Field of the invention

The present invention relates to the elimination of changes in weight mass, in particular of metal weights, where there is a high demand for accuracy, a device for executing this method, and a weight with surface modification for eliminating changes in the mass caused by contamination of the weight.

Background of the invention

The contamination of the surface of weights used in metrology represents a unsolved problem in the field of metrology. Due to the contamination of their surface, the mass of weights and even their primary standards change over time. Changes in their mass, primarily their increase, are only monitored at present and there exists no known method of effectively preventing this because the changes are dependent on many hardly predictable factors. The mass of primary standards is compared and monitored every year. Despite the fact that precise rules apply to the treatment of weights and standards, very often they are contaminated by contact with hands, dust, water, and other impurities. Consequently, the weights must be moved to lower classes of accuracy due to larger deviations from the required nominal value of the mass of the weights. Laboratory staff must then acquire new weights in the required class of accuracy in order to maintain other metrological parameters.

A significant portion of the increase in mass consists of adsorbed organic contamination from the surrounding air. A major problem is not only hydrocarbon contamination but also adsorbed water on the surface of the weight. Contamination on the surface of weights has thus far been impossible to remove. Various methods of removal have been tested, such as heating, laser cleaning, and plasma cleaning. Each of these methods, however, showed considerable disadvantages in the removal of not only the contaminated layer but also of the mass of the weights or the sorption of other contaminants etc., which resulted in changes in the mass of the weights and therefore to reductions in their accuracy.

The invention aims to provide a method for the elimination of changes in the mass of weights which would eliminate the aforementioned disadvantages and would allow for the cleaning of the decontaminated surface of the weights, without affecting the surface layer of the weights, and returning the mass of the weights to their initial nominal value.

Summary of the invention

This task is resolved by the creation of a method for eliminating changes in the mass of weights, in particular of metal weights, caused by the contamination of the surface of the weights. The essence of the invention consists in that the surface of the weight is provided with a photocatalytic layer onto which the impurities are adsorbed, and subsequently with electromagnetic radiation having a wavelength of 0.2 nm to 1000 nm acting on the photocatalytic layer and on the contamination on the surface of the weight During the light exposure of the electromagnetic radiation, a photocatalytic reaction takes place on the photocatalytic layer, during which the inorganic and/or organic impurities are converted into a gaseous phase and removed from the surface of the weight. The weight provided with the photocatalytic layer can then be periodically irradiated and thereby continuously removed of its impurities.

In a preferred embodiment, the surface of the weight with the photocatalytic layer Is acted upon by electromagnetic radiation alternately in doses with lower and higher intensity. The dose intensity of the electromagnetic radiation with lower intensity preferably reaches maximally 50% of the dose intensity of electromagnetic radiation with higher intensity.

In another preferred embodiment of the method in accordance with the invention, the electromagnetic radiation acts alternately in doses with a lower wavelength and a longer wavelength, wherein the energy of the dose of electromagnetic radiation with lower wavelength lies outside the energy values corresponding to the width of the band gap of the photocatalytic layer. The exposure time of the dose of electromagnetic radiation lies in the range of 0.1 seconds to 180 minutes, depending on the degree of contamination of the surface of the weight. The times that the individual doses successively act may be the same length or different lengths.

It is preferred that the electromagnetic radiation acts on the photocatalytic layer of the weight in a vacuum chamber, and that the gaseous phase containing the impurities is discharged out of the vacuum chamber so as not to contaminate the surface of the weight again. The impurities contained in the gaseous phase, in a preferred embodiment of the method in accordance with the invention, is then bound to a getter material which does not release them further. in another preferred embodiment of the method in accordance with invention, the surface of the weight with the applied photocatalytic coating is heated to a temperature of 0 to 400° C. The heating accelerates the photocatalytic reaction process which can then take place over a shorter period.

The subject of the present invention is also a device for executing the elimination of the changes in the mass of weights, in particular of metal weights and of primary standards in the method as described above. The essence of the device consists in that it includes a source of electromagnetic radiation with a wavelength of 0.2 nm to 1000 nm, adapted for acting on weights provided with the photocatalytic layer and contaminated by surface impurities. The source is preferably adapted to generate doses of electromagnetic radiation of varying intensities and varying wavelengths. The device may preferably include a vacuum chamber in which there is disposed a source of electromagnetic radiation and which is provided with an outlet for discharging the gaseous phase with the impurities from the surface of the weight and from the vacuum chamber.

The subject of the present invention is also a design of a weight with surface modification for eliminating changes in its mass caused by contamination of the surface of the weight, especially metal weights or primary standards. The surface of the weight is provided with a photocatalytic layer for eliminating changes in its mass caused by contamination on the surface of the weight. There are many existing photocatalytic layers whose composition and methods of application are known to the expert. These layers may be e.g. TiO2, GaP, ΖrΌ2, CdS, KTaO3, CdSe, SrTi02, ZnO, Nb205 deposited by methods involving ion implantation, vacuum deposition, sputtering, plasma deposition, dipping, or spin coating from liquid precursors. In a preferred embodiment, the photocatalytic layer is fluorescent, which is advantageous in that it indicates the degree of contamination.

The advantages of the invention consist in that the photocatalytic layer on the surface of the weight allows for the regular and technologically simple treatment of the weight during which removal of the surface layer of the weight itself does not occur, thereby not resulting in changes in the mass of the weight. The service life of such weights, specifically highly accurate laboratory weights and primary standards, is thus significantly increased, resulting in cost savings in the purchase of new precision weights.

Examples of the preferred embodiments of the invention

It is understood that the hereinafter described specific examples of the realization of the invention are presented for illustrative purposes and not as a limitation of the examples of the realization of the invention to the cases shown herein. Experts who are familiar with the state of technology shall find, or using routine experimentation will be able to determine, a greater or lesser number of equivalents to the specific realizations of the invention which are specifically described here.

To the metal weight 1, during its manufacture, there is applied a photocatalytic layer 2 of T1O2. The photocatalytic layer 2 is applied as a continuous mass across the surface of the weight 1. The photocatalytic layer is applied using techniques such as e.g. vacuum evaporation, vacuum sputtering, plasma deposition, dipping, or spin coating from liquid precursors. In other examples of embodiments, other photocatalytic materials may be selected to form a photocatalytic layer, such as e.g. TiO2, GaP, ZrO2, CdS, KTaO3, CdSe, SrTiO2, ZnO, or Nb2O5. A layer from ZnO may be created as fluorescent for visual indication of the level of contamination of the weight i. The weight 1, after contamination caused by manual manipulation with the weight 1, is cleaned by the action of doses of electromagnetic radiation 9 after placing the weight 1 into the vacuum chamber 4. The source 7 of the electromagnetic radiation 9, which is by way of example a UV lamp, irradiates the surface of the weight 1 alternately in doses with lower and higher intensity and with higher and lower wavelengths continuously for a duration of 20 minutes. The intensity of the electromagnetic radiation 9 with lower intensity is maximally 50% of the intensity of the dose of electromagnetic radiation with higher intensity. The energy of the dose of electromagnetic radiation 9 with lower wavelength is selected so as to lie outside the energy value corresponding to the width of the band gap of the photocatalytic layer 2, depending on the material of the photocatalytic layer used. The application time of the individual doses of electromagnetic radiation are identical, but in other examples of the embodiment may be of different lengths.

The ongoing photocatalytic reaction decomposes the contaminants into gases that bind to the getter material deposited in the vacuum chamber 4, or the gaseous phase 10 is discharged outside the vacuum chamber 4 where it can also bind to a suitable getter material. The getter material chemically binds or adsorbs the atoms or molecules of the gas and at the given conditions no longer releases them.

Irradiation by electromagnetic radiation 9 starts a photocatalytic reaction. The primarily forming free electron-hole pair and the hydroxyl radicals secondarily formed by contact of the excited photocatalytic molecules and water vapor, or water adsorbed on the surface of the weight 1, decompose the present organic and inorganic substances. The impurities 3 are converted into a gaseous phase 10 and in this gaseous phase 10 are discharged outside the weight 1 and are discharged outside the vacuum chamber 4 through the outlet 8. During the irradiation, the surface of the weight 1 with the coated photocatalytic layer 2 is heated to a temperature of 200° C, which improves the efficiency of the transfer of impurities 3 into the gaseous phase 10.

The weight 1 is treated in a specially constructed device 5. The device 5 is equipped with a source 7 of electromagnetic radiation 9. The source 7 is a semiconductor source, LED, or a UV radiation discharge tube. The source 7 is located in the vacuum chamber 4. In the event that in the vacuum chamber 4 there is only one source 7 of electromagnetic radiation 9, inside it there is located a rotary table 6 for storing the weight 1 during the exposure to the electromagnetic radiation 9 on the photocatalytic layer 2 of the weight 1. The rotation of the weight 1 allows for the uniform exposure of the electromagnetic radiation 9 on the entire surface of the weight 1. The effect of the electromagnetic radiation 9 initiates a photocatalytic reaction which decomposes impurities 3 on the surface of the weight 1. The vacuum chamber 4 is provided with an outlet 8 for discharging the gaseous phase 10. The photocatalytic reaction can also take place in the atmosphere; neither the source 7 nor the weight 1 need be placed in the vacuum chamber 4. In another embodiment of the invention, there may be arranged at least two sources 7 of electromagnetic radiation in the vacuum or reaction chamber 4 to provide irradiation to the entire surface of the weight 1. 1 n this case, it is not necessary to equip the chamber 4 with a rotary table 6. To heat the weight 1 , the vacuum chamber 4 may be provided with a heating coil 11.

Industrial applicability

The method of eliminating changes in the mass of weights according to the present invention can be used for treating the surface of weights, in particular primary standards or precision laboratory weights, and for maintaining them at their nominal value in the requested class of accuracy.

Overview of the positions used in the drawings

1 weight

2 photocataJytic layer

3 impurities

4 vacuum chamber

5 device for executing the elimination of changes in the mass of weights

6 rotary table

7 source of electromagnetic radiation

8 outlet for draining the gaseous phase

9 electromagnetic radiation

10 gaseous phase

11 heating coil