Sintering Behavior and Properties of NiFe2O4 Ceramic Inert Anode Toughened by Adding NiFe2O4 Nanopowder

doi:10.15541/jim20150602

Abstract

Abstract:

NiFe₂O₄ ceramic inert anode for aluminum electrolysis, strengthened by adding NiFe₂O₄nanopowder, was prepared via powder metallurgy method. The effects of NiFe₂O₄ nanopowder content on sintering behavior and properties of NiFe₂O₄ ceramic inert anode were studied. Linear shrinkage and scanning electron microscope (SEM) were employed to characterize the sintering property and microstructure. The results show that the sintering shrinkage degree increases gradually as increase of NiFe₂O₄ nanopowder content, while the sintering temperature and apparent activation energy of initial stage of sintering decrease. When nanopowder content is 40%, the sharp sintering shrinkage begins from 900℃ and the apparent activation energy of initial stage of sintering drops to 291.43 kJ/mol. Volume density, bending strength and fracture toughness are enhanced firstly and then decreased with the increase of nanopowder content, while the porosity and static corrosion rate display opposite tendency. The maximum value of fracture toughness is 3.12 MPa•m^1/2 with nanopowder content of 30%, which is 2.14 times that of without adding nanopowder. The toughening effect is realized by the elevated fracture surface energy, which is attributed to the enhanced grain boundary cohesive bond and the reduced porosity with addition of NiFe₂O₄ nanopowder.

Key words: NiFe2O4, linear shrinkage, activation energy, fracture surface energy, toughening

CLC Number:

TQ174

ZHANG Zhi-Gang, YAO Guang-Chun, LUO Hong-Jie, ZHANG Xiao, MA Jun-Fei, XU Jian-Rong. Sintering Behavior and Properties of NiFe₂O₄ Ceramic Inert Anode Toughened by Adding NiFe₂O₄ Nanopowder[J]. Journal of Inorganic Materials, 2016, 31(7): 761-768.

Figures/Tables 13

Table 1 Design of particle gradation

Main granule (500-355 μm)	Filler granule (105-74 μm)	Fine granule (<74 μm)	Nanopowder (30-65 nm)
42wt%	18wt%	40wt%	0
		30wt%	10wt%
		20wt%	20wt%
		10wt%	30wt%
		0	40wt%

Fig. 1 XRD pattern (a) and TEM image (b) of NiFe2O4 nanopowders prepared by low temperature solid-state reaction

Fig. 2 Effect of nanopowder content on linear shrinkage of inert anodes as a function of temperature

Table 2 Linear shrinkage of samples prepared by adding different amount of nanopowders at 1300℃

Nanopowder content/wt %	0	10	20	30	40
Linear shrinkage/ %	-5.23	-6.09	-6.93	-9.41	-10.41

Fig. 3 Effect of nanopowder content on density and porosity

Fig. 4 ln(△L/L0)T versus lnC for samples without nanopowders

Table 3 Values of slope and linear regression coefﬁcient (R) of relationship between ln(△L/L0)T and lnC for samples without nanopowders under different temperatures

T/℃	1150	1175	1200	1225	1250	Average
-1/(m+1)	-0.352	-0.338	-0.362	-0.373	-0.365	-0.358
R	0.991	0.994	0.985	0.987	0.992	-

Fig. 5 ln[(△L/L0)/T] versus 1/T relation graph for sample without nanopowders

Table 4 Values of slope (a) and linear regression coefﬁcient (R) of relationship between ln[(△L/L0)/T] and 1/T for samples without nanopowders under different heating rates

Heating rate/(K·min^-1)	5	10	20	Average
a	-16731	-17165	-15889	-16595
R	0.978	0.985	0.981	-

Table 5 Values of exponent and apparent activation energy for samples with various contents of NiFe2O4 nanopowders at the early-stage sintering

Nanopowder content /wt%	0	10	20	30	40
Exponent m	1.793	1.648	1.564	1.486	1.453
Apparent activation energy, Q/(kJ·mol^-1)	385.35	349.52	324.27	302.69	291.43

Fig. 6 Effect of nanopowder content on bending strength and fracture toughness

Fig. 7 SEM images of fracture surfaces of NiFe2O4 ceramic inert anodes with various contents of nanopowder

Fig. 8 Effect of nanopowder content on the static corrosion rate of inert anodes

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Sintering Behavior and Properties of NiFe₂O₄ Ceramic Inert Anode Toughened by Adding NiFe₂O₄ Nanopowder

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