Sintered shaped body reinforced with platelets

Details Sintered shaped body reinforced with platelets Sintered shaped body reinforced with platelets

2000-07-06

2002-09-17

Hoang, Tu Ba (Department: 3742)

Industrial electric heating furnaces

Resistance furnace device

Lining

C051S309000, C501S105000

Reexamination Certificate

active

06452957

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject-matter of the present invention is a sintered shaped body consisting of a matrix material that contains an aluminium oxide/chromium oxide mixed crystal and which is in situ reinforced with platelets.
2. Description of Related Art
The use of an oxide ceramic material for pressing-tools for shaping components of glass or ceramic material containing glass is specified in DE-A-36 08 854. In addition to cubic and tetragonal zirconium dioxide, aluminium oxide, chromium oxide, spinel and an Al-Cr-mixed oxide (AlCr
2
O
3
) that is not defined with regard to its quantitative composition are also specified as matrix materials. The individual proposals for the matrix components enjoy equality in this connection so there is not offered any teaching for the selection of a particular matrix component or for the proportion of the quantity of, for example, zirconium dioxide to be incorporated in the matrix. Stabilizing oxides, such as, for example, yttrium oxide (Y
2
O
3
) in a quantity of 3.5 to 12, preferably 8 to 10, or magnesium oxide (MgO) in a quantity of 6.0 to 16, preferably 8 to 14 mol %, and cerium oxide (CeO
2
) in a quantity of 3.5 to 12 mol %, preferably 8 to 10 mol %, relative can also be present in addition to the components mentioned above. A size between 5 and 5000 nm, corresponding to 0.005 to 5 &mgr;m, is mentioned as the particle size for the particles incorporated in a polycrystalline matrix.
A further proposal for a so-called “conversion-reinforced” ceramic composition, in which a finely distributed solid solution of ZrO
2
—HfO
2
in a solid solution of either aluminium oxide, containing chromium oxide, or mullite, containing chromium oxide, is specified, is found in WO 85/01936 and in that case is put forward for high-temperature fields of application, such as, for example, for diesel engines and gas turbines. The proportion of chromium oxide considered between 3 and 30 mol %, in particular a proportion of 20 mol % chromium oxide, cooperating with a proportion of 10 to 20 mol % hafnium dioxide, is to be used to improve the hardness and to set a low level of thermal conductivity. Rising proportions of chromium oxide and hafnium dioxide result in a decrease in the thermal conductivity. Noticeable increases in hardness are first found when there are comparatively high concentrations of chromium oxide—approximately 20 mol %, relative to 20 mol % HfO
2
. An order of magnitude of 5 &mgr;m is specified for the grain size of the incorporated ZrO
2
—HfO
2
phase in the examples of this specification, and the fact that tetragonal modification is not obtained is attributed to the fact that there not been achieved any success in obtaining the dispersed ZrO
2
—HfO
2
solid solution with the sufficient degree of fineness. No addition of stabilizing oxides is mentioned in this specification. The fracture-toughness values attained lie in the range between 5 and approximately 6.5 MPavm.
EP-A-199 459 relates to ceramic compositions with high levels of toughness and provides for the cooperation of zirconium dioxide, partly stabilized zirconium dioxide, solid solutions of zirconium dioxide/hafnium dioxide, solid solutions of partly stabilized zirconium dioxide/hafnium dioxide, partly stabilized hafnium dioxide and hafnium dioxide with mixtures of metal oxides, in particular yttrium niobium oxide (YNbO
4
) or yttrium tantalum oxide (YTaO
4
), with the yttrium ion of the mixed oxides even being replaced in part by a cation of a rare earth metal, for example La
+3
, Ce
+4
, Ce
+3
, Pr
+2
, Tm
+3
. According to a further variant of this specification, the ceramic alloy that is described, that is, for example ZrO
2
, can be mixed, whilst adding YNbO
4
in a quantity of at least 5 % by volume, with, for example, &agr;-aluminium oxide or even Al
2
O
3
—Cr
2
O
3
, mullite or titanium carbide. The disadvantage of this known composition can be seen in the fact that, as a consequence of the mixed oxides containing Nb or Ta that are produced, a further grain-boundary develops with the ceramic products and a softening point sets in that is not yet at a sufficiently high level for many fields of application.
Similarly, U.S. Pat. No. 4,770,673 describes a ceramic cutting tool, 20 to 45% of which consists of a zirconium dioxide alloy, containing 1 to 4 mol % of a mixed metal oxide, and 55 to 80% by weight of which consists of a hard ceramic composition, with the mixed metal oxides consisting of the group of YNbO
4
, YTaO
4
, MNbO
4
, MTaO
4
and mixtures thereof, and M consisting of a cation, which is provided for the substitution of the yttrium cation, and being selected from Mg
+2
, Ca
+2
, Sc
+3
and rare earth metal ions, consisting of the group LA
+3
, Ce
+4
, Ce
+3
, Pr
+3
, Nd
+3
, Sm
+3
, Eu
+3
, Gd
+3
, Tb
+3
, Dy
+3
, HO
+3
, Er
+3
, Tm
+3
, Yb
+3
and Lu
+3
and mixtures thereof. In addition to aluminium oxide and, for example, sialon, SiC, Si
3
N
4
, as a hard ceramic material Al
2
O
3
—Cr
2
O
3
also comes into consideration, in which a proportion of Cr
2
O
3
of up to approximately 5 mol % is provided. Here again, as previously, there is the disadvantage that too low a softening range results in the ceramic material on account of the alloying constituents that are added to the ZrO
2
in the form of the mixed oxides which contain niobium or tantalum.
U.S. Pat. No. 4,316,964 relates to a composition that is also taken into consideration for the production of cutting plates and which consists of 95-5% by volume aluminium oxide and 5-95% by volume zirconium dioxide with the addition of approximately 0.5-5.5 mol % yttrium oxide, 0.5 to 10 mol % cerium oxide, 0.4 to 4 mol % erbium oxide and 0.5 to 5 mol % lanthanum oxide, relative to zirconium dioxide.
A sintered shaped body that is also provided for use as a cutting plate in accordance with EP-A-282 879 consists of a matrix containing whiskers and, moreover, particles of, for example, silicon carbide, silicon nitride, sialon, aluminium oxide and zirconium dioxide. The whiskers can be made of the same materials as the particles. Zirconium dioxide is mentioned here as the matrix material in addition to mullite and aluminium oxide. Moreover, the sintered shaped body can also contain the usual sintering aids, such as, for example, the oxides of magnesium, chromium or yttrium. Of the rare earth oxides that are suitable those which are preferred are the oxides of lanthanum, samarium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Fracture-toughness values of more than 10 MPam
½
are specified.
A ceramic material with very high levels of toughness and wear-resistance for use as a metal-removing cutting tool is known from DE-A-35 29 265. The composition provides, in addition to 20 to 50% by weight titanium carbide and 18 to 79.9% by weight aluminium oxide, 0.1 to 2% by weight of a sintering aid which is selected from the group: MgO, CaO, SiO
2
, ZrO
2
, NiO, Th
2
O
3
, AIN, TiO, TiO
2
, Cr
2
O
3
and/or at least one oxide of the rare earths. Y
2
O
3
, Dy
2
O
3
, Er
2
O
3
, Ho
2
O
3
, Gd
2
O
3
and/or Tb
4
O
7
are mentioned as rare earth oxides. The sintering aids are used to prevent the grain growth in the case of the aluminium oxide and enter into combination with the latter, promoting the sintering process of the ceramic material.
A sintered body containing 40 to 99 mol % partly stabilized zirconium dioxide and 1 to 60 mol % aluminium oxide and, furthermore, as sintering aids, small quantities of the oxides of Mn, Fe, Co, Ni, Cu and Zn for the acceleration of the sintering process, is known from EP-A-214 291. The oxides of yttrium, magnesium, calcium or cerium are proposed for the purpose of setting a tetragonal phase proportion of 65 % or more. 1.3 to 4 mol % is mentioned as the quantity of yttrium oxide that is to be added and which can be replaced completely or partly by the other stabilizing oxides in a quantity of 0.01 to 12 mol %.
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