Synthesis for ancient blue pigments and in particular Egyptian Blue and Han Blue

Description

Description of the Industrial Invention having for title: “SYNTHESIS FOR THE ANCIENT AND IN BLUE PIGMENTS DETAIL OF EGYPTIAN BLUE AND HAN BLUE” 5 in the name of: University of Palermo, of Italian nationality, with headquarters in Piazza Marina 61 – 90129 Palermo. Designated Inventors: Saladino Maria Luisa - Armetta Francesco – Lo Bianco Alessandro 10 Filed under no. DESCRIPTION The invention relates to the development of a synthesis method for ancient blue pigments and in especially for Egyptian Blue and Han Blue. 15 Egyptian Blue is historically known for having been one of the first synthetic pigments of humanity, appeared in Egypt during the age of bronze, around 3100 BC and spread throughout the ancient world, also thanks to the presence of Rome 20 in the following centuries, until slowly falling into disused in the Middle Ages. The material was composed of cuprorivaite, which is a copper tetrasilicate and calcium, CaCuSiO , and some phases of silica 4 10 such as cristobalite or tridymite, which can 25 determine a variability in the final color of the material. In the seventh book of De Architectura of Vitruvius reports one of the most detailed ancient recipes for preparing blue cheese Egyptian, where sand was used, as 5 source of silica, and metallic copper which were “cooked” at very high temperatures between the 850 to 950°C. In Egypt, the addition of a mixture of salts called natron, rich in sodium carbonate, was 10 instead used as a flow agent. The pigment was also used for its particular stability over time, so much so that in many finds are found in excellent condition conservation. The stability characteristics in the 15 time, resistance to the action of acids and bases, resistance to high temperatures (~1000°C), the non toxicity, the ability to emit in the infrared with high quantum yields, they made it and it make it a very promising material for various 20 modern applications, from around the world of anti-counterfeiting, to that of bioimaging or of photovoltaics. Today's summaries predict a quality better in the choice of reagents and the possibility 25 to have ovens and muffles available that allow for better control of the synthesis and so the final product, although always in the range temperature 850÷950°C and treatment times greater than 10 hours. These conditions make the 5 quite expensive pigment, with a price that varies between 1400 and 1900 euros per kilogram. Similar to Egyptian Blue, Han Blue, also known as Chinese Blue, is an ancient material originally from China, used as a pigment since 10 since ancient times. Han Blue was used in production of inks and paints, contributing to the richness and diversity of colors in the Chinese artwork. It was used in ancient China during the Warring States Period (475- 15 221 BC) until the end of the Han Dynasty (206 BC-220 AD), from which it takes its name. It was first discovered on ancient Chinese artifacts from Fitzhugh in 1983. The blue of Han is a double-layered barium copper silicate, 20 BaCuSi O of Effenbergerite crystalline structure, 4 10 structurally similar to the CaCuSiO present in 4 10 2+ Egyptian Blue, containing Ba ions instead of 2+ About . Despite these similarities, Han Blue is 25 was developed in China over two thousand years after the Egyptian blue, suggesting an evolutionary history independent. In modern times, numerous researches scientific evidence shows that, in addition to a high chemical and physical stability, has excellent properties 5 emission optics in the infrared range and therefore it is widely used in analysis biomedical, among the imaging techniques Multispectral for archaeology, in optical sensors and in photocatalysis. 10 The synthesis procedure is similar to that of the Egyptian Blue and predicts high temperatures and long treatment times. These conditions make the quite expensive pigment, with a price that varies between 500 and 1900 euros per kilogram depending on the 15 shades of color. The purpose of this invention is to propose a suitable method to reduce drastically the production costs of said Blue Egyptian and Han Blue. 20 The above and other purposes are achieved with a synthesis method and device, respectively compliant with claims 1 and 10. The synthesis method for obtaining pigments of 25 antique blue color, especially Egyptian Blue and Han Blue, whose main components are copper and calcium tetrasilicate respectively, CaCuSiO , and copper barium tetrasilicate, 4 10 BaCuSiO , is a two-step solid-state synthesis: 4 10 5 - phase 1: a first treatment with microwaves; - phase 2; a second treatment in a muffle. The reagents, previously crushed and homogenized in an agate mortar are: - a copper salt [malachite CuCO (OH) ]; 2 3 2 10 - a silicon oxide (SiO ); - a mixture of sodium salts (natron) [mixture comprising sodium sulfate (NaSO), carbonate 2 4 sodium (NaCO), sodium bicarbonate (NaHCO), 2 3 3 sodium chloride (NaCl)]; 15 a carbonate salt. If the carbonate salt is calcium (CaCO ) the The resulting pigment is Egyptian Blue. Instead, if the carbonate salt is barium (BaCO ), the pigment obtained is the Blue of Han. 20 The synthesis device comprises a first crucible in which the reagents are inserted to synthesize said pigments, said first crucible being inserted into a second crucible partially filled with a susceptor, called 25 first crucible being partially immersed in said susceptor and said second crucible being covered with a lid. This methodology involves an initial treatment of the reagents in a microwave oven operating at 5 rated power of 750W for 30-60 minutes; and a second treatment in a muffle at 950°C for 1 now. Since the characteristics of the products obtained are identical to those of the two pigments blue prepared by the conventional procedure, 10 reducing preparation times, this method reduces production costs. Preferred embodiments and variants non-trivial aspects of the present invention form the subject of the dependent claims. 15 It is understood that all claims attached form an integral part of this document. description. The invention solves the main problem, if not the only one, which is to have a high 20 production cost, which is mainly linked to the treatment time that is excessively long. In fact, the pigments are obtained following a microwave treatment for about 30 minutes and a subsequent heat treatment at 950° for 25 approximately 1 hour, with a higher time reduction 90%, maintaining the structure and properties of the similar pigments. Other advantages are the ease preparation and lower energy consumption electric. 5 It will be immediately obvious that one can make countless variations to what has been described and changes (for example relating to materials and operations with equivalent functionality) without to move away from the protection field 10 of the invention, as appears from the claims attached. The present invention will be better described from a preferred embodiment, provided to by way of example and not by way of limitation, with 15 reference to the attached drawings, in which: - FIG. 1 shows a synthesis device in the which reaction of the reagents takes place pigment production. - FIG. 2 shows the synthesis device in 20 a microwave oven with some fire bricks coverage; - FIG. 3 shows the crucible in a furnace muffle. A procedure will be described below 25 suitable for the artisanal production of small amount of pigment. The expert technician of the sector will have no difficulty in transferring to productions on any scale, the concepts that will be expressed. 5 With reference to FIG. 1, with (1) is indicated a device for the synthesis of the following pigments: Egyptian Blue and Han Blue. The said synthesis device (1) comprises a first crucible (2) of alumina in which are 10 reagents (3) inserted to synthesize the pigments. The first crucible (2) is inserted into a second crucible (4) of ceramic, of dimensions larger, partially filled with a susceptor 15 (5) (carbon or graphite), called first crucible (2) being partially immersed in said susceptor (5). The second crucible (4) is, in turn, covered with a ceramic lid (6). For the synthesis of Egyptian Blue, the reagents 20 (3) which are placed inside the first melting pot (2) are: - calcium carbonate (CaCO , ACS reagent, ≥ 99.0% CAS 471-34-1); - malachite (CuCO (OH), Sigma-Aldrich, reagent 2 3 2 25 grade CAS 12069-69-1); - silica gel (SiO , Sigma-Aldrich high purity grade CAS 112926-00-8). These reagents are dosed according to the stoichiometric ratios 1:1:8, homogenized and 5 crushed for 5 minutes using a mortar of agate. To the above reagents is added, as fluxing agent, 50% natron by weight compared to the weight of malachite (Cu CO(OH)), 2 3 2 10 also measured and added to the mixture during homogenization. Natron is a mixture of the following salts sodium (In mole ratio Sodium Sulfate : Sodium Carbonate : Sodium Bicarbonate : Chloride 15 of sodium equal to 1:1.171:1.171:1.750): - sodium sulfate (NaSO , ACS reagent, ≥ 99.5% 2 4 CAS 7757-82-6); - sodium carbonate (NaCO , ACS reagent, ≥ 2 3 99.5% CAS 497-19-8); 20 - sodium bicarbonate (NaHCO , ACS reagent, ≥ 99.5% CAS 144-55-8); - sodium chloride (NaCl, ACS reagent, ≥ 99.8% CAS 7647-14-5). After homogenization, the reagents (3) and the 25 natrons are placed in the said first crucible (2). The synthesis heat treatment follows which is takes place in two phases. Phase 1 - The synthesis device (1) so loaded and covered with said ceramic lid 5 (6) is placed in a microwave oven (10) and surrounded by refractory bricks (11) (FIG 2). The materials contained in the first being crucible (2) non-conductors, do not interact with microwaves and therefore would not heat up if in 10 second crucible (4) was not present said susceptor (5), which interacts with the microwaves heats and, by conduction, heats the first crucible (2). Microwave treatment is conducted in 15 a conventional microwave oven (e.g. Whirlpool Easy Pool) at a nominal power of 150 W for 30-60 minutes and per gram of susceptor. Phase 2 - The powders obtained in phase 1 and contained in the crucible (2) are treated in a 20 muffle furnace (20) at 950°C for 1 hour (e.g. GEFRAN 1001 ME320 220 Volt Temp. Max 1100°C) (FIG. 3). Han Blue is obtained with the same procedure, but replacing the calcium carbonate 25 (CaCO , ACS reagent, ≥ 99.0% CAS 471-34-1) with the barium carbonate (BaCO , ACS reagent, ≥ 99.0% CAS 513-77-9) and using the carbonate ratios barium, malachite, silica 1:1:4. To these reagents natron is then added (50% by weight compared to 5 to the weight of malachite (Cu CO(OH) )). 2 3 2 To carry out a quality assessment of the pigments obtained as described above, the two pigments were also prepared according to the known technique, i.e. by solid-state synthesis 10 which involves mixing the reagents and a heat treatment in a muffle furnace at 950°C for 24 hours. The evaluation result shows that the characteristics of the pigments obtained are similar. 15 It is therefore confirmed that the method according to the invention does not lead to new pigments, but drastically reduces production time, with a very significant reduction in costs production. 20 A preferred form of has been described implementation of the invention, but of course it is subject to further changes and variations within the scope of the same inventive idea. In In particular, experts in the field will find it clear 25 immediately evident numerous variants and modifications, functionally equivalent to the previous ones, which fall within the scope of protection of the invention, as highlighted in the attached claims in which the signs of 5 references placed in brackets cannot be interpreted as meaning to limit the claims themselves. Furthermore, the word “comprising” does not exclude the presence of elements and / or phases other than those listed in the 10 claims. The article "un," "one," or "a" preceding an element does not exclude the presence of a plurality of such elements. The simple fact that some features are mentioned in different dependent claims between them 15 indicates that a combination of these characteristics cannot be advantageously used.

Claims

CLAIMS 1. A synthetic method for obtaining antique blue pigments, in particular Egyptian Blue and Han Blue, the main components of which are respectively copper calcium tetrasilicate, CaCuSi4O10, and copper barium tetrasilicate, BaCuSi4O10, of the type which involves a high-temperature treatment of previously crushed and homogenized reagents, characterized in that said reagents comprise: - a carbonate salt; - a copper salt [malachite Cu2CO3(OH)2]; - ​​a silicon oxide (SiO2); a flow agent being added to said reagents, and that the treatment occurs in two phases: - phase 1: a first treatment with microwaves; - phase 2: a second treatment in an oven at a temperature of 950 °C for a treatment duration of 1 hour.

2. Synthesis method for obtaining ancient blue pigments, in particular Egyptian Blue and Han Blue, according to claim 1, characterised in that said reagents are contained in a first crucible (2) inserted in a second crucible (4), of larger dimensions, partially filled with a susceptor (5).

3. Synthetic method for obtaining antique blue pigments, in particular Egyptian Blue and Han Blue, according to claim 1, characterised in that said flow agent is a mixture of sodium salts (natron), or a mixture comprising sodium sulphate (Na2SO4), sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), sodium chloride (NaCl).

4. Synthetic method for obtaining antique blue pigments, in particular Egyptian Blue and Han Blue, according to claim 3, characterised in that said sodium salts are present in the mixture with the following mole ratios: - sodium sulphate (Na2SO4):(1); - sodium carbonate (Na2CO3):(1.171); - sodium bicarbonate (NaHCO3):(1.171); - sodium chloride (NaCl):(1.750).

5. Synthetic method for obtaining antique blue pigments, in particular Egyptian Blue and Han Blue, according to at least one of claims 1 to 4, characterised in that said phase 1 of the microwave treatment occurs under the following conditions: power: 150 W per gram of susceptor; - duration of the treatment: 30 min.

6. Synthetic method for obtaining antique blue pigments, in particular Egyptian Blue and Han Blue, according to claim 1, characterised in that said phase 2 of the oven treatment takes place under the following conditions: - temperature: 950°C; - duration of the treatment: 1 hour.

7. Synthetic method for obtaining Egyptian Blue pigments, according to claim 1, characterized in that said carbonate salt is a calcium carbonate (CaCO3).

8. Synthetic method for obtaining Egyptian Blue pigments, according to at least one of claims 1 to 7, characterized in that the reagents: - calcium carbonate (CaCO3); - malachite Cu2CO3(OH)2; - silicon oxide (SiO2); are dosed according to stoichiometric ratios of 1:1:

8.

9. Synthetic method for obtaining Han Blue color pigments, according to at least one of claims 1 to 8, characterized in that said carbonate salt is a barium carbonate (BaCOs).

10. Synthetic method for obtaining Han Blue pigments, according to at least one of claims 1 to 9, characterized in that the reagents: - barium carbonate (BaCO3); - malachite Cu2CO3(OH)2; - silicon oxide (SiO2); are dosed according to stoichiometric ratios of 1:1:

4.

11. Synthesis device (1), for obtaining antique blue pigments, in particular Egyptian Blue and Han Blue, according to at least one of claims 1 to 10, characterised in that it comprises a first crucible (2) in which reagents (3) are inserted to synthesise said pigments, said first crucible (2) being inserted in a second crucible (4) partially filled with said susceptor (5), said first crucible (2) being partially immersed in said susceptor (5) and said second crucible (4) being covered with a lid (6).

12. Synthesis device (1), for obtaining ancient blue pigments, in particular Egyptian Blue and Han Blue, according to claim 11, characterised in that said susceptor (5) is carbon or graphite.