Li-Ti Ferrite Research Articles

ANALYSIS OF THE APPLICABILITY OF PHYSICAL MODELS TO DESCRIBE DENSIFICATION OF LITHIUM FERRITE COMPACTS DURING SINTERING IN THE FIELD OF INTENSE ELECTRON BEAM

The paper analyzes the possibility of describing the accelerated sintering of lithium-titanium compacts under high-power radiation effects in terms of classical physical models developed by Kuczynski and Johnson based on the kinetic analysis of ferrite compact densification. LiTi ferrites synthesized by ceramic technology in laboratory conditions were investigated. The first portion of the compacts was sintered in air in thermal ovens at 900–1100°C for 30 minutes at a heating rate of 900 °C/min. The second portion of the compacts was sintered in a similar mode but using a radiation-thermal method: the exposure to pulsed electron beam with energy of 1.5–2.0 MeV using the ILU-6 accelerator. The geometrical dimensions of the compacts were measured before and after sintering to determine shrinkage. Mathematical approximation of the experimental shrinkage data showed the discrepancy of both models to describe sintering of LiTi ferrite samples both under thermal sintering conditions and radiationthermal effect.

Wetting behavior and bonding characteristics of bismuth-based glass brazes used to join Li-Ti ferrite systems

Abstract A series of bismuth-based glass brazes were used to join Li-Ti ferrite. The wetting behavior and bonding characteristics of glass brazes utilized to join Li-Ti ferrite were systematically investigated. The glass brazes feature a good CTEs match, and a favorable wetting ability over Li-Ti ferrite mating surfaces. Upon brazing, the Bi-rich phases (Bi 46 Fe 2 O 72 , Bi 12 SiO 2 and Bi 24 B 2 O 39 ) and Zn-rich phase (ZnO) were observed in the Li-Ti ferrite/Bi40 and Li-Ti ferrite/Bi35 joints. The Zn 2 SiO 4 , ZnFe 2 O 4 and Bi 5 Ti 3 FeO 15 whiskers were detected in the Li-Ti ferrite/Bi25, Li-Ti ferrite/Bi20 and Li-Ti ferrite/Bi25-BC joints, respectively. No crystalline phase was detected in the Li-Ti ferrite/Bi30-BF joint. Multiple factors impact the joint strength, such as the three-point bending strength of glass brazes, the CTE match of the glass braze and the Li-Ti ferrite, as well as the crystal phases within the seam. The joint strength has the maximum value of 86 MPa for a Li-Ti ferrite/Bi25-Ba couples. The main impact is attributed to the strengthening effect of Bi 5 Ti 3 FeO 15 whiskers. The dielectric properties of Li-Ti ferrite/glass braze joints show a stronger frequency dependence than that of Li-Ti ferrite at low frequency. This is attributed to the formation of new interfaces. The glass matrix or a crystal phase with a higher dielectric constant could counteract the decrease in the dielectric constant of heat-treated Li-Ti ferrite. Therefore, the dielectric constant of joint, especially that of Li-Ti ferrite/Bi25-BC joint, would be near that of the original Li-Ti ferrite at a high frequency. Meanwhile, no increase in the dielectric loss tangent of a joint takes place.

An influence of a Glass Braze Composition on the Properties of Li-Ti Ferrite Joints

The influence of the chemical composition of Bi2O3-B2O3-SiO2-ZnO glass brazes on (i) the microstructure, (ii) the mechanical and (iii) the dielectric properties of Li-Ti ferrite joints was systematically investigated. The Bi5(Ti3Fe)O15 whisker and a white block phase consisting of Bi12SiO2 and Bi24B2O39 were observed in the joints of Li-Ti ferrite/Bi25-Ba and Li-Ti ferrite/glass brazes, respectively, containing a higher content of Bi2O3. No crystalline phase was detected in the Li-Ti ferrite/Bi25 and Li-Ti ferrite/Bi20 joints. The joint strength reached the maximum of 48 MPa in the Li-Ti ferrite/Bi25-Ba couples. It is assumed that this is mainly due to the strengthening effect of Bi5(Ti3Fe)O15 whiskers. The bonding temperature (700°C) had little effect on the dielectric properties of Li-Ti ferrite. Moreover, compared to the Bi25-Ba glass brazes, the Bi25 and Bi20 glass brazes had a less pronounced influence on the dielectric properties of joints. Different glass brazes can be tailored to different requirements depending on specific application and joint property requirements.

Microstructural evolution of Li-Ti ferrite/composite braze/Li-Ti ferrite joints reinforced by Bi5(Ti3Fe)O15 whiskers

The composite brazes consisting of (i) Bi2O3-B2O3-SiO2 glass and (ii) Li-Ti ferrite powder were used to join the Li-Ti ferrite. The microstructural evolution and resulting mechanical strength of the joint were systematically investigated. Both needle-like and plate-like Bi5(Ti3Fe)O15 phases were observed in the joint. With a sufficiently pronounced Ti concentration gradient, the Bi5(Ti3Fe)O15 crystal nucleuses evolve into whiskers along the c-axis orientation. Contrary to that, the Bi5(Ti3Fe)O15 plates were observed when the Ti concentration gradient was small enough to make the driving force of the preferential growth markedly weaker in comparison to the attraction between the (Bi2O2)2+ and (Am−1BmO3m+1)2− domains in a bismuth layer-perovskite structure. The Bi5(Ti3Fe)O15 whiskers having a large size could potentially absorb the fracture force by deflecting or stopping its propagation. The highest shear strength of 81.0MPa was obtained for the joint with the composite braze containing 10.0wt% of Li-Ti ferrite powder.

Structural, thermoelectric power and magnetization measurements of Nd-doped Li–Ti ferrite by combustion synthesis

Nd-doped Li–Ti ferrites with compositional formula Li0.4Ti0.1Fe2.5−xNdxO4 (where x = 0.0, 0.025, 0.05, 0.075 and 0.10) are prepared at 450 °C by combustion synthesis. X-ray analysis showed the limit of Nd-concentration for formation of single phase cubic is 0.075 and thereafter a secondary phase of FeNdO3 is observed. As the Nd-concentration increased to 0.075 the lattice parameter increased, which is attributed to the incorporation of larger ionic radius of Nd3+ ions in place of smaller ionic radius of Fe3+ in the spinel lattice. When Nd-concentration is 0.10, some of the Nd3+ ions diffuse to the grain boundaries, which can be correlated from scanning electron microscope analysis. The infrared spectra have shown three strong absorption bands in the range 400–600 cm−1 and confirming the occupancies of Nd3+ into the spinel lattice. We explained for n-type semiconductors the Seebeck coefficient should be negative only. Saturation magnetization (MS) value increases with increase in Nd-concentration indicating that Nd3+ ions are replacing the Fe3+ ions in the spinel lattice.

Investigation of microstructure and mechanical property of Li–Ti ferrite/Bi2O3–B2O3–SiO2 glass/Li–Ti ferrite joints reinforced by FeBi5Ti3O15 whiskers

The Bi2O3–B2O3–SiO2 glass solder was used to join the Li–Ti ferrite. SEM micrographs of the joints showed the formation of FeBi5Ti3O15 whiskers at the interface. The formation mechanism was that the elements Fe and Ti reacted with [BiO6] units and came out as needle-like FeBi5Ti3O15 whiskers during cooling when the Ti content in the seam reached the critical concentration of crystallization. The quantity and morphology of the FeBi5Ti3O15 whiskers could be controlled by adjusting the bonding temperature and applied pressure, which could decide the Ti content in the seam. The deciduous ferrite ceramic particles were observed at the interface due to the formation of the FeBi5Ti3O15 whiskers continually consumed the elements Fe and Ti. Under the combined influence of the elements diffusion and interfacial reactions, nearly defect-free joints were obtained and a maximum in the shear strength of 92MPa was achieved at 750°C for 30min under 100Pa applied pressure.

The study of the ferroelectric properties of lithium-titanium ferrite

Loop-shaped dependences of the electric polarization on the electric field strength (the dielectric hysteresis) are registered for the first time for polycrystalline Li-Ti ferrite. Temperature evolution of the hysteresis loop parameters is investigated for ferrite samples. A thermal Barkhausen effect is detected during heating and cooling of ferrite specimens prepolarized in an electric field. The results obtained can be interpreted from the viewpoint of the Maxwell-Wagner relaxation polarization or induced ferroelectric-like state in the electric ferrite subsystem.

Experimentally Investigated Microstrip Circular Patch Antenna Fabricated on LiTi Ferrite Substrate

Experimental study of microstrip circular patch antenna which has been fabricated on LiTi ferrite substrate is presented. Obtained results have also been compared with same structure of antenna on dielectric substrate for the X band. The structure of antenna has been optimized with IE3D and lithographed on 2 mm thickness ferrite substrate. The radiation patterns have been measured in anechoic chamber and plotted for both E-plane and H-plane. Using ferrite material the patch size reduced about 63 % as compared to antenna printed on dielectric substrate. Obtained values of return loss and VSWR for antenna on ferrite substrate have positive results than the antenna on dielectric substrate but the bandwidth, directivity, gain and quality factor of antenna have been affected negatively. For this work the polycrystalline LiTi ferrite has been synthesized using solid state reaction technique and characterized its electric and magnetic properties.

Investigation into the special features of the dielectric and polarization properties of lithiumtitanium ferrite ceramics

Loop-shaped dependences of the electric polarization on the electric field strength (the dielectric hysteresis) are registered for the first time for polycrystalline Li–Ti ferrite. Temperature evolution of the hysteresis loop parameters is investigated for ferrite samples. The results obtained can be interpreted from the viewpoint of the Maxwell–Wagner relaxation polarization or induced ferroelectric-like state in the electric ferrite subsystem.

On switching behavior of ferrite substrate with magnetostatic and spin wave exchange term

Due to the generation of magnetostatic and spin waves, switching phenomena of ferrite substrate with a normal magnetic biasing field is presented. Generally below the X-band of microwave range, the Pozar’s quasi TEM waves (extraordinary waves) were studied, but for the study of X-band there should be an inclusion of spin wave exchange term (ωr) in the magnetostatic wave analysis which depends upon the static internal field (Hex). This term is included in analysis because the wavelength of microwave approach is the inter-atomic distance of ferrite material. In this work we synthesize LiTi ferrite through Solid State Reaction Technique (SSRT) and obtained electric and magnetic properties for the analysis. Absorbing and transmission power coefficients have been calculated to obtain the power loss and transmitted power through the substrate, respectively. The absorbing power coefficient verifies the switching behavior of substrate for certain range of applied external magnetic field (H o) which depends on the resonance line width parameter (ΔH) of ferrite material.

Dressing of Monolayer Brazed Diamond Wheel for Grinding Li-Ti Ferrite

The monolayer brazed diamond tools have recently been used increasingly in hard-brittle materials grinding because of their excellent grinding performances as long tool life, high material removal rate and large inter-grit chip space, etc. However, they possess an inherent shortcoming of the high roughness of the grinding surface. This work is an attempt to reduce the over-protruded grits of the monolayer brazed diamond wheel so that precision grinding operations can be executed effectively. In this investigation, the monolayer brazed diamond wheels with regular distribution pattern of grit have been dressed by a special conditioning process and used in precision grinding experiments on Li-Ti ferrite. The outcome of this attempt appeared highly encouraging. A substantial improvement of the ground surface roughness could be achieved with the dressed monolayer brazed diamond wheels.

The Experiment Research of Precision Grinding of Li-Ti Ferrite with Graphite Grinding Wheel

Li-Ti ferrite used in aviation occasions needs good surface quality. In conventional grinding it is difficult to meet the surface demand. Accordingly, this paper proposed a new grinding process to change the situation. The process employed graphite grinding wheel which is always used in ultra-precision grinding of steel piece. The process can obtain good surface quality and ensure certain material removal rate. The ground surface appearance is nearly mirror-like. The lowest surface roughness of Ra value of the ground surface is 0.05μm in the experiment. The ground surface morphology is made up of spread glazed area and dispersed minute pits. The ductile regime dominates the material removal mechanism and no surface damage is induced in the process. In consideration of the results in the experiment it can be seen that grinding with graphite grinding wheel is a good finishing procedure in ferrite machining because of its obtained high surface quality.

Relaxation Polarization of Li-Ti Ferrite Ceramics

Relaxation Polarization of Li-Ti Ferrite Ceramics

Temperature Dependences of the Electrophysical Parameters of a Li–Ti Ferrite

Temperature dependences of real and imaginary parts of the complex permeability of a Li–Ti ferrite were obtained by measuring its capacitance and total electrical conductivity by the bridge method at temperatures lying in the range 77–500 K. The measurements were carried out at a frequency of 1 MHz and a standard signal voltage of 250 mV. Dipoles of two types are identified. The static permittivity, activation energy, and pre-exponential factors characterizing the reorientation time constants of each dipole and also of the quantities describing the charge-carrier transfer in an electric field are estimated by the method of regression analysis of the obtained dependences.

Field and temperature dependence of magnetic viscosity in randomly canted Li-Ti ferrite

The magnetic viscosity of the spinel system Li 0.5 + 0.5 t Fe 2.5 − 1.5 t Ti t O 4 ( t = 1.25) has been studied as function of temperature, applied field and waiting time before switching off the field, on samples with different local order. The magnetic viscosity depends strongly on the applied field but does not appear to be influenced by the waiting time. The temperature dependence of the viscosity has an unusual behavior and the properties are explained from a thermally activated model based on the relaxation time of the transverse spin component.

Effect of aluminium substitution on electric, magnetic, and microwave properties of LiTi ferrite

Effects of substitution of diamagnetic Al3+ ion in LiTi ferrite on its electric and magnetic properties are reported. These parameters are studied as a function of temperature, frequency, and concentration. The dielectric data are verified with a modified relation of Koops' two layer model. Other fundamental properties like hysteresis loop parameters viz. coercive force and remanence ratio, and Curie temperature are also found to be affected by Al3+ substitution. FMR linewidth and spin wave line width show a very slow increase with addition of aluminium. The activation energy is found to decrease with the increase in Al3+ concentration and frequency. Es werden die Einflusse einer Substitution von diamagnetischen Al3+-Ionen in LiTi-Ferrit auf dessen elektrische und magnetische Eigenschaften mitgeteilt. Diese Parameter werden als Funktion der Temperatur, Frequenz und Konzentration untersucht. Die dielektrischen Daten werden mit einer modifizierten Beziehung des Koopschen Zwei-Schichtenmodells verifiziert. Es wird ebenfalls gefunden, das andere fundamentale Eigenschaften der Hystereseschleifenparameter, Koerzitivkraft und Remanenzverhaltnis, und die Curietemperatur durch Al3+-Substitution beeinflust werden. FMR-Linienbreite und Spinwellenlinienbreite zeigen einen sehr flachen Anstieg bei Zugabe von Aluminium. Es wird gefunden, das die Aktivierungsenergie mit Zunahme der Al3+-Konzentration und Frequenz abnimmt.