Patent Application
20110228265
The present invention provides a method of determining whether an aqueous solution is in the solid or the liquid phase.
To be more precise, the present invention relates to a method of determining the liquid or solid state of a substance containing at least a possibly minimal quantity of water.
There are very numerous and highly diverse situations in which it is important to know whether a substance containing at least a minimum quantity of water is in the solid state or the liquid state or, to be more precise, whether the portion of water contained in the substance is in the liquid or the solid state, or possibly whether that water is in a transition state between the solid state and the liquid state.
One field in which making this determination is particularly important is that of monitoring the state of roads during winter.
It is well known that, during periods in which below-freezing temperatures may occur, the competent services responsible for the roads make use of aqueous solutions of sodium chloride at higher or lower concentration, or, more rarely, aqueous solutions of other salts.
After this spreading, it is important for the competent services to be able to check periodically that the aqueous solution remains in liquid form in order to prevent the risk of ice or frost forming on the road.
It goes without saying that the risk of frost or ice forming varies greatly from one road area to another. Thus, it is very important, especially for road safety, to detect whether the spread aqueous solution has locally changed to the solid state.
Clearly, manual or visual checking for the possible occurrence of such a situation is laborious, costly, and random.
Checks that are purely statistical or too localized in the geographical sense run the risk of leaving portions of the road that are very dangerous.
Furthermore, when those checks have to be carried out in poor light, visual checking is somewhat ineffective.
Thus, there exists a real need for a technique, particularly, but not exclusively, for checking the state of roads in winter, making it possible to determine the solid or liquid state of a substance containing water, in particular, by means that do not rely on visual observation, manual checking, or making a measurement that is geographically too localized or not representative of a route.
The first object of the invention is to provide a method of determining whether an aqueous solution, or, more generally, a substance containing water, is in the solid or the liquid phase and to provide a method that satisfies the conditions set out above.
To achieve this object, the method of the invention for determining the solid/liquid phase of an aqueous solution is characterized in that it comprises the following steps:
a) subjecting said aqueous solution to a beam of photons;
b) recording the Raman spectrum of the photons scattered by said solution in the wave number range 2500 per centimeter (cm−1) to 4000 cm−1; and
Clearly, the means for implementing the method comprise only a source of photons, a Raman spectrometer, and information processing means.
As a result of this, there need not be any contact between the means for implementing the method and the substance of phase that is being determined.
Another result of this is that all of the means for implementing the method may be moving relative to the substance to be checked or relative to a support on which the substance is located.
A final result of this is that such determination can be undertaken regardless of the conditions external to the substance.
In the situation referred to above of checking the state of a road, all of the necessary means may be onboard a vehicle moving along the road.
When checking frozen food products, the food products may be located on a conveyor belt, or the like, with the means for implementing the method being stationary.
In a preferred implementation of the method, to implement the step c):
In one implementation of the method, to implement the step c):
In a first implementation of the method, the phase determination method is characterized in that, in order to determine the reference curve of said phase ratio:
In a second implementation of the method, the phase determination method is characterized in that in order to determine the reference curve of said phase ratio:
The phase determination method is preferably characterized in that said two specific wave numbers are chosen so that one of said wave numbers is chosen in the sub-range of wave numbers corresponding to symmetrical stretching of the OH bonds and the other in the sub-range of wave numbers corresponding to asymmetrical stretching of the OH bonds.
The method may be applied to a large number of aqueous solutions including, in particular, a chloride, an acetate, a formate, urea, or a mixture of some or all of these salts.
More generally, the invention applies to any substance producing an anion when it is dissolved in water.
A second object of the invention is to provide the application or use of the above-defined method in its different variants for determining the state of a road.
The benefit of such a method of checking is explained above.
A third object of the invention is to provide the application or use of the above-defined method to checking the frozen state of food products, notably, but not exclusively, food products producing brine.
By checking the solid or liquid phase of the water contained in the food product, it is possible to determine its frozen state. This is made economically and technically possible, in particular, by the fact that the method is non-destructive and may be effected through the packaging of the food product.
A fourth object of the invention is to provide the application or use of the method for the purpose of detecting the occurrence or the presence of ice in a pipe transporting a substance containing at least a fraction of water.
Other features and advantages of the invention become more apparent on reading the following description of several embodiments of the invention given as non-limiting examples.
The description refers to the appended figures, in which:
As explained above, the method of the invention uses Raman spectrometry.
This technique is well known in itself and thus need not be described in detail.
It suffices to outline its general principle.
When a sample is subjected to a monochromatic electromagnetic wave, a small part of the light is scattered.
Frequency analysis of the scattered light shows up a component of the same wavelength as the incident light (elastic scattering) and a component comprising wavelengths different from the incident beam (inelastic scattering).
It is this second component that is used in Raman spectrometry. The Raman spectrum of the scattered beam is characteristic of the medium to which the electromagnetic beam was applied.
The method of determining the solid or liquid phase of a completely identified aqueous solution is described below.
Implementing the method includes a preliminary step of constructing a reference curve followed by a step of determining the real liquid or solid phase of the substance to be tested.
The total range PL of wave numbers, which extends from 2500 cm−1 to 4000 cm−1, may be divided into two sub-ranges PL1 and PL2 respectively corresponding to symmetrical stretching of the OH bonds of water, which is representative of the solid state, and asymmetrical stretching of the OH bonds of water, which corresponds to the liquid state.
A first wave number S1 in the sub-range P1 and a second value S2 in the sub-range P2 are chosen.
The discrimination that can be made based on the reference curve is improved by choosing the pair of wave numbers S1 and S2 appropriately.
To the wave numbers S1 and S2, there correspond points P1 and P2 on the curve S. There is associated with each point P1 or P2 a magnitude representative of its Raman intensity. This may be the intensity itself I1 or I2, or the area A1 or A2 between the curve S and the abscissa axis for a limited curve portion around the point P1 or P2. The phase ratio Rp between these representative magnitudes is then calculated.
The same operation is effected for different temperatures in the range of temperatures concerned.
A reference curve CR(T) may be drawn by plotting temperature T along the abscissa axis and the phase ratios Rp up the ordinate axis.
In this figure, it can be seen that the curve CR includes a first part Z1 corresponding to the solid state, a second part Z2 corresponding to the liquid state, and an intermediate portion Z3 corresponding to the solid/liquid transition.
For the curve CR1, Rp was determined by calculating the ratio of the areas A1 (3,080 cm−1 to 3,200 cm−1) and A2 (3,300 cm−1-3,420 cm−1). For the curve CR2, Rp was calculated from the areas A1 (3,080 cm−1-3,200 cm−1) and A2 (3,350 cm−1-3,500 cm−1).
For the curve CR3, Rp was calculated from the intensities I1 and 12 respectively corresponding to S1=3,135 cm−1 and S2=3,425 cm−1.
Note that whatever method is used to determine the reference curve, all the curves obtained are of the same general shape.
After establishing the reference curves CR corresponding to the aqueous solution to be tested and the range of temperatures concerned, the liquid or solid phase of the aqueous solution is determined in situ by recording the Raman spectrum for that solution. From the recording of that spectrum, the phase ratio Rp specific to the solution is calculated, naturally while using the same parameters as were used to establish the reference curve CR (same values of S1 and S2, use of intensities or areas).
By plotting the value of the phase ratio Rp determined in this way on the reference curve CR, it is possible to deduce whether the aqueous solution is in the liquid phase, the solid phase, or the transition phase.
In the above description, the different steps of the method of determining the phase of an aqueous solution are explained.
The method includes a preliminary step of preparing the reference curve CR and a measurement step as such linked to the example of an aqueous solution of phase that is to be determined.
The preliminary step does not require access to the example to be tested. It suffices to have available a sample of aqueous solution identical to the solution that is to be tested.
Where the determination step as such is concerned, this requires only acquisition of the Raman spectrum of the sample for testing followed by mathematical and logical processing of the acquired spectrum. This therefore requires no contact with the aqueous solution for testing, nor any particular conditioning of the solution.
The method of the invention is therefore highly flexible in use.
By way of non-limiting example, there follows a description of equipment for determining the phase of an aqueous solution of de-icing substances (for example, NaCl) spread over a road.
As shown in
The instrumentation may comprise a laser source 20 and a Raman spectrometer 22 connected to the optical fibers 16. The spectrometer 22 sends information to a processor unit 24, which information corresponds to the successively established Raman spectra. The information capture instants may be generated automatically by the processor unit 24.
The processor unit 24 is associated with a memory 26 for storing data relating to the reference curve CR, the wave numbers S1 and S2, and software for processing received Raman spectra.
For each received spectrum, a phase ratio Rp is calculated and the reference curve is compared to the calculated phase ratio Rp in order to deduce the phase of the aqueous solution. A display screen 28 enables the operator to view the results. These results may equally constitute control data for another device or method and may thus feed into the control loop of those devices or methods.
Of course, uses of the method may be envisaged other than those referred to above. It suffices that they rely on determining the solid or liquid phase of a substance, in particular an aqueous solution, provided it contains a sufficient quantity of water.
As indicated above, the method may be applied to very numerous salts in aqueous solution in the sense defined above.
To illustrate these possibilities,
| Number | Date | Country | Kind |
|---|---|---|---|
| 0857090 | Oct 2008 | FR | national |
This is a 371 national phase application of PCT/FR2009/051976 filed 16 Oct. 2009, claiming priority to French Patent Application No. 0857090 filed 17 Oct. 2008, the contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR09/51976 | 10/16/2009 | WO | 00 | 5/31/2011 |
