Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2000-01-26
2002-02-26
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
Reexamination Certificate
active
06350712
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention refers to a glass composition and a method for the commercial production of a colored glass composition, that it highly desirable for use in the construction industry and mainly in the automotive industry. More particularly, this invention relates to a glass composition that utilizes ferric oxide, titanium oxide and chromium oxide to produce a glass suitable for use in automotive industry with a thickness of about 2.8 millimeters to about 4.0 millimeters.
2. Description of the Related Art
Several patents have been developed for obtaining colored glass, using a standard soda-lime glass base composition.
For automotive use, it is highly desirable that the glass has a high level or percentage of visible light transmission, in order to provide a good vision area of a vehicle, such as a windshield and side and rear windows.
Similarly, it is highly desirable that the glass have the necessary absorption properties to absorb damaging infrared (IR) and ultraviolet (UV) solar light, so as to reduce the excessive heating within the vehicles on sunny days, and to protect the interior of the vehicle from the degradation caused by ultraviolet radiation.
Also, it is well-known that the transmitting characteristics of the glass of different wavelengths can be controlled by adding several absorbent coloring agents in the initial manufacturing mix.
Consequently, for vehicle applications, it has been desirable to use colorants to produce a glass that is able to filter a large portion of the damaging ultraviolet rays from the sun, lower than 39% (measured in the wavelength of &lgr; 300-400 nm and air mass 2 or less than 35% in the same wavelength range with air mass equals 1.5), but that permits the largest possible visible amount (of the luminous rays) up to 70% or more.
The iron is generally present in the glass as both ferrous oxide (FeO) and ferric oxide (Fe
2
O
3
) imparting to the glass a clear green color. The balance between ferrous and ferric oxide has a direct a material effect on the color and transmittance properties of the glass. In this way, in a glass composition, the total amount of iron is present as both ferric oxide (Fe
2
O
3
) and as ferrous oxide (FeO) since, even when pure ferric oxide is used in the basic raw material during the glass forming process, a portion of the ferric oxide is reduced and is transformed into ferrous oxide.
Normally, the total amount of iron in the glass and its amount of ferrous oxides are expressed as being bases on Fe
2
O
3
. It is also standard in this industry to express the quantity of ferrous or ferric oxide as a percentage of the total iron, namely:
%
Fe
+
2
(
FERROUS
)
=
Fe0
×
100
Total
Fe
2
O
3
%
Fe
+
3
(
FERRIC
)
=
Fe
2
O
3
×
100
Total
Fe
2
O
3
The iron oxides (ferric and ferrous) impart different optical properties to the glass, the total quantity of iron present and its equilibrium as ferric or ferrous have a direct impact on the color, light transmission and absorption of infrared and ultraviolet radiations.
The ferric oxide absorbs ultraviolet energy (low transmission level), and at the same time it has a high levels of light transmission, and of infrared energy transmission.
By contrast, ferrous oxide absorbs infrared energy (low transmission level), has a high level of ultra-violet transmission, and a lower level of light transmission and possesses a more intense blue color.
Therefore, the greater the quantity of Fe
2
O
3
present in the glass, the greater will be the absorption of ultraviolet radiation, and the light transmission is increased but, as the contents of FeO is increased as a result of the chemical reduction of Fe
2
O
3
, the absorption of the infrared radiation will increase, but the absorption of the ultraviolet radiation is decreased and the light transmission is also (undesirable) decreased.
On the other hand, the greater the concentration of FeO in relation to Fe
2
O
3
, results in a change in the color of the glass. The shift toward a higher concentration of FeO in relation to the Fe
2
O
3
causes a change of color of the glass from a yellow or yellow-green to a darker blue-green undesirable, because it reduces the light transmission of the glass.
Therefore, in order to manufacture a glass with determined properties and color, one must have the correct proportion of Fe
2
O
3
and FeO, taking into account that what is increased on the ferrous side, will diminish on the ferric one, and consequently one must arrive at a compromise of properties since improving (lowering) the value of one property will worsen (rise) the value of the other properties.
In order to increase the absorption of the infrared and ultraviolet radiation without sacrificing the transmission of the visible spectrum, it has been necessary to lower the total content of the iron which is highly reduced from ferric to ferrous, to less than 0.70% of total iron expressed as Fe
2
O
3
.
Depending on the state of reduction of the glass, the coloring changes as follows:
LOW FERROUS (12%)—YELLOW—HIGH LIGHT TRANSMISSION (HIGH FERRIC)
YELLOW-GREEN
GREEN-YELLOW
GREEN (DESIRABLE)
GREEN-BLUE
BLUE-GREEN
BLUE
HIGH FERROUS (75%)—AMBER—LOW LIGHT TRANSMISSION (LOW FERRIC)
Additionally, it is known that the oxides of titanium, molybdenum and the cerium, principally of cerium, also are colorants, and when they are used in combination with the Fe
2
O
3
, it is possible to obtain an additional reduction of the ultraviolet light transmission to a point where the sought for visibility transmission is achieved. It does, however, suffer from the disadvantage of its high cost, which makes the formulation very expensive, and has a tendency to oxidize the iron to Fe
2
O
3
.
In addition, while the use of CeO
2
in quantities from 0.1 to 0.5%, provides absorption of ultraviolet radiation, it has the disadvantage that it tends to change the most desirable green color, to an unacceptable yellowish hue.
In order to control the reduction of the glass formulation, metallic tin, stannic chloride, and mainly coal, have been employed as reducing agents, introduced them in the charge. Coal is used in a finely divided state in an amount of 0.01 to 0.05%, preferably 0.025% of the total amount of the charge.
For maintain a constant ferrous value and conserve the green color of the glass, the amount of coal required to counter the oxidizing effect provoked by the introduction of 1% cerium oxide in a typical glass with a low content of iron, is between the range of 0.9 kilograms per ton of glass. Pursuant to the opinion of some researchers in the field, this level of coal interferes with the humidification action of the silica of the saline cake and, therefore, it results in the formation of silica slag in the smelting furnace.
Similarly, in order to maintain the ferrous value constant, thus counteracting the oxidizing effect, of a constant amount of cerium oxide is added as the content of iron in the glass increases. For example, up to 0.80% of total iron added, it was foreseen that the same amount of coal should be added due to the fact that the level of cerium oxide is constant, or that the requirement of coal should be much greater due to the fact that the equilibrium of the ferrous value would lessen with the greater addition of iron.
Many papers have been published on colored glass compositions with infrared and ultraviolet radiation absorbing characteristics. W. A. Weyl in the book Coloured Glasses, Society of Glass Technology, reprinted 1992, describes diverse theories of colour in glasses related to the current views of the structure and constitution of glass. The use of chromium and its compounds for coloring glasses is described in this book. In the glass industry the chromium is added to the raw materials to obtain a color emerald green which is typical of Cr
3+
. The chromium can be present as Cr
6+
as CrO
4
2−
to obtain a lightly yellow color and as Cr
2+
throug
Abelman ,Frayne & Schwab
Group Karl
Vitro Corporativo, S.A. DE C.V.
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