SE461980B - PROCEDURES FOR CHEMICAL INDICATION OF VANADINOXIDE FILMS - Google Patents

Description

LS 20 IN) 461 980 35 percent of six millimeters thick clear s.k. float glass. Vanadium oxide films containing V 2 O 5 can also be prepared by chemical vapor deposition according to the present invention. These films can then be reduced to form thermochromic films containing V02.

DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the optical change of a vanadium oxide (VO 2) film formed directly by chemical vapor deposition.

Figure 2 illustrates the electoresistive change that accompanies the optical change illustrated in Figure 1.

Figure 3 illustrates the optical change of a doped vanadium oxide film by comparing the solar energy transmittance of a coated glass sample at room temperature with the transmittance of the sample heated above its transition temperature.

Figure 4 illustrates the transition temperature range of a doped vanadium oxide film by showing the resistance as a function of temperature.

SUMMARY OF THE INVENTION The present invention relates more particularly to a process for the chemical vapor deposition of vanadium oxide films, which process is characterized by: a. Heating a glass substrate to a sufficient temperature to convert an organovanadine compound to vanadium oxide; b. vaporizes a liquid organovanadine compound; c. contacting a surface of the heated glass substrate with the vapor of said vanadium compound to deposit a vanadium oxide film on the glass surface.

According to another aspect of the invention, there is provided a process for producing a conductive coated glass part, which process is characterized in that: a. A glass substrate is heated to a temperature of at least about 40 ° C; b. vaporizes vanadium n-propylate; c. transporting the vaporized vanadium n-propylate to the substrate in a stream of nitrogen; d. contacting a surface of the heated glass substrate with the vaporized vanadium n-propylate to deposit a film containing V 2 O 3 thereon; and 10 15 20 25 30 55 461 980 e. cools the coated glass particle in an atmosphere which is insufficiently oxidizing to convert VZO3 to VO2.

DETAILED DESCRIPTION OF PURED PAINTED METHODS Numerous metal and / or metal oxide coatings are known to be useful for solar energy control. Such coatings typically reflect a large proportion of the incident solar energy to minimize heating inside a structure or building, while allowing sufficient transmission of the visible part of the spectrum to be bright inside said building. A particularly desirable architectural window for passive solar energy regulation would be a window with variable transmittance, which would minimize the transmittance in summer, when the temperature is high and the incident solar energy is. greatest, but transmit solar energy when the temperature is low. Variable transmittance in a glass pane can be achieved with the help of photochromism, which means that the pane is darkened by the sun's ultraviolet rays, typically using silver halides. However, absorption of solar radiation by the glass over the entire spectral range results in heating and fading, which spoils the photochromic properties of the glass. According to the present invention, variable transmittance is achieved by means of a thermochromic response, which is the result of an optical change when a vanadium oxide film is heated by absorbed solar energy.

Vanadium oxide (VO2) undergoes a phase transition from the monoclinic crystallographic class to the tetragonal one at a nominal temperature of 68 ° C. This phase transition is accompanied by a rapid reversal or change of the electrical resistivity from semiconductor behavior to metallic one, a resistivity change of about 103 to 105-fold in a single crystal. In addition to the change in electrical conductivity, a vanadium oxide (VO2) film also undergoes significant optical change in the infrared spectral range, as shown in Figures 1 and 2, along with a minor change in the spectral range of visible light.

Thus, vanadium oxide films are prepared according to the present invention by chemical vapor deposition from organovanadine compounds such as liquid vanadium isopropylate and vanadium n-propylate.

To be useful as a thermochromic window for passive solar energy regulation, the vanadium oxide coating should provide greater optical change within the solar infrared spectral range, a temperature range for the change that is related to the actual temperatures achieved by a window that exposed to solar radiation, as well as sufficient change properties at a film thickness that is small enough to avoid iridescence. Preferably, the film thickness is in a range of from about 100 to 1500 Ångström. These properties can be achieved by vanadium oxide films prepared in accordance with the present invention.

Thin vanadium oxide films can be prepared on glass substrates by chemical vapor deposition using a variety of organovanadine compounds, preferably those in liquid form at standard temperature and pressure. Soda-lime-silica float glass and borosilicate glass are useful as substrates. The glass substrates are preheated, typically to a temperature of at least about 350 ° C, in a conventional tube furnace, which is open at both ends for feeding and discharging the substrates. An air-powered feed arm can be used to feed a substrate in and feed it out of the heating zone onto a conveyor belt which carries the substrate to a CVD coating chamber located below an exhaust hood. The CVD coating chamber contains an organovanadine compound, such as liquid vanadium isopropylate or vanadium n-propylate, which is heated to a sufficiently high temperature for the vanadium compound to evaporate. The vapor of the organovanadine compound is passed in a gas stream to the heated substrate, whereupon the organovanadine compound pyrolyzes to form vanadium oxide.

According to a preferred embodiment of the present invention, vanadium isopropylate is evaporated and passed in a stream of non-oxidizing gas such as nitrogen or forming gas to a heated glass substrate. A vanadium oxide coating is formed on the glass, which is then introduced into a tunnel purged with forming gas to a cooling surface or quenching surface, where the coated glass is cooled to ambient temperature or room temperature. When VO 2 is formed from vanadium isopropylate, the resulting vanadium oxide coated glass is semiconducting at ambient temperature with a solar infrared transmittance typically above 30% at wavelengths of between 0.8 and 2.2 .mu.m, while the VO 2 -containing film above the transition temperature, nominally 68 ° C, is characteristically conductive and has a total solar infrared transmission that is less than about 15%. 46 15 980 To improve the optical response of a vanadium oxide film, it may be useful to prime the glass surface prior to the chemical vapor deposition of the vanadium oxide coating. Optimal primer can be obtained with a tin oxide coating, typically from 700 to 800 Å thick. The tin oxide primer is preferably prepared by pyrolytic deposition of an organotin compound. Silica and titanium dioxide films are also useful as primers. The use of such base films, especially SnO2, seems to improve the crystallinity and formation of VO2 rather than other vanadium oxides, resulting in a VO2-rich film which has very good optical change properties.

The optical change or reversal properties of the vanadium oxide coating are determined by scanning the transmittance pattern with a Cary 14 spectrophotometer (comparable spectrophotometers now available from Varian Associates) over the spectral range 0.8 to 2.2 μm. The vanadium oxide coated glass sample is held in an insulated holder with an opening for jet passage. Two cylindrical 25 watt heaters in contact with the glass edges immediately outside the beam passage opening were used to heat the vanadium oxide coated glass sample through the change or switching temperature range. A spectral scan is performed both before and after heating without moving the sample. Typical results are shown in Figures 1 and 2.

The temperature range of the optical change is determined in a separate experiment, which also gives a measure of the thermoresistive change. A flat-head probe for an Omega Amprove fixed-temperature measuring device (marketed by Omega Engineering, Inc., Stanford, Connecticut) is clamped onto a narrow strip of vanadium oxide film surface. In the immediate vicinity on each side of the probe, there are terminals connected to an ohm meter for measuring the resistance. The resistance is measured as a function of the temperature when the coated sample is heated through the transition temperature range. A sample measurement is illustrated in Figure 3.

In general, it turns out that of the 103 to 105-fold thermoresistivity change capacity of vanadium oxide (VO 2), a thermoresistive change of the order of about two-fold is sufficient to effect optical change of the required magnitude for passive solar energy control in the spectral range 0.8. to 2.2 .mu.m. The temperature range for optical change, 10 461 980 around the nominal value 68 ° C which is known for relatively pure single crystals of vanadium oxide (VO,), is close to the range of about 45 - 60 ° C which is actually achieved in windows in summer in the south.

Furthermore, it turns out that optical change properties can be achieved with vanadium oxide films that are thin enough to avoid visible iridescence or blast wave effect.

V02 films with reduced change temperatures can be prepared by doping with niobium, molybdenum, iridium, tantalum or tungsten oxides, these metal cations having a larger ionic radius than vanadium.

According to a variant of such a process, the glass substrate is immersed in a solution containing 1 part by volume of vanadium isopropylate, 3 parts by volume of 2-propanol and about 2.5 to 4 g per liter of WOCl 4 at room temperature. Film formation takes place by hydrolysis in ambient air. The coated glass is then heated, preferably in a reducing atmosphere, more preferably in an atmosphere of forming gas containing an aromatic hydrocarbon, to a sufficient temperature and for a sufficient period of time to form a thermochromic VO 2 film which changes within a temperature range above rising room temperature but below the characteristic value 68 ° C.

The VO 2 film is semiconductive at ambient temperatures or room temperature, the total solar infrared transmittance being as shown in Figure 3, while the VO 2 -containing film over the transition temperature range is typically conductive and has a solar infrared transmittance of less than about 10%. as shown in Figure 4.

A larger size thermoresistive change can be achieved by using liquid vanadium isopropylate supported in nitrogen to form highly oxidized vanadium oxide (VZOS) on a glass surface heated to at least about 300 ° C. The vanadium oxide-coated glass is transported inside a tunnel flushed with air to a cooling surface, which is also flushed with air, where the coated glass is cooled to ambient temperature or room temperature. The resulting vanadium oxide coating is mainly V205. To obtain thermochrome VO 2, the vanadium oxide coating is reduced in a reducing atmosphere, preferably forming gas containing a small proportion of aromatic hydrocarbon at a temperature of from about 325 to 475 ° C.

The thermochromic V02 film thus formed is semiconducting at ambient temperature with a solar infrared transmittance as illustrated in Figure 2, while the VO2 film over the transition temperature is characteristically conductive with a total solar infrared transmission of 10 46. less than about 10%. The thermoresistive change is approximately 1000-fold as shown in Figure 3.

Conductive thin films of vanadium oxide containing VZOS can be prepared by chemical deposition using vanadium n-propylate. Glass substrates are preheated, typically to a temperature of at least about 450 ° C, in a conventional tube furnace open at both ends for feeding and discharging the substrates. Liquid vanadium n-propylate is evaporated and carried in a stream of nitrogen to the heated substrate, whereupon the organovanadine compound pyrolyzes to form vanadium oxide. The vanadium oxide coated glass passes through a tunnel purged with forming gas to a cooling surface, which is also purged with forming gas, where the coated glass is cooled to room temperature. The resulting conductive V203 film is typically gray in transmission compared to yellow to brown for V02 and typically has a resistance of approximately 200 to 300 ohms per square. Preferred film thicknesses vary from about 200 to 1500 Ångström. _.

The present invention will be further apparent from the following description of embodiments.

EXAMPLE I A glass substrate is heated to a temperature of about 6.3500 and brought into contact with a solution containing two parts by volume of dibutyltin diacetate and one part by volume of methanol. A tin oxide coating, which is from about 700 to 800 Å thick, forms on the glass surface.

The tin oxide-based glass passes through a chemical vapor deposition chamber containing liquid vanadium isopropylate, which is heated to 127 ° C to evaporate organovanadine compound.

The organovanadine vapors are fed in nitrogen to the moving glass substrate, which is maintained at a temperature of about 530 ° C. The vanadium oxide film formed on the glass substrate is yellow when transmitted in fluorescent light. The vanadinoxide film shows a transition over the temperature range from about 55 to 75 ° C. The electrical change for this film is from about 13,000 ohms at room temperature to about 5,000 ohms above the transition temperature range. The associated optical change is shown in Figure 1. EXAMPLE II Vanadium isopropylate is heated to 127 ° C in a chemical vapor deposition chamber. The organovanadine vapors are passed in nitrogen to a moving glass substrate, which is preheated to a temperature of about 400 ° C, to deposit a vanadium oxide film on the unfounded glass substrate. The coated glass is cooled to room temperature in air, resulting in a vanadium oxide composition containing V 2 O 5. The VZOS film is reduced to thermochrome VO 2 by heating at a temperature of from about 450 to 463 ° C for about 23 minutes in a forming gas atmosphere containing an aromatic hydrocarbon (obtained by heating to 160 ° C on a Califlux TT bath). which is a process oil marketed by Witco Chemical Corp., Los Angeles, California). The VO 2 film exhibits an electrical change from more than 105 ohms at room temperature to about 500 to 800 ohms above 68 ° C with an optical change to less than 10% transmittance of solar radiation between 0.8 and 2.2 μm, as shown in Figure 2.

EXAMPLE 3 Vanadium n-propylate is heated to 127 ° C to form vapors which are passed in nitrogen to a moving glass substrate which is preheated to a temperature of about 530 ° C. A conductive vanadium oxide (V 2 O 3) film is formed on the glass substrate. The coated glass is cooled in an atmosphere of forming gas. The vanadium oxide film is gray when transmitted in fluorescent light and has a resistance at room temperature of about 150 to 190 ohms per square at a thickness that gives a clear transmittance of about 24%.

EXAMPLE IV A clear sheet of float glass is immersed in a solution containing one part by volume of vanadium isopropylate, three parts by volume of 2-propanol and about 4 g per liter of WOCl 4 at room temperature. The glass is taken up and hydrolysis is allowed to proceed in ambient air to form a clear film, which turns yellow on transmission. The coated glass is then heated to 375 ° C in forming gas. For a period of 1 minute, the coated glass is exposed to hydrocarbon vapors, which are carried by a stream of forming gas. The hydrocarbon vapors are obtained by heating to 160 ° C a bath of Califlux TT, which is a process oil marketed by Witco Chemical Corp., Los Angeles, California. The resulting vanadium oxide (VO 2) coated glass exhibits optical change as shown in Figure 3 and has a transition temperature as shown in Figure 4.

The above examples are given for the purpose of illustrating the present invention. Various other substrates, such as borosilicate glass, can also be used in the manufacture of vanadium oxide films of the present invention. Other organovanadine compounds, such as vanadium ethylate and butylate and vanadium oxychloride, VOCl3, can also be used. Post-deposition reduction of V 2 O 5 can be avoided by incorporating a reducing agent, such as an aromatic hydrocarbon, into the atmosphere of the chamber during deposition. Other dopants such as niobium, molybdenum, iridium and tantalum compounds, as well as other tungsten compounds, may also be used. The chemical vapor deposition method of the present invention is particularly useful for coating a moving strip of glass, such as in a continuous float glass process. Useful methods and apparatus for chemical vapor deposition are described in U.S. Pat. Nos. 3,850,679 and 3,951,100, the contents of which are hereby incorporated by reference. Different atmospheres can be used; oxidizing atmospheres such as air, inert atmospheres such as nitrogen or argon and reducing atmospheres such as forming gas or other mixtures of inert gas and reducing agent. Other coating methods, such as vacuum deposition, can be used. The thermochromic V02 films are preferably used in window units with a plurality of panes for solar energy control by variable transmittance of infrared radiation.

A preferred multi-glass unit configuration is described in US-A 3,919,023, the contents of which are hereby incorporated into the present text.

The scope of the present invention is defined by the following claims.

Claims (14)

/ 0 461 980 PATENT CLAIMS A process for the chemical vapor deposition of vanadium oxide films, characterized in that: a. Heating a glass substrate to a sufficient temperature for the conversion of an organovanadine compound to vanadium oxide; b. vaporizes a liquid organovanadine compound; c. contacting a surface of the heated glass substrate with the steam of said vanadium compound to deposit a vanadium oxide film on the glass surface. A process according to claim 1, characterized in that the vanadium compound is vanadium isopropylate. 3. Process according to claim 1 or 2, characterized in that the glass substrate is coated with a primer layer selected from the group consisting of tin oxide, silicon and titanium oxide before the chemical vapor deposition of vanadium oxide. 4. A process according to claim 2 or 3, characterized in that the vaporized vanadium isopropylate is brought into contact with the glass surface in a non-oxidizing atmosphere and that a thermochromic film containing VO 2 is formed. p Process according to one of Claims 1 to 3, characterized in that the vanadium compound and the glass substrate are exposed to an oxidizing atmosphere and that a film containing VZOS is formed. The method of claim 5, characterized in that the V 2 O 5 coated glass is further exposed to a reducing atmosphere to reduce V 2 O to V 2 O 2. 7. A process according to claim 1, characterized in that the organovanadine compound is vanadium n-propylate. A method according to claim 7, characterized in that the vanadium oxide coated glass is exposed to a non-oxidizing atmosphere and that an electrically conductive film containing vzos is formed. \ 9. A method according to any one of the preceding claims, characterized in that the vanadium oxide film is deposited to a thickness of from about 100 to 1500 Angstroms. Process according to Claim 1, characterized in that the glass substrate is heated to a temperature of at least about 350 ° C, in that the liquid organovanadine compound is vanadium isopropylate, in that the evaporated vanadium isopropylate is transported to the glass surface and contacting it therewith in a non-oxidizing atmosphere and cooling the vanadium oxide coated glass in a reducing atmosphere to obtain a thermochromic film containing VO 2. A process according to claim 1, characterized in that the glass substrate is heated to a temperature of at least SOOOC, that the organovanadine compound is vanadium isopropylate; that the vaporized vanadium compound is transported in an inert gas, and that the vanadium oxide coated glass is cooled in air to obtain a film containing V 2 O 5. 12. A method according to claim 11, characterized in that VZOS is reduced to VO 2 in a reducing atmosphere. Process according to claim 1, characterized in that the organovanadine compound is vanadium n-propylate, and that the evaporated vanadium n-propylate is transported to and brought into contact with the glass surface in an atmosphere sufficiently oxidizing to form a film of V02 but insufficiently oxidizing to form a film that is not thermochromic due to the proportion of V205. 14. A process for producing a conductive coated glass part, characterized in that: a. Heating a glass substrate to a temperature of at least about 40,000; b. vaporizes vanadium n-propylate; c. transporting the vaporized vanadium n-propylate to the substrate in a stream of nitrogen; d. contacting a surface of the heated glass substrate with the vaporized vanadium n-propylate to deposit a film containing V 2 O 3 thereon; and e. cooling the coated glass particle in an atmosphere that is insufficiently oxidizing to convert V 2 O 3 to VO 2.