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Dross
 
 
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Dross is a mass
Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
 of solid
Solid

A solid object is in the states of matter characterized by resistance to deformation and changes of volume. In other words, it has high values both of Young's modulus and of shear modulus; this contrasts e.g....
 impurities
Impurity

Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical composition of the material or compound....
 floating on a molten metal. It appears usually on the melting of low melting point
Melting point

The melting point of a solid is the temperature range at which it changes states of matter from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium....
 metal
Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
s or alloy
Alloy

An alloy is a partial or complete solid solution of one or more chemical element in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history....
s such as tin
Tin

Tin is a chemical element with the symbol Sn and atomic number 50. Tin is obtained chiefly from the mineral cassiterite, where it occurs as an oxide, SnO2....
, lead
Lead

Lead is a main-group Chemical element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metal ....
, zinc
Zinc

Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal of the group 12 element of the periodic table....
 or aluminium
Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
, or by oxidation
Redox

Redox describes all chemical reactions in which atoms have their oxidation number changed.This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane , or it can be a complex process such as the oxidation of sugar in the human body through a ser...
 of the metal(s). It can also consist of impurities such as paint leftovers. It can easily be skimmed off the surface before pouring the metal into a mold
Molding (process)

Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....
 or casting flask.

With tin and lead the dross can also be removed by adding sodium hydroxide
Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
 pellets, which dissolve the oxides and form a slag
Slag

Slag is a partially vitreous by-product of smelting ore to purify metals. They can be considered to be a mixture of metal oxides; however, they can contain metal sulfides and metal atoms in the elemental form....
.

Dross, as a solid, is distinguished from slag, which is a liquid.






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Dross is a mass
Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
 of solid
Solid

A solid object is in the states of matter characterized by resistance to deformation and changes of volume. In other words, it has high values both of Young's modulus and of shear modulus; this contrasts e.g....
 impurities
Impurity

Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical composition of the material or compound....
 floating on a molten metal. It appears usually on the melting of low melting point
Melting point

The melting point of a solid is the temperature range at which it changes states of matter from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium....
 metal
Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
s or alloy
Alloy

An alloy is a partial or complete solid solution of one or more chemical element in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history....
s such as tin
Tin

Tin is a chemical element with the symbol Sn and atomic number 50. Tin is obtained chiefly from the mineral cassiterite, where it occurs as an oxide, SnO2....
, lead
Lead

Lead is a main-group Chemical element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metal ....
, zinc
Zinc

Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal of the group 12 element of the periodic table....
 or aluminium
Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
, or by oxidation
Redox

Redox describes all chemical reactions in which atoms have their oxidation number changed.This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane , or it can be a complex process such as the oxidation of sugar in the human body through a ser...
 of the metal(s). It can also consist of impurities such as paint leftovers. It can easily be skimmed off the surface before pouring the metal into a mold
Molding (process)

Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....
 or casting flask.

With tin and lead the dross can also be removed by adding sodium hydroxide
Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
 pellets, which dissolve the oxides and form a slag
Slag

Slag is a partially vitreous by-product of smelting ore to purify metals. They can be considered to be a mixture of metal oxides; however, they can contain metal sulfides and metal atoms in the elemental form....
.

Dross, as a solid, is distinguished from slag, which is a liquid. Dross product is not entirely waste material; aluminium dross, for example, is used in secondary steelmaking
Steelmaking

Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the Pig iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required....
 for slag deoxidation
Deoxidizer

A deoxidizer is a chemical used in a reaction or process to remove oxygen. In comparison with antioxidants, deoxidizers are not used for stabilization during storage but for oxygen removal during manufacture....
, reducing processing costs by minimizing use of pure aluminum.

In the electronic wave soldering
Wave soldering

Wave soldering is a large-scale soldering process by which electronic components are soldered to a printed circuit board to form an electronic assembly....
 process, dross can account for over 50% of the metal required. With the advent of lead-free solder
Solder

A solder is a fusible alloy metal alloy with a melting point or melting range of 90 to 450 ?Celsius , used in a process called soldering where it is melted to join metallic surfaces....
s, the cost of replacing metal lost to dross has become unacceptably high. Dross also reduces the expected quality of the solder joint as measured in defects per million opportunities
Defects per million opportunities

In process improvement efforts, defects per million opportunities or DPMO is a measure of process performance. It is defined asA defect is defined as a nonconformance of a quality characteristic to its specification....
 (DPMO). With the advent of the lead-free soldering process, the cost of the new alloys are so high that accepting dross in the process has become a significant cost issue.

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