摘要:
The present invention employs poly(ethyloxazoline) as a temporary binder and lubricant during the preparation of greenware articles. According to the present invention, molten poly(ethyloxazoline) promotes the compressibility of the powder used to form the greenware article, thus improving the density and strength of both the greenware and the abrasive article. The molten poly(ethyloxazoline) acts as a lubricant to permit a more efficient grain rearrangement under applied pressure and thereby increases the average density of the greenware article by 6 to 8 percent as compared to standard cold pressing.
摘要:
Reactive ceramic-metal compositions are described that include a ceramic phase of at least 70 percent by volume, 95 percent of theoretical density and a metal phase that retains its chemical reactivity with the ceramic phase after the composition has been fully densified. The composition may be heat treated after densification to form additional ceramic phases in a controllable manner. Preferred ceramic metal compositions wherein the metal and ceramic components retain reactivity after densification include boron carbide ceramic and Al or Mg metals. The process employed in forming said compositions requires first forming a sintered porous body of the ceramic material followed by contacting with the metal component, which may be in chip or solid bar form. The system is then heated to the melting point of the metal and a pressure of at least 200 MPa is employed such that the porous body is filled with metal and the composition is substantially fully densified. Subsequent heating reacts the metal with the ceramic to form additional B-C-metal phases as desired.
摘要:
A process for preparing a self-reinforced silicon nitride ceramic body of high fracture toughness comprising hot-pressing a powder mixture containing silicon nitride, a densification aid such as sodium oxide, a conversion aid such as lanthanum oxide and a compound, such as gallium oxide, which enhances growth of .beta.-silicon nitride whiskers-under conditions such that densification and the in situ formation of .beta.-silicon nitride whiskers having a high aspect ratio occur. A novel silicon nitride ceramic of high fracture toughness and high fracture strength is disclosed comprising a .beta.-silicon nitride crystalline phase wherein at least about 20 volume percent of the phase is in the form of whiskers having an average aspect ratio of at least about 2.5; a glassy second phase containing the densification aid, the conversion aid, the compound which enhances growth of .beta.-silicon nitride whiskers, and an amount of silica; and not greater than about 10 weight percent of the total weight as other phases. The glassy phase may also include a minor amount, e.g., up to 5.0 weight percent, based upon total weight of the ceramic, of aluminum nitride or boron nitride.
摘要:
A process for preparing a self-reinforced silicon nitride ceramic body of high fracture toughness comprising hot-pressing a powder mixture containing silicon nitride, magnesium oxide, yttrium oxide and calcium oxide under conditions such that densification and the in situ formation of .beta.-silicon nitride whiskers having a high aspect ratio occur. A novel silicon nitride ceramic of high fracture toughness is disclosed comprising a .beta.-silicon nitride crystalline phase wherein at least about 20 volume percent of the phase is in the form of whiskers having an average aspect ratio of at least about 2.5; a glassy second phase containing magnesium oxide, yttrium oxide, calcium oxide, and silica in a total amount not greater than about 35 weight percent; and not greater than about 10 weight percent of the total weight as other phases.
摘要:
A process for preparing a self-reinforced silicon nitride ceramic body of high fracture toughness comprising hot-pressing a powder mixture containing silicon nitride, magnesium oxide, yttrium oxide and calcium oxide under conditions such that densification and the in situ formation of .beta.-silicon nitride whiskers having a high aspect ratio occur. A novel silicon nitride ceramic of high fracture toughness is disclosed comprising a .beta.-silicon nitride crystalline phase wherein at least about 20 volume percent of the phase is in the form of whiskers having an average aspect ratio of at least about 2.5; a glassy second phase containing magnesium oxide, yttrium oxide, calcium oxide, and silica in a total amount not greater than about 35 weight percent; and not greater than about 10 weight percent of the total weight as other phases.
摘要:
A mullite body comprising: a plurality of crystals, wherein about 70 percent or greater of the crystals have a crystal diameter that is within about 3 microns or less of an average diameter of the plurality of crystals, and a porosity of 55 percent or greater; and made using a process comprising: mixing precursor materials together with an average aggregate particle size of about 3 microns or smaller measured using a particle size analyzer; heating greenware in air to a first temperature such that the greenware is dried and forms calcineware, heating the calcineware in a silicon tetrafiouride atmosphere to form flurotopaz, and heating to a second temperature so that a mullite structure is formed.
摘要:
A mullite body comprising: a plurality of crystals, wherein about 70 percent or greater of the crystals have a crystal diameter that is within about 3 microns or less of an average diameter of the plurality of crystals, and a porosity of 55 percent or greater; and made using a process comprising: mixing precursor materials together with an average aggregate particle size of about 3 microns or smaller measured using a particle size analyzer; heating greenware in air to a first temperature such that the greenware is dried and forms calcineware, heating the calcineware in a silicon tetrafiouride atmosphere to form flurotopaz, and heating to a second temperature so that a mullite structure is formed.
摘要:
An improved aluminum-boron carbide (ABC) composite has been discovered that is comprised of a continuous network of AlB24C4 and boron carbide grains having therein other isolated aluminum-boron carbide reactive phases and at most 2% by volume of isolated metal. The improved ABC composite may be formed by forming boron carbide particulates into a porous body that has a porosity of at most about 35%, where the boron particulates have been heat treated to a temperature of 1200° C. to 1800° C., infiltrating the porous body with aluminum or aluminum alloy until an infiltrated aluminum-boron carbide body is formed that has at most about 1% porosity, heat treating the infiltrated body for at least 25 hours at 1000° C. to 1100° C. to form an aluminum boron carbide composite having a continuous network of AlB24C4 and boron carbide, and subsequently heat-treating to 700° C. to 900° C. to form the improved aluminum boron carbide composite.
摘要:
A skin is applied to a ceramic honeycomb. The skin is formed by applying a skin-forming composition and drying it. The skin-forming composition includes a carrier liquid, colloidal silica and/or colloidal alumina, and an inorganic filler. The filler includes an inorganic fiber. The filler may contain low aspect ratio particles that have the same or nearly the same CTE as the inorganic fiber. The filler may include a small proportion of a low aspect ratio filler particle that has a different CTE than the inorganic fiber.
摘要:
In one embodiment, a composition (10) to be mixed with a molten metal to make a metal matrix composite, the composition characterized by: a ceramic reinforcing filler (12), the ceramic reinforcing filler not being wettable by molten aluminum and/or not being chemically stable in molten aluminum, the ceramic reinforcing filler being coated with a ceramic material, the ceramic material being wettable by and chemically stable in molten aluminum. In a related embodiment, a composition (20) to make a porous preform to be infiltrated by molten metal to make a metal matrix composite, the composition characterized by: a ceramic reinforcing filler (23), the ceramic reinforcing filler not being wettable by molten aluminum, the ceramic reinforcing filler being coated with a ceramic material (22) and optionally with a metal (21) such as nickel, the ceramic material being wettable by molten aluminum. The ceramic material can be coated on the ceramic reinforcing filler by a vacuum deposition technique such as vacuum sputtering.