Thermodynamics of formation of simple spinels

Navrotsky, Alexandra; Kleppa, O. J.

doi:10.1016/0022-1902(68)80475-0

Cited by 316 publications

(110 citation statements)

References 18 publications

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“…Fast-sintering conditions with 50 deg/min heating rate do not lead to more shrinkage. Although the solid state reaction forming the spinel NiMn204 is endothermic (for thermodynamic values see [5]), it is so fast even at low heating rates that rate controlled sintering with 0.1/~m/s shrinkage rate was not possible.…”

Section: Influence Of Compactionmentioning

confidence: 99%

Thermoanalytic characterization of NiMn2O4 formation

Jung

Töpfer

Feltz

1990

Journal of Thermal Analysis

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Comparative thermogravimetric and heat-flux DSC investigations of phase formations by heating of sinteractive powders, which were prepared by thermal decomposition of a NiCO3 : MnCO3 = 1 : 2 mixture and thermal decomposition of oxalate mixed crystals NiMn2(C204)3.6H20, show the metastability of the defect spinel from the oxalate precursor and its high reactivity.Dilatometric shrinkage measurements show that reaction sintering leads to the shrinkage and maximum shrinkage rate at lower temperatures. Decomposition of the spinel NiMn204 under NiO separation and 02 release at 975 ~ in oxygen atmosphere is in contrast to the known phase diagram. Utilization of the thermodynamic driving force of the primarily formed metastable oxide phase and the NiMn204 formation leads, supported by a sinteradditire, to high density semiconductor ceramics.Ni-Mn-spinels are important in semiconductor ceramic materials. The phase relations were investigated in 1964 by Wickham [1]. Recently the formation of defect spinels after thermal decomposition of oxalate mixed crystals was described [2].Subject of this paper is the investigation of spinel formation in powders in connection with the sinter densification. As oxygen from the sintering atmosphere participates, thermogravimetry and differential thermal analysis are useful to observe the phase formation processes.

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Section: Influence Of Compactionmentioning

confidence: 99%

Thermoanalytic characterization of NiMn2O4 formation

Jung

Töpfer

Feltz

1990

Journal of Thermal Analysis

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“…Thus, it appears that no appreciable interchange among A and B sites by Cu 2+ and Cr 3+ ions occurs in this spinel even at a temperature of 1273 K. The plausible reasons for this may be (i) strong affinity of C1 "z+ ion for B site or (ii) a larger lattice energy of normal CuCr20~ than that of inverse CuCr2Oa at all temperatures. Since the energy difference between normal and inverse spinels is quite small [12], (ii) may not be the deciding factor here and it is the strong affinity of Cr z+ ions for B sites, even at temperatures above 1200 K, which prevents the c/a ratio from changing in quenched CuCrzO~. Thus, it may be concluded that the tetragonal to cubic transition in CuCr204 is a first order, diffusionless, reversible and very fast transition, not only at 860 K but also at higher temperatures.…”

Section: Resultsmentioning

confidence: 99%

Thermal effects on cation distribution of CuCr2O4

Ghose

Murthy

1981

Journal of Thermal Analysis

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Thermal studies on CuCr204 spinel indicated the phase present above 870 K to be cubic CuCr~O~. However, when the substance was quenched from 1023 K, 1173 K, 1273 K and 1473 K, only the tetragonal phase of CuCr204 was obtained. This is because the first-order, diffusionless, tetragonal to cubic phase transition at 865 K occurs reversibly at a very fast rate. The c/a ratio for CuCr204 present in the various quenched samples did not change when the quenching temperature was raised. A strong preference of the Cr ~+ ion for the B site prevents it from interchanging sites with Cu z* ions, thus keeping the lattice parameters c and a unchanged.Copper(II) chromite (CuCr~O4) and copper(II) ferrite (CuFe~Oa) are tetragonally distorted spinels with c]a < 1 and c]a > 1, and the transition to the cubic form occurs at 873 K and 633 K, respectively [1][2][3][4]. The distortion in these spinels is due to the Cu 2+ Jahn-Teller ion [5,6]. Cr ~+ and Cu e+ both have a strong preference for octahedral coordination, but the former has a comparatively higher octahedral site preference energy [7] and so Cu[Cr2]O4 is a normal spinel, whereas Fe[CuFe]O4 is almost an inverse spinel. However, the degree of inversion of CuFe~O4 changes at higher temperatures, due to a change in the cation distribution, as indicated by the c/a values of CuFe2Oa quenched from various temperatures, and cubic CuFe204 can be obtained by quenching from above 1033 K [4]. Such changes in cation distribution at higher temperatures may also be expected in CuCr204 and the present work is an attempt to study the thermal effect on the cation distribution of CuCr~O~, and the preparation of quenched cubic CuCr204.

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“…According to the earlier reports, the increase in the crystallite size can be attributed to the increase in the enthalpy of formation. The enthalpy of formation of Nickel ferrite (−1.22 kcal/mol) is more than that of Zinc ferrite (−2.67 kcal/mol) [30]. Therefore, the formation of Zinc ferrite is more exothermic as compared to the formation of nickel ferrite.…”

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confidence: 87%

Mössbauer Spectroscopic Studies of NiZn Ferrite Prepared by the Sol-Gel Method

Niyaifar¹,

Mohammadpour²,

Rodriguez³

2015

Journal of Magnetics

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This study was aimed to study the effect of Zn content on the hyperfine parameters and the structural variation of Ni 1-x Zn x Fe 2 O 4 for x = 0, 0.2, 0.4, 0.6, and 0.8. To achieve this, a sol-gel route was used for the preparation of samples and the obtained ferrites were investigated by X-ray diffraction, scanning electron microscopy, and Mössbauer spectroscopy. The formation of spinel phase without any impurity peak was identified by X-ray diffraction of all the samples. Moreover, the estimated crystallite size by X-ray line broadening indicates a decrease with increasing Zn content. This result was in agreement with the scanning electron microscopy result, indicating the reduction in grain growth with further zinc substitution. The room-temperature Mössbauer spectra show that the hyperfine fields at both the A and B sites decreased with increasing Zn content; however, the rate of reduction is not the same for different sites. Moreover, the best fit parameter showed that the quadrupole splitting values of B site increased from the pure nickel ferrite to the sample with x = 0.8.

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Thermodynamics of formation of simple spinels

Cited by 316 publications

References 18 publications

Thermoanalytic characterization of NiMn2O4 formation

Thermoanalytic characterization of NiMn2O4 formation

Thermal effects on cation distribution of CuCr2O4

Mössbauer Spectroscopic Studies of NiZn Ferrite Prepared by the Sol-Gel Method

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