Thermodynamic studies on lithium ferrites

Thermodynamic studies on ternary oxides of Li-Fe-O systems were carried out using differential scanning calorimetry, Knudsen effusion mass spectrometry, and solid-state electrochemical technique based on fluoride electrolyte. Heat capacities of LiFe₅O₈(s) and LiFeO₂(s) were determined in the temperature range 127-861 K using differential scanning calorimetry. Gibbs energies of formation of LiFe₅O₈(s) and LiFeO₂(s) were determined using Knudsen effusion mass spectrometry and solid-state galvanic cell technique. The combined least squares fits can be represented as

Δ_fG_m^o(LiFe₅O₈,s,T)/kJ mol⁻¹ (±6)=−2341+0.6764(T/K) (588≤T/K≤971)     

Volumetric determination of lithium in lithium carbonate and nitrate and in lithium ferrites in non-aqueous media

Summary Lithium carbonate was titrated after dissolution in a glacial acetic acid/carbon tetrachloride mixture with 0.05 N perchloric acid in glacial acetic acid in the presence of gentian violet indicator. In the case of lithium nitrate the nitrate was firts reduced with ascorbic acid and the lithium titrated in an acetic anhydride/glacial acetic acid medium with the same measuring solution and indicator. The lithium content of lithium ferrites and lithium-nickel-zinc ferrites was measured after the extraction of iron and nickel by means of methyl-isobutyl ketone in a glacial acetic acid/carbon tetrachloride solution in the presence of tropeoline OO/methylene blue indicator mixture.

---

Volumetrische Bestimmung von Lithium in Lithiumcarbonat und -nitrat sowie in Lithiumferriten in nichtwärigem Medium

Zusammenfassung Lithiumcarbonat wird nach Auflösung in Eisessig/Tetrachlorkohlenstoff mit 0,05 N Perchlorsäure in Eisessig titriert, wobei Gentianaviolett als Indicator dient. Bei der Analyse von Lithiumnitrat wird zunächst das Nitrat mit Ascorbinsäure reduziert und dann die Titration mit Perchlorsäure gegen Gentianaviolett durchgeführt. Im Falle von Lithium- und Lithium-Nickel-Zink-Ferriten werden Eisen und Nickel durch Extraktion mit Isobutylmethylketon abgetrennt und anschließend wird mit Perchlorsäure in Eisessig/Tetrachlorkohlenstoff gegen ein Indicatorgemisch aus Tropäolin OO und Methylenblau titriert. Die Fehler liegen bei ± 0,5% für Carbonat und Nitrat und 0,5–1% für Ferrite.

     

Investigation of structural and magnetic properties of nanocrystalline manganese substituted lithium ferrites

Nanocrystalline manganese substituted lithium ferrites Li_0.5Fe_2.5−xMn_xO₄ (2.5≤x≥0) were prepared by sol-gel auto-combustion method. X-ray diffraction patterns revealed that as the concentration of manganese increased, the cubic phase changed to tetragonal. Magnetic properties were measured by hysteresis loop tracer technique. All the compositions indicated ferrimagnetic nature. The surface morphology of all the samples was studied by using scanning and transmission electron microscopy. The substitution of manganese ions in the lattice affected the structural as well as magnetic properties of spinels.     

Chemical and instrumental analysis of ferrites

More than thirty years since the manufacture of the first commercial ferrites, research and development efforts continue to produce ferrites with enhanced performance and new applications. Analytical chemistry has maintained a substantial role in the ferrite industry in the characterization of both raw materials and products, and the analytical literature of ferrites has grown accordingly. The continuing importance of ferrites to the electronic device industry requires further development of analytical methods suitable for characterization of ferrites so that their chemical composition may be related to performance and to the manufacturing processes used. As modem analytical techniques have been developed, their application to the characterization of ferrites and the detection of heterogeneity in these materials is increasing.     

Application of thermal analysis for the investigation of calcium ferrites

Investigations of metallurgical materials such as blast furnace sinters and pellets require the syntheses of the standard phases contained in these materials.Synthetic pure and calcium-doped iron oxides were studied Calcium ferrite phases originated in the intergranular space and strongly affected the reducibility of the sinter, besides haematite and magnetite.Studies of the formation and physicochemical properties of the synthetic calcium ferrites CaFe₂O₄ and Ca₂Fe₂O₅, identified in polycrystalline calciomagnetite and calciowustite samples, are described.

---

Zusammenfassung Die Untersuchungen einiger metallurgischer Stoffe wie z.B. Hochofensinter und Pellets bedingen eine künstliche Herstellung von Standardphasen, die in den genannten Materialien vorkommen.Es wurden synthetische reine und mit Calcium versetzte Eisenoxide untersucht. Calciumferrit wurde neben Haematit und Magnetit als diejenigen Phasen befunden, die im intergranularen Raum entstehen und die Reduzierbarkeit der Sinter stark beeinflussen.Es werden hier Untersuchungen von Herstellungsprozessen als auch der physikalischchemischen Eigenschaften der synthetischen Calciumferrite CaFe₂O₄ und Ca₂Fe₂O₅ beschriebenen.

     

Ab initio analysis of lithium dimethylaminoborohydride

Ab initio calculations were used to determine the equilibrium geometries and energies of lithium dimethylaminoborohydride. Relative energies of the monomeric and dimeric species were calculated in the gas phase and for the dimethyl ether microsolvated molecules. The most stable structure was a dimer in which the lithium and boron atoms were bridged by two hydrogen atoms, similar to the three-center two-electron bonds in diborane. This hydrogen bridging was maintained in the lithium dimethylaminoborohydride bis(dimethyl ether) microsolvate.     

Neutron activation analysis of lithium niobate

A radiochemical neutron activation analysis procedure for the determination of Ta, W, Ir, Pt, Au, Cu, Cr, Co and Zn in lithium niobate has been developed. The method involves a one-step removal of radioactive nuclides of Nb, Ta and W representing the dominating radioactivity of the irradiated sample. After irradiation, the sample is fused with inactive carriers and Na₂O₂ in a nickel crucible. The fused cake is dissolved in HCl–H₂O₂ and Nb, Ta and W are homogeneously precipitated. The impurities are separated by combinations of precipitation and ion-exchange separations for precise -ray measurements with an overall chemical yield of 70% to 90%. The results are discussed.     

Trace analysis of lithium metal by PIXE

A rapid method is described for simultaneous trace determination of metallic impurities in lithium metal by Particle Induced X-ray Emission (PIXE) technique. The impurities were preconcentrated by ion-exchange separation using a weak cation exchanger, Bio Rex-70 and analyzed by 2.34 MeV protons. The reliability of the method was tested by analyzing synthetic samples having several metallic impurities at 1–5 ppm range.     

Vibrational spectroscopic analysis of lithium hydrazinium sulfate

The low temperature polarized Raman spectra of lithium hydrazinium sulfate, LiN₂H₅SO₄, have been measured in the range 5–3500 cm⁻¹. The symmetry-based assignments for the observed modes are given. The room temperature polarized i.r. reflectivity spectra in the range 200–4000 cm⁻¹ were also measured to verify the presence of extensive TO—LO splitting in the sulfate ion ν₃ and ν₄ internal optic modes. In the lattice mode region, the lithium ion external optic modes are identified, and the spectra of the deuterated analog allow the identification of several modes due primarily to the external motions of either the sulfate or hydrazinium ions. Other lattice modes are found to be a mixture of sulfate and hydrazinium ion external motions. Coupling of the sulfate ion ν₃ modes and the hydrazinium ion group bending modes prevents an unambiguous assignment of the bands in the 1050–1200 cm⁻¹ spectral region. The N—H stretching region spectra contain a larger number of modes than predicted by a factor group analysis. These extra modes are discussed in terms of resonance interactions of the N—H stretching fundamental modes with overtones and combination modes.     

Effect of highly filled ferrites on non-isothermal crystallization behavior of polyamide 6 bonded ferrites

The aim of this study is to characterize the non-isothermal crystallization of polyamide 6 bonded highly filled ferrites which were prepared by the melt extrusion. Especially, the effect of ferrite concentration and its surface property on the non-isothermal crystallization were investigated by means of differential scanning calorimetry. The highly filled ferrite particles acting as obstacles could severely hinder the motion of surrounding chain segments, which were irrespective of surface nature. The ferrite could be modified by silane and obtain a visually enhanced interaction with polymer matrix which evoked the heterogeneous nucleation. Increasing this enhanced interfacial area between polymer-particle can promote the heterogeneous nucleation. However, a strong interaction can slow the motion of surrounding chain segments of particles, thereby producing a competitive effect on the crystallization rate and crystallinity. The plot of crystallization activation energy against concentration also can evaluate dispersion performance of hydrophilic fillers within hydrophobic polymer.     

Determination of lithium by instrumental neutron activation analysis

The fast transfer system in the DR 2 reactor for irradiation at a thermal neutron flux density of 10¹³ n·cm⁻²·sec⁻¹ was used for the determination of lithium by the⁷Li(n, γ)⁸Li reaction. β-counting with a large perspex Cerenkov detector begun at 0.3 s after the end of irradiation, and multi-scaler data was accumulated in 300 channels at 0.1 s per channel. With a suitable choice of discrimination level only¹⁶N and background interfere, and the 0.84 s half-life of⁸Li was resolved by the method of weighted least squares. Results are presented for 36 international geochemical reference materials, and for a few biological samples, including BOWEN's kale and the NBS Standard Reference Material 1571 Orchard Leaves.     

八面体尖晶石型铁氧体的水热法制备

尖晶石型铁氧体(MeFe2O4,M为金属离子Co2+,Mn2+,Ni2+,Zn2+等)作为一类重要的功能材料,广泛应用于电子、通讯和化工行业[1].铁氧体的制备方法很多,经典的方法是陶瓷方法,需要很高的温度和很长的反应时间,而且伴随研磨,这就导致了杂质的产生.     

Determination of bound oxygen in ferrites

Summary A method has been worked out for the determination of the bound oxygen content of ferrites.The non-aqueous acid mixture used consisted of phosphoric acid—dichloroacetic Acid—acetic acid after dehydration with acetic anhydride. When ferrites are dissolved in this mixture water is liberated in a quantity equivalent to the bound oxygen of the system. This water can be determined with Karl Fischer's reagent. Erroes amount to about ±1%.

---

Zusammenfassung Es wird ein Verfahren beschrieben zur Bestimmung von gebundenem Sauerstoff in Ferriten. Hierbei wird die Probe in einem nichtwäßrigen Gemisch von Phosphor-, Dichloressig- und Essigsäure (nach Entwässerung mit Essigsäureanhydrid) gelöst und das dabei freigesetzte Wasser (das dem gebundenen Sauerstoff äquivalent ist) mit Karl Fischer-Reagens bestimmt. Die Fehler betragen etwa ±1%

---

---

Part of Mrs. Hochmann-Fischer's dissertation for the doctor's degree, prepared at the Department of Pharmaceutical Chemistry (Prof. Dr. Antal Végh), Medical School, Budapest University.     

Multiferroid properties of hexagonal barium ferrites

Samples of BaFe₁₂O₁₉ with high multiferroid properties at room temperature (maximum polarization P_m = 48.0–9.5 μQ/cm², residual polarization P_r = 28.0–29.5 μQ/cm², and electric coercive field Е_c = 115–120 kV/m) have been obtained for the first time using a modified ceramic technology (based on highpurity raw materials and sintering in an oxygen atmosphere with a B₂O₃ addition). A mechanism for the explanation of the multiferroid properties obtained has been suggested; the large practical importance of the results obtained is noted.     

Thermal analysis of lithium peroxide prepared by various methods

Behavior of lithium peroxide samples at heating in air was studied by the methods of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). In the temperature range from 32 to 82°C all the studied samples we found to react with water vapor forming lithium peroxide monohydrate as confirmed by the methods of chemical analysis and of qualitative X-ray phase analysis. It was found experimentally that in the temperature range from 340 to 348°C lithium peroxide began to decompose into lithium oxide and oxygen, the starting temperature depended on the method of preparation of lithium peroxide. For all the studied samples polymorphism in the temperature range from 25 to 340°C was not detected.     

Study on electro-conductance and thermal analysis of lithium carnallite

Lithium carnallite is a hydrated double salt containing lithium and magnesium chlorides. The processes of thermal dehydration and thermal decomposition of lithium carnallite during heating has been studied by the conductance-thermoanalysis which was designed according to Berg and-Wendlandt, and an interpretation of the conductance-thermoanalytical curve has been suggested.     

Simultaneous determination of boron and lithium by activation analysis

Simultaneous determination of boron and lithium is done by double irradiation with protons. One irradiation with 1.55 MeV protons and another with 7.4 MeV protons, measuring in both cases the amount of⁷Be formed /⁷Li/p,n/⁷Be and¹⁰B/p,/⁷Be/. Deuteron bombardment was not found to be of much advantage.     

Determination of lithium in graphite by neutron activation analysis

Trace impurities of lithium in graphite is one of the sources of tritium in high-temperature reactors. To determine contents of less then 1ng/g a procedure based on the (n,)-reaction of⁶Li was developed. The samples are irradiated in a reactor and then ignited in a Wickbold apparatus. Thereby the tritium produced by the (n,)-reaction is completely converted in HTO, which can be easily purified by distillation and, if necessary, by a scavenger precipitation step. Several types of graphite have been investigated and the lowest content measured was 0.2 ng/g.