Corrosion properties of soldered joints. Part II: Corrosion pattern of dental solder and dental nickel-chromium alloy Naofumi Satoshi
DDS, PhD,a Toshiyuki
Shigeto, Murakami,
DDS,C
and Taizo
Yanagihara,
Hamada,
DDS,
BEng,b PhDd
Hiroshima University, Schoolof Dentistry, Hiroshima, Japan Six nickel-chromium (Ni-Cr) alloys joined with two solders were evaluated for degree of corrosion after they were immersed in corrosive solution for 100 days. The corroded surface of the Ni-Cr alloy and the cross section of the soldered joint were observed and the solution of nickel and copper (Cu) ions in each combination was measured, No corrosion was observed in the high-resistant Ni-Cr alloys with high Cr content. Pitting corrosion was seen on low-resistant Ni-Cr alloys, which had less Cr content. In the cross section of the joint, the joint of silver solder became porous by corrosion and the corrosion advanced especially along the interface. Solution of Ni ions was detected in all of the combinations of Ni-Cr alloys and solders with exception of the combination of high-resistant Ni-Cr alloys and gold solder. On the other hand, solution of Cu ions was detected in all of the combinations with silver solder. (J PROSTHETDENT 1991;66:607-10.)
S
oldering is commonly used to assemble crown and fixed partial denture prostheses. Improvement has been made in investments, fluxes, and heating equipment. Many studies have reported joint strength and microstructure of the soldered joint.lw3 However, corrosion (such as tarnish, discoloration, and dissolution of the soldered joint) has not received a complete evaluation. Nickel-chromium (Ni-Cr) alloys with varing percentages of Cr have been evaluated for degree of corrosion by use of an electrochemical method.4 Although the experimental methodology is interesting, the study did not demonstrate a real corrosion pattern. Corrosion at the soldered joint, if improper combination of metals and fluxes are used, may produce an unsatisfactory result (fracture, discoloration of the joint, or plaque accumulation). This study evaluated the corrosion patterns of actual soldered joints made up of six kinds of Ni-Cr alloys containing different amounts of Cr and two different types of solders (gold solder and silver solder).
MATERIAL AND Alloy specimens
METHODS
The compositions of dental Ni-Cr alloys and dental solders used in this study are shown in Tables I and II. Each alloy was cast to produce samples 3 X 1.5 X 20 mm; the small end of the casting was ground with emery paper and an alumina suspension and sandblasted by fine alumina abrasives. The polished surfaces of two castings were abutted to *AssociateProfessor,Department of Prosthetic Dentistry. bInstructor, Department of Prosthetic Dentistry. cGraduate student, Department of Prosthetic Dentistry. dProfessorand Chairman, Department of Prosthetic Dentistry. 1Of1f3137c-J
THE
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OF PROSTHETIC
DENTISTRY
each other with a clearance of 0.3 mm in a furnace. Lo-Temp flux (Jeneric Gold Co., Wallingford, Corm.) was used. The soldered block was cut to 20 mm length to position the joint in the center of the sample and was invested with a polyester resin. The exposed portion of the joint was polished with emery paper and an alumina suspension. The term alloy A-gold solder means that two blocks of alloy A were soldered with gold solder. The term alloy A-silver solder means that two blocks of alloy A were soldered with silver solder. Other combinations were similarly identified.
Observation A saline solution (0.9 “/o NaCl) was adjusted to pH 7 and used as the corrosive solution in which specimens were immersed at 37” C for 100 days. The surface was observed with a microscope for any corrosion and then crosssectioned through the joint for observation.
Measurement
of nickel
and copper
ions
The concentrations of Ni and Cu ions that bad eluted into the corrosive solution after the immersion test were measured by use of atomic absorption and emission spectrometry (type 207, Hatachi, Ltd., Tokyo, Japan).
RESULTS Observation
of Ni-Cr
alloy
surface
Corroded surfaces of Ni-Cr alloys immersed in the corrosive solution for 100 days are shown in Figs. I and 2. On the surface of alloy A, pittings 0.1 to 0.4 mm in diameter were seen on the specimen. Corrosion of silver solder was greater than that of gold solder. Pitting on the surfaces of alloys B and C was less than on alloy A. No pitting corrosion was observed on the surfaces of alloys D, E, and F.
607
CORROSION
PATTERN
OF SOLDERED
JOINTS
3. Photomicrographs of pitting on surface of cross section of soldered joints between Ni-Cr alloys (A through F) and silver solder (SS). Top end in each photomicrograph shows surface exposed to corrosive solution. No pitting on surfaces of cross section of soldered joints between Ni-Cr alloy-gold solder combinations. Fig.
ABCDEF
Alloy-gold
solder
combination
Fig. 4. Dissolution of Ni ion from Ni-Cr alloy (A through F) and gold solder combinations.
.-5
3
2 :: g
2
.z
1 0 A
6
Alloy-silver
C
solder
D
E
F*
combination
Fig. 5. Dissolution of Ni ion from Ni-Cr alloy (A through F) and silver solder combinations.
connected in air to the measuring equipment mentioned in the former report.4 When the Ni-Cr alloy and solder are actually joined together, current density values of galvanic currents on the surfaces of the Ni-Cr alloy and the solder are different from each other in proportion to distances THE
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0
ABCDEF
Alloy-silver
solder
combination
Fig. 6. Dissolution of Cu ion from Ni-Cr alloy (A through 5’) and silver solder combinations. No Cu ions were detected from Ni-Cr alloy and gold solder combinations.
from the soldered interface. The actual sol should be evaluated for corrosion after immersion in the corrosive solution for a long term. Pitting on the surface of the Ni-Cr alloy was seen in alloys A, B, and C combined with gold or silver solder. These alloys were low in corrosion resistence in view of the values of Cr and molybdenum (MO) content. The existence ofpitting was not related to the position in distan joint. The shape of pitting was probably dendritic structure of each Ni-Cr alloy casting. Corrosion of the cross section of the joint was observe in silver solder combined with all Ni-Cr alloys because the solder was low in corrosion resistence. It was noted that the solder was more significantly corroded than the Ni-Cr alloys particularly from the exposed surface to the Enside. One study implied that the soldered joint between the nonprecious alloy and silver solder was a mechanical con-
of Ni and Cu ions in each combination was measured by use of atomic absorption and emission spectrometry. The following results were obtained: 3.. No corrosion was observed in the higb-resistant Ni-@I= alloys of D, E, and F (high Cr content) when they were coupled with either of the two kinds of solder. 2. Pitting corrosion was seen on low-resistant Ni-@r ailays of A, B, and C (less Cr content) w en they were coupled with any of the solders. 3. In the cross section of the joint with silver solder, the joint beea porous by corrosion that advanced along the interface. corrosion was seen with gold solder. 4. Elution of Ni ions was detected in all of the combinations of Ni-Cr alloys and solders, with the exception of the ~ornbi~at~o~ of alloys D, E, and F with gold solder. On the other hand, elution of Cu ions was detected in all of the ~o~bi~at~ons with silver solder, but not with gold solder. REFE
CES
1. Lautenschiager Dent
E?. Strength
mechanism
of dentai
soldered
joints.
J
Kes :974;53:1m-7.
2. Brudvik JS, Nicholls JI. Soldering of removable partial dentures. d PR~STBET DENT 1983;49:762-5. 3. Kayiakie WG, Brukl CE. Comparative tens& strengths of nonnobie dental alioy solders. J PROSTKET DENT 1985:53:455-62. 4. Shigeto hi, Yanagihara T, Hamada T, Bud&J$rgensen E. Corrosicm properties of soidered joints. Part I: electfochemical action of dentai solder and dental nickel-chromium alloy. J PROSTHET DENT 1959; 62512-5.
5. Walters FM. A photomicrographic evaluation of the solder joint between precious and nonprecious metai. J PROSTWET DENT 1976;35:689-92. 6. Townsend LWA, Vermilyea SG, Griswold WH. Soldering nonnoble ai10~s. J PROSTHET DENT M43:50:51-3. 7. Skinner EW, Phillips KW. The science of dentai materials. Pbiladelphia: WB Saunders CO, 1967;287-97.
Reprintrequestato: Six kinds cd Ni-Cr aBoy soldere dess were im.meraed in sa%ine s&&ion for 100 days. The CQrroaed surface of the Ni-cr alloy and the cross section af t‘he soldered joint were ob3efved with a microscope. Elutinn
DR.NAOFUMI HIROSHIMA
SHIGETQ UNIVERSITY,
KWJMI 1-2-3, MINAMI-KC' HIR~SWIMA~~~ *JAPAN
Scx-100~ OF
DENTISTRY
DDS, PhD,a Toshiyuki
Shigeto, Murakami,
DDS,C
and Taizo
Yanagihara,
Hamada,
DDS,
BEng,b PhDd
Hiroshima University, Schoolof Dentistry, Hiroshima, Japan Six nickel-chromium (Ni-Cr) alloys joined with two solders were evaluated for degree of corrosion after they were immersed in corrosive solution for 100 days. The corroded surface of the Ni-Cr alloy and the cross section of the soldered joint were observed and the solution of nickel and copper (Cu) ions in each combination was measured, No corrosion was observed in the high-resistant Ni-Cr alloys with high Cr content. Pitting corrosion was seen on low-resistant Ni-Cr alloys, which had less Cr content. In the cross section of the joint, the joint of silver solder became porous by corrosion and the corrosion advanced especially along the interface. Solution of Ni ions was detected in all of the combinations of Ni-Cr alloys and solders with exception of the combination of high-resistant Ni-Cr alloys and gold solder. On the other hand, solution of Cu ions was detected in all of the combinations with silver solder. (J PROSTHETDENT 1991;66:607-10.)
S
oldering is commonly used to assemble crown and fixed partial denture prostheses. Improvement has been made in investments, fluxes, and heating equipment. Many studies have reported joint strength and microstructure of the soldered joint.lw3 However, corrosion (such as tarnish, discoloration, and dissolution of the soldered joint) has not received a complete evaluation. Nickel-chromium (Ni-Cr) alloys with varing percentages of Cr have been evaluated for degree of corrosion by use of an electrochemical method.4 Although the experimental methodology is interesting, the study did not demonstrate a real corrosion pattern. Corrosion at the soldered joint, if improper combination of metals and fluxes are used, may produce an unsatisfactory result (fracture, discoloration of the joint, or plaque accumulation). This study evaluated the corrosion patterns of actual soldered joints made up of six kinds of Ni-Cr alloys containing different amounts of Cr and two different types of solders (gold solder and silver solder).
MATERIAL AND Alloy specimens
METHODS
The compositions of dental Ni-Cr alloys and dental solders used in this study are shown in Tables I and II. Each alloy was cast to produce samples 3 X 1.5 X 20 mm; the small end of the casting was ground with emery paper and an alumina suspension and sandblasted by fine alumina abrasives. The polished surfaces of two castings were abutted to *AssociateProfessor,Department of Prosthetic Dentistry. bInstructor, Department of Prosthetic Dentistry. cGraduate student, Department of Prosthetic Dentistry. dProfessorand Chairman, Department of Prosthetic Dentistry. 1Of1f3137c-J
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
each other with a clearance of 0.3 mm in a furnace. Lo-Temp flux (Jeneric Gold Co., Wallingford, Corm.) was used. The soldered block was cut to 20 mm length to position the joint in the center of the sample and was invested with a polyester resin. The exposed portion of the joint was polished with emery paper and an alumina suspension. The term alloy A-gold solder means that two blocks of alloy A were soldered with gold solder. The term alloy A-silver solder means that two blocks of alloy A were soldered with silver solder. Other combinations were similarly identified.
Observation A saline solution (0.9 “/o NaCl) was adjusted to pH 7 and used as the corrosive solution in which specimens were immersed at 37” C for 100 days. The surface was observed with a microscope for any corrosion and then crosssectioned through the joint for observation.
Measurement
of nickel
and copper
ions
The concentrations of Ni and Cu ions that bad eluted into the corrosive solution after the immersion test were measured by use of atomic absorption and emission spectrometry (type 207, Hatachi, Ltd., Tokyo, Japan).
RESULTS Observation
of Ni-Cr
alloy
surface
Corroded surfaces of Ni-Cr alloys immersed in the corrosive solution for 100 days are shown in Figs. I and 2. On the surface of alloy A, pittings 0.1 to 0.4 mm in diameter were seen on the specimen. Corrosion of silver solder was greater than that of gold solder. Pitting on the surfaces of alloys B and C was less than on alloy A. No pitting corrosion was observed on the surfaces of alloys D, E, and F.
607
CORROSION
PATTERN
OF SOLDERED
JOINTS
3. Photomicrographs of pitting on surface of cross section of soldered joints between Ni-Cr alloys (A through F) and silver solder (SS). Top end in each photomicrograph shows surface exposed to corrosive solution. No pitting on surfaces of cross section of soldered joints between Ni-Cr alloy-gold solder combinations. Fig.
ABCDEF
Alloy-gold
solder
combination
Fig. 4. Dissolution of Ni ion from Ni-Cr alloy (A through F) and gold solder combinations.
.-5
3
2 :: g
2
.z
1 0 A
6
Alloy-silver
C
solder
D
E
F*
combination
Fig. 5. Dissolution of Ni ion from Ni-Cr alloy (A through F) and silver solder combinations.
connected in air to the measuring equipment mentioned in the former report.4 When the Ni-Cr alloy and solder are actually joined together, current density values of galvanic currents on the surfaces of the Ni-Cr alloy and the solder are different from each other in proportion to distances THE
JOURNAL
OF PROSTHETIC
DENTISTRY
0
ABCDEF
Alloy-silver
solder
combination
Fig. 6. Dissolution of Cu ion from Ni-Cr alloy (A through 5’) and silver solder combinations. No Cu ions were detected from Ni-Cr alloy and gold solder combinations.
from the soldered interface. The actual sol should be evaluated for corrosion after immersion in the corrosive solution for a long term. Pitting on the surface of the Ni-Cr alloy was seen in alloys A, B, and C combined with gold or silver solder. These alloys were low in corrosion resistence in view of the values of Cr and molybdenum (MO) content. The existence ofpitting was not related to the position in distan joint. The shape of pitting was probably dendritic structure of each Ni-Cr alloy casting. Corrosion of the cross section of the joint was observe in silver solder combined with all Ni-Cr alloys because the solder was low in corrosion resistence. It was noted that the solder was more significantly corroded than the Ni-Cr alloys particularly from the exposed surface to the Enside. One study implied that the soldered joint between the nonprecious alloy and silver solder was a mechanical con-
of Ni and Cu ions in each combination was measured by use of atomic absorption and emission spectrometry. The following results were obtained: 3.. No corrosion was observed in the higb-resistant Ni-@I= alloys of D, E, and F (high Cr content) when they were coupled with either of the two kinds of solder. 2. Pitting corrosion was seen on low-resistant Ni-@r ailays of A, B, and C (less Cr content) w en they were coupled with any of the solders. 3. In the cross section of the joint with silver solder, the joint beea porous by corrosion that advanced along the interface. corrosion was seen with gold solder. 4. Elution of Ni ions was detected in all of the combinations of Ni-Cr alloys and solders, with the exception of the ~ornbi~at~o~ of alloys D, E, and F with gold solder. On the other hand, elution of Cu ions was detected in all of the ~o~bi~at~ons with silver solder, but not with gold solder. REFE
CES
1. Lautenschiager Dent
E?. Strength
mechanism
of dentai
soldered
joints.
J
Kes :974;53:1m-7.
2. Brudvik JS, Nicholls JI. Soldering of removable partial dentures. d PR~STBET DENT 1983;49:762-5. 3. Kayiakie WG, Brukl CE. Comparative tens& strengths of nonnobie dental alioy solders. J PROSTKET DENT 1985:53:455-62. 4. Shigeto hi, Yanagihara T, Hamada T, Bud&J$rgensen E. Corrosicm properties of soidered joints. Part I: electfochemical action of dentai solder and dental nickel-chromium alloy. J PROSTHET DENT 1959; 62512-5.
5. Walters FM. A photomicrographic evaluation of the solder joint between precious and nonprecious metai. J PROSTWET DENT 1976;35:689-92. 6. Townsend LWA, Vermilyea SG, Griswold WH. Soldering nonnoble ai10~s. J PROSTHET DENT M43:50:51-3. 7. Skinner EW, Phillips KW. The science of dentai materials. Pbiladelphia: WB Saunders CO, 1967;287-97.
Reprintrequestato: Six kinds cd Ni-Cr aBoy soldere dess were im.meraed in sa%ine s&&ion for 100 days. The CQrroaed surface of the Ni-cr alloy and the cross section af t‘he soldered joint were ob3efved with a microscope. Elutinn
DR.NAOFUMI HIROSHIMA
SHIGETQ UNIVERSITY,
KWJMI 1-2-3, MINAMI-KC' HIR~SWIMA~~~ *JAPAN
Scx-100~ OF
DENTISTRY
