RU2054596C1 - Fluorescent material and method of preparation of impregnating solution - Google Patents

Abstract

FIELD: incandescent lighting engineering. SUBSTANCE: fluorescent material is formed by mixing the zirconium oxide, calcium oxide and ceric oxide at the following percentage in moles: zirconium oxide, 75 to 87; calcium oxide, 12 to 24; ceric oxide, 1 to 1.5. Fluorescent material may contain one of oxides of chemical elements of the lantanide series: holmium oxide, thulium oxide, erbium oxide or mixture of these oxides. Percentage of each oxide ranges from 0.05 to 0.3 and total percentage of their mixture ranges from 0.1 to 0.3. Method consists in solving the zirconium oxide, calcium oxide and ceric oxide forming the solution of preset concentration; salts are dissolved in aqueous solution of hydrochloric acid at concentration of 0.05 in moles of hydrogen chloride. Salts are dissolved in sequence corresponding to descending order of their concentration in the solution. EFFECT: enhanced efficiency. 4 cl

Description

 The invention relates to light-glowing technology and can be implemented in the manufacture of glow grids used in kerosene, alcohol and gas lamps light sources.

 Known luminescent materials (luminoform), the preparation of which is based on impregnation with a mixture of substances of an organic base, which is a knitted stocking, the knitting of which is made from cotton or viscose yarn.

 When firing a heating net in fuel vapor, its organic base burns out. The substances used for impregnation (usually acid salts) are converted to oxides and sintered to form a thermoluminescent material in the form of a sufficiently strong and ductile ceramic frame that reproduces the pattern of knitted knitting.

 When heated in the products of fuel combustion, the framework of the glow grid emits bright light, the spectrum of which is usually somewhat shifted to the infrared region.

 To ensure high performance, the heating grid must meet the following requirements: have high thermoluminescent properties; Do not collapse in the entire range of operating temperatures; be resistant to mechanical stress in the form of shock and shock, which inevitably occur during operation.

 At the initial stage of the development and creation of luminescent materials, radioactive elements such as; thorium, uranium, and moderately toxic strontium in combination with insignificant additives of rare earth elements, for example, cerium, yttrium, lanthanum, praseodymium, etc. Rare earth elements acted as original “activators” that significantly increased the energy of light radiation and at the same time added a certain color shade to the emitted light.

 Glow nets containing radioactive elements are known (see German patents CL 26, 4-1 N 92021, 1896, N 117755, 1899, N 74745, 1900, N 41945, 1900, etc.

 Around the same time, luminescent materials without radioactive elements were found (see German Patents, CL 26, 4-1 N 39162, 1885, N 66117, 1891; N 218333, 1909).

 However, to date, the most widespread are nevertheless precisely the "thorium" glow networks, which possess light radiation that is unsurpassed in strength.

However, the "thorium" glow grid has the following disadvantages:
1. Radioactivity in the form of α-radiation. It is known that when a substance with α-radiation enters the body, it is approximately 1000 times more harmful than γ-radiation (Nekrasov B.V. Fundamentals of General Chemistry, vol. 2, p. 532, M. Chemistry, 1973).

 2. The ionizing effect of α-radiation. It causes, respectively, β- and γ-radiation of other substances. In addition, the radioactive decay products of thorium also have β- and γ-radiation.

 3. During the operation of a glow lamp together with the products of fuel combustion, although in small amounts, radon gas is radioactive.

 4. The global consumption of thorium in the production of glow gauzes is measured in tens of tons. A failed heat network is usually thrown away, which leads to a gradual dispersion of thorium and an increase in the general radiation background.

 These shortcomings prompt manufacturers of heating systems to look for other thermoluminescent materials that do not contain radioactive elements. Unfortunately, to this day there are no theoretical developments that allow “designing” thermo-luminescent material with predetermined properties. This is usually done experimentally.

 More than 100 years of experience in the development of such materials has identified a range of non-radioactive substances suitable for use in glowing grids. These include oxides: zirconium, aluminum, calcium, chromium, manganese, vanadium and other substances, in combination with oxides of rare earth elements. Moreover, not only the mutual combination of some substances with others is of great importance, but also their strict proportional composition, which determines the color shade, the strength of the emitted light and the mechanical strength of the framework of the glow grid.

 The methods for preparing the impregnating solutions are almost identical and consist in dissolving the salts of the elements in solvents.

 Among recent developments, US Pat. No. 4,533,317, cl. 21 Н 3/00, where yttrium, aluminum, manganese and cerium oxides are used, as well as French patent N 2518218, 21 Н 1/02, 3/00, 1981, where zirconium and calcium oxides are used as the basis for the thermoluminescent material, and a method for producing an impregnating solution is proposed. This patent is selected as a prototype.

 In accordance with the first paragraph of the prototype formula, the luminescent material is composed of an oxide mixture and contains in gram molecules: 75.90% zirconium oxide, 10.25% calcium oxide, 0.5% aluminum oxide, 0.1% of all, one or more oxides of iron, manganese, praseodymium or cerium.

 A method of preparing an impregnating solution consists in dissolving in water salts of zirconium, calcium, aluminum and one or more substances: iron, manganese, praseodymium, cerium.

 The authors conducted an experimental verification of the luminescent properties of the proposed material and the method of preparation of the impregnating solution, as a result of which the following was established.

 All versions of the luminescent material, with the exception of material with the addition of magnesium oxide, ensure reliable operation of the framework of the glow grid. Even a slightly greater thermo-mechanical resistance was recorded than that of a framework based on thorium oxides. However, the framework of a luminescent material with the addition of magnesium oxide, as a rule, is destroyed during the first few minutes of operation. In cases of destruction of the frame with magnesium oxide, attention is also paid in the patent.

 The main and significant drawback of the luminescent material stated in the patent is that all variants of its composition are significantly inferior to the "thorium" material in terms of the energy of light radiation.

 The discovered discrepancy between the patent data and the results of the experimental verification is due to the fact that the authors of the patent compared the luminescent properties of the proposed material with pure thorium material in the form of 100% thorium oxide.

At the same time, it is known that thorium luminescent materials necessarily contain activators, for example, cerium oxide CeO ₂ . Consequently, the comparison was made with “thorium” material, which has obviously worse luminescent properties.

 The disadvantage of the proposed method for the preparation of an impregnating solution is that all impurities contained in the starting chemicals enter the solution and then into the composition of the luminescent material. In this case, we mean impurities of iron, which, having fallen into the composition of the luminescent material, give a reddish tint to the emitted light.

 Thus, the known bestorium-free luminescent materials are characterized by low radiation intensity, and the methods for producing impregnating solutions do not provide the optimal composition of the resulting phosphor.

 The aim of the invention is to obtain a phosphor with higher luminescent properties.

 The technical result that can be obtained by carrying out the invention is to increase the energy of light radiation and the exclusion of a red tint from the emitted light.

 The essential features of the luminescent material common with the prototype are: the content of zirconium oxide in the mixture is 75.87%; the content of calcium oxide is 12-24%; the presence of cerium oxide in the mixture.

 Salient features of a method for preparing an impregnating solution common with the prototype are: dissolution of zirconium, calcium and cerium salts with the formation of a solution of a given concentration.

 The essential features of the material, distinguishing from the prototype and sufficient in all cases, are: the content of cerium oxide in a mixture of 1-1.5% (gram-molecular).

 The essential features of the method, distinctive from the prototype and sufficient in all cases, are: dissolution of salts in an aqueous solution of hydrochloric acid with its concentration in moles of hydrogen chloride of 0.05-0.15.

The essential features of substances that are distinguishing from the prototype and sufficient in particular cases of its implementation are: the presence in the mixture of one or more of the oxides of the chemical elements of a number of lanthanides: holmium, thulium, erbium; the content of each oxide is 0.05-0.3%; the total content of the mixture of these oxides in the luminescent material is 0.1-0.3%
Salient features of the method, distinctive from the prototype and sufficient in particular cases of its implementation, are: the consistent dissolution of salts in the order of decreasing their concentration.

 A causal relationship between the set of essential features and the technical result achieved is as follows: increasing the cerium oxide content from 0-1% in the prototype to 1-1.5% in the proposed phosphor promotes the excitation of resonant vibrations of phosphor atoms, in connection with which it increases light return. Obviously, for the “tuning” into resonance, it is extremely important to have a well-defined percentage of the “activator” and within rather narrow limits.

 Oxides of holmium thulium, erbium, and mixtures thereof have a similar effect on light output.

In addition to the above, the intensity of light radiation is favorably influenced by the combination of emission spectra and absorption of substances included in the proposed phosphor composition;
The zirconium-calcium mixture, which is the basis of the phosphor, has a stable cubic crystal lattice such as CaF ₂ fluorite. Such a crystalline structure is not susceptible to phase transitions in the operating temperature range of the heating network and therefore ensures its reliable operation (under the editorship of A. Mendelkorn, “Nonstoichiometric Compounds”, M. Chemistry, 1971; Kolong. Nestochiometriya, M. Mir, 1974). The use of an aqueous solution of hydrochloric acid with a concentration of 0.05-0.15 hydrogen chloride in moles makes it possible to remove iron compounds from the phosphor due to the conversion of iron contained in chemical impurities into compounds with chlorine and its subsequent evaporation during firing grids. Successive dissolution of salts in decreasing order of their concentration in the impregnating solution eliminates the negative effect of hydrochloric acid on salt concentration.

The proposed substance contains oxides of zirconium, calcium and cerium with their content (gram-molecular percent), respectively: 75-87, 12-24, 1-1.5. In addition, the substance may contain oxides of the chemical elements holmium, thulium, erbium, or a mixture of these oxides. When the content of each oxide is 0.05-0.3% and with a total content of their mixture in the luminescent material 0.1-0.3%
The substance can be obtained as follows (for example, the manufacture of a heating grid, glow lamps).

 First of all, a solution is prepared, for example, aqueous, hydrochloric acid and nitric salts of the above chemical elements. A knitted “stocking” knitted from cotton or viscose yarn should be prepared in advance. The base of the mesh is placed in a solution and, after impregnation, dried in air. The resulting glow grid is fired in fuel vapor, directly on the glow lamp. During firing, the organic basis of the mesh burns out, and the substances used during its impregnation pass into oxides and, sintering, form a luminescent material.

 The method is as follows. Prepare an aqueous solution of hydrochloric acid with a concentration in moles of hydrogen chloride of 0.05-0.15. Salts of zirconium, calcium and cerium are dissolved in the specified solution to achieve from a given concentration.

 These salts are dissolved sequentially in order of decreasing concentration.

 It is known that the red tint in the light emitted by the phosphor is in particular caused by the presence of iron compounds (oxides). Iron as an impurity is present in all chemicals, without exception. In the production of glowing nets, affordable and relatively cheap technologically pure chemicals are used. Such chemicals contain a sufficient amount of iron impurities to give a red tint to the emitted light.

 In this regard, iron compounds are removed from the phosphor, for which the following method is used.

When preparing an aqueous solution for the impregnation of glowing grids, a predetermined amount of hydrochloric acid was introduced into it. In this case, the iron present in the solution combines with chlorine. When firing a potassium grid, iron and chlorine compounds having a boiling point of 1012 ^о С (FeCl ₂ ) and 315 ^о С (FeCl ₃ ) evaporate.

 Thus, the presence of iron compounds in the finished phosphor is sharply reduced.

 Hydrochloric acid, introduced into the solution, also reacts with compounds of zirconium, calcium and cerium. In this case, the main components of the solution are consumed and their concentration changes. For a component having a concentration in the mixture from 20 to 80%, this effect is small and can be neglected. However, for components with a low concentration, treatment with hydrochloric acid can lead to a sharp decrease in their content. The negative effect of hydrochloric acid can be reduced in two ways: by increasing the concentration of substances in the initial solution or by applying the method of sequential dissolution. The last way is preferred and is carried out as follows.

 Since all chemical compounds used in the preparation of the impregnating solution have approximately the same degree of purity, a larger amount of iron impurities enters the solution with the reagent that has a large initial concentration. In this regard, the solution of this reagent should be primarily treated with hydrochloric acid. To this end, in the preparation of the impregnating solution, the reagents do not dissolve in water, but in a previously prepared aqueous solution of hydrochloric acid of a given concentration and in the order of decreasing their concentration in the finished solution.

 The experiments allowed us to establish that when the radiation intensity of the prototype is approximately 7-16 mA, the radiation intensity of the proposed phosphor is from 16.4 to 20.6 mA, which is at least 30% higher than the similar indicator of the prototype.

 In addition, a red tint is excluded from the emission spectrum.

 Thus, the developed luminescent material and the method for producing an impregnating solution make it possible to obtain an environmentally friendly phosphor having the highest emissivity and a radiation spectrum favorable for the human eye.

Claims (4)

 1. Luminescent material, consisting of a mixture of zirconium, calcium and cerium oxides, and the percentage in gram molecules is: zirconium oxide - 75 - 87%, and calcium oxide - 12 - 24%, characterized in that the percentage in gram molecules the cerium oxide content in the mixture is 1-1.5%.  2. The material according to claim 1, characterized in that it additionally contains one of the oxides of chemical elements of a number of lanthanides: holmium, thulium, erbium, or a mixture of these oxides when each oxide contains 0.05-0.3% of each oxide and the total the content of their mixture in the luminescent material is 0.10 - 0.3%.  3. The method of preparation of the impregnating solution, which consists in dissolving the salts of zirconium, calcium and cerium with the formation of a solution of a given concentration, characterized in that the salts are dissolved in an aqueous solution of hydrochloric acid with its concentration in moles of hydrogen chloride of 0.05 - 0.15.  4. The method according to claim 3, characterized in that the salts are dissolved sequentially in the order of decreasing their concentration in the solution.