Salt sintering method

Abstract

The present invention relates to a method for sintering a salt of formula Na1-xMgx / 2Cl, where x is a number between 0.001 and 0.5, in order to obtain a part made of said salt, the method comprising the following steps: a) grinding the salt in order to obtain a powder having a particle size less than or equal to that of the salt; b) vibrating the ground powder in a mould; c) compacting the resulting powder at a pressure of between 600 bar and 800 bar in order to form a compacted part; d) heating the compacted part at a temperature of between 600°C and 750°C for a period of between 2 h and 20 h.

Description

[0001] SALT SINTERING PROCESS

[0002] FIELD OF INVENTION

[0003] The present invention relates to a salt sintering process, in particular the sintering of MgCh-doped salt.

[0004] STATE OF THE ART

[0005] Sintering is a manufacturing process widely recognized for its ability to produce solid and homogeneous parts. Used primarily for the manufacture of metal and ceramic components, as well as in artisanal applications such as pottery firing, it relies on the "welding" of powder grains under the effect of heat, promoting their bonding by chemical diffusion and thus ensuring the cohesion of the resulting part.

[0006] However, the application of this technique to unusual materials such as salt remains rare, despite its promising potential. The creation of objects from salt, while aesthetically pleasing and unique, is limited by the objects' low mechanical strength, due to the lack of cohesion between the salt grains. This problem is exacerbated by variations in humidity, making these objects vulnerable outside their original dry environment.

[0007] To date, no industrialized process exists that can overcome these structural defects while fully exploiting the artistic and economic potential of salt as a basic material.

[0008] The invention therefore relates to a salt sintering process to obtain a compact and solid piece of salt over time, resistant to mechanical, chemical and climatic stresses in the context of use.

[0009] SUMMARY The invention relates to a salt sintering process of type Nai- x Mgx / 2Cl, x being a number between 0.001 and 0.5, in order to obtain one piece of said salt, the process comprising the following steps:

[0010] a) grinding the salt to obtain a powder with a particle size less than or equal to that of the salt;

[0011] b) vibrating the ground powder in a mold;

[0012] c) compacting the powder obtained at a pressure between 600 bars and 800 bars in order to form a compacted part;

[0013] d) heating the compacted piece to a temperature between 600°C and 750°C for a period of between 2h and 20h.

[0014] According to one embodiment, the molar doping level of the salt with MgCh is between 1% and 10%, preferably close to 1%, for example, 1%. According to one embodiment, the step of vibrating the ground powder before compaction lasts between 15 seconds and 240 seconds at a frequency between 5 Hz and 60 Hz. According to one embodiment, the compaction step includes imprinting a relief pattern on at least one face of the compacted part. According to one embodiment, the heating step includes three heating sequences:

[0015] a first heating sequence at a temperature below 650°C; a second heating sequence at a temperature between 650°C and 700°C;

[0016] a third heating sequence at a temperature above 700°C.

[0017] In one embodiment, compaction is carried out using a hydraulic press or an isostatic press. In one embodiment, the compacted part has the shape of a disc, cylinder, cube, hollow tube, freeform shape, or parallelepiped. A freeform shape is a shape without a predefined structure, which may be organic, exhibit irregularities, or asymmetries. In other words, any freeform shape consists of continuous curves or surfaces with a generally regular appearance, the shape of which is not governed, a priori, by any particular equation. In one embodiment, the process includes an additional step of shaping the part. In one embodiment, the salt part has a thickness of between 1 mm and 50 mm, preferably between 2 mm and 10 mm. In another embodiment, the salt part has a dimension of between 5 mm and 100 mm, preferably between 10 mm and 50 mm.

[0018] The invention also relates to a piece of salt with the formula Nai- x Mg x / 2Cl, x being a number between 0.001 and 0.5 obtained by the process according to any one of claims 1 to 10.

[0019] DEFINITIONS

[0020] In the present invention, the terms below are defined as follows:

[0021] “Piece of salt” refers to any object made of salt using the process described below.

[0022] DETAILED DESCRIPTION

[0023] All examples and conditional language cited in this document are intended for educational purposes to assist the reader in understanding the principles of disclosure and the concepts brought by the inventor to the advancement of the art, and should be interpreted as not being limited to those specifically cited examples and conditions.

[0024] Furthermore, all statements of principles, aspects, and achievements of disclosure, as well as specific examples, are intended to encompass their structural and functional equivalents. These equivalents include both currently known equivalents and those developed in the future—that is, all developed elements that fulfill the same function, regardless of their structure.

[0025] The present invention relates to a process for sintering salt of formula Nai-xMg^Cl, x being a number between 0.001 and 0.5, in order to obtain a piece of said salt.

[0026] The said sintering process includes in particular the following steps: a) grinding of the salt to obtain a powder with a particle size less than or equal to that of the salt;

[0027] b) vibrating the ground powder in a mold;

[0028] c) compacting the powder obtained at a pressure between 600 bars and 800 bars in order to form a compacted part;

[0029] d) heating the compacted piece to a temperature between 600°C and 750°C for a period of between 2h and 20h.

[0030] This salt sintering process relies on consolidating the cohesion of a granular stack through key steps, from grain preparation to the firing of the resulting piece.

[0031] The first step is to grind the salt to reduce its particle size, improve its homogeneity and facilitate its compaction and stability by promoting better densification and cohesion of the grains during sintering.

[0032] Before firing, vibrating the powder followed by compaction plays a crucial role. Vibrating the salt grains in the compaction mold effectively expels air from the interstices, maximizes contact between grains of varying sizes, and promotes optimal granular packing. Vibration also allows the smaller grains to fill the gaps between the larger ones, improving the internal distribution of the material and ensuring a more uniform surface distribution, thus enhancing the final part's appearance. This step is essential for obtaining a precise and homogeneous part, both in terms of density and shape. The pressure then applied to the salt, ideally exceeding 600 bar, reduces porosity by maximizing the number of contacts between grains of different sizes.

[0033] During heating, chemical diffusion is activated by thermal energy. This diffusion is facilitated by the natural structural defects of the salt, particularly vacancies, which increase at high temperatures. It allows the formation of strong bridges between the grains, consolidating the whole through coalescence. The finer and more compact the grains, the more efficient and rapid the sintering, resulting in a homogeneous, resistant, and less friable final material.

[0034] This process, by combining grinding, vibration, compaction, and cooking of the salt, makes it possible to obtain salt pieces of unprecedented quality, suitable for a variety of uses, ranging from decorative objects to architectural applications. In particular, the resistance of these pieces to mechanical stress and humidity is greatly improved.

[0035] The molar doping level of the salt with MgCh can be between 1% and 10%, i.e., x between 0.02 and 0.2; preferably, the doping level of the salt with MgCh can be equal to 1%, i.e., x equal to 0.02. Such doping advantageously creates more vacancies and facilitates the diffusion of species during sintering. In the case of MgCh doping, the Mg cations 2+ are of higher valence than Na cations + thus two Na cations + are replaced by a Mg cation 2+ and a gap.

[0036] The salt can be sea salt or salt extracted from the Salar de Uyuni in Bolivia. Being naturally rich in MgCh, the latter is particularly well-suited to the sintering process described here.

[0037] The process may optionally contain, upstream of step a), an additional salt doping step, e.g., a salt doping step with MgCh, in order to adjust the salt composition.

[0038] During step a), the salt can be ground using a mortar or a mechanical grinder.

[0039] For example, salt can be ground using a mechanical grinder at 450 revolutions per minute for a period of between 1 minute and 10 minutes, preferably for 3 minutes.

[0040] The particle size class of the ground powder, i.e., obtained in step a), can be that of the "fillers." A particle size class is expressed by the pair d / D or 0 / D, where d is the smaller dimension of the aggregate and D is the larger dimension of the aggregate. The "fillers" class is expressed as 0 / D, with D < 2 mm, with at least 85% passing through 1.25 mm and 70% passing through 0.063 mm. The particle size class impacts the texture and surface appearance of the final part. Thus, the smaller the grain, the smoother the surface texture and the higher the mechanical strength of the final part. When the grain is larger, the surface of the final part is less homogeneous; each grain of salt is individually visible, highlighting its bright, crystalline appearance and revealing a pattern that reflects the grain structure.

[0041] Preferably, the particle size of the ground powder is less than or equal to 0.71 mm.

[0042] During step b), the ground powder can be vibrated before compaction for a period of between 15 seconds and 240 seconds at a frequency between 5 Hz and 60 Hz, preferably between 50 Hz and 60 Hz.

[0043] The compaction mold can be in two parts, i.e., it can include at least an upper part and a lower part. This advantageously allows for easier demolding of the salt piece, reducing the risk of breakage or cracking of said piece during demolding.

[0044] The mold may include at least one identical upper and lower part. Advantageously, this makes it possible to obtain a piece of salt with a uniform surface finish across its entire surface.

[0045] Alternatively, the mold may comprise at least one upper and one lower part that differ in terms of surface relief or surface finish. Advantageously, this makes it possible to obtain a piece of salt having an upper and a lower face, opposite to each other, exhibiting a different surface relief or surface finish.

[0046] The mold can comprise at least four parts, including an upper part, a lower part, and two side parts. Advantageously, this allows for the modulation of the surface finish of at least three faces of the salt piece in terms of different surface relief or surface textures.

[0047] During step c), the powder is compacted preferably at a pressure between 700 and 800 bar. Compaction can be carried out with a hydraulic press or an isostatic press. A uniaxial hydraulic press is advantageous for producing fine salt pieces. An isostatic press allows for compressing a larger quantity of material, up to 1 kg of salt.

[0048] In the case of compaction using a uniaxial hydraulic press, the powder is preferably compacted at a pressure of 800 bars.

[0049] In the case of compaction using an isostatic press, the powder is preferably compacted at a pressure of 700 bar. In this case, a rubber sleeve is filled with ground powder in a predetermined quantity (depending on the desired part diameter). The filled sleeve is sealed and vibrated before being introduced into the press's compression chamber, which contains water. Once the compression chamber is closed, the press is operated until the required compaction pressure is reached. The sleeve is then removed from the chamber, and the part, which will have an elongated cylindrical shape, can be demolded.

[0050] The compacted piece can have the shape of a disc, cylinder, cube, hollow tube, free or parallelepiped.

[0051] At least one surface of the compacted part may have a gloss level belonging to the high gloss, medium gloss, or low gloss class. The gloss of a surface is measured using a glossmeter that measures gloss levels for surfaces without micro-relief, from high gloss to medium gloss to low gloss (at 20°, 45°, 60°, 75°, and 90° angles). A highly polished black glass surface with a defined refractive index and a specular reflectance of 100 UB at a given angle is taken as the reference. This reference is used to establish a maximum calibration point of 100, with the minimum point set at 0 for a perfectly matte surface.

[0052] At least one surface of the compacted piece may exhibit at least one micro-relief, which is described by amplitude parameters between the highest and lowest points, i.e., between a peak and a valley, relative to a reference level that defines micro-hollows and micro-peaks. Such an amplitude can range from 40 pm to 300 pm, preferably between 50 pm and 250 pm. The shape of the micro-peak describes (e.g., plateau, dome, peak) the shape of the valley and the slope;

[0053] The compaction step includes imprinting a raised pattern on at least one face of the compacted part. The relief can be imprinted on at least one face of the compacted part using the compaction mold (one face of which bears the negative of the relief to be imprinted) or a punch.

[0054] When using a punch, after the vibration stage, a punch with the pattern is inserted into the compression mold. The patterned side must be in contact with the salt. The mold is then closed, and the powder is compacted. The punch can be made of a polymer such as polymethyl methacrylate (PMMA). The punch has a diameter equal to that of the part to be manufactured, i.e., equal to the diameter of the compaction mold, and can have a thickness between 1 mm and 10 mm. The embossed pattern is preferably engraved onto the punch.

[0055] The raised motif can be a bas-relief design. A bas-relief design is slightly raised from the flat surface of the piece. This type of design offers the advantage of greater durability, as the motifs are less prone to wear over time.

[0056] Alternatively, the embossed motif can be a high-relief motif. A high-relief motif is much more prominent, projecting significantly from the surface of the piece. The details are more pronounced and dramatic, creating a more striking and artistic visual effect.

[0057] The compacted piece may include a bas-relief motif on one face and a high-relief motif on the opposite face. It may also include a bas-relief or high-relief motif on both faces.

[0058] During step d), the compacted part is heated to a temperature below its melting point, namely 801 °C. Advantageously, this prevents the harmful release of hydrochloric acid that occurs when salt melts in the presence of water vapor, and the evaporation of salt that would deposit on the furnace surfaces and damage the heating elements of electric furnaces.

[0059] Preferably, the compacted piece is heated to a temperature between 630°C and 730°C. Firing at a temperature above 730°C results in a brown discoloration of the underside of the compacted piece. At these temperatures, a settling of the calcinate from the earth contained in the salt is likely to occur.

[0060] The heating stage may include three heating sequences:

[0061] a first heating sequence at a temperature below 650°C, preferably at 600°C;

[0062] a second heating sequence at a temperature between 650°C and 700°C, preferably at 650°C;

[0063] a third heating sequence at a temperature above 700°C, preferably at 730°C.

[0064] Depending on a preferred configuration, the heating stage can include three heating sequences:

[0065] an initial heating sequence at 600°C for 3 hours;

[0066] a second heating sequence at 650°C for 3 hours;

[0067] a third heating sequence at 730°C for 9 hours.

[0068] The process according to the invention may further include an additional step of shaping the part. During this step, the piece of salt can be shaped by various methods such as, for example, cutting (e.g., with a band saw), milling (using a digital milling machine, for example a 3D milling machine), turning, or a combination thereof, so as to obtain a complex shape.

[0069] The invention also relates to a piece of salt with the formula Nai- x Mg x / 2Cl, where x is a number between 0.001 and 0.5, obtained by the process described above. The term "piece" here is a generic term designating any salt object obtained by the described process, for example, a pellet, a cylinder or sausage, or a coin. The salt piece can have a thickness between 1 mm and 50 mm, preferably between 2 mm and 10 mm, and more preferably between 2 mm and 5 mm.

[0070] The piece of salt can have at least one dimension between 5 mm and 100 mm, preferably between 10 mm and 50 mm.

[0071] The piece of salt can have a diameter between 5 mm and 100 mm, preferably between 10 mm and 50 mm.

[0072] The piece of salt can have an average densification of between 75% and 95%, preferably between 85% and 90%.

[0073] The salt coin can be in the shape of a disc, cylinder, cube, hollow tube, free-standing object, or parallelepiped. The salt coin is preferably a disc (also called a pellet).

[0074] The piece of salt may include at least one through hole, preferably in its center.

[0075] In a particular method, the through hole has a diameter between 1 mm and 5 mm.

[0076] The salt coin can be a decorative type object (tableware, furniture...), a functional type object (accessories, containers...) or a monetary type object (coin).

[0077] The salt coin is preferably a coin (also called "jayu").

[0078] The salt cube can be a micro cube of salt usable in cooking as a replacement for pinches of salt.

[0079] The invention also relates to an assembly of pieces of salt linked to each other by joining elements, preferably textile fibers.

[0080] The assembly can be of the articulated orthogonal type. This assembly allows the salt pieces to be positioned in an orthogonal grid. This arrangement is not completely compact. Similarly, the joining elements are not rigid (macrame). This allows for articulated movement between the pieces that make up the object.

[0081] Alternatively, the assembly can be of the hexagonal close-packed type. This assembly allows the parts to be positioned within a hexagonal close-packed structure. This hexagonal assembly is, in turn, a geometric representation of the type of atomic packing in the salt's close-packed structure, giving particular meaning and relevance to salt objects created with this structure. Thus, the object represents, on a magnified scale, the molecular structure of the material from which it was made.

[0082] The arrangement can include patterns created by transparency. A single grain of salt is naturally translucent, even transparent. The arrangement of salt grains within an object results in a material that is more opaque the thicker the object. In this way, an arrangement made with pieces of salt of varying thicknesses can generate patterns or designs when the objects are backlit, patterns or designs that are not visible under normal lighting conditions.

[0083] BRIEF DESCRIPTION OF THE FIGURES

[0084] Figure 1 is a diagram representing the cohesion of the salt grains according to the different stages of the process according to one embodiment.

[0085] Figure 2 is a photograph showing a coin obtained by the sintering process, said coin including a high-relief design on one of its faces.

[0086] Figure 3 is a photograph showing a coin obtained by the sintering process, said coin including a bas-relief motif on one of its faces.

[0087] Figure 4 is a representation of an orthogonal articulated assembly of salt pieces (circles in the figure) linked to each other by joining elements, preferably textile fibers (lines in the figure), each piece having a central through hole.

[0088] Figure 5 is a representation of a compact hexagonal assembly of salt pieces (circles in the figure) linked to each other by joining elements, preferably textile fibers (lines in the figure), each piece having a central through hole. Figure 6 is a representation of an assembly of salt pieces including a pattern seen through the transparency, the gray salt pieces representing pieces of greater thickness than the white salt pieces.

[0089] Figure 7 is a representation of an assembly of salt pieces including a transparency pattern, the grey salt pieces representing pieces of greater thickness than the white salt pieces, and the black salt pieces representing pieces of greater thickness than the grey salt pieces.

[0090] Figure 8 is a photograph showing an articulated orthogonal assembly of salt pieces linked together by textile fibers, each piece having a central through hole.

[0091] Figure 9 is a photograph showing an articulated hexagonal assembly of salt pieces linked together by textile fibers, each piece having a central through hole.

[0092] Figure 10 is a photograph showing two French table salt fritters, one cut with a band saw and hollowed out with a metal lathe (left), the other with a granular outer texture (right).

[0093] Figure 11 is a photograph showing a French table salt frit machined with a digital milling machine.

[0094] Figure 12 is a photograph showing a salt fritter from the Salar d'Uyuni exhibiting folds.

[0095] Figure 13 is a photograph showing "Tunupa", a proof of concept of the robustness of salt sintering in the face of digital milling.

[0096] Figure 14 is a photograph showing different milling stages to form the machined sinter "Tunupa" shown in Figure 13.

[0097] As illustrated in Figure 1, the cohesion of the salt grains increases during the different stages of the process described here: grinding and vibration (El);

[0098] compaction (E2); and

[0099] cooking (E3).

[0100] In an embodiment illustrated in Figure 2, the piece of salt obtained by the process described above may include a high-relief motif on one of its faces. This motif represents the Tunupa volcano as seen from the Salar de Uyuni, with the typical hexagonal structures of the Salar's soil in the foreground.

[0101] Alternatively, in an embodiment illustrated in Figure 3, the piece of salt obtained by the process described above may include a bas-relief motif on one of its faces. This motif represents the Tunupa volcano as seen from the Salar de Uyuni, with the typical hexagonal structures of the Salar's soil in the foreground.

[0102] Figures 4 to 9 represent or illustrate assemblies that can be obtained from salt pieces made using the process described above. The modularity of the pieces and their assembly is particularly advantageous for creating complex objects. The salt pieces can vary in diameter and thickness. For example, the prototype shown in Figure 9 was made with elements 25 mm in diameter and between 4 and 10 mm thick. Each piece has a 3 mm diameter hole drilled in its center, allowing them to be joined using textile techniques such as macrame or tapestry weaving. The hexagonal assembly shown in Figure 9 is compact and therefore more structured for creating objects than the orthogonal assembly shown in Figure 8, which is articulated and gives the final result greater flexibility.Furthermore, as illustrated by Figures 6, 7, by playing on the variations in thickness of the pieces of salt composing the assemblages, it is possible to compose surfaces capable of revealing subtle patterns, perceptible for example when backlit.

[0103] This modular system enables the creation of geometric patterns that are both functional and decorative. The illustrated prototypes should be considered a proof of concept, showcasing both the assembly qualities and the tactile properties of the material. Beyond its decorative aspect, this modular system opens up diverse possibilities: it could inspire creations in the fields of furniture, tableware, textile design, and even surfaces with controlled deformation.

[0104] EXAMPLES

[0105] The present invention will be better understood by reading the following examples which illustrate the invention in a non-limiting way.

[0106] Example 1:

[0107] Commercial salt is compacted without being crushed using a 4-tonne uniaxial hydraulic press, which operates at 800 bars of pressure. The surface is smooth to the touch, but the individual salt grains are visible to the eye. The visible salt grains have a slightly shiny appearance, like micro-crystals.

[0108] Example 2:

[0109] Commercial salt is ground using a mechanical mill at 450 revolutions per minute for 3 minutes: the resulting particle size corresponds to the "filler" category. The ground powder is compacted using a 4-tonne uniaxial hydraulic press, i.e., at 800 bar pressure. The surface appearance is homogeneous, white in color, and smooth and satiny in texture.

[0110] Example 3:

[0111] Salt extracted from the Salar de Uyuni, naturally rich in magnesium chloride (MgCh), is ground using a mechanical mill at 450 revolutions per minute for 3 minutes: the resulting particle size corresponds to the "filler" category. The ground powder is compacted using a 4-ton uniaxial hydraulic press, which operates at 800 bars of pressure. The surface appearance is homogeneous, off-white in color, and smooth and satiny in texture. The difference in color compared to French salt is due to the fact that Salar salt contains small particles of soil, which make it slightly less glossy.

[0112] Example 4: 20 salt tablets with a diameter of 25 mm and a thickness of 8 mm (tablets 1-10) or 4 mm (tablets 11-20) were prepared according to the following process:

[0113] a) grinding of the salt to obtain a powder with a particle size smaller than that of the salt, here a particle size of the class of "fillers";

[0114] b) vibrating the ground powder in a mold for a period of between 15 seconds and 240 seconds;

[0115] c) compacting the resulting powder at a pressure of 800 bar using a uniaxial hydraulic press to form a compacted pellet; d) heating the compacted part according to the following heating sequences:

[0116] a first heating sequence at 600°C for 3 hours; a second heating sequence at 650°C for 3 hours; a third heating sequence at 730°C for 9 hours.

[0117] Densification rate measurements were carried out on these pellets and the results are presented in Table 1 (8 mm thick pellets) and Table 2 (4 mm thick pellets).

[0118] From the measurements of each pellet (diameter, thickness, and weight), the maximum and minimum volume (V) and density (d) of the pellet are calculated. This allows these measurements to be positioned relative to the reference density for pure salt at normal atmospheric pressure (2.161 g / cm³) and thus the percentage densification of each pellet to be calculated.

[0119] Table 1 - Density measurements and calculations for 8mm pellets

[0120]

[0121]

[0122] Table 2 - Density measurements and calculations for 4 mm pellets

[0123]

[0124]

[0125] The results of these calculations allow us to determine an average density of 87% regardless of the thickness of the pellet.

[0126] Example 5: Compressive strength

[0127] 4 mm cubed salt was made from 4 mm thick salt pellets such as pellets 11-20 of example 4 by cutting the lateral faces.

[0128] Compression tests were carried out on these salt cubes: each cube is placed in the center of the compression plate of the Instron 5966 - lOkN machine and then the following conditions are applied:

[0129] Charging speed: 160 Newtons per min

[0130] End of test: 3000 Newtons

[0131] Across all the salt cubes, the maximum compressive stress that the material can withstand ranges between 50 MPa and 60 MPa, or between 510 and 610 kg.cm' 2 .

[0132] It has been observed that when a cube of salt is subjected to this compression, initially the edges of the cube appear to flex slightly and round outwards. Subsequently, no further changes are observed until, upon reaching a compression of 50 MPa–60 MPa, the entire cube collapses, as if, under this compressive stress, the majority of its constituent grains detach and disintegrate.

[0133] The machine, programmed to apply pressure based on the material's response, suddenly encounters no resistance from the material. It descends rapidly, searching for the missing counterforce, and is only stopped by the machine's safety mechanism just before reaching the bearing surface. Example 6: Resistance to Friction

[0134] The friction resistance of the salt pieces was evaluated by a friction test. This test determines the degradation of the salt pieces according to two parameters: time and frequency of friction.

[0135] Frequency is defined as the number of times a periodic phenomenon repeats itself per unit of time. Here, it is the number of times a first piece of salt (a) rubs against a second piece of salt (b) per minute. The pieces of salt are in the form of pellets. The degradation of an imprinted pattern (in low relief and high relief) on one face of a salt pellet is measured at a frequency x over increasing time intervals (1 minute, 4 minutes, and 5 minutes).

[0136] Each first pellet (a) is placed on a support that holds it in a fixed position. A second pellet (b) is placed above it and set in bidirectional rectilinear motion at a constant speed (60 and 120 passes per minute). After each time interval (1 minute, 4 minutes, and 5 minutes), the tested sample is observed, photographed, and any alteration is described and characterized.

[0137] Three tests were carried out at 89% relative humidity:

[0138] a) Rubbing two small discs with high-relief patterns,

[0139] b) Rubbing two small discs with bas-relief patterns,

[0140] c) Rubbing a lozenge with a high-relief pattern and a lozenge with a low-relief pattern.

[0141] Each pair of lozenges was tested at 4 intervals:

[0142] 1. 60 passes per minute

[0143] 2. 60 passes per minute

[0144] 3. 120 passes in 1 minute

[0145] 4,480 passes in 4 minutes

[0146] 5,600 passes in 5 minutes

[0147] The results are shown in Table 3.

[0148] Table 3 - Density measurements and calculations for 8mm pellets

[0149]

[0150]

[0151]

[0152]

[0153] Following the tests, the degradation of the sintered material due to friction remained relatively limited. On the contrary, these tests revealed an interesting and unexpected property of the material: its ability to be polished to a glossy finish. Friction seems to enhance the tested samples, giving them an elegant patina and a visually improved appearance.

[0154] Example 7: Demonstrations of shaping pieces of salt by material removal (cutting, turning, digital milling).

[0155] Large-scale sintering (for example, approximately 1 kg of salt, versus 1 to 20 grams for pellets) produces a homogeneous material in a solid form (or hollow, provided a thickness of at least one centimeter is guaranteed), with a parallelepiped, cylindrical, or slightly conical shape, and a base identical to the apex, the latter possibly being slightly rounded (Figure 1). This initial form exhibits a variety of surface qualities depending on multiple parameters such as: the salt grain size, its moisture content at the time of compression, the type of machining, etc.

[0156] French table salt, characterized by its very white color and a grain size belonging to the family of sands (standard XP P 18-540 indicates the usual terminology of Sands according to their dimensions: Sands 0 / D: D < 1 mm) allows obtaining a homogeneous cylindrical shape with a slightly shiny granular texture on the outside and a smooth and satiny appearance when machined (Figures 1, 2).

[0157] The salt used for crafts from the Salar de Uyuni gives the sintered forms a characteristic slightly pink color. Due to its grain size, which belongs to the filler family (standard XP P 18-540 indicates the usual terminology for fillers according to their dimensions: Fillers 0 / D: D < 2 mm), the resulting sintered form does not have the textured graininess of the French sample, but rather a surface that is both smooth and rough, and matte. The shape of the sample is not as homogeneous, but exhibits folds, giving the material a textile-like, plastic appearance (Figure 3). The homogeneity of the cylinder's shape depends on the moisture content and, consequently, on the absence of lumps present in the salt.The salt from the Salar de Uyuni (from which the sintered salt shown in Figure 3 with folds was made), due to its imperfect storage conditions in the laboratory, absorbed ambient moisture, creating agglomerations of salt grains that we will call "lumps." These lumps make the stacking of the salt grains during compression less orderly and homogeneous, hence the visible folds.

[0158] At this scale, sintered salt can be worked in the same way as soft stone. It can be cut with a band saw, machined on a lathe, or by a CNC milling machine. The possibilities for creating 2D and 3D shapes are similar to the capabilities of material removal processes starting from simple 3D geometric shapes.

[0159] Tunupa is a proof of concept (POC) that tests the feasibility of CNC milling for salt sintering. Using a 3D model of the Tunupa volcano, located on the shores of the Salar de Uyuni, a sample of sintered salt was machined (Figure 4). Figure 5 shows the machining process: a first roughing pass followed by a fine pass. As a precaution, salt residue was vacuumed up as the milling cutter removed material. The main risk in this test was breaking or cracking the material due to contact with the rotating cutter and the inherent vibrations of the process. Not only did the material withstand these risks without breakage or cracking, but a very high level of precision and detail was achieved on the part. The surface is smooth and satin-like, with no material removal. This proof of concept demonstrates that such machining processes are feasible.

Claims

DEMANDS 1. Sintering process of salt of formula Nai- x Mg x / 2Cl, x being a number between 0.001 and 0.5, in order to obtain one piece of said salt, the process comprising the following steps: a) grinding the salt to obtain a powder with a particle size less than or equal to that of the salt; b) vibrating the ground powder in a mold; c) compacting the powder obtained at a pressure between 600 bars and 800 bars in order to form a compacted part; d) heating the compacted piece to a temperature between 600°C and 750°C for a period of between 2h and 20h.

2. A method according to claim 1, wherein the molar doping rate of the salt in MgCh is between 1% and 10%, preferably the doping rate of the salt in MgCh is equal to 1%.

3. A method according to claim 1 or 2, wherein the step of vibrating the ground powder before compaction lasts between 15 seconds and 240 seconds at a frequency between 5 Hz and 60 Hz.

4. A method according to any one of claims 1 to 3, wherein the compaction step includes the impression of a relief pattern on at least one face of the compacted part.

5. A method according to any one of claims 1 to 4, wherein the heating step comprises three heating sequences: a first heating sequence at a temperature below 650°C; a second heating sequence at a temperature between 650°C and 700°C; a third heating sequence at a temperature above 700°C.

6. A method according to any one of claims 1 to 5, wherein the compaction is carried out with a hydraulic press or an isostatic press.

7. A method according to any one of claims 1 to 6, wherein the compacted part has the shape of a disc, cylinder, cube, hollow tube, free or parallelepiped.

8. A method according to any one of claims 1 to 7, comprising an additional step of shaping the part.

9. A method according to any one of claims 1 to 8, wherein the piece of salt has a thickness of between 1 mm and 50 mm, preferably between 2 mm and 10 mm.

10. A method according to any one of claims 1 to 9, wherein the piece of salt has at least one dimension between 5 mm and 100 mm, preferably between 10 mm and 50 mm.

11. Piece of salt of formula Nai-xMg^Cl, x being a number between 0.001 and 0.5 obtained by the process according to any one of claims 1 to 10.

Images