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Thermal studies on CuCr2O4 spinel indicated the phase present above 870 K to be cubic CuCr2O4. However, when the substance was quenched from 1023 K, 1173 K, 1273 K and 1473 K, only the tetragonal phase of CuCr2O4 was obtained. This is because the first-order, diffusionless, tetragonal to cubic phase transition at 865 K occurs reversibly at a very fast rate. Thec/a ratio for CuCr2O4 present in the various quenched samples did not change when the quenching temperature was raised. A strong preference of the Cr3+ ion for the B site prevents it from interchanging sites with Cu2+ ions, thus keeping the lattice parametersc anda unchanged.

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The effect of electric fields on the thermal dehydration of amorphous hydrated iron(III) oxide under oxidizing, inert and reducing atmospheres was studied by X-ray diffractometry. In oxidizing and inert atmospheres, the transformation toα-Fe2O3 was enhanced by electric fields, especially at the negative electrode. The crystallite size of the product was also greatest at the negative electrode. Both results are explained in terms of the migration of protons to the negative electrode, where they subsequently form water which acts as a nucleating agent for the crystalline phase. In reducing atmospheres the formation of Fe3O4 and FeO at the expense of Fe2O3 is facilitated by electric fields, particularly at the negative electrode. Possible reaction mechanisms are considered, and the role of protons in stabilizing defect-spinel intermediates and products is discussed.

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Introduction The synthesis of metal chromites with spinel structures is a subject that acquired keen researcher interest from early times because of their technological applications [ 1 ]. In the last decade, the synthesis of

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smaller average grain size of α-Cr 2 O 3 scales and higher scale plasticity. This mechanism is also valid for alumina scale forming alloys, but to a lesser extent. There is evidence that RE containing spinels form in the growing scale, depleting

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Journal of Thermal Analysis and Calorimetry
Authors: Vittorio Berbenni, Chiara Milanese, Giovanna Bruni, Alessandro Girella, and Amedeo Marini

exceeding 700 °C [ 2 ]. The spinel compound Mg 2 SnO 4 has been recently proposed for applications in electronic ceramics: an example of such applications is the use of this material in manufacturing dielectric plates for cellular phones and high speed

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nanoparticles that could be used for high density magnetic recording sensors etc., has attracted many workers toward the cubic spinel-structured cobalt ferrite of variable particle size in which Co 2+ and Fe 3+ occupy tetrahedral/octahedral sites in the fcc

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2 O 4 ) 3 ]} ∞ has resulted into a spinel oxide—Mn 1.5 Cr 1.5 O 4 at ∼ 500 °C [ 8 ]. Recently, thermal degradation of one analogous molecular ferrimagnetic material {N( n -C 4 H 9 ) 4 [Fe II Fe III (C 2 O 4 ) 3 ]} ∞ has been reported to lead to

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NiAl 2 O 4 spinels, synthesized by citrate precursor method and annealed at 450 and 650 °C . J Therm Anal Calorim . 107 : 205 – 210 10.1007/s10973-011-1860-7 . 20. Singh , RK , Yadav

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Further heating to 925–950 °C converts metakaolin to a defect, aluminum-silicon spinel (Si 3 Al 4 O 12 ), which is also referred to as a gamma-alumina type structure. Upon calcination to around 1050 °C, the spinel phase (Si 3 Al 4 O 12

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Journal of Thermal Analysis and Calorimetry
Authors: Hou-yin Zhao, Yan Cao, Zhi-zhong Kang, Yau-bang Wang, and Wei-ping Pan

showed the new formation of CuAl 2 O 4 spinel during the redox cycles. Figure 3 shows that the fresh oxygen carrier was composed of CuO and Al 2 O 3 . After the first reduction, it was reduced to Cu while after first oxidation, it was oxidized to CuAl

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