Reactive synthesis of alumina-boron nitride ..
Kanzaki, “Boron Carbide and Nitride as Reactants for In Situ Synthesis of Boride-Containing Ceramic Composites,” J.
Reaction Synthesis of Aluminum Nitride–Boron Nitride ..
In situ (Al2O3-Si)/Al composites with a reinforcement volume fraction of 10% were synthesized from the Al-SiO2 system using low energy ball milling and reaction hot pressing. Differential thermal analysis was used to investigate the reaction mechanisms between SiO2 and Al. X-ray diffraction results revealed that the reaction between Al and SiO2 took place completely at 900°C with a holding time of 2 h, thereby forming Al2O3 and Si. Scanning electron microscopic, energy dispersive X-ray spectroscopic, and transmission electron microscopic (TEM) results showed that the in situ synthesized Al2O3 and Si particles, whose sizes are less than 2 µm, were polygonal in shape and dispersed uniformly in the matrix. Moreover, Al2O3 particle size showed a tendency to increase from ~2 to ~6 µm when the synthesis temperature was increased. Furthermore, TEM observation showed that the interface between the reinforcements and Al matrix is clean. The yield strength, ultimate tensile strength, and Brinell hardness of the in situ (Al2O3-Si)/Al composite was significantly higher than the aluminum matrix. Mechanisms governing the tensile fracture process are discussed.
Hexagonal BN can be prepared in the form of fibers, structurallysimilar to , by thermal decomposition of extruded (B3N3H6) fibers with addition ofboron oxide in a nitrogen atmosphere at 1800 °C. An alternativemethod is thermal decomposition of fibers impregnated with boric acidor ammonium tetraborate in an atmosphere of ammonia and nitrogenabove 1000 °C. Boron nitride fibers are used as reinforcement in , with the matrix materials ranging from organicresins to ceramics to metals (see ).
In‐Situ Reaction Synthesis of Oxide‐Boron Nitride Composites
Low-pressure deposition of thin films of cubic boron nitride ispossible. As in diamond growth, the major problem is to suppressthe growth of hexagonal phases (h-BN or graphite, respectively).Whereas in diamond growth this is achieved by adding hydrogen gas, is used for c-BN. , , , , and other methods are used as well.
Intermetallic compound TiAl-base composites have been prepared by the hot isostatic pressing (HIP) reactive sintering technique. These composites have been synthesized from a powder mixture of titanium, aluminum and boron nitride, and contain Ti2AlN and TiB2 strengthening particles. Nearly spherical particles of Ti3Al and Ti2AlN of about 20 μm in diameter have been embedded in the TiAl phase. The composite has been found with a dual phase matrix structure. The Ti2AlN phase is composed of about 300–500 nm grains and includes dispersion of nano scaled TiB2 particles (about 50–100 nm). Both compression tests and hardness measurements have revealed that this composite material attains higher strength as compared with non-reinforced TiAl. The insufficient bending ductility, however, hinders its bending fracture strength at ambient temperature.
Reactive Hot-Pressed Alumina–Boron Nitride Composites …
Because of excellent thermal and chemical stability, boronnitride ceramics are traditionally used as parts ofhigh-temperature equipment. Boron nitride has a great potential innanotechnology. Nanotubes of BN can be produced that have astructure similar to that of , i.e. graphene (or BN)sheets rolled on themselves, however the properties are verydifferent: whereas carbon nanotubes can be metallic orsemiconducting depending on the rolling direction and radius, a BNnanotube is an electrical insulator with a wide bandgap of ~5.5 eV(same as in diamond), which is almost independent of tube chiralityand morphology. Similar to other BN forms, BN nanotubes are morethermally and chemically stable than carbon nanotubes which favorsthem for applications.
Boron nitride has been produced in an amorphous (a-BN) andseveral crystalline forms. The most stable crystalline form is the one, also calledh-BN, α-BN, or g-BN (graphitic BN). It has a layered structuresimilar to graphite. Within each layer, boron and nitrogen atomsare bound by strong , whereas the layers areheld together by weak . Theinterlayer "registry" of these sheets differs, however, from thepattern seen for graphite, because the atoms are eclipsed, withboron atoms lying over and above nitrogen atoms. This registryreflects the polarity of the B-N bonds. Still, h-BN and graphiteare very close neighbors and even the BC6N hybrids havebeen synthesized where carbon substitutes for some B and Natoms.
Reactive Hot-Pressed Alumina–Boron Nitride Composites with Y ..
Low-cost preparation of boron nitride ceramic …
Low-cost preparation of boron nitride ceramic ..
Synthesis of boron nitride nanotubes via chemical …
High-Performance Ceramics III: Reaction Synthesized Boron Nitride-Containing Composites (BNCC)
10/04/2015 · Synthesis of boron nitride nanotubes ..
Boron Nitride | Carbon Nanotube | Boron - Scribd
synthesis of alumina-boron nitride composites ..
As diamond is less stable than graphite, cubic BN is less stablethan h-BN, but the conversion rate between those forms isnegligible at room temperature. The cubic form has the crystalstructure, same as diamond structure, and is also called β-BN orc-BN. The BN form(w-BN) has similar structure as lonsdaleite, rare hexagonalpolymorph of carbon. In both c-BN and w-BN boron and nitrogen atomsare grouped into , but the angles betweenneighboring tetrahedra are different.
Synthesis of boron nitride nanotubes by boron ink …
The partly structure ofBN layers in h-BN reduces covalency and electrical conductivity,whereas the interlayer interaction increases resulting in higherhardness of h-BN relative to graphite. The reducedelectron-delocalization in hexagonal-BN is also indicated by itsabsence of color and a large . Very different bonding - strongcovalent within the basal planes (planes where boron and nitrogenatoms are covalently bonded) and weak between them - causes high of mostproperties of h-BN. For example, the hardness, electrical andthermal conductivity are much higher within the planes thanperpendicular to them. On the contrary, the properties of c-BN andw-BN are more homogeneous. Those materials are extremely hard, withthe hardness of c-BN being slightly smaller and w-BN even higherthan that of diamond.Because of much better stability to heat and metals, c-BN surpassesdiamond in mechanical applications.The thermal conductivity of BN is among the highest of all electricinsulators (see table).
Boron Nitride Nanotubes Reinforced Aluminum Composites ..
Boron nitride is insoluble in usual acids, but is soluble inalkaline molten salts and nitrides, such as LiOH, KOH,NaOH-Na2CO3, NaNO3,Li3N, Mg3N2,Sr3N2, Ba3N2 orLi3BN2, which are therefore used to etchBN.
Synthesis of boron nitride nanotubes by self …
h-BN parts can be fabricated inexpensively by hot-pressing withsubsequent machining. The parts are made from boron nitride powdersadding for better compressibility. Thin films of boron nitridecan be obtained by from and nitrogen precursors.Combustion of boron powder in nitrogen at 5500 °C yields boron nitride used forlubricants and .
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