Nickel sulfide inclusion
Encyclopedia
A nickel sulfide inclusion, (also abbreviated to NiS), occurs during the process of manufacturing float glass
(normal window glass).
, contaminants that contain nickel
might be present, (e.g. stainless steel
.)
These can combine with sulfur
to form nickel sulfide inclusions. Furnaces produce hundreds of tons of glass every day, so it is difficult to completely eliminate any contaminants. This causes a problem later in the manufacturing process.
While total elimination is difficult, specific controlled processes can significantly reduce the formation of NiS in the float glass. These are actions taken by US flat glass manufacturers supplying to the automotive industry in the early 1990s:
a) all green sand (silica, transported by railroads from Wyoming USA) shipments were processed through multiple screens (to filter out any nickel bearing materials either mineral or stainless steel tools, nuts, bolts, washers) since stainless steel cannot be detected by magnets.
b) all other bulk materials including recycled glass were inspected similarly to (a).
c) every maintenance procedure and all training was very focused on the need for every worker to prevent contamination of the float furnace or the float glass tank with NiS.
d) use of any nickel containing tool or material anywhere in the Ford Glass float facility was closely controlled to prevent contamination.
e) any float glass suspected to have NiS (it could only be found with a Scanning Electron Microscope) was destroyed and landfilled as it could not be re-introduced to glass used for any purpose.
The process of tempering float glass
can cause a NiS to change from its normal state (known as a low-temperature structure) to a different high-temperature, crystalline structure. When the glass
is cooled quickly (as part of the process) the NiS particle is unable to change back to its original form.
Over a certain period of time NiS will slowly convert to the original low temperature structure. This means the NiS increases in size, and the mechanical stresses caused by this cause the tempered pane to shatter, for no apparent reason (hence spontaneous glass breakage
).
Float glass
Float glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass...
(normal window glass).
Occurrence
In a batch of glassGlass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
, contaminants that contain nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
might be present, (e.g. stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
.)
These can combine with sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
to form nickel sulfide inclusions. Furnaces produce hundreds of tons of glass every day, so it is difficult to completely eliminate any contaminants. This causes a problem later in the manufacturing process.
While total elimination is difficult, specific controlled processes can significantly reduce the formation of NiS in the float glass. These are actions taken by US flat glass manufacturers supplying to the automotive industry in the early 1990s:
a) all green sand (silica, transported by railroads from Wyoming USA) shipments were processed through multiple screens (to filter out any nickel bearing materials either mineral or stainless steel tools, nuts, bolts, washers) since stainless steel cannot be detected by magnets.
b) all other bulk materials including recycled glass were inspected similarly to (a).
c) every maintenance procedure and all training was very focused on the need for every worker to prevent contamination of the float furnace or the float glass tank with NiS.
d) use of any nickel containing tool or material anywhere in the Ford Glass float facility was closely controlled to prevent contamination.
e) any float glass suspected to have NiS (it could only be found with a Scanning Electron Microscope) was destroyed and landfilled as it could not be re-introduced to glass used for any purpose.
The process of tempering float glass
Float glass
Float glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass...
can cause a NiS to change from its normal state (known as a low-temperature structure) to a different high-temperature, crystalline structure. When the glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
is cooled quickly (as part of the process) the NiS particle is unable to change back to its original form.
Over a certain period of time NiS will slowly convert to the original low temperature structure. This means the NiS increases in size, and the mechanical stresses caused by this cause the tempered pane to shatter, for no apparent reason (hence spontaneous glass breakage
Spontaneous glass breakage
Spontaneous glass breakage is a phenomenon by which toughened glass may spontaneously break without any apparent reason.The most common causes are:...
).