The invention concerns a cleaning product to clean titanium surfaces and its application in a procedure to clean titanium surfaces such as titanium facades and panels.
The excellent resistance of titanium and its alloys to corrosion is due to the formation of a protective film of oxides, which is continuous, stable and adheres strongly to the surface. Owing to the high affinity of titanium for oxygen, this film of oxides forms spontaneously as soon as a recent cut of the material is exposed to the atmosphere.
The nature, composition and thickness of the layer of protective oxides formed on the surface of the titanium depend on environmental conditions. In most aqueous environments, the oxide formed is TiO2, although also a mixture of TiO2, Ti2O3 and TiO can also be formed. The naturally formed oxide films reach thicknesses of around 10 nm, which are not visible with the naked eye.
Some factors can alter the characteristics and composition of the TiO2 layer, including the temperature or affinity of titanium for certain gases. Also, the presence of contamination or dirt on the metal surface can produce discontinuities in the surface that can give rise to severe localized corrosion processes. In the case of titanium panels used in construction and exposed to aggressive environmental, industrial and urban atmospheres, this type of phenomenon, which alters the surface characteristics of the panels and their composition, has been observed.
Cleaning and surface passivation methods used in normal conditions to eliminate this type of oxide and surface contamination require immersion processes that use different types of solutions. These include acid pickling, electropolishing or mechanical processes. These methods are not viable in panels used for construction purposes owing to their high cost and because they can alter the surface characteristics of the original panels.
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There is, therefore, the need for a new method to clean surfaces containing titanium, such as the titanium panels used in construction, that can help to overcome all or most of the problems described here.
The invention, in general, deals with the problem of providing a method to clean titanium surfaces such as the titanium panels used to build facades.
The solution provided by the invention is based on the development of a cleaning product that includes, separately, (i) a descaling substance, which contains an active agent that acts on the metal surface, composed of a mixture of inorganic acids, and (ii) a fixative, which inhibits and neutralizes the action of the descaling substance, and also in the application of this cleaning product to clean titanium surfaces.
The application of the cleaning product and the cleaning method provided by this invention permit easy and precise cleaning of the titanium surface without damaging it.
This cleaning product and its application to clean titanium surfaces are both the objectives of this invention.
The invention provides a cleaning product, useful for cleaning titanium surfaces, that includes, separately, (A) a descaling or cleaning substance, from hereon called the descaling substance, which contains an active agent that acts on the metal surface, which is composed of a mixture of inorganic acids, and, (B) a fixative or neutralizer, from hereon referred to as the fixative, which inhibits and neutralizes the action of the descaling substance.
More specifically, the cleaning product of the invention corresponds, separately, to:
The composition of the descaling substance consists of water, an active agent and auxiliary agents (thickener, surfactant and indicator), as well as a propellant.
The active agent is comprised of a mixture of nitric and hydrofluoric acid, and acts on the metal surface (Ti), providing the chemical reaction responsible for eliminating the contamination, impurities and oxides. Beneficially, the active agent also has a protective effect to prevent progression of the cleaning chemical reaction on the metal substrate. The active agent, usually added in the form of an aqueous solution, is present in the descaling substance in a concentration ranging from 1 to 20% in weight relative to the total descaling composition. In a specific application, this active agent consists of a mixture of nitric acid and hydrofluoric acid that contains between 1% and 10% in weight of nitric acid compared to the total descaling composition and between 0.1% and 1% in weight of hydrofluoric acid relative to the total descaling composition, and the weight ratio of nitric acid: hydrofluoric acid is 10:1.
The thickener is introduced in the descaling substance as a stabilizer, also giving it viscosity and selected rheological characteristics. As a thickening agent, a water-soluble organic pseudoplastic thickener can be used, for example, of cellulotic type or a natural gum, for example xanthane gum. The thickening agent can be present in the descaling substance in a concentration ranging from 0.1% to 1% in weight relative to the total descaling composition.
The surfactant alters the surface tension of the descaling substance, favoring the formation of foam, stabilization of this substance and dispersion of its components. Potential surfactants include ionic ones (anionic or cationic), in concentrations ranging from 0.1 to 1% in weight compared to the total descaling composition. In one specific application this surfactant is sodium dodecyl sulphate.
The indicator is introduced in the descaling substance to indicate, by a color change, the time of neutralization of the descaling substance applied on the metallic surface by the fixative substance. The indicator is present in the descaling substance at a concentration less than 0.1% in weight relative to the total weight of descaling substance. In one application the indicator used is phenolphthalein.
The water present in the descaling substance can come from the active agent (if the acids present are supplied in aqueous solution) and/or from the auxiliary agents (if these are provided dissolved or suspended in water) and/or from water added to make up the descaling solution.
The descaling substance can take one of several different forms, for example, it can be a foam, gel or a spray gel. Depending on its form of preparation and packaging, the descaling substance may or may not contain a propellant.
The propellant is a substance that provides the packaged descaling substance with a high internal pressure that results in its forced ejection onto the metallic surface to be cleaned. The propellant can be a liquated or compressed gas.
Liquated gases are substances that are liquid at ambient temperature, due to the effect of pressure, and that become gaseous at atmospheric pressure. At a specific temperature, the high working pressure is constant and equals the vapor pressure of the liquated propellant. Vaporization of the propellant into the atmosphere favors spray formation or conversion into fine droplets of the non-volatile compounds in solution favoring the formation of microfoams. Examples of liquated gases include hydrocarbons and hydrofluorocarbons (HFC), which can be used at a concentration ranging from 5% to 20% in weight relative to the total descaling composition. In one specific application, the propellant is hydrofluorocarbon identified as HFC 134a (1,1,1,2-tetrafluoroethane).
Compressed gases are substances injected at appropriate pressures that maintain the excess pressure on the surface of the descaling substance in the container, forcing this to the exterior in the same way as an embolus that acts on the surface of a liquid, especially in the case of insoluble gases. As the contents are discharged, the gas occupies an increasingly larger volume, its initial pressure is reduced and, therefore, the initial working conditions change. Nitrogen, carbon dioxide, nitrous oxide and air can be used in appropriate amounts at the required working pressure.
As mentioned previously, the preparation and packaging of the descaling compound depends on the form or type of viscous vehicle concerned. As an example, this descaling compound can take the form of:
The foam and spray gel products are prepared in pressurized containers resistant to acid media, from the following components [active agent, auxiliary agents (in gel form or as an aqueous mixture of thickener, surfactant and indicator), water and gas propellant, in the proportions appropriate to satisfy the percentages defined for the final desired product]. In this case, application of the descaling substance is done, for example, by spraying with a gun, with a maximum interval of 3 hours between filling the container and application of the product, preferably less than 1 hour.
The gel type product is prepared in acid-resistant containers from the following components [active agent, gel or aqueous mixture of auxiliary agents (thickener, surfactant and indicator) and water, in appropriate proportions to satisfy the percentages defined for the final desired product]. In this case, application of the product is done, for example by sponge trowel, with a maximum time interval between filling the container and using the product of 3 hours, and preferably under 1 hour.
The fixative is comprised of a neutralizing active agent that stops the action of the descaling agent, neutralizing it, some auxiliary agents (thickener and surfactant), water and a propellant.
The neutralizing active agent inhibits the action of the acid present in the descaling substance when the fixative is applied to the metallic surface thus reducing the likelihood of a too aggressive attack of the acid on the metallic surface, neutralizing the cleaning product and favoring its collection and elimination. As a neutralizing active agent, a base can be used, generally in the form of an aqueous solution, capable of neutralizing the acid present in the descaling substance. As an example, this base can be an alkaline metal hydroxide, for example, sodium hydroxide, in a concentration of between 1% and 20% in weight relative to the total fixative composition, or trisodium phosphate, in a concentration of between 1% and the maximum permitted concentration relative to the fixative.
The thickener has the same function as mentioned previously relative to the descaling substance. In this case, as a thickening agent, preferentially, inorganic products with a silicate base are used, for example, sepiolite, at a concentration ranging from 1 to 8% in weight relative to the total fixative composition, since this type of thickener can also neutralize the hydrofluoric acid of the descaling substance.
The surfactant fulfils the same function as that mentioned for the descaling substance. The surfactant present in the fixative can correspond to ionic surfactants (anionic or cationic), that can be the same or different to those used in the descaling substance. The surfactant can be present in the fixative in a concentration ranging from 0.1 to 1% in weight relative to the total fixative composition.
The water present in the fixative can either come from the neutralizing active agent (if the base is supplied in aqueous solution) and/or from auxiliary agents (in the case that these are supplied dissolved or suspended in water) and/or of water that is incorporated to make up the volume of the fixative.
The propellant, which can be a liquated gas or a compressed gas, fulfils the same function as that mentioned previously relative to the descaling substance. The propellant present in the fixative compound can be the same as or different to that used in the descaling substance(if this contains propellant). The propellant can be present in the fixative substance in a concentration ranging from 5 to 20% in weight relative to the total fixative composition when the propellant is a liquated gas, for example, a hydrocarbon or a HFC, such as HFC 134a. Alternatively, when the propellant is a compressed gas, for example, nitrogen, carbon dioxide, nitrous oxide or air, this propellant is used, as mentioned previously, in the appropriate quantity at the working temperature required.
The fixative can take any suitable form of presentation such as foam(FF) when the propellant is a liquated gas or in the form of spray gel (SGF) when the propellant is a compressed gas.
Both products (foam and spray gel) are kept in pressurized containers resistant to alkaline media, and are composed of the following components [neutralizing active agents, auxiliary agents (in the form of gel or an aqueous mixture of thickener and surfactant) in proportions that satisfy the percentages defined for the final desired product and propellant gas]. Application of the fixative substance is done, for example, by spraying with a gun, with a maximum interval between filling the container and application of the product of 3 hours, but preferably less than 1 hour.
In one specific application, the invention provides a cleaning product, useful for cleaning titanium surfaces, that also has, separately, the characteristics listed in Table 1.
In one specific application of the cleaning product the composition of which is recorded in Table 1, in the descaling composition the active agent is a mixture of 60%HNO3 and 48% HF, the thickening agent is xanthane gum, the surfactant is sodium dodecyl sulphate, the indicator is phenolphthalein and the propellant (liquated gas) is HFC 134a.
Similarly, in one specific application of the cleaning product the composition of which is shown in Table 1, in the fixative composition, the base is sodium hydroxide, the thickening agent is sepiolite, the surfactant is sodium dodecyl sulfate and the propellant (liquated gas) is HFC 134a.
The cleaning product of the invention is useful for cleaning titanium surfaces, especially, titanium building facades. Therefore, the invention provides a method to clean titanium surfaces that consists of using the cleaning product of this invention. More specifically, this method corresponds to the following stages of:
Stage a) or the descaling stage consists in applying the descaling substance of the cleaning product of the invention, homogeneously over the whole titanium surface to be cleaned, which is preferentially dry. Where necessary, the titanium surface is dried using instruments that do not cause mechanical damage of the metallic surface. Depending on the form of presentation of the descaling substance, this is administered in one way or another. For example, foam descaling substances (FD) and spray gel descaling substances (SGD) are applied using the appropriate spray gun, while the gel descaling substance (GD) is applied with a sponge trowel taking care not to cause mechanical damage of the metallic surface. After applying the descaling substance to the metallic surface this should be left to act for a period ranging from 15 seconds to 10 minutes before applying the fixative.
Stage b) or the fixative stage consists in applying the fixative of the cleaning product of the invention to the metallic surface previously treated with the descaling substance in stage a) ensuring that the surface is completely and homogeneously covered. The fixative as foam (FF) and spray gel (SGF) are applied using an appropriate spray gun. After applying the fixative, this is left to act for 30 seconds to 5 minutes before proceeding to the following stage, confirming beforehand that the active neutralizing agent of the fixative substance has neutralized the acid present in the fixative, indicated by the color change of the indicator, or, alternatively, by the use of pH paper indicator strips.
After the fixation stage, stage c) or the aspiration stage is carried out, in which the previously treated titanium surfaces are aspirated to remove the cleaning products from this previously treated surface. This aspiration is applied carefully using the appropriate equipment to avoid producing chemical or mechanical damage to the metallic surface.
Finally, after aspiration, step d) or the rinsing is carried out, in which a water jet at a temperature between 5 and 30°C is applied to eliminate the remains of products used in previous stages.
In one specific application, the titanium surface to be cleaned is a titanium building facade or titanium panels to be used for the construction of facades.
The following example illustrates application of the invention and should not in any way be considered to limit its scope of application.
Several cleaning products were prepared with formulations included among the compositions recorded in Table 2.
Both the descaling substance and the fixative are prepared and packaged in foam form by incorporating different compounds in the desired amounts.
Titanium panels will be cleaned using cleaning products prepared according to Example 1.1. This will be done by following the protocol described below:
The cleaning products tested showed their efficacy at cleaning the treated titanium panels.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.