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Description:
Iridium Power Technology
Fifty million years ago, an asteroid composed almost entirely of the precious metal Iridium (Ir-77) struck the earth creating the Gulf of Mexico. From this catastrophe came a metal with properties ideal for spark plug construction. Using this element, DENSO has evolved spark plug design to a new level.

Patented Technologies
The U-Groove Design
In 1972, we received a patent for the popular U-Groove ground electrode design. This electrode was developed to meet the demand for improved ignitability, which is necessary for an increase of efficiency in emission gas purification and fuel consumption. The U-Groove gives the flame a groove to grow in, thereby creating a larger flame front for a more complete combustion even in the case of lean air-fuel mixture. A conventional, flat ground electrode design of regular plugs crushes the flame preventing full spark potential.

Iridium Alloy
In a never-ending effort to improve upon success, DENSO developed an Iridium alloy that is superior to platinum based on hardness, strength and melting point. The new Iridium alloy is composed primarily of Iridium with rhodium mixed in for oxidation wear. Pure Iridium has a melting point of almost 700ºC higher than platinum, and had the greatest potential for resistances against wear. Iridium by itself is susceptible to oxidation wear at temperatures over 900ºC, however, ordinary driving around town an engine would never reach these temperatures. Further testing proved that Iridium alone would not meet DENSO's demanding standards. After testing other pure metals combined with Iridium, rhodium proved to be the best choice to meet the needs of DENSO's spark plug engineers.

Ultra Fine Electrode
By harnessing the power of Iridium, DENSO is suddenly able to shrink the surface area of the center electrode - the critical component of a spark plug. Unlike a typical platinum plug that has a 1.1mm diameter center electrode, DENSO Iridium Power plugs have the world's smallest center electrode measuring 0.4mm in diameter. This means that the voltage requirements are decreased while firing performance is greatly improved.

U-Groove Technology
Our patented U-Groove design changed the industry standard in the mid 1970s by providing a better design that virtually eliminates erratic starts caused by poor fuel mixture. The U-Groove results in less flame dissipation making the spread of the flame nucleus easier and therefore yielding greater firing energy. It gives the flame a groove to grow in, thereby creating a larger flame front for a complete combustion.
On a conventional plug, the flat electrode design crushes the spark, and the overall volume of the flash front is smaller.
The conventional method to improve firing was to increase the spark gap. This has a negative effect on the spark. With a U-Groove firing can be greatly improved without increasing the spark gap.

Tapered Cut
To help improve ignitability DENSO minimized the portion of the ground electrode that comes in contact with the flame nucleus. Because the area of the ground electrode where the tapered cut comes into contact with the flame nucleus is small, the heat lost to the electrode is lessened and firing performance improves dramatically. The surface area and weight of the ground electrode tip is reduced along with the load in terms of heat and vibrations. This means the spark plug can cope with heavier driving conditions.

Origin Of Iridium
A Long Time Ago...
Approximately 50 million years ago an asteroid, some 10km in diameter slammed into what is now Mexico's Yucatan Peninsula near the town of Chicxulub. The resulting dust cloud destroyed most living things and ended the dinosaurs reign on earth. The evidence for this has been known for some time, with the deposits of Iridium-rich clay found at the boundary of Cretaceous and Tertiary deposits (known as the K/T Boundary) all over the world.
On July 2 1992, Alan R. Hildebrand of the Geological Survey of Canada presented a scientific paper to the General Assembly of the Royal Astronomical Society of Canada entitled "The Cretaceous/Tertiary Boundary Impact". Some of his findings are summarized here.
The K/T boundary layer, sometimes known as the iridium bearing clay layer, has a global distribution and consists of at least two layers of impact material.
The upper layer, known as the Fireball layer averages 3mm thickness and represents 1500 cubic kilometers of debris deposited globally with no apparent variation in thickness.
The lower layer termed the ejecta layer, averages about 2cm in thickness.

A Major Impact on Earth?
Many scientists believe that the enormous impact put enough dust into the upper atmosphere to darken and hence cool the Earth for several years. This was theorized to result in shutting off global photosynthesis, with the resulting collapse of the global food chain. As a result nothing larger than 25 kg survived the boundary.
Iridium is found all over the world in the K/T layer and is not an unknown metal (commodity), however; its ability to be used in a manufacture type environment is unique. The current products that use Iridium are cellular telephones (Motorola), sunglasses (Oakley), and now spark plugs (DENSO). The reason for only a few companies using this precious metal is its difficulty to be manipulated in a cost-effective manner.
DENSO's experience with Iridium in the development of the complete line of original equipment platinum spark plugs helped in the development of the patented DENSO Iridium alloy, where the Iridium becomes the primary metal complimented by rhodium (Atomic Symbol: Rh) to increase oxidation wear resistance.

Laser Welding
The 0.4mm Iridium tip that generates the high performance of Iridium Power is an alloy with a very high melting point. Therefore, ordinary resistance welding cannot be used because the Iridium alloy does not melt enough and adequate weld strength cannot be guaranteed.
The DENSO patented 360° Laser Welding process employs a high-energy laser so reliable that the electrode resists wear in the worst conditions.

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