WO2007083248A1 - Method of making a gos ceramic using single-axis hot pressing and a flux aid - Google Patents

Method of making a gos ceramic using single-axis hot pressing and a flux aid Download PDF

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Publication number
WO2007083248A1
WO2007083248A1 PCT/IB2007/050052 IB2007050052W WO2007083248A1 WO 2007083248 A1 WO2007083248 A1 WO 2007083248A1 IB 2007050052 W IB2007050052 W IB 2007050052W WO 2007083248 A1 WO2007083248 A1 WO 2007083248A1
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WIPO (PCT)
Prior art keywords
pressing
hot
present
temperature
sintering
Prior art date
Application number
PCT/IB2007/050052
Other languages
French (fr)
Inventor
Cornelis Reinder Ronda
Herbert Schreinemacher
Guenter Zeitler
Norbert Conrads
Simha Levene
Original Assignee
Philips Intellectual Property & Standards Gmbh
Koninklijke Philips Electronics N.V.
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Application filed by Philips Intellectual Property & Standards Gmbh, Koninklijke Philips Electronics N.V. filed Critical Philips Intellectual Property & Standards Gmbh
Priority to JP2008550881A priority Critical patent/JP2009523689A/en
Publication of WO2007083248A1 publication Critical patent/WO2007083248A1/en

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    • C04B35/547—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on sulfides or selenides or tellurides
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Definitions

  • the present invention is directed to a fluorescent ceramic having the general formula Gd 2 O 2 S doped with M, whereby M represents at least one element selected from the group Ce, Pr, Eu, Tb, Yb, Dy, Sm and/or Ho and a method of making such a fluorescent ceramic.
  • the invention further relates to a method for manufacturing a fluorescent ceramic using single-axis hot pressing.
  • the invention still further relates to a detector for detecting ionizing radiation.
  • the invention still further relates to a use of said detector for detecting ionizing radiation.
  • Fluorescent members for detecting high energy radiation contain a phosphor that can absorb the radiation and convert it into visible light.
  • the luminescent emission thereby generated is electronically acquired and evaluated with the assistance of light sensitive systems such as photodiodes or photomultipliers.
  • Such fluorescent members can be manufactured of single-crystal materials, for example, doped alkali halides.
  • Non-single-crystal materials can be employed as powdered phosphor or in the form of ceramic members manufactured therefrom.
  • a method of manufacturing such a fluorescent ceramic is e.g. disclosed in WO 2005/110943 Al which is hereby enclosed by reference.
  • this method suffers from the drawback that e.g. for some applications an increased pressure is needed.
  • the object of the present invention is to provide a method for manufacturing a scintillating ceramics with a still further improved light output and afterglow characteristics.
  • a method for manufacture of a fluorescent ceramic material using a single-axis hot-pressing comprises the step of selecting a pigment powder Of Gd 2 O 2 S doped with M, and M represents at least one element selected from the group of Eu, Tb, Yb, Dy, Sm, Ho, Ce and/or Pr, and said hot-pressing is carried out at a maximum temperature of >900°C to ⁇ 1500° C; and/or a maximum pressure of >75 MPa to ⁇ 300 MPa; whereby hot-pressing is carried out with a sintering and/or flux aid.
  • hot uniaxial pressing as used in the context of the present invention is well recognised in the art and to be understood as involving the compaction of powder into a rigid mould by applying pressure in a single axial direction through a rigid die or piston under the application of heat.
  • a "sintering and/or flux aid" in the sense of the present invention means, describes and/or includes especially a material or an mixture of materials, which show at least one of the following features:
  • Decomposes to form the actual flux below or in the temperature region of hot- pressing e.g. Li 2 GeF 6 decomposes into 2 LiF and GeF 4 ).
  • Some of the decomposition products are gaseous, in this way they can easily leave the mixture to be sintered.
  • a melting point in the temperature region used for the hot-pressing A boiling point which lies well beyond the temperature region used for the hot- pressing to prevent evaporation of the flux from the mixture to be sintered.
  • a high solubility for the Gd 2 O 2 S pigment powder used within the molten flux aid is non-soluble in the Gd 2 O 2 S material or only in minute amounts soluble. Etches the surface to enhance surface reactivity during hot pressing to facilitate sintering.
  • Can preferably be used in very minute amounts, to prevent contamination of the mixture to be sintered, which may lead to undesired effects like afterglow or light yield reduction.
  • the sintering and/or flux aid is added homogeneously prior the hot-pressing step using an appropriate admixing method; according to a different embodiment of the present invention, the sintering and/or flux aid and the pigment powder are mixed and vacuum-sealed prior to the hot-pressing.
  • the sintering and/or flux aid comprises a fluoride.
  • fluoride in the sense of the present invention means, describes and/or includes especially a material or an mixture of materials, which contains fluorine.
  • the sintering and/or flux aid comprises an alkali and/or earth alkali fluoride.
  • alkali and/or earth alkali fluoride in the sense of the present invention means, describes and/or includes especially a material or an mixture of materials, which contains at least one alkali and/or earth alkali metal and fluorine, either in form of an simple fluoride or in form of more complex structures e.g. in form of a "double-fluoride” together with one or more additional metal compounds.
  • the sintering and/or flux aid comprises LiF and/or Li 2 GeF 6 and/or Li 2 SiF 6 and/or Li 3 AlF 6 .
  • the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >50:l to ⁇ 20000:l.
  • the term "F converted value of the sintering and/or flux aid” means the amount (in wt.) of F " ions that are present in the flux during the hot-pressing step.
  • the F converted value of the sintering and/or flux aid is 1.9 g (since the molecular weight of LiF is 26 g/mole).
  • the F converted value of the sintering and/or flux aid is 380 mg (since two F " ions are released per Li 2 GeF 6 and the molecular weight OfLi 2 GeF 6 is 200 g/mole).
  • the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >1000:l to ⁇ 10000:l.
  • the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >2000:l to ⁇ 8000:l.
  • the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >3000:l to ⁇ 7000:l.
  • the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >4000:l to ⁇ 6000:l.
  • the hot pressing is carried out at maximum pressure and/or maximum temperature for >30 to ⁇ 600 minutes.
  • At maximum pressure and/or maximum temperature in the sense of the present invention means, describes and/or includes especially that the above given time describes the pressing time when the maximum pressure and/or maximum temperature is reached; however, according to an embodiment of the present invention, the overall hot-pressing step can be quite longer as will be described later on.
  • the maximum pressure and maximum temperature are reached essentially at the same time; according to an embodiment of the present invention, the maximum pressure and maximum temperature are reached with a delay.
  • the hot pressing is carried out at maximum pressure and/or maximum temperature for > 100 to ⁇ 400 minutes.
  • the hot pressing is carried out at maximum pressure and/or maximum temperature for > 150 to ⁇ 300 minutes.
  • hot-pressing is performed in that way that the factor A is set to be > 45000 to ⁇ 540000, whereby A fulfils the equation
  • A t * T, with t being the time for which the hot-pressing is carried out at maximum pressure and T being the maximum temperature (in 0 C) during the time t (in minutes).
  • the temperature T is kept constant during the time period t; if the temperature is varied during the time period t, the temperature T is the maximum temperature which is set during the time t.
  • hot-pressing is performed in that way that the factor A (dimension [ 0 C* minutes]) is set to be > 45000 to ⁇ 540000
  • hot-pressing is performed in that way that the factor A is set to be > 50000 to ⁇ 450000.
  • hot-pressing is performed in that way that the factor A is set to be > 60000 to ⁇ 400000.
  • hot-pressing is performed in that way that the factor A is set to be > 70000 to ⁇ 300000.
  • the hot-pressing is performed at a maximum temperature of > 1000° C to ⁇ 1400° C. According to an embodiment of the present invention, the hot-pressing is performed at a maximum temperature of >1100° C to ⁇ 1300° C.
  • the hot-pressing is performed at a maximum temperature of > 1200° C to ⁇ 1250° C.
  • the hot-pressing is performed at a maximum pressure of >75 MPa to ⁇ 300 MPa.
  • the hot-pressing is performed at a maximum pressure of >90 MPa to ⁇ 150 MPa.
  • the hot-pressing is performed at a maximum pressure of > 100 MPa to ⁇ 125 MPa.
  • the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >0.1 K/min to ⁇ 40 K/min.
  • the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >5 K/min to ⁇ 25 K/min.
  • the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >10 K/min to ⁇ 20 K/min.
  • the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >0.2 K/min to ⁇ 5 K/min.
  • the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >1 K/min to ⁇ 4 K/min.
  • the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >1.5 K/min to ⁇ 2.5 K/min.
  • the hot-pressing is performed in that way that the maximum temperature is reached at least partly via at least one first heating step which involves a raise in temperature with >0.1 K/min to ⁇ 40 K/min, then a dwelling step, in which the temperature is not changed and then via at least one second heating step which involves a raise in temperature with >0.2 K/min to ⁇ 5 K/min.
  • the raise in temperature is >5 K/min to ⁇ 25 K/min.
  • the raise in temperature is >10 K/min to ⁇ 20 K/min.
  • the raise in temperature is >1 K/min to ⁇ 4 K/min.
  • the raise in temperature is >1.5 K/min to ⁇ 2.5 K/min.
  • the dwelling step is performed after reaching a temperature of >600°C to ⁇ 1100 0 C.
  • the dwelling step is performed after reaching a temperature of >700°C to ⁇ 900 0 C.
  • the dwelling step is performed after reaching a temperature of >750°C to ⁇ 850 0 C.
  • the dwelling step is performed for >5 min to ⁇ 30 min.
  • the dwelling step is performed for >10 min to ⁇ 20 min.
  • the hot-pressing is performed in that way that the maximum pressure is reached at least partly via a pressuring step which involves a raise in pressure with >0.5 MPa/min to ⁇ 10 MPa/min.
  • the hot-pressing is performed in that way that the maximum pressure is reached at least partly via a pressuring step which involves a raise in pressure with >1 MPa/min to ⁇ 5 MPa/min. According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum pressure is reached at least partly via a pressuring step which involves a raise in pressure with >1.5 MPa/min to ⁇ 3 MPa/min.
  • the hot-pressing is performed in that way that the maximum pressure is released at least partly via a pressure releasing step which involves a decline in pressure with >5 MPa/min to ⁇ 35 MPa/min.
  • the hot-pressing is performed in that way that the maximum pressure is released at least partly via a pressure releasing step which involves a decline in pressure with >10 MPa/min to ⁇ 25 MPa/min.
  • the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >2 K/min to ⁇ 5 K/min.
  • the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >3 K/min to ⁇ 3.5 K/min.
  • the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >2 K/min to ⁇ 5 K/min until a temperature of >300°C to ⁇ 600°C is reached.
  • the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >3 K/min to ⁇ 3.5 K/min until a temperature of >300°C to ⁇ 600°C is reached.
  • the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >2 K/min to ⁇ 5 K/min until a temperature of >350°C to ⁇ 450°C is reached.
  • the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >3 K/min to ⁇ 3.5 K/min until a temperature of >350°C to ⁇ 450°C is reached.
  • the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >2 K/min to ⁇ 5 K/min until a temperature of approx . 400 0 C is reached.
  • the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >3 K/min to ⁇ 3.5 K/min until a temperature of approx. 400 0 C is reached.
  • the hot-pressing is performed in that way that the temperature releasing step is performed after the pressure releasing step.
  • the grain size of said pigment powder used for hot-pressing is of > 1 ⁇ m to ⁇ 20 ⁇ m
  • the pigment powder Of Gd 2 O 2 S comprises an amount of M from > 0.1 ppm to ⁇ 2000 ppm (weight fraction).
  • M represents the total added weight fractions of said elements.
  • the fluorescent ceramic after the step of single-axis hot-pressing under vacuum, can be further treated by air annealing at a temperature of 700° C to 1200° C, preferably of 800° C to 1100° C, more preferably of 900° C to 1000° C; whereby said time period for air annealing treatment is 0.5 hours to 30 hours, preferably 1 hours to 20 hours, more preferably 2 hours to 10 hours and most preferably 2 hours to 4 hours.
  • Gd 2 O 2 S material with an average grain size in the range of 1 ⁇ m to 20 ⁇ m can be commonly purchased by manufactures of the fluorescent ceramics as a raw material and do not need to be broken up to finer particles of less than 100 nm.
  • Gd 2 O 2 S pigment powder used according to the present invention has an average grain size in the range of 2 ⁇ m to 10 ⁇ m and more preferably of 4 ⁇ m to 6 ⁇ m. Moreover, due to the method of the invention no specific powder production process is necessary, as conventionally available powders may be successfully used for manufacturing of luminescent ceramics.
  • - a total transparency in the range of 0 to 80%, preferably 10% to 70%, still preferably 20-35% measured for a wavelength of 513 nm.
  • the ceramics of the present invention can be advantageously used for manufacturing x-ray luminescent ceramics that serve as raw material in fabrication of medical computer tomographs (CT).
  • CT computer tomographs
  • an additional step comprises annealing fluorescent ceramic under vacuum at a temperature of 1000° C to 1400° C for a period of time of 0.5 hours to 30 hours.
  • the annealing temperature is selected in the range of 1100° C to 1300° C, more preferably of 1200° C to 1250° C.
  • the time period for vacuum annealing can be preferably set to 1 hours to 20 hours, more preferably to 2 hours to 10 hours and most preferably 3 hours to 5 hours.
  • an undoped Gd 2 O 2 S powder is mixed with a composition comprising at least one element of the group of rare earth ions comprising Pr, Ce, Eu, Tb, Yb, Dy, Sm and/or Ho.
  • Pr or Ce are selected as envisaged dopants
  • an introduction of Pr or Ce ions can be carried out using aqueous solutions of corresponding salts: PrCl 3 , PrBr 3 , PrI 3 , Pr(NO 3 ) 3 , Pr 2 (SO 4 ) 3 , CeCl 3 , CeBr 3 , CeI 3 , Ce(NO 3 ) 3 , Ce 2 (SO 4 ) 3 , etc.
  • dopant ions can be carried out during a mechanical mixture of powders Of Gd 2 O 2 S with insoluble compositions comprising the dopant, like oxides, for example Pr 6 On, Pr 2 O 3 , Ce 2 O 3 , CeO 2 .
  • Gd 2 O 2 S powder may be mechanically mixed with water insoluble salts of the dopant, like PrF 3 , Pr 2 S 3 , Pr 2 O 2 S, Pr 2 (CO 3 ) 3 , Pr 2 (C 2 O 4 ) 3 , CeF 3 , Ce 2 O 2 S, Ce 2 (CO 3 ) 3 , Ce 2 (C 2 O 4 ) 3 , and the like.
  • This principle of a dopant introduction may be used for introduction of ions such as Tb, Eu and other rare earth elements. Additionally, ions of other elements not being rare earth ions may be introduced accordingly.
  • a suitable sintering aid is co-mixed prior to hot-pressing.
  • the invention further relates to ceramics being represented by a chemical formula of Gd 2 O 2 S doped with M, whereby M represents at least one element selected from the group Pr, Ce, Eu, Tb, Yb, Dy, Sm and/or Ho, whereby said fluorescent ceramic comprises a single phase in its volume.
  • the fluorescent ceramic of the present invention can have a significantly increased relative light yield or light output relative to ceramic fluorescent material that is available on the market. The difference is especially seen for a ceramic thickness of equal or more than 1.5 mm.
  • the light output can be a factor of 2.3 higher than that of cadmium tungstate crystals of the same thickness.
  • the doped pigment powder of Gd 2 O 2 S can have a surface according to BET in the range of > 0.01 m 2 /g and ⁇ 1 m 2 /g, preferably of > 0.05 m 2 /g and ⁇ 0.5 m 2 /g and more preferably of > 0.1 m 2 /g and ⁇ 0.2 m 2 /g.
  • the Gd 2 O 2 S can be doped by at least one element selected from the group of Ce, Pr, Eu, Tb, Yb, Dy, Sm and/or Ho. It is preferred that the Gd 2 O 2 S powder is doped by one element selected from the group of Ce, Pr, Eu, Tb, Yb, Dy, Sm and Ho only. Most preferred is the use of an element of Ce or Pr.
  • the content of Ce in the Gd 2 O 2 S powder in a weight fraction can be from 0.1 ppm to 100 ppm , preferably 5 ppm to 50 ppm and more preferably 10 ppm to 25 ppm and/or the content of Pr in the Gd 2 O 2 S powder can be from 100 ppm to 2000 ppm , preferably 300 ppm to 1200 ppm and more preferably 500 ppm to 800 ppm.
  • the Gd 2 O 2 S fluorescent ceramics of the present invention can have a significantly reduced afterglow in the range of 1 x 10 "6 to 8 x 10 "5 at 500 ms, relative to the initial light output.
  • the fluorescent ceramic of the present invention can preferably have an afterglow in the range of 1.0 x 10 "6 to 6 x 10 "5 at 500 ms, preferably of 1.0 x 10 "6 to 5 x 10 "5 at 500 ms and more preferred of 1.0 x 10 "6 to 3.0 x 10 "5 at 500 ms, again relative to the initial light output.
  • the fluorescent ceramics of the present invention can provide a good transparency in the optical range. It is therefore preferred that the fluorescent ceramic manufactured according to the present invention has a density of > 99.0 %, preferably of > 99.5 % and more preferred > 99.7 % and ⁇ 100 %.
  • the fluorescent ceramic manufactured according to the present invention can have a significantly increased relative light yield or light output in the range of 0.74 to 1.00, preferably of 0.80 to 1.00 and more preferably of 0.84 to 1.00.
  • the size of the crystallites of the fluorescent ceramic manufactured according to the present invention is preferably higher compared with the grain size of the starting powder of the M doped Gd 2 O 2 S grains. It is preferred that > 50 %, preferably > 70 % and more preferred > 90 % of the M doped Gd 2 O 2 S crystallites of the fluorescent ceramic should have a crystallite size of 1 to 300 ⁇ m, preferably of 10 to 100 ⁇ m.
  • the fluorescent ceramic manufactured according to the present invention can have a texture in the plane 001, which corresponds to a plane in a lattice oriented substantially perpendicular to a direction of a pressure applied during a process of uniaxial pressing.
  • the process involves the following steps a) placing a first solid into a mould, preferably out of graphite and/or TZM; b) placing a molybdenum foil onto the first solid of step a); c) placing a mixture of the pigment powder and the sintering and/or flux aid onto the molybdenum foil of step b); d) if desired, placing additional alternating layers of molybdenum foil and mixture of the pigment powder and the sintering and/or flux aid onto the mixture of the pigment powder and the sintering and/or flux aid of step c); e) alternatively, if desired, placing alternating layers of molybdenum foil, mixture of the pigment powder and the sintering and/or flux aid and further solid(s) onto the ceramic powder of step c); f) arranging the second to last layer of the resultant stack to be molybdenum foil; g) arranging the last layer of the resultant stack to be a solid with the same
  • a fluorescent ceramic manufactured according to the present invention can be used for example in a scintillator or fluorescent member for detecting ionizing radiation, preferably x-rays, gamma rays and electron beams; and/or an apparatus or device used in the medical field, preferably for a computer tomography (CT).
  • a scintillator or fluorescent member for detecting ionizing radiation, preferably x-rays, gamma rays and electron beams
  • an apparatus or device used in the medical field preferably for a computer tomography (CT).
  • CT computer tomography
  • At least one fluorescent ceramic manufactured according to the present invention can be used for a detector or apparatus adapted for medical imaging.
  • a fluorescent ceramic made according to the present invention can be used for any detector known in the medical field.
  • detectors are for example X-ray detector, CT-detector, Electronic Portal Imaging detector and the like.
  • Fig. 1 shows an apparatus suitable for the method according to the present invention designed for hot uniaxial pressing with pressure being applied from one direction.
  • Fig. 2 shows a further apparatus suitable for the method according to the present invention designed for hot uniaxial pressing with pressure being applied from two directions.
  • Fig.3 shows a temperature and pressure diagram over time for a hot uniaxial pressure step according to a first embodiment of the present invention.
  • Figure 1 shows an apparatus (1) suitable to be used according to the present invention designed for hot uniaxial pressing with pressure being applied from one direction. Such an apparatus is also described in the EP 05 110 054.3 which is hereby incorporated by reference.
  • a piston (2) transfers pressure onto a die (3).
  • This die (3) fits inside a mould (5).
  • a second die (6) On the bottom of the mould (5), a second die (6), which is in a fixed position, is located.
  • This arrangement is heated by a heater (4).
  • ceramic powder (9) Inside the mould there are layers of ceramic powder (9) who are in contact with molybdenum foil (8).
  • the molybdenum foil layers in turn are in contact with layers of graphite solids (7).
  • piston (2), dies (3) and (6), heater (4), mould (5) and the layers of graphite (7), molybdenum foil (8) and ceramic powder (9) are arranged in a cylinder symmetric fashion around a vertical symmetry axis.
  • FIG. 2 shows further apparatus (10) according to the present invention designed for hot uniaxial pressing with pressure being applied from two directions.
  • a piston (2) transfers pressure onto a die (3).
  • This die (3) fits inside a mould (5).
  • a further die (11) which is movable and driven by a second piston (12), is located.
  • This arrangement is heated by a heater (4).
  • ceramic powder (9) who are in contact with molybdenum foil (8).
  • the molybdenum foil layers in turn are in contact with layers of graphite solids (7).
  • a Gd 2 O 2 SiPr pigment powder with a Pr concentration of 500-1000 wt ppm was used with Ce furthermore present as an impurity in an concentration of about 20 wt ppm. 3kg of said pigment powder were admixed with 0.0055 g of LiF as sintering and/or flux aid.
  • the mixture of the pigment powder and the LiF were filled in an apparatus according to Fig. 1 and the hot-pressing was performed as shown in Fig. 3.
  • the temperature was raised with approx. 2OK/ min until 800 0 C was reached, upon which a dwelling step of 25 min was performed.
  • the pressure was raised by 2.5 MPa/min until approx 50 MPa was reached.
  • the temperature was again raised by 10K/min to reach 1050 0 C, followed by a simultaneous increase in temperature of 2K/min and pressure of 1 MPa/min until the maximum pressure of 150 MPa and the maximum temperature of 1250 0 C were reached.

Abstract

The present invention relates to method of producing a fluorescent ceramic having the general formula Gd2O2S doped with M, whereby M represents at least one element selected from the group Ce, Pr, Eu, Tb, Yb, Dy, Sm and/or Ho involving a uniaxial hot-pressing step in the presence of a sintering and/or flux aid.

Description

METHOD OF MAKING A GOS CERAMIC USING SINGLE-AXIS HOT PRESSING AND A FLUX AID
The present invention is directed to a fluorescent ceramic having the general formula Gd2O2S doped with M, whereby M represents at least one element selected from the group Ce, Pr, Eu, Tb, Yb, Dy, Sm and/or Ho and a method of making such a fluorescent ceramic.
The invention further relates to a method for manufacturing a fluorescent ceramic using single-axis hot pressing.
The invention still further relates to a detector for detecting ionizing radiation.
The invention still further relates to a use of said detector for detecting ionizing radiation.
Fluorescent members for detecting high energy radiation contain a phosphor that can absorb the radiation and convert it into visible light. The luminescent emission thereby generated is electronically acquired and evaluated with the assistance of light sensitive systems such as photodiodes or photomultipliers. Such fluorescent members can be manufactured of single-crystal materials, for example, doped alkali halides. Non-single-crystal materials can be employed as powdered phosphor or in the form of ceramic members manufactured therefrom.
A method of manufacturing such a fluorescent ceramic is e.g. disclosed in WO 2005/110943 Al which is hereby enclosed by reference. However, this method suffers from the drawback that e.g. for some applications an increased pressure is needed. The object of the present invention is to provide a method for manufacturing a scintillating ceramics with a still further improved light output and afterglow characteristics.
The above-described objective can be achieved according to Claim 1 of the present invention. Accordingly, a method for manufacture of a fluorescent ceramic material using a single-axis hot-pressing is provided, whereby said inventive method comprises the step of selecting a pigment powder Of Gd2O2S doped with M, and M represents at least one element selected from the group of Eu, Tb, Yb, Dy, Sm, Ho, Ce and/or Pr, and said hot-pressing is carried out at a maximum temperature of >900°C to <1500° C; and/or a maximum pressure of >75 MPa to <300 MPa; whereby hot-pressing is carried out with a sintering and/or flux aid. The term "hot uniaxial pressing" as used in the context of the present invention is well recognised in the art and to be understood as involving the compaction of powder into a rigid mould by applying pressure in a single axial direction through a rigid die or piston under the application of heat.
A "sintering and/or flux aid" in the sense of the present invention means, describes and/or includes especially a material or an mixture of materials, which show at least one of the following features:
Decomposes to form the actual flux below or in the temperature region of hot- pressing (e.g. Li2GeF6 decomposes into 2 LiF and GeF4).
Some of the decomposition products are gaseous, in this way they can easily leave the mixture to be sintered.
A melting point in the temperature region used for the hot-pressing. A boiling point which lies well beyond the temperature region used for the hot- pressing to prevent evaporation of the flux from the mixture to be sintered.
A high solubility for the Gd2O2S pigment powder used within the molten flux aid. On the other hand the flux aid itself is non-soluble in the Gd2O2S material or only in minute amounts soluble. Etches the surface to enhance surface reactivity during hot pressing to facilitate sintering.
Easily diffuses through the mixture during hot pressing that is ensured in case of a pronounced wetting behaviour.
Can preferably be used in very minute amounts, to prevent contamination of the mixture to be sintered, which may lead to undesired effects like afterglow or light yield reduction.
According to an embodiment of the present invention, the sintering and/or flux aid is added homogeneously prior the hot-pressing step using an appropriate admixing method; according to a different embodiment of the present invention, the sintering and/or flux aid and the pigment powder are mixed and vacuum-sealed prior to the hot-pressing.
According to an embodiment of the present invention, the sintering and/or flux aid comprises a fluoride.
The term "fluoride" in the sense of the present invention means, describes and/or includes especially a material or an mixture of materials, which contains fluorine.
According to an embodiment of the present invention, the sintering and/or flux aid comprises an alkali and/or earth alkali fluoride.
The term "alkali and/or earth alkali fluoride" in the sense of the present invention means, describes and/or includes especially a material or an mixture of materials, which contains at least one alkali and/or earth alkali metal and fluorine, either in form of an simple fluoride or in form of more complex structures e.g. in form of a "double-fluoride" together with one or more additional metal compounds.
According to an embodiment of the present invention, the sintering and/or flux aid comprises LiF and/or Li2GeF6 and/or Li2SiF6 and/or Li3AlF6.
According to an embodiment of the present invention, the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >50:l to ≤20000:l. In the sense of the present invention, the term "F converted value of the sintering and/or flux aid" means the amount (in wt.) of F" ions that are present in the flux during the hot-pressing step.
I.E. in case the sintering and/or flux aid is LiF and 2.6 g LiF are used, the F converted value of the sintering and/or flux aid is 1.9 g (since the molecular weight of LiF is 26 g/mole). In case the sintering and/or flux aid is Li2GeF6 and 2.0Og OfLi2GeF6 are used, the F converted value of the sintering and/or flux aid is 380 mg (since two F" ions are released per Li2GeF6 and the molecular weight OfLi2GeF6 is 200 g/mole).
According to an embodiment of the present invention, the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >1000:l to ≤10000:l.
According to an embodiment of the present invention, the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >2000:l to ≤8000:l.
According to an embodiment of the present invention, the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >3000:l to ≤7000:l.
According to an embodiment of the present invention, the ratio (in wtwt) of pigment powder to the F converted value of the sintering and/or flux aid is >4000:l to ≤6000:l.
According to an embodiment of the present invention, the hot pressing is carried out at maximum pressure and/or maximum temperature for >30 to <600 minutes.
The term "at maximum pressure and/or maximum temperature" in the sense of the present invention means, describes and/or includes especially that the above given time describes the pressing time when the maximum pressure and/or maximum temperature is reached; however, according to an embodiment of the present invention, the overall hot-pressing step can be quite longer as will be described later on.
According to an embodiment of the present invention, the maximum pressure and maximum temperature are reached essentially at the same time; according to an embodiment of the present invention, the maximum pressure and maximum temperature are reached with a delay.
According to an embodiment of the present invention, the hot pressing is carried out at maximum pressure and/or maximum temperature for > 100 to <400 minutes.
According to an embodiment of the present invention, the hot pressing is carried out at maximum pressure and/or maximum temperature for > 150 to <300 minutes.
According to an embodiment of the present invention, hot-pressing is performed in that way that the factor A is set to be > 45000 to <540000, whereby A fulfils the equation
A = t * T, with t being the time for which the hot-pressing is carried out at maximum pressure and T being the maximum temperature (in 0C) during the time t (in minutes).
Preferably, the temperature T is kept constant during the time period t; if the temperature is varied during the time period t, the temperature T is the maximum temperature which is set during the time t.
According to an embodiment of the present invention, hot-pressing is performed in that way that the factor A (dimension [0C* minutes]) is set to be > 45000 to < 540000
According to an embodiment of the present invention, hot-pressing is performed in that way that the factor A is set to be > 50000 to <450000.
According to an embodiment of the present invention, hot-pressing is performed in that way that the factor A is set to be > 60000 to <400000.
According to an embodiment of the present invention, hot-pressing is performed in that way that the factor A is set to be > 70000 to <300000.
According to an embodiment of the present invention, the hot-pressing is performed at a maximum temperature of > 1000° C to <1400° C. According to an embodiment of the present invention, the hot-pressing is performed at a maximum temperature of >1100° C to <1300° C.
According to an embodiment of the present invention, the hot-pressing is performed at a maximum temperature of > 1200° C to < 1250° C.
According to an embodiment of the present invention, the hot-pressing is performed at a maximum pressure of >75 MPa to <300 MPa.
According to an embodiment of the present invention, the hot-pressing is performed at a maximum pressure of >90 MPa to <150 MPa.
According to an embodiment of the present invention, the hot-pressing is performed at a maximum pressure of > 100 MPa to <125 MPa.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >0.1 K/min to <40 K/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >5 K/min to <25 K/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >10 K/min to <20 K/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >0.2 K/min to <5 K/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >1 K/min to <4 K/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >1.5 K/min to <2.5 K/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is reached at least partly via at least one first heating step which involves a raise in temperature with >0.1 K/min to <40 K/min, then a dwelling step, in which the temperature is not changed and then via at least one second heating step which involves a raise in temperature with >0.2 K/min to <5 K/min.
According to an embodiment of the present invention, in the at least one first heating step the raise in temperature is >5 K/min to <25 K/min.
According to an embodiment of the present invention, in the at least one first heating step the raise in temperature is >10 K/min to <20 K/min.
According to an embodiment of the present invention, in the at least one second heating step the raise in temperature is >1 K/min to <4 K/min.
According to an embodiment of the present invention, in the at least one second heating step the raise in temperature is >1.5 K/min to <2.5 K/min.
According to an embodiment of the present invention, the dwelling step is performed after reaching a temperature of >600°C to <1100 0C.
According to an embodiment of the present invention, the dwelling step is performed after reaching a temperature of >700°C to <900 0C.
According to an embodiment of the present invention, the dwelling step is performed after reaching a temperature of >750°C to <850 0C.
According to an embodiment of the present invention, the dwelling step is performed for >5 min to <30 min.
According to an embodiment of the present invention, the dwelling step is performed for >10 min to <20 min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum pressure is reached at least partly via a pressuring step which involves a raise in pressure with >0.5 MPa/min to <10 MPa/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum pressure is reached at least partly via a pressuring step which involves a raise in pressure with >1 MPa/min to <5 MPa/min. According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum pressure is reached at least partly via a pressuring step which involves a raise in pressure with >1.5 MPa/min to <3 MPa/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum pressure is released at least partly via a pressure releasing step which involves a decline in pressure with >5 MPa/min to <35 MPa/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum pressure is released at least partly via a pressure releasing step which involves a decline in pressure with >10 MPa/min to <25 MPa/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >2 K/min to <5 K/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >3 K/min to <3.5 K/min.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >2 K/min to <5 K/min until a temperature of >300°C to <600°C is reached.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >3 K/min to <3.5 K/min until a temperature of >300°C to <600°C is reached.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >2 K/min to <5 K/min until a temperature of >350°C to <450°C is reached.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >3 K/min to <3.5 K/min until a temperature of >350°C to <450°C is reached.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >2 K/min to <5 K/min until a temperature of approx . 4000C is reached.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the maximum temperature is lowered at least partly via a temperature releasing step which involves a decline in temperature with >3 K/min to <3.5 K/min until a temperature of approx. 4000C is reached.
According to an embodiment of the present invention, the hot-pressing is performed in that way that the temperature releasing step is performed after the pressure releasing step.
According to an embodiment of the present invention, the grain size of said pigment powder used for hot-pressing is of > 1 μm to <20 μm,
According to an embodiment of the present invention, the pigment powder Of Gd2O2S comprises an amount of M from > 0.1 ppm to <2000 ppm (weight fraction).
In case that more than one element is used, M represents the total added weight fractions of said elements.
The fluorescent ceramic, after the step of single-axis hot-pressing under vacuum, can be further treated by air annealing at a temperature of 700° C to 1200° C, preferably of 800° C to 1100° C, more preferably of 900° C to 1000° C; whereby said time period for air annealing treatment is 0.5 hours to 30 hours, preferably 1 hours to 20 hours, more preferably 2 hours to 10 hours and most preferably 2 hours to 4 hours. Another advantage of the present invention is that Gd2O2S material with an average grain size in the range of 1 μm to 20 μm can be commonly purchased by manufactures of the fluorescent ceramics as a raw material and do not need to be broken up to finer particles of less than 100 nm. In an embodiment it is preferred that Gd2O2S pigment powder used according to the present invention has an average grain size in the range of 2 μm to 10 μm and more preferably of 4 μm to 6 μm. Moreover, due to the method of the invention no specific powder production process is necessary, as conventionally available powders may be successfully used for manufacturing of luminescent ceramics.
Following ceramics parameters have been achieved with the method according to the invention:
- an afterglow in the range of 1 x 10"6 to 8 x 10"5 at 500 ms (using the experimental method described in WO 2005110943 Al); and/or
- a total transparency in the range of 0 to 80%, preferably 10% to 70%, still preferably 20-35% measured for a wavelength of 513 nm.
The ceramics of the present invention can be advantageously used for manufacturing x-ray luminescent ceramics that serve as raw material in fabrication of medical computer tomographs (CT).
It is found to be advantageous to introduce the vacuum annealing step for still further improving optical properties of resulting ceramics. During this step a further grain growth in the ceramics takes place which further improves transparency due to a decrease in porosity. Next to this, due to the grain growth an additional diffusion of dopant atoms in the lattice of oxysulfide enables still further improving scintillating properties of the ceramics.
Therefore, according to one embodiment of the method according to the present invention between the hot-pressing and the annealing an additional step can be carried out, which comprises annealing fluorescent ceramic under vacuum at a temperature of 1000° C to 1400° C for a period of time of 0.5 hours to 30 hours.
Preferably, the annealing temperature is selected in the range of 1100° C to 1300° C, more preferably of 1200° C to 1250° C. The time period for vacuum annealing can be preferably set to 1 hours to 20 hours, more preferably to 2 hours to 10 hours and most preferably 3 hours to 5 hours.
In a still further embodiment of the method according to the present invention an undoped Gd2O2S powder, according to an embodiment with a grain size between 1 μm and 20 μm, is mixed with a composition comprising at least one element of the group of rare earth ions comprising Pr, Ce, Eu, Tb, Yb, Dy, Sm and/or Ho.
This technical measure still further simplifies a process of ceramics manufacturing as a broad range of available materials can be used. For example, in case Pr or Ce are selected as envisaged dopants, an introduction of Pr or Ce ions can be carried out using aqueous solutions of corresponding salts: PrCl3, PrBr3, PrI3, Pr(NO3)3, Pr2(SO4)3, CeCl3, CeBr3, CeI3, Ce(NO3)3, Ce2(SO4)3, etc. Alternatively, the introduction of dopant ions can be carried out during a mechanical mixture of powders Of Gd2O2S with insoluble compositions comprising the dopant, like oxides, for example Pr6On, Pr2O3, Ce2O3, CeO2.
Still alternatively Gd2O2S powder may be mechanically mixed with water insoluble salts of the dopant, like PrF3, Pr2S3, Pr2O2S, Pr2(CO3)3, Pr2(C2O4)3, CeF3, Ce2O2S, Ce2(CO3)3, Ce2(C2O4)3, and the like.
This principle of a dopant introduction may be used for introduction of ions such as Tb, Eu and other rare earth elements. Additionally, ions of other elements not being rare earth ions may be introduced accordingly. Preferably, a suitable sintering aid is co-mixed prior to hot-pressing.
The invention further relates to ceramics being represented by a chemical formula of Gd2O2S doped with M, whereby M represents at least one element selected from the group Pr, Ce, Eu, Tb, Yb, Dy, Sm and/or Ho, whereby said fluorescent ceramic comprises a single phase in its volume.
Further it has been found that the fluorescent ceramic of the present invention can have a significantly increased relative light yield or light output relative to ceramic fluorescent material that is available on the market. The difference is especially seen for a ceramic thickness of equal or more than 1.5 mm. The light output can be a factor of 2.3 higher than that of cadmium tungstate crystals of the same thickness.
The doped pigment powder of Gd2O2S can have a surface according to BET in the range of > 0.01 m2/g and < 1 m2/g, preferably of > 0.05 m2/g and < 0.5 m2/g and more preferably of > 0.1 m2/g and < 0.2 m2/g.
The Gd2O2S can be doped by at least one element selected from the group of Ce, Pr, Eu, Tb, Yb, Dy, Sm and/or Ho. It is preferred that the Gd2O2S powder is doped by one element selected from the group of Ce, Pr, Eu, Tb, Yb, Dy, Sm and Ho only. Most preferred is the use of an element of Ce or Pr.
The content of Ce in the Gd2O2S powder in a weight fraction can be from 0.1 ppm to 100 ppm , preferably 5 ppm to 50 ppm and more preferably 10 ppm to 25 ppm and/or the content of Pr in the Gd2O2S powder can be from 100 ppm to 2000 ppm , preferably 300 ppm to 1200 ppm and more preferably 500 ppm to 800 ppm.
It has been found that the Gd2O2S fluorescent ceramics of the present invention can have a significantly reduced afterglow in the range of 1 x 10"6 to 8 x 10"5 at 500 ms, relative to the initial light output. The fluorescent ceramic of the present invention can preferably have an afterglow in the range of 1.0 x 10"6 to 6 x 10"5 at 500 ms, preferably of 1.0 x 10"6 to 5 x 10"5 at 500 ms and more preferred of 1.0 x 10"6 to 3.0 x 10"5 at 500 ms, again relative to the initial light output.
According to a preferred embodiment of the pressing invention, during the uniaxial hot pressing the polycrystalline brick is compacted preferably down to density values close to theoretical density of prei> 99.7% ptheor- Due to the high densities, the fluorescent ceramics of the present invention can provide a good transparency in the optical range. It is therefore preferred that the fluorescent ceramic manufactured according to the present invention has a density of > 99.0 %, preferably of > 99.5 % and more preferred > 99.7 % and < 100 %.
Further it has been surprisingly found that the fluorescent ceramic manufactured according to the present invention can have a significantly increased relative light yield or light output in the range of 0.74 to 1.00, preferably of 0.80 to 1.00 and more preferably of 0.84 to 1.00. The size of the crystallites of the fluorescent ceramic manufactured according to the present invention is preferably higher compared with the grain size of the starting powder of the M doped Gd2O2S grains. It is preferred that > 50 %, preferably > 70 % and more preferred > 90 % of the M doped Gd2O2S crystallites of the fluorescent ceramic should have a crystallite size of 1 to 300 μm, preferably of 10 to 100 μm.
The fluorescent ceramic manufactured according to the present invention can have a texture in the plane 001, which corresponds to a plane in a lattice oriented substantially perpendicular to a direction of a pressure applied during a process of uniaxial pressing.
According to an embodiment of the present invention, the process involves the following steps a) placing a first solid into a mould, preferably out of graphite and/or TZM; b) placing a molybdenum foil onto the first solid of step a); c) placing a mixture of the pigment powder and the sintering and/or flux aid onto the molybdenum foil of step b); d) if desired, placing additional alternating layers of molybdenum foil and mixture of the pigment powder and the sintering and/or flux aid onto the mixture of the pigment powder and the sintering and/or flux aid of step c); e) alternatively, if desired, placing alternating layers of molybdenum foil, mixture of the pigment powder and the sintering and/or flux aid and further solid(s) onto the ceramic powder of step c); f) arranging the second to last layer of the resultant stack to be molybdenum foil; g) arranging the last layer of the resultant stack to be a solid with the same material as the solid of step a); h) covering the last layer with a graphite solid; i) creating a vacuum of > IxIO"8 bar to ≤ IxIO"3 bar within the pressing apparatus; j) performing the hot-pressing step as described above. A fluorescent ceramic manufactured according to the present invention can be used for example in a scintillator or fluorescent member for detecting ionizing radiation, preferably x-rays, gamma rays and electron beams; and/or an apparatus or device used in the medical field, preferably for a computer tomography (CT).
Most preferred at least one fluorescent ceramic manufactured according to the present invention can be used for a detector or apparatus adapted for medical imaging.
However, a fluorescent ceramic made according to the present invention can be used for any detector known in the medical field. Such detectors are for example X-ray detector, CT-detector, Electronic Portal Imaging detector and the like.
The aforementioned components, as well as the claimed components and the components to be used in accordance with the invention in the described embodiments, are not subject to any special exceptions with respect to their size, shape, material selection and technical concept such that the selection criteria known in the pertinent field can be applied without limitations.
Additional details, characteristics and advantages of the object of the invention are disclosed in the subclaims, the figures and the following description of the respective figures and examples, which —in an exemplary fashion— show two preferred embodiments of an apparatus suitable according to the invention and one example of manufacturing according to the method of the present invention.
Fig. 1 shows an apparatus suitable for the method according to the present invention designed for hot uniaxial pressing with pressure being applied from one direction. Fig. 2 shows a further apparatus suitable for the method according to the present invention designed for hot uniaxial pressing with pressure being applied from two directions. Fig.3 shows a temperature and pressure diagram over time for a hot uniaxial pressure step according to a first embodiment of the present invention.
Figure 1 shows an apparatus (1) suitable to be used according to the present invention designed for hot uniaxial pressing with pressure being applied from one direction. Such an apparatus is also described in the EP 05 110 054.3 which is hereby incorporated by reference.
A piston (2) transfers pressure onto a die (3). This die (3) fits inside a mould (5). On the bottom of the mould (5), a second die (6), which is in a fixed position, is located. This arrangement is heated by a heater (4). Inside the mould there are layers of ceramic powder (9) who are in contact with molybdenum foil (8). The molybdenum foil layers in turn are in contact with layers of graphite solids (7). It is to be noted that piston (2), dies (3) and (6), heater (4), mould (5) and the layers of graphite (7), molybdenum foil (8) and ceramic powder (9) are arranged in a cylinder symmetric fashion around a vertical symmetry axis. It is further to be noted that heater (4), mould
(5) and layers of graphite (7), molybdenum foil (8) and ceramic powder (9) are arranged in a mirror symmetric fashion around a horizontal symmetry axis.
Figure 2 shows further apparatus (10) according to the present invention designed for hot uniaxial pressing with pressure being applied from two directions. A piston (2) transfers pressure onto a die (3). This die (3) fits inside a mould (5). On the bottom of the mould (5), a further die (11), which is movable and driven by a second piston (12), is located. This arrangement is heated by a heater (4). Inside the mould there are layers of ceramic powder (9) who are in contact with molybdenum foil (8). The molybdenum foil layers in turn are in contact with layers of graphite solids (7). It is to be noted that pistons (2) and (12), dies (3) and (11), heater (4), mould (5), second die
(6) and the layers of graphite (7), molybdenum foil (8) and ceramic powder (9) are arranged in a cylinder symmetric fashion around a vertical symmetry axis and in a mirror symmetric fashion around a horizontal symmetry axis. The invention will furthermore be understood according to the following Example which - in a merely illustrative fashion - shows a process of manufacturing a fluorescent ceramic according to the present invention.
EXAMPLE I
In the Example, a Gd2O2SiPr pigment powder with a Pr concentration of 500-1000 wt ppm was used with Ce furthermore present as an impurity in an concentration of about 20 wt ppm. 3kg of said pigment powder were admixed with 0.0055 g of LiF as sintering and/or flux aid.
The mixture of the pigment powder and the LiF were filled in an apparatus according to Fig. 1 and the hot-pressing was performed as shown in Fig. 3.
First, the temperature was raised with approx. 2OK/ min until 800 0C was reached, upon which a dwelling step of 25 min was performed. During part of the dwelling step, the pressure was raised by 2.5 MPa/min until approx 50 MPa was reached.
Afterwards, the temperature was again raised by 10K/min to reach 10500C, followed by a simultaneous increase in temperature of 2K/min and pressure of 1 MPa/min until the maximum pressure of 150 MPa and the maximum temperature of 12500C were reached.
At this point, the hot-pressing was performed for 240 min.
After the pressing was finished, first the pressure was reduced by 5 MPa/min and then the temperature by 3 K/min until ambient temperature and pressure were reached.
To provide a comprehensive disclosure without unduly lengthening the specification, the applicant hereby incorporates by reference each of the patents and patent applications referenced above.
The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings with other teachings in this and the patents/applications incorporated by reference are also expressly contemplated. As those skilled in the art will recognize, variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed.

Claims

CLAIMS:
1. A method for manufacture of a fluorescent ceramic material using a single-axis hot-pressing, said method comprising the step of selecting a pigment powder of Gd2O2S doped with M, and M represents at least one element selected from the group of Eu, Tb, Yb, Dy, Sm, Ho, Ce and/or Pr, and said hot-pressing is carried out at
a maximum temperature of >900°C to <1500° C; and/or a maximum pressure of >75 MPa to <300 MPa; whereby hot-pressing is carried out with a sintering and/or flux aid.
2. A method according to claim 1, whereby the sintering and/or flux aid comprises a fluoride.
3. A method according to claims 1 or 2, wherein the sintering and/or flux aid comprises LiF and/or Li2GeF6 and/or Li2SiF6 and/or Li3AlF6.
4. A method according to any of the claims 1 to 3, wherein the ratio (in wt:wt) of pigment powder to the F converted value of the sintering and/or flux aid is >50:l to <20000:l.
5. A method according to any of the claims 1 to 4, wherein the hot pressing is carried out at maximum pressure and/or maximum temperature for >30 to <600 minutes.
6. A method according to any of the claims 1 to 5, wherein the hot-pressing is performed in that way that the factor A is set to be > 45000 to <540000, whereby A fulfils the equation
A = t * T, with t being the time for which the hot-pressing is carried out at maximum pressure and T being the maximum temperature (in 0C) during the time t (in minutes).
7. A method according to any of the claims 1 to 6, wherein the hot-pressing is performed in that way that the maximum temperature is reached at least partly via a heating step which involves a raise in temperature with >0.1 K/min to <40 K/min.
8. A fluorescent ceramic prepared by a method according to claims 1 to 7.
9. A detector arranged for detecting ionizing radiation, said detector comprising a fluorescent ceramic according to claim 8.
10. Use of a detector according to claim 9 in an apparatus adapted for medical imaging.
PCT/IB2007/050052 2006-01-18 2007-01-08 Method of making a gos ceramic using single-axis hot pressing and a flux aid WO2007083248A1 (en)

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US9067304B2 (en) 2011-09-16 2015-06-30 Baker Hughes Incorporated Methods of forming polycrystalline compacts
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US8981311B2 (en) 2010-05-24 2015-03-17 Koninklijke Philips N.V. CT detector including multi-layer fluorescent tape scintillator with switchable spectral sensitivity
US9322935B2 (en) 2011-07-28 2016-04-26 Koninklijke Philips N.V. Terbium based detector scintillator
US9067304B2 (en) 2011-09-16 2015-06-30 Baker Hughes Incorporated Methods of forming polycrystalline compacts
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US10350563B2 (en) 2011-09-19 2019-07-16 Baker Hughes, A Ge Company, Llc Methods of forming polycrystalline diamond compacts
US9816028B2 (en) 2014-08-14 2017-11-14 Tsinghua University Process for the preparation of gadolinium oxysulfide (Gd2O2S) scintillation ceramics

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