Electro-static dissipative ceramic products and methods

Abstract

The invention provides partially stabilised zirconia and alumina based electro-static dissipative or ESD ceramic compositions. The proposed ceramic compositions include specific amounts of dopants comprising one or more metal oxides selected from iron oxide, chromium oxide and titanium oxide. The proposed ESD ceramic materials are made into useful industrial products by injection moulding and sintering technology. A novel binder system may optionally be used to make injection mouldable feedstock. Useful products produced by the invention include, for example, ESD ceramic tweezers tips, ESD ceramic dispensing needles, ESD ceramic scissors and blades and ESD ceramic wire bonding capillaries which retain their ESD properties at relatively low temperatures, for example, service temperatures from 25 to 500° C.

1 . An ESD ceramic composition based on partially stabilised zirconia and dopant, the composition comprising 70-98 wt % zirconia partially stabilised with 5.2 wt % of yttria and 2-30% by weight of dopant, the dopant being one or more metal oxides selected from the group comprising iron oxide, chromium oxide, titanium oxide and aluminium oxide.  
   
   
       2 . (canceled)  
   
   
       3 . A method for forming useful articles using the ceramic composition of  claim 1 , the selected composition made suitable for use in powder injection moulding technology by blending with a binder system to form the injection mouldable feedstock, injecting the feedstock into a metal die set to form oversized bodies, then subjecting the bodies to debinding and sintering in air, at 1350° C. to 1450° C. for 2-4 hours followed by heat treatment, the said heat treatment comprising heating the bodies to about 1000° C. in a reducing atmosphere and holding before cooling down in a reducing atmosphere to room temperature.  
   
   
       4 . A method for forming useful articles using the ceramic composition of  claim 1 , the selected composition made suitable for use in powder injection moulding technology by blending with a binder system to form the injection mouldable feedstock, injecting the feedstock into a metal die set to form oversized bodies, then subjecting the bodies to debinding and sintering in a reducing atmosphere or in a vacuum of 1 to 10 −2  torr, at 1350° C. to 1400° C. for 2-3 hours, whereby an after treatment is not required.  
   
   
       5 . (canceled)  
   
   
       6 . (canceled)  
   
   
       7 . The method according to  claim 3 , further comprising the step of subjecting the bodies, before sintering and heat treatment, to solvent or thermal process to remove the binders.  
   
   
       8 . The method according to  claim 4 , further comprising the step of subjecting the bodies, before sintering and heat treatment, to solvent or thermal process to remove the binders.  
   
   
       9 . (canceled)  
   
   
       10 . (canceled)  
   
   
       11 . The method according to  claim 3 , wherein the binder comprises thermally degradable polymers, polyolefin, surfactants and waxes, specifically wherein the polymers are high density polyethylene (HDPE) or ethylene vinyl alcohol (EVA), in the range of 40-70 wt %, the polyolefin comprising peanut oil, vegetable oil, or fish oil in the range of 2-10 wt %, the surfactant being stearic acid, in the range of 1-5 wt %, and the waxes selected from the group comprising polyethylene wax, paraffin wax, bee wax and the like in the range of 25-50 wt %.  
   
   
       12 . The method according to  claim 4 , wherein the binder comprises thermally degradable polymers, polyolefin, surfactants and waxes, specifically wherein the polymers are high density polyethylene (HDPE) or ethylene vinyl alcohol (EVA), in the range of 40-70 wt %, the polyolefin comprising peanut oil, vegetable oil, or fish oil in the range of 2-10 wt %, the surfactant being stearic acid, in the range of 1-5 wt %, and the waxes selected from the group comprising polyethylene wax, paraffin wax, bee wax and the like in the range of 25-50 wt %.  
   
   
       13 . (canceled)  
   
   
       14 . (canceled)  
   
   
       15 . The composition of  claim 1 , wherein pure alumina is added to strengthen the base zirconia ceramic and the dopant is only a single metal oxide from the group.  
   
   
       16 . (canceled)  
   
   
       17 . An article comprising an ESD ceramic tweezers tip made of 80-90 wt % of yttria partially stabilised zirconia and 10-20 wt % of titania of purity greater than 99.9%, formed using injection moulding and sintering and heat treatment, having electrical surface resistivity in the range of 3×10 6  to 8×10 9  ohm/square at 10V and 100V of applied voltages; static decay time of <1.0 s from +/−1000V to +/−10V and discharge current at 500V being <10 mA.  
   
   
       18 . An article comprising an ESD ceramic dispensing needle, made of 85-95 wt % of yttria partially stabilised zirconia and 5-15 wt % of titania of purity greater than 99.9%, formed using injection moulding and sintering and heat treatment, having electrical surface resistivity in the range of 2×10 7  to 9×10 9  ohm/square at 10V and 100V of applied voltages.  
   
   
       19 . An article comprising an ESD ceramic scissors blade made from 80-90 wt % of strengthened zirconia and 10-20 wt % of titania of purity greater than 99.9%, formed using injection moulding and sintering and heat treatment, having electrical surface resistivity in the range of 5×10 6  to 9×10 9  ohm/square at 10V and 100V of applied voltages.  
   
   
       20 . An article comprising an ESD ceramic wire bonding capillary, made of 80-95 wt % of toughened alumina (purity >99.95%, toughened with 5-25 wt % of partially stabilised zirconia) and 5-20 wt % of titania (purity >99.9%), formed using injection moulding and sintering and finishing, having electrical surface resistivity in the range of 6×10 6  to 8×10 9  ohm/square at 10V and 100V of applied voltages, which remains unchanged when subjecting to service temperatures from 25 to 500° C.  
   
   
       21 . The article of  claim 17 , wherein following sintering there is a heat treatment, the heat treatment comprising heating the article to about 1000° C. in a reducing atmosphere and holding for 1-3 hours before cooling down in a reducing atmosphere to room temperature.  
   
   
       22 . The article of  claim 18 , wherein following sintering there is a heat treatment, the heat treatment comprising heating the article to about 1000° C. in a reducing atmosphere and holding for 1-3 hours before cooling down in a reducing atmosphere to room temperature.  
   
   
       23 . The article of  claim 19 , wherein following sintering there is a heat treatment, the heat treatment comprising heating the article to about 1000° C. in a reducing atmosphere and holding for 1-3 hours before cooling down in a reducing atmosphere to room temperature.  
   
   
       24 . The article of  claim 20 , wherein following sintering there is no heat treatment, the sintering is done under vacuum of 1 to 10 −2  torr.  
   
   
       25 . A composition for the injection moulding of ESD zirconia based ceramic articles, the composition comprising 80-98 wt % partially stabilised zirconium oxide (stabilised with 5.2 wt % of yttria) and 2-20 wt % titanium oxide.  
   
   
       26 . A composition for the injection moulding of ESD strengthened zirconia based ceramic articles, the composition comprising 70-85 wt % partially stabilised zirconium oxide (stabilised with 5.2 wt % of yttria), 5-25 wt % aluminium oxide and 10-25 wt % titanium oxide.  
   
   
       27 . A composition for the injection moulding of ESD alumina based ceramic articles, the composition comprising 80-95 wt % pure aluminium oxide and 5-20 wt % titanium oxide.  
   
   
       28 . A composition for the injection moulding of ESD toughened alumina based ceramic articles, the composition comprising 65-85 wt % pure aluminium oxide, 5-25 wt % of partially stabilised zirconium oxide (stabilised with 5.2 wt % of yttria) and 10-25 wt % titanium oxide.  
   
   
       29 . The composition of  claim 1 , further comprising a binder to facilitate the injection moulding process, the binder comprising thermally degradable polymers, polyolefin, surfactants and waxes, wherein the polymers are high density polyethylene (HDPE) and ethylene vinyl alcohol (EVA), in the range of 40-70 wt %, the polyolefin comprising peanut oil, vegetable oil, or fish oil in the range of 2-10 wt %, the surfactant being stearic acid, in the range of 1-5 wt %, and the waxes selected from the group comprising polyethylene wax, paraffin wax, bee wax and the like in the range of 25-50 wt %.  
   
   
       30 . (canceled)