Oxygen-generating compositions comprising thermally treated (Li,Fe,Mg)O

Abstract

The present disclosure provides an oxygen-generating composition comprising an oxygen source and mixed-metal oxide of formula: (Li,Fe,Mg)O, wherein said mixed-metal oxide is in at least partially crystalline form.

Claims

1. An oxygen-generating composition comprising: an oxygen source; and a mixed-metal oxide of formula: (Li,Fe,Mg)O, wherein said mixed-metal oxide is in at least partially crystalline form.

2. The composition as claimed in claim 1, wherein said mixed-metal oxide is a thermally treated oxide.

3. The composition as claimed in claim 1, wherein at least 50% of the mixed-metal oxide is crystalline.

4. The composition as claimed in claim 1, wherein said mixed-metal oxide comprises 0.1 to 1.0 at. % Fe and 0.1 to 1.0 at. % Li.

5. The composition as claimed in claim 1, wherein said mixed-metal oxide is in the form of nano-particles.

6. The composition as claimed in claim 5, wherein said nano-particles have a diameter of less than or equal to 500 nm.

7. The composition as claimed in claim 1, wherein said oxygen source is selected from alkali metal chlorates, alkali metal perchlorates, alkaline earth metal chlorates, alkaline earth metal perchlorates and mixtures thereof.

8. The composition as claimed in claim 1, wherein said oxygen source comprises sodium chlorate and/or lithium perchlorate.

9. The composition as claimed in claim 1, wherein said composition consists essentially of said oxygen source and said mixed-metal oxide.

10. The composition as claimed in claim 1, wherein 90 to 99.9 wt. % of said composition is said oxygen source.

11. The composition as claimed in claim 1, wherein 0.1 to 10 wt. % of said composition is said mixed-metal oxide.

12. A method for generating oxygen, said method comprising decomposing an oxygen source in the presence of a mixed-metal oxide of formula: (Li,Fe,Mg)O, wherein said mixed-metal oxide is in at least partially crystalline form.

13. A chemical oxygen-generator comprising an oxygen-generating composition as claimed in claim 1.

14. The chemical oxygen-generator as claimed in claim 13 wherein said generator comprises a container for containing the oxygen-generating composition and a primer for starting decomposition of the oxygen-generating composition.

15. The chemical oxygen-generator as claimed in claim 13 wherein said chemical oxygen-generator is a chemical oxygen candle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One or more non-limiting examples will now be described, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a flow-chart outlining the method for preparing the mixed-metal oxides of the present disclosure as described further in Example 1.

(3) FIG. 2 shows decomposition of sodium chlorate using thermally treated (Li,Fe,Mg)O, according to Example 2.

(4) FIG. 3 shows decomposition of lithium perchlorate using thermally treated (Li,Fe,Mg)O, according to Example 3.

(5) As shown in FIG. 1, mixed-metal oxides according to the present disclosure can be formed by precipitation. An aqueous solution of Mg(NO3)2.6H2O is prepared by dissolving Mg(NO3)2.6H2O in distilled H2O. A solution of Fe(NO3)3.9H2O is prepared in the same way. The nitrate solutions are concurrently added drop-wise to a stirred ammonia solution while keeping the pH value above 11. The gelatinous precipitates can be separated by centrifugation and rinsed with distilled H2O in a cleansing step. In order to incorporate Li into the mixed-metal oxide, the resulting precipitate is mixed with an aqueous LiOH solution (LiOH.xH2O) with appropriate Li concentrations (chosen to influence the amount of Li in the eventual oxide) in a tubular mixer and homogenised. In order to produce nano-powder, the suspension can be quick-frozen using liquid nitrogen. Afterwards, it may be freeze-dried over at least 12 hours using a freeze-dryer. The combination the above mentioned precipitation, quick-freezing and freeze-drying steps produces nano-particles. Optionally a further crushing step may be used, although the method allows production of nano-particles without any crushing step.

(6) In order to produce a thermally treated/crystalline oxide, the material is then heated, e.g. at 900 C. for 1 hour in MgO crucibles.

(7) It will be understood that the description above relates to a non-limiting example and that various changes and modifications may be made from the arrangement shown without departing from the scope of this disclosure, which is set forth in the accompanying claims.

(8) The disclosure will now be further described by way of the following non-limiting Examples:

EXAMPLE 1

(9) Preparation of Mixed-Metal Oxides

(10) Aqueous solutions of Mg(NO3)2.6H2O were prepared by dissolving Mg(NO3)2.6H2O in distilled H2O. A solution of Fe(NO3)3.9H2O was prepared in the same way. The nitrate solutions were concurrently added drop-wise to a stirred ammonia solution while keeping the pH value above 11. The gelatinous precipitates were rinsed with distilled H.sub.2O and mixed with aqueous LiOH solution (LiOH.1H2O) with appropriate Li concentrations (chosen to influence the amount of Li in the eventual oxide) in a tubular mixer.

(11) Finally, the solution was quick-frozen using liquid N2. Afterwards, it was freeze-dried over at least 72 hours using a freeze-dryer. (Li,Fe,Mg)O semi-crystalline powders were produced.

(12) After thermal treatment at 900 C. for 1 h in MgO crucibles, crystalline (Li,Fe,Mg)O powders were produced. Crystallinity was greater than 50%. The ratio of Li:Fe:Mg is determined by preparation process.

(13) The Li-content of the different samples was quantified via atomic absorption spectroscopy, using an AASNovAA400G device from Analytik Jena via flame. The Fe content was determined via inductively coupled plasma atomic emission spectroscopy, using a Horiba Scientific ICP Model Ultima 2. The specific surface area was determined by a Micromeritics Gemini III 2375 Surface Area Analyzer, using N2 adsorption at 196 C. Before measuring, the samples were degassed at 300 C. and 0.15 mbar at least for 30 minutes. The surface areas were calculated by the method of Brunauer, Emmett and Teller. Powder X-Ray diffractograms were obtained (CuK1 radiation, with a wavelength 0.154 nm) using a Bruker AXS D8 ADVANCE X-ray diffractometer. EPR experiments were performed with a BRUKER E680 spectrometer. The spectrometer was operated in conventional continuous wave (cw) as well as in pulsed mode. Data were taken from as prepared compounds.

(14) In Table 1 an overview over the target and the actual loading of Li and the Fe-content, the BET surface area and the present phases, detected via XRD is given. The intended and the loading of Li and Fe of the prepared catalysts agree very well. The ratio Fe/Li is in both cases near 1 and the BET surface area does not vary too strongly. The FeLi/MgO sample showed solely the XRD peaks of the MgO phase indicating an entire incorporation of the Li and Fe ions in MgO (Fe3+, ionic radius: 55 pm for coordination number 6). The peak positions of the MgO pattern were marginally affected. An overview of the detected phases is shown in Table 1.

(15) TABLE-US-00001 TABLE 1 Li and Fe-content of the catalyst, the ratio dopant (Fe) to Li, the specific surface area, determined before reaction, the sample colour and the detected phases. Measured Target-content content Atom Li Fe Li Fe ratio BET XRD Catalyst [at. %] [at. %] [at. %] [at. %] [Fe/Li] [m.sup.2/g] Colour phases FeLi/ 0.5 0.5 0.5 0.5 1 29 Light yellow MgO MgO

(16) Co-doping of Li/MgO catalysts with charge compensating Fe ions was therefore performed with a constant atomic ratio of Li to dopant of approximately 1:1. These aliovalent Fe ions turned out to occupy Mg2+ sites in the lattice. The solubility of Fe3+ in MgO was shown to be unlimited. The anticipated Li stabilization by co-doping Li/MgO with Fe.sup.3+ appears to take place. As shown in the following Examples, the co-doping results in active catalytic materials.

EXAMPLE 2

(17) Decomposition of Sodium Chlorate Using Thermally Treated (Li,Fe,Mg)O

(18) Thermally treated nano-sized non-toxic (Li,Fe,Mg)O (Li 0.5 at. %; Fe 0.5 at. %) was prepared according to Example 1. It was combined with sodium chlorate (98.7 wt. % sodium chlorate and 1.3 wt. % oxide) by dry mixing (any method) and subsequently uniaxial pressed to form a chlorate candle of comparable size and weight to those commercially available. Production of oxygen via decomposition of sodium chlorate in the presence of the thermally treated (Li,Fe,Mg)O was monitored and compared to a commercially available chlorate candle of comparable size and weight. As shown in FIG. 2, the oxygen flow rate using the thermally treated (Li,Fe,Mg)O (modified; dashed line; gas flow: 7.6 to 8.4 L/min, i.e. in line with industry recommendations that oxygen flow is 4 litres per minute) was significantly smoother and at a higher rate than that achieved using the commercially available candle (standard; solid line; gas flow: 6.6 to 8.6 L/min). Moreover, the mixed-metal oxide of the present disclosure also acts as a binder and fuel, thus removing the need for further components to perform these functions and is non-toxic.

EXAMPLE 3

(19) Decomposition of Lithium Perchlorate Using Thermally Treated (Li,Fe,Mg)O

(20) Thermally treated nano-sized non-toxic (Li,Fe,Mg)O (Li 0.5 at. %; Fe 0.5 at. %) was prepared according to Example 1. It was combined with lithium perchlorate (98.7 wt. % lithium perchlorate and 1.3 wt. % oxide) by dry mixing. Production of oxygen via decomposition of lithium perchlorate in the presence of the thermally treated (Li,Fe,Mg)O was monitored and is shown in FIG. 3. Although the candle used was smaller than commercially available candles, the oxygen flow rate using the thermally treated (Li,Fe,Mg)O was 7.6 to 9.7 L/min, i.e. in line with industry recommendations that oxygen flow is 4 litres per minute and was relatively smooth. Moreover, the mixed-metal oxide of the present disclosure also acts as a binder and fuel, thus removing the need for further components to perform these functions and is non-toxic.