E-IJPM: Vol. 44/4 - MPIF

TUNGSTEN FILAMENTS—THE FIRST MODERN PM PRODUCT
46
day, and one lamp calls for four feet of my wire.”
On March 11, 1907, he wrote: “Dear Mother, it
looks now as though I have made a great improvement
in my filament method. Unless a bug develops
(and I don’t expect it now) my improved
method will be very hard to beat, and for the large
filaments at any rate I very much doubt whether
anything can touch it. The improvement consists
in the addition of a small quantity of another
metal, bismuth, to my mixture. It cuts the time
per filament from minutes down to four seconds.”
One month later he wrote, “I am also pleased to
see that I am getting the credit for my recent discovery
that tungsten is a ductile metal below red
heat. I found that these filaments which are so
brittle cold can readily be bent into any shape by
heating slightly.”
EARLY COOLIDGE BULB AND MAZDA BULBS
GE made the first public announcement of ductile
tungsten wire in 1910 but changed over to the
Coolidge process during late 1910. The company
scrapped about $500,000 worth of equipment as
well as another $500,000 worth of unsold filament
lamps.
In 1907, 90 percent of domestic incandescent
lamp sales were carbon. By 1916 an estimated 85
percent were made from tungsten. Lamps made
with ductile tungsten filaments were marketed by
GE in 1911 under the Mazda brand in 25, 40, 60,
100, and 150 watt levels, lasting up to 1,000 h,
Figure 5 and Figure 6.
A GE advertisement for Edison Mazda Lamps
said: “For the same money that you now pay for
the old-style carbon lamp, you can have your
choice of three times as much light in each room.”
COOLIDGE PATENTS
Coolidge began filing patents in 1909 on dies
and die supports, and was awarded the patent for
ductile tungsten (U.S. Patent 1,082,933) on
December 30, 1913, Figure 7. GE granted licenses
to several companies to make ductile-tungsten
wire for incandescent electric lamps. However,
Coolidge’s 1913 patent was challenged by the
Independent Lamp & Wire Co., Weehawken, New
Jersey, and invalidated in 1927 because it was
not an invention as defined by patent law.
Many competitors joined the business including
the Independent Lamp & Wire Company producing
wire for Sylvania bulbs. Callite Tungsten
Corporation followed, as well as Westinghouse,
Mallory Metallurgical, and GTE Sylvania, Inc.
OTHER TUNGSTEN DEVELOPMENTS
Coolidge’s seminal work on tungsten filaments
opened the door to inventing a vacuum tube for
generating X-rays known as the “Coolidge tube.”
It became the first stable and controllable X-ray
generator for medical and dental use and replaced
gas-filled tubes with platinum targets. Another
well-known GE researcher, Irving Langmuir,
found that he could obtain a controllable electron
emission from one of Coolidge’s hot tungsten filaments
in a high vacuum instead of a gas. Coolidge
installed a heated tungsten filament in an X-ray
tube with a tungsten filament cathode and a
tungsten target. He also developed tungsten contacts
for electrical switches used in automotive
ignition systems. Many other commercially successful
tungsten products followed.
Figure 5. Early
Coolidge bulb
Figure 6. Mazda
brand GE
light bulbs,
1911–1913
Volume 44, Issue 4, 2008
International Journal of Powder Metallurgy