Compositions – Electrically conductive or emissive compositions
Reexamination Certificate
1999-12-20
2001-06-26
Marcantoni, Paul (Department: 1755)
Compositions
Electrically conductive or emissive compositions
C252S508000, C252S509000, C501S126000, C501S127000, C501S128000
Reexamination Certificate
active
06251306
ABSTRACT:
The present invention relates to novel ceramic materials that are capable of generating continuous infrared (IR) radiation. More particularly, it relates to refractory ceramic materials that have enhanced thermal, chemical, and physical stability as well as enhanced resistance to thermocycling and that can be used for drying things, for quickly and efficiently sterilizing various objects, for treating cardiovascular disorders, for conveying gases and liquids, for air purification, in cooling systems, in systems where conductivity varies in pulses, in high-temperature heaters, and in lining materials.
Ceramic materials are known of the general formula RCrO
3
, where R is a rare-earth oxide such as yttrium oxide, described in U.S. Pat. No. 3,475,352. These materials, although successfully used where conductance is essential, e.g. in electrodes, have low chemical stability when exposed to high (over 1600° C.) temperatures, low resistance to thermocycling at temperatures above 1500° C., and cannot be heated at high rates. Furthermore, they have relatively low radiating capacity. These shortcomings have limited the use of these materials in applications where the stability of properties is important.
A device is known for sterilizing a hose coupling for an artificial kidney (see U.S. Pat. No. 4,774,415, Class 250-455.1). The ceramic material of the sterilizer has an insufficient radiating power in the infrared range, which results in insufficient sterilization of some parts of the coupling which do not get the necessary exposure. Increasing the time of sterilization does not help, since it may result in overheating the parts of the coupling most susceptible to TR radiation. In this case articles made of metal and glass may melt, or change colour due to the formation of an oxide film.
A ceramic Composition having more stable thermal, physical and chemical properties is one based on chromium oxide Cr
2
O
3
(up to 44.7 wt %) and iron oxide Fe
2
O
3
(up to 35 wt %) and also containing a large amount of silicon oxide SiO
2
(10~20 wt %) and Al
2
O
3
, CuO, CaO and MgO as additives (see U.S. Pat. No. 5,350,927, published 27.09.1994, national classification 250-504R, Radiation emitting ceramic materials and devices containing the same), chosen as the prototype. The said ceramic material receives either pulse IR radiation from another ceramic material generating only pulse IR radiation, made in the form of a screen, or radiation from a lamp, a heating coil, and so on, and generates continuous IR radiation used in sterilizers. A shortcoming of the ceramic is the relatively low efficiency of conversion of primary radiation, which severely limits its application in the many fields listed in the preamble.
The object of the present invention is to create a ceramic material that will be capable of uniform IR radiation and have an increased radiating capacity. This goal is achieved by supplementing a ceramic material containing Cr
2
O
3
, Fe
2
O
3
, SiO
2
, MgO, Al
2
O
3
, CaO, and CuO, with CaCO
3
, in the following ratio of ingredients, wt %:
Cr
2
O
3
28.0 ~ 32.0
CaCO
3
7.0 ~ 10.0
Fe
2
O
3
33.0 ~ 35.0
SiO
2
16.0 ~ 17.5
MgO
4.0 ~ 6.0
CaO
2.5 ~ 3.0
Al
2
O
3
0.5 ~ 2.0
CuO
0.5 ~ 1.0
It has turned out that it is precisely the addition of CaCO
3
in the amount given, with a simultaneous decrease, relative to the prototype, in Cr
2
O
3
, CaO and CuO to the amounts indicated and the amounts of the remaining ingredients held constant, that allows one to obtain a ceramic material capable of generating continuous IR radiation with a radiating power exceeding that of known ceramic materials on the basis of chromium oxide by 23 to 49%.
The ceramic material being claimed is prepared following a conventional route. The ingredients arc milled to a fine powder, mixed until homogeneity is achieved, and placed in the crucible of a solar furnace, where they are melted. The melting is usually done in conditions where the loss of oxygen from the resulting powder is kept to a minimum. As a rule, these ceramic compositions on the basis of chromium oxide are melted at about. 2 600° C. It is desirable that the melting be carried out in an oxidizing atmosphere, preferably in air.
The melt drips into a cooling tank containing water. The resultant material is ground to a grain size of 160 &mgr;m and then the powder is pressed into desired articles.
REFERENCES:
patent: 3585390 (1971-06-01), Ishikawa
Abelman ,Frayne & Schwab
Marcantoni Paul
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