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Low and high temperature electric Lehrs
are released by the splktting of uranium-235 atoms during the chain reaction. By absorbing the neutrons, the glass tubes, encased in stainless steel, help maintain a constant level of neutron activity in th#e reactor and a controlled burning rate fo’r the uranium fuel. More than 1,000 such tubes might be used in one haht-water nuclear reactor. This type of Reactor, 43 of which are now hcensed in the U.S., gets its name from its use of ordinary- water ‘(two hydrogen atoms plus one oxygen atom) to transfer he’at from the fissioning of uranium to a steam turbine. Another application for borosilicate glass is proposed for the storage of spent reactor fuel rods. Few reprocessing centers exist for reclaliming used fuel rods. Thus, the rods must be stored by utilities in specially designed water pools that contain the rods’ hazardous raidioactivity yest prevent spontaneous chain reactions. The rods are now piling UP at a rate of 150 tons a month’, and some utilities are threatened with shutdown of their relactors because they have no additional space for storage. It has been ryrooosed that fuel rods be stored between borosihcate glass tubes or sheets. The glass would absorb neutrons and prevent the rods from reaching a critical fission level. This would allow the tubes to be stored closer together, thus increasing storage capacity.
SEMI
probe analyses show that the calcium content of the glaze is reduced during firing on porcelain. It is concluded that the higher ionic conductivity of glazes fired in contact with porcelain is a result of the dealetion of calcium ions in the glass network. These ions are known to block the mobility of Na+ Beiow 300% and K+ ions in glasses. the conduction mechanism in the glaze is electronic for which the activation energy and hence the TQ depends on the method of meaarina the alazes. For example, glazes made from”tin oxide doped with antimony have Tllz of about 150-200°C whereas those in which St0 and Sb,O, are added separately have T’/2 of 80°C. Transmission electron microscopy shows sub-micron grains of SnOZ which tend to be more uniformly distributed the lower the loading of the gl’aze. Scanning electron microscopy illustrates the homogenous nature of the glazes, and shows relatively conducting and relatively insulating regions. These observations show that conduction in these glazes cannot be entirely via a continuous network of contacting grains of semi-conducting tin oxide but must allso take place through the glassy regions surrounding the grains. A possible mechanism is that these regions contain dissolved tin and antimony ions in more than one valence state to permit hopping-type conduction, but tunnelling between the conducting grains many also play a role when the grains are close enough together.
LAZES
investigations into tin oxide semiconducting glazes have been conducted at the materials development division of AERE Harwell. These materials have applications in controlling flash-over on hiah tension insulators, particularly when pJlution results in sait solutions condensing on the insulator surface. The most satisfactory glazes developed to date make use of the semi-canducting properties of antimony-doped tin oxide dispersed in an aluminosilicate glaze but many properties of these glazes remain poorly characterised. The conductivity and the temperature coefficient of resistivity are important parameters for a glaze; the latter property should be less to avoid thermal runaway and is normally expressed in is the temperaterms of TM, which ture at which the resistivity falls to haif its value at room temperature. Various studies of tin oxide glazes have been made on sections of commercial insulators; laboratory glazes fired on electrical porcelain tiles; glazes fired on high alumina tiles, and bulk glazes fired in alumina boats. The electrical conductivity and transport number of the glazes have been measured and structural information has been derived from scanning electron microscopy, high voltage transmission electron micromicroprobe analysis and chescopy, mical analysis. It has been fourrd that conduction in the glazes above about 300°C is predominantly ionic, with the ionic conductivity of glazes fired on porcelain being somewhat higher than for the same glazes fired on alumina. There is evidence for some ~~a~~-~orce’~a~~ body ~~t~ractio~s and chemicai and micro-
BTU Engineering Corporation has developed two new lines of electric lehrs for glass processing, electronic display sealing, and epoxy curing. Available in both low and high temperature ranges (up to lOOO”C), the new lehrs are offered in belt widths from I2 to 48 inches. Control accuracy across the full1 width of the 48 inch belt is %5”C, or *2”C with an optional control arrangement. Shielded heaters mounted in fibrous ceramic material both insulate, and prevent interaction between heater coils and harmful effluents emanatmg ,from the product, Larger size lehrs have staggered hearth sections and randomly located pier supports to prevent longitudinal line sha, dowing of the prv-luct during processing. Double-walled constructrvn throughout the length of the lehr enhances aoaea.~ rance and keeps outer surfaces ‘safe to the touch. Easily removable heat shields provide convenient access to thermocouples and heater wiring. For further Corporation, MA 01862.
Allison Div. of General Motors Corp., Indianapolis, Ind. The $43 million contract extends an effort started under an earlier contract and will continue through 1983. NASA-Lewis Research Center awarded GM thle contract in suaoort of DOE. Special m’aterials composed of abundant elements such as silicon, nitrogen and carbon will be desiqned into comoonents used in gas turbine engines; techniques will be developed to fabricate the components; and components will be integrated into advanced turbine engine h’ardware. -~I
I
3M Ceramic Fibers is a space age insulatina material beina fabricated in the form of protective sleeving by Santa Fe Textiles, Inc. Specific aopjications for SF2600 include protecting cables from open flames an’d shielding thermocouple wires as they measure the heat in ovens. In ‘addition, thle sleeves protect hoses from molten metals ,in steel plants, guard fire control insulate furnace components systems, to cut down on heat loss and serve as the slleevin’g over wire mesh for gaskets on the Space Shuttle. A majo’r advantage of the product is its ability to protect against temperatures to 2600°F for extended periods and to 3000°F for short aerio’ds. The material offers good dielectric strength, durabilitv and reliability IanId retains ‘its tensile strength and flexibility at elevated temperatures. The ceramic fibers which Santa Fe braids into high temperature sleeving represent a major advancement in fiber technology. They are continuous ceramic that can be converted into filaments a variety of textile forms: tapes, conveyor belts, fabrics, etc.
KING BEAM FklRNAG CO-FIRING CERAMIC BTU Engineelring Colrporation offers a new 1800°C Walkino Beam furnace for volume co-firing of -ceramic substrates. Molybdenum or ,tungsten pastes are screened onto the green alumina sub”, strates, Pressled into multilayers, and fired to form conductive circuits.
information: BTU Engineering Esquire Road, N. Billerica,
A contract to advance development of ceramic materials, fabrication techniiques and components for use in new, energyefficient automobile gas turbine engines has been awarded to Detroit Bisesej
The advantages of processing ceramic components in Walking BeNam furnaces are increasingly recognized in the field. For example: the simplified bseam movereatest capacity for ment has the
SEMI
probe analyses show that the calcium content of the glaze is reduced during firing on porcelain. It is concluded that the higher ionic conductivity of glazes fired in contact with porcelain is a result of the dealetion of calcium ions in the glass network. These ions are known to block the mobility of Na+ Beiow 300% and K+ ions in glasses. the conduction mechanism in the glaze is electronic for which the activation energy and hence the TQ depends on the method of meaarina the alazes. For example, glazes made from”tin oxide doped with antimony have Tllz of about 150-200°C whereas those in which St0 and Sb,O, are added separately have T’/2 of 80°C. Transmission electron microscopy shows sub-micron grains of SnOZ which tend to be more uniformly distributed the lower the loading of the gl’aze. Scanning electron microscopy illustrates the homogenous nature of the glazes, and shows relatively conducting and relatively insulating regions. These observations show that conduction in these glazes cannot be entirely via a continuous network of contacting grains of semi-conducting tin oxide but must allso take place through the glassy regions surrounding the grains. A possible mechanism is that these regions contain dissolved tin and antimony ions in more than one valence state to permit hopping-type conduction, but tunnelling between the conducting grains many also play a role when the grains are close enough together.
LAZES
investigations into tin oxide semiconducting glazes have been conducted at the materials development division of AERE Harwell. These materials have applications in controlling flash-over on hiah tension insulators, particularly when pJlution results in sait solutions condensing on the insulator surface. The most satisfactory glazes developed to date make use of the semi-canducting properties of antimony-doped tin oxide dispersed in an aluminosilicate glaze but many properties of these glazes remain poorly characterised. The conductivity and the temperature coefficient of resistivity are important parameters for a glaze; the latter property should be less to avoid thermal runaway and is normally expressed in is the temperaterms of TM, which ture at which the resistivity falls to haif its value at room temperature. Various studies of tin oxide glazes have been made on sections of commercial insulators; laboratory glazes fired on electrical porcelain tiles; glazes fired on high alumina tiles, and bulk glazes fired in alumina boats. The electrical conductivity and transport number of the glazes have been measured and structural information has been derived from scanning electron microscopy, high voltage transmission electron micromicroprobe analysis and chescopy, mical analysis. It has been fourrd that conduction in the glazes above about 300°C is predominantly ionic, with the ionic conductivity of glazes fired on porcelain being somewhat higher than for the same glazes fired on alumina. There is evidence for some ~~a~~-~orce’~a~~ body ~~t~ractio~s and chemicai and micro-
BTU Engineering Corporation has developed two new lines of electric lehrs for glass processing, electronic display sealing, and epoxy curing. Available in both low and high temperature ranges (up to lOOO”C), the new lehrs are offered in belt widths from I2 to 48 inches. Control accuracy across the full1 width of the 48 inch belt is %5”C, or *2”C with an optional control arrangement. Shielded heaters mounted in fibrous ceramic material both insulate, and prevent interaction between heater coils and harmful effluents emanatmg ,from the product, Larger size lehrs have staggered hearth sections and randomly located pier supports to prevent longitudinal line sha, dowing of the prv-luct during processing. Double-walled constructrvn throughout the length of the lehr enhances aoaea.~ rance and keeps outer surfaces ‘safe to the touch. Easily removable heat shields provide convenient access to thermocouples and heater wiring. For further Corporation, MA 01862.
Allison Div. of General Motors Corp., Indianapolis, Ind. The $43 million contract extends an effort started under an earlier contract and will continue through 1983. NASA-Lewis Research Center awarded GM thle contract in suaoort of DOE. Special m’aterials composed of abundant elements such as silicon, nitrogen and carbon will be desiqned into comoonents used in gas turbine engines; techniques will be developed to fabricate the components; and components will be integrated into advanced turbine engine h’ardware. -~I
I
3M Ceramic Fibers is a space age insulatina material beina fabricated in the form of protective sleeving by Santa Fe Textiles, Inc. Specific aopjications for SF2600 include protecting cables from open flames an’d shielding thermocouple wires as they measure the heat in ovens. In ‘addition, thle sleeves protect hoses from molten metals ,in steel plants, guard fire control insulate furnace components systems, to cut down on heat loss and serve as the slleevin’g over wire mesh for gaskets on the Space Shuttle. A majo’r advantage of the product is its ability to protect against temperatures to 2600°F for extended periods and to 3000°F for short aerio’ds. The material offers good dielectric strength, durabilitv and reliability IanId retains ‘its tensile strength and flexibility at elevated temperatures. The ceramic fibers which Santa Fe braids into high temperature sleeving represent a major advancement in fiber technology. They are continuous ceramic that can be converted into filaments a variety of textile forms: tapes, conveyor belts, fabrics, etc.
KING BEAM FklRNAG CO-FIRING CERAMIC BTU Engineelring Colrporation offers a new 1800°C Walkino Beam furnace for volume co-firing of -ceramic substrates. Molybdenum or ,tungsten pastes are screened onto the green alumina sub”, strates, Pressled into multilayers, and fired to form conductive circuits.
information: BTU Engineering Esquire Road, N. Billerica,
A contract to advance development of ceramic materials, fabrication techniiques and components for use in new, energyefficient automobile gas turbine engines has been awarded to Detroit Bisesej
The advantages of processing ceramic components in Walking BeNam furnaces are increasingly recognized in the field. For example: the simplified bseam movereatest capacity for ment has the