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Influence of heat treatment and coatings on time stability of coercive force of the amorphous Fe80.5B12Si6.5C1 alloys
Journal of Magnetism and Magnetic Materials 109 (1992} 27-33 North-Holland
Influence of heat treatment and coatings on time stability of coercive force of the amorphous Fes0.sBa2Si6.sC 1 alloys A. Ko~turiak Department of Phys. and Analytical Chemistry, Faculty of Sciences, Moyzesora 11, 041 54 Ktogice, Czechosloeakia
O. Du,~a a n d J. G a j d u g e k Department of Exp. Phys., Faculty of Sciences, ndm. Feor. ef~azstt,a 9, 041 54 Ko~ice, Czechoslovakia Received 11 July 1991; in revised torm 1 October 1991
The influence of both heat treatment in various atmospheres and eleclrotechnical coatings on the coercive torce and its long time stability for amorphous Fes0.sBt2Si6.sC l alloys was studied. A number of factors, predominantly chemical processes, acting at the heat treatment and the coating deposition, are diseussed.
1. Introduction It is well established that various macroscopic magnetic properties of amorphous metal ferromagnets prepared by the rapid quenching method are dependent to a considerable extent on the physical and chemical state of a surface [1-5]. The coercive force, H c, is one of such basic magnetic characteristics indicating the possibility of a material application [6-8]. The time stability of properties of amorphous ferromagnetic alloys appears to be a poor characteristic as compared with classic type materials. The coating of amorphous materials by a thin surface layer (anorganic or organic) which acts simultaneously as an electroinsulating, anticorrosive and magnetic stimulating factor, should serve to a stability increase [3,4,9]. Amorphous Fes0.sBt2Si6.5C 1 alloys exhibit extremely low magnetic losses (p~.3v=(0.105_+ 0.004) W kg-1; Pt.4T = (0.129 _+ 0.003) W kg -~ at f = 5 0 Hz [10]. The first problem for coatings application leads one to finding e[eetrotechnical coatings (EC) to decrease magnetic losses or at least not to increase it. The aim of this paper is to present the influ-
ence of heat treatment, phosphate and borate coatings on H c and its time stability.
2. Experimental Amorphous Fes05Bl:Si,~Ci ribbon was prepared by rapid quenching from the melt onto a rotating wheel at the Nippon Steel Corp. Laboratory. Its sample number is A 030-B. From this ribbon, given to us, samples were cut having length l = 130 ram, width w = 25 mm and thickness d = (23.8 +_ 1) × 10 -6 m. Heat treatment was realized in air under conditions of EC formation, in a furnace with a nitrogen atmosphere at a temperature of about 360°C for 60 rain and in an argon atmosphere. During work with both atmospheres temperature and time were kept the same. Before deposition of EC samples were defatted in an organic solvent, then immersed in a deposition solution for a few seconds and at last placed in a furnace with air at the temperature about 400°C for 5-10 rain. Phosphate solutions involved water-ethylalcohol solutions of o-phosphoric acid with the addition of oxidation-reduc-
0304-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
A. Kogtudak et al. / Heat treatment and coatings of Feeo.sBt2Si6.5Cl alloys
28
tion components and others [11]. The basic glassforming element of borate solutions for EC was boric acid and its salts including oxidation-reduction components, too [12]. Information about treatment of samples is resumed in table 1. H e was measured by a fluxmeter and H e variations were investigated during six years time. For reproducibility reasons three samples of each set were prepared.
Table 1 Information about treatment sample amorphous Fes0.sB~2 Si~.sC 1 alloys Set rio.
Sample processing as initial state heat treatment in air under conditions of EC formation heat treatment in N 2 under conditions given by NSC heat treatment in Ar under conditions as for no. 3 deposition by phosphate coatings deposition by phosphate coatings with higher H3PO 4 content than for no. 5 deposition by borate coatings with oxidation component added deposition by borate coatings with redaction component added
3. Results and discussion H c was measured at several values of the applied magnetic field, Ha, corresponding to sample polarizations in the nonsaturated or the saturated state. The influence of technological parameters on H c measured at H a = 30 and 630 A / m including its time changes is shown in tables 2 and 3. To examine the effect of technological parameters H e of the processed samples (table 4) was compared with Hc for samples of the initial state. Changes of H c (Hc~ --- Hcx - Hey, where Hcx, H~v are for samples x, y, respectively) m e a s u r e d ira-
mediately after processing show large differences in comparison with deviations of measurements s (tables 2 and 3). At higher magnetic fields (6300 and 20000 A / m ) the H c values were equal to those at H, = 630 A / m within the measuring accuracy and therefore they are ommited.
Table 2 The H(. values at applied magnetic field H,, = 30 A / m . The number of samples for each set n = 3. All data are in units of A / m . HeM is a mean of tt c, measured, tlcc is calculated by the least squa;e methods, s M is the deviation involving both the
measurement repeating and reproducibility Set
0 year
no.
UcM
2 years
SM
Hcc 1 2 3 4 5 6 7 8
1.73 t.71 2.59 2.53 0.48 0.47 1.35 1.23 1.57 1.44 2.27 2.26 1.74 !.23 1.02 0.94
HcM
4 years
sM
Hcc 0.07 0.13 0,06 0.16 0.12 0.27 0. I 1 0.03
2.37 2.34 3.10 3.18 9.79 0.8l 1.68 1 82 1.91 2.10 3.08 3.01 1.88 1.97 1.20 1.33
HeM
6 years
sM
0.13 0.18 0.06 0.11 0.13 0.16 0.13 0.05
3.03 2.31 3.87 4.01 1.37 1.41 2.74 2.g8 2.90 3.08 3.83 4.01 3.43 3.17 1.79 1.88
HCM
SM
Ucc
Hcc 0.15 0,15 0.08 0.31 0.2b 0.15 0.25 0.19
4.60 4.41 5.21 5.06 2.54 2.46 4.72 4.40 4.86 4.50 5.46 5.34 4.94 5.09 2.84 2.65
0.60 0.23 0.17 0.20 0.35 0.12 0.65 0.10
A. Kogturiak et al. / Heat treatment and coatings of Fe so.5B l2Sit~.sC1 alloys
29
Table 3 The H c values at applied magnetic field H a = 630 A / m . The number of samples for each set n = 3. All data are in units of A/re. HCM is a mean of H c measured. Hcc is calculated by the least square methods, s M means the deviation involving both the measurement repeating and reproducibilit3,
Set
0 year
no.
Hc i
2 years s~,t
HCM
Hcc 1
3 4 5 6 7 8
sM
Hcc
5.40 5.34 5,23 5,18 0.87 0.81 2,03 2.06 4.87 4.72 5.54 5.30 2.05 2.14 2.10 2.00
2
4 years
0.28
0.05 0.02 0.12 0.44 0.18 0.05
sM
nci
Hcc
6.77 6.81 6.59 6.63 1.26 1.34 3.46 3.31 5.43 5.50 6.47 6.53 3.54 3.40 2.37 2.48
0,25
HCM
6 years
0.35 0.31 0.06 0.06 0.15 0.32 0.26 0. i 6
3.1. Influence of heat treatment From comparison of Hot (initial state) with He2 (heat treated under conditions of EC formation) it can be seen that differences occur within measurements accuracy only. It can be stated that heat treatment under these conditions does not influence H c changes. However, the difference
SM
Hcc
8.57 8.70 8A0 8.49 2.00 2.20 5.10 5.31 6.27 6.56 7.80 8.04 5.87 5.40 2.94 3.08
0.40
11.29 11.09 11.02 10.88 3.85 3.62 8.67 8.53 8.01 7.74 10.13 9.98 8.13 8.56 4.01 3.82
0.52 0.10 0.04 0.15 0.26 0 40 0.21
0.17 0.75 0.22 0.33 0.25 0.21 1.04 0.30
He41 (He4 is for samples heat treated in argon atmosphere) is very large as compared to the measurements errors. We assume it to be due to diffuse and microcrystalline processes taking place in amorphous ferromagnets. These processes are supported by both temperature and time, differing from those for samples 2. This assumption is also confirmed by the comparison of He3 with
Table 4 Statistic parameters characterizing the dependence log H c = f ( t ) of amorphous Fes0.sBt2Si6.sC1 alloys measured in external magnetieal sphere 30 A m - 1. Total n u m b e r of measurements taken for the calculation of each series N = 12. b is the slope oI dependence, s b is the decisive deviation of slope b, a is the intercept of dependence, s a is the decisive deviation of intercept, EA z is the sum of squared deviations between the measured and by the method least squares calculated values of log H~, r is the coefficient of correlation Set iio.
b
st,
a
sa
E,~ 2
r
1 2 3 4 5 6 7 8
0.0687 0.0502 O.1202 0.0927 0.0827 0.0624 0.1030 0.0751
0.0045 0.0031 0.0043 0.0066 0.0064 0.0037 0.0057 0.0057
0.2320 0.4024 - 0.3312 0.0900 0.1577 0.3531 0.0881 0.0257
0.0035 0.0022 0.0033 0.0046 0.0046 0.0026 0.0041 0.0040
0.0123 0.0057 0.0128 0.0257 0.0250 0.0084 0.0138 0.0196
0.97q 0.982 0.993 0.976 0.971 0.982 0.985 0.972
A. Kogturiak et aL / Heat treatment and coatings of Feso.sBuSi6 sCt alloys
31+)
tte~ corresponding to samples heat treated for the same temperature and time, but for samples 3 a N 2 atmosphere was applied. We can see that Hot 3 = 4.57 A / m (table 3). The effect of formation of nitrogen nitrides with iron at the surface is involved to this difference. This process may be expressed by the equation 16Fe+N, .
w, ~ FemN 2
,,." , 2 FeN 4 + 8 Fe,
(1) where w t is a reaction rate of the formation of metastable tetragonal Fet~N 2 which one transforms with a reaction rate w 2 to the stable Fe4N [13]. Hence, He34 = 1.2 A / m corresponds to the formation of the stable cubic nitride.
H PO4 "
3.2. Influence of" electrotechnical coatings 7"0 separate the EC contribution to H c we have compared the samples coated with borate and phosphate layers in respect to samples 2. Table 3 shows the values of Hc27 and Hc2s to be about 3.15 A / m . This difference is very large in
F
+'--;- . . . . . . .
7 . . . . . . . .
T..........
7
t°+Hc!
T--
.....
comparison with measurements errors and may be explained by a suitable variation of the chemical and physical state of a sample surface due to its reaction with borate solutions. On the other hand, from the comparison both He5 and He6 with Hc2, it turns out that phosphate coatings do not contribute remarkably to the change of H c. We propose it to be caused by the higher reactivity of o-phosphoric acid [14], in contrast to boric acid. This can be understood by analyzing the powers of both acids. Their measured values, as it is well known, are dependent on the dissociate constant K. O-phosphoric acid dissociates aecording to the reaction scheme:
~
2.23
US+ H2PO -
+ HPO42- ~
12.32
7.21
H÷
H + + PO43- ,
(2)
where pK is the negative logarithm of K. Boric acid dissociates according to the scheme:
H~BO~ ~ " - 9.2 + HBO2_
l
•
I
H++ H2BO ~ pK.a 13.8
pK~> 12.7
H+ + B O ~ - .
H+ (3)
We can see that PKH3PO4 << pK H3BO3 thus H3PO 4 reactivity with the surface of samples is many times greater than that of H3BO 3 z,nd wetting effect occurs. To confirm this effect we compare Hc5 with Hc6.
:!
3.3. Influence of technological parameters on time variations of He From an analysis of results it turns out that H 2 is increasing nonlinearly with time. This dependence can be described by the relation M
*'C +.+t.
O
I
I
2
.....
1
I
4
I
__
I
t [ymor]
Fig. 1. The dependence log H c as a function of time for some samples heat treated. (1) as initial state, (2) heat treated in air u n d e r conditions - f formation ot electrotechnical coatings, (3) heat treated in atmosphere N 2 / 3 6 0 ° C / 6 0 min, (4) heat treated in atmosphere A r / 3 6 0 ° C / 6 0 rain.
= I4
aacO
C kt.
E4"~ k
J
In fig. 1 the dependence log H c as a function of time for some samples heat treated is shown. Fig. 2 shows the log H¢-t dependence for some samples with coatings. From the tables 4 and 5 it is evident that the values of coefficients of correlation are sufficiently high (0.993-0.960) to con-
31
A. Ko~turiak et al. / Heat treatment and coatings o[ Fe so.,sBuSi o ~C ~ alloys I
I
I
t°g~ 1' 0, 9 -
07
0,5
0.3 I
I
I
0
2
t,
I
t[yeari
Fig. 2. The dependence log He as a function of tirr,e for some samples with coatings. (2) heat treated in air under conditions of EC coatings, (5) deposited by phosphate coatings, (6) deposited by phosphate coatings with higher HzPO a amount than for no. 5, (7) deposited by borate coatings with oxidation component added, (8) deposited by borate coatings having reduction component added.
firm the possibility of formal description with maturing of samples of proceeding rctions by used relation (4). The adequatly low values Z j 2 prove it. The log Hc-t dependence may bc from the chemical kinetics point of view formaly taken as a monomolecular reaction described by a kinetic equation of first order. In fact, the description of chemical processes taking place at techno-
logical treatment as well as natural aging is more complicated. It is supported also by the various influences of technological parameters on the H~ of the same set, For example H~t and 2 (tables 2 and 3). Such irregularities are even mere plausible for H c measured after 6 years time of natural aging, e.g. H a vs. H¢7 (table 3, fig. 2). In this case, the anomaly seems to be due to various stabilizing effects of borate coatings having oxidation components. In agreement with that, the slope at the log H¢ vs. t function for sample 7 is greater than that for sample 5. Hence phosphate coatings exhibit a far better stabilizing influence on physical and chemical actions taking place at a sample surface. As it is known [15] the processes which act at the surface during aging may be characterized as a heterogeneous, competitive, catalytic reaction. These processes are very complicated with a great number of interfering factors contributing to He. It means that the values of slopes b (tables 4 and 5) express in logarithmic form the reaction rate. Together with the intercept values it is possible with relation (4) to calculate the total rate constants (table 6) quantifying the time change H c tn the investigated samples. However, the number values of slopes b as well as rate constants k, do not allow to decide about the influence of the physicochemical state of the surface to the time stability of He. We can cot, sider H~. to be composed of two parts as follows: He = H ° + H2,
(5)
where H ° is a nearly constant part limited substantially by conditions of a material processing.
Table 5 Statistic parameters characterizing the dependence log H c = f ( t ) of amorphous Fes0.sB12Sio.5C1 alloys measured in external magnetical sphere 630 A m - t . Total number of measurements taken for the c: Iculation of in each series N = 12 Set
b
sb
0.0530 0.0537 0.1081 0.1030 0.0358 0.0452 0.1003 0.0468
0.0036 0.0030 0.0053 0.0031 0.0026 0.0029 0.0064 0.0044
a
sa
E,l 2
r
0.0028 0.0{t21 0.0037 0.0022 0.0018 0.0021 0.0045 0.0031
l).0176 0.1)053 tl.01 fit% 0.0057 0.0040 0.0049 0.0025 0.01 i 5
0.978 0.085 0.988 0.996 0.975 0.980 0.980 0.960
no.
1 2 3 4 5 6 7 8
0.7273 0.7142 - 9.0900 0.3133 0.6737 0.7244 0.3310 0.3009
32
A. Ko~turiak et al. / Heat treatment and coatings of Feso sBt,Si6.sC l alloys
H~~ forms in a relative short time. H2 is a time dependent component limited mainly by physical and chemical processes occuring at the surface during aging. Average time gains of H~ allow us to decide about this influence (table 6). The time gains are related to an external magnetic field of 630 A/re. On the basis of time stability values of Hc1 we can arrange the samples into the following series: stabilisating influence of surface
0.303~s~< 0.151o~ < 0.503~s~ < 0.767~ < 0.947~, < 0.g670~ < 1.049~7~< 1.079{47 ,,)
destabilisating influence of surface
This order is congruent with experimentally observed time changes of H c (table 3). It expresses the fact that borat coatings made from applied solutions containing substances of reducing nature have the highest stabilizating influence ot H~. Taking into account the fact that using borat depositing solutions which consist of substances of oxidative nature to make coatings destabilizing H~, we can see the main influence of oxido-reducing processes on the surface of these ferromagnetic materials to the time stability of H c. With regard to the adequatly low value of H ° and electroisolating resistance of borat coatings, samples 8 seem to be the most appropiate for practical applications, even more advantageous than samples 3 with nitridic layer on their surface, what shows minimal electroisolating properties. In an external magnetic field 30 A / m the order of samples on the first two place" does not change. But the washing effect of o-phosphoric acid has a destabilizing influence on Hc in low fields. Although in this work there is not sufficient amount of proof to explicit some of the existing anomalies, the evaluation of depicted magnetica! properties of these materials will help to reveal them. F~r practical use, particularly, it is possible taking into account approximate relations. As a time stability measure we have taken a slope k in the linear dependence: H c = H e + kt. The time stability measure k is show,l in table 6 for both H~ measured and calculated. This phenomenon
representing the mean time increase of H i shows that the borate coatings from solutions with reduction components have the strongest effect on He. In contrast, the borate solutions having oxidation components form coatings with an apparent destabilizing effect. With regards to a relatively low H e and an appropriate electroinsulating resistivity samples 8 seem to be the most suitable ones. It is the case, even as compared with samples 3 having similar stability, but minimal electroinsulating properties. At low magnetic fields (table 2) the destabilizing wetting effect of o-phosphoric acid appears to influence the time stability. Is should be noted, in addition to effects discussed, that there is a number of other factors to be taken into account. Therefore further work is in progress to study other magnetic properties since the anomalies mentioned before are expected to be explained.
4. Conclusions
The influence of heat treatment and electrotechnical coatings on coercive force H e of amorphous Fes0.sB12Si6.sC1 alloys was investigated during 6 years time. On the basis of experimental results and statistical analysis it was shown that H c arises in a complicated process. From a chemical and physical point of view this process can be considered as a heterogeneous competitive, catalytic reaction and can be described by a kinetic equation of first order for homogeneous monomolecule reactions. H c measured, in principle, may be divided into 2 parts: (1) H °, arising during a relative short time interval affected mainly by technological conditions of sample treatment (temperature, annealing atmosphere, chemical properties of deposition solutions, etc.). (2) Hi, occurring during a long time interval affected predominantly by the chemical and physical properties of the metal ferromagnetic surface. The analysis of technological conditions shows the limiting influence of these parameters on
He°:
A. Ko~turiak et al. / Heat treatmem and coatings of Fe so.s Bt2Si 6.sC I alloys
(a) temperature and time of heat treatment, supporting diffuse and crystallization processes; (b) annealing atmosphere that makes it possible that qualitatively new types of compounds at the surface occur. This change immediately leads to variations of physical properties of material surfaces; (e) chemical composition of deposition solutions, which react with the surface of amorphous samples during a transformation to eleetroteehnieal coatings. As a consequence of that their physical and chemical properties are changed considerable and thus basic material properties as well. On the other hand, the analysis of parameters limiting H i affecting the surface properties shows: (a) considerable stabilizing effect of phosphate coatings, (b) partly destabilizing effect of o-phosphoric acid, (e) remarkable destabilizing effect of oxidation elements at borate coatings, (d) remarkable destabilizing effect of the long time heat treatment leading to the arising of crystallization centres, in particular, at the surface of basic materials. ~ased on the results obtained it comes out that for practical use of these materials H c is suitable to be minimized not only with regards to its value measured after preparation but also from point of view of its time stability. Therefore, the most suitable properties exhibit samples 8.
33
References [1] I. Nagyi, T. Tarnoczi, M. Hosso and F. Pavlyak, Conf, on Metallic Glasses, Science and Technology, Kultura, Budapest (1980) p. 223. [2] Y.J. Wang and H. KronmiiUer, Phys. Stat. Sol (a) 70 (1982) 415. [3] A. Ko~turiak, J. DanieI-Szab6, M. Kon~ and A. Zentko, Proe. Conf. Pure Chemicals, Vol. 1 (in Slovak), Dora techniM SVTS, Bratislava (1982) p. 59. [4] A. Zentko, A. Ko~turiak and P. Duhaj, IEEE Trans. Magn. MAG-20 (1984) 1326. [5] V.V. Nemogkalenko et al., Amorfnyje metalli eskije splaw (in Russian) (Naukova Dumka, Kiev, 1987). [61 H. Kronmiiller, J. Magn. Magn. Mater. 24 (1981) 159. [7] Z. Jur~nek, P. Koll~ir, L. Potoek~ and L. Nov~k, Acta Phys. Slovaca 38 (1988) 261. [8] W. Grimm, B. Metzer and H. Hubert, J. Magn. Magn. Mater. 27 (1984) 171. [9] D. Nathasingh and A. Datta, Digest of Int. May. Conf., Hamburg, Germany (1984) p. 59. [10] M. Kawashima, Manager Nippon Steel Corporation, private communications. [11] A. Ko§turiak, A. Zentko and M. Kon~, Czech. pat. AO 221 1982. [12] A. Ko~turiak, Czech. pat. AO 245 108. [13] V. Hajko, A. Ko~turiak and M. Trenkler, Br. Ind. Sci. Int. Met. Soc. 1"7, 295 (London, 1978) p. 1. [14] A. Zentko, A. Ko~turiak and P. Duhaj, Digest of Int. Magn. Cont., Hamburg, Germany (1984) p. 54. [15] J.C Jungers et al., Chemical Kinetics (Czech. iransl.) (SAV, Prague, 1963).
Influence of heat treatment and coatings on time stability of coercive force of the amorphous Fes0.sBa2Si6.sC 1 alloys A. Ko~turiak Department of Phys. and Analytical Chemistry, Faculty of Sciences, Moyzesora 11, 041 54 Ktogice, Czechosloeakia
O. Du,~a a n d J. G a j d u g e k Department of Exp. Phys., Faculty of Sciences, ndm. Feor. ef~azstt,a 9, 041 54 Ko~ice, Czechoslovakia Received 11 July 1991; in revised torm 1 October 1991
The influence of both heat treatment in various atmospheres and eleclrotechnical coatings on the coercive torce and its long time stability for amorphous Fes0.sBt2Si6.sC l alloys was studied. A number of factors, predominantly chemical processes, acting at the heat treatment and the coating deposition, are diseussed.
1. Introduction It is well established that various macroscopic magnetic properties of amorphous metal ferromagnets prepared by the rapid quenching method are dependent to a considerable extent on the physical and chemical state of a surface [1-5]. The coercive force, H c, is one of such basic magnetic characteristics indicating the possibility of a material application [6-8]. The time stability of properties of amorphous ferromagnetic alloys appears to be a poor characteristic as compared with classic type materials. The coating of amorphous materials by a thin surface layer (anorganic or organic) which acts simultaneously as an electroinsulating, anticorrosive and magnetic stimulating factor, should serve to a stability increase [3,4,9]. Amorphous Fes0.sBt2Si6.5C 1 alloys exhibit extremely low magnetic losses (p~.3v=(0.105_+ 0.004) W kg-1; Pt.4T = (0.129 _+ 0.003) W kg -~ at f = 5 0 Hz [10]. The first problem for coatings application leads one to finding e[eetrotechnical coatings (EC) to decrease magnetic losses or at least not to increase it. The aim of this paper is to present the influ-
ence of heat treatment, phosphate and borate coatings on H c and its time stability.
2. Experimental Amorphous Fes05Bl:Si,~Ci ribbon was prepared by rapid quenching from the melt onto a rotating wheel at the Nippon Steel Corp. Laboratory. Its sample number is A 030-B. From this ribbon, given to us, samples were cut having length l = 130 ram, width w = 25 mm and thickness d = (23.8 +_ 1) × 10 -6 m. Heat treatment was realized in air under conditions of EC formation, in a furnace with a nitrogen atmosphere at a temperature of about 360°C for 60 rain and in an argon atmosphere. During work with both atmospheres temperature and time were kept the same. Before deposition of EC samples were defatted in an organic solvent, then immersed in a deposition solution for a few seconds and at last placed in a furnace with air at the temperature about 400°C for 5-10 rain. Phosphate solutions involved water-ethylalcohol solutions of o-phosphoric acid with the addition of oxidation-reduc-
0304-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
A. Kogtudak et al. / Heat treatment and coatings of Feeo.sBt2Si6.5Cl alloys
28
tion components and others [11]. The basic glassforming element of borate solutions for EC was boric acid and its salts including oxidation-reduction components, too [12]. Information about treatment of samples is resumed in table 1. H e was measured by a fluxmeter and H e variations were investigated during six years time. For reproducibility reasons three samples of each set were prepared.
Table 1 Information about treatment sample amorphous Fes0.sB~2 Si~.sC 1 alloys Set rio.
Sample processing as initial state heat treatment in air under conditions of EC formation heat treatment in N 2 under conditions given by NSC heat treatment in Ar under conditions as for no. 3 deposition by phosphate coatings deposition by phosphate coatings with higher H3PO 4 content than for no. 5 deposition by borate coatings with oxidation component added deposition by borate coatings with redaction component added
3. Results and discussion H c was measured at several values of the applied magnetic field, Ha, corresponding to sample polarizations in the nonsaturated or the saturated state. The influence of technological parameters on H c measured at H a = 30 and 630 A / m including its time changes is shown in tables 2 and 3. To examine the effect of technological parameters H e of the processed samples (table 4) was compared with Hc for samples of the initial state. Changes of H c (Hc~ --- Hcx - Hey, where Hcx, H~v are for samples x, y, respectively) m e a s u r e d ira-
mediately after processing show large differences in comparison with deviations of measurements s (tables 2 and 3). At higher magnetic fields (6300 and 20000 A / m ) the H c values were equal to those at H, = 630 A / m within the measuring accuracy and therefore they are ommited.
Table 2 The H(. values at applied magnetic field H,, = 30 A / m . The number of samples for each set n = 3. All data are in units of A / m . HeM is a mean of tt c, measured, tlcc is calculated by the least squa;e methods, s M is the deviation involving both the
measurement repeating and reproducibility Set
0 year
no.
UcM
2 years
SM
Hcc 1 2 3 4 5 6 7 8
1.73 t.71 2.59 2.53 0.48 0.47 1.35 1.23 1.57 1.44 2.27 2.26 1.74 !.23 1.02 0.94
HcM
4 years
sM
Hcc 0.07 0.13 0,06 0.16 0.12 0.27 0. I 1 0.03
2.37 2.34 3.10 3.18 9.79 0.8l 1.68 1 82 1.91 2.10 3.08 3.01 1.88 1.97 1.20 1.33
HeM
6 years
sM
0.13 0.18 0.06 0.11 0.13 0.16 0.13 0.05
3.03 2.31 3.87 4.01 1.37 1.41 2.74 2.g8 2.90 3.08 3.83 4.01 3.43 3.17 1.79 1.88
HCM
SM
Ucc
Hcc 0.15 0,15 0.08 0.31 0.2b 0.15 0.25 0.19
4.60 4.41 5.21 5.06 2.54 2.46 4.72 4.40 4.86 4.50 5.46 5.34 4.94 5.09 2.84 2.65
0.60 0.23 0.17 0.20 0.35 0.12 0.65 0.10
A. Kogturiak et al. / Heat treatment and coatings of Fe so.5B l2Sit~.sC1 alloys
29
Table 3 The H c values at applied magnetic field H a = 630 A / m . The number of samples for each set n = 3. All data are in units of A/re. HCM is a mean of H c measured. Hcc is calculated by the least square methods, s M means the deviation involving both the measurement repeating and reproducibilit3,
Set
0 year
no.
Hc i
2 years s~,t
HCM
Hcc 1
3 4 5 6 7 8
sM
Hcc
5.40 5.34 5,23 5,18 0.87 0.81 2,03 2.06 4.87 4.72 5.54 5.30 2.05 2.14 2.10 2.00
2
4 years
0.28
0.05 0.02 0.12 0.44 0.18 0.05
sM
nci
Hcc
6.77 6.81 6.59 6.63 1.26 1.34 3.46 3.31 5.43 5.50 6.47 6.53 3.54 3.40 2.37 2.48
0,25
HCM
6 years
0.35 0.31 0.06 0.06 0.15 0.32 0.26 0. i 6
3.1. Influence of heat treatment From comparison of Hot (initial state) with He2 (heat treated under conditions of EC formation) it can be seen that differences occur within measurements accuracy only. It can be stated that heat treatment under these conditions does not influence H c changes. However, the difference
SM
Hcc
8.57 8.70 8A0 8.49 2.00 2.20 5.10 5.31 6.27 6.56 7.80 8.04 5.87 5.40 2.94 3.08
0.40
11.29 11.09 11.02 10.88 3.85 3.62 8.67 8.53 8.01 7.74 10.13 9.98 8.13 8.56 4.01 3.82
0.52 0.10 0.04 0.15 0.26 0 40 0.21
0.17 0.75 0.22 0.33 0.25 0.21 1.04 0.30
He41 (He4 is for samples heat treated in argon atmosphere) is very large as compared to the measurements errors. We assume it to be due to diffuse and microcrystalline processes taking place in amorphous ferromagnets. These processes are supported by both temperature and time, differing from those for samples 2. This assumption is also confirmed by the comparison of He3 with
Table 4 Statistic parameters characterizing the dependence log H c = f ( t ) of amorphous Fes0.sBt2Si6.sC1 alloys measured in external magnetieal sphere 30 A m - 1. Total n u m b e r of measurements taken for the calculation of each series N = 12. b is the slope oI dependence, s b is the decisive deviation of slope b, a is the intercept of dependence, s a is the decisive deviation of intercept, EA z is the sum of squared deviations between the measured and by the method least squares calculated values of log H~, r is the coefficient of correlation Set iio.
b
st,
a
sa
E,~ 2
r
1 2 3 4 5 6 7 8
0.0687 0.0502 O.1202 0.0927 0.0827 0.0624 0.1030 0.0751
0.0045 0.0031 0.0043 0.0066 0.0064 0.0037 0.0057 0.0057
0.2320 0.4024 - 0.3312 0.0900 0.1577 0.3531 0.0881 0.0257
0.0035 0.0022 0.0033 0.0046 0.0046 0.0026 0.0041 0.0040
0.0123 0.0057 0.0128 0.0257 0.0250 0.0084 0.0138 0.0196
0.97q 0.982 0.993 0.976 0.971 0.982 0.985 0.972
A. Kogturiak et aL / Heat treatment and coatings of Feso.sBuSi6 sCt alloys
31+)
tte~ corresponding to samples heat treated for the same temperature and time, but for samples 3 a N 2 atmosphere was applied. We can see that Hot 3 = 4.57 A / m (table 3). The effect of formation of nitrogen nitrides with iron at the surface is involved to this difference. This process may be expressed by the equation 16Fe+N, .
w, ~ FemN 2
,,." , 2 FeN 4 + 8 Fe,
(1) where w t is a reaction rate of the formation of metastable tetragonal Fet~N 2 which one transforms with a reaction rate w 2 to the stable Fe4N [13]. Hence, He34 = 1.2 A / m corresponds to the formation of the stable cubic nitride.
H PO4 "
3.2. Influence of" electrotechnical coatings 7"0 separate the EC contribution to H c we have compared the samples coated with borate and phosphate layers in respect to samples 2. Table 3 shows the values of Hc27 and Hc2s to be about 3.15 A / m . This difference is very large in
F
+'--;- . . . . . . .
7 . . . . . . . .
T..........
7
t°+Hc!
T--
.....
comparison with measurements errors and may be explained by a suitable variation of the chemical and physical state of a sample surface due to its reaction with borate solutions. On the other hand, from the comparison both He5 and He6 with Hc2, it turns out that phosphate coatings do not contribute remarkably to the change of H c. We propose it to be caused by the higher reactivity of o-phosphoric acid [14], in contrast to boric acid. This can be understood by analyzing the powers of both acids. Their measured values, as it is well known, are dependent on the dissociate constant K. O-phosphoric acid dissociates aecording to the reaction scheme:
~
2.23
US+ H2PO -
+ HPO42- ~
12.32
7.21
H÷
H + + PO43- ,
(2)
where pK is the negative logarithm of K. Boric acid dissociates according to the scheme:
H~BO~ ~ " - 9.2 + HBO2_
l
•
I
H++ H2BO ~ pK.a 13.8
pK~> 12.7
H+ + B O ~ - .
H+ (3)
We can see that PKH3PO4 << pK H3BO3 thus H3PO 4 reactivity with the surface of samples is many times greater than that of H3BO 3 z,nd wetting effect occurs. To confirm this effect we compare Hc5 with Hc6.
:!
3.3. Influence of technological parameters on time variations of He From an analysis of results it turns out that H 2 is increasing nonlinearly with time. This dependence can be described by the relation M
*'C +.+t.
O
I
I
2
.....
1
I
4
I
__
I
t [ymor]
Fig. 1. The dependence log H c as a function of time for some samples heat treated. (1) as initial state, (2) heat treated in air u n d e r conditions - f formation ot electrotechnical coatings, (3) heat treated in atmosphere N 2 / 3 6 0 ° C / 6 0 min, (4) heat treated in atmosphere A r / 3 6 0 ° C / 6 0 rain.
= I4
aacO
C kt.
E4"~ k
J
In fig. 1 the dependence log H c as a function of time for some samples heat treated is shown. Fig. 2 shows the log H¢-t dependence for some samples with coatings. From the tables 4 and 5 it is evident that the values of coefficients of correlation are sufficiently high (0.993-0.960) to con-
31
A. Ko~turiak et al. / Heat treatment and coatings o[ Fe so.,sBuSi o ~C ~ alloys I
I
I
t°g~ 1' 0, 9 -
07
0,5
0.3 I
I
I
0
2
t,
I
t[yeari
Fig. 2. The dependence log He as a function of tirr,e for some samples with coatings. (2) heat treated in air under conditions of EC coatings, (5) deposited by phosphate coatings, (6) deposited by phosphate coatings with higher HzPO a amount than for no. 5, (7) deposited by borate coatings with oxidation component added, (8) deposited by borate coatings having reduction component added.
firm the possibility of formal description with maturing of samples of proceeding rctions by used relation (4). The adequatly low values Z j 2 prove it. The log Hc-t dependence may bc from the chemical kinetics point of view formaly taken as a monomolecular reaction described by a kinetic equation of first order. In fact, the description of chemical processes taking place at techno-
logical treatment as well as natural aging is more complicated. It is supported also by the various influences of technological parameters on the H~ of the same set, For example H~t and 2 (tables 2 and 3). Such irregularities are even mere plausible for H c measured after 6 years time of natural aging, e.g. H a vs. H¢7 (table 3, fig. 2). In this case, the anomaly seems to be due to various stabilizing effects of borate coatings having oxidation components. In agreement with that, the slope at the log H¢ vs. t function for sample 7 is greater than that for sample 5. Hence phosphate coatings exhibit a far better stabilizing influence on physical and chemical actions taking place at a sample surface. As it is known [15] the processes which act at the surface during aging may be characterized as a heterogeneous, competitive, catalytic reaction. These processes are very complicated with a great number of interfering factors contributing to He. It means that the values of slopes b (tables 4 and 5) express in logarithmic form the reaction rate. Together with the intercept values it is possible with relation (4) to calculate the total rate constants (table 6) quantifying the time change H c tn the investigated samples. However, the number values of slopes b as well as rate constants k, do not allow to decide about the influence of the physicochemical state of the surface to the time stability of He. We can cot, sider H~. to be composed of two parts as follows: He = H ° + H2,
(5)
where H ° is a nearly constant part limited substantially by conditions of a material processing.
Table 5 Statistic parameters characterizing the dependence log H c = f ( t ) of amorphous Fes0.sB12Sio.5C1 alloys measured in external magnetical sphere 630 A m - t . Total number of measurements taken for the c: Iculation of in each series N = 12 Set
b
sb
0.0530 0.0537 0.1081 0.1030 0.0358 0.0452 0.1003 0.0468
0.0036 0.0030 0.0053 0.0031 0.0026 0.0029 0.0064 0.0044
a
sa
E,l 2
r
0.0028 0.0{t21 0.0037 0.0022 0.0018 0.0021 0.0045 0.0031
l).0176 0.1)053 tl.01 fit% 0.0057 0.0040 0.0049 0.0025 0.01 i 5
0.978 0.085 0.988 0.996 0.975 0.980 0.980 0.960
no.
1 2 3 4 5 6 7 8
0.7273 0.7142 - 9.0900 0.3133 0.6737 0.7244 0.3310 0.3009
32
A. Ko~turiak et al. / Heat treatment and coatings of Feso sBt,Si6.sC l alloys
H~~ forms in a relative short time. H2 is a time dependent component limited mainly by physical and chemical processes occuring at the surface during aging. Average time gains of H~ allow us to decide about this influence (table 6). The time gains are related to an external magnetic field of 630 A/re. On the basis of time stability values of Hc1 we can arrange the samples into the following series: stabilisating influence of surface
0.303~s~< 0.151o~ < 0.503~s~ < 0.767~ < 0.947~, < 0.g670~ < 1.049~7~< 1.079{47 ,,)
destabilisating influence of surface
This order is congruent with experimentally observed time changes of H c (table 3). It expresses the fact that borat coatings made from applied solutions containing substances of reducing nature have the highest stabilizating influence ot H~. Taking into account the fact that using borat depositing solutions which consist of substances of oxidative nature to make coatings destabilizing H~, we can see the main influence of oxido-reducing processes on the surface of these ferromagnetic materials to the time stability of H c. With regard to the adequatly low value of H ° and electroisolating resistance of borat coatings, samples 8 seem to be the most appropiate for practical applications, even more advantageous than samples 3 with nitridic layer on their surface, what shows minimal electroisolating properties. In an external magnetic field 30 A / m the order of samples on the first two place" does not change. But the washing effect of o-phosphoric acid has a destabilizing influence on Hc in low fields. Although in this work there is not sufficient amount of proof to explicit some of the existing anomalies, the evaluation of depicted magnetica! properties of these materials will help to reveal them. F~r practical use, particularly, it is possible taking into account approximate relations. As a time stability measure we have taken a slope k in the linear dependence: H c = H e + kt. The time stability measure k is show,l in table 6 for both H~ measured and calculated. This phenomenon
representing the mean time increase of H i shows that the borate coatings from solutions with reduction components have the strongest effect on He. In contrast, the borate solutions having oxidation components form coatings with an apparent destabilizing effect. With regards to a relatively low H e and an appropriate electroinsulating resistivity samples 8 seem to be the most suitable ones. It is the case, even as compared with samples 3 having similar stability, but minimal electroinsulating properties. At low magnetic fields (table 2) the destabilizing wetting effect of o-phosphoric acid appears to influence the time stability. Is should be noted, in addition to effects discussed, that there is a number of other factors to be taken into account. Therefore further work is in progress to study other magnetic properties since the anomalies mentioned before are expected to be explained.
4. Conclusions
The influence of heat treatment and electrotechnical coatings on coercive force H e of amorphous Fes0.sB12Si6.sC1 alloys was investigated during 6 years time. On the basis of experimental results and statistical analysis it was shown that H c arises in a complicated process. From a chemical and physical point of view this process can be considered as a heterogeneous competitive, catalytic reaction and can be described by a kinetic equation of first order for homogeneous monomolecule reactions. H c measured, in principle, may be divided into 2 parts: (1) H °, arising during a relative short time interval affected mainly by technological conditions of sample treatment (temperature, annealing atmosphere, chemical properties of deposition solutions, etc.). (2) Hi, occurring during a long time interval affected predominantly by the chemical and physical properties of the metal ferromagnetic surface. The analysis of technological conditions shows the limiting influence of these parameters on
He°:
A. Ko~turiak et al. / Heat treatmem and coatings of Fe so.s Bt2Si 6.sC I alloys
(a) temperature and time of heat treatment, supporting diffuse and crystallization processes; (b) annealing atmosphere that makes it possible that qualitatively new types of compounds at the surface occur. This change immediately leads to variations of physical properties of material surfaces; (e) chemical composition of deposition solutions, which react with the surface of amorphous samples during a transformation to eleetroteehnieal coatings. As a consequence of that their physical and chemical properties are changed considerable and thus basic material properties as well. On the other hand, the analysis of parameters limiting H i affecting the surface properties shows: (a) considerable stabilizing effect of phosphate coatings, (b) partly destabilizing effect of o-phosphoric acid, (e) remarkable destabilizing effect of oxidation elements at borate coatings, (d) remarkable destabilizing effect of the long time heat treatment leading to the arising of crystallization centres, in particular, at the surface of basic materials. ~ased on the results obtained it comes out that for practical use of these materials H c is suitable to be minimized not only with regards to its value measured after preparation but also from point of view of its time stability. Therefore, the most suitable properties exhibit samples 8.
33
References [1] I. Nagyi, T. Tarnoczi, M. Hosso and F. Pavlyak, Conf, on Metallic Glasses, Science and Technology, Kultura, Budapest (1980) p. 223. [2] Y.J. Wang and H. KronmiiUer, Phys. Stat. Sol (a) 70 (1982) 415. [3] A. Ko~turiak, J. DanieI-Szab6, M. Kon~ and A. Zentko, Proe. Conf. Pure Chemicals, Vol. 1 (in Slovak), Dora techniM SVTS, Bratislava (1982) p. 59. [4] A. Zentko, A. Ko~turiak and P. Duhaj, IEEE Trans. Magn. MAG-20 (1984) 1326. [5] V.V. Nemogkalenko et al., Amorfnyje metalli eskije splaw (in Russian) (Naukova Dumka, Kiev, 1987). [61 H. Kronmiiller, J. Magn. Magn. Mater. 24 (1981) 159. [7] Z. Jur~nek, P. Koll~ir, L. Potoek~ and L. Nov~k, Acta Phys. Slovaca 38 (1988) 261. [8] W. Grimm, B. Metzer and H. Hubert, J. Magn. Magn. Mater. 27 (1984) 171. [9] D. Nathasingh and A. Datta, Digest of Int. May. Conf., Hamburg, Germany (1984) p. 59. [10] M. Kawashima, Manager Nippon Steel Corporation, private communications. [11] A. Ko§turiak, A. Zentko and M. Kon~, Czech. pat. AO 221 1982. [12] A. Ko~turiak, Czech. pat. AO 245 108. [13] V. Hajko, A. Ko~turiak and M. Trenkler, Br. Ind. Sci. Int. Met. Soc. 1"7, 295 (London, 1978) p. 1. [14] A. Zentko, A. Ko~turiak and P. Duhaj, Digest of Int. Magn. Cont., Hamburg, Germany (1984) p. 54. [15] J.C Jungers et al., Chemical Kinetics (Czech. iransl.) (SAV, Prague, 1963).