Home » Photos » Nickel Sulfide Inclusion: A tiny speck that destroys tempered glass
A rare impurity known as a nickel sulfide inclusion is a tiny metallic ball that grows over time with sufficient force that it can catastrophically shatter tempered glass. This is what nickel sulfide inclusions look like.
Shattered sliding door
Shattered sliding door
This glass sliding glass door in a Chicago high-rise spontaneously broke one day with nobody home. It was the inner lite of an insulated glass unit. The outer lite was fine, so no impact came from the outside.
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Tempered glass break
Tempered glass break
Tempered glass breaks into thousands of pieces by design. The small "cubes" are safer than large glass shards. The breakage pattern has a focal point where the major lines converge. This is the origin of the fracture.
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Butterfly pattern in tempered glass
Butterfly pattern in tempered glass
At the center of the glass fracture pattern, two polygons can be found bordering one another. These polygons are typical of the breakage pattern caused by a nickel sulfide inclusion. The inclusion, a tiny dot, can be seen on the break between the two polygons. This pattern is also called a "butterfly pattern"
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04.jpg
04.jpg
Magnified 20x, the dot on the border between the two polygons can be seen as a small sphere. This is the nickel sulfide inclusion. It is hard to imagine that this tiny dot caused an entire sliding door glass to shatter, but it's true. The phenomenon of nickel sulfide inclusions causing tempered glass breakage has been known by manufacturers since the late 1940's and was first identified in an industry article in 1961.
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Reflection pattern at nickel sulfide inclusion
Reflection pattern at nickel sulfide inclusion
Varying the light in the picture, the light reflection reveals stress waves emanating from the inclusion. The stress is the cause of the glass failure. It developed slowly as the nickel sulfide inclusion grew over time, pressing against the unyielding encasing glass. One researcher estimated that this stress could reach 100,000 pounds per square inch. When the stress exceeded the ability of the glass to contain it, the glass failed catastrophically. Why catastrophically? Because tempered glass, by design, has a permanent internal tug-of- war to the tune of 10,000 pounds per square inch everywhere in the glass plate. Disrupt that structure, and you get...pop!
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Stress waves at nickel sulfide inclusion
Stress waves at nickel sulfide inclusion
Another view of stress waves emanating from the nickel sulfide inclusion. The stress waves are in the shape of four teardrops pointing to one another, converging at the nickel sulfide inclusion. The small teardrops aim toward the glass surface, where the localized stress was quickly relieved as the fracture made its way to the surface. The taller teardrops stretched their way along the length of the fracture.
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Nickel sulfide inclusion - impurities - vents
Nickel sulfide inclusion - impurities - vents
At 200x magnification, more activity can be seen in the glass. The inclusion doesn't look spherical at all, but rather like a bird diving into water. The birdlike shape is a combination of the nickel sulfide inclusion, other impurities around it, and vents (small cracks) emanating from it.
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Glass ripples at NiS inclusion
Glass ripples at NiS inclusion
Now we change the focus to observe the waves and ripples in the break immediately surrounding the nickel sulfide inclusion. Was this phenomenon the inspiration for similar patterns we see in the works of Chagall and Van Gogh?
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Mirror at NiS inclusion
Mirror at NiS inclusion
The bird-like shape has a round head, and a body. The smooth surface it is swimming in is shiny like a mirror. In glass fractography, the incredibly smooth part of the break is actually called the mirror.
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Wallner lines at NiS inclusion
Wallner lines at NiS inclusion
This nickel sulfide inclusion is quite unique - it has a typical spherical ball, at right, but then it has an unusual elongated impurity. We'll call that the tail. Curved lines in the mirror are called Wallner lines. They indicate the direction of crack propagation. Since the inclusion is at the center of the break, the Wallner lines emanate in many directions.
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NiS inclusion breaks glass
NiS inclusion breaks glass
This graceful swimming bird is a minute imperfection that singlehandedly broke an entire piece of glass.
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NiS inclusion hidden in glass reflection
NiS inclusion hidden in glass reflection
Now we are going to start rotating the view. The triangular shape at the right of the inclusion is actually a ridge that has such strong reflective properties, that it can hide the inclusion almost completely when viewed from a different angle.
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Nis inclusion hidden behind fracture mirror
Nis inclusion hidden behind fracture mirror
Here almost the entire NiS inclusion is hidden behind a mirror-smooth ridge in the fracture surface. The ridge is reflecting light in such a way that it obscures the inclusion.
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NiS inclusion embedded in glass edge
NiS inclusion embedded in glass edge
When you view from a different angle, the inclusion looks like a gnarly insect embedded in the glass edge
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Inclusion on mirror smooth glass
Inclusion on mirror smooth glass
Here we see the inclusion insect floating on mirror-smooth glass with lazy ripples conveying movement
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NiS inclusion with impurities
NiS inclusion with impurities
Here we see the inclusion with other impurities in the glass with small cracks, known as vents, emanating from it
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Spherical nickel sulfide inclusion ball
Spherical nickel sulfide inclusion ball
Finally, a shiny spherical shape becomes visible, That shiny metal ball is the nickel sulfide inclusion.
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NiS inclusion and corner fracture
NiS inclusion and corner fracture
The inclusion (lower left) seems to swim its way to the very first instance where the fracture branches (at right), creating a beautiful, intricate corner shape. This corner conveys explosiveness and structure all at once. It has a very natural look, yet glass is a man-made material.There is much beauty in this tiny little world.
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NiS inclusion SEM image
NiS inclusion SEM image
This beautiful scanning electron microscope image of a nickel sulfide inclusion was provided by Jianjun Yang of Xinyi Glass, Dongguan City, Guangdong Province, China
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NiS SEM chemical analysis
NiS SEM chemical analysis
Jianjun Yang provided this image of a nickel sulfide inclusion. The encircled area is being analyzed for chemical composition. See next two images for results.
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Nickel sulfide inclusion and other impurities
Nickel sulfide inclusion and other impurities
Graph showing composition of nickel sulfide inclusion with other impurities. The graph shows spikes of nickel and sulfur, as well as other elements.
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NiS inclusion chemical composition
NiS inclusion chemical composition
Chemical analysis of nickel sulfide inclusion. In addition to nickel (Ni) and sulfur (S), the glass impurities also include oxygen (O), sodium (Na), silicon (Si), potassium (K) and calcium (Ca).Thanks to Jianjun Yang, Xinyi Glass and South China University of Technology for these images.
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