 28 and 50 nm. From this, we can guess that the complexing agent participates in the reaction and has a certain influence on the particle size of the sample. Elemental analysis showed that all the six samples prepared contained magnesium, cobalt, iron, and oxygen, and then we quantitatively analyzed the sample to find that the prepared sample was the target product. The BET test shows that a sample is prepared with glucose as the complexing agent, the specific surface area of it can be increased. The VSM data show that magnesium–cobalt ferrite powder with high saturation magnetization, residual magnetization, and coercivity can be prepared by selecting glucose as the complexing agent.
Vibration monitoring is one of the most effective approaches for bearing fault diagnosis. Within this category of techniques, sparsity constraint-based regularization has received considerable ...attention for its capability to accurately extract repetitive transients from noisy vibration signals. The optimal solution of a sparse regularization problem is determined by the regularization term and the data fitting term in the cost function according to their weights, so a tradeoff between sparsity and data fidelity has to be made inevitably, which restricts conventional regularization methods from maintaining strong sparsity-promoting capability and high fitting accuracy at the same time. To address the limitation, a stepwise sparse regularization (SSR) method with an adaptive sparse dictionary is proposed. In this method, the bearing fault diagnosis is modeled as a multi-parameter optimization problem, including time indexes of the sparse dictionary and sparse coefficients. Firstly, sparsity-enhanced optimization is conducted by amplifying the regularization parameter, making the time indexes and the number of atoms adaptively converge to the moments when impulses occur and the number of impulses, respectively. Then, fidelity-enhanced optimization is carried out by removing the regularization term, thereby obtaining the high-precision reconstruction amplitudes. Simulations and experiments verify that the reconstruction accuracy of the SSR method outperforms other sparse regularization methods under most noise conditions, and thus the proposed method can provide more accurate results for bearing fault diagnosis.
The present experimental investigation aims to discover the effect of hydrothermal aging on the mechanical properties of virgin and recycled PSU, as well as the effect of hydrothermal aging on the ...long-term durability including stress relaxation and creep properties of virgin and recycled PSU. Virgin and recycled PSU specimens were exposed to pure hot water at temperatures of 98 °C for 1, 1.5, 3, 4.5, 6, 9, and 12 months, respectively. Mechanical test of tensile, three-point bending, impact, and fracture toughness was carried out on those aged specimens. To obtain the long-term stress relaxation and creep property, a series of short-time stress relaxation and creep tests were performed by using dynamic mechanical analysis (DMA), and the master curve of long-term stress relaxation modulus and creep compliance was drawn by shifting those short relaxation and creep curve based on the time–temperature superposition principle (TTSP). It was finally concluded that the virgin PSU exhibits excellent hydrothermal aging resistance in tensile, flexural, impact and fracture toughness, stress relaxation, and creep properties, even if it was aged in 98 °C hot water for 1 year. Although the tensile and flexural properties of the unaged recycle PSU are similar to those of virgin PSU, the hydrothermal aging resistance in tensile, flexural, stress relaxation, and creep properties of recycled PSU is worse than that of virgin PSU. In addition, the activation energy required for stress relaxation of PSU is same with that for creep.
X-ray diffraction, X-ray electron spectroscopy and magnetic measurement techniques were used to study the structure and magnetic properties of ferrites. The sample was prepared by the sol–gel method ...under the conditions of different doses of drugs, and then annealed at 900 °C to improve the microstructure of the sample. For spinel ferrite, cations on its microstructure are replaced to improve magnetic properties. Doping with non-magnetic Al
3+
ions to study the change of the properties of the sample by the zero magnetic moment ions. Al
3+
ion doping has an effect on the microstructure and magnetic properties of the sample. The doped sample still has a pure phase structure without forming an impurity phase, which confirms the purity of the sample. The shape of the hysteresis loops of all samples indicates that they are hard magnetic. This above all proves that Al
3+
ions enter the crystal lattice because it is smaller than the particle radius of Fe
3+
ions.
In this paper, sol-gel self-propagation is used as the experimental method, and glucose is used as the complexing agent to prepare magnesium–cobalt ferrite (Mg
0.1
Co
0.9
FeO
4
). In the experiment, ...the annealing temperature of the sample is changed to study the annealing temperature on the ferrite. The influence of the microstructure and magnetic properties. In order to explore the samples, (X-ray diffractometer) XRD, (Fourier infrared spectrometer) FTIR, (scanning electron microscope) SEM and (vibrating sample magnetometer) VSM are usually used to characterize the sample. The characterization results of the samples are analyzed to prove the changes in the microstructure and magnetic properties. There are several obvious diffraction peaks in the XRD diffraction patterns of the five samples. Analysis of the positions of the diffraction peaks can prove that the prepared samples have a pure phase spinel structure. In the Fourier infrared spectroscopy, there is an obvious absorption peak around 580 cm
−1
. The presence of this absorption peak can also prove that the sample has a spinel structure. The morphology of the sample in the SEM photograph of the sample is round or elliptical, and the particle distribution is obvious, and the size is 100 ~ 200 nm. Vsm tested the magnetic properties of the samples. On the hysteresis loop of each sample, can see that the saturation magnetization and the residual magnetization of the sample reached the maximum when the annealing temperature was 500 °C. When the annealing temperature was 600 °C the coercive force and magnetic susceptibility of the sample reached maximum.
A series of chemical sample with formulae Ni
0.2
Mg
0.2
Co
0.6
Fe
2−
x
Cr
x
O
4
(0.00 ≤
x
≤ 0.1; step 0.025) were prepared by sol–gel automatic combustion at 950 °C. X-ray diffraction analysis ...found that the sample has characteristic peaks belonging to spinel, and Fourier transform infrared (FTIR) analysis found that the sample has a characteristic absorption band indicating the structure of spinel. This above findings can confirm that all samples belong to the single-phase cubic spinel structure. The average crystallite size and the lattice constant increase first and then decrease with the increase of Cr
3+
ion content. Surface morphology analysis observed that the shape of the ferrite sample was spherical nanoparticles. The surface morphology of the sample and the stoichiometric ratio of each element contained in it are analyzed by energy-dispersive spectrometer. The sample was subjected to an external magnetic field of 15 KOe at room temperature, and a vibrating sample magnetometer was used to measure the magnetic properties of Ni
0.2
Mg
0.2
Co
0.6
Fe
2−
x
Cr
x
O
4
nano-ferrite. Compared with other samples doped Cr
3+
ion, the magnetic properties of the sample reach to best when the doping content is
x
= 0.025, and the
M
s
,
M
r
and
S
* (coercivity squareness) also reach the maximum at the same time.
After characterizing Ni-Mg-Co magnetic ferrite nanoparticles doped with Al
3+
, La
3+
, Ce
3+
, Pr
3+
and Sm
3+
, the structure, magnetic properties, and other aspects of both the doped and pure ...samples show, through comparative analysis, the characteristic peaks and absorption bands belonging to the spinel structure, which proves that the prepared samples have a single-phase spinel structure. According to the Debye–Scherrer formula, the calculated average crystallite size decreased from 56.7 to 36.6 nm after doping with rare-earth ions, while doping with Al
3+
caused the average crystallite size to increase to 90.7 nm. Doping nickel-magnesium-cobalt ferrite with Al
3+
and rare-earth ions has a certain effect on its magnetic properties. The remanent magnetization (M
r
), square degree (M
r
/M
s
), coercivity rectangle degree (S
*
) and anisotropy constant (K) all increase after doping with rare-earth ions, but they decrease after doping with Al
3+
.
The injection and accumulation of space charge in the bulk of XLPE insulation will be intensified due to the ageing of HVDC cable insulation which will affect the normal operation of the HVDC cable. ...In this paper, the effects of thermal stress of different endurance time and temperature on the space charge distribution of HVDC cable were studied. The samples used in the tests were all slices of 160 kV DC cable insulation and the thermal stress temperatures were 90 and 135 °C, which represented the low temperature thermal stress and high temperature stress, respectively. The Pulsed Electro-Acoustic (PEA) method was used to measure the space charge accumulation and decay characteristics of the samples. And then, the electron trap properties of the test samples were analyzed based on the PEA space charge decay model. Meanwhile, in order to further understand the influence of thermal stress on the physicochemical property of the samples, Fourier Transform Infrared Spectrum (FTIR) and Differential Scanning Calorimetry (DSC) tests were conducted in this paper. The results showed that the 90 °C thermal treating could help to improve the crystalline morphologies of the XLPE at the early stage which led to the decrease of electro traps and space charge density. However, for a much longer thermal stress, the total amount of space charge would trend to increase with the gradually degradation of the XLPE caused by long term thermal stress. Besides, the high temperature thermal stress of 135 °C caused the rapid degradation of the XLPE molecular structure, reducing the crystallinity, creating more deep traps in the insulation and resulting in the accumulation of space charge. With more deep electron traps, the de-trapping process became much more difficult and slower.
Cr
3+
ion-doped Ni–Ba–Co ferrite with the chemical formula Ni
0.2
Ba
0.1
Co
0.7
Fe
2-x
Cr
x
O
4
was prepared by the sol–gel route. The X-ray diffraction analysis confirmed spinel-phase structure of ...the prepared Cr
3+
ion-doped Ni–Ba–Co ferrite. By Scherrer’s formula, the average crystallite size was calculated. Meanwhile, from Fourier transform infrared spectroscopy, the absorption peaks around 590 cm
− 1
were found; it can be inferred that the prepared samples had spinel structure. Transmission electron microscopy images showed that the prepared particles had spherical cube shape and were in the nanosize range. EDS analyzed the elements and ingredients of samples. Vibrating sample magnetometer results revealed that the values of Ms, Mr and Hc increased with Cr
3+
ions doping level from 0 to 0.075; when x = 0.1, the above three slightly decreased. This indicates that proper doping content can enhance the magnetic properties. The material can be used for audio, videotape and high-density digital recording disk in information storage industry.
