Boron nitride particles of spherical geometry and process for making thereof
A low viscosity filler boron nitride agglomerate particles having a generally spherical shape bound together by an organic binder and to a process for producing a BN powder composition of spherically shaped boron nitride agglomerated particles having a treated surface layer which controls its viscosity. In one embodiment, the composition of spherically shaped boron nitride agglomerated particles are further heat-treated for the binder to decompose, forming a coating layer on the spherical BN agglomerates and significantly improving its thermal conductivity property.
1 . A powder composition comprising a plurality of spherical agglomerated boron nitride particles having an average diameter greater at least 1 microns and a tap density of at least about 0.287 g/cc,
wherein the spherical agglomerated boron nitride particles are formed by spray drying a slurry comprising irregular shaped boron nitride particles, a binder, and a base for maintaining the slurry basic; and
wherein spherical agglomerated boron nitride particles are heat-treated at a sufficiently high temperature for a sufficiently long period of time for the binder to decompose forming at least a coating layer on at least a surface on the spherical agglomerated boron nitride particles surface.
2 . The composition of claim 1 , wherein the binder comprises at least one of oxides, nitrates, acetates, sulfates of boron, aluminum, titanium, zirconium, silicon, nickel, rare earth and alkaline earth metallic elements, and mixtures thereof.
3 . The composition of claim 2 , wherein the spherical agglomerated boron nitride particles are heat-treated at a temperature of at least 1200° C. for at least ½ hour.
4 . The composition of claim 3 , wherein the spherical agglomerated boron nitride particles are heat-treated at a temperature of at least 1200° C. for at least 1 hour.
5 . The composition of claim 4 , wherein the spherical agglomerated boron nitride particles are heat-treated at a temperature of at least 1500° C. for at least 1 hour.
6 . The composition of claim 3 , wherein the binder comprises at least one of calcium acetate, calcium sulfate, or calcium nitrate, sodium acetate, sodium sulfate, sodium nitrate, magnesium acetate, magnesium sulfate, magnesium nitrate, nickel acetate, nickel sulfate, nickel nitrate, copper acetate, copper sulfate, copper nitrate, zinc acetate, zinc sulfate, zinc nitrate, strontium acetate, strontium sulfate, strontium nitrate, yttrium acetate, yttrium sulfate, yttrium nitrate, zirconium acetate, zirconium sulfate, zirconium nitrate, hafnium sulphate, hafnium nitrate, titanium sulfate, molybdenum acetate, molybdenum sulfate, vanadium acetate, vanadium sulfate, vanadium nitrate, chromium acetate, chromium sulfate, chromium nitrate, manganese acetate, manganese sulfate, manganese nitrate, ferrous acetate, ferrous sulfate, ferrous nitrate, cobalt acetate, cobalt sulfate, cobalt nitrate, cadmium acetate, cadmium sulfate, cadmium nitrate, silver acetate, silver sulfate, silver nitrate, palladium acetate, palladium sulfate, palladium nitrate, rhodium acetate, rhodium sulfate, rhodium nitrate, colloidal silica, aluminum sulfate, aluminum propoxide, aluminum silicate, aluminum acetate, and mixtures thereof.
7 . The composition of claim 6 , wherein the binder is selected from the group of aluminum acetate and aluminum sulfate.
8 . The composition of claim 7 , wherein the binder comprises aluminum acetate.
9 . The composition of claim 8 , wherein the spherical agglomerated boron nitride particles are heat-treated at a temperature of at least 1500° C. for at least 1 hour.
10 . The composition of claim 1 , wherein the coating layer formed by the decomposition of the binder comprises from about 0.5 to about 10 wt. % of the total weight of the BN agglomerates.
11 . The composition of claim 10 , wherein the coating layer comprises from about 1 to about 7 wt. % of the total weight of the BN agglomerates.
12 . The composition of claim 11 , wherein the coating layer comprises from about 2 to about 5 wt. % of the total weight of the BN agglomerates.
13 . The composition of claim 1 , wherein the binder is aluminum acetate and the coating layer comprises aluminum oxide.
14 . A polymer composition comprising the spherical agglomerated boron nitride powder of claim 1 .
15 . The polymer composition of claim 14 , wherein the polymer is selected from the group of a melt-processable polymer, a polyester, a phenolic, a silicone polymer, a silicone rubber, an acrylic, a wax, a thermoplastic polymer, a low molecular weight fluid, an epoxy molding compound, and blends thereof.
16 . The polymer composition of claim 15 , wherein the polymer is a silicone polymer.
17 . The polymer composition of claim 14 , having a thermal conductivity ranging from 1 W/mK to about 40 W/mK.
18 . The polymer composition of claim 14 , having a thermal conductivity ranging from 10 W/mK to about 30 W/mK.
19 . The polymer composition of claim 14 , comprising from about 30 wt. % to about 80 wt. % the spherical agglomerated boron nitride powder.
20 . The polymer composition of claim 19 , comprising from about 50 wt. % to about 80 wt. % the spherical agglomerated boron nitride powder.
20 . An article comprising the spherical agglomerated boron nitride powder of claim 1.