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Inorganic Dielectrics Research

A ceramic of very fine crystal size (0.2 - 0.5 micron) was produced by devitrification from a finely powdered barium titanate glass. An evaluation of industrial hot pressed boron nitride revealed that it is both porous and soluble which causes deterioration of its electrical properties under high humidity conditions. Alumina bodies were fired in four atmospheres; hydrogen, oxygen, argon or vacuum, and evaluated for density, moisture absorption, total porosity and translucency. Microscopic methods were used to determine grain and pore size. Development of low loss ceramics with dielectric constants in the range of 12 to 15 was pursued. The lanthana-alumina-silica system was selected for study. Electrical properties of composition within the system are given. Correlations of these properties with regard to crystal and glass content, crystalline types and porosity are also presented. A brief review of the work on hot extrusion of ceramic materials is presented.

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  • "A ceramic of very fine crystal size (0.2 - 0.5 micron) was produced by devitrification from a finely powdered barium titanate glass. An evaluation of industrial hot pressed boron nitride revealed that it is both porous and soluble which causes deterioration of its electrical properties under high humidity conditions. Alumina bodies were fired in four atmospheres; hydrogen, oxygen, argon or vacuum, and evaluated for density, moisture absorption, total porosity and translucency. Microscopic methods were used to determine grain and pore size. Development of low loss ceramics with dielectric constants in the range of 12 to 15 was pursued. The lanthana-alumina-silica system was selected for study. Electrical properties of composition within the system are given. Correlations of these properties with regard to crystal and glass content, crystalline types and porosity are also presented. A brief review of the work on hot extrusion of ceramic materials is presented."@en
  • "The report discusses results and problems in the production of hot-pressed specimens of high purity SrTiO3. Also described are procedures for the incorporation of minor substitutions in SrTiO3 and the electrical properties obtained from -40 to +80C at 1 KHz. Equipment and test procedures are described for determining electrical properties and change of permittivity with biasing voltages for a number of materials including: unannealed and annealed single crystal SrTiO3, pure polycrystalline SrTiO3, polycrystalline SrTiO3 with minor substitutions, CaTiO3, BaZrO3 and lithium thallium tartrate. Electrical properties of bodies with BaO to TiO2 ratios between 1:1 and 1:3 are discussed. Positive, negative, and nearly zero temperature coefficients of capacitance were obtained depending upon composition and firing temperature. Also discussed are compositions in the CaTiO3-MgTiO3-La2O3.2TiO2 system. Results on specimens of BaTi3O7 are reported. (Author)."@en
  • "Low loss microwave ceramic dielectrics on compounds were investigated in the ternary system La2O3-SiO2-Al2O3. In work on low loss boron nitride ceramic dielectrics bodies containing boron nitride and two undevitrifiable glasses were prepared and evaluated. Hot pressing and sintering were employed in an effort to produce dense translucent aluminum oxide bodies. Theoretical density was achieved by hot pressing but the specimens were contaminated with graphite from the mold used. Temperatures reached in gas firing were not high enough to produce maximum density. Results of thermal conditioning of micromodule wafers having BaTiO3 and TiO2 as their chief crystalline phase are reported. The effects of conditioning upon camber and electrical properties are discussed. The results obtained in the conditioning of wafers are compared with those obtained in the earlier work on rod-shaped specimens. Work on high temperature extrusion of barium titanate is in preliminary stages. A review of the progress made in this area is reported along with a resume of the work reported by Nuclear Metals, Inc. A 150 ton press has been ordered to continue this work. AD-287 1689N3 +++Properties of ceramic dielectric materials for possible use in microwave equipment; crystal formation and methods of preparation of glass containing these materials; mechanical and electrical properties."@en
  • "Devitrified barium titanate ceramics on flame spraying barium titanate into distilled water, in order to make a glass, approximately 3.5% baria desolves in the water. This occurred with the several barium titanates investigated. Attempts to minimize or eliminate the solution of baria during this operation have failed. Ultra low loss ceramics: the system Lanthana-AluminaSilica was evaluated for ceramic bodies. Crystallinge ceramics research is discussed. Study of boron nitride and the effect of additives on its hygrosc6picity: the cause of the deterioration of electrical properties of hot pressed boron nitride is reported along with a procedure for making hot pressed boron nitride. A program for tying-up certain loss producing ions is discussed. (Author)."@en
  • "LOW LOSS MICROWAVE CERAMIC DIELECTRICS: Three compositions in the La2O3-Al2O3-SiO2 system were hot-pressed and the electrical properties measured at several frequencies and temperatures. A study was made of the crystalline phases appearing in a number of compositions within the system. Two lanthanum silicate compounds, lanthanum aluminate and mullite were found in the various compositions. Attempts to form each lanthanum silicate compound by itself are being made in order to evaluate their electrical properties. This information will be used in attempting to tailor bodies to meet the specific require ents of this project. TRANSPARENT POLYCRYSTALLINE CERAMICS: Specimens of pure alumina were pressed and sintered using a twofire procedure. For the initial firing, one set of specimens was fired in air and one set was fired in A. The second firing of both sets was performed in A. Bulk densities of the 2 sets of specimens were measured and compared. Specimens which were initially fired in air were less dense than those fired wholly in A. HOT EXTRUSION: The hot extrusion apparatus is described and results of 3 extrusion attempts are described. (Author)."@en
  • "Devitrified Ferroelectrics: Devitrified bodies made from C.P. grade flame-sprayed BaTiO3 were evaluated. The Curie temperature was shifted to higher temperatures depending upon thermal history. Under certain conditions the dielectric constant retained its higher value above the Curie temperature. Results were compared to those of C.P. solid phase reacted BaTiO3 bodies and capacitor grade devitrified bodies. Devitrified BaTiO3 bodies result in the formation of extremely small crystals as compared to the large ones of the solid phase reacted BaTiO3. Low loss BN ceramic dielectrics: A method for testing electrical properties under humidity conditions was developed. By use of surface resistance measurements it was indicated that the problem is one of a surface nature. Structural studies of polycrystalline ceramics: Metallization of micromodule substrates was compatible with thermal conditioning treatment. The 2 processes can be combined within a single operation to result in greatly strengthened substrates. (Author)."@en
  • "Time temperature firings as determined from the crystallization behavior of the barium titanate glass were made as a possible method of controlling crystal size. The dielectric constants and bulk densities of the devitrified composition was increased but the Curie temperature remained in the vicinity of 150 deg C and the crystal size remained unchanged. Dielectric constant versus temperature measurements of the glass were made and are discussed. Thermal expansions of the glass and crystalline phases of the devitrified bodies were determined. A careful X-ray examination reveals that the only crystalline phase present in the devitrified composition is tetragonal barium titanate, which appears more tetragonal than conventional barium titanate."@en
  • "Pulverized BaTiO3 glass specimens were fired in an O atmosphere which resulted in raising the bulk density to 5.64 g/cc. An impurity level study was conducted to determine the contamination added by processing. No more than 0.1% impurities was added to the 99.8% pure BaTiO3. A study of the electrical hysteresis vs. temperature, and structure vs. temperature, is presented proving that the structural Curie temperature is at 120 C while the dielectric Curie temperature is at approximately 150 C. Deterioration of the electrical properties of hot pressed BN was studied. A furnace capable of being fired up to 1900 C using H or an inert atmosphere was constructed. It utilizes induction heating. Alumina specimens fired to date reached 98% of true density, and theoretical density should be produced when higher temperature firings are accomplished. Several procedures for preparing lanthanum alumino silicate dielectrics are discussed. A procedure was devised by which the compositions are prereacted, reduced to a fabricating particle size, specimens prepared and fired to maturity. A second firing is being utilized to develop low loss characteristics. (Author)."@en
  • "The program includes four phases. Under High Temperature Extrusion of Ferroelectric Materials, coextrusion of Bi4Ti3O12 in 1018 steel resulted in dense but non-uniform ceramics. BaTiO3 plus 2.5% BaO3 gave similar results while additions of 5% resulted in good ceramics. Boron nitride shows promise as a separating media, which along with a thin monel sheath, allows for easy removal of the ceramic from the coextruded can. Under Low Loss Microwave Ceramic Dielectrics, selected compositions in the BaTiO3. MgTiO3. FeSnO3 system have been made and evaluated for their T.C. properties, and are compared to several other compositional systems exhibiting zero T.C. characteristics. The high frequency (8.6 KMc) properties of several compositions are presented. Under Devitrification Techniques For Ferroelectric Materials, the melting and specimen forming operations are discussed along with results realized for compositions evaluated in the BaO. TiO2.B2O3 system. Electrical and T.C. Properties are reported. Under Structure Studies of High Density Polycrystalline Ceramics, specimens made of the three ultra-pure barium titanates have been fired to several additional temperatures thus extending the range under study from 1325 to 1525 C. The T.C. properties have been determined. In general the dielectric constants range from 1750 to 2100 with some volumes up to 2700. The power factors range from .008 to above .020. (Author)."@en
  • "A comparative study is reported on a boron phosphate silica type composition prepared as a glass, a devitrified body and hot pressed body. The electrical properties versus temperature and frequency indicate that this type composition approaches fused silica. Specimens of lanthanum aluminate were prepared by sintering and hot pressing. A dielectric constant of 25 was obtained for this material. The as-received strength of random samples of 10 types of micromodule wafers is reported. The two approaches to making barium titanate glass are the use of new glass formers and faster frit quenching methods in order to produce a good glass free of devitrified material. A calcium boro-aluminate frit was substituted as the glass former and the flame spraying of 100% BaTiO3 was tried both in an oxygen-hydrogen flame and an oxygenacetylene flame. A study was initiated to attempt to remove the glass forming oxide (B2O3) from the barium titanate-boric oxide frit. The object is to increase the barium titanate content in order to improve the dielectric properties of this type of ferroelectric."@en
  • ";Contents: Low loss microwave ceramic dielectrics; Nonlinear low loss, voltage variable dielectrics; Advanced ceramic processing techniques."@en
  • "A summary of status of the 100% devitrified barium titanate type compositions is presented. Alumina bodies were fired in four atmospheres: hydrogen, oxygen, argon, and vacuum, using a two fire procedure, and a differen tmosphere for each fire. Fired specimens were tested for speci fic gravity, moisture absorption, total porosity, and translucency. Microscopic examinations were used to determine grain and pore size. Specimens fired in vacuum exhibited the best results, while poorest properties were obtained with argon. A number of experimental attempts to hot coextrude lead zirconate titanate and barium titanate in steel co-extrusion cans are described. An attempt to slowly hot extrude lead zirconate titanate at low pressure is also discussed. In order to aid in the development of materials with very low losses in the microwave frequency range, a study is initiated of single crystals, ceramics, and glasses for which extensive electrical data have been obtained. (Author)."@en

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  • "Inorganic Dielectrics Research"@en
  • "INORGANIC DIELECTRICS RESEARCH"@en

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