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Determination of pore size and shape distribution from porosimetric hysteresis curves
Powder Technology-Ekvkr
Sequoia SA,
Iausanne-Pdntal
in ihc Netherlands
345
Determination of Pore Size End Shape Distribution from Porosimetric Hysteresis Curves M. SVATi%
@kceived September 2. 1971)
Summary The Reverberi method, eArrating the pore sire distribution of pores of irregular cross-section from the diifference between the ascending and descending branches of the porosimetric hysteresis loops, was tested with regard to its applicability for measuring powder metallurgical compacts The method was found applicable, provided ihat the samples were coated with protecttie jZms zo prer;ent Ihe interaction of mercury with the metal during the long-lasting measurements
IXTRODUCTION Since
the measurement
of pore
size distribution
by mercury penetration was proposed by Washburn’ and the first experimental data published by Ritter and Drake’, the Washburn equation, based on the model of cylindrical pores, has generally been accepted for evaluating the results- In compar-
ing these to the results of other independent methods, the fact that many solids fail to meet the Washburn model criteria has repeatedly been mentioned3-5, especially when working with samples containing irregular pores or so called “ink-bottle” pores, as is the case in powder metallurgy- Attempts have therefore been made to replace the Washburn model by more sophisticated models, e.g. the model of packed spheres3, whose applicability to powder metallurgical compacts has already been discussed’_ As has been found, this model gives good agreement with reality in samples formed from classified metal powders. whose porosity does not exceed 45%. In samples of a higher porosity, or those prepared with the aid of a filler. the criteria of the packed spheres model are no longer met and the method is therefore not applicable. A method aiming to solve the problem of measurement of varying pore radii withoat the former limitations is the Reverb&
method’- This method allows one to determine independent!y the broad and narrow parts of the pores from porosimetric hysteresis loops. Hysteresis in mercury porosimetry is due just to the existence of the ink-bottle poress-g. Such a pore consists ofa big cavity connected with the remaining pore system by a narrow neck. When pressing mercury into such a pore. ihe cavity is invaded at the same pressure as the neck, ie_ at a pressure which is higher than that corresponding to its radius_ When decreasing the pressure, the cavity releases the mercury at a pressure corresponding to its proper size, ie- a pressure lower than that at which it was filled. The hysteresis branch, ie. that part of the curve which is obtained by decreasing the pressure, is consequently shifted to larger radii as compared to the ascending branch_ Reverberi proposed a method utilizing the difference between the ascending and descending branches of the curve for evaluating the broad and narrow parts of the pores independently of one another_ The essence of his method is as follows: The ascending branch of the curve is measured in the usual way_ The descending branch is measured in such a way that the highest pressure reached is again lowered in several steps, always beginning from the maximum pressure reached; the pressure is lowered to a certain pre-set value and then increased again to the maximum value_ The procedure may best be seen in Fig. 1. After having reached the point O_ the. pressure is decreased to point A value, corresponding to the pore radius r,. At this point, all pores and cavities of rtr,, are emptied If the pressure is increased a,oa;l, the pores and necks in the interval (rA’; rJ4ashed curve-are fiiled; in the interval from A’ to X7 tie pores of a radius in the interval (rA.; rA-) are filled but at the same time also the cavities of a radius between r,,- and r,, having the neck size of the radius of rA-.-rA-_ After decreasing the pressure to point B, all pores of a radius r c r, are freed. On increasing the pressure a,oain. the
M. SVATA
346 pores of a radius between r,. and r, are filled first, then at point B” the necks rw- to r,. are filled but at the same time the cavities of the size r,. to r,, having a neck in the interval rP to rS_ The volume increment between A and A’ is the volume of “cylindrical”
and in some unfavourable cases may be as high as 100°~. It is evident that the Reverberi method is not suited for these samples. It is the aim of the present paper to determine the possibility of applying the Reverberi method to metal systems currently encountered in a powder metallurgist’s practice.
EXPERIMENTAL
Fi_g 1. Reverb& porosimetric tuna obtained on pressed carbon11 iron. Orerall ascending and descending branches are drawn in full, individual pressuresteps arc dashed. pores of a radius r,- to r,; the volume increment
from B’ to B” stands for the sum of the cylindrical pore vo!umes of a radius from r,. to r, and ink-bottle pores of a radius from rW to r,... The difference between the two increments is thus the volume of the ink-bottle pores of a radius from r,- to r,--_ Continuing in this way through the whole interval measured, one obtains a series of radii and volumes whose
sum
must
be identical
with
the total
differ-
ence between the point 0 and E, i.e. it must be equal to the total quantity of mercury freed from the sample after decreasing the pressure to its zero value. As is seen from the plot, this quantity is lower than the total value pressed into the sample. The difference, called “retention”, varies a great deal according to the material and structure of the sample. In some materials where the surface is soft or wetted by mercury, the mercury surface may be contaminated after a certain time and the contact angle may thus be influenced- In systems, containing very fine and at the same time very large pores, or in systems with very non-uniform pore walls, the mercury cohnnn may, after a rapid decrease in pressure, be tom similarly as in a thermometer, and the quantity of the mercury flowing out may vary from one determination to the next. The quantity of the mercury retained by the sample thus varies in a broad range
A series of compacts, representative of the systems encountered in our practice, was prepared: (1) Carbonyl iron powder, grain size below 8 m was impregnated with a 1 o/0solution of rubber in benzene, dried, and pressed at 3 t/cm’(2) Carbonyl nickel powder, stated grain size 3-5 ,um, was pressed at 500 kg/cm’ and sintered in a hydrogen atmosphere at 45@C for 90 min. (3) Carbonyl nickel powder as under (2) was mixed with 10% by weight of ammonium oxalate as a pore-forming agent, grain size 2@-40 jnn, and pressed and sintered as under (2) (4) Electrolytical copper powder, grain size above 40 pm, was pressed at 100 kg/cm’(5) Carbonyl nickel powder, stated grain size 3-5 jun, was mixed with 45% by weight of ammonium oxalate, sieve fraction 10-20 m pressed at SO0 kg/cm’ and sintered at 300°C in a hydrogen atmosphere for 70 min. On these samples porosimetric curves were measured in the usual way; on samples 2-5 another series of measurements was made after pre-treating the compacts with a 1 0/0solution of stearic acid in chloroform and with a 1% solution of rubber in benzene.
RESULTS AND DISCUSSION
The porosimetric curves obtained by the Reverberi method on sample I will be found in Fig. 1 and their analysis in Table 1. In measuring the ascending branches the pressure was increased in 5-min intervals, whereas at least 10 min waiting time was necessary when measuring the descending branches. This was necessary due to the large changes in temperature occurring in the pressure vessel of the porosimeter after decompression. The overall ascending and descending branches of the curve are drawn in full, the partial CUN~~ are dashed_ It will be observed that the retention of the mercury is extremely low Powder
TecZmoZ_
5 (1971/72)
PORESIZE AND SHAPE DIS-IRIBUTION
347
TABLE 1 Carbonyl iron : mutual relation of broad and narrow curves Volumes in em3- IO-‘/g
parts of the pores in a porous. compact_ obtained
from porosimetric
A
B
C
D
E
3.s64.05
4.os-L20
4.20436
4.36453
4.53-5.7s
288-3.70 3.70-3.86 3.864.05 4.0.5-4_I?0 4.204.36 4.36-4.53 4.533_78
0.4 0.3 0.3
0.9 0.1 0.7 04
Total
1.0
kJ r2 (A,
in this case, amounting to only 9%_ As was found later, this was due to the pre-treatment of the powder with rubber. The individual pressure cycles were selected in such a way to divide the x axis into approximately equal sections. This of course is not necessary; the number and intervals of the cycles will change according to the shape of the curve and the information required The shorter the pressure intervals, the more detailed is the information obtained_ The analysis of the curves was done according to the procedure outlined above and the data obtained are compiled in Table 1. Horizontal lines in the table given the volumes of the mercury corresponding to the radii of the cavities (r,), the columns contain the volumes corresponding to the necks or to the constant radii pores (rz), in both cases in cm3 - 10-‘/g. According to the ascending branch of the curve. the most frequent pore radius is of the size log r= 4.2; the descending branch, however, points to 4.35. The mutual ratio of both the values may be read off from the partial curves. Of the total volume (0.123 cm’) O-028 crn3, ie 23 “/, belongs to the necks and to the constant cross-section pores; the remainder arc the cavities and the broad parts of the pores As was to be expected in a sample prepared by pressing classified metal powder, the difference between the cavities and necks is not too pronounced In other words, there are no big spaces present which would be closed by very narrow passages The overall picture is, therefore, the following: the largest volum2 belongs to the pores in the interval 4.36 c log r < 4.53 (0.042 cm”). Of this volume 80 %
2.1
0.9 1’ 0.6
27
1.7 1.6 0.9
42
hysterezis
l-oral
0.8 o-9 0.6
13 0.4 1.9 3.3 3.1.8 0.6
73
123
(0.033 cm’) are accessible through a neck of a smaIler size. The mutual ratio of both the sizes is approximately 2: 1. When measuring the nickel samples (2 and 3). it was found that the retention of mercurywas too high to permit the measurement to be carried out. It seems that although the solubility of niche1 in mercury is only about 10-““A, a change in the contact angle does occur due to the interaction of the nicke1 and mercury after longer periods of contact_ This is not decisive in current porosimetric measurcments taking several tens of minutes, but in the case of the Reverberi method, taking up to several
O.ZJ
030
Fig. 2 Hysteresis curves of nickel samples 3 and 3. mcasurcd ox., untreated samples (ful1) and after treatment with steak acid (dashed). The ascending branch6 of the rrured and onrreatcd samples are identical.
M_ SVATA
348 days, the phenomenon makes itself apparent. For this reason it was found necessary to provide the nickel and also the other materal surfaces with a protective film. This was done by pre-treating the samples with a 1 o/0solution of stearic acid in chloroform; a 1% rubber solution in benzene was also tested but proved too viscous to penetrate into the interior of the sample. The samples were first dried, then shaken iu the protective solution for six hours, filtered off, and dried at 12@C. It will be observed in Fig. 2 that this procedure revealed itself in a decrease of the amount of the mercury retained by the sample from 109 to 8% in sample 2 and from 95 to 22 % in sample 3. The same pre-treatment was
Fig 3. Reverberi curves obtained on electrolytic copper cornpacts pi-e-treated Fiitbsteak acid.
TABLE
2
Carbonyl nickel 3-S pm with ammonium oxalatc IO-2Opm diameter; mutual relation of broad and narrow parts of the pores in the compact, obtained from porosimetric hysteresis eurv~ Volumes
in cuts- 10-‘/g
425-4.65
4.6.5-4.78
42S4.45 4.45-454 4.564.65 4-65-4.78 4.78-50
1.4 26 20
1.0 26 1.0 28
Total
6.0
7.4
k7
r.2
(A,
4.78-s-o
TOtUl
6.2 0.2 1.0
24 5.2 9-Z 3.0 LO
7-4
20-S
applied to the copper compacts. Although copper is sufficiently protected by its natural oxide film to allow current measurements to be made, for the Reverberi procedure it has to be provided with protection_ A Reverberi curve of sample 4 is given in Fig. TJ.It will be noted that no amalgamation of the copper surface occurred, as is proved by the coincidence of the individual ascending and descending branches. Figure 4 depicts the Reverberi curve of sample 5 whose analysis is contained in Tabie 2. As may be seen, the maximum volume belongs to pores of a radius of 6-10 qn (log r=4_78-5; 0.062 cm3) whose necks are in the range of 3.545 m (log r=4.54-4.65). That suggests that the tiller formed an interconnected network of pores, as only a small volume of pores (0.024 cm3) is completely closed and accessible only through the intergranular voids of T= l-84-5 q (log r=4.254_45). Since the compact was prepared by pressing a powder of 35 m and a filler of 10-20 m diameter grain size, respectively, this may be considered very accurate information.
CONCLUSION
Fig 4. Reverberi -es fromnick=1 powder 35 size
obtained on nickel compacts prepared pm and spacing agent IO-20 pm grain
The Reverberi method gives very detailed information on the porous structure which may, in many instances, be worth the time-consuming determination. It is applicable to all samples which are not wetted by and have a low retention of mercuryFor powder metallurgical compacts the interaction between mercury and the surface of the sample may be eliminated by the formation of a thin film of stearic acid on the metal surface.
PORE
SIZE AND
SHAPE
DIS7RIBUIION
REFERENCES I E W. Washburn. Proc Nat Acad St5 USA. 7 (1921) 115. 2 EL L Rittcr and L C Draks Ind Eng. Chemq AnaL EL+ 17 (12) (1945) 789 3 R P. Meyer and R A Stow, J. Colloid Sci. 20 (I%E,893. 4 0. S Ksenzhek, Z/am_ Fiz. Khim_ 37 (1963) 1297. 5 K- Micka and U SK&, CoZlecrion Czech Chem Commun. 32 (1967) 3493.
349 6 M. Svati and Z Eb-kj; Pomicr TechmL 3 (1970) 294. 7 A Rcverbai, G. Faraiolo and A Pclosq Ann China_ 56 (1966) 1552 8 J. Frcundiicb Ekctrochim Acta. 6 (1962) 35. 9 N. M Kamakin hfem& isskdmxmi~n szruktuq r~sokod~ pemqzh i porist~ch fel Izd Akad Nat i SSSR Mostia 1958. p_ 47.
Powder Techol.
5 (1971p_)
Sequoia SA,
Iausanne-Pdntal
in ihc Netherlands
345
Determination of Pore Size End Shape Distribution from Porosimetric Hysteresis Curves M. SVATi%
@kceived September 2. 1971)
Summary The Reverberi method, eArrating the pore sire distribution of pores of irregular cross-section from the diifference between the ascending and descending branches of the porosimetric hysteresis loops, was tested with regard to its applicability for measuring powder metallurgical compacts The method was found applicable, provided ihat the samples were coated with protecttie jZms zo prer;ent Ihe interaction of mercury with the metal during the long-lasting measurements
IXTRODUCTION Since
the measurement
of pore
size distribution
by mercury penetration was proposed by Washburn’ and the first experimental data published by Ritter and Drake’, the Washburn equation, based on the model of cylindrical pores, has generally been accepted for evaluating the results- In compar-
ing these to the results of other independent methods, the fact that many solids fail to meet the Washburn model criteria has repeatedly been mentioned3-5, especially when working with samples containing irregular pores or so called “ink-bottle” pores, as is the case in powder metallurgy- Attempts have therefore been made to replace the Washburn model by more sophisticated models, e.g. the model of packed spheres3, whose applicability to powder metallurgical compacts has already been discussed’_ As has been found, this model gives good agreement with reality in samples formed from classified metal powders. whose porosity does not exceed 45%. In samples of a higher porosity, or those prepared with the aid of a filler. the criteria of the packed spheres model are no longer met and the method is therefore not applicable. A method aiming to solve the problem of measurement of varying pore radii withoat the former limitations is the Reverb&
method’- This method allows one to determine independent!y the broad and narrow parts of the pores from porosimetric hysteresis loops. Hysteresis in mercury porosimetry is due just to the existence of the ink-bottle poress-g. Such a pore consists ofa big cavity connected with the remaining pore system by a narrow neck. When pressing mercury into such a pore. ihe cavity is invaded at the same pressure as the neck, ie_ at a pressure which is higher than that corresponding to its radius_ When decreasing the pressure, the cavity releases the mercury at a pressure corresponding to its proper size, ie- a pressure lower than that at which it was filled. The hysteresis branch, ie. that part of the curve which is obtained by decreasing the pressure, is consequently shifted to larger radii as compared to the ascending branch_ Reverberi proposed a method utilizing the difference between the ascending and descending branches of the curve for evaluating the broad and narrow parts of the pores independently of one another_ The essence of his method is as follows: The ascending branch of the curve is measured in the usual way_ The descending branch is measured in such a way that the highest pressure reached is again lowered in several steps, always beginning from the maximum pressure reached; the pressure is lowered to a certain pre-set value and then increased again to the maximum value_ The procedure may best be seen in Fig. 1. After having reached the point O_ the. pressure is decreased to point A value, corresponding to the pore radius r,. At this point, all pores and cavities of rtr,, are emptied If the pressure is increased a,oa;l, the pores and necks in the interval (rA’; rJ4ashed curve-are fiiled; in the interval from A’ to X7 tie pores of a radius in the interval (rA.; rA-) are filled but at the same time also the cavities of a radius between r,,- and r,, having the neck size of the radius of rA-.-rA-_ After decreasing the pressure to point B, all pores of a radius r c r, are freed. On increasing the pressure a,oain. the
M. SVATA
346 pores of a radius between r,. and r, are filled first, then at point B” the necks rw- to r,. are filled but at the same time the cavities of the size r,. to r,, having a neck in the interval rP to rS_ The volume increment between A and A’ is the volume of “cylindrical”
and in some unfavourable cases may be as high as 100°~. It is evident that the Reverberi method is not suited for these samples. It is the aim of the present paper to determine the possibility of applying the Reverberi method to metal systems currently encountered in a powder metallurgist’s practice.
EXPERIMENTAL
Fi_g 1. Reverb& porosimetric tuna obtained on pressed carbon11 iron. Orerall ascending and descending branches are drawn in full, individual pressuresteps arc dashed. pores of a radius r,- to r,; the volume increment
from B’ to B” stands for the sum of the cylindrical pore vo!umes of a radius from r,. to r, and ink-bottle pores of a radius from rW to r,... The difference between the two increments is thus the volume of the ink-bottle pores of a radius from r,- to r,--_ Continuing in this way through the whole interval measured, one obtains a series of radii and volumes whose
sum
must
be identical
with
the total
differ-
ence between the point 0 and E, i.e. it must be equal to the total quantity of mercury freed from the sample after decreasing the pressure to its zero value. As is seen from the plot, this quantity is lower than the total value pressed into the sample. The difference, called “retention”, varies a great deal according to the material and structure of the sample. In some materials where the surface is soft or wetted by mercury, the mercury surface may be contaminated after a certain time and the contact angle may thus be influenced- In systems, containing very fine and at the same time very large pores, or in systems with very non-uniform pore walls, the mercury cohnnn may, after a rapid decrease in pressure, be tom similarly as in a thermometer, and the quantity of the mercury flowing out may vary from one determination to the next. The quantity of the mercury retained by the sample thus varies in a broad range
A series of compacts, representative of the systems encountered in our practice, was prepared: (1) Carbonyl iron powder, grain size below 8 m was impregnated with a 1 o/0solution of rubber in benzene, dried, and pressed at 3 t/cm’(2) Carbonyl nickel powder, stated grain size 3-5 ,um, was pressed at 500 kg/cm’ and sintered in a hydrogen atmosphere at 45@C for 90 min. (3) Carbonyl nickel powder as under (2) was mixed with 10% by weight of ammonium oxalate as a pore-forming agent, grain size 2@-40 jnn, and pressed and sintered as under (2) (4) Electrolytical copper powder, grain size above 40 pm, was pressed at 100 kg/cm’(5) Carbonyl nickel powder, stated grain size 3-5 jun, was mixed with 45% by weight of ammonium oxalate, sieve fraction 10-20 m pressed at SO0 kg/cm’ and sintered at 300°C in a hydrogen atmosphere for 70 min. On these samples porosimetric curves were measured in the usual way; on samples 2-5 another series of measurements was made after pre-treating the compacts with a 1 0/0solution of stearic acid in chloroform and with a 1% solution of rubber in benzene.
RESULTS AND DISCUSSION
The porosimetric curves obtained by the Reverberi method on sample I will be found in Fig. 1 and their analysis in Table 1. In measuring the ascending branches the pressure was increased in 5-min intervals, whereas at least 10 min waiting time was necessary when measuring the descending branches. This was necessary due to the large changes in temperature occurring in the pressure vessel of the porosimeter after decompression. The overall ascending and descending branches of the curve are drawn in full, the partial CUN~~ are dashed_ It will be observed that the retention of the mercury is extremely low Powder
TecZmoZ_
5 (1971/72)
PORESIZE AND SHAPE DIS-IRIBUTION
347
TABLE 1 Carbonyl iron : mutual relation of broad and narrow curves Volumes in em3- IO-‘/g
parts of the pores in a porous. compact_ obtained
from porosimetric
A
B
C
D
E
3.s64.05
4.os-L20
4.20436
4.36453
4.53-5.7s
288-3.70 3.70-3.86 3.864.05 4.0.5-4_I?0 4.204.36 4.36-4.53 4.533_78
0.4 0.3 0.3
0.9 0.1 0.7 04
Total
1.0
kJ r2 (A,
in this case, amounting to only 9%_ As was found later, this was due to the pre-treatment of the powder with rubber. The individual pressure cycles were selected in such a way to divide the x axis into approximately equal sections. This of course is not necessary; the number and intervals of the cycles will change according to the shape of the curve and the information required The shorter the pressure intervals, the more detailed is the information obtained_ The analysis of the curves was done according to the procedure outlined above and the data obtained are compiled in Table 1. Horizontal lines in the table given the volumes of the mercury corresponding to the radii of the cavities (r,), the columns contain the volumes corresponding to the necks or to the constant radii pores (rz), in both cases in cm3 - 10-‘/g. According to the ascending branch of the curve. the most frequent pore radius is of the size log r= 4.2; the descending branch, however, points to 4.35. The mutual ratio of both the values may be read off from the partial curves. Of the total volume (0.123 cm’) O-028 crn3, ie 23 “/, belongs to the necks and to the constant cross-section pores; the remainder arc the cavities and the broad parts of the pores As was to be expected in a sample prepared by pressing classified metal powder, the difference between the cavities and necks is not too pronounced In other words, there are no big spaces present which would be closed by very narrow passages The overall picture is, therefore, the following: the largest volum2 belongs to the pores in the interval 4.36 c log r < 4.53 (0.042 cm”). Of this volume 80 %
2.1
0.9 1’ 0.6
27
1.7 1.6 0.9
42
hysterezis
l-oral
0.8 o-9 0.6
13 0.4 1.9 3.3 3.1.8 0.6
73
123
(0.033 cm’) are accessible through a neck of a smaIler size. The mutual ratio of both the sizes is approximately 2: 1. When measuring the nickel samples (2 and 3). it was found that the retention of mercurywas too high to permit the measurement to be carried out. It seems that although the solubility of niche1 in mercury is only about 10-““A, a change in the contact angle does occur due to the interaction of the nicke1 and mercury after longer periods of contact_ This is not decisive in current porosimetric measurcments taking several tens of minutes, but in the case of the Reverberi method, taking up to several
O.ZJ
030
Fig. 2 Hysteresis curves of nickel samples 3 and 3. mcasurcd ox., untreated samples (ful1) and after treatment with steak acid (dashed). The ascending branch6 of the rrured and onrreatcd samples are identical.
M_ SVATA
348 days, the phenomenon makes itself apparent. For this reason it was found necessary to provide the nickel and also the other materal surfaces with a protective film. This was done by pre-treating the samples with a 1 o/0solution of stearic acid in chloroform; a 1% rubber solution in benzene was also tested but proved too viscous to penetrate into the interior of the sample. The samples were first dried, then shaken iu the protective solution for six hours, filtered off, and dried at 12@C. It will be observed in Fig. 2 that this procedure revealed itself in a decrease of the amount of the mercury retained by the sample from 109 to 8% in sample 2 and from 95 to 22 % in sample 3. The same pre-treatment was
Fig 3. Reverberi curves obtained on electrolytic copper cornpacts pi-e-treated Fiitbsteak acid.
TABLE
2
Carbonyl nickel 3-S pm with ammonium oxalatc IO-2Opm diameter; mutual relation of broad and narrow parts of the pores in the compact, obtained from porosimetric hysteresis eurv~ Volumes
in cuts- 10-‘/g
425-4.65
4.6.5-4.78
42S4.45 4.45-454 4.564.65 4-65-4.78 4.78-50
1.4 26 20
1.0 26 1.0 28
Total
6.0
7.4
k7
r.2
(A,
4.78-s-o
TOtUl
6.2 0.2 1.0
24 5.2 9-Z 3.0 LO
7-4
20-S
applied to the copper compacts. Although copper is sufficiently protected by its natural oxide film to allow current measurements to be made, for the Reverberi procedure it has to be provided with protection_ A Reverberi curve of sample 4 is given in Fig. TJ.It will be noted that no amalgamation of the copper surface occurred, as is proved by the coincidence of the individual ascending and descending branches. Figure 4 depicts the Reverberi curve of sample 5 whose analysis is contained in Tabie 2. As may be seen, the maximum volume belongs to pores of a radius of 6-10 qn (log r=4_78-5; 0.062 cm3) whose necks are in the range of 3.545 m (log r=4.54-4.65). That suggests that the tiller formed an interconnected network of pores, as only a small volume of pores (0.024 cm3) is completely closed and accessible only through the intergranular voids of T= l-84-5 q (log r=4.254_45). Since the compact was prepared by pressing a powder of 35 m and a filler of 10-20 m diameter grain size, respectively, this may be considered very accurate information.
CONCLUSION
Fig 4. Reverberi -es fromnick=1 powder 35 size
obtained on nickel compacts prepared pm and spacing agent IO-20 pm grain
The Reverberi method gives very detailed information on the porous structure which may, in many instances, be worth the time-consuming determination. It is applicable to all samples which are not wetted by and have a low retention of mercuryFor powder metallurgical compacts the interaction between mercury and the surface of the sample may be eliminated by the formation of a thin film of stearic acid on the metal surface.
PORE
SIZE AND
SHAPE
DIS7RIBUIION
REFERENCES I E W. Washburn. Proc Nat Acad St5 USA. 7 (1921) 115. 2 EL L Rittcr and L C Draks Ind Eng. Chemq AnaL EL+ 17 (12) (1945) 789 3 R P. Meyer and R A Stow, J. Colloid Sci. 20 (I%E,893. 4 0. S Ksenzhek, Z/am_ Fiz. Khim_ 37 (1963) 1297. 5 K- Micka and U SK&, CoZlecrion Czech Chem Commun. 32 (1967) 3493.
349 6 M. Svati and Z Eb-kj; Pomicr TechmL 3 (1970) 294. 7 A Rcverbai, G. Faraiolo and A Pclosq Ann China_ 56 (1966) 1552 8 J. Frcundiicb Ekctrochim Acta. 6 (1962) 35. 9 N. M Kamakin hfem& isskdmxmi~n szruktuq r~sokod~ pemqzh i porist~ch fel Izd Akad Nat i SSSR Mostia 1958. p_ 47.
Powder Techol.
5 (1971p_)