Tube furnace
Encyclopedia
A tube furnace is an electric heating
device used to conduct syntheses and purifications of inorganic compound
s and occasionally in organic synthesis
. The usual design consists of a cylindrical cavity surrounded by heating coils
, which are embedded in a thermally insulating matrix. Temperature is controlled via feedback
from a thermocouple
. More elaborate tube furnaces have two (or more) heating zones useful for transport experiments
. Some digital controllers allow RS232 interface and permit the operator to program up to 126 segments, such as ramping, soaking, sintering, and more. Also, advances in materials for heating elements, such as molybdenum disilicide offered in certain models by Vecstar, can now produce working temperatures up to 1800 °C, which facilitate more sophisticated metallurgical applications. Most commonly, the tubes are made of Pyrex
or fused quartz
.
The tube furnace was invented in the first decade of the 20th century and was originally used to manufacture ceramic
filaments
for Nernst lamp
s and glowers
.
. A mixture of finely powdered CuO, BaO, and Y2O3, in the appropriate molar ratio, contained in a platinum or alumina "boat," heated in a tube furnace at several hundred degrees under flowing oxygen
. Similarly tantalum disulfide is prepared in a tube furnace followed by purification, also in a tube furnace using the technique of chemical vapor transport. Because of the availability of tube furnaces, chemical vapor transport has become a popular technique not only in industry (see van Arkel process) but also in the research laboratory.
Tube furnaces can also be used for thermolysis reactions, involving either organic or inorganic reactants. One such example is the preparation of ketene
s which may employ a tube furnace in the 'ketene lamp'. Flash vacuum pyrolyses often utilize a fused quartz tube, usually packed with quartz or ceramic beads, which is heated at high temperatures.
Joule heating
Joule heating, also known as ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. It was first studied by James Prescott Joule in 1841. Joule immersed a length of wire in a fixed mass of water and measured the temperature...
device used to conduct syntheses and purifications of inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
s and occasionally in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
. The usual design consists of a cylindrical cavity surrounded by heating coils
Heating element
A heating element converts electricity into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element....
, which are embedded in a thermally insulating matrix. Temperature is controlled via feedback
Feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...
from a thermocouple
Thermocouple
A thermocouple is a device consisting of two different conductors that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a...
. More elaborate tube furnaces have two (or more) heating zones useful for transport experiments
Chemical transport reaction
In chemistry, a chemical transport reaction describes a process for purification and crystallization of non-volatile solids. The process is also responsible for certain aspects of mineral growth from the effluent of volcanoes. The technique is distinct from chemical vapor deposition, which...
. Some digital controllers allow RS232 interface and permit the operator to program up to 126 segments, such as ramping, soaking, sintering, and more. Also, advances in materials for heating elements, such as molybdenum disilicide offered in certain models by Vecstar, can now produce working temperatures up to 1800 °C, which facilitate more sophisticated metallurgical applications. Most commonly, the tubes are made of Pyrex
Pyrex
Pyrex is a brand name for glassware, introduced by Corning Incorporated in 1915.Originally, Pyrex was made from borosilicate glass. In the 1940s the composition was changed for some products to tempered soda-lime glass, which is the most common form of glass used in glass bakeware in the US and has...
or fused quartz
Fused quartz
Fused quartz and fused silica are types of glass containing primarily silica in amorphous form. They are manufactured using several different processes...
.
The tube furnace was invented in the first decade of the 20th century and was originally used to manufacture ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
filaments
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...
for Nernst lamp
Nernst lamp
Nernst lamps were an early form of electrically powered incandescent lamps. Nernst lamps did not use a glowing tungsten filament. Instead, they used a ceramic rod that was heated to incandescence...
s and glowers
Nernst glower
The Nernst glower is an obsolete device for providing a continuous source of infrared radiation for use in spectroscopy. Typically it was in the form of a cylindrical rod or tube composed of a mixture of certain oxides such as zirconium oxide , yttrium oxide and erbium oxide at a ratio of...
.
Illustrative applications
An example of a material prepared using a tube furnace is the superconductor YBa2Cu3O7Yttrium barium copper oxide
Yttrium barium copper oxide, often abbreviated YBCO, is a crystalline chemical compound with the formula YBa2Cu3O7. This material, a famous "high-temperature superconductor", achieved prominence because it was the first material to achieve superconductivity above the boiling point of liquid...
. A mixture of finely powdered CuO, BaO, and Y2O3, in the appropriate molar ratio, contained in a platinum or alumina "boat," heated in a tube furnace at several hundred degrees under flowing oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. Similarly tantalum disulfide is prepared in a tube furnace followed by purification, also in a tube furnace using the technique of chemical vapor transport. Because of the availability of tube furnaces, chemical vapor transport has become a popular technique not only in industry (see van Arkel process) but also in the research laboratory.
Tube furnaces can also be used for thermolysis reactions, involving either organic or inorganic reactants. One such example is the preparation of ketene
Ketene
A ketene is an organic compound of the form R'RC=C=O. The term is also used specifically to mean ethenone, the simplest ketene, where R' and R are hydrogen atoms.Ketenes were first studied as a class by Hermann Staudinger.-Formation:...
s which may employ a tube furnace in the 'ketene lamp'. Flash vacuum pyrolyses often utilize a fused quartz tube, usually packed with quartz or ceramic beads, which is heated at high temperatures.