Using a high-tech but low-cost technique, a Johns
Hopkins undergraduate has tested tiny samples of four metal
alloys to find the best blend for use in platinum jewelry.
After evaluating the metal mixtures, student researcher
Christopher Kovalchick determined that platinum combined
with a small amount of chromium in a cold-rolled and heat
treatment process displayed the greatest strength.
The finding is important because pure platinum is too
soft for use in a durable piece of jewelry. Yet many
countries mandate that platinum jewelry must contain at
least 95 percent of the precious metal by weight. With just
5 percent left to work with, jewelers are looking for the
best platinum blend to produce strong and durable products.
In addition to the metallic mix, platinum alloy makers can
also employ various production methods such as heat
treatment and cold-rolling techniques to affect mechanical
properties such as hardness and elasticity.
Kovalchick's testing method, pioneered by his faculty
adviser, helped him keep costs low because it used
ultra-thin samples, each smaller than a child's thumbnail,
rather than the large, expensive chunks required in
conventional testing. The engineering mechanics major
estimated that each platinum alloy microsample used in his
tests cost $200. A traditional platinum-based test sample,
measuring about 10 inches long, 1 inch wide and a half-inch
thick, would cost nearly $50,000, the student said.
"This is a very useful technique," Kovalchick said.
"It's [not only] less expensive, but what we learn from the
microsamples will also apply to larger amounts of the
material."
His presentation on platinum testing won first place
in the student competition at the annual conference of the
Society for Experimental
Mechanics, held recently in Portland, Ore. Kovalchick,
a Hamilton, N.J., resident who will begin his senior year
next month, was the only undergraduate entrant, competing
against 17 graduate students.
His project began in March 2004, when Kovalchick asked
William N. Sharpe
Jr., the Alonzo G. Decker Professor of
Mechanical
Engineering, to sponsor him in applying for a
Provost's Undergraduate Research
Award. The professor, an internationally recognized
leader in microsample testing, proposed a collaboration
with the Centre for Materials Engineering at the University
of Cape Town, South Africa, where researchers wanted an
independent lab to test platinum alloys. South Africa is a
leading source of platinum and boasts a growing platinum
jewelry industry.
The Cape Town researchers sent 32 specimens of four
alloys for testing by Kovalchick under Sharpe's
supervision. Each sample was only 200 to 400 microns thick,
roughly three or four times the thickness of a human hair.
For testing purposes, each was shaped like a tiny dog
biscuit, about 3 centimeters long.
Each microsample was placed carefully between two
grips. A motor pulled on one end, and a device called a
50-pound load cell measured the amount of force the sample
withstood before breaking. The researchers also measured
strain, the metal's ability to stretch without breaking.
This was done by a technique invented by Sharpe called
interferometric strain/displacement gage. In this method, a
laser is aimed at two small indentations in the metal
specimen. The light bounces off the indentations, producing
patterns that change as the metal is stretched. These
changes, captured by photosensors, give the researchers
data to measure the strain characteristics.
Kovalchick tested four alloys: a cold-rolled platinum
blend containing 5 percent copper; a cold-rolled platinum
blend containing 3.2 percent chromium; a 3.2 percent
platinum-chromium blend that was cold rolled and then
heated to 300 C for three hours; and a 3.2 percent
platinum-chromium blend that was recrystalized by heating
it for six hours at 800 C.
The student researcher determined that among these
alloys, the platinum-chromium mix that underwent cold
rolling and three hours of heating displayed the greatest
strength. The recrystalized alloy was the weakest. His
detailed findings will be given to researchers in South
Africa and are expected to be the focus of a scientific
journal article.
"Because each microspecimen was a little different,
this project turned out to be more involved and more
complicated than we'd ever anticipated," said Sharpe,
Kovalchick's faculty adviser. "But Chris finished the work,
and he gave a fine presentation before the judges at the
student competition."
Kovalchick said he was well-prepared because Sharpe
and other engineering professors had grilled him with
questions during a meeting before the science conference.
"It was a great learning experience," the student said.
"This is what Hopkins prides itself on — giving
undergraduates a chance to do research. This will give me a
leg up when I go to grad school."
In addition to his engineering studies, Kovalchick is
pursuing a second degree, in violin performance at
Peabody. During
his freshman and sophomore years, he was concertmaster of
the Peabody Concert Orchestra. He is currently a principal
in the Peabody Symphony Orchestra.
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