Au-Amalgam Alloy: Effect of Annealing and Splat Cooling MANOHAR L. MALHOTRA* Department of AMaterials Science, University of Virginia, Charlottesville, Virginia 22903, USA
Recently, conxlentional AgenSn alloy has been modified by replacing Ag in part by Au in an attempt to obtain an amalgam of y, (Snt75Hg). The preseit svuik denonstrates that the annealed alloy (59 xst% Ag, 26 wst%, Sn, and 15 wt% Au) shows two distinct phases whereas the splat cooled ribbon of the same alloy composition showis a single phase, homogeneous material. Figure 1 shows an optical micrographi of a polished suirface of the alloy inigot annealed at 470 C for tvo weeks. The microstructure shows large sized grains (-375 micrometers [,tcm])
ZG
o
..........
sur-
Thiis itnvestigation wsas supported by Grant No. DE021 11 from the National Institute of Dental Researchi, National Institutes of Health, Bethesda, Md. This wvork was in partial fulfillment of the doctor of
he
philosophiy degree. Received for publication January 15. 1976. Accepted for publication May 12, 1976. Present address: School of Dentistry, University of M-ichigan, Ann Arbor, Mich.
~~~~~~~~FiG2.-Typical scanning electron micrograph splat-cooled ribbon alloy surface showing x.ell -defned small-sized y gi separated by ....sharp boundaries.
t
of
...
sounued by black rings and separated by bound-
ais regions. Electron microprobe analysis has ~~~confiimed that Au is distributed uniformly all 6,), 4.~ ~ ~ ~ ~ ~ ~ ~~~~oe the -y (Ag,5Sn) grains, and that black rings surroundling the grains an-d also boundary regionis between the grains coirespond to an 4 ~~(Au-Sni) 2phase. a 4 igure shiows scanning electron micrograph ....of a spatcooled ribbon surface of the same alloy A. compositioni. The microstructuie shows small...14 sized grains ('-3.5 1um) defined by sharp grain boouncdaries. Electron microprobe analysis has conifis med the homogenieity of this alloy ribbon suirface and also has shown that Au is distributed tiniiformly all over the -y grains. Thus, it is concluded that the dental amalgam madle from small-sized, single-phase, homogenecous alloy particles obtained by the splat. gq~cooling process ensures improved mechanical properties. However, the annealing process prodluces opposite effects compared with the splat20o ftm cooling process and the results are of no significance so far as dental amalgam FieG I.-Typical optical micrograph of an- ispiactical concerne(l. It is thus believed that the neaed llo sufae sowig lrg y rais sratnalgam made out of alloy powder from splatasby rouned y blck ing andals by ounary cooled ribbons will show a good clinical behavior. regions of (Au-Sn) phase. .......
-.
..
c~~~~~~-
neanded ally surace shoings large grainsdsry
J Dent Res November-December 1976, Vol 55 No. 6 Downloaded from jdr.sagepub.com at Harvard Libraries on June 26, 2015 For personal use only. No other uses without permission.
1141
Recently, conxlentional AgenSn alloy has been modified by replacing Ag in part by Au in an attempt to obtain an amalgam of y, (Snt75Hg). The preseit svuik denonstrates that the annealed alloy (59 xst% Ag, 26 wst%, Sn, and 15 wt% Au) shows two distinct phases whereas the splat cooled ribbon of the same alloy composition showis a single phase, homogeneous material. Figure 1 shows an optical micrographi of a polished suirface of the alloy inigot annealed at 470 C for tvo weeks. The microstructure shows large sized grains (-375 micrometers [,tcm])
ZG
o
..........
sur-
Thiis itnvestigation wsas supported by Grant No. DE021 11 from the National Institute of Dental Researchi, National Institutes of Health, Bethesda, Md. This wvork was in partial fulfillment of the doctor of
he
philosophiy degree. Received for publication January 15. 1976. Accepted for publication May 12, 1976. Present address: School of Dentistry, University of M-ichigan, Ann Arbor, Mich.
~~~~~~~~FiG2.-Typical scanning electron micrograph splat-cooled ribbon alloy surface showing x.ell -defned small-sized y gi separated by ....sharp boundaries.
t
of
...
sounued by black rings and separated by bound-
ais regions. Electron microprobe analysis has ~~~confiimed that Au is distributed uniformly all 6,), 4.~ ~ ~ ~ ~ ~ ~ ~~~~oe the -y (Ag,5Sn) grains, and that black rings surroundling the grains an-d also boundary regionis between the grains coirespond to an 4 ~~(Au-Sni) 2phase. a 4 igure shiows scanning electron micrograph ....of a spatcooled ribbon surface of the same alloy A. compositioni. The microstructuie shows small...14 sized grains ('-3.5 1um) defined by sharp grain boouncdaries. Electron microprobe analysis has conifis med the homogenieity of this alloy ribbon suirface and also has shown that Au is distributed tiniiformly all over the -y grains. Thus, it is concluded that the dental amalgam madle from small-sized, single-phase, homogenecous alloy particles obtained by the splat. gq~cooling process ensures improved mechanical properties. However, the annealing process prodluces opposite effects compared with the splat20o ftm cooling process and the results are of no significance so far as dental amalgam FieG I.-Typical optical micrograph of an- ispiactical concerne(l. It is thus believed that the neaed llo sufae sowig lrg y rais sratnalgam made out of alloy powder from splatasby rouned y blck ing andals by ounary cooled ribbons will show a good clinical behavior. regions of (Au-Sn) phase. .......
-.
..
c~~~~~~-
neanded ally surace shoings large grainsdsry
J Dent Res November-December 1976, Vol 55 No. 6 Downloaded from jdr.sagepub.com at Harvard Libraries on June 26, 2015 For personal use only. No other uses without permission.
1141
