Method and apparatus for producing hollow microspheres

A method for making filamented, hollow glass microspheres having a high contained vacuum, which comprises heating glass to form molten glass, forming a liquid film of molten glass across an orifice of a coaxial blowing nozzle, said blowing nozzle having an inner nozzle to convey metal vapor blowing gas to the inner surface of the liquid film and an outer nozzle to convey molten glass to said orifice, the lower portion of said outer nozzle being tapered inwardly to form with the outer edge of the inner nozzle a fine gap, feeding the molten glass under pressure through said gap and forming said thin film of molten glass across said orifice of the blowing nozzle, applying said metal vapor blowing gas through said inner nozzle at positive pressure on the inner surface of the liquid film to blow the film downwardly and outwardly to form the microsphere, continuously feeding said molten glass to said outer nozzle while said microsphere is being formed, directing an entraining fluid at said coaxial blowing nozzle, at a linear velocity in the region of microsphere formation of about 1 to 50 feet per second to obtain connecting glass filaments between microspheres, and at an angle relative to a line drawn through the center axis of said coaxial blowing nozzle, said entraining fluid passing over and around said coaxial blowing nozzle to fluid dynamically induce a pulsating or fluctuating pressure fluid having periodic oscillations at the opposite or lee side of the blowing nozzle in the wake or shadow of said blowing nozzle, said entraining fluid acting on the microsphere to pinch and close-off the microsphere at a point proximate to the coaxial blowing nozzle and said entraining fluid acting to detach the microsphere from the coaxial blowing nozzle, surface tension forces causing the detached microsphere to form a spherical shape, and cooling, solidifying and hardening said microsphere to obtain microspheres of 500 to 6,000 microns diameter and 0.5 to 400 microns wall thickness, said microspheres being connected by thin filamented portions that are continuous with the glass microspheres, and depositing said metal vapor as a thin metal coating 50.degree. to 600.degree. A. thick on the innerwall surface of the microspheres to form filamented microspheres having a contained vacuum having a pressure at ambient temperature which is about the vapor pressure of said metal at ambient temperature.

A method for making hollow glass microspheres which comprises heating glass to form molten glass, forming a liquid film of molten glass across an orifice of a coaxial blowing nozzle, said blowing nozzle having an inner nozzle to convey an inert gas or metal vapor blowing gas to the inner surface of the liquid film and an outer nozzle to convey said molten glass at a temperature of 2000.degree. to 2800.degree. F., to said orifice, applying said inert gas or a metal vapor blowing gas through said inner nozzle at positive pressure on the inner surface of the liquid film to blow the film downwardly and outwardly to form an elongated cylinder shaped liquid film of molten glass which is closed at its outer end and connected at its inner end to the outer edge of the orifice of said blowing nozzle, continuously feeding said molten glass to said nozzle while said elongated cylinder is being formed, directing an entraining fluid at said coaxial blowing nozzle at an angle of 25.degree. to 75.degree. relative to a line drawn through the center axis of said coaxial blowing nozzle, said entraining fluid passing over and around said coaxial blowing nozzle to fluid dynamically induce a pulsating or fluctuating pressure field having periodic oscillations at the opposite or lee side of the blowing nozzle in the wake or shadow of said blowing nozzle, whereby said entraining fluid envelops and acts on the elongated cylinder to flap, fold, pinch and close-off said elongated cylinder at its inner end at a point proximate to the coaxial blowing nozzle and said entraining fluid acting through drag forces on said cylinder to detach the cylinder from the coaxial blowing nozzle whereby surface tension forces cause the cylinder to form a spherical shape microsphere and directing a quench fluid into contact with said microsphere to rapidly cool and solidify said microsphere.

A method for making hollow glass microspheres which comprises heating glass to form molten glass, forming a liquid film of molten glass across an orifice of a coaxial blowing nozzle, said blowing nozzle having an inner nozzle to convey a blowing gas to the inner surface of the liquid film and an outer nozzle to convey said molten glass to said orifice, applying said blowing gas through said inner nozzle at positive pressure on the inner surface of the liquid film to blow the film downwardly and outwardly to form the microsphere, continuously feeding said molten glass to said outer nozzle while said microsphere is being formed, directing an entraining fluid at said coaxial blowing nozzle at an angle relative to a line drawn through the center axis of said coaxial blowing nozzle, said entraining fluid passing over and around said coaxial blowing nozzle to fluid dynamically induce a pulsating or fluctuating pressure field having periodic oscillations at the opposite or lee side of the blowing nozzle in the wake or shadow of said blowing nozzle, said entraining fluid acting on the microsphere to pinch and close-off the microsphere at a point proximate to the coaxial blowing nozzle and said entraining fluid acting to detach the microsphere from the coaxial blowing nozzle, surface tension forces causing the detached microsphere to form a spherical shape, and cooling and solidifying said microsphere.

A method for making hollow glass microspheres having a high contained vacuum which comprises heating glass to form molten glass, forming a liquid film of molten glass across an orifice of a coaxial blowing nozzle, said blowing nozzle having an inner nozzle to convey metal vapor blowing gas to the inner surface of the liquid film and an outer nozzle to convey molten glass to said orifice, the lower portion of said outer nozzle being tapered inwardly to form with the outer edge of the inner nozzle a fine gap, feeding the molten glass under pressure through said gap and forming said thin film of molten glass across said orifice of the blowing nozzle, applying said metal vapor blowing gas through said inner nozzle at positive pressure on the inner surface of the liquid film to blow the film downwardly and outwardly to form the microsphere, continuously feeding said molten glass to said outer nozzle while said microsphere is being formed, directing an entraining fluid at said coaxial blowing nozzle at an angle relative to a line drawn through the center axis of said coaxial blowing nozzle, said entraining fluid passing over and around said coaxial blowing nozzle to fluid dynamically induce a pulsating or fluctuating pressure field having periodic oscillations at the opposite or lee side of the blowing nozzle in the wake or shadow of said blowing nozzle, said entraining fluid acting on the microsphere to pinch and close-off the microsphere at a point proximate to the coaxial blowing nozzle and said entraining fluid acting to detach the microsphere from the coaxial blowing nozzle, surface tension forces causing the detached microsphere to form a spherical shape, and cooling, solidifying and hardening said microsphere to obtain microspheres of 500 to 6,000 microns diameter and 0.5 to 400 microns wall thickness, and depositing said metal vapor as a thin metal coating 50.degree. to 600.degree. A. thick on the innerwall surface of the microspheres to form microspheres having a contained vacuum having a pressure at ambient temperature which is about the vapor pressure of said metal at ambient temperature.