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Specific features of copper and nickel oxides obtained under extreme conditions by CO2 laser irradiation of inorganic salts
Materials Science and Engineering, A 168 (1993) 71-73
71
Specific features of copper and nickel oxides obtained under extreme conditions by CO2 laser irradiation of inorganic salts C. P o p e s c u LACECA Research Centre, Str. Siret 95, Sector 1, 78308, Bucharest (Romania) R. A l e x a n d r e s c u , I. M o r j a n a n d I. V o i c u Institute for Atomic Physics, P.O. Box MG-6, Bucharest-M6gurele (Romania)
Abstract Several experiments showed that nickel and copper salts are decomposed to oxides by irradiation with a continuous wave CO 2 laser. The processes are characterized by an extremely high heating rate which develops within the impact region of the laser beam with the substrate. The salts were also decomposed under controlled heating conditions. A difference was noticed concerning the size and isotropy of final crystallites obtained by laser irradiation as compared with thermal heating. The magnitude of this difference seems to be related to the laser quanta absorptivity of the salts.
1. Introduction
2. Experimental details
The interaction of high-power laser radiation with solid systems is often investigated using a thermochemical approach, in which the strong localized action of the laser beam imposes the characteristics of the processes [1 ]. In earlier works [2, 3] it was shown that the decomposition of inorganic salts exposed to IR laser radiation takes place under unusual heating conditions, characterized by high heating rates developing within the impact region of the laser beam. Compared with the reaction products obtained in classical thermal decomposition, the oxides produced using laser processes exhibited peculiarities of structure and morphology. A correlation was found between these features and the absorptivity of the initial salts to the wavelength of laser radiation. In this paper we present new results on the laser decomposition of some copper salts. The similarities of their behaviour and that of nickel salts under the same conditions are revealed. The salts were also decomposed under controlled heating. Crystallographic investigations of the oxides produced (CuO and NiO) revealed differences in the size and isotropy of crystallites produced from laser experiments compared with those obtained by thermal heating. The high heating rates which characterize the laser processes together with the absorptivity of the substance to the laser wavelength should both be involved in the kinetics of the reactions.
Different nickel and copper salts of analytical purity grade were used. Their IR spectral characteristics within the range of CO2 laser emission (10.6/zm) were investigated and the results are given in Table 1. Laser irradiation experiments were performed using a continuous wave CO2 laser of beam intensity 400-600 W c m -2. The salts, in powdered form, were evenly distributed as a thin layer in a metal reaction cell, which was moved perpendicular to the beam at various speeds. After each passage through the laser beam the samples were weighed (accuracy + 5 x 10- 5g) until constant weight was achieved. A Q 1500 D MOM derivatograph was used for the thermal analysis experiments. Heating rates of 5 and 10 K rain- 1 were used.
0921-5093/93/$6.00
TABLE I. Absorptivity values of nickel and copper salts at 10.6/~m Substance
Code
Absorptivity (%)
NiCO 3 •Ni(OH) 2 •H20 Ni(NO3) 2"6H20 NiC12 "6H20 NiSO 4 •7H20
K A C S
42 2 0 8
Cu2CO3(OH)2
K' A' S' C'
15 5 13 1-2
Cu(CH3COO)2 "H20 CuSO 4.51t20 CuCI: •2H20
© 1993 - Elsevier Sequoia. All rights reserved
72
C Popescu et aL
/
Cu and Ni oxides obtained using CO2 laser
X-ray diffraction measurements were taken using a Philips diffractometer, with Cu K a radiation.
3. Results and discussion The salts were processed in the laser beam, until a constant weight was observed. The weight losses v s . time can be used to study the kinetics of the laserinduced reactions [3]. The same salts were thermally decomposed in the derivatograph and the recorded thermogravimetric data were processed to give a kinetic analysis of the thermal reactions [4]. Table 2 presents the mass losses for the copper salts, decomposed thermally and by laser radiation. Thermal experiments all give CuO as the final product (in the limits of our experimental method). From laser experiments, either a non-stoichiometric oxide CUOx, x < 1, is obtained, or, more likely, a mixture of oxides Cu20 and CuO. Crystallographic investigations of both nickel and copper oxides by X-ray diffraction showed that the crystallites of laser-treated samples were larger than those obtained thermally and that this difference increased for salts with higher absorptivity to the wavelength of laser radiation. The mean size of the oxide crystallites was determined along the [111] and [200] crystallographic directions using the Debye-Sherrer
TABLE 2. Mass losses in laser and thermal experiments, compared with stoichiometric losses Substance
Thermal Laser Theoretical mass mass loss mass loss loss (%) (%) (%) To Cu20 To CuO
CuSO4"5H20 Cu2CO3(OH)2 CuC12"2H20 Cu(CH3COO)2"H20
68.5 29.3 84.6 60.2
69.6 33.2 61.4 a
71.3 35.3 58.1 64.2
68.1 28.1 53.4 60.15
aThe salt was scattered by the laser beam.
TABLE 3. Size of CuO crystallites obtained from thermal and laser processes, from different inorganic salts Substance
Cu2CO3(OH)2
CuSO4.5H20 Cu(CH3COO)2H20 CuC12'2HzO
Thermal process
Laser process
DIll (/~)
D2oo(A) D l l
383 540 416 573
392 561 434 563
580 572 656 556
I (A)
D2oo(A) 680 690 723 561
tma)
%
70t 6at 50~ 40~ 30C t00
tooo
1~ooo.
Fig. 1. Mean sizes of NiO x crystallites, thermally treated (e) and laser treated (o).
*~(A), 650J
5J0
°3
,so
i,o
iso
15o =~o(A)
Fig. 2. Mean sizes of CuO x crystallites obtained thermally (e) and by laser irradiation (o).
formula with corrections calculated as indicated by Kaelbe [5]. The sizes of CuO crystallites obtained in laser and thermal experiments are listed in Table 3. From the plots of Fig. 1 and Fig. 2 one may note that the crystallites produced by laser experiments have different sizes along the [111] and [200] crystallographic directions. For NiO~ crystallites (Fig. 1) [3], the largest anisotropy of shape is exhibited sample K (nickel hydroxycarbonate) which was the most absorbant to laser radiation. Very similar behaviour is observed for CuOx crystallites in Fig. 2, obtained from copper salts with increased absorptivity in the order/~ < S' < K' (see Table 1 ). The crystallites obtained from non-absorbing salts (such as copper chloride) are situated towards the line of isotropy in both figures (Figs. 1 and 2). We may conclude that the more the initial substance absorbs the laser radiation, the larger are the size and anisotropy of the oxide crystallites obtained (different lengths along the directions 3200 a n d D i l 1). Further support for the influence of salt absorptivity on the laser effect is given in Fig. 3, which shows the dependence of the mean crystallite size on the speed of passage through the laser beam. For the salt with high absorptivity (nickel hydroxycarbonate) the size of
C. Popescu et al.
/
Cu and Ni oxides obtained using CO2 laser
tO00 ~C
0
0~
00
0e
0a
,0
is v(m~/,)
Fig. 3. Dependence of the mean size of NiO~ crystailites obtained on the speed of passage through the laser beam: × nickel hydroxycarbonate; + nickel nitrate.
crystallites in the direction D200 decreases as the speed increases [3], but remains unchanged for nickel nitrate. A qualitative explanation of the effect of the laser on oxide morphology could be found by analysing the dynamics of the laser heating process. The laser irradiation area is characterized by extremely high heating rates ( 1 0 0 0 - 1 5 0 0 K is easily reached in a short time interval with a medium-power CO 2 laser). The heating rate of the laser-induced reactions is strongly related to the quanta absorbed by the substance, i.e. to the absorptivity of the salt at 10.6 /~m, the power of the
73
source, the speed of the cell through the laser beam, etc. Obviously the heating rate for the laser experiments is a non-linear function of temperature, and different heating rate functions (i.e. different powers, speeds, etc.) will lead to different physical forms of the final products. Thus, it is expected that substances with higher absorptivities will experience higher changes in the heating rates (as shown in Fig. 3) with the consequence that the crystallites grow larger and are more anisotropic. For the case of salts with lower absorptivity, the laser heating is more uniform, with increased dissipative losses through the metal walls of the cell; the reaction products look like those which have undergone pure thermal decomposition.
References 1 D. Bauerle (ed.), Laser Processing and Diagnostics, Springer, Berlin, 1985. 2 C. Popescu, V. Jianu, R. Alexandrescu, I. N. Mih~tilescuand I. Morjan, Thermochim. Acta, 129 (1988) 269. 3 C. Popescu, I. Ursu, M. Popescu, R. Alexandrescu, I. Morjan and I. N. Mihfiilescu, Thermochim. Acta, 164 (1990) 79. 4 C. Popescu, R. Alexandrescu, I. Morjan and M. Popescu, Thermochim. A cta, 184 (1991) 73. 5 D. Negoiu, Treatise of Inorganic Chemistry, Tehnica, Bucharest, 1972 (in Romanian).
71
Specific features of copper and nickel oxides obtained under extreme conditions by CO2 laser irradiation of inorganic salts C. P o p e s c u LACECA Research Centre, Str. Siret 95, Sector 1, 78308, Bucharest (Romania) R. A l e x a n d r e s c u , I. M o r j a n a n d I. V o i c u Institute for Atomic Physics, P.O. Box MG-6, Bucharest-M6gurele (Romania)
Abstract Several experiments showed that nickel and copper salts are decomposed to oxides by irradiation with a continuous wave CO 2 laser. The processes are characterized by an extremely high heating rate which develops within the impact region of the laser beam with the substrate. The salts were also decomposed under controlled heating conditions. A difference was noticed concerning the size and isotropy of final crystallites obtained by laser irradiation as compared with thermal heating. The magnitude of this difference seems to be related to the laser quanta absorptivity of the salts.
1. Introduction
2. Experimental details
The interaction of high-power laser radiation with solid systems is often investigated using a thermochemical approach, in which the strong localized action of the laser beam imposes the characteristics of the processes [1 ]. In earlier works [2, 3] it was shown that the decomposition of inorganic salts exposed to IR laser radiation takes place under unusual heating conditions, characterized by high heating rates developing within the impact region of the laser beam. Compared with the reaction products obtained in classical thermal decomposition, the oxides produced using laser processes exhibited peculiarities of structure and morphology. A correlation was found between these features and the absorptivity of the initial salts to the wavelength of laser radiation. In this paper we present new results on the laser decomposition of some copper salts. The similarities of their behaviour and that of nickel salts under the same conditions are revealed. The salts were also decomposed under controlled heating. Crystallographic investigations of the oxides produced (CuO and NiO) revealed differences in the size and isotropy of crystallites produced from laser experiments compared with those obtained by thermal heating. The high heating rates which characterize the laser processes together with the absorptivity of the substance to the laser wavelength should both be involved in the kinetics of the reactions.
Different nickel and copper salts of analytical purity grade were used. Their IR spectral characteristics within the range of CO2 laser emission (10.6/zm) were investigated and the results are given in Table 1. Laser irradiation experiments were performed using a continuous wave CO2 laser of beam intensity 400-600 W c m -2. The salts, in powdered form, were evenly distributed as a thin layer in a metal reaction cell, which was moved perpendicular to the beam at various speeds. After each passage through the laser beam the samples were weighed (accuracy + 5 x 10- 5g) until constant weight was achieved. A Q 1500 D MOM derivatograph was used for the thermal analysis experiments. Heating rates of 5 and 10 K rain- 1 were used.
0921-5093/93/$6.00
TABLE I. Absorptivity values of nickel and copper salts at 10.6/~m Substance
Code
Absorptivity (%)
NiCO 3 •Ni(OH) 2 •H20 Ni(NO3) 2"6H20 NiC12 "6H20 NiSO 4 •7H20
K A C S
42 2 0 8
Cu2CO3(OH)2
K' A' S' C'
15 5 13 1-2
Cu(CH3COO)2 "H20 CuSO 4.51t20 CuCI: •2H20
© 1993 - Elsevier Sequoia. All rights reserved
72
C Popescu et aL
/
Cu and Ni oxides obtained using CO2 laser
X-ray diffraction measurements were taken using a Philips diffractometer, with Cu K a radiation.
3. Results and discussion The salts were processed in the laser beam, until a constant weight was observed. The weight losses v s . time can be used to study the kinetics of the laserinduced reactions [3]. The same salts were thermally decomposed in the derivatograph and the recorded thermogravimetric data were processed to give a kinetic analysis of the thermal reactions [4]. Table 2 presents the mass losses for the copper salts, decomposed thermally and by laser radiation. Thermal experiments all give CuO as the final product (in the limits of our experimental method). From laser experiments, either a non-stoichiometric oxide CUOx, x < 1, is obtained, or, more likely, a mixture of oxides Cu20 and CuO. Crystallographic investigations of both nickel and copper oxides by X-ray diffraction showed that the crystallites of laser-treated samples were larger than those obtained thermally and that this difference increased for salts with higher absorptivity to the wavelength of laser radiation. The mean size of the oxide crystallites was determined along the [111] and [200] crystallographic directions using the Debye-Sherrer
TABLE 2. Mass losses in laser and thermal experiments, compared with stoichiometric losses Substance
Thermal Laser Theoretical mass mass loss mass loss loss (%) (%) (%) To Cu20 To CuO
CuSO4"5H20 Cu2CO3(OH)2 CuC12"2H20 Cu(CH3COO)2"H20
68.5 29.3 84.6 60.2
69.6 33.2 61.4 a
71.3 35.3 58.1 64.2
68.1 28.1 53.4 60.15
aThe salt was scattered by the laser beam.
TABLE 3. Size of CuO crystallites obtained from thermal and laser processes, from different inorganic salts Substance
Cu2CO3(OH)2
CuSO4.5H20 Cu(CH3COO)2H20 CuC12'2HzO
Thermal process
Laser process
DIll (/~)
D2oo(A) D l l
383 540 416 573
392 561 434 563
580 572 656 556
I (A)
D2oo(A) 680 690 723 561
tma)
%
70t 6at 50~ 40~ 30C t00
tooo
1~ooo.
Fig. 1. Mean sizes of NiO x crystallites, thermally treated (e) and laser treated (o).
*~(A), 650J
5J0
°3
,so
i,o
iso
15o =~o(A)
Fig. 2. Mean sizes of CuO x crystallites obtained thermally (e) and by laser irradiation (o).
formula with corrections calculated as indicated by Kaelbe [5]. The sizes of CuO crystallites obtained in laser and thermal experiments are listed in Table 3. From the plots of Fig. 1 and Fig. 2 one may note that the crystallites produced by laser experiments have different sizes along the [111] and [200] crystallographic directions. For NiO~ crystallites (Fig. 1) [3], the largest anisotropy of shape is exhibited sample K (nickel hydroxycarbonate) which was the most absorbant to laser radiation. Very similar behaviour is observed for CuOx crystallites in Fig. 2, obtained from copper salts with increased absorptivity in the order/~ < S' < K' (see Table 1 ). The crystallites obtained from non-absorbing salts (such as copper chloride) are situated towards the line of isotropy in both figures (Figs. 1 and 2). We may conclude that the more the initial substance absorbs the laser radiation, the larger are the size and anisotropy of the oxide crystallites obtained (different lengths along the directions 3200 a n d D i l 1). Further support for the influence of salt absorptivity on the laser effect is given in Fig. 3, which shows the dependence of the mean crystallite size on the speed of passage through the laser beam. For the salt with high absorptivity (nickel hydroxycarbonate) the size of
C. Popescu et al.
/
Cu and Ni oxides obtained using CO2 laser
tO00 ~C
0
0~
00
0e
0a
,0
is v(m~/,)
Fig. 3. Dependence of the mean size of NiO~ crystailites obtained on the speed of passage through the laser beam: × nickel hydroxycarbonate; + nickel nitrate.
crystallites in the direction D200 decreases as the speed increases [3], but remains unchanged for nickel nitrate. A qualitative explanation of the effect of the laser on oxide morphology could be found by analysing the dynamics of the laser heating process. The laser irradiation area is characterized by extremely high heating rates ( 1 0 0 0 - 1 5 0 0 K is easily reached in a short time interval with a medium-power CO 2 laser). The heating rate of the laser-induced reactions is strongly related to the quanta absorbed by the substance, i.e. to the absorptivity of the salt at 10.6 /~m, the power of the
73
source, the speed of the cell through the laser beam, etc. Obviously the heating rate for the laser experiments is a non-linear function of temperature, and different heating rate functions (i.e. different powers, speeds, etc.) will lead to different physical forms of the final products. Thus, it is expected that substances with higher absorptivities will experience higher changes in the heating rates (as shown in Fig. 3) with the consequence that the crystallites grow larger and are more anisotropic. For the case of salts with lower absorptivity, the laser heating is more uniform, with increased dissipative losses through the metal walls of the cell; the reaction products look like those which have undergone pure thermal decomposition.
References 1 D. Bauerle (ed.), Laser Processing and Diagnostics, Springer, Berlin, 1985. 2 C. Popescu, V. Jianu, R. Alexandrescu, I. N. Mih~tilescuand I. Morjan, Thermochim. Acta, 129 (1988) 269. 3 C. Popescu, I. Ursu, M. Popescu, R. Alexandrescu, I. Morjan and I. N. Mihfiilescu, Thermochim. Acta, 164 (1990) 79. 4 C. Popescu, R. Alexandrescu, I. Morjan and M. Popescu, Thermochim. A cta, 184 (1991) 73. 5 D. Negoiu, Treatise of Inorganic Chemistry, Tehnica, Bucharest, 1972 (in Romanian).